Fabrication of Ti-PDA nanoparticles with enhanced absorption and photocatalytic activities for hexavalent chromium Cr(VI) removal

This article prepared a nanoparticle (NP) Ti-PDA made from bis (2-hydroxy propionic acid) diammonium titanium hydroxide (Ti-BALDH) chelating dopamine (DA), as a photocatalyst to absorb and reduce hexavalent chromium (Cr(VI)) under visible light with recycling ability from waste water. Ti-PDA NPs with part of TiO2-like structure can perform some function of TiO2, while participation of PDA will not only broaden absorption spectrum from UV to visible light, but offer the ability to absorb Cr(VI). Compared with TiO2 Ti-PDA NPs would make full use of sunlight, increasing the photocatalytic efficiency. The adsorption results of Ti-PDA NPs for Cr(VI) showed that the adsorption capacity of Ti-PDA NPs can reach 500.24 mg/g when the concentration of Cr(VI) was 300 mg/L, and the adsorption data matched well with the Langmuir isotherm model, and confirmed to a quasi-second-order dynamics. Under visible light irradiation, Ti-PDA NPs could reduce Cr(VI) to Cr(III) within 30 min, and can almost completely reduce Cr(VI) within 15 min even at pH = 4. After three cycles, photocatalytic reduction efficiency was still 95.02%. Thereby the toxic Cr(VI) can be effectively eliminated by Ti-PDA NPs from sewage. As a result, Ti-PDA will be a promising green photocatalyst to remove Cr(VI) in disposal of water pollution.