Engineering oxygen into ultrathin graphitic carbon nitride: synergistic improvement of electron reduction and charge carrier dynamics for efficient photocatalysis

The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C₃N₄) materials in the field of photocatalytic hydrogen (H₂) evolution. Here, ultrathin oxygen (O) engineered g-C₃N₄ (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H₂ evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H₂ evolution (93.78 μmol h^?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h^?1. Furthermore, the H₂ evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h^?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C₃N₄ to achieve efficient photocatalytic H₂ evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation.     

Semi-chemical interaction between graphitic carbon nitride and Pt for boosting photocatalytic hydrogen evolution

Owing to the exorbitant overpotential and serious carrier recombination of graphitic carbon nitride （gC₃N₄）,noble metal （NM） is usually served as the H₂evolution co-catalyst.Although the NM （such as Pt）nanoparticles can reduce the H₂evolution overpotential,the weak van der Waals interaction between Pt and g-C₃N₄makes against the charge transfer.Herein,the solvothermal method is developed to achieve semi-chemical interaction betwee...     

Two-step calcination synthesis of Z-scheme α-Fe2O3/few-layer g-C3N4 composite with enhanced hydrogen production and photodegradation under visible light

Solar photocatalytic technology is of great significance for adjusting energy structure and environmental improvement. Developing an efficient and low-cost photocatalyst is key to realizing the conversion of solar to chemical energy. In this study, α-Fe₂O₃-modified few-layer g-C₃N₄ hybrids (α-Fe₂O₃/FL g-C₃N₄) were successfully prepared by a two-step calcination route with a mixture of α-Fe₂O₃ and melamine. The samples were characterized by Thermogravimetric analysis, X-ray diffraction, Fourier transform infrared, scanning electron microscope, transmission electron microscope, High-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, UV–Vis absorption spectrum, photoluminescence, and Time-resolved photoluminescence spectroscopy; furthermore, their photoelectrochemical measurements and their photocatalytic performances were evaluated by visible light-driven hydrogen evolution and degradation of RhB. The results showed that the hydrogen production activity and degradation ability of α-Fe₂O₃/FL g-C₃N₄ were significantly enhanced compared with those of α-Fe₂O₃ / multilayer g-C₃N₄ (α-Fe₂O₃/ML g-C₃N₄) and FL g-C₃N₄. The enhanced photoactivities were mainly attributed to the synergistic effect between the increased visible-light absorption, enhanced surface area, and highly efficient electron transfer and separation on the Z-type heterojunction interface. This work not only provides evidence for the formation of FL g-C₃N₄ nanosheets using a thermal exfoliation method but also provides new insights into the interfacial charge carrier dynamics of Z-scheme α-Fe₂O₃/FL g-C₃N₄ heterostructures for photocatalytic H₂ generation and pollutant degradation.     

Advantageous Interfacial Effects of AgPd/g-C3N4 for Photocatalytic Hydrogen Evolution: Electronic Structure and H2O Dissociation

Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C₃N₄ sample has superior activity to Ag/g-C₃N₄ and Pd/g-C₃N₄ photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C₃N₄, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H₂O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H₂O dissociation to radical species on the AgPd/g-C₃N₄ photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C₃N₄, that is, Pd^δ−⋅⋅⋅Ag^δ+, and the activation energy of H₂O molecule dissociation on AgPd/g-C₃N₄ is the lowest, which is the main contributor to the enhanced photocatalytic H₂ evolution.     

Novel PtPd alloy nanoparticle-decorated g-C3N4 nanosheets with enhanced photocatalytic activity for H2 evolution under visible light irradiation

PtPd bimetallic alloy nanoparticle (NP)-modified graphitic carbon nitride (g-C₃N₄) nanosheet photocatalysts were synthesized via chemical deposition precipitation. Characterization of the photocatalytic H₂ evolution of the g-C₃N₄ nanosheets shows that it was significantly enhanced when PtPd alloy NPs were introduced as a co-catalyst. The 0.2 wt% PtPd/g-C₃N₄ composite photocatalyst gave a maximum H₂ production rate of 1600.8 μmol g^–1 h^–1. Furthermore, when K₂HPO₄ was added to the reaction system, the H₂ production rate increased to 2885.0 μmol g^–1 h^–1. The PtPd/g-C₃N₄ photocatalyst showed satisfactory photocatalytic stability and was able to maintain most of its photocatalytic activity after four experimental photocatalytic cycles. In addition, a possible mechanism for the enhanced photocatalytic activity was proposed and verified by various photoelectric techniques. These results demonstrate that the synergistic effect between PtPd and g-C₃N₄ helps to greatly improve the photocatalytic activity of the composite photocatalyst.     

