Novel g-C3N4/CoO Nanocomposites with Significantly Enhanced Visible-Light Photocatalytic Activity for H2 Evolution

SERS activity of silver nanoparticles and silver-modified 2D graphitic carbon nitride towards ciprofloxacin drug

Herein, silver nanoparticles (AgNPs) and silver-loaded graphitic carbon nitride (Ag@g-C3N4) nanocomposites have been synthesized and used as an effective surface-enhanced Raman scattering (SERS) substrates for the detection of low concentrations (10-14 M) of ciprofloxacin (CIP), a commonly bioactive medication used to treat bacterial illnesses. A combined approach of vibrational spectroscopy and density functional theory (DFT) has been developed to understand the possible modes of analyte (CIP) and SERS substrate (AgNPs and Ag@g-C3N4) interactions. Furthermore, it has been noticed that the behavior of drug molecules in terms of SERS response and energetics of interaction changed significantly when interacted with the noble metal AgNPs decorated onto the g-C3N4 framework in comparison to only AgNPs as substrate. The most prominent interaction scenario between AgNPs and CIP is likely to be through the -NH moiety of drug molecule with an interaction energy of -306 kcal/mol. Whereas, the CIP molecules adsorbed onto Ag@g-C3N4 nanocomposite were more flexible with interaction energy of -107 kcal/mol, suggesting a greater association of analyte with the skeletal modes of substrate leading to Raman enhancements in the low wavenumber region i.e. below 600 cm-1. Hence, the Ag@g-C3N4 nanocomposite-based SERS substrates investigated served two distinct spectral ranges, making them complementary of each other in terms of SERS detection of CIP. The characteristics of the computed frontier molecular orbitals indicated a pronounced amount of charge transfer between the drug and the substrate, highlighting the significance of the chemical mechanism of the overall process. These results represent a successful approach to have an extended spectral range that covers lower wavenumber shifts by applying simple and meaningful modifications to the normally utilized noble metal-based nanoparticles, which can lead to more effective and reliable detection of bioactive drugs.

Developing a highly sensitive electrochemical sensor for malathion detection based on green g-C3N4@LiCoO2 nanocomposites

Nowadays, developing pesticide-free agriculture is highly demanded by society. The development of electrochemical sensors to monitor and control pesticides is an effective step toward this desired goal. The current research has faced this issue by modifying of glassy carbon electrodes (GCEs) with green g-C3N4@LiCoO2 nanocomposites to probe malathion, an organophosphate pesticide. The g-C3N4@LiCoO2 modified GCE showed higher current than the net GCE, as a result of improved electrocatalytic performance of the modified GCE to oxidize malathion. Increased malathion concentration enhanced the malathion oxidation anodic peak current at +410 mV caused by the g-C3N4@LiCoO2 modified GCE. The developed probe showed an excellent linear response for malathion detection in the 5-120 nM (R 2 = 0.994) range and recorded a limit of detection of 4.38 nM. Besides, the modified GCE reveals considerable stability and reproducibility, which offers a cost-effective, sensitive, and selective electrode for malathion probing.

Construction of S/g-C3N4@β-Bi2O3 heterojunction and its photocatalytic degradation of toluene in the gas phase

In this paper, a modification of g-C3N4 was carried out by combining non-metal doping with the construction of heterojunctions, and a type II heterojunction composite, S/g-C3N4@β-Bi2O3, was prepared. The phase structure, morphology, elemental composition, valence band structure, and light absorption performance of the photocatalyst were analyzed using characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The performance of the composite photocatalyst in the photocatalytic degradation of gaseous toluene, one of the typical volatile organic compounds (VOCs), under simulated solar light was studied. The effects of preparation conditions, toluene concentration, and recycling on the photocatalytic performance of the composite photocatalyst were investigated. The results show that under the optimal preparation conditions, S/g-C3N4@β-Bi2O3 achieved a degradation efficiency of 74.0% for 5 ppm toluene after 5 h of light irradiation. Although the degradation efficiency decreased to 61.2% after five cycles, it maintained 83% of its initial activity, indicating good stability of the composite photocatalyst. Free radical quenching experiments demonstrated that h+ was the main active species in the photocatalytic degradation of toluene, followed by ·O2-. Based on all experimental results, the migration law of photo-generated charges was analyzed, and a possible photocatalytic mechanism was proposed. In this study, a new material was obtained for the photocatalytic removal of VOCs by improving the photocatalytic properties of g-C3N4.

