P. Gomathisankar

Cu-doped TiO2 nanoparticles for photocatalytic disinfection of bacteria under visible light

Two percent Cu-doped TiO(2) nanoparticles were prepared by a modified ammonia-evaporation-induced synthetic method, calcined at 450°C, and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, ESR spectroscopy, scanning electron microscopy, UV-visible diffuse reflectance spectrum, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Doping shifts the optical absorption edge to the visible region but increases the charge-transfer resistance and decreases the capacitance. Under visible light, the composite nanoparticles very efficiently catalyze the disinfection of Escherichia coli. The prepared oxide is selective in photocatalysis; under UV light, its photocatalytic activity to degrade sunset yellow, rhodamine B, and methylene blue dyes is less than that of the undoped one.

Enhanced phenol-photodegradation by particulate semiconductor mixtures: interparticle electron-jump.

Degradation of phenol on suspended TiO(2), ZnO, CdO, Fe(2)O(3), CuO, ZnS and Nb(2)O(5) particles under UV-A light exhibit identical photokinetic behavior; follow first-order kinetics, display linear dependence on the photon flux and slowdown with increase of pH. All the semiconductors show sustainable photocatalytic activity. Dissolved O(2) is essential for the photodegradation and oxidizing agents like H(2)O(2), Na(2)BO(3), K(2)S(2)O(8), KBrO(3), KIO(3) and KIO(4), reducing agents such as NaNO(2) and Na(2)SO(3) and sacrificial electron donors like hydroquinone, diphenyl amine and trimethyl amine enhance the degradation. However, the photocatalysis is insensitive to pre-sonication. Two particulate semiconductors present together, under suspension and at continuous motion, enhance the photocatalytic degradation up to about four-fold revealing interparticle electron-jump.

Photoproduction of iodine with nanoparticulate semiconductors and insulators

The crystal structures of different forms of TiO2 and those of BaTiO3, ZnO, SnO2, WO3, CuO, Fe2O3, Fe3O4, ZrO2 and Al2O3 nanoparticles have been deduced by powder X-ray diffraction. Their optical edges have been obtained by UV-visible diffuse reflectance spectra. The photocatalytic activities of these oxides and also those of SiO2 and SiO2 porous to oxidize iodide ion have been determined and compared. The relationships between the photocatalytic activities of the studied oxides and the illumination time, wavelength of illumination, concentration of iodide ion, airflow rate, photon flux, pH, etc., have been obtained. Use of acetonitrile as medium favors the photogeneration of iodine.

Nanostructures and optical, electrical, magnetic, and photocatalytic properties of hydrothermally and sonochemically prepared CuFe2O4/SnO2

The hydrothermal preparation of CuFe2O4/SnO2 yields nanospindles of a high aspect ratio bound to nanoblocks. The nanospindles grow to about 800 nm with a diameter of ∼110 nm. The sonochemically obtained CuFe2O4/SnO2 nanocomposite lacks a regular shape and is about 40 nm in size. X-ray diffractograms (XRD) and selected area electron diffractograms (SAED) show tetragonal SnO2 and tetragonal CuFe2O4 as the components of the hydrothermally prepared nanostructure. Although the XRD of the sonochemically obtained CuFe2O4/SnO2 shows the presence of tetragonal CuFe2O4 only the SAED reveals the existence of tetragonal SnO2 also. The sonochemically prepared composite lacks a perfect nanocrystalline surface. The hydrothermally obtained nanostructure is rich in SnO2 (80% mol.) and the other is rich in CuFe2O4 (91% mol.). Both the nanostructures absorb visible light and exhibit emission at 600 nm. The solid state complex impedance spectra display truncated semicircular arcs, which is similar to that of SnO2. The hydrothermally synthesized CuFe2O4/SnO2 is superparamagnetic, while both the nanostructures exhibit bactericidal activity the visible light-photocatalytic activity of the hydrothermally prepared nanostructure is much larger than that of the other. The contrasting photocatalytic activities are explained in terms of the nanostructures. The present study shows that the sonochemical method provides a coating of SnO2 on CuFe2O4 nanoparticles, whereas it is an ordered growth of SnO2 on CuFe2O4 in the hydrothermal preparation.

Phenol-photodegradation on ZrO2. Enhancement by semiconductors

On illumination with light of wavelength 365 nm phenol undergoes degradation on the surface of ZrO(2). The rate of degradation enhances linearly with the concentration of phenol and also the light intensity but decreases with increase of pH. The photonic efficiency of degradation is higher with illumination at 254 nm than with 365 nm. The diffuse reflectance spectral study suggests phenol-sensitized activation of ZrO(2) with 365 nm light. TiO(2), Fe(2)O(3), CuO, ZnO, ZnS, Nb(2)O(5) and CdO particles enhance the photodegradation on ZrO(2), indicating inter-particle charge-transfer. Determination of size of the particles under suspension, by light scattering technique, shows agglomeration of particles supporting the proposition of charge-transfer between particles.

