Sustain. Chem., Volume 6, Issue 4 (December 2025) – 19 articles

The old spectral displacement method can be suitably revitalized for a didactic experimental approach to fundamental concepts of supramolecular chemistry and to the study of complex equilibria in general. In particular, the case of the β-cyclodextrin/phenolphthalein/adamantane ternary system has been taken into account as a viable and impressive example due to the remarkable color changes that can be observed when performing the experiments. A new method for data regression analysis is proposed, with a smart trick able to overcome the mathematical difficulties arising whenever multiple equilibria must be considered. Hence, some aspects of the reliability of fitting procedures are discussed. Full article

Mercury (Hg²⁺) contamination in water systems poses a severe environmental and health hazard due to its high toxicity and bioaccumulation potential. In this study, a novel adsorbent was developed by sequentially modifying kaolin via acid–base treatment, titanium dioxide (TiO₂) incorporation, and 3-aminopropyltriethoxysilane (APTES) grafting. Batch adsorption experiments revealed that the fully modified kaolin (TiO₂-loaded and APTES grafted) exhibited the highest adsorption capacity (25.6 mg/g) compared to the acid–base-treated (5.8 mg/g) and TiO₂-loaded (17.7 mg/g) kaolin. Under optimal conditions (75 mg adsorbent dosage; 70 mg/L Hg²⁺; pH 5), the fully modified kaolin maintained its performance even in the presence of varying ionic strengths, natural organic matter, and competing metal ions. Adsorption kinetics followed a pseudo-second-order model, and the equilibrium data were well fitted by the Langmuir isotherm. Antibacterial activity assay revealed that the TiO₂-loaded kaolin effectively inhibited S. aureus (minimum inhibitory concentration = 2.5 mg/mL) and showed moderate activity against E. coli (BL21) (minimum inhibitory concentration = 5 mg/mL). However, antibacterial activity decreased after amine functionalization, indicating a compromise between enhancing adsorption capacity and preserving antibacterial functionality. This study presents a promising cost-efficient approach for the simultaneous removal of Hg²⁺ ions from water matrices and inhibiting bacterial growth, aligning with SDG 6 (Clean Water and Sanitation). Full article

Deep eutectic solvents (DES) were selected for the extraction of anthocyanins from red grape skins as an efficient and environmentally friendly solvent alternative to traditional mixtures based on methanol. In silico studies (COSMO-RS) were employed as screening tools to identify the most suitable options, significantly reducing the chemical space of potential DES to be studied. A total of 30,132 DES combinations were assessed. The DESs selected were polyalcohols (ethyleneglycol, glycerol, 1,2-propanediol, and 1,6-hexanediol) and carboxylic acids (citric, oxalic, malic, and lactic acid) as hydrogen bond donors (HBD) and choline chloride, betaine, or salts (potassium carbonate, sodium acetate, and propionate), as hydrogen bond acceptors (HBA). Choline chloride:glycerol and choline chloride:oxaclic acic were selected as solvents to optimize time, temperature, and water content in ultrasound- and microwave-assisted extraction of anthocyanins. In both cases, around 20 wt% of water was found to be the optimum to maximize the extractions, whereas extraction time and temperature depended on the type of anthocyanin. The amount of malvidin-3-O-glucoside extracted by microwave-assisted extraction with choline chloride: oxalic acid was 172 ± 7 mg/kg and 119.5 ± 0.5 mg/kg by ultrasound-assisted extraction with choline chloride: glycerol, which means an increase in performance of, respectively, 64 and a 13% compared to the traditional method. Full article

