Rejoint of Carbon Nitride Fragments into Multi-Interfacial Order-Disorder Homojunction for Robust Photo-Driven Generation of H2 O2

Facile preparation of a 3D rGO/g-C3N4 nanocomposite loaded with Ag NPs for photocatalytic degradation

Graphene-based and g-C3N4-based nanocomposites can effectively remove organic pollutants from water. However, the reasonable design and scale preparation of hybrid nanomaterials of reduced graphene oxide (rGO), g-C3N4 and silver nanoparticles (Ag NPs) with improved performance for practical application need to be further explored. Herein, a 3D rGO/g-C3N4 nanocomposite loaded with Ag NPs was successfully fabricated through a facile three-step synthetic route. The microstructure and morphology of GO, g-C3N4, rGO/g-C3N4 and rGO/g-C3N4 nanocomposite loaded with Ag NPs were characterized and analyzed. The experimental results show that the as-prepared nanocomposite loaded with Ag NPs has excellent activity to remove methylene blue (MB) from water under visible light irradiation, and its maximum removal capacity is high as 49.60 mg g-1 within 60 min. Based on its possible catalytic process and kinetic analysis, the adsorption and catalytic performance of this nanocomposite may be attributed to a synergistic effect of rGO, g-C3N4 and Ag NPs. In addition, it can provide a useful reference for the rational design and scale preparation of rGO/g-C3N4 nanocomposite for practical applications.

Single-electron effects regulate the electronic structure of carbon nitride to enhance photocatalytic hydrogen peroxide generation and pollutant degradation performance

Photocatalysis technology can convert H2O and O2 into H2O2 by using solar energy; however, the efficiency of photocatalytic H2O2 production is limited by the high electron-hole recombination rate, poor oxygen reduction ability, and weak O2 adsorption capacity. Herein, we construct a phosphorus (P)-doped graphitic carbon nitride (g-C3N4, i.e., CN) photocatalyst, denoted as P-CN, by adjusting the bandgap and electronic structure of CN to improve its charge distribution, increase its separation efficiency for photogenerated carriers, and enhance its oxygen reduction ability. In addition, P doping forms two lone pairs of electrons on the CN surface, considerably enhancing the adsorption and activation of O2, thereby synergistically facilitating the photocatalytic production of H2O2. Results demonstrate that the H2O2 yield of 7.5 % P-CN can reach 719.68 µmol·L-1, which is 2.2 times that of CN. Considering the reaction pathway, intermediate structure of H2O2 production, and density functional theory (DFT) results, the mechanism of the single electron effects to improve O2 adsorption as well as H2O2 yield was proposed. In addition, the single-electron effect caused by P doping facilitates both the degradation activity of CN and efficiency there for hydrogen production, which provides new ideas for designing and regulating the electronic structure of catalysts and improving their reaction performance.

Regulation of the Endocytosis System Using Ultrathin g-C3N4 Nanosheets for Enhanced Photodynamic Therapy of Glioma

Glioma is the most aggressive form of brain cancer. Photodynamic therapy (PDT) has emerged as a promising treatment method for glioma; however, its efficacy is often hindered by the blood-brain barrier (BBB) and the need for precise tumor cell targeting. In the present study, a facile strategy is found to enhance the penetration of the BBB and the internalization efficiency by exfoliating the (100) crystal plane of g-C3N4 (CN) using liquid nitrogen, resulting in ultrathin graphitic carbon nitride (CN12) nanosheets with hydroxyl-rich surfaces. These CN12 nanosheets significantly enhanced the permeability of the BBB, increased the endocytosis efficiency by four times, and elevated reactive oxygen species (ROS) in vivo by 2.5 times. The as-formed CN12 nanosheets successfully targeted the mitochondrial function of tumor cells, promoted ROS generation, and induced apoptosis. Moreover, the combination of CN12 nanosheets with photoelectrode implantation completely eradicated tumors within 10 d without recurrence or severe side effects.

