Depolymerization to Decontamination: Transforming PET Waste into Tailored MOFs for Advanced Pollutant Adsorption

Abstract

Plastic waste and water pollution demand circular economy-driven innovations. This review examines metal–organic framework (MOF) synthesis from polyethylene terephthalate (PET) waste for wastewater treatment. Depolymerized PET yields terephthalic acid and ethylene glycol—essential MOF precursors. We evaluate the following: (1) PET depolymerization (hydrolysis, glycolysis, ammonolysis) for monomer recovery efficiency; (2) MOF synthesis (solvothermal, microwave, mechanochemical) using PET-derived linkers; (3) performance in adsorbing heavy metals, dyes, and emerging contaminants. PET-based MOFs match or exceed commercial adsorbents in pollutant removal while lowering costs. Their tunable porosity and surface chemistry enhance selectivity and capacity. By converting waste plastics into functional materials, this strategy tackles dual challenges: diverting PET from landfills and purifying water. The review underscores the environmental and economic benefits of waste-sourced MOFs, proposing scalable routes for sustainable water remediation aligned with zero-waste goals.

1. Introduction

Polyethylene terephthalate (PET) is one of the most widely used synthetic polymers, playing a pivotal role in liquid beverage packaging, textile manufacturing, and electronic devices due to its lightweight nature, durability, and versatile properties. However, the exponential growth in PET consumption has precipitated a global waste management crisis, with improper disposal causing severe environmental harm [1]. Conventional degradation of PET waste can take centuries, exacerbating its accumulation in landfills and marine ecosystems. To mitigate this crisis, recycling strategies—including re-extrusion (primary), mechanical (secondary), chemical (tertiary), and incineration (quaternary) processes—have been developed [2,3]. Among these, chemical recycling via solvolysis (hydrolysis and glycolysis) is particularly promising, as it depolymerizes PET into reusable monomers such as terephthalic acid and bis(2-hydroxyethyl) terephthalate (BHET). These monomers serve as valuable precursors for synthesizing advanced materials, including metal–organic frameworks (MOFs). MOFs, characterized by their ultrahigh surface areas, tunable porosity, and versatile chemical functionalities, have demonstrated exceptional potential in gas storage, catalysis, and environmental remediation. Their adsorption capabilities are especially relevant for wastewater treatment, targeting contaminants such as organic dyes, heavy metals, pharmaceuticals, and agricultural pollutants [4,5]. However, the performance of MOFs is critically influenced by synthesis parameters, including precursor purity, metal–ligand coordination geometry, and textural properties, as well as host–guest interactions such as hydrogen bonding and π-complexation [4]. Despite extensive research on MOFs for environmental remediation, reviews specifically addressing PET-derived MOFs remain limited, with existing works often overlooking key technical challenges in PET depolymerization and monomer purification. Shanmugam et al. (2022) reviewed the upcycling of PET waste into MOFs for CO₂ capture, hydrogen production, and water purification but overlooked critical technical challenges in PET-to-monomer conversion [5]. Similarly, Cherian et al. (2025) focused on MOF-aided plastic degradation but offered minimal discussion on PET recycling realities [6]. These gaps underscore the need for a comprehensive analysis bridging PET depolymerization and MOF synthesis. This review systematically evaluates the sustainable transformation of PET waste into functional MOFs, with dual emphasis on (1) optimizing hydrolysis/glycolysis for high-yield monomer recovery and (2) advancing MOF design for superior adsorption performance. By critically assessing synthesis methodologies, structural properties, and application efficacy, we provide a roadmap for leveraging PET waste in next-generation environmental remediation materials, addressing both plastic pollution and resource scarcity.

2. PET: Presentation and Recycling

2.1. PET: Presentation

PET is a highly durable engineering thermoplastic renowned for its exceptional mechanical strength, dimensional stability, and chemical resistance to acids, bases, and solvents [7]. These superior properties, combined with its thermal stability (withstanding temperatures up to 80 °C), make PET indispensable across multiple industries, particularly in food/beverage packaging, pharmaceutical containers, and protective electronic components [8]. The material’s unique combination of transparency, lightweight nature, and processability further expands its applications to textiles, automotive parts, and construction materials [9]. Notably, PET’s recyclability presents significant environmental advantages, enabling closed-loop production systems that reduce waste in textile manufacturing and other sectors [10]. Global polyester production currently reaches 61 million tons annually, primarily for synthetic fibers [10]. The packaging industry consumes 30% of PET output, with bottles representing the second-largest plastic packaging category [11]. Alarmingly, much of this single-use packaging becomes waste, with over 8 million tons entering oceans yearly [12]. This pollution crisis demands comprehensive solutions, including improved recycling systems, source reduction initiatives, and active cleanup of existing ocean plastic debris.

2.2. Recycling Strategies of PET

PET recycling is a crucial solution to reduce plastic waste and mitigate the crisis. The important recycling techniques of PET are mechanical recycling, chemical recycling, energetic recycling, and biological recycling (Figure 1). PET recycling is essential for sustainability and resource preservation.

2.2.1. Mechanical Recycling

Mechanical recycling represents the most widely adopted method for PET waste recovery, involving the physical reprocessing of materials without chemical modification. The process begins with the collection and sorting of post-consumer PET products, followed by shredding into flakes. These flakes undergo rigorous washing to remove contaminants, including labels, adhesives, and food residues, before being dried to eliminate moisture [13]. The purified flakes are then melted and extruded into pellets or directly molded into new products such as beverage bottles, textile fibers, or packaging films. As the most energy-efficient PET recycling method, mechanical processing reduces greenhouse gas emissions by up to 75% compared to virgin PET production while conserving petroleum resources [14]. This closed-loop approach significantly diverts plastic waste from landfills and marine environments, supporting circular economy objectives. However, the method faces limitations, including (i) degradation of polymer chains during thermal processing, (ii) sensitivity to feedstock contamination, (iii) color limitations in recycled products, and (iv) decreasing quality with multiple recycling cycles. These constraints necessitate strict quality control measures to maintain material integrity for high-value applications.

2.2.2. Energetic Recycling

Energy recovery utilizes plastic waste as an energy source by capitalizing on its high calorific value, comparable to conventional fuels. This process significantly reduces waste volume by making it effective for non-recyclable plastics. Energy can be recovered through direct incineration (with heat/electricity generation) or thermochemical conversion, including pyrolysis (thermal decomposition at 300–900 °C in oxygen-free conditions to produce liquid fuel), gasification, and hydrothermal processing [15]. However, these methods face environmental challenges. Incineration emits toxic pollutantsand greenhouse gases, requiring advanced flue gas treatment. Pyrolysis and gasification, while cleaner, still produce hazardous ashes and tars. Despite these drawbacks, energy recovery remains crucial for managing contaminated or mixed plastic waste, complementing mechanical/chemical recycling in a circular economy framework.

2.2.3. Chemical Recycling

Chemical recycling represents a transformative approach for PET waste management through thermolysis (pyrolysis and gasification) or depolymerization through chemical reactions, including hydrolysis, glycolysis, methanolysis, aminolysis, and ammonolysis [16,17] into fundamental monomers like purified terephthalic acid (PTA) [15]. This process overcomes quality limitations of mechanical recycling by enabling infinite recyclability without molecular degradation. Advanced solvolysis methods (hydrolysis, glycolysis, methanolysis) break PET polymers into high-purity raw materials suitable for reproducing virgin-quality PET or synthesizing higher-value products [17]. Notably, recovered monomers serve as precursors for emerging materials like MOFs, creating valuable applications in adsorption and catalysis. This technology establishes a true circular economy for PET while addressing current recycling challenges of contamination and material downgrading. The following section analyzes chemical pathways to recover high-purity monomers—terephthalic acid (TPA) and bis(2-hydroxyethyl) terephthalate (BHET)—from post-consumer PET for MOF synthesis.

2.3. Chemical Recycling of PET for Metal–Organic Framework Ligand Recovery

Chemical depolymerization of PET utilizes selective solvolysis methods to recover high-purity monomers. Aminolysis with amines produces terephthalamides, while hydrolysis (neutral/acidic/alkaline) yields terephthalic acid (TPA). Glycolysis using ethylene glycol generates bis(2-hydroxyethyl) terephthalate (BHET), the preferred monomer for industrial PET repolymerization due to its high yield and compatibility with existing infrastructure [3].

Table 1. Comparative analysis of PET waste depolymerization methods [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41].

Method	Operation Conditions	Advantages	Disadvantages	Chemical Mechanism
Glycolysis	Ethylene glycol (primary) Temp: 110–270 °C	Direct repolymerization Closed-loop recycling	High energy input Requires catalyst (e.g., Zn acetate) Purification needed	Nucleophilic acyl substitution: Ethylene glycol hydroxyl groups attack electron-deficient carbonyl carbons in PET ester bonds, facilitated by metal catalysts that polarize the C=O bond, forms BHET through a tetrahedral intermediate that collapses, releasing polymer fragments.
Alcoholysis	Methanol/ethanol Temp: 160–350 °C	Low solvent cost High DMT/DET purity (>90%) Scalable industrially	Extreme conditions Methanol toxicity Safety risks	Transesterification cascade: Alcohol nucleophiles (methanol/ethanol) attack proton-activated ester linkages. Smaller alcohol molecules penetrate polymer crystallites more effectively, but require metal catalysts to stabilize the transition state.
Neutral Hydrolysis	Water (5:1 mass ratio) Temp: 200–250 °C	No solvents Eco-friendly TPA suitable for MOFs	Slow (Energy-intensive TPA purification costly	Hydrolysis: Water molecules act as nucleophiles under subcritical conditions (200–250 °C). The rate-determining step involves water penetration into PET amorphous regions, with proton transfer stabilizing the carboxylate intermediate.
Alkaline Hydrolysis	NaOH/KOH (4–20%) Temp: 100–225 °C	Fast, Mild conditions High TPA yield	Corrosive	Base-catalyzed saponification: Hydroxide ions initiate chain scission through direct nucleophilic attack on ester groups. The reaction proceeds via a concerted mechanism where C-O bond cleavage coincides with carboxylate formation.
Acid Hydrolysis	H2SO4/HNO3 (7–14 M) 60–100 °C	No pressure needed TPA purity	Reactor corrosion Toxic byproducts Acid disposal	Strong acids protonate ester oxygens, making carbonyl carbons more susceptible to nucleophilic attack. The reaction proceeds through an acid-stabilized carbocation intermediate that undergoes nucleophilic capture by water.

provides a comprehensive comparison of PET waste depolymerization methods, including hydrolysis, glycolysis, aminolysis, and methanolysis. For each technique, the table systematically presents reaction products, experimental conditions (temperature, solvent, catalyst), and chemical mechanisms. Additionally, it evaluates the advantages and limitations of each method.

