Metastable β-Bi2O3 Nanoparticles with Potential for Photocatalytic Water Purification Using Visible Light Irradiation

Photocatalytic studies under visible light irradiation using nanosized β-Bi₂O₃ are reported. β-Bi₂O₃ nanoparticles are prepared starting from the well-defined bismuth oxido cluster [Bi₃₈O₄₅(OMc)₂₄(DMSO)₉]⋅2 DMSO⋅7 H₂O (OMc=O₂CC₃H₅) using a straightforward hydrolysis and annealing protocol. Powder X-ray diffraction studies, transmission electron microscopy, diffuse reflectance UV/Vis spectroscopy and nitrogen adsorption measurements (using the Brunauer–Emmett–Teller (BET) theory) are used for the characterization of the as-prepared β-Bi₂O₃. By time-dependent annealing, the crystallite size can be controlled between (17±2) nm and (45±5) nm with BET surface areas of 7 to 29 m² g⁻¹. The indirect band gap of the as-prepared β-Bi₂O₃ amounts to (2.15±0.05) eV. The decomposition rates for rhodamine B (RhB) solutions are in the range of 2.46×10⁻⁵ to 4.01×10⁻⁴ s⁻¹ and depend on the crystallite size, amount of catalyst and concentration of RhB. Photocorrosion experiments have shown the formation of Bi₂O₂CO₃ after several catalytic cycles. However, the catalyst can be recycled to phase-pure β-Bi₂O₃ nanoparticles by annealing for one hour under argon atmosphere at 380 °C. Furthermore, the photocatalytic activity of as-prepared β-Bi₂O₃ nanoparticles for the decomposition of phenol, 4-chlorophenol, 2,4-dichlorphenol, 4-nitrophenol, triclosan and ethinyl estradiol is demonstrated.

Adsorption of poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) polymers on zinc, zinc oxide, iron, and iron oxide surfaces

The adsorption of poly(vinyl formamide) (PVFA) and the statistic copolymers poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) onto zinc and iron metal particles as well as their oxides was investigated. The adsorbates were characterized by means of XPS, DRIFT spectroscopy, wet chemical analysis, and solvatochromic probes. Dicyano-bis-(1,10-phenanthroline)-iron(II) (1), 3-(4-amino-3-methylphenyl)-7-phenyl-benzo-[1,2-b:4,5-b']difuran-2,6-dione (2), and 4-tert-butyl-2-(dicyano-methylene)-5-[4-(diethylamino)-benzylidene]-Δ(3)-thiazoline (3) as solvatochromic probes were coadsorbed onto zinc oxide to measure various effects of surface polarity. The experimental findings showed that the adsorption mechanism of PVFA and PVFA-co-PVAm strongly depends on the degree of hydrolysis of PVFA and pH values and also on the kind of metal or metal oxide surfaces that were employed as adsorbents. The adsorption mechanism of PVFA/PVFA-co-PVAm onto zinc oxide and iron oxide surfaces is mainly affected by electrostatic interactions. Particularly in the region of pH 5, the adsorption of PVFA/PVFA-co-PVAm onto zinc and iron metal particles is additionally influenced by redox processes, dissolution, and complexation reactions.

Linear Solvation Energy Parameters for Model Tropospheric Aerosol Surfaces

Excited-state absorption spectra for several coumarin derivatives adsorbed to aerosol particles provide linear solvation energy (LSE) relationships for the aerosol surfaces. This study focuses on NaCl and (NH4)2SO(4) particles as models for tropospheric aerosol. We investigate several others, including NH(4)Cl, NaBr, KI, Na(2)SO(4), NaNO(3), Al(2)O3, and CaCO(3), to establish trends and understand the factors that control polarity for surfaces. The Kamlet-Taft dipolarity/polarizability parameter, pi*, for these particles ranges from 0.73 to 1.69. The values are high compared to most homogeneous molecular solvents and are attributable to ion-dipole forces, especially at defect sites. We also find that the smaller values of pi* (1.01 for (NH4)2SO(4) and 0.73 for NH(4)Cl) correlate with appreciable hydrogen bond donor acidity in the surface (alpha = 0.23 and 1.06, respectively). Strong hydrogen bonds with the surface lead to a drop in overall polarity either by making interaction with very polar defect sites less likely or orienting the probe molecule away from the surface. Adsorbed water layers mainly alter the alpha value of the surface, but can have indirect effects on pi* by changing the interaction of the adsorbed molecule with the surface.