Enhanced photocatalytic performance at a Au/N-TiO2 hollow nanowire array by a combination of light scattering and reduced recombination.

We demonstrate one-step gold nanoparticle (AuNP) coating and the surface nitridation of TiO2 nanowires (TiO2-NWs) to amplify visible-light photon reflection. The surface nitridation of TiO2-NW arrays maximizes the anchoring of AuNPs, and the subsequent reduction of the band gap energy from 3.26 eV to 2.69 eV affords visible-light activity. The finite-difference time-domain (FDTD) simulation method clearly exhibits the enhancement in the strengths of localized electric fields between AuNPs and the nanowires, which significantly improves the photocatalytic (PC) performance. Both nitridation and AuNP decoration of TiO2-NWs result in beneficial effects of high (e(-)/h(+)) pair separation through healing of the oxygen vacancies. The combined effect of harvesting visible-light photons and reducing recombination in Au/N-doped TiO2-NWs promotes the photocatalytic activity towards degradation of methyl orange to an unprecedented level, ∼4 fold (1.1 × 10(-2) min) more than does TiO2-NWs (2.9 × 10(-3) min(-1)). The proposed AuNP decoration of nitridated TiO2-NW surfaces can be applied to a wide range of n-type metal oxides for photoanodes in photocatalytic applications.

Adsorption studies of arsenic on Mn-substituted iron oxyhydroxide.

Mn-substituted iron oxyhydroxide (Mn(0.13)Fe(0.87)OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m2 g(-1) and a pore volume of 0.35 cm3 g(-1). Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 degrees C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g(-1), respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases, adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15-24 and 45-67 kJ mol(-1) for arsenate and arsenite, respectively.

Adsorption of arsenate on synthetic goethite from aqueous solutions.

Goethite was synthesized from the oxidation of ferrous carbonate precipitated from the double decomposition of ferrous sulfate doped with sodium lauryl sulfate (an anionic surfactant) and sodium carbonate in aqueous medium. The specific surface area and pore volume of goethite were 103 m(2) g(-1) and 0.50 cm(3) g(-1). Batch experiments were conducted to study the efficacy of removal of arsenic(V) using this goethite as adsorbent for solutions with 5-25 mg l(-1) of arsenic(V). The nature of adsorption was studied by zeta-potential measurements. The adsorption process followed by Langmuir isotherm and diffusion coefficient of arsenate was determined to be 3.84 x 10(11)cm(2)s(-1). The optimum pH of adsorption was found to be 5.0. The kinetics of adsorption was evaluated with 10 mg l(-1) and 20 mg l(-1) of As(V) solutions and activation energy of adsorption, as calculated from isoconversional method was in the range of 20 kJ mol(-1) to 43 kJ mol(-1). This suggests that the adsorption process is by diffusion at the initial phase and later through chemical control. FT-IR characterization of arsenic treated goethite indicated the presence of both AsOFe and AsO groups and supported the concept of surface complex formation.