Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols

A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C₃N₄ catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C₃N₄-OH) has been prepared from graphitic carbon nitride (g-C₃N₄) scaffold by converting the residual –NH₂ and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C₃N₄-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N₂ adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C₃N₄-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C₃N₄-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%).     

A simple and rapid route for synthesizing the nanosized g-C3N4 materials with narrow bandgap and their photocatalytic activity

The graphitic carbon nitride (g-C₃N₄) materials with many intriguing properties have attracted much attention in photocatalysis. The photocatalytic activity of g-C₃N₄ is hindered by serious aggregation and limited exposed active sites. Herein is shown that nanosized g-C₃N₄ can be simply obtained by a superfast high-pressure homogenization approach. The high-pressure homogenization treatment can provide strong force to cut and/or to exfoliate the bulk g-C₃N₄ into nanosized g-C₃N₄ with good dispersion. Moreover, choosing different solvents during treatment can cause a different surface structure of as-prepared nanosized g-C₃N₄. In addition, the narrow bandgap properties, the high photogenerated charge carrier separation, and the transport abilities are achieved in as-prepared nanosized g-C₃N₄ because of the retaining conjugated C₃N₄ system. Specifically, the photocatalytic activities of as-prepared nanosized g-C₃N₄ have been significantly enhanced in terms of degradation of organic dye Rhodamine B (RhB) under visible light irradiation (10 times higher than that of bulk g-C₃N₄). These findings can provide a promising and simple approach to the exfoliation, nanonization, and surface functionalization of 2D layered materials.     

Ag nanoparticles loaded on porous graphitic carbon nitride with enhanced photocatalytic activity for degradation of phenol

Highly efficient photocatalyst of visible-light-driven Ag nanoparticles loaded on porous graphitic carbon nitride (g-C₃N₄) was prepared by the reduction of Ag ions on porous g-C₃N₄. The obtained Ag/porous g-C₃N₄ composite products were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflection spectra (DRS), thermal gravimetric analysis (TGA). The results demonstrated that a homogeneous distribution of Ag NPs of 10 nm was attached onto the surface of the porous g-C₃N₄. The prepared Ag/porous g-C₃N₄ samples were applied for catalyzing the degradation of phenol in water under visible light irradiation. Porous g-C₃N₄ demonstrated an excellent support for the formation and dispersion of small uniform Ag NPs. When the weight percentage of Ag reaches 5%, the nanohybrid exhibits superior photocatalytic activities compared to bulk g-C₃N₄, porous g-C₃N₄, and 2% Ag/porous g-C₃N₄ hybrids. The enhanced photocatalytic performance is due to the synergic effect between Ag and porous g-C₃N₄, which suppressed the recombination of photogenerated electron-hole pairs.     

氮缺陷石墨相氮化碳的制备及其光催化降解环境有机污染物性能

通过在三聚氰胺热分解过程中加入NaHCO₃制备出具有氮缺陷的石墨相氮化碳（g-C₃N₄）,利用X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）、N₂吸附-脱附、X射线光电子能谱（XPS）、紫外-可见漫反射光谱（UV-vis DRS）和固体荧光光谱（PL）等方法对其进行表征,并在可见光（λ> 420nm）照射下,以水相中罗丹明B（RhB）的降解为模型反应,研究了该氮缺陷g-C₃N₄对有机污染物降解的光催化活性。结果表明,引入氮缺陷可以提高g-C₃N₄对可见光的吸收以及电子-空穴对的分离效率,进而提高g-C₃N₄的可见光催化活性。催化剂CNK0.005、CNK0.01和CNK0.05在30min内对RhB的降解率分别为79.8%、100.0%和87.6%;而在相同条件下,没有氮缺陷的g-C₃N₄对RhB的降解率仅为59.8%。     

Gold/monolayer graphitic carbon nitride plasmonic photocatalyst for ultrafast electron transfer in solar-to-hydrogen energy conversion