2.3.1. Glycolysis

Glycolysis is the breakdown of PET chains through the insertion of glycols such as ethylene glycol (EG), diethylene glycol, or dipropylene glycol, yielding bis(hydroxyethyl) terephthalate (BHET). As the oldest and most extensively studied PET depolymerization method, glycolysis has significant commercial applications [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. First patented in 1965 [19], this process typically operates at 110–270 °C and 1–25 atm pressure. Catalysts like zeolites and metal acetates (manganese, zinc, and magnesium) enhance the reaction, with zinc and manganese acetates being the most effective. Glycolysis remains a key industrial approach for PET recycling due to its efficiency and scalability.

2.3.2. Alcoholysis

PET alcoholysis was originally developed to recover isooctyl terephthalate (DOTP), a valuable plasticizer, from PET waste. This chemical recycling process involves depolymerizing PET through reaction with various alcohols, including methanol, pentaerythritol, 1-butanol, and 1-pentanol, producing corresponding terephthalate esters and ethylene glycol (EG) as primary products (Table 1). The most extensively researched method is methanolysis, where PET reacts with methanol under severe conditions (180–280 °C, 20–40 atm) to yield dimethyl terephthalate (DMT) and EG [23]. Ethanolysis follows a similar mechanism, generating diethyl terephthalate (DET) instead. The methanolysis process was first commercialized by Gruschke et al. (1968) [24], who demonstrated complete PET depolymerization to DMT and EG at 210 °C without catalysts. While methanolysis remains industrially important due to its high efficiency, significant safety concerns exist regarding methanol’s toxicity. Recent studies suggest ethanolysis as a safer alternative, offering comparable depolymerization efficiency while eliminating methanol-related hazards [25].

2.3.3. Hydrolysis

The hydrolysis of esters in neutral and acidic media is a well-established process. The reaction begins with protonation of the ester carbonyl group, followed by nucleophilic attack by water, leading to cleavage of the ester bond and formation of carboxyl and hydroxyl-ester intermediates, which further degrade into carboxylic acids and alcohols (Figure 1). PET hydrolysis can be performed under three main conditions: alkaline, acidic, or neutral hydrolysis [26]. Alkaline hydrolysis uses strong bases (e.g., NaOH) for rapid degradation, while acid hydrolysis (e.g., H₂SO₄) is effective but corrosive. Neutral hydrolysis, requiring only water and heat though slower, is environmentally favorable. Each method influences reaction rate, yield, and product purity.

Neutral Hydrolysis

Neutral hydrolysis of polyethylene terephthalate (PET) is typically carried out in an aqueous medium under high-temperature conditions (above 245 °C) with a water-to-PET mass ratio exceeding 5.1:1 [26]. This process occurs in the molten phase of PET, where water molecules attack the ester bonds, breaking them into terephthalic acid (TPA) and ethylene glycol (EG). However, a major drawback of neutral hydrolysis is the requirement for expensive high-pressure reactors and prolonged reaction times due to the extreme conditions (200–250 °C) [26]. After hydrolysis, TPA can be recovered through acidification and filtration. To enhance reaction efficiency, recent studies have explored the use of catalysts, microwave irradiation, and ultrasonic treatment. Common catalysts include zinc acetate and sodium zincate, which are also used in transesterification reactions. These catalysts function by destabilizing the PET-water interface, increasing the accessible surface area for hydrolysis [21]. Additionally, alternative methods such as microwave-assisted hydrolysis have demonstrated significant improvements. For instance, Ikenaga et al. (2016) achieved complete PET degradation in just 30 min by combining microwave heating with a high-pressure reactor (223–232 °C, 2.3–3.0 MPa) [26]. Recent research has also investigated environmentally friendly hydrolysis methods. Stanica-Ezeanu & Matei, (2021) demonstrated that PET waste can undergo natural hydrolysis in seawater, with an activation energy of 73.5 kJ/mol [27]. This process is facilitated by metallic ions (Na⁺, Mg²⁺, Ca²⁺, K⁺) present in seawater, which weaken ester bonds and promote random depolymerization [27]. Such findings highlight the potential for sustainable PET recycling methods that reduce energy consumption and operational costs.

Alkaline Hydrolysis

The alkaline hydrolysis of PET is typically conducted using aqueous solutions of sodium hydroxide (NaOH, 4–20 wt%) or potassium hydroxide (KOH), with NaOH being preferred due to its superior effectiveness and cost efficiency [30]. The alkaline hydrolysis produces disodium terephthalate and ethylene glycol (EG) as the primary reaction products [28]. Subsequent acidification of the resulting solution to pH 2 using strong mineral acids yields pure terephthalic acid (TPA) while maintaining EG in solution [29]. The foundational research on PET alkaline hydrolysis was established by Pitat et al., who developed a process utilizing an 18 wt% NaOH solution at a PET-to-NaOH weight ratio of 1:20, achieving complete hydrolysis within 2 h at 100 °C [31]. Subsequent studies by Lazarus et al. demonstrated that even dilute 4% NaOH solutions could effectively hydrolyze Nylon-6/PET blends (70:30 w/w) at 230 °C and 17 atm pressure, yielding 97.4% TPA [30]. However, complete PET conversion under reflux conditions requires approximately 24 h when employing 4 molar equivalents of KOH relative to the benzene dicarboxylate (BDC) units [30]. Recent advancements have focused on developing milder reaction conditions through various innovative approaches. Phase-transfer catalysts, particularly quaternary ammonium salts, have proven highly effective in accelerating reaction rates by 2.3 to 9 times compared to conventional methods, enabling efficient depolymerization at temperatures below 100 °C [29]. Microwave-assisted hydrolysis has shown promising results, with studies reporting 47% conversion of 3 g of PET in 30 mL of 1 M NaOH after 12 h of irradiation [27]. The incorporation of ethanol as a co-solvent in a 60:40 vol% ethanol-water mixture containing 5 wt% NaOH has achieved approximately 95% yield in less than 20 min at 80 °C [31]. Ultrasound-assisted alkaline hydrolysis has also demonstrated significant improvements, reducing the required reaction time from 65 min to just 45 min at 90 °C while maintaining complete PET depolymerization [32]. The reaction kinetics of PET hydrolysis can be effectively described using the shrinking-core model, which correlates the reaction rate with the available surface area of unreacted PET [17]. Current research efforts are increasingly focused on combining these various techniques, with particular emphasis on integrating phase-transfer catalysts with ultrasound irradiation to simultaneously reduce both reaction time and temperature requirements [27,32]. These technological developments are proving crucial for advancing sustainable plastic waste management solutions by addressing the economic and environmental challenges associated with PET depolymerization processes.

Acid Hydrolysis of PET

Acid hydrolysis of polyethylene terephthalate (PET) is commonly performed using concentrated sulfuric, nitric, or phosphoric acid, with terephthalic acid recovered via crystallization. Unlike alkaline hydrolysis, this method avoids the need for an additional acidification step when the reaction proceeds to completion. Early work by Pusztaseri (1987) demonstrated PET depolymerization using highly concentrated sulfuric acid (>14.5 M H₂SO₄) [33]. In contrast, nitric acid hydrolysis produces 2-nitroterephthalic acid (NO₂-BDC), as verified by ¹H NMR analysis [33]. Recent developments have expanded the feasibility of acid hydrolysis under milder conditions. Microwave-assisted reactions, for instance, allow the use of lower H₂SO₄ concentrations while improving efficiency. One study showed that depolymerizing 3 g of PET with 1–2 equivalents of HCl per benzene dicarboxylate (BDC) unit resulted in a 12 h induction period, after which hydrolysis accelerated markedly. Yoshioka et al. (2001) proposed that this delay arises from microcrack formation on PET surfaces, increasing reactive contact between the polymer and acid [16]. However, using more than twoequivalents of HCl slowed the reaction due to TPA precipitation, which formed a passivating layer that inhibited further degradation [16]. Notably, alkaline hydrolysis with NaOH does not induce similar surface cracking, underscoring a fundamental mechanistic difference between acid- and base-catalyzed PET degradation. Acid strength also plays a critical role: while oneequivalent of HCl led to carbon black formation as a side product, twoequivalents of NaOH not only prevented carbonization but also enhanced hydrolysis rates, yielding BDC more efficiently. These findings highlight key trade-offs in acid hydrolysis. Although strong acids enable rapid depolymerization, side reactions and passivation effects can reduce efficiency. Emerging approaches, such as microwave-assisted reactions, may help address these challenges, offering a more scalable route for industrial PET recycling.

2.3.4. Aminolysis

This process involves the nucleophilic attack of primary amines, such as ethanolamine or hydrazine hydrate, on PET ester bonds, yielding monomers like bis(2-hydroxyethylene) terephthalamide (BHETA), terephthalic dihydrazide (TDH), and various oligomers, having various uses in high-value applications, including polyurethanes, anticorrosive coatings, and epoxy resins. However, despite its inherent advantages, aminolysis remains underutilized in industrial-scale PET recycling due to persistent challenges in optimizing reaction conditions and ensuring economic feasibility.

