Development of filter modified by polyelectrolyte multilayers as adsorbent for herbicides

Abstract

At present, herbicides are used in agriculture in order to obtain higher production yields. Unfortunately, their chemical residues contaminates environment. In this study, polyelectrolyte multilayer was used to modify polypropylene membrane and water filter cartridge to enhance the effectiveness on the removal of water contaminated with paraquat and glyphosate. Poly(diallyl dimethyl ammonium chloride) (PDADMAC) as a polycations and poly(styrene sulfonic acid-co-maleic acid) (PSSMA) as polyanions and humic acid (HA) as a macromolecule were fabricated using layer-by-layer (LbL) technique. Sodium chloride concentration and pH solution were optimized to achieve the best film growth condition. The growth was monitored via Uv-Vis, FT-IR, SEM and AFM. The optimized fabrication condition delivering the thickest PDADMAC/PSSMA and PDADMAC/HA multilayers film were 1 M NaCl, HA pH 7 and PSSMA pH 5.5. However, the PDADMAC/HA could remove more herbicides comparing to PDADMAC/PSSMA. Thus, the PDADMAC/HA multilayers film was used in the performance study of the modified filters on the herbicides removal. The optimum number of the polyelectrolyte multilayers was 16th layers and flow rate was found to be at 0.5 mL/min as the best performance. Regarding paraquat removal, the maximum capacity of non-modified membrane is 8.24 ± 0.37 µg, while PDADMAC/HA modified membrane is 16.89 ± 0.45 µg (2.0-fold increase). For glyphosate removal, maximum capacity of non-modified membrane is 56.32 ± 0.54 µg and PDADMAC/HA modified membrane is 64.43 ± 0.26 µg (1.1-fold increase). The water filter cartridge was fabricated with the optimized condition previously found. For tap water, the amount of herbicides removal was increased from 0.20 ± 0.37 to 0.67 ± 0.45 mg (3.4-fold increase) for paraquat and from 1.03 ± 0.26 to 1.49 ± 0.34 mg (1.5-fold increase) for glyphosate. For groundwater, the amount of herbicides removal was increased from 0.15 ± 0.42 to 0.55 ± 0.26 (3.7-fold increase) in paraquat spiked sample and from 0.69 ± 0.25 to 1.26 ± 0.44 mg (1.8-fold increase) for glyphosate. This study showed the success on the fabrication of polyelectrolyte multilayers films on all types of substrates and the effectiveness on the removal of water contaminated with herbicides.