Catalyst Recovery Research Articles

Thin film photo(electro)catalysts for the generation of energetic vectors: success cases and challenges, a brief review

Abstract Thin-film semiconductors are excellent candidates for converting solar energy into chemical energy via water splitting because of their outstanding physical and chemical properties. This review aims to provide the most recent findings on the production of energetic vectors from photo-(electro-)catalytic water splitting using thin-film semiconductors as catalysts. Recent successful cases are discussed to provide the scientific community with a guide for the design of new and advanced thin-film semiconductors with maximum efficiency for scaling the process. In addition, the use of coatings to provide a higher amount of catalyst for photo(electro)catalytic H2 production is discussed. Some of the most critical challenges in this reaction, such as charge recombination, light absorption, catalyst recovery, and stability, have been effectively addressed by applying thin films. In addition, the design of adequate thin-film photo(electro)chemical reactors is a critical step in improving efficiency and avoiding mass transfer limit steps. However, further research is required to provide continuous and low-cost manufacturing deposition techniques that favor optimal conditions to produce clean and renewable H2.

Iron(III) Bis(Phenol) Amine Complex Supported on Functionalized Graphene Oxide Nanosheets as an Efficient and Recoverable Catalyst for Room Temperature Epoxidation of Alkenes

ABSTRACTIron(III) bis(phenol) amine complex immobilized on the surface of functionalized graphene oxide nanosheets (FeLGDC‐AP/GO) has introduced as a highly active and recoverable catalyst for the epoxidation of alkenes. Optimizing different parameters in the oxidation of styrene as a model substrate revealed that 100% conversion and selectivity were obtained toward styrene oxide in the presence of H2O2 (28 wt%) as oxidant and water/acetone (3:1) as a solvent system in a bicarbonate buffer system. Furthermore, the catalyst displayed 54%–100% conversion and 90%–100% selectivity for the epoxidation of various aromatic and aliphatic alkenes under optimized reaction conditions at room temperature. The recycling experiment showed that FeLGDC‐AP/GO could be easily recovered by simple filtration and recycled six times without loss of the activity and selectivity. The high catalytic activity and selectivity of the developed catalyst could be attributed to the well‐designed coordination sphere around the iron core as well as the presence of GO support, which facilitates the electron transfer process beside the catalyst recovery.

Microwave-Powered Liquid Metal Degradation of Polyolefins.

Upcycling waste plastics is highly promising to tackle global white pollution while achieving sustainable development. However, prevailing approaches often encounter challenges in scalable engineering practices due to either insufficient plastic upcycling capability or arduousness in the separation, recovery, and purification of catalysts, which inevitably augments the cost of plastic upcycling. Here, the microwave-powered liquid metal synergetic depolymerization is presented to facilitate low-cost plastic upcycling. By leveraging the fluidity of liquid metals and their exceptional chemical-bond activation ability under microwave field, this method efficiently converts various polyolefins into narrowband hydrocarbon oil (Oil yield: 81 wt.% for polypropylene (PP), 85.9 wt.% for polyethylene (PE)) and high-value olefin monomers (C2-4  selectivity: 50% for PE, 65.3% for PP) over 30 successive cycles, resulting in a high turnover frequency of 2.83 kgPlastic mLLiquid metal -1. These captivating advantages offered by electromagnetically-powered liquid metals are also supported by their self-separation features, thereby paving the way for large-scale engineering solutions in waste plastic upcycling.

