Facile synthesis of the Z-scheme graphite-like carbon nitride/silver/silver phosphate nanocomposite for photocatalytic oxidative removal of nitric oxides under visible light

Boosting photocatalytic NO oxidation mediated by high redox charge carriers from visible light-driven C3N4/UiO-67 S-scheme heterojunction photocatalyst

The construction of CN/UiO-67 (CNU) S-scheme heterojunction composites through in situ formation of UiO-67 on carbon nitride (C3N4) helps to address the limitations of carbon nitride (CN) in photocatalytic NO elimination. The optimized CNU3 demonstrates superior photocatalytic efficiency, which is attributed to electronic channels constructed by Zr-N bonds and S-scheme electron transport mechanism, effectively promoting the efficient separation of photogenerated charge carriers with high redox potentials. Density Functional Theory (DFT) calculations reveal redistributed electronic orbitals in CNU3, with progressive and continuous energy levels near the Fermi level, which bolsters electronic conduction. Comprehensive quenching experiments, Electron Paramagnetic Resonance (EPR), and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analyses highlight a synergistic interplay of electrons, holes, and superoxide radicals in CNU3, inhibiting the generation of toxic nitrogen oxide intermediates and culminating in highly efficient photocatalytic NO oxidation. This study not only elucidates the mechanisms underpinning the enhanced performance of CNU3 heterojunctions but also offers new perspectives on the preparation and interfacial charge separation of heterojunction photocatalysts.

Recent advances in ternary Z-scheme photocatalysis on graphitic carbon nitride based photocatalysts

Due to its excellent photocatalytic performance over the last few years, graphitic-like carbon nitride (g-C3N4) has garnered considerable notice as a photocatalyst. Nevertheless, several limitations, including small surface area, the rates at which photo-generated electrons and holes recombine are swift, and the inefficient separation and transport of photoexcited carriers continue to impede its solar energy utilization. To overcome those limitations in single-component g-C3N4, constructing a heterogeneous photocatalytic system has emerged as an effective way. Among the various studies involving the incorporation of hetero composite materials to design heterojunctions, among the most promising approaches is to assemble a Z-scheme photocatalytic configuration. The Z-scheme configuration is essential because it facilitates efficient photocarrier separation and exhibits superior redox ability in separated electrons and holes. Moreover, ternary composites have demonstrated enhanced photocatalytic activities and reinforced photostability. Ternary Z-scheme heterostructures constructed with g-C3N4 possess all the above-mentioned merits and provide a pioneering strategy for implementing photocatalytic systems for environmental and energy sustainability. A summary of the latest technological advancements toward design and fabrication in ternary all-solid-state Z-scheme (ASSZ) and direct Z-scheme (DZ) photocatalysts built on g-C3N4 is presented in this review. Furthermore, the review also discusses the application of ternary Z-scheme photocatalytic architecture established on g-C3N4.

Advances in photocatalytic NO oxidation by Z-scheme heterojunctions

The fast development of urbanisation and industrialisation has led to a rise in nitrogen oxide (NOx) emissions, specifically nitric oxide (NO). One effective method for reducing the harmful effects of this dangerous air pollutant on both human health and the environment is the photocatalytic oxidation of NO. Z-scheme heterojunctions enhance incident light utilisation and increase photocatalytic activity, eventually leading to better NO oxidation performance by encouraging the effective separation of charges and migration. A comprehensive discussion of Z-scheme-based heterojunctions is provided in this review paper, with a focus on their applications in the photocatalytic oxidation of NO. Significant progress has been made in the fabrication of efficient photocatalytic devices in recent years, with Z-scheme-based heterojunctions proving to be particularly successful. The review looks into the various methodologies used to create Z-scheme-based heterojunctions as well as photocatalytic NO oxidation mechanisms. Recent studies on photocatalysts employing Z-scheme heterojunctions for the photocatalytic oxidation of NO are also discussed. The possibilities for new opportunities as well as the present challenges, barriers, advances, and solutions have been emphasized.

Recent Advances in g-C3N4-Based Photocatalysts for NOx Removal

Nitrogen oxides (NOx) pollutants can cause a series of environmental issues, such as acid rain, ground-level ozone pollution, photochemical smog and global warming. Photocatalysis is supposed to be a promising technology to solve NOx pollution. Graphitic carbon nitride (g-C3N4) as a metal-free photocatalyst has attracted much attention since 2009. However, the pristine g-C3N4 suffers from poor response to visible light, rapid charge carrier recombination, small specific surface areas and few active sites, which results in deficient solar light efficiency and unsatisfactory photocatalytic performance. In this review, we summarize and highlight the recent advances in g-C3N4-based photocatalysts for photocatalytic NOx removal. Firstly, we attempt to elucidate the mechanism of the photocatalytic NOx removal process and introduce the metal-free g-C3N4 photocatalyst. Then, different kinds of modification strategies to enhance the photocatalytic NOx removal performance of g-C3N4-based photocatalysts are summarized and discussed in detail. Finally, we propose the significant challenges and future research topics on g-C3N4-based photocatalysts for photocatalytic NOx removal, which should be further investigated and resolved in this interesting research field.

