Preparation of TiO2-Ag heterostructure via tannic acid-assistance and its immobilization on PVDF membrane for the degradation of dye under visible light

In this work, PVDF/TiO2-Ag hybrid membranes were fabricated by immobilizing TiO2-Ag nanoparticles on the Polyvinylidene fluoride (PVDF) membrane surface via covalent bonding. Interestingly, not only Ag nanoparticles were in-situ reduced on the TiO2 surface by tannic acid (TA) and lead to the construction of tightly coupled TiO2-Ag heterostructures, but also the TiO2-Ag nanoparticles and the membrane matrix were bridged by TA. The photo-response range of the hybrid membrane was broadened to visible light through the surface plasmon resonance (SPR) effect. The impact of the Ag precursor solution species on the microstructure of the TiO2-Ag nanoparticles was compared and the photocatalytic properties was thoroughly studied. The smaller particle size and more uniform distribution of Ag further enhanced the SPR effect, reduced the band gap, and inhibited the photogenerated electron-hole recombination. Finally, the photocatalytic degradation efficiency (η) for RhB reached 97.8 % under visible light, while the reaction rate constant was as high as 0.156 mL min−1 cm−2. In addition, the value of η remained above 90 % even after 8 recycling cycles. The fabrication conditions of TiO2-Ag nanoparticles were optimized using the response surface methodology technique. Our work provides valuable insights for the purposeful design and optimization of TiO2-based photocatalytic membranes.