The VSC Adsorption on Hydrotalcite through Topochemical Reactions

Abstract

Volatile sulfur compounds (VSCs) such as hydrogen sulfide (H2S), methyl mercaptan and dimethyl sulfide produced in mouth. Some oral (Gram-negative) bacteria produce VSCs, which induces permeability of mucous membrane, cause the oral malordor, dental caries, color change of the dental fillings. Thus, material which adsorbs VSCs should be useful to keep health in mouth. Previously, we reported the H2S adsorptive properties of zeolite and hydrotalcite materials having micro pores. The amount of H2S adsorbed on the zeolite or hydrotalcite at room temperature was found to be around 300-400 ppm, and and 3 % of H2S was desorbed when heated at 400 °C. The hydrotalcite, whose compositon is Mg1-xAlx(OH)2Ax/n·mH2O, where A is CO32-, and x is 0.25, was heat-treated at 500 °C, and put into aqueous solution containing H2S. In this study, the relation between heat-treatment tempearture and the sulfide adsorption on hydrotalcite in aqueous solution was investigated. The hydrotalcite materials were hydrothermally synthesized and identified by powder X-ray diffraction method. The change in concentrations of H2S in aqueous solution was measured using FPD gas chromatography (GC). The concentrations of H2S was decreased with time for the hydrotalcite heated at 500 °C or 600 °C, and fell to 20 % for 12 hours. But, the concentration was decreased by 40% for 12 hours for the hydrotalcite materials heated at higher temperatue. XRD and FT-IR analysis revealed that the sulfides were into or out of the hydrotalcite structure through topochemical reactions.