Phosphorus-Doped Carbon Nitride Tubes with a Layered Micro-nanostructure for Enhanced Visible-Light Photocatalytic Hydrogen Evolution

Visible-light-prompted photoelectrochemical sensors fabricated using Er3NbO7/P@g-C3N4/SnS2 nanocomposite for detecting mercury ion in environmental water samples

Photoelectrochemical (PEC) detection technology is key for fighting pollution, leveraging the photoelectric conversion of the photoelectrode material. A specialized photoelectrode was developed to detect Hg2+ ions with exceptional sensitivity, utilizing an anodic PEC sensor composed of Er3NbO7/P@g-C3N4/SnS2 ternary nanocomposite. Rare earth metal niobates (RENs) were chosen due to their underexplored potential, whose performance was enhanced through bandgap engineering and surface modification, facilitated by P@g-C3N4 as an immobilization matrix and SnS2, belonging to the I-IV semiconductors category fostering hybrid heterojunction formation for boasting optical properties and suitable redox potentials. Introducing Hg2+ into the system, a specific amalgamation reaction occurs between reduced Hg and Sn. This reaction obstructs electron transfer to the FTO electrode surface, leading to the recombination of charges. The proposed PEC sensor exhibited remarkable analytical performance for Hg2+ detection, high sensitivity, a detection limit of 0.019 pM, excellent selectivity, and a detectable concentration range of 0.002-0.15 nM. Additionally, it demonstrated good recovery and low relative standard deviation when analyzing Hg2+ in water samples, highlighting the potential application of the heterostructure in detecting heavy metal ions via PEC technology.

Advances in the heterostructures for enhanced hydrogen production efficiency: a comprehensive review

The growing global energy demand and heightened environmental consciousness have contributed to the increasing interest in green energy sources, including hydrogen production. However, the efficacy of this technology is contingent upon the efficient separation of charges, high absorption of sunlight, rapid charge transfer rate, abundant active sites and resistance to photodegradation. The utilization of photocatalytic heterostructures coupling two materials has proved to be effective in tackling the aforementioned challenges and delivering exceptional performance in the production of hydrogen. The present article provides a comprehensive overview of operational principles of photocatalysis and the combination of photocatalytic and piezo-catalytic applications with heterostructures, including the transfer behavior and mechanisms of photoexcited non-equilibrium carriers between the materials. Furthermore, the effects of recent advances and state-of-the-art designs of heterostructures on hydrogen production are discussed, offering practical approaches to form heterostructures for efficient hydrogen production.

Silver and g-C3N4 co-modified biochar (Ag-CN@BC) for enhancing photocatalytic/PDS degradation of BPA: Role of carrier and photoelectric mechanism

Photocatalytic property of nano Ag is weak and its enhancement is important to enlarge its application. Herein, a novel strategy of constructing silver g-C3N4 biochar composite (Ag-CN@BC) as photocatalyst is developed and its photocatalytic degradation of bisphenol A (BPA) coupled with peroxydisulfate (PDS) oxidation process is characterized. Characterization result showed that silver was evenly embedded into the g-C3N4 structure of the nitrogen atoms format, impeding agglomeration of Ag by distributing stably on biochar. In optimum condition, BPA of 10 mg/L could be degraded completely at pH of 9.0 with a 0.5 g/L photocatalyst, 2 mM PDS in Ag-CN@BC-2 (Ag/melamine molar ratio of 0.5)/PDS system (99.2%, k = 4.601 h-1). Ag-CN@BC shows superior mineralization ratio in degrading BPA to CO₂ and H₂O via active radical way, including holes (h⁺), superoxide radicals (•O2⁻), sulfate radicals (SO4•⁻), and hydroxyl radicals (•OH). Proper amount of silver can be dispersed effectively by gC3N4, which is responsible for improving the visible-light absorbing capability and accelerate charge transfer during activation of PDS for BPA degradation, while biochar as carrier in the composite is supposed to enhance the photoelectric degradation of BPA by reducing the band gap and increasing the photocurrent of Ag-CN@BC catalyst. Ag-CN@BC exhibits excellent catalyst stability and photocatalytic activity for treatment of toxic organic contaminants in the environment.

Selective and stable visible-light-prompted scavenger-free photoelectrochemical strategy based on a ternary ErVO4/P@g-C3N4/SnS2 nanocomposite for the detection of lead ions in different water samples

Lead ions (Pb2+) are heavy metal environmental pollutants that can significantly impact biological health. In this study, the synthesis of a ternary nanocomposite, ErVO4/P@g-C3N4/SnS2, was achieved using a combination of hydrothermal synthesis and mechanical grinding. The as-fabricated photoelectrochemical (PEC) sensor was found to be an ideal substrate for Pb2+ detection with high sensitivity and reliability. The ErVO4/P@g-C3N4/SnS2/FTO was selected as the substrate because of its remarkable and reliable photocurrent response. The Pb2+ sensor exhibited a low detection limit of 0.1 pM and a broad linear range of 0.002-0.2 nM. Moreover, the sensor exhibited outstanding stability, selectivity, and reproducibility. In real-time applications, it exhibited stable recovery and a low relative standard deviation, ensuring reliable and accurate measurements. The as-prepared PEC sensor was highly stable for the detection of Pb2+ in different water samples. This promising characteristic highlights its significant potential for use in the detection of environmental pollutants.

Precise Defect Engineering on Graphitic Carbon Nitrides for Boosted Solar H2 Production

Defect engineering has been regarded as an "all-in-one strategy" to alleviate the insufficient solar utilization in g-C3N4. However, without appropriate modification, the defect benefits will be partly offset due to the formation of deep localized defect states and deteriorated surface states, lowering the photocarrier separation efficiency. To this end, the defective g-C3N4 is designed with both S dopants and N vacancies via a dual-solvent-assisted synthetic approach. The precise defect control is realized by the addition of ethylene glycol (EG) into precursor formation and molten sulfur into the pyrolysis process, which simultaneously induced g-C3N4. with shallow defect states. These shallow defect energy levels can act as a temporary electron reservoir, which are critical to evoke the migrated electrons from CB with a moderate trapping ability, thus suppressing the bulky photocarrier recombination. Additionally, the optimized surface states of DCN-ES are also demonstrated by the highest electron-trapping resistance (Rtrapping) of 9.56 × 103 Ω cm2 and the slowest decay kinetics of surface carriers (0.057 s-1), which guaranteed the smooth surface charge transfer rather than being the recombination sites. As a result, DCN-ES exhibited a superior H2 evolution rate of 4219.9 µmol g-1 h-1, which is 29.1-fold higher than unmodified g-C3N4.

