Photocatalytic Properties Of g-C3N4 Research Articles

Research on Graphitic Carbon Nitride (g-C3N4) prepared by template-based method and its photocatalytic properties

Abstract. The Graphitic Carbon Nitride (g-C3N4), a non-metallic polymer photocatalytic material, has a wide range of raw materials and a simple preparation process. Due to its unique electronic structure and excellent photocatalytic performance, g-C3N4 has attracted wide attention in the field of environmental purification and energy conversion in recent years. However, g-C3N4 faces a lot of challenges, including a wide band gap, many interlayer defects, and poor interlayer electron transport. Nevertheless, its unique semiconductor structure and chemical stability still provide the possibility to explore the effect of its piezoelectric properties on photocatalysis, which paves the way for a novel approach to environmentally friendly hydrogen production. Therefore, the paper delves into the application of different template methods in the preparation of g-C3N4 by reviewing the related literature, and analyzes the role of different template materials in the preparation. In addition, in this paper, the photocatalytic properties of g-C3N4 are explored, which are mainly reflected in the photocatalytic water separation performance and photocatalytic degradation of organic dyes. It is found that the g-C3N4 shows great potential in the fields of photocatalytic water decomposition for hydrogen production and degradation of organic pollutants due to its unique band gap, nontoxicity, low cost and wide range of sources. Future research should continue to explore more kinds of template materials and their preparation processes, with the aim of realizing further enhancement of the performance of g-C3N4 photocatalysts and promoting their practical applications in the fields of environment and energy.

Electrically enhanced adsorption and photocatalytic properties of g-C3N4/TiO2 heterostructure for removal of tetracycline in water: A study by molecular dynamics simulation and experiment

Here, molecular dynamics (MD) simulations and experimental studies were carried out to investigate the effect and mechanism of external applied electric fields on the adsorption efficiency of g-C3N4/TiO2 heterostructure for removing tetracycline (TC) from water. The MD simulation results indicate that the electric fields in the X and Y directions have little effect, while the electric field in the Z direction has a significant impact on the adsorption system. The Z direction electric field significantly reduces the number of water molecules near the surface of the heterostructure, improves the adsorption energy between the heterostructure and TC molecules, and thereby enhances the adsorption effect. The experimental research results show that the removal rate of tetracycline increases from 26 % to 33 % in 90 min when an electric field of 3000 V/m is applied, which indicates that the presence of an external electric field can improve the adsorption and removal performance of g-C3N4/TiO2 heterostructure for TC in water, and verifies the research conclusion of MD simulations. Alkaline conditions are more conducive to the removal of TC. In addition, applying an external electric field can effectively improve the light absorption performance of heterostructures, thereby enhancing the photocatalytic degradation efficiency of TC.

Enhanced photocatalytic properties of s-triazine-based-g-C3N4/BlueP and g-C3N4/G/BlueP vdW heterostructures: A DFT study

Constructing a Z-scheme heterostructure from selected semiconductors has been proved to be an effective route for attaining the strong redox capability and broad light absorption range simultaneously. In this work, we investigated the electronic, optical and photocatalytic properties of g-C3N4/BlueP and g-C3N4/G/BlueP van der waals heterostructures (vdWHs) by density functional theory (DFT) calculations. The staggered band alignment and the interfacial built-in electric field originated from the charge transfer from g-C3N4 to BlueP depict the Z-scheme photocatalytic mechanism of the g-C3N4/BlueP vdWH. Meanwhile, the vdWH shows an enhanced absorbance at the ultraviolet and visible light range compared to the individual g-C3N4 and BlueP monolayers. Furthermore, the intercalation of Graphene monolayer between g-C3N4 and BlueP is proved to modulate the interfacial built-in electric field, while retaining the staggered band alignment simultaneously. The significant enhancement of the visible light region absorption efficiency promoted by the gap-state of intercalated Graphene manifests the co-catalytic effect of Graphene and the applicable prospect of the constructed ternary heterostructure in photocatalysis area.