Facile construction of efficient WO3/V2O5 coupled g-C3N4 ternary composite photocatalyst for environmental emergent aqueous pollutant degradation: Stability, degradation reaction pathway and effect of pH evaluation

Currently, one of the primary challenges that human society must overcome is the task of decreasing the amount of energy used and the adverse effects that it has on the environment. The daily increase in liquid waste (comprising organic pollutants) is a direct result of the creation and expansion of new companies, causing significant environmental disruption. Water contamination is attributed to several industries such as textile, chemical, poultry, dairy, and pharmaceutical. In this study, we present the successful degradation of methylene blue dye using g-C3N4 (GCN) mixed with WO3 and V2O5 composites (GCN/WO3/V2O5 ternary composite) as a photocatalyst, prepared by a simple mechanochemistry method. The GCN/WO3/V2O5 ternary composite revealed a notable enhancement in photocatalytic performance, achieving around 97% degradation of aqueous methylene blue (MB). This performance surpasses that of the individual photocatalysts, namely pure GCN, GCN/WO3, and GCN/V2O5 composites. Furthermore, the GCN/WO3/V2O5 ternary composite exhibited exceptional stability even after undergoing five consecutive cycles. The exceptional photocatalytic activity of the GCN/WO3/V2O5 ternary composite can be ascribed to the synergistic effect of metal-free GCN and metal oxides, resulting in the alteration of the band gap and suppression of charge recombination in the ternary photocatalyst. This study offers a better platform for understanding the characteristics of materials and their photocatalytic performance under visible light conditions.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

A two dimensional Co(OH)2 catalytic gravity-driven membrane for water purification: a green and facile fabrication strategy and excellent water decontamination performance

Cobalt-based materials are reported to be the most efficient catalysts in sulfate radical advanced oxidation processes (SR-AOPs). A green and facile method was developed in this work to prepare uniform Co(OH)2 hexagonal nanosheets, which was void of any organic solvents via mere ambient temperature stirring. The obtained nanosheets were assembled into a catalytic gravity-driven membrane, through which the removal efficiency of a typical pharmaceutical contaminant, ranitidine (RNTD), could reach ∼100% within 20 min. Meanwhile, the catalytic membrane also demonstrated effective removal performance towards various pollutants. In order to augment the long-term stability of catalytic membranes, Co(OH)2/rGO composites were fabricated using the same strategy, and a Co(OH)2/rGO catalytic membrane was prepared correspondingly. The Co(OH)2/rGO membrane could maintain a ∼100% removal of RNTD over a constant reaction period lasting for up to 165 hours, which was approximately 11 times that of the sole Co(OH)2 membrane (15 h). Analysis of element chemical states, metal ion concentration in filtrates, and quenching experiments suggested that the combination with rGO could promote the electron transfer to accelerate the Co(II) regeneration, restrain the cobalt dissolution to alleviate the active site loss, and contribute to the production of 1O2via synergistic effects of oxygen-containing groups in rGO. Toxicity assessment was performed on RNTD and its degradation intermediates to confirm the reduction in ecotoxicity of the treated feed. Overall, this work not only offered guidance for the application of nanosheets in AOP membranes, but also had implications for the environmentally-friendly preparation protocol to obtain functional metal hydroxides.

Organic Donor-Acceptor Systems for Photocatalysis

Organic semiconductor materials are considered to be promising photocatalysts due to their excellent light absorption by chromophores, easy molecular structure tuning, and solution-processable properties. In particular, donor-acceptor (D-A) type organic photocatalytic materials synthesized by introducing D and A units intra- or intermolecularly, have made great progress in photocatalytic studies. More and more studies have demonstrated that the D-A type organic photocatalytic materials combine effective carrier separation, tunable bandgap, and sensitive optoelectronic response, and are considered to be an effective strategy for enhancing light absorption, improving exciton dissociation, and optimizing carrier transport. This review provides a thorough overview of D-A strategies aimed at optimizing the photocatalytic performance of organic semiconductors. Initially, essential methods for modifying organic photocatalytic materials, such as interface engineering, crystal engineering, and interaction modulation, are briefly discussed. Subsequently, the review delves into various organic photocatalytic materials based on intramolecular and intermolecular D-A interactions, encompassing small molecules, conjugated polymers, crystalline polymers, supramolecules, and organic heterojunctions. Meanwhile, the energy band structures, exciton dynamics, and redox-active sites of D-A type organic photocatalytic materials under different bonding modes are discussed. Finally, the review highlights the advanced applications of organic photocatalystsand outlines prospective challenges and opportunities.

4-Methyl-5-vinyl thiazole modified Ni-MOF/g-C3N4/CdS composites for efficient photocatalytic hydrogen evolution without precious metal cocatalysts

The construction of heterojunction systems is an effective way to efficiently generate hydrogen by water photolysis. In this work, Ni-MOF (trimesic acid, (BTC)) and g-C3N4 (denoted as CN) were combined, and then Ni-MOF/CN was modified by 4-Methyl-5-vinyl thiazole (denoted as MVTh). Finally, CdS was loaded on the surface of Ni-MOF/CN/MVTh to prepare the photocatalyst Ni-MOF/g-C3N4/MVTh/CdS (denoted as Ni/CN/M/Cd) with a triangular closed-loop path heterojunction for the first time. As a photocatalyst without precious metal cocatalysts, Ni/CN/M/Cd displayed high H2 evolution (17.844 mmol·g-1·h-1) under an optimum CdS loading of 40 wt%. The H2 evolution rate was approximately 79 times that of Ni-MOF/CN and exceeded those of almost all catalysts based on MOF/CN in the literature. The triangular closed-loop heterojunction formed between Ni-MOF, g-C3N4, and CdS could realize the directional migration of photocarriers and significantly diminished the transfer resistance of carriers. The Ni2+ in Ni-MOF provided many cocatalytic sites for H2 evolution via g-C3N4 and CdS. Furthermore, charge carrier separation in Ni-MOF/CN/CdS improved after the innovative addition of MVTh. This study provides a reference for the construction of a closed-loop heterojunction system without precious metal cocatalysts.

