Recycling Tests Research Articles

Tandem Oxidation-Condensation Tandem Catalysis via a Multifunctional Cu-Based Metal-Organic Framework.

The development of heterogeneous catalysts for tandem reactions remains a significant challenge for practical applications, primarily due to the need for multiple isolated catalytic sites. This study presents a novel metal-organic framework (MOF), Cu-AIPA, formulated as Cu(AIPA)(DMF)2 (AIPA: 2-amino isophthalic acid, DMF: N, N-dimethylformamide). The Cu-AIPA framework integrates three distinct catalytic mechanisms: redox activity, Brønsted basicity, and Lewis acidity. The structure of Cu-AIPA features redox-active Cu(II) centers and Brønsted basic sites, enabling the sequential transformation of alcohols to aldehydes and their subsequent condensation into imines. The close spatial arrangement of these redox-active/Lewis acidic and basic sites within the confined pores of Cu-AIPA facilitates efficient tandem catalysis. This process involves oxidizing benzyl alcohol to benzaldehyde using TEMPO without requiring an external base, followed by amine condensation. Compared with HKUST-1, another Cu-based MOF with a high surface area, Cu-AIPA demonstrated superior catalytic performance at room temperature. Recyclability tests revealed that Cu-AIPA retained over 90% conversion efficiency across at least three catalytic cycles. This study highlights the potential of MOFs incorporating multiple catalytic sites and confined pore structures for tandem reactions, emphasizing their potential for scalable and sustainable industrial applications.

Catalytic Performance of Oxydianiline-Derived Polybenzoxazine in the Cycloaddition of CO2 with Epoxides for Selective and Cleaner Production of Cyclic Carbonates

Benzoxazine-based polymer (PBZ) acts as a catalyst for converting CO2 into cyclic carbonates. PBZ-ODA was successfully synthesized and examined for its catalytic efficiency, proving to be effective under milder conditions with higher yields at room temperature without solvents. Various terminal monoepoxides showed good to excellent conversion rates, while epoxides with aromatic or bulky groups and second oxirane rings also were able to produce corresponding cyclic carbonates. Recyclability tests demonstrated that regenerated PBZ-ODA retained 93% of its catalytic activity. Overall, there was a low catalyst deactivation, as investigated by chemical experiments, SEM-EDX, TGA, FT-IR, XPS, XRD and NMR. The catalyst is reusable and suitable for use in flow or batch reactors.

Non‐Covalent Immobilization of Chiral Rhodium Catalysts on Carbon Nanotubes for Asymmetric Hydrogenation

AbstractSupported chiral catalysts were prepared by ionic anchoring of two cationic rhodium complexes (A and B) onto functionalized carbon nanotubes (CNTs). The immobilization of the Rh complexes was done by applying two ionic anchoring strategies: i) electrostatic interaction with the negatively charged surface of carboxylate‐functionalized CNTs (CNT‐COO−); ii) electrostatic interaction through a heteropoly acid (HPA) spacer previously grafted at the CNTs surface (CNT‐HPA). The characterization of the obtained CNT‐COO−@complex A, CNT‐COO−@complex B, CNT‐HPA@complex A, and CNT‐HPA@complex B materials by ICP, TEM and XPS showed the successful anchoring of the Rh complexes onto the supports. The HPA spacer was found to increase the catalyst's stability and to limit the effect of the CNT surface on the catalytic performances of the immobilized Rh complexes. CNT‐HPA@complexes performed the hydrogenation of dimethyl itaconate into methyl succinate with high conversions (83–100 %) and good enantioselectivities (58–63 %). The recyclability tests showed the catalysts were less active but still enantioselective after recycling.

