Surfactant modification of chitosan hydrogel beads for Ni@NiO core-shell nanoparticles formation and its catalysis to 4-nitrophenol reduction

Abstract

Chitosan (CS) in its hydrogel bead form is widely used to remove metal ions from aqueous medium. In the present work CS gel beads were modified with sodium dodecyl sulfate (SDS), an anionic surfactant, in a novel way, with formation of bilayer (admicelle) on to it. The concentration of SDS used for CS bead modification was 6000mg/L. These surfactant-modified chitosan beads were designated as POSTCS beads. In the next step, Ni(II) was loaded on the SDS bilayer present in the POSTCS beads through a process called ‘adsolubilization'. The loading of nickel was ∼4 times higher in POSTCS beads compared to that in normal CS beads. The property of surfactant to form admicelle helped in enhanced Ni(II) adsorption, and its stabilization. Further Ni@NiO core-shell type particles were formed on POSTCS beads by borohydride reduction. The particles were characterized by XRD, FTIR, SEM/EDX and TEM analysis. The as-prepared particles exhibited excellent catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of borohydride. The reduction was carried out with various catalyst doses, and it was found to follow first order rate. The turn over number (TON) and turn over frequency (TOF) of the catalyst at a dose of 2.0g/L and 1×10−4M 4-NP concentration were found to be 3.0115×1019 molecules/g and 5.019×1016 molecules/g/s, respectively.