Graphitic C2N3: An Allotrope of g-C3N4 Containing Active Azide Pentagons as Metal-Free Photocatalyst for Abundant H2 Bubble Evolution

Molybdenum diselenide/polymeric carbon nitride dual-homojunction photocatalyst with multi-step charge transfer for efficient catalytic carbon dioxide reduction

Due to the high dissociation energy of carbon dioxide (CO2) and sluggish charge transfer dynamics, photocatalytic CO2 reduction with high performance remains a huge challenge. Herein, we report a novel dual-homojunction photocatalyst comprising of cyano/cyanamide groups co-modified carbon nitride (CN-TH) intramolecular homojunction and 1 T/2H-MoSe2 homojunction (denoted as 1 T/2H-MoSe2/CN-TH) for enhanced photocatalytic CO2 reduction. In this dual-homojunction photocatalyst, the intramolecular CN-TH homojunction could promote the intralayer charge separation and transfer owing to the strong electron-withdrawing capabilities of the two-type cyanamide, while the 1 T/2H-MoSe2 homojunction mainly contributes to a promote interlayer charge transport of CN-TH. This could consequently induce a tandem multi-step charge transfer and accelerate the charge transfer dynamics, resulting in enhanced CO2 reduction activities. Thanks to this tandem multi-step charge transfer, the optimized 1 T/2H-MoSe2/CN-TH dual-homojunction photocatalyst presented a high CO yield of 27.36 μmol·g-1·h-1, which is 3.58 and 2.87 times higher than those of 1 T/2H-MoSe2/CN and 2H-MoSe2/CN-TH single homojunctions, respectively. This work provides a novel strategy for efficient CO2 reduction via achieving a tandem multi-step charge transfer through designing dual-homojunction photocatalyst.

Unveiling the potential of MXene-fabricated catalysts: an effective approach for H2 generation from water splitting

Hydrogen has enough potential and can be successfully used as an alternative to the conventional fuel. It can be successfully produced from water that is not only a sustainable source but exists everywhere on earth. Additionally, its combustion releases water that is quite safe and environment friendly. The current project was designed to generate hydrogen from catalytic water splitting on TiO2@Ti3C2T x catalysts. To obtain the required catalytic characteristics, titania was engineered on Ti3C2T x surfaces in situ using an ethanol-assisted solvothermal approach. After careful recovery, the catalysts were characterized and assessed for the photoreaction. All photoreactions were performed in a quartz reactor (150 mL), where hydrogen evolution activities were monitored on GC-TCD (Shimadzu-JP). The comparative activities indicated that TiO2@C and TiO2@Ti3C2T x catalysts deliver 9.37 and 18.57 mmol g-1 h-1 of hydrogen, respectively. The higher activities of TiO2@Ti3C2T x were attributed to the existence of higher active sites (charge trapping centres) on the multilayer MXene that progressively promote and facilitate redox reactions. Reason is that existence of titania on MXene interfaces develops heterojunctions that rectify the charge transfer; hence reduce the charge recombination (i.e., back reaction). On the basis of encouraging activities, it has been concluded that the aforementioned approach holds promise to replace the costly and conventional hydrogen generation technologies.

Enhanced tetracycline degradation by novel Mn-FeOOH/CNNS photocatalysts in a visible-light-driven photocatalysis coupled peroxydisulfate system

Recently, photocatalysis combined peroxydisulfate activation under visible light (PC-PDS/Vis) was developed as a promising technology for removing antibiotics in water. Herein, Mn doped FeOOH (Mn-FeOOH) nanoclusters were grown in-situ on the surface of graphitic carbon nitride nanosheets (CNNS) using a wet chemical method, which served as a visible-light-driven photocatalyst for peroxydisulfate (PDS) activation. Photovoltaic property characterizations revealed that Mn-FeOOH/CNNS owned superior light capture ability and carrier separation efficiency. According to DFT calculations, the synergistic effect between Mn and Fe species was proved to enhance the adsorption and activation of PDS. 99.7% of tetracycline (TC) was rapidly removed in 50 min in the PC-PDS/Vis system. In addition, Mn-FeOOH/CNNS exhibited high recycling stability with low iron leaching, attributed to the interaction between Mn-FeOOH clusters and carbon species. Quenching experiments and electron spin resonance (ESR) tests unveiled that •O2- played a significant role in TC removal, while •OH and SO4•- acted as additional roles contributing to the overall process. These findings given a new strategy for antibiotics degradation by photocatalysis, offering deeper insights for the advancement of sustainable and cutting-edge wastewater treatment technologies.