Preparation and photocatalytic properties of g-C3N4/WO3–SiO2 composite photocatalyst for methylene blue and methyl orange degradation

WO3–SiO2 gel was prepared by sol-gel method using ethyl orthosilicate and sodium tungstate dihydrate as raw materials, and a series of g-C3N4/WO3–SiO2 composite photocatalysts with different g-C3N4 loading loads were prepared on WO3–SiO2 gel. The photocatalytic degradation performance of methylene blue (MB) and methyl orange (MO) was investigated under 464 nm light source. According to the findings, the degrading effect of the g-C3N4/WO3–SiO2 composite catalyst is optimum when the load of g-C3N4 is 1.3 wt%, and the degradation rates of MB and MO are 95.62 % and 98.09 %, respectively. The characterization results show that the excellent photocatalytic performance is due to the formation of g-C3N4/WO3 heterojunction by the introduction of g-C3N4, which effectively promotes the migration and separation of photogenerated carriers, increases the number of active electrons and holes, and thus enhances its photocatalytic activity. In addition, according to the analysis of the energy band structure of the catalyst, the possible mechanism of g-C3N4/WO3–SiO2 degradation of MB (MO) is proposed as S-type heterojunction mechanism.

B-doping on the electronic structure and photocatalytic properties of g-C3N4/Janus PtSSe heterojunctions: A first-principles study

The effect of B doping on the stability, electronic structure, work function, and optical properties of g-C3N4/Janus PtSSe heterojunctions has been investigated based on the density-functional theory plane-wave ultrasoft pseudopotential approach. It is shown that the binding energy of g-C3N4/PtSSe after B doping is negative and has a low layer spacing and lattice mismatch rate. It is stable at a room temperature of 300 K, proving its structural and thermodynamic stability. B-atom doping of g-C3N4/SPtSe and g-C3N4/SePtS heterojunctions leads to the upward shift of the Fermi energy level resulting in a significant reduction of the band gap and significant orbital hybridization. The impurity band near the Fermi energy level easily transfers electrons from the valence band into the conduction band, which makes electron leaps easier. Different built-in electric fields are formed when the g-C3N4 and Se(S) atomic layers are in contact. The reduction of the bandgap after B doping enables the photogenerated electron-hole pairs between the heterojunction interfaces to be better separated under the action of the built-in electric field, which reduces the composite rate of the electron-hole pairs and greatly improves the carrier migration and photocatalytic performance. The absorption and reflection coefficients of g-C3N4/SPtSe-BNC and g-C3N4/SePtS-BNC are the highest and decrease slowly in the visible region, which indicates that they have the optimal photocatalytic performance, and they can effectively broaden the range of light absorption and promote the utilization of light. The introduction of the B–B bonding effectively improves the photocatalytic activity of the heterojunction.

Influence of the calcination duration of g-C3N4/TiO2 “veggie-toast-like” photocatalyst on the visible-light triggered photocatalytic oxidation of bisphenol A

Two commercially available TiO2 (hexagonal-like and spherical-like particles) were used to investigate the effect of g-C3N4 “melting” on the photocatalytic properties of g-C3N4/TiO2 composites. Improvement in the contact between the components was observed when they were thermally treated at 350 °C for an extended period of time (between 2 and 72 h) due to the partial melting and phase fusion of g-C3N4. Consequently, the enhanced contact between the phases allows easier injection of photogenerated electrons from the conduction band of g-C3N4 into TiO2, improving charge carrier separation. The prepared composites were tested for bisphenol A degradation under visible-light illumination, which showed that the components that had been calcined for 24 h performed better due to the improved charge carrier separation. Superoxide anionic radicals and photogenerated holes were identified as active species in the photooxidation experiments conducted under visible-light illumination.