Integrating non-precious-metal cocatalyst Ni3N with g-C3N4 for enhanced photocatalytic H2 production in water under visible-light irradiation

Photocatalytic H₂ production via water splitting in a noble-metal-free photocatalytic system has attracted much attention in recent years. In this study, noble-metal-free Ni₃N was used as an active cocatalyst to enhance the activity of g-C₃N₄ for photocatalytic H₂ production under visible-light irradiation (λ > 420 nm). The characterization results indicated that Ni₃N nanoparticles were successfully loaded onto the g-C₃N₄, which accelerated the separation and transfer of photogenerated electrons and resulted in enhanced photocatalytic H₂ evolution under visible-light irradiation. The hydrogen evolution rate reached ～305.4 μmol h^?1 g^?1, which is about three times higher than that of pristine g-C₃N₄, and the apparent quantum yield (AQY) was ～0.45% at λ = 420. Furthermore, the Ni₃N/g-C₃N₄ photocatalyst showed no obvious decrease in the hydrogen production rate, even after five cycles under visible-light irradiation. Finally, a possible photocatalytic hydrogen evolution mechanism for the Ni₃N/g-C₃N₄ system is proposed.     

分级孔结构g-C3N4光催化剂的制备及性能

以单分散SiO2为模板,通过简单的一步煅烧法制备具有分级孔结构的g-C3N4。与体相g-C3N4相比,分级孔结构的g-C3N4不仅可见光吸收性能和比表面积得到提高,而且更有利于光生电子-空穴的分离。此外,具有分级孔结构的g-C3N4具有明显增强的可见光驱动的光催化产氢活性,当SiO2和二氰二胺质量比为1∶1时,制备所得g-C3N4(C3N4-2)产氢速率几乎是体相g-C3N4的18倍。     

Controllable design of Zn-Ni-P on g-C3N4 for efficient photocatalytic hydrogen production

Synthesizing a stable and efficient photocatalyst has been the most important research goal up to now. Owing to the dominant performance of g-C₃N₄ (graphitized carbonitride), an ordered assemble of a composite photocatalyst, Zn-Ni-P@g-C₃N₄, was successfully designed and controllably prepared for highly efficient photocatalytic H₂ evolution. The electron transport routes were successfully adjusted and the H₂ evolution was greatly improved. The maximum amount of H₂ evolved reached about 531.2 μmol for 5 h over Zn-Ni-P@g-C₃N₄ photocatalyst with a molar ratio of Zn to Ni of 1:3 under illumination of 5 W LED white light (wavelength 420 nm). The H₂ evolution rate was 54.7 times higher than that over pure g-C₃N₄. Moreover, no obvious reduction in the photocatalytic activity was observed even after 4 cycles of H₂ production for 5 h. This synergistically increased effect was confirmed through the results of characterizations such as XRD, TEM, SEM, XPS, N₂ adsorption, UV-vis DRS, transient photocurrent, FT-IR, transient fluorescence, and Mott-Schottky studies. These studies showed that the Zn-Ni-P nanoparticles modified on g-C₃N₄ provide more active sites and improve the efficiency of photogenerated charge separation. In addition, the possible mechanism of photocatalytic H₂ production is proposed.     

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.     

NiFe2O4/g-C3N4 heterojunction composite with enhanced visible-light photocatalytic activity

Spinel structure nickel ferrite (NiFe₂O₄) doped graphitic carbon nitride (g-C₃N₄) photocatalyst NiFe₂O₄/g-C₃N₄ was synthesized by the coprecipitation route to enhance the photocatalytic activity for the visible-light driven degradation of methyl orange. The NiFe₂O₄ doping content is responsible for the microstructure and photocatalytic activity of NiFe₂O₄/g-C₃N₄ samples. Compared with pure NiFe₂O₄ and g-C₃N₄, the 2-NiFe₂O₄/g-C₃N₄ composite with NiFe₂O₄ doping of 2.0 wt% exhibited excellent photocatalytic activity and superior stability after five runs for degrading methyl orange under visible light irradiation. The catalytic activity of 2-NiFe₂O₄/g-C₃N₄ sample produced using the coprecipitation route was higher than those of conventional 2-NiFe₂O₄/g-C₃N₄ bulks prepared by the impregnation approach. The prepared samples for the photocatalytic degradation of methyl orange followed pseudo-first-order reaction kinetics. It’s ascribed to the synergistic effect between NiFe₂O₄ and g-C₃N₄, which can inhibit the recombination of photoexcited electron-hole pairs, accelerate photoproduced charges separation, and enhance the visible light absorption.     

