Search Results (1,203)

Accelerated industrialization and surging energy demands have led to continuously rising atmospheric CO₂ concentrations. Developing sustainable methods to reduce atmospheric CO₂ levels is crucial for achieving carbon neutrality. Concurrently, the rapid development of new energy vehicles has driven a significant increase in demand for lithium-ion batteries (LIBs), which are now approaching an end-of-life peak. Efficient recycling of valuable metals from spent LIBs represents a critical challenge. This study employs conventional hydrometallurgical processing to recover valuable metals from spent LIBs. Subsequently, Ni-doped Co₃O₄ (Ni:Co₃O₄) supported on the natural mineral attapulgite (ATP) was synthesized via a sol–gel method. The incorporation of a small amount of Ni into the Co₃O₄ lattice generates oxygen vacancies, inducing a localized surface plasmon resonance (LSPR) effect, which significantly enhances charge carrier transport and separation efficiency. During the photocatalytic reduction of CO₂, the primary product CO generated by the Ni:Co₃O₄/ATP composite achieved a high production rate of 30.1 μmol·g⁻¹·h⁻¹. Furthermore, the composite maintains robust catalytic activity even after five consecutive reaction cycles. Full article

The objective of this work is to evaluate how spent catalyst from fluid catalytic cracking (SCFCC) affects the physical, mechanical and durability properties of fly ash (FA) and blast furnace slag (BFS)-based alkali-activated materials (AAMs). Recycling of SCFCC by integrating it in a AAM matrix offers several advantages: valorization of the material, reducing its disposal in landfills and the landfill cost, and minimizing the environmental impact. Mineralogical, physical and mechanical characterization were carried out. The durability of the specimens was studied by performing acid attack and thermal stability tests. Mass variation, compressive strength and porosity parameters were determined to assess the durability. BFS- and FA-based AAMs have a different chemical composition, which contribute to variations in microstructure and physical and mechanical properties. Acid neutralization capacity was also determined to analyse the acid attack results. Porosity, including the pore size distribution, and the acid neutralization capacity are crucial in explaining the resistance of the AAMs to sulfuric acid attack and thermal degradation. Herein, a novel route was explored, the use of SCFCC to enhance the durability of AAMs under harsh operating conditions since results show that the compositions containing SCFCC showed lower strength decay due to the lower macroporosity proportions in these compositions. Full article

Plastic waste accumulation is one of the most pressing environmental challenges of the 21st century, owing to the widespread use of synthetic polymers and the limitations of conventional recycling methods. Among available strategies, chemical upcycling via depolymerization has emerged as a promising circular approach that converts plastic waste back into valuable monomers and chemical feedstocks. This article provides an in-depth narrative review of recent progress in the upcycling of major plastic types such as PET, PU, PS, and engineering plastics through thermal, chemical, catalytic, biological, and mechanochemical depolymerization methods. Each method is critically assessed in terms of efficiency, scalability, energy input, and environmental impact. Special attention is given to innovative catalyst systems, such as microsized MgO/SiO₂ and Co/CaO composites, and emerging enzymatic systems like engineered PETases and whole-cell biocatalysts that enable low-temperature, selective depolymerization. Furthermore, the conversion pathways of depolymerized products into high-purity monomers such as BHET, TPA, vanillin, and bisphenols are discussed with supporting case studies. The review also examines life cycle assessment (LCA) data, techno-economic analyses, and policy frameworks supporting the adoption of depolymerization-based recycling systems. Collectively, this work outlines the technical viability and sustainability benefits of depolymerization as a core pillar of plastic circularity and monomer recovery, offering a path forward for high-value material recirculation and waste minimization. Full article

