Long-Range Visible Fluorescence Tunability Using Component-Modulated Coupled Quantum Dots

A simple route for tailoring emissions in the visible wavelength region by chemically coupling quantum dots composed of ZnSe and CdS is reported. coupled quantum dots offer a novel route for tuning electronic transitions via band-offset engineering at the material interface. This novel class of asymmetric. coupled quantum structures may offer a basis for a diverse set of building blocks for optoelectronic devices, ultrahigh density memories, and quantum information processing.

Aryl monosulphides and symmetrical disulphides based second order nonlinear optical chromophores with transparency in the visible

A series of aryl monosulphides and disulphides have been synthesized and characterized. Their molecular hyperpolarizability (beta) has been measured in solution with the hyper-Rayleigh Scattering technique and also calculated by semiempirical AMI method. The trend in the observed and calculated values of first hyperpolarizability of these compounds has been found to be in good agreement. These compounds show moderate P values and excellent transparency in the visible region.

Unsymmetrical aryl disulfides with excellent transparency in the visible region for second order nonlinear optics

Several unsymmetrically substituted aromatic donor acceptor disulfides have been synthesized and analysed for their second order nonlinear optical properties. These molecules exhibit moderately high first hyperpolarizability (beta) with excellent transparency in the visible region. Most of the unsymmetrical disulfides have a cut-off wavelength below 420 nm. Calculations show that the molecules have an asymmetric charge distribution around the disulfide bond which is responsible for their high beta values. These results provide motivation for the design and synthesis of nonlinear optical chromophores with multiple disulfide bonds for large second order nonlinearity and excellent visible transparency.

Efficient visible light induced nuclease activity of a ternary mono-1,10-phenanthroline copper(II) complex containing 2-(methylthio)ethylsalicylaidimine

Ternary Schiff base copper(II) complex [CuL(phen)](ClO4), where HL is 2-(methylthio)ethylsalicylaldimine and phen is 1,10-phenanthroline, has been prepared and structurally characterized by X-ray crystallography. The complex shows a CuN3OS coordination in a square-pyramidal (4 + 1) geometry with the sulfur as an equatorial ligand. The complex is an avid binder to double-stranded DNA in the minor groove and exhibits both photonuclease and chemical nuclease activity. When exposed to UV light of 312 nm (96 W) or visible light of 532 nm (125 W) under aerobic conditions, the complex causes significant cleavage of supercoiled pUC19 DNA in the absence of any externally added reducing agent or H2O2.

Synthesis and characterization of carbon-covered alumina (CCA) supported TiO2 nanocatalysts with enhanced visible light photodegradation of Rhodamine B

The anatase phase of titania (TiO2) nano-photocatalysts was prepared using a modified sol gel process and thereafter embedded on carbon-covered alumina supports. The carbon-covered alumina (CCA) supports were prepared via the adsorption of toluene 2,4-diisocyanate (TDI) on the surface of the alumina. TDI was used as the carbon source for the first time for the carbon-covered alumina support system. The adsorption of TDI on alumina is irreversible; hence, the resulting organic moiety can undergo pyrolysis at high temperatures resulting in the formation of a carbon coating on the surface of the alumina. The TiO2 catalysts were impregnated on the CCA supports. X-ray diffraction analysis indicated that the carbon deposited on the alumina was not crystalline and also showed the successful impregnation of TiO2 on the CCA supports. In the Raman spectra, it could be deduced that the carbon was rather a conjugated olefinic or polycyclic hydrocarbons which can be considered as molecular units of a graphitic plane. The Raman analysis of the catalysed CCAs showed the presence of both the anatase titania and D and G band associated with the carbon of the CCAs. The scanning electron microscope micrographs indicated that the alumina was coated by a carbon layer and the energy dispersive X-ray spectra showed the presence of Al, O and C in the CCA samples, with the addition of Ti for the catalyst impregnated supports. The Brunauer Emmet and Teller surface area analysis showed that the incorporating of carbon on the alumina surface resulted in an increase in surface area, while the impregnation with TiO2 resulted in a further increase in surface area. However, a decrease in the pore volume and diameter was observed. The photocatalytic activity of the nanocatalysts was studied for the degradation of Rhodamine B dye. The CCA-TiO2 nanocatalysts were found to be more photocatalytically active under both visible and UV light irradiation compared to the free TIO2 nanocatalysts.

