Hierarchically Porous ZnO/g-C3N4 S-Scheme Heterojunction Photocatalyst for Efficient H2O2 Production

S-scheme electron transfer promoted by novel indium oxide quantum dot-loaded carbon nitride heterojunctions promoted using oxidized indium monomers

The graphitic carbon nitride (g-C3N4) photocatalysis has emerged as a clean method for cleaving lignin-linked bonds due to its mild and sunlight-driven reaction conditions. The fast electron-hole pair complex of g-C3N4 constrains its degradation efficiency, making the heterojunction construction a popular solution. The conventional methods of preparing g-C3N4 heterojunctions by physical mixing destroy π-conjugations in g-C3N4, reducing the adsorption of lignin containing benzene rings. In this study, a novel indium oxide (In2O3) quantum dot-g-C3N4 0D/2D heterojunction was prepared through the high-temperature oxidation of pre-prepared indium-doped g-C3N4. The introduction of In2O3 at the quantum dot level minimizes the interference with lignin adsorption capacity. The strong combination of the two (In2O3 and g-C3N4) increases the intersection interface area, promoting the S-scheme transfer route of the photogenerated electrons. Consequently, this enhances the photoelectric conversion efficiency and carrier lifetime of the heterojunction, and inhibits the rapid recombination of photogenerated electron-hole pairs in g-C3N4. The proposed heterojunction was 3 times more efficient than g-C3N4 alone for selective cleavage of lignin β-O-4 bonds after 2 h of sunlight irradiation. Combined with inhibitor experiments and gas chromatography-mass spectrometry analysis, this paper defines the reactive oxides and proposes a cleavage pathway for the lignin β-O-4 bonds in In2O3-g-C3N4 heterojunction system.

Synthesis of H2O2 to Self-Catalyzed Generation of •OH over ZnO/CuI/Cu Foam Electrode for the Self-Fenton Cleaning of Wastewater

A novel ZnO/CuI/Cu foam electrode was constructed, which demonstrated excellent photoelectrocatalytic activity for the self-Fenton degradation of tetracycline in water. The H2O2 yield was 405.0 μmol L-1 over ZnO/CuI/Cu foam (CIZ-3) under light irradiation (100 mW cm-2) for 5 h at -1.23 V (vs NHE), which was 1.7 times higher than that of ZnO/Cu foam and 1.6 times higher than that of CuI/Cu foam, respectively. The 99.0% of tetracycline was degraded by CIZ-3 due to its efficient yield of H2O2 to self-catalyzed generation of •OH. The results of the open-circuit potential between CuI and ZnO displayed that the electrons from the conduction band of CuI flowed to ZnO and the holes from the valence band of ZnO migrated to CuI. As a result, the photogenerated electron-hole pairs of ZnO/CuI were efficiently separated, which greatly promoted the photoelectrocatalytic activity of ZnO/CuI/foam. The toxicity of the aqueous tetracycline solution was significantly reduced by observing the growth of Escherichia coli in the treated wastewater.

Construction of a BiOCl/Bi2O2CO3 S-Scheme Heterojunction Photocatalyst via Sharing [Bi2O2]2+ Slabs with Enhanced Photocatalytic H2O2 Production Performance

The construction of a close contact interface is key to enhancing the photocatalytic activity in heterojunctions. In the work, the BiOCl/Bi2O2CO3 of sharing [Bi2O2]2+ slabs S-scheme heterojunction was prepared by a HCl in situ etching method. The optimal composite photocatalyst could accomplish sizable productivity of H2O2 to 2562.95 μmol g-1 h-1 under simulated solar irradiation, higher than that of primitive Bi2O2CO3 and BiOCl. Moreover, the synthesized catalysts showed good stability. The band structures of BiOCl and Bi2O2CO3 were determined, confirming the formation of BiOCl/Bi2O2CO3 S-scheme heterojunction The BiOCl/Bi2O2CO3, which obviously improved the separation efficiency of photoinduced carriers and effectively enhanced the redox ability of the photocatalyst. In addition, density functional theory (DFT) calculations were utilized to analyze the electron transfer properties and the constitution of the built-in electric field at the interface of BiOCl and Bi2O2CO3. The photocatalytic reaction process was further researched by electron paramagnetic resonance (EPR), indicating the active species in the photocatalytic production of hydrogen peroxide. Eventually, a feasible S-scheme electron transfer mechanism on the BiOCl/Bi2O2CO3 heterojunction during the photocatalytic H2O2 production process was proposed and discussed. This work provides a reliable strategy for the fine design of the S-scheme heterojunction.

Ag@MUT-16 nanocomposite as a Fenton-like and plasmonic photocatalyst for degradation of Quinoline Yellow under visible light

A new cobalt-based metal-organic framework with the chemical formula of [Co2(DClTPA)2(DABCO)]·(DMF)4 (MUT-16) containing 1,4-diazabicyclo[2.2.2]octane (DABCO) and 2,5-dichloroterephthalic acid (DClTPA) has been designed and prepared through a solvothermal method. MUT-16 (MUT = Materials from University of Tehran) crystallized in a tetragonal system with I41/acd space group, based on single-crystal X-ray analysis. The Ag@MUT-16 nanocomposite was prepared using Ag nanoparticles (NPs) loaded into/onto porous MUT-16via photoreduction route (PR). The MUT-16 and Ag@MUT-16 were characterized using various techniques, such as PXRD, FT-IR, FE-SEM, TEM, EDX, N2 adsorption-desorption isotherms, TGA, DRS, PL, EIS, and Mott-Schottky measurements. The Ag@MUT-16 nanocomposite showed photocatalytic activity of 87.75% in the degradation of Quinoline Yellow (QY) after 30 min under visible light irradiation. The distinctive characteristics of the Ag@MUT-16 nanocomposite, such as the Fenton-like effect of Co2+ ions, surface plasmon resonance (SPR) of Ag NPs, Schottky junction at interfaces between Ag NPs and MUT-16, and reduction of electron-hole recombination through electron trapping by Ag NPs as co-catalyst, all play significant roles in the photocatalytic degradation of Quinoline Yellow (QY).

