Preparation Of Titanium Dioxide By High-gravity Method And Photodegradation Of Volatile Organic Compounds

Volatile organic compounds?VOCs?are a general term for many low-boiling,volatile hydrocarbons.Their pollutants have a wide range of sources,complex components,great harms,and are difficult to degrade,which brings great harm to the human living environment and ecological environment.The photocatalytic oxidation method uses light as an energy source,and has the advantages of low energy consumption,thorough mineralization,and mild conditions.However,the photocatalyst's insufficient utilization of light energy and the short lifetime of photo-generated carriers seriously affect the photocatalytic efficiency.At the same time,it is difficult to prepare a nano-TiO₂ photocatalyst with a small particle size,a narrow distribution,and a high light energy utilization rate,resulting in higher costs.Therefore,it is necessary to develop a new method to facilitate the continuous preparation of high-quality,high photocatalytic efficiency of nano-TiO₂.Studies have shown that by uniformly doping,the range of light absorption of TiO₂ can be widened,and the carrier lifetime can be extended,thereby improving the photocatalytic efficiency.The chemical precipitation method has the advantages of simple process and cheap raw materials in the preparation of nano-TiO₂,but this method usually uses a traditional stirred reactor.Due to its limited micro-mixing,the prepared catalyst has a large particle size,a wide distribution,and uneven quality.Based on this,combined with the unique advantages of Impinging Stream-Rotating Packed Bed?IS-RPB?in enhancing liquid-liquid micro-mixing,this paper proposes to use high-gravity technology to strengthen the chemical precipitation process to prepare nano-TiO₂,and use its uniform micro-mixing characteristics to achieve uniformity doped.And finally,the catalyst performance was studied by photodegradation of volatile organic compounds.The main research contents include the following three parts:?1?The high-gravity technology was used to strengthen the micro-mixing in the chemical precipitation process,and TiOSO₄ was used as the titanium source,ammonia water was used as the precipitant,and IS-RPB was used as the reactor to successfully prepare nano-TiO₂.When the concentration of TiOSO₄ is 0.2 mol/L,the precipitant is 0.5 mol/L,the liquid flow rate is 60 L/h,and the packed bed speed is 800 rpm,the prepared TiO₂ has a particle size of 13 nm,and has a uniform distribution and good dispersibility.Calcination temperature has a greater effect on the crystal form and particle size of TiO₂.The higher the temperature,the larger the particle size,and a complete 100%anatase crystal form at 500?.?2?Based on the enhanced micro-mixing characteristics of IS-RPB,Fe³⁺-doped nano-TiO₂?Fe-TiO₂?was successfully prepared using TiOSO₄ as titanium source,ammonia as precipitant,FeCl₃·6H₂O as Fe³⁺source and IS-RPB as reactor.The results show that the doping of iron does not affect the crystal structure of TiO₂,there are a large number of hydroxyl groups before and after doping,iron exists in trivalent form and uniformly distributed in the grains,and the particle size of the catalyst with a Fe/Ti ratio of 5%is about11.3±1.9 nm.It is possible that partial iron doping into the lattice instead of part of Ti⁴⁺,results in the expansion of the light response range of the doped catalyst to visible light.The impurity energy level with low band gap is produced by doping,which reduces the band gap energy of the catalyst,and the Fe-TiO₂ prepared in IS-RPB has a mesoporous structure with narrow pore size distribution and a specific surface area larger than that of commercial P25.?3?UV lamp and xenon lamp were used as light sources to simulate UV and visible light,and toluene was used to simulate volatile organic compounds?VOCs?.The effects of different catalysts,initial concentration of toluene and the amount of catalyst on the degradation were investigated.The results show that under UV light,the performance of Fe-TiO₂ is better than commercial P25 and undoped TiO₂.When the molar ratio of Fe/Ti is 1.0%,the degradation rate of 4 h is 95.7%.Under visible light,commercial P25 and undoped TiO₂ have no photocatalytic activity.But Fe-TiO₂ show photocatalytic activity under visible light due to the expansion of light response range.PL spectra show that doping suppresses the photogenerated electron-hole recombination of the catalyst,resulting in the improvement of photoquantum efficiency,thus enhancing the photocatalytic performance.