Fabrication of a Novel Co/CoO@Fe2 V4 O13 Composite Catalyst as a Photoanode for Enhanced Photoelectrochemical Water Oxidation

Herein, the synthesis of a novel composite photocatalyst, Co/CoO@Fe2 V4 O13 , is reported by the deposition of CoO metal oxide nanoparticles on the surface of Fe2 V4 O13 bimetallic oxide. The synthesised photocatalyst exhibited a band gap of roughly 1.8 eV, rendering it responsive to the complete visible light spectrum of the sun, thereby enabling optimal absorption of solar radiation. The Co/CoO@Fe2 V4 O13 composites demonstrated an enhanced photoelectrochemical water oxidation capacity compared to pristine Fe2 V4 O13 when exposed to visible light. The enhanced performance is attributed primarily to the creation of a p-n junction at the interface of Fe2 V4 O13 and Co/CoO, as well as the Z-scheme charge transfer mechanism, which aids in the separation and transfer of photogenerated charge carriers. Light absorption by Co nanoparticles via plasmonic excitation and intra- and inter-band transitions in the composite structure is also likely, resulting in increased composite efficiency. Our findings indicate that Co/CoO@Fe2 V4 O13 composites show promising performance for solar water splitting applications and offer new perspectives for designing effective photocatalysts.

Controlled Ni doping on a g-C3N4/CuWO4 photocatalyst for improved hydrogen evolution

The development of a low-cost, environment-friendly and suitable semiconductor-based heterogeneous photocatalyst poses a great challenge towards extremely competent and substantial hydrogen evolution. A series of environment-friendly and proficient S-scheme Ni-doped CuWO4 nanocrystals supported on g-C3N4 nanocomposites (Ni-CuWO4/g-C3N4) were constructed to ameliorate the photocatalytic efficacy of pure g-C3N4 and Ni-CuWO4 and their activity in H2 generation through photocatalytic water splitting was evaluated. The Ni-CuWO4 nanoparticles were synthesized through doping of Ni2+ on wolframite CuWO4 crystals via the chemical precipitation method. An elevated hydrogen generation rate of 1980 μmol h-1 g-1 was accomplished over the 0.2Ni-CuWO4/g-C3N4 (0.2NCWCN) nanocomposite with an apparent quantum yield (AQY) of 6.49% upon visible light illumination (λ ≥ 420 nm), which is evidently 7.1 and 17.2 fold higher than those produced from pristine g-C3N4 and Ni-CuWO4. The substantial enhancement in the photocatalytic behaviour is primarily because of the large surface area, limited band gap energy of the semiconductor composite and magnified light harvesting capability towards visible light through the inclusion of g-C3N4, thus diminishing the reassembly rate of photoinduced excitons. Further, density functional theory (DFT) calculations were performed to investigate the structural, electronic and optical properties of the composite. Theoretical results confirmed that the Ni-CuWO4/g-C3N4 composite is a potential candidate for visible-light-driven photocatalysts and corroborated with the experimental findings. This research provides a meaningful and appealing perspective on developing cost-effective and very proficient two-dimensional (2D) g-C3N4-based materials for photocatalytic H2 production to accelerate the separation and transmission process of radiative charge carriers.

Boosted Tetracycline and Cr(VI) Simultaneous Cleanup over Z-Scheme WO3/CoO p-n Heterojunction with 0D/3D Structure under Visible Light

In this study, a Z-Scheme WO₃/CoO p-n heterojunction with a 0D/3D structure was designed and prepared via a simple solvothermal approach to remove the combined pollution of tetracycline and heavy metal Cr(VI) in water. The 0D WO₃ nanoparticles adhered to the surface of the 3D octahedral CoO to facilitate the construction of Z-scheme p-n heterojunctions, which could avoid the deactivation of the monomeric material due to agglomeration, extend the optical response range, and separate the photogenerated electronhole pairs. The degradation efficiency of mixed pollutants after a 70 min reaction was significantly higher than that of monomeric TC and Cr(VI). Among them, a 70% WO₃/CoO heterojunction had the best photocatalytic degradation effect on the mixture of TC and Cr(VI) pollutants, and the removing rate was 95.35% and 70.2%, respectively. Meanwhile, after five cycles, the removal rate of the mixed pollutants by the 70% WO₃/CoO remained almost unchanged, indicating that the Z-scheme WO₃/CoO p-n heterojunction has good stability. In addition, for an active component capture experiment, ESR and LC-MS were employed to reveal the possible Z-scheme pathway under the built-in electric field of the p-n heterojunction and photocatalytic removing mechanism of TC and Cr(VI). These results offer a promising idea for the treatment of the combined pollution of antibiotics and heavy metals by a Z-scheme WO₃/CoO p-n heterojunction photocatalyst, and have broad application prospects: boosted tetracycline and Cr(VI) simultaneous cleanup over a Z-scheme WO₃/CoO p-n heterojunction with a 0D/3D structure under visible light.