One-step hydrothermal synthesis of CeVO4/bentonite nanocomposite as a dual-functional photocatalytic adsorbent for the removal of methylene blue from aqueous solutions

Cerium vanadate/modified bentonite (CeVO4/mbt) nanocomposite with different composition percentages was synthesized through a simple one-step hydrothermal method at 180 ℃, and then its photocatalytic activity was evaluated by decolorizing methylene blue (MB) in an aqueous solution under light exposure. In order to increase the surface area as an important parameter in photocatalytic processes, bentonite was modified by ball mill method. The structural and optical properties of the synthesized composites were determined by XRD, FT-IR, DRS, FESEM, EDS, and BET measurements. XRD and EDS results confirmed the successful synthesis of pure CeVO4. FESEM images and EDS mapping showed a proper distribution of rice-like CeVO4 nanoparticles on bentonite. The removal efficiency of MB with only 0.1 g of CeVO4/mbt nanocomposite in 15 min was about 99%, which is significant compared to neat bentonite and pure CeVO4 with efficiency of 30% and 57%. The mentioned nanocomposite followed the first-order kinetics, had a reaction rate constant equal to 0.1483 min-1, and showed acceptable stability in five consecutive cycles.

S-Scheme Boron Phosphide/MoS2 Heterostructure with Excellent Light Conversion Ability for Solar Cells and Water Splitting Photocatalysts

Monolayer molybdenum disulfide (MoS2) with a suitable direct band gap and strong optical absorption is very attractive for utilization in solar cells and photocatalytic water splitting. Nevertheless, the broader utilization of MoS2 is impeded by its low carrier mobility and limited responsiveness to infrared light. To overcome these challenges, we constructed a variety of stackings for the boron phosphide (BP)/MoS2 van der Waals heterostructure (vdWH), all of which display S-scheme band alignments except for the AC' stacking. The constituent BP monolayer has superior carrier mobility and strong infrared and visible light response, which makes up for the shortcomings of MoS2. The study revealed that the AB stacking exhibits a remarkable power conversion efficiency of 22.27%, indicating its significant application prospect in solar cells. Additionally, the AB stacking also exhibits a promising application prospect in photocatalytic water splitting due to its suitable band structure, S-scheme band alignment, strong optical adsorption characteristic, high solar-to-hydrogen efficiency, and robust built-in electric field. Meanwhile, applying uniaxial tensile strains along the x-axis direction is more beneficial for photocatalytic water splitting. Hence, the AB-stacked BP/MoS2 vdWH shows significant potential for use in both solar cells and photocatalytic water splitting. This work paves the way for exploring the application of S-scheme heterostructures in solar energy conversion systems.

ZIF-8/g-C3N4 photocatalysts: enhancing CO2 reduction through improved adsorption and photocatalytic performance

Nowadays, the widespread concern over controlling CO2 emissions and mitigating the adverse effects of greenhouse gases on global climate has attracted significant attention. In this study, g-C3N4 was synthesized by thermopolymerizing urea. Subsequently, ZIF-8 was combined with g-C3N4 using an in situ deposition method, resulting in the fabrication of ZIF-8/g-C3N4 composite photocatalysts at various molar ratios. Effective incorporation of ZIF-8 into g-C3N4 suppressed the recombination of photogenerated electrons and holes, thereby enhancing CO2 capture capacity and preserving light absorption capabilities. The ZIF-8/g-C3N4 composite demonstrates excellent photocatalytic performance for CO2 reduction, where the optimized material exhibited a CO2 adsorption capacity 1.52 times that of pure g-C3N4 and increased the conversion of CO2 to CH4 by more than sevenfold. This study harnesses the superior CO2 adsorption properties of metal-organic frameworks to develop more efficient photocatalysts, enhancing CO2 conversion efficacy and offering insights for developing efficient photocatalysts that utilize CO2.

Solar-matched S-scheme ZnO/g-C3N4 for visible light-driven paracetamol degradation

In pursuit of an efficient visible light driven photocatalyst for paracetamol degradation in wastewater, we have fabricated the ZnO/g-C3N4 S-Scheme photocatalysts and explored the optimal percentage to form a composite of graphitic carbon nitride (g-C3N4) with zinc oxide (ZnO) for enhanced performance. Our study aimed to address the urgent need for a catalyst capable of environmentally friendly degradation of paracetamol, a common pharmaceutical pollutant, using visible light conditions. Here, we tailored the band gap of a photocatalyst to match solar radiation as a transformative advancement in environmental catalysis. Notably, the optimized composite, containing 10 wt.% g-C3N4 with ZnO, demonstrated outstanding paracetamol degradation efficiency of 95% within a mere 60-min exposure to visible light. This marked enhancement represented a 2.24-fold increase in the reaction rate compared to lower wt. percentage composites (3 wt.% g-C3N4) and pristine g-C3N4. The exceptional photocatalytic activity of the optimized composite can be attributed to the band gap narrowing that closely matched the maximum solar radiation spectrum. This, coupled with efficient charge transfer mechanisms through S-scheme heterojunction formation and an abundance of active sites due to increased surface area and reduced particle size, contributed to the remarkable performance. Trapping experiments identified hydroxyl radicals as the primary reactive species responsible for paracetamol photoreduction. Furthermore, the synthesized ZnO/g-C3N4 composite exhibited exceptional photostability and reusability, underscoring its practical applicability. Thus, this research marks a significant stride towards the development of an effective and sustainable visible light photocatalyst for the removal of pharmaceutical contaminants from aquatic environments.

