Investigation of manganese distribution between MnOx surface segregation and SnO2 crystal structure in SnO2/MnOx nanocomposites by inductively coupled plasma mass spectrometry

An approach to the determination of manganese separately on the surface and in the volume of SnO₂/MnO_x nanocomposites is proposed to establish the «synthesis conditions – composition» relationship. The approach includes the determination of the total content of Mn and Sn in solutions of composite and Mn on its surface by the ICP MS, followed by the calculation of the additive content in the volume of the material. Solutions of HCl, H₂C₂O₄, Na₄P₂O₇, and formaldoxime were studied as acid reduction etching reagents for the determination of manganese on the surface. It is shown that when the surface of the samples is treated with a formaldoxime solution at 20°C, manganese dissolves on the surface of the sample, while tin does not pass into the solution. A 4- step temperature program transferring SnO₂ synthesized at high temperature to a solution using a mixture of acids in an autoclave with microwave intensification has been developed for subsequent determination of the Mn and Sn content by the ICP MS method. It is shown that the application of internal Mn/Cu and Sn/Rh standards makes it possible to reduce the relative standard deviation of the analysis results (s_r) to 0.02. Based on the obtained results of the determination of Mn and Sn on the surface and the total content, the distribution of manganese in SnO₂/MnO_x composites between the surface and volume is calculated. It is shown that manganese is distributed unevenly between the volume and the surface of the samples. As the annealing time increases, the manganese content on the surface of the composite decreases due to the diffusion of the additive into the SnO₂ particle.

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