Search Results (150)

Metal-free polymeric semiconductor graphitic carbon nitride (g-C₃N₄) was synthesized via thermal polycondensation using cyanamide with PVP as a medium, using SiO₂ nanospheres as sacrificial templates to suppress bulk agglomeration. Structural analysis using X-ray diffraction (XRD) confirmed the conservation of the g-C₃N₄ structure, while diffuse reflectance UV-Vis spectroscopy (DRS) showed that there is a slight change in optical absorption, modifying the band gap energy of g-C₃N₄ with the addition of SiO₂. Transmission electron microscopy (TEM) evidenced the formation of interconnected porous architectures, facilitating charge migration. Photocatalytic activity was evaluated under simulated solar irradiation using acetaminophen (ATP) as a model pharmaceutical pollutant. Kinetics experiments demonstrated that the sample containing 7% SiO₂ nanospheres achieved 65% degradation for 180 min. The best photocatalytic performance is attributed to the pore volume, which favors better adsorption, facilitating the degradation of acetaminophen. The participation of different reactive species during the photocatalytic degradation of ATP was determined. Experiments with scavenger agents indicate that the photogenerated holes are the predominant oxidizing reactive species. These results highlight the potential of g-C₃N₄ modified with SiO₂ nanospheres as an efficient photocatalyst for the degradation of emerging contaminants, thus advancing sustainable water treatment technologies. Full article

The selective photocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) into high-value 2,5-diformylfuran (DFF) under green conditions is a promising route toward carbon neutrality. However, achieving high efficiency and selectivity in pure water remains challenging due to limited oxygen solubility and nonselective radical reactions. In this study, a series of amorphous MoS₃-modified Zn₃In₂S₆ nanoflowers (x%MS/ZIS) with varying MoS₃ loadings were successfully synthesized via a one-step hydrothermal method and served as the photocatalysts for the highly selective oxidation of HMF to DFF. The incorporation of MoS₃ significantly enhances visible-light absorption, promotes efficient separation of photogenerated carriers, and accelerates surface reaction kinetics. Under visible light irradiation, the optimized 2.4%MS/ZIS catalyst achieves 64.7% HMF conversion and 89.5% DFF selectivity in pure water within 6 h, ~39-fold enhancement in DFF yield compared to pristine Zn₃In₂S₆. Radical scavenging experiments and electron paramagnetic resonance analyses suggest that superoxide radicals (·O₂⁻) and photogenerated holes are the main reactive oxygen species governing the selective oxidation, while the absence of ·OH radicals suppresses overoxidation. This study demonstrates a viable and green strategy for the valorization of biomass platform molecules through visible-light-driven photocatalysis in pure water. Full article

This study explored the influence of high silver (Ag) loading (5–10 mol%) on the photocatalytic performance of zirconium (Zr) co-doped TiO₂ (AZT) with a low Zr content. Although various Ag/Zr ratios have been reported, the effect of high Ag loading combined with low Zr content remains largely unrevealed, particularly in low-temperature synthesis where the role of Zr as a phase inhibitor is less critical. To address this gap, the AZT photocatalyst was fabricated via a solvothermal method combined with organic-free peroxy route. Characterization indicated Zr⁴⁺ incorporated into the TiO₂ lattice, inducing structural distortions and promoting Ti³⁺ defect states. Simultaneously, silver existed as ternary Ag species, which functioned as visible light responsive co-catalysts that enhanced light absorption via Surface Plasmon Resonance (SPR) and facilitated efficient charge separation. Photocatalytic performance was evaluated through Methylene Blue (MB) decolorization under household LED lamp. The optimized 7% Ag loaded catalyst achieved 99.4% removal efficiency within 6 h, with a reaction rate ten times higher than the Zr-doped sample. This superior activity was attributed to a p-n heterojunction and the SPR effect, narrowing the optical band gap to 2.60 eV. Radical scavenger experiments confirmed that the process was primarily driven by photogenerated holes. Full article