Enhanced Visible-Light H2O2 Production over Pt/g-C3N4 Schottky Junction Photocatalyst

Photocatalytic for hydrogen peroxide (H2O2) production is thought as a promising technology owing to its clean and green properties with the cheap and easily available raw materials of H2O and O2. Herein, Pt/g-C3N4 Schottky junction photocatalysts with ultralow Pt contents (0.025-0.1 wt %) were successfully fabricated by an impregnation-reduction method. It can efficiently reduce O2 to generate H2O2 without a sacrificial agent under visible-light irradiation. The yield of H2O2 produced over Pt0.05/g-C3N4 with the optimal 0.05 wt % Pt reached 31.82 μM, which was 2.46 times that of g-C3N4 and higher than most of those in the literature. It also showed good stability in three repeated tests. The deposition of highly dispersed metal Pt nanoparticles with low and limited content can expose enough active Pt atoms, significantly enhance the separation efficiency of photogenerated carriers, and reduce its negative effect on H2O2 decomposition, resulting in improved and outstanding efficiency of H2O2 production. The ·O2- radicals were found to be the main active species. The mechanism of photocatalytic H2O2 production was confirmed to be a two-step single electron route (O2 + e-→ ·O2- → H2O2).

A Visible Light-Driven α-MnO2/UiO-66-NH2 S-Scheme Photocatalyst toward Ameliorated Oxy-TCH Degradation and H2 Evolution

Photocatalytic hydrogen production and pollutant degradation using a heterogeneous photocatalyst remains an alternative route for mitigating the impending pollution and energy crisis. Hence, the development of cost-effective and environmentally friendly semiconducting materials with high solar light captivation nature is imperative. To overcome this challenge, α-MnO2 nanorod (NR)-modified MOF UiO-66-NH2 (UNH) was prepared via a facile solvothermal method, which is efficient toward H2 evolution and oxy-tetracycline hydrochloride (O-TCH) degradation. The field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HR-TEM) results of the α-MnO2@UNH (MnU) hybrid reveals its nanorod embedded in MOF matrix, and the X-ray photoelectron spectroscopy (XPS) result confirms the interaction of UNH moiety with α-MnO2 NRs. Additionally, the outstanding separation of photogenerated excitons and the charge-transfer efficacy are further validated by photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical impedance spectroscopy (EIS), and transient photocurrent analysis, which are the key causes for photoactivity augmentation in the MnU composites. The MnU-2 composite shows a superior O-TCH degradation efficiency of 93.23% and an excellent H2 production rate of about 410.6 μmol h-1 upon light irradiation. This study provides significant evidence in favor of the suggested mediator-free S-scheme-adapted charge migration path, and it effectively explains the enhanced exciton separation leading to extraordinary catalytic efficiency of the proposed composite.

Green synthesis of ZnO nanoparticles from ball moss (Tillandsia recurvata) extracts: characterization and evaluation of their photocatalytic activity

Green synthesis (GS), referred to the synthesis using bioactive agents such as plant materials, microorganisms, and various biowastes, prioritizing environmental sustainability, has become increasingly relevant in international scientific practice. The availability of plant resources expands the scope of new exploration opportunities, including the evaluation of new sources of organic extracts, for instance, to the best of our knowledge, no scientific articles have reported the synthesis of zinc oxide nanoparticles (ZnO NPs) from organic extracts of T. recurvata, a parasitic plant very common in semiarid regions of Mexico.This paper presents a greener and more efficient method for synthesizing ZnO NPs using T. recurvata extract as a reducing agent. The nanoparticles were examined by different techniques such as UV-vis spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and BET surface analysis. The photocatalytic and adsorptive effect of ZnO NPs was investigated against methylene blue (MB) dye in aqueous media under sunlight irradiation considering an equilibrium time under dark conditions. ZnO nanoparticles were highly effective in removing MB under sunlight irradiation conditions, showing low toxicity towards human epithelial cells, making them promising candidates for a variety of applications. This attribute fosters the use of green synthesis techniques for addressing environmental issues.This study also includes the estimation of the supported electric field distributions of ZnO NPs in their individual spherical or rounded shapes and their randomly oriented organization, considering different diameters, by simulating their behavior in the visible wavelength range, observing resonant enhancements due to the strong light-matter interaction around the ZnO NPs boundaries.

Visible Light Motivated the Photocatalytic Degradation of P-Nitrophenol by Ca2+-Doped AgInS2

4-Nitrophenol (4-NP) is considered a priority organic pollutant with high toxicity. Many authors have been committed to developing efficient, green, and environmentally friendly technological processes to treat wastewater containing 4-NP. Here, we investigated how the addition of Ca2+ affects the catalytic degradation of 4-NP with AgInS2 when exposed to light. We synthesized AgInS2 (AIS) and Ca2+-doped AgInS2 (Ca-AIS) with varying amounts of Ca2+ using a low-temperature liquid phase method. The SEM, XRD, XPS, HRTEM, BET, PL, and UV-Vis DRS characteristics were employed to analyze the structure, morphology, and optical properties of the materials. The effects of different amounts of Ca2+ on the photocatalytic degradation of 4-NP were investigated. Under visible light illumination for a duration of 120 min, a degradation rate of 63.2% for 4-Nitrophenol (4-NP) was achieved. The results showed that doping with an appropriate amount of Ca2+ could improve the visible light catalytic activity of AIS. This work provides an idea for finding suitable cheap alkaline earth metal doping agents to replace precious metals for the improvement of photocatalytic activities.

Optical, Dielectric, Magnetic, Photocatalytic, and Antibacterial Properties of Ga-Doped BiGaxFe1-xO3 Synthesized by the Microemulsion Approach

The effect of Ga-substitution on bismuth ferrite BiGaxFe1-xO3 (x = 0, 0.05, 0.10, 0.15, 0.20, and 0.25) properties was investigated, which was fabricated using a microemulsion route. X-ray diffraction analysis confirmed that specimens had a single-phase rhombohedral structure with space group R3̅c. The concentration of Ga had an impact on various properties such as structural parameters, crystalline size, porosity, and unit cell volume. The samples exhibited notable values for the dielectric constant, tangent loss, and dielectric loss in the low-frequency range, which declined as the frequency increased due to different polarizations. The increment in the AC conductivity was associated with rise in frequency. The P-E loops demonstrated that the samples became more resistive as the Ga concentration increased. The retentivity (Mr) and saturation magnetization (Ms) values reduced as the Ga content increased, although all samples had Hc values within the range for electromagnetic materials. The Ga-substitution had a synergistic effect on the electrochemical characteristics of BiGaxFe1-xO3, resulting in greater conductivity than that of undoped BiFeO3. These enhanced properties contributed to their higher photocatalytic activity in the degradation of crystal violet under visible light irradiation. The doped BiGaxFe1-xO3 exhibited 79% dye degradation after 90 min of illumination compared to 54% for pure BiFeO3. Recycling experiments confirmed the stability and reusability of the synthesized nanoparticles. The antibacterial activity of the samples was certified against various microbes, and the doped BiGaxFe1-xO3 showed promising activity. Thus, doped materials are good candidates for memories, dielectric resonators, and photovoltaics because of their high dielectric constant and AC conductivity, while their higher photocatalytic activity under visible light makes them promising photocatalysts for removing noxious and harmful effluents from wastewaters.

