Green Chemical Technology Open Access

Chemical Recycling and Upcycling of Waste Plastics: A Review

The indiscriminate disposal of plastic waste represents a significant environmental hazard. Conventional remediation techniques, such as landfilling and incineration, also encounter limitations and are unable to adequately address the pollution issue. Chemical recycling and upcycling represent an effective method for the degradation of plastics into oligomers and subsequent transformation into other product substances. This review provides an overview of the various chemical treatment methods currently in use, from the earliest thermal degradation techniques to the emerging strategies. The conventional techniques for thermal degradation of discarded plastics frequently encounter difficulties due to the necessity for elevated temperatures, substantial energy consumption, and the generation of a heterogeneous product mixture. Significant advances have been made in the fields of catalytic solvolysis, hydrotreating, and oxidative cleavage for the recycling and upcycling of plastics under mild conditions. This review provides a comprehensive overview of the chemical treatment methods currently employed for plastics, with a particular focus on the principles and current developments, as well as the reaction mechanisms involved. Additionally, it offers a detailed introduction to various advanced catalytic technologies and the catalysts utilized. Finally, it presents prospective outlooks for different methods, based on their current development status and the gap between actual needs.

Comparative Study: Biodegradable Chelating Agents vs. Aqua Regia for Extraction of Indispensable Elements from Pyrite Ore of Bagrot, Gilgit Baltistan

This study investigates the optimization of metal extraction from Bagrot pyrite ore, with a focus on gold recovery. Initial characterization using X-ray fluorescence (XRF) provided a comprehensive elemental profile of the ore. Fire assaying was employed to establish a baseline gold concentration. Systematic leaching experiments were conducted, varying parameters such as reaction time, temperature, and stirring speed, and the results were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Among the chelating agents tested Ethylenediamine N-N′ disuccinic acid (EDDS), Ethylenediaminetetraacetic acid (EDTA), and Diethylenetriaminepentaacetic acid (DTPA) only limited efficacy in gold extraction was observed. In contrast, ammonium thiosulfate demonstrated substantial potential for effective gold recovery. Mercaptobenzothiazole (MBT) and N,N-Dimethylglycine (DMG) were determined to be ineffective for metal leaching under the tested conditions. This research highlights the critical role of reagent selection and parameter optimization in enhancing the efficiency and sustainability of gold extraction processes, positioning ammonium thiosulfate as a promising alternative to traditional cyanide-based methods.

Adsorption and High-Value Transformation of Volatile Fatty Acids from Microbial Fermentation Products: A Review

To mitigate the aforementioned global environmental issues, the concept of carbon capture and storage is crucial in addressing the necessity for carbon peaking and carbon neutrality. The buildup of volatile fatty acids during anaerobic fermentation is a primary factor contributing to the suboptimal performance or outright failure of anaerobic digestion systems. In response to the pressing demand for volatile organic acid recovery and high-value conversion, we primarily outlined the sources, recovery techniques, adsorption materials, and methods for high-value conversion of volatile fatty acids. The methods of adsorbing volatile acetic acid were presented, encompassing adsorption materials, mechanisms, and interfacial modifications of the adsorbent. Furthermore, drawing from recent research advancements, we have synthesized the high-value conversion techniques for volatile fatty acids and evaluated the research challenges and future prospects in this domain.

The Discovering of Rapid Formation La(OH)₃ from LaH₃

It was found that the single crystal of LaH₃ specimen with $${Fm\overline{3}m}$$ (No.225) will decompose into powders within 24 h, which is later characterized to be La(OH)₃ by single crystal X-ray diffraction (SXRD) measurements. The discovery motivates the examination of three possible transition paths by comparing formation enthalpy with first-principles calculations and employing a custom- designed hydrogen detection setup. Furthermore, the most suitable adsorption position of O₂ molecules on the (111) surfaces has been investigated by comparing the adsorption enthalpy from different candidate positions by utilizing first-principles calculations, implying the pivotal role of O₂ molecules played in the rapid formation of La(OH)₃ along the optimal transition path.

Recent Progress of High Safety Separator for Lithium-Ion Battery

With the rapid increase in quantity and expanded application range of lithium-ion batteries, their safety problems are becoming much more prominent, and it is urgent to take corresponding safety measures to improve battery safety. Generally, the improved safety of lithium-ion battery materials will reduce the risk of thermal runaway explosion. The separator is a key component of lithium-ion batteries. It plays a crucial role in battery safety, serving as one of the most effective measures against internal short circuits.Separator failure is a direct cause of the thermal runaway and can be specifically divided into three categories: puncture, melting, and thermal shrinkage. The requirements for an ideal lithium-ion battery separator have a synergistic effect on the electrochemical performance, safety, and scalability of lithium-ion batteries. Focus on the separator, this review summaries the mechanism of separator in thermal runaway process, and reports the recent progress of high safety separator from the perspective of material preparation.

