A study on removal of Cr(III) from aqueous solution using biomass of Cymbopogon flexuosus immobilized in sodium alginate beads and its use as hydrogenation catalyst

Abstract A novel strategy for wastewater recycling by removing Chromium [Cr(III)] from water, utilizing the treated water for agricultural purposes and the saturated adsorbent used as the catalyst for p-nitrophenol reduction was successfully incorporated for sustainable environmental application. Removal of Cr(III) by adsorption on Cymbopogon flexuosus waste material entrapped within sodium alginate beads was investigated. Sorption behavior of Cr(III) on to the biosorbent phase showed to follow pseudo first order kinetic model. The thermodynamic variables such as ∆G (−2.59 kJ mol −1 ), ∆H (4.57 kJ mol −1 ) & ∆S (0.024 J mol −1 K −1 ) was evaluated and the corresponding values ensure on favoring endothermic nature of adsorption. Isotherm studies strongly supports on Freundlich model (R 2  = 0.99) rather than Langmuir isotherm model (R 2  = 0.93), Temkin (R 2  = 0.89) and Dubinin-Radushkevich (R 2  = 0.77) confirming on multilayer chemisorption behaviour with immobilized Cymbopogon flexuosus having the maximum loading capacity of 121.64 mg.g −1 . The sorption of Cr(III) by immobilized Cymbopogon flexuosus was quantitative (99.9%) at the optimum condition: Cr(III) concentration:50 ppm, pH:4.5, agitation speed:150 rpm, temp.:298 K. The above sorption mechanism was well supported by the intraparticle diffusion model. Response Surface Methodology (RSM) was also introduced to investigate for optimization of process parameters during removal of Cr(III) from aqueous solution. The adsorbent material saturated with Cr(III) ascertained first order kinetics with k app value of 2.5 × 10 −1 min −1 for catalytic reduction of toxic p-nitrophenol to p-aminophenol. The phytotoxicity study of treated water on Zea mays plant has been analyzed and a considerable result obtained with regards to the usage of Cr(III) contaminated-water in plant growth. The change in the crystal structure, surface morphology and surface functional groups of the adsorbent before and after the process was analyzed and well ascertained by XRD, SEM and FTIR analysis. This investigation suggests the possible application of this low-cost material in fine chemical manufacturing.