Rational design of full-spectrum visible-light-responsive bimetallic sulfide Bi2S3/CoS2 composites for high-efficiency photocatalytic degradation of naproxen and bacterial inactivation

Photocatalytic water decontamination has emerged as a highly promising technology for efficient and rapid water treatment, harnessing sustainable solar energy as its driving force. In this study, we prepared visible-light active Bi2S3/CoS2 composites for the degradation of naproxen (NPX) and the inactivation of Escherichia coli (E. coli). The homogeneous dispersion of CoS2 was stably integrated with Bi2S3, resulting in a significant enhancement of the specific surface area, efficient utilization of visible light, and effective separation of photogenerated charge carriers. Consequently, this synergistic photocatalytic system greatly facilitated the successful degradation of NPX and the inactivation of E. coli under visible-light irradiation. Compared to the pure Bi2S3 and CoS2 catalysts, the Bi2S3/CoS2 (1:2) composites displayed significantly enhanced photodegradation activity, achieving 96.46% (k = 0.2847 min-1) degradation of NPX within 90 min and maintaining good recyclability with no significant decline after six successive cycles. Additionally, the photocatalytic inactivation of E. coli results indicated that Bi2S3/CoS2 composites exhibited excellent performance, leading to the inactivation of 7 log10 cfu mL-1 of bacterial cells after 150 min of visible-light exposure. Scanning Electron Microscopy (SEM) and K+ ions leakage tests demonstrated that the destruction of the E. coli cell membrane structure resulted in cell death. The outcomes of this work suggest that Bi2S3/CoS2 composites hold significant potential for treating water contaminated with antibiotic and microbial pollutants.

Rapid Charge Transfer Endowed by Interfacial Ni-O Bonding in S-scheme Heterojunction for Efficient Photocatalytic H2 and Imine Production

Cooperative coupling of H2 evolution with oxidative organic synthesis is promising in avoiding the use of sacrificial agents and producing hydrogen energy with value-added chemicals simultaneously. Nonetheless, the photocatalytic activity is obstructed by sluggish electron-hole separation and limited redox potentials. Herein, Ni-doped Zn0.2 Cd0.8 S quantum dots are chosen after screening by DFT simulation to couple with TiO2 microspheres, forming a step-scheme heterojunction. The Ni-doped configuration tunes the highly active S site for augmented H2 evolution, and the interfacial Ni-O bonds provide fast channels at the atomic level to lower the energy barrier for charge transfer. Also, DFT calculations reveal an enhanced built-in electric field in the heterojunction for superior charge migration and separation. Kinetic analysis by femtosecond transient absorption spectra demonstrates that expedited charge migration with electrons first transfer to Ni2+ and then to S sites. Therefore, the designed catalyst delivers drastically elevated H2 yield (4.55 mmol g-1  h-1 ) and N-benzylidenebenzylamine production rate (3.35 mmol g-1  h-1 ). This work provides atomic-scale insights into the coordinated modulation of active sites and built-in electric fields in step-scheme heterojunction for ameliorative photocatalytic performance.

Compositionally engineered Cd-Mo-Se alloyed QDs toward photocatalytic H2O2 production and Cr(VI) reduction with a detailed mechanism and influencing parameters

With the exceptional advantages of safety, greenness, and low cost, photocatalytic H2O2 generation has kindled a wonderful spark, although being severely hampered by the terrible photoinduced exciton recombination, migration, and surface decomposition. Here, employing reflux method, the Cd-Mo-Se quantum dots of varying molar ratios of Cd and Mo were synthesized using thioglycolic acid as the capping ligand to regulate their growth. This type of metal alloying promotes rapid charge migration, improves light harvesting, and reduces the rate of charge recombination. The improved optoelectronic properties and boosted activity of Cd-rich ternary CMSe-1 QDs led to the observed exceptional photocatalytic H2O2 yield of 1403.5 μmol g-1 h-1 (solar to chemical conversion efficiency, 0.27%) under visible light, outperforming the other ternary and Se-based QD photocatalysts. Additionally, CMSe-1 shows 93.6% (2 h) hazardous Cr(VI) photoreduction. The enhanced catalytic performance of CMSe-1 corresponds to effective charge carrier separation and transfer efficiency, well supported by PL, TRPL, and electrochemical measurements. Photocatalytic H2O2 production was also studied under varying experimental conditions and the scavenger test suggests a superoxide radical intermediate 2-step single electron reduction pathway. The catalyst-assisted Cr(VI) reduction is substantiated by the zero-order kinetics as well as the determination of the pHPZC value. The catalyst can be employed for a maximum of four times while retaining its activity, according to the photostability and reusability test outcomes. This research presents interesting approaches for producing ternary QDs and modified systems for efficient photocatalytic H2O2 production and Cr(VI) reduction.

Efficient Photocatalytic H2 O2 Production Ability of a Novel Graphitic Carbon Nitride/Carbon Composites under Visible Light

In the present work, using one-step calcination of a mixture made of potassium hydroxide (KOH), melamine, and microplastics, this work prepares a novel graphitic carbon nitride/carbon (g-C3 N4 /C) composite, which can be employed to photo-catalytically produce hydrogen peroxide (H2 O2 ) at a high rate up to 6.146 mmol g-1 h-1 under visible light irradiation. By analyzing the energy band structure of the catalyst, the production of H2 O2 in this system consists of two single-electron reactions. The modification of KOH makes abundant N-vacancies caused by cyano-groups in g-C3 N4 , enhancing the electron absorption ability. Moreover, the introduction of graphitic carbon increases its specific surface area and porosity and improves the adsorption ability of O2 . Simultaneously, their synergism reduces the g-C3 N4 band gap, making both the conduction-band and valence-band positions more negative, showing enhanced reduction ability, lowering the energy barrier for oxygen reduction, and greatly improving the photogeneration performance of H2 O2 .

