| Mesoporous TiO2(meso-TiO2),not simply a famous semiconductor material,also shows some excellent properties,including high specific surface area and pore volume and well-defined mesostructures,which exhibit great potential in photocatalysis,solar cells,sensors,etc.The research on meso-TiO2 is one of the hot topics in the field of functional materials.However,the related research on meso-TiO2 in the preparation and manipulation of mesoporous and crystalline structures still faces some challenges.This work aims to develop a novel templating system for the preparation of meso-TiO2 based on peroxotitanic acid(PTA)as titanium precursor and nonionic surfactants(e.g.,P123)as soft template.A ternary self-assembly system based on PTA/Pl23/H2O can thus be established for meso-Ti02 with tunable mesoporous and crystalline structures.In addition,the relationship between structure and photocatalytic property of meso-Ti02 will also be studied.The details are:In a low-temperature templating approach for the fabrication of meso-TiO2 using the PTA as precursor and Pluronic P123 as nonionic template,the results showed that after calcinations at 450?,the meso-TiO2 with high specific surface area up to 163 m2·g-1,large pore volume of 0.65 cm3·g-1 can be obtained.The mesopore sizes can be varied between 13.2 and 19.8 nm via this synthesis approach.The amounts of P123 in PTA/P123/H2O ternary self-assembly system and calcination conditions were found to have great influence on the mesoporous and anatase/rutile bi-crystalline structures of meso-TiO2,wherein the ratio of rutile is up to 17.0%(the rest is anatase).The photocatalytic activity testing in this work clearly shows that the high surface area and bi-crystallinity phases of meso-TiO2 play important roles in enhancing photocatalytic properties of meso-TiO2 in photo-decomposing Rhodamine B in water.Moreover,based on a novel high temperature and water-based evaporation-induced self-assembly(HW-EISA)approach,the same simple ternary templating system(PTA/P123/H2O)enable the facile and rapid synthesis of nanocrystalline meso-TiO2 with unusual structures:high surface areas(183?212 m2?g-1),high pore volumes(0.73?1.02 cm3·g-1),ultra-large mesopores(20.5?25.5 nm)and tunable bi-crystallinity(anatase plus rutile,10.6?20.2%rutile content),after calcination at 450 0C.The unusual templating and subsequent decomposition behaviors of P123 were newly unveiled to play crucial and multiple roles in inducing self-assembly between PTA and P123 for final meso-TiO2 with high pore volumes and ultra-large mesopores during the HW-EISA and helping preserve the integrity of mesostructures during calcination and rendering bi-crystallinity in the titania frameworks as well.After calcination at 550?,specific surface area of meso-TiO2 reaches 143 m2·g-1,its mesopore size and rutile content is 29.0 nm and 25.9%,respectively.Other PEO-based nonionic surfactants were also demonstrated to be applicable to produce similar mesostructures.The photocatalytic testing results showed that both high surface areas and the synergistic effects of bi-crystallinity of anatase plus rutile are of great significance in enhancing the photocatalytic properties of meso-TiO2.Additionally,via a modified HW-EISA process,a facile and controllable multi-templating approach based on a solo nonionic surfactant P123 and PTA was reported for the preparation of bimodal meso-mesoporous titania(BMM-TiO2)with high surface area(179?243 m2·g-1),high pore volume(0.29?0.57 cm3 g-1),large mesopore sizes spanning from 5.3 to 12.9 nm(BJH pore size),and high&tunable crystallinity(anatase or anatase+rutile),after calcination at 400 ?.The BMM-TiO2 was shown to be a homogeneous 'mixture' of two series of wormhole mesostructures with two modes of mesopore sizes that depend on both the contents of P123 and synthetic conditions.The formation of BMM structures was proposed to arise from both the formation of differentiated micellar structures of P123(dual soft-templating)and their subsequent different mesostructural shrinkages driven by prolonged drying process(i.e.,100 ? for 12 h)in the presence of PTA.The low-temperature crystallization behaviours of PTA,unusual hard-templating effect of P123 and its carbon derivatives(3rd fold templating)are all believed to be responsible for the high thermal stability of the obtained BMM-TiO2.P123 was also confirmed to be a prerequisite for the formation bi-crystalline BMM-TiO2,after calcination at 550?,its specific surface area was 147 m2·g-1 and its mesopore size was 16.1 nm,showned a good thermal stability.In the photodegradation test of Rhodamine B in water by UV irradiation,other than the high surface area and synergistic effect between anatase and rutile phases,the BMM structures were also found to be advantageous to enhance the photocatalytic properties of meso-TiO2.Finally,meso-TiO2 with controllable mesoporous and crystalline structures were also demonstrated to be facilely prepared by using poly(ethylene glycol)(PEG)as structure-directing(SD)agent and PTA as precursor.Meso-TiO2 with high BET surface area(157 m2·g-1)and pore volume(0.45 cm3·g-1)after calcination at 450? can be obtained,with large mesopore size of 13.9 nm and tunable anatase/rutile bi-crystallinity structure(the rutile ratio up to 13.4%).After calcination at 550?,the specific surface area of mesoporous TiO2 was 114 m2·g-1 and its rutile content is 16.6%,showing the good thermal stability.PEG was thus demonstrated to be a suitable low-cost SD agent for the preparation of meso-Ti02 with controllable mesoporous and bi-crystalline structures. |
PDF Full Text Request