Structural, electronic, optical properties and adsorption energy of BiVS4 photocatalyst used in wastewater treatment and comparison with a standard Photocatalyst BiVO4 computationally

Abstract

Earth is gifted with abundant quantity of clean water, air and green environment. But concurrent time, the world has found in severe risk on environmental and economic stability due to the enormous population from household and industries with the growth of the advance technology. Among these, the textile, leather, cosmetics, plastic, paper, ink, ceramic and food processing industries are the most responsible candidate from which the organic dyes are extensively used materials that causes the contamination both aquatic and non aquatic environments [1-3].

Some of the semiconductor based Metal oxides represent ideal catalysts for solar-driven hydrogen production and other photocatalytic relevance due to their low cost and high stability in aqueous solution even any kind of ambivalence situation of any of the environments. In this case, the BiVO₄ is well examined photocatalyst but there are few limitations such as wide band gap, low stability, low  absorption capacity, less than 5% UV light irradiation and  small surface area capacity [4-5]. In view of the surface area, the oxygen atom has replaced and designed the BiVS₄ to examine the computational data.

The electronic structure and optical properties of BiVS₄ were calculated and compared with the parent crystal BiVO₄. First of all, the five functionals, such as GGA with PBE, GGA with RPBE, GGA with PW91, GGA with WC and GGA with PBESOL were used for primary screening of electronic band structure and structural geometry for BiVO4 while the band gaps were evaluated to be 2.418 eV, 2.474 eV, 2.389 eV, 3.385 eV and 2.375 eV, respectively. It is worthy to mention that the experimental band gap for BiVO₄ is 2.40 eV [6] so that the GGA with PBE showed the overlapping value of band gap. The band gap for four others, such as GGA with PBE, GGA with RPBE, GGA with PW91, GGA with WC and GGA with PBESOL functionals, were computed to be 0.285 eV, 0.314 eV, 0.267 eV and 0.261 eV and 0.250 eV, respectively. For their orbitals contributed for each atom on this crystal, the density of state and the partial density of state for BiVS₄ and BiVO₄ crystals were simulated through the GGA with PBE method as standard regarding the calculation of band gap study comparison with experimental ones.

The first-principles study on the electronic structure demonstrates the BiVS₄ a promising photocatalyst for hydrogen generation. BiVS₄ is found to have an indirect band gap semiconductor. There remains, a vast coupling between 6s orbital of Bi and 2p orbital of sulphur atom with an upward dispersion of the valence band at the zone boundary; however, an indirect gap is maintained via coupling between 3d orbital V, 2p orbital of O, and 6p orbital of Bi, which conveys the lower contribution of conduction band. These interactions result in symmetric hole and electron are produced to activate the organic pollution degradation as photocatalyst. In addition, the optical properties, such as absorption, reflection, refractive index, conductivity, dielectric function and loss function were calculated, and made a comparative study between BiVO₄ and BiVS₄. To explain the catalytic nature, the total energy, adsorption energy, rigid adsorption energy, deformation energy and energy of catalyst have also determined. From the observe findings of this work, It may conclude that the BiVS₄ is the better photocatalyst than BiVO_4.