g-C3N4 Composites Research Articles

A Breakthrough in Photocatalytic Wastewater Treatment: The Incredible Potential of g-C3N4/Titanate Perovskite-Based Nanocomposites.

Water pollution has emerged as a major global environmental crisis due to the massive contamination of water resources by the textile dyeing industry, organic waste, and agricultural residue. Since water is fundamental to life, this grave disregard puts lives at risk, making the protection of water resources a serious issue today. Recent research has shown great interest in improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) for wastewater treatment. However, the photocatalytic removal activity of pure g-C3N4 is poor, owing to its minimal surface area, fast recombination of photo-generated electron-hole pairs, and poor light absorption. Recently, titanate perovskites (TNPs) have attracted significant attention in both environmental remediation and energy conversion due to their exceptional structural, optical, physiochemical, electrical, and thermal properties. Accordingly, TNPs can initiate a variety of surface catalytic reactions and are regarded as an emerging category of photocatalysts for sustainability and energy-related industries when exposed to illumination. Therefore, in this review article, we critically discuss the recent developments of extensively developed g-C3N4/TNPs that demonstrate photocatalytic applications for wastewater treatment. The different synthetic approaches and the chemical composition of g-C3N4/TNP composites are presented. Additionally, this review highlights the global research trends related to these materials. Furthermore, this review provides insight into the various photocatalytic mechanisms, including their potential impact and significance. Also, the challenges faced by such materials and their future scope are discussed.

Novel in-situ composites of chlorine-doped CQDs and g-C3N4 with improved interfacial connectivity and accelerated charge transfer to enhance photocatalytic degradation of tetracycline and hydrogen evolution

The photocatalytic performance of graphite-phase carbon nitrides (g-C3N4) composites is severely limited by poor interfacial connectivity and a narrow visible light response range. Although carbon quantum dots (CQDs) can enhance the visible light absorption of g-C3N4, it is difficult to produce effective interfacial connectivity due to their different properties. Herein, a novel “in-situ composite modified by chlorine-doped CQDs” strategy was proposed to further enhance the photocatalytic redox capability of g-C3N4. Specifically, chlorine-doped CQDs (Cl-CQDs) were prepared from mulberry branch powder and sulfoxide chloride directly, and the novel metal-free photocatalyst (Cl-CCN) was prepared by in-situ compounding the Cl-CQDs with g-C3N4. Cl-CCN shows superior photocatalytic tetracycline degradation rate (0.0269 min−1) and hydrogen production rate (1397.5 µmol g−1h−1), which are 14.9 and 2.75 times higher than those of g-C3N4, respectively. The characterization and DFT calculation results reveal that the C − Cl covalent bonds serve as fast electronic channels to bridge the hydrophilic Cl-CQDs and hydrophobic g-C3N4 and significantly enhance the interfacial coupling and charge transfer. On this basis, a possible mechanism for tetracycline degradation and hydrogen production photocatalyzed by Cl-CCN is proposed. This study provides a concise and economical method for modifying and enhancing the photocatalytic activity of composites CQDs/g-C3N4.

Heterostructure α-Fe2O3(0 0 1)/g-C3N4(0 0 2) adsorbent to remove As2O3 in simulated coal flue gas: Experimental and DFT study

