Selective separation of dye/salt mixture using diatomite-based sandwich-like membrane

A novel nanofiltration membrane was developed by entrapping a layer of modified diatomaceous earth between two layers of electrospun polysulfone (E-PSf) nanofibers. The diatomaceous earth particles and the fabricated membrane were characterized using FTIR, SEM, EDS, zeta potential, and water contact angle techniques. The static adsorption and dynamic separation of pristine E-PSF and sandwich-like membranes for methylene blue (MB) with/without salt were investigated under different operating conditions. The Langmuir model suited the MB adsorption isotherm data with a linear regression correlation coefficient (R2) >0.9955. As pH increased, both flux and MB rejection of the sandwich-like membrane improved by up to 183.8 LMH and 99.7%, respectively, when operated under gravity. The water flux of the sandwich-like membrane was sharply increased by increasing the pressure up to 19,518.2 LMH at 4.0 bar. However, this came at the expense of MB rejection (10.93%) and reduced its practical impact. At a high salt concentration, the sandwich-like membrane also indicated remarkable dye/salt separation with a higher permeation of salt (<0.2% NaCl rejection) and MB rejection (>99%). The performance of the regenerated diatomaceous material and membrane was maintained during five cycles of operation compared to that of the original ones.

Automated summary

A novel nanofiltration membrane with a layer of modified diatomaceous earth between two layers of electrospun polysulfone nanofibers was developed. The diatomaceous earth particles and the fabricated membrane were characterized using various techniques. The sandwich-like membrane showed improved flux and methylene blue (MB) rejection as pH increased, with a high water flux at increased pressure but reduced MB rejection. Moreover, the sandwich-like membrane exhibited remarkable dye/salt separation at high salt concentration, with higher permeation of salt and high MB rejection. The performance of the regenerated diatomaceous material and membrane was maintained during five cycles of operation.