Optimising sodium silica gel for Ferroin immobilization

Abstract

The addition of compounds like enzymes or catalysts in silica gel matrix expand its applications as sensor material, controlled drug-delivery and photo-active material, as well as it allows the study of pattern generation in oscillating chemical reactions in dependence on spatial catalyst structures. Creating catalyst structures requires at the moment photolithography or emulsions. A simpler way of creating spatial catalyst structures in silica gels is spotting the catalyst onto the gel matrix. The result of this procedure mainly depends on the ability of the gel to absorb the catalyst and immobilise it in the desired structure in aqueous solutions. We investigate if the addition of polymers into the silica gel can enhance the immobilization of Ferroin, which is an indicator for redox potentials and a standard catalyst for the Belousov–Zhabotinsky reaction. Polyethylenglycol (PEG), poly-styrene sodium sulfate and poly-styrenesulfate-co-maleic acid sodium salt (PSS-co-PM) were tested. By optical measurements the immobilization was analyzed and scanning electron microscopy, energy dispersive X-ray spectroscopy and nuclear magnetic resonance measurements were applied for microstructure and chemical element analysis. We found that PEG and PSS-co-PM enhance the stability of Ferroin spots in silica gels. Thereby, PEG changes the silica gel microstructure without being incorporated into the solid gel, whereas PSS-co-PM is incorporated into the silica gel and (chemically) interacts with Ferroin.