C. Karunakaran

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.

Nonquenching of charge carriers by Fe3O4 core in Fe3O4/ZnO nanosheet photocatalyst.

Fe3O4-implanted ZnO and pristine ZnO nanosheets have been synthesized hydrothermally. High-resolution scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping, selected area electron diffractometry, powder X-ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, solid state impedance spectroscopy, UV-visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy show implantation of Fe3O4 in ZnO nanosheets. Fe3O4 core with ZnO shell is of type I core/shell heterostructure which is to quench charge carriers and suppress photocatalysis. But the photocatalytic activity is not suppressed on implantation of Fe3O4 in ZnO nanosheets, and time controlled single photon counting lifetime spectroscopy shows that the photogenerated charge carriers are not quenched by the Fe3O4 core in the ZnO nanosheets. The composite nanosheets are photostable, reusable, and magnetically recoverable, revealing potential application in mineralization of organic pollutants.

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.

Molybdenum(VI) catalysis of perborate or hydrogen peroxide oxidation of iodide ion

SummaryPerborate in aqueous solution generates H2O2; in its presence the molybdenum(VI) catalysed oxidation of iodide ion is first order with respect to the oxidant and catalyst, and is independent of [I−] and [H+]. Kinetic studies point to peroxymolybdenum(VI) species as the oxidizing species.

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.

Photoinduced electron-transfer from imidazole derivative to nano-semiconductors

Bioactive imidazole derivative absorbs in the UV region at 305 nm. The interaction of imidazole derivative with nanoparticulate WO3, Fe2O3, Fe3O4, CuO, ZrO2 and Al2O3 has been studied by UV-visible absorption, FT-IR and fluorescence spectroscopies. The imidazole derivative adsorbs strongly on the surfaces of nanosemiconductor, the apparent binding constants for the association between nanomaterials and imidazole derivative have been determined from the fluorescence quenching. In the case of nanocrystalline insulator, fluorescence quenching through electron transfer from the excited state of the imidazole derivative to alumina is not possible. However, a possible mechanism for the quenching of fluorescence by the insulator is energy transfer, that is, energy transferred from the organic molecule to the alumina lattice. Based on Forsters non-radiation energy transfer theory, the distance between the imidazole derivative and nanoparticles (r0∼2.00 nm) as well as the critical energy transfer distance (R0∼1.70 nm) has been calculated. The interaction between the imidazole derivative and nanosurfaces occurs through static quenching mechanism. The free energy change (ΔGet) for electron transfer process has been calculated by applying Rehm-Weller equation.

Photosensitization of Imidazole Derivative by ZnO Nanoparticle

A sensitive imidazole based fluorescent sensor like 4, 5-diphenyl-2(E)-styryl-1H-imidazole, for ZnO has been designed and synthesized via simple steps. The absorption, fluorescence, SEM, EDX and IR studies indicate that imidazole derivative is bound on the surface of ZnO semiconductor. Based on photo-induced electron transfer (PET) mechanism, fluorescent enhancement has been explained and apparent binding constant has been calculated. Ligand adsorption on ZnO nanoparticle lowers of the HOMO and LUMO energy levels of imidazole derivative and the chemical affinity between the nitrogen atom of the imidazole and zinc ion on the surface of the nano oxide may be a reason for strong adsorption of the ligand on nanoparticle. The electron injection from photo excited imidazole derivative to the ZnO conduction band (S*→S+ + eCB−) accounts for the enhanced fluorescence.

Selectivity in photocatalysis by particulate semiconductors

TiO2, Fe2O3, CuO, ZnO, ZnS, Nb2O5, MoO3, CdO, CdS, Sb2O3, CeO2, HgO, Pb2O3, PbO2 and Bi2O3 microparticles exhibit band gap excitation with UV-A light but they are selective to photodegrade phenols. While TiO2 anatase and ZnO photocatalyze the degradation of phenol, o-aminophenol, m-aminophenol, p-aminophenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-nitrophenol, p-nitrophenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol and quinol, MoO3 does not photodegrade any of the fifteen phenols. Fe2O3, CuO, ZnS, Nb2O5, CdO, CdS, Sb2O3, CeO2, HgO, Pb2O3, PbO2 and Bi2O3 are selective in photodegrading the fifteen phenols; however, the phenols get adsorbed over all sixteen particulate semiconductors.