Ultrasonic-assisted Sol-gel Using In Synthesis Of TiO₂-SiO₂ Composite Aerogel And Its Performance For P-nitrophenol Photodegradation Application

TiO₂-SiO₂ composite aerogel is a photocatalytic material with visible light response,which is prepared by ultrasonic assisted sol-gel method with tetra-butyl titanate as titanium source and rice husk ash as silicon source.By X-ray diffraction（XRD）,field emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM）,automatic specific surface area analysis（BET）,laser Raman spectroscopy（LRS）,Fourier transform infrared（FTIR）,X-ray photoelectron spectroscopy（XPS）and ultraviolet-visible diffuse reflection spectrum（UV-Vis DRS）characterization methods such as the preparation of state and after heat treatment was studied of TiO₂-SiO₂ aerogel composite morphology structure and catalytic performance differences.The effects of TiO₂-SiO₂ composite aerogels on interface structure,surface morphology and photocatalytic performance were investigated.The photodegradation of PNP by ultrasonic dark reaction-photocatalysis was compared with that by TiO₂-SiO₂ composite aerogel catalyst.The research results are as follows:（1）Under the conditions of n（Ti:Si）= 3:1,2:1,1:1,1:2,1:3 with different TiO₂-SiO₂ composite aerogel ratios obtained by ultrasound-assisted method,the photodegradation effect of n（Ti:Si）= 2:1 on nitrophenol was the best under ultraviolet light source and simulated sunlight light source.（2）With the increase of Ti content in TiO₂-SiO₂ composite aerogel,the content of anatase phase TiO₂ increases,and SiO₂ always exists in the aerogel in an amorphous form.Titanium silicon exists in the form of Ti-O-Si.（3）The results of TiO₂-SiO₂ composite aerogel prepared with different ultrasonic powers showed that when the ultrasonic power was 350W,the crystallinity of anatase phase TiO₂ in TiO₂-SiO₂ composite aerogel was the best,which was better than the samples prepared with other ultrasonic powers,so that its treatment had the best effect on nitrophenol,and the degradation rate of 80%could be reached after 40min of light reaction.Ultrasound helps to form Ti3+,which provides surface oxygen vacancy and improves photocatalytic efficiency of catalyst.（4）The comparison of TiO₂-SiO₂ composite aerogel after heat treatment at different temperatures shows that SiO₂ exists in amorphous form in TiO₂-SiO₂ composite aerogel.In the temperature range from 350 ℃ to 750 ℃ pyrolysis,TiO₂ all exist in anatase phase;Starting from 850 ℃,TiO₂-SiO₂ composite aerogel began rutile phase crystal phase structure;In the temperature range from 850 ℃ to 1150 ℃ pyrolysis,TiO₂ in anatase and rutile phase exists in the form of mixed crystal phase;With the increase of pyrolysis temperature,the grain size of each phase increased obviously.（5）Ultrasonic assisted sol-gel TiO₂ up in TiO₂-SiO₂ composite aerogel by anatase phase shift for the rutile phase temperature range of 750 ℃ to 850 ℃;Compared with the results of other researchers on the phase transition temperature of TiO₂,the introduction of Sio2 can inhibit the phase transition of TiO₂.（6）The TiO₂-SiO₂ aerogel prepared by ultrasound-assisted sol-gel method can effectively reduce hole collapse in the process of atmospheric pressure drying.Ultrasonic cavitation energy can enable the aerogel to form Ti-O-Si bond and broaden the TiO₂ light response range to the visible region.Ultrasonic dark reaction-photocatalysis method can effectively reduce the apparent activation of PNP molecules and increase the photocatalytic efficiency.（7）Experimental results of free radical capture showed that ·O₂--and ·OH were the main active substances in the photodegradation PNP system,and ·O₂-played a major role in the system.The mechanical action of ultrasound is helpful for the catalyst to obtain more opportunities to contact·O₂-in the sound wave of medium vibration,and it is helpful for the catalyst to attach·O₂-on the surface,so as to generate a large amount of ·O₂-in the light reaction stage,thus improving the photocatalytic degradation efficiency.