Structural investigation of phosphonium-based ionic liquid impregnated mesostructured silica nanoparticles and application towards the adsorption of Pb(II)

Abstract

Adsorption has been widely used in waste water treatment due to its simplicity and cost-effective process. One of the popular adsorbent was silica due to their advantageous properties. Immobilizing additive onto particular adsorbent is one of the way to enhance adsorption capacity. Immobilizing ionic liquid (IL) onto silica-based support could alleviate the drawbacks of IL and enhance the adsorption capacity. Thus, silica-based materials, silica and mesostructured silica nanoparticle (MSN), were impregnated with a phosphonium-based ionic liquid (IL), trioctyldodecylphosphonium bromide (P8,8,8,12Br), which was designated as IL@SIL and IL@MSN. The structural variation of the support greatly impact the adsorbent performance. The results showed that IL@MSN with superior surface properties exhibit a faster reaction kinetic and lower thermodynamic barrier for the adsorption of Pb(II). Both adsorbents followed a pseudo second-order kinetic and chemically adsorbed Pb(II). IL@MSN showed a higher adsorption capacity in both batch and column adsorption than that of IL@SIL. The equilibrium data of both adsorbents fitted well with the Freundlich isotherm model with maximum adsorption capacity of 256.4 and 142.9 mg g-1 for IL@MSN and IL@SIL, respectively. In agreement with the batch experiment, IL@MSN showed a higher adsorption capacity in column adsorption than that of IL@SIL (325.6 and 242.2, respectively). Column adsorption with IL@MSN was able to achieve 94% removal of Pb(II) while IL@SIL achieved 70%. Superior surface properties of IL@MSN allowed a longer duration of column exhaustion than that of IL@SIL. The column experimental data showed a good fit with the Thomas model. Immobilized IL on silica based materials has potential as an adsorbent for heavy metals and structural variation over the support material played an important role.