Ti-based layered double hydroxides: Efficient photocatalysts for azo dyes degradation under visible light

• Different Ti-based LDH materials with good crystal structure have been synthesized.
• The band gap of LDH materials follow the order: Zn/Ti > CeO2/ZnTi > Zn/Al–Ti/SB.
• The degradation performance of MO/MB follow the order: CeO2/ZnTi > Zn/Al–Ti/SB > Zn/Ti.
• Mechanism and intermediates for photocatalytic degradation on MO has been presumed.
• Zn/Al–Ti/SB–LDHs after MO/MB degradation was feasible at least three cycles.

Three types of Ti-based Layered Double Hydroxides (Zn/Ti–NO3–LDHs with Ti element on LDH sheet, Zn/Al–Ti/Schiff–base–LDHs with Ti element in LDH interlayer and CeO2/ZnTi–LDH composite containing TiO2) were synthesized by different environmental friendly methods. Their activities of photocatalytic degradation of Methyl orange and Methylene blue under visible light were tested. Ti-based LDHs were characterized by XRD, FT-IR, BET and ICP-AES, confirming the formation of pure LDH phase with good crystal structure. The as-synthesized Ti-based LDH materials showed the narrow band gap (all smaller than 3.0 eV) and high removal efficiency for Methyl orange and Methylene blue under visible light, and the decomposition performance of these dyes decreased in the order of CeO2/ZnTi–LDH composite > Zn/Al–Ti/Schiff–base–LDHs > Zn/Ti–NO3–LDHs. In addition, the kinetics and possible mechanisms for photocatalytic degradation on Methyl orange and Methylene blue were also discussed in details. Moreover, the thermal regeneration for re-use of Zn/Al–Ti/SB–LDHs after photoreaction was feasible for at least three cycles (degradation amount still over 85%).

The electron–hole pair (e−/h+), which yield from the excited electrons of LDH material, will react with water and dissolved oxygen to produce hydroxyl radicals (OH). Then, the MO molecules can be oxidized and decomposed into intermediates of p-amino-N,N-dimethylaniline and p-aminobenzene sulfonic acid by the OH radicals and photon generated electrons (e−). Finally, the intermediates can be further decomposed into inorganic micromolecules, like CO2 and H2O.Figure optionsDownload as PowerPoint slide