Hydrogen production and photocatalytic activity of g-C3N4/Co-MOF (ZIF-67) nanocomposite under visible light irradiation

Herein, cobalt (Co)-based metal–organic zeolitic imidazole frameworks (ZIF-67) coupled with g-C₃N₄ nanosheets synthesized via a simple microwave irradiation method. SEM, TEM and HR-TEM results showed that ZIF-67 were uniformly dispersed on g-C₃N₄ surfaces and had a rhombic dodecahedron shape. The photocatalytic properties of g-C₃N₄/ZIF-67 nanocomposite were evaluated by photocatalytic dye degradation of crystal violet (CV), 4-chlorophenol (4-CP) and photocatalytic hydrogen (H₂) production. In presence of visible light illumination, the photocatalytic dye results showed that 95% CV degradation and 53% 4-CP degradation within 80 min. The H₂ production of the g-C₃N₄/ZIF-67 composite was 2084 μmol g⁻¹, which is 3.84 folds greater than that of bare g-C₃N₄ (541 μmol g⁻¹).     

In Situ Synthesis of Cu3P/P-Doped g-C3N4 Tight 2D/2D Heterojunction Boosting Photocatalytic H2 Evolution†

Heterojunction design in a two-dimensional (2D) fashion has been deemed beneficial for improving the photocatalytic activity of g-C₃N₄ because of the promoted interfacial charge transfer, yet still facing challenges. Herein, we construct a novel 2D/2D Cu₃P nanosheet/P-doped g-C₃N₄ (PCN) nanosheet heterojunction photocatalyst (PCN/Cu₃P) through a simple in-situ phosphorization treatment of 2D/2D CuS/g-C₃N₄ composite for photocatalytic H₂ evolution. We demonstrate that the 2D lamellar structure of both CuS and g-C₃N₄ could be well reserved in the phosphorization process, while CuS and g-C₃N₄ in-situ transformed into Cu₃P and PCN, respectively, leading to the formation of PCN/Cu₃P tight 2D/2D heterojunction. Owing to the large contact area provided by intimate face-to-face 2D/2D structure, the PCN/Cu₃P photocatalyst exhibits significantly enhanced charge separation efficiency, thus achieving a boosted visible-light-driven photocatalytic behavior. The highest rate for H₂ evolution reaches 5.12 μmol·h^–1, nearly 24 times and 368 times higher than that of pristine PCN and g-C₃N₄, respectively. This work represents an excellent example in elaborately constructing g-C₃N₄-based 2D/2D heterostructure and could be extended to other photocatalyst/co-catalyst system.      

BiOBr/g-C3N4 S型异质结无H2O2光-自芬顿高效催化降解RhB

通过焙烧-超声混合法成功地制备了BiOBr/g-C₃N₄S型异质结复合光催化剂。采用多种表征手段对样品物理属性进行了表征,包括X射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)。研究了所制备样品有/无Fe³⁺的光-自芬顿催化/光催化降解罗丹明B(RhB)性能。通过捕获实验确定了光催化反应中的主要活性物种,提出了光-自芬顿反应的降解机理。研究结果表明,BiOBr/g-C₃N₄S型异质结能原位生成H₂O₂,添加Fe³⁺后,H₂O₂被原位活化成活性物种且光生电流和载流子分离效率获得显著提高。该光-自芬顿过程能高效降解RhB,其反应速率常数为0.208 min^-1,约为无Fe³⁺光催化反应速率常数的5.3倍,在光-自芬顿循环使用过程中表现出良好的稳定性。Fe...     

Photocatalytic desulfurization of thiophene base on molecular oxygen and zinc phthalocyanine/g-C3N4

Oxidative desulfurization is considered to be one of the promising new methods for super-deep desulfurization of fuel oil. Herein, zinc phthalocyanine/g-C₃N₄ (g-C₃N₄/ZnTcPc) composites were synthesized by a facile in situ hydrothermal technique, utilizing g-C₃N₄, Zn(CH₃COO)₂ and 1,2,4-benzenetricarboxylic anhydride as the precursors. The crystal structure, morphology and chemical environment of the catalysts were respectively confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the resulting g-C₃N₄/ZnTcPc composites was evaluated by desulfurization of thiophene in fuel under visible light with molecular O₂ as the oxidant. Compared with pure g-C₃N₄ and ZnTcPc, g-C₃N₄/ZnTcPc presented a significantly enhanced photocatalytic activity for the degradation of thiophene in fuel under visible irradiation. Sulfur content of model gasoline (800 ppm) after desulfurization for 90 min was decreased to 125 ppm. The possible preparation pathway of g-C₃N₄/ZnTcPc has been proposed according to the results of XRD and TEM. The formation mechanism of g-C₃N₄/ZnTcPc–O₂ complex is proposed to be desulfurization by molecular oxygen.

