Search Results (399)

In this study, nine barium sulfate (BaSO₄)-supported heterogeneous catalysts (C1–C9) were synthesized via three modification strategies: stearic acid coating (C1–C3), physical doping (C4, C6, and C8), and sol-gel processing with calcination (C5, C7, and C9). Their comprehensive characterization revealed that sol-gel-synthesized C7 exhibited the most favorable surface properties, including well-dispersed Al–O–Si species, tetrahedrally coordinated Al³⁺, and abundant Brønsted acid sites. Their catalytic performance was evaluated in the chlorination of toluene, fluorobenzene, bromobenzene, and iodobenzene, using hydrochloric acid (HCl) as the chlorine source and either hydrogen peroxide (H₂O₂) or ammonium persulfate ((NH₄)₂S₂O₈) as the oxidant. C7 achieved complete toluene conversion (100%) at 60 °C under optimized conditions and exhibited high conversions of fluorobenzene (55%), bromobenzene (76%), and iodobenzene (46%). Notably, ammonium persulfate enabled a unique in situ halogen exchange pathway, yielding chlorobenzene as the exclusive product from bromobenzene and iodobenzene. XRD and XPS analysis of crystalline by-products confirmed the formation of NH₄HSO₄, BaSO₄, and NH₄Cl, providing evidence for the persulfate-driven radical mechanism. Iodine detection in upper-layer crystals confirmed iodobenzene products, while the absence of chlorine signals in the upper layer confirmed separation of organic and inorganic species. The detection of barium sulfate peaks confirms that the catalyst support retains its structural integrity under harsh reaction conditions, demonstrating chemical stability and reusability potential. Collectively, these findings establish a clear structure–activity relationship and demonstrate that the synergy between modified BaSO₄ surfaces and persulfate-generated radicals provides an efficient, sustainable platform for aromatic chlorination, offering significant potential for pharmaceutical, agrochemical, and fine chemical manufacturing applications. Full article

Biochar-supported rare earth oxides are herein assessed as heterogeneous catalysts for the UV-assisted Catalytic Wet Peroxide Oxidation (UV-CWPO) treatment of pharmaceuticals under mild conditions. Catalysts were synthesized by two different pyrolysis methods (activated carbon-assisted oxygen-limited pyrolysis in a muffle furnace, and inert-gas pyrolysis in a tubular furnace under nitrogen flow), and characterized by XRD, SEM, and N₂ adsorption–desorption isotherms. Their performance in assisting 385 nm UVA-LED CWPO treatment of acetaminophen (ACE), diclofenac (DCF), and metamizole (MTZ) was assessed under circumneutral pH conditions. The biochar-supported cerium-loaded catalyst prepared by oxygen-limited pyrolysis reported the highest activity, achieving 80% ACE and 70% DCF removals within 120 min of treatment, whereas MTZ was completely removed in less than 10 min, with only 16% of the removal attributable to adsorption. Superoxide radicals dominated the degradation mechanism, and photogenerated holes and hydroxyl radicals contributed moderately. Catalyst stability (minimal activity loss and negligible cerium leaching) was confirmed over five consecutive reuses. Degradation efficiency decreased ≈12–18% because of radical scavenging losses caused by the content of inorganic ions and organic matter in tap, river, and WWTP effluent waters. Treated effluents addressed lower toxicity than untreated solutions, reinforcing the environmental safety of this treatment strategy. Full article

Next-generation waste degradation and valorization technologies are increasingly developed as integrated platforms for pollutant removal, resource recovery, and circular manufacturing. This review critically evaluates degradation and valorization routes for liquid, organic solid, and inorganic/electronic waste streams from an engineering perspective. For liquid waste, advanced oxidation processes, photocatalysis, electrochemical oxidation, plasma treatment, and hybrid systems are assessed with emphasis on radical utilization, photon and electron efficiency, catalyst stability, byproduct formation, and reactor hydrodynamics. For organic solid waste, biological, thermochemical, catalytic, enzymatic, and mechanical pathways are compared for agricultural residues, textile waste, and industrial polymers, including fermentation, pyrolysis, hydrogenolysis, solvolysis, enzymatic depolymerization, and mechanical recycling. Their practical viability depends strongly on feed purity, product selectivity, monomer or fuel recovery, and the energy and separation requirements of downstream processing. For inorganic and electronic waste, hydrometallurgical, pyrometallurgical, biohydrometallurgical, and physical separation routes are examined for the recovery of critical metals, mineral phases, and non-metallic fractions. Industrially mature integrated flowsheets generally offer greater feed tolerance, whereas emerging selective routes provide improved recovery potential but remain constrained by reagent consumption, reaction rate, and scale. Across all waste classes, the review identifies reactor design, process intensification, reaction–separation integration, techno-economic analysis, and life-cycle assessment as essential tools for translating laboratory performance into scalable, economically competitive, and environmentally sustainable processes. Full article

