Effect of the Method of Synthesis on the Photocatalytic and Sorption Properties for Potassium Polytitanates Doped with D
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HESIS AND PROPERTIES OF INORGANIC COMPOUNDS
Effect of the Method of Synthesis on the Photocatalytic and Sorption Properties for Potassium Polytitanates Doped with Di- and Trivalent Metal Ions N. A. Morozova, *, O. Yu. Sinelshchikovaa, N. V. Besprozvannykha, and T. P. Maslennikovaa a
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, 199034 Russia *e-mail: [email protected] Received February 3, 2020; revised March 19, 2020; accepted March 27, 2020
Abstract—The paper describes the results of a physicochemical study of materials obtained in the K2O– MO(M2O3)–TiO2 systems (M = Ni, Mg, Al, Fe, Cr) by pyrolysis of citrate–nitrate compositions and by coprecipitation followed by hydrothermal treatment. It was shown that the nanoparticles formed in the hydrothermal process have a high sorption capacity towards the model dye (methylene blue), but do not show a noticeable photocatalytic activity. The use of the citrate–nitrate method for the synthesis of nanopowders provides materials with a markedly lower sorption capacity, but with a higher photocatalytic activity. Spectral studies were performed to estimate the band gap width of the synthesized samples. As a result, the optimal compositions for obtaining sorbents and photocatalysts in these systems were identified. Keywords: citrate, nitrate method, hydrothermal treatment, spectrophotometry, nanotubes DOI: 10.1134/S0036023620080124
INTRODUCTION Quite a number of publications of the last several decades were devoted to various forms of titanate nanomaterials. Depending on the composition and structure, these materials can be applied in various fields: power engineering where they were proposed for lithium ion and solar batteries; environment protection for the treatment of water and air using sorption, filtering, and photocatalytic processes; as special photochromic coatings possessing controlled wettability; and as friction materials [1–3]. The pristine titanium oxide is the most studied and demanded photocatalyst for decomposition of organic contaminants. The TiO2 band gap (3 eV for rutile; 3.2 eV for anatase; and 3.3 eV for brookite) is such that ultraviolet irradiation leads to excitation of electron–hole pairs. This process is used in solar batteries and in various photocatalytic reactions [4–8]. However, radiation absorbed by titanium oxide spans only 4–5% of the solar spectrum; therefore, the main goal of the current research is to make TiO2 absorb in the visible region. This can be attained by either an appropriate shift of the absorption edge, which is characteristic of complex titanium oxides, or sensitization of TiO2 by surface additives [9–12]. A key factor affecting the catalytic, photocatalytic, and sorption activity of materials in heterogeneous processes is the particle size and morphology. The preparation of compounds in the nano-sized state can increase the specific surface area
by a factor of tens [13–15] and decrease the probability of electron–hole recombination in photocatalytic reactions [
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