Atomically Contacted Cs3Bi2Br9 QDs@UiO-66 Composite for Photocatalytic CO2 Reduction

Metal halide perovskite quantum dots (QDs) are widely studied in the field of photocatalytic CO2 due to their strong light absorption and long carrier migration length. However, it can not exhibit high catalytic performance because of the radiative recombination and the lack of effective catalytic sites. Metal organic frameworks (MOFs) encapsulated QDs can not only solve the aforementioned problems, but also maintain their own unique characteristics with ultra-high specific surfaces area and abundant metal sites. In this work, lead-free bismuth-based halide perovskite QDs are encapsulated into Zr-based MOF (UiO-66), which combines the advantages with high power conversion efficiency of QDs and the high surface area and porosity of UiO-66. In addition, benefiting from the close contact between the Cs3Bi2Br9 QDs and the UiO-66 enables the photogenerated electrons in the QDs to be rapidly transferred to the MOF. As a result, the Cs3Bi2Br9@UiO-66 composite exhibits a higher yield for photocatalytic CO2 reduction than that of the prepared large-sized composite of Cs3Bi2Br9 and UiO-66.

Supercritical CH3OH-Triggered Isotype Heterojunction and Groups in g-C3N4 for Enhanced Photocatalytic H2 Evolution

The structure tuning of bulk graphitic carbon nitride (g-C3N4) is a critical way to promote the charge carriers dynamics for enhancing photocatalytic H2-evolution activity. Exploring feasible post-treatment strategies can lead to effective structure tuning, but it still remains a great challenge. Herein, a supercritical CH3OH (ScMeOH) post-treatment strategy (250-300 °C, 8.1-11.8 MPa) is developed for the structure tuning of bulk g-C3N4. This strategy presented advantages of time-saving (less than 10 min), high yield (over 80%), and scalability due to the enhanced mass transfer and high reactivity of ScMeOH. During the ScMeOH post-treatment process, CH3OH molecules diffused into the interlayers of g-C3N4 and subsequently participated in N-methylation and hydroxylation reactions with the intralayers, resulting in a partial phase transformation from g-C3N4 into carbon nitride with a poly(heptazine imide)-like structure (Q-PHI) as well as abundant methyl and hydroxyl groups. The modified g-C3N4 showed enhanced photocatalytic activity with an H2-evolution rate 7.2 times that of pristine g-C3N4, which was attributed to the synergistic effects of the g-C3N4/Q-PHI isotype heterojunction construction, group modulation, and surface area increase. This work presents a post-treatment strategy for structure tuning of bulk g-C3N4 and serves as a case for the application of supercritical fluid technology in photocatalyst synthesis.

Progress on enhancing the charge separation efficiency of carbon nitride for robust photocatalytic H2 production

Solar-driven H2 production from water splitting with efficient photocatalysts is a sustainable strategy to meet the clean energy demand and alleviate the approaching environmental issues caused by fossil fuel consumption. Among various semiconductor-based photocatalysts, graphitic carbon nitride (g-C3N4) has attracted much attention due to its advantages of long term-stability, visible light response, low cost, and easy preparation. However, the intrinsic Coulombic attraction between charge carriers and the interlayer electrostatic barrier of bulk g-C3N4 result in severe charge recombination and low charge separation efficiency. This perspective summarizes the recent progress in the development of g-C3N4 photocatalytic systems, and focuses on three main modification strategies for promoting charge transfer and minimizing charge recombination, including structural modulation, heterojunction construction, and cocatalyst loading. Based on this progress, we provide conclusions regarding the current challenges of further improving photocatalytic efficiency to fulfill commercial requirements, and propose some recommendations for the design of novel and satisfactory g-C3N4 photocatalysts, which is expected to progress the solar-to-hydrogen conversion.

