Fabrication of High-Performance Thin-Film Composite Nanofiltration Membrane by Dynamic Calcium-Carboxyl Intra-Bridging during Post-Treatment.

Hongyi Han,Ruobin Dai,Zhiwei Wang

doi:10.3390/membranes10070137

Abstract

Widespread applications of nanofiltration (NF) and reverse osmosis (RO)-based processes for water purification and desalination call for high-performance thin-film composite (TFC) membranes. In this work, a novel and facile modification method was proposed to fabricate high-performance thin-film composite nanofiltration membrane by introducing Ca2+ in the heat post-treatment. The introduction of Ca2+ induced in situ Ca2+-carboxyl intra-bridging, leading to the embedment of Ca2+ in the polyamide (PA) layer. This post modification enhanced the hydrophilicity and surface charge of NF membranes compared to the pristine membrane. More interestingly, the modified membrane had more nodules and exhibited rougher morphology. Such changes brought by the addition of Ca2+ enabled the significant increase of water permeability (increasing from 17.9 L·m−2·h−1·bar−1 to 29.8 L·m−2·h−1·bar−1) while maintaining a high selectivity (Na2SO4 rejection rate of 98.0%). Furthermore, the intra-bridging between calcium and carboxyl imparted the NF membranes with evident antifouling properties, exhibiting milder permeability decline of 4.2% (compared to 16.7% of NF-control) during filtration of sodium alginate solution. The results highlight the potential of using Ca2+-carboxyl intra-bridging post-treatment to fabricate high-performance TFC membranes for water purification and desalination.

Highlights

We proposed to use the intra-bridging between calcium and carboxyl groups in PA layer for modification of NF membrane during post-treatment, since calcium ion is capable of complexing with carboxyl groups [23]
Various NF membranes were synthesized via an interfacial polymerization (IP) process followed by the dynamic thermal post-treatment with addition of CaCl2
The images demonstrate that the PA selective layers had a nodular structure, which is the typical structure of PIP based PA layer [25,26]

Summary

Introduction

Water purification and desalination can be an effective route to address the water shortage and crisis worldwide [1,2,3,4]. Membrane-based processes have attracted much attention due to their high efficiency for wastewater reclamation, desalination, and water purification [5,6]. Nanofiltration (NF) and reverse osmosis (RO)-based processes play a dominant role in water harvesting applications [7,8,9]. In these applications, thin-film composite (TFC) membranes have experienced the tremendous development for a few decades and each layer of TFC membrane can be independently controlled and optimized to achieve expected selectivity and permeability. The membranes hold the key to the performance and cost-effectiveness of the processes [10,11]

Methods

Results

Conclusion