Preparation of a positive porous polyvinylidene fluoride membrane and its removal of mercury containing wastewater

There are few porous membrane technologies for removing heavy metals from water. A porous polyvinylidene fluoride (PVDF) membrane modified by blending with polycationic liquid was prepared with positively charged surface. The membranes were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy analysis and the surface properties including the water contact angle, mechanical strength, pure water flux and zeta potentials were also tested. The hydrophilicity of the membrane was improved by blending more additive. The water contact angle of the modified membrane N3 (24 wt.%, 7/3) was decreased from 81.9° (pure PVDF membrane) to 55.0°. The increase of the concentration of the casting solution enhanced the mechanical strength, the pure water flux of the membrane N3 was decreased to 136.87 L/m 2 ∙h, and the membrane porosity was enlarged to 81.30%. Because of the positively charged surface, all blend membranes showed no adsorption on the positive Rhodamine 6G, but had a certain adsorption capacity on the negative Orange IV. In addition, results showed that adding 5 wt.% of N,N-dimethylformamide into the coagulation bath effectively enhanced the retention of hydrophilic additives on the membrane surface, and the optimum membrane N4 (24 wt.%, 8/2) demonstrated a strong retention for Hg(II) at low pH, as high as 89.8% (pH=1), that is, the prepared positive porous membrane has certain engineering application potential in the removal of heavy metal wastewater.