Abstract
Zeolite adsorbents and ion exchangers reducing the concentrations of contaminants in aqueous medium, containing bioactive metals and endowed with bactericidal properties are promising for application in environmental protection practice and medicine. Phillipsite has a high ion exchange capacity and can be used to produce such materials. Silver-, copper-, and zinc-containing micro-mesoporous zeolite materials have been prepared on the basis of natural phillipsite from the Shukhuti field, Western Georgia(Saqartvelo), using ion-exchange reactions between grinded and washed by dilute hydrogen chloride solution zeolite and a salt of a corresponding transition metal in the solid phase followed by washing with distilled water. Synthesized in such way adsorbent-ion-exchangers are characterized by chemical analysis and sorption data (nitrogen adsorption-desorption isotherms at 77 K and water vapour sorption at room temperature), powder X-ray diffraction patterns, Fourier transform infra-red spectra, and scanning electron microscope images. Obtained materials keep the crystal structure and general sorption and ion-exchange properties of phillipsite, they contain up to 230 mg/g of silver, 66 mg/g of copper, and 86 mg/g of zinc, which is several times higher than the content of bioactive metals in the cation-exchange forms of clinoptilolite and synthetic zeolites obtained by ion exchange in the liquid phase described in the literature. Prepared silver-, copper-, and zinc-containing phillipsites show bactericidal and bacteriostatic activity towards Escherichia coli regardless of whether the number of released ions of the bioactive metal reaches the minimum inhibitory concentration in solution. The procedure of dry ion-exchange synthesis leads to an increase in the dispersion of the material, but does not affect the developed mesoporous system of phillipsite and the total pore volume averaging 0.285 cm 3 /g. The compliance of proposed method for preparation of silver-, copper-, and zinc-containing forms of phillipsite with high environmental standards is confirmed by its low Sheldon’s factor E in comparison with the similar green chemistry metrics of conventional methods of the ion exchange in solutions.
Highlights
The environmental use of zeolites, alunimosilicates with the general formula MenSixAlnO2(n+x)·mH2O (Me = Na, K, ... 1⁄2Ca, 1⁄2Mg, ...), is based on the complex of their properties, especially on the capability of zeolites to enter into ion exchange reactions with the participation of Me+n ions compensating the negative charge of the crystal lattice constructed from alternating SiO4 and AlO4– tetrahedra.Many different studies have demonstrated effectiveness of zeolites in reducing the concentrations of contaminants in water [1,2,3,4,5,6].The complexity of aquatic systems demands special attention in the selection and preparation of materials for water purification
Chemical composition of natural phillipsite and its modified forms with a maximum silver, copper or zinc content are listed in the Table 2 in terms of the empirical formulas x(MaNabKcCadMgeMef)[AlxSiyO32]·nH2O, where Me+ ion corresponds to the impurity metals, M = Ag+, 1⁄2Cu2+, or 1⁄2Zn2+, and deviations are given in parentheses
Degree of replacement is quite high, the obtained modified forms contain a large amount of transition metals – up to 230 mg/g (2.14 mmol per 1 g of zeolite) of silver in the AgPSH sample, up to 66 mg/g (~1 mmol per 1 g of zeolite) of copper in the CuPSH sample, and up to 86 mg/g (~1.3 mmol per 1 g of zeolite) of zinc in the ZnPSH sample
Summary
Many different studies have demonstrated effectiveness of zeolites in reducing the concentrations of contaminants (heavy metals, anions and organic matter) in water [1,2,3,4,5,6]. The chemical behaviour of natural zeolites in different aqueous environments depends on the structural characteristics and chemical composition [5, 6]. The possibilities of using natural and synthetic zeolites to extract ammonium ions and heavy metals from water were well studied in the last century [7,8,9,10], but research into specific natural zeolites continues [11,12,13,14] including studies of adsorbents for the removal of organic pollutants [15]. Nowadays, modified natural zeolites are increasingly used for biological treatment of water, precisely for surface binding of biological agents from water
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