Tubular g‐C3N4 Isotype Heterojunction: Enhanced Visible‐Light Photocatalytic Activity through Cooperative Manipulation of Oriented Electron and Hole Transfer

A tubular g‐C₃N₄ isotype heterojunction (TCNH) photocatalyst was designed for cooperative manipulation of the oriented transfer of photogenerated electrons and holes to pursue high catalytic performance. The adduct of cyanuric acid and melamine (CA·M) is first hydrothermally treated to assemble into hexagonal prism crystals; then the hybrid precursors of urea and CA·M crystals are calcined to form tubular g‐C₃N₄ isotype heterojunctions. Upon visible‐light irradiation, the photogenerated electrons transfer from g‐C₃N₄ (CA·M) to g‐C₃N₄ (urea) driven by the conduction band offset of 0.05 eV, while the photogenerated holes transfer from g‐C₃N₄ (urea) to g‐C₃N₄ (CA·M) driven by the valence band offset of 0.18 eV, which renders oriented transfer of the charge carriers across the heterojunction interface. Meanwhile, the tubular structure of TCNH is favorable for oriented electron transfer along the longitudinal dimension, which greatly decreases the chance of charge carrier recombination. Consequently, TCNH exhibits a high hydrogen evolution rate of 63 μmol h^?1 (0.04 g, λ > 420 nm), which is nearly five times of the pristine g‐C₃N₄ and higher than most of the existing g‐C₃N₄ photocatalysts. This study demonstrates that isotype heterojunction structure and tubular structure can jointly manipulate the oriented transfer of electrons and holes, thus facilitating the visible‐light photocatalysis.     

基于g–C3N4光催化型抗菌包装纸的制备及其抗菌性研究

目的 解决g–C3N4存在的比表面积小,电子–空穴复合速率快从而导致光催化性能不佳等问题。方法 以尿素和硫脲为前驱体材料,通过热解聚辅助水蒸气活化合成S掺杂石墨相氮化碳(g–C3N4),并用界面聚合制备出光催化型抗菌包装纸。利用扫描电镜(SEM)、红外光谱(FTIR)、水接触角(WCA)、热重分析(TGA)、光催化抗菌实验等对抗菌包装纸的形态结构、表面官能团、纸张性质、光催化抗菌性进行详细研究。结果 致密的g–C3N4层有效提高了抗菌包装纸的疏水性和热稳定性。可见光照射下,光催化型抗菌包装纸对大肠杆菌和金黄色葡萄球菌的杀灭率达100%。未经可见光照射的原纸比光催化型包装纸的抗菌性差。结论 g–C3N4光催化型抗菌包装纸具有良好的广谱抗菌性,为绿色抗菌包装材料的制备提供了新思路。     

Preparation of Carbon‐Rich g‐C3N4 Nanosheets with Enhanced Visible Light Utilization for Efficient Photocatalytic Hydrogen Production

Exfoliation of layered bulk g‐C₃N₄ (CNB) to thin g‐C₃N₄ sheets in nanodomains has attracted much attention in photocatalysis because of the intriguing properties of nanoscaled g‐C₃N₄. This study shows that carbon‐rich g‐C₃N₄ nanosheets (CNSC) can be easily prepared by self‐modification of polymeric melon units through successively thermally treating bulk g‐C₃N₄ in an air and N₂ atmosphere. The prepared CNSC not only retain the outstanding properties of nanosheets, such as large surface area, high aspect ratios, and short charges diffusion distance, but also overcome the drawback of enlarged bandgap caused by the quantum size effect, resulting in an enhanced utilization of visible light and photoinduced electron delocalization ability. Therefore, the as‐prepared CNSC show a high hydrogen evolution rate of 39.6 µmol h^?1 with a turnover number of 24.98 in 1 h at λ > 400 nm. Under irradiation by longer wavelength of light (λ > 420 nm), CNSC still exhibit a superior hydrogen evolution rate, which is 72.9 and 5.4 times higher than that of bulk g‐C₃N₄ and g‐C₃N₄ nanosheets, respectively.     

