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In this work, we carried out in-depth study of the structural, electronic, and optical properties of intrinsic, fluorine (F)- and chlorine (Cl)-doped SnO2, using a pseudo-potential plane-wave scheme in the framework of the density functional theory. We found that the substitution of oxygen by F or Cl elements slightly modified the crystalline parameters without altering the stability of SnO2 compounds. The doping of tin oxide by these two halogens is confirmed by the displacement of the Fermi level position to the conduction band. Consequently, the doped materials are strongly degenerated as illustrated by the Moss-Burstein shift: 2.310 and 2.332 eV for F:SnO2 and Cl:SnO2, respectively. On the other hand, the density of states and Mulliken population analysis show that the covalent character of Sn–O bond is maintained after doping, while Sn–X (X = F or Cl) bond reveals an ionic nature. In terms of optical properties after doping, intrinsic SnO2 exhibits low absorption, while the doped ones are transparent in the visible range, making them more efficient in photovoltaic applications. Moreover, in the ultraviolet (UV) scale, pure and doped tin oxide compounds show better absorption, which may be beneficial for use in devices of protection against UV light and UV absorbers or sensors. Finally, the plasma frequencies of 28.22, 29.16, and 27.67 eV for pure, F-, and Cl-doped SnO2, respectively, were obtained. [ABSTRACT FROM AUTHOR]

The effluents emanating from industries such as paper, plastics, textile, and leather contain many dyes which are toxic and carcinogenic. The treatment of these effluents has become very important to reduce the potential toxicity of their pollutants and minimize their concentration prior to their discharge. This paper presents a comparative study between adsorption and biosorption processes for the red dye bimacid removal from aqueous solution. The experimental results show that the removal efficiency of the red bimacid using biosorption process which uses immobilized anaerobic sulfate-reducer cells onto a physical adsorbent is more significant (up to 91%) as compared to the adsorption process using bentonite and pozzolana powders. The kinetics of biosorption and the adsorption isotherms of the red dye bimacid on these materials showed great affinities to adsorbent-adsorbate. The pH of the aqueous solution influences positively the rate of the dye removal in the case of adsorption; however, it is a limiting factor in the case of biosorption. [ABSTRACT FROM PUBLISHER]

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The structures and vibrational spectra of inorganic aerosols, including ammonium sulfate (NH4)2SO4, ammonium nitrate NH4NO3, and sodium nitrate NaNO3 are investigated at the periodic ab initio quantum mechanical level with the CRYSTAL code, which is based on Gaussian basis sets. Local density (LDA), gradient-corrected (PW91), and hybrid (B3LYP) density functionals have been used and the results are compared with experiment. All three functionals reproduce the equilibrium geometry of these aerosols to a high level of accuracy. The calculations of the frequencies gave a mean absolute deviation from experiment of 3% for B3LYP, clearly showing that this functional performs extremely well in this case. The mean absolute deviation is about 7% and 6% for PW91 and LDA, respectively. [ABSTRACT FROM AUTHOR]