Search Results (400)

This study addresses the urgent issue of nitrate-contaminated water by investigating Ni-Pt and Co-Pt catalysts supported on TiO₂, with the aim of improving both photocatalytic efficiency and reaction selectivity. The influence of adding non-noble metal co-catalysts to TiO₂, in addition to Pt, was explored. The synthesized samples were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), diffuse reflectance UV–Vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The assessment of catalytic performance was conducted during the catalytic hydrogenation of nitrate, followed by an evaluation of the photocatalytic performance achieved when the aqueous nitrate solution was irradiated with UV light. The focus is on assessing the synergistic effects of the catalysts supported on TiO₂ in nitrate reduction, as well as their selectivity towards benign reaction products during the photocatalytic process, in contrast to the reactions occurring in the absence of light. Despite the selectivity for nitrite being preserved, the photocatalytic experiments indicated that the selectivity for N₂ reached around 68%, which is about 1.5 times higher than the values observed during the dark catalytic reaction. In contrast, the selectivity for ammonium saw a notable reduction. The findings were discussed in relation to the characteristics of the synthesized materials. Full article

Photocatalytic CO₂-to-CH₄ conversion is usually assessed through catalyst activity, selectivity, and methane formation rate, although the practical usefulness of the resulting gas stream also depends on methane recovery from CO₂-rich mixtures. Here, a phenomenological Langmuir–Hinshelwood reactor model was used to evaluate batch gas-phase CO₂ photoreduction under different reactor thicknesses, water-availability conditions, photocatalyst activities, and idealized methane-selective extraction configurations. The model considered competitive adsorption, transient gas-phase balances, finite or buffered water supply, and a lumped selective CH₄ extraction term. Under finite vapor inventory, water depletion limited reaction progress, particularly in thin reactors. Buffered-water operation increased CO₂ conversion and methane formation, while reactor thickness produced a trade-off: thin reactors favored apparent conversion and methane enrichment, whereas thicker reactors provided a larger CO₂ reservoir and higher cumulative methane formation. At the baseline kinetic condition, methane extraction strongly decreased the in-reactor CH₄ fraction but only modestly increased methane formation. When photocatalyst activity was increased, the non-membrane thin reactor reached a product-accumulation-limited regime, and methane-selective extraction became kinetically relevant. These results indicate that methane-selective extraction concepts should be evaluated not only as separation devices, but as conditional reactor-intensification tools whose relevance depends on water availability, reactor geometry, catalyst productivity, and product dilution. Full article

The use of solar energy and semiconductor photocatalysts to reduce carbon dioxide (CO₂) into high-value fuels and chemicals is a promising approach to alleviate the current energy crisis and climate change. Layered double hydroxides (LDHs) are a special two-dimensional anionic clay material with a brucite-like structure. They have excellent properties such as adjustable layer cation types, interlayer anion types, and layer ratio. LDHs have been widely used in catalytic fields such as carbon dioxide reduction, water splitting, and ammonia synthesis, and are considered safe and green new photocatalysts. In recent years, researchers have conducted in-depth studies on the photocatalytic CO₂ reduction performance of hydrotalcite-like materials and have made certain progress. However, the low carrier mobility and low light utilization efficiency of pure LDHs greatly limit their catalytic reaction ability and further applications. More and more scientists are exploring methods based on regulating the structure of LDHs to improve the conversion efficiency and light utilization of products, such as changing the layer composition of LDHs, introducing vacancies in LDH structures, or coupling different types of semiconductors to construct heterojunctions. This article first summarizes the development history and structural properties of LDHs; Secondly, the mechanism of photocatalytic reduction of carbon dioxide was summarized; Thirdly, the application of LDH-based materials in photocatalytic reduction of CO₂ was classified and summarized. Although LDH-based photocatalysts have made significant progress in the field of photocatalytic reduction of CO₂, further exploration is still needed to investigate their photocatalytic active sites, mechanisms of action, synergistic mechanisms between components, and interfacial reaction mechanisms. Full article