Biodiesel production from waste cooking oils, non-edible oils and other low-grade lipid feedstocks is constrained by free fatty acids, water, salts, oxidation products, and the poor miscibility of triglycerides with short-chain alcohols. Carbon–inorganic hybrid catalysts are attractive because the inorganic phase can provide strong acid or base sites, while the carbon phase can alter dispersion, wettability, pore accessibility, microenvironment polarity, leaching, and recovery. Yet the term hybrid is often applied to materials for which the carbon component has not been shown to affect catalysis. This critical review therefore focuses on one defined reaction scenario: esterification and transesterification for biodiesel production from low-grade lipid feedstocks. The discussion is organized by the catalytic problem rather than by an unrestricted catalogue of materials. Carbon-supported CaO and MgO, carbon-coupled layered-double-hydroxide-derived mixed oxides, sulfonated carbon–inorganic acids, bifunctional acid–base systems, magnetically recoverable ferrite/carbon catalysts, and graphenic supports are compared through structure–activity relationships, reaction conditions, feedstock quality, FAME yield, heterogeneity, reusability, and post-reaction evidence. Particular attention is given to the distinction between a true interfacial effect and activity caused by leached Ca, K, Na or sulfonic species. A minimum evidence hierarchy is proposed, requiring carbon-only, inorganic-only, and physical-mixture controls, hot-filtration tests, elemental analysis of the liquid phase, recovered-mass accounting, and post-reaction structural characterization. The literature shows that high first-cycle yield is common, whereas water tolerance, low leaching, retained active-site density, and continuous operation remain uncommon. The most defensible future direction is therefore not greater compositional complexity, but simpler hybrid architectures designed around a specific failure mode and validated under realistic feedstock and reactor conditions. Full article

Biopolymers have emerged as effective stabilizing and capping agents in the green synthesis of metal nanoparticles due to their biocompatible, hydrophilic, and eco-friendly nature. Among these, bacterial polysaccharides, particularly exopolysaccharides (EPSs), offer distinct advantages over plant, algal, and fungal derived polymers, owing to their unique chemical structure rich in negatively charged functional groups that facilitate interactions with metal ions and enhance nanoparticles’ stability. Despite their properties, the practical application of AgNPs is often limited by aggregation, colloidal instability, and uncontrolled ion release. To address these challenges, in the present study, EPS-stabilized silver nanoparticles (AgNPs) were synthesized using a green approach. The synthesized biogenic AgNPs were immobilized with natural zeolite, a porous inorganic material, to improve stability and regulate functionality. The resulting catalytic material was partially characterized using structurally using spectrophotometry (UV-Vis), scanning electron microscope - energy dispersive X-ray analysis (SEM-EDAX), dynamic light scattering (DLS), and Fourier-transform infrared spectroscopy (FTIR). Furthermore, the synthesized green catalyst was evaluated for its photocatalytic degradation against synthetic dyes (methylene blue). In addition, its antibacterial potential was also assessed through determination of inhibitory concentration (IC₉₀) and minimum bactericidal concentration (MBC₉₉), highlighting its potential as a multifunctional biomaterial for environmental and biomedical applications. Full article