Acetonitrile-Based Local High-Concentration Electrolytes for Advanced Lithium Metal Batteries

Acetonitrile (AN) is a compelling electrolyte solvent for high-voltage and fast-charging batteries, but its reductive instability makes it incompatible with lithium metal anodes (LMAs). Herein, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is used as the diluent to build an AN-based local high-concentration electrolyte (LHCE) to realize dense, dendrite-free, and stable LMAs. Such LHCE exhibits an exceptional electrochemical stability window close to 6 V (vs Li+/Li), excellent wettability, and promising flame retardancy. Compared to a baseline carbonate-based electrolyte, its electrochemical performance is prominent: the overpotential of lithium nucleation is minimal (only 24 mV), the average half-cell coulombic efficiency (CE) reaches 99.5% at 0.5 mA cm-2, and its practicality in full cells with LiFePO4 (LFP) and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes is also demonstrated. Compounding factors are identified to decipher the superiority of the AN-based LHCE. From the respect of solvation structures, both the elimination of free AN molecule and the diluent separation would contribute to prevention of anodic AN decomposition. Based on cryogenic electron microscopy (Cryo-EM) characterization and theoretical simulations results, the produced solid-electrolyte interphase (SEI) layer is uniform and compact. Thus, this work demonstrates a successful application of AN-based electrolytes in LMAs-traditionally deemed impractical-via the combined regulation of solvation and SEI structures.

Metal-free functionalized carbon nitride as a photocatalyst driven by sunlight for acetal synthesis and selective regeneration of NAD(P)H cofactor

Nicotinamide Adenine Dinucleotide Phosphate (NAD(P)H) plays an important role in numerous biologically significant redox reactions. The photochemical restoration of its oxidized form (NAD(P)+) under physiological conditions is intriguing in the context of integrated photo and catalysis. Herein, we report the functionalized graphitic carbon-based solar light active photocatalyst by doping boron and fluorine in the native graphitic carbon nitride (GCN) (nonfunctionalized) for the regeneration of enzymatically visible light active coenzyme and in photo-acetalization reactions. The metal-free functionalized photocatalyst systems such as BFGCN-x leads to higher yield NADH and NADPH regeneration. They are also capable of catalyzing acetal reactions in the absence of any Lewis and Bronsted acids. The current research endeavor provides the advancement and the application of functionalized GCN-based photocatalysts for NADH (61.89%), NADPH (59.84%) regeneration, and photo-acetalization reactions.

Anisotropic Dual S-Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response

The design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S-scheme heterojunction artificial photosynthetic system composed of Bi2O3-BiOBr-AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55-fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag-based materials, this dual S-scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Effects of Phosphorus Doping on Amorphous Boron Nitride's Chemical, Sorptive, Optoelectronic, and Photocatalytic Properties

Amorphous porous boron nitride (BN) represents a versatile material platform with potential applications in adsorptive molecular separations and gas storage, as well as heterogeneous and photo-catalysis. Chemical doping can help tailor BN's sorptive, optoelectronic, and catalytic properties, eventually boosting its application performance. Phosphorus (P) represents an attractive dopant for amorphous BN as its electronic structure would allow the element to be incorporated into BN's structure, thereby impacting its adsorptive, optoelectronic, and catalytic activity properties, as a few studies suggest. Yet, a fundamental understanding is missing around the chemical environment(s) of P in P-doped BN, the effect of P-doping on the material features, and how doping varies with the synthesis route. Such a knowledge gap impedes the rational design of P-doped porous BN. Herein, we detail a strategy for the successful doping of P in BN (P-BN) using two different sources: phosphoric acid and an ionic liquid. We characterized the samples using analytical and spectroscopic tools and tested them for CO2 adsorption and photoreduction. Overall, we show that P forms P-N bonds in BN akin to those in phosphazene. P-doping introduces further chemical/structural defects in BN's structure, and hence more/more populated midgap states. The selection of P source affects the chemical, adsorptive, and optoelectronic properties, with phosphoric acid being the best option as it reacts more easily with the other precursors and does not contain C, hence leading to fewer reactions and C impurities. P-doping increases the ultramicropore volume and therefore CO2 uptake. It significantly shifts the optical absorption of BN into the visible and increases the charge carrier lifetimes. However, to ensure that these charges remain reactive toward CO2 photoreduction, additional materials modification strategies should be explored in future work. These strategies could include the use of surface cocatalysts that can decrease the kinetic barriers to driving this chemistry.

Thermal Exfoliation and Phosphorus Doping in Graphitic Carbon Nitride for Efficient Photocatalytic Hydrogen Production

Photocatalytic H2 evolution has been regarded as a promising technology to alleviate the energy crisis. Designing graphitic carbon nitride materials with a large surface area, short diffusion paths for electrons, and more exposed reactive sites are beneficial for hydrogen evolution. In this study, a facile method was proposed to dope P into a graphitic carbon nitride framework by calcining melamine with 2-aminoethylphosphonic acid. Meanwhile, PCN nanosheets (PCNSs) were obtained through a thermal exfoliation strategy. Under visible light, the PCNS sample displayed a hydrogen evolution rate of 700 μmol·g-1·h-1, which was 43.8-fold higher than that of pure g-C3N4. In addition, the PCNS photocatalyst also displayed good photostability for four consecutive cycles, with a total reaction time of 12 h. Its outstanding photocatalytic performance was attributed to the higher surface area exposing more reactive sites and the enlarged band edge for photoreduction potentials. This work provides a facile strategy to regulate catalytic structures, which may attract great research interest in the field of catalysis.

Assembling carbon nitride quantum dots into hollow fusiformis and loading CoP for photocatalytic hydrogen evolution

The self-assembled carbon nitride quantum dots (CNQDs) has been largely advanced owing to the structure-relative photocatalytic activities, especially its electronic structure, which can be regulated by defects, functional groups, and doping. However, there are still issues such as wide band gaps for the assembles and severe recombination of photoinduced charges. Herein, we demonstrate the self-assembly of CNQDs into fusiform hollow superstructures (CNFHs), induced by hydrogen bonding between the terminal functional groups (-OH, -COOH, and -NH2). During the top-down assembly process, the hydrogen bonding dominates and initiates lateral cross-linking between adjacent CNQDs, which further twist into fusiform hollow structures. Benefitted greatly from the ultrathin and hollow nature of the superstructure that provides more exposed active sites, coupled with the introduction of phosphorus doping atoms into the framework induced narrowed band gap, CNFHs exhibits an 18-fold higher activity than the bulk counterpart toward photocatalytic hydrogen evolution after loading the CoP co-catalyst. This work presents a new platform to design and manipulate carbon nitride superstructures.