The efficiency of PET aminolysis is critically dependent on several key process parameters. The PET-to-solvent ratio, for instance, significantly influences the depolymerization yield, with higher solvent ratios generally improving efficiency by enhancing the interaction between PET and the amine solvent. Studies have indicated optimal ratios ranging from 1:4 to 1:20 (PET:amine), with ethanolamine (EA) being the most commonly employed solvent. For example, Vinitha et al. (2022) achieved an impressive 94% BHETA yield at a 1:20 PET:EA ratio, further augmented by the use of Sn-doped ZnO nanoparticles as catalysts [34]. Hydrazine monohydrate, due to its dual amine groups, can achieve high TDH yields (84%) even at lower ratios (1:3), as demonstrated by George and Thomas (2015) [35]. Reaction time is another crucial factor. While conventional heating methods typically require 3–4 h for complete PET conversion, microwave irradiation has been shown to drastically reduce this to mere minutes (Parab et al., 2012) [36]. For instance, microwave-assisted aminolysis, when coupled with a sodium sulfate catalyst, achieved an 86% TDH yield in just 10 min, a stark contrast to the 4 h required under conventional heating conditions [36]. Although slower (taking up to 21 days), solar-driven aminolysis offers significant energy savings, highlighting its potential for sustainable operations [37]. The judicious selection of catalysts is also essential for enhancing the efficiency of aminolysis.

Sodium acetate and zinc acetate are widely used for their ability to reduce both reaction time and temperature. More recently, deep eutectic solvents (DES) like choline chloride-ZnCl₂ have shown considerable promise, yielding up to 97% BHETA in just 30 min under relatively mild conditions [38]. The products derived from PET aminolysis exhibit remarkable versatility, finding applications across diverse industries. The primary products include BHETA, which is extensively utilized in polyurethane foams [39], as PVC plasticizers [40], and in the formulation of anticorrosive paints [37]. Beyond these primary applications, the versatility of aminolysis products extends to secondary uses. Polyurethane formulations enhanced with BHETA exhibit improved mechanical properties [39], while BHETA-based paints demonstrate superior adhesion and corrosion resistance [37].

3. MOF from Waste PET

Metal–organic Frameworks (MOFs) represent a revolutionary class of porous crystalline materials formed through the coordination of metal ions or clusters (e.g., Zn²⁺, Cu²⁺, and Fe³⁺) with multifunctional organic linkers such as carboxylates, sulfonates, or nitrogen-rich heterocycles (Figure 2). These hybrid materials exhibit unparalleled structural diversity, where the judicious selection of metal centers and ligand geometries (linear, trigonal, or tetrahedral) enables precise control over framework architecture, pore size (0.5–5 nm), and surface functionality [42]. As illustrated in Figure 2, the fundamental building blocks of MOFs consist of metal nodes interconnected by organic spacers, creating tunable periodic networks with exceptional surface areas. This structural versatility underpins their remarkable performance in gas storage (H₂, CO₂, CH₄), heterogeneous catalysis, controlled drug delivery, and molecular separation technologies.

3.1. Early Development of PET Waste-Derived MOFs

The early exploration into synthesizing metal–organic frameworks (MOFs) from polyethylene terephthalate waste marked a pivotal advancement in the field of sustainable materials. These pioneering efforts, particularly those documented by Huang et al. (2011), illuminated both the immense potential and inherent challenges associated with utilizing depolymerized PET as a source of terephthalic acid linkers for the preparation of the organic–inorganic hybrid NTHU-2 [42]. Remarkably, the resulting NTHU-2 crystals maintained a composition and structure identical to those produced using conventional precursors. However, they exhibited distinct photoluminescence properties, a finding that underscored the potential for waste-sourced linkers to impart unique functional characteristics to MOFs. This discovery hinted at the possibility of creating MOFs with properties not easily achievable when using commercially available raw materials [43]. After five years, investigations pioneered by Lo et al., 2016 focused on a range of MOF structures, including, MIL-47, MIL-53(Cr), MIL-53(Al), and MIL-53(Ga), providing crucial insights into the intricate interplay of synthesis parameters and their impact on the structural outcomes of PET-derived MOFs [43]. The synthesis of MIL-47 from PET waste proved to be relatively straightforward, showcasing the direct applicability of PET-derived BDC as a substitute for commercial BDC in certain MOF syntheses. Standard hydrothermal conditions, involving VCl₃ and hydrofluoric acid (HF) at 200 °C for four days, successfully yielded the desired MIL-47 framework without requiring significant modifications [44]. This demonstrated a promising pathway for valorizing PET waste into functional materials. However, the path to synthesizing more complex MOFs, such as those in the MIL-53 family, presented greater challenges, emphasizing the need for meticulous optimization of synthesis conditions. For MIL-53(Cr), initial attempts using Cr(NO₃)₃ and HF at 220 °C resulted only in an amorphous material. Researchers successfully overcame this hurdle by strategically substituting Cr(NO₃)₃ with CrCl₃, increasing the concentration of HF, and lowering the reaction temperature to 160 °C. These crucial adjustments led to the crystallization of MIL-53(Cr). Despite this success, the product contained trapped BDC within its pores, necessitating an additional vacuum drying step at 200 °C to achieve purity. This experience highlighted the critical importance of selecting appropriate metal precursors and precisely controlling reaction conditions when incorporating PET-derived linkers. Similar complexities were encountered during the synthesis of MIL-53(Al). An initial attempt at 220 °C resulted in an undesirable mixture of MIL-53(Al) and aluminum oxyhydroxide (boehmite) byproducts. By reducing the reaction temperature to 160 °C, researchers successfully suppressed boehmite formation, thereby obtaining phase-pure MIL-53(Al). This demonstrated how even subtle alterations in synthesis parameters could significantly influence the quality and purity of the final product [44]. The case of MIL-53(Ga) further underscored the profound impact of reaction conditions and the choice of acid modulators [44]. The initial HF-mediated synthesis failed to produce the target MOF, yielding only unreacted BDC. However, by strategically switching from HF to hydrochloric acid (HCl) as a modulator, researchers successfully achieved the crystallization of MIL-53(Ga). This revealed that the selection of the mineral acid could profoundly influence the assembly of the MOF framework. In the same year, Deleu et al. (2016) developed, in parallel, two primary methods: a one-pot hydrothermal synthesis and a two-step process [44]. In the one-pot method, PET undergoes simultaneous hydrolysis and MOF formation under microwave heating at 200 °C in water, successfully yielding stable frameworks like MIL-53(Al) and MIL-47(V). The MIL-53(Al) product, after activation at 400 °C, achieved a high BET surface area of 1481 m²/g, demonstrating the method’s viability for producing porous materials with industrial potential. However, this approach is limited to thermally robust MOFs, as less stable metals (e.g., Fe and Cr) tend to form oxides under the harsh reaction conditions. To circumvent this, the team introduced a two-step synthesis where PET is first hydrolyzed—either with NaOH or under acidic conditions—to release BDC, followed by MOF crystallization at milder temperatures (e.g., 80 °C). This adaptation enabled the synthesis of more sensitive frameworks like MIL-88B(Fe), albeit with additional purification steps. A key innovation was the direct growth of MOF coatings on PET surfaces by partially depolymerizing the polymer with nitric acid, creating carboxylate anchors for crystal formation. This technique transformed PET bottles into functional reactors, yielding adherent layers of MIL-53(Al) and UiO-66(Zr) without requiring solvent-intensive processes. Collectively, these foundational studies unequivocally demonstrated that while PET-derived BDC could indeed serve as an effective substitute for commercial BDC in MOF synthesis, the process often demanded meticulous optimization of various reaction parameters. These included careful consideration of temperature, the specific choice of metal precursors, and the type of acid modulators employed.

3.2. Method of Preparation of MOF Derived PET

The synthesis of metal–organic frameworks from PET waste can be achieved through two primary approaches: direct and indirect methods. Each method has distinct advantages and limitations in terms of process efficiency, product quality, and scalability (

Table 2. Direct vs. Indirect MOF Synthesis from PET waste: Key process comparisons.

Parameter	Direct Method	Indirect Method (Depolymerization First)
Process Steps	1-step: PET → MOF	2-step: PET → Terephthalic acid → MOF
Reaction Conditions	Precence of acid modulator for depolymerization	Technique of depolymerization
Yield	Low	moderate
Time Required	Depolymerization and MOF synthesis at the same time	Time of depolymerization + time of MOF synthesis
Purity Control	Moderate (impurities from additives)	High if terephthalic acid or BHET pure
Crystallinity	Lower (defect-rich)	Higher (more ordered structures)
Energy Consumption	Lower (one-pot synthesis)	Higher (multiple steps)

and Figure 3).

Direct Method (PET → MOF in One Step)

The direct method involves converting PET waste into MOFs in a single step, where depolymerization and MOF formation occur simultaneously. This approach typically requires the presence of an acid modulator (e.g., formic acid and acetic acid) to break down PET while coordinating the resulting monomers with metal nodes (e.g., Zr, Cr, and Zn) [45,46,47]. Key advantages of this method include reduced reaction time (since depolymerization and MOF synthesis happen concurrently) and lower energy consumption due to the elimination of intermediate purification steps. However, the direct method often suffers from lower yields and moderate purity control, as residual additives (e.g., plasticizers and dyes) from PET can introduce defects in the MOF structure. The resulting MOFs tend to have lower crystallinity and surface area compared to those synthesized via the indirect route. Despite these drawbacks, the direct method is more scalable for industrial applications, as it simplifies production by avoiding multiple processing stages.