Natural bentonite, dominated by montmorillonite-type layered aluminosilicates, is increasingly considered as an inexpensive and environmentally acceptable support or catalyst for the thermochemical conversion of waste carbon streams. Its relevance to catalysis arises from a combination of cation-exchange capacity, swelling behavior, hierarchical porosity after modification, and the possibility of generating Brønsted, Lewis, redox and metallic active sites. This review critically evaluates bentonite modification strategies—acid activation, alkaline and sodium exchange, inorganic oxide pillaring, transition- and noble-metal impregnation, organosilane or surfactant functionalization, and carbon-based hybridization—with emphasis on their consequences for texture, acidity, thermal stability, metal dispersion and catalytic behavior. The review then connects these structure–property relationships with the emerging application of modified bentonites in plastic-waste thermocatalysis and hydrogen-rich product formation. The recent literature indicates that acid-modified bentonite can substantially improve liquid hydrocarbon formation from polyethylene, binder-free bentonite pellets can operate at kilogram-batch scale for drop-in fuels, and Ni-, Fe- or Ni–Fe-modified bentonite-type catalysts can promote tar cracking, reforming and gas upgrading. However, direct evidence for high hydrogen yields from plastic waste over bentonite remains narrower than the evidence for liquid-fuel production, biomass pyrolysis or model-compound reforming. Therefore, this article distinguishes between direct plastic-waste evidence and transferable evidence from biomass, acetic acid, tar and hydrocarbon reforming studies. The analysis identifies Ni-impregnated acid-activated or pillared bentonite, Ni–Fe/bentonite, and La/Ca-promoted Ni/bentonite as the most promising routes for plastic-derived hydrogen-rich syngas, while acid activation alone is best regarded as a pretreatment rather than a complete catalyst design. Key limitations include catalyst deactivation by coke, metal sintering, chloride poisoning from PVC, inconsistent reporting of gas yields, and insufficient life-cycle and techno-economic analysis. A roadmap is proposed for designing reproducible, scalable bentonite catalysts for circular plastic-waste valorization. Full article

Hybrid biological–inorganic (HBI) systems that integrate hydrogen-oxidizing bacteria (HOBs) with inorganic water-splitting catalysts have been developed as bioelectrochemical platforms for CO₂ conversion. This study used an HBI system to enrich HOBs under atmospheric air or a high CO₂ concentration. The HBI system operated with two different bioreactor configurations: a high-CO₂ condition, in which the bioreactor was sealed with an air-tight stopper and the headspace gas was replaced with CO₂ (100%), and an atmospheric air condition, in which the bioreactor was sealed with an air-permeable cap, gas exchange was allowed, and contamination was prevented. These bioreactors were inoculated with six rhizosphere soil samples, which were additionally enriched with a conventional gas-fermentation mixture. 16S rRNA gene amplicon sequencing revealed enrichment of the bacterial lineages mostly related to three main families under the high-CO₂ condition. On the contrary, the open-air system facilitated enrichment of aerobic HOBs, potentially occurring through the enrichment of more diverse bacterial lineages. The different enrichment conditions imposed distinct selective pressures on HOBs. The obtained results indicated that HBI systems provide an alternative enrichment platform for expanding the diversity of HOBs applicable to CO₂-based biomanufacturing. Full article

The oxygen reduction reaction (ORR) is the cathode cornerstone of fuel cells and metal-air batteries. Its inherent spin mismatch between triplet O₂ and singlet products causes sluggish kinetics that conventional catalyst designs cannot fully overcome. This review critically summarizes the past three years’ breakthroughs in spin-regulated ORR electrocatalysis and offers a fresh perspective beyond traditional electronic and geometric optimization. We first dissect the physical mechanism of spin-selective electron transfer required for the 4e⁻ pathway. We then systematically present four strategies for modulating the spin state of transition-metal active sites, namely strain engineering, defect engineering, heteroatom doping, and interfacial heterostructures. Subsequently, we highlight the emerging chirality-induced spin selectivity effect, where chiral organic molecules or intrinsically chiral inorganic materials act as spin filters without an external magnetic field, enabling spin-matched electron transfer and enhanced ORR performance. At the end of our review, we identify several key challenges, including the lack of in situ techniques to dynamically track spin states under operating conditions, the limited stability and universality of chiral catalysts, and the insufficient understanding of synergistic effects between spin control and traditional design parameters. We also outline future research directions, such as developing operando spin characterization, constructing robust chiral inorganic nanostructures, and employing high-throughput computational screening to integrate spin, geometric, and electronic level design. Our review provides a timely and comprehensive framework that bridges spin physics with electrocatalyst design, offering critical mechanistic insights and practical guidelines. Full article

