Highly recyclable and super-tough hydrogel mediated by dual-functional TiO2 nanoparticles toward efficient photodegradation of organic water pollutants

A novel photocatalytic hydrogel was prepared by loading TiO2 nanoparticles (TiO2 NPs) onto the surface of 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO)-oxidized chitin nanofibers (TOCNs), which were further incorporated into the polyacrylamide (PAM) matrix. The resultant hydrogel exhibited a macro-porous structure with a low density (similar to 1.45 g/cm(3)) and high water content (similar to 80%). The well-dispersed TiO2 NPs not only acted as a crosslinking agent for bridging the three-dimensional porous network structure, but also endowed the hydrogel with good catalytic activity. After the introduction of TiO2 accounting for 10 wt% of the hydrogel mass, the hydrogels showed compressive strength of 1.46 MPa at 70% strain, tensile stress of 316 kPa, tensile strain of 310%, toughness of 47.25 kJ/m(3) and fatigue resistance. Compared with neat TOCN-PAM hydrogel, the uniaxial compressive and tensile strengths of the TiO2-TOCN-PAM10 hydrogel increased 6.35-fold and 3.70-fold, respectively. Furthermore, the removal of methyl orange (MO) was attributed to the synergistic effect of the adsorption and photocatalytic degradation of the hydrogels. The hydrogels adsorbed up to 8.5% of MO after 150 min of adsorption and a photocatalytic degradation rate of 97.3% achieved after 90 min of UV irradiation at pH = 2. Especially, the TiO2 -TOCN-PAM10 hydrogel exhibited excellent recycling performance: its MO removal efficiency was around 96% even after 10 reuse cycles. The as-prepared hydrogels, with characteristics of excellent stretchability, photocatalytic activity and recyclability, are expected to be used in alleviating organic pollutants in practical wastewater treatments. (C) 2019 Elsevier Inc. All rights reserved.