Preparation Of Silicate Nanomaterials And Exploration Of Photocatalytic Performance

Silicates are ubiquitous materials with abundant reserves,and have been widely used as industrial catalysts.In the presence of transition-metal cations the SiO₄ tetrahedra in silicates can be easily distorted and get polarized,which can promote the charge-separation efficiency and photocatalytic activity.Furthermore,the presence of several different coordination environments for transition-metal cations can enhance not only the preferential migration of photogenerated charge carriers from one metal-oxygen polyhedra to another but also the optical absorption at various wavelengths.Therefore,it is highly desirable to search for novel silicate photocatalyst.In this dissertation,we have explored some silicate photocatalyst such as Zn₂SiO₄,amorphous sodium iron silicate and NaFeSi₂O₆ nanowires and studied their application in wastewater treatment.The specific research contents are as follows:?1?Zn₂SiO₄ nanocrystallines were synthesized by a low-temperature hydrothermal method,in which the composition and morphology were tailored by changing the hydrothermal temperature and pH value.Well-crystallized Zn₂SiO₄ can be obtained at a low temperature of120°C.The Zn₂SiO₄ prepared at 130°C has a nest-like and hollow structure,and numerous bundle-like particles constructed by large nanorods are obtained at 180°C.Zn₂SiO₄ was applied as novel photocatalyst to degrade various organic pollutants and it exhibited excellent photocatalytic activity and stability under UV light irradiation.The better photocatalytic performance of Zn₂SiO₄than ZnO can be attributed to the stronger oxidation ability of h⁺,the higher concentration of active·O₂^-radicals and the more stable polyhedral structure.?2?The amorphous sodium ferric silicate nanosheets were synthesized through a simple solvothermal method using ferric nitrate and sodium silicate.The specific surface areas of the sample was 135.19 m² g^-1.The adsorption affinity of the as-prepared sample toward a variety of dyes in water was analyzed and investigated.The high selective adsorption performance of cationic dyes was mainly due to the strong electrostatic attraction between them because they had opposite charges.The equilibrium adsorption data of methylene blue?MB?on the as-prepared sample was further investigated by Langmuir and Freundlich models,indicating that the Langmuir model was much more suitable for the experimental data.The sample showed the highest adsorption capacity with 239.6 mg g^-1.The experimental data were then fitted using pseudo-second order kinetics,suggesting that pseudo-second order kinetics could well describe the adsorption of MB on composites.The catalytic activity of the prepared amorphous sodium ferric silicate was evaluated using Rhodamine B?RhB?as the target pollutant.The results indicated that under visible irradiation the higher catalytic activity of the sample was observed in the photo-Fenton-like process.?3?NaFeSi₂O₆ was synthesized by a hydrothermal method,in which the composition and morphology were tailored by changing the reaction solvent and pH value.NaFeSi₂O₆ nanowires with length of 0.8-1.2?m and diameter of about 5 nm are obtained at 180°C and pH=12.The morphological evolution process of the NaFeSi₂O₆ nanowires involves a nucleation–ripening process.The catalytic activity of the prepared NaFeSi₂O₆ nanowires was evaluated using Rhodamine B?RhB?as the target pollutant.The results indicated that under visible irradiation the higher catalytic activity of the sample was observed in the photo-Fenton-like process.