Temperature and Surfactant Tuned Mesoporous Undoped TiO2 Monoliths for the Visible-Light Photocatalytic Degradation of Fabric Dye Pollutants

Abstract

Porous TiO₂ monolith with controlled mesopore structural morphologies exhibits good physical and chemical properties, which are important in photocatalytic wastewater treatment [1]. In this study, a first of its kind attempt has been carried out in preparing visible-light responsive mesoporous TiO₂ monoliths via. a liquid-crystal template approach, using various surface directing agents (SDAs) namely non-ionic triblock copolymers (Pluronic F108, P123 and F127) by sol-gel assisted hydrothermal process [2]. The resulting TiO₂ monoliths are calcined at different temperatures (450°C, 550°C and 650°C) to obtain the desired material with superior structural and porosity features that promotes the photocatalysis efficiency. The structural properties and surface morphology of worm-like TiO₂ monoliths are determined by HR-SEM, EDAX, p-XRD, UV-Vis-DRS, TG/DTA, PLS and BET/BJH measurements. The results show that the monoliths derived from the SDAs show a pure anatase (photo-active) phase, with an average crystalline size of 5.4 nm, at a calcination temperature of 450°C. However, at calcination temperatures of 550°C and 650°C, the TiO₂ monoliths display the presence of a mixed phases (anatase and rutile). The formation of ordered mesoporous monolithic framework ensures that the anatase TiO₂ monolith exhibits visible light activity without any doping process. The potential photocatalytic properties of the synthesized worm-like TiO₂ monolithic materials are systematically studied by visible-light (300 W/cm²) irradiation on Reactive Brown 10 (RB-10) - an organic azo fabric dye. The critical analysis on the impact of various physio-chemical parameters such as, the effect of surface directing an agent, solution pH, dye concentration, photocatalyst quantity, light intensity, the role of oxidizers, etc., are examined. Based on the results, under optimized conditions, the synthesized TiO₂ monoliths show faster degradation kinetics (≤ 40 min) for complete mineralization of 20 ppm of RB-10, using only 100 mg of photocatalyst.