Comparing the Photocatalytic Activity of Suspended and Floating Ag-decorated TiO2 for Dye Removal

We proposed a two-step synthesis process to fabricate floating TiO2 and Ag-decorated TiO2 (Ag/TiO2) photocatalysts. In the first step, an ultrasound-assisted sol-gel method followed by spray drying was adopted to synthesize powder photocatalysts. Next, the powder samples were immobilized onto a floating polyurethane foam (PUF) support with an ultrasound-assisted impregnation method. The photocatalytic activity of TiO2 and Ag/TiO2 was evaluated to remove methyl orange (MO) as a dye pollutant in two suspended and floating photocatalytic systems. Ag decoration on TiO2 improved the optical and textural properties by narrowing the bandgap energy to 2.9 eV and increasing the surface area from 10 m2/g to 30 m2/g. Ag/TiO2 exhibited higher photocatalytic activity compared to TiO2 for MO removal, which was 98% for suspended and 95% for floating catalysts under simulated sunlight irradiation. In addition, floating photocatalysts exhibited higher photocatalytic activity over five cycles of reuse. Floating Ag/TiO2@PUF maintained 89% of its initial photoactivity, while suspended Ag/TiO2 lost 50% after the five cycles. Moreover, we investigated the effect of operating conditions on the photocatalytic performance of floating Ag/TiO2@PUF. Optimal conditions for the complete removal of MO below detection limits were obtained as follows: Ag/TiO2@PUF loading = 0.4:200 g/mL, initial MO concentration = 5 mg/L, time = 90 min, and pH = 4 under simulated sunlight irradiation. This study highlights the potential of floating photocatalyst systems as a sustainable, reusable, and scalable approach for wastewater treatment, addressing challenges in catalyst recovery and efficiency under real-world conditions.

The synergistic effect of Co atomic clusters and single atoms facilitates the fenton-like reaction on A- and R-TiO2

The regulation of single atom (SA) sites is crucial for the promotion of advanced oxidation processes (AOPs). Here A- and R-TiO2 with Co mixed sites (clusters and single atoms, CS) were prepared to degrade sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS). Co CS/A-TiO2+PMS system can completely remove SMX within 14 min under secondary effluent and dark conditions, and its rate constant (0.4926 min-1) was 4.4, 3.2 and 2.5 times higher than that of Co SA/R-TiO2, Co SA/A-TiO2 and Co CS/R-TiO2 systems, respectively. Experiments and calculations verified that the electron configuration of Co SA was optimized by Co clusters, facilitating the adsorption, conversion and desorption of PMS by Co SA, leading to the enhancement of Fenton-like activity. Co CS/A-TiO2 catalytic sponges exhibited exceptional degradation performance in microreactor treatment experiment. This work reveals the synergistic effect between SA and clusters at atomic level and provides an all-purpose strategy (catalytic sponge) for the recovery of non-magnetic catalysts in wastewater treatment.

Carbon-Chalcogenide Cross-Coupling Reactions in Water

: Over the past two decades, researchers have witnessed the synthesis of diaryl sulfides and diaryl selenides via transition metals-mediated carbon-heteroatom cross-coupling reactions in the presence of various organic and inorganic solvents. The use of water as a clean and environmentally friendly solvent in cross-coupling chemistry of C-S/Se bond formations has attracted profound interest owing to its availability, non-toxicity, low cost and renewability. The most commonly used solvents have been recognized as being of environmental concern, but the use of green and eco-friendly solvents like water is frequently considered with respect to the recovery of catalysts, isolation of products, and recycling. The fundamental interactions between the water and the transition metal catalysts or ligands are viewed from mechanistic aspects, which mostly favours the rational selection of high-performance and safe solvents. In this article, the authors intended to focus extensively on the critical role of water in various transition metals mediated C-S/Se cross-coupling methodologies.

Surface- and substrate-coated catalytic membrane for mitigating interference of water matrix species in intensified micropollutant confinement oxidation