This study investigated the effect of KOH activation on biochar, with a focus on how porosity and potassium content influence microwave-assisted catalytic biodiesel production, using experimental design approaches. Activated biochar was synthesized from oat hull waste through KOH activation, followed by pyrolysis under controlled conditions. The biochar was characterized through chemical, morphological, and physical analyses, and its catalytic performance in converting used waste cooking oil (WCO) into biodiesel was evaluated using methanol as the acyl acceptor and microwave irradiation to optimize the reaction via experimental design. Results revealed that increasing the KOH/biomass ratio significantly enhanced the specific surface area (SSA) of the catalyst, achieving a maximum SSA of 637.28 m²/g under optimal pyrolysis conditions: 600 °C for 3 h with a KOH/biomass ratio of 2. A maximum fatty acid methyl ester (FAME) yield of 100% was achieved within 1 min of microwave-assisted reaction using an optimized catalyst dosage of 2.5%, a WCO/MeOH molar ratio of 1/12, and a reaction temperature of 150 °C, with the catalyst being successfully recycled across three cycles. An economic and energy evaluation estimated a catalyst production cost of USD 176.97/kg and a biodiesel production cost of USD 8.9/kg of FAMEs. This research provides a straightforward and cost-effective approach for biofuel production. Full article

This review surveys recent advances and emerging prospects in phase-transfer catalysis (PTC) for fuel desulfurization. In response to increasingly stringent environmental regulations, the removal of sulfur from transportation fuels has become imperative for curbing SO_x emissions. Conventional hydrodesulfurization (HDS) operates under severe temperature–pressure conditions and displays limited efficacy toward sterically hindered thiophenic compounds, motivating the exploration of non-hydrogen routes such as oxidative desulfurization (ODS). Within ODS, PTC offers distinctive benefits by shuttling reactants across immiscible phases, thereby enhancing reaction rates and selectivity. In particular, PTC enables efficient migration of organosulfur substrates from the hydrocarbon matrix into an aqueous phase where they are oxidized and subsequently extracted. The review first summarizes the deployment of classic PTC systems—quaternary ammonium salts, crown ethers, and related agents—in ODS operations and then delineates the underlying phase-transfer mechanisms, encompassing reaction-controlled, thermally triggered, photo-responsive, and pH-sensitive cycles. Attention is next directed to a new generation of catalysts, including quaternary-ammonium polyoxometalates, imidazolium-substituted polyoxometalates, and ionic-liquid-based hybrids. Their tailored architectures, catalytic performance, and mechanistic attributes are analyzed comprehensively. By incorporating multifunctional supports or rational structural modifications, these systems deliver superior desulfurization efficiency, product selectivity, and recyclability. Despite such progress, commercial deployment is hindered by the following outstanding issues: long-term catalyst durability, continuous-flow reactor design, and full life-cycle cost optimization. Future research should, therefore, focus on elucidating structure–performance relationships, translating batch protocols into robust continuous processes, and performing rigorous environmental and techno-economic assessments to accelerate the industrial adoption of PTC-enabled desulfurization. Full article

Metal–organic frameworks (MOFs), particularly ZIF-8, have emerged as promising materials due to their high porosity, tunability, and chemical stability. In this study, we report the synthesis of ZnFe₂O₃-doped ZIF-8 composites with 10 wt% loading via a solvothermal method to enhance their optical and photocatalytic performance. Structural analyses confirmed the successful incorporation of ZnFe₂O₃ without disrupting the ZIF-8 framework. Optical studies revealed enhanced absorption in the visible range, a narrowed bandgap (4.26 eV vs. 4.37 eV for pristine ZIF-8), and an increased extinction coefficient, indicating superior light-harvesting potential. The photocatalytic activity was evaluated by methylene blue (MB) degradation under visible light, where the 10 wt% ZnFe₂O₃-ZIF-8 composite achieved 90% degradation efficiency, outperforming pristine ZIF-8 (67.8%). The catalyst also demonstrated excellent recyclability over five cycles and a proposed degradation mechanism involving ·OH and ·O₂⁻ radical formation. These findings demonstrate the potential of highly doped ZnFe₂O₃@ZIF-8 composites for environmental remediation and photonic applications. Full article

