A dendrimer-like hyper branched chitosan beads toward fluoride adsorption from water.

The present study reports a novel approach for the preparation of polyamidoamine grafted chitosan beads (PAAGCB) via Michael addition followed by protonation of PAAGCB to get protonated PAAGCB (H(+)-PAAGCB). Various metal ions viz., Al(3+), Ce(3+), La(3+) and Zr(4+) have been loaded onto the PAAGCB in order to get respective Al-PAAGCB, Ce-PAAGCB, La-PAAGCB and Zr-PAAGCB. All these sorbents were used to remove the fluoride ions from aqueous solution. Ethylenediamine is used for amination purpose of chitosan beads through Michael addition. The results showed that Zr-PAAGCB was more selective with the maximum defluoridation capacity of 17.47 mg/g than the other metal ion loaded chitosan beads. The sorbents were characterized using FTIR, XRD, SEM and EDAX. The fluoride sorption was reasonably explained using Freundlich and Langmuir isotherm models. The mechanism concerned in the adsorption of fluoride ions is by physisorption on heterogeneous materials according to the results obtained by fitting the data to various isotherm models. Temperature study carried out at 303, 313 and 323K revealed that the adsorption process was spontaneous and endothermic in nature. The applicability of the sorbents studied has been tested with field sample collected from fluoride endemic area.