苝四羧酸二酰亚胺修饰增强g-C_(3)N_(4)光催化性能EI北大核心CSCD

以3,4,9,10-苝四甲酸二酐和L-天冬氨酸为原料,合成水溶性苝二酰亚胺衍生物N,N′-二(2-丁二酸基)-3,4,9,10-苝四羧酸二酰亚胺(PASP)。采用水热法将PASP接枝在g-C_(3)N_(4)上,制备PASP改性g-C_(3)N_(4)复合光催化剂(g-C_(3)N_(4)-PASP)。通过X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FT-IR)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见光漫反射光谱(UV-Vis DRS)和固体荧光光谱等对g-C_(3)N_(4)-PASP的组成、结构、形貌和光学性质等进行表征,考察g-C_(3)N_(4)-PASP对水溶液中模型污染物亚甲基蓝(MB)的光催化降解活性。结果表明:g-C_(3)N_(4)与PASP经水热反应,可通过酰胺键共价结合;相比纯g-C_(3)N_(4),g-C_(3)N_(4)-PASP比表面积显著增大,吸收带边红移至614 nm,同时PASP修饰可促进g-C_(3)N_(4)材料表面光生电子和空穴分离,进而有效提升光催化活性。在可见光(λ>420 nm)照射下,g-C_(3)N_(4)-PASP对MB的降解率60 min内可达99.4%,降解速率常数k约为g-C_(3)N_(4)的2倍。     

Faster Electron Injection and More Active Sites for Efficient Photocatalytic H2 Evolution in g‐C3N4/MoS2 Hybrid

Herein, the structural effect of MoS₂ as a cocatalyst of photocatalytic H₂ generation activity of g‐C₃N₄ under visible light irradiation is studied. By using single‐particle photoluminescence (PL) and femtosecond time‐resolved transient absorption spectroscopies, charge transfer kinetics between g‐C₃N₄ and two kinds of nanostructured MoS₂ (nanodot and monolayer) are systematically investigated. Single‐particle PL results show the emission of g‐C₃N₄ is quenched by MoS₂ nanodots more effectively than MoS₂ monolayers. Electron injection rate and efficiency of g‐C₃N₄/MoS₂‐nanodot hybrid are calculated to be 5.96 × 10⁹ s^?1 and 73.3%, respectively, from transient absorption spectral measurement, which are 4.8 times faster and 2.0 times higher than those of g‐C₃N₄/MoS₂‐monolayer hybrid. Stronger intimate junction between MoS₂ nanodots and g‐C₃N₄ is suggested to be responsible for faster and more efficient electron injection. In addition, more unsaturated terminal sulfur atoms can serve as the active site in MoS₂ nanodot compared with MoS₂ monolayer. Therefore, g‐C₃N₄/MoS₂ nanodot exhibits a 7.9 times higher photocatalytic activity for H₂ evolution (660 µmol g?¹ h^?1) than g‐C₃N₄/MoS₂ monolayer (83.8 µmol g^?1 h^?1). This work provides deep insight into charge transfer between g‐C₃N₄ and nanostructured MoS₂ cocatalysts, which can open a new avenue for more rationally designing MoS₂‐based catalysts for H₂ evolution.     

Strongly Coupled g‐C3N4 Nanosheets‐Co3O4 Quantum Dots as 2D/0D Heterostructure Composite for Peroxymonosulfate Activation

The development of effective approaches for the preparation of 0D quantum dots (QDs)/2D nanosheets (NSs) heterostructures, which have been proven to be favorable for heterogeneous catalysis, is highly desirable but remains a great challenge. Herein, 0D metal oxide nanocrystals–2D ultrathin g‐C₃N₄ nanosheets (Co₃O₄/CNNS) heterostructures are synthesized via a facile chemical reaction, followed by annealing in air. Ultrafine Co₃O₄ QDs (≈2.2–3.2 nm) are uniformly and tightly attached on the surface of g‐C₃N₄ nanosheets. Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline (TC) via peroxymonosulfate (PMS) activation. The optimal catalyst, namely, Co₃O₄/CNNS‐1100, exhibits excellent performance and ≈98.7% TC can be degraded under visible light irradiation. Moreover, TC degradation is almost completely insusceptible to several real water samples. Meanwhile, other dye pollutants can also be efficiently degraded by the Co₃O₄/CNNS‐1100/PMS/vis system. The quenching tests display that that the h⁺, ?OH, O₂^??, and SO₄^?? are responsible for TC removal. The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic‐ and chemical‐processes in the PMS activation. This work gives an insight into the development of multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification.     

