First-principles-driven catalyst design protocol of 2D/2D heterostructures for electro- and photocatalytic nitrogen reduction reaction

Ammonia synthesis from nitrogen is a vital process and a necessity in a variety of applications including energy, pharmaceutical, agricultural, and chemical applications. The electro- and photocatalytic nitrogen reduction reactions (NRRs) are promising sustainable processes operated under milder conditions than the conventional Haber-Bosch process. However, the main pain points of these catalytic processes are their low selectivity and low efficiency. This perspective presents the recent status and the design protocols for developing promising 2D/2D heterojunction catalysts for the NRR, using the first-principles approach. The current theoretical studies are briefly discussed, and available methods are suggested for the development and design of new potential 2D/2D heterojunctions as efficient electro- and photo-NRR catalysts.

Semiconductor photocatalysts: A critical review highlighting the various strategies to boost the photocatalytic performances for diverse applications

The photocatalytic technology illustrates an eco-friendly and sustainable route to overcome environmental and energy issues. The successful construction of a photocatalyst depends on four key elements: light absorption ability, the density of active sites, redox capacity, and photoinduced electron-hole recombination rate. Sincemost of intrinsic semiconductor photocatalysts cannot meet all these requirements, they are often modified to boost their photocatalytic properties. Many strategies have been adopted to design novel and efficient photocatalysts for diverse applications. Herein, we review the most efficient of these strategies and methods focused on effectively overcoming the efficiency limitations of photocatalysts to promote their large-scale application. Subsequently, a particular aim is put on the most current studies for photocatalytic applications, including CO₂ reduction, N₂ fixation, H₂ evolution, and pollutants degradation. Finally, key challenges and future perspectives in designing and implementing semiconductor photocatalysts for large-scale applications are discussed. Therefore, it is foreseen that this review will work as a guide for future research and provides a variety of strategies to develop novel and high-performance photocatalysts for various applications.

Synergistic catalysis of ozonation and photooxidation by sandwich structured MnO2-NH2/GO/p-C3N4 on cephalexin degradation

Antibiotics such as cephalexin (CLX) are often detected in water and sewage, and advanced oxidation processes (AOPs) are usually the most effective method to degrade them. Currently, the synergy of AOPs has raised lively interest in water and wastewater treatment. Here the sandwiched catalyst of MnO₂-NH₂/GO/p-C₃N₄ (MN/GO/CN) is synthesized, in which graphene oxide (GO) acts as "core layer" connecting aminated MnO₂ (MnO₂-NH₂) for catalytic ozonation and proton-functionalized g-C₃N₄ (p-C₃N₄) for photocatalysis. The MN/GO/CN combines the AOPs of catalytic ozonation and photocatalysis, initiates hydroxyl radicals 4.2 times the sum of catalytic ozonation and photocatalysis, and achieves the first order kinetics constant of 2.4 × 10^-2/s, which is 2.7, 8.1 and 20.1 times that of catalytic ozonation, photo ozonation, and photocatalysis, respectively, and consequently reduces CLX from 1.0 mg/L to below the detection limit within 2.5 min, demonstrating the strong synergism between the AOPs. The sandwich structure enables GO to mediate the electron transfer between p-C₃N₄ and MnO₂-NH₂, which not only hinders electron-hole recombination on p-C₃N₄, but also speeds redox electron cycle on MnO₂ to promote the catalytic activity. The simultaneous catalytic ozonation and photocatalysis by sandwiched bifunctional catalyst to obtain synergistic effect will find its broad prospect in water and wastewater treatment.

Recent Advances in Application of Graphitic Carbon Nitride-Based Catalysts for Photocatalytic Nitrogen Fixation

Ammonia, the second most-produced chemical, is widely used in agricultural and industrial applications. However, traditional industrial ammonia production dominated by the Haber-Bosch process presents huge resource and environment issues due to the massive energy consumption and CO₂ emission. The newly emerged nitrogen fixation technology, photocatalytic N₂ reduction reaction (p-NRR), uses clean solar energy with zero-emission, holding great prospect to achieve sustainable ammonia synthesis. Although great efforts are made, the p-NRR catalysts still suffer from poor N₂ adsorption and activation, inferior light absorption, and fast recombination of photocarriers. Due to the tunable electronic structure of the metal-free polymeric graphitic carbon nitride (g-C₃ N₄ ), the above-mentioned issues can be significantly alleviated, making it the most promising p-NRR photocatalyst. This review summarizes the recent development of g-C₃ N₄ -based catalysts for p-NRR, including the working principle of p-NRR catalysts, the challenges of developing p-NRR catalysts, and corresponding solutions. Particularly, the roles of defect engineering and heterojunction construction on g-C₃ N₄ to the enhancement of photocatalytic performances are emphasized. In addition, computational studies are introduced to deepen the understanding of reaction pathways. At last, perspectives are provided on the development of p-NRR catalysts.

