| Semiconductor titania is an important photocatalyst and has been widely employed in photodegradation of organic pollutants and air purification for the advantages of cheap,non-toxic and high oxidation activity.Because the powder titania cannot be separated and recycled,there has been an increasing interest in the preparation of film to solve this problem and overcome the instability and poisoning of suspended phase.In the paper,we firstly described the utility of the quartz capillary with hydroxyl silicon on the inner wall as the substrate for titania films and their application for photodegradation of organic compound.Titania capillary column was prepared by sol-gel method.In the process of sol preparation,using tetrabutoxytitanium as a source,ethanol and deionized water as solvent and reactant respectively,acetic acid as stabilizer to control the reaction speed,and polyethylene glycol as dispersant.Through a sol-gel method,the titania films were deposited on the inner wall of the capillary based on the condensation reaction between hydroxyl silicon and hydroxy titanium.SEM,XRD,HRTEM and BET were used to characterize the morphology and structure of titania monolithic column.The photodegradation experiments were conducted with Rhodamine B to investigate influences of the thickness,crystal form and specific surface area on photocatalytic performance using titania films as catalyst.The reaction kinetics and photodegradation mechanism of Rhodamine B was also analyzed.The titania sol was prepared from a solution containing tetrabutoxytitanium as a source,ethanol as solvent,deionized water as reactant,and acetic acid as stabilizer to control the reaction speed.Influences of water,acetic acid and reaction temperature on gel time were investigated.It concluded that the sol preparation conditions were as follows:the volume ratio of tetrabutoxytitanium,acetic acid,water and ethanol is 5:4:2:20,and the reaction temperature is 50 ℃.The prepared transparent precursor solution was injected into the pretreated capillaries and the titania capillary monolithic column was prepared by aging,washing and calcination.The film thickness on the capillary was controlled by changing the amount of tetrabutoxytitanium.To obtain a smooth,compact and porous film,a certain amount of polyethylene glycol as dispersant and porogen was added into the mixture to prevent cracks by reducing the surface tension between the titania particles and increase specific surface area.The effect of calcination temperature on the crystal form of titania was studied.The optimal preparation conditions of film were determined through photocatalytic performance experiment.As a consequence,we acquired a maximum thickness of 361 nm and a good mesoporous structure of 8.7 nm with specific surface area of 47.72 m2/g for titania films in the presence of 15.15%TBOT and PEG 1000.The base structure of the films is nearly spherical particles with a 10 nm diameter and anatase phase as calcined for 5 h at 500 ℃.For a Rhodamine B solution of 15 mg/L,photodegradation efficiency is 98.33%in 30 min,indicating that TiO2 film catalyst could almost completely degrade macromolecular organics.Effect of initial Rhodamine B concentration on its photodegradation was discussed in the paper.The results show that the degradation efficiency decreases with Rhodamine B concentration increases.The catalysts could be reused up to eight times with the photodegradation efficiency of 96.6%,indicating a firm immobilization of films on the inner wall of the capillary.Which is very significant in terms of avoidance of secondary pollution and cost savings.A large number of experiments and mass spectrometry data proved that Rhodamine B photodegradation was a process including gradual deethylation and decarboxylation,and breakage of double bond on the benzene ring caused by the attack of hydroxyl radical... |
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