Graphitic Carbon Nitride Nanosheets Decorated with Zinc-Cadmium Sulfide for Type-II Heterojunctions for Photocatalytic Hydrogen Production

In this study, we fabricated graphitic carbon nitride (g-C3N4) nanosheets with embedded ZnCdS nanoparticles to form a type II heterojunction using a facile synthesis approach, and we used them for photocatalytic H2 production. The morphologies, chemical structure, and optical properties of the obtained g-C3N4-ZnCdS samples were characterized by a battery of techniques, such as TEM, XRD, XPS, and UV-Vis DRS. The as-synthesized g-C3N4-ZnCdS photocatalyst exhibited the highest hydrogen production rate of 108.9 μmol·g-1·h-1 compared to the individual components (g-C3N4: 13.5 μmol·g-1·h-1, ZnCdS: 45.3 μmol·g-1·h-1). The improvement of its photocatalytic activity can mainly be attributed to the heterojunction formation and resulting synergistic effect, which provided more channels for charge carrier migration and reduced the recombination of photogenerated electrons and holes. Meanwhile, the g-C3N4-ZnCdS heterojunction catalyst also showed a higher stability over a number of repeated cycles. Our work provides insight into using g-C3N4 and metal sulfide in combination so as to develop low-cost, efficient, visible-light-active hydrogen production photocatalysts.

Photosynthesis of Hydrogen Peroxide Based on g-C3 N4 : The Road of a Cost-Effective Clean Fuel Production

Emerging artificial photosynthesis promises to offer a competitive means for solar energy conversion and further solves the energy crisis facing the world. Hydrogen peroxide (H2 O2 ), which is considered as a benign oxidant and a prospective liquid fuel, has received worldwide attention in the field of artificial photosynthesis on account of the source materials are just oxygen, water, and sunlight. Graphitic carbon nitride (g-C3 N4 )-based photocatalysts for H2 O2 generation have attracted extensive research interest due to the intrinsic properties of g-C3 N4 . In this review, research processes for H2 O2 generation on the basis of g-C3 N4 , including development, fabrication, merits, and disadvantages, and the state-of-the-art methods to enhance the performance are summarized after a brief introduction and the mechanism analysis of an efficient catalytic system. Also, recent applications of g-C3 N4 -based photocatalysts for H2 O2 production are reviewed, and the significance of active sites and synthetic pathways are highlighted from the view of reducing barriers. Finally, this paper ends with some concluding remarks to reveal the issues and opportunities of g-C3 N4 -based photocatalysts for producing H2 O2 in a high yield.

Melamine-Formaldehyde Polymer-Based Nanocomposite for Sunlight-Driven Photodegradation of Multiple Dyes and Their Mixture

Cadmium sulfide (CdS)-decorated, cross-linked melamine-formaldehyde polymer-based nanocomposite (MFP-CdS) has been synthesized. MFP-CdS is utilized here as a photoactive material for the photodegradation of six model organic dyes and their mixture in an aqueous medium in the presence of sunlight. The half-life values from the kinetic study of multiple dyes strongly support the importance of sunlight on the fast degradation of all six dyes compared to bulb light and control (dark) conditions. A comparative ¹H NMR analysis of the dyes and their degraded products has been performed to support the breakdown of the aromatic framework of organic dyes using MFP-CdS in sunlight. The mechanisms involved in the photodegradation of dyes have been investigated based on radical trapping studies that support the significant involvement of superoxide radicals along with holes. Moreover, the dye removal efficiency using MFP-CdS from real industrial wastewater samples is evaluated via the external spiking of organic dyes and their mixture in unknown industrial effluents where they showed similar photodegradation results. Based on the high recyclability of MFP-CdS, these are used for multiple cycles.

Optical, Photocatalytic, Electrochemical, Magnetic, Dielectric, and Ferroelectric Properties of Cd- and Er-Doped BiFeO3 Prepared via a Facile Microemulsion Route

A series of Cd- and Er-doped bismuth ferrites were synthesized using a simple microemulsion technique. The influence of Cd and Er doping on the structural, ferroelectric, photocatalytic, and dielectric properties of bismuth ferrite (BFO) was examined in this research. The prepared materials were examined by X-ray diffraction, Raman, scanning electron microscopy, and UV-vis techniques. The XRD patterns reflected the formation of a monophasic rhombohedral structure with the space group R3^-c and an average crystallite size calculated to be in the range of 29 to 32 nm. The saturation polarization (P_s), coercivity (H_c), and retentivity (P_r) of the materials were investigated by a hysteresis loop (P-E), and it was perceived that increasing the dopant contents improved the P_s and P_r values, which may be due to the variation of metal cation valence states. In accordance with the photoluminescence (PL) spectra, a highly substituted material displayed lower recombination and increased charge separation rate (e^--h⁺), which eventually contributed to a higher photocatalytic degradation performance of the prepared NMs. Furthermore, as the frequency and dopant concentration increased, the dielectric loss decreased, which could be due to different types of polarization. Bi_1 - xCd_xFe_1 - yEr_yO₃ showed well-saturated hysteresis loops (P-E) with enhanced saturation polarization near 9.7 × 10^-4 μC·cm^-2. The remnant polarization of the BFO and BFOCE NPs was 2.26 × 10^-4 and 8.11 × 10^-4 μC·cm^-2, respectively, under a maximum electric field, which may be due to the variation of the metal cation valence states. The improved ferroelectric and dielectric properties of Bi_1 - xCd_xFe_1 - yEr_yO₃ NPs are attributed to the reduced concentration of defects, the different domain behavior, and the valence state of Cd and Er ions. The electrochemical (crystal violet (CV) and I-V) properties of Bi_1 - xCd_xFe_1 - yEr_yO₃ were all influenced by the dopant concentrations (Cd and Er). The synergistic effects of Cd and Er on the substituted material enhanced the specific capacitance in comparison to undoped BiFeO₃. The photocatalytic activity to degrade CV under visible irradiation increased in BFOCE as the dopant (x,y) concentration increased from 0 to 0.25 by showing 84% dye degradation in comparison to pristine BiFeO₃ (53% only) within 120 min under visible light. Moreover, the stability of these prepared nanoparticles was confirmed using recycling experiments, with the results indicating that the synthesized nanomaterials demonstrated promising stability and reusability.