Recent advances and challenges in 2D/2D heterojunction photocatalysts for solar fuels applications

Although photocatalytic technology has emerged as an effective means of alleviating the projected future fuel crisis by converting sunlight directly into chemical energy, no visible-light-driven, low-cost, and highly stable photocatalyst has been developed to date. Due to considerably higher interfacial contact with numerous reactive sites, effective charge transmission and separation ability, and strong redox potentials, the focus has now shifted to 2D/2D heterojunction systems, which have exhibited effective photocatalytic performance. The fundamentals of 2D/2D photocatalysis for different applications and the classification of 2D/2D materials are first explained in this paper, followed by strategies to improve the photocatalytic performance of various 2D/2D heterojunction systems. Following that, current breakthroughs in 2D/2D metal-based and metal-free heterojunction photocatalysts, as well as their applications for H₂ evolution via water splitting, CO₂ reduction, and N₂ fixation, are discussed. Finally, a brief overview of current constraints and predicted results for 2D/2D heterojunction systems is also presented. This paper lays out a strategy for developing efficient 2D/2D heterojunction photocatalysts and sophisticated technology for solar fuel applications in order to address the energy issue.

Recent developments in architecturing the g-C3N4 based nanostructured photocatalysts: Synthesis, modifications and applications in water treatment

Water pollution is becoming an inevitable problem in today's world. Tons and tons of wastewater with hazardous pollutants are getting discharged into the clean water bodies every day. In this regard, photocatalytic environmental remediation using nanotechnology such as the use of organic, metal and non-metal based semiconductor photocatalysts for photodegradation of pollutants has gained enormous attention in the past few decades. This review is focused particularly on graphitic carbon nitride (g-C₃N₄) which is a cheap, metal-free, polymeric photoactive compound and it is used as a potential photocatalyst in wastewater treatment. Though, pristine g-C₃N₄ is a good photocatalyst, it has certain drawbacks such as poor visible light absorption capacity, quicker recombination of photoelectrons and holes, delayed mass and charge transfer, etc. As a result, the pristine g-C₃N₄ catalyst is modified into novel 0D, 1D, 2D and 3D morphologies such as nano-quantum dots, nanorods, nanotubes, nanowires, nanosheets, nanoflakes, nanospheres, nanoshells, etc. It was also tailored into novel composites along with various compounds through doping, metal deposition, heterojunction formation, etc., to enhance the photocatalytic property of pure g-C₃N₄. The modified catalysts showed promising photocatalytic performance such as degradation of majority of pollutants in the environment. It also showed excellent results in the removal or reduction of heavy metals. This review provides a detailed record of g-C₃N₄ and its diverse photocatalytic applications in the past years and it provides knowledge for the development of such similar novel compounds in the future.

Self-assembly hybridization of COFs and g-C3N4: Decipher the charge transfer channel for enhanced photocatalytic activity

Organic semiconductors have been recognized as a new generation of photocatalysts for pollutants degradation and energy production. Herein, organic heterojunction (TpMa/CN) consisting of carbon nitride and β-ketoenamine-based covalent organic framework is fabricated via a controllable self-assembly approach. The as-prepared TpMa/CN heterojunctions show enlarged visible-light absorption. The optimum TpMa/CN-5 photocatalyst achieves the highest photocatalytic activity towards tetracycline degradation, and its photocatalytic degradation rate is improved by 2.3 and 4.3 times than TpMa and CN, respectively. As a multifunctional photocatalyst, TpMa/CN-5 sample also shows remarkable photocatalytic activity for hydrogen peroxide production (880.494 μM h^-1), which is 49 times higher than that of CN. Experimental and theoretical investigations indicate that a built-in electric field is formed at the interface of composite, which enables an accelerated charge transfer and separation. This work develops an effective strategy to design difunctional photocatalyst and deciphers the electronic properties and mechanisms of g-C₃N₄-based organic photocatalysts, which spurs further interests for organic heterojunction photocatalysts in the future.

