Natural rubber as a template for making hollow silica spheres and their use as antibacterial agents

Abstract

A method is reported for synthesizing hollow silica spheres (HSS) using skimmed natural rubber (NR) latex as template. Tetraethyl orthosilicate (TEOS) and (3-aminopropyl) triethoxysilane (APTES) were used as the silica source and the co-structure directing agent, respectively. Effects of the TEOS/APTES mole ratio, the synthesis pH, and the total silica content relative to rubber, on HSS formation were observed through transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Skimmed NR latex proved to be a suitable natural template because the rubber particles in it were generally spherical and the ammonia (NH 3 ) conventionally added to the latex as a preservative served as the catalyst for the synthesis of silica. The suitable pH range for forming the hollow structures was 7–10, so long as the TEOS/APTES mole ratio was satisfactory and the total silica available was sufficient. The optimal conditions for forming HSS with robust shells were a TEOS/APTES mole ratio of 1:1, pH 10, and a total silica content of 200 phr. The silver-loaded HSS had excellent antibacterial activity against Escherichia coli . • Skimmed natural rubber latex was used to make hollow silica spheres (HSS). • A sol-gel process with tetraethyl orthosilicate as the silica source was used. • The co-structure directing agent was (3-aminopropyl) triethoxysilane. • A method was developed for loading the HSS with silver ions (Ag + ). • Ag-loaded HSS had superior antibacterial activity compared to a solution of AgNO 3 .