S-Scheme Heterojunction Photocatalysts for H2O2 Production

Photocatalysis opens a new door to H₂O₂ formation via a low-cost, clean, mild, and sustainable process, which holds great promise for the next generation of massive H₂O₂ production. However, fast photogenerated electron-hole recombination and slow reaction kinetics are the main obstacles for its practical application. An effective solution is to construct the step-scheme (S-scheme) heterojunction, which remarkably promotes carrier separation and boosts the redox power for efficient photocatalytic H₂O₂ production. Considering the superiority of S-scheme heterojunctions, this Perspective summarizes the recent advances of S-scheme photocatalysts for H₂O₂ production, including photocatalysts for building S-scheme heterojunctions, H₂O₂-production performance, and S-scheme photocatalytic mechanisms. Lastly, some prospects are given to motivate future research in this promising field, other promising strategies are provided to further improve H₂O₂ yields, and future research directions are suggested.

Synthesis of β-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (β-FeOOH/PANI, about 1.0 μm) could be successfully composed by polyaniline (PANI, (C₆H₇N)_n, 200-300 nm) and akaganéite (β-FeOOH, FeO(OH)_1-xCl_x, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the β-FeOOH/PANI composite (compared with β-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H₂O₂ oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h⁺ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H₂O molecule and CO₂. The β-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

A Cu medium designed Z-scheme ZnO-Cu-CdS heterojunction photocatalyst for stable and excellent H2 evolution, methylene blue degradation, and CO2 reduction

Solar photocatalysis has emerged as a pollution-free and inexhaustible technique that has been extensively researched in the domains of environmental remediation and energy production. Herein, we have integrated ZnO and CdS nanoparticles through Cu as a solid-state electron mediator to design a ZnO-Cu-CdS Z-scheme heterosystem via a sol-gel route and further tested this as a photocatalyst for dye degradation, H₂ evolution, and CO₂ reduction. Within 60 min of visible light exposure, about 97% of methylene blue (MB) is degraded with a degradation rate constant of 0.042 min^-1 for the ZnO_0.45Cu_0.1CdS_0.45 catalyst. The MB degradation with this catalyst is 84, 21, 4.8, and 2 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. The ZnO-Cu-CdS catalyst manifests an H₂ evolution efficiency of 5579 μmol h^-1 g^-1, which is 169, 41, 3.9, and 3.5 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. Using H₂ as a reducing agent, the CO production rate over the ZnO_0.45Cu_0.1CdS_0.45 catalyst reaches 770 μmol h^-1 g^-1, which is 3 and 1.8 times higher than those of ZnO_0.5CdS_0.5 and Cu_0.1ZnO_0.9 catalysts. Besides, the optimal CH₄ production rate over ZnO_0.45Cu_0.1CdS_0.45 reaches 890 μmol h^-1 g^-1. The improved photocatalytic response of the ZnO-Cu-CdS catalyst is assigned to the delayed recombination of photoexcited charge carriers through a Z-scheme charge transport mode, maintaining the photocarriers with strong redox potentials and the dual role of Cu to serve as a conductive bridge to accelerate the charge transfer rate and enhance the light absorption due to its SPR phenomenon. This research offers a promising strategy for developing binary/ternary Z-scheme heterojunction photocatalytic systems for different photocatalytic applications.

Synthesis of Ag3PO4/Ag4P2O7 by microwave-hydrothermal method for enhanced UV-visible photocatalytic performance

Ag₃PO₄/Ag₄P₂O₇ photocatalysts were successfully synthesized by microwave-hydrothermal method. Tuning the properties of photocatalysts was achieved using different amount of acetic acid (CH₃COOH) and sodium hydroxide (NaOH) to adjust pH value of precursor solution (pH = 4, 7, 10 and 12). The crystal structure, morphology and optical property of samples were characterized and explained. The photocatalytic activity of sample was determined by degradation of rhodamine B (RhB) and methyl orange (MO) under a wavelength range of 350-700 nm irradiation. The results demonstrated that the change in shape of particles was not observed whereas the average particle size was decreased with increasing pH value because of the high hydroxide ions (OH^-). The sample synthesized in the solution with the pH of 10 exhibited excellent photocatalytic performance and stability because of the highest surface area and the present of Ag₄P₂O₇ on the surface of particles. The highest photodegradation efficiency was 99.34 and 96.12% by degrading RhB and MO, respectively. The enhancement of photocatalytic performance of Ag₃PO₄/Ag₄P₂O₇ was discussed. The active species trapping experiments showed that the h⁺ was the main active species to decompose the dye molecules.

Construction of a novel double S-scheme structure WO3/g-C3N4/BiOI: Enhanced photocatalytic performance for antibacterial activity

In recent years, the threat to human health from bacteria in wastewater has attracted attention, and photocatalytic technology has emerged as a promising strategy for inactivating bacteria in water. Therefore, it is of great research value to develop a novel high-efficiency photocatalytic system with the visible light response. We successfully designed a double S-scheme heterojunction composite WO₃/g-C₃N₄/BiOI (WCB) in this paper. The preparation of WCB composites was demonstrated by a series of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The antibacterial effects of photocatalysts against representative Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) were tested under LED light irradiation. The novel photocatalyst presented excellent antibacterial properties, inactivating E. coli in 12 min and S. aureus in 20 min. The bacterial cell inactivation process was studied by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). Active species capture experiments show that the active species present in the WCB composites in the process of inactivating bacteria are h⁺, e^-, OH and O₂^-. In conclusion, the synthesized double S-scheme WCB photocatalyst exhibits remarkable photocatalytic antibacterial activity under LED light and has broad prospects for practical application in water antibacterial treatment.