The development of sustainable technologies capable of simultaneously addressing environmental pollution and renewable energy production remains a major scientific challenge. In this work, titanium dioxide nanoparticles (GTiO₂) were synthesized through a plant-extract-assisted route using Punica granatum (pomegranate) peel extract and subsequently modified with platinum nanoparticles (Pt NPs) to obtain an efficient photocatalyst for the photoreforming of organic pollutants. The resulting Pt-GTiO₂ material exhibited an anatase crystal structure with an average crystallite size of approximately 12 nm and a specific surface area of about 140 m² g⁻¹. Comprehensive characterization using XRD, BET, TEM, FTIR, Raman, and photoluminescence spectroscopy (PL) revealed favorable structural and optoelectronic properties that promote efficient charge separation. The photocatalytic performance of Pt-GTiO₂ was evaluated through the simultaneous degradation of 2-naphthol, a priority aromatic pollutant, and hydrogen evolution under simulated solar irradiation in anaerobic conditions. Under the investigated conditions, Pt-GTiO₂ effectively promoted 2-naphthol degradation, with substantial but incomplete mineralization, as confirmed by TOC removal. The synthesized catalyst showed degradation efficiency higher than Pt-UV100 and comparable to Pt-P25, while exhibiting superior hydrogen evolution when compared with Pt-P25. Mechanistic investigations combining scavenger experiments, electron paramagnetic resonance (EPR) spectroscopy, and the identification of reaction intermediates suggest that photogenerated holes play a major role in the initial oxidation step under the mechanistic test conditions. The detected intermediates indicate that photoreforming proceeds via multiple pathways, including hydroxylation, ring-opening, reduction, and fragmentation. These findings highlight the potential of biogenic TiO₂-based photocatalysts for converting hazardous organic pollutants into clean hydrogen fuel while simultaneously achieving wastewater purification, offering a promising route toward sustainable environmental and energy technologies. Full article

The development of highly efficient and stable photoanodes is essential for advancing photoelectrochemical cathodic protection towards practical applications. Herein, a novel ternary sulfide heterojunction was engineered through the construction of a three-dimensional interlocked architecture of ZnIn₂S₄ on SnIn₄S₈ nanosheets via a sequential hydrothermal synthesis. This unique three-dimensional interlocked configuration creates an intimate interface and continuous charge transfer highways, effectively addressing the slow electron movement and poor interfacial contact that plague conventional photoelectrodes. Spectroscopic and electrochemical analyses verified the formation of a Type-II band alignment, which drives the directional migration of photogenerated electrons from ZnIn₂S₄ to SnIn₄S₈ under an intrinsic built-in electric field. Upon coupling with 304 stainless steel, the ZnIn₂S₄/SnIn₄S₃ heterojunction exhibited outstanding photoelectrochemical cathodic protection performance. It delivered impressive photocurrent densities of 15.22, 19.76, and 72.27 μA·cm⁻² in 3.5 wt% NaCl, 0.1 M Na₂S₂O₃, and 0.1 M Na₂S/NaOH electrolytes, respectively, along with a prominent 720 mV cathodic potential shift in the Na₂S/NaOH system. Most importantly, its good activity and stability in the scavenger-free 3.5 wt% NaCl solution and natural seawater highlight the strong practical potential of this 3D interlocked photoanode for sustainable marine metal corrosion control. Through a strategic multi-electrolyte assessment, the underlying protection mechanisms were decoupled, revealing that the synergy between the heterojunction-induced charge separation enabled by the three-dimensional interlocked structure and electrolyte-specific hole scavenging is key to the enhanced performance. Full article

In this review, some special characteristics of the reactions in semiconductor photocatalysis are presented. At first, since a pair of the redox reactions take place at the same particle, a particle-based kinetic method was presented and applied for the Langmuir–Hinshelwood kinetics to describe the photocatalytic oxidation as a function of both the reactant concentration and the light intensity. Since the surface electron transfer (ET) reactions are the subject of electrochemistry, the difference in the characteristics from particulate semiconductor photocatalysis was pointed out by showing each electric potential near the solid surface. Different from ET in electrochemistry, the ET frequency is limited by the photon absorption in photocatalysis. In the estimation of the reaction rate, the validity of Marcus theory in photocatalysis was argued. Almost all photocatalytic reactions are irreversible, because, before the charge recombination, the oxidation and/or reduction must take place at the same particle. Then, the kinetics for irreversible reaction was discussed. As an exception, the reversible reduction reaction of methylviologen with a hole scavenger was presented. By changing pH, the energy levels of thermalized electrons in TiO₂ particles were estimated, and the difference of the flat band potentials between anatase and rutile was clearly explained. Thus, various uniqueness of photocatalytic reactions in aqueous suspension of semiconductor particles were demonstrated. Full article

