Abstract
The most environmentally friendly protocol for obtaining mesoporous SiO2–TiO2 catalysts has been sought. Water has been employed as a green solvent, the energy input has been minimized, and three further principles (1, 3, and 12) of Green Chemistry have been considered. Four different modes for promoting the reaction have been comparatively evaluated, namely near-infrared and microwave electromagnetic irradiations, ultrasound, and traditional mantle heating. Brunauer–Emmett–Teller (BET) analyses of the catalysts produced revealed that the non-conventional activation modes afforded both large surface areas (335–441 m2 g−1) and smaller crystal sizes (7.2–15.3 nm) than the mantle heating process. These modes also generated the catalysts in shorter reaction times than traditional mantle heating, 10–30 min versus 3 h, with anatase as the sole crystalline phase. The photocatalytic degradation of 4-chlorophenol has been carried out to assess the catalytic efficiencies of the hybrid materials. The catalyst synthesized with microwave assistance showed the best mineralization activity (97%), followed by those prepared with ultrasound, near-infrared, and mantle heating. The materials have been extensively characterized by FTIR, XRD, DRS-UV/Vis, SEM, 29Si MAS NMR, and BET analyses. To the best of our knowledge, this is the first such comparative assessment of green energetic alternatives in developing a sol–gel process.
Highlights
The sol–gel process is one of the most prevalent routes for producing oxide materials with control of their textural and surface properties, furnishing them with high purity and homogeneity.[1,2,3] Due to their mesoporous structures, oxide materials are important in many industrial processes, for example as catalysts,[4] absorbents,[5] gas sensors,[6] and photocatalysts.[7]
Considering the intensities of the bands assigned to the Si–OH moiety (3379–3326 cmÀ1) in Fig. 1, an intense broad band is seen for the sample prepared by the MW method, indicating a catalyst with higher surface area and higher titania content in comparison to those prepared with NIR, US, or mantle heating (MH) assistance, respectively
The Si–OH band was more intense for the samples prepared with MW and NIR assistance; less intense bands for those prepared with US and MH were probably due to a lower titania content, and less retention of undissociated water
Summary
The sol–gel process is one of the most prevalent routes for producing oxide materials with control of their textural and surface properties, furnishing them with high purity and homogeneity.[1,2,3] Due to their mesoporous structures, oxide materials are important in many industrial processes, for example as catalysts,[4] absorbents,[5] gas sensors,[6] and photocatalysts.[7]. Researchers strive to design chemicals and chemical manufacturing processes that pose insigni cant risk to human health and the environment, it must be conceded that no activity is risk-free.[15]
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