Efficient photocatalytic hydrogen peroxide production induced by the strong internal electric field of all-organic S-scheme heterojunction

Light-driven reaction of oxygen and water to hydrogen peroxide (H₂O₂) is an environmental protection method, which can convert solar energy into green products. In this work, perylene-3, 4, 9, 10-tetracarboxylic diimide (PDINH) could be recrystallized in situ on the surface of porous carbon nitride (PCN), to obtain an all-organic S-scheme heterojunction (PDINH/PCN). The design of the hierarchical porous photocatalyst improved the mass transfer, enhanced the light absorption and increased specific surface area. Moreover, the construction of the S-scheme heterojunction at the interface of PDINH and PCN exhibited suitable band, which facilitated the separation and transfer of carriers. The H₂O₂ production rate was up to 922.4 μmol g^-1h^-1, which was 2.6 and 53.3 times higher than that of PCN and PDINH. Therefore, the all-organic S-scheme heterojunction provides an insight for improving the photocatalytic H₂O₂ production.

Photocatalytic Hydrogen Production and Tetracycline Degradation Using ZnIn2S4 Quantum Dots Modified g-C3N4 Composites

In this work, ZnIn₂S₄/g-C₃N₄ (ZIS/CN) composites were synthesized by in-situ growth method, which showed excellent photocatalytic activity in the degradation of tetracycline and hydrogen production from water under visible light irradiation. ZnIn₂S₄ quantum dots (ZIS QDs) tightly combined with sheet g-C₃N₄ (CN) to accelerate the separation and transportation of photogenerated charges for enhanced photocatalytic activity. Among the prepared nanocomposites, 20%ZnIn₂S₄ QDs/g-C₃N₄ (20%ZIS/CN) delivered the highest photocatalytic activity. After 120 min of irradiation, the degradation rate of tetracycline with 20%ZIS/CN was 54.82%, 3.1 times that of CN while the rate of hydrogen production was 75.2 μmol·g^-1·h^-1. According to the optical and electrochemical characterization analysis, it was concluded that the excellent photocatalytic activities of the composite materials were mainly due to the following three points: enhancement in light absorption capacity, acceleration in the charge transport, and reduction in the carrier recombination rate through the formation of S-scheme heterojunction in the composite system. The high photocatalytic activity of ZIS/CN composites provides a new idea to develop highly efficient photocatalysts.

Hydroxyl-/Carboxyl-Rich Graphitic Carbon Nitride/Graphene Oxide Composites for Efficient Photodegradation of Reactive Red 195 and Antibacterial Applications

In this work, a protonated graphitic carbon nitride (P-g-C₃N₄)-coated graphene oxide (GO) composite (GO/P-g-C₃N₄) was prepared via wet-chemistry exfoliation, followed by a freeze-drying process. The GO/P-g-C₃N₄ composite was found to have an outstanding photodegradation performance effect on the reactive red 195 (RR195) dye and very strong antibacterial properties. Both the GO structure and the dispersed state of P-g-C₃N₄ were found to play a significant role in enhancing the photocatalytic activity of GO/P-g-C₃N₄. The GO/P-g-C₃N₄ obtained via freeze-drying retained a large number of oxygen-containing groups and showed higher catalytic activity and reusability than the reduced GO (rGO)/g-C₃N₄ obtained via thermal reduction. Characterization of the samples indicates that GO/P-g-C₃N₄ has a higher specific surface area and photocurrent density than rGO/g-C₃N₄; it is likely that these properties lead to the superior photocatalytic activity observed in GO/P-g-C₃N₄. Adsorption energy calculations indicate that O₂ can be readily adsorbed onto the GO surface, which results in stronger oxidizing superoxide anion radicals (^•O₂^-) and holes (h⁺); these active radicals can rapidly degrade RR195 dyes. Moreover, broad-spectrum antibacterial activity (demonstrated against Staphylococcus aureus and Escherichia coli) was observed in the case of the GO/P-g-C₃N₄ composite irradiated with visible light. This work offers new insights into the design of cost-effective g-C₃N₄-based photocatalysts for environmental remediation.

Potassium-Derived Charge Channels in Boron-Doped g-C3N4 Nanosheets for Photocatalytic NO Oxidation and Hydrogen Evolution

The application of graphitic carbon nitride (g-C3N4) in photocatalytic NO oxidation was limited due to severe recombination of photogenerated carriers and low concentration of oxidizing species. In this work, K and B were introduced into the interlayer and in-plane framework of g-C3N4 to address this challenge through the thermal polymerization process. The synthesized K-doped B-g-C3N4 nanosheets exhibited expanded light absorption and low charge recombination efficiency. In addition, the doping of K and B reduced the band gap of g-C3N4, which corresponded to enhanced light absorption. B was introduced into the in-plane structure by replacing C atoms, which adjusted the in-plane electron distribution. K was inserted into the interlayer by binding to the N and C atoms of adjacent layers. K-derived electron transfer channels were constructed, which increased electron delocalization and expanded the π-conjugate system. More electrons were transferred through the interlayer channels and were involved in the reaction process. The severe carrier recombination and weak transfer were improved due to the synergistic effect of K and B doping. K-doped B-g-C3N4 nanosheets exhibited enhanced generation of superoxide radicals and hydroxyl radicals, which played a key role during NO oxidation. The photocatalytic NO oxidation efficiency of codoped g-C3N4 nanosheets reached 61%, which was 2.1 and 1.2 times of that of pristine g-C3N4 and B-doped g-C3N4, respectively. The codoped g-C3N4 sample still exhibited stable photocatalytic NO oxidation efficiency after five cycles. This result provided a potential idea for improving the charge distribution and transfer of layered materials by codoping metallic and nonmetallic elements and for photocatalytic NO oxidation.