Simultaneous photocatalytic tetracycline oxidation and Cr(VI) reduction by a 0D/3D hierarchical Bi2WO6@CoO Z-scheme heterostructure: In situ interfacial engineering and charge regulation mechanism

Constructing visible-light driven semiconductor heterojunction with high redox bifunctional characteristics is a promising approach to deal with the increasingly serious environmental pollution problems, especially the coexistence of organic/heavy metal pollutants. Herein, a simple in-situ interfacial engineering strategy for the fabrication of 0D/3D hierarchical Bi₂WO₆@CoO (BWO) heterojunction with an intimate contact interface was successfully developed. The superior photocatalytic property was reflected not only in individual tetracycline hydrochloride (TCH) oxidation or Cr(VI) reduction, but also in their simultaneous redox reaction, which could be predominantly attributed to the outstanding light-harvesting, high carrier separation efficiency and enough redox potentials. In the simultaneous redox system, TCH acted as a hole-scavenger for Cr(VI) reduction, replacing the additional reagent. Interestingly, superoxide radical (·O₂^-) played the role as oxidants in TCH oxidation but as electron transfer media in Cr(VI) reduction. On account of the interlaced energy band and tight interfacial contact, a direct Z-scheme charge transfer model was established, which was verified by the active species trapping experiments, spectroscopy, and electrochemical tests. This work provided a promising strategy for the design/fabrication of highly efficient direct Z-scheme photocatalysts in environmental remediation.

ZnSnO3 based gas sensors for pyridine volatile marker detection in rice aging during storage

This study reports the development of ZnSnO₃ based gas sensors for pyridine detection in rice aging. Pyridine is one of heterocyclic markers formed via Maillard reaction and lipid oxidation. Herein, graphitic carbon nitride (g-C₃N₄) decorated ZnSnO₃ microstructures were obtained through a template-free approach. And the sensing results reveal that 5 wt%g-C₃N₄ decorated ZnSnO₃ exhibited a high sensitivity (47.9), a short response/recovery time (14/120 s) and a low detection limit (0.45 ppm), which is due to the catalysis of g-C₃N₄ nanosheets, the decorated microstructure and the formation of heterojunctions. Meanwhile, the practical experiment demonstrates that the sensitivity towards volatiles generated from Japonica rice aging is 48.7, which is around 4 and 2.5 times higher than those of Indica rice and Polished Glutinous rice, indicating that the sensor has anticipated application in the development of a high-performance E-nose for the quality inspection of rice and other products.

Rational Design of Monolithic g-C3N4 with Floating Network Porous-like Sponge Monolithic Structure for Boosting Photocatalytic Degradation of Tetracycline under Simulated and Natural Sunlight Illumination

In order to solve the problems of powder g-C₃N₄ catalysts being difficult to recycle and prone to secondary pollution, floating network porous-like sponge monolithic structure g-C₃N₄ (FSCN) was prepared with a one-step thermal condensation method using melamine sponge, urea, and melamine as raw materials. The phase composition, morphology, size, and chemical elements of the FSCN were studied using XRD, SEM, XPS, and UV-visible spectrophotometry. Under simulated sunlight, the removal rate for 40 mg·L^-1 tetracycline (TC) by FSCN reached 76%, which was 1.2 times that of powder g-C₃N₄. Under natural sunlight illumination, the TC removal rate of FSCN was 70.4%, which was only 5.6% lower than that of a xenon lamp. In addition, after three repeated uses, the removal rates of the FSCN and powder g-C₃N₄ samples decreased by 1.7% and 2.9%, respectively, indicating that FSCN had better stability and reusability. The excellent photocatalytic activity of FSCN benefits from its three-dimensional-network sponge-like structure and outstanding light absorption properties. Finally, a possible degradation mechanism for the FSCN photocatalyst was proposed. This photocatalyst can be used as a floating catalyst for the treatment of antibiotics and other types of water pollution, providing ideas for the photocatalytic degradation of pollutants in practical applications.

The enhanced visible light driven photocatalytic activity of zinc porphyrin/g-C3N4 nanosheet for efficient bacterial infected wound healing

Graphitic carbon nitride (g-C₃N₄) has received much attention as a metal-free polymeric two-dimensional photocatalyst for antibiotic-free antibacterial application. However, the weak photocatalytic antibacterial activity of pure g-C₃N₄ stimulated by visible light limits its applications. Herein, g-C₃N₄ is modified with Zinc (II) meso-tetrakis (4-carboxyphenyl) porphyrin (ZnTCPP) by amidation reaction to enhance the utilization of visible light and reduce the recombination of electron-hole pairs. The composite (ZP/CN) is used to treat bacterial infection under visible light irradiation with a high efficacy of 99.99% within 10 min due to the enhanced photocatalytic activity. Ultraviolet photoelectron spectroscopy and density flooding theory calculations indicate the excellent electrical conductivity between the interface of ZnTCPP and g-C₃N₄. The formed built-in electric field is responsible for the high visible photocatalytic performance of ZP/CN. In vitro and in vivo tests have demonstrated that ZP/CN not only possesses excellent antibacterial activity upon visible light irradiation, but also facilitates the angiogenesis. In addition, ZP/CN also suppresses the inflammatory response. Therefore, this inorganic-organic material can serve as a promising platform for effective healing of bacteria-infected wounds.

