Optimization of isotropic MoS₂/PES membranes for efficient treatment of industrial oily wastewater

Elimination of tiny oil droplets nearly miscible with wastewater can be realized using membrane technology through ultrafiltration. The novelty of this work was to blend different phases of molybdenum disulfide (MoS₂) in isotropic polyethersulfone (PES). We prepared isotropic PES membranes by optimizing nonsolvent vapour-induced phase separation (VIPS). Membranes were blended with MoS₂ nanosheets of different phases to promote separation performance and antifouling resistance. FE-SEM revealed the flower-like surface morphology of MoS₂ nanosheets. HR-TEM of MoS₂ revealed 2H domains in the monolayer, flakes of a few layers and a d-spacing of 0.22 nm. Raman spectroscopy could be used to distinguish mixed-phase MoS₂ from single-phase MoS₂. Isotropic PES membranes modified with 70% 1T/2H MoS₂ had a significantly high permeance to pure water (6911 kg m^-2 h bar). The same membrane possessed a high efficiency of oil rejection of 98.78%, 97.85%, 99.83% for emulsions of industrial crude oil at 100, 1000 and 10 000 mg L^-1, respectively. Removal of oil droplets from wastewater was dominated by a mechanism based on size exclusion. Isotropic PES modified with 2H MoS₂ possessed superior oleophilicity, which resulted in low rejection of crude oil. Modified membranes showed excellent fouling resistance for three successive filtration cycles, as evidenced by enhanced antifouling parameters. Our study reveals how the phase composition of MoS₂ nanosheets can significantly affect the performance of isotropic PES membranes during the ultrafiltration of oily wastewater.