Sorption action of silicon-containing samples against bacteria

Abstract

Silicon-containing amorphous substances, such as silicon dioxide (silica) and aluminosilicates, have a wide range of applications due to their porosity, chemical inertness and thermal stability. These materials are conventionally produced from quartz, diatomite and silicates of various compositions. However, the existing methods for isolating pure compounds are quite expensive and energy intensive. Renewable biological waste containing large amounts of silicon, e.g. rice husks and straw (Oryza sativa), can be used as an alternative raw material. The main advantages of such a material consist in its low cost, almost constant chemical composition, as well as simple and relatively inexpensive processing methods. Due to the high content of silicon dioxide in rice husks and straw, their recycling products are effective adsorbents of many types of pollutants from aqueous solutions. Although some publications describe interaction processes between microorganisms and highly-dispersive synthetic materials based on silicon dioxide of mineral origin, there is a lack of information on the biogenic forms of silica and aluminosilicates obtained from rice production wastes. In previous studies, we established the ability of a number of silicon-containing samples isolated from rice production wastes, depending on the raw material (husk or straw) and production conditions, to bind different bacteria, e.g. Escherichia coli, Streptococcus aureus, Candida albicans, Pseudomonas aeruginosa and Bacillus subtilis. In this work, we studied the sorption action of amorphous silicon dioxide and aluminosilicates obtained from rice husks and straw against the test cultures of Escherichia coli and Bacillus subtilis. The reference materials were such commercial products as expanded vermiculite (natural aluminosilicate) and the ‘White Coal’ sorbent containing approximately equal proportions of silica and microcrystalline cellulose. The obtained results were discussed in the context of the physicochemical parameters of the studied substances, including their chemical composition, IR absorption spectra, characteristics of the acid-base properties of the surface assessed by the methods of pH-metry and adsorption of acid-base indicators (Hammett's method). It was established that the sorption capacity of a sorbent in relation to bacteria depends on the initial material, its composition and production method.