Arsenic has strong migration and enrichment in flue gas and can produce serious arsenic pollution, so it is urgent to control the arsenic emission in flue gas. In this study, α-Fe2O3/g-C3N4 composites with heterostructure were prepared by hybrid calcination, which was innovatively used to combine As2O3(g) adsorption experiment and microscopic computational analysis. The experimental results show that FC2 (α-Fe2O3:g-C3N4 = 14%, Wt%) has a better As2O3(g) adsorption capacity within 400–500 °C. At 450 °C, FC2 has almost twice the adsorption capacity of As2O3(g) than α-Fe2O3 with an adsorption capacity of 2870.93 mg/kg. When the temperature rises to 500 °C, the adsorption amount of FC2 to As2O3(g) reaches 3450.80 mg/kg, which can be attributed to the more active points than α-Fe2O3. At the same time, with the increase of the adsorption time, the As(III) in the sample tends to be gradually oxidized to As(V). The results of density functional theory (DFT) show that in the heterostructure of α-Fe2O3(001)/g-C3N4(002), the electron transfers 0.614 e from g-C3N4 to α-Fe2O3, which establishes the electron transmission channel, thus enhancing the adsorption capacity of As2O3(g). Finally, the oxidation mechanism of As(III) is deduced, and the removal of As2O3 by α-Fe2O3/g-C3N4 can be understood as adsorption before catalysis. Firstly, As2O3(g) is adsorbed to Fe and O on the surface and generates chemical bonds, subsequently binding to the cleaved O2. Part of As(III) is oxidized to As(V), and the other part of As is still As(III) although the As-O bond is broken but combines with O of O2.

A two-dimensional Cu(II) metal-organic framework and its g-C3N4 heterojunction composite for high efficient photodegradation of organic dyes

A two-dimensional Cu(II) MOF {[Cu2(OH)(mtrb)(suc)1.5(H2O)2]·H2O·0.5DMA}n (Cu(mtrb)) (mtrb = 1,3-bis((1,2,4-triazol-4-ylmethyl)benzene, H2suc = succinic acid, DMA = N, N-dimethylacetamide) was obtained using solvothermal synthesis. Cu(mtrb) has a two-dimensional (6,3) network with the point symbol of 63. A series of Cu(mtrb)/wt%g-C3N4 composites were obtained by coupling Cu(mtrb) and semiconductor g-C3N4 to give heterojunctions by the grinding method. The composite samples were investigated with XRD, FT-IR, SEM, EDS, XPS, TGA, UV–Vis, PL and EIS to analyze the purity, functional groups, surface morphology, elemental distribution, valence electron, thermal stability, visible-light absorption and electron-hole pair separation status. Photocatalytic degrade methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) were investigated. Cu(mtrb) can degrade 93.6% MB in 30 min, 87.0% MO in 135 min and 92.0% RhB in 90 min. Cu(mtrb)/10%g-C3N4 could degrade 96.2% MB in 15 min, 87.0% MO in 45 min and 92.3% RhB in 60 min, respectively. The coupling of Cu(mtrb) with g-C3N4 resulted in the formation of heterojunctions in Cu(mtrb)/wt%g-C3N4 composites and inhibited the rapid recombination of electron-hole pairs. The main reactive species for MB degradation were •OH and h+. Cu(mtrb) and Cu(mtrb)/10%g-C3N4 composites are the good photocatalysts.

The g-C3N4-TiO2 nanocomposite for non-volatile memory and artificial synaptic device applications

Recently, 2D layered materials like graphitic carbon nitride (g-C3N4) are gaining significant attention due to their excellent structural and electronic properties. Metal oxide and g-C3N4 composite can enhance chemical and electronic properties which can ultimately enhance device performance. Given this, we report the synthesis of g-C3N4–TiO2 nanocomposite by the ex-situ (solid state reaction) method for resistive switching (RS) applications. Initially, the TiO2 nanoparticles (NPs) were optimized by using annealing them at different temperatures and composited with the g-C3N4. The devices fabricated using g-C3N4–TiO2 nanocomposite shows good RS properties at very low SET and RESET voltages (< 0.5 V), similar to the biological voltage scale. The distribution of switching voltages of all devices was studied using the cumulative probability and Weibull distribution techniques. Moreover, switching voltages were modeled and predicted using the statistical time series analysis method. All fabricated devices demonstrated the double-valued charge flux characteristics, suggesting the presence of a non-ideal memristor effect. The optimized g-C3N4-TiO2 (TiO2 NPs annealed at 450 °C) device shows good endurance and retention memory properties. Moreover, the optimized g-C3N4-TiO2 device can mimic the various bio-synaptic properties such as potentiation-depression, excitatory postsynaptic current, and paired-pulse facilitation. The charge transport results reveal that Ohmic and Child's square law dominated the conduction of the device. Based on electrical and charge transport results, a plausible filamentary RS effect is presented. This study suggested that the g-C3N4-TiO2 is beneficial for both memory and neuromorphic computing applications.

