RESUMO
Layer by layer (LbL) assembly can be regarded as an emerging technology for the separation of organic micro-pollutants from water. Direct assembly of polyelectrolytes (PEs) under LbL mode on natural support material is rare. Here we report the integration of LbL to one of the most resourceful support materials that might have an enduring impact on water treatment in color industry. A low-cost adsorbent is developed from chitosan (CHI) and polyacrylic acid (PAA) through LbL deposition on coir fiber (CF) by alternate exposure to their aqueous solutions. Their layer dependent formation is characterized by spectroscopic and microscopic techniques. CHI/PAA multilayer coated coir fiber or simply, layered coir fiber (LCF) showed high loading of cationic and anionic dyes both at acidic and alkaline loading pH. The loading was between 70% and 99% at the acidic pH 3 which is attributed to the binding between LCF and dye molecules by electrostatic and hydrophobic forces. The performance of LCF in presence of NaCl, Na2SO4 and sodium dodecyl sulfate (SDS) in dye solution is discussed. Textile industrial waste water showed significant reduction in dye (81%) content along with COD (84%) and TDS.
RESUMO
The development of a sustainable membrane surface based on chitosan/poly(acrylic acid) (CHI/PAA) multilayers suitable for applications in analytical separations is reported here. Bilayers are constructed on polyamide microfiltration membranes at a pH combination of 3/3 (CHI pH/PAA pH) through a layer by layer approach. A 12.5 bilayer yielded a thickness of 400 nm. Low pressure (10 psi) filtrations through a 5.5 bilayered membrane exhibited high flux (7 m(3) m(-2) day(-1)) and selectivity (NaCl/reactive black 5 (RB5) selectivity >8000). The selectivity and flux observed here are the highest reported to date for low pressure filtrations through membranes. The increase in flux with increasing feed salt concentration is correlated with morphological transformations. Salt content above 7500 ppm causes some perturbation of surface layers. The presence of RB5, a model dye in the feed, restores the surface to maintain sustainability. A skin layer as thin as 50 nm imparts a large separation window. An RB5 feed concentration of 500 ppm results in 98.64% rejection with a flux of 25.79 m(3) m(-2) day(-1). The increase in flux with feed dye concentration supports the plasticizing action of RB5. The transport studies with large feed dye concentrations indicate that at a dye concentration of 500 ppm, the linear growing region (pre-exponential, 5.5 bilayer) itself provides a separation window similar to that of 100 ppm. At the same time, 1000 ppm requires a 9.5 bilayer that falls in the nonlinear growing region. Scanning electron microscopy images show the increase in porosity with respect to feed dye. Interesting morphologies that show the sustainable nature of the membrane surfaces along with the transport data of RB5 are presented.
