Photocatalytic degradation of dimethoate using LbL fabricated TiO2/polymer hybrid films

Degradation of dimethoate under UV irradiation using TiO2/polymer films prepared by the layer-by-layer (LbL) method was investigated. The thin films were fabricated on glass slides and the surface morphology and roughness of the thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of lamp intensity, catalyst loading in the layers, number of bilayers, pH and initial dimethoate concentration on the degradation of dimethoate was systematically studied. The degradation was monitored using high performance liquid chromatography (HPLC) analysis and total organic carbon (TOC) measurements as a function of irradiation time, to see the change in concentration of dimethoate and mineralization, respectively. Complete degradation of dimethoate was achieved under TiO2 optimum loading of 4 g/L at an UV irradiation time of 180 min. Increase in the lamp intensity, catalyst loading and number of bilayers increased the rate of degradation. At a pH of 4.62, complete degradation of dimethoate was observed. The degradation efficiency decreased with increase in initial dimethoate concentration. The degradation byproducts were analyzed and confirmed by gas chromatography-mass spectra (GC-MS). Toxicity of the irradiated samples was measured using the luminescence of bacteria Vibrio fischeri after 30 min of incubation and the results showed more toxicity than the parent compound. Catalyst reusability studies revealed that the fabricated thin films could be repeatedly used for up to ten times without affecting the photocatalytic activity of the films. The findings of the present study are very useful for the treatment of wastewaters contaminated with pesticides. (C) 2011 Elsevier B.V. All rights reserved.

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.

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO2) nanowires have been synthesized at a low substrate temperature of 450 degrees C via vapor-liquid-solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2-4 mu m and diameter of 20-60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO2 nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO2 nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 x 10(-4) mbar suggested that a temperature equal to or greater than 450 degrees C was the best condition for phase pure SnO2 nanowires growth. The SnO2 nanowires grown on a SiO2 substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO2 NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 mu W/cm(2) UV lamp (330 nm) intensity on the photo detector.

Near-infrared photoactive Cu2ZnSnS4 thin films by co-sputtering

The thin films of Cu2ZnSnS4 (CZTS) were grown by co-sputtering further the structural, optical and electrical properties were analyzed and confirmed the CZTS phase formation. The photo response of CZTS in near IR photodectection has been demonstrated. The detector response was measured employing both the IR lamp and IR laser illuminations. The calculated growth and decay constants were 130 m sec and 700 m sec followed by the slower components upon lamp illumination. The external quantum efficiency of 15%, responsivity of 13 AW(-1) makes CZTS a suitable candidate for the IR photodectection.

Facile synthesis of Cu2CoSnS4 nanoparticles exhibiting red-edge-effect: Application in hybrid photonic devices

Cu2CoSnS4 (CCTS) quaternary semiconducting nanoparticles with size distribution from 20 nm to 60 nm were synthesized by one-pot low temperature time and surfactant dependent hydrothermal route. Nanoparticles were characterized structurally and optically. Excitation dependent fluorescence exhibited a dynamic stoke shift referring to the Red-Edge-Effect with peak shifting by a greater magnitude (>100 nm) towards red side, in all the samples. Hybrid devices, fabricated from CCTS nanoparticle inorganic counterparts benefitting from the conjugation of organic P3HT polymer matrix, were demonstrated for photodetection under infra-red and A. M 1.5 solar light illuminations. Faster rise and decay constants of 37 ms and 166 ms, with one order photocurrent amplification from 1.6 x 10(-6) A in the dark to 6.55 x 10(-5) A, upon the 18.50 mW cm(-2) IR lamp illumination, make CCTS a potential candidate for photodetector and photovoltaic applications. (C) 2013 AIP Publishing LLC.

Near-infrared photoactive Cu3BiS3 thin films by co-evaporation

Semiconducting Cu3BiS3 (CBS) thin films were deposited by co-evaporation of Cu, Bi elemental metallic precursors, with in situ sulphurisation, using a quartz effusion cell. Cu3BiS3 thin films were structurally characterized by XRD and FE-SEM. The chemical bonding of the ions was examined by XPS. As deposited films were demonstrated for metal-semiconductor-metal near IR photodectection under lamp and laser illuminations. The photo current amplified to three orders and two orders of magnitude upon the IR lamp and 60 m W cm(-2) 1064 nm IR laser illuminations, respectively. Larger grains, made up of nano needle bunches aided the transport of carriers. Transport properties were explained based on the trap assisted space charge conduction mechanism. Steady state detector parameters like responsivity varied from 1.04 AW(-1) at 60 m Wcm(-2) to 0.22 AW(-1) at 20 m Wcm(-2). Detector sensitivity of 295 was found to be promising and further could be tuned for better responsivity and efficiency in utilization of near infra-red photodetector. (C) 2014 AIP Publishing LLC.

