Short communicationAmorphous nanostructured composites Al2O3:nC with enhanced sorption affinity to La(III), Ce(III), U(VI) ions in aqueous solution
Graphical abstract
Introduction
Anthropogenic emissions of heavy and radioactive metals in industrial waste water lead to their accumulation in the environment, which may in time become a threat to ecosystems and human health since these pollutants cannot be biodegraded into non-hazardous components [1]. Therefore, waste water treatment aimed at its recycling is of vital importance. The modern technologies for removal of heavy and radioactive metal ions make use of some traditional methods including chemical deposition, reverse osmosis, electrochemical treatment methods, ion exchange, membrane filtration, coagulation, extraction, radiation and adsorption [2]. The adsorption method based on the use of low-cost natural and synthetic sorbents holds much promise due to its profitability, high efficiency and ease of operation [3], [4], [5], [6], [7]. It can be used in combination with the corresponding desorption method, which opens a prospect not only of ground disposal, but also of recovery of metals extracted from solution. Synthetic sorbents include porous oxide and carbon materials that have long been in use and proved to be effective for removal of Cr(VI), Pb(II), Cd(II), Ni(II), Eu(III), Cm(III), U(VI) ion micro impurities from aqueous solutions [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. However, most of these materials have a low sorption capacity and selectivity limiting the scale of their application.
Recently, in order to realize the synergistic effect based on the combination of the properties of metal oxide and carbon, attempts were made to synthesize composites of the nominal composition MexOy:nC, which would possess a higher stability and enhanced sorption properties compared to individual components. Here, the primary focus of specialists was on the development of synthesis methods allowing one to control the dimensional, microstructural and morphological characteristics of materials, which affect their functional properties. It was shown that the produced recently oxide–carbon nanocomposites Al2O3:nC with a spherical shape of aggregates can be applied for removal of heavy metals, as well as uranium and americium, from solutions [20], [21], [22]. In comparison with pure aluminum oxide, Al2O3:nC nanocomposites are characterized by a higher sorption activity with respect to cations of toxic and radioactive elements in aqueous solutions. However, judging by the available literature data, the synthesis of such nanostructures with a special morphology and microstructure of aggregates is usually a complex resource-consuming process with a low product yield unfavourable to large-scale production.
In order to meet the increasing demands of industry and ecology for new sorption materials, it is extremely important to develop effective methods of synthesis, which would make it possible to control the dimensional, morphological and microstructural characteristics of particles and thereby to form a set of functional properties peculiar to intended practical applications. This was the main prerequisite for choosing the aim of this work – synthesis of novel nanostructured composite materials of the nominal composition Al2O3:nC that will be applied as sorbents in technologies for removal of heavy and radioactive metals from aqueous solutions. Ce(III) and La(III), as well as U(VI) ions were chosen for the evaluate the performance of Al2O3:nC composite as a sorbent in aqueous medium.
Section snippets
Experimental methods
Al2O3:nC was synthesized by thermolysis of the precursor produced by thermal treatment of aluminum nitrate Al(NO3)3·9H2O solution (99.95%) in ethylene glycol (99.5%). Generally, 37.5 g aluminum nitrate was dissolved in 50 ml ethylene glycol at 40 °C. The resulting transparent solution was heated at 120 °C until it transformed into a bulk viscous mass and then into a white loose powder, which was used as a precursor. To produce Al2O3:nC, the precursor was heated in helium atmosphere at 700, 900
Results and discussion
At first, the precursor was obtained by heating of aluminum nitrate with ethylene glycol. This process was accompanied by formation of gaseous products, among which, judging by their yellowish color and specific smell, there is nitrogen dioxide. The obtained precursor is an X-ray amorphous material. The IR spectrum of the precursor produced is shown in Fig. 1. The intensive wide bands with absorption maxima at 3397 cm−1 and 2961 cm−1 observed in the IR spectrum correspond to the stretching
Conclusion
We report a new procedure for the synthesis of nanostructured oxide–carbon composites of the nominal composition Al2O3:nC, built from jointly grown layers of amorphous aluminum oxide and carbon having a morphology similar to that of multilayer graphene. In helium atmosphere, the amorphous state of aluminum oxide in the composite is preserved up to 1000 °C, above which it crystallizes with the formation of γ-Al2O3 nanoparticles (<10 nm in diameter). This synthesis procedure allows to enhance
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The X-ray study was carried out at the Multiple–Access Centre for X–ray Structure Analysis at the Institute of Solid State Chemistry, UB RAS. The UV-Vis spectra were recorded on equipment of the Center for Joint Use “Spectroscopy and Analysis of Organic Compounds” at the Postovsky Institute of Organic Synthesis, UB RAS. This work was carried out in accordance with the scientific and research plans and the state assignment of the Institute of Solid State Chemistry, UB RAS (grant No.
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