g-C3N4 Semiconductor Research Articles

Ionic liquid-assisted synthesis of Br-modified g-C3N4 semiconductors with high surface area and highly porous structure for photoredox water splitting

Coping with the gradually increasing worldwide energy and environmental issues, it is urgent to develop efficient, cheap and visible-light-driven photocatalysts for hydrogen production. Here, we present a facile way to synthesize bromine doped graphitic carbon nitride (CN-BrX) with highly porous structure by using ionic liquid (1-butyl-3-vinylimidazolium bromide) as the Br source and soft-template for the first time, which applied in hydrogen evolution under visible light irradiation. A systematic study is conducted on the optimization in the doping amount. The results find that the as-fabricated CN-BrX photocatalysts possess a uniform porous network with thin walls due to the release of volatile domains and decomposition of ionic liquids. The highly porous structure with the large surface area (≤150 m2/g) benefits the exposure of active sites. Moreover, the bromine modification and porous structure can narrow the band gap, enhance the transportation capability of photogenerated electrons, improve the optical and conductive properties of CN, thus contribute to an outstanding H2 evolution rate under visible light irradiation (120 μmol h−1), which is about 3.6 times higher than pure CN. This work provides a new insight for designing the novel g-C3N4 based photocatalysts for hydrogen production, CO2 conversion and environmental remediation.

Metal-free heterojunction of graphitic carbon nitride composite with superior and stable visible-light active photocatalysis

A highly active isotype graphitic carbon nitride (g-C3N4) derivatives were fabricated by a one-step thermal treatment with the aim to promote the charge separation. The molecular composite precursor melamine-urea, melamine-thiourea, and urea-thiourea were treated simultaneously under the same thermal conditions, in situ creating a novel heterojunction. Coupling of g-C3N4 with different electronic band structure precursor produces different isotype heterojunctions. Different characterizations were studied using Fourier transform infrared spectroscopy, X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and UV–visible diffused reflectance spectroscopy. The prepared metal-free isotype heterojunction evidenced the separation of photoinduced charges, which promote the photocatalytic activity for degrading Methylene Blue (MB) under visible-light irradiation. The hetereojunction system shows 99% photodegradation for MB which is about 10% higher when compared to single precursor g g-C3N4 semiconductor. Moreover, photoactivity of the controlled bandgap design g-C3N4 composite semiconductors was greatly enhanced and possessed excellent stability even after four recycles.

Porous Mn doped g-C3N4 photocatalysts for enhanced synergetic degradation under visible-light illumination

Photocatalytic degradation by semiconductors is an ideal way to solve the environmental problem. Here, the porous Mn doped g-C3N4 photocatalyst was synthesized by the calcination-refluxing method. The as-prepared g-C3N4 exhibits the high activity of photocatalytic degradation under visible light irradiation ( > 400nm) in the mixed system of Cr(VI) and organic pollutants. Especially, the photocatalytic activity of Cr(VI) reduction was increased from 9.5% to 76.5%, while that of Rhodamine B(RhB) degradation was enhanced from 15.3% to 88.9% after 60min irradiation. The porous Mn doped g-C3N4 still keeps the high degradation efficiency of mixed pollutants in the 7th running. Based on the computational modeling, the Mn doping and carboxyl modification affect the atomic arrangement and molecular orbital distribution of the g-C3N4 semiconductor, leading to the enhancement of photo-induced carrier separation. Additionally, the active oxygen species and intermediates in the photoreaction process were discovered by ESR measurement and UV–vis test. The RhB degradation in synergistic photocatalysis not only inhibits the reverse reaction of Cr(VI) reduction, but also validly supply the photogenerated electrons by the photosensitization effect. This work may be useful for rationally designing photocatalysts and providing illuminating insights into the photocatalytic mechanism.

Constructing Multifunctional Metallic Ni Interface Layers in the g-C3N4 Nanosheets/Amorphous NiS Heterojunctions for Efficient Photocatalytic H2 Generation.