Soil Respiration of Paddy Soils Were Stimulated by Semiconductor Minerals

Large quantities of semiconductor minerals on soil surfaces have a sensitive photoelectric response. These semiconductor minerals generate photo-electrons and photo-hole pairs that can stimulate soil oxidation-reduction reactions when exposed to sunlight. We speculated that the photocatalysis of semiconductor minerals would affect soil carbon cycles. As the main component of the carbon cycle, soil respiration from paddy soil is often ignored. Five rice cropping areas in China were chosen for soil sampling. Semiconductor minerals were measured, and three main semiconductor minerals including hematile, rutile, and manganosite were identified in the paddy soils. The identified semiconductor minerals consisted of iron, manganese, and titanium oxides. Content of Fe₂O₃, TiO₂, and MnO in the sampled soil was between 4.21-14%, 0.91-2.72%, and 0.02-0.22%, respectively. Most abundant semiconductor mineral was found in the DBDJ rice cropping area in Jilin province, with the highest content of Fe₂O₃ of 14%. Soils from the five main rice cropping areas were also identified as having strong photoelectric response characteristics. The highest photoelectric response was found in the DBDJ rice cropping area in Jilin province with a maximum photocurrent density of 0.48 μA/cm². Soil respiration was monitored under both dark and light (3,000 lux light density) conditions. Soil respiration rates in the five regions were (from highest to lowest): DBDJ > XNDJ > XBDJ > HZSJ > HNSJ. Soil respiration was positively correlated with semiconductor mineral content, and soil respiration was higher under the light treatment than the dark treatment in every rice cropping area. This result suggested that soil respiration was stimulated by semiconductor mineral photocatalysis. This analysis provided indirect evidence of the effect semiconductor mineral photocatalysis has on the carbon cycle within paddy soils, while exploring carbon conversion mechanisms that could provide a new perspective on the soil carbon cycle.

Photocatalytic degradation mechanism of phenanthrene over visible light driven plasmonic Ag/Ag3PO4/g-C3N4 heterojunction nanocomposite

Visible light driven plasmonic Ag/Ag₃PO₄/g-C₃N₄ heterojunction nanocomposite with regular morphology was prepared via a modified facile method. The two-dimensional ultrathin g-C₃N₄ nanosheet is uniformly wrapped on the surface of Ag₃PO₄ nanopolyhedron. A charge transfer bridge was built between Ag₃PO₄ nanopolyhedron and g-C₃N₄ nanosheet due to the reduction of Ag nanoparticles. This structure can inhibit the recombination of photogenerated electron-hole pairs and promote the transfer of photogenerated carriers, so as to produce more active species for participating in the photocatalytic reaction. In addition, the surface plasmon resonance (SPR) of appropriate Ag nanoparticles enhanced the absorption and utilization of visible light. Compared with Ag₃PO₄ and Ag/Ag₃PO₄, Ag/Ag₃PO₄/g-C₃N₄ showed higher photocatalytic activity. Under visible light irradiation, the degradation rate of phenanthrene (PHE) was 0.01756 min^-1, which was 3.14 times and 2.38 times that of Ag₃PO₄ and Ag/Ag₃PO₄, respectively. After four cycles of photocatalytic reaction, the Ag/Ag₃PO₄/g-C₃N₄ photocatalyst still maintained high photocatalytic activity. The active sites of PHE were predicted by Gaussian simulation calculation and combined with intermediate products identification of GC-MS, the possible degradation pathway of PHE was speculated. This research has reference significance for the construction of plasmonic heterojunction photocatalyst in the field of environmental pollution remediation.