Advances and challenges in the modification of photoelectrode materials for photoelectrocatalytic water splitting

With the increasing consumption of fossil fuels, the development of clean and renewable alternative fuels has become a top priority. Hydrogen (H2) is an ideal primary clean energy source for its extremely high gravimetric energy density, carbon-free combustion, and abundant natural resources. Photoelectrocatalytic (PEC) water splitting is among the most promising approaches for converting sunlight and water into H2. However, the cost-effectiveness and the overall solar to hydrogen conversion efficiency of PEC water splitting are still big challenges. In the past few decades, several studies have been devoted to this technology, and it is essential to develop economical photoelectrocatalysts with high conversion efficiency. Therefore, there is an urgent need for a comprehensive and updated review of recent advances in the design, manufacture, and modification of efficient PEC water splitting systems. This review first starts with the basic mechanism of photoelectrochemical water splitting. Then the problems in PEC water splitting are discussed, and the methods of photoelectrode modulation such as nanostructure fabrication, doping engineering, surface modification, and heterojunction construction are introduced. Finally, the critical challenges and future trends/perspectives in the PEC water splitting are discussed.

Cyanuric Acid-Assisted Synthesis of Hierarchical Amorphous Carbon Nitride Assembled by Ultrathin Oxygen-Doped Nanosheets for Excellent Photocatalytic Hydrogen Generation

Amorphous carbon nitride with typical short-range order arrangement as an effective photocatalyst is worth exploring but remains a great challenge because its disordered structure induces severe recombination of photogenerated charge carriers. Herein, for the first time, we demonstrate that a hierarchical amorphous carbon nitride (HACN) with structural oxygen incorporation can be synthesized via a cyanuric acid-assisted melem hydrothermal process, accompanied by freeze-drying and pyrolysis. The complex composed of melem and cyanuric acid exhibiting a unique 3D self-supporting skeleton and significant phase transformation is responsible for the formation of an interconnected hierarchical framework and amorphous structure for HACN. These features are beneficial to enhance its visible light harvesting by the multiple-reflection effect within the architecture consisting of more exposed porous nanosheets and introducing a long band tail absorption. The well-designed morphology, band tail state, and oxygen doping effectively inhibit rapid band-to-band recombination of the photogenerated electrons and holes and facilitate subsequent separation. Accordingly, the HACN catalyst exhibits exceptional visible light (λ > 420 nm)-driven photoreduction for hydrogen production with a rate of 82.4 μmol h-1, which is 21.7 and 9.5 times higher than those of melem-derived carbon nitride and crystalline nanotube carbon nitride counterparts, respectively, and significantly surpasses those of most reported amorphous carbon nitrides. Our controlling of rearrangement of the in situ supramolecular self-assembly of melem oligomer using cyanuric acid directly instructs the development of highly efficient amorphous photocatalysts for converting solar energy into hydrogen fuel.

Progress of charge carrier dynamics and regulation strategies in 2D CxNy-based heterojunctions

Two-dimensional carbon nitrides (CxNy) have gained significant attention in various fields including hydrogen energy development, environmental remediation, optoelectronic devices, and energy storage owing to their extensive surface area, abundant raw materials, high chemical stability, and distinctive physical and chemical characteristics. One effective approach to address the challenges of limited visible light utilization and elevated carrier recombination rates is to establish heterojunctions for CxNy-based single materials (e.g. C2N3, g-C3N4, C3N4, C4N3, C2N, and C3N). The carrier generation, migration, and recombination of heterojunctions with different band alignments have been analyzed starting from the application of CxNy with metal oxides, transition metal sulfides (selenides), conductive carbon, and Cx'Ny' heterojunctions. Additionally, we have explored diverse strategies to enhance heterojunction performance from the perspective of carrier dynamics. In conclusion, we present some overarching observations and insights into the challenges and opportunities associated with the development of advanced CxNy-based heterojunctions.

Enhancing CO2 Hydrogenation Using a Heterogeneous Bimetal NiAl-Deposited Metal-Organic Framework NU-1000: Insights from First-Principles Calculations