The Direct Air Synthesis of Hydrogen Peroxide Induced by The Giant Built-In Electric Field of Trz-CN

Graphitic carbon nitride (C3N4) has been identified as an optimal material for hydrogen peroxide (H2O2) photosynthesis, although its utility is hampered by a high photocarrier recombination rate. Herein, a novel carbon nitride material with a giant built-in electric field (BEF), Trz-CN, is synthesized through a hydrothermal-calcination tandem strategy. The giant BEF (4.8-fold) induced by the large dipole moment facilitated the efficient separation and directional migration of photogenerated carriers. Trz-CN exhibited an H2O2 production rate of 569.9 µmol·g-1·h-1 using O2 as feedstock under visible light (λ > 420 nm), marking an impressive 11.2-fold enhancement compared to bulk C3N4. Utilizing air instead of pure O2 as feedstock resulted in a trivial 1.6% decrease in the H2O2 generation by Trz-CN while maintaining a substantial production rate of 560.6 µmol·g-1·h-1. Notably, Trz-CN showcased a sterilization rate of 99.9% against Escherichia coli (E. coli) in natural seawater. Density functional theory (DFT) calculations revealed that incorporating a nitrogen-rich skeleton into the C3N4 enhanced its oxygen adsorption capacity and lowered the energy barrier for H2O2 formation. This leads to enhanced photocatalytic performance for H2O2 generation under ambient air conditions. Trz-CN provides a new exploratory idea for direct air synthesis of H2O2 and ballast water treatment.

Dynamic in-situ reconstruction of active site circulators for photo-Fenton-like reactions

Developing efficient and stable heterogeneous catalysts for the continuous activation of oxidants is crucial to mitigating the global water resource crisis. Guided by computational predictions, this research achieved this goal through the synthesis of a modified graphitic carbon nitride with enhanced catalytic activity and stability. Its intrinsic activity was further amplified by dynamic in-situ reconstruction using the I-/I3- redox mediator system during photoreactions. Impressively, this reconstructed catalyst demonstrated the capability for at least 30 regeneration cycles while maintaining high purification efficacy. The mechanism underlying the in-situ reconstruction of active sites for periodate functionalization was elucidated through theoretical calculations, coupled with semi-in-situ X-ray photoelectron spectroscopy (XPS) and electrochemical analyses. The system's capacity to detoxify recalcitrant pollutants was demonstrated through successful Escherichia coli cultivation and Zebrafish embryo experiments. The economic feasibility and environmental impacts are quantitatively assessed by the Electrical Energy per Order (EE/O) metric and Life Cycle Assessment (LCA), confirming the system's scalability and applicability in real-world scenarios. This dual-site constrained interlayer insertion, and controllable in-situ catalyst reconstruction achieve durable robustness of the photocatalyst, paving the way for the development of sustainable catalytic water purification technologies.

Benzene Ring Engineering of Graphitic Carbon Nitride for Enhanced Photocatalytic Dye Degradation and Hydrogen Production from Water Splitting

The photocatalytic activity of graphitic carbon nitride (g-C3N4) strongly depends on its electronic structure. To design the photocatalysts with efficient charge separation and transfer property, here a benzene ring-doped g-C3N4 via one-pot thermal polycondensation of dicyandiamide and 2,4-diaminobenzenesulfonic acid is reported. The carbon-rich benzene ring is embedded into g-C3N4, which enables the asymmetric modification of the heptazine units in g-C3N4 and the extension of the π-conjugate system without altering its long-range order structure significantly. Such molecular structure optimization effectively improves the visible light harvesting and charge carriers separation ability. A high photocatalytic hydrogen evolution rate and dye degradation performance is achieved under visible light irradiation (λ > 420 nm), which is about 8.4 and 4.4-fold higher than that of pristine g-C3N4, respectively. The reason for enhanced photocatalytic performance is ascribed to a favorable optical property, suppressed charge carrier recombination, and efficient charge transfer processes. This work provides a green and economical method to functionalize g-C3N4 using low-content organic carbon molecule for efficient energy conversion-related applications.

Improved H2O2 Photogeneration on KBr Doped-Polymeric Carbon Nitride Via Optimize the Oxygen Reduction Path

The photosynthesis of hydrogen peroxide (H2O2) from oxygen (O2) represents a promising catalytic pathway, the limited efficiency of the oxygen reduction constitutes a primary barrier to enhancing production. In this content, alkali metal potassium (K+) and Br-doped g-C3N4 photocatalysts (K-CN) were successfully constructed by one-pot method. The introduction of K+ is not only beneficial to the transmission of space charge and the separation efficiency of photogenerated carriers, but also promotes the efficient production of H2O2 by 2e- oxygen reduction reaction. The introduction of Br- promotes O2 converted to triplet state and triggers energy transfer process to increase 1O2 production, O2 adsorption was facilitated through regulating the oxygen evolution (O2→1O2), which is beneficial to the subsequent oxygen reduction process. The results showed that the H2O2 yield of 0.05 K-CN catalyst reached 26.0 mmol g-1 h-1, which was more than 5 times that of pure g-C3N4.

