Desalination of dye utilizing carboxylated TiO2/calcium alginate hydrogel nanofiltration membrane with high salt permeation

In order to recover dyes from textile wastewater, a self-supported carboxylated titanium dioxide/calcium alginate (TiO 2 -COOH/CaAlg) hydrogel nanofiltration membrane was prepared using TiO 2 -COOH as the reinforcing agent. The Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX) mapping scanning spectra were employed to characterize the distribution of TiO 2 -COOH nanoparticles on the membrane surface. The pore size distribution, zeta potential and mechanical performance of the membrane were evaluated. The rejections for single dye solutions, salt solutions and dye/salt mixture solutions were also examined. The results indicate that the TiO 2 -COOH nanoparticles are dispersed uniformly on the membrane surface. Compared to CaAlg membrane, the tensile strength of 20 wt% TiO 2 -COOH/CaAlg membrane is enhanced by 328%. At the operating pressure of 0.1 MPa, the rejection ratios of 20 wt% TiO 2 -COOH/CaAlg membrane for 100 mg/L Brilliant blue G250, Direct black 38 and Congo red are 98.4%, 96.8% and 95.9% respectively, and the permeate flux is about 14.1 L·m −2 ·h −1 . Meanwhile, this membrane possesses the low rejection ratios for inorganic salts (16.1%, 15.6%, 12.3% and 9.0% for MgSO 4 , Na 2 SO 4 , MgCl 2 and NaCl, respectively), excellent dye anti-fouling property and good stability in the long-term filtration for dye/salt mixture solution.