Synergy of photocatalysis and adsorption for simultaneous removal of Cr(VI) and Cr(III) with TiO₂ and titanate nanotubes.
An one-step efficient simultaneous removal of Cr(VI) and Cr(III) was achieved with mixture of TiO₂ and titanate nanotubes (TNTs). Unlike the conventional two-step Cr removal with a first photocatalytic reduction of Cr(VI) and a subsequent adsorption of Cr(III), the proposed single process significantly reduced reaction time (over 50%). The synergy of photocatalysis and adsorption played an important role in enhancing Cr removal process. The synergetic mechanism was interpreted and indirectly confirmed with H₂O₂ variation during photocatalysis. The instant transfer of the reduced Cr from TiO₂ surface to TNTs interlayer greatly promoted the release of photocatalytic sites of TiO₂, which in turn considerably enhanced photocatalytic activity of TNTs by inhibiting electron-hole pairs recombination. The optimum condition for the whole process was at pH 5. Adsorption of Cr(III) was primarily in the interlayer of TNTs at pH ≤ 5. However, higher pH would lead to precipitation of Cr(OH)₃ onto TNTs as observed by X-ray photoelectron spectroscopy (XPS). Addition of Ca(2+) could promoted photocatalysis owing to its ionic bridging function and form of ≡TiOH(+)-Cr(VI)-Ca(2+)-Cr(VI) linkages, while SO₄(2-) only slightly inhibited photo-reduction of Cr(VI), indicating good synergy of photocatalysis and adsorption even at high ionic strength of electrolyte. Besides, the desorbed TNTs could be easily regenerated by remedying the damaged tubular structure and reused for Cr removal with excellent performance. The outstanding synergetic effects with essential explanation of the mechanism make this study not only fundamentally important but also potentially practical applicable.
Shenzhen Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China; The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Department of Environmental Engineering, Peking University, Beijing 100871, China.
Wen
W
Liu
Shenzhen Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China; The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Department of Environmental Engineering, Peking University, Beijing 100871, China. Electronic address: nijinren@iee.pku.edu.cn.
Jinren
J
Ni
The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Department of Environmental Engineering, Peking University, Beijing 100871, China.
Xiaochen
X
Yin
D000327:Adsorption; D002857:Chromium / Q000737:chemistry*; D004573:Electrolytes; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste / Q000032:analysis; D053768:Metal Nanoparticles / Q000737:chemistry*; D010782:Photolysis; D014025:Titanium / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D004573:Electrolytes; D007220:Industrial Waste; D014874:Water Pollutants, Chemical; D002857:Chromium; C009495:titanium dioxide; C074702:chromium hexavalent ion; D014025:Titanium
Adsorption; Chromium; Photocatalysis; Synergy; Titanate nanotubes