BiFeO3/g-C3N4/f-CNF ternary nanocomposite as an efficient photocatalyst for methylene blue dye degradation under solar light irradiation

The development of Perovskite oxide photocatalysts with superior dye degradation efficiency under solar light irradiation has gained attention in recent years, owing to their extraordinary flexibility, chemical composition, and tunability. Herein, we report the facile synthesis of a novel ternary composite composed of BiFeO3 (BFO) perovskite, g-C3N4, and functionalized carbon nanofibers (f-CNF), referred to as BFO/g-C3N4/f-CNF using a simple solution method as a photocatalyst to accelerate the degradation of methylene blue dye. Detailed structural and microstructural features confirm the formation of a ternary composite composed of BFO nanoparticles and f-CNFs mounted on g-C3N4 nanosheets. The photocatalytic activity of the sample for the degradation of methylene blue dye was studied in solar light using UV–visible spectroscopy. The BFO/g-C3N4/f-CNF ternary composite displays excellent photocatalytic activity with a degradation rate of 87 % after illumination for 120 min under solar light than BFO, g-C3N4, and binary composites BFO/g-C3N4 and BFO/f-CNF. The highest rate constant (k = 0.01675 min−1) for BFO/g-C3N4/f-CNF further confirms improved photocatalytic efficiency. The red shift in the UV–visible absorption spectrum of BFO/g-C3N4/f-CNF indicates a reduced band gap (1.9 eV) compared to that of pure BFO (2.28 eV) and g-C3N4 ( 2.72 eV). A decrease in the photoluminescence intensity of the ternary composite compared to that of BFO indicates the inhibition of photoexcited electron recombination which results in the availability of more charge carriers for the photocatalytic process. The enhanced efficiency of BFO/g-C3N4/f-CNF can be explained by the synergistic effect between BFO and g-C3N4 and the incorporation of f-CNF further promotes the migration rate of electrons from BFO to g-C3N4.

Efficient removal of levofloxacin by iron (II) phthalocyanine/g-C3N4 activated peroxymonosulfate under high salinity conditions: Role of high-valent iron-oxo species

Efficient and selective removal of organic contaminants using traditional radical-dominated Advanced Oxidation Processes (AOPs) in complex environmental matrices is challenging, especially under high salinity conditions. This study proposes an alternative approach using iron (II) phthalocyanine-supported g-C3N4 composite (FePc/CN) as a peroxymonosulfate (PMS) activator to efficiently remove organic contaminants. The FePc/CN-PMS process was selective towards the elimination of various organic contaminants, and those compounds with lower ionization potential value can be effectively degraded after reaction for 10 min. Results from radical quenching experiments, electron spin resonance (ESR), and PMSO chemical probe indicated that the dominant active species in the FePc/CN-PMS process are high-valent iron-oxo species (FeIVO2+), rather than the long-recognized SO4•− and •OH radical. A total of 22 intermediate products resulting from the degradation of levofloxacin (LVF) were identified by LC-MS. Additionally, two degradation pathways of LVF were proposed, with the piperazine ring of LVF being the primary site of degradation. The 5%FePc/CN-PMS system demonstrates resistance to ubiquitous inorganic anions and dissolved organic matter (DOM) in an aquatic environment, enabling efficient removal of (LVF) even under high salinity conditions. Furthermore, the 5%FePc/CN catalyst exhibits good chemical stability and reusability, making it a viable option for practical water remediation.

Graphitic carbon nitride (g–C3N4)–assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g–C3N4)–based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g–C3N4– photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g–C3N4–based photocatalysts and sensors with practical applications.