Nitrate pollution in freshwater has become an increasing concern for both environmental sustainability and human health, especially in water reuse systems and intensive aquaculture. Photocatalytic reduction in nitrate to nitrogen gas (N₂) represents a promising low-chemical treatment strategy that can operate under sunlight or LED irradiation, and in general, enable nitrate removal without generating concentrated waste streams. Over the past decade, the development of advanced photocatalytic materials, including heterojunction semiconductors, plasmonic catalysts, and single-atom co-catalysts, has significantly enhanced visible-light absorption and overall photocatalytic performance. Despite these advances in photocatalyst design and synthesis, several critical challenges still limit the large-scale implementation of photocatalytic nitrate reduction to N₂. First, selectivity toward N₂ remains limited, as competing reaction pathways often lead to the formation of undesirable byproducts, such as nitrite (NO₂⁻), ammonium (NH₄⁺), and nitrous oxide (N₂O). Second, nitrogen reaction pathways are often uncertain, because many studies lack isotopic labeling or nitrogen mass balances, making it difficult to verify that the detected N₂ originates from nitrate reduction. Third, practical implementation is restricted by several technical challenges, including catalyst fouling or leaching, limitations in reactor design, excessive addition of hole scavengers, and the relatively high energy demand associated with indoor LED-driven systems. This review critically surveys advances from 2015 to 2025 in photocatalytic materials and reaction mechanisms for nitrate conversion to N₂. It highlights best practices for reliable product quantification and reaction pathway validation, and evaluates the feasibility of integrating these systems into recirculating aquaculture systems (RAS), where effective nitrate management is essential. In addition, the potential role of modern inline nitrate sensors (optical and electrochemical) and automated process control is discussed, outlining pathways toward hybrid photocatalytic–biological nitrate removal systems for sustainable aquaculture applications. Full article

Zinc oxide (ZnO) and zinc sulfide (ZnS) nanocomposites represent promising multifunctional photocatalysts due to their complementary band structures and synergistic charge separation. ZnO–ZnS nanocomposites with varied ZnS content were synthesized to elucidate the composition–structure–property relationships governing their multifunctional performance. Structural characterization using XRD, SEM/EDS, Raman spectroscopy, and XPS confirmed the coexistence of wurtzite crystalline phases of ZnO and ZnS. SEM analysis revealed ZnS fine deposition on the ZnO surface. XPS measurements showed a gradual increase in the amount of ZnS on the ZnO surface with increasing sulfide content and a shift in the valence band maximum from 2.32 eV (pure ZnO) to 0.77 eV (pure ZnS). Optical measurements (IR, UV–Vis diffuse reflectance, photoluminescence) demonstrated that, despite the evolution of vibrational and luminescence features characteristic of ZnS, the apparent band gap remained nearly constant at 3.16–3.18 eV across the series. Photocatalytic methylene blue (MB) degradation followed pseudo-first-order kinetics, peaking for ZN_2 (1% ZnS, k_app = 103 × 10⁻³ min⁻¹), which is 1.7 times higher than for pure ZnO. This enhanced performance is consistent with an S-scheme-like heterojunction that facilitates electron migration to the ZnS conduction band while retaining ZnO valence band holes for oxidation. Scavenging experiments confirmed that electrons dominate MB degradation (k_app up to 185.1 × 10⁻³ min⁻¹ with EDTA/t-BuOH/Ar), outperforming hole-mediated pathways. Antibacterial assays against Staphylococcus aureus revealed good antimicrobial activity for all nanoparticles. The nanocomposite’s antibacterial activity was similar across all samples and was only slightly lower than that of pure ZnS and ZnO. Full article

A synergistic and magnetically recoverable NiFe₂O₄–MWCNT–CA nanocomposite was developed for efficient UV-driven photodegradation of hazardous organic pollutants. Biogenic NiFe₂O₄ nanoparticles synthesized using Costus speciosus extract exhibited a crystallite size of 32.5 nm, which increased to 83.6 nm upon incorporation into the MWCNT–cellulose acetate matrix. XRD confirmed the preservation of the cubic spinel structure, while VSM analysis showed maintained ferrimagnetic behavior with a saturation magnetization of 9.64 emu/g, enabling rapid magnetic separation. Although BET analysis revealed a reduction in surface area from 112.46 to 30.99 m²/g due to hybridization, the conductive MWCNT network significantly enhanced charge separation and interfacial electron transport. The composite displayed a widened optical bandgap of 5.3 eV, necessitating UV excitation for photocatalytic activity. Under UV irradiation, it achieved rapid degradation of methylene blue (97%) and Congo red (91%) at 20 mg/L, with corresponding rate constants of 0.119 and 0.076 min⁻¹. Scavenger experiments confirmed hydroxyl radicals (•OH) as the dominant reactive species, followed by photogenerated holes (h⁺). These results demonstrate a robust and synergistically engineered photocatalyst with high efficiency in removing organic pollutants under UV illumination. Full article