Gold (Au) plasmonic nanoparticles were grown evenly on monolayer graphitic carbon nitride (g-C₃N₄) nanosheets via a facile oil-bath method. The photocatalytic activity of the Au/monolayer g-C₃N₄ composites under visible light was evaluated by photocatalytic hydrogen evolution and environmental treatment. All of the Au/monolayer g-C₃N₄ composites showed better photocatalytic performance than that of monolayer g-C₃N₄ and the 1% Au/monolayer g-C₃N₄ composite displayed the highest photocatalytic hydrogen evolution rate of the samples. The remarkable photocatalytic activity was attributed largely to the successful introduction of Au plasmonic nanoparticles, which led to the surface plasmon resonance (SPR) effect. The SPR effect enhanced the efficiency of light harvesting and induced an efficient hot electron transfer process. The hot electrons were injected from the Au plasmonic nanoparticles into the conduction band of monolayer g-C₃N₄. Thus, the Au/monolayer g-C₃N₄ composites possessed higher migration and separation efficiencies and lower recombination probability of photogenerated electron-hole pairs than those of monolayer g-C₃N₄. A photocatalytic mechanism for the composites was also proposed.     

Tuning band structure of graphitic carbon nitride for efficient degradation of sulfamethazine: Atmospheric condition and theoretical calculation

Numerous approaches have been used to modify graphitic carbon nitride（g-C₃N₄） for improving its photocatalytic activity. In this study, we demonstrated a facial post-calcination method for modified graphitic carbon nitride（g-C₃N₄-Ar/Air） to direct tuning band structure, i.e., bandgap and positions of conduction band（CB）/valence band（VB）, through the control of atmospheric condition without involving any additional elements or metals or semiconductors. ...     

钾离子掺杂对石墨型氮化碳光催化剂能带结构及光催化性能的影响

以双氰胺和氢氧化钾为原料制备了能带可控的钾离子掺杂石墨型氮化碳(g-C3N4)光催化剂,并与碱处理的g-C3N4及g-C3N4/KOH复合催化剂进行了对比。采用X射线衍射(XRD)光谱、紫外-可见(UV-Vis)光谱、傅里叶变换红外(FTIR)光谱、N2吸附、电感耦合等离子体-原子发射光谱(ICP-AES)、荧光(PL)光谱、X 光电子能谱(XPS)等分析手段对制备的催化剂进行了表征。结果表明,钾离子含量对氮化碳催化剂的价带及导带位置有显著影响。此外,钾离子的引入抑制了氮化碳晶粒的生长,提高了氮化碳的比表面积以及对可见光的吸收,降低了光生电子-空穴对的复合几率。以染料罗丹明B的降解为探针反应系统研究了钾离子掺杂对g-C3N4在可见光下催化性能的影响,研究了光催化反应机理。结果表明,钾离子掺杂后氮化碳的光催化性能显著提高。制备的钾离子掺杂氮化碳催化剂表现出良好的结构及催化稳定性。     

Synthesis g-C3N4 of high specific surface area by precursor pretreatment strategy with SBA-15 as a template and their photocatalytic activity toward degradation of rhodamine B

Using SBA-15 as a template, high surface area porous graphitic carbon nitrides (g-C₃N₄) were successfully synthesized by pretreating melamine using hydrochloric acid, and fully characterized by Fourier-Transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron micrographs (SEM), N₂ adsorption-desorption, ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL) spectrum. The results of these analyses indicated that the g-C₃N₄ synthesized from HCl-pretreated melamine with SBA-15 as a template has enhanced specific surface area and increased the separation rate of the photogenerated electrons and holes compared with bulk g-C₃N₄, but didn’t change the structure of bulk g-C₃N₄. The photocatalytic activity of samples was evaluated by the degradation of rhodamine B (RhB) under xenon lamp. The results indicated that the activity was improved significantly with the increase of specific surface area. The rate constant for CN-3（HCl pretreatment melamine precursor and SBA-15 as a template） was 13 times as high as g-C₃N₄. Furthermore, the CN-3 catalyst exhibited outstanding structural and catalytic stability.     

A facile single-step approach to achieve in situ expanded g-C3N4 for improved photodegradation performance

Improved graphitic carbon nitride (g-C₃N₄) was synthesized through a unique one-step cost-effective technique involving a dynamic gas bubbling phenomenon using ammonium chloride (NH₄Cl) as a bubbling agent. An extensive investigation was carried out to optimize the weight ratio of NH₄Cl and melamine during the thermal pyrolysis process. Here, we report an improved form of g-C₃N₄ namely “expanded g-C₃N₄” with increased interlayer distance and remarkable volume expansion. The surface area of this improved version has notably increased leading to higher photocatalytic efficiency as compared with its counterpart, an synthesized without adding NH₄Cl. Synthesized photocatalyst materials were further used to study the Rhodamine B photodegradation under visible light. It was observed that the expanded g-C₃N₄ showed a 2.4 times higher photodegradation rate than its counterpart and degraded 94% of the dye in just 30 min.     

