Synthesis and Characterization of Polymer Beads and Hydrogel Metal Nanoparticle Composites for Adsorption and Catalytic Applications

Abstract

This work concerns with the synthesis, characterization and applications of hydrogels and polymer beads. Hydrogels of micron dimension and of different chemical compositions were prepared. Poly(methacrylic acid) (p(MAc)), poly(methacrylic acid-co- acrylonitrile) (p(MAc-co-AN)), poly(sulfobetain methacrylate) (p(SBMA)) microgels were prepared. Modification of nitrile groups to amidoxime groups was accomplished by treating with hydroxylamine hydrochloride. The prepared hydrogels were used as microreactors for the synthesis of monometallic Cu, Co, and Ni nanoparticles as well as bimetallic Co-Fe nanoparticles. The catalytic applications of the hydrogel metal nanoparticles composites were investigated for the reduction of nitro compounds such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP) and 4-nitroaniline (4-NA). Catalytic activities of the prepared composites were also studied for the reduction of cation and anionic dyes such as eosine Y (EY), methyl orange (MO), and methylene blue (MB). Simultaneous reductions of two or three compounds like 4-NP, EY and MB were also carried out in the presence of the prepared catalysts. The bare (p(MAc-co-AN) microgels and their magnetic composites were also used as adsorbents for the removal of heavy metal ions such as Cd (II) and Cr (III), industrial dyes like MB and rhodamine 6 G (R6G) and a widely used herbicide paraquat (PQ) from aqueous medium. Tremendous increase in the adsorption capacity was observed after the conversion of nitrile to amidoximes. The magnetic microgels were found to retain their magnetic characteristics even after adsorption of pollutants. The poly(acrylonitrile) (p(AN)) beads were prepared and the nitrile groups were converted to amidoximes. The adsorption ability of the p(AN) beads was investigated by using them as adsorbents for the removal of Cd (II), MB, R6G and PQ from aqueous medium. Another type of modifiable poly (vinylbenzyl chloride) (p(VBC)) beads were prepared and the reactive vinyl chloride groups were treated with 3, 3ʹ-iminodipropionitrile (IDPN) to introduce two nitrile groups on each reactive site. The nitrile groups were then converted to amidoxime groups. These amidoximated beads were then applied as adsorbents for the removal of anionic dyes such as MO and EY as well as for the removal of toxic dichromate and arsenate from aqueous medium. Three adsorption isotherms; Langmuir, Freundlich, and Temkin adsorption isotherms were applied on the adsorption data to find the nature of adsorption. The pseudo first order and iipseudo second order kinetics was also applied to investigate the kinetics of the adsorption experiments. The catalytic and adsorption results of this work are much better as compared to the previously reported work. To sum up, the microgels that can be employed for the synthesis of inherently magnetic, highly stable and reusable nano catalysts have been prepared. The most important outcome from this work is that the prepared microgel composite catalysts can be used for individual and simultaneous degradation of nitrophenols and cationic/anionic dyes pairs or in the triple combinations that may exist in the contaminated aquatic environments. In addition, polymer beads which can be easily modified and complete adsorption task within 45 minutes and can be easily removed from the adsorption medium are reported.