Pure ZnO and ZnO/Gd₂O₃ (1 and 2 mol %) nanoneedles were synthesized via a sonochemical route and evaluated as catalytic materials for the degradation of paracetamol using glass and PTFE (Teflon) stirring rods. The morphology and elemental composition of the obtained nanostructures were investigated by SEM and EDS analyses, confirming the formation of anisotropic rod-like architectures and the successful incorporation of gadolinium species into the ZnO matrix. The optical and defect-related properties were further examined by photoluminescence and UV–Vis spectroscopy, revealing defect-related modifications in the electronic structure and improved charge carrier behavior in the gadolinium-modified samples. Comparative catalytic experiments showed higher degradation efficiencies in the system employing the glass stirring bar compared to the PTFE. However, the differences between these two setups are not limited solely to the stirring bar material, but also involve variations in interfacial contact conditions during operation. Therefore, the observed differences in catalytic activity cannot be attributed to a single mechanistic origin such as mechanically induced effects, but rather reflect the combined influence of catalyst–surface interactions and the specific nature of the stirring medium. The influence of inorganic ions on paracetamol degradation was also investigated using distilled water and aqueous solutions containing sodium chloride, sodium sulfate, and sodium hydrogen carbonate. In both systems, the ZnO/Gd₂O₃ samples exhibited higher degradation efficiency than pristine ZnO, indicating that Gd incorporation plays a key role in enhancing catalytic performance. This improvement can be associated with a modified defect structure and more favorable charge carrier dynamics in the doped material. The mineralization efficiency of the treated solutions was additionally evaluated through chemical oxygen demand (COD) measurements, confirming a significant reduction in organic load after treatment. Full article

The hydrogen evolution reaction (HER) plays a pivotal role in electrochemical water splitting for sustainable hydrogen production. However, its practical implementation is hindered by sluggish kinetics and the reliance on costly noble-metal catalysts. In this work, a conductive polymer-inorganic hybrid electrode based on vanadium pentoxide (V₂O₅) and polyaniline (PANI) is rationally designed and fabricated on carbon cloth via a combined hydrothermal synthesis and electropolymerization strategy. Initially, hierarchical V₂O₅ nanoflowers were synthesized, followed by controlled PANI deposition through cyclic voltammetry at varying cycle numbers to tailor the interfacial architecture and electronic properties. Morphological and structural analyses reveal the formation of well-defined V₂O₅ nanoflowers uniformly decorated with PANI nanorods, establishing an interconnected conductive network. Among the prepared samples, the optimized V₂O₅-PANI-2 electrode exhibits superior interfacial integration and structural homogeneity. Electrochemical evaluation in 1.0 M KOH demonstrates that V₂O₅-PANI-2 achieves a low overpotential of 79.9 mV at −10 mA cm⁻², accompanied by a small Tafel slope of 46.6 mV dec⁻¹, indicating accelerated HER kinetics. Furthermore, the electrode shows reduced charge-transfer resistance and an enhanced electrochemically active surface area (ECSA), facilitating efficient charge transport and abundant active site exposure. The catalyst also delivers excellent durability, maintaining stable performance over 5000 CV cycles and prolonged 24 h operation. The enhanced HER performance is attributed to the synergistic interaction between V₂O₅ and the conductive PANI matrix, which promotes charge redistribution, improves electrical conductivity, and optimizes the adsorption/desorption energetics of hydrogen intermediates. Full article

Water pollution caused by the continuous emergence of organic contaminants poses increasing challenges to conventional treatment technologies. Although advanced oxidation processes (AOPs) based on nanoconfined materials show great promise, their practical application remains constrained by short radical lifetimes, mass transfer limitations, and catalyst deactivation. This review systematically summarizes the critical role of nanoconfinement effects in AOPs. Through size exclusion and electrostatic regulation, confined spaces promote reactant enrichment and interference exclusion, while confined mass transfer and capillary-driven effects accelerate reaction kinetics. Particular emphasis is placed on multidimensional nanoconfined systems, ranging from zero-dimensional to three-dimensional structures and catalytic membranes, and on how structural design improves reaction microenvironments and active-site accessibility. The synergistic integration of confined structures with external fields, such as electric fields, is further discussed, highlighting their ability to regulate the electronic structure of active sites and shift reaction pathways from non-selective radical oxidation to efficient and highly selective non-radical routes. By optimizing parameters such as pH and catalyst-to-oxidant ratio, nanoconfined systems can achieve efficient pollutant degradation under near-neutral conditions while maintaining strong anti-interference capability and stability in real water matrices containing natural organic matter and inorganic ions. Full article