Experimental Study on A Novel Organic/Inorganic Green Deep Eutectic Solvents: Thermophysical Properties, Thermal Stability, and Utilization in Nanofluids

In response to the performance limitations of traditional heat transfer fluids under extreme conditions, a series of organic/inorganic deep eutectic solvents (DES), composed of ethylene glycol and different types of acetates, have been developed, and their downstream thermophysical properties, as well as their potential applications in nanofluids, have been explored. It is found that the prepared DESs significantly broaden the liquid phase temperature range, which ranges from −14~196 °C to −40~201 °C. The initial decomposition temperature increases from 85 °C to 130 °C, and the peak decomposition rate shifts from 175 °C to 206 °C. Subsequently, nanofluids were prepared by employing the selected ethylene glycol: potassium acetate-5:1 DES with carbon nanotube as nanofiller. The results reveal that the thermal conductivity of the nanofluid could be increased by approximately 3% compared to the base fluid, and the specific heat capacity was enhanced by 7.5% with a photothermal conversion efficiency reaching up to 42.7%. These results highlight the promising thermal stability and heat transfer properties of ethylene glycol-acetate DESs. Moreover, the nanofluids prepared from those DESs as base fluids provide useful references for the development of novel, green, and high-efficiency energy transportation fluids.

Green Chemical Technology: A New Journal for Green Engineering and Green Technology

Magnetic Solid Phase Extraction of Paeonol and Paeonoflorin from Moutan Bark with Magnetic Graphene Oxide

Herbal medicine plays an important role in modern medicine and separation of the active ingredients from herbal medicine is vital for convenient and safe usage. Paeonol and paeonoflorin are the active ingredients in the widely used herbal medicine of moutan bark. In this study, the composite of graphene oxide-Fe₃O₄ nanoparticles (GO-Fe₃O₄) was synthesized and used as a magnetic absorbent to extract paeonol and paeonoflorin from the herbal medicine of moutan bark. The adsorption of paeonol and paeoniflorin on GO-Fe₃O₄ rapidly reached equilibrium (within 10 min) due to the high absorption capability of GO. Thermodynamics and kinetics for the absorption process were studied. The optimal condition for the elution of the target compound from GO-Fe₃O₄ was the use of 2 mL of a mixed solvent (methanol and dichloromethane, 1:1 by volume) with 0.2% formic acid for 5 min. The GO-Fe₃O₄ adsorbent possesses the advantages of rapid adsorption and convenient separation. GO-Fe₃O₄ can be used over 6 times without losing absorbing capacity. This method is efficient, convenient and rapid, thus possesses a high potential for the separation of active ingredients from herbal medicine.

Mini Review on the Photocatalytic Removal of Gaseous Ammonia: Current Status and Challenges

Ammonia gas (NH₃) is a notorious malodorous pollutant released mainly in agriculture and industry. With the increasing demand for ammonia, environmental pollution caused by ammonia discharge has seriously threatened human health and safety. Due to the discrete emission and low concentration of NH₃, photocatalytic oxidation is an economical and efficient treatment strategy. TiO₂, as a common photocatalyst, has been widely used by researchers for the photocatalytic removal of NH₃. In addition, surface modification, element doping, semiconductor recombination and metal loading are used to improve the utilization rate of solar energy and carrier of TiO₂ so as to find a catalyst with high efficiency and high N₂ selectivity. Further, at present, there are three main removal mechanisms of NH₃ photocatalytic oxidation: ·NH₂ mechanism, iSCR mechanism and N₂H₄ mechanism. Among them, N₂H₄ mechanism is expected to be the main removal path of NH₃ photocatalytic oxidation in the future because the removal process does not involve NO_x and nitrate. This review summarizes recent studies on the photocatalytic oxidation of NH₃, focusing primarily on NH₃ removal efficiency, N₂ selectivity, and the underlying removal mechanisms. Additionally, the potential future applications of NH₃ photocatalytic oxidation are discussed.

