2.5. Separation experiments
The pure water permeance of the membranes was measured by filtering the ultrapure water through the membranes and calculated by
\(J=V/(\text{Apt})\) (2)
where J is the permeance (L m-2h-1 bar-1), V is the volume of the solution through the membranes (L), A is the effective filtration area of the membranes (m2), p is the pressure difference across the membranes (bar), and t is the filtration time (h).
Six organic dye molecules were used as probes to evaluate nanofiltration performances of the membranes, including TMPyP (Mw 1363.60), direct yellow 50 (DY,Mw 956.82), EB (Mw897.88), congo red (CR, Mw 696.68), oil red (OR,Mw 408.50) and MB (Mw373.89). MgSO4 and NaCl were also used to evaluate desalination performances. 50 mL of dye solution (10 μg mL-1) or salt solution (1 mg mL-1) was filtered under continuous stirring. When about one third of the solution passed through the membranes, the concentration of dyes in the feed, the retentate and the permeate was measured by the ultraviolet-visible (UV-vis) absorption spectrometer (UV-1800, Shimadzu, Japan) while the concentration of salts in the feed, the retentate and the permeate was measured by the conductivity meter (CON700, Eutech, USA). The rejection was calculated by
\(R=(C_{f}-C_{p})/C_{f}\times 100\%\) (3)
where R is rejection (%), Cf andCp are the concentration of solutes in the feed and the permeate (g L-1), respectively.