Harnessing Janus structures: enhanced internal electric fields in C3N5 for improved H2 photocatalysis

Homojunction engineering holds promise for creating high-performance photocatalysts, yet significant challenges persist in establishing and modulating an effective junction interface. To tackle this, we designed and constructed a novel Janus homojunction photocatalyst by integrating two different forms of triazole-based carbon nitride (C3N5). In this design, super-sized, ultrathin nanosheets of carbon-rich C3N5 grow epitaxially on a nitrogen-rich honeycomb network of C3N5, creating a tightly bound and extensive interfacial contact area. This arrangement enhances the built-in internal electric field (IEF) between the two forms of C3N5, facilitating faster directional transfer of photogenerated electrons and improved visible-light harvesting. Consequently, Janus-C3N5 achieves a remarkable H2 evolution rate of 1712.4 μmol h-1 g-1 under simulated sunlight, which is approximately 5.58 times higher than that of bulk C3N5 (306.8 μmol h-1 g-1) and 14.1 times higher than another form of bulk C3N5 (121.2 μmol h-1 g-1). This work offers a new approach to design efficient homojunction-based photocatalysts.

Donor-Acceptor Type Carbon Nitride Photocatalysts in Photocatalysis: Current Understanding, Applications and Challenges

The exploration of photocatalytic materials with efficient charge separation has always been a prominent area of research in photocatalysis. In the preceding years, the strategy of constructing donor-acceptor (D-A) structured materials has gradually been developed in photocatalytic systems, becoming a new research crossroads and attracting extensive interdisciplinary focus. Polymeric carbon nitride (PCN) has gradually been recognized as the primary photocatalytic material for constructing D-A structures due to its attractive exceptional physicochemical stability, electronic band structure, and cost-effectiveness. However, few reports have summarized the research on D-A type PCN at the molecular level. This review focuses on the molecular level design strategies and the performance enhancement mechanisms of D-A type PCN are emphasized from two main aspects: intramolecular D-A and intermolecular D-A. In addition, the concept of dual D-A type PCN is introduced, proposing a new direction for advancing the efficacy of photocatalysts. Subsequently, this review summarizes the application scenarios of D-A type PCN in energy transformation and environmental amelioration. Finally, by elaborating on the main difficulties and opportunities in this hot field, this review can provide inspiration and innovative strategies for developing D-A type PCN and resolving energy and environmental issues.

Alkali metal cation adsorption-induced surface polarization in polymeric carbon nitride for enhanced photocatalytic hydrogen peroxide production

Photocatalytic hydrogen peroxide (H2O2) generation on the catalyst surface from oxygen is an electron-demanding process, making the construction of an electron-rich surface highly advantageous. In this study, a localized electric field was observed on the surface of polymeric carbon nitride (g-C3N4) when alkali metal cations were adsorbed onto it. These fields effectively inhibited surface carrier recombination and extended their lifespan, thereby enhancing H2O2 production. As a result, g-C3N4 achieved a superior H2O2 yield of 2.25 mM after 1 h in a 0.25 M K+ solution, which was 2.06 times greater than that (1.09 mM) achieved in a pure solvent. Notably, the increase in photocatalytic efficiency showed a remarkable dependence on ion species. At low concentrations, H2O2 generation efficiency was in the order of Li+ < Na+ < K+ < Rb+ < Cs+. However, after optimizing the ion concentration, the highest H2O2 production was achieved in a solution containing K+ instead of Cs+. Molecular dynamics simulations and temperature-dependent photocatalysis experiments revealed that the synergistic interaction between adsorption energy and adsorption distance was crucial in governing the extent to which alkali metal cation adsorption enhanced g-C3N4 photocatalytic H2O2 production. This study provides theoretical insights for the design of materials for electron-demanding photocatalysis and aids in understanding variations in photocatalytic behavior in natural waters.

