Hybrid nanofiltration thin film hollow fiber membranes with adsorptive supports containing bentonite and LDH nanoclays for boron removal

This study focused on removal of boron from water via hybrid nanofiltration (NF) thin film composite (TFC) hollow fiber (HF) membranes. To do so, nanocomposite polyvinyl chloride (PVC) HF membranes containing bentonite and layered double hydroxide (LDH) nanoparticles as natural and synthetic adsorbents were fabricated as the adsorptive support layers with high efficiency in boron removal. The phase inversion behavior of dope solutions and mechanical strength of the adsorptive nanocomposite PVC HF membranes were investigated and the results showed that LDH interacts better with PVC polymeric chains than bentonite. It was found that LDH with smaller pores and better adsorption capability in comparison with bentonite results in more hydrophilic membranes with better performance. On the other hand, bentonite tends to become agglomerated at above 1.5 wt%. Moreover, the fabricated membranes containing LDH have lower MWCO and more uniform pore size distribution which make them better options as support for the TFC layer formation to fabricate NF TFC membranes. The selective TFC layer was then fabricated via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5-benzenetricarbonyl trichloride (TMC) on the outer layer of the nanocomposite PVC HF membranes. Boron removal, and recovery and reusability of the fabricated NF TFC membranes were investigated by Na2CO3 solution. It was found that the NF TFC membranes containing LDH with boron removal of more than 83.6% and water flux of 16.1 L/m(2).h at 4 bar operational pressure exhibit better performance than the NF TFC membranes containing bentonite.