Facile synthesis of self-healing poly-acrylic acid/TiO2 hybrid hydrogel for photocatalytic hydrogenation of 4-nitrophenol to 4-aminophenol

Self-healing poly-acrylic acid/TiO2 (PT) hybrid hydrogel with different water amount have been simply fabricated by UV light irradiation. The cross-linking (matrix) formation of PT hydrogels was formed due to UV light absorption by TiO2 generating the radical species to polymerize acrylic acid monomer to poly-acrylic acid. XRD analysis successfully revealed the presence of TiO2 in the hydrogel. Meanwhile, the polymerization of acrylic acid to poly-acrylic acid was revealed by FTIR analysis. It is obvious that the physical appearance of as-prepared PT hydrogels with different water amount was different, where a rigid hydrogel was obtained with less water amount and a spongy hydrogel was formed with more water amount. The highest self-healing efficiency achieved ∼85% exhibited by PT-4 hydrogel in which the self-healing ability is due to hydrogen bond occurred between TiO2 and carboxylic functional groups in poly-acrylic acid. For the application, the healed PT-4 hydrogel demonstrated the capability to convert toxic 4-nitrophenol to 4-aminophenol through photocatalytic hydrogenation reaction within 2 h UV light irradiation.