A macroscopic study of the retention capacity of copper by polyaniline coated onto silica gel and natural solid materials

Synthesised polyaniline coated onto silica gel and other natural materials such as peanut, almond, nut shells, apricot and olive seeds, etc., have been tested for the ability to retain metallic pollutants. Two adsorbents have been tested, namely silica gel and peanut shells, with copper as the metallic pollutant. In the absence of the polymer, both adsorbents have shown an extremely low capacity of retention, inversely to the case where they are coated with polyaniline, where the retention is very important. In fact the kinetic study of metal retention has shown that both polyaniline coated sorbents exhibit a rapid phase of adsorption before saturation is reached. However it should be noted that the peanut shells have shown a more rapid kinetic of retention than silica gel. The influence of different parameters like the contact time between the liquid and solid phases and the solution pH, on the capacity of retention, has been considered. The main result obtained from this study is that, macroscopically, the introduction of polyaniline onto the surface of silica gel and peanut shells, has largely improved the retention capacity of copper, practically from a zero value to nearly hundred per cent.

The main conclusion which can be drawn from this study, is that the technique of adsorption presents very large perspectives as far as the resolution of environmental problems are concerned. For instance, as seen in this work, toxic heavy metals can be efficiently removed from aqueous solutions by polyaniline coated silica gel and even more interesting, by polyaniline coated peanut shells which do not present any cost and are abundant. This can be a stimulating factor to evaluate many other natural materials from fruit shells or stones, which are also free, abundant and not destined for any immediate specific use. In the future, a microscopic explanation of the retention phenomenon will be attempted in order to systematise the strategies of modifying surface properties of solid materials in order to improve their adsorption capacities towards micro pollutants.