Immaculate composite of g-C3N4/TiO2/polypyrrole as a facile super-capacitive electrode material for energy accumulation

A series of g-C3N4/TiO2/PPy (GTP) nanocomposites were prepared after in-situ chemical polymerization of pyrrole and the optimized dosage of g-C3N4 and TiO2 was intercalated with diverse polypyrrole (PPy) to get various composites. Super-capacitive functionality of the structurally and morphologically analysed fabricated electrodes was optimized for energy storage purpose. Electrochemical studies were performed in 1 M H2SO4 electrolyte. Among the different compositions of synthesized composites, GTP 1.0 exhibited good specific capacitance, 1216 F/g at 2 mV/s, accord well with that of the GCD results. Excellent cyclic stability of 93% was observed after 10,000 cycles. Power density and energy density for the GTP 1.0 composite in three electrode system were found to be 249.9 W/kg and 65.6 Wh/kg respectively at 0.5 A/g, thus providing promising results for energy storage. GTP//AC (Activated Charcoal) supercapacitor device was designed owing energy density as 15.6 Wh/kg and power density as 232.3 W/kg.

Synergistic degradation of chlorobenzene using intimate coupling of visible-light responsive TiO2/oxygenous groups decorated g-C3N4 composites and Ralstonia sp. XZW-1

The effective and economic treatment of chlorobenzenes has become one of the most intractable issues in the field of air pollution control. Herein, a visible-light photocatalysis coupled with biodegradation (VPCB) system was developed by integrating an innovative visible-light responsive TiO2/oxygenous groups decorated g-C3N4 (TiO2/OCN) with polyurethane carriers immobilized with Ralstonia sp. XZW-1 for chlorobenzene removal. Performance tests showed that light intensity, preparation of the MICs, catalyst dosage and composition of the TiO2/OCN cast significant influence on chlorobenzene removal efficiency, with the degradation efficiency, mineralization and dechlorination ratios of VPCB achieving 100%, 35.5%, and 99.4% under the optimal conditions, respectively, outcompeting the sum of visible-light photocatalytic system and biodegradation protocols. Cycling tests further demonstrated the excellent stability of VPCB. Mechanism analysis found that increased reactive sites, improved visible-light harvesting, accelerated charge transfer and separation, and the resulting abundant active species jointly contributed to the enhanced photocatalytic activity of TiO2/OCN. Photogenerated holes were most significant active species for chlorobenzene removal, followed by OH and O2− radicals. The carriers could effectively protect microorganisms from light illumination and strong oxidizing species, allowing the further microbial metabolism of chlorobenzene photocatalytic oxidation intermediates with good biodegradability, not only greatly promoting the microbial growth and activity, but further enhancing chlorobenzene photocatalytic degradation. Plausible synergistic mechanism for chlorobenzene degradation between photocatalysis and biodegradation was also revealed. Furthermore, the VPCB system constructed presented wide applicability towards various pollutants, and its performance was found closely related with the hydrophobicity of pollutants. This work provided insight into the design and application of the VPCB system for the efficient and economic treatment of refractory pollutants.

Construction of α-MnO2/g-C3N4 Z-scheme heterojunction for photothermal synergistic catalytic decomposition of formaldehyde

Formaldehyde (HCHO), as the most common indoor air pollutant, undoubtedly poses a huge threat to people's health. It is of practical importance to achieve complete decomposition of HCHO to harmless CO2 at room temperature. Herein, α-MnO2/g-C3N4 Z-scheme heterojunction was constructed through the in-situ growth of α-MnO2 nanowires on the surface of g-C3N4 nanosheets. Owing to the construction of Z-scheme heterojunction, α-MnO2/g-C3N4 composite exhibits excellent photothermal catalytic activity, achieving complete mineralization of HCHO with the illumination of 191 mW/cm2 solar-light at GHSV of 180 L/gcat·h. Particularly, even under one sun and visible light radiation, the α-MnO2/g-C3N4 composite can still maintain 60% and 68% HCHO conversion, respectively. The formation of α-MnO2/g-C3N4 Z-scheme heterojunction not only effectively inhibits the photogenerated electron-hole pairs recombination, but also overcomes the band defects of the individual component. Furthermore, the mechanism of the photothermal catalysis of α-MnO2/g-C3N4 composite was discovered to be thermal-assisted photocatalytic process rather than solar-light driven thermalcatalysis. On the one hand, the thermal energy generated from light radiation can accelerate the migration of photo-generated carriers and improve the separation efficiency of photogenerated electrons from vacancies; on the other hand, it can decrease the activation energy of lattice oxygen and produce more surface-active oxygen species. This work provides cost-effective strategies and suggestions for decomposing HCHO and other VOCs in indoor air at room temperature.

