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The hybrid hydrogel materials meet important social challenges, including the photocatalytic purification of water and bio-medical applications. Here, we demonstrate two scenarios of polyacrylamide-TiO2 (PAAm@TiO2) composite hydrogel design using calcium alginate (Alg-Ca) or Keplerate-type polyoxometalates (POMs) {Mo132} tuning the polymer network structure. Calcium alginate molding allowed us to produce polyacrylamide-based beads with an interpenetrating network filled with TiO2 nanoparticles Alg-Ca@PAAm@TiO2, demonstrating the photocatalytic activity towards the methyl orange dye bleaching. Contrastingly, in the presence of the POM, the biocompatible PAAm@TiO2@Mo132 composite hydrogel was produced through the photo-polymerization approach (under 365 nm UV light) using vitamin B2 as initiator. For both types of the synthesized hydrogels, the thermodynamic compatibility, swelling and photocatalytic behavior were studied. The influence of the hydrogel composition on its structure and the mesh size of its network were evaluated using the Flory–Rehner equation. The proposed synthetic strategies for the composite hydrogel production can be easily scaled up to the industrial manufacturing of the photocatalytic hydrogel beads suitable for the water treatment purposes or the biocompatible hydrogel patch for medical application.

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A comparative study on the photocatalytic activity was done for TiO 2 /poly(acrylamide-co-potassium acrylate) composite hydrogels with varying content of potassium acrylate monomer units. The presence of the acrylate units led to the increase in the swelling ratio of hydrogel and to the enhancement of the diffusion of the methyl orange probe dye to the surface of the embedded TiO 2 particles. However, the photocatalytic activity was not improved. Microcalorimetry data showed that while the enthalpy of polymer adhesion to the TiO 2 particles surface was positive in the case of polyacrylamide and it became negative if acrylate units were included in the polymer network. Likely, the adhesion enhancement occurred due to the electrostatic interaction among acrylate monomer units and surface of TiO 2 particles. As a result of polymer adhesion to the active surface of the catalyst particles was partly blocked and the photocatalytic activity of the composite hydrogel diminished.

Adsorption equilibriums in aqueous aluminum and iron oxides nanosuspensions stabilized by SDBS and TX-100 were investigated using UV spectrophotometry. It was established that the non-ionic surfactant TritonX-100 is not adsorbed from aqueous solution on a hydrophilic surface of both aluminum and iron oxide nanoparticles. At the same time adsorption of the anionic surfactant SDBS was observed in both oxides nanoparticles. In the investigated range of concentrations adsorption isotherms SDBS from aqueous solution on the surfaces of nanoparticles Al2O3 and γ-Fe2O3 not reach saturation. The share of the particles surface occupied by surfactant molecules were estimated based on the value of an area of molecules SDBS in the adsorption layer, which was derived from the isotherm of surface tension (0.10 nm2). The calculations showed that at the investigated concentrations SDBS Al2O3 employed approximately 30 % of surface of nanoparticles, and for γ-Fe2O3 – up to 10%.

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