The construction of exceptionally robust and high-quality semiconductor-cocatalyst heterojunctions remains a grand challenge toward highly efficient and durable solar-to-fuel conversion. Herein, novel graphitic carbon nitride (g-C3N4) nanosheets decorated with multifunctional metallic Ni interface layers and amorphous NiS cocatalysts were fabricated via a facile three-step process: the loading of Ni(OH)2 nanosheets, high-temperature H2 reduction, and further deposition of amorphous NiS nanosheets. The results demonstrated that both robust metallic Ni interface layers and amorphous NiS can be utilized as electron cocatalysts to markedly boost the visible-light H2 evolution over g-C3N4 semiconductor. The optimized g-C3N4-based photocatalyst containing 0.5 wt % Ni and 1.0 wt % NiS presented the highest hydrogen evolution of 515 μmol g-1 h-1, which was about 2.8 and 4.6 times as much as those obtained on binary g-C3N4-1.0%NiS and g-C3N4-0.5%Ni, respectively. Apparently, the metallic Ni interface layers play multifunctional roles in enhancing the visible-light H2 evolution, which could first collect the photogenerated electrons from g-C3N4, and then accelerate the surface H2-evolution reaction kinetics over amorphous NiS cocatalysts. More interestingly, the synergetic effects of metallic Ni and amorphous NiS dual-layer electron cocatalysts could also improve the TEOA-oxidation capacity through upshifting the VB levels of g-C3N4. Comparatively speaking, the multifunctional metallic Ni layers are dominantly favorable for separating and transferring photoexcited charge carriers from g-C3N4 to amorphous NiS cocatalysts owing to the formation of Schottky junctions, whereas the amorphous NiS nanosheets are mainly advantageous for decreasing the thermodynamic overpotentials for surface H2-evolution reactions. It is hoped that the implantation of multifunctional metallic interface layers can provide a versatile approach to enhance the photocatalytic H2 generation over different semiconductor-cocatalyst heterojunctions.

A facile synthesis of Br-modified g-C3N4 semiconductors for photoredox water splitting

Hydrogen production by semiconductor photocatalysis using abundant sunlight and water is an ideal method to address the globe energy and environment issues. Here, we present a facile synthesis of bromine doped graphitic carbon nitride (g-C3N4) photocatalysts for hydrogen evolution with visible light irradiation. Bromine modification is shown to enhance the optical, conductive and photocatalytic properties of g-C3N4, while still keeping the poly-tri-s(triazine) core structure as the main building blocks of the materials. This modification method can be generally applicable to several precursors of g-C3N4, including urea, dicyandiamide, ammonium thiocyanide, and thiourea. The optimal sample CNU-Br0.1 shows more than two times higher H2 evolution rates than pure CNU sample under visible light irradiation, with high stability during the prolonged photocatalytic operation. Results also found that the photocatalytic O2 evolution activity of CNU-Br0.1 was promoted when the sample was subjected to surface kinetic promotion by loading with cobalt oxide as a cocatalyst. This study affords us a feasible modification pathway to rationally design and synthesize g-C3N4 based photocatalysts for a variety of advanced applications, including CO2 photofixation, organic photosynthesis and environmental remediation.

Post-annealing reinforced hollow carbon nitride nanospheres for hydrogen photosynthesis.

Hollow-structured g-C3N4 polymers with a high thermal stability up to 550 °C and an enhanced photocatalytic activity have been developed by post-annealing treatment, which effectively modifies the textural, crystal, and electronic properties of the g-C3N4 semiconductors without extra chemical assistance. This is a unique example of thermally and chemically stable conjugated polymers with hollow nanostructures and optoelectronic properties, promising the development of functional hollow g-C3N4 nanocomposites by chemical modifications like doping, surface grafting, and coupling with other inorganic/polymeric semiconductors with the aid of thermal treatment at high temperatures.

Noble-metal-free g-C3N4/Ni(dmgH)2 composite for efficient photocatalytic hydrogen evolution under visible light irradiation

We report an economic photocatalytic H2 generation system consisting of earth-abundant elements only by coupling graphitic carbon nitride (g-C3N4) with Ni(dmgH)2 sub-microwires that serve as effective co-catalysts for H2 evolution. This composite photocatalyst exhibits efficient hydrogen evolution under visible-light irradiation in the presence of triethanolamine as electron donor. The optimal coupling of 3.5wt% Ni(dmgH)2 to g-C3N4 (5mg composite) allows for a steady H2 generation rate of 1.18μmol/h with excellent stability. This study demonstrates that the combination of polymeric g-C3N4 semiconductor and small proportion of transition-metal-based co-catalyst could serve as a stable, earth-abundant and low-cost system for solar-to-hydrogen conversion.

Photodegradation performance of methylene blue aqueous solution on Ag/g-C3N4 catalyst

The graphitic carbon nitride (g-C3N4) was synthesized by the polymerization of dicyandiamide, then silver hybrid g-C3N4 (Ag/g-C3N4) catalyst was prepared by photodeposition, deposition-precipitation, and doping methods. The first two methods deposited silver nanoparticles on the surface of g-C3N4 semiconductor, while the last one embedded silver atom into the g-C3N4 matrix without destroying the host structure. The photodegradation behavior of methylene blue (MB) aqueous solution over Ag/g-C3N4 catalyst was performed to evaluate the photocatalytic activity of the as-prepared samples. The samples were characterized by XRD, UV-vis spectroscopy, FT-IR spectroscopy, elemental analysis and TEM. The experiment results indicate that the Ag/g-C3N4 prepared by the doping method possesses the best photocatalytic activity, which can be explained by promoting the transfer of electron due to the formation of organic-metal hybrid material.