One-pot synthesis of porous graphitic carbon nitride with rich nitrogen vacancies and oxygen heteroatoms for boosting photocatalytic performance

Graphitic carbon nitride (g-C3N4), as an attractive photocatalyst, has been applied in environmental pollution control and energy conversion. However, its photocatalytic performance was plagued owing to the insufficient light absorption and poor photocarrier separation and transportation efficiencies. Herein, a porous g-C3N4 with rich nitrogen vacancies and oxygen heteroatoms was fabricated using a one-pot thermal polymerization method. Such method involves molecular homogenization of urea and ammonium bicarbonate, recrystallization of urea, and subsequent polycondensation and thermal stripping of g-C3N4 lamellas. The resultant g-C3N4 presents enriched exposed edges and interconnected open diffusion channels, and possesses abundant nitrogen vacancies and oxygen heteroatoms. This unique structure and composition of g-C3N4 contribute to exposure of active sites, migration of substrate and products, and visible light absorption in photocatalytic reactions. As expected, the design of nitrogen vacancies and oxygen heteroatoms in g-C3N4 modulated its electronic structure, thereby accelerating the photocarrier separation and further accelerating the output of •O2− radicals under light irradiation. The optimal g-C3N4 exhibited an extraordinary photodegradation performance for high concentration (C0 = 50 mg/L) of Rhodamine B. The photodegradation efficiencies are 97.5% and 99% in 90 min under visible light and sunlight irradiation, respectively. The work provides a porous g-C3N4 photocatalyst with intensified photocatalytic performance for environmental pollution control and emerging energy conversion.

Integration between CuMOF and g-C3N4 for effective suppressing charge recombination in photocatalytic peroxymonosulfate activation

In this work, CuMOF and graphite phase carbon nitride (g-C3N4) composite was synthesized, and tetracycline hydrochloride (TC) in water was degraded under simulated solar light irradiation with the assistance of peroxymonosulfate (PMS). The prepared g-C3N4/CuMOF samples were characterized by XRD, FT-IR, SEM, TEM and XPS. It is found that the introduction of CuMOF into g-C3N4 was not only beneficial to the charge separation of g-C3N4, but also greatly accelerated the activation of PMS. Through the initial pH value, PMS concentration, catalyst concentration, catalyst repeated use and other factors, the degradation performance of g-C3N4/CuMOF was studied. The photocatalytic experiment results showed that in the presence of PMS, the degradation rate of TC reached 90 % within 30 min. In addition, the reaction mechanism of the g-C3N4/CuMOF/PMS system was studied by using scavenging experiments and electron spin resonance (ESR) technology. This work provides a promising way for the rational design of high-performance and low-cost photocatalysts for environmental remediation.

Efficient degradation of ciprofloxacin by Cu2O/g-C3N4 heterostructures with different morphologies driven under the visible light

