Biomolecules mediated synthesis of magnetite nanoparticles and their application in efficient removal of heavy metals

Abstract

Due to rapid industrialisation, the wastewater released from various industries such as tannery, mining and metallurgical contain toxic contaminants including heavy metal ions which cause serious health hazards to human and other biological systems. In this thesis, magnetite nanoparticles (MNPs) were synthesised by chemical co-precipitation method modified with biomolecules such as starch and casein with an aim toward increase of the stability and prevent aggregation of nanoparticles for efficient heavy metal ions removal from wastewater. The synthesised magnetite nanoparticles were characterised by various physicochemical methods. Here, heavy metal ions such as lead and chromium solution were used for the adsorption/removal study using coated (starch coated magnetite nanoparticles, MNPST and casein coated magnetite nanoparticles, MNPCS) as well as uncoated MNPs. Parameters such as temperature, pH, contact time, and adsorbent dosage were optimised. Furthermore, we observed that the temperature of 308 K ( for Pb2+ and Cr6+), pH of 6.0 (for Pb2+ ) and 4.0 (for Cr6+), contact time of 30 min (Pb2+)and 60 min (Cr6+) and adsorbent dosage of 0.2 g (Pb2+ and Cr6+) were the optimal conditions for the maximum adsorption of metal ions. We further observed that removal of both Pb2+ and Cr6+follows pseudo-second-order kinetic model. However, experimental data fits better with Langmuir isotherm that indicates that monolayer adsorption took place and maximum adsorption capacities(Qm) were calculated and found that MNPST showing highest adsorption capacity for metal ions with 120.48 mg/g for Pb2+ and 99.0 mg/g for Cr6+. The regeneration and reusability study proved that magnetic nanoadsorbents can be reused for multiple cycles with a reduction of removal efficiency only by 12%. In conclusion,our study revealed that starch capped magnetite nanoadsorbents can demonstrate great potential to remove heavy metal ions from wastewater with excellent regeneration efficiency.