ReS2 with unique trion behavior as a co-catalyst for enhanced sunlight hydrogen production

The interfacial catalytic reaction plays a crucial role in determining hydrogen production efficiency of a photocatalyst. In this work, hollow spherical nano-shell composite (g-C₃N₄/CdS/ReS₂) formed by graphitic carbon nitride (g-C₃N₄), cadmium sulfide (CdS), and rhenium disulfide (ReS₂) was prepared for photocatalytic hydrogen production, with ReS₂ introduced as a relatively inexpensive co-catalyst with excellent performance. It was found that two-electron catalytic reaction took place in this photocatalytic system due to the unique trion behavior of ReS₂ co-catalyst, which greatly enhances the rate of photocatalytic hydrogen production. The tightly bound excitons in the ReS₂ co-catalyst could easily capture the photogenerated electrons in the photocatalytic system to form trions, while g-C₃N₄ in the inner shell and CdS in the middle shell provided sufficient electrons for the formation of trions. The active edge sites of ReS₂ also facilitated the generation and desorption of hydrogen, which creates conditions favoring two-electron catalytic reaction. In addition, oxidation and reduction reactions occurred inside and outside of the hollow spherical nano-shell, respectively, which effectively inhibits the recombination of photogenerated carriers. The unique trion behavior of ReS₂ alters the interfacial catalytic reaction compared to the widely used platinum (Pt) co-catalyst in photocatalytic hydrogen production, which provides a new approach for enhancing the activity of photocatalytic systems.

Solar-induced efficient propylparaben photodegradation by nitrogen vacancy engineered reticulate g-C3N4: Morphology, activity and mechanism

Propylparaben (PrP) has attracted extensive concerns due to its wide occurrence in wastewater and potential health risk. Herein, nitrogen vacancy engineered reticulate g-C₃N₄ (Nv-RCN) was successfully synthesized for the photodegradation of PrP. Nv-RCN exhibited larger specific surface area, greater light absorption ability, higher transfer and separation efficiency of charge carriers in comparison with bulk g-C₃N₄ (CN). According to the characterization results and DFT calculation, nitrogen vacancy could capture electrons and facilitate oxygen adsorption. The Nv-RCN exhibited an outstanding PrP removal efficiency of 94.3 %, and the corresponding apparent rate constant of Nv-RCN was 3.37 times higher than that of CN. High O₂ concentration (8 mg/L) and low pH value (pH = 3) promoted PrP photodegradation based on Box-Behnken Design. The O₂^- was the major radical during PCOP of Nv-RCN, and could oxidize PrP by decarbonylation and dealkylation. This study provided new insights to the improvement of photodegradation performance of g-C₃N₄ for parabens removal and related environmental remediation.

Visible light-driven H2O2 synthesis over Au/C3N4: medium-sized Au nanoparticles exhibiting suitable built-in electric fields and inhibiting reverse H2O2 decomposition

Visible light-driven H₂O₂ production presents the unique merits of sustainability and environmental friendliness. The size of noble metal nanoparticles (NPs) determines their dispersion and electronic structure and greatly affects their photocatalytic activity. In this work, a series of sized Au NPs over C₃N₄ were modulated for H₂O₂ production. The results show that there is a volcanic trend in H₂O₂ with the decrease of Au particle size, and the highest H₂O₂ production rate of 1052 μmol g^-1 h^-1 is obtained from medium-sized Au particles (∼8.7 nm). The relationship between structure and catalytic performance is supported by experimental and theoretical methods. (1) First, medium-sized Au NPs promote photon absorption, and have a suitable built-in electric field at the heterojunction, which can be successfully tuned to achieve a more efficient h⁺-e^- spatial separation. (2) Second, medium-sized Au NPs enhance O₂ adsorption, and create selective 2e^- O₂ reduction reaction sites. (3) Particularly, medium-sized Au NPs promote the desorption of produced H₂O₂ and inhibit H₂O₂ decomposition, finally leading to the highest H₂O₂ selectivity. Excellent catalytic performance will be obtained by finely optimizing the particle size in a certain range. This work provides a new idea for preparing high efficiently photocatalysts for H₂O₂ production.

Highly Selective Electrochemical CO2 Reduction to C2 Products on a g-C3N4-Supported Copper-Based Catalyst

Herein, a novel approach used to enhance the conversion of electrochemical CO₂ reduction (CO₂R), as well as the capacity to produce C₂ products, is reported. A copper oxide catalyst supported by graphite phase carbon nitride (CuO/g-C₃N₄) was prepared using a one-step hydrothermal method and exhibited a better performance than pure copper oxide nanosheets (CuO NSs) and spherical copper oxide particles (CuO SPs). The Faradaic efficiency reached 64.7% for all the C₂ products, specifically 37.0% for C₂H₄, with a good durability at -1.0 V vs. RHE. The results suggest that the interaction between CuO and the two-dimensional g-C₃N₄ planes promoted CO₂ adsorption, its activation and C-C coupling. This work offers a practical method that can be used to enhance the activity of electrochemical CO₂R and the selectivity of C₂ products through synergistic effects.

