Rapid Preparation Of TiO₂ Aerogel By Mechanical Ball Milling Assisted Method And Its Photocatalytic Performance

TiO₂ aerogel has good chemical stability,high specific surface area and porosity,and is a functional material with excellent adsorption and catalytic properties.It,however,still has some challenges in practical preparation and application.On the one hand,the gel aging and solvent replacement processes consume long time and require the use of a large amount of organic solvents,which is not conducive to the large-scale industrial production of TiO₂ aerogel.On the other hand,the high compounding rate of photogenerated carriers generated by photoexcitation of pure TiO₂ aerogel materials leads to their low photocatalytic efficiency.To address the above problems,this study innovatively developed a mechanical ball milling method to assist the gel aging and solvent replacement process in the TiO₂ aerogel preparation process,which significantly shortened the preparation time of TiO₂ aerogel and reduced the solvent consumption.It is investigated the effects of three factors,such as ball milling time,ball milling speed and solvent consumption,on the structure and properties of TiO₂ aerogel materials,and the mechanism of mechanical ball milling-assisted gel aging and solvent replacement process,and the optimization of process parameters.Based on the optimized process parameters,the Sn-TiO₂ aerogel was prepared by mechanical ball milling with the control of Ti/Sn molar ratio and calcination temperature,which has excellent photocatalytic properties.Physical adsorption/desorption（BET）,X-ray polycrystalline diffractometer（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,thermogravimetric analyzer（TGA）,Fourier transform infrared spectrometer（FT-IR）,X-ray photoelectron spectroscopy（XPS）and ultraviolet-visible diffuse reflectance spectrometer（UV-Vis DRS）were used.The TiO₂ aerogel materials fabricated under different process parameters were characterized,and the photocatalytic activities of TiO₂aerogel and Sn-TiO₂ aerogel were investigated with tetracycline hydrochloride（TC-HCl）as the target contaminant.The conclusions of the study are as follows:（1）A process method for the rapid preparation of TiO₂ aerogel materials assisted by mechanical ball milling is proposed.The preparation process is as follows:TiO₂ gel is prepared by ultrasonically assisted sol-gel method,and then TiO₂ gel aging and solvent replacement process is assisted by mechanical ball milling method,followed by vacuum drying,grinding and calcination to finally produce TiO₂ aerogel with good photocatalytic properties.（2）Investigated the effects of three process parameters,ball milling time,ball milling rotational speed and solvent consumption,on the structure and properties of TiO₂ aerogels in the mechanical ball milling-assisted preparation process.Suitable ball milling time and ball milling speed can promote gel aging and increase the mechanical strength of TiO₂gel network,but too long ball milling time or too large ball milling speed can cause agglomeration of gel particles,which is not conducive to the formation of gel network.The appropriate amount of hexane solvent can replace the high surface tension solvent and weaken the capillary force during gel drying,while the excessive amount of solvent will weaken the efficiency of mechanical ball milling.（3）The process parameters of TiO₂ aerogel preparation by mechanical ball milling assisted method were optimized.When the ball milling time was 30 min,the ball milling speed was 300 rpm,and the solvent consumption was 60 m L,the structure of the prepared TiO₂ aerogel material was optimal,and the specific surface area was 465.573 m2·g-1,the total pore volume was 0.3522 cc·g-1,and the average pore diameter was3.026 nm.The gel aging and solvent replacement time was shortened from15 h to 30 min,and the amount of hexane used for solvent replacement was reduced by 25%.（4）The mechanism of the mechanical ball milling-assisted preparation process affecting the structure of TiO₂ aerogels was analyzed.The decisive factor affecting the structure of TiO₂ aerogel is the degree of destruction of TiO₂ gel network by capillary forces during the drying process,where the ball milling time and ball milling speed affect the mechanical strength of TiO₂ gel network by influencing the degree of gel aging,and the solvent consumption affects the degree of TiO₂ gel solvent replacement,which in turn affects the capillary forces destroying TiO₂ gel network during the drying process.（5）Sn-TiO₂ aerogel was successfully prepared by applying the mechanical ball milling-assisted preparation method proposed in this study.Based on the optimized process parameters,when the Ti/Sn molar ratio was 20:1 and the calcination temperature was 500℃,the produced Sn-TiO₂ aerogel had the best adsorption and photocatalytic performance,and the total removal rate of 20 mg·L-1 tetracycline hydrochloride under UV light conditions reached 94.54%,compared with pure TiO₂ aerogel,the rate constant of the primary photocatalytic reaction was enhanced from 0.0561min-1 to 0.0771 min-1.