The hydrogenation of CO2 to high-value-added liquid fuels is crucial for greenhouse gas emission reduction and optimal utilization of carbon resources. Developing supported heterogeneous catalysts is a key strategy in this context, as they offer well-defined active sites for in-depth mechanistic studies and improved catalyst design. Here, we conducted extensive first-principles calculations to systematically explore the reaction mechanisms for CO2 hydrogenation on a heterogeneous bimetal NiAl-deposited metal-organic framework (MOF) NU-1000 and its catalytic performance as atomically dispersed catalysts for CO2 hydrogenation to formic acid (HCOOH), formaldehyde (H2CO), and methanol (CH3OH). The present results reveal that the presence of the NiAl-oxo cluster deposited on NU-1000 efficiently activates H2, and the facile heterolysis of H2 on Ni and adjacent O sites serves as a precursor to the hydrogenation of CO2 into various C1 products HCOOH, H2CO, and CH3OH. Generally, H2 activation is the rate-determining step in the entire CO2 hydrogenation process, the corresponding relatively low free energy barriers range from 14.5 to 15.9 kcal/mol, and the desorption of products on NiAl-deposited NU-1000 is relatively facile. Although the Al atom does not directly participate in the reaction, its presence provides exposed oxygen sites that facilitate the heterolytic cleavage of H2 and the hydrogenation of C1 intermediates, which plays an important role in enhancing the catalytic activity of the Ni site. The present study demonstrates that the catalytic performance of NU-1000 can be finely tuned by depositing heterometal-oxo clusters, and the porous MOF should be an attractive platform for the construction of atomically dispersed catalysts.

In-situ grown carbon as charge transfer medium for enhanced photoinduced electrons extraction from polymer carbon nitride toward TiO2

Interfacial charge transfer resistance is one of the main limiting factors for realizing high photocatalytic efficiency of heterostructures system. Herein, an activated carbon layer is successfully introduced between the interface of polymer carbon nitride (CN) and TiO2 heterostructure (CNP-x) as charge transfer medium by in situ pyrolysis carbonization method. Because of the lower spatial resistance of the crystalline/amorphous interface and the fast carrier transportation character of activated carbon, the efficiency of TiO2 in extracting photoinduced electrons from CN was significantly improved. That is, the separation/transport of photocarriers in CNP-x heterostructure is accelerated, and the recombination time of photogenerated electrons and holes is prolonged. The CNP-1 exhibits a H2 evolution rate of 1298.5 μmol h-1 with apparent quantum yield (AQY) of 34.5 %, 20.3 % and 12.6 % at 365 nm, 380 nm and 400 nm, respectively. This work offers a novel and unique strategy to promote interface charge separation and transport of CN-based heterostructures by accurately introduction charge transfer medium.

n→π* Electron Transitions and Directional Charge Migration Synergistically Promoting O2 Activation and Holes Utilization on Carbon Nitride for Efficiently Photocatalytic Degradation of Organic Contaminants

Stimulating electron transitions and promoting exciton dissociation are crucial for improving the photocatalytic performance of polymeric carbon nitride (CN) yet still challenging. Herein, a novel CN with C dopant and asymmetric structure (CC-UCN2 ) is ingeniously synthesized. The obtained CC-UCN2 not only reinforces the intrinsic π→π* electron transitions, but also successfully awakens additional n→π* electron transitions. Besides, charge centers dislocation caused by symmetry breaking induces a spontaneous polarized electric field, effectively breaking the constraints of Coulomb electrostatic interaction between electrons and holes and driving their directional migration. Along with the spatial separation of reduction and oxidation sites, CC-UCN2 shows exceptional O2 activation and holes oxidation efficiency, thus exhibits a high degradation rate constant (0.201 min-1 ) and mineralization rate (80.1%) for bisphenol A (BPA)(far outperforming pristine and other modified CNs). This work proposes a novel perspective for developing high-efficiency photocatalysts and comprehending the underlying mechanism of O2 activation and holes oxidation for pollutant degradation.

DNAzyme-Mediated Biodeposition Coupling Adjustable Cascade Electric Fields for Photoelectrochemical Telomerase Activity Monitoring