In this study, Cu2O/g-C3N4 composite with photocatalytic activity was successfully prepared by chemical precipitation method. The catalytic degradation of ciprofloxacin (CIP) by Cu2O and Cu2O/g-C3N4 composites with different morphologies was investigated. The effective structure and properties of Cu2O/g-C3N4 composites were tested by a series of characterization methods. The photocatalytic test results show that the Cu2O/g-C3N4 composite photocatalyst has good stability and good photocatalytic performance, which is attributed to the effective hetero-junction structure formed by the combination of Cu2O and g-C3N4, which promotes the interfacial charge separation. The addition of g-C3N4 can reduce the crystal size of Cu2O, improve the crystal morphology, and increase its light utilization. Among the synthesized catalysts, the Cu2O-3(20%)/g-C3N4 composite has the highest catalytic activity, and the photocatalytic oxidation efficiency of CIP is 96%. By free radical capture and ESR analysis, it was verified that OH, h+ and O2− radicals may be the main active substances involved in CIP photodegradation. Finally, various degradation products and intermediates of CIP were identified by LC-MS, and the possible conversion pathways were proposed.

Visible-light-assisted activation of peroxymonosulfate (PMS) over CoOx @C/g-C3N4 composite for efficient organic pollutant degradation

As a promising advanced oxidation process, photo-assisted peroxymonosulfate (PMS) activation for wastewater treatment has attracted widespread attentions. However, rational design of synergetic and recyclable catalysts for PMS photo-activation remains a big challenge. In this study, a carbon layer-coated amorphous CoOx supported on graphitic carbon nitride (CoOx @C/g-C3N4) composite was fabricated to drive visible-light-assisted activation of PMS for efficient organic pollutant degradation. Amorphous CoOx nanoparticles were in-situ grown on two-dimensional g-C3N4 substrate, among which a carbon layer serves as a high-speed electron transmission channel, facilitating the separation of photogenerated electron-hole pairs and accelerating the Co3+/Co2+ redox cycle. Simultaneously, the carbon layer provides a protective film to suppress Co leaching, thereby improving the catalytic activity and reusability. Owing to the unique heterostructure and synergetic effect, the optimized 6% CoOx @C/g-C3N4 composite exhibits superior catalytic efficiency and excellent cycling stability towards the degradation of various organic pollutants, which displays nearly 100% elimination of tetracycline (TC) within 80 mins. The h+, SO4•- and •OH are determined as the main contributors in the visible light-assisted PMS activation system, and the possible catalytic mechanism is also proposed. This work demonstrates a feasible strategy for constructing synergetic and effective photo-activation PMS catalysts for water remediation.

Study on g-C3N4/BiVO4 Binary Composite Photocatalytic Materials

Recent studies have shown that the composite of semiconductor photocatalytic materials and g-C3N4 can effectively inhibit photocatalytic carrier recombination and enhance the adsorption performance of the composite photocatalytic materials, so that the composite photocatalyst has stronger photocatalytic activity. In this paper, three kinds of graphitic carbon nitride photocatalyst g-C3N4 with different morphologies were prepared using the same precursor system by the chemical cracking method. After characterization and application, the sample with the most significant photocatalytic activity was selected and the g-C3N4/BiVO4 heterostructure was synthesized by the simple solvent evaporation method, then the photocatalytic experiment was carried out. The results show that, when the content of BiVO4 in the composite sample is 1%, the photocatalytic activity of RhB was the highest, and the degradation rate could reach 90.4%. The kinetic results showed that the degradation of RhB was consistent with the quasi-primary degradation kinetic model. The results of the photocatalytic cycle experiment show that the photocatalytic performance remains unchanged and stable after four photocatalytic cycles. The existence of a g-C3N4/BiVO4 binary heterojunction was confirmed by UV/Visible diffuse reflection (UV-DRS) and photoluminescence (PL) experiments. Owing to the Z-type charge process between BiVO4 and g-C3N4, efficient carrier separation was achieved, thus enhancing the photocatalytic capacity. This work provides a new idea for the study of heterojunction photocatalytic materials based on g-C3N4.

