Structure-activity relationship of nanosized porous PEG-modified TiO2 powders in degradation of organic pollutants

This study aims to gain insights in structure-activity relationship of TiO2 photocatalysts. For this purpose photocatalysts were synthesized via classical sol-gel method using titanium isopropoxide as a precursor and polyethylene glycols (PEGs) of different molecular mass (M-n = 200, 600, 2000, 10,000) as a template agents. Incorporating PEG into TiO2 network enhanced not only catalyst porous structure, but also increased the fraction of anatase phase. The use of low-molecular-weight PEGs resulted in catalysts with increased anatase content and enlarged specific surface area. The catalyst photoactivity was estimated through degradation of organic pollutants: Reactive Black 5, arylazo pyridone dye and phenol. The results revealed that the photoactivity was following the same order independently of target pollutant: TiO2/P600 > TiO2/P200 > TiO2/P2000 > TiO2/P10000 > TiO2. BET surface area and anatase fraction, rather than pore diameter or pore volume, were found to be predominant catalyst property determining the activity for particular reaction system. The existence of synergistic effect between anatase and rutile phases was confirmed for the most active catalysts TiO2/P200 and TiO2/P600. These catalysts showed similar activity in dye degradation, while TiO2/P200 displayed significantly lower activity in phenol degradation, which was attributed to its lower sorption capacity and lower UV light utilization. The difference in the reactivity between investigated pollutants was discussed in relationship with their size, structure and sorption ability.