Improved photocatalytic degradation of methyl violet dye and pathogenic bacteria using g-C3N4 supported phosphotungstic acid heterojunction

The g-C3N4/PTA photocatalyst composite was prepared by immobilizing high redox ability phosphotungstic acid (PTA) as an efficient acceptor of photogenerated electrons, on metal-free graphitic carbon nitride (g-C3N4). The photocatalytic property of g-C3N4/PTA composite was tested by photodegradation of methyl violet (MV) dye as a simulated organic contaminant in water. In presence of visible light illumination, the results showed high MV degradation (95.63 %) has been incredibly achieved after short irradiation time and at specific conditions (g-C3N4/PTA photocatalyst dose = 0.5 g/l, pH = 6.8 and MV dye concentration = 10 ppm). Antibacterial results exhibited that the synthesized g-C3N4/PTA heterostructure had high ability to decrease the density of E. coli pathogenic bacterium after 180 min of visible light irradiation. The enhanced photocatalytic degradation activities were attributed to the impact of synergistic of PTA and g-C3N4 in the synthesized hybrid, which increases the separation of photogenerated electrons and holes.

The charge transfer pathway of g-C3N4 decorated Au/Ni3(VO4)2 composites for highly efficient photocatalytic hydrogen evolution

The photocharge carrier separation and migration within the heterostructure interface plays a pivotal role in the photoelectrocatalytic hydrogen production and the photocatalytic degradation activity. Herein, a series of the 2D/3D g-C3N4/Ni3(VO4)2 photocatalyst were successfully fabricated via a facile hydrothermal method. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The highest photocatalytic hydrogen production rate of g-C3N4/Au/Ni3(VO4)2 was about 3345 μmol g−1 h−1, which largely beyond that obtained of g-C3N4/Ni3(VO4)2 (501 μmol g−1 h−1), and pristine g-C3N4 (14 μmol g−1 h−1). The optimal apparent quantum efficiency was counted to be 6.8 % at λ = 420 nm and 1.1 % at λ = 600 nm. Moreover, the photocatalytic property of g-C3N4/Au/Ni3(VO4)2 could remain unchanged almost with 50 h in 5 cycles. The improvement of photocatalytic H2 yield is attributed to the result of rapid separation of photogenic carriers in space and surface plasmon resonance effect of Au nanoparticles.

Effects of vacancies on the electronic structures and photocatalytic properties of g-C3N4

The geometric structures, electronic structures and photocatalytic properties of g-C3N4 with different vacancies are studied by the first-principles calculations. These calculations suggest that introducing different vacancies can cause the relaxation of these adjacent atoms, the formation of dangling bonds, and the deformation of these building blocks. And these band gaps of the heptazine-based graphitic C3N4 sheets are narrowed by different vacancies. The energetic preferability of the heptazine-based g-C3N4 sheets with different vacancies is assessed as functions of the environmental factors, including nitrogen partial pressure and temperature. It is indicated that VC2 and VN2 are the respectively stable vacancies over the investigated nitrogen partial pressure. A transition from VN2 to VC2 should occur at ultrahigh vacuum pN2≥∼10−23atm at 1000 K, and move to higher nitrogen partial pressure with the increasing temperature. According to the calculated absorption coefficient, these g-C3N4 sheets with VC2 and VN2 vacancies have larger absorption than the perfect structure over the visible wavelength range, suggesting that vacancies can increase the catalytic efficiency of graphitic C3N4. These results show that introducing defects, especially vacancies, is an effective approach to enhance the sunlight absorption efficiency of graphitic carbon nitride.

