Rapid selective separation and recovery of a specific target dye from mixture consisted of different dyes by magnetic Ca-ferrites nanoparticles
Graphical abstract
CaFe2O4 magnetic nanoparticles (MNPs) as a novel selective adsorbent showed an excellent high affinity to anionic congo red (CR) in multi-component dye wastewater.
Introduction
There are significant amounts of unused dyes in the wastewater released from the textile, rubber, plastic, paper printing and dyeing industries [1]. The dyes in effluents have caused serious concerns for their adverse effects on living bodies and ecosystems, and can be toxic and carcinogenic to organisms and humankind. In order to decrease the loss of dyes and diminish the pollution, it is very necessary to recover and treat the dye containing effluents before discharge. Various physicochemical methods have been successfully applied for dyes removal, such as precipitation, flocculation, ion-exchange, photodegradation, chemical oxidation and even microbiological treatment [2], [3], [4], [5]. Among these approaches, adsorption is regarded as one of the competitive strategies because of its high efficiency, economic feasibility and simplicity of operation [6], [7].
Numerous studies have considered adsorption process for single component systems [8], [9], [10], and few studies have been performed in multi-component systems [11], [12]. Due to the co-existence of multiple components in real dye containing effluents and the limited adsorption capacity of adsorbents, the treatment of dye wastewater is troublesome and cost-consuming. Indeed, little attention has been paid to the selective adsorption of multi-dye systems. Recently, based on their efforts on the selective adsorption of dyes [13], Gao et al. demonstrated that anionic methylene orange in effluents could be selectively separated and retrieved by mesoporous Cu2O submicro-spheres. Liang et al. reported that SnNb2O6 nanosheet would selectively remove cationic dyes from a mixture [14]. Kyzas et al. prepared two water-compatible molecularly imprinted polymers (MIPs) for selective separation of basic and reactive dyes from simulated effluents [15]. Zhao et al. reported that CR-containing cationic dye mixtures would be selective removed from a dye wastewater mixture by in-situ hybridization with growing calcium carbonate [16]. The achievement of selective removal of targeted pollutants among the mixture may enhance the economical feasibility of the adsorption process in wastewater treatment. However, controlling adsorption of targeted pollutants via adsorbents is a challenging issue since it is difficult to choose a more appropriate adsorbent with molecular recognition property. Consequently, the development of adsorption materials with a high performance to selectively adsorb targeted molecular species is of great significance.
To achieve the molecular recognitive adsorption efficiently, adsorbents should show high selectivity for targeted organic molecules and possess high surface area to provide more active adsorption sites. Based on this idea, we synthesized a novel spinel magnetic ferrite, i.e. p-type CaFe2O4 magnetic nanoparticles which can be prepared from low-cost materials such as iron and calcium. The magnetic characteristics make CaFe2O4 easier to separate and recycle upon the application of an external magnetic field. It is expected that CaFe2O4 nanoparticles can be applied as promising adsorbents for selective removal or enrichment of targeted dye from mixture consisted of different dyes.
In this work, magnetic nano-CaFe2O4 was applied to the selective adsorption for the first time. CaFe2O4 exhibited molecular recognitive adsorption for CR dye from the ternary dye system, suggesting significantly high selectivity of the adsorbent. The selective adsorption mechanism was also studied in detail. Meanwhile, we have put forward preferable reuse of the adsorbents as well as the dyes. The results gained in this study could be useful for further applications of system design in the treatment of practical dye-containing effluents.
Section snippets
Materials and analysis method
Anionic congo red (CR) and methyl orange (MO) dyes and cationic rhodamine b (RhB) dye were selected as adsorbates to investigate the adsorption selectivity. The chemical structures of the dyes are shown in Fig. 1. These dyes were purchased from Sinopharm Chemical Reagent Co., Ltd. China, and used without further purification.
The dye concentration was analyzed using a UV–vis–NIR cary 5000 spectrophotometer (Varian, USA) at their corresponding maxima wavelength. The mixed dyes were also detected
Characterization of CaFe2O4 MNPs
Fig. 2a shows XRD patterns of as-synthesized ferrite powders calcined at different temperatures. It was observed that the diffraction peaks could be well indexed to the cubic spinel CaFe2O4 and the crystallinity was improved with increase of calcinations temperature. When calcinations temperature was above 673 K, some new diffraction peaks appeared, which indicated the presence of α-Fe2O3. The grain sizes (Dc) of the synthesized CaFe2O4 MNPs were calculated using the Debye–Scherrer equation [18]
Conclusions
In conclusion, the CaFe2O4 MNPs were synthesized by a simple sol–gel process. The synthesized CaFe2O4 MNPs were first used for the selective removal of CR from multi-component dye system. A good adsorption selectivity with a high separation factor was achieved in the CR-MO-RhB ternary mixture. H-bonding interaction between the functional groups (NH2) in CR and OH of absorbent surface was conceived as the main force involved in the selective adsorption. Moreover, the CaFe2O4 MNPs demonstrated
Acknowledgements
This project was supported by the National Nature Science Foundation of China (NSFC51178212), Liaoning Provincial Department of Education Innovation Team Projects (LT2012001), the Shenyang Science and Technology Plan Project (F12-277-1-69 and F13-289-1-00), China, the Foundation of 211 Project for Innovative Talent Training, Liaoning University and the Foundation for Young Scholars of Liaoning University (No. 2012LDQN06). The authors also thank their colleagues and other students who
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