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In this article, we report the fabrication of various morphological bismuth oxides (α-Bi2O3) by a self-assembly process using bismuth oxalates as precursors. Barlike Bi2(C2O4)3·7H2O and microrod-like (BiOHC2O4)2·H2O were synthesized by using bismuth nitrate with oxalic acid in a simple mixing and hydrothermal process and are hereafter referred to as bismuth oxalate-1 and bismuth oxalate-2, respectively. The thermal decomposition of bismuth oxalate-2 at 300 and 400 °C for 2 h yields aggregate-free honeycomb brushlike and wormlike morphological Bi2O3, respectively. We first report the formation of both the above-mentioned novel morphological bismuth oxides. However, the decomposition of bismuth oxalate-1 results in microspheres with bundle-shaped particles and wormlike bundles with microflower morphologies at 300 and 400 °C, respectively. The influences of hydrothermal temperature, time, and bismuth precursor on the formation of bismuth oxalate-2 were investigated. The synthesized bismuth oxalates and Bi2O3 were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and nitrogen adsorption analysis. The XRD patterns indicated that well-crystallized α-Bi2O3 was formed in the thermal decomposition process from both precursors. The FE-SEM images indicated the formation of well-organized honeycomb brush-like and worm-like morphologies. The photocatalytic degradation of Acid Orange 7 (AO7) dye by using the synthesized bismuth oxides was investigated, and the results showed superior photocatalytic activity of the honeycomb brushlike Bi2O3. We propose a plausible mechanism for the formation of various morphologies of Bi2O3.

MnO2 typically coexists with iron oxides as either discrete particles or coatings in soils and sediments. This work examines the effect of Aldrich humic acid (AHA), alginate, and pyromellitic acid (PA) as representative natural organic matter (NOM) analogues on the oxidative reactivity of MnO2, as quantified by pseudo-first-order rate constants of triclosan oxidation, in mixtures with goethite or hematite. Adsorption studies showed that there was low adsorption of the NOMs by MnO2, but high (AHA and alginate) to low (PA) adsorption by the iron oxides. Based on the ATR-FTIR spectra obtained for the adsorbed PA on goethite or goethite + MnO2, the adsorption of PA occurred mainly through formation of outer-sphere complexes. The Fe oxides by themselves inhibited MnO2 reactivity through intensive heteroaggregation between the positively charged Fe oxides and the negatively charged MnO2; the low solubility of the iron oxides limited surface complexation of soluble Fe(3+) with MnO2. In ternary mixtures of MnO2, Fe oxides, and NOM analogues, the reactivity of MnO2 varied from inhibited to promoted as compared with that in the respective MnO2 + NOM binary mixtures. The dominant interaction mechanisms include an enhanced extent of homoaggregation within the Fe oxides due to formation of oppositely charged patches within the Fe oxides but an inhibited extent of heteroaggregation between the Fe oxide and MnO2 at [AHA] < 2-4 mg-C/L or [alginate/PA] < 5-10 mg/L, and an inhibited extent of heteroaggregation due to the largely negatively charged surfaces for all oxides at [AHA] > 4 mg-C/L or [alginate/PA] > 10 mg/L.

This paper presents the results of visible light assisted photocatalytic ozonation and other related oxidation processes for the removal of Orange II dye from water using Bi 2 O 3 and Au/Bi 2 O 3 nanorods prepared using microwave irradiation which was found effective compared to Bi 2 O 3 particles prepared by conventional heat treatment method at 90 °C. Particularly, in the photocatalytic ozonation using Au/Bi 2 O 3 nanorods, a fourfold increase in the rate was observed as compared to that in the absence of Au/Bi 2 O 3 . This is because tuning semiconductor materials into nanosize could create high quantum confinement of electron and hole to increase the illumination efficiency. In addition, the deposition of nanomaterial can also be employed to enhance the mechanical strength of devices. That is, deposited Au nanoparticles act as electron traps to impede electron/hole recombination.

This paper describes a highly efficient and rapid approach of synthesizing different CuO nanostructures in aqueous solutions using ultrasound irradiation of copper(II) acetate with urea/sodium hydroxide in the presence of polyvinylpyrrolidone (PVP), as stabilizing polymer. Field emission scanning electron microscope images clearly indicate the formation of CuO quasi-spherical microarchitectures and long-straw like structure in the presence of urea and sodium hydroxide. Other characterization techniques such as TEM, XRD and XPS are also provided to support the formation of such structures. One of the reasons for the formation of such CuO nanostructures may be due to the formation of a polymer-metal complex with the stabilizing polymer (PVP).