Exited State Absorption Upconversion Induced by Structural Defects for Photocatalysis with a Breakthrough Efficiency

The nitrogen-deficient graphitic carbon nitride (g-C₃N₄) has been prepared, a new excited state absorption (ESA) up-conversion mode is discovered, which is directly induced by structural defects, showing distinct chemical characteristics from those based on lanthanide ions and triplet states chromophores. The abundant N_2C vacancies in g-C₃N₄ nanosheets work as the crucial intermediate excitation states, which lead to g-C₃N₄ upconverted emitting at the wavelength of 436 nm excited by the light with the wavelength of 800 nm. This process is proven to proceed via a two-photon involved ESA mode with a breakthrough quantum efficiency of 0.64 %. Further, we combine N_2C vacancies enriched g-C₃N₄ with In₂S₃ and CdS, and successfully achieved an infrared light driven photocatalytic reactions. These findings offered a new family of up-conversion materials; more semiconductors with various structural defects are potential complementary members.     

MoS_2/g-C_3N_4复合材料的制备及可见光催化性能

首先在N-甲基吡咯烷酮溶液中超声剥离得到少层的MoS_2,将其与石墨相氮化碳(g-C_3N_4)复合,制得MoS_2/g-C_3N_4复合材料。采用X射线衍射(XRD),扫描电镜(SEM),X射线光电子能谱(XPS),傅里叶变换红外光谱(FTIR),Raman光谱,紫外-可见漫反射吸收光谱(DRS)和光致荧光(PL)技术对复合材料进行表征。可见光下考察MoS_2/g-C_3N_4复合材料光催化降解罗丹明B(Rh B)的活性,结果表明:将少量MoS_2与g-C_3N_4复合可明显提高光催化活性,且1%(w/w)MoS_2/g-C_3N_4复合物的光催化活性最高,可能的原因是MoS_2和g-C_3N_4匹配的能带结构,增大了界面间电荷的传输,降低了光生电子-空穴的复合,进而提高了光催化活性。     

MoS2/g-C3N4复合材料的制备及可见光催化性能

首先在N-甲基吡咯烷酮溶液中超声剥离得到少层的MoS₂,将其与石墨相氮化碳（g-C₃N₄）复合,制得MoS₂/g-C₃N₄复合材料。采用X射线衍射（XRD）,扫描电镜（SEM）,X射线光电子能谱（XPS）,傅里叶变换红外光谱（FTIR）,Raman光谱,紫外-可见漫反射吸收光谱（DRS）和光致荧光（PL）技术对复合材料进行表征。可见光下考察MoS₂/g-C₃N₄复合材料光催化降解罗丹明B（RhB）的活性,结果表明：将少量MoS₂与g-C₃N₄复合可明显提高光催化活性,且1%（w/w）MoS₂/g-C₃N₄复合物的光催化活性最高,可能的原因是MoS₂和g-C₃N₄匹配的能带结构,增大了界面间电荷的传输,降低了光生电子-空穴的复合,进而提高了光催化活性。     

Graphitic carbon nitride embedded hydrogels for enhanced gel electrophoresis

Here, we show, for the first time, the use of graphitic carbon nitride (g-C₃N₄) nanosheets to improve the resolution and efficiency of protein separation in gel electrophoresis. By loading 0.04% (m/v) g-C₃N₄ nanosheets into the polyacrylamide gel at 25 °C, the thermal conductivity increased approximately 80% which resulted in 20% reduction in Joule heating and overall increase of separation efficiency. Also, polymerization of acrylamide occurred in the absence of tetramethylethylenediamine (TEMED) when the polyacrylamide gel contained g-C₃N₄ nanosheets. Hence, the g-C₃N₄ act simultaneously as a polymerization catalyst as well as heat sinks to lower Joule heating effect on band broadening.     