The photoreduction of CO₂ is a growingly interesting research topic due to the intriguing possibility of producing solar fuels from a concerning pollutant. TiO₂ photocatalysts were the first materials used for this application, but since then, various strategies have been developed to optimise the catalytic performance and operating conditions to obtain competitive yield. This review presents the findings of the last decade of research on different semiconductors, TiO₂ and g-C₃N₄ and their composites. The main features of the reaction and its key issues are first overviewed, focusing on the effect of different reaction conditions on the performance and recalling the mechanism of the reaction. The strategies developed to overcome the challenges of this demanding reaction are described in the following paragraphs, including the use of dopants or co-catalysts, heterojunctions between different semiconductors and the use of electron transfer mediators. Finally, some unifying concepts are summarised, suggesting the calculation of the stored energy amount and the relative efficiency to allow a safer comparison between literature data collected under widely variable conditions and leading to different products. Full article

Photocatalysis is widely used for toxic air and water pollutant degradation, water slitting and H₂ production, and the reduction of CO₂ to useful hydrocarbons. Hollow fibers (HFs) have been widely used as photocatalyst immobilizers for advanced oxidation and reduction applications under batch conditions, with active semiconductors either applied on their surface or incorporated into their matrix. Photocatalytic hollow fiber membranes (HFMs), the porous version of the above-mentioned fibers, which exhibit dual functionality in the degradation and physical separation of contaminants, are currently applied under flow conditions for wastewater recycling and reuse. This work provides a concise overview of all the studies encountered in the literature on photocatalytic HFs and HFMs, categorizes them with respect to their materials and fabrication methods and aspires to serve as a guide for anyone wanting to prepare and use them in photocatalytic batch or flow reactors. Full article

To address the insufficient visible-light absorption of Bi₄O₅Br₂ photocatalysts, first-principles density functional theory (DFT) calculations were employed to systematically investigate the effects of I doping at different concentrations (12.5%, 25%, 50%, 75%, 87.5%, and 100%) on the geometric structure, electronic structure, optical properties, and photocatalytic CO₂ reduction performance of Bi₄O₅Br₂. Formation energy calculations and Ab initio molecular dynamics (AIMD) simulations indicate that the I-doped systems possess good thermodynamic and kinetic stability. Geometric analysis shows that I doping leads to a gradual expansion of lattice parameters along the c-axis (from 14.80 Å to 15.16 Å), due to the larger ionic radius of I⁻ compared to Br⁻. Electronic structure results reveal that all doped systems remain indirect band gap semiconductors, with the band gap decreasing from 2.56 eV for the pristine system to 2.25 eV at 87.5% doping. This reduction is mainly attributed to the progressive substitution of Br 4p states by I 5p states near the valence band maximum, which modifies the valence band structure. Differential charge density analysis shows electron transfer from Bi to I, enhancing local polarization effects. Optical property calculations demonstrate a pronounced red shift in the absorption edge and significantly enhanced absorption intensity in the visible region after I doping. The real and imaginary parts of the dielectric function also exhibit red shifts and increased peak intensities in the low-energy region. Gibbs free energy analysis indicates that the Gibbs free energy for *COOH formation decreases from 2.83 eV in the pristine system to 2.68 eV after I doping, while the free energy of the *CO intermediate decreases from 1.28 eV to 0.98 eV, significantly improving the CO₂ reduction pathway. This study provides a theoretical basis for improving the optical response and the thermodynamics of the CO₂ reduction reaction through halogen substitution, suggesting a promising strategy for enhancing the photocatalytic potential of Bi₄O₅Br₂. Full article

