Preparation Of TiO₂ Sol And Nano TiO₂ Powder And Their Comparison In Adsorption And Photocatalysis

Sol is a well-dispersed mixture.Compared with nano-powder,sol is more difficult to agglomerate and has good dispersion,and does not need to be calcined.At present,there are few reports on the direct use of sol to study adsorption and photocatalysis,and there is no literature to compare sol and nano-powder in adsorption and photocatalysis.In this paper,TiO₂ sol and nano TiO₂powder as the main research system,through the study of dye adsorption and photocatalytic performance,TiO₂ sol and nano TiO₂powder properties of the difference.In this paper,neutral TiO₂ sol and acidic TiO₂ sol were prepared with inorganic titanium source and organic titanium source respectively,the prepared sol was characterized by field emission scanning electron microscope,x-ray diffraction（XRD）,TG-DSC and transmission electron microscope.Then the diluted TiO₂ sol and nano TiO₂powder were obtained by diluting and drying the prepared TiO₂ sol.Finally,the dye adsorption and photocatalytic properties of TiO₂ sol and nano TiO₂powder were studied,and the differences of adsorption and photocatalytic properties between TiO₂ sol and nano TiO₂powder were compared.The results show that:（1）adsorption and photocatalytic selectivityThe neutral TiO₂ sol and nano TiO₂powder prepared with inorganic titanium source have great difference in the adsorption and photocatalysis of four kinds of dyes.However,the adsorption and photocatalytic activity of acidic TiO₂ sol and nano TiO₂powder prepared from organic titanium source have no significant difference.Both neutral TiO₂ sol and nano TiO₂powder have higher adsorption and degradation rate for malachite green,and the next is fuchsin,but they have no adsorption and photocatalytic activity for orange G and congo red dyes,this is because the negative potential of the nano TiO₂band provides the electrostatic interaction between the cationic dye and the nano-material.Acid TiO₂ sol and nano TiO₂powder have adsorption and photocatalysis on four kinds of dyes.Hydrochloric acid in acid TiO₂ sol changes the interfacial charge properties and the surface charge distribution of TiO₂particles in solution,this may be due to the acidic nature of the TiO₂ sol prepared from organic titanium sources,which changes the interfacial charge properties and the charge distribution on the particle surface in the solution.Therefore,the adsorption and photocatalytic activity of the dye on the surface were affected.（2）adsorption kineticsNeutral TiO₂ sol prepared from inorganic titanium source and acidic TiO₂ sol prepared from organic titanium source were dried to adsorb four kinds of dyes,the kinetic data show that the adsorption of dye on neutral TiO₂and acidic TiO₂are more consistent with the quasi-second-order kinetics.The adsorption equilibrium and adsorption rate of neutral TiO₂increase with the increase of temperature.At 298.15K,it takes 2h for the adsorption to reach equilibrium,while at 335.15K,it takes 1h for the adsorption to reach equilibrium.At the same temperature,the order of the adsorption capacity of the three nano TiO₂materials is nano TiO₂ sol?diluted nano TiO₂ sol?nano TiO₂powder.With the increase of the dark time,the adsorption equilibrium of nano TiO₂could be reached at 30min,and at the same temperature,the adsorption rate of nano TiO₂ to malachite green was higher than that of nano TiO₂powder only when it was diluted,the adsorbability of the other three dyes is that the nano TiO₂powder is larger than the diluted TiO₂ sol.（3）adsorption thermodynamicsNeutral TiO₂ sol prepared from inorganic titanium source adsorbed four kinds of dyes after drying,thermodynamic data show that three kinds of nano TiO₂materials adsorbed the standard mole gibbs free energy（35）_adsmG^o-of malachite green Dye,it decreases with the increase of temperature and belongs to physical adsorption.The standard molar adsorption enthalpyΔ_adsH_m^-oand standard molar adsorption entropy（35）^o_adsmS^-of three kinds of nano TiO₂for malachite green dye are positive,which means the process is endothermic.（4）photocatalysis kineticsThe neutral TiO₂ sol prepared from inorganic titanium source and the acidic TiO₂ sol prepared from organic titanium source were dried and the photocatalysis experiments were carried out on the four dyes,the results show that the photocatalytic degradation of neutral TiO₂and acid TiO₂is more consistent with the first-order kinetics,and the photocatalytic degradation rate constant of neutral nano TiO₂powder is larger than that of diluted neutral TiO₂ sol.With the extension of irradiation time,the photocatalytic degradation reached equilibrium at 480 min.The degradation rate of neutral nano TiO₂powder to malachite green and basic fuchsin dyes was higher than that of diluted neutral TiO₂ sol.The rate constant of photocatalytic degradation of four dyes by acidic nano TiO₂powder is less than that by diluted acidic TiO₂ sol.With the extension of irradiation time,the photocatalytic degradation reached equilibrium at 150 min.The degradation rate of the diluted acidic TiO₂ sol is higher than that of the acidic nano TiO₂powder.The neutral TiO₂ sol and acidic TiO₂ sol prepared in this paper can provide guidance for the adsorption and photocatalysis under different conditions,the comparison of the adsorption and photocatalytic properties of TiO₂ sol and nano TiO₂ sol can provide an important reference for the application of TiO₂materials.