Nano-TiO₂ Immobilized On Sepiolite: Preparation,Crystal Facet Regulation And Photocatalytic Properties

The development of efficient,inexpensive,and stable photocatalytic materials is the basis and core for the widespread application of photocatalytic technology.TiO₂has been extensively studied due to its high chemical stability,chemical resistance and environmental friendliness.However,wide band gaps,ease of aggregation,high recombination of electron-hole pairs,and difficulty in separating TiO₂ powder suspended in solution limit its application.In this paper,the combination of sepiolite with excellent adsorption properties and high phocatalytic activity of TiO₂nanocrystals to form TiO₂/sepiolite composite solves the above problems.The TiO₂nanoparticles can be embedded in the sepiolite,which could improve the problems of solid-liquid separation and easy aggregation of nano-TiO₂;and electron-hole separation was further promoted by the crystal plane modulation of the supported TiO₂.The visible photocatalytic activity was further enhanced by the surface plasmon resonance?SPR?effect.At the same time,the structure-effect relationship between chemical composition,elemental valence,pore structure,morphology and phtocatalytic properties of the material was studied.The photodegradation mechanism was further discussed.The specific research contents of this paper are as follows:?1?Micro-mesoporous structure TiO₂/sepiolite?TiMS?composites were prepared by hydrolysis-precipitation method using modified sepiolite?MS?as carrier.The effects of calcination temperature,TiO₂/MS weight ratio,HCHO initial concentration and environmental relative humidity on the degradation of HCHO by TiMS were studied.It was proved that the presence of sepiolite can improve the photocatalytic efficiency and stability of nano-TiO₂,and the photocatalytic mechanism of TiMS for degradation of HCHO was finally proposed.?2?The single-crystal TiO₂/sepiolite composite gel?TiSG?with exposed{001}and{101}facets was synthesized by one-step solvothermal method.The CTAB content,solvothermal temperature,solvothermal time,and HAc content played crucial roles in the morphological and exposed facet of TiSG.A possible mechanism for the formation of TiSG was further proposed.CTAB as capping/shape-controlling agent can strongly bind to the more reactive?001?facet of TiO₂ and then mitigate the thermodynamically favored?001?plane growth.Eventually,the truncated octahedral TiO₂ was obtained by controlling the growth rates in<001>and<101>directions.Sepiolite as a cross-linking agent provided sufficient crosslinking sites for TiO₂ to induce three-dimensional?3D?network formation,thereby generating the composite gel.TiSG exhibited higher catalytic activity than TiO₂ and P25 for the following reasons.The 3D network structure is advantageous to light reflection and refraction,which can greatly improve the utilization rate of light;The surface heterojunction between?001?and?101?planes is formed,which promotes separation of photoexcited electrons and holes;The presence of sepiolite increases the specific surface area and adsorption capacity of the material.?3?High activity mesocrystalline TiO₂/sepiolite?TiS?composites were prepared by controlling the titanium source and acetic acid concentration.via a solvothermal process.Thereinto each TiO₂ mesocrystal comprised many[001]-oriented anatase nano single crystals.The parameters such as reaction time and sepiolite content were adjusted to optimize the photocatalytic activity of TiS.The differences in the photocatalytic degradation mechanisms of MO and MB were described,which was related to the charge of the surface of the material and the main active species in the photocatalytic process.?4?To optimize the visible light catalytic performance,a novel ternary Ag-decorated TiO₂/sepiolite?AgTiS?composite was prepared by sepiolite loading-assisted SPR technology.Compared with TiO₂,P25,sepiolite and TiO₂/sepiolite,the designed AgTiS exhibits enhanced visible light catalytic activity.The degradation kinetics exhibit pseudo-first-order behavior.Holes and superoxide radicals are the main active species in the photodegradation of MO.Based on the role of sepiolite and Ag,the possible photocatalytic mechanism of AgTiS composites was proposed under visible light.