Zr(IV) loaded cross-linked chitosan beads with enhanced surface area for the removal of nitrate and phosphate

• Silica dissolution method has been introduced to enhance the surface area of the cross-linked chitosan beads.
• The removal of nitrate and phosphate using Zr(IV) loaded cross-linked chitosan beads was not studied elsewhere.
• The adsorbent reported in this study has exhibited higher nitrate and phosphate adsorption capacities.
• The anion adsorbed SD-ZrCB was regenerated using 0.025 M NaCl up to 10 cycles without much drop in adsorption capacities.

In this work, a new method namely silica dissolution method, has been adapted to increase the surface area of the cross-linked chitosan beads. Zr(IV) was loaded in the cross-linked chitosan beads in order to make it selective for the nitrate and phosphate anions from aqueous solutions. Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB) and silica dissolution method (SD-ZrCB) were characterised using N2 adsorption/desorption studies, SEM, EDAX, XRD, FTIR, TGA, DTA and water regain property. The SD-ZrCB exhibited higher N2 adsorption, water regain property as well as anion adsorption capacity than ZrCB. Batch method was adapted for the adsorption studies. The nitrate and phosphate adsorbed SD-ZrCB was regenerated using 0.025 M NaCl solution. There was not much drop in adsorption capacities up to 10th regeneration cycle. Freundlich adsorption isotherm was the best fit adsorption isotherm among Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms which have been used to fit the nitrate and phosphate adsorption data. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process.

A new method namely silica dissolution method has been introduced to enhance the surface area of the chitosan beads cross-linked with glutaraldehyde. The N2 adsorption, water regain property as well as nitrate and phosphate adsorption capacity of Zr(IV) loaded cross-linked chitosan beads prepared by and silica dissolution method (SD-ZrCB) was significantly higher than that of Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB).Figure optionsDownload as PowerPoint slide