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.
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.
Water Res. 2014 Apr 15;53:12-25. doi: 10.1016/j.watres.2013.12.043. Epub 2014 Jan 18.
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.
一步法高效去除 Cr(VI) 和 Cr(III) 用 TiO₂ 和钛酸盐纳米管 (TNTs) 的混合物实现。与传统的两步法 Cr 去除方法（首先光催化还原 Cr(VI)，然后吸附 Cr(III)）不同，所提出的单一过程显著缩短了反应时间（超过 50%）。光催化和吸附的协同作用在增强 Cr 去除过程中起着重要作用。协同机制通过光催化过程中 H₂O₂ 的变化进行了解释和间接证实。从 TiO₂ 表面到 TNTs 层间还原的 Cr 的即时转移极大地促进了 TiO₂ 光催化位点的释放，从而通过抑制电子-空穴对复合来极大地增强了 TNTs 的光催化活性。整个过程的最佳条件是在 pH 5 下。在 pH ≤ 5 时，Cr(III)的吸附主要在 TNTs 的层间进行。然而，较高的 pH 会导致 Cr(OH)₃在 TNTs 上沉淀，这可以通过 X 射线光电子能谱 (XPS) 观察到。添加 Ca(2+) 可以促进光催化作用，因为它具有离子桥接功能，并形成 ≡TiOH(+)-Cr(VI)-Ca(2+)-Cr(VI)键，而 SO₄(2-) 只是略微抑制 Cr(VI)的光还原，表明即使在电解质的高离子强度下，光催化和吸附也具有良好的协同作用。此外，通过修复受损的管状结构，易于再生解吸的 TNTs，并可重复用于 Cr 去除，具有优异的性能。这种协同作用具有显著的效果，并对机制进行了必要的解释，不仅在基础理论上具有重要意义，而且在实际应用中也具有潜在的价值。