Self-Assembled Silver Nanoparticles Decorated on Exfoliated Graphitic Carbon Nitride/Carbon Sphere Nanocomposites as a Novel Catalyst for Catalytic Reduction of Cr(VI) to Cr(III) from Wastewater and Reuse for Photocatalytic Applications

Silver nanoparticles decorated on an exfoliated graphitic carbon nitride/carbon sphere (AgNP/Eg-C₃N₄/CS) nanocomposites were synthesized by an adsorption method with a self-assembled process. These nanoparticles were characterized by different techniques like UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Raman spectroscopy, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), electrochemical impedance spectroscopy (EIS), and ζ potential. AgNP/Eg-C₃N₄/CS nanocomposites showed a higher catalytic reduction activity for the conversion of Cr(VI) into Cr(III) with formic acid (FA) at 45 °C when compared to bulk graphitic carbon nitride (Bg-C₃N₄, Eg-C₃N₄, CS, and Eg-C₃N₄/CS). The kinetic rate constants were determined as a function of catalyst dosage, concentration of Cr(VI), pH, and temperature for the AgNP/Eg-C₃N₄/CS nanocomposite. This material showed higher reduction efficiency (98.5%, k = 0.0621 min^-1) with turnover frequency (0.0158 min^-1) for the reduction of Cr(VI) to Cr(III). It also showed great selectivity and high stability after six repeated cycles (98.5%). Further, the reusability of the Cr(III)-AgNP/Eg-C₃N₄/CS nanocomposite was also investigated for the photocatalytic degradation of methylene blue (MB) under visible light irradiation with various time intervals and it showed good degradation efficiency (α = 97.95%). From these results, the AgNP/Eg-C₃N₄/CS nanocomposite demonstrated higher catalytic activity, improved environmental friendliness, lower cost for the conversion of toxic Cr(VI) to Cr(III) in solutions, and also good reusability.

A Comparative Study of the Effect of Graphene Oxide, Graphitic Carbon Nitride, and Their Composite on the Photocatalytic Activity of Cu3SnS4

Photocatalysis has shown high potential in dealing with the ever-broadening problem of wastewater treatment, escalated by the increasing level of recalcitrant chemicals often referred to as emerging contaminants. In this study, the effect of support material on the photocatalytic activity of copper tin sulfide (Cu3SnS4) nanoparticles for the degradation of tetracycline as an emerging contaminant is presented. Graphene oxide, protonated graphitic carbon nitride, and a composite of graphitic carbon nitride and graphene oxide were explored as support materials for Cu3SnS4 nanoparticles. The nanoparticles were incorporated with the different carbonaceous substrates to afford graphene-supported Cu3SnS4 (GO-CTS), protonated graphitic carbon nitride-supported Cu3SnS4 (PCN-CTS), and graphene oxide/protonated graphitic carbon nitride-supported Cu3SnS4 (GO/PCN-CTS). Physicochemical, structural, and optical properties of the prepared nanocomposites were characterized using techniques such as Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis near infrared, and fluorescence spectrophotometry. The compositing of the Cu3SnS4 nanoparticles on the support materials was confirmed by the characterization techniques, and the optical properties of the composites were found to be influenced by the nature of the support material. The incorporation of CTS into the support materials resulted in a reduction in band gap energy with evaluated band gaps of 1.65, 1.46, 1.43 eV, and 1.16 eV. The reduction in band gap energy suggests the potential of the composites for enhanced photocatalytic activity. From the photocatalytic study, the degradation efficiency of tetracycline by CTS, PCN-CTS, GO-CTS, and PC/GO-CTS was 74.1, 85.2, 90.9, and 96.5%, respectively. All the composites showed enhanced activity compared to pristine CTS, and the existence of a synergy between GO and PCN when both were employed as support materials was observed. Based on the charge carrier recombination characteristics and the band edge potential calculations from the composites, a possible mechanism of action of each composite was proposed. This study therefore confirms the possibility of modulating the mechanism of action and subsequently the efficiency of semiconductor materials by altering the nature of the support material.

