Synergistic effect of efficient adsorption g-C3N4/ZnO composite for photocatalytic property

Novel g-C₃N₄/ZnO composite photocatalyst was synthesized from an oxygen-containing precursor by direct thermal decomposition urea in air without any other templates assistance. Different percentages of g-C₃N₄ were hybridized with ZnO via the monolayer-dispersed method. The prepared g-C₃N₄/ZnO composites were characterized by XRD, SEM, UV–vis diffuse reflectance spectra (DRS), FT-IR, TEM and XPS. The composites showed much higher efficiency for degradation of Rhodamine B (RhB) than ZnO under UV and visible light irradiation. Especially, the photocatalytic efficiency was the highest under UV light irradiation when the percentage of g-C₃N₄ was 6%. The improved photocatalytic activity may be due to synergistic effect of photon acquisition and direct contact between organic dyestuff and photocatalyst. Then, effective separation of photogenerated electron–hole pairs at the interface of g-C₃N₄ is an important factor for improvement of photocatalytic activity. This work indicates that g-C₃N₄ hybrid semiconductors photocatalyst is a promising material in pollutants degradation.     

A facile in situ solvothermal method for two-dimensional layered g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/SnS<Subscript>2</Subscript> p-n heterojunction composites with efficient visible-light photocatalytic activity

To overcome the fast recombination rate of electron-hole pairs of individual SnS₂, p-n heterojunction g-C₃N₄/SnS₂ composites were fabricated as high-efficiency visible-light photocatalyst to photodegradate the organic dye MB. The morphologies, structures, compositions, and photocatalytic properties were characterized. The SnS₂ shows two-dimensional layer structure with an average thickness of 20 nm and diameter size of about 2 μm, and the g-C₃N₄ nanoflakes were uniformly deposited on the surface of SnS₂ nanosheets. In comparison with the bare g-C₃N₄ and SnS₂, the composites show improved photocatalytic activity under visible light, which is sensitive to the content of g-C₃N₄. In particular, the 15% g-C₃N₄/SnS₂ composites exhibit the highest photocatalytic activity and outstanding reusability, which can degrade 88.01% MB after only 1 h in the visible light (λ?>?420 nm) range. The g-C₃N₄/SnS₂ heterojunction composites show outstanding reusability after four times cycling experiments. The improved photocatalytic activities of composites are attributed to abundant active species, increased charge separation, and decreased electron-hole pair recombination, which originated from the large specific surface area and efficient interfacial transport of photo-induced charge carriers between SnS₂ and g-C₃N₄. These results suggest that the two-dimensional layered g-C₃N₄/SnS₂ p-n heterojunction composites are promised to be a high-efficiency visible-light photocatalyst.     

石墨相氮化碳的制备条件优化用以提高其在可见光下的光催化活性

通过染料的光降解实验和敏感性数学分析探讨了石墨相氮化碳(g-C₃N₄)的制备条件与其稳定性和光催化活性之间的联系. 结果表明,相比于焙烧时间,焙烧温度的改变更为显著地影响了g-C₃N₄ 的光催化活性. 制备条件优化之后的g-C₃N₄在可见光照射下催化降解罗丹明B(RhB)的活性比未优化时提高了约100倍,归因于材料比表面积的增大和表面光生电子-空穴迁移速度的增强.     

The synthesis of graphene-TiO<Subscript>2</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> super-thin heterojunctions with enhanced visible-light photocatalytic activities

In this paper, an efficient strategy for the synthesis of graphene nanobelt-titanium dioxide/graphitic carbon nitride (graphene-TiO₂/g-C₃N₄) heterostructure photocatalyst was applied to fabricate a kind of visible-light-driven photocatalyst. The heterostructure shows higher absorption edge towards harvesting more solar energy compared with pure TiO₂ and pure g-C₃N₄ respectively. Furthermore, the as-prepared graphene-TiO₂/g-C₃N₄ heterostructure can show enhanced photocatalytic activity under visible-light irradiation. These outstanding performances of photocatalytic activities for graphene-TiO₂/g-C₃N₄ composites can be attributed to the heterojunction interfaces which can separate the electron-hole pairs and impede the recombination of electrons and holes more efficiently. This study conclusively demonstrates a facile and environmentally friendly new strategy to design highly efficient graphene-TiO₂/g-C₃N₄ heterostructure photocatalytic materials for potential applications under visible-light irradiation.

