Synthesis Of ZnS Nanoparticles By Sol-gel Combustion Method And Application In Photocatalylysis

Sol-gel auto combustion method is a new synthesis method for powder materials,which combines sol-gel method and combustion synthesis.It is widely applied in the synthesis of kinds of oxide powder material with many advantages such as accurate stoichiometric control,simple and energy saving process,short reaction time,high homogeneity product,small particle size and large specific surface area.ZnS is one of the most widely studied photocatalytic materials,which can produce electron hole pairs rapidly under the condition of optical excitation,and has high catalytic activity for decomposing organic pollutants in water under UV irradiation.The synthesis of ZnS nanomaterials by conventional methods,such as solvothermal method,hydrothermal method and chemical vapor deposition method,show disadvantages of complex synthesis process,low yield and high cost,which is not suitable for large-scale synthesis,and limits the application of ZnS nanoparticles as photocatalytic materials.Therefore,it is of great academic and practical value to study the synthesis and photocatalytic properties of ZnS nanomaterials by sol-gel combustion method.It has been found that if the sulfur containing organic compounds such as thiourea is used as the complexing agent in the precursor,the sulfuration atmosphere will be formed at the combustion,and the corresponding metal sulfides are obtained.In preliminary study,based on this idea,ZnS nanoparticles are synthesized by sol-gel combustion method using thiourea as complexing agent.However,the homogeneity of particle size and morphology is poor;making the synthetic method is lack of practicality.In this thesis,first we successfully synthesized the ZnS nanoparticles with homogeneous size and morphology by the addition of glycine as complexing agent and ethylene glycol as dispersing agent into the precursor.Then we studied the influence of the ratio of fuel/oxidant,dispersing/complexing agent and Zn/S in the precursor on the morphologyof ZnS nanoparticles by statistical analysis of the experimental dat.The study results show that: 1.ZnS particles with homogeneous size and shape can be obtained by adjusting the ratio of dispersant/complexing agent under different fuel/oxidant.Moreover,the ratio of dispersant/complexing agent for best sample gradually decreased,with the ratio of fuel/oxidant ratio increasing.2.The average size of the nanoparticles with best morphology changes for different ratio of fuel/oxidant.3.With fixed fuel/oxide,the influence of changing the ratio of Zn/S on the ratio of dispersing/complexing agent for best sample is negligible as the same as that on average size of the nanoparticles.Based on the study,we suppose the role of glycine and ethylene glycols in the optimization of particle morphology are as follows: 1.glycine is a better complexing agent than thiourea o form a complex crosslinking network in the dry gel with the presence of ethylene glycol.The complex crosslinking network in the dry gel is favorable for the homogeneously heat conducting in combustion,providing a homogeneous thermal environment for the growth of nanoparticles.2.Ethylene glycol also works as dispersing agent in the dry gel.The simple structure and small molecular weight make ethylene glycol molecules being homogeneously dispersed between complexes.Moreover,the binding between ethylene glycol and the complex group is weak and easy to be break at the high temperature in combustion,which is favorable for the homogeneous sulfurization of Zinc nanoparticles.In addition,beside the study od the synthesis of ZnS nanoparticles,we also studied the influence of morphology control factors on the photocatalytic performance of ZnS nanoparticles for decomposing organic dyes under UV light.The study results show that the photocatalytic ability is not related to the morphology homogeneity,the ratio of oxidant / fuel and ethylene glycol /complexing agent cannot independently control the photocatalytic ability,but the ratio of thiourea / zinc nitrate show prominent influence on the photocatalytic ability of the as synthesized ZnS nanoparticles.Therefore,the photocatalytic properties of ZnS nanoparticles are determined not only by morphology but also by other factors.The research in this paper not only provides a new and efficient method for the synthesis of ZnS nanoparticles,but also provides a theoretical and experimental basis for the further application of sol-gel auto combustion method in the synthesis of sulfide nanomaterials.