Synthesis, characterization, optoelectronic and photocatalytic properties of Sr2Bi2O5/SrCO3 and Sr3Bi2O6/SrCO3 heterostructures with varying SrCO3 content

Revisiting the BaBiO3 semiconductor photocatalyst: synthesis, characterization, electronic structure, and photocatalytic activity

This article revisits the properties of BaBiO₃ examined extensively in the last two decades because of its electronic properties as a superconductor and as a semiconductor photocatalyst. Solid-state syntheses of this bismuthate have often involved BaCO₃ as the barium source, which may lead to the formation of BaBiO₃/BaCO₃ heterostructures that could have an impact on the electronic properties and, more importantly, on the photocatalytic activity of this bismuthate. Accordingly, we synthesized BaBiO₃ by a solid-state route to avoid the use of a carbonate; it was characterized by XRD, SEM, and EDX, while elemental mapping characterized the composition and the morphology of the crystalline BaBiO₃ and its thin films with respect to structure, optoelectronic, and photocatalytic properties. XPS, periodic DFT calculations, and electrochemical impedance spectroscopy ascertained the electronic and electrical properties, while Raman and DRS spectroscopies assessed the relevant optical properties. The photocatalytic activity was determined via the degradation of phenol in aqueous media. Although some results accorded with earlier studies, the newer electronic structural data on this bismuthate, together with the photocatalytic experiments carried out in the presence of selective radical trapping agents, led to elucidating some of the mechanistic details of the photocatalytic processes that previous views of the BaBiO₃ band structure failed to address or clarify. Analytical refinement of the XRD data inferred the as-synthesized BaBiO₃ adopted the C_2/m symmetry rather than the I_2/m structure reported earlier, while Tauc plots from DRS spectra yielded a bandgap of 2.05 eV versus the range of 1.1-2.25 eV reported by others; the corresponding flatband potentials were 1.61 eV (E_VB) and - 0.44 eV (E_CB). The photocatalytic activity of BaBiO₃ was somewhat greater than that of the well-known Evonik P25 TiO₂ photocatalyst under comparable experimental conditions.

Photocatalytic Activity of S-Scheme Heterostructure for Hydrogen Production and Organic Pollutant Removal: A Mini-Review

Finding new technologies and materials that provide real alternatives to the environmental and energy-related issues represents a key point on the future sustainability of the industrial activities and society development. The water contamination represents an important problem considering that the quantity and complexity of organic pollutant (such as dyes, pesticides, pharmaceutical active compounds, etc.) molecules can not be efficiently addressed by the traditional wastewater treatments. The use of fossil fuels presents two major disadvantages: (1) environmental pollution and (2) limited stock, which inevitably causes the energy shortage in various countries. A possible answer to the above issues is represented by the photocatalytic technology based on S-scheme heterostructures characterized by the use of light energy in order to degrade organic pollutants or to split the water molecule into its components. The present mini-review aims to outline the most recent achievements in the production and optimization of S-scheme heterostructures for photocatalytic applications. The paper focuses on the influence of heterostructure components and photocatalytic parameters (photocatalyst dosage, light spectra and intensity, irradiation time) on the pollutant removal efficiency and hydrogen evolution rate. Additionally, based on the systematic evaluation of the reported results, several perspectives regarding the future of S-scheme heterostructures were included.