一步法合成磷掺杂石墨相氮化碳及其光催化性能

以尿素(CO(NH₂)₂)和磷酸氢二铵((NH₄)₂HPO₄)作为原料, 通过热聚合法制备了磷(P)掺杂石墨相氮化碳(g-C₃N₄)材料(P-CN)。通过X射线衍射、红外光谱、X射线光电子谱、扫描电子显微镜、透射电子显微镜、紫外可见漫反射光谱和N₂吸附-脱附对样品进行了表面形貌及结构表征, 通过对罗丹明B(RhB)的降解实验, 研究了样品的可见光催化性能, 对其催化机理进行了分析。结果表明, 合成过程中磷原子的掺杂会取代g-C₃N₄中的C原子, 从而改变g-C₃N₄的表面形貌和电子结构。在可见光条件下, P-CN材料表现出优异的光催化性能, 其对RhB的降解速率明显优于纯氮化碳。其中3%P-CN样品催化活性最高, 反应30 min时, RhB降解率达到96.8%。分析认为, P原子对g-C₃N₄中的C原子的取代使P-CN样品表面处于富电子状态, 并导致P-CN样品导带位置升高, 光电子还原性增强。这些电子与水中的溶解氧形成超氧自由基(·O₂^-), 从而使得光催化性能显著提高。     

Single Ni Atoms Anchored on Porous Few‐Layer g‐C3N4 for Photocatalytic CO2 Reduction: The Role of Edge Confinement

It is greatly intriguing yet remains challenging to construct single‐atomic photocatalysts with stable surface free energy, favorable for well‐defined atomic coordination and photocatalytic carrier mobility during the photoredox process. Herein, an unsaturated edge confinement strategy is defined by coordinating single‐atomic‐site Ni on the bottom‐up synthesized porous few‐layer g‐C₃N₄ (namely, Ni₅‐CN) via a self‐limiting method. This Ni₅‐CN system with a few isolated Ni clusters distributed on the edge of g‐C₃N₄ is beneficial to immobilize the nonedged single‐atomic‐site Ni species, thus achieving a high single‐atomic active site density. Remarkably, the Ni₅‐CN system exhibits comparably high photocatalytic activity for CO₂ reduction, giving the CO generation rate of 8.6 µmol g^?1 h^?1 under visible‐light illumination, which is 7.8 times that of pure porous few‐layer g‐C₃N₄ (namely, CN, 1.1 µmol g^?1 h^?1). X‐ray absorption spectrometric analysis unveils that the cationic coordination environment of single‐atomic‐site Ni center, which is formed by Ni‐N doping‐intercalation the first coordination shell, motivates the superiority in synergistic N–Ni–N connection and interfacial carrier transfer. The photocatalytic mechanistic prediction confirms that the introduced unsaturated Ni‐N coordination favorably binds with CO₂, and enhances the rate‐determining step of intermediates for CO generation.     

In Situ Synthesis of Few‐Layered g‐C3N4 with Vertically Aligned MoS2 Loading for Boosting Solar‐to‐Hydrogen Generation

In artificial photocatalytic hydrogen evolution, effective incident photon absorption and a high‐charge recombination rate are crucial factors influencing the overall efficiency. Herein, a traditional solid‐state synthesis is used to obtain, for the first time, novel samples of few‐layered g‐C₃N₄ with vertically aligned MoS₂ loading (MoS₂/C₃N₄). Thiourea and layered MoO₃ are chosen as precursors, as they react under nitrogen atmosphere to in situ produce the products. According to the quasi‐Fourier transform infrared reflectance and X‐ray diffraction measurements, the detailed reaction process is determined to proceed through the confirmed formation pathway. The two precursor units MoS₂ and C₃N₄ are linked by Mo? N bonds, which act as electronic receivers/conductors and hydrogen‐generation sites. Density functional theory is also carried out, which determines that the interface sites act as electron‐accumulation regions. According to the photoelectrochemical results, MoS₂/C₃N₄ can achieve a current of 0.05 mA cm^?2, which is almost ten times higher than that of bare g‐C₃N₄ or the MoS₂/C₃N₄‐R reference samples. The findings in the present work pave the way to not only synthesize a series of designated samples but also thoroughly understand the solid‐state reaction.     