Eosin Y Post-Decorated Metal-Organic Framework as a Selectivity Regulator for the Alcohols Oxidation

The selective oxidation of alcohols into aldehydes is a basic and significant procedure, with great potential for scientific research and industrial applications. However, as an important factor in the C(sp3)-H activation process, high selectivity is generally difficult to achieve due to the fact that the more easily activated properties of aldehydes are compared to alcohols. Herein, by the ingenious decoration of eosin Y into a Zr-based metal-organic framework (MOF-808), EY@MOF-808 was prepared as a selectivity regulator for the aerobic oxidation of the benzyl alcohols into corresponding aldehydes, possessing applicability for the benzylic alcohols with various substituents. By anchoring eosin Y on Zr6O4(OH)4 clusters of MOF-808 and maintaining open metal nodes with selective binding effects, the benzyl alcohol substrates were selectively coordinated to the unsaturated metal clusters adjacent to eosin Y, which ensured that the excited eosin Y rapidly activated substrates to generate carbon radicals by the hydrogen atom transfer (HAT) process. The rapid electron transfer (ET) simultaneously produced reactive oxygen species (O2•-) and then a combination of both to further promote the generation of benzaldehydes. The weak interaction of benzaldehydes with the skeleton allowed it to dissociate rapidly, thus preventing overoxidation. Under the catalysis of EY@MOF-808, the selectivity of various benzaldehydes was more than 99%. In contrast, eosin Y gave only benzoic acid products under the same conditions, which demonstrated the superiority of regulatory selectivity of EY@MOF-808. Taking advantage of the heterogeneity of the MOF, EY@MOF-808 was recycled four times without a decrease in its selectivity and avoided the quenching effect of eosin Y. The organic functional units postdecorated MOF-based photocatalyst strategy exhibits a promising new perspective approach to sustainably regulating the selectivity of inert oxidation.

Creation of Interfacial S4-Sn-N2 Electron Pathways for Efficient Light-Driven Hydrogen Evolution

Establishing effective charge transfer channels between two semiconductors is key to improving photocatalytic activity. However, controlling hetero-structures in situ and designing binding modes pose significant challenges. Herein, hydrolytic SnCl2·2H2O is selected as the metal source and loaded in situ onto a layered carbon nitriden supramolecular precursor. A composite photocatalyst, S4-Sn-N2, with electron pathways of SnS2 and tubular carbon nitriden (TCN) is prepared through pyrolysis and vulcanization processes. The contact interface of SnS2-TCN is increased significantly, promoting the formation of S4-Sn-N2 micro-structure in a Z-scheme charge transfer channel. This structure accelerates the separation and transport of photogenerated carriers, maintains the stronger redox ability, and improves the stability of SnS2 in this series of heterojunctions. Therefore, the catalyst demonstrated exceptional photocatalytic hydrogen production efficiency, achieving a reaction rate of 86.4 µmol h-1, which is 3.15 times greater than that of bare TCN.

Photocatalytic Synthesis of Ammonia from Hollow Coral-Like Graphitic Carbon Nitride/FeOCl Loaded with Fe-1T MoS2 Nanosheets as Cocatalysts

Photocatalytic ammonia synthesis (PAS) represents an emerging environmentally friendly approach to ammonia production. In this work, we employed Fe doping to modify the cocatalyst 1T MoS2, enhancing the active N2 sites on Fe-1T MoS2 by inducing defects on the surface of 1T MoS2. Afterward, Fe-1T MoS2 was loaded onto a hollow coral-like graphitic carbon nitride (CCN)/FeOCl composite. Under simulated sunlight, the efficiency of 5% Fe-1T MoS2@CCN/FeOCl (Fe-MCN/FeOCl) reached 367.62 μmol g-1 h-1, surpassing 1T MoS2@CCN(MCN) by 3.2 times, CCN by 16.9 times, and g-C3N4 by 32.5 times, where 5% means the doping amount of Fe in 1T MoS2. The good performance of Fe MCN/FeOCl should be attributed to the Fe doping in Fe-MCN/FeOCl which not only increases the separation efficiency of active sites and charge carriers, but also reduces the sample impedance significantly through the heterojunction formed between CCN and FeOCl. This work also presents a method for creating more efficient and stable photocatalysts for ammonia synthesis.

Supramolecular assembly activated single-molecule phosphorescence resonance energy transfer for near-infrared targeted cell imaging

Pure organic phosphorescence resonance energy transfer is a research hotspot. Herein, a single-molecule phosphorescence resonance energy transfer system with a large Stokes shift of 367 nm and near-infrared emission is constructed by guest molecule alkyl-bridged methoxy-tetraphenylethylene-phenylpyridines derivative, cucurbit[n]uril (n = 7, 8) and β-cyclodextrin modified hyaluronic acid. The high binding affinity of cucurbituril to guest molecules in various stoichiometric ratios not only regulates the topological morphology of supramolecular assembly but also induces different phosphorescence emissions. Varying from the spherical nanoparticles and nanorods for binary assemblies, three-dimensional nanoplate is obtained by the ternary co-assembly of guest with cucurbit[7]uril/cucurbit[8]uril, accompanying enhanced phosphorescence at 540 nm. Uncommonly, the secondary assembly of β-cyclodextrin modified hyaluronic acid and ternary assembly activates a single intramolecular phosphorescence resonance energy transfer process derived from phenyl pyridines unit to methoxy-tetraphenylethylene function group, enabling a near-infrared delayed fluorescence at 700 nm, which ultimately applied to mitochondrial targeted imaging for cancer cells.

High-Efficiency Ag-Modified ZnO/g-C3N4 Photocatalyst with 1D-0D-2D Morphology for Methylene Blue Degradation

Photocatalysts with different molar ratios of Ag-modified ZnO to g-C3N4 were prepared through an electrostatic self-assembly method and characterized through techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The resulting Ag-ZnO/g-C3N4 photocatalysts exhibited a unique 1D-0D-2D morphology and Z-type heterojunction. Moreover, g-C3N4 nanosheets with large layer spacing were prepared using acid treatment and thermal stripping methods. The Z-type heterostructure and localized surface plasmon resonance effect of Ag nanowires enabled high-speed electron transfer between the materials, while retaining large amounts of active substances, and broadened the light response range. Because of these features, the response current of the materials improved, and their impedance and photoluminescence reduced. Among the synthesized photocatalysts, 0.05Ag-ZnO/g-C3N4 (molar ratio of g-C3N4/ZnO: 0.05) exhibited the highest photocatalytic performance under UV-visible light. It degraded 98% of methylene blue in just 30 min, outperforming both g-C3N4 (21% degradation in 30 min) and Ag-ZnO (84% degradation in 30 min). In addition, 0.05Ag-ZnO/g-C3N4 demonstrated high cycling stability.

