Preparation And Application Of TiO₂/NiO Nanocomposites

In this paper,TiO₂/NiO double-shell hollow spheres with p-n heterostructures were successfully prepared by sol-gel method and hydrothermal method.Firstly,SiO₂nanospheres were prepared by a simple St?ber method.Subsequently,SiO₂ nanospheres were used as templates,and TiO₂ was coated on the surface of SiO₂ by sol-gel method.Then,the prepared SiO₂/TiO₂ nanocomposite microspheres were calcined at high temperature.After cooling,the template SiO₂ was etched away with the sodium hydroxide solution to obtain the TiO₂ hollow sphere.Next,TiO₂/NiO double-shell hollow sphere nanocomposite with p-n heterojunction was prepared by hydrothermal coating NiO on the surface of TiO₂ hollow sphere.The inner diameter of TiO₂/NiO double-shell hollow sphere is about 270 nm,the shell thickness of TiO₂ is about 20 nm,and the shell thickness of NiO increases from 10 nm to 25 nm with the increase of nickel source.Therefore,the total diameter of the TiO₂/NiO double-shell hollow is330–360 nm.According to XRD test analysis,the crystal form of TiO₂ is anatase,and the crystal form of NiO is hexagonal.The specific surface area test results of the sample show that the material has a large specific surface area,which can provide more active sites for the catalytic reaction.The prepared pure TiO₂ hollow spheres and TiO₂/NiO double-shell hollow spheres of four different NiO content were applied to photocatalytic degradation of papermaking wastewater,methylene blue and methyl orange.The results show that the degradation effect of TiO₂/NiO double-shell hollow spheres with p-n heterojunction is better than the pure TiO₂ hollow spheres.The TiO₂/NiO double-shell hollow sphere with 5 wt.%NiO content has the best degradation effect.When the papermaking wastewater is degraded,the chemical oxygen demand removal rate of papermaking wastewater is close to 98.1%after 6 hours of ultraviolet light irradiation.Therefore,5wt.%of NiO is used as the optimum loading of the p-n heterostructure TiO₂/NiO double-shell hollow sphere photocatalyst.This excellent photocatalytic performance can be attributed to two reasons:?1?At a low loading amount of NiO,photocatalytic activity is low due to the formation of only a few p-n junctions.?2?With the increase of NiO loading,the dispersion degree of the NiO particles on the surface of TiO₂ decreased,resulting in large NiO particles.Given that the surface recombination phenomenon is more likely to occur in large particles,photocatalytic activity can be reduced.And the blocking effect of the redundant NiO particles on TiO₂ may negatively influence the photoactivity of the p-n heterostructured TiO₂/NiO double-shelled hollow spheres.In addition,the influencing factors affecting photocatalytic degradation of papermaking wastewater were also explored.The optimal conditions for catalyst degradation of papermaking wastewater were pH 5 and photocatalyst dosage is 1.0 g L^–1.The results of three photocatalytic degradation of papermaking wastewater cycle experiments show that the prepared photocatalyst has good stability and reusability,which is of great significance for the practical application of papermaking wastewater treatment.