Adsorption of Bisphenol A and 2,6-Dichlorophenol in Water Using Magnetic Phosphogypsum Composite Materials

Phenolic pollutants in water bodies pose a huge threat to human health and environmental safety. In this paper, a hydrophobicity-enhanced magnetic C-SiO₂/MPG composite was prepared by a two-step method to remove bisphenol A (BPA)and 2,6-dichlorophenol (2,6-DCP), typical phenolic trace pollutants in livestock wastewater and natural water bodies. The results of pH gradient experiments showed that C-SiO₂/MPG showed a stable removal effect on BPA in the pH range of 2–11. The adsorption of 2,6-DCP by C-SiO₂/MPG peaked at pH = 2, while the adsorption of 2,6-DCP by C-SiO₂/MPG was severely inhibited under alkaline conditions. The PSO kinetic model and the Langmuir isotherm model can better describe the adsorption process of BPA and 2,6-DCP on C-SiO₂/MPG, indicating that the monolayer chemical adsorption has a rate-controlling step. With the Langmuir equation fitting, the maximum adsorption capacity of C-SiO₂/MPG for BPA and 2,6-DCP at 298 K was calculated to be 561.79 mg/g and 531.91 mg/g, respectively. The results of adsorption thermodynamics indicated that the adsorption of BPA and 2,6-DCP on C-SiO₂/MPG was spontaneous, accompanied by a process of entropy decrease. C-SiO₂/MPG showed good environmental resistance and repeated use stability for BPA and 2,6-DCP in electrolyte ion interference, actual water samples and cycle experiments. Mechanism analysis showed that the adsorption of BPA and 2,6-DCP on C-SiO₂/MPG was mainly controlled by hydrogen bonding and hydrophobic interactions. This study designed an efficient adsorbent for phenolic pollutants that can be used in actual wastewater and broadened the resource utilization of industrial waste phosphogypsm.

Chemical Recycling and Upcycling of Waste Plastics: A Review

The indiscriminate disposal of plastic waste represents a significant environmental hazard. Conventional remediation techniques, such as landfilling and incineration, also encounter limitations and are unable to adequately address the pollution issue. Chemical recycling and upcycling represent an effective method for the degradation of plastics into oligomers and subsequent transformation into other product substances. This review provides an overview of the various chemical treatment methods currently in use, from the earliest thermal degradation techniques to the emerging strategies. The conventional techniques for thermal degradation of discarded plastics frequently encounter difficulties due to the necessity for elevated temperatures, substantial energy consumption, and the generation of a heterogeneous product mixture. Significant advances have been made in the fields of catalytic solvolysis, hydrotreating, and oxidative cleavage for the recycling and upcycling of plastics under mild conditions. This review provides a comprehensive overview of the chemical treatment methods currently employed for plastics, with a particular focus on the principles and current developments, as well as the reaction mechanisms involved. Additionally, it offers a detailed introduction to various advanced catalytic technologies and the catalysts utilized. Finally, it presents prospective outlooks for different methods, based on their current development status and the gap between actual needs.utf-8

Recent Progress of High Safety Separator for Lithium-Ion Battery

With the rapid increase in quantity and expanded application range of lithium-ion batteries, their safety problems are becoming much more prominent, and it is urgent to take corresponding safety measures to improve battery safety. Generally, the improved safety of lithium-ion battery materials will reduce the risk of thermal runaway explosion. The separator is a key component of lithium-ion batteries. It plays a crucial role in battery safety, serving as one of the most effective measures against internal short circuits.Separator failure is a direct cause of the thermal runaway and can be specifically divided into three categories: puncture, melting, and thermal shrinkage. The requirements for an ideal lithium-ion battery separator have a synergistic effect on the electrochemical performance, safety, and scalability of lithium-ion batteries. Focus on the separator, this review summaries the mechanism of separator in thermal runaway process, and reports the recent progress of high safety separator from the perspective of material preparation.utf-8

Adsorption and High-Value Transformation of Volatile Fatty Acids from Microbial Fermentation Products: A Review

To mitigate the aforementioned global environmental issues, the concept of carbon capture and storage is crucial in addressing the necessity for carbon peaking and carbon neutrality. The buildup of volatile fatty acids during anaerobic fermentation is a primary factor contributing to the suboptimal performance or outright failure of anaerobic digestion systems. In response to the pressing demand for volatile organic acid recovery and high-value conversion, we primarily outlined the sources, recovery techniques, adsorption materials, and methods for high-value conversion of volatile fatty acids. The methods of adsorbing volatile acetic acid were presented, encompassing adsorption materials, mechanisms, and interfacial modifications of the adsorbent. Furthermore, drawing from recent research advancements, we have synthesized the high-value conversion techniques for volatile fatty acids and evaluated the research challenges and future prospects in this domain.utf-8

Efficient Removal of Glyphosate from Aqueous Solution by Cerium Dioxide Loaded Biochar