Photocatalytic Conversion of Methane to Ethanol at a Three-Phase Interface with Concentration-Matched Hydroxyl and Methyl Radicals

The direct oxidation of CH4 to C2H5OH is attractive but challenging owing to the intricate processes involving carbon-chain growth and hydroxylation simultaneously. The inherent difficulty arises from the strong tendency of CH4 to overoxidize in the commonly used pressurized powder suspension systems rich in reactive oxygen radicals (ROR), which are specifically designed for CH4 concentration and activation. Meanwhile, the strong tendency of nucleophilic attack of potent ROR on the C-C bond of the resulting product C2H5OH ultimately leads to a higher selectivity for C1 oxygenates. This study addresses this multifaceted issue by designing a three-phase interface based on a hydrophilic floating Fe(III)-cross-linked macroporous alginate hydrogel film encapsulated with C3N4 [Fe(III)@ACN] to simultaneously enhance the accessibility of H2O and CH4 molecules to the active sites and species within the macroporous channel. The hydrophilic properties of Fe(III)@ACN allow the in situ production of H2O2 from C3N4 through the water oxidation reaction under irradiation. The concurrent photoinduced Fe(II) triggers Fenton reaction with H2O2 to produce •OH. The enhanced mass transfer of CH4 at the three-phase interface ensures the efficient formation of •CH3 by reacting with •OH, ultimately facilitating carbon-chain growth in the conversion pathway from CH4 to CH3OH and finally to C2H5OH with •CH3 and •OH present in comparable concentrations. Thus, the Fe(III)@ACN catalyst exhibits a remarkable 96% selectivity for alcohol, achieving a 90% selectivity for C2H5OH in the alcohol products. The C2H5OH production rate reaches 171.7 μmol g-1 h-1 without the need for precious-metal additive.

Template-Free Synthesis of Boron-Doped Graphitic Carbon Nitride Porous Nanotubes for Enhanced Photocatalytic Hydrogen Evolution

The photocatalytic activity of g-C3N4 can be enhanced by improving photoinduced carrier separation and exposing sufficient reactive sites. In this study, we synthesized B-doped porous tubular g-C3N4 (BCNT) using a H3BO3-assisted supramolecular self-template method, wherein H3BO3 helped in B-doping, building a porous structure, and maintaining one-dimensional nanotubes. The tubular structure had an ultrathin tube wall and large aspect ratio, which are conducive to the directional transmission and separation of photogenerated carriers; moreover, the abundant pore structure of the tube wall could fully expose the reactive sites. The introduction of B and the cyano group modulated the bandgap of g-C3N4 and elevated the position of the conduction band, thus enhancing the photoreduction ability and effectively improving the hydrogen evolution performance. Consequently, the hydrogen evolution of BCNT-2 (220.8, 53.2 μmol·h-1) was 1.82 and 1.54 times that of ultrathin g-C3N4 nanosheets (CNN, 121.3, 34.6 μmol·h-1) under simulated sunlight and LED lamp irradiation, respectively. Thus, this work provides in-depth insights into the rational design of one-dimensional g-C3N4 nanotubes with high hydrogen evolution activity under visible irradiation.

Efficient removal of U(VI) from aqueous solution by CNN/UiO-66 under simulated sunlight irradiation: the synergy of adsorption and photocatalysis

The reduction of soluble U(VI) to insoluble and less toxic U(IV) by photocatalysis is an effective method to control uranium contamination. The graphitic carbon nitride nanosheet (CNN)/UiO-66 composites (CNNU) were prepared by thermal polymerization and solvothermal methods for the removal of U(VI). The morphology, crystal structure and optical properties of composites were analyzed by SEM, XRD, BET, UV-DRS, PL and EIS. The results showed the introduction of UiO-66 increased the specific surface of CNN from 9.07 m2/g to 46.24 m2/g, and effectively suppressed the recombination of photogenerated electrons and holes and improved the photocatalytic activity. The U(VI) removal capacity by adsorption and photocatalysis of CNNU was reached 779.47 mg/g, which significantly higher than that of adsorption (478.38 mg/g). The adsorption process was found to conform to the pseudo-second-order kinetic model and the Langmuir isothermal model. Meanwhile, U(VI) adsorbed on the CNNU was reduced to U(IV) via e- and ·O2- generated in the photocatalytic process. Therefore, this outstanding performance of CNNU in U(VI) removal is attributed to the synergistic effect of adsorption and photocatalytic reduction.

P-N Heterojunction Embedded CuS/TiO2 Bifunctional Photocatalyst for Synchronous Hydrogen Production and Benzylamine Conversion

The coupling of photocatalytic hydrogen production and selective oxidation of benzylamine is a topic of significant research interest. However, enhancing the bifunctional photocatalytic activity in this context is still a major challenge. The construction of Z-scheme heterojunctions is an effective strategy to enhance the activity of bifunctional photocatalysts. Herein, a p-n type direct Z-scheme heterojunction CuS/TiO2 is constructed using metal-organic framework (MOF)-derived TiO2 as a substrate. The carrier density is measured by Mott-Schottky under photoexcitation, which confirms that the Z-scheme electron transfer mode of CuS/TiO2 is driven by the diffusion effect caused by the carrier concentration difference. Benefiting from efficient charge separation and transfer, photogenerated electrons, and holes are directedly transferred to active oxidation and reduction sites. CuS/TiO2 also exhibits excellent bifunctional photocatalytic activity without noble metal cocatalysts. Among them, the H2 evolution activity of the CuS/TiO2 is found to be 17.1 and 29.5 times higher than that of TiO2 and CuS, respectively. Additionally, the yields of N-Benzylidenebenzylamine (NBB) are 14.3 and 47.4 times higher than those of TiO2 and CuS, respectively.

Schottky junction enhanced H2 evolution for graphitic carbon nitride-NiS composite photocatalysts

As one of the most promising photocatalysts for H2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H2 evolution rate of 752.9 μmol g-1 h-1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the SH bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H2 evolution activity.

An ultra-porous g-C3N4 micro-tube coupled with MXene (Ti3C2TX) nanosheets for efficient degradation of organics under natural sunlight

It remains as a challenge for realizing efficient photo-responsive catalysts towards large-scale degradation of organic pollutants under natural sunlight. This work reports a new pore engineering strategy for creating ultra-porous g-C3N4 micro-tubes with an unprecedentedly high specific surface area of 152.96 m2/g. This is mainly associated with releasing internal vapor pressure in the autoclave where the hydrothermal treatment of the urea/melamine mixture is processed. Supported by microscopic observation, porosity measurement and spectroscopic characterization, it is found that releasing the pressure at halfway of hydrothermal process is vital for forming exfoliated rod-like precursors and the de-aggregation of these rods presents substantial benefits on the production of mesopores on g-C3N4 micro-tubes during the calcination of precursors. This offers a large number of reactive sites required by photocatalytic reaction. Coupling these micro-tubes with Ti3C2TX nanosheets via electrostatic interaction yields a 1D/2D heterojunction with a close interfacial contact. The addition of metallically conductive Ti3C2TX nanosheets accelerates the separation between electrons and holes, and also enhances the light absorption. All these merits of structural design lead to forming a group of highly efficient catalysts demonstrating an excellent photocatalytic degradation rate of k = 0.0560 min-1 for RhB dyes under 100 mW/cm2 visible light radiation that micks sunlight outdoors. This laboratory valuation is further supported by an outdoor test that shows a fast degradation rate of 0.0744 min-1 under natural sunlight.

