Surface chemical properties and adsorption of Cu (II) on nanoscale magnetite in aqueous solutions
Research highlights
► In-depth characterization for magnetite studied. ► The maximum adsorption capacity was found to be 0.1354 m mol/g for adsorbent at 25 °C. ► Adsorption reached the equilibrium before 60 min for this adsorbent. ► The adsorption process was found to be pH dependent. Also, the adsorption behavior was a function of the concentration and type of supporting electrolyte. ► The adsorption data were fitted by several kinetic and isothermal equations.
Introduction
Environmental contamination by heavy metals is of growing concern because of health risks on humans and animals. Bivalent copper (Cu (II)) is a priority pollutant [1] and can cause hemolysis, liver and kidney damage, irritation of upper respiratory tract, gastrointestinal disturbance, diarrhea. The main anthropogenic pathway through which Cu (II) enters the water bodies is via waters from various industrial processes such as dyeing, paper, petroleum, copper/brass-plating and copper-ammonium rayon [2]. Conventional methods for removing heavy metals ions from aqueous solutions principally include chemical precipitation, ion-exchange, reverse osmosis and adsorption. Although the effectiveness of these processes has been sufficiently proven, they present some inconveniences and limitations due to high energy requirements, incomplete metal removal, and a large amount of sludge production [3].
Recently, new technology researches involving the removal of heavy metals from wastewaters have directed attention to nanosorbents based on their large specific area and chemical functional groups. Removal of heavy metals by nanoparticles would provide significant reductions in cost, time, and labor to industry and results in improved environmental stewardship [4]. Magnetite is widespread in the environment and recently, some researches have focused on utilization of nanoscale magnetite to remove heavy metals mainly including Cr (VI) [3], [5], [6], Hg (II) [7], As (V) [8], Sb (V) [9], Se (IV) [10], and V (V) [5]. These studies mainly investigated the reaction mechanism (oxidation–reduction interactions) on the magnetite surface.
Nano-technology has been considered as one of the most important recent advancements in science and technology. In recent years, great interests have arisen in the application of nanoporous adsorbents for environmental remediation technologies. Magnetite is the most widely used adsorbent for the removal and separation of proteins and other biological molecules, such as bovine serum albumin, etc. The adsorption characteristics of the material accompanied by its magnetic nature make magnetite a good choice for remediation technologies based on High Gradient Magnetic Separation (HGMS) [11]. However, very few experimental studies were reported in the literature on the other common heavy metal ions (e.g. Cu (II)) interactions with nanoscale magnetite. In this work, the magnetite nanoparticles were tested for removal of Cu (II) from aqueous solution. The overall purpose is to study the effectiveness of magnetite nanoparticles on the removal of Cu (II) by investigating the adsorption kinetics and mechanism of Cu (II) onto magnetite nanoparticles. In addition, an in-depth understanding of the dependence of metal adsorption on ionic strength and electrolyte type is critical to unraveling the role of metal adsorption in nature because wastewaters are composed of many types of electrolytes [12]. Accordingly, the effects of ionic strength and electrolyte types on Cu (II) uptake were also investigated.
Section snippets
Materials and methods
All chemical reagents used were of analytical grade or better. All glassware was washed with 1 mol/L HNO3 and rinsed thoroughly with deionized water prior to use. Solutions were made with deionized water purified by passage through a milli-Q water system. The magnetite samples were purchased from Nanjing Emperor Nano Material Co., Ltd, China and used as received.
Particle characterization
The magnetite sample applied was characterized by X-ray powder diffraction (XRD) as illustrated in Fig. 1 and the result shows that diffraction patterns and relative intensities of all diffraction peaks match well with those of JCPDS card 72–2303 for magnetite. Also, the sample has the characteristics of bulk magnetite crystallite phase and the broad peaks suggest the nanocrystallite nature of magnetite particles [14]. The resulting mean particle diameter was approximately 10 nm for the
Conclusions
The magnetite nanoparticles were applied effectively in the removal of Cu (II) from aqueous solutions due to higher surface area and reactive hydroxyl surface sites. Surface chemical properties of magnetite at 25 °C in aqueous suspensions were investigated. The removal efficiency of Cu (II) strongly depended on pH, ionic strength and supporting electrolyte types. The adsorption process was found to follow the pseudo-second-order equation and the Fractional power equation. The equilibrium data
Acknowledgements
This work was supported by China National Science Foundation (grant 20977040).
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