First-principles study of nitrogen defect g-C3N4/WS2 heterojunction on photocatalytic activity

In this work, first-principles density functional theory simulations have been performed to investigate the influence of nitrogen (N) defect on the supercell structure, electronic structure and photocatalytic properties of g-C3N4/WS2 heterojunctions. Analyses of calculated binding energies and the lattice mismatch ratios led us to confirm that N-deficient g-C3N4 and WS2 were in parallel contact and form a stable heterojunction. Furthermore, the work functions, molecular dynamics simulations, charge density differences, band structures, DOS, electronic and optical properties and absorption spectra of different g-C3N4/WS2 heterojunctions have been analyzed in detail. It is revealed that the compositing of N-deficient g-C3N4 with WS2 improves the separation of photoinduced electron-hole pairs. N-defect enhances the visible light absorption of the heterojunction, due to the introduction of impurity energy levels. Moreover, the introduction of defect species further improves the photocatalytic performance of g-C3N4/WS2 heterojunction in the visible region.

In situ fabrication of a novel CdS/ZnIn2S4/g-C3N4 ternary heterojunction with enhanced visible-light photocatalytic performance.

In this study, a novel g-C3N4-based ternary heterojunction was rationally designed and constructed by the in situ growth of ZnIn2S4 nanosheets and CdS nanoparticles onto the g-C3N4 nanosheets using a facile two-step oil-bath method. Through optimizing the proportion of ZnIn2S4 and CdS component, g-C3N4 nanosheets coupled with ZnIn2S4 nanosheets and CdS nanoparticles (denoted as CdS/ZnIn2S4/g-C3N4) exhibited obviously higher photocatalytic properties for RhB removal than the single-component and dual-component systems. Among the as-obtained ternary photocatalysts, it was found that the ternary CdS/ZnIn2S4/g-C3N4-0.2 photocatalyst displayed the optimum photocatalytic property (96%) within a short time (30 min), which was almost 27.42 and 1.17 times higher than that of pure g-C3N4 and binary ZnIn2S4/g-C3N4-0.7 composite. The excellent activity of the ternary CdS/ZnIn2S4/g-C3N4 heterostructure is assigned to the synergetic effects of CdS nanoparticles, ZnIn2S4 nanosheets and g-C3N4 nanosheets, which not only broaden the visible-light absorption range, but also improve the charge mobility and separation rate, thus boosting the visible-light-driven photocatalytic property of g-C3N4.

Facile construction of S-scheme SnO2/g-C3N4 photocatalyst for improved photoactivity

The SnO2/g-C3N4 composites were fabricated via an annealing mixture of g-C3N4 and SnO2, which were obtained from calcinating melamine and hydrothermal treatment of SnCl4 solution, respectively. The photocatalytic properties of g-C3N4/SnO2 were studied over the degradation of Rhodamine B (RhB) under visible light, which exhibits a significantly improved photocatalytic activity compared to the single components, g-C3N4 and SnO2. The enhancement in photocatalytic activity of SnO2/g-C3N4 could be described by the S-scheme pathway, in which the effective charge transfer between components is demonstrated toward the suppression in recombination of the photogenerated electron-hole pairs within redox potential conservation. Besides, a new criterion, photochemical space-time yield, was applied to evaluate the photocatalytic performance of our samples.

Preparation and photocatalytic properties of g-C3N4/BiOCl heterojunction

g-C3N4 is a polymer semiconductor material with visible-light response capability, BiOCl has a unique layered structure and indirect band gap transition mode, which can be effectively separated photoelectron-hole generation and charge transfer. This paper prepared the heterostructure of g-C3N4/BiOCl by hydrothermal method, and explored under what ratio g-C3N4/BiOCl can more effectively remove methylene blue (MB) in visible-light. The results show that BiOCl is well dispersed on the g-C3N4 layered structure, forming g-C3N4/BiOCl heterostructure, which has higher photocatalytic activity than single g-C3N4 and BiOCl. The degradation efficiency of 90 % g-C3N4/BiOCl was 91.53% when the photocatalysis progressed to 240 min.

