Anhydrous proton conductor consisting of pectin-inorganic composite material

Selective Accumulation of Rare-Earth and Heavy Metal Ions by a Fucoidan-Inorganic Composite Material

The accumulation of rare-earth and heavy metal ions from wastewater is important for industrial technology. However, practical accumulators of metal ions are expensive with respect procurement of raw materials, synthesis, and preparation. Therefore, it is preferable to accumulate metal ions using sustainable resources, such as natural polymers. Fucoidan, a water-soluble natural polymer, is a sulfated polysaccharide from the cell-wall of brown algae. Therefore, fucoidan behaves as an acidic polysaccharide in an aqueous solution. We prepared a fucoidan-inorganic composite material by mixing fucoidan and a silane coupling reagent, bis(3-(trimethoxysilyl)propyl)amine (SiNSi). This fucoidan-SiNSi (F-SiNSi) composite material showed a water-insoluble property. This is due to the encapsulation of fucoidan into a three-dimensional network of SiNSi with siloxane bonding. When the F-SiNSi composite material is immersed in a metal ion-containing aqueous solution, the composite material accumulated the metal ions. The binding affinity of each metal ion was Ca(II), Mg(II) << Nd(III) < Cu(II), Zn(II), Ni(II), La(III) < In(III) < Y(III). Additionally, the maximum-accumulated amounts of the Nd(III), Cu(II), Zn(II), Ni(II), La(III), In(III), and Y(III) ions were 140, 200, 190, 200, 200, 230, and 270 nmol per mg of fucoidan, respectively. Furthermore, the molar ratios of the acidic groups (the sulfate and carboxyl groups) in the fucoidan and accumulated metal ions, were 0.081–0.156. Therefore, the F-SiNSi composite material showed a selectivity for rare-earth and heavy metal ions. The accumulation mechanism of the rare-earth and heavy metal ions was related to the carboxyl groups in the fucoidan.

Preparation of Gellan Gum-Inorganic Composite Film and Its Metal Ion Accumulation Property

Gellan gum is one of the water-soluble anionic polysaccharides produced by the bacteria Sphingomonas elodea. In this study, we prepared gellan gum-inorganic composite films by mixing the gellan gum and a silane coupling reagent—3-glycidoxypropyltrimethoxysilane (GPTMS). These gellan gum-GPTMS composite films were stable in an aqueous solution and showed a thermal stability. In addition, these composite films indicated a mechanical strength by the formation of the three-dimensional network of siloxane. We demonstrated the accumulation of metal ions from a metal ion-containing aqueous solution by the composite film. As a result, although the composite film indicated the accumulation of heavy and rare-earth metal ions, the light metal ions, such as Mg(II) and Al(III) ions, did not interact with the composite material. Therefore, the accumulative mechanism of metal ions using a composite film was evaluated by IR measurements. As a consequence, although the accumulation of heavy and rare-earth metal ions occurred at both the −COO− group and the −OH group in the gellan gum, the accumulation of light metal ions occurred only at the −OH group.