CO2 adsorption study of the zeolite imidazolate framework (ZIF-8) and its g-C3N4 composites

CO2 adsorption study of the zeolite imidazolate framework (ZIF-8) and its g-C3N4 composites

Enhanced photocatalytic degradation performance of In2O3/g-C3N4 composites by coupling with H2O2

Environmental pollution by organic pollutants poses a great threat to the ecosystem and human development. Solar-powered catalytic oxidation technology can solve the existing energy and pollution crisis. Hence, in this work, cubic nano-In2O3 modified g-C3N4 composite was synthesized by in situ calcination, then it was coupled with hydrogen peroxide for the degradation of antibiotic under visible light. The results of SEM and XPS showed that In2O3 and g-C3N4 were closely combined. The catalytic oxidation efficiency of the antibiotic doxycycline was greatly improved when the as-prepared compound was coupled with hydrogen peroxide, and 88.2% of doxycycline was degraded within 80 min. By designing the active species inhibition test, it was found that a large number of hydroxyl radicals were generated in the system after adding hydrogen peroxide, which accelerated the degradation of the target. Hydrogen peroxide not only acts as a source of hydroxyl radical, but also as an active electron acceptor, which promotes the separation of photogenerated electron-hole pairs in the composite photocatalyst. Therefore, the double oxidation system formed by In2O3/g-C3N4 coupled with hydrogen peroxide can degrade the target at a higher rate. This work provided a research basis for the synthesis of In2O3 with regular morphology and simplified synthesis of In2O3/g-C3N4, and explored the practicability of the coupling method of double advanced oxidation for pollutant degradation.

Significantly improved photocatalytic H2O2 generation over PDA-modified g-C3N4 via promoting charge-carriers separation and oxygen adsorption

Recently, graphitized carbon nitride (g-C3N4) is widely used as a metal-free photocatalyst for photocatalytic hydrogen peroxide (H2O2) generation. However, its photocatalytic activity still suffers from the poor separation efficiency of charge carrier and weak adsorption ability towards dioxygen. Herein, a series of polydopamine (PDA) surface-modified g-C3N4 composites (CNPX) are successfully fabricated through a self-assembled method. The optimum material, i.e. CNP40, produced H2O2 of 69.0 μM/L under visible-light irradiation for 3 h, demonstrating 4.6-fold higher activity in comparison with the pristine g-C3N4. Meanwhile, the apparent quantum yield (AQY) reached as high as 1.91% over CNP40 under monochromatic irradiation of 420 nm, which is 6.2-fold higher than CN. It is identified that the remarkably increased photocatalytic activity is contributed to the significantly promoted charge separation and dioxygen adsorption. This present work could provide a novel environmental-friendly material for the efficient photocatalytic H2O2 production.

In-situ synthesis of novel dual S-scheme AgI/Ag6Mo7O24/g-C3N4 heterojunctions with tandem structure for photocatalytic degradation of organic pollutants

The controllable design of multivariate heterojunction with sequential structures is of significant relevance for breaking the performance limit of binary composite photocatalysts. In this work, the novel dual S-scheme ternary-component AgI/Ag6Mo7O24/exfoliated g-C3N4 (ECN) composite was prepared by a two-step in-situ synthetic strategy. The energy band bending at the heterointerface and the formation of dual built-in electric field could be observed due to distinct work functions of different components in the ternary composite. Benefiting from the sequential heterojunction structure, the AgI/Ag6Mo7O24/ECN composite achieved 98.7% removal efficiency of 2-nitrophenol (2-NP) within 70 min under visible light irradiation, and AgI/Ag6Mo7O24/ECN also showed higher degradation efficiency for a variety of organic pollutants such as methylene blue (MB), rhodamine B (RhB), methyl orange (MO), 4-nitrophenol (4-NP), 2-sec-butyl-4,6-dinitrophenol (DNBP) and tetracycline (TC). Notably, •OH and •O2− played dominant roles in the AgI/Ag6Mo7O24/ECN set up, which was consistent with the dual S-scheme charge transfer mechanism. In-depth insights for the photodegradation of 2-NP were presented based on a combined DFT study and GC-MS analysis. Additionally, the photoreduction of Ag+ in AgI/Ag6Mo7O24/ECN was also evaded by the fast transfer of photogenerated electrons through the dual S-scheme pathway, achieving the effect of killing two birds with one stone.