Layer-by-Layer Self-Assembled Metal-Ion- (Ag-, Co-, Ni-, and Pd-) Doped TiO2 Nanoparticles: Synthesis, Characterisation, and Visible Light Degradation of Rhodamine B

Metal-ion- (Ag, Co, Ni and Pd) doped titania nanocatalysts were successfully deposited on glass slides by layer-by-layer (LbL) self-assembly technique using a poly(styrene sulfonate sodium salt) (PSS) and poly(allylamine hydrochloride) (PAH) polyelectrolyte system. Solid diffuse reflectance (SDR) studies showed a linear increase in absorbance at 416 nm with increase in the number of m-TiO2 thin films. The LbL assembled thin films were tested for their photocatalytic activity through the degradation of Rhodamine B under visible-light illumination. From the scanning electron microscope (SEM), the thin films had a porous morphology and the atomic force microscope (AFM) studies showed ``rough'' surfaces. The porous and rough surface morphology resulted in high surface areas hence the high photocatalytic degradation (up to 97% over a 6.5 h irradiation period) using visible-light observed. Increasing the number of multilayers deposited on the glass slides resulted in increased film thickness and an increased rate of photodegradation due to increase in the availability of more nanocatalysts (more sites for photodegradation). The LbL assembled thin films had strong adhesion properties which made them highly stable thus displaying the same efficiencies after five (5) reusability cycles.

Remarkable photocytotoxicity of curcumin in HeLa cells in visible light and arresting its degradation on oxovanadium(IV) complex formation

Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400-700 nm giving IC50 = 8.2 +/- 0.2 mu M and its degradation is arrested on formation of photocytotoxic dipyridophenazine (dppz) complex VO(cur)(dppz)Cl] (IC50 = 3.3 +/- 0.4 mu M), while both are less toxic in the dark.

Extracting Three Dimensional Surface Model of Human Kidney from the Visible Human Data Set using Free Software

Three dimensional digital model of a representative human kidney is needed for a surgical simulator that is capable of simulating a laparoscopic surgery involving kidney. Buying a three dimensional computer model of a representative human kidney, or reconstructing a human kidney from an image sequence using commercial software, both involve (sometimes significant amount of) money. In this paper, author has shown that one can obtain a three dimensional surface model of human kidney by making use of images from the Visible Human Data Set and a few free software packages (ImageJ, ITK-SNAP, and MeshLab in particular). Images from the Visible Human Data Set, and the software packages used here, both do not cost anything. Hence, the practice of extracting the geometry of a representative human kidney for free, as illustrated in the present work, could be a free alternative to the use of expensive commercial software or to the purchase of a digital model.

Visible light photocatalytic inactivation of Escherichia coli with combustion synthesized TiO2

The photocatalytic inactivation of Escherichia coil was studied with combustion synthesized TiO2 photocatalysts in the presence of visible light. A series of 400W lamps irradiating in the visible region of the solar spectrum was used. The effect of various parameters, such as catalyst loading, light intensity, presence of inorganic ions, addition of hydrogen peroxide and pH, on the photocatalytic inactivation of E. coil was investigated. Photolysis alone had a small effect on inactivation while the dark experiment resulted in no inactivation and Ag/TiO2 showed the maximum inactivation. At a catalyst loading of 0.25 g/L, all the combustion synthesized catalysts showed better inactivation of E. coil compared to commercial Degussa P-25 (DP-25) TiO2 catalyst. An improved inactivation was observed with increasing lamp intensity and addition of H2O2. A negative effect on inactivation was observed by addition of inorganic ions such as HCO3-, SO42-, Cl-, NO3-, Na+, K+ and Ca2+. The photocatalytic inactivation of E. coli remained unaltered at different pH of the solution. The inactivation of E. coli was modeled with power law kinetics and was observed to follow first order kinetics. (C) 2012 Elsevier B.V. All rights reserved.