Fenton oxidation can contribute to meeting effluent standards for COD in actual wastewater treatment plant effluents. However, Fenton oxidation is prone to produce iron sludge waste. The application of heterogeneous Fenton-like systems based on Fenton iron mud carbon in wastewater treatment plants is essential for Fenton iron mud reduction and recycling. In this study, a Fenton iron mud carbon catalyst/Ferrate salts/H₂O₂ (FSC/Fe(VI)/H₂O₂) system was developed to remove chemical oxygen demand (COD) from secondary effluents at the pilot scale. The results showed that the FSC/Fe(VI)/H₂O₂ system exhibited excellent COD removal performance with a removal rate of 57% under slightly neutral conditions in laboratory experiments. In addition, the effluent COD was stabilized below 40 mg·L⁻¹ for 65 days at the pilot scale. Fe(IV) and ¹O₂ were confirmed to be the main active species in the degradation process through electron paramagnetic resonance (EPR) and quenching experiments. C=O, O-C=O, N sites and Fe⁰ were responsible for the generation of Fe(IV) and ¹O₂ in the FSC/Fe(VI)/H₂O₂ system. Furthermore, the cost per ton of water treated by the pilot-scale FSC/Fe(VI)/H₂O₂ system was calculated to be only 0.6209 USD/t, further confirming the application potential of the FSC/Fe(VI)/H₂O₂ system. This study promotes the engineering application of heterogeneous Fenton-like systems for water treatment. Full article

Traditional covalently cross-linked solid-state electrolytes exhibit desirable mechanical durability but suffer from limited processability and recyclability due to their permanent network structures. Incorporating dynamic covalent bonds offers a promising solution to these challenges. In this study, we report a reprocessable and recyclable polymer electrolyte based on a dynamic ester bond network, synthesized from commercially available materials. Polyethylene glycol diglycidyl ether (PEGDE) and glutaric anhydride (GA) were cross-linked and cured in the presence of benzyl dimethylamine (BDMA), forming an ester-rich polymer backbone. Subsequently, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was introduced as a transesterification catalyst to facilitate network rearrangement. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was incorporated to establish efficient ion transport pathways. By tuning the cross-linking density and catalyst ratio, the electrolyte achieved an ionic conductivity of 1.89 × 10⁻⁵ S/cm at room temperature along with excellent reprocessability. Full article

The sludge produced by the Fenton process contains mixed-valence iron particulates (hereafter called Fenton wastes). Using a solvothermal method, we fabricated a new heterogeneous photo-Fenton catalyst using Fenton wastes and metal–organic frameworks (MOFs). Nanoporous metal carboxylate (MIL-88) MOF impregnated with Fenton waste was functionalized using 2,5-dihydroxyterephthalic acid (x-HO-MIL-88-C, x, concentration of the 2,5-dihydroxyterephthalic acid). The efficiency of x-HO-MIL-88-C was examined under visible light radiation using methylene blue (MB) as an index pollutant. We observed the best catalytic performance for MB degradation by 4-HO-MIL-88-C. In the photo-Fenton process, the simultaneous presence of singlet oxygen, superoxide, and hydroxyl radicals is confirmed by free radical quenching and electron spin resonance spectral data. These free radicals associate with holes in the non-selective degradation of MB. The 4-HO-MIL-88-C catalyst shows good stability and reusability, maintaining over 80% efficiency at the end of five consecutive cycles. This work opens up a new path for recycling Fenton wastes into usable products. Full article

