Dual functional styrene-maleic acid copolymer beads: Toxic metals adsorbent and hydrogen storage

Abstract

When the concentration of heavy toxic metals exceeds the constraint, adverse health effects in human as well as in other living organisms materialize. Even though the entire evading of exposure to such metals is not possible, abstraction of such metals is effected by either physical or chemical processes such as adsorption, electrochemical methods, chemical precipitation, ultrafiltration and coagulation floatation. Precipitation or oxidation-reduction methods which convert the metal ions to insoluble compounds or extortionate sludges during the metal ion isolation may lead to a secondary pollution. Of these methods, adsorption is accepted as one of the most adequate and fiscal methods for the abstraction of metal ions at low ion concentrations. This chapter spotlights on the cross-linked styrene-maleic acid copolymeric beads for the adsorption of toxic heftily ponderous metal ions from aqueous systems and a material for hydrogen storage at room temperature. The suspension polymerized adsorbents were highly cross-linked to achieve better mechanical properties, and the porosity is introduced in the copolymer matrix. Discrete metal ions such as Cu(II), Co(II), Ni(II), Zn(II) and Au(III) and dyes such as Congo red (CR) were magnificently adsorbed by the highly crosslinked styrene-maleic acid copolymeric beads. XRD and SAXS results verified that these copolymer beads are additionally highly efficacious in in situ reduction of Au (III) ions from dihydrogen monoxide to Au (0) nanogold formation. The obtained experimental data were interpreted utilizing distinct adsorption isotherms and kinetic models such as Freundlich isotherm, Langmuir isotherm, Temkin isotherm, pseudo-first-order kinetic model, pseudo-second-order kinetic model and intraparticle diffusion models. Langmuir and Freundlich isotherm models were fitting for the adsorption of metal ions and are followed by pseudo-first-order kinetics in the initial stages and pseudo-second-order kinetics in the later stage of adsorption. Adsorption of metal ions was governed by intraparticle diffusion, and the desorption of metal ions was carried out utilizing dilute HCl. To assess the adsorption of Congo red dye molecules, composites of SMA with sugarcane molasses and sawdust were additionally synthesized, and the composite exhibits exceptional adsorption of Congo red dye which was validated utilizing distinct isotherm and kinetic models. The adsorption of hydrogen by the cross-linked SMA copolymer beads at room temperature withal was evaluated. The augmented rate of hydrogen adsorption was prosperously accomplished by the prelude of highly cross-linked interpenetrating networks inside the microspheres and porosity prelude into the copolymer network. The rate of hydrogen adsorption is virtually commensurable for the various cross-linked polymers and is independent of their divinylbenzene content. Even with perpetuated exposure of upto 65 hours, saturation cannot be accomplished; thus the slow micropore opening mechanism being involved that is more immensely colossal pores are filled first is envisaged. Enhanced cross-linked SMA beads modified with metal-organic frameworks (MOF) were synthesized by the slow diffusion of TEA. Maleic acid, which is a dicarboxylic acid, will influence the morphology of the MOFs composed in the polymer matrix and thus the hydrogen storage capacity. SMA functionalized with MOF samples exhibit hydrogen storage capacities where Zn-SMA complexes exhibit hydrogen storage capacity of 0.57 wt% at 300 K and 0.61bars. The ethanol adsorption and retention of the modified beads can be scrutinized for a cache of liquid hydrogen in fuel cells. Advantages in the utilization of these polymer beads in fuel cell encompass embedded catalyst activity, low cost, efficacious solvent and simultaneous hydrogen storage and operation at higher temperatures, thus providing a solution for current fuel cells.