Visible light photocatalytic degradation of water-soluble organic pollutants in aqueous solution by thulium copper oxide nanostructures: sonochemical synthesis, characterization, optimization of conditions, and mechanisms

The problem of water contamination has grown significantly in recent years, and the development of novel materials capable of effectively removing these toxins is imperative. The Tm2Cu2O5 nanophotocatalyst for the decolorization of various organic pollutants that are soluble in water is presented in the current study. A quick and easy sonochemical process was used to create Tm2Cu2O5 nanostructures, which had an appropriate bandgap of 1.6 eV according to DRS spectroscopy. The BET result indicated type III isotherm with H3 hysteresis and the specific surface area of 5.9788 m2 g−1. To get the maximum effectiveness, a number of variables were carefully examined, including the pH of the medium, the concentrations of organic pollutants, the types of organic contaminants, and the doses of Tm2Cu2O5. The outcomes demonstrated that Tm2Cu2O5 was very successful in eliminating various organic pollutants from water. For instance, 100% of the erythrosine was destroyed when 50 mg of Tm2Cu2O5 and 10 ppm dye were utilized under visible irradiation for 35 min. Subsequent analysis utilizing Tm2Cu2O5 as a photocatalyst showed that hydroxyl radicals were the main cause of pollutant photodegradation. The recyclability test showed that Tm2Cu2O5 is very stable and after five cycles, the degradation performance reduced by 7.8% from the first cycle (100.0%) to about 92.2%. According to this research, Tm2Cu2O5 is a promising choice for creating novel materials that efficiently eliminate water pollutants.

Ketjenblack-Supported and Unsupported ZrO2-ZrN Nanoparticle Systems for Enabling Efficient Electrochemical Nitrogen Reduction to Ammonia.

Artificial N2 fixation via the electrocatalytic nitrogen (N2) reduction reaction (NRR) has been recently promoted as a rational route toward reducing energy consumption and CO2 emission as compared with the traditional Haber-Bosch process. Nevertheless, optimizing NRR relies on developing highly efficient electrocatalysts. Herein, we report on the reliable and reproducible synthesis of two promising electrocatalysts in either the presence or absence of Ketjenblack (KB), namely, ZrO2-ZrN@KB and ZrO2-ZrN systems, synthesized through the nitriding of Zr. Both materials had never previously been considered for NRR, to the best of our knowledge. Nevertheless, both of these electrocatalysts incorporated a combination of tetragonal ZrO2, ZrON, and cubic ZrN and showed excellent activity and durability toward NH3 formation. Moreover, the maximum NH3 production rate of 84.1 μg h-1 mg-1 at -0.7 V vs a reversible hydrogen electrode (RHE) was achieved with the ZrO2-ZrN electrocatalyst with an impressive Faradaic efficiency of 21.2% at -0.6 V vs RHE, indicating a high selectivity associated with the NRR. Additionally, the catalysts demonstrated excellent stability during the electrolysis process and recycling tests. We postulate that the combination of exposed active sites of ZrN and ZrO2 likely contributes to the enhanced NRR performance attributed to ZrO2-ZrN.

Adsorption and Removal of 2,4,6-Trinitrotoluene by a Glycoluril-Derived Molecular-Clip-Based Supramolecular Organic Framework.

A glycoluril-derived molecular-clip-based supramolecular organic framework (clip-SOF) with intrinsic porosity was prepared. The clip-SOF was used for the adsorption and removal of 2,4,6-trinitrotoluene (TNT) driven by noncovalent interactions. The efficiency of TNT removal by clip-SOFs is up to 88.5% in adsorption equilibrium, and the TNT adsorption capacity of clip-SOFs is about 40.2 mg/g at 25.0 °C. Clip-SOFs have good reusability, exhibiting almost no loss in performance in ten consecutive recycling tests. This work not only provides a new method for adsorbing energetic materials, but also promotes the application of supramolecular hosts in crystal engineering.

Coupling UiO-66 MOF with a Nanotubular Oxide Layer Grown on Ti-W Alloy Accelerates the Degradation of Hormones in Real Water Matrices.

