Synthesis of Silver Nanoparticles-Modified Graphitic Carbon Nitride Nanosheets for Highly Efficient Photocatalytic Hydrogen Peroxide Evolution

As a promising metal-free photocatalyst, graphitic carbon nitride (g-C₃N₄) is still limited by insufficient visible light absorption and rapid recombination of photogenerated carriers, resulting in low photocatalytic activity. Here, we adjusted the microstructure of the pristine bulk-g-C₃N₄ (PCN) and further loaded silver (Ag) nanoparticles. Abundant Ag nanoparticles were grown on the thin-layer g-C₃N₄ nanosheets (CNNS), and the Ag nanoparticles decorated g-C₃N₄ nanosheets (Ag@CNNS) were successfully synthesized. The thin-layer nanosheet-like structure was not only beneficial for the loading of Ag nanoparticles but also for the adsorption and activation of reactants via exposing more active sites. Moreover, the surface plasmon resonance (SPR) effect induced by Ag nanoparticles enhanced the absorption of visible light by narrowing the band gap of the substrate. Meanwhile, the composite band structure effectively promoted the separation and transfer of carriers. Benefiting from these merits, the Ag@CNNS reached a superior hydrogen peroxide (H₂O₂) yield of 120.53 μmol/g/h under visible light irradiation in pure water (about 8.0 times higher than that of PCN), significantly surpassing most previous reports. The design method of manipulating the microstructure of the catalyst combined with the modification of metal nanoparticles provides a new idea for the rational development and application of efficient photocatalysts.     

钴、碳共掺杂氮化碳的制备及其光催化分解水产氢性能

针对氮化碳可见光利用率低和在光催化过程中光生电子与空穴易于复合的缺点,通过钴、碳共掺杂提升其光催化性能。以尿素为前驱体,维生素B12（VB12）为钴源和碳源,将二者的混合物进行一步煅烧,制备钴、碳共掺杂氮化碳（CNCoC）。结果表明,钴、碳共掺杂对氮化碳的微观形貌、骨架结构和官能团都没有造成明显影响;但是增大了产物的比表面积,调节了产物的能带结构,增加了其对可见光的吸收。更重要的是,相比于单一元素碳的掺杂,钴、碳共掺杂具有协同作用,能够更有效地提升光生电子和空穴的分离和传递效率。因此,加入6 mg VB12制备的CNCoC-6的可见光光催化分解水产氢速率达到了56.1 μmol·h^-1,是纯氮化碳（CN）的3.05倍;而碳掺杂氮化碳（CNC-6）的产氢速率仅为CN的2.55倍。     

Electron Configuration Modulation of Nickel Single Atoms for Elevated Photocatalytic Hydrogen Evolution

The emerging metal single‐atom catalyst has aroused extensive attention in multiple fields, such as clean energy, environmental protection, and biomedicine. Unfortunately, though it has been shown to be highly active, the origins of the activity of the single‐atom sites remain unrevealed to date owing to the lack of deep insight on electronic level. Now, partially oxidized Ni single‐atom sites were constructed in polymeric carbon nitride (CN), which elevates the photocatalytic performance by over 30‐fold. The 3d orbital of the partially oxidized Ni single‐atom sites is filled with unpaired d‐electrons, which are ready to be excited under irradiation. Such an electron configuration results in elevated light response, conductivity, charge separation, and mobility of the photocatalyst concurrently, thus largely augmenting the photocatalytic performance.     

氧掺杂氮化碳纳米片的制备及其光解水制氢性能

以草酸为氧源,二聚氰胺和尿素为原料,采用两步热聚合方式合成氧掺杂氮化碳纳米片催化剂(CNO)。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见吸收光谱(UV-Vis)、X射线光电子能谱分析(XPS)、荧光光谱(PL)及电化学测试等技术对催化剂进行结构表征分析。在可见光照射下通过分解水制氢反应对CNO的光催化还原性能进行评价。结果表明,草酸中的O元素通过取代氮化碳三嗪环结构中N原子直接键合到sp~2杂化碳上,形成O掺杂CNO。经O掺杂改性后的氮化碳具有良好的层状堆积结构,可见光吸收性明显提高,同时禁带宽度降低。O掺杂的引入加速了光生电子-空穴对的分离和传输,能大幅度提高氮化碳的光催化分解水制氢性能,在可见光照下达88.6μmol·h~(-1),是未掺杂CN的3.91倍。     

