Abstract

Magnetite nanoparticles were synthesized by a simple and ecofriendly method using onion peel (MNp-OP) and corn silk extract (MNp-CS), in order to develop new low-cost adsorbents for arsenic removal from groundwater. As a point of comparison, magnetite nanoparticles were also synthesized with a conventional chemical process (MNp-CO). The antioxidant potential of onion peel and corn silk extracts was determined using ferric reducing antioxidant power (FRAP) and free radical (DPPH) scavenging assays, including the total phenolics, flavonoids and tannins contents. The synthesized magnetite nanoparticles were characterised using different techniques (Scanning electron microscope/Energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) surface area analyzer). The adsorption capacity of MNp-OP and MNp-CS and the arsenic removal mechanism of these novel adsorbents was investigated through kinetic and equilibrium experiments and their corresponding mathematical models. Characterisation of MNp-OP and MNp-CS shows high BET specific surface areas of 243 m2/g and 261 m2/g, respectively. XRD and FTIR analysis confirmed the formation and presence of magnetite nanoparticles. The arsenic adsorption mechanism on MNp-OP, MNp-CS and MNp-CO involves chemisorption, intraparticle and external diffusion. Maximal adsorption capacities of MNp-OP, MNp-CS and MNp-CO were 1.86, 2.79, and 1.30 mg/g respectively. The green synthesis applied using onion peel and corn silk extracts was cost effective and environmentally friendly, and results in adsorbents with a high capacity for arsenic and magnetic properties, making them a very promising alternative approach in the treatment of arsenic contaminated groundwater.

Highlights

  • The presence of arsenic in groundwater, either from anthropogenic or natural sources, is a serious problem in many different parts of the world

  • It can be seen that the surfaces of all three materials are rough and contain a large number of particles that are irregular in shape and size

  • A large number of aggregated particles on the surface of these materials could be attributed to nanostructures and magnetic properties, which contribute a tendency for agglomeration and aggregation

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Summary

Introduction

The presence of arsenic in groundwater, either from anthropogenic or natural sources, is a serious problem in many different parts of the world. Mostly in rural and developing countries, are exposed to high levels of arsenic via the intake of arsenic rich groundwater [1]. Various technologies have been employed for arsenic removal from groundwater including coagulation, membrane separation, ion exchange and adsorption [4]. Among these techniques, adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities, and generally lower operation costs [5,6,7,8]

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