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g-C3N4/SnS2异质结构:一类有潜力的光解水催化剂

采用第一性原理方法研究了层间耦合作用对g-C₃N₄/SnS₂异质结构的电子结构和吸光性质的影响.发现g-C₃N₄/SnS₂是一类典型的范德瓦异质结构,能有效吸收可见光,其价带顶和导带底与水的氧化还原势匹配,且由于电荷转移而导致的界面处极化场有利于光生载流子的分离.这些理论研究结果表明g-C₃N₄/SnS₂异质结构是一类非常有潜力的光解水催化材料.     

Ag3PO4/rectorite nanocomposites: Ultrasound-assisted preparation,characterization and enhancement of stability and visible-light photocatalytic activity

To overcome the drawback of low stable brought by the transformation of Ag⁺ into Ag, a highly efficient and stable photocatalyst Ag₃PO₄/rectorite composite was successfully synthesized by ultrasound-assisted precipitation method. The as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N₂ adsorption-desorption, room-temperature photoluminescence spectra, Fourier transform infrared spectrum measurements and UV–vis diffuse reflectance spectra. The absorption edges of the Ag₃PO₄/rectorite display a noticeable shift to the visible light region as compared to that of the Ag₃PO₄. Compared with bare Ag₃PO₄, the Ag₃PO₄/rectorite composite by ultrasound-assisted precipitation process exhibits significantly enhanced photocatalytic activity and stable for methyl orange (MO) degradation under visible light irradiation. The improved activity of the Ag₃PO₄/rectorite photocatalyst could be attributed to the expanded visible light absorption, the enhanced interfacial charge transfer and the inhibited recombination of electron-hole pairs. Therefore, the facile ultrasound-assisted preparation process provides some insight into the application of Ag₃PO₄/rectorite nanocomposites in photocatalytic degradation of organic pollutants.     

高比表面积TiO2与g-C3N4复合材料的光催化性能及机理研究

本文通过简单的溶剂热法制备了g-C₃N₄与高比表面积的TiO₂复合材料,该方法操作简单且能耗低. 甲基橙降解实验结果表明,高比表面积的TiO₂有效提高了光催化活性. 光电化学测试结果表明,与g-C₃N₄复合后,TiO₂的电荷载流子迁移速率得到明显改善. g-C₃N₄/高比表面积-TiO₂的光催化活性很强,在100分钟内,6%-g-C₃N₄/高比表面积-TiO₂对甲基橙的降解程度可达92.44%. 6%-g-C₃N₄/高比表面积-TiO₂不仅具有良好的光催化降解性能,还具有较高的稳定性. 本文对6%-g-C₃N₄/高比表面积-TiO₂的光催化机理也进行了系统的研究.     

g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity

Novel g-C₃N₄ modified Bi₂O₃ (g-C₃N₄/Bi₂O₃) composites were synthesized by a mixing-calcination method. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent-time measurement (PT). The photocatalytic activity of the composites was evaluated by degradation of Rhodamine B (RHB) and 4-chlorophenol (4-CP) under visible light irradiation (>400 nm). The results indicated that the g-C₃N₄/Bi₂O₃ composites showed higher photocatalytic activity than that of Bi₂O₃ and g-C₃N₄. The enhanced photocatalytic activity of the g-C₃N₄/Bi₂O₃ composites could be attributed to the suitable band positions between g-C₃N₄ and Bi₂O₃. This leads to a low recombination between the photogenerated electron–hole pairs. The proposed mechanism for the enhanced visible-light photocatalytic activity of g-C₃N₄/Bi₂O₃ composites was proven by PL and PT analysis.     