Indirect Method (PET → Terephthalic Acid/BHET → MOF)

The indirect method follows a two-step process: (1) depolymerization of PET into purified terephthalic acid (TPA) or bis(2-hydroxyethyl) terephthalate (BHET), followed by (2) MOF synthesis using these monomers. Common depolymerization techniques include acid/alkaline hydrolysis, glycolysis, or enzymatic degradation. The major advantage of this approach is the higher purity of the resulting MOF, as the intermediate TPA or BHET can be rigorously purified before MOF assembly. This leads to better crystallinity, higher surface area, and more uniform pore structures, making the indirect method preferable for high-performance applications (e.g., catalysis and gas storage). However, the process is more time-consuming (due to separate depolymerization and synthesis steps) and energy-intensive, as it requires additional solvent use and purification. Despite these challenges, the indirect method allows for greater control over MOF properties, enabling the synthesis of complex frameworks (e.g., MIL-101 and rare-earth MOFs) that are difficult to achieve via direct conversion.

3.3. Techniques of Synthesis

The synthesis of metal–organic frameworks has seen the development of diverse synthetic approaches, which can be broadly categorized into three main classes: conventional solvothermal methods and unconventional methods [46]. Conventional solvothermal synthesis remains the most widely employed approach, typically involving the reaction of metal precursors with organic linkers in organic solvents at elevated temperatures and pressures. This method offers excellent control over crystallinity and pore structure but often requires long reaction times and high energy input. Unconventional methods have emerged to address these limitations, encompassing microwave-assisted synthesis, electrochemical routes, and mechanochemical approaches that can significantly reduce reaction times and improve energy efficiency.

3.3.1. Conventional Synthesis Method (Solvothermal and Hydrothermal Methods)

Conventional solvothermal methods remain the most widely employed technique for MOF synthesis, involving the reaction of metal precursors with organic linkers—often terephthalic acid (BDC) or its derivatives—under elevated temperature and pressure in sealed vessels such as autoclaves. While these methods offer excellent control over MOF crystallinity, morphology, and pore structure, they typically require long reaction times and considerable energy input [48,49]. Hydrothermal synthesis, a water-based variant of the solvothermal approach, provides an eco-friendlier alternative, particularly beneficial for generating water-stable MOFs [50]. Recent research has significantly advanced the use of solvothermal and hydrothermal methods for PET-derived MOFs, showcasing a sustainable “Waste-to-MOFs” model. For example, Dubey et al. (2023) utilized solvothermal synthesis to produce Cu-, Ti-, and Zr-based MOFs [48]. These MOFs incorporated benzene dicarboxylate linkers extracted from waste PET bottles, specifically for application as supercapacitor electrodes. Among these, the Cu-MOF demonstrated superior electrochemical performance, achieving a specific capacitance of 104.8 F/g and retaining 87% capacitance after 10,000 cycles. This impressive performance was attributed to the Cu-MOF’s high surface area and low internal resistance, highlighting the dual benefit of recycling PET waste while concurrently producing efficient energy storage materials.

Similarly, Villarroel-Rocha et al. (2022) successfully synthesized MOF-5 using terephthalic acid derived from recycled PET [51]. Their work confirmed that the structural integrity and ligand quality of the PET-derived MOF-5 were comparable to those synthesized from commercial sources. The synthesized MOF-5 exhibited excellent CO₂ adsorption capacity, with static adsorption of 2.5 mmol/g and dynamic adsorption of 2 mmol/g at 35 °C. This demonstrates the significant potential of PET-derived MOFs, synthesized via solvothermal routes, for critical environmental remediation applications. These studies collectively underscore the effectiveness of solvothermal and hydrothermal methods in converting non-degradable PET waste into valuable, high-performance MOF materials for diverse applications, ranging from energy storage to gas adsorption.

3.3.2. Unconventional Methods of Synthesis

To address the drawbacks of lengthy and energy-intensive conventional methods, unconventional synthesis techniques have been developed, offering rapid, energy-efficient, and greener alternatives.

Mechanochemical Synthesis

Mechanochemical synthesis is an innovative, solvent-free, and energy-efficient method for preparing metal–organic frameworks that has gained considerable attention in recent years. This technique employs mechanical energy—typically through ball milling or grinding—to drive the reaction between metal salts and organic ligands without requiring solvents [52]. Mechanical force disrupts the molecular bonds of reactants, facilitating their direct interaction and leading to the rapid formation of MOFs, often within just 10–16 min. This solid-state process offers several distinct advantages over conventional solution-based methods, such as significantly reduced energy consumption, minimal waste generation, and complete elimination of organic solvents. Mechanochemical synthesis is particularly efficient when hydrated metal salts with essential anions are combined with low-melting-point organic reactants, as the mechanical force promotes efficient mixing and reaction. Mild heating after mechanical activation helps remove volatile byproducts like water, further enhancing product purity [47]. First applied to MOFs in 2006 by Pichon et al., who demonstrated the solvent-free synthesis of a microporous framework [53]. This method has since evolved into a scalable production technique. Its simplicity, low environmental impact, and ability to avoid high temperatures make it a promising route for industrial-scale MOF production, suitable for a wide range of framework types. Recently, D’Amato et al., 2021 presented a mechanochemical “shake-and-bake” method using PET-derived bis(2-hydroxyethyl) terephthalate as an organic linker for synthesizing UiO-66(Zr) [54]. The solvent-free process involves manually grinding BHET with zirconium precursors, followed by baking at 130 °C for 0.5–12 h. This approach eliminates the need for organic solvents, reduces synthesis time, and operates under milder conditions compared to traditional solvothermal methods. Hydrolysis of BHET to terephthalate ions facilitates MOF crystal growth. The method is energy-efficient, scalable, and yields MOFs with applications in catalysis and energy storage, advancing green chemistry and plastic recycling.

Sonochemical Synthesis

Utilizing ultrasonic waves to promote crystallization via acoustic cavitation, sonochemical synthesis rapidly produces a wide range of MOFs. Bang and Suslick (2010) demonstrated this for nanostructured materials, and adapting this technique for PET-derived ligands promises further process intensification [55].

Electrochemical Synthesis

Electrochemical synthesis of MOFs offers significant industrial advantages over traditional solvothermal methods. This approach operates at lower temperatures, achieves faster reaction rates, and avoids the production of corrosive anion byproducts (e.g., nitrate and chloride), making it a more environmentally friendly alternative [56,57]. Unlike conventional methods that require metal salts, electrochemical synthesis generates metal ions directly through anodic dissolution. When voltage is applied, the metal electrode dissolves, releasing metal ions into the reaction mixture containing organic linkers and electrolyte [58]. These freshly generated metal ions rapidly react with linkers near the electrode surface, enabling the formation of MOF structures without contamination from salt-derived impurities. Moreover, this method allows precise control over MOF properties, as the voltage and current density can be adjusted to modulate growth rates, crystal sizes, and morphologies. The use of electrons as the sole source of metal ions not only eliminates chemical waste but also aligns with green chemistry principles, making electrochemical synthesis an efficient, scalable, and sustainable strategy for MOF production in various industrial applications.

3.4. Recent Synthesis and Applications Studies in PET-Derived MOF (2024–2025)

Table 3. Summary of PET-derived MOF synthesis methods, properties, and applications from recent studies (2024–2025).

Metal Source	MOF Synthesis Method	MOF Type	Key Synthesis Conditions	Yield/Purity	Application	Study
Zn from used batteries	Solvothermal + GO modification	GO-MOF	120 °C, 24 h	High-purity TPA	Photodegradation of pesticides	[59]
Mn salts	Solvothermal	Mn-PET-MOF	Standard conditions	Comparable to commercial (8.27 mg/g)	Tetracycline adsorption	[70]
Co(NO3)2·6H2O	Solvothermal	ZnO@Co-BDC	180 °C, 6 h	87.5% MB degradation	Dye photocatalysis	[71]
Fe salts	Solvothermal + PANI composite	Fe-MOF@PANI	100 °C, 12 h	258 mg/g Pb(II)	Heavy metal adsorption	[60]
Ni salts	Electrochemical	Ni-MOF	1.47 V, RT	94% Faradaic efficiency	Formic acid production	[61]
Al salts	One-step hydrothermal	MIL-53(Al)	200 °C, water solvent	71.25% conversion	Dye adsorption	[72]
Fe salts	Hydrothermal	MIL-101(Fe)/MOF-235	80 °C, 24 h	93.3% efficiency	Material synthesis	[68]
Fe from galvanizing waste	Room-temperature	MIL-88B(Fe)	RT, 1 h	87% TC degradation	Photocatalysis	[63]
Fe from wastewater	Microwave-assisted	MagMOF	30 min, 300 W	94% purity	Azo dye degradation	[64]
Cu/Ni salts	Solvothermal	Cu-Ni-PET	Standard conditions	806 F/g capacitance	Hydrogen generation	[69]
Ag salts	Solvothermal	Ag-MIL-101	Standard conditions	93% in 8 min	Dye degradation	[62]
Cu/Ni salts	Solvothermal + BiOI	Ni/Cu-MOF@BiOI	Sunlight 4 h	99% MB degradation	Dye photocatalysis	[67]
Co/Tb salts	Electrodeposition	TbCo-MOF/NF	1.55 V cell	161 mV HER	H2 production	[65]
Zr	Alkaline depolymerization	UiO-66	Ethanol modulation Room-temperature coating	-	Superhydrophobic textile coatings	[73]
Al salts	Hydrothermal	MIL-53(Al)	Standard conditions	826 mg/g	Phosphate removal	[74]
Cr/Al/Fe salts	One/two-pot	MIL-101(Cr) etc.	200 °C, 60 min	95.6% yield	Water adsorption	[75]
Zn salts	Solvothermal	MOF-5	120 °C, 24 h	2325 mg/g TC	Tetracycline adsorption	[66]

summarizes recent studies (2024–2025) on PET-derived MOFs, highlighting synthesis conditions and applications. Recent studies demonstrate significant progress in depolymerizing PET for MOF synthesis, with alkaline hydrolysis remaining the dominant method due to its high terephthalic acid yield and scalability [59,60]. However, alternative glycolysis [61,62] isgaining prominence for itsfaster reaction kinetics and compatibility with waste-derived metal sources. The field shows a clear shift toward sustainable synthesis, with room-temperature [63] and microwave-assisted methods [64,65] emerging as energy-efficient alternatives to traditional solvothermal processes. A particularly noteworthy trend involves the utilization of non-traditional metal sources, including zinc from spent batteries [59], iron from galvanizing waste [63], and transition metals from industrial wastewater [64], demonstrating the potential for circular economy approaches in MOF production. These innovations have enabled remarkable performance in environmental applications, such as the 2325 mg/g tetracycline adsorption capacity achieved by MOF-5 [66] and 93–99% efficiency in dye degradation using waste-derived MOFs [67,68]. Applications have expanded beyond adsorption to include energy-related uses, exemplified by the 806 F/g supercapacitor performance of Cu-Ni-PET [69] and the 161 mV overpotential for hydrogen evolution reaction achieved by TbCo-MOF/NF [65], 2024). Bimetallic systems, such as RuxMn1.2Co0.8Oy [62] and Cu-Ni-PET [69], have shown particular promise for enhanced functionality through synergistic effects. While these advancements are impressive, challenges remain in scaling these processes for industrial adoption and further reducing energy requirements.