Emerging Materials and Methods toward Ammonia-Based Energy Storage and Conversion

Efficient storage and conversion of renewable energies is of critical importance to the sustainable growth of human society. With its distinguishing features of high hydrogen content, high energy density, facile storage/transportation, and zero-carbon emission, ammonia has been recently considered as a promising energy carrier for long-term and large-scale energy storage. Under this scenario, the synthesis, storage, and utilization of ammonia are key components for the implementation of ammonia-mediated energy system. Being different from fossil fuels, renewable energies normally have intermittent and variable nature, and thus pose demands on the improvement of existing technologies and simultaneously the development of alternative methods and materials for ammonia synthesis and storage. The energy release from ammonia in an efficient manner, on the other hand, is vital to achieve a sustainable energy supply and complete the nitrogen circle. Herein, recent advances in the thermal-, electro-, plasma-, and photocatalytic ammonia synthesis, ammonia storage or separation, ammonia thermal/electrochemical decomposition and conversion are summarized with the emphasis on the latest developments of new methods and materials (catalysts, electrodes, and sorbents) for these processes. The challenges and potential solutions are discussed.

A Comprehensive Review on the Recent Development of Ammonia as a Renewable Energy Carrier

Global energy sources are being transformed from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind, solar and hydrogen. The biggest challenge with hydrogen as a renewable energy carrier is the storage and delivery system’s complexity. Therefore, other media such as ammonia for indirect storage are now being considered. Research has shown that at reasonable pressures, ammonia is easily contained as a liquid. In this form, energy density is approximately half of that of gasoline and ten times more than batteries. Ammonia can provide effective storage of renewable energy through its existing storage and distribution network. In this article, we aimed to analyse the previous studies and the current research on the preparation of ammonia as a next-generation renewable energy carrier. The study focuses on technical advances emerging in ammonia synthesis technologies, such as photocatalysis, electrocatalysis and plasmacatalysis. Ammonia is now also strongly regarded as fuel in the transport, industrial and power sectors and is relatively more versatile in reducing CO2 emissions. Therefore, the utilisation of ammonia as a renewable energy carrier plays a significant role in reducing GHG emissions. Finally, the simplicity of ammonia processing, transport and use makes it an appealing choice for the link between the development of renewable energy and demand.

Surface chemistry-dependent activity and comparative investigation on the enhanced photocatalytic performance of graphitic carbon nitride modified with various nanocarbons

Organic contaminants, dyes and antibiotics, discharged in wastewater systems, have posed great threats to the sustainability of the ecosystem. This study was performed to prepare graphitic carbon nitride (GCN) nanocomposites modified by nanocarbons, including carbon quantum dots (CQD), carbon nanotube (CNT), reduced graphene oxide (rGO), and carbon nanospheres (CNS), by a straightforward one-pot method. The characterization results suggest that after the modification with nanocarbons, GCN demonstrated slight red shift and stronger light absorption. The resultant photocatalysts revealed prominent performances for total photodegradation of organic contaminants. The degradation processes were investigated by in situ electron paramagnetic resonance (EPR). The mechanistic studies on the enhanced photoelectrochemical and photocatalytic performances were also conducted. Results indicate that GCN modified by the nanocarbon spheres displayed a substantial improvement in the degradation of sulfachloropyridazine (SCP) and dyes, compared favourably with other GCN samples modified by carbon nanotubes, quantum dots and layered graphene oxide. The photocatalytic degradation difference is mainly stemmed from the higher contents of COOH and CO functional groups. The intimate contact or interaction between the two phases of GCN and nanocarbon in the nanocomposites may further improve the activity. This work provides insight in the design of highly efficient metal-free photocatalysts to better utilise the clean and free solar energy for environmental remediation.

Facile photo-ultrasonic assisted synthesis of flower-like Pt/N-MoS2 microsphere as an efficient sonophotocatalyst for nitrogen fixation

Semiconductor photocatalytic technology is a sustainable and less energy consuming one for nitrogen (N₂) reduction to produce ammonia (NH₃). In this study, flower-like hierarchical N doped MoS₂ (N-MoS₂) microsphere was synthesized as a photocatalyst by one-step solvothermal method, which was assembled by numerous interleaving nanosheets petals with thin thickness. Besides, Pt nanoparticles were loaded on the surface of N-MoS₂ via photo-ultrasonic reduction method. The as-prepared Pt/N-MoS₂ photocatalyst exhibited higher N₂ fixation ability than that over pure MoS₂ and N-MoS₂, which can be attributed to that the N doping narrows the band gap, and the Schottky barrier due to the existence of Pt nanoparticles improves the charge transfer and carrier separation. The reduction of N₂ with ultrasonic irradiation was also investigated under visible light irradiation to evaluate the sonophotocatalytic activity of the Pt/N-MoS₂ microsphere. The results showed that the N₂ reduction rate of sonophotocatalysis (133.8 µmol/g_(cat)h) was higher than that of sonocatalysis and photocatalysis, which can be ascribed to the synergistic effect of ultrasound and visible light irradiation. The effects of catalyst dosage, ultrasonic power and ultrasonic pulse on the photocatalytic efficiency were also studied. Meanwhile, a possible mechanism for improved sonophotocatalytic performance was also proposed.

