Preparation Of Functional SnO₂ Hollow Nanospheres And Their Removal Of Nitrate From Water

With the rapid development of modern industry and agriculture,nitrate pollution has become a major environmental problem on the globe scale.Nitrate seriously threatens water environment security and human health due to its high solubility and stability.How to efficiently remove nitrate from water has become a research hotspot.SnO₂ has been widely used in the field of water treatment because of its chemical stability,non-toxicity,environmental friendliness,low cost and easy availability.In this paper,monodisperse SnO₂ hollow spheres were prepared by a one-step hydrothermal method and a series of modifications were made to prepare functional materials based on SnO₂ hollow spheres.Functional materials that can be used for nitrate removal were screened by adjusting the physical and chemical properties of the synthesized samples.The main research results are as follows:SnO₂@?-Fe(Zr)OOH hollow nanospheres were successfully synthesized by two-step hydrothermal method,which was used to adsorb nitrate in water.The structure and properties of samples which synthesized in this work were analyzed by means of XRD,SEM,TEM,XPS,BET and Zeta potential systematically.Moreover,the effects of initial nitrate concentration,p H,time and temperature on nitrate removal were also investigated.The amount of nitrate nitrogen adsorbed by the SnO₂@?-Fe(Zr)OOH nanocomposite was14.0 mg·g^-1 in the first 30 minutes.The adsorption kinetics and adsorption isotherms are in accordance with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model,respectively.The adsorption thermodynamic studies were carried out to prove that the reaction process is a spontaneous endothermic reaction.After six adsorption-desorption cycles,the composite still has an adsorption capacity of 80%.Flower-like Ag/SnO₂@?-Ni(OH)₂ hollow nanospheres is successfully fabricated by hydrothermal method,chemical precipitation method,and photodeposition method.The SnO₂@?-Ni(OH)₂hierarchical Z-scheme system displays remarkably improved photocatalytic nitrate reduction activity compared to pristine SnO₂ hollow nanospheres.Coupled with the surface plasmon resonance effect of Ag nanoparticles,it has a higher nitrate conversion(93.4%)rate and N₂ selectivity(99.2%).Ag/SnO₂@?-Ni(OH)₂still maintains high nitrate conversion rate(85.1%)and N₂selectivity(95.5%)after six cycles.The enhanced photocatalytic activity of Z-scheme system can be attributed to its unique feature of accelerating the reduction process,including:(i)The superiority of hollow structure,(ii)the construction of hierarchical Z-scheme heterojunction,(iii)the production of Ni⁰ co-catalyst that can act as a charge transfer center,and(iv)the SPR effect of Ag nanoparticles.The hierarchical Ag/SnO₂@?-Ni(OH)₂ photocatalytic system designed by this research provides a new path for the photocatalytic reduction of nitrate to N₂.