Nowadays, organic, inorganic, and microbial pollutants are listed as a substantial threat to the environment as well as public health, leading to water contamination. Green technologies such as photocatalytic and photoelectrocatalytic processes have appeared as favorable tools for water remediation, leading to effective degradation of pollutants under environmentally relevant operating conditions. With the rapid development of photocatalysis in the 21st century, heterogeneous catalysts have been extensively engineered to improve light utilization and promote surface redox reactions. This review presents an overview of recent advances in the synthesis, design, and application of heterogeneous catalysts for water purification. Key reaction mechanisms, material modifications, and hybrid processes are discussed. Also, the growing need for environmentally friendly, sustainable, and cost-effective catalytic materials is underlined. Attention was given to the role of molecular modeling in understanding catalytic mechanisms and guiding the design of efficient and sustainable catalytic materials. By critically analyzing contemporary progress, limitations, and emerging trends, this review directs future research activities towards increasingly efficient and scalable water purification methods. Full article

The cleavage of cumene hydroperoxide (CHP) via the Hock rearrangement is a cornerstone process in the chemical industry, responsible for over 90% of global phenol and acetone production. Despite its industrial significance, the conventional use of homogeneous sulfuric acid catalysis presents critical drawbacks, including severe equipment corrosion, generation of hazardous waste, and the need for complex neutralization steps. This review explores the transition toward heterogeneous solid acid catalysts as a sustainable alternative, emphasizing the relationship between catalyst structure, surface acidity, and reaction performance. Key catalyst families—such as ion-exchange resins, zeolites, and heteropolyacids—are systematically evaluated, with a focus on how Brønsted acid site density and porous architecture influence catalytic activity and selectivity. Particular attention is given to deactivation mechanisms, including coking, leaching of active species, and poisoning by inorganic cations, alongside mitigation strategies enabled by rational catalyst design and regeneration protocols. Additionally, we highlight recent progress in reactor engineering, particularly the integration of solid acid catalysts in reactive distillation and microchannel configurations. These insights offer a strategic perspective for developing more efficient and environmentally benign industrial processes for the Hock cleavage of cumene hydroperoxide. Full article

In recent years, Metal–Biomass Carbon (M–BC) hybrids have been widely studied as promising, cost-effective, and sustainable catalysts for persulfate activation in the degradation of emerging organic contaminants. M–BC systems offer advantages such as good performance and the sustainable use of biomass waste. Despite the considerable attention they have received, significant uncertainty remains regarding their precise catalytic mechanisms. A primary concern is the inherent complexity of biomass precursors, which frequently render the resulting catalytic structures ill-defined or akin to a “black box”. To address this challenge, this review critically evaluates the current state of mechanistic research, focusing on the debate between radical and non-radical pathways. In this paper, five fundamental challenges to clear mechanistic understanding are identified, including interference of inherent inorganic species, lack of precursors standardization and inherent heterogeneity, ambiguous overlapping active sites, methodological limitations in chemical quenching due to competitive adsorption, and conductivity-related constraints on non-radical pathways. Among these, the interference from inherent inorganic species is of primary concern, as the available evidence suggests it frequently confounds reported synergistic effects. Additionally, the future research directions for improving the experimental standardization and mechanistic understanding of M–BC catalysts are proposed. This review enriches the field by providing a clear path toward rigorous mechanistic understanding and the rational design of M–BC catalysts for water remediation. Full article

Pharmaceuticals and personal care products (PPCPs), as persistent organic pollutants, are widely present in various aquatic environments. Their long-term presence in aquatic environments poses a potential threat to ecosystems and human health. This study established an efficient, green, and cost-effective photocatalytic method using P25 titanium dioxide (P25TiO₂) to simultaneously degrade five representative PPCPs (methyl paraben (MeP), carbamazepine (CBZ), bisphenol A (BPA), diclofenac (DFC), and triclosan (TCS), while elucidating the reaction mechanisms. Under sunlight irradiation, degradation rates for all five PPCPs reached 100%, achieving near-complete mineralization with total organic carbon (TOC) removal rates exceeding 95%. This demonstrates the system’s exceptional capability to not only degrade the parent compounds but to thoroughly convert them into benign inorganic substances. We systematically investigated the effects of catalyst concentration, initial pollutant concentration, light intensity, pH, and various common inorganic anions (chloride, sulfate, bicarbonate, phosphate) and humic acid (HA) on the degradation process. Additionally, mechanistic studies indicated that hydroxyl radicals (·OH) are the primary active species in the system. The degradation rate differences among various persistent organic pollutants (DFC > BPA > TCS > CBZ > MeP) primarily stem from variations in the reactivity of different functional groups within their molecular structures toward ·OH. In summary, this study provides a promising and practical solution for treating complex medical wastewater containing five typical PPCPs. Full article