P. Vinayagamoorthy

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.

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.

Magnetically recoverable Fe3O4-implanted Ag-loaded ZnO nanoflakes for bacteria-inactivation and photocatalytic degradation of organic pollutants

Fe3O4-implanted Ag-loaded (0.3 at%) perforated ZnO nanoflakes have been synthesized by a two-step method. Scanning electron and high resolution transmission electron micrographs (HRTEM) display the morphology and the energy dispersive X-ray spectrum confirms the presence of the constituent elements. HRTEM reveals the core/shell structure and Ag-deposition. Selected area electron diffraction pattern displays the presence of Fe3O4, ZnO and metallic Ag. The X-ray diffractograms and Raman spectrum are characteristic of the Ag-deposited ZnO lattice. The M–H loop confirms the presence of a magnetic core and the charge transfer resistance of the composite is less than that of pristine ZnO. The nanoflakes display moderate visible light absorption. The UV absorption and emission spectra of the composite are similar to those of pristine ZnO. The decay of photogenerated charge carriers in the nanocomposite is not significantly different from that in pristine ZnO. The composite nanoflakes are magnetically recoverable and inactivate bacteria such as E. coli in the absence of illumination and photocatalytically degrade dyes such as methylene blue effectively. Thus the synthesized composite nanoflakes address (i) bacteria disinfection, (ii) mineralization of organic pollutants and (iii) magnetic recovery of the nanomaterial.

Enhanced photocatalytic activity of magnetically separable bactericidal CuFe2O4-embedded Ag-deposited ZnO nanosheets

Mineralization of organic pollutants by semiconductor-photocatalysis is an emerging technique but recovery of the photocatalyst nanoparticles is a hindrance for putting this technology into practice. Magnetic separation is feasible if a magnetic core is implanted in the photocatalyst particle. An iron oxide core, because of the conduction and valence band potentials, promotes electron–hole recombination in the core/shell photocatalyst and thus suppresses the photocatalytic activity. Here we present for the first time, the synthesis of magnetically recoverable bactericidal CuFe2O4-encapsulated Ag-deposited ZnO nanosheets for enhanced photocatalytic mineralization of dyes; the CB edge of the CuFe2O4 core does not induce charge carrier recombination. The nanosheets were obtained by a two-step synthesis of a hydrothermal method followed by photodeposition. High resolution scanning and transmission electron microscopies, selected area electron and X-ray diffractometries, vibrating sample magnetometry, and energy dispersive X-ray, Raman, solid state electrochemical impedance, UV visible diffuse reflectance, photoluminescence and time-correlated single photon counting lifetime spectroscopies show encapsulation of CuFe2O4 in Ag-deposited ZnO nanosheets. The synthesized composite nanosheets show enhanced photocatalytic activity. The synthesized nanosheets are a trifunctional material. The photocatalyst is photostable, reusable and magnetically separable. Furthermore, it exhibits excellent bactericidal activity.

Electrical, optical, photocatalytic, and bactericidal properties of polyethylene glycol-assisted sol–gel synthesized ZnTiO3-implanted ZnO nanoparticles

ZnTiO3-implanted ZnO nanoparticles were prepared by sol–gel method employing polyethylene glycol (PEG) 4000 and 20 000. The high resolution transmission electron micrographs, selected area electron diffraction pattern, energy dispersive x-ray spectra and powder x-ray diffractograms show the prepared materials as core/shell nanoparticles. Increase of the molecular mass of PEG decreases the d-spacing in ZnO of ZnTiO3-implanted ZnO and pristine ZnO nanoparticles. The charge transfer resistances of ZnTiO3-implanted ZnO nanoparticles are larger than those of pristine ZnO and precursor ZnTiO3 nanoparticles. The optical properties of ZnTiO3/ZnO nanoparticles are similar to those of pristine ZnO nanoparticles. The photocatalytic activity of ZnO is enhanced by the presence of ZnTiO3 core in the ZnO lattice. The bactericidal activity of core/shell ZnTiO3/ZnO nanoparticles is not less than that of ZnO nanoparticles.

Styryl phenanthrimidazole-fluorescence switched on by core/shell BaTiO3/ZnO and Mn-doped TiO2/ZnO nanospheres and switched off by the core nanoparticles

Absorption, fluorescence and lifetime spectral studies have been carried out to probe the interaction of fluorophore (E)-1-phenyl-2-styryl-1H-phenanthro[9,10-d]imidazole with sol–gel synthesised BaTiO3/ZnO and Mn-doped TiO2/ZnO core/shell and pristine ZnO nanospheres and BaTiO3 and Mn-doped TiO2 nanoparticles. The emission of fluorophore is switched on by Mn-doped TiO2/ZnO and BaTiO3/ZnO core/shell and pristine ZnO nanospheres, and switched off by Mn-doped TiO2 and BaTiO3 nanoparticles owing to charge injection from the excited singlet state of fluorophore to the conduction band (CB) of the nanosemiconductors. The affinity of the fluorophore to ZnO results in the lowering of HOMO and LUMO energy levels of fluorophore, leading to emission at ∼420 nm. This is due to LUMO → HOMO, LUMO → CB and deep level emission (DLE) of ZnO resulting in the enhancement of fluorescence. The HOMO and LUMO energy levels of the fluorophore are unlikely to be influence by core BaTiO3 and Mn-doped TiO2 nanoparticles. This leads to quenching of fluorescence because of electron transfer from LUMO → CB.

Tri-functional Fe2O3-encased Ag-doped ZnO nanoframework: magnetically retrievable antimicrobial photocatalyst

Fe2O3-encased ZnO nanoframework was obtained by hydrothermal method and was doped with Ag through photoreduction process. Energy dispersive x-ray spectroscopy, transmission electron microscopy (TEM), high resolution TEM, selected area electron diffractometry, x-ray diffractometry and Raman spectroscopy were employed for the structural characterization of the synthesized material. While the charge transfer resistance of the prepared nanomaterial is larger than those of Fe2O3 and ZnO the coercivity of the nanocomposite is less than that of hydrothermally obtained Fe2O3 nanostructures. Although Fe2O3/Ag–ZnO exhibits weak visible light absorption its band gap energy does not differ from that of ZnO. The photoluminescence of the fabricated nanoframework is similar to that of ZnO. The radiative recombination of charge carriers is slightly slower in Fe2O3/Ag–ZnO than in ZnO. The synthesized Fe2O3-encased Ag-doped ZnO, under UV A light, exhibits sustainable photocatalytic activity to degrade dye and is magnetically recoverable. Also, the Fe2O3/Ag–ZnO nanocomposite disinfects bacteria effectively in absence of direct illumination.

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.