Hydrocarbon production by addition of Cu-ZnO on g-C3N4 for CO2 conversion

In this study, copper/zinc oxide/graphite nitrogen carbide (Cu/ZnO/g-C₃N₄) is prepared using a hydrothermal method and applied as a photocatalyst for CO₂ photoreduction. The morphology and structural properties of the obtained Cu/ZnO/g-C₃N₄ are systematically characterized through X-ray powder diffraction, ultraviolet–visible absorption spectroscopy, transmission electronic microscopy, and photoluminescence spectroscopy. A 3 wt% Cu/ZnO/g-C₃N₄ photocatalyst exhibits high CH₄ (40.7 μmol g⁻¹ hr⁻¹), CO (65.1 μmol g⁻¹ hr⁻¹), and CH₃OH (92.5 μmol g⁻¹ hr⁻¹) production rates, which are 38.3, 77.1, and 58.1 fold higher than the pure g-C₃N₄. The production rate is higher than those for bulk g-C₃N₄ and ZnO/g-C₃N₄. Finally, the reaction mechanism of Cu/ZnO/C₃N₄ is proposed in this study.     

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.     

A Metal-Organic-Framework-Derived g-C3N4/α-Fe2O3 Hybrid for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

As one of the most efficient systems for photocatalytic hydrogen evolution, the Z-Scheme system, consisting of different semiconductors with a reversible donor–acceptor pair, has attracted great attention. Considering the non-toxicity and low cost of photocatalysts, a series of g-C₃N₄/α-Fe₂O₃ hybrids were rationally constructed based on the Z-Scheme mechanism for the first time, using a metal-organic framework template approach that can fine tune the compositions and properties of the hybrids. An optimized hybrid, g-C₃N₄/α-Fe₂O₃-2, exhibited prominent photocatalytic water splitting performance with a visible light response. Under irradiation of visible light (λ>420 nm), the hybrid shows a high durability and superior hydrogen production rate of 2066.2 μmol g⁻¹ h⁻¹ from water splitting, which is approximately three times greater than that of bulk g-C₃N₄ because of the effective separation of photo-excited charge carriers by two narrow band gap semiconductors, tightly coupled with the Z-Scheme structural feature.     

Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D_3h-symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C₅₄N₆-COF) via Knoevenagel condensation with another D_3h-symmetric monomer 2,4,6-tris(4′-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C_2v-symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C₅₂N₆-COF). The octupolar conjugated characters of g-C₅₄N₆-COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C₅₂N₆-COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C₅₄N₆-COF enabled the two-half reactions of photocatalytic water splitting with an average O₂ evolution rate of 51.0 μmol h⁻¹ g⁻¹ and H₂ evolution rate of 2518.9 μmol h⁻¹ g⁻¹. Such values are among the highest of state-of-the-art COF photocatalysts.     

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<...     

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.     

A novel P-doped and NCDs loaded g-C3N4 with enhanced charges separation for photocatalytic hydrogen evolution

Graphite carbon nitride(g-C₃N₄) is a promising non-metal photocatalyst for photocatalytic hydrogen production, but its performance is still limited due to sluggish charges separation and low utilization of light.In this work, P-doped and N-doped carbon dots(NCDs) supported g-C₃N₄were successfully prepared via hydrothermal and polymerization reactions. The sub-bandgap formed by P-doping enhances the utilization of visible light, and the high electron de...     

Promoting Piezocatalytic H2O2 Production in Pure Water by Loading Metal-Organic Cage-Modified Gold Nanoparticles on Graphitic Carbon Nitride

Piezocatalytic hydrogen peroxide (H₂O₂) production is a green synthesis method, but the rapid complexation of charge carriers in piezocatalysts and the difficulty of adsorbing substrates limit its performance. Here, metal-organic cage-coated gold nanoparticles are anchored on graphitic carbon nitride (MOC-AuNP/g-C₃N₄) via hydrogen bond to serve as the multifunctional sites for efficient H₂O₂ production. Experiments and theoretical calculations prove that MOC-AuNP/g-C₃N₄ simultaneously optimize three key parts of piezocatalytic H₂O₂ production: i) the MOC component enhances substrate (O₂) and product (H₂O₂) adsorption via host–guest interaction and hinders the rapid decomposition of H₂O₂ on MOC-AuNP/g-C₃N₄, ii) the AuNP component affords a strong interfacial electric field that significantly promotes the migration of electrons from g-C₃N₄ for O₂ reduction reaction (ORR), iii) holes are used for H₂O oxidation reaction (WOR) to produce O₂ and H⁺ to further promote ORR. Thus, MOC-AuNP/g-C₃N₄ can be used as an efficient piezocatalyst to generate H₂O₂ at rates up to 120.21 μmol g⁻¹ h⁻¹ in air and pure water without using sacrificial agents. This work proposes a new strategy for efficient piezocatalytic H₂O₂ synthesis by constructing multiple active sites in semiconductor catalysts via hydrogen bonding, by enhancing substrate adsorption, rapid separation of electron-hole pairs and preventing rapid decomposition of H₂O₂.     