In this study, the photocatalytic performance of natural clinoptilolite was enhanced through copper modification, achieved via ion exchange followed by KOH-induced precipitation, leading to materials with different copper speciation. Physicochemical characterization using WDXRF, PXRD, FTIR and N₂ physisorption revealed a transition from exchanged Cu²⁺ species at low loading to the formation of copper-bearing phases such as brochantite, Cu(OH)₂ and CuO at higher alkalinity. The Cu-modified samples were evaluated for the photocatalytic degradation of Congo red under UV irradiation. Among them, sample NZ-Cu3 exhibited the highest activity, achieving approximately 91% dye degradation within 30–40 min. Kinetic analysis demonstrated that the degradation process is better described by the pseudo-second-order model, indicating that chemisorption plays a dominant role. Radical scavenger experiments revealed that photogenerated holes (h⁺) are the primary reactive species responsible for dye degradation, while hydroxyl radicals contribute to a lesser extent. The enhanced photocatalytic performance is attributed to the synergistic effect of photocatalytic degradation, improved charge separation and the presence of surface copper species, highlighting Cu-modified clinoptilolite as a promising low-cost photocatalyst for wastewater treatment. Full article

Water contamination by synthetic dyes is a pressing environmental and social issue, particularly in the textile industry, which is among the largest consumers of freshwater and sources of wastewater pollutants. Malachite green (MG), a synthetic triphenylmethane dye, was selected as a model contaminant due to its persistence, toxicity, and international regulatory restrictions. In this study, a spinel-type cobalt–manganese oxide (CoMn₂O₄) photocatalyst was synthesized by calcination at 500 °C and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirming the formation of the spinel phase with nanoscale morphology. Photocatalytic activity was evaluated under visible-light irradiation using UV-Vis spectrophotometry to monitor MG degradation. Control experiments and scavenger assays identified hydroxyl radicals (•OH), superoxide anions (O₂⁻), and photogenerated holes (h⁺) as the main reactive species. The catalyst achieved over 90% dye removal within 300 min and retained high activity over four consecutive reuse cycles, with only a slight decrease in efficiency from 97% to 94%. These results confirm both the efficiency and stability of CoMn₂O₄ under visible light. The study underscores the potential of this material as a sustainable option for wastewater treatment while contributing to environmental governance and supporting the fulfillment of the Human Right to Water. Full article

The development of photocatalyst material is vital for the practical application of environmental purification, solar energy conversion, and chemical production. In this work, a spherical Bi(C₆N₇O₃) photocatalyst is successfully prepared by replacing K⁺ of rod-shaped K₃[C₆N₇O₃] with Bi³⁺ ions through the ion exchange method, which demonstrates an improved homogeneous photodegradation efficiency over antibiotics in water compared to pristine K₃[C₆N₇O₃]. Under visible light irradiation, Bi(C₆N₇O₃) degraded 81% of tetracycline hydrochloride within 60 min, and the rate constant was 1.8 and 79.1 times greater than K₃[C₆N₇O₃] and bulk g-C₃N₄, respectively. Scavenger experiments revealed that superoxide radicals and holes are the primary active species in the photocatalytic process. This study presents a promising route for designing high-performance visible-light photocatalysts by a simple ion-exchange approach for environmental applications. Full article

