Incorporating silica-magnetite synthesized from natural resources into the cation exchange membranes

Abstract

Inorganic material-incorporated cation exchange membranes (CEMs) with improved properties have drawn attention for reverse electrodialysis (RED). This paper deals with improving CEMs properties by incorporating silica–magnetite inorganic materials from natural resources. First, silica and magnetite were extracted from rice husk and iron sand, respectively. CEMs were prepared using the phase inversion method by incorporating various ratios. The results showed that both silica and magnetite were in micron size with yields of 76.6% and 59.2% wt., respectively. The CEMs containing magnetite materials showed higher ion exchange capacity (IEC) and ionic conductivity than PVC membranes. However, they had a greater swelling degree. The presence of silica reduced the swelling degree from 18.38% to 7.15% leading to membrane strengthening. A maximum IEC and conductivity of CEMs of 0.26 meq/g and 0.524 S/cm were obtained for the membrane prepared with a SiO2/Fe3O4 ratio of 0:4, respectively. However, considering all aspects, the addition of a SiO2/Fe3O4 ratio of 1:3 was the most significant for increasing the fixed cation density and conductivity by 27.49% and 2815%, respectively, compared to other ratios. Thus, this SiO2/Fe3O4 ratio (1:3) should be considered for practical implementation. Performance examination using RED confirmed that the PVC/SiO2/Fe3O4 can be used as CEM for power generating and had comparable performance to commercial membrane.