Salt accumulation often occurs in conventional processes for textile wastewater treatment, which affects the dye removal efficiency and water recovery rate. Nanofiltration is a feasible way to fractionate dye/NaCl mixtures. In this study, to enhance the dye/salt separation efficacy, two-dimensional (2D) WS2 nanosheets were incorporated and coordinately bonded to polyelectrolytes for fabricating layer-by-layer hybrid nanofiltration membranes. The incorporation of WS2 enhanced the hydrophilicity and surface negativity of the membrane. Further, the stacking of WS2 nanosheets and their frictionless surface promoted water transportation in polyelectrolyte multilayers. WS2-incorporated membrane (2 wt %) exhibited the highest pure water flux and achieved separation factors of 7238 and 9036 during filtration of Conge red/NaCl and reactive black 5/NaCl binary solutions, respectively. Moreover, the instability of the multilayered polyelectrolyte membrane in high ionic strength solutions was overcome by the incorporation of WS2, and the WS2-incorporated membrane showed better antifouling performance toward model organic foulants.
Separation performance of nanofiltration (NF) membranes is constrained by the trade-off between permeability and selectivity. Herein, a facile and environmental friendly water activation before microwave heating was performed to improve the performance of NF membranes and overcome this trade-off. The water activation before microwave heating facilitated the hydrolysis of acyl chloride, resulting in a loose polyamide layer with enhanced hydrophilicity and surface charge. The activated NF membrane showed a permeance of 29.9 L m -2 h -1 bar -1 , which is almost 2 times higher than the control. The membrane possesses a Na 2 SO 4 rejection of 96.8% and high selectivity to antibiotics and NaCl. At the meantime, the fouling resistance to model foulants including bovine serum albumin and sodium alginate was significantly enhanced. The water activation before microwave heating is proved to be an adequate strategy for fabricating NF membranes.
Juan Li,Guijing Chen,Shanshan Luo,Huixia Pang,Chengtao Gao,Shaowen Huang,Shan Liu,Shuhao Qin
In this study, styrene-maleic anhydride copolymer/chlorinated polyvinyl chloride composite membranes were prepared via a non-solvent induced phase separation technique. Different porous morphologies of the composite membranes were obtained by controlling the temperature of coagulation bath water. With the coagulation bath temperature increasing, the porous morphology of membrane surface changed from co-continuous pores to isolated-round-pores, and its evolution mechanism was elaborated. The average pore size of membranes surface increased from 17.27 to 48.72 nm, the pure water flux increased from 225.50 to 624.47 L m −2 h −1 , and the rejection rate of Congo red and bovine serum albumin declined gradually with the increase of coagulation bath temperature, but the NaCl rejection was less than 1.0%. The surface segregation behavior of anhydride groups was affected by the phase separation process, which in turn affects the anti-fouling performance of membranes. The composite membranes obtained at the coagulation bath temperature of 20 and 30°C had large surface segregation of anhydride groups and excellent anti-fouling performance. The water flux recovery rate is higher than 90% and the irreversible pollution decline rate is about 5.0%. Meanwhile, the obtained membranes, especially the membrane fabricated at a coagulation bath temperature of 0°C, has good dye/NaCl salt separation performance and can be used for the pretreatment of textile wastewater.
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