In situ formation of silver nanowire networks on paper

Simple, universally adaptable techniques for fabricating conductive patterns are required to translate laboratory-scale innovations into low-cost solutions for the developing world. Silver nanostructures have emerged as attractive candidates for forming such conductive patterns. We report here the in situ formation of conductive silver-nanowire networks on paper, thereby eliminating the need for either cost-intensive ink formulation or substrate preparation or complex post-deposition sintering steps. Reminiscent of the photographic process of `salt printing', a desktop office printer was used to deposit desired patterns of silver bromide on paper, which were subsequently exposed to light and then immersed in a photographic developer. Percolating silver nanowire networks that conformally coated the paper fibres were formed after 10 min of exposure to light from a commercial halogen lamp. Thus, conductive and patterned films with sheet resistances of the order of 4 Omega/rectangle can be easily formed by combining two widely used processes - inkjet printing and photographic development.

Tailoring the Cu(In, Al)S-2 nanostructures for photonic applications

Solvent dependent and low temperature based Chalcopyrite CuIn1-xAlxS2 (CIAS) nano structures were synthesized by a simple one-pot solvothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and micro-Raman spectroscopy were used to characterize the nanostructures structurally and optically. CIAS hollow spheres were constructed from the nanoplates. Detailed formation mechanism of the hollow spheres was explained. Tentative optical phonon vibrational modes have been discussed. Steady state room temperature IR photodectection have been demonstrated with all the CIAS nanostructures under IR lamp illumination. Photo current was amplified by two orders and one order in case of nano needle like structures and hollow spheres respectively, which was explained based upon the trap assisted space charge. Growth and decay constants lasted for few milli seconds.

Nanocomposite Based Organic-Inorganic Cu3BiS3 High Sensitive Hybrid Photonic Devices

We report the synthesis and application Cu3BiS3 nanorods in infrared photodectection. Cu3BiS3 nano rods were characterized structurally, optically and electrically. The detailed IR photodectection properties in terms of photo response were demonstrated with IA lamp and 1064 nm laser illuminations. The rapid photocurrent time constants followed by the slower components, resulting due to the defect states. The photo detecting properties for different concentrations of nanorods blended with the conjugate polymer devices were demonstrated. Further the photocurrent was enhanced to threefold increase from 3.47 x 10(-7) A to 2.37 x 10(-3) A at 1 V for 10 mg nanorods embedded in the polymer device. Responsivity of hybrid device was enhanced from 0.0158 NW to 102 NW. The detailed trap assisted space charge transport properties were studied considering the different regimes. Hence Cu3BiS3 can be a promising candidate in the nano switchable near IA photodetectors.

Estimation of background carrier concentration in fully depleted GaN films

Buffer leakage is an important parasitic loss mechanism in AlGaN/GaN high electron mobility transistors (HEMTs) and hence various methods are employed to grow semi-insulating buffer layers. Quantification of carrier concentration in such buffers using conventional capacitance based profiling techniques is challenging due to their fully depleted nature even at zero bias voltages. We provide a simple and effective model to extract carrier concentrations in fully depleted GaN films using capacitance-voltage (C-V) measurements. Extensive mercury probe C-V profiling has been performed on GaN films of differing thicknesses and doping levels in order to validate this model. Carrier concentrations as extracted from both the conventional C-V technique for partially depleted films having the same doping concentration, and Hall measurements show excellent agreement with those predicted by the proposed model thus establishing the utility of this technique. This model can be readily extended to estimate background carrier concentrations from the depletion region capacitances of HEMT structures and fully depleted films of any class of semiconductor materials.

LOW RESISTANCE LIQUID MOTION FOR ENERGY HARVESTING

Low resistance motion of liquids on a well-defined path is beneficial for several MEMS based applications including energy harvesting and switching. By eliminating the contact line we demonstrate low resistance motion of a liquid bulge on pre-wetted strips. The bulge appears on wetted strips due to a morphological instability. The wetted strip confines the mercury bulge and defines its path of motion. Resistance to initiate motion of the bulge was studied experimentally and compared to other cases. An electret based energy harvesting device using bulge motion has been fabricated and tested.