Preparation And Microstructure Of Molybdenum Disulfide-halloysite Composites

Molybdenum disulfide has become a research hotspot in the field of photocatalysis in recent years because of the wide visible light response range and high carrier mobility.However,the nano-molybdenum disulfide with the large surface energy often agglomerates spontaneously,leading to a decreased number of active sites and thus a lower photocatalytic activity,which brings great challenges to the mass application.In this thesis,alkali-modified halloysite was used as a functional carrier to disperse molybdenum disulfide.The effects of the preparation conditions and surfactants on the microstructure of the molybdenum disulfide-halloysite composites were studied.Rhodamine B（Rh B）degradation was used as a probe reaction to evaluate the photocatalytic performance of the composites.On this basis,the possible growth mechanism of the composites was proposed,the degradation mechanism of the composites and the synergistic effect between molybdenum disulfide and halloysite were also revealed.The optimal preparation conditions for the preparation of composites by hydrothermal method were determined as follows:halloysite with 5 mol/L of modification concentration and 24 h of modification time,220°C of hydrothermal temperature,24 h of hydrothermal time,and 8 wt.%of halloysite additional content.The degradation rate of Rh B by the optimal composite reached 89.3%,roughly 2.3 times than that of pure molybdenum disulfide.It was found that molybdenum disulfide was converted from nano-microspheres to highly dispersed nanosheets with the addition of the modified halloysite,which effectively solved the problem of agglomeration of nano-molybdenum disulfide.The composites had the best morphology and properties with the addition of 1.5 mmol/L sodium dodecyl benzene sulfonate（SDBS）,and the degradation rate of Rh B reached 93.4%.The possible growth mechanism of the composites was as follow:the Na OH would attack the silicon-oxygen tetrahedral（Si O₄）units on the outer surface of the halloysite and thus produced lots of defects on the outer surface.Followingly,both the defects at outer surface and Al-OH at inner surface served as nucleation sites,which could adsorb a large amount of molybdate ions.These molybdate ions could react with H₂S gas generated by the hydrolysis of thiourea in the hydrothermal process to form molybdenum disulfide,which makes molybdenum disulfide grows into highly dispersed nanosheets on both outer surface and lumen of the modified halloysite during hydrothermal process.UV-vis diffuse reflectance spectra showed that the composites exhibited strong light absorption,and the experimental results of active species capture indicated that h⁺and·O^2-played a dominant role in the degradation of Rh B by the composites.The excellent absorption capability of the modified halloysite could promote the transfer of Rh B molecules to the active sites of molybdenum disulfide and thus accelerate the photocatalytic degradation process.The composites prepared in this work provide an effective strategy for the efficient utilization of halloysite and the low-cost preparation of highly dispersed two-dimensional materials.