A fantastic graphitic carbon nitride (g-C3N4) material: Electronic structure,photocatalytic and photoelectronic properties

As an analog of graphite, graphitic carbon nitride (g-C₃N₄) has been the hotspot in the materials science for its unique electronic structure. With medium band gap as well as thermal and chemical stability in ambient environment, it becomes one of the most promising photocatalytic materials. Intensive investigation has been focus on its photocatalytic performance for various reactions to date. What is more, controllable modulation of its electronic structure via doping or chemical functionalization is available. In addition, considerable attention has been paid on its photoelectronic application, such as light emitting device, photocathode, optical sensor, etc. Based on the electronic properties and pathway to modulate its electronic structure, in this review, we highlight the applications of g-C₃N₄ ranging from photocatalytic to photoelectronic materials.     

Fe掺杂g-C3N4的制备及其可见光催化性能

以硝酸铁和三聚氰胺为原料制备不同含铁量的Fe 掺杂石墨氮化碳（g-C₃N₄）. 采用X 射线衍射光谱（XRD）、紫外-可见（UV-Vis）光谱、傅里叶变换红外（FT-IR）光谱、电感耦合等离子体-原子发射光谱（ICP-AES）、荧光（PL）光谱、X光电子能谱（XPS）等分析手段对制备的催化剂进行了表征. 结果表明,铁以离子形式镶嵌在g-C₃N₄的结构单元中,影响了g-C₃N₄的能带结构,增加了g-C₃N₄对可见光的吸收,降低了光生电子-空穴对的复合几率. 以染料罗丹明B的降解为探针反应系统研究了不同含铁量对g-C₃N₄在可见光下催化性能的影响. 结果表明,m（Fe）/m（g-C₃N₄）=0.14%时,制备的Fe 掺杂g-C₃N₄表现出最佳的光催化性能,120 min 内罗丹明B的降解率高达99.7%,速率常数达到0.026 min^-1,是纯g-C₃N₄的3.2 倍. 以叔丁醇、对苯醌、乙二胺四乙酸二钠为自由基（·OH）、自由基（O₂^-·）和空穴（h_VB⁺）的捕获剂,研究了光催化反应机理.     

g-C3N4-BiOBr复合材料制备及可见光催化性能

利用原位沉积法将BiOBr纳米片生长到g-C₃N₄表面,制得g-C₃N₄-BiOBr p-n型异质结复合光催化剂。采用X射线衍射(XRD)、红外光谱(FTIR)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、紫外可见漫反射(UV-Vis-DRS)和荧光光谱(PL)等测试对光催化剂结构和性能进行表征。通过可见光辐照降解甲基橙水溶液检测评估复合光催化剂光催化活性。研究结果表明:复合光催化剂由BiOBr和g-C₃N₄两相组成,BiOBr纳米片在片状g-C₃N₄表面快速形核生长形成面-面复合结构。相比于纯相g-C₃N₄和BiOBr,g-C₃N₄-BiOBr复合材料具有更强可见光吸收能力,吸收带边红移。在可见光辐照100 min后,性能最佳的2:8 g-C₃N₄-BiOBr复合光催化剂光催化活性分别是纯相g-C₃N₄和BiOBr的1.8和1.2倍,经过4次循环实验后,其降解率仍达84%,说明复合结构光催化剂催化性能和稳定性增强。复合光催化剂的荧光强度显著降低,说明光生载流子复合得到了有效抑制。复合光催化剂催化性能的提高归因于p-n型异质结促进电荷有效分离、抑制电子-空穴复合和吸收光波长范围的扩展,相比单一成分材料具有更好的催化活性和稳定性。自由基捕获实验证明,可见光降解甲基橙光催化过程中的主要活性成分为空穴,并据此提出了可能的光催化机理。     

Exploring recent advances in silver halides and graphitic carbon nitride-based photocatalyst for energy and environmental applications