To enable the photoelectrocatalytic treatment of large volumes of water containing low concentrations of pollutants, this study introduces a hybrid photocatalyst, composed of nanotubular oxides grown on TixW alloy (x = 0.5 and 5.0 wt %) modified with UiO-66 MOF, for degradation of estrone (E1) and 17α-ethinyl estradiol (EE2). The oxide layer (Nt/TixW) was prepared via anodization, while UiO-66 nanoparticles were synthesized by using a solvothermal process. Different techniques for modifying nanotubular oxides were evaluated to maximize the photocatalytic activity and the sorption process. In photo(electro)catalytic experiments using low concentrations of E1 and EE2 synthetic solutions and UV-vis radiation (100 W/cm2), all modified materials exhibited approximately 40% higher degradation compared to the unmodified photocatalyst, keeping the same sequential performance of the photocatalysts (Nt/TiO2 < Nt/Ti-0.5W < Nt/Ti-5.0W) independent of the treatment. This enhancement was attributed to the MOF's increased hormone sorption, with no synergistic interaction observed between the photocatalyst and the adsorbent. In real water supply matrices, the photoelectrocatalytic removal rate of E1 using Nt/Ti-5.0W modified UiO-66 under UV-vis radiation and 1.3 V was 0.168 s-1, while for EE2, it was 0.310 min-1, approximately 1.78 and 18.21 times faster than obtained with the unmodified photocatalyst. The slower degradation rate of EE2 compared to that of E1 is attributed to the formation of denser intermediates that compete with smaller organic molecules in the real matrix. The cooperative effect between NT/TixW and UiO-66 favored the confinement of pollutants and by-products within the UiO-66 cavity, minimizing the diffusion effects and promoting the degradation of these compounds by the OH· radical generated at the oxide/solution interface. Among the tested electrodes, NT/Ti5W modified with UiO-66 demonstrated the highest efficiency and stability during the recycle tests. This highlights its promise for applications in photocatalytic processes for treating water supplies with low pollutant concentrations.

Remarkable recycling processes of conjugated polymers with titanium dioxide quantum dots as photocatalysts for photodegradation of hazardous industrial wastewater

This study presents the synthesis and characterization of a novel polyaniline-titanium dioxide quantum dot (PA-TQD) composite for enhanced photocatalytic degradation of hazardous industrial wastewater. The composite was synthesized via in-situ polymerization and characterized using FTIR, XRD, TEM, BET, and TGA, confirming the integration of TiO₂ quantum dots (2.8–5.3 nm) into the polyaniline matrix (particle size 35–40 nm). BET analysis revealed a surface area of 50.30 m²/g for PA-TQD, significantly higher than 28.18 m²/g for pure polyaniline, contributing to its improved photocatalytic activity. Photocatalytic degradation experiments on methyl orange dye demonstrated a 60.1% degradation efficiency under xenon irradiation, compared to 35% for polyaniline alone. The photocatalytic rate constant of PA-TQD was 0.032 min⁻¹, indicating enhanced performance.In recycling tests, PA-TQD retained 73.8% of its photocatalytic efficiency after four cycles, showcasing strong reusability. TGA analysis confirmed the composite's enhanced thermal stability, with minimal weight loss up to 250 °C. COD analysis of real industrial wastewater samples showed effective pollutant reduction, with COD values for PA-TQD ranging from 756 to 1212 ppm. However, further optimization is needed to meet regulatory limits set by Saudi environmental laws (<1000 ppm COD). The synergy between polyaniline and TiO₂ quantum dots enhances charge separation, increases active sites, and makes PA-TQD a promising recyclable photocatalyst for sustainable wastewater treatment applications.

Iron and Zinc Metallates Supported on Ion Exchange Resins: Synergistic Catalysts for the Solvent‐Free Cyclic Carbonate Synthesis from Epoxides and CO2

