Preparation and catalytic activity of Fe alginate gel beads for oxidative degradation of azo dyes under visible light irradiation

Fe alginate gel beads were prepared by adding sodium alginate aqueous solution drop-wise into the FeCl3 gelling solution using a syringe needle at room temperature, and measured in terms of size, mass and Fe content, then characterized using SEM, XRD, FT-IR, XPS and TGA, respectively. The gel beads were evaluated as the heterogeneous Fenton catalysts for oxidative degradation of two typical azo dyes, Reactive Blue 222 and Acid Black 234 in the presence of H2O2 under visible light irradiation. Some important factors affecting the preparation of the beads and their catalytic function such as FeCl3 concentration, irradiation intensity and pH value were examined. The results indicated that Fe3+ ions coordinated with oxygen atoms in carboxyl groups from glucose chains of alginates to form the Fe alginate gel beads. And Fe3+ ion was a central cation that has a coordination number of 6 in the complex. Higher concentration of FeCl3 solution caused the significant increase in the Fe content of the gel bead during preparation. Fe alginate gel beads showed a great catalytic role in the degradation of the azo dyes in a wide pH range of 3.0–8.0. Moreover, higher Fe content and increasing irradiation intensity could promote the catalytic performance of Fe alginate gel beads.