The integration of advanced oxidation processes (AOPs) with membrane technology offers benefits for catalyst recovery and reducing membrane fouling. However, the application of the hybrid process could be hampered by the background species in water matrix. This study addresses this challenge by developing catalytic ceramic membranes (CCMs) with dual mechanisms to intensify acetaminophen (ACT) removal in water. The CCMs effectively activated peroxymonosulfate (PMS), achieving ACT degradation of 85% and 93% in real water matrices (reverse osmosis retentate and settled water, respectively) and 99% in MQ water. The CCMs demonstrated consistent performance across multiple operational cycles, even in the presence of humic acid (HA) (96% ACT reduction). The CCM design features Co3O4 catalytic layer on CCM surface, facilitating surface oxidation, reducing fouling, and TiO2 intermediate rejection layers serving as barrier for bulk organic pollutants, achieving 50% HA removal through rejection and 70% with 1.5mM PMS. This design facilitates catalytic degradation at the membrane surface, allowing retention and degradation of bulk organic pollutants and intermediates, while ACT permeates into CCM substrate. The surface oxidation and rejection enhanced confinement oxidation within the Co3O4-coated macropores, minimizing interference from background species. LC-QTOF analysis identified multiple degradation pathways, including hydroxylation, acetyl-amino group cleavage, side chain oxidation and benzene ring cleavage, with intermediates showing reduced toxicity. Reactive oxygen species involved in the system were identified and PMS activation mechanism was proposed. This research highlights the potential of the hybrid process, enhancing micropollutant removal by mitigating interference from background species, providing practical implications in water treatment applications.

Interfacial microenvironment to construct a three-dimensional fluoride-modified cobalt oxyhydroxide/polyvinylidene fluoride for the PMS activation to remove antibiotics

The monolithic membrane reactor for purification of antibiotics-contained wastewater offers a bright means to vanquish technological challenges associated with catalyst recovery, reaction efficiency, and mass transfer typically encountered in powdered heterogeneous catalysts. Herein, a fluoride-modified cobalt oxyhydrooxide (FCO) is planted on polyvinylidene fluoride (PVDF) film via constructing a microenvironment of Co2+-F- interaction. This optimized monolithic PVDF-supported FCO (FCO-PVDF) can completely remove tetracycline, ciprofloxacin and sulfadiazine via the peroxy-monosulfate (PMS) activation within 6 min. Additionally, the FCO-PVDF maintains outstanding resistance to environmental interference and high activity stability without decay after 8 consecutive cycles. Our investigations reveal that such exceptional performance stems from the exposure of cobalt-contained active sites for PMS activation and enhanced mass transfer in 3-D structure, leading to efficient generation of active species. Experiment and characterization demonstrate 1O2 active species play the most crucial role in eliminating antibiotics, in which perform PMS decomposition at a cobalt-exposed interface of FCO-PVDF. This work underscores the significance of designing PVDF membrane integrated fluoride-modified cobalt oxyhydroxide by constructing a unique interface microenvironment for PMS activation towards antibiotics removal.

Mechanochemistry Strategy in Metal/Fe3O4 with High Stability for Superior Chemoselective Catalysis.

While noble metal nanoparticles (MNPs) exhibit remarkable performance in heterogeneous catalysis and their incorporation into crystalline materials can fully exploit the combined advantages of both, achieving introduction of nanoclusters during material crystallization, precisely controlling their interactions, and facilitating catalyst recovery remain significant challenges. In this study, Au NPs, Pt NPs, and Pd NPs are supported on magnetic Fe3O4, enabling the modulation of the electronic states of MNPs by adjusting the introduction method. Notably, the catalysts (Pt/Fe3O4, Au/Fe3O4, and Pd/Fe3O4) demonstrate excellent activity in chemoselective reactions: cinnamaldehyde (CAL) hydrogenation (turnover number: 20,135 h-1), nitrobenzene hydrogenation (with 99.9% selectivity for major nitrobenzene derivatives and robust stability at 19 cycles), and 3-nitrophenylacetylene (3-NPA) hydrogenation (yielding up to 98.4% 3-aminophenylacetylene (3-APA)), in stark contrast to the low activity of comparable catalysts. This paper proposes a novel and versatile solid-phase mechanochemistry strategy that achieves precise control over the microenvironment of MNPs while maintaining their inherent activity, thereby offering an effective approach to develop catalysts with high specificity and easy recovery capabilities.

