Development and optimization of low surface free energy of rGO-PVDF mixed matrix membrane for membrane distillation

Abstract

In this research work, mixed matrix membranes were fabricated by synthesising and blending reduced graphene oxide (rGO) in polyvinylidene fluoride (PVDF) membrane via a facile phase inversion process. Low and high loadings of rGO were incorporated into the PVDF membrane matrix to study its physicochemical properties which could be analysed using field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), surface analyser and atomic force microscopes (AFM). All fabricated mixed matrix membranes exhibit low surface free energy (SFE) properties compared with the pristine membrane which is suitable for the application in membrane distillation (MD) system. Besides, high rGO loadings in PVDF membrane resulted in a smaller membrane pore size and rougher membrane surface. The successful blend-in of rGO in PVDF membrane could be further confirmed with FESEM, EDX, SFE and AFM results. The performance of fabricated membranes was evaluated with a prolonged desalination process via direct contact membrane distillation (DCMD). It was found that low rGO-PVDF mixed matrix membranes exhibit a better permeate flux of 31.92 ± 2.85 L/m2.hr which has 31.79 % increase in flux compared with pristine membrane. All membranes have 99.99 ± 0.05 % of salt rejection for 40 h of DCMD operation. Membranes after the desalination process were analysed and it was found that the rGO is stable in the membrane matrix and low loadings of rGO in PVDF membrane could improve MD desalination performance. Besides, optimization of rGO loadings using response surface methods (RSM) was employed and the result showed that 1.36 wt% of rGO-loading in PVDF membrane matrix could result in 34.69 ± 2.74 L/m2.hr of permeate flux.