Insight into stability of dithiocarbamate-modified adsorbents: Oxidation of dithiocarbamate

We previously reported that monoalkyl dithiocarbamate-modified cellulose (DMC) exhibited excellent adsorption performance for arsenite (As^III), cadmium (Cd^II), lead (Pb^II), gold (Au^III), silver (Ag^I), platinum (Pt^IV), and palladium (Pd^II). However, its adsorption capability for As^III decreased by 96.4% after two weeks of storage at 40 °C under an air atmosphere. This decrease in adsorption ability could occur for other metals that dithiocarbamates can extract. In this study, we investigated the adsorption performance of DMC for various metals before and after storage and proposed a possible mechanism for this decrease. We found significant decreases in the adsorption abilities of Pb^II (11.4%), Ag^I (39.5%), Pt^IV (65.5%), and Pd^II (69.6%), whereas Au^III and Cd^II adsorption was largely retained, with decreases of 1.1% and 4.0%, respectively. FTIR analysis of the stored DMC revealed the formation of S-S bonds and the retention of dithiocarbamate peaks, indicating the formation of dithiocarbamate dimers (thiuram disulfides). To further support thiuram disulfide formation, dialkyl thiuram disulfides were tested for the adsorption of the seven employed metals. The metal adsorption behavior of dialkyl thiuram disulfides was almost identical to that of the stored adsorbent, ensuring thiuram disulfide formation. In conclusion, the loss of adsorption capability can be mainly attributable to the formation of thiuram disulfide.