Nano-structured composite calcium silicate and some novel applications

Composite nano-structured calcium silicate materials have been prepared by reaction of a silica-containing solution with calcium ions at elevated pH, characterised and tested in metal adsorption and anti-microbial applications. The material comprises nano-size platelets that self-assemble into particles of about 1–5 μm in size with an open framework structure. These exhibit a high pore volume and liquid absorption of about 500–600 g oil 100 g−1 silicate and a high accessible surface area of up to about 600 m2 g−1, both of which are controllable in the synthesis process. It has a high whiteness and brightness. XRD shows only short range order. The surface of the nano-size platelets contain both silanol (Si–OH) groups and Ca2+ ions which provide bonding sites for the adsorption of metal cations. As such, the nano-structured calcium silicate exhibits an excellent ability to recover metal cations from solutions such as Cu2+ down to the 1 mg kg−1 level, demonstrating its potential in environmental clean-up applications. Similarly, silver ions can be adsorbed with the resulting nano-structured calcium silicate–silver composites showing excellent antimicrobial activity against Staphylococcus aureus (ATCC 25923) down to very low silver levels of 1 mg kg−1. The silver cannot be leached out easily. These composite particles can be incorporated into surface coatings, plastics and food packaging as an easily useable, effective and durable anti-microbial agent.