Architecture and Kinetic Studies of Photocatalytic H2O2 Generation and H2 Evolution through Regulation of Spatial Charge Transfer via Z-Scheme Path over a (001) Facet Engineered TiO2@MXene/B-g-C3N4 Ternary Hybrid

Spatial charge separation and migration are the critical shortcomings dominating the core energy conversion corridors of photocatalytic systems. Here, a biomimetic multi-interfacial architecture providing strong coupled interaction and rapid charge transmission for photostable and competent photocatalytic H2O2 production and H2 evolution is proposed. The triple-hybrid all-solid-state Z-scheme system was formed with the (001) facet exposed TiO2 nanosheets derived from MXene layers and B-g-C3N4 nanosheets (M/(001)TiO2@BCN) through an electrostatic self-assembly strategy with intimate electronic interaction due to Ti orbital modulation and proper stacking among the hybrids. The metallic and highly conductive MXene layers act as solid state electron mediators in the Z-scheme heterojunction that promote electron-hole separation and migration efficiency. Specifically, the MTBCN-12.5 composite provides optimum yield of H2O2 up to 1480.1 μmol h-1 g-1 and a H2 evolution rate of 408.4 μmol h-1 (with ACE 6.7%), which are 4 and 20 fold greater than the pristine BCN, respectively. The enhanced photocatalytic performance is systematically identified by the increased surface area, higher cathodic and anodic current densities of -1.01 and 2.27 mA cm-2, delayed charge recombination as supported by PL and EIS measurement, and excellent photostability. The Z-scheme charge transfer mechanism is validated by time-resolved photoluminescence (TRPL) analysis, cyclic voltametric analysis, and the radical trapping experiment as detected by PL analysis. This research marks a substantial advancement and establishes the foundation for future design ideas in accelerating charge transfer.

Fabrication of a highly dispersed Co3O4-modified MOF-derived ZnO@ZnS porous heterostructure for efficient photocatalytic hydrogen production

A highly dispersed Co3O4-modified ZnO@ZnS porous heterostructure was prepared via a designed bimetallic ZnCo-ZIF@ZIF-8 precursor for water splitting.

Synergistic effect of exfoliation and substitutional doping in graphitic carbon nitride for photocatalytic H2O2 production and H2 generation: a comparison and kinetic study

The fabricated exfoliated e-BCN demonstrated stupendous H2O2 production and H2 generation owing to sufficient active surface area and enhanced aromatic π-conjugation, faster charge migration/separation efficiency.

Recent progress in the design of photocatalytic H2O2 synthesis system

Photocatalytic synthesis of hydrogen peroxide under mild reaction conditions is a promising technology. This article will review the recent research progress in the design of photocatalytic H₂O₂ synthesis systems. A comprehensive discussion of the strategies that could solve two essential issues related to H₂O₂ synthesis. That is, how to improve the reaction kinetics of H₂O₂ formation via 2e^- oxygen reduction reaction and inhibit the H₂O₂ decomposition through a variety of surface functionalization methods. The photocatalyst design and the reaction mechanism will be especially stressed in this work which will be concluded with an outlook to show the possible ways for synthesizing high-concentration H₂O₂ solution in the future.

Enhanced photodegradation of rifampicin and co-trimoxazole by ZnO/ZnMn2O4/ZnS-PVA and its genotoxicity studies on Allium cepa

Oxygen vacancies and its associated defect states have a great influence on the electronic and structural aspects of semiconductor photocatalysts, yet there is paucity of investigations about the influence of the defect states on their photocatalytic properties. Herein, this study reports the hierarchical fabrication of oxygen vacancy enriched ZnO/ZnMn₂O₄/ZnS-PVA nanocomposite (NCs) for the enhanced photodegradation of rifampicin and co-trimoxazole. The formation of lattice expansion induced oxygen vacancies and its associated Urbach tail energy, and n-p-n heterojunction-based S-scheme charge transfer path synergistically contributed to the boosted photocatalytic performance of the as prepared NCs. The photocatalytic performance of the nanomaterial towards rifampicin and co-trimoxazole has been determined to be 80% and 90% under visible light irradiation, respectively. Furthermore, various operating parameters including the concentration of NCs and drug, pH and interference of various ions have been evaluated. The degraded product intermediates have been elucidated by GC-MS analysis. The toxicity of the as-prepared nanomaterials has been evaluated by treating the samples with root tips of Allium cepa, where the NCs was found to be non-toxic. The study provides a new-fangled insight on the preparation and fabrication of non-toxic and defect rich nanomaterials which may help stimulate this area of research.

Three-Dimensional Hierarchical Seaweed-Derived Carbonaceous Network with Designed g-C3N4 Nanosheets: Preparation and Mechanism Insight for 4-Nitrophenol Photoreduction

The development of g-C₃N₄-based photocatalysts with abundant active sites is of great significance for photocatalytic reactions. Herein, a smart and robust strategy was presented to fabricate three-dimensional (3D) g-C₃N₄ nanosheet-coated alginate-based hierarchical porous carbon (g-C₃N₄@HPC), including coating melamine on calcium alginate (CA) hydrogel beads, freeze-drying hydrogel beads as well as pyrolysis at high temperatures. The resulting photocatalyst possessed a significantly high surface area and a large amount of interconnected macropores compared with porous carbon without the melamine coating. The unique structural features could effectively inhibit the curling and agglomeration of g-C₃N₄ nanosheets, provide abundant photocatalytic active sites, and promote mass diffusion. Therefore, the g-C₃N₄@HPC composite exhibited remarkable photocatalytic activity and outstanding stability toward the photoreduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH₄ under natural sunlight and simulated visible-light irradiation (λ > 420 nm) using a 300 W xenon lamp. Moreover, the mechanism toward the photocatalytic reaction was extensively studied by quenching experiments and electron spin resonance (ESR) experiments. The results showed that active hydrogen species were able to be achieved by following a dual-channel pathway in the NaBH₄ system, which included photocatalytic reduction of H⁺ ions and photocatalytic oxidation of BH₄^- ions. This work not only opens up a new way to design efficient photocatalysts for various reactions but also provides a reference for an in-depth study of the photoreduction mechanism.