Integration of separation and photocatalysis using an inorganic membrane modified with Si-doped TiO2 for water purification

An unsymmetrical inorganic membrane with Si-doped TiO2 layers was fabricated for the purpose of realizing filtration and photocatalysis in a single device in water purification process. Tetra-n-butyl titanate [Ti(OC4H9)4, TBOT] and tetraethyl orthosilicate [Si(OC2H5)4, TEOS] were used as precursors of TiO2 and Si element source, and Si-doped TiO2 photocatalytic layer was coated on a commercial Al2O3 membrane by sol–gel technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization demonstrated that the Si-doped TiO2 thin layer possessed nanoporous membrane structure. The results of UV–vis diffuse reflectance spectra (DRS) and X-ray diffraction (XRD) pattern indicated that a strong UV absorption of as-prepared membrane surface was ascribed to anatase phase of TiO2 materials. The thickness controllability of Si-doped TiO2 layer was conducted by repeated-coating procedure, and water permeability and polyethylene glycol (PEG) retention of membrane were related with thickness of the TiO2 layer. The removal efficiency of model pollutant, dye Reactive Red ED-2B (RR ED-2B), was improved obviously using the membrane under UV irradiation in comparison with photocatalysis or membrane separation alone, which demonstrated that the model pollutant was separated and degraded simultaneously. The multifunctional performance of composite membrane hints this unit may become more powerful in water purification process.