Green modification of outer selective P84 nanofiltration (NF) hollow fiber membranes for cadmium removal

Abstract

Outer-selective thin-film composite (TFC) hollow fiber membranes are normally made from interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC).However, the removal of excess MPD solution and the large consumption of alkane solvents are their technical bottlenecks. In this study, green methods to prepare the outer selective TFC hollow fiber membranes were explored by firstly modifying the membrane substrate with polyethyleneimine (PEI) and then by water soluble small molecules such as glutaraldehyde (GA) and epichlorohydrin (ECH). Using P84 polyimide as the substrate, not only do these modifications decrease substrate's pore size, but also vary surface charge by making the membranes less positively charged. As a result, the resultant membranes have higher rejections against salts such as Na 2 SO 4 , NaCl and MgSO 4 . The PEI and then GA modified membrane has the best separation performance with a NaCl rejection over 90 % and a pure water permeability (PWP) of 1.74 ± 0.01 Lm −2 bar −1 h −1 . It also shows an impressive rejection to CdCl 2 (94 %) during long-term stability tests. The CdCl 2 rejection remains higher than 90% at operating temperatures from 5 to 60 °C. This study may provide useful insights for green manufacturing of outer-selective nanofiltration (NF) hollow fiber membranes.

Green fabrication of a positively charged nanofiltration membrane by grafting poly(ethylene imine) onto a poly (arylene ether sulfone) membrane containing tertiary amine groups

“…The appearance of this peak suggests PEGDGE reacts with the tertiary amine groups, and was thus successfully grafted on the surface of the PES-TA membrane. Table 1 shows the atom percentage of oxygen, which increased from 12.24% in the unmodified PES-TA to 21.43% in PES-TA-PEGDGE, confirming that PEGDGE was grafted onto the PES-TA membrane surface. The XPS spectrum of the PES-TA-PEGDGE-PEI membrane is presented in Fig.…”

“…When the PEGDGE concentration exceeds 1 wt%, the flux increases with PEGDGE concentration. It has been shown previously that the PEGDGE graft monomer can cover the pore openings and narrow the pore radius on the membrane surface [21]. Thus, the membrane flux decreases and salt rejection increases initially (with 1 wt% PEGDGE).…”

“…Various post-modification methods have been investigated to improve the performance of asymmetric NF membranes without sacrificing mechanical properties. UV-photografting [18,19], ATRP grafting [20], and covalent bond grafting [21] have been widely used to obtain the desired high surface charge density to enhance the rejection of dyes and salts. Covalent bond grafting has also been shown to increase the antifouling properties of NF membranes [22].…”

“…Covalent bond grafting has also been shown to increase the antifouling properties of NF membranes [22]. In the grafting process, reducing the use of organic solvents is necessary to decrease manufacturing costs and to produce enable greener membrane-preparation processes [21].…”

Improved adsorption performance of activated carbon covalently functionalised with sulphur-containing ligands in the removal of cadmium from aqueous solutions

“…The removal of Cd(II) from aqueous systems is generally realised via different treatment technologies, namely adsorption (Attar et al 2018;Izidoro et al 2013;Huang et al 2013), reverse osmosis (Kheriji et al 2015;Pirsaheb et al 2017), nanofiltration (Gao et al 2016;Liu et al 2016;Saljoughi and Mousavi 2013) and precipitation (Islamoglu et al 2006;Tan et al 2013).…”