The photocatalytic conversion of carbon dioxide (CO₂) into methanol represents a promising strategy for both greenhouse gas mitigation and renewable fuel production. In this study, a niobium-based metal–organic gel (Nb-MOG) was employed as a photocatalyst for the reduction of CO₂ to methanol under UV irradiation in a batch photoreactor. A two-factor experimental design was conducted to evaluate the effects of sodium carbonate concentration and catalyst loading on methanol production. The Nb-MOG catalyst was dispersed in the reaction medium and irradiated with UV light for four hours. During the photocatalytic experiments, samples were periodically collected and analyzed by headspace gas chromatography coupled with flame ionization detection (HS-GC-FID) to quantify methanol production. The results showed that both the Na₂CO₃ concentration and catalyst loading exerted significant positive effects on methanol formation. The highest methanol yield was achieved at a Na₂CO₃ concentration of 0.10 mol·L⁻¹ and a catalyst loading of 0.50 g·L⁻¹. The experimental design results demonstrated a good fit of the statistical model to the experimental data, highlighting its predictive capability and confirming the reliability of the obtained results. Furthermore, Nb-MOG exhibited enhanced light-harvesting and charge-transfer properties, leading to measurable methanol production under the investigated conditions. These findings contribute to a better understanding of Nb-MOG’s photocatalytic behavior and demonstrate its potential for application in a sustainable CO₂ reduction system. Full article

Photocatalytic CO₂ reduction into CH₄ is a promising route for solar fuel production, but its efficiency is still limited by poor charge separation, insufficient CO₂ activation, and sluggish multi-electron transfer kinetics. Herein, Cu-modified TiO₂ (Cu/TiO₂) was prepared by calcining a Cu-modified defective MIL-125(Ti) precursor, denoted as Cu-MIL-125, through a temperature-controlled calcination strategy. The effects of calcination temperature on the structural evolution, surface chemical states, interfacial charge transport, and CO₂ photoreduction performance were examined. These results indicated that the Cu/TiO₂ was successfully prepared, while the crystallinity, porous structure, and interfacial electronic properties of Cu/TiO₂ were strongly dependent on the calcination temperature. Among the obtained samples, the Cu/TiO₂ sample obtained by calcining Cu-MIL-125 at 450 °C (450 Cu/TiO₂) exhibited the highest CH₄ formation rate, reaching 15.90 μmol g⁻¹ h⁻¹, corresponding to an approximately 9.8-fold enhancement over TiO₂ calcined from defective MIL-125(Ti) at 450 °C, together with a high CH₄ selectivity of 93.05%. Control experiments and ¹³CO₂ isotope-labeling tests confirmed that the detected carbon-containing products were generated from CO₂ under photocatalytic conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy measurements further revealed the formation of carbonate, bicarbonate and hydrogenated carbon-containing intermediates during the reaction. This work offers a practical route for constructing metal–organic framework-derived Cu/TiO₂ photocatalysts for selective CH₄ production from CO₂. Full article

This review aims to clarify the molecular design principles and operational challenges of photoinduced electron transfer (PET) and photoredox processes in metal complexes. The manuscript is structured to include a survey of established conventional systems, such as Ru complexes, followed by our own research on cost-effective photosensitizers for dye-sensitized solar cells (DSSCs) and carbon dioxide (CO₂) reduction. Crucially, our main conclusion emphasizes that achieving high optoelectronic efficiency requires the balanced optimization of excited-state lifetimes, orbital distributions, and matrix environments, rather than a simplistic “one-size-fits-all” approach. Finally, based on the fundamental principles of metal complexes and photocatalytic materials, we offer a critical analysis of the practical challenges and reasons behind our unsuccessful experimental outcomes. Thus, this study provides a perspective on unsuccessful molecular design, comparing typical examples. Full article