Ni-Co Bimetallic Hydroxide Nanosheet Arrays Anchored on Graphene for Adsorption-Induced Enhanced Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction can be implemented to use CO₂ , a greenhouse gas, as a resource in an energy-saving and environmentally friendly way, in which suitable catalytic materials are required to achieve high-efficiency catalysis. Insufficient accessible active sites on the catalyst surface and inhibited electron transfer severely limit the photocatalytic performance. Therefore, porous aerogels are constructed from composites comprising different ratios of Ni-Co bimetallic hydroxide (Ni_x Co_y ) grown on reduced graphene oxide (GR) into a hierarchical nanosheet-array structure using a facile in situ growth method. Detailed characterization shows that this structure exposes numerous active sites for enhanced adsorption-induced photocatalytic CO₂ reduction. Moreover, under the synergistic effect of Ni-Co bimetallic hydroxide, the CO₂ adsorption capacity as well as charge-carrier separation and transfer are excellent. As a result, the Ni₇ Co₃ -GR catalyst exhibits highly improved catalytic performance when compared with recently reported values, with a high CO release rate of 941.5 µmol h^-1  g^-1 and a selectivity of 96.3% during the photocatalytic reduction of CO₂ . This work demonstrates a new strategy for designing nanocomposites with abundant active sites structures.

Oxygen Vacancy-Induced Construction of CoO/h-TiO2 Z-Scheme Heterostructures for Enhanced Photocatalytic Hydrogen Evolution

Environmentally friendly catalysts with excellent performance and low cost are critical for photocatalysis. Herein, using hydrogenated TiO₂ (h-TiO₂) nanosheets with enriched oxygen vacancies as the support, two-dimensional CoO/h-TiO₂ Z-scheme heterostructures are fabricated for hydrogen production through photocatalytic water splitting. It is revealed that the oxygen vacancies in h-TiO₂ can inhibit the oxidation of Co²⁺ into high-valence Co³⁺ during the hydrothermal reaction and thermal treatment processes. A CoO/h-TiO₂ Z-scheme heterostructure possesses a space charge region and a built-in electric field at the interface, and oxygen vacancies in h-TiO₂ can provide more reactive sites, which synergistically improve the separation and transportation of photogenerated carriers. As a result, the photocatalytic hydrogen evolution rate achieves 129.75 μmol·h^-1 (with 50 mg of photocatalysts) on the optimized CoO/h-TiO₂ heterostructures. This work provides a new design idea for the preparation of excellent TiO₂-based photocatalysts.

Phosphor-Enhanced, Visible-Light-Storing g-C3N4/Ag3PO4/SrAl2O4:Eu2+,Dy3+ Photocatalyst Immobilized on Fractal 3D-Printed Supports

The combination of a phosphor with semiconductor photocatalysts can provide photoactivity in the dark. Indeed, the phosphor acts as a "light battery", harvesting photons during irradiation and later re-emitting light that can be used by the catalytic phase when in conditions of total darkness. This allows for continued activity of the composite catalyst, even in conditions of unstable light stimulation. In this study, we assess the use of a heterojunction, namely graphitic-C₃N₄/Ag₃PO₄, that enables efficient photoactivity specifically under visible light stimulation, in combination with a phosphor that exhibits green-blue phosphorescence (510 nm), that is SrAl₂O₄:Eu²⁺,Dy³⁺. Our findings showed that this combination was particularly interesting, noticeably displaying significant photoactivity in darkness, after short periods of activation by visible light. After finding the right combination and optimal ratios for maximum efficiency, the resulting catalyst composite was immobilized on resin supports with a fractal surface, printed by LCD-SLA 3D printing. The immobilization was effectuated via an aqueous-phase plasma-aided grafting (APPAG) process, using cold plasma discharge (CPD) and using vinylphosphonic acid (VPA) as a coupling agent. Whereas the colloidal photocatalyst displayed a serious problem of partial physical separation between the catalytic phase, g-C₃N₄/Ag₃PO₄, and the phosphor, the immobilization of the composite catalyst on polymer supports allowed solving this issue. Photodegradation assessments confirmed that the hybrid supported phosphor-enhanced catalyst was active, notably in dark conditions, as well as fairly photostable. This study offers new prospects for the fabrication of polymer-based panels for water purification, with round-the-clock activity and that are, in addition, extremely easy to recover and reuse, by comparison with colloidal catalysts.