This interdisciplinary study explores the potential of bioactive compounds from Aronia melanocarpa pomace, a juice industry by-product. The ethanol extract of the pomace was analyzed using HPLC, revealing key polyphenolic acids and anthocyanins. The extract exhibited outstanding antioxidant activity (100% as measured by the ABTS assay and 98.23% as measured by the DPPH assay) and >99% antibacterial efficacy against E. coli and S. aureus. This bioactive extract was utilized in a one-step process to dye and functionalize textiles (wool, silk, cellulose acetate, cotton, and viscose), with cotton and viscose suited for colored disposable bioactive textiles, particularly protective healthcare textiles, due to strong antioxidant (>97% as measured by the ABTS assay and >76% as measured by the DPPH assay) and antibacterial (>75% for E. coli and >80% for S. aureus) properties. The aronia pomace extract was also incorporated into newly synthesized starch/gelatin hydrogels with a compression modulus of 0.041–0.127 MPa and equilibrium swelling ratios of 3.33–4.26 g/g. Functionalized hydrogels demonstrated over 99% ABTS antioxidant activity, while the antibacterial efficacy against E. coli and S. aureus exceeded 70% and 97%, respectively. These properties, combined with the hydrogels’ ability to control the release of extract compounds, make them adequate for wound care applications. The extract’s effectiveness as a green inhibitor for carbon steel, with inhibition efficiency surpassing 94% at a concentration of aronia pomace extract of 100 ppm, was confirmed by electrochemical methods. Moreover, the extract predominantly retards the cathodic reaction. The current research represents the first exploration of alternative and green sustainable technologies for developing novel products based on aronia pomace extract. Full article

The burning of coal in thermal power plants throughout Serbia produces significant amounts of industrial waste, primarily in the form of fly ash, boiler ash, and slag. Given their annual production, availability, and fine grain structure, it is necessary that sustainable strategies are developed for their reuse, instead of depositing them directly in landfills. In this research, the possibility of using fly ash, slag, and diatomaceous earth as raw materials for the synthesis of geopolymers at low temperatures was examined, in order to replace cement in construction materials, with the aim of reducing carbon dioxide emissions. Special emphasis was put on the effect of addition of organic macromolecules—polyvinyl alcohol (PVA), chitosan, and starch—upon the structure and mechanical properties of the obtained materials. In addition, the behavior of the materials with regard to the leaching of heavy metals in different environmental conditions was examined. Chemometric methods of multivariate analysis were used to examine the correlations between the obtained physical–chemical parameters, while the dependence of mechanical properties on the composition of the raw mixture was analyzed using the Mixture Design of Experiments method. The results obtained indicate that the examined waste materials have potential to be used as an environmentally friendly alternative to cement. The addition of PVA and chitosan had a positive effect on the mechanical properties of the geopolymers, with the highest strength achieved in formulations based solely on fly ash, containing 2.5% PVA, which reached 12.6 MPa. It was also shown that the addition of 30% diatomaceous earth increases the density and compressive strength of the material, while reducing the number of microcracks present in its structure, with a compressive strength of 13 MPa. Full article

Catalytic upgrading of bioethanol via a C–C coupling reaction is a sustainable method of producing 1-butanol, a high-performance biofuel. This reaction was studied using a flow-through microreactor system with Pd/MgO-Al₂O₃ and bimetallic Pd-Cu/MgO-Al₂O₃ mixed oxide-based catalysts in a H₂ carrier gas at a pressure of 21 bar and temperatures ranging from 200 to 350 °C. The effect of the metal promoter(s) on the hydrogen transfer reaction steps in the overall reaction was investigated. The palladium promoter significantly improved the activity and butanol selectivity across the entire temperature range. However, the yield of liquid products decreased significantly at temperatures higher than 250 °C, primarily because the decarbonylation side reaction of the acetaldehyde intermediate accelerated. The promoting effect of Pd was most beneficial below 250 °C because the decarbonylation reaction was inhibited by the reversible poisoning effect of CO on multiple Pd sites responsible for decarbonylation. Diluting the Pd phase with Cu increased liquid yields due to gradually decreasing decarbonylation activity. However, the dehydrogenation–hydrogenation activity decreased as well, as did the promoting effect on the corresponding reaction steps in the coupling reaction. Additionally, the product distribution changed dramatically, decreasing 1-butanol selectivity, because metallic Cu can catalyze the formation of ethyl acetate and ketone products. Full article

