Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi2O3:M (M = S, Se, and Re).

δ-Bi2O3:M (M = S, Se, and Re) with an oxygen-defective fluorite-type structure is obtained by a coprecipitation method starting from the bismuth oxido cluster [Bi38O45(OMc)24(dmso)9]·2dmso·7H2O (A) in the presence of additives such as Na2SO4, Na2SeO4, NH4ReO4, Na2SeO3·5H2O, and Na2SO3. The coprecipitation of the starting materials with aqueous NaOH results in the formation of alkaline reaction mixtures, and the cubic bismuth(III)-based oxides Bi14O20(SO4) (1c), Bi14O20(SeO4) (2c), Bi14O20(ReO4.5) (3c), Bi12.25O16.625(SeO3)1.75 (4c), and Bi10.51O14.765(SO3)0.49(SO4)0.51 (5c) are obtained after microwave-assisted heating; formation of compound 5c is the result of partial oxidation of sulfur. The compounds 1c, 2c, 4c, and 5c absorb UV light only, whereas compound 3c absorbs in the visible-light region of the solar spectrum. Thermal treatment of the as-prepared metastable bismuth(III) oxide chalcogenates 1c and 2c at T = 600 °C provides a monotropic phase transition into their tetragonal polymorphs Bi14O20(SO4) (1t) and Bi14O20(SeO4) (2t), while compound 3c is transformed into the tetragonal modification of Bi14O20(ReO4.5) (3t) after calcination at T = 700 °C. Compounds of the systems Bi2O3-SOx (x = 2 and 3) and Bi2O3-Re2O7 are thermally stable up to T = 800 °C, whereas compounds of the system Bi2O3-SeO3 completely lose SeO3. Thermal treatment of 4c and 5c in air results in the oxidation of the tetravalent to hexavalent sulfur and selenium, respectively, upon heating to T = 400-500 °C. The as-prepared cubic bismuth(III)-based oxides 1c-5c were studied with regard to the photocatalytic decomposition of rhodamine B under visible-light irradiation with compound 3c showing the highest turnover and efficiency.