高分散Co0.2Ni1.6Fe0.2P助催化剂改性P掺杂g-C3N4纳米片高效光催化析氢的研究

随着化石燃料使用的增加和温室气体排放量持续上升,20世纪以来气温上升得更快。开发环境友好型能源取代传统化石燃料是当务之急。氢能源作为一种清洁、高效的能源,被认为是最有希望取代传统化石燃料的能源。光催化水分解水产氢作为为一种环保型技术被认为是最有前景的氢能生产方法。提高光生电子-空穴对分离效率是构建高效光催化剂的关键。然而,利用高度分散的助催化剂构建高效、稳定的产氢光催化剂仍然是一个挑战。本文首次成功地采用一步原位高温磷化法制备了高度分散的非贵金属三金属过度金属磷化Co_0.2Ni_1.6Fe_0.2P助催化剂(PCNS-CoNiFeP)掺杂P的石墨相氮化碳纳米片(PCNS)。有趣的是,PCNS-CoNiFeP与传统氢氧前驱体磷化法制备的CoNiFeP相比,没有聚集性,分散性高。X射线衍射(XRD)、X射线光电子能谱(XPS)、元素映射图像和高分辨率透射电镜(HRTEM)结果表明,PCNS-CoNiFeP已成功合成。紫外-可见吸收光谱结果表明,PCNS-CoNiFeP在200–800 nm波长范围内较PCNS略有增加。光致发光光谱、电化学阻抗谱(EIS)和光电流分析结果表明,CoNiFeP助催化剂能有效促进光生电子-空穴对的分离,加速载流子的迁移。线性扫描伏安法(LSV)结果还表明,负载CoNiFeP助催化剂可大大降低CNS的过电位。结果表明,以三乙醇胺溶液为牺牲剂的PCNS-CoNiFeP最大产氢速率为1200 μmol·h^-1·g^-1,是纯CNS-Pt (320 μmol·h^-1·g^-1)的4倍。在420 nm处的表观量子效率为1.4%。PCNS-CoNiFeP在光催化反应中也表现出良好的稳定性。透射电镜结果表明,6–8 nm的CoNiFeP高度分散在PCNS表面。高度分散的CoNiFeP比聚集的CoNiFeP具有更好的电荷分离能力和更高的电催化析氢活性。由此可见,聚合的CoNiFeP-PCNs (300 μmol·h^-1·g^-1)的产氢速率远低于PCNS-CoNiFeP。此外,CNS的P掺杂可以改善其电导率和电荷传输。     

Amorphous and Crystalline 2D Polymeric Carbon Nitride Nanosheets for Photocatalytic Hydrogen/Oxygen Evolution and Hydrogen Peroxide Production

Photocatalytic reactions, including hydrogen/oxygen generation, water splitting and hydrogen peroxide production, are regarded as a renewable and promising method to harvest and use solar energy. The key to achieving this goal is to explore efficient photocatalysts with high productivity. Recently, two‐dimensional (2D) polymeric carbon nitride nanosheets were reported as efficient photocatalysts toward various products because of their outstanding properties, such as high specific surface area, more reactive sites, the quantum effect in thickness and unique electronic properties. This minireview attempts to overview recent advances in the preparation, structure and properties of crystalline and amorphous carbon nitride nanosheets, and their applications in photocatalytic hydrogen/oxygen evolution, water splitting and hydrogen peroxide production. We also thoroughly discuss the effect of defects, dopants and composites on the photocatalytic efficiency of these carbon nitride nanosheets. Finally, we outlook the ongoing opportunities and future challenges for 2D carbon nitride nanosheets in the field of photocatalysis.     