Nanostructured catalysts have become a core component of energy conversion in electrocatalysis and photocatalysis; however, successfully translating their performance from laboratory scale to industrial applications remains a long-standing challenge. This paper provides a critical assessment of the field, systematically tracing the entire development trajectory from catalyst design to practical application. We focus on five major classes of catalysts—monometallic catalysts, bimetallic/multimetallic alloy catalysts, metal compound catalysts, carbon-based composite catalysts, and single-atom catalysts—and explore synthetic strategies for achieving precise structural control, including hydrothermal/solvothermal methods, electrodeposition, template-assisted and MOF-derived syntheses, high-temperature pyrolysis, and post-treatment defect engineering. This paper delves into the mechanisms and performance descriptors governing the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), urea oxidation, photocatalytic water splitting, and CO₂ reduction. Based on the above analysis, this paper lays the mechanistic foundation for five core strategies to improve catalyst performance: morphology control, elemental doping, heterostructure and interface engineering, defect and vacancy engineering, and support modification. Furthermore, this paper provides an in-depth evaluation of the applications of these catalysts in water splitting, CO₂ valorization, fuel cells, metal–air batteries, and energy-saving electrolysis, with a particular focus on earth-abundant alternatives to precious metals. We argue that in many well-studied reactions, intrinsic activity may no longer be the primary bottleneck restricting their development; instead, the core challenge now lies in maintaining excellent catalytic performance under harsh and industrially relevant conditions, especially under high-current densities, impurity-containing feed systems, and long-term operating conditions. In response to this shift in research focus, this paper clearly identifies the key obstacles hindering the industrial application of catalysts and proposes practical directions for future research. Full article

The development of sustainable, noble-metal-free photocatalytic systems for acceptorless dehydrogenation (ADH) of cyclic amines remains a significant challenge. Herein, we report a novel heterogeneous photocatalyst constructed by covalently grafting a cobaloxime-based proton reduction catalyst onto a photosensitive covalent organic framework (PT-COF). The tailored PT-COF scaffold, featuring a donor–acceptor architecture and uncondensed amino groups, serves as both an efficient visible-light harvester and a porous support for cobalt active sites. The resulting Co-PT-COF hybrid exhibits excellent photocatalytic activity for the ADH of a wide range of cyclic amines, affording the corresponding N-heteroarenes in 62–95% yields under an Ar atmosphere at 28 °C with blue LED irradiation for 12 h in water. Notably, the catalyst demonstrates outstanding recyclability over five consecutive cycles with minimal loss of activity or cobalt leaching. Comprehensive photoelectrochemical and spectroscopic studies reveal that enhanced charge separation and efficient electron transfer from the photoexcited COF to the cobalt centers underpin the superior performance. Mechanistic investigations, including in situ EPR spectroscopy, confirm the involvement of α-amino radical intermediates in the catalytic cycle. This work establishes a sustainable platform for solar-driven dehydrogenation chemistry and provides a versatile blueprint for integrating molecular catalysts with photoactive frameworks. Full article

This study investigates the simultaneous elimination of ethyl acetate (EA), a representative volatile organic compound (VOC), and Escherichia coli aerosols from indoor air using a continuous-flow dielectric barrier discharge (DBD) plasma reactor coupled with a photocatalytic luminous textile system (Cu/TiO₂-coated fibers). The effects of applied voltage, relative humidity, and air-flow rate on pollutant removal and disinfection performance were systematically evaluated. Optimal DBD operation at 18 kV, 1 m³ h⁻¹ airflow, and 70% relative humidity achieved single-process removal efficiencies of 77% for EA and 2 log reduction (CFU mL⁻¹) for E. coli. When photocatalysis was coupled with DBD plasma, a significant combined effect was observed, increasing EA degradation to 87% and bacterial inactivation to 3.8 log (CFU mL⁻¹). The coupling enhanced active-species generation, improved CO₂ selectivity (up to 53%), and reduced residual ozone concentration. Humidity positively affected microbial inactivation due to °OH radical formation but slightly decreased VOC degradation by limiting ozone regeneration. Results demonstrate the efficiency and scalability of the DBD–photocatalysis hybrid system for multi-pollutant indoor air purification, offering rapid, low-temperature treatment suitable for industrial-scale applications. Full article