Ammonia, widely regarded as the “hydrogen carrier of the future,” offers high hydrogen content, ease of production, and a well-established infrastructure for handling and transportation globally. Meanwhile, ammonia cracking requires a heat supply at high temperatures, and induction heating provides efficient, precise, and rapid heating to conductive materials of different shapes and sizes. Therefore, this work presents a proof of concept for ammonia cracking using induction heating with three different reactor configurations: (1) a 3D metal workpiece; (2) a 3D metal workpiece and Ni/Al₂O₃ catalyst; and (3) only Ni/Al₂O₃ catalyst. The performance of the inductively heated reactor is also compared to an electric furnace. The results showed that the reactor with the workpiece and the catalyst required 97 W to reach 650 °C, being the most efficient in terms of power usage when compared to the workpiece alone and the electric tube furnace, which required 39% and 132% more, respectively; the least efficient configuration is with just the catalyst, needing 138 W to reach just 116 °C. Overall, the introduction of the 3D workpiece allowed for fast and uniform conversion and heating within the reactor, enabling efficient and dynamic process control when applying induction heating to chemical reactors. Full article

Mesoporous materials have attracted increasing attention due to their ordered pore systems; tunable surface chemistry; and versatile applications in catalysis, adsorption, and environmental technologies. Among them, SBA-15 stands out for its large surface area, uniform mesopores, and high hydrothermal stability, which make it a promising platform for gas adsorption and mass transport studies. This review examines the functionalization of SBA-15 through strategies such as post-synthesis grafting and co-condensation, focusing on the introduction of amines, thiols, and organometallic species that enhance selectivity, adsorption capacity, and thermal stability. The discussion integrates classical diffusion models, including Fickian and Knudsen transport, with more advanced approaches such as the Maxwell–Stefan formalism, to describe molecular transport within mesoporous networks and highlight the role of van der Waals interactions in gas capture processes. Special emphasis is placed on the relationship between structural features and diffusive behavior, supported by recent advances in computational modeling and spectroscopic validation. Applications in CO₂ capture, heterogeneous catalysis, drug delivery, and environmental remediation are critically assessed to illustrate the versatility of functionalized SBA-15. This review concludes by outlining future perspectives on the rational design of hierarchical and multifunctional mesoporous materials for clean energy conversion, pollutant removal, and biomedical applications. Full article

This study reports the solvent-free mechanochemical synthesis of a novel series of 2-hydrazone-bridged benzothiazole derivatives 19–52 via the reaction of 2-hydrazinylbenzothiazole derivatives 4–6 with O-alkylated benzaldehydes 7–18. The stereostructure of the E-isomers was confirmed by 2D NOESY spectroscopy. The antiproliferative potential of these newly prepared 2-hydrazone derivatives of benzothiazole 19–52 was evaluated in vitro against eight human cancer cell lines. Several compounds demonstrated low micromolar IC₅₀ values, with some outperforming the reference drug etoposide. Among the most potent compounds, the 6-chloro-2-hydrazone(3-fluorophenyl)benzothiazole derivative 38 exhibited remarkable activity against pancreatic adenocarcinoma (Capan-1, IC₅₀ = 0.6 µM) and non-small cell lung cancer (NCI-H460, IC₅₀ = 0.9 µM). Structure–activity relationship analysis revealed that derivatives 45–52, featuring a methoxy group at position 6 of the benzothiazole ring and either a methoxy or fluorine substituent at position 3 of the phenyl ring, showed consistently strong antiproliferative effects across all tested cell lines (IC₅₀ = 1.3–12.8 µM). Furthermore, compounds bearing N,N-diethylamino or N,N-dimethylamino groups at position 4 of the phenyl ring generally exhibited superior activity compared to those with morpholine or piperidine moieties. However, as this study represents an initial screening, further mechanistic investigations are required to confirm specific anticancer pathways and therapeutic relevance. In addition to their in vitro anticancer properties, the antibacterial activity of the compounds was assessed against both Gram-positive and Gram-negative bacteria. Notably, compound 37 demonstrated selective antibacterial activity against Pseudomonas aeruginosa (MIC = 4 µg/mL). Overall, this work highlights the efficiency of a green, mechanochemical approach for synthesizing E-isomer hydrazone-bridged benzothiazoles and underscores their potential as promising scaffolds for the development of potent antiproliferative agents. Full article

