Electrospinning Preparation Of TiO₂ Nanofibers For Photocatalytic Air Purification

As the process of world industrial civilization accelerates,a large number of pollutants are discharged into the natural environment,causing serious environmental pollution problems.Semiconductor photocatalytic oxidation technology has received extensive attention because it can use solar energy and oxygen in the air to oxidize and decompose toxic pollutants.As the most typical semiconductor photocatalytic material,TiO₂ can not use visible light and photogenerated carriers are easily recombined,resulting in poor photocatalytic activity.Considering the excellent physical,chemical and biological properties of one-dimensional nanomaterials with easily recycling use,in this paper,high photoactive TiO₂ nanofibers were fabricated by electrospinning technique,and the photocatalytic air purification performance was investigated.The main contents of the research are as follows:1.TiO₂ Nanofibers with Large Specific Surface Area: In order to enhance the photocatalytic activity of ordinary TiO₂ nanofibers by increasing the specific surface area,we first prepared TiO₂ nanofibers using electrospinning technology and then converted them into titanate nanosheets by heat treatment in basic solution.After acid wash and followed by calcination,TiO₂ nanofibers assembly from TiO₂ nanosheets（TiO₂-NFs-NSs）with large BET surface area are obtained.The effect of heating time on the photocatalytic oxidation performance of acetone over TiO₂-NFs-NSs and photoelectric conversion efficiency of TiO₂-NFs-NSs film based dye-sensitized solar cells（DSSCs）were systematically investigated.The results showed that:（1）after heat treatment in basic solution for 3 h,the BET surface area of the obtained TiO₂-NFs-NSs sharply increased from 28 m²g^–1to 106 m²g^–1,improving 3.8 times;（2）TiO₂-NFs-NSs with 2.5 h of alkali heating treatment exhibited the highest photocatalytic activity.The rate constant for photocatalytic oxidation of acetone and the photoelectric conversion efficiency of DSSCs increased 3.1 times(from 1.11 ppm · min^-1to 3.41 ppm · min^-1)and 2.3 times（from 1.14% to 2.65%）,respectively.The reason for the enhanced activity of TiO₂-NFs-NSs compared with pristine TiO₂-NFs is the combined effects of enlarged BET surface area and enhanced light harvesting ability as the the sheet-like structures facilitate the scrattering of the incidental light.2.C-doped TiO₂ Nanofibers: Trace amount of element doping is beneficial to extend the photoresponsive range of TiO₂ and therefore improve the photocatalytic activity.During the calcination of the TiO₂ nanofiber precursor at certain temperature（300-800 ^oC）,carbon-doped TiO₂ nanofibers（C-TiO₂-NFs）were produced due to the carbonization of the PVP template.The photocatalytic activity of C-TiO₂-NFs was evaluated by photocatalytic reduction of CO₂.The results showed that:（1）TiO₂ nanofibers calcined at 400 ^oC（T400）showed the highest CH₄ generation rate(55 μmolg^-1h^-1),while TiO₂ nanofibers calcined at 500 ^oC（T500）exhibited the highest CO generation rate(4.7 μmolg^-1h^-1);（2）CH₄ and CO are the main products during the photocatalytic reduction of CO₂ over anatase TiO₂,while CO is the main product when rutile TiO₂ is used as the photocatalyst.The reasons for the high photoreactivity of C-TiO₂-NFs are extended visible light responsive range and promoted carrier separation rate due to carbon doping.3.N-doped TiO₂ Nanofibers: To improve the light absorption property of TiO₂ nanofibers,we synthesized N-doped TiO₂-NFs-NSs（N-TiO₂-NFs-NSs）by calcination the mixture of TiO₂-NFs-NSs and N-containing organic substances such as urea,melamine and dicyandiamide at 550 ^oC.The activity of the photocatalyst was evaluated by visible photocatalytic oxidation of NO.It was found that N-TiO₂-NFs-NSs can be synthesized whatever use urea,melamine or dicyandiamide as nitrogen sources,and N-TiO₂-NFs-NSs prepared with urea as the nitrogen source showed the highest photocatalytic activity towards NO oxidation.When compared with that of pristine TiO₂-NFs-NSs（NO removal rate from 39.4%）,the photoreactivity of N-TiO₂-NFs-NSs increased by 1.3 times（NO removal rate of 50.8%）.This is ascribed to the dopiong of N,which enhances light absorption and stimulates the seperatiom of photo-generated carriers.