Ag-based coordination polymer-enhanced photocatalytic degradation of ciprofloxacin and nitrophenol

Transition-metal coordination complexes have attracted wide attention in molecular chemistry, but their applications still confront a tremendous challenge. Herein, a novel silver coordination polymer with a formula of {[Ag9(TIPA)6](NO3)9·12H2O}n (Ag-TIPA) was prepared by a solvothermal reaction of silver nitrate with triangular tris(4-imidazolylphenyl)amine (TIPA). The crystalline molecular structure was determined by single-crystal X-ray diffraction, which showed that each Ag(I) was coordinated with two nitrogen atoms of TIPA ligands. Such Ag-TIPA was used as a catalyst for the photodegradation of ciprofloxacin and 4-nitrophenol under UV-visible light irradiation. The results exhibited excellent photocatalytic performance and reusability due to high structure stability in an acidic, neutral and alkaline environment. The experimental findings and density functional theory calculations revealed that metal-ligand charge transfer in Ag-TIPA extended the absorption range of light and improved the charge transfer properties of TIPA. To further understand the photodegradation process, the intermediates were predicted and analysed through electrostatic potential, orbital weighted dual descriptor, and liquid chromatography-mass spectrometry techniques. Based on these findings, a possible degradation mechanism was proposed. This study provides new insights into the design and synthesis of Ag-based coordination polymers with novel structures, excellent catalytic activity, and good durability.

Performance and characterization of snail adhesive mucus as a bioflocculant against toxic Microcystis

Toxic Microcystis blooms are widespread in aquatic bodies, posing major threats to aquatic and human life. Recently, bioflocculants have attracted considerable attention as a promising biomaterial for Microcystis management. In search of a novel organism that can produce an efficient bioflocculant for controlling harmful algae sustainably, the native gastropod Cipangopaludina chinensis was co-cultured continuously with toxic Microcystis under different initial algal cell densities. The bioflocculation effect of snail mucus on toxic Microcystis, microcystin removal, and toxin accumulation in snails was investigated. In addition, the properties of the adhesive mucus were characterized using microscopic, X-ray diffraction, infrared spectroscopy, and polysaccharide and proteome analyses. Microcystis cells were captured and flocculated by the snail mucus; removal efficiencies of up to 89.9% and 84.8% were achieved for microalgae and microcystin-leucine arginine (MC-LR), respectively, when co-cultured with C. chinensis for only one day. After nine-day exposure, less than 5.49 µg/kg DW microcystins accumulated in the snails, indicating safety for human consumption. The snail mucus contained 104.3 µg/mg protein and 72.7 µg/mg carbohydrate, which provide several functional groups beneficial for Microcystis bioflocculation. The main monosaccharide subunits of polysaccharides are galactose, galactosamine, glucosamine, fucose, glucose, and mannose. Most of them are key components of polysaccharides in many bioflocculants. Gene Ontology analysis indicated the protein enrichment in binding processes and catalytic activity, which may account for Microcystis bioflocculation via protein binding or enzymatic reactions. The findings indicate that native C. chinensis secretes adhesive mucus that can act as bioflocculant for toxic Microcystis from ambient water and can be an effective and eco-friendly tool for Microcystis suppression.

Bio-Inspired Supramolecular Self-Assembled Carbon Nitride Nanostructures for Photocatalytic Water Splitting

Fast production of hydrogen and oxygen in large amounts at an economic rate is the need of the hour to cater to the needs of the most awaited hydrogen energy, a futuristic renewable energy solution. Production of hydrogen through simple water splitting via visible light photocatalytic approach using sunlight is considered as one of the most promising and sustainable approaches for generating clean fuels. For this purpose, a variety of catalytic techniques and novel catalysts have been investigated. Among these catalysts, carbon nitride is presently deemed as one of the best candidates for the visible light photocatalysis due to its unique molecular structure and adequate visible-range bandgap. Its bandgap can be further engineered by structural and morphological manipulation or by doping/hybridization. Among numerous synthetic approaches for carbon nitrides, supramolecular self-assembly is one of the recently developed elegant bottom-up strategies as it is bio-inspired and provides a facile and eco-friendly route to synthesize high surface area carbon nitride with superior morphological features and other semiconducting and catalytic properties. The current review article broadly covers supramolecular self-assembly synthesis of carbon nitride nanostructures and their photocatalytic water-splitting applications and provides a comprehensive outlook on future directions.

Highly Hydrophilic and Defective Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

Graphitic carbon nitride (g-C3N4), as a kind of nonmetallic low-cost photocatalyst, has great potential in photocatalytic hydrogen (H2) evolution, but its poor hydrophilicity and nonwetting extremely limit its H2 evolution efficiency. Herein, highly hydrophilic and defective g-C3N4 photocatalysts (NH3-CN-P as a representative example) have been fabricated on the basis of the strategy of joint phosphorus doping and ammonia stripping. The dopant of phosphorus prefers to occupy the C atoms bonded to -NH2 groups in the g-C3N4 skeleton, which is conducive to the formation of N defects caused by the effects of electronegativity and charge balance. Moreover, ammonia stripping plays a dual role in exposing plentiful two-dimensional defective planar structure and implanting the hydrophilic groups on the surface. As expected, the photocatalytic H2 evolution property of NH3-CN-P reaches 11.31 mmol g-1 h-1, with an apparent quantum yield of 17.9% at 420 nm, outperforming the majority of the reported g-C3N4-based photocatalysts.

Eosin Y-Based Metal-Organic Framework Synergistic with Cobalt(II) Complex for Hydrogen Evolution through Photoinduced Intermolecular Electron Transfer

Photocatalytic hydrogen evolution reaction (HER) is a promising approach for producing clean energy and has the potential to play an important role in the transition toward a more sustainable and environmentally friendly energy system. Optimizing the photoinduced electron transfer (PET) process and increasing visible-light utilization play a central role in photocatalysis. Herein, we built a novel Eosin Y-based metal-organic framework (Zn-EYTP) by synergizing a cobalt(II) complex for boosting the H2 evolution efficiency through photoinduced intermolecular electron transfer. Under optimized conditions, the maximum H2 evolution efficiency for Zn-EYTP was determined to be a turnover number (TON) value of 11,100 under green LED irradiation. And the synthesized Zn-EYTP photocatalysts could be easily recycled to restore the initial photocatalytic activity even after 3 cycles. Detailed studies reveal that the significantly enhanced HER activity in Zn-EYTP could be ascribed to the effective separation of photogenerated charges and the synergistic intermolecular interaction between Zn-EYTP and [Co(bpy)3]Cl2. The present work enables a deeper understanding of the importance of the PET process for enhanced HER photocatalytic activities, which will provide a viable strategy for the development of highly efficient photocatalysts.