Characterization and optimization of Ce0.6Zr0.4−x Mn x O2 (x ≤ 0.4)

In situ synthesis method is used to synthesize g-C₃N₄-P25 composite photocatalysts with different mass rations. The experiment result shows that P25 particles with diameter at range of 20–30 nm were embedded homogenously in the sheets of g-C₃N₄. Coupling g-C₃N₄ with P25 can not only improve the visible light absorption, but also improve the visible light photocatalytic activity of P25. The g-C₃N₄-P25 nanocomposite has the higher photocatalytic activity than g-C₃N₄ under visible light. The optimal g-C₃N₄ content with the highest photocatalytic activity is determined to be 84 %, which is almost 3.3 times higher than that of individual g-C₃N₄ under the visible light. The enhanced visible light photocatalytic activity could be ascribed to the formation of g-C₃N₄ and TiO₂ heteojunction, which results in an efficient separation and transfer of photo-induced charge carriers. The electron spin resonance results show that the ^·O₂ ^? radicals are main active species for g-C₃N₄ and the g-C₃N₄-P25 nanocomposites.     

rGO supported self-assembly of 2D nano sheet of (g-C3N4) into rod-like nano structure and its application in sonophotocatalytic degradation of an antibiotic

Graphitic carbon nitride (g-C₃N₄) is an analog of graphite due to its unique electronic structure. g-C₃N₄ based materials have been used in photocatalytic applications. However, pure g-C₃N₄ suffers from major shortcomings which include poor disparity, low surface area and a high recombination rate of photo generated electron-hole pairs that significantly reduce its photocatalytic activity. In this work, self-assembly of g-C₃N₄ sheet into rod shaped g-C₃N₄ was developed via a simple polymerisation method. A composite made of g-C₃N₄ nanorods and rGO (rGO-RCN) was also prepared. The band gap g-C₃N₄ was shifted from 2.77 to 2.6 eV evidented by UV-DRS data. As a result, rGO-RCN showed a relatively high absorption in the visible region. Moreover, a fast electron transfer rate was observed with rGO-RCN composite as conformed from PL analysis and photocurrent measurement. The formation of nanorod and sheet morphologies was confirmed via TEM analysis. The photocatalytic activities of prepared sheet-g-C₃N₄ (SCN)_, Rod g-C₃N₄ (RCN), reduced graphene oxide supported sheet-g-C₃N₄ (rGO-SCN) and reduced graphene oxide supported Rod-g-C₃N₄ (rGO-RCN) were evaluated using a commonly used antibiotic (tetracycline). Among these catalysts, rGO-RCN nanocomposite showed sonophotocatalytic activity 3 times higher compared to pure g-C₃N₄. This superior sonophotocatalytic activity could be due to enhanced visible light absorption of the material, active sites generated by ultrasound, and the high electron transport property of rGO.     

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.     

One-pot synthesis of Ag+ doped BiVO4 microspheres with enhanced photocatalytic activity via a facile hydrothermal method

The Ag⁺/BiVO₄ photocatalyst was fabricated through a facile hydrothermal method by using K₆V₁₀O₂₈·9H₂O as the vanadium source. The impact of Ag⁺ on the product's structure and morphology was studied. It was shown that the amount of Ag⁺ has no effect on the product’s crystal phases but plays an important role on the morphology of the nanoparticles that construct the shell of BiVO₄ microspheres. In addition, the Ag⁺-doped photocatalysts have much higher photocatalytic activities in removing RhB and MB under the UV light illumination than the pure BiVO₄. A possible photocatalytic mechanism was proposed in photoexcitation of the BiVO₄ electrons which subsequently captured by the dopant. The present work may offer a novel route to reach higher photocatalytic activity by doping the Ag⁺ in the semiconductor catalysts.     

High vis-light photocatalytic property of g-C3N4 on four pollutants (RhB,MB, TC-HCl and P-Nitrophenol)

The g-C₃N₄ nanosheets were synthesized by a multistage program calcination with different heating rate, which was an easy, low-cost, and quick method. The morphology and structure of samples were characterized by various techniques. The performance evaluation of the samples was tested by degrading Rhodamine B, Methylene Blue, Tetracycline Hydrochloride and P-Nitrophenol in visible light. The results show that the photodegradation properties of TP-g-C₃N₄ prepared by multistage program calcination are the best than others. In particular, the degradation rate of TP-g-C₃N₄ to Rhodamine B reached 99.6% in just 4 min. TP-g-C₃N₄ catalyst has excellent stability and recycling performance. According to free radical capture experiments, •O₂⁻ may be the main active species for pollutant degradation. The possible photocatalytic degradation mechanism was also discussed. Due to the high specific surface area and a narrow band gap, the TP-g-C₃N₄ becomes a promising photocatalyst.     

