A new heterogeneous catalytic system for wastewater treatment: Fe-immobilized polyelectrolyte microshells for accumulation and visible light-assisted photooxidative degradation of dye pollutants

Fe-immobilized polyelectrolyte microshells have been successfully constructed by alternative adsorption of Fe(III) and alginate sodium (ALG) onto the precursor shells composed of chitosan (CHI) and ALG templated on melamine formaldehyde (MF) particles. Confocal laser scanning microscopy (CLSM) directly demonstrated that the as-synthesized (ALG/CHI)₄(ALG/Fe)_n (n = 1, 2) shells could accumulate efficiently rhodamine B (RhB), methylene blue (MB) and acridine orange (AO) in well-defined internal space under moderate conditions via a simple mix processing. Further, H₂O₂ could cross the Fe-immobilized shell walls and react with the dyes concentrated in the interior of shells under visible radiation. The photodegradation of dyes accumulated in the microshells in the presence of H₂O₂ was characterized by UV–vis adsorption spectra and CLSM. More importantly, the photooxidative reaction occurring in the Fe-immobilized microshells can be performed at a wide range of pH from acid to neutral media, which is superior to the conventional Fenton reaction that allows taking effect only under acid condition of pH <4. Electron paramagnetic resonance (EPR) and other studies into the mechanism of the light-activated reaction process give tentative evidence that distinct from the photoreaction occurring in neutral medium, the photoreaction taking place in confined microshells in acid medium proceeds mainly through HO radicals with high oxidative potential.