Polymeric Carbon Nitride Edged with Spatially Isolated Donor and Acceptor for Sunlight-Driven H2O2 Synthesis and In-Situ Utilization

On-site H2O2 activation attracts much attention in energy conversion and environment remediation et al., yet remains challenging in its highly efficient and sustainable synthesis. Herein, we grafted a pair of spatially isolated donor (methoxyphenyl unit) and acceptor (anthraquinone unit) in polymeric carbon nitride edges, which induce directional electron-hole transfer to the two spatially separated dual active centers. Specifically, photogenerated electrons in the anthraquinone unit facilitate the 2e- ORR, while the methoxyphenyl unit, which gathers photogenerated holes, enables rapid 4e- WOR. More impressively, the anthraquinone unit also exhibits strong proton extraction capabilities to boost the generation of *OOH intermediates and H2O2. Consequently, the synthesized donor-polymeric carbon nitride-acceptor (DPA) catalyst shows a remarkable H2O2 yield of 6497.1 μM h-1 g-1 in pure water, surpassing traditional DP and PA catalysts. Because of its high efficiency, the H2O2 product can efficiently degrade and mineralize various organic contaminants in a continuous-flow self-Fenton reactor under sunlight irradiation. Our work presents an unprecedented approach to designing photocatalysts with efficient H2O2 synthesis and practical application from a molecular engineering perspective.

Molten salt-assisted synthesis of boron-doped carbon nitride for photocatalytic hydrogen evolution

In this work, B and K were introduced into the heptazine structure of carbon nitride to synthesize the catalyst kalium-boron doped carbon nitride (KBCN) with a larger light absorption range and improved photogenerated carrier separation rate. Boron atoms are introduced into the carbon nitride heptazine units to optimize the electronic structure within the carbon nitride planes, and the B-N bonds formed by the heptazine units facilitate charge transfer. Potassium atoms are introduced into the carbon nitride interlayer as charge transfer channels to synergistically promote the transfer of photogenerated electrons. This work provides a potential idea for the doping of metallic and nonmetallic elements to jointly promote the charge distribution and transfer of carbon nitride.

Heteropoly blue-modified ultrathin bismuth oxychloride nanosheets with oxygen vacancies for efficient photocatalytic nitrogen fixation in pure water

Photocatalytic nitrogen reduction is a promising green technology for ammonia synthesis under mild conditions. However, the poor charge transfer efficiency and weak N2 adsorption/activation capability severely hamper the ammonia production efficiency. In this work, heteropoly blue (r-PW12) nanoparticles are loaded on the surface of ultrathin bismuth oxychloride nanosheets with oxygen vacancies (BiOCl-OVs) by electrostatic self-assembly method, and a series of xr-PW12/BiOCl-OVs heterojunction composites have been prepared. Acting as a robust support, ultrathin two-dimensional (2D) structure of BiOCl-OVs inhibits the aggregation of r-PW12 nanoparticles, enhancing the interfacial contact between r-PW12 and BiOCl. More importantly, the existence of oxygen vacancies (OVs) provides abundant active sites for efficient N2 adsorption and activation. In combination of the enhanced light absorption and promoted photogenerated carriers separation of xr-PW12/BiOCl-OVs heterojunction, under simulated solar light, the optimal 7r-PW12/BiOCl-OVs exhibits an excellent photocatalytic N2 fixation rate of 33.53 µmol g-1h-1 in pure water, without the need of sacrificial agents and co-catalysts. The reaction dynamics is also monitored by in situ FT-IR spectroscopy, and an associative distal pathway is identified. Our study demonstrates that construction of heteropoly blues-based heterojunction is a promising strategy for developing high-performance N2 reduction photocatalysts. It is anticipated that combining of different defects with heteropoly blues of different structures might provide more possibilities for designing highly efficient photocatalysis systems.

