SYNTHESIS, CHARACTERIZATION, AND EVALUATION OF OPTICAL PROPERTIES OF POTASSIUM NIOBATE (KNbO3) BY MICROWAVE-ASSISTED HYDROTHERMAL METHOD (MaHS)

Reference	Presenter	Authors (Institution)	Abstract
13-022	Tiago Bender Wermuth	Wermuth, T.B.(Universidade Federal do Rio Grande do Sul); BERGMANN, C.P.(UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL); Baibich, M.N.(Universidade Federal do Rio Grande do Sul); Americo, C.(Universidade Federal do Rio Grande do Sul); Ribeiro, T.M.(Universidade Federal do Rio Grande do Sul);	In this work, we evaluated the molar ratio effects of niobium and potassium precursors on the structure and morphology of potassium niobate powders prepared via microwave-assisted hydrothermal synthesis (MaHS). The raw materials used were niobium pentoxide (Nb2O5), potassium hydroxide (KOH), Milli-Q water and ethyl alcohol. Stoichiometric (Nb2O5: KOH – 1:2M) and non - stoichiometric (Nb2O5: KOH – 1:4; 1:8M) molar ratios were studied at different MaHS times (30, 60, 120 and 240 min) at 200 ºC. After the reaction, the system was inertially cooled to room temperature and the resulting product was washed with Milli-Q water and ethanol until complete pH stabilization, then centrifuged and dried at 60 °C for 12 hours. The obtained powders’ were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning (SEM) and transmission electronic microscopy (TEM). The average crystallite size calculated by the Scherrer equation agrees with the microscopy results. Also, the results show “nanotowers" formation in rather reduced synthesis times. Pure KNbO3 crystalline phases with orthorhombic symmetry were obtained at molar ratio 1:8M (Nb2O5: KOH), presenting a mean crystallite size ranging from 33.9 to 46.4 nm. KNbO3 light absorption curves were obtained using the diffuse reflectance (UV-Vis) spectrophotometry technique. The band-gap energy (Eg) was calculated using the Kubelka-Munk function. Different synthesis times presented values between 3.14 and 3.16 eV, indicating potential applications in photodegradation.
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