AbstractDespite extensive research into developing efficient and environmentally friendly catalysts for converting CO2 over the last decade, the search for a robust and cost‐effective catalytic system is ongoing. This study describes developing and applying a new catalytic system using inexpensive ferrate and zincate anions immobilized on easily available commercial ion exchange resins (IER) to produce cyclic carbonates from CO2 with high efficiency and low cost. Two polystyrene‐based anion exchange resins, AmberlystTM A26‐Cl (A26‐Cl) and AmberliteTM IRA‐400‐Cl (IRA400‐Cl), were compared. The results demonstrated the catalysts’ remarkable activity under mild conditions and demonstrated the synergistic effect between the polystyrene support and the active ammonium metallates, presenting a scalable, eco‐friendly method for cyclic carbonate production using waste CO2. A Design of Experiment (DoE) approach was implemented to optimize the catalytic cycloaddition of CO2. The reaction scale‐up to produce a 5 g batch of propylene oxide and conducting recycling tests demonstrated that the catalyst retained its activity over four cycles. The research also explored the use of various epoxides and found that terminal epoxides produced very good yields. In summary, this study introduces a cost‐effective, scalable method for converting CO2 into valuable cyclic carbonates, leveraging the synergistic effects of polystyrene supports and active ammonium metallates.

Visible light sensitive photocatalytic properties of Bi2WO6/Ag2CO3 heterojunction combined with reduced graphene oxide for the removal of organic dyes

Herein, an efficient Bi2WO6/Ag2CO3/rGO (BW/AC/rGO) heterojunction photocatalyst with different loadings of reduced graphene oxide (rGO) was synthesized by the simple hydrothermal process. The incorporated rGO serves as a redox mediator for promoting the transfer of electrons and improves the reunion time of photogenerated charge carriers. The structural analysis confirms the heterojunction formation and the optical analysis affirms the modulated bandgap and prolonged lifetime (309 ns) of charges favorable for visible light-sensitive photocatalysis. The photocatalytic studies reveal that the prepared BW/AC/rGO photocatalyst with 40 % loading of rGO exhibited a higher degradation efficiency of 97 % at 230 min in degrading rhodamine B dye. The recyclability test reveals that the photocatalyst is consistent in degrading with good photostability after four consecutive cycles. The radical trapping experiments proved that electrons and hydroxyl radicals play a crucial role in enhancing photocatalytic activity. These findings suggest that the heterojunction-designed BW/AC/rGO photocatalyst is a potential candidate for environmental remediation.

Oxygen Vacancy Sites Enable Efficient Photocatalytic Oxidation of Nitric Oxide: The Role of W/Mo Valence Transition in Bi2W(Mo)O6‐x

AbstractOxygen vacancy (Ov) sites play a critical role in the activation and deep oxidation of nitric oxide (NO). However, controlling the concentration and type of Ov remains a significant challenge. In this study, Bi2W(Mo)O6‐x is investigated as a model system and demonstrates that increasing the concentration of Ov substantially enhances the efficiency of air NO removal. Increasing the Ov concentrations in Bi2WO6‐x and Bi2MoO6‐x improves NO removal efficiency ≈12‐ and 11‐fold, respectively, compared to their low‐Ov counterparts. This enhancement is attributed to improved adsorption and activation of NO/O2 molecules, better separation and transfer of photogenerated carriers, and increased visible light absorption. Notably, Bi2WO6‐x remains highly stable over ten recycling tests for continuous air NO deep photooxidation, while Bi2MoO6‐x shows a 43.5% decrease in efficiency after ten runs. This sustained performance is attributed to stable Ovs without changes in metal ion valence, unlike Bi2MoO6‐x, where instability arises from the reduction of Mo6+ to Mo4+. In situ DRIFTS reveals possible pathways for the deep photooxidation of NO to nitrate (NO3−). This study provides valuable insights into designing high‐performance, durable catalysts by effectively controlling Ov concentration and type, paving the way for efficient photocatalytic air purification technologies.