Graphitic Carbon Nitride/Nitrogen‐Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts

An interconnected framework of mesoporous graphitic‐C₃N₄ nanofibers merged with in situ incorporated nitrogen‐rich carbon has been prepared. The unique composition and structure of the nanofibers as well as strong coupling between the components endow them with efficient light‐harvesting properties, improved charged separation, and a multidimensional electron transport path that enhance the performance of hydrogen production. The as‐obtained catalyst exhibits an extremely high hydrogen‐evolution rate of 16885 μmol h^?1 g^?1, and a remarkable apparent quantum efficiency of 14.3 % at 420 nm without any cocatalysts, which is much higher than most reported g‐C₃N₄‐based photocatalysts even in the presence of Pt‐based cocatalysts.     

泡沫状氮化碳的制备及其可见光分解水产氢性能

以三聚氰胺为前驱体,价格低廉、来源广泛的海泡石作为硬模板,制备出具有特殊空腔结构的泡沫状氮化碳。 通过透射电子显微镜、X射线粉末衍射、傅里叶变换红外光谱、N₂吸附-脱附、紫外可见漫反射光谱及荧光光谱等手段对样品的表面形貌和结构等物理性质进行表征,以光解水产氢性能考察其光催化活性,并通过电化学测试手段考察其光生电荷传输和分离情况。 结果表明,聚多巴胺能起到粘接剂作用,改善了前驱体与模板的结合,制备出的泡沫状氮化碳具有更大的比表面积;随模板用量增加,氮化碳的比表面积增大,当聚多巴胺改性海泡石与三聚氰胺质量比为2:1时,泡沬状氮化碳比表面积可达389.2 m²/g,其可见光产氢速率约为1061.87 μmol/(g·h),较体相氮化碳和未经多巴胺改性海泡石制备的氮化碳分别提高了7和2.6倍。 这表明大比表面积的泡沫状氮化碳为光催化反应提供了更多的活性位点,改善了多相光催化反应的传质扩散过程,提高了光生电子-空穴的分离效率,其特殊的空腔结构能有效地提高光的利用率,从而提高其光催化活性。     

碳自掺杂石墨相氮化碳纳米片的制备及其在可见光照射下的光解水产氢性能

石墨相氮化碳(g-C3N4)由于具有对可见光吸收范围较窄和光生载流子分离效率低等缺陷,其光解水产氢活性较差.我们采用简单的一步热共聚法,以尿素和2,4,6-三氨基嘧啶(TAPD)混合物为前驱物,制备碳自掺杂纳米片(CNNS-x,xmg代表掺入TAPD的质量).X射线衍射(XRD)、元素分析(EA)和X射线光电子能谱(X...     

Harvesting Solar Light with Crystalline Carbon Nitrides for Efficient Photocatalytic Hydrogen Evolution

Described herein is the photocatalytic hydrogen evolution using crystalline carbon nitrides (CNs) obtained by supramolecular aggregation followed by ionic melt polycondensation (IMP) using melamine and 2,4,6‐triaminopyrimidine as a dopant. The solid state NMR spectrum of ¹⁵N‐enriched CN confirms the triazine as a building unit. Controlling the amount and arrangements of dopants in the CN structure can dramatically enhance the photocatalytic performance for H₂ evolution. The polytriazine imide (PTI) exhibits the apparent quantum efficiency (AQE) of 15 % at 400 nm. This method successfully enables a substantial amount of visible light to be harvested for H₂ evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts.     

Efficient and Robust Hydrogen Evolution: Phosphorus Nitride Imide Nanotubes as Supports for Anchoring Single Ruthenium Sites

Amorphous phosphorus nitride imide nanotubes (HPN) are reported as a novel substrate to stabilize materials containing single‐metal sites. Abundant dangling unsaturated P vacancies play a role in stabilization. Ruthenium single atoms (SAs) are successfully anchored by strong coordination interactions between the d orbitals of Ru and the lone pair electrons of N located in the HPN matrix. The atomic dispersion of Ru atoms can be distinguished by X‐ray absorption fine structure measurements and spherical aberration correction electron microscopy. Importantly, Ru SAs@PN is an excellent electrocatalyst for the hydrogen evolution reaction (HER) in 0.5 m H₂SO₄, delivering a low overpotential of 24 mV at 10 mA cm^?2 and a Tafel slope of 38 mV dec^?1. The catalyst exhibits robust stability in a constant current test at a large current density of 162 mA cm^?2 for more than 24 hours, and is operative for 5000 cycles in a cyclic voltammetry test. Additionally, Ru SAs@PN presents a turnover frequency (TOF) of 1.67 H₂ s^?1 at 25 mV, and 4.29 H₂ s^?1 at 50 mV, in 0.5 m H₂SO₄ solution, outperforming most of the reported hydrogen evolution catalysts. Density functional theory (DFT) calculations further demonstrate that the Gibbs free energy of adsorbed H* over the Ru SAs on PN is much closer to zero compared with the Ru/C and Ru SAs supported on carbon and C₃N₄, thus considerably facilitating the overall HER performance.     

