Water Supply (Mar 2021)
Adsorption of nitrate and phosphate in an aqueous solution on composites of PVA and chitosan prepared from a Somanniathelphusa sinensis shell
Abstract
In this study, chitosan was prepared from the shell of Somanniathelphusa sinensis, which is a crab ubiquitous in Vietnam. The 3-level, 3-factor Box–Behnken design was applied to the preparation of chitosan to investigate effects of factors such as the HCl solution concentration, protein removal time and deacetylation time on the degree of deacetylation (%DD). Scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and gel permeation chromatography were employed to examine the chitosan structure, as well as pH titration and antibacterial testing of the chitosan solution. Results revealed that as-p chitosan comprises specific functional groups, with almost no impurities. Its average molecular weight was ∼225,000 g/mol, and %DD was ∼89.7%. The chitosan/PVA composite was prepared and investigated for the adsorption of nitrate and phosphate ions in water. Experimental results revealed that the adsorption capacity of a chitosan/PVA (1:2) composite is better than that of chitosan. Accordingly, the theoretical maximum adsorption capacities of nitrate and phosphate ions on chitosan were 122.0 mg/g and 344.8 mg/g, respectively. The corresponding values on the chitosan/PVA (1:2) composite were 135.1 mg/g and 384.6 mg/g. Adsorption kinetics data at 25 °C were well fitted to the pseudo-second-order model (R2 > 0.998). These results revealed that crab shell chitosan and the chitosan/PVA (1:2) composite can be used for the adsorption of nitrates and phosphates in aqueous solutions. HIGHLIGHTS The process of preparing chitosan from the shell of Somanniathelphusa Sinensis was optimized by Box-Behnken design.; The characterization of chitosan showed that it was successfully prepared with high DD value, moderate molecular weight, good antibacterial properties and no impurities.; Chitosan/PVA composites were prepared with uniform distribution, uniform particle size.; Crab shell chitosan and Chitosan/PVA (1:2) composite show good adsorption capacity of nitrate and phosphate ions in aqueous solution.;
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