Title: Engineering of wood-based membranes with excellent permeability or selectivity properties for forward osmosis process

Abstract

A novel lignin-based membrane with excellent water permeability and salt rejection characteristics was developed for forward osmosis (FO) processes. The overall FO membranes had three compartments including: (i) a bottom layer of nanofibrous electrospun sulfonated kraft lignin (SKL) (70 wt%) and polyvinyl alcohol (PVA) (30 wt%), (ii) an intermediate layer of PVA-glutaraldehyde (GA) hydrogel, and (iii) a top thin film of selective polyamide (PA) layer. The thickness of the electrospun underlying SKL-PVA mat was 50 μm where its super porous structure can quickly absorb water drops within the internal pores. We coated the surface of SKL-PVA support with four different concentrations of PVA hydrogel (0.25, 0.5, 1, and 2 wt%). Increasing the concentration of the PVA hydrogel, the thickness of the deposited layer was increased accordingly. After coating of PA layer, lignin-based thin film composite (LTFC-X) membranes were obtained in which X denotes the PVA hydrogel concentration. Among all synthesized membranes, the LTFC-0.5 membrane demonstrated the lowest structural parameter (S) of 191.67±5.88 μm which can result in a minimal internal concentration polarization (ICP) in this membrane. The FO performances of the fabricated membranes were evaluated in either of two different configurations including the active PA layer facing the feed solution (ALFS) or the PA layer facing the draw solution (ALDS). The LTFC-0.5 membrane had the maximum water flux (Jw) in both ALDS (61.33±2.85 LMH) and ALFS (56.60±2.99 LMH) modes. The specific salt flux (Js/Jw) shows the potential of a membrane in salt passage versus 1 L of permeated pure water. In the ALDS mode, the LTFC-0.5 membrane represented the lowest Js/Jw of 0.087±0.004 g/L among all fabricated membranes. However, the LTFC-1 membrane had the best performance in the ALFS mode with a minimal Js/Jw value of 0.090±0.011 g/L.