Few-Layer Black Phosphorus Nanosheets: A Metal-Free Cocatalyst for Photocatalytic Nitrogen Fixation

Exploiting an appropriate strategy to prepare fine crystal quality black phosphorus nanosheet (BPNS) catalyst is a major challenge for its practical application in catalysis. Herein, we address this challenge by developing a rapid electrochemical expansion strategy for scale preparation of fine crystal quality BPNSs from bulk black phosphorus, which was demonstrated to be an active cocatalyst for photocatalytic nitrogen fixation in the presence of CdS as a photocatalyst. The transient photocurrent and charge density studies show that the BPNSs can efficiently accelerate charge separation of CdS, leading to the enhanced photocatalytic activities of BPNS/CdS nanocomposites for nitrogen fixation. The 1.5% BPNS/CdS photocatalyst exhibits the highest photocatalytic activity for nitrogen fixation with an NH₃ evolution rate of 57.64 μmol·L^-1·h^-1. This study not only affords a rapid and simple strategy for scale synthesis of fine crystal quality BPNSs but also provides new insights into the design and development of black phosphorus-based materials as low-cost metal-free cocatalysts for photocatalytic nitrogen fixation.

Nitrogen-doped Carbon Nanospheres-Modified Graphitic Carbon Nitride with Outstanding Photocatalytic Activity

Metals and metal oxides are widely used as photo/electro-catalysts for environmental remediation. However, there are many issues related to these metal-based catalysts for practical applications, such as high cost and detrimental environmental impact due to metal leaching. Carbon-based catalysts have the potential to overcome these limitations. In this study, monodisperse nitrogen-doped carbon nanospheres (NCs) were synthesized and loaded onto graphitic carbon nitride (g-C₃N₄, GCN) via a facile hydrothermal method for photocatalytic removal of sulfachloropyridazine (SCP). The prepared metal-free GCN-NC exhibited remarkably enhanced efficiency in SCP degradation. The nitrogen content in NC critically influences the physicochemical properties and performances of the resultant hybrids. The optimum nitrogen doping concentration was identified at 6.0 wt%. The SCP removal rates can be improved by a factor of 4.7 and 3.2, under UV and visible lights, by the GCN-NC composite due to the enhanced charge mobility and visible light harvesting. The mechanism of the improved photocatalytic performance and band structure alternation were further investigated by density functional theory (DFT) calculations. The DFT results confirm the high capability of the GCN-NC hybrids to activate the electron-hole pairs by reducing the band gap energy and efficiently separating electron/hole pairs. Superoxide and hydroxyl radicals are subsequently produced, leading to the efficient SCP removal.

An overview of photocatalysis facilitated by 2D heterojunctions

Two-dimensional (2D) photocatalysts have attracted considerable research interest in the past decades due to their unique optical, physical and chemical properties. Constructing 2D/2D heterojunctions with large interface area has been considered as an effective approach to enhance the transfer rate and the separation efficiency of the charge carriers, leading to dramatic increase in the photocatalytic performance of the photocatalysts. Here, the state-of-the-art progress on heterojunctions based on 2D materials is reviewed, including the photocatalysis principles using 2D heterojunctions, the categories of 2D heterojunctions and their application in different photocatalytic reactions, and the theoretical studies of the 2D heterojunctions. Moreover, the advantages and disadvantages of the 2D heterojunctions are also discussed. Finally, the ongoing challenges and opportunities for the future development of 2D photocatalysts with built-in heterojunctions are proposed.