     

BiOBr/g-C3N4 S型异质结无H2O2光-自芬顿高效催化降解RhB

通过焙烧-超声混合法成功地制备了BiOBr/g-C₃N₄ S型异质结复合光催化剂。采用多种表征手段对样品物理属性进行了表征,包括X射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-VisDRS)。研究了所制备样品有/无Fe³⁺的光-自芬顿催化/光催化降解罗丹明B (RhB)性能。通过捕获实验确定了光催化反应中的主要活性物种,提出了光-自芬顿反应的降解机理。研究结果表明,BiOBr/g-C₃N₄ S型异质结能原位生成H₂O₂,添加Fe³⁺后,H₂O₂被原位活化成活性物种且光生电流和载流子分离效率获得显著提高。该光-自芬顿过程能高效降解RhB,其反应速率常数为0.208 min^-1,约为无Fe³⁺光催化反应速率常数的5.3倍,在光-自芬顿循环使用过程中表现出良好的稳定性。Fe³⁺的加入促进了光生电荷的分离和H₂O₂的活化,超氧阴离子自由基(·O₂^-)、空穴和羟基是光-自芬顿催化过程中的主要活性物种,且·O₂^-作用更大。     

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.     

Boron doped 1T phase MoS2 as a cocatalyst for promoting photocatalytic H2 evolution of g-C3N4 nanosheets

As one of the 2D transition metal sulfides,1T phase MoS₂ nanosheets (NSs) have been studied because of their distinguished conductivity and suitable electronic structure.Nevertheless,the active sites are limited to a small number of edge sites only,while the basal plane is catalytically inert.Herein,we report that boron (B) doped 1T phase Mo S₂NSs can replace precious metals as a co-catalyst to assist in photocatalytic H₂production of 2D layered g-C₃N<...     

Enhancement in the photocatalytic activity of TiO2 nanofibers hybridized with g-C3N4 via electrospinning

TiO₂/g-C₃N₄ nanofibers with diameter of 100–200 nm were prepared by electrospinning method after calcination at high temperature, using polyvinylpyrrolidone (PVP), Melamine (C₃H₆N₆), Ti(OC₄H₉)₄ as raw materials. The composite nanofibers were characterized by XRD, FT-IR, SEM, UV–vis and PL respectively. The effects of different g-C₃N₄ contents on structure and photocatalytic degradation of the composite nanofibers were investigated. The results indicated that with increasing g-C₃N₄ content, the diameter of the composite fibers increased and the morphology changed from uniform structure to a nonuniform one, containing beads. The composite nanofibers displayed the best photocatalytic degradation on RhB, when the g-C₃N₄ content was 0.8 wt%. The degree of degradation was up to 99% at the optimal conditions of 40 min. The degradation activity of the composite nanofibers on RhB, MB and MO was found to be higher than that of the TiO₂ nanofibers.     

Enhanced photocatalytic H2 production over dual-cocatalyst-modified g-C3N4 heterojunctions

Ag nanoparticles (NPs) were deposited on the surface of g-C₃N₄ (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H₂ generation performance under solar-light irradiation. An H₂ production rate of 9.728 mmol·g^?1·h^?1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C₃N₄, 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H₂ generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C₃N₄, which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H₂ production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C₃N₄-related composite photocatalysts for H₂ production by using different co-catalysts.     

Highly enhanced visible-light photocatalytic hydrogen evolution on g-C3N4 decorated with vopc through π-π interaction

Photocatalytic H₂ evolution reactions on pristine graphitic carbon nitrides (g-C₃N₄), as a promising approach for converting solar energy to fuel, are attractive for tackling global energy concerns but still suffer from low efficiencies. In this article, we report a tractable approach to modifying g-C₃N₄ with vanadyl phthalocyanine (VOPc/CN) for efficient visible-light-driven hydrogen production. A non-covalent VOPc/CN hybrid photocatalyst formed via π-π stacking interactions between the two components, as confirmed by analysis of UV-vis absorption spectra. The VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good stability. Under optimal conditions, the corresponding H₂ evolution rate is nearly 6 times higher than that of pure g-C₃N₄. The role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs effectively. It is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C₃N₄-based hybrid systems with strong light absorption and high-efficiency carrier separation.