To ensure the sustainable use of limited resources, it is essential to establish selective and efficient recycling technologies for platinum group metals (PGMs). This study focused on the selective precipitation-based separation of Pt(IV) from hydrochloric acid (HCl) solutions in the presence of various metal ions, using trans-1,4-bis(aminomethyl)cyclohexane (BACT) as a precipitating agent. By using BACT, we succeeded in the selective separation of Pt(IV) by precipitation from HCl solutions containing Pd(II) and Rh(III). Notably, selective and efficient recovery of Pt(IV) was accomplished across various HCl concentrations, with a small amount of BACT and within a short shaking time. To evaluate the practical applicability of the method, Pt(IV) was recovered and purified from the HCl leachate of spent automotive exhaust gas purification catalysts using BACT. As a result, a high Pt recovery of 95.6% and a high purity of 99.3% were achieved. Although Pt(IV) was recovered as a precipitate containing BACT, it was found that Pt black could be readily obtained by dissolving the precipitate in HCl solution followed by reduction with sodium borohydride. Detailed structural analysis of the Pt(IV)-containing precipitate revealed that it is an ionic crystal composed of [PtCl₆]²⁻ and protonated BACT. The selective formation of this ionic crystal in HCl solution, along with its stability under such conditions, is the key to the selective recovery of Pt(IV) using BACT. Full article

Rapid economic growth has led to an increase in the use of multilayer plastic packaging, which involves complex polymer compositions and hinders recycling. This study investigated the catalytic pyrolysis of plastic packaging waste in a 3000 cm³ semibatch reactor, aiming to optimize kerosene-like hydrocarbon production. The temperature (420–500 °C), N₂ flow rate (25–125 mL/min), and catalyst loading (5–20 wt.%) were examined individually and in combination with activated carbon and an Fe-doped dolomite (Fe/DM) catalyst. Central composite design (CCD) and response surface methodology (RSM) were used to identify the optimal conditions and synergistic effects. Pyrolysis product analysis involved simulation distillation gas chromatography (Sim-DGC), gas chromatography/mass spectrometry (GC/MS), and Fourier transform infrared (FT-IR) spectroscopy. The optimal conditions (440 °C, 50 mL/min N₂ flow, catalyst loading of 10 wt.% using a 5 wt.% Fe-doped dolomite-activated carbon 0.6:0.4 mass/molar ratio) yielded the highest pyrolysis oil (79.6 ± 0.35 wt.%) and kerosene-like fraction (22.3 ± 0.22 wt.%). The positive synergistic effect of Fe/DM and activated carbon (0.6:0.4) enhanced the catalytic activity, promoting long-chain polymer degradation into mid-range hydrocarbons, with secondary cracking yielding smaller hydrocarbons. The pore structure and acid sites of the catalyst improved the conversion of intermediate hydrocarbons into aliphatic compounds (C₅–C₁₅), increasing kerosene-like hydrocarbon production. Full article

As a renewable alternative to fossil fuels, the industrial production of biodiesel urgently requires the development of efficient and recyclable solid base catalysts. In this study, the physicochemical properties and catalytic performance differences between MgO/Na₂CO₃ and MgO/K₂CO₃ catalysts were systematically compared using soybean oil as the raw material. By regulating the calcination temperature (500–700 °C), alcohol-to-oil ratio (3:1–24:1), and metal carbonate loading (10–50%), combined with N₂ adsorption–desorption, CO₂-TPD, XRD, SEM-EDS, and cycling experiments, the regulatory mechanisms of the ionic radius differences between sodium and potassium on the catalyst structure and performance were revealed. The results showed that MgO/Na₂CO₃-600 °C achieved a FAME yield of 97.5% under optimal conditions, which was 1.7% higher than MgO/K₂CO₃-600 °C (95.8%); this was attributed to its higher specific surface area (148.6 m²/g vs. 126.3 m²/g), homogeneous mesoporous structure, and strong basic site density. In addition, the cycle stability of MgO/K₂CO₃ was significantly lower, retaining only 65.2% of the yield after five cycles, while that of MgO/Na₂CO₃ was 88.2%. This stability difference stems from the disparity in their solubility in the reaction system. K₂CO₃ has a higher solubility in methanol (3.25 g/100 g at 60 °C compared to 1.15 g/100 g for Na₂CO₃), which is also reflected in the ion leaching rate (27.7% for K⁺ versus 18.9% for Na⁺). This study confirms that Na⁺ incorporation into the MgO lattice can optimize the distribution of active sites. Although K⁺ surface enrichment can enhance structural stability, the higher leaching rate leads to a rapid decline in catalyst activity, providing a theoretical basis for balancing catalyst activity and durability in sustainable biodiesel production. Full article

