title: Nano modification of NZVI with an aquatic plant Azolla filiculoides to remove Pb(II) and Hg(II) from water: Aging time and mechanism study.
abstract: This paper reports the preparation and stabilization of nano zero valent iron (NZVI) on a modified aquatic plant, Azolla filiculoides, and investigates its potential for the adsorption/reduction of Pb(II) and Hg(II) ions from aqueous media even after six months of storage in the lab condition. XRD, TEM and zeta potential results demonstrated that the Azolla-NaOH could be a good stabilizer of aged NZVI (six months) and the green support suppressed the oxidation and aggregation of immobilized NZVI. Kinetic and equilibrium models for lead and mercury ions uptake were developed by considering the effect of the initial Pb(II) and Hg(II) concentrations, contact time, adsorbent dosage, initial pH and effect of temperature. The contact time to obtain equilibrium for maximum uptake by Azolla-OH-NZVI was 20min. The removal of toxic metal ions has been monitored in terms of pseudo-first- and -second-order kinetics, and the Freundlich and Langmuir isotherms models have also been utilized to the equilibrium uptake results. The uptake kinetics followed the mechanism of the pseudo-second-order equation for all systems studied, confirming chemical sorption as the rate-limiting step of adsorption mechanisms and not involving a mass transfer in solution. The thermodynamic results confirmed that the uptake of Pb(II) and Hg(II) ions were feasible, spontaneous and endothermic at 25-80°C. XRD and zeta potential data displayed the existence of Pb(0) and Hg(0) on the Azolla-OH-NZVI surface. The nanobioadsorbent revealed high recyclability due to its reasonable uptake efficiency after 7th adsorption-desorption cycles. The proposed nano biocomposite could also be utilized to uptake Pb(II) and Hg(II) ions from the real water (Anzali lagoon water). However, coated NZVI with Azolla filiculoides as a green and environmentally friendly support suppressed rapid oxidation and aggregation of the immobilized NZVI, therefore vastly enhancing the probability of environmental transport and reducing the sedimentation and potential for toxicity.
authors.affiliation: Department of Chemistry, Shiraz Branch, Islamic Azad University, P.O. Box 71955-149, Shiraz, Fars, Iran. Electronic address: mohammadarshadi@yahoo.com.
authors.forename: M
authors.initials: M
authors.lastname: Arshadi
authors.affiliation: Department of Chemistry, College of Arts and Sciences, University of Cincinnati, 404 Crosley Tower, Cincinnati, OH 45221-0172, United States.
authors.forename: M K
authors.initials: MK
authors.lastname: Abdolmaleki
authors.affiliation: Mehr Petrochemical Company, Phase (PSEEZ), Assaluyeh, Bushehr, Iran.
authors.forename: F
authors.initials: F
authors.lastname: Mousavinia
authors.affiliation: Department of Fishery, University of Guilan, P.O. Box 1144, Sowmesara, Iran.
authors.forename: S
authors.initials: S
authors.lastname: Foroughifard
authors.affiliation: Department of Chemical and Polymer Engineering, Yazd University, Yazd, Iran.
authors.forename: A
authors.initials: A
authors.lastname: Karimzadeh
mesh_terms: D000327:Adsorption; D059001:Aquatic Organisms; D029624:Ferns / Q000737:chemistry*; D005618:Fresh Water / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D007854:Lead / Q000302:isolation & purification*; D008628:Mercury / Q000302:isolation & purification*; D053761:Nanocomposites / Q000737:chemistry* / Q000648:ultrastructure; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D014874:Water Pollutants, Chemical; D007854:Lead; D007501:Iron; D008628:Mercury
keywords: Aquatic plant; Azolla filiculoides; Lead; Mercury; NZVI; Nanobioadsorbent