Chitosan-gold nanocomposite and its functionalized paper strips for reversible visual sensing and removal of trace Hg2+ in practice

To eliminate mercury contamination in aqueous environment, chitosan-gold nanocomposite and its functionalized paper strips were designed and developed for visual sensing and removal of trace Hg2+. By simply immersing a common filter paper into the resultant composite dispersion, gold nanochromophores could be well dispersed with minor aggregation by virtue of the dual supporting roles of the chitosan and the filter paper. Under optimized conditions, the colour of both the chitosan-gold nanocomposite and its functionalized paper strips could change from dark red to yellow upon addition of Hg2+, with a detection limit of 3.2 x 10(-9) mol L-1 and 5.0 x 10(-8) mol L-1, respectively. Importantly, the chitosan-gold nanocomposite was non-toxic and could be utilized repeatedly for sensing trace Hg2+ in both environmental aqueous solutions and some fruit or vegetable juice samples, with satisfactory results. Furthermore, using the resulting functionalized filter-paper, more than 93.5% Hg2+ in aqueous solution with an initial concentration as high as 1.0 x 10(-5) mol L-1 could be enriched and separated by a simple filtration process. The proposed operating mechanism is based on the reversible gold amalgam formation between the gold nanoparticles and Hg2+. This study will be the first report for paper-based sensing to visually detect, enrich and remove Hg2+ with minimal secondary pollution.