Ag2S nanoparticle encapsulated in mesoporous material nanoparticles and its application for photocatalytic degradation of dye in aqueous solution

Semiconductor loaded mesoporous materials in general possess greater photocatalytic activity than pure semiconductors. Hence, with an attempt to achieve higher photocatalytic activity, Ag₂S/MCM-41 photocatalysts were prepared by ion exchange method and used for the photocatalytic degradation of methylene blue. The materials were characterized by different analytical techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and BET (Brunauer-Emmert-Teller) experiments. The effect of Ag₂S, MCM-41 support and different wt% of Ag₂S over the support on the photocatalytic degradation and influence of parameters such as Ag₂S loading, catalyst a mount, pH and initial concentration of dye on degradation are evaluated. The degradation reaction follows pseudo-first order kinetics. It was seen that 0.6 g/L of photocatalyst is an optimum value for the dosage of photocatalyst. The degradation efficiency was decreased in dye concentration above 3.2 ppm for dye.     

Modified g-C3N4/TiO2 nanosheets/ZnO ternary facet coupled heterojunction for photocatalytic degradation of p-toluenesulfonic acid (p-TSA) under visible light

Novel ternary nanocomposites with facet coupled structure were synthesized by using modified g-C₃N₄, TiO₂ nanosheets and nano-ZnO. Nanosheet/nanosheet heterojunction structure was investigated by TEM, XPS and XRD. FT–IR and Nitrogen adsorption were illustrated for chemical/physical structure analyses. Solution of p-Toluenesulfonic acid (p-TSA) was chosen as target pollutant for visible light photodegradation and the excellent removal efficiency was achieved by this structurally modified g-C₃N₄/TiO₂/ZnO hybrid. The visible light absorption improvement and quantum efficiency enhancement, which were testified by UV–vis DRS, PL and p-TSA photodegradation measurements, due to the facet coupled structure and appropriate quantity of modified g-C₃N₄ in the nanocomposites.     

Mechanistic investigations on emission characteristics from g-C3N4, g-C3N4@Pt and g-C3N4@Ag nanostructures using X-ray absorption spectroscopy

An improved method for the preparation of g-C₃N₄ is described. Currently, heating (>400 C°) of urea is the common method used for preparing the g-C₃N₄. We have found that sonication of melamine in HNO₃ solution, followed by washing with anhydrous ethanol, not only reduce the crystallite size of g-C₃N₄ but also facilitate intriguing electronic structure and photoluminescence (PL) properties. Moreover, loading of metal (Pt and Ag) nanoparticles, by applying the borohydride reduction method, has resulted in multicolor-emission from g-C₃N₄. With the help of PL spectra and local electronic structure study, at C K-edge, N K-edge, Pt L-edge and Ag K-edge by X-ray absorption spectroscopy (XAS), a precise mechanism of tunable luminescence is established. The PL mechanism ascribes the amendments in the transitions, via defect and/or metal states assimilation, between the π* states of tris-triazine ring of g-C₃N₄ and lone pair states of nitride. It is evidenced that interaction between the C/N 2p and metal 4d/5d orbitals of Ag/Pt has manifested a net detraction in the δ*→LP transitions and enhancement in the π*→LP and π*→ π transitions, leading to broad PL spectra from g-C₃N₄ organic semiconductor compound.     

Computational study on the half-metallicity in transition metal—oxide-incorporated 2D g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets

In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C₃N₄ nanosheet (labeled C₃N₄–TM–O, TM = Sc–Mn). The results suggest that the TM–O binds to g-C₃N₄ nanosheets strongly for all systems. We found that the 2D C₃N₄–TM–O framework is ferromagnetic for TM = Sc, Ti, V, Cr, while it is antiferromagnetic for TM = Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures (T _c ) of the C₃N₄–TM–O (TM = Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C₃N₄ nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C₃N₄ nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.     