Biopurification systems are designed for the treatment of pesticide-containing agricultural wastewater; their biologically active matrix, the biomixture, can be modified to enhance the pesticide removal capacity. Two approaches, fungal bioaugmentation with Trametes versicolor and amendment with biochar, were applied for the potential improvement of biomixtures’ capacity to remediate myclobutanil-contaminated wastewater. The conventional biomixture (B) and its modifications, either bioaugmented with Trametes versicolor (biomixture BT) or supplemented with pineapple biochar (5% v/v) (biomixture BB), were spiked with myclobutanil at a very high concentration (10,000 mg/kg) to simulate extreme on-farm events such as the disposal or leakage of commercial formulations. The dissipation followed a bi-phasic behavior in every case. Both modifications of the conventional biomixture increased the dissipation rates, resulting in estimated DT₅₀ values of 61.9 (BB) and >90 days (BT) compared to biomixture B (DT₅₀ = 474 days). The assessment of biomixtures’ detoxification was carried out with two different bioindicators: a seed germination test in Lactuca sativa and an algal growth inhibition test. Some degree of detoxification was achieved for all biomixtures in both indicators, with the exception of the biochar-containing biomixture, which, despite showing the fastest myclobutanil dissipation, was unable to maintain a steady detoxification trend towards the algae over the course of the treatment, probably due to biochar adverse effects. This approach seems promising for removing persistent myclobutanil from agricultural wastewater and demonstrates the dissipation capacity of biomixtures at extremely high pesticide concentrations likely to take place at an on-farm level. Full article

Known for its excellent adsorption and molecular sieving properties, CHA-type zeolite is highly effective in separation technologies, including alcohol dehydration and gas separation. Despite their advantages, especially in terms of energy savings, the prolonged synthesis time of zeolite membranes limits their commercial adoption. The remarkably rapid synthesis of CHA membranes was demonstrated using an exceptionally small tubular reactor (ID: 4.0 mm, OD: 6.0 mm, L: 135 mm). The formation of membranes could be observed after 10 min of synthesis, and a membrane with a thickness of 0.65 µm, αH₂O/2-PrOH of 1662, and a total flux of 2.97 kg/(m² h), was produced after 40 min of synthesis in an oil bath. Using the synthesis time of 40 min and longer, membranes with good quality and enhanced reproducibility were produced, as the number of defects was reduced. These findings demonstrate the potential for rapid, scalable CHA membrane production, paving the way for broader industrial applications. Full article

The composite material lignocellulose makes up the majority of biomass on earth and is characterized by a high biological and chemical resistance, which is essentially caused by the phenylpropanoid polymer lignin. Thus, the removal and depolymerization of lignin to produce aromatic chemicals can significantly enhance the material usability of all lignocellulose constituents. This review summarizes the current state of knowledge on the nature of lignin, including its biosynthesis, structure, chemistry and biodegradation. Second, it attempts to derive implications regarding the technical valorization of lignin from native biomass through depolymerization. Finally, the consequences of the findings for conventional, recently developed and future processes valorizing lignocellulose are assessed, and the associated technical and economic hurdles are discussed. It becomes clear that lignin depolymerizability is restricted in established pulping processes, primarily due to repolymerization reactions. Strategies avoiding lignin repolymerization involve an increased process complexity and additional economic expenditure but might enable an increased value creation from lignocellulosic biomass. Full article