Regulating local molecular polarization of triazine-PDI based polymer for high-efficient photocatalytic coupling of benzylamine

Designing a robust built-in electric field (BF) is a charming strategy for enhancing the separation and transportation of charges via introducing large π-conjugated molecules. However, it has flexible or semiflexible geometries, which significantly disorder the crystalline and deteriorated the built-in electric field. Here, a straightforward tactic for creating a cyano-functionalized smaller D (benzene) - A (triazine) units in PDI- triazine based polymer (PDIMB) to enhance intrinsic molecule dipole has been proposed. The density functional theory (DFT) calculation revealed that the modification of smaller D-A groups destroyed the π-localization of charges, which enhanced the molecular dipole and the BF for promoting the exciton dissociation and charge transfer. Moreover, it not only exposed number of active sites, but also enhanced the interfacial molecular interacting. Therefore, PDIMB-2 exhibits high activity (24.5 mmol g-1 h-1) and selectivity (>99%) for the photooxidation of benzylamine to N-benzylidenebenzylamine under mild conditions. Our work offers a potential and simple synthetic option for enhancing the built-in electric field of polymer.

Self-assembly synthesis of hollow phosphorus-doped graphitic carbon nitride microboxes for the photodegradation of organic pollutants

The rational design of photocatalysts with efficiency and stability is highly desirable but remains challenging. Here, we report a supramolecular self-assembly strategy to construct hollow phosphorus-doped g-C3N4 microboxes (PCNMs). Considering the effects of multiple parameters on the structure and activity of samples, the orthogonal design is innovatively introduced to optimize technology parameters for screening high-performance g-C3N4. Under visible light irradiation (λ ≥ 420 nm), rhodamine B (RhB, 4 mg L-1) is completely degraded in just 80 seconds in the presence of the optimal PCNM. The kinetic rate constant of RhB degradation with the PCNM is 3.4633 min-1, demonstrating unprecedented activity that is about 112 times higher than that of bulk g-C3N4 (0.0309 min-1) synthesized by direct polycondensation of melamine. Additionally, the optimal PCNM also shows enhanced degradation efficiency for tetracycline. The outstanding properties are primarily attributed to the hollow architecture, high specific surface area, and phosphorus doping. This work advances the design of photocatalysts correlating various factors, opening an avenue for optimizing photocatalytic synthesis and activity.

Orthogonal Dual Photocatalysis of Single Atoms on Carbon Nitrides for One-Pot Relay Organic Transformation

Single-atom photocatalysis has shown potential in various single-step organic transformations, but its use in multistep organic transformations in one reaction systems has rarely been achieved. Herein, we demonstrate atomic site orthogonality in the M1/C3N4 system (where M = Pd or Ni), enabling a cascade photoredox reaction involving oxidative and reductive reactions in a single system. The system utilizes visible-light-generated holes and electrons from C3N4, driving redox reactions (e.g., oxidation and fluorination) at the surface of C3N4 and facilitating cross-coupling reactions (e.g., C-C and C-O bond formation) at the metal site. The concept is generalized to different systems of Pd and Ni, thus making the catalytic site-orthogonal M1/C3N4 system an ideal photocatalyst for improving the efficiency and selectivity of multistep organic transformations.

Carbon Nitrides from Supramolecular Crystals: From Single Atoms to Heterojunctions and Advanced Photoelectrodes

Carbon nitride materials (CN) have become one of the most studied photocatalysts within the last 15 years. While CN absorbs visible light, its low porosity and fast electron-hole recombination hinder its photoelectric performance and have motivated the research in the modification of its physical and chemical properties (such as energy band structure, porosity, or chemical composition) by different means. In this Concept we review the utilization of supramolecular crystals as CN precursors to tailor its properties. We elaborate on the features needed in a supramolecular crystal to serve as CN precursor, we delve on the influence of metal-free crystals in the morphology and porosity of the resulting materials and then discuss the formation of single atoms and heterojunctions when employing a metal-organic crystal. We finally discuss the performance of CN photoanodes derived from crystals and highlight the current standing challenges in the field.

Multifunctional carbon nitride nanoarchitectures for catalysis

Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.

Phosphorus-Doped Hollow Tubular g-C3N4 for Enhanced Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction is a tactic for solving the environmental pollution caused by greenhouse gases. Herein, NH4H2PO4 was added as a phosphorus source in the process of the hydrothermal treatment of melamine for the first time, and phosphorus-doped hollow tubular g-C3N4 (x-P-HCN) was fabricated and used for photocatalytic CO2 reduction. Here, 1.0-P-HCN exhibited the largest CO production rate of 9.00 μmol·g-1·h-1, which was 10.22 times higher than that of bulk g-C3N4. After doping with phosphorus, the light absorption range, the CO2 adsorption capacity, and the specific surface area of the 1.0-P-HCN sample were greatly improved. In addition, the separation of photogenerated electron-hole pairs was enhanced. Furthermore, the phosphorus-doped g-C3N4 effectively activated the CO2 adsorbed on the surface of phosphorus-doped g-C3N4 photocatalysts, which greatly enhanced the CO production rate of photocatalytic CO2 reduction over that of g-C3N4.

Atomically Dispersed FeN2 P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range

The past decade has witnessed the great potential of Fe-based single-atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long-term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high-density Fe atoms (3.97 wt%) are coordinated with square-planar para-positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as-crafted atomically dispersed Fe catalyst (denoted Fe-SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half-wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe-SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H2 SO4 , and only a minor negative shift of 40 mV detected in 0.1 M HClO4 , significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe-SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic-level insight into improving the activity and stability of non-noble metal ORR catalysts, opening up an avenue to craft the desired single-atom electrocatalysts.

Shear Stress Triggers Ultrathin-Nanosheet Carbon Nitride Assembly for Photocatalytic H2O2 Production Coupled with Selective Alcohol Oxidation

Coupled photocatalysis without cocatalysts can maximize the utilization of photons and atoms, which puts forward higher demands on photocatalysts. Polymeric carbon nitride (CN) has become the most promising photocatalyst, but still suffers from major drawbacks of insufficient catalytic sites and low quantum efficiency. Herein, we report a fluid shear stress-assisted molecular assembly to prepare ultrathin-nanosheet-assembled acanthosphere-like CN (ASCN) with nitrogen vacancy (Nv) and carbonyl modification. Shear stress breaks the stacking interactions between layers and cuts the stacked structure into ultrathin layers, which are further reassembled into acanthosphere bundles driven by "centrifugal force". Benefitted greatly from the ultrathin nature that provides more exposed active sites and improves charge carrier separation, ASCN-3 exhibits a 20-fold higher activity than the bulk counterpart toward oxygen reduction to H2O2 coupled with 4-methoxybenzyl alcohol (4-MBA) oxidation to anisaldehyde (AA), with significantly increased turnover frequency (TOF) values (TOF: 1.69 h-1 for H2O2 and 1.02 h-1 for AA). Significantly, ASCN-3 exhibits 95.8% conversion for 4-MBA oxidation with nearly 100% selectivity. High apparent quantum yields of 11.7% and 9.3% at 420 nm are achieved for H2O2 photosynthesis and 4-MBA oxidation. Mechanism studies suggest that carbonyl induces holes concentrated at the neighboring melem unit to directly oxidize the Cα-H bond of 4-MBA to produce carbon radicals, and Nv as oxygen adsorption active site traps electrons to form a superoxide radical that further combines with the shed protons into H2O2. This work presents a simple physical method to break the layered stack of CN for creating hierarchical assembly for coupled photocatalysis.