Peptide-Functionalized Gold Nanoparticles as Organocatalysts for Asymmetric Aldol Reactions

The use of high catalyst loading is required for most of the organocatalyzed asymmetric aldol reactions in organic synthesis, and this often presents challenges during purification and difficulties in catalyst recovery from the reaction mixture. The immobilization of the catalyst onto gold nanoparticles (AuNPs) can change the structural conformations of the catalyst, thereby improving its catalytic activity and reusability. Herein we report on the synthesis of aldolase mimetic peptide coupled to gold nanoparticles (AuNPs) as efficient organocatalysts for asymmetric aldol reaction. AuNPs were synthesized using the Turkevich method. The conjugation of the peptide to AuNPs was characterized using surface plasmon resonance (SPR), Raman and X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM) was used for particle size determination. The produced nanoparticles, whose sizes depended on the reduction method, were quasi-spherical with a relatively narrow size distribution. The peptide–AuNP conjugates were evaluated for aldol reaction catalytic activity between carbonyls p-nitrobenzaldehyde and cyclohexanone. The products were obtained with good yields (up to 85%) and enantioselectivity (up to 94%). The influence of organic solvents, pH and buffer solutions was also investigated. The results showed that the buffer solutions regulated the colloidal stability of AuNPs, resulting in a significant enhancement in the catalytic rate of the peptide–AuNP conjugate.

Environmentally benign synthesis of NiO nanoparticles: Potential catalysts for Knoevenagel condensation with promising anti-cancer and anti-diabetic activities

With rising environmental awareness, there is an increasing demand for sustainable practices, leading to the growing popularity of green synthetic methodologies that focus on simplicity and non-toxicity. The study presents an efficient eco-friendly route for synthesizing nickel oxide nanoparticles using the Punica granatum L. fruit juice extract. The synthesized nanoparticles were characterized by Ultraviolet–visible Diffuse Reflectance Spectroscopy (UV–Vis DRS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Dynamic Light Scattering (DLS), Zeta potential and Brunauer-Emmett-Teller (BET) analyses. The nanoparticles exhibited a face-centered cubic phase, with an average crystallite size of 10 nm and a nearly spherical shape. The specific surface area of the nanoparticles was found to be 113.73 m2/g. The nanoparticles served as highly effective, heterogeneous, and sustainable catalysts for the Knoevenagel condensation reactions involving various substituted aromatic aldehydes and active methylene compounds under non-toxic and moderate conditions. The reactions proceeded smoothly with excellent product yields in short time frames with convenient work-up procedures, and easy catalyst recovery, exhibiting high Turnover Number (TON) and Turnover Frequency (TOF). The catalytic performance of the nanoparticles remained consistent over five reaction cycles. The nanoparticles showcased significant cytotoxicity against the human liver cancer cell line (HepG2), achieving a 70.28 % inhibition at a concentration of 112.5 μg/mL. Moreover, the nanoparticles exhibited notable anti-diabetic properties by inhibiting the action of alpha-amylase enzyme. An enzyme inhibition of 52.04 % was attained at a nanoparticle concentration of 500 µg/mL, thereby promoting the hypoglycemic effect. Overall, this study showcases innovative applications of NiO nanoparticles synthesized from Punica granatum L. fruit juice extract, including their use as catalysts for the Knoevenagel condensation reactions, as anti-cancer agents against HepG2 cells, and as anti-diabetic agents through alpha-amylase inhibition.

