Strong enhancement on dye photocatalytic degradation by ball-milled TiO2: A study of cationic and anionic dyes

TiO2 particles with desirable properties were produced by undergoing specific durations of ball milling. Characterizations of the TiO2 particles before and after ball milling were investigated via X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), particle size analysis, zeta potential, and scanning electron microscope (SEM). The equilibrium adsorption data were well fitted to Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. Compared to the as-received TiO2 (mean particle size d50 = 0.78 μm, specific surface area = 88.17 m2 g−1, pore volume = 0.41 cm3 g−1), the 60 min ball-milled TiO2 (d50 = 0.55 μm, specific surface area = 99.48 m2 g−1, pore volume = 0.48 cm3 g−1) enhanced the adsorption quantity of congo red and methylene blue from 10.4 mg g−1 to 13.6 mg g−1, and from 17.0 mg g−1 to 22.2 mg g−1, respectively; and also improved the kinetic rates from k = 0.1325 to 0.2193, and k = 0.0944 to 0.1553, respectively. Dye adsorption and degradation efficiency of congo red was enhanced in acidic pH range (2-5.14), and methylene blue was enhanced in alkaline pH range (7.58-12).