Antifouling macrocyclic-engineered PVDF membrane for the low-pressure separation of surfactant-stabilized oily wastewater

Abstract

Fouling is a common phenomenon which affects the long-term efficacy of membranes in the practical treatment of oily wastewater. It often results in a dramatic decline in flux, and a consequent increase in maintenance and operational cost. To address this, various substrates have been incorporated during membrane fabrication to enhance the fouling resistance, and improve the separation efficiency. Herein, we report the fabrication of a novel symmetrical ball-copper phthalocyanine incorporated PVDF membrane (CuPc@PVDF) for the effective separation of surfactant-stabilized oil-in-water emulsions. The symmetrical ball-Cu phthalocyanine with four non-peripheral substituents synthesized ab-initio and characterized using UV–vis, FT-IR, 1H NMR, and MALDI-TOF spectroscopies was added to the casting solution during membrane fabrication resulting in the formation of highly hydrophilic and anti-fouling CuPc@PVDF membrane. In contrast to the PVDF membrane, having a water contact angle of 82.3° ± 0.7°, the CuPc@PVDF membrane demonstrated high hydrophilicity with a contact angle of 55.5° ± 0.5°, and pure water permeance up to 768 LMH at 3 bar. It further achieved 99.9 % rejection of oil with size in the range of 50–450 nm at 1 bar, and demonstrated high stability and excellent anti-fouling property during 10 cycles of continuous demulsification, with a flux recovery ratio (FRR) of 98.5 %, and extremely low irreversible flux of 1.5 %. Similarly, the CuPc@PVDF membrane exhibited high resistance to accelerated organic fouling, maintaining a steady flux and an FRR of 93.0 % during 1 hour of continuous operation with 10 ppm sodium alginate and Ca2+ ions. This study reports a novel strategy to enhance the fouling resistance of demulsification membranes, and could be further explored in the design of next generation of advanced membranes for the purification of oily wastewater.