Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi 2 O 3 :M (M = S, Se, and Re).

δ-Bi 2 O 3 :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 [Bi 38 O 45 (OMc) 24 (dmso) 9 ]·2dmso·7H 2 O ( A ) in the presence of additives such as Na 2 SO 4 , Na 2 SeO 4 , NH 4 ReO 4 , Na 2 SeO 3 ·5H 2 O, and Na 2 SO 3 . The coprecipitation of the starting materials with aqueous NaOH results in the formation of alkaline reaction mixtures, and the cubic bismuth(III)-based oxides Bi 14 O 20 (SO 4 ) ( 1c ), Bi 14 O 20 (SeO 4 ) ( 2c ), Bi 14 O 20 (ReO 4.5 ) ( 3c ), Bi 12.25 O 16.625 (SeO 3 ) 1.75 ( 4c ), and Bi 10.51 O 14.765 (SO 3 ) 0.49 (SO 4 ) 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 Bi 14 O 20 (SO 4 ) ( 1t ) and Bi 14 O 20 (SeO 4 ) ( 2t ), while compound 3c is transformed into the tetragonal modification of Bi 14 O 20 (ReO 4.5 ) ( 3t ) after calcination at T = 700 °C. Compounds of the systems Bi 2 O 3 -SO x ( x = 2 and 3) and Bi 2 O 3 -Re 2 O 7 are thermally stable up to T = 800 °C, whereas compounds of the system Bi 2 O 3 -SeO 3 completely lose SeO 3 . 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.