Glyphosate, which is one of the most widely used organophosphorus herbicides, poses a threat to the surrounding water environment. Traditional adsorbents were depicted to have poor capacities to eliminate it. CeO₂ embraces the potential to adsorb glyphosate efficiently. However, suitable carbonaceous composites were necessary to be employed as its support. In this paper, water hyacinth was used as the precursor to prepare CeO₂-loaded biochar (CeO₂/WHBC), which was employed to remove glyphosate from the aqueous solution via adsorption. The results showed that CeO₂/WHBC-3 illustrated the best adsorption performance for glyphosate with the capacity of 126.3 mg·g, which was prepared with per mmol CeO₂ loaded of 0.2 g WHCB. Static adsorption experiments demonstrated that glyphosate adsorption at different solution pH values followed the Langmuir isotherm model and quasi-second order kinetic model, indicating that the adsorption was monolayer adsorption and that the adsorbent’s surface active sites primarily controlled the rate. Coexisting ion interference experiments showed that common cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and anions (Cl⁻, NO₃⁻, SO₄²⁻) both promoted glyphosate adsorption on the CeO₂/WHBC-3 surface. Moreover, the prepared sorbent maintained a high adsorption capacity after five adsorption-desorption cycles. Dynamic adsorption experiments showed that the CeO₂/WHBC-3 packed column could efficiently remove glyphosate from aqueous solutions, even at high concentrations and fast flow rates. Zeta potentials and XPS analysis revealed that the adsorption mechanism of CeO₂/WHBC-3 for glyphosate is mainly through electrostatic adsorption and metal complexation.utf-8

Antifungal and Antibacterial Activity of Lathyrus aphaca L. Mediated Green Synthesized CdS Nanoparticles and Their Characterization

Cadmium Sulfide nanoparticles (CdS-LA hybrid nanoparticles) were synthesized here by a green approach using the precursor cadmium acetate and sodium sulphide along with the extract of a plant Lathyrus aphaca L. containing the phytochemicals which were responsible for surface modification of nanoparticles. The nanoparticle was used to evaluate their inhibition potential against species of bacteria and fungi. The nanoparticles were characterized by XRD, which demonstrates the hexagonal crystal structure. SEM confirms the homogenous surface appearance of the CdS-LA hybrid crystalline structure. EDX analysis confirms surface modification of nanoparticles by phytochemicals. FTIR confirmed the Cd-S linkage laterally with the related functional groups and the presence of metabolites on the surface of nanoparticles. The UV-visible spectroscopy confirmed the peak at the characteristic wavelength range, but a slight shift occurred in the peak of the CdS nanoparticles due to the presence of the phytochemicals. This study particularly provides an environment-friendly strategy to synthesize the CdS nanoparticles capped by Lathyrus aphaca L. extract that are biologically active due to the mediation of the plant extract. CdS-LA hybrid nanoparticles have shown inhibition potential against various species of bacteria and fungi and realize the biological importance of the green synthesis of nanoparticles especially mediated with the plant extract.utf-8

Fermentation of Wild Hydrolytic Bacteria Isolated from Opuntia ficus-indica, and Its Effect on Flow Behavior of Cladodes Flour Culture Media

The aim of this study was to evaluate the fermentation dynamics of two wild hydrolytic microorganisms and their effect on the flow behavior of a culture medium formulated with Opuntia ficus-indica cladode flour. Identified Acinetobacter pitti and Bacillus subtilis presented maximum values of specific hydrolytic activity (SHA) at 24 h of growth (0.21 ± 0.05 and 0.22 ± 0.01 IU, respectively). The apparent viscosity of cladode flour medium (CFM) measured by applying shear rates (66.7 s⁻¹–0.003 s⁻¹) in suspensions (20%) showed a significant decrease (60%) as a function of bacterial growth progressed. After fermentation, the CFM exhibited pseudoplastic (shear-thinning) behavior, which was linked to the enzymatic degradation of polysaccharides. The use of crude extracellular enzyme extracts from these wild bacteria effectively reduced medium viscosity by breaking down the plant matrix. These findings highlight the hydrolytic potential of native strains in modifying the rheological properties of cactus-based culture media, offering a low-cost alternative for biomass pretreatment and valorization in future biotechnological applications.utf-8

Harnessing Nature’s Colours: Experimental and Computational Insights into Bixa orellana Pigments for Next-Generation Dye-Sensitized Solar Cells