Construction of direct Z-scheme g-C3N4/TiO2 nanorod composites for promoting photocatalytic activity

Direct Z-scheme g-C₃N₄/TiO₂ nanorod composites were prepared for enhancing photocatalytic activity for pollutant removal. The characterization revealed that the g-C₃N₄/TiO₂ nanorod composite formed a close interface contact between g-C₃N₄ and TiO₂ nanorods, which was of benefit for the charge transfer and resulted in its high photocatalytic activity. The g-C₃N₄/TiO₂ nanorod composites exhibited higher photocatalytic activity for degradation of Rhodamine B (RHB) than bare g-C₃N₄ and TiO₂ nanorods. The high photocatalytic activity of g-C₃N₄/TiO₂ nanorod composites is attributed to the formation of the direct Z-scheme system, in which the electrons from the conduction band (CB) of TiO₂ combine with the holes from the valence band (VB) of C₃N₄ while the electrons from the CB of C₃N₄ and holes from the VB of TiO₂ with stronger redox ability are used to reduce and oxidize pollutants. Based on the radical-trapping experiments, the main reactive species for RHB degradation are O₂⁻ and · OH, which are produced by photoinduced electrons and holes with high redox ability. This work provides insights into the photocatalytic mechanism of composite materials for the photocatalytic removal of organic pollutants.     

Novel ternary g-C3N4/Ag3VO4/AgBr nanocomposites with excellent visible-light-driven photocatalytic performance for environmental applications

Novel visible-light-induced photocatalysts were fabricated by integration of Ag₃VO₄ and AgBr semiconductors with graphitic carbon nitride (g-C₃N₄) through a facile refluxing method. The fabricated photocatalysts were extensively characterized by XRD, EDX, SEM, TEM, FT-IR, UV–vis DRS, BET, TGA, and PL instruments. The photocatalytic performance of these samples was studied by degradations of three dye contaminants under visible-light exposure. Among the ternary photocatalysts, the g-C₃N₄/Ag₃VO₄/AgBr (10%) nanocomposite displayed the maximum activity for RhB degradation with rate constant of 1366.6 × 10⁻⁴ min⁻¹, which is 116, 7.23, and 38.5 times as high as those of the g-C₃N₄, g-C₃N₄/AgBr (10%), and g-C₃N₄/Ag₃VO₄ (30%) photocatalysts, respectively. The effects of synthesis time and calcination temperature were also investigated and discussed. Furthermore, according to the trapping experiments, it was found that superoxide anion radicals were the predominant reactive species in this system. Finally, the ternary photocatalyst displayed superlative activity in removal of the contaminants under visible-light exposure, displaying great potential of this ternary photocatalyst for environmental remediation, because of a facile synthesis route and outstanding photocatalytic performance.     

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.     

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。     

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...     

Defects Promote Ultrafast Charge Separation in Graphitic Carbon Nitride for Enhanced Visible-Light-Driven CO2 Reduction Activity

Fundamental photocatalytic limitations of solar CO₂ reduction remain due to low efficiency, serious charge recombination, and short lifetime of catalysts. Herein, two-dimensional graphitic carbon nitride nanosheets with nitrogen vacancies (g-C₃N_x) located at both three-coordinate N atoms and uncondensed terminal NH_x species were prepared by one-step tartaric acid-assistant thermal polymerization of dicyandiamide. Transient absorption spectra revealed that the defects in g-C₃N₄ act as trapped states of charges to result in prolonged lifetimes of photoexcited charge carriers. Time-resolved photoluminescence spectroscopy revealed that the faster decay of charges is due to the decreased interlayer stacking distance in g-C₃N_x in favor of hopping transition and mobility of charge carriers to the surface of the material. Owing to the synergic virtues of strong visible-light absorption, large surface area, and efficient charge separation, the g-C₃N_x nanosheets with negligible loss after 15 h of photocatalysis exhibited a CO evolution rate of 56.9 μmol g⁻¹ h⁻¹ under visible-light irradiation, which is roughly eight times higher than that of pristine g-C₃N₄. This work presents the role of defects in modulating light absorption and charge separation, which opens an avenue to robust solar-energy conversion performance.     

