Rational design and fabricate of protonated crosslinked chitosan adsorbent for boosting the removal of nitrite in water

Removing hazardous nitrite from water by chitosan has many advantages such as low cost, biocompatible, and abundant availability. However, its poor adsorption capacity for nitrite hinders its practical applications. More importantly, the strategies for improving the nitrite adsorption ability of chitosan are still elusive. In this work, a systematic strategy that considers adsorption sites, surface potential, and crystallinity was proposed to enhance the nitrite adsorption of chitosan. As a demonstration, a rationally designed amorphous adsorbent (H+/GCLchitosan) with imine adsorption sites and positive surface Zeta potential was synthesized via heterogeneous cross-linking with glutaraldehyde and then acidified in HCl solution. The obtained adsorbent exhibited a high nitrite adsorption capacity of 17.30 mg & sdot;N & sdot;g ? 1, far surpassing the previously-reported chitosan-based adsorbents. Theoretical calculations and mechanism studies indicated that the designed imine adsorption sites and positive surface Zeta potential are crucial for its excellent adsorption capacity. Furthermore, H+/GCL-chitosan can rapidly reach adsorption equilibrium within 3 min and maintain stable adsorption for 24 h, and the adsorbent can be regenerated effectively. To demonstrate its applications, two H+/GCL-chitosan adsorption devices achieved over 95 % of nitrite removal rate with the initial nitrite concentrations of 10 and 100 mg & sdot;N & sdot;L- 1 respectively, without any pretreatment of the polluted water. These results clearly show that H+/GCL-chitosan has an excellent ability for nitrite removal. Moreover, the surface engineering strategy proposed in this work may open up new possibilities for the efficient removal of nitrite from water using chitosan-based adsorbent.