Unlocking Topological Effects in Covalent Organic Frameworks for High-Performance Photosynthesis of Hydrogen Peroxide

Covalent organic frameworks (COFs) offer a compelling platform for the efficient photosynthesis of hydrogen peroxide (H2O2). Constructed with diverse topologies from various molecular building units, COFs can exhibit unique photocatalytic properties. In this study, three π-conjugated 2D sp2 carbon-linked COFs with distinctly different topologies (hcb, sql, and hxl) are designed to investigate the topological effect on the overall photosynthesis of H2O2 from water and oxygen. Despite their similar chemical and band structures, the QP-HPTP-COF with hxl topology outperformed other COFs in the photosynthesis of H2O2, demonstrating a remarkable solar-to-chemical conversion efficiency of 1.41%. Comprehensive characterizations confirmed that the hxl topology can substantially improve charge separation and transfer, thereby significantly enhancing photocatalytic performance. This study not only unravels the topology-directed charge carrier dynamics in COFs but also establishes a molecular engineering framework for developing high-performance photocatalysts for sustainable H2O2 production.

Merger of Single-Atom Catalysis and Photothermal Catalysis for Future Chemical Production

Photothermal catalysis is an emerging field with significant potential for sustainable chemical production processes. The merger of single-atom catalysts (SACs) and photothermal catalysis has garnered widespread attention for its ability to achieve precise bond activation and superior catalytic performance. This review provides a comprehensive overview of the recent progress of SACs in photothermal catalysis, focusing on their underlying mechanisms and applications. The dynamic structural evolution of SACs during photothermal processes is highlighted, and the current advancements and future perspectives in the design, screening, and scaling up of SACs for photothermal processes are discussed. This review aims to provide insights into their continued development in this rapidly evolving field.

From one to two: in situ construction of C3N5-poly(triazine imide) heterojunction for enhanced O2 activation

A novel C3N5-poly(triazine imide) (PTI) heterojunction was designed and constructed using a thermal polymerization process, and featured an intimate S-scheme interface coupling and a particularly good performance for H2O2 production. This work provides a new perspective for constructing metal-free C3N5-based heterojunctions to be used for selective molecular oxygen activation.

Photoinduced Zn-Air Battery-Assisted Self-Powered Sensor Utilizing Cobalt and Sulfur Co-Doped Carbon Nitride for Portable Detection Device

Most self-powered electrochemical sensors (SPESs) are limited by low open circuit voltage and power density, leading to a narrow detection range and low sensitivity. Herein, a photoinduced Zn-air battery-assisted SPES (ZAB-SPES) is proposed based on cobalt and sulfur co-doped carbon nitride with the cyano group (Co, S-CN). The cyano functionalization remarkably enhances visible light utilization, and the cyano moiety acts as an electron-withdrawing group to promote electron enrichment. Co and S co-doping can create a p-n homojunction within carbon nitride, enabling the efficient migration and separation of carriers, thereby significantly improving the performance of the oxygen reduction reaction. The synergistic effects endow Co, S-CN photocathode with an open circuit voltage of 1.85 V and the maximum power density of 43.5 µW cm-2 in the photoinduced ZAB. Employing heavy metal copper ions as the target model, the photoinduced ZAB-SPES exhibited dual-mode and sensitive detection. Furthermore, a portable detection device based on the photoinduced ZAB-SPES is designed and exhibits high linearity in the range of 5 ~ 600 nM with a detection limit of 1.7 nM. This work offers a portable detection method based on the photoinduced ZAB-SPES in the aquatic environment.

