Local structure and influence of bonding on the phase-change behavior of the chalcogenide compounds K1−xRbxSb5S8

High-Efficiency Visible Light Responsive Sulfide KSb5S8 Photocatalyst with a Layered Crystal Structure

The development of efficient photocatalysts for degrading environmental pollutants in wastewater has drawn considerable attention due to their great potential in industrial applications. Herein, we used a solvothermal method to prepare KSb5S8 with a layered crystal structure. The crystal structure of the as-synthesized samples was characterized by powder X-ray diffraction and transmission electron microscope imaging. Our UV-vis diffuse reflectance spectroscopy results indicated that KSb5S8 could absorb visible light, and its optical band gap was 1.62 eV. The photocatalytic activity of KSb5S8 was evaluated in the degradation of methyl orange. A degradation of 73% within 180 min was achieved under visible light irradiation, which was considerably higher than that of commercial P25 and g-C3N4. Theoretical calculations demonstrated that KSb5S8 was an indirect band gap semiconductor. The estimated effective mass of holes ( m h * ) was approximately two times greater than that of electrons ( m e * ) . The large ratio of m h * / m e * might promote separation of photo-induced carriers during the photocatalytic process. On the basis of the layered crystal structure and large m h * / m e * value, KSb5S8 was a high-performance photocatalyst capable of harvesting visible light. This study provides valuable insight that will aid the design of improved sulfide photocatalytic materials with layered crystal structures.

Wide Compositional and Structural Diversity in the System Tl/Bi/P/Q (Q = S, Se) and Observation of Vicinal P−Tl J Coupling in the Solid State

The compounds alpha-TlBiP2Se6 (I), beta-TlBiP2Se6 (II), TlBiP2S6 (III), Tl3Bi3(PS4)4 (IV), TlBiP2S7 (V), and Tl3Bi(PS4)2 (VI) were synthesized, and the structures of I-V were determined by single-crystal X-ray diffraction analysis. The structure of I features infinite chains. Those of compounds II, III, and V are layered. The structure of IV features a three-dimensional framework. Tl4Bi2(PS4)2(P2S6) (VII) was also prepared for comparison to the title compounds. The band gaps of each compound are 1.23, 1.27, 1.81, 1.88, 2.06, 1.98, and 1.97 eV for I-VII, respectively. Compounds I, III, IV, and VI melt congruently at 544, 595, 495, and 563 degrees C, respectively, and compounds II, V, and VII melt incongruently at 544, 509, and 600 degrees C, respectively. Solid-state 31P NMR spectroscopy of the reported compounds demonstrates chemical shifts and chemical shift anisotropies in line with related chalcophosphate materials. Evidence for two-bond P-Tl J coupling was observed in 31P NMR spectra (J=481-1781 Hz), and to the best of our knowledge, this is the first example of two-bond P-Tl J coupling and the first example of P-Tl coupling in the solid state. It was possible to assign chemical shifts of inequivalent 31P atoms from the same [PxQy]z- anion type based on different modes of metal ion coordination to the chalcogen. These assignments provide information about the vicinal metal ion contribution to the 31P chemical shift.