Telomerase, as a specialized reverse transcriptase, plays a vital role in early cancer diagnostics and prognosis; thus, developing efficient sensing technologies is of vital importance. Herein, an innovative "signal-on-off" photoelectrochemical (PEC) sensing platform was developed for ultrasensitive evaluation of telomerase activity based on an electron-transfer tunneling distance regulation strategy and DNAzyme-triggerable biocatalytic precipitation. Concretely, cascade internal electric fields between CuInS2 quantum dots (QDs), graphitic carbon nitride nanosheets (g-C3N4 NSs), and TiO2 nanorod arrays (NRAs) were developed to realize cascade electron extraction and hole transfer. Enabled by such a design, an effective "signal-on" state to gain a progressively enhanced PEC output was designed by suppressing the photogenerated electron-hole pair recombination. With the introduction of hairpin probe H2 and the subsequent extension of the primer sequence driven by the target telomerase, the CuInS2 QDs labeled with hairpin probe H1 were programmatically unfolded, resulting in CuInS2 QDs' close proximity to the working electrode away from the cascade interface, accompanied by the formation of G-quadruplex/hemin complexes. The gradual undermining of tunneling distance and implantation of DNAzyme-initiating biocatalytic precipitation tremendously induced the sluggish migration kinetics of the photoinduced charge, accompanied by the photocurrent intensity decrement, leading to the "signal-off" state. Under optimized conditions, the as-prepared PEC biosensor realizes ultrasensitive detection of telomerase activity from 10 to 105 cell·mL-1 with a detection limitation of 3 cells·mL-1. As a proof of concept, this well-designed method provides new insights into signal amplification for telomerase activity evaluation and also presents promising potential for further development in drug screening, healthcare diagnostics, and biological assays.

Hydrogen Evolution Activity of Nitrogen-Rich g-C3-xN4+x Synthesized by Solid-Gas Interface Method

Synthesis of a metal-free carbon nitride (g-C3N4) photocatalyst in the form of nitrogen-rich g-C3-xN4+x derivatives is desirable for efficient solar to hydrogen conversion and remains a challenging task to achieve. Herein we report the development of homogeneous sheets of nitrogen-rich graphitic carbon nitride samples from melamine by a solid-gas interface approach. Using this method, pure g-C3N4 (CN), g-C3-xN4+x under ammonia flow (CN-NH3) and g-C3-xN4+x under nitrogen flow (CN-N2) are prepared. The g-C3-xN4+x (CN-NH3) sample shows better surface conductivity, wide optical absorbance in the visible region, reduced recombination and high electron donor density, and higher performance toward photoelectrochemical hydrogen evolution (HER). The g-C3-xN4+x (CN-NH3) generates a photocurrent of 2.06 μA cm-2, which is 2.5 times higher than that of the pure g-C3N4 (CN) sample (0.85 μA cm-2). It also shows higher photocatalytic water splitting ability compared to the CN and CN-N2 samples, generating 634 μmol g-1 hydrogen without cocatalyst and 1163 μmol g-1 of hydrogen with Pt cocatalyst. Density functional calculations suggest that the progressive band gap reduction with the increase in the N-dopant percentage can be attributed to the gradual increase in the partial π-occupations, which can lead to a significant stabilization of the conduction band minima. The theoretical modeling, however, indicates a saturation in the band gap effect after 75% of N-dopant. The onset potential of g-C3-xN4+x for HER appears at η = 0.43 V in dark and η = 0.34 V vs Ag/AgCl under solar light illumination of 1 sun.

Double-Shelled Porous g-C3 N4 Nanotubes Modified with Amorphous Cu-Doped FeOOH Nanoclusters as 0D/3D Non-Homogeneous Photo-Fenton Catalysts for Effective Removal of Organic Dyes

Graphite phased carbon nitride (g-C₃ N₄ ) has attracted extensive attention attributed to its non-toxic nature, remarkable physical-chemical stability, and visible light response properties. Nevertheless, the pristine g-C₃ N₄ suffers from the rapid photogenerated carrier recombination and unfavorable specific surface area, which greatly limit its catalytic performance. Herein, 0D/3D Cu-FeOOH/TCN composites are constructed as photo-Fenton catalysts by assembling amorphous Cu-FeOOH clusters on 3D double-shelled porous tubular g-C₃ N₄ (TCN) fabricated through one-step calcination. Combined density functional theory (DFT) calculations, the synergistic effect between Cu and Fe species could facilitate the adsorption and activation of H₂ O₂ , and the separation and transfer of photogenerated charges effectively. Thus, Cu-FeOOH/TCN composites acquire a high removal efficiency of 97.8%, the mineralization rate of 85.5% and a first-order rate constant k = 0.0507 min^-1 for methyl orange (MO) (40 mg L^-1 ) in photo-Fenton reaction system, which is nearly 10 times and 21 times higher than those of FeOOH/TCN (k = 0.0047 min^-1 ) and TCN (k = 0.0024 min^-1 ), respectively, indicating its universal applicability and desirable cyclic stability. Overall, this work furnishes a novel strategy for developing heterogeneous photo-Fenton catalysts based on g-C₃ N₄ nanotubes for practical wastewater treatment.