The potential of Bixa orellana (annatto) pigments, specifically bixin and norbixin, as sensitizers for dye-sensitized solar cells (DSSCs) was investigated. The pigments were extracted using various solvents (acetone, methanol, ethanol, and hexane), and their optical and photo-electrical properties were investigated using UV-Vis spectroscopy and photoelectrical analysis. Results indicate that acetone extract (a-AP) exhibited the highest power conversion efficiency (PCE) of 0.786%, attributed to its broad absorption spectrum and optimal electronic properties. Quantum chemical calculations revealed that both bixin and norbixin exhibit favourable frontier orbital energies and energy gaps, making them well-suited for efficient electron injection and light absorption. These findings position Bixa orellana pigments as promising, eco-friendly alternatives to conventional synthetic sensitizers, offering a pathway toward more sustainable, locally adaptable, and efficient solar energy harvesting.utf-8

Upcycling of Waste Poly(ethylene terephthalate) into 2,4-Pyridine Dicarboxylic Acid by a Tandem Chemo-Microbial Process

This study presents a chemo-microbial cascade process for the upcycling of waste poly(ethylene terephthalate) (PET) into valuable compound 2,4-pyridine dicarboxylic acid (2,4-PDCA). Initially, waste PET undergoes efficient hydrolysis to terephthalic acid (TPA) with a high yield of 92.36%, catalyzed by p-toluenesulfonic acid (PTSA). The acid catalyst exhibits excellent reusability, maintaining activity over five cycles. Subsequently, a one-pot, two-step whole-cell conversion system utilizing genetically modified Escherichia coli strains (E. coli PCA and E. coli 2,4-PDCA) converts the generated TPA into 2,4-PDCA. By integrating the PET hydrolysis module with the 2,4-PDCA biosynthesis module, the study achieves an impressive overall efficiency of 94.01% in converting challenging PET waste into valuable 2,4-PDCA. Our research presents a rational design strategy for PET upcycling and 2,4-PDCA synthesis methods. This research provides a systematic approach to PET upcycling, demonstrating its feasibility and potential for industrial application.utf-8

Mini Review on the Photocatalytic Removal of Gaseous Ammonia: Current Status and Challenges

Ammonia gas (NH₃) is a notorious malodorous pollutant released mainly in agriculture and industry. With the increasing demand for ammonia, environmental pollution caused by ammonia discharge has seriously threatened human health and safety. Due to the discrete emission and low concentration of NH₃, photocatalytic oxidation is an economical and efficient treatment strategy. TiO₂, as a common photocatalyst, has been widely used by researchers for the photocatalytic removal of NH₃. In addition, surface modification, element doping, semiconductor recombination and metal loading are used to improve the utilization rate of solar energy and carrier of TiO₂ so as to find a catalyst with high efficiency and high N₂ selectivity. Further, at present, there are three main removal mechanisms of NH₃ photocatalytic oxidation: ·NH₂ mechanism, iSCR mechanism and N₂H₄ mechanism. Among them, N₂H₄ mechanism is expected to be the main removal path of NH₃ photocatalytic oxidation in the future because the removal process does not involve NO_x and nitrate. This review summarizes recent studies on the photocatalytic oxidation of NH₃, focusing primarily on NH₃ removal efficiency, N₂ selectivity, and the underlying removal mechanisms. Additionally, the potential future applications of NH₃ photocatalytic oxidation are discussed.
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Preparation, Characterization and Performance Assessment of Metal Complexes of Curcuma longa Extract as Sensitizers for Dye-Sensitized Solar Cells

The dye extract of Curcuma longa (turmeric), which is very rich in curcumin, was chemically modified by complexation reaction with Zn²⁺, Cu²⁺, and Fe³⁺ ions to enhance its stability, electron transfer and photovoltaic performance. The dye and complexes were characterized by Ultraviolet-Visible (UV-Vis) absorption and Fourier Transform Infra-Red (FTIR) spectroscopy of potential chromophores and functional groups. The spectral data obtained indicated that the curcuminoid ligands were successfully coordinated with the metal centers, resulting in red-shifted absorption bands from beyond 460 nm and C=O vibrational frequency decreasing below 1650 cm⁻¹. Complexation reaction resulted in improved photochemical response and enhanced light-harvesting potential. When compared, the solar cells fabricated with titanium dioxide (TiO₂) photoanodes sensitized by the complexes afforded improvement in the magnitude of short-circuit current density as well as power conversion efficiency compared to the devices sensitized with the crude extract. Among the three complexes, the Zn-complex afforded the highest efficiency (1.20%), attributed to favourable electronic coupling and reduced recombination losses. Computational studies conducted through quantum chemical calculations based on the curcumin structure supported the experimental findings. The findings from this study demonstrate that metal ions-natural dye complexes have potential for application as low-cost, eco-friendly and sustainable sensitizers, thereby opening a novel horizon in green photovoltaic technologies.utf-8