3.5. Ligand Variants from PET in MOF Synthesis

Figure 4 illustrates various methods for recuperating monomers from PET waste, which are then utilized in the synthesis of MOFs. This comprehensive diagram outlines four distinct pathways to break down PET waste into valuable precursors. While terephthalic acid (TPA) remains the most commonly employed ligand derived from PET waste for MOF synthesis, recent research has explored alternative PET-derived organic linkers and innovative preparation methods to enhance MOF functionality and sustainability. One notable alternative is bis(2-hydroxyethyl) terephthalate (BHET), a key intermediate in PET glycolysis. In a groundbreaking study, BHET was recovered from PET waste via solvent-free melt depolymerization and subsequently hydrolyzed into TPA. Both BHET and TPA were employed to synthesize cerium-based metal–organic frameworks (Ce-MOFs) for energy applications [76]. Characterization techniques such as FTIR, NMR, FE-SEM, and EDX confirmed the structural integrity and purity of the recovered products and MOFs. The BHET and TPA-Ce-MOF exhibited specific capacitances of 91.5 and 220.1 F/g, respectively, highlighting their potential in energy storage while promoting environmental benefits [76]. The versatility of BHET as a dual-functional ligand is further emphasized, as it not only serves as an effective coordination site but also promotes easier crystal growth, making it an attractive alternative for sustainable MOF fabrication.

In a different approach, disodium terephthalate (DST)—a salt form of terephthalic acid—has been employed to prepare MOF composites [77]. Moumen et al. (2024) synthesized Fe-based MOF composites using DST derived from PET waste instead of free TPA [77]. This method yielded shaped MOF composites exhibiting high phosphate adsorption efficiency, offering a novel valorization pathway that integrates PET waste recycling with water purification technologies [77]. The use of DST as a ligand precursor presents practical advantages, including enhanced solubility and reactivity under synthesis conditions, thereby streamlining large-scale MOF production [77]. Beyond DST, other PET-derived intermediates, such as ethylene glycol (recovered during depolymerization), have been repurposed as solvents or co-ligands in MOF synthesis, further closing the loop in plastic waste upcycling. These advancements underscore the dual environmental and economic benefits of PET-derived MOFs. For instance, MIL-53(Al) synthesized from PET bottles demonstrated comparable performance to commercial TPA-based MOFs in adsorbing tetracycline, while UiO-66 coatings from polyester/Spandex textiles achieved superhydrophobicity (contact angle ≥ 150°) [70,77]. Such innovations align with circular economy principles, transforming non-recyclable PET waste into high-value materials for pollution remediation, catalysis, and energy storage [70,76,77]

3.6. Sustainable Synthesis of MOFs from PET and Metallic Waste Precursors

The preceding sections have conclusively demonstrated the viability of producing high MOFs using terephthalic acid and BHET derived from PET waste. This approach simultaneously tackles two critical environmental issues: plastic pollution and resource conservation (eliminating the need for petroleum-derived linkers). Advanced synthesis strategies now integrate multiple waste streams, employing not only PET-derived organic ligands but also metal ions recovered from industrial byproducts (e.g., electroplating sludge, and spent batteries) and mining effluents. As summarized in

Table 4. MOF Types Derived from Heavy Metal Waste and Their Environmental Applications.

MOF Type	Heavy Metal Source	Key Characteristics	Performance Metrics	Mechanistic Insights and Performance	Reference
CrNiFe-MOF	Stainless steel waste (Cr, Ni, Fe)	Mesoporous, defect-rich structure; pH-stable (2–10)	Phosphate adsorption: 126 mg/g; STY: 5760 g m−3 day−1	The trimetallic oxo-clusters (Cr/Ni/Fe) provide high-density Lewis acid sites for selective phosphate binding via ligand exchange. The mesoporous defective structure enhances diffusion kinetics, achieving 98% removal from eutrophic water.	[79]
Ni-MOF	Electroplating sludge (Ni2+, Fe3+, Cu2+)	Tolerant to impurity ions; nanocrystalline morphology	CO2 photoreduction: 9.68 × 103 μmol h−1 g−1 CO (96.7% selectivity); AQY: 1.36% (420 nm)	Visible light excitation generates electrons that migrate to Ni2+ nodes, reducing adsorbed CO2 through a proton-coupled electron transfer pathway. The reaction proceeds via CO2•− and formate intermediates, ultimately yielding CO with 96.7% selectivity. Fe3+/Cu2+ impurities from the sludge optimize the Ni sites’ electronic structure, suppressing H2 evolution and stabilizing key intermediates. The MOF’s high surface area and defect-rich framework enhance charge separation, contributing to its superior activity (9.68 × 103 μmol h−1 g−1 CO) and stability.	[80]
Zn-MOF (W-MOF)	Zn-C batteries (Zn2+)	GO-modified composite; visible-light active	Pesticide degradation: >95% (chlorpyrifos/profenofos); stable for multiple cycles	Zn2+ nodes and terephthalate linkers form a photoactive framework. Under visible light, charge separation generates •OH radicals, which cleave P−O bonds GO integration reduces electron–hole recombination, boosting degradation efficiency to 95% in 60 min (pH 5).	[59]

, these waste-sourced MOFs achieve performance comparable to conventional MOFs. Al Busafi et al., 2021 present a green synthesis method for aluminum-based metal–organic frameworksusing waste materials [78]. PET bottles were chemically recycled by alkaline hydrolysis to produce TPA [78]. Simultaneously, aluminum scraps were dissolved in hydrochloric acid (HCl) to form aluminum chloride hexahydrate (AlCl₃·6H₂O). The two recycled products were then combined in a dimethylformamide (DMF) solution with acetic acid under reflux for three days, leading to the formation of MIL-53 (Al). The reaction produced a white crystalline MOF, which was purified through filtration and washing. The prepared MIL-53 (Al) exhibited excellent thermal stability, maintaining its structure even above 300 °C. Characterization using IR revealed distinct bands corresponding to the functional groups, while XRD confirmed its crystalline nature. SEM showed a brick-like crystal morphology with sizes ranging from 100 to 500 nm. Elemental analysis indicated an aluminum content of 13.82%, aligning with the expected MOF composition. More recent work focuses on developing streamlined processes with improved environmental profiles. Boukayouht et al. (2024) pioneered an ultrarapid, sustainable method for synthesizing trimetallic CrNiFe-MOF using stainless steel waste and PET-derived disodium terephthalate [79]. The room-temperature coprecipitation approach achieves an exceptional space-time yield of 5760 g m⁻³ day⁻¹, demonstrating industrial-scale potential. Characterization revealed mesoporous, defect-rich nanoparticles with superior phosphate adsorption capacity across wide pH ranges. Density functional theory calculations revealed that Cr sites enhance binding affinity, with adsorption energies increasing at higher pH due to the predominance of divalent and trivalent phosphate species. The mechanism involves electrostatic attraction and ligand exchange, where phosphate displaces water molecules coordinated to the metal centers. The MOF maintained stability in real eutrophic water samples, outperforming many conventional adsorbents. Very recently, Yeganeh et al., 2025 present a sustainable synthesis of GO/MOF nanocomposites using waste-derived materials [59]. Zinc ions were recovered from spent Zn-C batteries, while terephthalic acid was obtained from PET plastic waste bottles through chemical treatment. The waste-originated MOF was synthesized by combining these recovered precursors under optimized conditions. Subsequently, graphene oxide was incorporated to enhance photocatalytic properties. The resulting GO/MOF composite demonstrated excellent performance in degrading organophosphorus pesticides (chlorpyrifos and profenofos) under visible light, achieving high removal efficiency at optimal conditions (pH 5, 0.6 g/L catalyst dose, 60 min irradiation). The synthesis method represents a circular economy approach, transforming two problematic waste streams into a valuable photocatalyst. The composite maintained high stability through multiple reuse cycles, confirming the robustness of both the synthesis method and resulting material. Under visible light, the composite generates electron–hole pairs, with electrons reducing oxygen to superoxide radicals and holes oxidizing water to hydroxyl radicals. These reactive oxygen species degrade organophosphorus pesticides via oxidative cleavage of P-O and C-S bonds. The MOF’s porous structure facilitates pollutant adsorption, while graphene oxide improves charge separation, leading to efficient degradation and excellent recyclability. Song et al., 2021 address the green synthesis of Ni-MOF nanocrystals using electroplating sludge (EPS) and PET waste as dual precursors [80]. The method successfully converts problematic industrial wastes into functional MOFs while tolerating impurities like Fe³⁺ and Cu²⁺ coexisting with Ni²⁺ ions from EPS.