Photocatalytic properties of novel two-dimensional B4C3/g-C3N4 van der Waals heterojunction with moderate bandgap and high carrier mobility: A theoretical study

Developing two-dimensional heterojunctions is an excellent approach to achieve exceptional optical, electrical, and photocatalytic properties. Here, we used the periodic density functional theory simulations to engineer the electronic band structure, charge separation efficiency, as well as the photocatalytic properties of g-C3N4 and B4C3 based two-dimensional van der Waals heterojunctions. The effect of strain on the band edge energy and band structure was investigated in detail. The effective mass of electrons (me*/mо = 0.76) and holes (mh*/mо = 1.16) in the B4C3/g-C3N4 heterojunction predicted a superior mobility than in isolated g-C3N4 monolayer (me* = 0.98; mh* = 1.34). The ΔGH* value (-0.10 eV) of the atomic hydrogen on B4C3/g-C3N4 heterojunction confirmed the superior HER performance in contrast to isolated g-C3N4 (ΔGH* =0.108 eV) and B4C3 (ΔGH* = -0.22 eV) monolayers. Our study offers possibilities to produce a novel B4C3/g-C3N4 heterojunction for the photocatalytic water splitting and optoelectrical applications.

Design and Performance of Novel Self-Cleaning g-C3N4/PMMA/PUR Membranes.

In the majority of photocatalytic applications, the photocatalyst is dispersed as a suspension of nanoparticles. The suspension provides a higher surface for the photocatalytic reaction in respect to immobilized photocatalysts. However, this implies that recovery of the particles by filtration or centrifugation is needed to collect and regenerate the photocatalyst. This complicates the regeneration process and, at the same time, leads to material loss and potential toxicity. In this work, a new nanofibrous membrane, g-C3N4/PMMA/PUR, was prepared by the fixation of exfoliated g-C3N4 to polyurethane nanofibers using thin layers of poly(methyl methacrylate) (PMMA). The optimal amount of PMMA was determined by measuring the adsorption and photocatalytic properties of g-C3N4/PMMA/PUR membranes (with a different PMMA content) in an aqueous solution of methylene blue. It was found that the prepared membranes were able to effectively adsorb and decompose methylene blue. On top of that, the membranes evinced a self-cleaning behavior, showing no coloration on their surfaces after contact with methylene blue, unlike in the case of unmodified fabric. After further treatment with H2O2, no decrease in photocatalytic activity was observed, indicating that the prepared membrane can also be easily regenerated. This study promises possibilities for the production of photocatalytic membranes and fabrics for both chemical and biological contaminant control.

Junction of porous g-C3N4 with BiVO4 using Au as electron shuttle for cocatalyst-free robust photocatalytic hydrogen evolution

Z-scheme g-C3N4/Au/BiVO4 photocatalyst has been prepared successfully by assembling gold nanoparticles on the interface of super-thin porous g-C3N4 and BiVO4, which exhibits outstanding photocatalytic performance toward hydrogen evolution and durable stability in the absence of cocatalyst. The highest photocatalytic hydrogen production rate of g-C3N4/Au/BiVO4 was about 410.0 μmol g−1 h−1, which largely beyond that obtained of g-C3N4/BiVO4 (23.3 μmol g−1 h−1), Au/g-C3N4 (244.6 μmol g−1 h−1) and pristine g-C3N4 (2.2 μmol g−1 h−1). The optimal apparent quantum efficiency was counted to be 6.8% at λ = 420 nm and 1.1% at λ = 600 nm. Moreover, the photocatalytic property of g-C3N4/Au/BiVO4 could remain unchanged almost with 50 h in 5 cycles. The improvement of photocatalytic H2 yield is attributed to the result of rapid separation of photogenic carriers in space and surface plasmon resonance effect of Au nanoparticles. In combination of photoelectrochemical measurement, active species capture experiment and electron paramagnetic resonance spectra, the underlying mechanism was illuminated. The pathway of charge carrier migration between semiconductor photocatalysts could be changed to Z-system through Au as an electron intermediate, which could not only benefit to maintain outstanding redox capability but also help to accelerate photo-generated carrier separation, and thus improve the photocatalytic activity.