石墨相氮化碳纳米管的合成及光催化产氢性能

通过硬模板法,采用氰胺前驱物和二氧化硅纳米管(SiO₂-NTs)模板,合成石墨相氮化碳纳米管(CN-NTs)光催化剂。采用扫描电镜(SEM)、透射电镜(TEM)、X射线粉末衍射(XRD)、傅立叶变换红外光谱(FT-IR)、氮气吸附/脱附测试、紫外可见漫反射光谱(UV-Vis DRS)、荧光光谱、热重分析(TGA)等手段对CN-NTs催化剂的结构与性能进行表征。结果表明,CN-NTs的化学组成是石墨相氮化碳(g-C₃N₄),形貌为均匀的纳米管,且是介孔材料。与体相氮化碳(B-CN)和介孔石墨相氮化碳(mpg-CN)相比,CN-NTs的光吸收带边蓝移到440 nm,荧光发射谱的峰强减弱。在可见光(λ>420 nm)照射下,CN-NTs具有较高的光催化分解水活性,产氢速率为58 μmol/h,且表现出良好的光催化活性稳定性和化学结构稳定性。研究结果表明纳米管状结构能有效促进g-C₃N₄半导体激子解离,提高光生电子-空穴的分离效率,进而显著优化g-C₃N₄的光催化产氢性能。     

Silver Single Atom in Carbon Nitride Catalyst for Highly Efficient Photocatalytic Hydrogen Evolution

Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag-N₂C₂/CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag-N₂C₂ configuration have been identified by aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and extended X-ray absorption. Experiments and DFT calculations further verify that Ag-N₂C₂ can reduce the H₂ evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag-N₂C₂/CN catalyst exhibits much better H₂ evolution activity than the N-coordinated Ag single atom in CN (Ag-N₄/CN), and is even superior to the Pt nanoparticle-loaded CN (Pt_NP/CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.     

Hollow Carbon Sphere-Modified Graphitic Carbon Nitride for Efficient Photocatalytic H2 Production

A novel hybrid photocatalyst composed of hollow carbon nanospheres (NCS) and graphitic carbon nitride (CN) curly nanosheets has been prepared by the calcination of a NCS precursor and freeze-dried urea. The optimized photocatalyst exhibits an efficient photocatalytic performance under visible light irradiation with a highest H₂ generation rate of 3612.3 μmol g⁻¹ h⁻¹, leading to an apparent quantum yield of 10.04 % at 420 nm, five times higher than the widely reported benchmark photocatalyst CN (2.01 % AQY). The materials characterization shows that NCS-modified CN curly nanosheets can promote photoelectron transfer and suppress charge recombination through their special coupling interface and NCS as an electron acceptor, which significantly improves the photocatalytic efficiency. Thus, this study provides an efficient strategy for the design of highly efficient photocatalyst, particularly suitable for a totally metal-free photocatalytic system.     

超薄石墨相氮化碳纳米片的构建及其光催化作用

通过简单调整g-C_3N_4的热聚合方式,一步构筑了超薄氮化碳纳米片,厚度在0.2~0.4 nm左右,分布均匀,比表面积可以达到99 m~2·g~(-1)。光催化性能测试结果表明,随着纳米片比表面积的增大,材料除了表现出优异的光解水性能以外,还在微生物领域表现出一定的抗菌性能,且活性随着聚合温度的升高、纳米片层的变薄而逐渐提高。     

