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In the present study, we report the synthesis of two different Kegging-type polyoxometalates (POMs), ammonium heptamolybdate (AHM) and phosphotungstic acid (PWA), loaded hydrogel beads formed from chitosan (Chi), chitosan/methylcellulose (Chi/MC) and chitosan/gelatin (Chi/Gel). The addition of negatively charged POMs results in cross-linking between positively charged chitosan chains through electrostatic attraction. Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal gravimetric analysis were used to characterize the as-prepared hydrogel beads. Rheological measurements provided the mechanical and self-healing properties. Swelling properties of the as-prepared hydrogels were determined at pH 6.8, showing a maximum swellabilty of around 4000% in the case of chitosan/gelatin-PWA composite hydrogel. The hydrogels showed low cytotoxicity on HeLa cancer cells but became significant at higher dose levels. The embedded POMs within the biopolymer hydrogel beads had a significant enhancement of their antibacterial action against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus. The hydrogel beads containing AHM showed reversible photochromic properties with rapid UV detection and inkless erasable printing properties. The hydrogel beads had a significant catalytic effect on the reaction of o-phenylenediamine and aldehydes employing hydrogen peroxide as an oxidant under ultrasound irradiation at room temperature. These results show that the POM-hydrogel (as-prepared) beads had significant potential as functional soft materials in different application areas like catalysis, photochromism, UV sensing, and the development of antibacterial soft systems.
Shaheen et al. (Thu,) studied this question.