The synthesized Ni-MOF nanocrystals demonstrate exceptional photocatalytic performance for CO₂ reduction, achieving: (1) High CO production rate (9.68 × 10³ μmol h⁻¹ g⁻¹), (2) Outstanding selectivity (96.7% CO over H₂), and (3) Superior quantum efficiency (1.36% at 420 nm) compared to similar systems. Visible light excitation generates electrons that migrate to Ni²⁺ nodes, reducing adsorbed CO₂ through a proton-coupled electron transfer pathway. The reaction proceeds via CO₂•⁻ and formate intermediates, ultimately yielding CO with 96.7% selectivity. Fe³⁺/Cu²⁺ impurities from the sludge optimize the Ni sites’ electronic structure, suppressing H₂ evolution and stabilizing key intermediates. The MOF’s high surface area and defect-rich framework enhance charge separation, contributing to its superior activity (9.68 × 10³ μmol h⁻¹ g⁻¹ CO) and stability.

3.7. General Considerations on the Quality of PET-Derived MOFs

In general, metal–organic frameworks synthesized from PET waste demonstrate comparable structural integrity to those prepared from commercial terephthalic acid, though with distinct differences in crystallinity, porosity, and functional performance. Recent studies reveal that PET-derived MOFs like MIL-53(Al) exhibit nearly identical XRD patterns to commercial counterparts when optimized, confirming their structural similarity. However, impurities from incomplete PET depolymerization can introduce minor defects or secondary phases, such as the observed AlOOH byproduct in MIL-53(Al) synthesis [72]. In contrast, commercial TPA-derived MOFs consistently achieve higher phase purity due to standardized linker quality, as demonstrated by Mn-TPA-MOF’s sharper XRD peaks and uniform morphology compared to its PET-derived equivalent [70]. Advanced purification techniques like reactive crystallization have narrowed this gap, enabling PET-derived UiO-66 with crystallinity matching commercial benchmarks [81]. The porosity characteristics of these MOFs reveal significant variations. PET-derived versions typically show lower Brunauer-Emmett-Teller (BET) surface areas due to residual oligomers; for instance, MIL-53(Al) from PET displayed only 0.45 m²/g versus ~1000 m²/g for commercial samples [72]. This limitation stems from challenges in completely removing PET additives during depolymerization. Nevertheless, some PET-MOFs develop advantageous hierarchical porosity, as seen in defective MIL-88A(Fe) with 0.6 nm micropores and 1.95 nm mesopores that enhance mass transfer [82]. Commercial TPA-MOFs maintain superior consistency in pore structure, reflected in their higher adsorption capacities—Mn-TPA-MOF adsorbed 15.92 mg/g tetracycline versus 13.51 mg/g for PET-derived Mn-MOF [70]. However, the intentional defect engineering possible in PET-MOFs often compensates through additional active sites, as evidenced by Fe-MOF@PANI’s exceptional lead adsorption (258.59 mg/g) attributed to unsaturated metal centers [60]. Functional performance comparisons highlight context-dependent advantages. In photocatalytic applications, PET-derived GO-W-MOF achieved 87.5% methylene blue degradation, rivaling commercial catalysts [67]. The defective structures of PET-MOFs prove particularly effective for targeted applications; D-MIL-88A removed 93.4% methylmercury due to tailored pore chemistry [82]. Conversely, commercial TPA-MOFs exhibit better thermal stability, with Cu-Ni-C MOF maintaining 766 F/g capacitance over multiple cycles compared to PET-derived variants [69]. Synthetic methodologies further differentiate these materials. PET-MOFs often employ greener routes like solvent-free microwave synthesis (MagMOF) or room-temperature preparation (MIL-88B(Fe)), significantly reducing environmental impact [63,64]. Commercial TPA-MOFs rely on conventional solvothermal methods that ensure reproducibility but require higher energy inputs. Emerging PET depolymerization techniques, such as ball-milling and phase-transfer catalysis, are addressing purity challenges while maintaining sustainability [68]. The economic and environmental implications favor PET-derived MOFs, which transform waste into high-value materials while avoiding petroleum-based TPA. Life-cycle analyses indicate PET-MOFs can reduce carbon footprints by 30–40% compared to conventional synthesis [75].

4. Application for Water Treatment

The global water pollution crisis has reached unprecedented levels, with approximately 80% of wastewater discharged untreated into ecosystems worldwide, contaminating vital water resources with complex mixtures of industrial dyes, pharmaceutical residues, heavy metals, and emerging organic pollutants [83]. Conventional water treatment systems struggle to address these persistent contaminants due to limitations in removal efficiency, operational costs, and secondary pollution risks [83]. This challenge has driven the development of advanced adsorption technologies, particularly MOFs, which offer exceptional surface areas and tunable pore architectures for targeted contaminant removal. Recent innovations have further enhanced the sustainability of MOF technology by utilizing waste PET bottles as feedstock, transforming environmental liabilities into high-performance water treatment materials. PET-derived MOFs leverage recovered terephthalic acid as organic linkers, eliminating the need for hazardous synthesis chemicals while maintaining superior adsorption capacities.

4.1. Heavy Metal Removal

The growing threat of heavy metal contamination in water resources represents one of the most pressing environmental challenges of our time. Metals like arsenic, lead, and mercury persist indefinitely in ecosystems and accumulate in biological tissues, causing severe health impacts even at trace concentrations [84].

Table 5. Adsorptive performance and operational properties of MOF-derived PET waste for heavy metal removal.

Heavy Metal	MOF Type	Source of Metal Node	Adsorption Capacity (mg/g)	Optimal pH	Removal Efficiency	Regeneration Cycles	Key Mechanism	Reference
Arsenic (As)	La-MOF	Lanthanum salts	114.28	4–10	>90% (500→10 μg/L)	4	Ligand exchange, oxophilicity	[87]
Uranium (U)	Ca-BDC	Marble waste	829.18	5	98–99%	5	Monolayer chemisorption	[90]
Thorium (Th)	Ca-BDC	Marble waste	273.16	5	98–99%	5	Monolayer chemisorption	[90]
Copper (Cu)	Ca-BDC	Calcium salts	204.2	5–7	>95%	4	Chemical interaction, RSM-optimized	[91]
Arsenate (AsO43−)	Sn(II)-MOF	Tin salts	90.90	3–7	>99%	5	Electrostatic attraction	[92]

presents a summary of various MOF-derived waste PET used for the adsorption of heavy metals from aqueous solutions. It highlights MOF types, metal sources, adsorption capacities, pH ranges, removal efficiencies, regeneration capabilities, and the key adsorption mechanisms involved, providing valuable insights into their environmental remediation performance. Arsenic exposure alone affects approximately 200 million people worldwide through contaminated groundwater, leading to increased risks of cancers, cardiovascular diseases, and developmental disorders [85]. Conventional remediation methods such as coagulation, ion exchange, and activated carbon filtration face significant limitations, including poor selectivity, sludge generation, and high operational costs [86]. In this context, metal–organic frameworks derived from recycled polyethylene terephthalatebottles have emerged as a transformative solution that simultaneously addresses plastic waste accumulation and water pollution challenges through innovative materials science. Recent advances demonstrate that PET-derived MOFs outperform conventional adsorbents in both removal capacity and operational efficiency. Lanthanum-based MOFs synthesized from waste bottles achieve exceptional arsenate adsorption capacities of 114.28 mg/g through ligand exchange mechanisms that exploit lanthanum’s strong oxophilicity [87]. These materials consistently reduce arsenic concentrations from 500 μg/L to below the WHO guideline of 10 μg/L in column tests, maintaining over 90% efficiency through four regeneration cycles. Comparative studies reveal significant advantages over mesoporous alumina, which shows lower capacity (39.06 mg/g), narrower pH tolerance (3.9–6.6 vs. 4–10), and slower kinetics (720 min vs. minutes for MOFs) despite having higher surface area (~200 m²/g vs. 61.8 m²/g) (Han et al., 2013 [80]). This counterintuitive finding highlights how the strategic selection of metal centers in MOFs can outweigh the importance of pure surface area in adsorption performance. The superiority of PET-derived MOFs extends to comparisons with activated carbon systems. While iron-impregnated activated carbons can achieve capacities up to 204.2 mg/g under optimal conditions, most conventional carbons show much lower performance (1–60 mg/g) [88]. PET-MOFs maintain consistent effectiveness across pH 4–10, unlike activated carbons that require acidic conditions for optimal performance. Both material types follow pseudo-second-order kinetics, but MOFs achieve equilibrium orders of magnitude faster (minutes vs. hours) while demonstrating better regenerability (<10% capacity loss after 4 cycles) and lower ecological impact (<2.5% Daphnia magna mortality) [88]. The circular economy benefits of PET-derived MOFs further enhance their environmental value. The conversion of waste bottles into functional adsorbents addresses the global plastic crisis, where over 400 million tons of PET waste are generated annually [89]. Synthesis temperatures of 200–220 °C for MOFs compare favorably with the 600–800 °C required for activated carbon production, reducing both energy costs and carbon footprint. This dual benefit of waste valorization and water treatment creates a sustainable materials lifecycle that aligns with global sustainability goals. Beyond arsenic removal, PET-derived MOFs show exceptional performance for other toxic metals. Calcium-terephthalate frameworks synthesized from PET and marble waste achieve remarkable uranium (829.18 mg/g) and thorium (273.16 mg/g) removal capacities, with 98–99% elimination in just 10–15 min at optimal pH 5 [90]. These materials maintain effectiveness through five regeneration cycles while demonstrating minimal environmental impact, making them practical solutions for radioactive contamination. The Box–Behnken optimized synthesis ensures reproducible performance, while Langmuir isotherm modeling confirms monolayer chemisorption as the dominant mechanism. For copper removal, response surface methodology has optimized calcium-terephthalate MOF performance, with pseudo-second-order kinetics indicating chemical interaction mechanisms [91]. Similarly, tin(II)-MOFs derived from PET bottles demonstrate exceptional arsenate removal (90.90 mg/g) with >99% efficiency in both synthetic and real water samples [92]. These materials maintain high selectivity even in the presence of competing anions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻) and retain 78–86% capacity after five regeneration cycles. The positive surface charge of Sn(II)-MOFs facilitates electrostatic attraction of arsenate anions at pH 3–7, while Langmuir isotherm fitting confirms monolayer coverage.