Sustainable Design and Revolutionary Synthesis of Highly Recyclable Sulfonic Acid–Based Magnetic Nanoparticles as a Solid Acid for Synthesis of 2‐Substituted Benzimidazole and Bis Indole Methane Derivatives

ABSTRACTConcerning the objectives of green chemistry, silica‐coated magnetite nanoparticles provide a new way to implement an efficient and effective system for assisting catalyst recovery across multiple organic reactions. With Fe3O4 spheres serving as the core shell, the synthesis of sulfonic acid‐functionalized silica‐coated magnetic nanoparticles is presented in this paper. FTIR, PXRD, SEM, TEM, EDX, TGA, XPS, and VSM techniques were used to assess the prepared catalyst. The proposed nanocatalyst was employed to produce biological relevance 2‐substituted benzimidazole and bis indole methane derivatives. High yield, quick reaction time, soothing reaction conditions, extended functional group tolerance, and an accessible workup approach are the main advantages of synthesized nanoparticles. Furthermore, the present nanocatalyst may be recovered using an external magnet and retaining its effectiveness for up to six cycles. These are distinctive functions of the present approach.

Catalytically Active Site Mapping Realized through Energy Transfer Modeling.

The demands of a sustainable chemical industry are a driving force for the development of heterogeneous catalytic platforms exhibiting facile catalyst recovery, recycling, and resilience to diverse reaction conditions. Homogeneous-to-heterogeneous catalyst transitions can be realized through the integration of efficient homogeneous catalysts within porous matrices. Herein, we offer a versatile approach to understanding how guest distribution and evolution impact the catalytic performance of heterogeneous host-guest catalytic platforms by implementing the resonance energy transfer (RET) concept using fluorescent model systems mimicking the steric constraints of targeted catalysts. Using the RET-based methodology, we mapped condition-dependent guest (re)distribution within a porous support on the example of modular matrices such as metal-organic frameworks (MOFs). Furthermore, we correlate RET results performed on the model systems with the catalytic performance of two MOF-encapsulated catalysts used to promote CO2 hydrogenation and ring-closing metathesis. Guests are incorporated using aperture-opening encapsulation, and catalyst redistribution is not observed under practical reaction conditions, showcasing a pathway to advance catalyst recyclability in the case of host-guest platforms. These studies represent the first generalizable approach for mapping the guest distribution in heterogeneous host-guest catalytic systems, providing a foundation for predicting and tailoring the performance of catalysts integrated into various porous supports.

Catalytically Active Site Mapping Realized through Energy Transfer Modeling

AbstractThe demands of a sustainable chemical industry are a driving force for the development of heterogeneous catalytic platforms exhibiting facile catalyst recovery, recycling, and resilience to diverse reaction conditions. Homogeneous‐to‐heterogeneous catalyst transitions can be realized through the integration of efficient homogeneous catalysts within porous matrices. Herein, we offer a versatile approach to understanding how guest distribution and evolution impact the catalytic performance of heterogeneous host–guest catalytic platforms by implementing the resonance energy transfer (RET) concept using fluorescent model systems mimicking the steric constraints of targeted catalysts. Using the RET‐based methodology, we mapped condition‐dependent guest (re)distribution within a porous support on the example of modular matrices such as metal–organic frameworks (MOFs). Furthermore, we correlate RET results performed on the model systems with the catalytic performance of two MOF‐encapsulated catalysts used to promote CO2 hydrogenation and ring‐closing metathesis. Guests are incorporated using aperture‐opening encapsulation, and catalyst redistribution is not observed under practical reaction conditions, showcasing a pathway to advance catalyst recyclability in the case of host–guest platforms. These studies represent the first generalizable approach for mapping the guest distribution in heterogeneous host–guest catalytic systems, providing a foundation for predicting and tailoring the performance of catalysts integrated into various porous supports.