Electronic Structure and Functions of Carbon Nitride in Frontier Green Catalysis

ConspectusGraphitic carbon nitride-based materials have emerged as promising photocatalysts for a variety of energy and environmental applications owing to their "earth-abundant" nature, structural versatility, tunable electronic and optical properties, and chemical stability. Optimizing carbon nitride's physicochemical properties encompasses a variety of approaches, including the regulation of inherent structural defects, morphology control, heterostructure construction, and heteroatom and metal-atom doping. These strategies are pivotal in ultimately enhancing their photocatalytic activities. Previous reviews with extensive examples have mainly focused on the synthesis, modification, and application of carbon nitride-based materials in photocatalysis. However, there has been a lack of straightforward and in-depth discussion to understand the electronic characteristics and functions of various engineered carbon nitrides as well as their precise tailoring strategies and ultimately to explain the regularity and specificity of their improved performance in targeted photocatalytic systems. In the past ten years, our group has conducted extensive investigations on carbon nitride-based materials and their application in photocatalysis. These studies demonstrate the close yet intricate relationship between the electronic structure of carbon nitride materials and their photocatalytic reactivity. Understanding the electronic structure and functions of carbon nitride, as well as different engineering strategies, is essential for the improvement of photocatalytic processes from fundamental study to practical applications.To this end, in this Account, we first delve into the nature of the electronic properties of carbon nitride, highlighting the electronic structures, including band structure, density of states, molecular orbitals, and band center, as well as its electronic functions, such as the charge distribution, internal electric field, and external electric force. Subsequently, based on recent research in our group, we present a detailed discussion of the strategic modifications of carbon nitride and the consequential impacts on the physicochemical properties, particularly the optical properties and intrinsic electronic characteristics, for enhancing the photocatalytic performance. These modifications are categorized as follows: (i) component changing, which involves intralayer and interface heterojunctions as well as homojunctions, to modulate the band-edge potentials and reactivity of photoinduced electrons and holes toward surface redox reactions; (ii) dimensional tuning, which engineers the dimensional structure of carbon nitride, to influence the electron transfer direction; (iii) defect and heteroatom modification, which introduces a symmetry break in the carbon nitride framework, to promote charge redistribution for altering the charge density and electronic structure; and (iv) anchoring of single-atom metals to facilitate orbital hybridization and charge transfer enhancement through the unique metal-N coordination configurations. Finally, we propose an appraisal of the prospects and challenges in the precise manipulation and characterization of the electronic structure and functions of carbon nitride. The integration of in situ electronic structure analysis, theoretical calculation based on machine learning, and precise mechanism study may propel its substantial development in the light-driven circular economy. We hope this Account aspires to offer novel insights and perspectives into the operational mechanisms and tailored structure of carbon nitride-based materials in photocatalysis.

Effective Interfacing of Surface Homojunctions on Chemically Identical g-C3N4 for Efficient Visible-Light Photocatalysis without Sacrificial Agents

Developing efficient homojunctions on g-C3N4 promises metal-free photocatalysis to realize truly sustainable artificial photosynthesis. However, current designs are limited by hindered charge separation due to inevitable grain boundaries and random formation of ineffective homojunctions embedded within the photocatalyst. Here, efficient photocatalysis is driven by introducing effective surface homojunctions on chemically and structurally identical g-C3N4 through leveraging its size-dependent electronic properties. Using a top-down approach, the surface layer of bulk g-C3N4 is partially exfoliated to create sheet-like g-C3N4 nanostructures on the bulk material. This hierarchical design establishes a subtle band energy offset between the macroscopic and nanoscopic g-C3N4, generating homojunctions while maintaining the chemical and structural integrities of the original g-C3N4. The optimized g-C3N4 homojunction demonstrates superior photocatalytic degradation of antibiotic pollutants at >96% efficiency in 2 h, even in different real water samples. It achieves reaction kinetics (≈0.041 min-1) up to fourfold better than standalone materials and their physical mixture. Mechanistic studies highlight the importance of the unique design in boosting photocatalysis by effectively promoting interfacial photocarrier manipulation and utilization directly at the point-of-catalysis, without needing co-catalysts or sacrificial agents. This work presents enormous opportunities for developing advanced and green photocatalytic platforms for sustainable light-driven environmental, energy, and chemical applications.

High Sensitive and Stable UV-Vis Photodetector Based on MoS2/MoO3 vdW Heterojunction

The development of new high-performance photodetectors (PDs) is currently focused on achieving small size, low power consumption, low cost, and large bandwidth. Two-dimensional (2D) materials and heterostructures offer promising approaches for the future development of optoelectronic devices. However, there has been limited research on 2D wide-bandgap semiconductor heterostructures. In this study, we successfully constructed a MoS2/MoO3 vdW heterojunction PD. This PD exhibited excellent response and significant photovoltaic behavior in the ultraviolet (UV) to visible (Vis) range. Under 365 nm UV light and 1 V bias voltage, the PD demonstrated a high responsivity of 645 mA/W, a high specific detectivity of 8.98 × 1010 Jones, and fast response speeds of 55.9/59.6 ms. At 0 V bias voltage, the responsivity reached as high as 157 mA/W. Furthermore, the PD exhibited remarkable stability in its performance. These outstanding characteristics can be attributed to the strong internal electric field created by the type II heterojunction structure and the chemical stability of the materials. This work opens a route for the application of 2D wide-bandgap semiconductor materials in optoelectronic devices.