4.2. Pharmaceutical Contaminants

The increasing presence of pharmaceutical contaminants in global water systems has escalated into a critical public health emergency, with antibiotic pollution emerging as a particularly severe threat. According to the landmark O’Neill report, antimicrobial resistance fueled by pharmaceutical pollution is projected to cause 10 million deaths annually by 2050 [93]. This crisis stems from the widespread use and improper disposal of antibiotics, with approximately 5500 tons consumed yearly in the US and Europe alone—of which 50–80% enter aquatic ecosystems unmetabolized [93]. These persistent compounds not only drive the development of resistant bacterial strains but also disrupt aquatic ecology, creating an urgent need for advanced remediation technologies that can effectively address this complex challenge. Recent innovations in materials science have demonstrated that metal–organic frameworks derived from PET waste show exceptional promise for pharmaceutical removal through two complementary mechanisms: adsorption and catalytic degradation. For adsorption applications, magnetic α-Fe/Fe@C composites derived from PET waste achieve unprecedented tetracycline hydrochloride uptake (671.14 mg/g) through synergistic π-π stacking and cation-π bonding, with superparamagnetic properties enabling efficient recovery [94]. Even more impressive are defective MIL-68(Al) frameworks synthesized from plastic bottles, which show record nitroimidazole antibiotic removal by capturing 555.6 mg/g with 97% elimination achieved in just 10 s [95]. These ultrafast kinetics (2.84 g mg⁻¹ min⁻¹) result from engineered defects that create additional pores (~1.95 nm) and active sites while significantly enhancing mass transfer. Catalytic approaches using PET-derived MOFs demonstrate equally remarkable capabilities. Carbonized Co-MOF activates peroxymonosulfate to degrade 90.94% tetracycline within 20 min through non-radical pathways that overcome the pH limitations of conventional oxidation methods [96]. This system maintains effectiveness across a broad pH range (3–9), contrasting sharply with traditional methods that operate within narrow pH windows. Perhaps most striking is the advancement represented by PET-derived MOF-5 encapsulated in alginate hydrogel, which achieves a phenomenal tetracycline adsorption capacity of 2325.55 mg/g while solving practical handling challenges associated with powdered adsorbents [66]. This composite maintains 85.51% regeneration efficiency after five cycles through optimized hydrogen bonding and ionic interactions, as confirmed by XPS and FTIR analysis. The environmental advantages of these PET-MOF systems extend far beyond their technical performance metrics. By converting plastic waste into high-value water treatment materials, they create a circular economy solution that simultaneously addresses two pressing environmental problems. Field-relevant testing has shown these materials maintain effectiveness through multiple regeneration cycles (4–5 cycles with <30% efficiency loss) while demonstrating minimal ecological impact, addressing key concerns for practical implementation [95]. Innovative approaches continue to emerge in this field. Cho et al. (2021) developed a method to directly upcycle PET waste bottles into α-Fe₂O₃-incorporated MIL-53(Al), which is subsequently annealed to form Al₂O₃/Fe₃O₄-encapsulated magnetic carbon composites for pharmaceutical pollutant removal [97]. This process leverages simultaneous PET depolymerization and MOF synthesis at 220 °C under self-generated pressure [97], demonstrating exceptional removal efficiency for non-steroidal anti-inflammatory drugs (NSAIDs): ibuprofen (96.31%), naproxen (87.83%), ketoprofen (90.07%), and diclofenac (66.84%). Using response surface methodology, diclofenac adsorption was optimized to 92.94% at pH 5.0 with 1.21 g/L adsorbent over 15 h, closely matching theoretical predictions (93.15%), with the material retaining >85% efficiency through multiple cycles. Their neutral aqueous system achieves 95.6% terephthalic acid yield at 200 °C within 60 min—a significant improvement over conventional methods requiring corrosive solvents. The resulting PET-derived MOFs demonstrate exceptional properties: MIL-101(Cr) shows remarkable water adsorption capacity (1327.3 mg g⁻¹), while MIL-53(Al,Fe) removes >90% tetracycline within 60 min via photocatalysis, outperforming petroleum-based MOF catalysts. Further expanding the applications of waste-derived materials, Chen et al. (2023) developed a method to functionalize waste polyester into Cr-MOF for synergistic interfacial solar evaporation and organic pollutant degradation [82].

4.3. Dye Removal

The textile industry’s staggering annual discharge of approximately 200,000 tons of synthetic dyes has created a global water pollution crisis of unprecedented scale [98]. Conventional wastewater treatment systems fail to adequately address this challenge, removing only 50–70% of these persistent pollutants, leaving behind significant ecological and public health risks [98]. The complex molecular structures of synthetic dyes, designed for durability in fabrics, render them resistant to natural degradation processes, with concentrations as low as 1 mg/L capable of disrupting aquatic ecosystems by blocking sunlight penetration and impairing photosynthesis [99]. More alarmingly, many commercial dyes contain toxic aromatic amines and heavy metals that bioaccumulate in food chains, with certain azo dyes decomposing into known carcinogens like benzidine and naphthylamine, linked to bladder cancer, liver damage, and severe allergic reactions in humans [99]. Traditional treatment methods, including biological degradation, coagulation-flocculation, and chemical oxidation, face fundamental limitations in addressing this challenge. Biological systems struggle with the non-biodegradable nature of many synthetic dyes, while coagulation processes generate excessive sludge requiring costly disposal, and advanced oxidation methods risk creating toxic byproducts [99].

Table 6. Removal of synthetic dyes using MOF-Based materials: Adsorption capacities, regeneration, and mechanisms.

MOF Type	Dye Type	Adsorption Capacity (mg/g)	Regeneration Efficiency	Mechanism	Reference
MIL-101(Cr)	Reactive Red 2	662.87	>90%	Electrostatic, π-π stacking	[100]
MIL-101(Cr)	Reactive Blue 19	863.67	>90%	Electrostatic, π-π stacking	[100]
MIL-101(Cr)	Acid Blue 92	2176	>85%	Electrostatic interactions	[101]
Ni/Cu-MOF@BiOI	Methylene Blue	99% degradation	High	Photocatalytic degradation	[67]
Ca-TPA-MOF	Alizarin Red S	979.0	High	Chemisorption	[102]
Cu-Zn-MOF	Multiple Dyes	>95% degradation	-	Catalytic degradation	[103]

provides an overview of different MOF-based materials applied for dye removal from aqueous solutions. It outlines MOF types, target dye types, adsorption capacities, degradation efficiencies, regeneration performance, and underlying removal mechanisms, demonstrating their effectiveness and versatility in wastewater treatment applications. The pioneering work of Cheng et al. (2025) exemplifies this dual-benefit approach through their development of MIL-101(Cr) using terephthalic acid derived from waste PET [100]. This innovative synthesis method eliminates the need for hazardous hydrofluoric acid traditionally required in MOF production, while achieving remarkable adsorption capacities of 662.87 mg g⁻¹ for reactive red 2 and 863.67 mg g⁻¹ for reactive blue 19. Detailed characterization through X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed a sophisticated adsorption mechanism combining electrostatic interactions at chromium sites, hydrogen bonding with oxygen functional groups, and π-π stacking between aromatic systems [100]. The material maintained over 90% regeneration efficiency through multiple cycles using sodium carbonate as eluent, demonstrating both economic viability and environmental sustainability. Recent advancements have pushed the boundaries of dye removal performance even further. Keshta et al. (2024) developed a MIL-101(Cr) variant achieving unprecedented adsorption capacity (2176 mg/g for acid blue 92) through precise engineering of mesoporous structures optimized for electrostatic interactions [101]. Meanwhile, Karamat et al. (2024) adopted an alternative photocatalytic approach, creating Ni/Cu-MOF@BiOI heterostructures from PET waste that demonstrated 99% degradation of methylene blue under natural sunlight—a significant breakthrough in overcoming the energy intensity limitations of conventional UV-based systems [67]. These developments highlight the versatility of MOF-based solutions across different dye removal mechanisms. The field has also seen significant progress in optimizing MOF performance for specific dye removal applications. Farahani and Zolgharnein, (2022)employed advanced statistical modeling (Box–Behnken and Taguchi designs) to optimize a calcium-terephthalate MOF derived from PET waste for alizarin red S removal, achieving a maximum capacity of 979.0 mg g⁻¹ [102]. Their thermodynamic analysis confirmed the spontaneous, exothermic nature of the adsorption process (ΔH° = −13 kJ mol⁻¹, ΔG° = −2.6 to −1.5 kJ mol⁻¹), providing fundamental insights into the chemisorption mechanism. In parallel, Yarahmadi et al. (2023) developed a bimetallic Cu-Zn-MOF catalyst from PET-derived terephthalic acid that achieved >95% degradation of multiple dyes within 6–12 min, with impressive rate constants of 0.30–0.58 min⁻¹, demonstrating the potential for rapid, catalytic treatment systems [103]. Despite these remarkable advances, challenges remain in translating laboratory successes to industrial-scale applications. The economic viability of large-scale MOF production continues to be a significant consideration, with current synthesis costs potentially limiting widespread adoption.