Oxygen vacancies-enriched spent lithium-ion battery cathode materials loaded catalytic membrane for effective peracetic acid activation and organic pollutants degradation

Advanced oxidation processes combined with membrane filtration technique offer a promising approach for pollution mitigation and catalyst recovery. Herein, a waste ternary lithium-ion battery cathode material of LiNixCoyMnzO2 (LNCM) loaded polytetrafluoroethylene (PTFE) membrane was synthesized for peracetic acid (PAA) activation (LNCM-PTFE/PAA) and 2,4,6-trichlorophenol (TCP) degradation. Such a novel membrane, with a catalyst loading of 10 mg (0.796 mg/cm2) of LNCM achieved 96.4 % removal of TCP (2 mg/L) within 20 min in neutral pH. The redox cycles of surface metals (such as Co3+/Co2+, Ni3+/Ni2+, and Mn4+/Mn3+/Mn2+) in spent LNCM efficiently enhance charge transfer and mediated PAA activation. And intrinsic oxygen vacancies in LNCM facilitated PAA adsorption and its cleavage. The resulting carbon-centered radicals (R-C•, CH3C(O)OO•) and 1O2 are identified as the primary reactive species that collaboratively participate in TCP degradation. Quantitative structure-activity relationship analysis demonstrated a substantial reduction in product toxicity. The successful practical application of the LNCM-PTFE/PAA membrane was exemplified by treating chlorophenol industrial wastewater. This study presents a new LNCM-PTFE/PAA catalytic membrane for high-efficiency water treatment and a novel perspective for green utilization of waste LNCM.

Ultrafast complete dechlorination enabled by ferrous oxide/graphene oxide catalytic membranes via nanoconfinement advanced reduction

Chlorinated organic pollutants widely exist in aquatic environments and threaten human health. Catalytic approaches are proposed for their elimination, but sluggish degradation, incomplete dechlorination, and catalyst recovery remain extremely challenging. Here we show efficient dechlorination using ferrous oxide/graphene oxide catalytic membranes with strong nanoconfinement effects. Catalytic membranes are constructed by graphene oxide nanosheets with integrated ultrafine and monodisperse sub-5 nm nanoparticles through simple in-situ growth and filtration assembly. Density function theory simulation reveals that nanoconfinement effects remarkably reduce energy barriers of rate-limiting steps for iron (III)-sulfite complex dissociation to sulfite radicals and dichloroacetic acid degradation to monochloroacetic acid. Combining with nanoconfinement effects of enhancing reactants accessibility to catalysts and increasing catalyst-to-reactant ratios, the membrane achieves ultrafast and complete dechlorination of 180 µg L−1 dichloroacetic acid to chloride, with nearly 100% reduction efficiency within a record-breaking 3.9 ms, accompanied by six to seven orders of magnitude greater first-order rate constant of 51,000 min−1 than current catalysis. Meanwhile, the membranes exhibit quadrupled permeance of 48.6 L m−2 h−1 bar−1 as GO ones, because nanoparticles adjust membrane structure, chemical composition, and interlayer space. Moreover, the membranes show excellent stability over 20 cycles and universality for chlorinated organic pollutants at environmental concentrations.

Ecofriendly magnetic nanocomposite (Fe3O4/SiO2/Ag) fabrication for sustainable dye wastewater management: catalysis and SERS for a cleaner approach.

Our study focuses on sustainable dye wastewater management through catalysis, scrutinized by surface-enhanced Raman spectroscopy (SERS) using an ecofriendly magnetic nanocomposite (Fe3O4/SiO2/Ag (FSA)). To our knowledge, the use of green synthesis for fabricating nanocomposites from a single source, namely Nerium oleander leaves, has not been extensively explored. This poses a distinctive and challenging approach, differentiating it from conventional chemical methods. Analytical investigations confirm the nanocomposite morphology, featuring Fe3O4 cubic cores with SiO2 spheres and silver nanoparticles (AgNPs) decoration. Efficient catalysis rapidly degrades unary and binary dye systems (MB, RhB, and MB + RhB), with high efficiency in short durations (MB: 96% in 10min, RhB: 94% in 2min, MB + RhB: 96% MB and 91% RhB in 9min) and with elevated "k" values. SERS monitors water quality, revealing complete degradation and quenching of dye fingerprints with fabricated nanocomposite FSA. The nanocomposite exhibits reusability over four cycles by easy recovery of catalyst with external magnet. The nanocomposite achieved 89.7% degradation efficiency in real-time household wastewater treatment. The proposed research aligns with UN SDGs 6 and 15 and this approach holds promise for advancing industrial waste management.