The pore structure of a hydrotreating catalyst plays a pivotal role in hydrodemetallization (HDM) reactions. To effectively construct a meso-macroporous catalyst, we employed a CTAB-guided in situ TEOS hydrolysis approach to prepare silica-coated γ-Al₂O₃@SiO₂ composite supports. The silica shell incorporation significantly enhances specific surface area and reduces the metal–support interactions, thereby improving the dispersion of NiMo active components and boosting the deposition of metal impurity. Hence, the NiMo/Al₂O₃@SiO₂ catalyst (2.8 wt.% NiO, 4.3 wt.% MoO₃) exhibits much higher HDM activity than that of NiMo/Al₂O₃. This is evidenced by markedly higher demetallization rate constant (1.38 h⁻¹) and turnover frequency (0.56 h⁻¹) of the NiMo/Al₂O₃@SiO₂. The NiMo/Al₂O₃@SiO₂ catalyst further demonstrates excellent recyclability during sequential HDM reactions. This superior catalytic behavior stems from the hierarchical meso-macroporous structure, which simultaneously facilitates the deposition of metal impurities and mitigates deactivation by pore blockage. Full article

The sludge pyrolysis technology for biochar production delivers dual environmental benefits, addressing both sludge disposal challenges and enabling environmental remediation through the utilization of the resultant biochar. However, the complex multi-step procedures and low catalyst output in previous studies constrain the practical implementation of this technology. A facile sludge pyrolysis method was constructed to achieve the batch production of municipal sludge biochar (MSB) in this study. Compared to municipal sludge (MS), the resultant MSB showed a higher BET surface area, more well-developed pore channel architecture, and plentiful active sites for activating peroxymonosulfate (PMS). Under the optimized conditions (C_MSB = C_PMS = 0.2 g/L), 93.34% of Acid Red G (ARG, 20 mg/L) was degraded after 10 min, posing an excellent rate constant of 0.278 min⁻¹. Additionally, MSB demonstrated excellent broad pH adaptability, ion interference resistance, reusability, and recyclability for ARG elimination. It was primary Fe sites that excited PMS to generate ${\mathrm{O}}_2^{•-}$ and Fe-oxo species (Fe^IV=O) for ARG degradation. The reaction process exhibited minimal heavy metal leaching, indicating limited environmental risk. Therefore, the practical applicability of the sludge biochar production, coupled with its scalable manufacturing capacity and exceptional catalytic activity, collectively demonstrated that this study established a viable pyrolysis methodology for municipal sludge, offering critical insights for sludge disposal and resource reutilization. Full article

2,5-Furandicarboxylic acid (FDCA) is a bio-based platform chemical with high potential to replace terephthalic acid in polymer production, particularly for polyethylene furanoate (PEF), a biopolymer with superior thermal and barrier properties. This study investigates the selective oxidation of 5-hydroxymethylfurfural (HMF) into FDCA using nickel-based heterogeneous catalysts, aiming at a cost-effective and sustainable alternative to noble metal catalysts. A series of nickel oxide catalysts were synthesized and screened. The NiOx catalyst synthesized without thermal treatment via Route B showed the best performance, achieving a FDCA yield of 11.77%, selectivity of 27.41%, and concentration of 0.9 g/L under preliminary conditions. Reaction kinetics revealed that the controlled addition of NaClO enhanced FDCA yield by 2.28 times. Optimization using a 2³ factorial design identified the optimal conditions as 6% (w/v) catalyst concentration, 25 °C, and a NaClO:HMF molar ratio of 12:1, leading to 34.14% yield and 42.57% selectivity. The NiOx catalyst maintained its activity over five successive cycles, indicating good recyclability. Moreover, NiOx demonstrated catalytic activity with crude HMF derived from glucose dehydration, confirming its practical applicability. These results support the potential of nickel-based catalysts in sustainable FDCA production, contributing to the advancement of bio-based polymer synthesis. Full article