4.4. Pesticides

The widespread use of persistent pesticides in modern agriculture has created a global water contamination crisis, with recent studies detecting these toxic compounds in 90% of monitored waterways worldwide [104,105]. Chlorpyrifos and atrazine represent particularly concerning contaminants due to their exceptional environmental persistence, exhibiting aquatic half-lives exceeding 100 days and demonstrating resistance to conventional water treatment methods [106]. This persistence stems from their complex molecular structures and low biodegradability, which challenge traditional removal technologies through membrane fouling and poor selectivity in complex agricultural runoff containing mixed contaminants. The environmental and health impacts of these pesticides are severe, with demonstrated effects ranging from endocrine disruption in aquatic organisms to neurotoxicity in humans, driving urgent demand for advanced remediation solutions [106]. Recent technological advances have demonstrated the remarkable potential of MOF-derived waste PET through two primary application approaches: membrane filtration systems and direct adsorption technologies. In membrane applications, Prabhakar et al. (2025) achieved a breakthrough by developing MIL-53(Al)/PMMA nanofiber composite membranes using terephthalic acid recovered from PET waste [107]. These membranes demonstrated exceptional performance, rejecting 86.8% of chlorpyrifos and 60.48% of atrazine while maintaining high water flux (18.68 Lm⁻² h⁻¹). The membranes’ outstanding antifouling properties (95.45% flux recovery ratio) proved particularly valuable for treating real agricultural runoff, where they maintained over 80% pesticide rejection efficiency in field tests containing high dissolved organic matter (10–15 mg/L TOC) [108]. This performance stems from the precisely engineered pore structures (0.8–1.2 nm) that selectively exclude larger organic molecules while allowing water permeation, combined with exposed aluminum sites that provide additional coordination bonding with pesticide molecules. An alternative approach developed by Semyonov et al. (2021) bypasses PET depolymerization entirely by growing UiO-66 MOF crystals directly on waste PET bottle substrates [109]. This PET@UiO-66 hybrid material demonstrates superior imidacloprid adsorption capacity compared to conventional sorbents, while its engineered form factor solves practical implementation challenges [109]. The composite’s enhanced permeability (100× greater than powdered UiO-66) enables effective use in fixed-bed columns, overcoming a major limitation of MOF powders in flow-through systems. Importantly, the material’s structural integrity prevents microplastic leaching—a critical consideration for water treatment applications. This technology exemplifies the dual environmental benefits achievable through waste valorization, simultaneously addressing plastic pollution and water contamination while simplifying manufacturing by eliminating PET breakdown steps. The environmental advantages of PET-derived MOFs extend well beyond their technical performance metrics. Life cycle assessments reveal these materials can reduce the carbon footprint of water treatment systems by 30–40% compared to conventional adsorbents, primarily through lower synthesis temperatures (200–250 °C vs. 600–800 °C for activated carbon) and avoided plastic waste disposal impacts [109]. The circular economy potential is further enhanced by recent work demonstrating the feasibility of using multiple waste streams as MOF precursors. Yeganeh et al. (2025) developed an innovative photocatalytic system using zinc recovered from spent batteries and terephthalic acid from PET bottles to create a graphene oxide-modified MOF (GO-W-MOF) that efficiently degrades organophosphates like chlorpyrifos under visible light [59]. This approach achieved complete pesticide degradation within 60 min while demonstrating excellent recyclability, representing a significant advance in sustainable catalyst design. The removal mechanisms of PET-derived MOFs for pesticides involve multiple synergistic interactions that contribute to their exceptional performance. X-ray diffraction and spectroscopic analyses reveal that beyond the primary π-π stacking between terephthalate linkers and pesticide aromatic rings, exposed metal sites (Al³⁺, Zr⁴⁺, Zn²⁺) provide additional coordination bonds with pesticide functional groups [62,92]. The precisely tuned pore sizes (0.8–1.2 nm) enable molecular sieving effects that exclude larger organic matter responsible for membrane fouling, while surface charges can be optimized for electrostatic attraction of target pesticides. These multifunctional interactions collectively provide both high capacity and selectivity that surpass conventional adsorbents.

4.5. Phosphate Pollution

The increasing occurrence of phosphate pollution in water systems, primarily from agricultural runoff and wastewater discharge, has led to severe environmental consequences such as eutrophication and algal blooms. Recent advancements in sustainable materials science have demonstrated that MOFs derived from waste sources offer an effective solution for phosphate removal while addressing plastic waste accumulation. Boukayouht et al. (2024) developed an innovative CrNiFe-MOF using waste polyethylene terephthalate (PET) converted to disodium terephthalate and stainless steel as a source of metal ions [79]. This trimetallic MOF, synthesized through room-temperature coprecipitation, exhibited exceptional phosphate adsorption capacity (126 mg/g) across a broad pH range (2–10), with density functional theory (DFT) calculations confirming preferential binding of HPO₄²⁻/PO₄³⁻ at chromium sites. The material demonstrated industrial-scale productivity (5760 g m⁻³ day⁻¹) while maintaining 85% adsorption capacity after five regeneration cycles, showcasing its potential for large-scale water remediation applications. Addressing practical implementation challenges, Moumen et al. (2024) incorporated PET-derived Fe-MOF into composite chips, significantly improving material recoverability while maintaining high phosphate adsorption capacity (72.16 mg/g) [77]. Systematic evaluation under varying environmental conditions (pH, temperature, concentration) confirmed robust performance across different water treatment scenarios. This approach overcomes the limitations of powdered MOFs in real-world applications while maintaining the sustainability benefits of waste-derived materials. Ghosh and Das, (2021) presented another sustainable approach by synthesizing Sn(II)-MOF using PET-derived terephthalic acid [92]. The material demonstrated excellent phosphate removal (126.58 mg/g capacity, >88% efficiency) through electrostatic interactions between the positively charged MOF and anionic phosphate species, with optimal performance at pH 3–7 [92]. Remarkably, the adsorbent showed minimal interference from common coexisting anions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻) and maintained 76–81% efficiency through five regeneration cycles, highlighting its selectivity and reusability.

5. Conclusions

The global challenges of plastic pollution and water contamination demand innovative, sustainable solutions that align with circular economy principles. This review has systematically explored the transformation of polyethylene terephthalate (PET) waste into high-performance metal–organic frameworks (MOFs) for advanced water treatment applications, demonstrating how waste valorization can address both environmental crises simultaneously. By critically analyzing PET depolymerization techniques, MOF synthesis methodologies, and pollutant removal performance, we highlight the immense potential of this approach in sustainable materials science and environmental remediation. PET, one of the most widely used plastics, poses a significant environmental burden due to its slow degradation and accumulation in landfills and marine ecosystems. Conventional recycling methods, such as mechanical and energetic recycling, often result in downcycled products or hazardous emissions. In contrast, chemical recycling—particularly hydrolysis, glycolysis, and aminolysis—enables the recovery of high-purity monomers like terephthalic acid (TPA) and bis(2-hydroxyethyl) terephthalate (BHET), which serve as ideal organic linkers for MOF synthesis. The conversion of PET waste into MOFs not only mitigates plastic pollution but also reduces reliance on petroleum-derived precursors, lowering the carbon footprint of MOF production. Recent advances in depolymerization techniques, such as microwave-assisted hydrolysis, phase-transfer catalysis, and mechanochemical methods, have improved monomer recovery efficiency while minimizing energy consumption and hazardous solvent use. These innovations ensure that PET-derived MOFs are both environmentally and economically viable alternatives to conventional adsorbents. MOFs synthesized from PET waste can be produced via direct (one-pot) or indirect (two-step) methods. The direct method integrates PET depolymerization and MOF formation in a single step, offering simplicity and reduced processing time. However, it often yields MOFs with lower crystallinity and surface area due to residual impurities. In contrast, the indirect methodwhere PET is first converted to purified TPA or BHET before MOF assemblyproduces materials with superior structural integrity, porosity, and adsorption performance. Emerging unconventional synthesis techniques, including mechanochemical, sonochemical, and electrochemical methods, further enhance the sustainability of MOF production. These approaches minimize solvent use, reduce energy requirements, and enable scalable manufacturing. For instance, mechanochemical “grind-and-bake” methods have successfully produced UiO-66(Zr) from BHET without organic solvents, while electrochemical synthesis eliminates corrosive byproducts, aligning with green chemistry principles. PET-derived MOFs exhibit structural integrity comparable to those made from commercial terephthalic acid (TPA), though differences exist in crystallinity, porosity, and performance. While optimized PET-MOFs like MIL-53(Al) show similar XRD patterns to commercial versions, impurities from incomplete depolymerization can introduce defects or secondary phases, including AlOOH. Commercial TPA-MOFs generally achieve higher purity and sharper crystallinity, but advanced purification methods like reactive crystallization have improved PET-MOF quality, as seen with UiO-66. Porosity varies significantly, with PET-MOFs often displaying lower BET surface areas due to residual oligomers. However, some develop hierarchical porosity, enhancing mass transfer. Commercial MOFs maintain more consistent pore structures and higher adsorption capacities, though PET-MOFs can compensate through defect-engineered active sites, improving performance in applications like heavy metal adsorption

ET-derived MOFs have demonstrated remarkable efficacy in adsorbing a wide range of water contaminants, including heavy metals, pharmaceuticals, dyes, pesticides, and phosphates. Their tunable porosity, high surface area, and functionalizable metal sites enable selective and efficient pollutant capture through mechanisms such as electrostatic interactions, π-π stacking, hydrogen bonding, and chemisorption. The integration of waste PET into MOF production offers significant sustainability benefits, primarily by reducing the carbon footprint due to lower synthesis temperatures (200–250 °C for MOFs compared to 600–800 °C for activated carbon), thereby decreasing energy consumption. This approach also excels in waste valorization, diverting PET from landfills and oceans and transforming it into high-value materials for water purification. Furthermore, PET-derived MOFs demonstrate cost-effectiveness, matching or surpassing the performance of commercial adsorbents while simultaneously lowering raw material costs. Despite these advancements, several challenges persist, including the need for optimizing industrial-scale production for cost and energy efficiency (scalability), managing impurities like residual additives in PET waste, which can lead to defects, and validating the long-term stability, reusability, and mechanical robustness of these MOFs for real-world water treatment applications.