Efficient Nitrogen Fixation Catalyzed by Gallium Nitride Nanowire Using Nitrogen and Water

Ammonia is one of the most important bulk chemicals in modern society. However, the highly energy-extensive contemporary industrial production of ammonia was developed in the early 20th century and requires extensive heating of highly pressurized flammable hydrogen gas, whose global production still relies heavily on non-sustainable petroleum. The development of "sustainable" nitrogen fixation process represents a grand aspirational chemical pursuit concerning our future human well-being. Herein, we report an ultra-stable nitride-based photosensitizing semiconductor that enables efficient, sustainable, and mild photochemical nitrogen fixation. The catalyst exhibits strong chemisorption of nitrogen and enables immediate electron donation from its surface vacancy to nitrogen. In addition, it was also demonstrated that the nitride-based semiconductor possesses the potential to minimize electron-hole recombination.

Carbon Nanomaterials for Energy and Biorelated Catalysis: Recent Advances and Looking Forward

Along with the wide investigation activities in developing carbon-based, metal-free catalysts to replace precious metal (e.g., Pt) catalysts for various green energy devices, carbon nanomaterials have also shown great potential for biorelated applications. This article provides a focused, critical review on the recent advances in these emerging research areas. The structure-property relationship and mechanistic understanding of recently developed carbon-based, metal-free catalysts for chemical/biocatalytic reactions will be discussed along with the challenges and perspectives in this exciting field, providing a look forward for the rational design and fabrication of new carbon-based, metal-free catalysts with high activities, remarkable selectivity, and outstanding durability for various energy-related/biocatalytic processes.

One-pot fabrication of a double Z-scheme CeCO3OH/g-C3N4/CeO2 photocatalyst for nitrogen fixation under solar irradiation

A ternary photocatalyst CeCO₃OH/g-C₃N₄/CeO₂ was synthesized by an in situ self-sacrificing method, and its N₂ photofixation performance was investigated.

Research on the techniques of ultrasound-assisted liquid-phase peeling, thermal oxidation peeling and acid-base chemical peeling for ultra-thin graphite carbon nitride nanosheets

Graphite phase carbon nitride (g-C₃N₄) composite structure materials, as a kind of stable compound with graphite-like structure, has attracted more and more attention due to its excellent properties, such as being able to absorb solar energy, stable chemical and optical properties and having a suitable oxidation potential. However, its application in the field of photocatalysis is limited by its small specific surface area and poor dispersibility. To solve this problem, ultra-thin g-C₃N₄ nanosheets are often prepared using peeling methods. In this paper, the current status and mechanism of thermal oxidation peeling, ultrasound-assisted liquid-phase peeling and acid-base chemical peeling are reviewed in detail. In addition, the future research directions of ultra-thin graphite-like carbon nitride nanosheets are discussed.

New opportunities for efficient N2 fixation by nanosheet photocatalysts

Catalytic ammonia synthesis from dinitrogen (N2) under mild conditions has been considered to be the "holy grail" of N2 fixation, which is one of the most important chemical processes in the agriculture, biological and industrial fields. Given that current artificial N2 fixation is still dominated by the energy-intensive Haber-Bosch process, solar N2 fixation represents an encouraging and fascinating route for carbon-free and energy-saving N2 fixation. However, its practical application is seriously hampered by surface sluggish reaction kinetics. In this minireview, we share our perspectives on the use of two-dimensional (2D) nanosheets for the manipulation of photocatalytic N2 fixation. Nanosheet photocatalysts serve as the perfect platform for the engineering of surface active sites, including defects and iron, all of which can not only bolster photon-exciton interaction toward robust charge carriers generation upon light absorption, but also mimic the function schemes of MoFe-cofactor in nitrogenase toward sufficient N2 binding and activation. These merits endowed by nanosheets photocatalysts provide instructive information on exploring the rich nitrogen photochemistry on solid surfaces and offer new opportunities for the design of novel photocatalysts towards efficient N2 fixation.

Creating Graphitic Carbon Nitride Based Donor-π-Acceptor-π-Donor Structured Catalysts for Highly Photocatalytic Hydrogen Evolution