Improved photocatalytic property of lignin-derived carbon nanofibers through catalyst synergy

Converting lignin into high value-added products is essential to reduce our dependence on petroleum resources and protect our environment. In this work, TiO₂ and g-C₃N₄ are loaded in the lignin-derived carbon nanofibers (LCNFs) and an efficient LCNFs-based photocatalytic material (TiO₂/g-C₃N₄@LCNFs) is developed. The spinnability of lignin solution, the chemical structure and morphology of the LCNFs, and the catalytic degradation property of the TiO₂/g-C₃N₄@LCNFs for Rhodamine B (RhB) are systematically investigated. The TiO₂/g-C₃N₄@LCNFs achieve a 92.76 % degradation rate of RhB under UV-vis irradiation, which is close to or higher than most reported carbon fiber-based photocatalysts. The excellent degradation property of the photocatalysts can be ascribed to the synergy of TiO₂ and g-C₃N₄, which improves the excitation efficiency of electron and hole, and prolongs the lifetime of electron-hole pairs. We envision that our work will provide some guidance for the development of efficient photocatalysts based on biomass-derived fiber materials.

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.

Construction of a heterojunction with fast charge transport channels for photocatalytic hydrogen evolution via a synergistic strategy of Co-doping and crystal plane modulation

Carrier spatial separation efficiency and active electron density are the key factors affecting photocatalytic hydrogen evolution activity. Heterojunction catalysts with fast charge separation and directed electron transport systems were successfully prepared by a synergistic modification strategy of transition metal (Co) doping and crystal plane modulation. The optimized electronic structure and enhanced reaction kinetics enabled unidirectional electron transfer. Photocatalytic results show that CdS(002)/Co-C₃N₄ exhibits remarkable hydrogen evolution activity (991.2 μmol h^-1 g^-1) in the absence of a co-catalyst, which is 37.0 and 3.4 times higher than that of C₃N₄ (26.8 μmol h^-1 g^-1) and Co-C₃N₄ (294.6 μmol h^-1 g^-1), respectively. Density functional theory (DFT) calculations indicate that the enhanced catalytic activity of CdS(002)/Co-C₃N₄ is attributed to the reduced electron-hole recombination rate and the increased electron density at the active site. This work provides a new idea for the design of photocatalysts with directed charge transport channels from the perspective of re-optimizing heterojunctions.

High-yield and crystalline graphitic carbon nitride photocatalyst: One-step sodium acetate-mediated synthesis and improved hydrogen-evolution performance

To avoid the drawbacks (such as multi-step operations and causing big quality loss) of currently reported molten salt-assisted strategy for the preparation of crystalline graphitic carbon nitride (g-C₃N₄) photocatalysts, in this study, an innovative and one-step sodium acetate (CH₃COONa)-mediated synthesis strategy has been designed to synthesize a high-yield and crystalline g-C₃N₄ photocatalyst. It is found that CH₃COONa can strongly combine with dicyandiamide (DCDA) to availably prevent the massive sublimation of DCDA and the following intermediates, causing the high-efficiency transformation of DCDA into g-C₃N₄ with a high yield (52.2 wt%). In addition to the promoted denitrification and quick polymerization of DCDA via CH₃COONa, the produced Na₂CO₃ from CH₃COONa decomposition at a higher temperature can further accelerate the polymerization reaction of 3-s-triazine units, leading to the final production of highly ordered and crystalline g-C₃N₄. Consequently, the resultant high-yield and crystalline g-C₃N₄ shows an obviously strengthened hydrogen (H₂)-evolution rate, about 2.4 times higher than that of bulk g-C₃N₄, which is due to the synergetic function of highly crystalline structure, reduced band gap and cyano-groups. The current one-step CH₃COONa-mediated synthesis strategy may open a novel horizon for the facile preparations and various applications of crystalline g-C₃N₄ materials.

