Study of the physical-chemical and sorption properties of SnO2 prepared by mechanochemical and microwave routes

Abstract

There are many methods for synthesis of tin dioxide SnO 2 , namely sol-gel, precipitation. However, these methods do not allow to regulate the physical-chemical properties in wide limits in the synthesis stage. The most commonly obtained samples are predominantly microporous as a rule. On the other hand, the meso-macroporous structure is required for the effective use of tin dioxide in sorption processes. The mechanochemical and microwave treatments can be used for eliminating mentioned above disadvantages. Therefore, the purpose of this work was to study the influence of the mechanochemical and microwave treatments on the physical-chemical and sorption properties of SnO 2 prepared by heterogeneous precipitation. SnO 2 gels and xerogels have been obtained by heterogeneous precipitation. The mechanochemical treatment was carried out in air and water at 300 rpm for 0.5 h in the form of dried xerogel as well as wet gel using a planetary ball mill Pulverisette-7. Initial wet gel was subjected to microwave treatment for 1 h using a high-pressure reactor «NANO 2000». We used XRD and DTA-TG analysis, FTIR spectroscopy, adsorption-desorption of nitrogen for characterization of initial and modified samples. The initial sample corresponds to the composition tin oxohydroxide with gross formula Sn 3 O 4 (OH) 4. For the modified samples a partial removal of the structural OH groups occurs. The initial sample is characterized by high values of specific surface area and high content of micropores. The specific surface area, total volume of pores, mesoporous size are increased as a result of the mechanochemical and microwave treatments. Formation of the secondary porosity that presented by meso-and macropores is peculiarity of xerogel milling in water. The cation exchange capacity under the most optimal conditions for the sorption of U(VI) ions (pH = 5-6, no background, cationic forms of uranium) for the initial sample was 0.82 mEq/g UO 2 2+. The mechanochemical and microwave treatments result in drastic increase in sorption capacity of tin oxohydroxide in relation to U(VI) ions. The greatest effect was observed for sample milled in the form of wet gel, the sorption capacity А of which increases almost in three times while distribution coefficient K d increases almost 70 times. In case of sorption on the background of 0.1 M NaHCO 3 (pH 8, model of block water of the Chernobyl Nuclear Power Plant), the sorption capacity of sample after mechanochemical treatment of gel increases by 43 % compared to initial sample from 0.31 to 0.43 mEq/g UO 2 2+. Thus, modified samples can remove both cationic and anionic forms of U(VI) ions in the solution. At the same time, for sorption of Cs(I) and Sr(II) ions, it has been found, that in both cases the mechanochemical and microwave treatments negatively affect to their removal in comparison with initial sample.

The Effect of Hydrothermal, Microwave, and Mechanochemical Treatments of Tin Phosphate on Sorption of Some Cations

“…However, the authors of these works pay attention to the conditions of the sorption of these cations but do not sufficiently study the influence of the physicochemical characteristics of adsorbents, the porous structure in particular, on their sorption properties. The study of this aspect was attempted by the authors of References [ 22 , 23 , 24 , 25 , 26 , 27 ] using tin, titanium, and zirconium dioxides and phosphates for the sorption of some cations.…”

“…As shown in studies [ 31 , 32 , 33 , 35 , 36 , 37 ], hydrothermal, microwave, and mechanochemical treatments provide the formation of just such a porous structure and, as a consequence, an improvement in the adsorption properties of some materials. The results of References [ 22 , 23 ] are remarkable in that the microwave and mechanochemical treatments of tin dioxide contribute to a significant increase in the sorption capacity, as well as the distribution coefficient of cesium, strontium, and uranium cations. The main reason for this is an increase in the volume and size of the mesopores, even with a reduction in the specific surface area measured using nitrogen adsorption.…”