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

Abstract

δ-Bi 2 O 3 :M (M = S, Se, and Re) with an oxygendefective f luorite-type structure is obtained by a coprecipitation m e t h o d s t a r t i n g f r o m t h e b i s m u t h o x i d o c l u s t e r [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 ) ( 1 c ) , B i 1 4 O 2 0 ( S e O 4 ) (2 c ) , B i 1 4 O 2 0 ( R e O 4 . 5 ) (3 c ) , 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.

Dielectric and Optical Properties of δ‐Bi2O3 Quaternary Semiconducting Solid Solutions

“…Here, part of the W 6+ is replaced by Sc 3+ , increasing the oxygen vacancies. [ 25 ] Compared to other binary compositions, the lattice parameters are similar, [ 26 ] which implies that different cations in the site increase the disorder degree, but it is reached by doping that site with less doping concentration for the Bi 2 O 3 .…”

“…In terms of the optical bandgap, the quaternary system discussed here can be compared in part with the Re‐doped Bi 2 O 3 systems that absorb UV light only. [ 26 ] However, our materials could have applications in photocatalysis and water splitting, due to the absorption in the UV and visible region.…”

“…[25] However few compositions with quaternary systems have been studied. [26][27][28] Despite the number of research articles on quaternary compositions, up to this date, the Sc 3þ contribution on Bi 2 O 3 is still unknown because this cation in the ZrO 2 cubic structure increases the ionic conductivity. [29] As Bi 2 O 3 has the same fluorite symmetry, it is expected an increase in the transport properties at intermediate temperatures.…”

Discovery of Unconventional Proton‐Conducting Inorganic Solids via Defect‐Chemistry‐Trained, Interpretable Machine Learning

“…Bi 12 SiO 20 sillenite features a network of soft and distorted BiO 5 polyhedra, which are stabilized by a few rigid SiO 4 tetrahedra. [ 57 ] In this structure, protons occupy and conduct near the corner‐shared oxygen of the soft BiO 5 polyhedra while avoiding the rigid SiO 4 tetrahedra (Figure 5a–c). The proton conduction pathways formed in the sillenite are distinct from known compounds.…”

Ultrathin sillenite nanosheets with wide-spectrum response and high photocatalytic oxidation performance

“…Most prepared sillenites are in the format of nanoparticles that tend to agglomerate together and exhibit high concentrations of defects, which can act as recombination centers for photogenerated charges. [12][13][14] As a result, they show relatively low activity. At present, the prepared sillenite photocatalysts are all nanoparticles in structure.…”