Formation of flaky carbon nitride and beta-Indium sulfide heterojunction with efficient separation of charge carriers for enhanced photocatalytic carbon dioxide reduction

The flaky carbon nitride containing nitrogen defects (NDCN) could effectively perform the photocatalytic reduction of carbon dioxide (CO₂) due to its abundant active sites. Reducing the recombination of electrons and holes was also a method of semiconductor photocatalyst design. A nanosphere ball-flower Indium sulfide (In₂S₃) was synthesized via a simple hydrothermal approach, and then calcined to obtain the β-In₂S₃/NDCN heterojunction photocatalyst and applied for CO₂ photocatalytic reduction. The best total yield (carbon monoxide, CO: 20.32 μmol·g^-1·h^-1; methane, CH₄: 2.12 μmol·g^-1·h^-1) could be obtained at the optimized 20% β-In₂S₃/NDCN under near room temperature and pressure and without using any sacrificial agents or promoters, almost 1.7 times higher compared with NDCN. The composite catalyst still exhibited excellent stability after four cycles. The improvement of excellent performance was due to not only the enhancement of fine CO₂ adsorption/activation and the light absorption ability, but also attributed to the formation of heterojunction, which accelerated the effective separation of electrons and holes. This work might provide a novel approach to design carbon nitride heterojunction photocatalysts with nitrogen defects for CO₂ utilization.

Photocatalytic Air Purification Using Functional Polymeric Carbon Nitrides

The techniques for the production of the environment have received attention because of the increasing air pollution, which results in a negative impact on the living environment of mankind. Over the decades, burgeoning interest in polymeric carbon nitride (PCN) based photocatalysts for heterogeneous catalysis of air pollutants has been witnessed, which is improved by harvesting visible light, layered/defective structures, functional groups, suitable/adjustable band positions, and existing Lewis basic sites. PCN-based photocatalytic air purification can reduce the negative impacts of the emission of air pollutants and convert the undesirable and harmful materials into value-added or nontoxic, or low-toxic chemicals. However, based on previous reports, the systematic summary and analysis of PCN-based photocatalysts in the catalytic elimination of air pollutants have not been reported. The research progress of functional PCN-based composite materials as photocatalysts for the removal of air pollutants is reviewed here. The working mechanisms of each enhancement modification are elucidated and discussed on structures (nanostructure, molecular structue, and composite) regarding their effects on light-absorption/utilization, reactant adsorption, intermediate/product desorption, charge kinetics, and reactive oxygen species production. Perspectives related to further challenges and directions as well as design strategies of PCN-based photocatalysts in the heterogeneous catalysis of air pollutants are also provided.

Graphitic Carbon Nitride as a New Sustainable Photocatalyst for Textile Functionalization

As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C₃N₄) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has already been beneficially used in the fields of environmental remediation, biological applications, healthcare, energy conversion and storage, and fuel production. Despite the recognized potential of g-C₃N₄, there is still a knowledge gap in the application of g-C₃N₄ in the field of textiles, with no published reviews on the g-C₃N₄-functionalization of textile materials. Therefore, this review article aims to provide a critical overview of recent advances in the surface and bulk modification of textile fibres by g-C₃N₄ and its composites to tailor photocatalytic self-cleaning, antibacterial, and flame retardant properties as well as to create a textile catalytic platform for water disinfection, the removal of various organic pollutants from water, and selective organic transformations. This paper highlights the possibilities of producing g-C₃N₄-functionalized textile substrates and suggests some future prospects for this research area.

Highly active Z-scheme heterojunction photocatalyst of anatase TiO2 octahedra covered with C-MoS2 nanosheets for efficient degradation of organic pollutants under solar light

The construction of a Z-scheme photocatalyst by coupling semiconductors with conductors is an efficient way to achieve high pollutant degradation efficiency. In this study, a hydrothermal approach was used to fabricate a Z-scheme photocatalyst consisting of C-MoS₂ sheets wrapped around octahedral anatase TiO₂ nanocrystals. The catalyst showed excellent photocatalytic efficiency (99%) for methylene blue degradation with low catalyst loading (0.2 g L^-1) under the simulated solar light within 60 min. High photocatalytic degradation efficiencies were also observed for Rhodamine B, methyl orange, and tetracycline under solar irradiation. The C-MoS₂ acts as an electron mediator and serves as a carrier transmission bridge for the efficient electron-hole separation. The electron-rich (101)-faceted TiO₂ benefits the Z-scheme recombination of electrons from the conduction band of TiO₂ and holes at the valence band of MoS₂. The semiconductor coupling of (101)-exposed octahedral TiO₂ and 2H-MoS₂ as well as the introduction of solid-state electron mediators, 1T-MoS₂ and carbon, resulted in increased light absorption and accelerated charge transfer at the contact interface, which enhanced the photocatalytic activity of the photocatalyst significantly compared to those of P25, MoS₂/TiO₂, and C-MoS₂. The efficient separation of electron-hole pairs prolongs their lifetime for oxidation and reduction reactions in the degradation process.