Carrier and phonon transport in 2D InSe and its Janus structures

Recently, two-dimensional (2D) Indium Selenide (InSe) has been receiving much attention in the scientific community due to its reduced size, extraordinary physical properties, and potential applications in various fields. In this review, we discussed the recent research advancement in the carrier and phonon transport properties of 2D InSe and its related Janus structures. We first introduced the progress in the synthesis of 2D InSe. We summarized the recent experimental and theoretical works on the carrier mobility, thermal conductivity, and thermoelectric characteristics of 2D InSe. Based on the Boltzmann transport equation (BTE), the mechanisms underlying carrier or phonon scattering of 2D InSe were discussed in detail. Moreover, the structural and transport properties of Janus structures based on InSe were also presented, with an emphasis on the theoretical simulations. At last, we discussed the prospects for continued research of 2D InSe.

Graphitic carbon nitride-based photocatalysts in the applications of environmental catalysis

Semiconductor photocatalytic technology has shown great prospects in converting solar energy into chemical energy to mitigate energy crisis and solve environmental pollution problems. The key issue is the development of high-efficiency photocatalysts. Various strategies in the state-of-the-art advancements, such as heterostructure construction, heteroatom doping, metal/single atom loading, and defect engineering, have been presented for the graphitic carbon nitride (g-C₃N₄)-based nanocomposite catalysts to design their surface chemical environments and internal electronic structures to make them more suitable for different photocatalytic applications. In this review, nanoarchitecture design, synthesis methods, photochemical properties, potential photocatalytic applications, and related reaction mechanisms of the modified high-efficiency carbon nitride-based photocatalysts were briefly summarized. The superior photocatalytic performance was identified to be associated with the enhanced visible-light response, fast photoinduced electron-hole separation, efficient charge migration, and increased unsaturated active sites. Moreover, the further advance of the visible-light harvesting and solar-to-energy conversions are proposed.

Two-Dimensional Ultrathin Graphic Carbon Nitrides with Extended π-Conjugation as Extraordinary Efficient Hydrogen Evolution Photocatalyst

Construction of 2D graphic carbon nitrides (g-CN_x ) with wide visible light adsorption range and high charge separation efficiency concurrently is of great urgent demand and still very challenging for developing highly efficient photocatalysts for hydrogen evolution. To achieve this goal, a two-step pyrolytic strategy has been applied here to create ultrathin 2D g-CN_x with extended the π-conjugation. It is experimentally proven that the extension of π-conjugation in g-CN_x is not only beneficial to narrowing the bandgap, but also improving the charge separation efficiency of the g-CN_x . As an integral result, extraordinary apparent quantum efficiencies (AQEs) of 57.3% and 7.0% at short (380 nm) and long (520 nm) wavelength, respectively, are achieved. The formation process of the extended π-conjugated structures in the ultrathin 2D g-CN_x has been investigated using XRD, FT-IR, Raman, XPS, and EPR. Additionally, it has been illustrated that the two-step pyrolytic strategy is critical for creating ultrathin g-CN_x nanosheets with extended π-conjugation by control experiments. This work shows a feasible and effective strategy to simultaneously expand the light adsorption range, enhance charge carrier mobility and depress electron-hole recombination of g-CN_x for high-efficient photocatalytic hydrogen evolution.

Functionalized MOF-Based Photocatalysts for CO2 Reduction

Metal-organic frameworks (MOFs) materials have become a research forefront in the field of photocatalytic CO₂ reduction attributed to their ultra-high specific surface area, adjustable structure, and abundant catalytic active sites. Particularly, MOFs can be facilely tuned to match CO₂ photoreduction by utilizing post-modification of metal nodes, functionalization of organic linkers, and combination with other active materials. Herein, the recent advances in the construction strategy of MOF-based photocatalysts materials for CO₂ reduction are highlighted. Some systematic modification strategies on MOF-based photocatalysts are also discussed, such as modification of metal sites and organic ligands, construction of heterojunction, introduction of single/dual-atom, and strain engineering. Finally, the future development directions of MOF-based photocatalysts in the field of CO₂ reduction are presented.