Enhanced Raman Spectroscopy of Molecules Adsorbed on Carbon-Doped TiO2 Obtained from Titanium Carbide: A Visible-Light-Assisted Renewable Substrate

Titanium carbide (TiC) is an electrically conducting material with favorable electrochemical properties. In the present studies, carbon-doped TiO2 (C-TiO2) has been synthesized from TiC particles, as well as TiC films coated on stainless steel substrate via thermal annealing under various conditions. Several C-TiO2 substrates are synthesized by varying experimental, conditions and characterized by UV-visible spectroscopy, photoluminescence, X-ray diffraction and X-ray photoelectron spectroscopic techniques. C-TiO2 in the dry state (in powder form as well as in film form) is subsequently used as a substrate for enhancing Raman signals corresponding to 4-mercaptobenzoic acid and 4-nitrothiophenol by utilizing chemical enhancement based on charge-transfer interactions. Carbon, a nonmetal dopant in TiO2, improves the intensities of Raman signals, compared, to undoped TiO2. Significant dependence of Raman intensity on carbon doping is observed. Ameliorated performance obtained using C-TiO2 is attributed to the presence of surface defects that originate due to carbon as a dopant, which, in turn,, triggers charge transfer between TiO2 and analyte. The C-TiO2 substrates are subsequently regenerated for repetitive use by illuminating an analyte-adsorbed substrate with visible light for a period of 5 h.

Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO2) nano-photocatalysts, with different phases, prepared using a modified sol-gel process were employed in the degradation of rhodamine at 10 mg L-1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450 degrees C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K-app) of 0.023 min(-1). The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024 min(-1) for 450, 500, 550 and 600 degrees C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017 min(-1), which is similar to that of the commercial titania.

ZnO/Poly(3,4-ethylenedioxythiophene) Poly(styrenesulfonate) Based Ultraviolet and Visible Photodetectors: Role of Defects

Here, we report the ZnO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) based photodetectors that can response to ultraviolet as well as visible light. The temporal response of the heterostructures for various excitations in the ultraviolet (UV) and visible range are performed. The time constants are found to be excitation-dependent, the response to visible light is better as compared to UV. The reason behind the better response to UV light is the high level of defects present in ZnO as confirmed by the photoluminescence (PL) measurements. This is corroborated by the time resolved fluorescence (TRF) measurements which provides sufficient information behind the slow response time under the UV excitations. The possible explanation being the non-radiative recombinations occurring due to the traps or impurities present in the film which slows down the photoresponse.

Effect of Metal Ions (Ag, Co, Ni, and Pd) on the Visible Light Degradation of Rhodamine B by Carbon-Covered Alumina-Supported TiO2 in Aqueous Solutions

Metal-ion (Ag, Co, Ni, and Pd) doped TiO2 nanocatalysts were successfully embedded on carbon-covered alumina supports. The CCA-embedded catalysts were crystalline and had a high surface area compared to the free metal-ion doped titania nanocatalysts while they still retained the anatase phase of the core TiO2. These catalysts were photocatalytically active under solar light irradiation. Rhodamine B was used as a model pollutant and the reactivity followed a pseudo-first-order reaction kinetics. The reaction rate of the CCA-supported catalysts was Pd > Ag > Co > Ni. Among the ratios of the CCA:catalyst used, it was found that the 1:1 ratio had the fastest reaction rate, followed by the 1:2 ratio, while the 2:1 ratio exhibited the lowest reaction rate. The CCA/metal-ion doped titania were found to have photocatalytic activities comparable with those of CCA-supported titania.