Photocatalytic degradation of 1-naphthol by oxide ceramics with added bacterial disinfection

1-Naphthol photodegrades on the surfaces of TiO(2), ZnO, CeO(2), CdO, WO(3), Co(3)O(4), Sb(2)O(3), ZrO(2), La(2)O(3), Y(2)O(3), Pr(6)O(11), Sm(2)O(3) and Al(2)O(3), albeit at different efficiencies, and all the oxides show sustainable photocatalytic activity. The degradation conforms to the Langmuir-Hinshelwood kinetic model and enhances with the intensity of illumination. Dissolved oxygen is essential for the degradation. ZnO and TiO(2) anatase are the most efficient photocatalysts to degrade 1-naphthol. ZnO wurtzite, besides serving as an effective photocatalyt to degrade 1-naphthol, also acts as a bactericide; it inactivates E.coli even in absence of direct light. At a loading of 0.8 g L(-1), it kills about 44% of 2.5x10(12) CFU mL(-1) E. coli in (1/2) h under dark condition.

Optical, Electrical, and Photocatalytic Characteristics of Sol-Gel–Derived CuO-TiO2 Nanocomposite

CuO-TiO2 nanocomposite prepared by sol-gel method does not photocatalyze dye degradation under UV-A as well as visible light. Powder X-ray diffractogram shows the presence of monoclinic CuO and anatase TiO2 in the nanocomposite. The composite displays photoconductance confirming photogeneration of charge carriers. Absence of photocatalysis is attributed to CuO-mediated electron-hole recombination.

Photocatalytic Degradation of Dyes by Al2O3-TiO2 and ZrO2-TiO2 Nanocomposites

Al2O3-TiO2 and ZrO2-TiO2 nanocomposites have been prepared by sol-gel method using polyvinylpyrrolidone-polyethylene glycol (PVP-PEG) as templating agents. While Al2O3 in the former is of end-centered monoclinic crystal structure ZrO2 in the latter is a 4:1 blend of monoclinic and tetragonal phases. In both the composites TiO2 is present as anatase. The energy dispersive X-ray spectra provide the compositions of the composites as Al:Ti::1:12 and Zr:Ti::1:1. Scanning electron micrographs display the sizes of Al2O3-TiO2 and ZrO2-TiO2 particles as 30-77 and 38-57 nm, respectively. The diffuse reflectance spectra of both the composites show band gap excitation in the UV-A region. Both the composites display similar photoluminescence and the observed near band gap emission and deep level emission agree with those of TiO2. The impedance spectral studies reveal that the charge-transfer resistance of ZrO2-TiO2 is less than that of Al2O3-TiO2. Both the composites exhibit photoconductance. The photocatalytic activities of the prepared nanocomposites depend on the dye employed. While both the composites degrade methylene blue and rhodamine B effectively under UV-A light the photodegradation of methyl orange is slow. Rhodamine B degrades on both the nanocomposites under visible light also, which is through dye-sensitized photocatalytic mechanism.

Photocatalytic Activity of Sol-Gel Derived Bi2O3-TiO2 Nanocomposite

Bi2O3-TiO2 nanocomposites were obtained by sol-gel method using tween 80 (T-80) or polyvinyl pyrrolidone-polyethylene glycol (PVP-PEG) as templating agent. The powder X-ray diffraction (XRD) patterns of both the composites reveal the crystal structure of Bi2O3 as primitive tetragonal and TiO2 is in anatase phase. The energy dispersive X-ray (EDX) spectra provide the composition of Bi2O3 in Bi2O3-TiO2 (T-80) and Bi2O3-TiO2 (PVP-PEG) as 3.8 and 20.4 mol. %, respectively. The average crystallite sizes of Bi2O3-TiO2 (T-80) and Bi2O3-TiO2 (PVP-PEG), derived from XRD, are 9 and 17 nm, respectively. The scanning electron microscopic (SEM) images show the spherical shape of Bi2O3-TiO2 (T-80) and the composites are polycrystalline. The diffuse reflectance spectra (DRS) of the composites display faint absorption of visible light and strong absorption in UV-A region. The photoluminescence (PL) spectra of both the composites are similar and the observed near band gap emission (NBE) and deep level emission (DLE) agree with those of TiO2. The impedance spectra show that the charge-transfer resistances of the composites do not differ significantly. The visible light photoimpedance spectra display the photoconductance of Bi2O3-TiO2 (PVP-PEG) but not that of Bi2O3-TiO2 (T-80). Although the visible light-photocatalytic activities of the two nanocomposites to degrade dye do not differ significantly Bi2O3-TiO2 (T-80) under UV-A light degrades dyes faster than Bi2O3-TiO2 (PVP-PEG).