Prediction of Two-Dimensional Group IV Nitrides AxNy (A = Sn, Ge, or Si): Diverse Stoichiometric Ratios, Ferromagnetism, and Auxetic Mechanical Property

In this work, we unveiled a new class of two-dimensional (2D) group IV nitride A_xN_y (A = Sn, Ge, or Si) prototypes, C2/m A₄N, P3̅m1 A₃N, P3m1 A₂N, P3̅m1 A₃N₂, P6̅m2 AN, P3̅m1 AN, P6̅2m A₃N₄, P3m1 A₂N₃, P4̅2₁m AN₂, and P3̅m1 AN₃, by using evolutionary algorithms combined with first-principles calculations. Using HSE06 functional calculations, a wide range of band gaps from metal to semiconductor (0.405-5.050 eV) and ultrahigh carrier mobilities (1-24 × 10³ cm² V^-1 s^-1) were evidenced in these 2D structures. We found that 2D P3m1 Sn₂N₃, Ge₂N₃, and Si₂N₃ are intrinsic ferromagnetic semiconductors with gaps of 0.677, 1.285, and 2.321 eV, respectively. The lattice symmetry and Si-to-N₂ charge transfer upon strain lead to large anisotropic negative Poisson's ratios (-0.281 to -0.146) along whole in-plane directions in 2D P4̅2₁m SiN₂. Our findings not only enrich the family of 2D nitrides but also highlight the promising optoelectronic and nanoauxetic applications of 2D group IV nitrides.

SiP Nanosheets: A Metal-Free Two-Dimensional Photocatalyst for Visible-Light Photocatalytic H2 Production and Nitrogen Fixation

Two-dimensional (2D) semiconductors for photocatalysis are more advantageous than the other photocatalytic materials since the 2D semiconductors generally have large specific surface area and abundant active sites. Phosphorus silicon (SiP), with an indirect bandgap in bulk and a direct bandgap in the monolayer, has recently emerged as an attractive 2D material because of its anisotropic layered structure, tunable bandgap, and high charge carrier mobility. However, the utilization of SiP as a photocatalyst for photocatalysis has been scarcely studied experimentally. Herein, we reported the synthesis of SiP nanosheets (SiP NSs) prepared from bulk SiP by an ultrasound-assisted liquid-phase exfoliation approach which can act as a metal-free, efficient, and visible-light-responsive photocatalyst for photocatalytic H₂ production and nitrogen fixation. In a half-reaction system, the maximal H₂ and NH₃ generation rate under visible light irradiation achieves 528 and 35 μmol·h^-1·g^-1, respectively. Additionally, the apparent quantum yield for H₂ production at 420 nm reaches 3.56%. Furthermore, a Z-scheme photocatalytic overall water-splitting system was successfully constructed by using Pt-loaded SiP NSs as the H₂-evolving photocatalyst, Co₃O₄/BiVO₄ as the O₂-evolving photocatalyst, and Co(bpy)₃^3+/2+ as an electron mediator. Notably, the highest H₂ and O₂ generation rate with respect to Pt/SiP NSs achieves 71 and 31 μmol·h^-1·g^-1, respectively. This study explores the potential application of 2D SiP as a metal-free visible-light-responsive photocatalyst for photocatalysis.

Molecular-functionalized engineering of porous carbon nitride nanosheets for wide-spectrum responsive solar fuel generation

Carbon nitride (C₃N₄) is a promising metal-free photocatalyst for solar-to-energy conversion, but bulk carbon nitride (BCN) shows insufficient light absorption, sluggish photocarrier transfer and moderate activity for photocatalysis. Herein, a facile strategy to significantly increase solar spectrum absorption of the functionalized porous carbon nitride nanosheets (MFPCN) via molecule self-assembly engineering coupled thermal polymerization is reported. This strategy can greatly enhance the wide-solar-spectrum absorption of MFPCN up to 1000 nm than most reported carbon nitride-based photocatalysts. Experimental characterizations and theoretical calculations together display that this strategy could introduce hydroxyl groups into the structure of MFPCN as well as the rich pores and active sites at the edges of framework, which can narrow the bandgap and accelerate the transfer and separation of photoinduced carries. As a result, the optimal MFPCN photocatalyst exhibit the excellent photocatalytic hydrogen evolution rate of 7.745 mmol g^-1h^-1 under simulated solar irradiation, which is ≈13 times that of BCN with remarkable durable CO₂ reduction activities. New findings in this work will provide an approach to extend solar spectrum absorption of metal-free catalysts for solar fuel cascades.

Visible-light-responsive Z-scheme system for photocatalytic lignocellulose-to-H2 conversion

A Z-scheme system was successfully constructed for visible-light-driven photocatalytic H₂ production from lignocelluloses, the highest H₂ evolution rate of this Z-scheme system is 5.3 and 1.6 μmol h^-1 in α-cellulose and poplar wood chip aqueous solutions, respectively, under visible light irradiation.