This study explores the development of a water-based hybrid thermoelectric (TE) material composed of Sb₂Te₃ nanoparticles (NPs) and polyethylene oxide (PEO). Sb₂Te₃ NPs were synthesized via the microwave-assisted colloidal route, where X-ray diffraction confirmed the purity and quality of the Sb₂Te₃ NPs. Key properties, including the Seebeck coefficient (S), electrical conductivity (σ), power factor (PF), and long-term stability, were studied. X-ray photoelectron spectroscopy (XPS) analysis revealed that exposure to water and oxygen leads to NP oxidation, which can be partially mitigated by hydrochloric acid (HCl) treatment, though this does not halt ongoing oxidation. Scanning electron microscopy (SEM) images displayed a percolation network of NPs within the PEO matrix. While the initial σ was high, a decline occurred over eight weeks, resulting in similar conductivity among all samples. The effect of surface treatments, such as 1,6-hexanedithiol (HDT), was demonstrated to enhance long-term stability. The results highlight both the challenges and potential of Sb₂Te₃/PEO hybrids for TE applications, especially regarding oxidation and durability, and underscore the need for improved synthesis and processing techniques to optimize their performance. This study provides valuable insights for the design of next-generation hybrid TE materials and emphasizes the importance of surface chemistry control in polymer–inorganic nanocomposites. Full article

Antimony (Sb), bismuth (Bi), and arsenic (As) are common contaminants of copper (Cu) electrolyte and anodes, necessitating strict control of their concentrations. The purification of Cu electrolytes is required and demands the application of appropriate techniques. This paper presents the methodology of selective precipitation, applied for Sb, Bi, and As recovery from the acidic eluate of a Cu electrolyte purification plant. An important aspect was the change in solution type from chloride to sulfate, prior to arsenic sequestration. A facile precipitation method, preceded by a reduction in As(V) and Sb(V), was applied. The primary objectives are focused on the preparation of three distinct concentrates: antimony oxychloride, bismuth oxychloride, and iron(III) arsenate(V), emphasizing optimal recovery and purity. The processes were performed in a specially designed, cascade-lined pilot scale installation, with a daily capacity of approximately 2.5 m³. In total, 22 m³ of eluate was processed, yielding 191 kg of Sb concentrate, 97 kg of Bi concentrate, and 163 kg of scorodite. The recovery of Sb was as high as 98%, with antimony content up to 50% in the concentrate. The recovery of bismuth varied from 60 to 99%, depending on the process parameters. The elimination of arsenic from the eluate was close to 100%. Full article

This study evaluated the extraction of oils from the seeds of bacupari (Garcinia brasiliensis Mart.) and leiteira (Tabernaemontana catharinensis), using carbon dioxide (CO₂) in the supercritical state. The effects of temperature (40, 50, and 60 °C) and pressure (20, 24, and 28 MPa) on the yield and extraction kinetics were investigated. The results indicated that, within the studied limits, temperature had a negligible influence on the process, while pressure had a greater impact on the yields owing to its effect on the density of supercritical CO₂ and the solubility of the extracted compounds. The maximum yields obtained were 14.8% for bacupari and 15.2% for leiteira, with most of the oil extracted within the first 30 min, indicating initial rapid extraction. Chemical composition analysis revealed relevant bioactive compounds in bacupari, including oleic acid (35%) and delta-tocopherol (19.6%). In leiteira, the main compounds identified were hexanedioic acid (29.2%) and stigmast-5-ene (7.95%). These results suggest the potential application of these oils in the pharmaceutical, cosmetic, and food sectors, while also highlighting the feasibility of using supercritical CO₂ as an extraction method for these plant matrices. Full article

The substitution of hazardous, environmentally persistent solvents (NMP and DMAc) with more sustainable alternatives (ETAc and GBL) in fabricating flat sheet polyactic acid (PLA) membranes via nonsolvent-induced phase separation for air filtration applications was the focus of this study. The polymer-solvent affinity was first evaluated using Hansen solubility parameters, confirming suitable Relative Energy Difference (RED) values (<1) for all solvent candidates. Dope solutions prepared with biodegradable solvents demonstrated higher viscosity compared to those prepared with environmentally persistent solvents. These biodegradable solvent systems also exhibited slower precipitation rates during membrane formation. This resulted in spongelike cross-sectional morphologies, contrasting with the combined fingerlike and spongelike structures observed in membranes fabricated with environmentally persistent NMP and DMAc. Thermal analysis revealed that membranes fabricated with biodegradable solvents exhibited superior thermal stability with higher glass transition temperatures (Tg = 54.39–55.34 °C) compared to those made with environmentally persistent solvents (Tg = 49.97–50.71 °C). Membranes fabricated with ethyl acetate (ETAc) showed the highest hydrophobicity (contact angle = 115.1 ± 9°), airflow rate (12.7 ± 0.28 LPM at 0.4 bar) and maintained filtration efficiency at values greater than 95% for 0.3 μm aerosols. Full article

