Polyurethane foam membranes filled with humic acid-chitosan crosslinked gels for selective and simultaneous removal of dyes

Abstract

Polyurethane foam membrane filled with humic acid-chitosan crosslinked gels (HA-CS-PUF) for dye removal was prepared by soaking the foams into humic acid-chitosan (HA-CS) crosslinked gels and hot-pressing them into membranes. Scanning electron microscope, derivative thermogravimetry and X-ray photoelectron spectroscopy were used to characterize the HA-CS-PUF membrane. Results showed that the interaction of HA and CS was mainly through ionic cross-linking between carboxyl and protonated amino groups. Three types of dyes, including positively charged methylene blue (MB), neutrally charged rhodamine B (RB) and negatively charged methyl orange (MO), were used to test membranes properties through static adsorption and membrane filtration experiments. It revealed that adsorption process was better fitted with Pseudo-second-order and Freundlich model. In membrane filtration experiments, we found that the retention rates of membrane 1 (ratio of HA to CS was 0:1) to MO and RB were 99.7% and 65%, respectively, and nearly no retention to MB. While membrane 4 (ratio of HA to CS was 0.2:1) can retain 97.7% of MO, 71.6% of RB and 62.1% of MB. Based on the experimental results, membrane 1 possessed the ability of selectively separating MB from MO/MB and RB/MB solutions, and membrane 4 can simultaneously retain RB and MB from RB/MB solution.