Photocatalytic Activity Improvement of g-C3N4 under Visible Light by Optimizing Preparation Conditions

Graphite-like C₃N₄ (g-C₃N₄) is ané cient visible-light-driven photocatalyst which is com-monly used in pollutant degradation. The photoreactivity of g-C₃N₄ depends on the prepa-ration conditions to a large extent. In this work, we linked the preparation conditions of g-C₃N₄ to its stability and photocatalytic activity through dye photodegradation experi-ments and sensitivity mathematical analyses. The sensitivity mathematical analyses show that the effect of calcination temperature is more significant than calcination time on the photoreactivity of g-C₃N₄. The photocatalytic activity of optimized g-C₃N₄ in rhodamine B (RhB) degradation under visible light was 100 times higher than that of non-optimized one. The enhanced performance can be attributed to the increased specific surface area of g-C₃N₄ and the increased migration velocity of photogenerated electron-hole pairs on the surface. This work deepens the understanding of the relation between preparation conditions and the charateristics of g-C₃N₄, and provides an extremely simple method for significantly improving the photoreactivity of g-C₃N₄.     

A Piezo-Fenton System with Rapid Iron Cycling and Hydrogen Peroxide Self-Supply Driven by Ultrasound

The piezo-Fenton system has attracted attention not only because it can enhance the Fenton reaction activity by mechanical energy input, but also because it is expected to realize a class of stimuli-responsive advanced oxidation systems by regulating energy input and hydrogen peroxide self-supply, thus greatly enriching the application possibilities of Fenton chemistry. In this work, a series of Fe-doped g-C₃N₄ (g-C₃N₄-Fe) as a piezo-Fenton system were synthesized where the iron stably immobilized through Fe−N interaction. The piezo-induced electrons generate on g-C₃N₄ matrix support the conversion of Fe(III) to Fe(II) and promote rate-limiting step of Fenton reaction. With the optimal Fe loading, g-C₃N₄-0.5Fe can achieve methylene blue (MB) degradation under ultrasonic treatment with first-order kinetic rate constants of 75×10⁻³ min⁻¹. Most importantly, the g-C₃N₄-Fe can maintain good catalytic activity in a wide pH range (pH=2.0∼9.0) and be cyclic used without iron leaching to solution (<0.001 μg ⋅ L⁻¹), overcoming the disadvantage of traditional Fe-based Fenton catalysts that can only be applied under acidic conditions and prone to secondary pollution. In addition, g-C₃N₄-0.5Fe also exhibits antibacterial properties of Escherichia coli and Staphylococcus aureus under ultrasound. Hydroxyl radicals mainly contribute to the degradation of MB and the sterilization process. Our work is an attempt to clarify the role of g-C₃N₄-Fe in the conversion of mechanical energy to ROS and provide inspirations for the piezo-Fenton system design.     

Strong-Base-Assisted Synthesis of a Crystalline Covalent Triazine Framework with High Hydrophilicity via Benzylamine Monomer for Photocatalytic Water Splitting

Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF-HUST-A1 with a benzylamine-functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF-HUST-A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200 μmol g⁻¹ h⁻¹). Photocatalytic overall water splitting is achieved by depositing dual co-catalysts in CTF-HUST-A1, with H₂ evolution and O₂ evolution rates of 25.4 μmol g⁻¹ h⁻¹ and 12.9 μmol g⁻¹ h⁻¹ in pure water without using sacrificial agent.     

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.     

Flower-like shaped Bi12TiO20/g-C3N4 heterojunction for effective elimination of organic pollutants: Preparation,characterization, and mechanism study

Flower-like shaped Bi₁₂TiO₂₀ (Bismuth Titanate)/g-C₃N₄ (graphite-like carbon nitride) heterojunction was prepared through hydrothermal and sonification methods for the degradation of organic pollutants by visible-light irradiation. The preparation process, chemical structures, and the mechanism of photocatalytic enhancement of the heterostructures were studied systematically. Under visible-light irradiation, the novel flower-like shaped Bi₁₂TiO₂₀/g-C₃N₄ heterojunction demonstrates prominent activities for the degradation of rhodamine B and p-nitrophenol, with the introduction of flower-like shaped Bi₁₂TiO₂₀ into g-C₃N₄ composites greatly increasing the activity of pure g-C₃N₄. This activity enhancement for the heterojunction could be mainly attributed to its low recombination speed of electron–hole pairs, high adsorption ability of organic pollutants, and better optical absorption ability. Moreover, in the visible-light system of Bi₁₂TiO₂₀/g-C₃N₄, ^•OH also contributed to the degradation of pollutants, which may explain the enhanced photocatalytic activity after the introduction of Bi₁₂TiO_20, as ^•OH is inactive in pure g-C₃N₄. Furthermore, 10 wt.% Bi₁₂TiO₂₀/g-C₃N₄ showed not only high activity but also good stability for degradation of aqueous organic pollutants, implying potential applications prospect.