Conjugated polymers with tailored donor-acceptor units have recently attracted considerable attention in organic photovoltaic devices due to the controlled optical bandgap and retained favorable separation of charge carriers. Inspired by these advantages, an effective strategy is presented to solve the main obstructions of graphitic carbon nitride (g-C₃ N₄ ) photocatalyst for solar energy conversion, that is, inefficient visible light response and insufficient separation of photogenerated electrons and holes. Donor-π-acceptor-π-donor polymers are prepared by incorporating 4,4'-(benzoc 1,2,5 thiadiazole-4,7-diyl) dianiline (BD) into the g-C₃ N₄ framework (UCN-BD). Benefiting from the visible light band tail caused by the extended π conjugation, UCN-BD possesses expanded visible light absorption range. More importantly, the BD monomer also acts as an electron acceptor, which endows UCN-BD with a high degree of intramolecular charge transfer. With this unique molecular structure, the optimized UCN-BD sample exhibits a superior performance for photocatalytic hydrogen evolution upon visible light illumination (3428 µmol h^-1 g^-1 ), which is nearly six times of that of the pristine g-C₃ N₄ . In addition, the photocatalytic property remains stable for six cycles in 3 d. This work provides an insight into the synthesis of g-C₃ N₄ -based D-π-A-π-D systems with highly visible light response and long lifetime of intramolecular charge carriers for solar fuel production.

Controllable synthesis of graphitic carbon nitride nanomaterials for solar energy conversion and environmental remediation: the road travelled and the way forward

This review discusses advances in the synthesis and design of g-C₃N₄-based nanomaterials and their various photocatalytic and photoredox applications.

2D Hybrid Nanomaterials for Selective Detection of NO2 and SO2 Using "Light On and Off" Strategy

In order to distinguish NO₂ and SO₂ gas with one sensor, we designed a paper chip assembled with a 2D g-C₃N₄/rGO stacking hybrid fabricated via a layer-by-layer self-assembly approach. The g-C₃N₄/rGO hybrid exhibited a remarkable photoelectric property due to the construction of a van der Waals heterostructure. For the first time, we have been able to selectively detect NO₂ and SO₂ gas using a "light on and off" strategy. Under the "light off" condition, the g-C₃N₄/rGO sensor exhibited a p-type semiconducting behavior with a low detection limit of 100 ppb of NO₂, but with no response toward SO₂. In contrast, the sensor showed n-type semiconducting behavior which could detect SO₂ at concentration as low as 2 ppm under UV light irradiation. The effective electron transfer among the 2D structure of g-C₃N₄ and rGO nanosheets as well as highly porous structures could play an important role in gas sensing. The different sensing mechanisms at "light on and off" circumstances were also investigated in detail.

Molecular Design of Polymer Heterojunctions for Efficient Solar-Hydrogen Conversion

Semiconducting photocatalytic solar-hydrogen conversion (SHC) from water is a great challenge for renewable fuel production. Organic semiconductors hold great promise for SHC in an economical and environmentally benign manner. However, organic semiconductors available for SHC are scarce and less efficient than most inorganic ones, largely due to their intrinsic Frenkel excitons with high binding energy. In this study the authors report polymer heterojunction (PHJ) photocatalysts consisting of polyfluorene family polymers and graphitic carbon nitride (g-C₃ N₄ ) for efficient SHC. A molecular design strategy is executed to further promote the exciton dissociation or light harvesting ability of these PHJs via alternative approaches. It is revealed that copolymerizing electron-donating carbazole unit into the poly(9,9-dioctylfluorene) backbone promotes exciton dissociation within the poly(N-decanyl-2,7-carbazole-alt-9,9-dioctylfluorene) (PCzF)/g-C₃ N₄ PHJ, achieving an enhanced apparent quantum yield (AQY) of 27% at 440 nm over PCzF/g-C₃ N₄ . Alternatively, copolymerizing electron-accepting benzothiadiazole unit extended the visible light response of the obtained poly(9,9-dioctylfluorene-alt-benzothiadiazole)/g-C₃ N₄ PHJ, leading to an AQY of 13% at 500 nm. The present study highlights that constructing PHJs and adapting a rational molecular design of PHJs are effective strategies to exploit more of the potential of organic semiconductors for efficient solar energy conversion.

Controllable TiO2 heterostructure with carbon hybrid materials for enhanced photoelectrochemical performance

A TiO₂/RGO/C₃N₄ heterostructure has been successfully designed and fabricated, and the narrow bandgap and conductivity of RGO and C₃N₄ could be beneficial for the generation and separation of photocharges.

Preparation of an ultrathin 2D/2D rGO/g-C3N4 nanocomposite with enhanced visible-light-driven photocatalytic performance

An ultrathin 2D/2D rGO/g-C₃N₄ nanocomposite was constructed using thermally exfoliated g-C₃N₄ nanosheets and graphene oxide (GO) as precursors by a simple solvent method.