Hierarchically-porous resin for the adsorption of organic matter in raffinate produced by solvent extraction from the vanadium industry

Solvent extraction wastewater contains high concentrations of organic pollutants and metal ions, making it difficult to treat. This paper presents a method of using hierarchically-porous adsorption resin to recover organics from raffinate and regenerate the resin, addressing secondary pollution in extraction processes. The chosen resin, WS6108, removes over 95 % of organics from raffinate, with high metal ion concentrations enhancing its adsorption efficiency. The article conducted an optimization experiment and mechanism study on WS6108 resin for adsorbing organic matter in vanadium raffinate (OIVR), followed by desorption and recycling tests. Results showed WS6108 resin achieved a 96.7 % adsorption efficiency at a solid–liquid ratio of 24 g/L after optimization. The chosen methanol desorbent achieves over 99 % desorption efficiency for the WS6108 cycle under specific conditions. The resin’s performance remains stable for up to 45 cycles. Adsorption isotherms and kinetic experiments indicate that OIVR adsorption by WS6108 resin is endothermic, non-spontaneous and entropy increasing. Moreover, the adsorption kinetics of OIVR by WS6108 resin followed a pseudo-second-order model, based on the activation energy, liquid film diffusion was considered the main rate-controlling step. A column experiment was conducted to verify that WS6108 resin can be used in real vanadium raffinate to remove organics. Density functional theory (DFT) revealed that strong hydrogen bonding, π-π stacking and excellent adsorption diffusion behavior drive OIVR adsorption. This study aims to increase the use of adsorption to treat oily wastewater generated by solvent extraction.

Green synthesis of benzimidazole derivatives using copper(II)-supported on alginate hydrogel beads

The study addresses the challenge of developing sustainable and efficient catalytic systems for the synthesis of benzimidazole derivatives, which are of significant importance in the field of medicinal chemistry due to their diverse biological activities. The objective is to develop a recyclable and environmentally friendly catalyst utilizing copper(II)-loaded alginate hydrogel beads, which can facilitate the synthesis of these compounds while minimizing environmental impact. The preparation process entails crosslinking sodium alginate with copper(II) ions to form hydrogel beads, which are then washed and characterized through techniques such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Inductively coupled plasma (ICP), and Zeta potential to analyses the morphology, composition and porosity of the beads. The catalytic performance is evaluated through recycling tests, which demonstrate the catalyst's ability to maintain selectivity and activity over multiple reaction cycles. The Cu(II)-Alg hydrogel beads were used for synthesizing substituted benzimidazole derivatives in a water-ethanol solvent at room temperature. This method offers significant advantages, including extremely mild reaction conditions, short reaction times (<1 h), high yields (70–94 %), and ease of processing. The most significant results indicate that the Cu(II)-alginate catalyst exhibits a high loading capacity and retains its catalytic efficiency for at least 3 cycles, thereby highlighting its potential for sustainable applications in organic synthesis.

Enhanced and prolonged adsorption of ammonia gas by zeolites derived from coal fly ash.

In this study, zeolites were synthesized from coal fly ash (CFA) using NaOH (Na-X type) and KOH (chabazite-K type) and used for the adsorption of ammonia gas in a fixed-bed reactor. Magnetic separation was used to decrease the Fe impurity content from 6.84 to 2.37 wt.%, and to increase the Si and Al content in non-magnetic fly ash (NMFA). BET surface areas of the zeolites increased significantly to 425.28 m2/g with an increase in micropore volume (ca. 0.12 cm3/g). FTIR and NH3-TPD analyses revealed that the increased surface area provided more acidic sites for enhanced ammonia gas adsorption. In particular, the zeolite (i.e., ZNF-X) synthesized from NMFA and NaOH showed the highest ammonia gas adsorption capacity (64.9 mg/g), owing to its high BET surface area and micropore volume. Although the initial adsorption capacity of commercial 13X zeolite (74.5 mg/g) was higher than that of ZNF-X, a much higher recycling efficiency for ZNF-X (92.0%) was achieved than for 13X (31.5%) during the five recycling tests because of the lower ammonia desorption temperature of ZNF-X. The results provide new insights into the synthesis of zeolites by upcycling of CFA and demonstrate the potential use of the generated materials for enhanced and prolonged removal of ammonia gas.

Photocatalytic degradation of cetirizine hydrochloride using polypyrrole decorated zinc ferrite nanohybrids under visible light irradiation.

