Green synthesis of titanium dioxide/acrylamide-based hydrogel composite, self degradation and environmental applications

A green polymerization using TiO2 as an inorganic photoinitiator to synthesize titanium dioxide/poly[acrylamide-co-(acrylic acid)] hydrogel composite was successfully achieved. FTIR and SEM/EDXS characterizations indicated that the hydrogel composites were the crosslinked copolymer composed of acrylamide and acrylic acid in TiO2 particles. TiO2 hydrogel composites could adsorb up to 90% of 5 ppm methylene blue dye solution. Decolorization of methylene blue by the hydrogel composites was evaluated by colorimetry in term of K/S value. Approximately 83% of methylene blue was decolorized in 8 h by 5% TiO2 hydrogel composite and 90% decolorization in 8 h for 10% TiO2 hydrogel composites. The maximum color fading of methylene blue in the hydrogel composites at various UV irradiation times was observed by the slope of the linear region at different amounts of TiO2. It reveals that AMAA5050T10C1 gave the highest methylene blue fading of 91.6% with an R2 of 0.9999. The slope of 5 ppm Congo red in AM-T20-C1 adsorbent obeying a Pseudo-first order gave the highest dye removal of 44.8% with an R2 of 0.9572. This technique meets the criteria of green chemistry because the reaction does not need any organic photoinitiator or co-photoinitiator and the reaction takes place at room temperature. Congo red in polyacrylamide hydrogel composite containing 20% TiO2 obeyed a Pseudo-first order kinetics giving qe,exp = 2.22 mg g−1 (qe,cal = 2.24 mg g−1) while methylene blue in poly[acrylamide-co-(acrylic acid)] hydrogel composite at 50:50 monomer weight ratio containing 5% TiO2 followed a Pseudo-second order kinetics having qe,exp = 4.86 mg g−1 (qe,cal = 4.73 mg g−1). The rheological measurement of the TiO2/poly[arylamide-co-(acrylic acid)] hydrogel composites revealed a strong gel-like material and the self-degradation of the hydrogel composites evolved under UVA irradiation. TiO2/poly[(acrylamide)-co-(acrylic acid)] hydrogel composites synthesized in current work can be used as a model for both green synthesis of the hydrogel composites using an ionic photocatalyst, TiO2, and for degradation of organic dyes and self-degradation of the composites upon UV irradiation.