Hydroxyl-Bonded Co Single Atom Site on Boroncarbonitride Surface Realizes Nonsacrificial H2O2 Synthesis in the Near-Infrared Region

Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 and H2O under near-infrared light is a sustainable renewable energy production strategy, but challenging reaction. The bottleneck of this reaction lies in the regulation of O2 reduction path by photocatalyst. Herein, the center of the one-step two-electron reduction (OSR) pathway of O2 for H2O2 evolution via the formation of the hydroxyl-bonded Co single-atom sites on boroncarbonitride surface (BCN-OH2/Co1) is constructed. The experimental and theoretical prediction results confirm that the hydroxyl group on the surface and the electronic band structure of BCN-OH2/Co1 are the key factor in regulating the O2 reduction pathway. In addition, the hydroxyl-bonded Co single-atom sites can further enrich O2 molecules with more electrons, which can avoid the one-electron reduction of O2 to •O2 -, thus promoting the direct two-electron activation hydrogenation of O2. Consequently, BCN-OH2/Co1 exhibits a high H2O2 evolution apparent quantum efficiency of 0.8% at 850 nm, better than most of the previously reported photocatalysts. This study reveals an important reaction pathway for the generation of H2O2, emphasizing that precise control of the active site structure of the photocatalyst is essential for achieving efficient conversion of solar-to-chemical.

Oxygen-Centered Organic Radicals-Involved Unified Heterogeneous Self-Fenton Process for Stable Mineralization of Micropollutants in Water

Removing organic micropollutants from water through photocatalysis is hindered by catalyst instability and substantial residuals from incomplete mineralization. Here, a novel water treatment paradigm, the unified heterogeneous self-Fenton process (UHSFP), which achieved an impressive 32% photon utilization efficiency at 470 nm, and a significant 94% mineralization of organic micropollutants-all without the continual addition of oxidants and iron ions is presented. In UHSFP, the active species differs fundamentally from traditional photocatalytic processes. One electron acceptor unit of photocatalyst acquires only one photogenerated electron to convert into oxygen-centered organic radical (OCOR), then spontaneously completing subsequent processes, including pollutant degradation, hydrogen peroxide generation, activation, and mineralization of organic micropollutants. By bolstering electron-transfer capabilities and diminishing catalyst affinity for oxygen in the photocatalytic process, the generation of superoxide radicals is effectively suppressed, preventing detrimental attacks on the catalyst. This study introduces an innovative and cost-effective strategy for the efficient and stable mineralization of organic micropollutants, eliminating the necessity for continuous chemical inputs, providing a new perspective on water treatment technologies.

Efficient Proton Transfer and Charge Separation within Covalent Organic Frameworks via Hydrogen-Bonding Network to Boost H2O2 Photosynthesis

Photocatalytic synthesis based on the oxygen reduction reaction (ORR) has shown great promise for H2O2 production. However, the low activity and selectivity of 2e- ORR result in a fairly low efficiency of H2O2 production. Herein, we propose a strategy to enhance the proton-coupled electron transfer (PCET) process in covalent organic frameworks (COFs), thereby significantly boosting H2O2 photosynthesis. We demonstrated that the construction of a hydrogen-bonding network, achieved by anchoring the H3PO4 molecular network on COF nanochannels, can greatly improve both proton conductivity and photogenerated charge separation efficiency of COFs. Thus, COF@H3PO4 exhibited superior photocatalytic performance in generating H2O2 without sacrificial agents, with a solar-to-chemical conversion efficiency as high as 0.69%. Results indicated that a much more localized spatial distribution of energy band charge density on COF@H3PO4 led to efficient charge separation, and the small energy barrier of the rate-limiting step from *OOH to H2O2 endowed COF@H3PO4 with higher 2e- ORR selectivity.