硅藻土/g-C3N4复合材料的制备及其可见光增强活性

采用浸渍-焙烧法制备了具有可见光响应活性的硅藻土/g-C₃N₄复合光催化材料。利用TG、XRD、FE-SEM、HR-TEM、FT-IR、XPS、UV-Vis-DRS 和 PL谱等手段对其物相组成、形貌和光吸收特性进行表征。以RhB的光催化降解为探针反应评价催化剂的活性。光催化结果表明, 2.32wt%硅藻土/g-C₃N₄复合材料对RhB有较高的催化活性, 光催化降解的速率常数是纯g-C₃N₄的1.9倍。自由基捕获实验表明, ·O₂^-是RhB在硅藻土/g-C₃N₄复合材料上光催化降解的主要活性物种。光催化活性提高的主要原因在于硅藻土和g-C₃N₄之间静电作用有利于光生电子-空穴在g-C₃N₄表面的迁移, 进而提高g-C₃N₄的光催化活性。     

g-C3N4/高岭土复合材料的制备及其光催化性能研究

以水洗高岭土为载体, 采用盐酸对g-C₃N₄进行质子化处理, 通过浸渍法制备了g-C₃N₄/高岭土复合光催化材料。采用X射线衍射(XRD)、场发射扫描电镜(FESEM)和紫外-可见吸收光谱(UV-Vis)等手段对复合材料的晶体结构、微观形貌和光学性能进行了表征, 并以罗丹明B为目标降解物, 研究了复合材料在可见光下的光催化性能。结果表明: 当高岭土和g-C₃N₄的质量配比为6︰3时, g-C₃N₄/高岭土具有较优的光催化性能, 其光催化速率是纯g-C₃N₄的8.62倍; 高岭土和g-C₃N₄通过静电吸引力紧密结合在一起, 该复合结构能够有效地降低光生电子和空穴的复合几率, 改善了纯g-C₃N₄光催化材料的吸附性能, 进而有效提高了其光催化性能。     

Photoassisted Construction of Holey Defective g‐C3N4 Photocatalysts for Efficient Visible‐Light‐Driven H2O2 Production

Holey defective g‐C₃N₄ photocatalysts, which are easily prepared via a novel photoassisted heating process, are reported. The photoassisted treatment not only helps to create abundant holes, endowing g‐C₃N₄ with more exposed catalytic active sites and crossplane diffusion channels to shorten the diffusion distance of both reactants from the surface to bulk and charge carriers from the bulk to surface, but also introduces nitrogen vacancies in the tri‐s‐triazine repeating units of g‐C₃N₄, inducing the narrowing of intrinsic bandgap and the formation of defect states within bandgap to extend the visible‐light absorption range and suppress the radiative electron–hole recombination. As a result, the holey defective g‐C₃N₄ photocatalysts show much higher photocatalytic activity for H₂O₂ production with optimized enhancement up to ten times higher than pristine bulk g‐C₃N₄. The newly developed synthetic strategy adopted here enables the sufficient utilization of solar energy and shows rather promising for the modification of other materials for efficient energy‐related applications.     

Co_3O_4/mpg-C_3N_4催化剂的制备及其可见光催化性能研究

采用浸渍法制备了载钴介孔石墨相氮化碳(Co3O4/mpg-C3N4)催化剂,并对其进行X射线衍射(XRD),红外光谱(FT-IR),N2吸附脱附,紫外漫反射光谱(UV-vis DRS)和光生电流的表征。结果显示,Co3O4的引入提高了mpg-C3N4的光吸收性能,利于其表面光生电子和空穴的分离。将制得的Co3O4/mpg-C3N4用于可见光催化降解水中的亚甲基蓝(MB),其催化效率远高于mpg-C3N4,且最佳的钴负载量为3%。