超薄石墨相氮化碳纳米片的构建及其光催化作用

通过简单调整g-C₃N₄的热聚合方式,一步构筑了超薄氮化碳纳米片,厚度在0.2~0.4 nm左右,分布均匀,比表面积可以达到99 m²·g^-1。光催化性能测试结果表明,随着纳米片比表面积的增大,材料除了表现出优异的光解水性能以外,还在微生物领域表现出一定的抗菌性能,且活性随着聚合温度的升高、纳米片层的变薄而逐渐提高。     

Photocatalytic Hydrogen Evolution Performance for Hydroxyl-rich Porous Carbon Nitride

Metal-free photocatalyst C₃N₄ has been well investigated, while how to create hydroxyl-rich porous C₃N₄ remains a great challenge. Herein, we report a facile approach to address this issue by developing a novel two-step process:(i) precursor achieved via freeze-drying the mixture of urea, thiourea and NH₄Cl; (ii) subsequent thermal polydensation of the precursor. Systematic sample characterization demonstrated the formation of C₃N₄ featured by unique hydroxyl-rich porous structure with an extended tri-s-triazine unit. When applied as photocatalyst for water splitting under UV-Vis light irradiation, the sample displays a high hydrogen evolution rate of 243.4 μmol·g^-1·h^-1, about 4 times higher than that of C₃N₄ prepared by conventional method. Such a performance enhancement could be due to the porous structure and surface hydroxyl-rich functional groups that promote multiple-times reflection and light absorption, increase the active site numbers, and improve carrier transfer/separation efficiency.     

Carbon Quantum Dot Implanted Graphite Carbon Nitride Nanotubes: Excellent Charge Separation and Enhanced Photocatalytic Hydrogen Evolution

Graphite carbon nitride (g‐C₃N₄) is a promising candidate for photocatalytic hydrogen production, but only shows moderate activity owing to sluggish photocarrier transfer and insufficient light absorption. Herein, carbon quantum dots (CQDs) implanted in the surface plane of g‐C₃N₄ nanotubes were synthesized by thermal polymerization of freeze‐dried urea and CQDs precursor. The CQD‐implanted g‐C₃N₄ nanotubes (CCTs) could simultaneously facilitate photoelectron transport and suppress charge recombination through their specially coupled heterogeneous interface. The electronic structure and morphology were optimized in the CCTs, contributing to greater visible light absorption and a weakened barrier of the photocarrier transfer. As a result, the CCTs exhibited efficient photocatalytic performance under light irradiation with a high H₂ production rate of 3538.3 μmol g^?1 h^?1 and a notable quantum yield of 10.94 % at 420 nm.     

Controlled Carbon Nitride Growth on Surfaces for Hydrogen Evolution Electrodes

Efficient and low‐cost electrocatalysts for the hydrogen evolution reaction are highly desired for future renewable energy systems. Described herein is the reduction of water to hydrogen using a metal‐free carbon nitride electrocatalyst which operates in neutral and alkaline environments. An efficient, easy, and general method for growing ordered carbon nitride on different electrodes was developed. The metal‐free catalyst demonstrates low overpotential values, which are comparable to those of non‐noble metals, with reasonable current densities. The facile deposition method enables the fabrication of many electronic and photoelectronic devices based on carbon nitride for renewable energy applications.     

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

Phosphorus‐doped hexagonal tubular carbon nitride (P‐TCN) with the layered stacking structure was obtained from a hexagonal rod‐like single crystal supramolecular precursor (monoclinic, C2/m). The production process of P‐TCN involves two steps: 1) the precursor was prepared by self‐assembly of melamine with cyanuric acid from in situ hydrolysis of melamine under phosphorous acid‐assisted hydrothermal conditions; 2) the pyrolysis was initiated at the center of precursor under heating, thus giving the hexagonal P‐TCN. The tubular structure favors the enhancement of light scattering and active sites. Meanwhile, the introduction of phosphorus leads to a narrow band gap and increased electric conductivity. Thus, the P‐TCN exhibited a high hydrogen evolution rate of 67 μmol h^?1 (0.1 g catalyst, λ >420 nm) in the presence of sacrificial agents, and an apparent quantum efficiency of 5.68 % at 420 nm, which is better than most of bulk g‐C₃N₄ reported.