Self-Powered Immunoassay of Norovirus in Human Stools by π-Electron-Rich Homojunction for Enhanced Charge Transfer

Norovirus (NoV) stands as a significant causative agent of nonbacterial acute gastroenteritis on a global scale, presenting a substantial threat to public health. Hence, the development of simple and rapid analytical techniques for NoV detection holds great importance in preventing and controlling the outbreak of the epidemic. In this work, a self-powered photoelectrochemical (PEC) immunosensor of NoV capsid protein (VP1) was proposed by the π-electron-rich carbon nitride homojunction (ER-CNH) as the photoanode. C4N2 ring derived from π-rich locust bean gum was introduced into the tri-s-triazine structure, creating a large π-delocalized conjugated carbon nitride homojunction. This strategy enhances the C/N atomic ratio, which widens light utilization, narrows the bandgap, and optimizes the electronic band structure of carbon nitride. By introduction of a π-rich conjugated structure, p-type domains were induced within n-type domains to build the internal electric field at the interface, thus forming a p-n homojunction to boost carrier separation and transfer. The ER-CNH photoanode exhibited excellent photoelectric performance and water oxidation capacity. Since VP1 inhibits the water oxidation of the ER-CNH photoanode, the open-circuit potential of the as-prepared PEC immunosensor system was reduced for detecting NoV VP1. The self-powered PEC immunosensor achieved a remarkably low detection limit (∼5 fg mL-1) and displayed high stability and applicability for actual stool samples. This research serves as a foundation concept for constructing immunosensors to detect other viruses and promotes the application of self-powered systems for life safety.

Recent developments in photocatalytic production of hydrogen peroxide

Hydrogen peroxide (H2O2), an environmentally friendly strong oxidant and energy carrier, has attracted widespread attention in photocatalysis. Artificial photosynthesis of H2O2 using water and oxygen as raw materials, solar energy as an energy source, and semiconductor materials as catalysts is considered a promising technology. In the past few decades, encouraging progress has been made in the photocatalytic production of H2O2. Therefore, we summarize the research achievements in this field in recent years. This review first briefly introduces the reaction pathway, detection techniques and evaluation metrics. Then, the recent advances in photocatalysts are highlighted. Furthermore, the existing challenges and possible solutions in this field are presented. At last, we look forward to the future development direction of this field. This review provides valuable insights and guidance for efficient photocatalytic H2O2 production.

Metal-organic framework-based S-scheme heterojunction photocatalysts

Photocatalysis is a promising technology to resolve energy and environmental issues, where the design of high-efficiency photocatalysts is the central task. As an emerging family of photocatalysts, semiconducting metal-organic frameworks (MOFs) with remarkable features have demonstrated great potential in various photocatalytic fields. Compared to MOF-based photocatalysts with a single component, construction of S-scheme heterojunctions can render MOFs with enhanced charge separation, redox capacity and solar energy utilization, and thus improved photocatalytic performance. Herein, an overview of the recent advances in the design of MOF-based S-scheme heterojunctions for photocatalytic applications is provided. The basic principle of S-scheme heterojunctions is introduced. Then, three types of MOF-based S-scheme heterojunctions with different compositions are systematically summarized including MOF/non-MOF, MOF-on-MOF and MOF-derived heterojunctions. Afterwards, the enhanced performances of MOF-based S-scheme heterojunctions in hydrogen production, CO2 reduction, C-H functionalization, H2O2 production and wastewater treatment are highlighted. Lastly, the current challenges and future prospects regarding the design and applications of MOF-based S-scheme heterojunctions are discussed to inspire the further development of this emerging field.

Order-Disorder Engineering of Carbon Nitride for Photocatalytic H2O2 Generation Coupled with Pollutant Removal

Highly crystalline carbon nitride (CCN), benefiting from the reduced structural imperfections, enables improved electron-hole separation. Yet, the crystalline phase with insufficient inherent defects suffers from a poor performance toward the reaction intermediate adsorption with respect to the amorphous phase. Herein, a crystalline-amorphous carbon nitride (CACN) with an isotype structure was constructed via a two-step adjacent calcination strategy. Through specific oxygen etching and crystallization, the formation of a built-in electric field at the interface could drive charge transfer and separation, thus promoting photoredox reaction. As expected, the optimized CACN exhibited a H2O2 generation efficiency as high as 2.15 mM gcat-1 h-1, paired with a promoted pollutant degradation efficiency, which outperform its crystalline (CCN) and amorphous [amorphous carbon nitride (ACN)] counterparts. The detailed electron/hole transportation via a built-in electronic field and free radical formation based on the enhanced adsorption of oxygen were considered, and the synchronous reaction pathway was carried out. This work paves a novel pathway for the synthesis of carbon nitride with an isotype structure from the perspective of interfacial engineering.