Engineering visible light active photocatalytic systems for renewable energy production and environmental remediation has always been a promising technology to counter overall energy demands and pollution challenges. As a fascinating conjugated polymer graphitic carbon nitride (g-C₃N₄) has been developed as a hotspot in the research field as a metal-free semiconducting material with the appealing band gap of 2.7 eV. Recently, g-C₃N₄ has gained tremendous interest in photocatalytic wastewater abatement as well as for hydrogen (H₂) generation, carbon dioxide (CO₂) reduction, and pollutant degradation, under exposure to visible light. Plasmonic silver halides (AgX) such as AgCl, AgBr, and AgI as plasmonic photocatalyst have received immense research interest owing to their escalating photocatalytic efficacy and strong surface plasmon resonance effect (SPR). AgX is the photosensitive, broad bandgap semiconducting materials with effectual antimicrobial properties. This review summarizes the heterostructure of carbonaceous g-C₃N₄ with plasmonic AgX, to reduce the recombination of photo-generated charge carriers, thus enhancing the natural light absorption. g-C₃N₄ grafted AgX nanoarchitectures can be utilized for several potential applications, for instance, overall water splitting (OWS), CO₂ conversion to hydrocarbon fuels, pollutant exclusion, and antibacterial disinfection. This review focuses on the evolution of g-C₃N₄ as well as AgX, facile, and synthetic routes for fabrication of g-C₃N₄ tailored AgX, construction of nano-junctions (AgX/g-C₃N₄) with various photocatalytic applications. Finally, we provided a viewpoint of current hassles and some perceptions of novel trends in this exciting as well as developing research arena.     

Facile and efficient fabrication of g-C3N4 quantum dots for fluorescent analysis of trace copper(II) in environmental samples

The facile preparation of g-C₃N₄ QDs with high fluorescent performance has become an important direction in the last decade. Herein, we develop a facile, rapid approach to synthesize highly fluorescent QDs based on recrystallization and ultrasonic exfoliation. Size-controllable graphitic carbon nitride (g-C₃N₄) QDs can be obtained from the precursor of recrystallized dicyandiamide, only 90 min is needed and the size of QDs is adjusted from 5 nm to 200 nm by controlling the ultrasonic time. Moreover, better fluorescent efficiency is also obtained comparing to traditional g-C₃N₄ QDs. The obtained g-C₃N₄ QDs responds to Cu(II) in the 0.5 nmol/L to 30 μmol/L concentration range, with a 0.3 nmol/L detection limit. The method was applied to the determination of Cu(II) in different environmental water samples.     

Nanocavity-assisted single-crystalline Ti3+ self-doped blue TiO2(B) as efficient cocatalyst for high selective CO2 photoreduction of g-C3N4

Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) has invoked significant interest for photocatalytic applications for its excellent features such as high surface area, visible light absorption, and easy transportation of photogenerated charge carriers, but the most reported g-C₃N₄ show relatively low photoactivity due to inferior conductivity and rapid recombination of carriers. These can be overcome by inducing porosity in g-C₃N₄, followed by exfoliation and combining with other materials. Herein, we synthesize nanocavity-assisted oxygen-deficient Ti³⁺ self-doped blue TiO₂(B) nanorods (BT) and integrate them on exfoliated porous g-C₃N₄ (PCN). The synthesized materials are tested for photocatalytic conversion of CO₂ into solar fuels (H₂, CO, and CH₄). The fabricated BT/PCN heterostructures exhibit higher photocatalytic CO₂ conversion activity and 92% CO-evolving selectivity than BT and PCN. The enhancement in activity of BT/PCN can be attributed to the efficient separation and transportation of charge carriers, facilitated by the unique properties of BT, PCN, and their synergistic interactions. We believe that these results can contribute to the improvement of cost-effectiveness, feasibility, and overall performance for real photocatalytic systems.     

Novel CaCO3/g-C3N4 composites with enhanced charge separation and photocatalytic activity

A novel CaCO₃/graphitic carbon nitride (g-C₃N₄) photocatalyst was synthesized for the first time via a facile calcination method using CaCO₃ and melamine as precursors. The as-prepared samples were characterized using various techniques, such as scanning and transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, as well as Fourier-transform infrared, X-ray photoelectron, photoluminescence, and UV–vis diffuse reflectance spectroscopy. The results of the experiments confirm the successful coupling of CaCO₃ to g-C₃N₄. The photocatalytic activity of the synthesized CaCO₃/g-C₃N₄ composites was evaluated by assessing their performance in the photocatalytic degradation of crystal violet (CV) in water under visible light irradiation. The analysis shows that CaCO₃/g-C₃N₄ exhibits higher photocatalytic activity towards CV degradation (76.0%) than pristine g-C₃N₄ (21.6%) and CaCO₃ (23.2%). Radical trapping and electron spin resonance experiments show that hydroxyl radicals (OH) and holes (h⁺) are the key reactive species in the photocatalytic process. The enhanced photocatalytic activity of the composite is mainly attributed to the efficient separation rate of electron-hole pairs achieved through the incorporation of CaCO₃.