Synergistic photosensitized removal of Cr(VI) and Rhodamine B dye on amorphous TiO2 under visible light irradiation

► Am-TiO2 was prepared at room temperature. ► Am-TiO2 exhibited more significant synergistic effect than commercial P25-TiO2. ► Heat pretreatment of Am-TiO2 led to decreased synergistic activity. ► Specific surface area dominates the synergistic degradation dynamics. ► Am-TiO2 can be simply reused with negligible loss of activity. Amorphous TiO2 (Am-TiO2) was prepared at room temperature by hydrolysis of Ti(OBu)4 in water without addition of strong acids or organic solvents. Results from XRD and TEM revealed that the as-prepared Am-TiO2 was composed of amorphous structure. For the simultaneous photosensitized removal of Cr(VI) and zwitterionic Rhodamine B (RhB) dye, Am-TiO2 exhibited more significant synergistic effect than commercial P25-TiO2. The removal efficiencies for RhB and Cr(VI) after 100min visible light irradiation were 97.8% and 53.5% on Am-TiO2, respectively. While 88.2% RhB and 42.1% Cr(VI) were removed on P25-TiO2. Decreased synergistic activities as well as smaller surface areas were observed when Am-TiO2 was pretreated at high temperatures (200–700°C). Thus, it was the larger specific surface area rather than better crystallinity dominated the synergistic degradation dynamics under visible light irradiation with lower pH (2), greater catalyst loading amount (2g/L), proper RhB/Cr(VI) ratios (1:8) and higher light intensity (500W). Better synergistic performance was also obtained on Am-TiO2 than P25-TiO2 when Cr(VI) coexists with cationic dyes, while negligible difference was observed in the presence of anionic dyes. Superior stability and simplicity of Am-TiO2 was also exhibited in the cyclic runs.