The present work reports photocatalytic degradation of cetirizine hydrochloride (CTZ-HCl) utilizing polypyrrole (PPy) nanohybrids with ZnFe2O4 (ZnFe) nanoparticles. The synthesized materials were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectroscopy, BET, and scanning electron microscopy (SEM) techniques. UV diffuse reflectance studies (UV-DRS) revealed that the band gap was found to decrease with increase in the loading of PPy and Kubelka-Munk plots confirmed the bandgap values to be 2.14eV for ZnFe, 1.94eV for 1% PPy/ZnFe, 1.66eV for 3% PPy/ZnFe, and 1.38eV for 5% PPy/ZnFe. The photocatalytic performance against CTZ-HCl degradation was performed under visible light irradiation for 60min. The effect of catalyst dosage and the effect of drug concentration were investigated to confirm degradation behavior of the PPy/ZnFe photocatalysts. The degradation followed the pseudo-first-order kinetics model. Maximum photocatalytic degradation was observed to be 98% within 60min using 5% PPy/ZnFe as the photocatalyst. The recyclability tests revealed that the 5% PPy/ZnFe photocatalyst was reusable up to 4 cycles. Radical scavenging studies confirmed the generation of ●OH radicals that were responsible for the drug degradation. The degraded fragments were analyzed using LCMS technique and the tentative mechanism of degradation was proposed.

Copper Catalysts Anchored on Cysteine-Functionalized Polydopamine-Coated Magnetite Particles: A Versatile Platform for Enhanced Coupling Reactions.

Cysteine plays a crucial role in the development of an efficient copper-catalyst system, where its thiol group serves as a strong anchoring site for metal coordination. By immobilizing copper onto cysteine-modified, polydopamine-coated magnetite particles, this advanced catalytic platform exhibits exceptional stability and catalytic activity. Chemical modification of the polydopamine (PDA) surface with cysteine enhances copper salt immobilization, leading to the formation of the Fe3O4@PDA-Cys@Cu platform. This system was evaluated in palladium-free, copper-catalyzed Sonogashira coupling reactions, effectively catalyzing the coupling of terminal acetylenes with aryl halides. Additionally, the Fe3O4@PDA-Cys@Cu platform was employed in click reactions, confirming the enhanced catalytic efficiency due to increased copper content. The reusability of the platform was further investigated, demonstrating improved performance, especially in recyclability tests in click reaction, making it a promising candidate for sustainable heterogeneous catalysis.

Noble metal-free tandem catalysis enables efficient upcycling plastic waste into liquid fuel components

The lack of effective approaches for upcycling waste plastic has led to severe environmental pollution and squandering of carbon resources. While hydrocracking macromolecular polyolefins over typical metal-zeolite catalyst produces high quality liquid fuel components, the limited activity of base metal and restricted accessibility of acid sites within microporous zeolite renders this process still not in practical scale. A tandem catalyst comprising Ni-WO3/Al2O3 and Beta zeolite was developed for consecutive hydrocracking polyolefins, achieving a yield of 86.2 % of primarily gasoline-jet ranged hydrocarbons (mainly C5-C16 and minor C16+) at 280 °C. The incorporation of tungsten species onto Ni/Al2O3 largely enhances the surface acidity and accelerates the primary cracking process that converts polyethylene (PE) into medium-sized intermediates, which would readily diffuse into the pore networks of Beta and undergo further cracking to yield desired liquid hydrocarbons. In addition, this tandem catalyst also promotes facile hydrocracking of consumer-grade plastic waste and maintains excellent stability over 5 recycling tests. The noble-metal-free catalyst achieves an impressive liquid formation rate of 5.74 g·gcat.−1·h−1, rivaling the noble metal-based catalyst and demonstrating high application prospects.