Dual plasmonic Au and TiN cocatalysts to boost photocatalytic hydrogen evolution

Employing a suitable cocatalyst is very important to improve photocatalytic H2 evolution activity. Herein, two plasmonic cocatalysts, Au nanoparticles and TiN nanoparticles were in-situ coupled over the g-C3N4 nanotube to form a ternary 0D/0D/1D Au/TiN/g-C3N4 composite via a successive thermal polycondensation and chemical reduction method. The g-C3N4 nanotube acted as a support for the growth of Au and TiN nanoparticles, leading to intimate contact between g-C3N4 nanotube with Au nanoparticles and TiN nanoparticles. As a result, multiple interfaces and dual-junctions of Au/g-C3N4 Schottky-junction and TiN/g-C3N4 ohmic-junction were constructed, which helped to promote the charged carriers' separation and enhanced the photocatalytic performance. Furthermore, loading plasmonic cocatalysts of Au nanoparticles and TiN nanoparticles can enhance the light absorption capacity. Consequently, the Au/TiN/g-C3N4 composite exhibited significantly enhanced photocatalytic H2 evolution activity (596 μmol g-1 h-1) compared to g-C3N4 or binary composites of Au/g-C3N4 and TiN/g-C3N4. This work highlights the significant role of cocatalysts in photocatalysis.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

Effects of various alcohol sacrificial agents on hydrogen evolution based on CoS2@SCN nanomaterials and its mechanism

Visible light induced photocatalysis converted solar energy to chemical energy in the form of hydrogen. g-C₃N₄ modified by thermal oxidation etching, doped S, and nonprecious metal cocatalyst CoS₂ (CoS₂@SCN) were used for photocatalytic hydrogen production. And then the charge transfer behavior and mechanism of various alcohol sacrificial agents on hydrogen evolution was analyzed by optical characterization, impedance analysis, Mott-Schottky, and photocurrent tests. The relationship between the structure and catalytic performance was also explored using characterization methods. The results showed that CoS₂ significantly improved the light absorption of g-C₃N₄, and carrier migration and separation. And when the sacrificial agent was triethanolamine, the nanocomposite CoS₂@SCN exhibited best catalytic performance with the highest hydrogen activity of 223.6 μmol g^-1 h^-1, the minimum volume in-phase charge transfer resistance with 55.19 Ω and the maximum photocurrent and photocurrent density with 5.5 μA cm^-2 and 0.63 mA cm^-2. The more negatively charged surface of organic alcohols were, the easier they were to react with holes, thus enhanced charge transfer and hydrogen production efficiency. This report provides guidance for the selection of hydrogen producing sacrificial agents and preparation of highly charge-efficient catalysts. And it also provides a theoretical basis for hydrogen production from wastewater and environmental remediation.

Hematite nanoparticles decorated nitrogen-doped reduced graphene oxide/graphitic carbon nitride multifunctional heterostructure photocatalyst towards environmental applications

The carcinogenic heavy metals and aromatic organic compounds linger as wastewater pollutants implying great menace to the ecological balance. To solve these environmental pollution problems, the photocatalytic process is an...

Facile construction of dual heterojunction CoO@TiO2/MXene hybrid with efficient and stable catalytic activity for phenol degradation with peroxymonosulfate under visible light irradiation

Photocatalysis and peroxymonosulfate (PMS) based advanced oxidation processes (AOP) are emerging technology for the degradation of refractory organic pollutant in the field of water treatment. Here we report a novel CoO@TiO₂/MXene (CTM) hybrid through a facile sonication-hydrothermal method for efficient degradation of phenol via an integrated PMS activation-photocatalysis process. Benefiting from the proper position and superior suitability of the band structure, a dual interfacial charge transport channel was constructed, boosting the separation of photo-generated charge carriers and generating sufficient potential difference for redox reaction. Accordingly, the CTM hybrid not only possessed the outstanding photocatalytic activity but also dramatically accelerated PMS activation to generate considerable reactive radicals. As a result, over 96% phenol degradation was achieved in the 10% CTM/PMS/Vis system within 15 min. The radical quenching test and EPR analysis reveal that SO₄^•-, O₂^•- and ¹O₂ were predominant reactive species involved in the catalytic process. Moreover, the damaged chemical structure of CoO during PMS activation could be healed by the photo-actuated Co(II) regeneration to allow for continuous and stable catalytic process. This study offers a promising perspective for the rational design of competent and stable hybrid heterojunction catalyst to construct PMS activation-photocatalysis processes for the efficient degradation of organic contaminants.

Emerging Cocatalysts on g-C3 N4 for Photocatalytic Hydrogen Evolution

Over the past few decades, graphitic carbon nitride (g-C₃ N₄ ) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g-C₃ N₄ severely inhibits the further large-scale application of g-C₃ N₄ . In this case, the utilization of cocatalysts is a novel frontline in the g-C₃ N₄ -based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high-performance cocatalysts based on g-C₃ N₄ toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.

Facile preparation of metallic 1T phase molybdenum selenide as cocatalyst coupled with graphitic carbon nitride for enhanced photocatalytic H2 production

Low-cost, highly active and efficient alternative co-catalysts that can replace precious metals such as Au and Pt are urgently needed for photocatalytic hydrogen evolution reaction (HER). Herein, we show that 1T phase MoSe₂ can act as the co-catalyst in the 1T-MoSe₂/g-C₃N₄ composites and we synthesize this composite by a one-step hydrothermal method to promote photocatalytic H₂ generation. Our prepared 1T-MoSe₂/g-C₃N₄ composite exhibits highly enhanced photocatalytic H₂ production compared to that of g-C₃N₄ nanosheets (NSs) only. The 7 wt%-1T-MoSe₂/g-C₃N₄ composite presents a considerably improved photocatalytic HER rate (6.95 mmol·h^-1·g^-1), approximately 90 times greater than that of pure g-C₃N₄ (0.07 mmol·h^-1 g^-1). Moreover, under illumination at λ = 370 nm, the apparent quantum efficiency (AQE) of the 7 wt%-1T-MoSe₂/g-C₃N₄ composite reaches 14.0%. Furthermore, the 1T-MoSe₂/g-C₃N₄ composites still maintain outstanding photocatalytic HER stability.