The effectiveness of periodate-assisted photocatalysis in removing the cationic dye Safranin O (SO) was evaluated using a UV/TiO₂/IO₄⁻ process operated at room temperature under near-neutral pH conditions. Under base conditions ([IO₄⁻] = 0.15 mM, [TiO₂] = 0.4 g/L, [SO] = 10 mg/L), the ternary system achieved a pseudo-first-order rate constant of 0.6212 min⁻¹, outperforming the UV/TiO₂ and UV/IO₄⁻ processes by approximately 21- and 29-fold, respectively. This yielded a synergy ratio of about 12 compared to the sum of the binary processes. Targeted quenching experiments revealed the operative pathways. Strong inhibition by ascorbic acid and phenol indicates that interfacial holes and ^•OH are key oxidants. Methanol caused a moderate slowdown, consistent with ^•OH and hole scavenging. Benzoquinone and oxalate suppressed removal by intercepting the electron and O₂^•− pathways, respectively. Dichromate markedly inhibited the process via optical screening and competition for electrons. Azide had little effect, suggesting a minor role for singlet oxygen. Matrix studies showed progressively slower kinetics from deionized water to mineral water to seawater. This was due to halides, sulfate, alkalinity, and TiO₂ aggregation driven by ionic strength. Additional tests confirmed that the dominant modulators of performance were humic acid (site fouling and light screening), chloride and sulfate (radical speciation and surface effects), nitrite (near-diffusion radical quenching), and bicarbonate at pH 8.3 (conversion of ^•OH to CO₃^•−). Nonionic surfactants (Tween 80, Triton X-100) also depressed SO removal through micellar sequestration and competitive adsorption on TiO₂. The study confirms the potential of UV/TiO₂/IO₄⁻ as a tunable AOP capable of delivering rapid and reliable dye degradation under a wide range of water quality conditions. The mechanistic mapping unifies two roles for IO₄⁻, an electron acceptor that inhibits recombination and a photochemical precursor of iodine centered and ^•OH radicals and connect these roles to the observed synergy and to the trend across deionized water, mineral water, and seawater. The scavenger outcomes assign the main oxidant flux to holes and ^•OH radicals with a contributory electron or O₂^•− branch from IO₄⁻ reduction. Full article

This study compares the structural, morphological, magnetic, and photocatalytic properties of a pure SiO₂ matrix, a ZnFe₂O₄-doped SiO₂ nanocomposite (both synthesized via the sol-gel method), and bulk ZnFe₂O₄ produced by thermal decomposition. Thermogravimetric analysis (TGA) reveals that metal oxalates form below 200 °C and decompose into metal oxides, which subsequently form ferrite. Fourier-transform infrared (FTIR) spectroscopy confirms the embedding of both undoped and ZnFe₂O₄-doped nanoparticles into the SiO₂ matrix at all investigated annealing temperatures. X-ray diffraction (XRD) consistently reveals the formation of crystalline ZnFe₂O₄, with the crystallite size increasing from 48 to 93 nm upon annealing. Atomic force microscopy (AFM) shows spherical ferrite nanoparticles surrounded by an amorphous layer, with particle growth observed at higher temperatures. Structural parameters derived from XRD (e.g., crystallite size, density, porosity, lattice constant, unit cell volume) and AFM (e.g., particle size, coating thickness) as well as magnetic parameters (saturation magnetization, remanence, anisotropy, coercivity) demonstrate clear dependence on both dopant presence and annealing temperature. Magnetic measurements reveal enhanced properties with increasing ferrite content and heat treatment, with a transition from superparamagnetic behavior at 700 °C to ferrimagnetic behavior above 1000 °C. Scavenger experiments confirmed the involvement of holes, hydroxyl radicals, and superoxide radicals in the photocatalytic process. The photocatalytic efficiency, as evaluated by the Rhodamine B degradation under visible light, highlights the promising potential of the obtained nanocomposite for advanced environmental and technological applications. Full article

This work explores the influence of material properties and experimental conditions on both biological and photocatalytic nitrate reduction processes. For the biological route, results demonstrate that carbon supports, specifically carbon gels, with open porosity, slight acidity, and high purity enhance E. coli adhesion and promote the formation of highly active bacterial colonies. However, carbon supports of bacteria, produced from waste biomass, emerge as a sustainable and cost-effective alternative, improving scalability and environmental value. The complete conversion of nitrates to nitrites, followed by full nitrite reduction, is achieved under optimized conditions. Photocatalytic nitrate reduction under solar radiation is also proposed as a promising and ecofriendly upgrade method to conventional wastewater treatment. Graphene oxide (GO) was used to enhance the photocatalytic activity of TiO₂ nanoparticles for the degradation of nitrates. The efficiency of nitrate reduction is found to be highly sensitive to solution pH and the physicochemical nature of the photocatalyst surface, which governs nitrate interactions through electrostatic forces. TiO₂–GO composites achieved up to 80% nitrate removal within 1 h and complete removal of 50 mg/L nitrate within 15 min under optimized conditions. The screening of hole scavengers revealed that formic acid, in combination with the TiO₂–GO composite, delivered exceptional performance, achieving complete nitrate reduction in just 15 min under batch conditions at an acidic pH. Full article