Synthesis Of Mesoporous Microcrystalline TiO₂ Assisted By Deep Eutectic Solvent

Mesoporous titanium dioxide has good thermal stability,large specific surface area,easy surface modification,and can effectively enhance its photocatalysis,photoelectric conversion and other functions.Therefore,it can be widely used in water treatment,air purification,solar cells and nanomaterials.Currently,the synthesis methods of nano-mesoporous materials mainly include hydrothermal synthesis,sol-gel method and microwave synthesis.Among them,the sol-gel method has been widely used in recent years due to its mild reaction conditions,controllability and biocompatibility.The preparation of nano-mesoporous materials by sol-gel method is generally carried out by a combination of template techniques.The basic process is to use different types of structure-directing agents to form a supramolecular structure in the form of template,sol-gel,etc.under the interface of inorganic and organic materials to form nano-porous materials with narrow distribution and regular pores.Among them,ionic liquids have been widely used as templating agents in material preparation due to their low surface tension,small interfacial energy,easy formation of hydrogen bonds,and good performance of synthetic materials.However,due to the high cost of ionic liquids,complex synthesis processes,and the need for high purification,in order to solve these problems,we use low-cost,easy-to-synthesize eutectic solvents instead of ionic liquids as templating agents to synthesize nano-mesoporous titania microcrystals.In this paper,nano TiO₂ was synthesized by sol-gel method,and the preparation conditions were optimized by single factor experiment.Two kinds of deep eutectic solvents?DES?were prepared as template by molecular design.Anatase-type high specific surface area mesoporous titania microcrystals were used for photocatalytic degradation of methyl orange.Combined with density functional theory calculation,the mechanism of DES formation in mesoporous titanium dioxide was analyzed.The specific research contents are as follows:?1?Using titanium tetrabutyl titanate as titanium source,ethanol as solvent and acetic acid as pH adjuster,nano-titanium dioxide was prepared by sol-gel method.Theratio of anhydrous ethanol,deionized water and pH was investigated by single factor experiment.The optimum reaction ratio was determined by the influence of the particle size of titanium dioxide agglomeration.The results show that the ratio of reactants is n?TBT?:n?C2H5OH?:n?H2O?=1:9:4,X-ray diffraction?XRD?,dynamic light scattering?DLS?particle size when pH is 2.5.The distribution and BET analysis results showed that the product was a single crystal anatase phase with an average particle size of 13.2 nm but no pore structure.?2?According to the structure and mechanism of DES,two kinds of amphiphilic DES,namely choline chloride-phenol and choline chloride-phenylpropionic acid,were prepared as templating agents in the preparation process of sol-gel method.Porous titanium dioxide crystallites.The results show that the designed DES has a good mesoporous structure guiding effect when the molar ratio of choline chloride-phenol,choline chloride-phenylpropionic acid and tetrabutyl titanate is 0.3:1 and 0.1:1,respectively.The prepared nano titanium dioxide is an anatase phase with good crystallinity and has a mesoporous structure,wherein the specific surface area of titanium dioxide prepared by using choline chloride-phenylpropionic acid as a template is 70.94m²/g.The pore diameter was 4.47 nm and the pore volume was 0.079 cm³/g.The results of methyl orange degradation experiments show that the mesoporous titanium dioxide product has good photocatalytic performance,and the degradation rate of methyl orange degradation in the same time is 28.1%higher than that of titanium dioxide not prepared by using DES.?3?There is indeed a hydrogen bond between Cl of choline chloride and O-H in phenol.After DES formed by choline chloride-phenol,H of O-H in choline chloride in DES can also be combined with Ti?OH?₄ unit cell.The O-H forms a hydrogen bond,and the hydrogen bonds formed are medium-intensity hydrogen bonds and weak hydrogen bonds;as the number of atoms increases,the number of weak hydrogen bonds gradually increases,which is also because electrostatic attraction and repulsion effects are enhanced.This leads to a weakening of the hydrogen bond strength.