Novel prism shaped C3N4-doped Fe@Co3O4 nanocomposites and their dye degradation and bactericidal potential with molecular docking study

Novel prism shaped C₃N₄-doped Fe@Co₃O₄ nanocomposites were fabricated via a co-precipitation route for effective removal of organic pollutants from water and for bactericidal applications. Doping of C₃N₄ in the heterojunction significantly enhanced the photocatalytic and sonocatalytic activity against methylene blue ciprofloxacin (MBCF) dye. The main purpose of doping Fe atoms in the cobalt lattice was to generate crystal and surface defects. Moreover, the optimum doping amount of C₃N₄ for maximum degradation performance was evaluated. A detailed examination of the prepared nanocomposites was carried out systematically using various characterization tools for better understanding. HR-TEM images revealed the formation of novel prism shaped structures that exhibited outstanding degradation of the organic dye in water. Significant bactericidal potential was also observed for the synthesized nanocomposites against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. In silico, molecular docking studies against β-lactamase, DHFR and FabI enzymes served to elucidate the mechanism governing the bactericidal activity of the as-synthesized nanoparticles (NPs). Furthermore, a scavenging study by DPPH (2,2-diphenyl-1-picrylhydrazyl) assay and COD (chemical oxygen demand) analysis was performed in order to evaluate active species and the anti-oxidant potential of prepared composites.

This study provides new insights into the use of cobalt-based heterojunction photocatalysts for dye degradation and antibacterial applications (a) synthesis mechanism of C₃N₄ (b) schematic of synthesis route adopted for fabrication of nanocomposites.

In-situ fabrication of 3D hierarchical flower-like β-Bi2O3@CoO Z-scheme heterojunction for visible-driven simultaneous degradation of multi-pollutants

Development of an efficient heterojunction catalyst with a superior visible-light driven activity is regarded as a promising strategy to decontaminate organic wastewater. Herein, a novel direct Z-scheme β-Bi₂O₃@CoO heterojunction was well designed and successfully fabricated by in situ incorporating the two energy band-matched semiconductors. The obtained β-Bi₂O₃@CoO hybrid presented a unique 3D hierarchical structure with a mass of open channels and mesoporous, which afforded not only rapid mass transfer of targets but also good light-harvesting in view of the multiple reflections. Compared to the pristine β-Bi₂O₃ and CoO, the β-Bi₂O₃@CoO hybrid exhibited remarkably improved photocatalytic activity towards the simultaneous degradation of chlorotetracycline (CTC), tetracycline hydrochloride (TCH), oxytetracycline (OTC) and nitrobenzene (NB) under visible-light irradiation. The possible intermediates and degradation pathways were also tracked by mass spectra (MS) analysis. Moreover, a direct Z-scheme charge transfer mechanism in the intimate contact interface between β-Bi₂O₃ and CoO was verified for the improved catalytic activity, endowing the effective separation/transportation of the photo-excited charge carriers and maintenance of the strong redox ability in β-Bi₂O₃@CoO heterojunction. The present work affords a simple approach to design and construct 3D hierarchical direct Z-scheme photocatalysts with promising applications in water environment remediation.

Oxidative desulfurization of dibenzothiophene via layered graphitic carbon nitride-coordinated transition metal as a catalyst

In this study, graphitic carbon nitride (g-C3N4) has been synthesized. The cobalt-doped (CoO/g-C3N4) samples prepared by the impregnation method and their catalytic property were investigated on the ODS process.

Cd0.8Mn0.2S/MoO3 composites with an S-scheme heterojunction for efficient photocatalytic hydrogen evolution

High-performance and noble metal-free MoO3/Cd0.8Mn0.2S nanocomposites were synthesized via a simple direct physical mixing process. Consequently, from the many characterization methods, the obtained MoO3/Cd0.8Mn0.2S composites exhibited excellent photocatalytic hydrogen production performance and stability. The enhanced photocatalytic activity of the MoO3/Cd0.8Mn0.2S catalyst could be ascribed to the close contact interfaces and well-matched band structure of MoO3 and Mn0.8Cd0.2S, which is beneficial to the transport and separation of photonic excitons. Besides, the hydrogen production performance of the MoO3/Cd0.8Mn0.2S composite catalyst was 1.7 times higher than that of the pure MoO3. Based on the results of time-resolved fluorescence (TRPL) and electrochemical measurements, the possible S-scheme heterojunction mechanism of the photocatalytic hydrogen evolution of MoO3/Cd0.8Mn0.2S was proposed. This work has contributed to the transformation of solar energy into chemical energy.