Advancement in Heterogeneous Catalysts for the Synthesis of Benzothiazole Derivatives

AbstractBenzothiazole derivatives, a class of heterocyclic compounds, hold significant relevance in medicinal chemistry, materials science, and agrochemicals due to their diverse biological activities and applications. The conventional synthetic routes often involve harsh conditions and generate significant waste, prompting the exploration of more sustainable approaches. This work offers a comprehensive analysis of the developments in the use of heterogeneous catalysts for the production of benzothiazole derivatives, covering research from 2013 onward. Compared to traditional techniques, heterogeneous catalysts provide improved sustainability, efficiency, and recyclability. The review covers many heterogeneous catalysts and discusses their selectivity, recyclability, and catalytic activity. The utilization of heterogeneous catalysts is noteworthy as it facilitates the synthesis process's overall sustainability by allowing for milder reaction conditions, less environmental effect, and easier catalyst separation and recovery. The potential of heterogeneous catalysis in promoting the production of benzothiazole derivatives and satisfying the increasing need for these substances in various industrial applications is also highlighted.

A Kinetic and Mechanistic Study of Ir (III)-Catalyzed Oxidation of Methionine by HCF (III) in an Aqueous Alkaline Medium

Introduction: The kinetic study of Ir (III) chloride-catalyzed oxidation of methionine by hexacyanoferrate (abbreviated as HCF) III ions in aqueous alkaline medium was performed spectrophotometrically at constant ionic strength of 0.5 moldm-3 and temperature of 35±0.1°C. Methods: The progress of the reaction was found to be first-order rate dependence kinetics with respect to [HCF (III)], [OH-], and [IrCl3]. The rate of reaction was found to decrease with an increased concentration of methionine. The ionic strength of the reaction mixture showed a positive salt effect on the reaction rate. Different activation parameters were also evaluated by studying the reaction at four different temperatures. The stoichiometry of the reaction showed Methionine: HCF (III) = 1:4. Result: The oxidation product of the reaction was found to be methionine sulphone, which was identified by an organic solvent method and IR Spectroscopy. Further, a suitable mechanism was proposed to explain all the experimental results. Conclusion: It is assumed that the reaction proceeded through complex formation between substrate (oxidant) and iridium trichloride. A rate law was derived, which verified the results. CH3-S-(CH2)2-CH (NH2)-COO- + 4HCF (III) Ir (III), H2O→ CH3-SO2-(CH2)2-CH-(NH2)-COO- + 4HCF (II)

Oxidative degradation of chitosan by Fe-MCM-41 heterogeneous Fenton-like system

We herein disclosed an efficient multiphase Fenton-like catalytic system for oxidative degradation of chitosan. By utilizing Fe-MCM-41, featured with regular mesoporous structure and high specific surface area, the activation efficiency of H2O2 was significantly enhanced and the chitosan degradation efficiency proved by 28.1% higher than the conventional system using H2O2 alone. Under optimized conditions (5 g/L chitosan, 0.5 g/L Fe-MCM-41, 0.16 mol/L CH3COOH, 0.86 mol/L H2O2, 50 °C, 140 min), the viscosity reduction rate of chitosan reached an impressive 98.2%. Among the catalysts tested, Fe-MCM-41 with a loading factor of x = 0.12 demonstrated optimal degradation performance. After four recycles, the degradation efficiency maintained > 93.6%, demonstrating its excellent stability and recyclability for potential industrial applications. Kinetic studies provided further elucidation of the reaction mechanism, which indicated that the degradation process of chitosan followed a first-order kinetic model, with an apparent activation energy (Ea) of 48.91 kJ/mol. This novel and efficient strategy for chitosan degradation, addressed the challenges of catalyst recovery and secondary pollution typically associated with traditional Fenton systems, and posed broad application potential for polysaccharide material processing.