Regulation of Polymerization Kinetics to Improve Crystallinity of Carbon Nitride for Photocatalytic Reactions

Carbon nitride (CN) polymers exhibit tunable and fascinating physicochemical properties and are thus an essential class of photocatalytic materials with potential applications. Although significant progress has been made in the fabrication of CN, the preparation of metal-free crystalline CN via a straightforward method remains a considerable challenge. Herein, we describe a new attempt to synthesize crystalline carbon nitride (CCN) with a well-developed structure through regulation of the polymerization kinetics. The synthetic process involves the pre-polymerization of melamine to remove most of the ammonia and further calcination of the pre-heated melamine in the presence of copper oxide as an ammonia absorbent. Copper oxide can decompose the ammonia produced by the polymerization process, thereby promoting the reaction. These conditions facilitate the polycondensation process while avoiding carbonization of the polymeric backbone at high temperatures. Owing to the high crystallinity, nanosheet structure, and efficient charge-carrier transmission capacity, the as-prepared CCN catalyst shows much higher photocatalytic activity than its counterparts. Our study provides a novel strategy for the rational design and synthesis of high-performance carbon nitride photocatalysts by simultaneously optimizing polymerization kinetics and crystallographic structures.

TiO2/BP/g-C3N4 heterojunction photocatalyst for the enhanced photocatalytic degradation of RhB

The efficiency of graphite carbon nitride (g-C3N4, CN) as a photocatalyst is limited due to its quick recombination of photogenerated carriers and layer re-stacking. To enhance its photocatalytic activity, a multi-heterojunction photocatalyst was developed using TiO2 and black phosphorus (BP) coupled with CN through a liquid-phase ultrasonic method. The composite, TiO2/BP/CN, demonstrated a wider range of light response and higher photo-induced carrier separation efficiency. The presence of TiO2 nanoparticles on CN nanolayers reduced interlayer stacking and increased specific surface area, thereby providing more reactive sites. As a result, the optimized TiO2/BP/CN composite demonstrated enhanced photocatalytic efficiency for the degradation of Rhodamine B (RhB), with a first-order kinetic constant of 2.8, 4.3, and 6.4 times that of CN, TiO2, and BP, respectively. Active substance capture experiments confirmed that superoxide radical (·O2) was the primary reactive species. This study highlights the potential of the developed TiO2/BP/CN composite as a promising photocatalyst for environmental remediation applications.

Template-Free Synthesis of Phosphorus-Doped g-C3 N4 Micro-Tubes with Hierarchical Core-Shell Structure for High-Efficient Visible Light Responsive Catalysis

This work reports a new form of tubular g-C₃ N₄ that is featured with a hierarchical core-shell structure introduced with phosphorous elements and nitrogen vacancies. The core is self-arranged with randomly stacked g-C₃ N₄ ultra-thin nanosheets along the axial direction. This unique structure significantly benefits electron/hole separation and visible-light harvesting. A superior performance for the photodegradation of rhodamine B and tetracycline hydrochloride is demonstrated under low intensity visible light. This photocatalyst also exhibits an excellent hydrogen evolution rate (3631 µmol h^-1 g^-1 ) under visible light. Realizing this structure just requires the introduction of phytic acid into the solution of melamine and urea during hydrothermal treatment. In this complex system, phytic acid plays as the electron donor to stabilize melamine/cyanuric acid precursor via coordination interaction. Calcination at 550 °C directly renders the transformation of precursor into such hierarchical structure. This process is facile and shows the strong potential toward mass production for real applications.

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.

Boosting charge separation in graphdiyne quantum dots/hollow tubular carbon nitride heterojunction for water pollutant degradation

Non-desirable solar energy absorption and poor charge transfer efficiency are two problems that limit the peroxymonosulfate (PMS) photocatalytic techniques. Herein, a metal-free boron-doped graphdiyne quantum dot (BGDs) modified hollow tubular g-C₃N₄ photocatalyst (BGD/TCN) was synthesized to activate PMS and achieved effective space separation of carriers for degradation of bisphenol A. With 0.5 mM PMS, the degradation rate of bisphenol A (20 ppm) was 0.0634 min^-1, 3.7-fold higher than that of TCN itself. The roles of BGDs in the distribution of electrons and photocatalytic property were well identified by experiments and density functional theory (DFT) calculations. The possible degradation intermediate products of bisphenol A were monitored by mass spectrometer and demonstrated to be nontoxic using ecological structure activity relationship modeling (ECOSAR). Finally, this newly-designed material was successfully applied in actual water bodies, which further renders its promising prospect for actual water remediation.

Improved Plasmonic Hot-Electron Capture in Au Nanoparticle/Polymeric Carbon Nitride by Pt Single Atoms for Broad-Spectrum Photocatalytic H2 Evolution

Rationally designing broad-spectrum photocatalysts to harvest whole visible-light region photons and enhance solar energy conversion is a "holy grail" for researchers, but is still a challenging issue. Herein, based on the common polymeric carbon nitride (PCN), a hybrid co-catalysts system comprising plasmonic Au nanoparticles (NPs) and atomically dispersed Pt single atoms (PtSAs) with different functions was constructed to address this challenge. For the dual co-catalysts decorated PCN (PtSAs-Au2.5/PCN), the PCN is photoexcited to generate electrons under UV and short-wavelength visible light, and the synergetic Au NPs and PtSAs not only accelerate charge separation and transfer though Schottky junctions and metal-support bond but also act as the co-catalysts for H2 evolution. Furthermore, the Au NPs absorb long-wavelength visible light owing to its localized surface plasmon resonance, and the adjacent PtSAs trap the plasmonic hot-electrons for H2 evolution via direct electron transfer effect. Consequently, the PtSAs-Au2.5/PCN exhibits excellent broad-spectrum photocatalytic H2 evolution activity with the H2 evolution rate of 8.8 mmol g-1 h-1 at 420 nm and 264 μmol g-1 h-1 at 550 nm, much higher than that of Au2.5/PCN and PtSAs-PCN, respectively. This work provides a new strategy to design broad-spectrum photocatalysts for energy conversion reaction.