Rare earth elements (REEs) make up integral components in personal electronics, healthcare instrumentation, and modern energy technologies. REE leaching with organic acids is an environmentally friendly alternative to traditional extraction methods. Our previous study demonstrated that batch ultrasound-assisted organic acid leaching of REEs can significantly decrease environmental impacts compared to traditional bioleaching. The batch method is limited to small volumes and is unsuitable for industrial implementation. This study proposes a novel approach to increase reaction volume using a continuous ultrasound-assisted organic acid leaching method. Laboratory experiments showed that continuous ultrasound-assisted leaching increased the leaching rate (µg/h) 11.3–24.5 times compared to our previously reported batch method. Techno-economic analysis estimates the cost of the continuous approach using commercially purchased organic acids is $9465/kg of extracted REEs and $4325/kg of extracted REEs, using gluconic acid and citric acid, respectively. The sensitivity analysis reveals that substituting commercially purchased organic acids with microbially produced biolixiviant can reduce the process cost by approximately 99% while minimally increasing energy consumption. Environmental assessment shows that most of the emissions stemmed from the energy required to power the ultrasound reactor. We concluded that increased leaching capacity using a continuous ultrasound-assisted approach is feasible, but process modifications are needed to reduce the environmental impact. Full article

The confectionery industry produces effluents with diverse and complex compositions and high organic loads, which are typically not treated by conventional treatment plants. In this context, the Fenton process presents itself as an advanced chemical treatment alternative due to its ease of application, cost-effectiveness, and ability to improve the degradability of challenging effluents. This study addressed the question: How can Fenton’s reagent be applied as a pretreatment to reduce the organic load in real effluents from the food industry? The research evaluated this chemical pretreatment for effluents from a starch-based gummy candy production process, aiming to reduce the organic load and aid subsequent conventional treatments. Parameters such as COD, total dissolved solids (TDS), temperature, pH, electrical conductivity, dissolved oxygen, and degrees Brix (°Bx) were monitored before and after 2 and 4 h of pretreatment. The results showed that Fenton pretreatment reduced COD by more than 31%, with efficiency influenced by effluent composition and concentration. This removal can reduce discharge rates and operating costs, providing an economic advantage. The process proved to be a promising pretreatment option, contributing to the initial removal of pollutants and improving the performance of wastewater treatment systems, thus supporting sustainable industrial practices. Full article

Bimetallic mesoporous photocatalysts were synthesized via a wet impregnation method using SBA-15 as a support, and characterized by UV–visible diffuse reflectance spectroscopy, low-angle X-ray diffraction and N₂ physisorption. Among the tested materials, the Ti/Mn combination exhibited the highest photocatalytic activity in azo dye degradation. To understand this enhanced performance, catalysts with varying Mn loads and calcination ramps were evaluated. Additionally, experiments with radical scavengers (isopropanol, chloroform) and under N₂ insufflation were conducted to identify the active radical species. Catalysts prepared with low Mn content and higher calcination ramps showed the greatest activity, which significantly decreased with isopropanol, indicating hydroxyl radicals as the main reactive species. In contrast, samples with higher Mn content and quicker heating displayed reduced activity in the presence of chloroform, suggesting superoxide radical involvement. Spectroscopic analyses (XPS, UV–Vis DRS) revealed that increasing Mn load promotes the formation of Mn²⁺ over Mn⁴⁺ species and lowers the band gap energy. These findings highlight the direct correlation between synthesis parameters, surface composition and optical properties, providing a strategy for fine-tuning the performance of a photocatalyst. Full article