Preparation And Visible-light Photocatalytic Performance Of Silver-based Graphitic Carbon Nitride Composite Photocatalysts

Photocalaytic technologies, due to its potential utilization of solar energy for hazardous environmental pollutants degradation and traditional hydrogen production by water-splitting, have attracted extensive attention in recent decades. Owing to the special electronic structure and excellent chemical and thermal stability, graphitic carbon nitride（g-C₃N₄） is a novel visible-light metal-free polymeric photocatalyst. In addition, silver-based material is an efficient visible-light photocatalyst, such as Ag-AgCl, Ag3PO4, Ag₂CO₃, etc. However, some self-defects still limit their practical application when they are used alone, such as low quantum efficiency and serious photocorrosion etc. In order to solve these matters, accelerating the development of photocatalytic technology in environmental purification and other fields, in this paper, we carry out on the optimum preparation, structure assembling and property enhancement of g-C₃N₄ and silver-based photocatalyst, the major research points are summarized as follows:（1） The synthesis and controlled visible-light photocatalytic selectivity of ternary graphene oxide（rGO） /g-C₃N₄/Ag-AgCl（GCA） hybrids towards the azo dyes degradation. Firstly, the pure g-C₃N₄ nanosheets were synthesized by a simple thermal condensation method using melamine and urea as raw materials. Subsequently, the rGO/ g-C₃N₄/Ag-AgCl composites were successfully prepared by a combined depositionprecipitation and in situ photoreduction method. The prepared ternary graphenesemiconductor-metal photocatalysts exhibited enhanced photocatalytic visible-light activity and controlled selectivity for the azo dyes degradation in water. The enhanced visible-light photocatalytic activity of GCA sample may be attributed to the positive synergistic effect of the well electronic mobility of rGO sheets and the surface plasmon resonance of Ag-AgCl nanoparticles. This effect efficiently accelerated the separation of photogenerated electron-hole pairs and enhanced visible-light adsorption efficiency. In addition, the controlled photocatalytic selectivity of rGO/g-C₃N₄/Ag-AgCl composites can be modulated by tuning their surface charges to change the adsorption properties, which achieved selective degradation of preferential adsorbed molecules.（2） Ag₂CO₃ particles were fabricated for different precursors via a facile precipitation methods, the particle size of these Ag₂CO₃ distributed in 2 μm- 3 μm or 3 μm- 5 μm. The as-prepared Ag₂CO₃ particles showed decent visible-light photocatalytic activity for MO degradation. Based on the characterization method of X-ray diffraction（XRD）, scanning electron microscopy（SEM）, Nitrogen adsorption-desorption isotherms measured and UV-vis diffuse reflection spectra（UV-vis DRS）, a possible mechanism for the enhancement and deactivation of Ag₂CO₃ photocatalysts were also proposed. The result indicated that the trace amounts of Ag Nanoparticles（NPs） deposited on the surface of Ag₂CO₃ could act as the electron trapping centers to promote the separation rate of photoinduced charge carriers, but the photocatalytic activity of Ag₂CO₃ decreased with the presence of excessive Ag NPs. It was attributed to the shielding effect by Ag layers on the surface of Ag₂CO₃ declining the utilization rate of solar energy of samples, which leaded to the photo-corrosion of Ag₂CO₃ samples. Results from current study may provide a new light on the synthesis of more stable and efficient Ag₂CO₃ photocatalysts and their composite materials.