A Review of Phosphorus Structures as CO2 Reduction Photocatalysts

Effective photocatalytic carbon dioxide (CO₂ ) reduction into high-value-added chemicals is promising to mitigate current energy crisis and global warming issues. Finding effective photocatalysts is crucial for photocatalytic CO₂ reduction. Currently, metal-based semiconductors for photocatalytic CO₂ reduction have been well reviewed, while review of nonmetal-based semiconductors is almost limited to carbon nitrides. Phosphorus is a promising nonmetal photocatalysts with various allotropes and tunable band gaps, which has been demonstrated to be promising non-metallic photocatalysts. However, no systematic review about phosphorus structures for photocatalytic CO₂ reduction reactions has been reported. Herein, the progresses of phosphorus structures as photocatalysts for CO₂ reduction are reviewed. The fundamentals of photocatalytic CO₂ reduction, corresponding properties of phosphorus allotropes, photocatalysts with phosphorus doping or phosphorus-containing ligands, research progress of phosphorus allotropes as photocatalysts for CO₂ reduction have been reviewed in this paper. The future research and perspective of phosphorus structures for photocatalytic CO₂ reduction are also presented.

Effect of Functional Group Modifications on the Photocatalytic Performance of g-C3 N4

In recent years, photocatalysis has received increasing attention in alleviating energy scarcity and environmental treatment, and graphite carbon nitride (g-C₃ N₄ ) is used as an ideal photocatalyst. However, it still remains numerous challenges to obtain the desirable photocatalytic performance of intrinsic g-C₃ N₄ . Functional group functionalization, formed by introducing functional groups into the bulk structure, is one of the common modification techniques to modulate the carrier dynamics and increases the number of active sites, offering new opportunities to break the limits for structure-to-performance relationship of g-C₃ N₄ . Nevertheless, the general overview of the advance of functional group modification of g-C₃ N₄ is less reported yet. In order to better understand the structure-to-performance relationship at the molecular level, a review of the latest development of functional group modification is urgently needed. In this review, the functional group modification of g-C₃ N₄ in terms of structures, properties, and photocatalytic activity is mainly focused, as well as their mechanism of reaction from the molecular level insights is explained. Second, the recent progress of the application of introducing functional groups in g-C₃ N₄ is introduced and examples are given. Finally, the difficulties and challenges are presented, and based on this, an outlook on the future research development direction is shown.

Interfacial Chemical Bond Engineering in a Direct Z-Scheme g-C3N4/MoS2 Heterojunction

The Z-scheme heterojunction shows great potential in photocatalysis due to its superior carrier separation efficiency and strong photoredox properties. However, how to regulate the charge separation at the nanometric interface of heterostructures still remains a challenge. Here, we take g-C₃N₄ and MoS₂ as models and design the Mo-N chemical bond, which connects exactly the CB of MoS₂ and VB of g-C₃N₄. Thus, the Mo-N bond could act as an atomic-level interfacial "bridge" that provides a direct migration path of charge carriers between g-C₃N₄ and MoS₂. Experiments confirmed that the Mo-N bond and the internal electric field promote greatly the photogenerated carrier separation. The optimized photocatalyst exhibits a high hydrogen evolution rate that is about 19.6 times that of the pristine bulk C₃N₄. This study demonstrates the key role of an atomic-level interfacial chemical bond design in heterojunctions and provides a new idea for the design of efficient catalytic heterojunctions.

Chemical Etching and Phase Transformation of Nickel-Cobalt Prussian Blue Analogs for Improved Solar-Driven Water-Splitting Applications

Although Prussian blue and its analogs (PB/PBAs) have open framework structures, large surface areas, uniform metal active sites, and tunable compositions, and have been investigated for a long time, owing to their unfavorable visible light responsiveness, they rarely been reported in photocatalysis. This largely limits their applications in solar-to-chemical energy conversion. Here, a continuous-evolution strategy was conducted to convert the poor-performance NiCo PBA (NCP) toward high-efficiency complex photocatalytic nanomaterials. First, chemical etching was performed to transform raw NCP (NCP-0) to hollow-structured NCP (including NCP-30, and NCP-60) with enhanced diffusion, penetration, mass transmission of reaction species, and accessible surface area. Then, the resultant hollow NCP-60 frameworks were further converted into advanced functional nanomaterials including CoO/3NiO, NiCoP nanoparticles, and CoNi₂S₄ nanorods with a considerably improved photocatalytic H₂ evolution performance. The hollow-structured NCP-60 particles exhibit an enhanced H₂ evolution rate (1.28 mol g^-1h^-1) compared with the raw NCP-0 (0.64 mol g^-1h^-1). Furthermore, the H₂ evolution rate of the resulting NiCoP nanoparticles reached 16.6 mol g^-1h^-1, 25 times that of the NCP-0, without any cocatalysts.

Stable multifunctional aluminum phosphides at high pressures

Phosphides have been used in a wide range of applications due to their excellent optical, mechanical, and catalytic properties. Using an effective unbiased structure searching method combined with first-principles calculations, the phase diagram and physical and chemical properties of aluminum phosphides have been determined at high pressures. The results reveal that the unconventional stoichiometries of Al₂P, AlP₂, and AlP₃ remain stable above 66, 91, and 116 GPa, respectively. Interestingly, the analysis of the phonon spectrum suggests that AlP₂ with P2₁ symmetry can be dynamically stable at atmospheric pressure. In addition, the band gap of 1.51 eV at the HSE06 level and the estimated Vickers hardness of ∼10.54 GPa make P2₁-AlP₂ a hard photoelectric material. Moreover, our electronic properties show that AlP₃ with Immm symmetry and AlP₂ with I4/mmm structure are metallic at high pressures and further electron-phonon coupling calculations indicate Immm-AlP₃ and I4/mmm-AlP₂ are superconductors with estimated T_c values of 3.9 K at 150 GPa and 10.2 K at 100 GPa, respectively. Our work provides significant inputs toward understanding novel chemical bonding in aluminum phosphides and gives a direction for the experimental synthesis of multifunctional materials at high pressures.

Removing unreacted amino groups in graphitic carbon nitride through residual heating to improve the photocatalytic performance

In most of the research about graphitic carbon nitride (g-C₃N₄), g-C₃N₄ is prepared through the calcination of nitrogen-rich precursors. However, such a preparation method is time-consuming, and the photocatalytic performance of pristine g-C₃N₄ is lackluster due to the unreacted amino groups on the surface of g-C₃N₄. Therefore, a modified preparation method, calcination through residual heating, was developed to achieve rapid preparation and thermal exfoliation of g-C₃N₄ simultaneously. Compared with pristine g-C₃N₄, the samples prepared by residual heating had fewer residual amino groups, a thinner 2D structure, and higher crystallinity, which led to a better photocatalytic performance. The photocatalytic degradation rate of the optimal sample for rhodamine B could reach 7.8 times higher than that of pristine g-C₃N₄.