Narrow Results

This work presents the results of synthesis and characterization of polycrystalline $n$-type Bi₂S₃ thin films. The films were grown through a chemical reaction from co-evaporation of their precursor elements in a soda-lime glass substrate. The effect of the experimental conditions on the optical, morphological structural properties, the growth rate, and the electrical conductivity $(\sigma )$ was studied through spectral transmittance, X-ray diffraction (XRD), atomic force microscopy (AFM) and $\sigma$ versus $T$ measurements, respectively. The results showed that the films grow only in the orthorhombic Bi₂S₃ bismuthinite phase. It was also found that the Bi₂S₃ films present an energy band gap $(E_g)$ of about 1.38 eV. In addition to these results, the electrical conductivity of the Bi₂S₃ films was affected by both the transport of free carriers in extended states of the conduction band and for variable range hopping transport mechanisms, each one predominating in a different temperature range.

The Bi₂S₃-TiO₂-RGO composites were synthesized by a facile one-step hydrothermal method and applied for the photocatalytic degradation of Rhodamine B (Rh B) under the visible light. The Bi₂S₃-TiO₂-RGO composites were characterized by transmission electron microscopy, X-ray diffraction, Raman and Fourier transform infrared spectrometer. The results indicated that the Bi₂S₃-TiO₂-RGO composites were successfully prepared, and Ti-O-C and S-C bonds were existing among Bi₂S₃, TiO₂ as well as RGO. Furthermore, the photocatalytic ability of Bi₂S₃-TiO₂-RGO composites was excellent under visible light due to its responding to the whole visible light region, low recombination rate of photogenerated electron–hole pairs and relatively negative conduction band. Rh B photocatalytic degradation rate was 99.5% after 50min and still could reach 98.4% after five cycles. Finally, a formation mechanism as well as a photocatalytic mechanism of Bi₂S₃-TiO₂-RGO composites were proposed based on the experimental results.

Here, the lamellar-shaped Bi₂S₃ grown on a porous TiO₂ monolith was obtained by a two-step method including a sol–gel route and hydrothermal treatment. The photocatalytic activity of the as-synthesized Bi₂S₃/TiO₂ composites was evaluated for photodegradation of methylene blue (MB) dye in aqueous solution under the visible-light irradiation. Based on our experimental results, 5% (molar ratio of Bi₂S₃ to TiO${}_2)$ Bi₂S₃/TiO₂ photocatalysts exhibited a maximum photodegradation rate of MB up to 96.9% under visible-light irradiation for 120 min. Our findings indicated that the lamellar-shaped Bi₂S₃ can extend the light absorption up to visible areas, and porous TiO₂ can provide enhanced specific surface area and more mass transfer pathway to enhance the photodegradation efficiency. Furthermore, porous TiO₂ can accept the electrons from the Bi₂S₃ conduction band due to the relatively positive electrode potential to impede the photoproduced electron and hole combination to result in advanced photocatalytic performance.

Photocatalytic decomposition of water is a potential way to obtain hydrogen directly from solar energy. Of all the potential semiconductors, Bi₂S₃has attracted much attention due to its high utilization of sunlight. In this paper, Bi₂S₃nanowires with different morphologies and crystallinities were synthesized by a modified composite molten salt (M-CMS) method over different reaction times. Through the systematic characterization of the samples, it was found that Bi₂S₃samples with a longer synthesis times tend to form nanowires with a uniform morphology, clean surface, good crystallinity and lower photogenerated carrier recombination rate, and they can achieve efficient utilization of solar energy and high catalytic hydrogen production efficiency. The Bi₂S₃nanowires synthesized over 72 h had the best hydrogen production of 392 $\mu$mol/g within 2 h, and they still maintained an efficiency of 89% after four cycles.