Preparation And Visible-light Photocatalytic Activities Of Grraphite-like Carbon Nitride/Silver Bromide Composite Photocatalyst

With the development of society, the energy crisis and environmental pollution problems have attracted high attentions from many countries in the world. As one of utilization methods of solar energy, the preparation and technological development of visible-light photocatalyst materials has become a prosperous research area in the fields of chemistry, material and environment scienceRecently, a graphite-like carbon nitride (g-C3N4) semiconductor is regarded as a cheap and stable promising photocatalyst due to its appropriate band gap (2.7 eV), excellent chemical/thermal stability and abundant in source, thus being widely used in photolysis aquatic hydrogen and degradation of organic pollutants. However, the g-C3N4 synthesized by traditional solid-phase method often results in a low specific surface area and poor quantum efficiency, thereby severely restricting its large-scale applications in environment and energy fields. To deal with these problems, the ultrasonic treatment was used to refine the particle size of bulk g-C3N4 particles; On this base, a porous g-C3N4 was obtained by hydrothermal method in the presence of sulfuric acid based on protonation effect; Finally, silver bromide (AgBr) nanoparticles were loaded on the porous g-C3N4 matrix, to fabricate the g-C3N4/AgBr composite photocatalyst. The related properties and mechanisms were also studied, the main research contents and results are as follows:(1) The effects of ultrasonic treatment on the structure, morphology and properties of g-C3N4A simple ultrasonic technology was used to treat g-C3N4 in isopropyl alcohol. And a series of characterizations were adopted to analyze the particle size, crystal structure, functional groups, surface morphology and photoabsorption properties of the treated g-C3N4. The visible-light photocatalytic activities of the treated g-C3N4 were evaluated by decomposing rhodamine B in aqueous solution. The results show that ultrasonic treatment can effectively refine the particle size of g-C3N4 to increase its contact area with dye, and the surface cracks and flaws produced by ultrasonic wave can offer more active sites for photocatalysis, therefore enhancing the visible-light photocatalytic property of g-C3N4.(2) Template-free preparation and properties of porous g-C3N4Based on the ultrasonic treatment of g-C3N4, a novel template-free method was presented to fabricate a porous g-C3N4 by hydrothermal modification in the presence of sulfuric acid. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), Thermogravimetric Analysis (TGA) and UV-vis diffuse reflectance spectra (DRS) were adopted to analyze the structure, morphology and properties of the porous g-C3N4. The adsorption capacity and visible-light photocatalytic activities of the porous g-C3N4 were evaluated by absorbing and decomposing methyl orange and rhodamine B in aqueous solution, respectively. Based on electrochemical analysis, electron paramagnetic resonance (EPR) and reactive species trapping measurement, the photocatalytic mechanism of hydrothermal modified g-C3N4 was investigated. The results show that the protonation treatment under hydrothermal conditions in the presence of sulfuric acid is favorable to improve the porosity of g-C3N4, which can increase its ability to absorb pollutants and inhibit the recombination of photo-generated carriers, thereby enhancing the visible-light photocatalytic property ofg-C3N4.(3) Preparation and properties of g-C3N4/AgBr nanocomposite photocatalystA facile method was proposed to fabricate g-C3N4/AgBr composite photocatalyst by loading AgBr nanoparticles on the g-C3N4 matrix, which was protonated under hydrothermal conditions in the presence of sulfuric acid. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), Mott-schottky analysis (MS) and UV-vis diffuse reflectance spectra (DRS) were adopted to analyze the structure and properties of g-C3N4/AgBr composite photocatalyst. The photocatalytic activities of the as-prepared samples were evaluated by decomposing methyl orange and rhodamine B in aqueous solution under visible light illumination. In addition, the reusability was also investigated. The results show that the protonation pretreatment of g-C3N4 matrix can not only increase porosity of g-C3N4 matrix, but also provide growth sites for AgBr grains. Therefore, the AgBr nanoparticles can be uniformly loaded on the surface of g-C3N4 matrix. Combining the results of EIS Nyquist plots, PL photoluminescence, EPR spectroscopy, reactive species trapping measurement and ·OH trapping PL spectra, a Z-scheme charge transfer mechanism is proposed.