Ultrasonic irradiation preparation of graphitic-C3N4/polyaniline nanocomposites as counter electrodes for dye-sensitized solar cells

In this research, polyaniline/graphitic carbon nitride (PANI/g-C₃N₄) nanocomposites were synthesized via in-situ electrochemical polymerization of aniline monomer whit different number of cyclic voltammetry scans (10, 20 and 30 cycles) after electrode surface pre-preparation using a potential shock under ultrasonic irradiation. PANI/g-C₃N₄ nanocomposites with two values of g-C₃N₄ (0.010 wt% and 0.015 wt%) were deposited on the surface of the transparent conducting film (FTO glass) by immersing FTO into the aniline solution and g-C₃N₄ during the electro-polymerization. The resulting PANI/g-C₃N₄ films were characterized by Fourier transformed infra-red (FTIR), power X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) techniques. The prepared electrodes were applied as counter electrode in dye-sensitized solar cells. Among them, the prepared electrode with 10 cycles and 0.01 wt% g-C₃N₄ showed the best efficiency. These hybrids show good catalytic activity in elevating tri-iodide reduction and due to the synergistic effect of PANI and g-C₃N₄, PANI/g-C₃N₄ nanocomposite electrode shows power conversion efficiency about 1.8%.     

Ultrasound wave assisted removal of Ceftriaxone sodium in aqueous media with novel nano composite g-C3N4/MWCNT/Bi2WO6 based on CCD-RSM model

The aim of this study was ultrasound assisted removal of Ceftriaxone sodium (CS) based on CCD model. Using sonochemical synthesized Bi₂WO₆ implanted on graphitic carbon nitride/Multiwall carbon nanotube (g-C₃N₄/MWCNT/Bi₂WO₆). For this purpose g-C₃N₄/MWCNT/Bi₂WO₆ was synthesized and characterized using diverse approaches including XRD, FE-SEM, XPS, EDS, HRTEM, FT-IR. Then, the contribution of conventional variables including pH, CS concentration, adsorbent dosage and ultrasound contact time were studied by central composite design (CCD) under response surface methodology (RSM). ANOVA was employed to the variable factors, and the most desirable operational conditions mass provided. Drug adsorption yield of 98.85% obtained under these defined conditions. Through conducting five experiments, the proper prediction of the optimum point were examined. The respective results showed that RSD% was lower than 5% while the t-test confirmed the high quality of fitting. Langmuir isotherm equation fits the experimental data best and the removal followed pseudo-second order kinetics. The estimation of the experimentally obtained maximum adsorption capacities was 19.57 mg.g⁻ of g-C₃N₄/MWCNT/Bi₂WO₆ for CS. Boundary layer diffusion explained the mechanism of removal via intraparticle diffusion.     

Preparation of graphitic carbon nitride with large specific surface area and outstanding N2 photofixation ability via a dissolve-regrowth process

Nitrogen fixation is the second most important chemical process in nature next to photosynthesis. Here, we report a convenient dissolve-regrowth method for synthesizing graphitic carbon nitride (g-C₃N₄) with a large surface area and nitrogen vacancies by HCl treatment. XRD, N₂adsorption, SEM, TEM, UV–Vis spectroscopy, EPR, N₂-TPD, Photoluminescence and Photocurrent were used to characterize the prepared catalysts. The results indicate that HCl treatment does not influence the crystal phase of g-C₃N₄ but change the morphology and optical property, leading to the smaller particle size, larger surface area and increased bang gap energy. It is deduced by N₂-TPD, Photoluminescence, Photocurrent and DFT simulations that the nitrogen vacancies formed by the HCl treatment not only serve as active sites to adsorb and activate N₂ molecules but also promote interfacial charge transfer from g-C₃N₄to N₂ molecules. The HCl treated g-C₃N₄ catalyst exhibits outstanding nitrogen photofixation ability under visible light, which is 13.4-fold higher than that of bulk g-C₃N₄ without nitrogen vacancy. The possible reaction mechanism is proposed.