Revisiting structural and photocatalytic properties of g-C3N4/TiO2: Is surface modification of TiO2 by calcination with urea an effective route to “solar” photocatalyst?

g-C3N4/TiO2 derived from the surface modification of TiO2 by calcination with urea has been widely studied as a “visible-light-active” photocatalyst for environmental remediation. However, few attentions have been paid to the structure characterization and the photocatalytic properties of the resultant nanocomposite photocatalysts under a practical sunlight irradiation. Here we employ various characterization techniques, including TGA, XRD, TEM, XPS, UV–vis spectrum, and N2-sorption analysis to characterize the evolutions in phase crystal structure, microstructure and optical properties of g-C3N4/TiO2 nanohybrids synthesized through calcining a mechanical mixture of urea and Evonik Aeroxide P-25 TiO2 (P25) at 350–500 °C. The thermal pyrolysis of urea leads to the surface decoration of TiO2 with graphitic carbon nitrate (g-C3N4) at temperatures above 400 °C. The photocatalytic properties of the resultant g-C3N4/TiO2 nanoparticles are evaluated through photocatalytic decoloration of methylene blue (MB) and reduction of Cr (VI) to Cr (III) under visible (420 nm), UV (365 nm), and simulated solar light irradiations. The nanohybrid photocatalysts, as most previous studies reported, show much higher photocatalytic activity under visible light irradiation than the single-component counterparts, i.e. P25 or g-C3N4. However, under solar and UV irradiation, no considerable improvements are found, which is caused by the decrease in redox potential upon interfacial charge carrier transfer between g-C3N4 and TiO2. Moreover, g-C3N4/TiO2 shows an ultralow photocatalytic activity in Cr (VI) reduction. The surface modification with organic g-C3N4 is assumed to tune the surface properties (e.g. hydrophilicity) of TiO2. Our results demonstrate that photocatalytic activity in UV range is as important as that in visible range, and developing efficient “solar” photocatalysts should balance the photocatalytic activities at both ranges since they might be incompatible with each other.

The synergistic effect of non-metal doping or defect engineering and interface coupling on the photocatalytic property of g-C3N4: First-principle investigations

The light response range, redox potential, and consequently, the photo-reactivity of a semiconductor photocatalyst for solar-to-hydrogen are intrinsically dominated by its electronic structure. Introducing chemical impurities, structural defects, and construction of heterostructures have been considered as the widely adopted strategies to modify the electronic structures of two-dimensional photocatalyst. Up to now, however, the synergetic effect of these strategies on the photocatalytic property of photocatalyst remains unknown. In our work, using first-principles calculations, we systemically studied the effect of non-metal (sulfur) doping, vacancy engineering and interface coupling, as well as their synergetic effect on the electronic structure of g-C3N4. Results indicate that the introduction of doped S atom or C (N)-vacancy in g-C3N4 could extend the light response range by narrowing the band gap or creating gap states, while the coupling effect at interface of g-C3N4/MoS2 is able to tune the band edge potentials of g-C3N4. Incorporation of these strategies, a g-C3N4 with appropriate band gap and suitable band edge potentials can be obtained. Moreover, we also found that these modification strategies can influence the spatial electron distribution corresponded to the band edges, which would be beneficial to inhibiting the recombination of photogenerated electron-hole pairs. Therefore, incorporating doping or defect engineering with interface coupling should be an experimentally attainable way to improve the photo-reactivity of 2D semiconductors for overall photocatalytic water splitting.

Preparation and Visible Light Photocatalytic Property of g-C3N4/MoS2 Nanosheets/GO Ternary Composite Photocatalyst

Preparation and Visible Light Photocatalytic Property of g-C₃N₄/MoS₂ Nanosheets/GO Ternary Composite Photocatalyst

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.