Pure Bi₂O₃ is a favorable photocatalyst for visible-light-driven processes; however, the rapid recombination of photogenerated charge carriers limits its practical performance. In this work, Co-doped Bi₂O₃ nanoparticles, Co_xBi_2−xO₃ (x = 0–0.1), were produced through a sol–gel combustion route to enhance their visible-light photocatalytic activity. As demonstrated by XRD analysis, Co was successfully incorporated into the Bi₂O₃ lattice, along with changes to the crystal structure, crystallite size (up to ~88 nm), and lattice strain. Optical measurements revealed that Co-doping induces a clear absorption edge’s red shift, resulting in a systematic reduction of the optical band gap from 3.9 eV for pure Bi₂O₃ to approximately 3.1 eV for the doped samples. This band gap narrowing enhances visible-light absorption and improves photocatalytic efficiency. Photocatalytic activity was assessed by measuring the degradation of MB under visible-light irradiation. Incorporation of Co consistently enhanced the performance across all doped samples compared to the pristine oxide counterpart. The Co_0.1Bi_1.9O₃ composition demonstrated the best performance, achieving a removal efficiency of 94.5% within 120 min, compared with 73.0% for pure Bi₂O₃. Kinetic analysis indicated pseudo-first-order behavior, with the optimal sample showing a rate constant of 0.0240 min⁻¹—more than twice that of the undoped material (0.0105 min⁻¹). These results validate that Co-doping is an actual approach for engineering the electronic structure of Bi₂O₃, leading to enhanced visible-light absorption, improved charge-carrier separation, and significantly higher photocatalytic efficiency for environmental remediation applications. Full article

Calcium copper titanate (CaCu₃Ti₄O₁₂, abbreviated as CCTO) has emerged as a versatile, high-performance material distinguished by its remarkable dielectric, photocatalytic, and environmental properties, positioning it at the forefront of ongoing research and technological innovation. This review provides a comprehensive analysis of CCTO, emphasizing its growing relevance in catalytic and environmental applications. Beginning with an overview of its unique structural and dielectric properties, we discuss how these attributes underpin CCTO’s multifunctionality. Various synthesis methods are examined for their effects on CCTO’s microstructure and performance. Furthermore, we investigate the photocatalytic potential of CCTO under visible light, particularly for applications such as water splitting, CO₂ reduction, and degradation of organic pollutants. Environmental applications, including gas sensing and wastewater treatment, are also evaluated, highlighting CCTO’s chemical robustness and suitability under diverse operating conditions. Lastly, key challenges in scalability, cost, and environmental adaptability are discussed, along with future directions, including hybrid composite development and machine-learning-assisted material design. Together, these insights position CCTO as a promising material for advancing sustainable technologies in energy and the environment. Full article

The rational configuration of electronic band structures through deep-seated structural disorder remains a formidable challenge in sustainable solar-to-fuel conversion. Herein, we report a transformative kinetic strategy to “freeze” an extraordinary density of non-equilibrium structural defects within an integrated Cu₄MgO₅/ZnO nanocomposite. Synthesized via a chitosan-assisted coordination-combustion route followed by rapid thermal quenching, the material preserves a record crystallographic dislocation density of 1.09 × 1015 m⁻² and significant lattice microstrain (1.04 × 10⁻³). This engineered structural disorder induces a profound reconfiguration of the electronic landscape, generating a continuous manifold of sub-bandgap “tail states” that narrow the optical bandgap to a remarkable 1.34 eV. Consequently, the defect-rich architecture facilitates unprecedented dual-channel photocatalytic performance under simulated solar irradiation in an aqueous solution containing 5 vol% triethanolamine (TEOA) as a sacrificial electron donor; the catalyst achieved a hydrogen evolution rate of 17,700.0 µmol g⁻¹ h⁻¹ and a methane production rate of 172.50 µmol g⁻¹ h⁻¹—representing a 36.3-fold and 43.1-fold enhancement over commercial ZnO, respectively. With an apparent quantum yield of 8.42% at 420 nm and robust photostability—maintaining 95.3% of its activity over five consecutive cycles (25 h total)—this noble-metal-free ternary system bypasses the limitations of traditional heterojunctions. Our findings establish a new benchmark for defect-engineered catalysts, providing a scalable blueprint for high-efficiency carbon neutrality and solar fuel production. Full article