Boosted direct electrochemical reduction of As(III) from arsenic wastewater via Cu(II)-assisted codeposition on a CuIn alloy electrode

Arsenic contamination is a severe environmental problem. A promising strategy for addressing this issue is the direct conversion of highly toxic As(III) to less toxic elemental arsenic (As(0)) using electrochemical reduction technology. In this study, a novel CuIn alloy nanoparticles-modified copper foam (CuIn NPs/CF) was prepared as an efficient cathode for the electrocatalytic reduction of highly mobile As(III) to solid As(0). Density functional theory (DFT) results revealed that the Cu-In bimetallic system exhibited weaker H atom bonding, and the Cu-ln surface was more favorable for the adsorption of *AsO₃ species than the Cu surface. Compared to the pristine CF electrode, CuIn NPs/CF was demonstrated to effectively suppressed the hydrogen evolution reaction with an enlarged hydrogen evolution potential of 1.45 V, and displayed a superior As(0) recovery yield. The conversion of As(III) to As(0) was further enhanced by adding Cu²⁺ to the electrolyte, facilitating a Cu-As co-deposition process. Notably, the CuIn NPs/CF electrode achieved an As(0) recovery yield of 5.38 mg cm⁻² after eight successive recycling tests. This work not only presents a green and sustainable strategy for As(III) removal, but also provides valuable insights into the rational design of Cu-based alloy cathodes for electrocatalytic reduction.

Hydrothermal Valorization of Biosugars with Heterogeneous Catalysts: Advances, Catalyst Deactivation, Mitigation Strategies and Perspectives.

Sustainable production of valuable biochemicals and biofuels from lignocellulosic biomass necessitates the development of durable and high-performance catalysts. To assist the next-stage catalyst design for hydrothermal treatment of biosugars, this paper provides a critical review of (1) recent advances in biosugar hydrothermal valorization using heterogeneous catalysts, (2) the deactivation process of catalysts based on recycling tests of representative biosugar hydrothermal treatments, (3) state-of-the-art understandings of the deactivation mechanisms of heterogeneous catalysts, and (4) strategies for preparing durable catalysts and the regeneration of deactivated catalysts. Based on the review, challenges and perspectives are proposed. Some remarkable achievements in heterogeneous catalysis of biosugars are highlighted. The understanding of catalyst durability needs to be further enhanced based on full examination of the catalytic performance based on the conversion of substrates, the yield, and selectivity of products. Further, a full examination of the physiochemical changes based on multiple characterization techniques is required to eclucidate the relationships between treatment variables and catalyst durability. Collectively, a clear understanding of the relationships between chemical reaction pathways, treatment variables, and the physiochemistry of catalysts is encouraged to be gained to advise the development of heterogeneous catalysts for long-term and efficient hydrothermal upgrading of biosugars.

Anchoring TiO2 and CuO nanoparticles on SnO2 nanotube arrays to construct ternary heterostructure for visible-light-driven photocatalytic degradation of green malachite dye

Designing and constructing heterostructure photocatalysts is necessary to facilitate the long-term separation of photogenerated charge carriers and enhance photocatalytic efficiency. Herein, a ternary nanocomposite photocatalyst based on SnO2, TiO2 and CuO semiconductors was successfully synthesized and employed as a highly effective photocatalyst for the malachite green (MG) dye degradation under visible light irradiation. According to the results, the ternary SnO2/TiO2/CuO nanocomposite demonstrated impressive photocatalytic activity (98.4 %) compared to pristine SnO2 nanotubes (40.3 %), binary SnO2/TiO2 (76 %) and SnO2/CuO nanocomposites (88 %), when exposed to 90 min of visible illumination. The photoreaction rate constant of SnO2/TiO2/CuO nanocomposite (0.0482 min−1) was found to be ∼8.5 times faster than SnO2 nanotubes (0.0057 min−1) against MG dye. This enhancement in photocatalytic performance can be attributed to the introduction of TiO2 and CuO which effectively suppress the recombination of photogenerated electron-hole pairs, accelerate the transfer of charge carriers, increase the active sites, and improve the optical absorption properties. Scavengers were used to elucidate the photocatalytic mechanism, exhibiting the pivotal role of •O2− and h+ in the photodegradation process. Besides, recyclability tests showed acceptable results after four cycles, confirming the stability and durability of the SnO2/TiO2/CuO nanocomposite against RhB dye degradation.