N.T.R.N. Kumara

Sputtered copper oxide (CuO) thin films for gas sensor devices

Copper oxide (CuO) thin films were deposited using a reactive DC sputtering method for gas sensor applications. The structure of the films determined by means of an x-ray diffraction method indicates that the phase of copper oxide can be synthesized in the total pressure and temperature ranges of 6?8.5?mbar and 151?192??C, respectively. The resistivity of the film synthesized at a substrate temperature of 192??C increases from 0.104 to 0.51???m after absorbing CO2 gas at 135??C. The gas sensitivity of the film synthesized at the substrate temperature of 192??C increases up to 5.1 in the presence of CO2 gas at 160??C. The gas sensitivity in the presence of N2 gas reaches only 1.43 even at 200??C.

Potential natural sensitizers extracted from the skin of Canarium odontophyllum fruits for dye-sensitized solar cells.

Possibility of use of dye extract from skin samples of a seasonal, indigenous fruit from Borneo, namely Canarium odontophyllum, in dye sensitized solar cells (DSSCs) are explored. Three main groups of flavonoid pigments are detected and these pigments exhibit different UV-vis absorption properties, and hence showing different light harvesting capabilities. When applied in DSSCs. The detected pigment constituents of the extract consist of aurone (maritimein), anthocyanidin (pelargonidin) and anthocyanidin (cyanidin derivatives). When tested in DSSC, the highest conversion efficiency of 1.43% is exhibited by cyanidin derivatives, and this is followed by conversion efficiencies of 0.51% and 0.79% for aurone and pelargonidin, respectively. It is shown that individual pigments, like cyanidin derivatives and pelargonidin, exhibit higher power conversion efficiency when compared to that of C.odontophyllum skin pigment mixture (with a conversion efficiency of only 0.68%). The results indicate a possibility of masking effects of the pigments when used as a mixture. The acidification of C.odontophyllum skin pigments with concentrated hydrochloric acid improves the conversion efficiency of the mixture from 0.68% to 0.99%. The discussion in this paper will draw data and observations from the variation in absorption and adsorption properties, the HOMO-LUMO levels, the energy band gaps and the functional group compositions of the detected flavonoids.

Study of the Enhancement of Cell Performance of Dye Sensitized Solar Cells Sensitized With Nephelium lappaceum (F: Sapindaceae)

We have studied the performance of dye sensitized solar cells sensitized with pigments extracted from the fruit sheath of Nephelium lappaceum (F: Sapindaceae). The pH of the pigment solution used for impregnation was controlled by adding concentrated HCl (50:0.2 v/v). The UV-Vis spectroscopic results revealed that the extract consists of the pigment of Anthocyanin, with an additional absorption peak appearing around 540nm at a lower pH of the pigment solution. Also the band gap of the pigment was reduced by 1eV at low pH conditions. The solar cells fabricated with pigment extracted from the fruit sheath of Nephelium lappaceum showed photo-response with the conversion efficiency of 0.26%, with an open-circuit voltage (VOC) of 453mV, short-circuit current density (ISC) of 1.17mA cm � 2 , and fill factor (ff) of 0.48. The conversion efficiency was significantly enhanced when pH of the pigment solution was lowered by adding concentrated HCl. The conversion efficiency of the dye sensitized solar cells (DSSCs) sensitized after HCl treatment of the pigment was increased to 0.56%, with an open-circuit voltage (VOC )o f 404mV, short-circuit current density (ISC) of 2.71mA cm � 2 , and fill factor (ff) of 0.35. The HOMO level of the pigment at low pH was shown to be shifted towards more positive values with respect to vacuum level, giving rise to an enhanced DSSC efficiency. The overall efficiency enhancement of the low pH pigment was due to the combined effect of increased UV-Vis absorption and efficient adsorption of dye molecules onto the TiO2 semiconductor surface. [DOI: 10.1115/1.4023877]

Equilibrium Isotherm Studies of Adsorption of Pigments Extracted from Kuduk-kuduk (Melastoma malabathricum L.) Pulp onto TiO2 Nanoparticles

The adsorption of natural pigments onto TiO2 nanoparticles was investigated. The pigments were extracted from the dark purple colored pulp of the berry-like capsule of Kuduk-kuduk (Melastoma malabathricum L.). The Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models were used to analyze the equilibrium experimental data. Data correlated well with the Sips isotherm model, where the heterogeneity factor ( ) indicated heterogeneous adsorption characteristics, with a maximum adsorption capacity of 0.0130 mg/g. The heterogeneous adsorption character was further supported by results obtained from zeta-potential measurements. When a dye-sensitized solar cell (DSSC) was sensitized with the extracted pigment, the photo-energy conversion efficiency was measured to be 0.83%, thus proving the suitability of Kuduk-kuduk fruit pulp as a sensitizer in DSSCs.

DFT/TDDFT and Experimental Studies of Natural Pigments Extracted from Black Tea Waste for DSSC Application

We report results of combined experimental and theoretical studies of black tea waste extract (BTE) as a potential sensitizer for TiO2-dye-sensitized solar cells (DSSCs). UV-vis absorption data revealed that BTE contains theaflavin. DSSC sensitized with pigment complexes of BTE showed a photon-energy conversion efficiency of %, while a significant increase (%) is observed when pH of the pigment solution was lowered. The HOMO and LUMO energy levels were calculated using experimental data of UV-vis absorption and cyclic voltammetry. These calculations revealed a reduction of the band gap by 0.17 eV and more negativity of HOMO level of acidified pigment, compared to that of original pigment. Combined effect of these developments caused the enhanced efficiency of DSSC. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computational calculations were carried out to study the four theaflavin analogues which are responsible for the dark colour of BTE. According to the calculations, two theaflavin analogues, theaflavin and theaflavin digallate, are the most probable sensitizers in this dye-sensitized solar cell system.

Tailoring surface plasmon resonance and dipole cavity plasmon modes of scattering cross section spectra on the single solid-gold/gold-shell nanorod

Tunable surface plasmon resonance (SPR) and dipole cavity plasmon modes of the scattering cross section (SCS) spectra on the single solid-gold/gold-shell nanorod have been numerically investigated by using the finite element method. Various effects, such as the influence of SCS spectra under x- and y-polarizations on the surface of the single solid-gold/gold-shell nanorod, are discussed in detail. With the single gold-shell nanorod, one can independently tune the relative SCS spectrum width by controlling the rod length and rod diameter, and the surface scattering by varying the shell thickness and polarization direction, as well as the dipole peak energy. These behaviors are consistent with the properties of localized SPRs and offer a way to optically control and produce selected emission wavelengths from the single solid-gold/gold-shell nanorod. The electric field and magnetic distributions provide us a qualitative idea of the geometrical properties of the single solid-gold/gold-shell nanorod on plasmon resonance.

Impacts of temperature on the stability of tropical plant pigments as sensitizers for dye sensitized solar cells.

Natural dyes have become a viable alternative to expensive organic sensitizers because of their low cost of production, abundance in supply, and eco-friendliness. We evaluated 35 native plants containing anthocyanin pigments as potential sensitizers for DSSCs. Melastoma malabathricum (fruit pulp), Hibiscus rosa-sinensis (flower), and Codiaeum variegatum (leaves) showed the highest absorption peaks. Hence, these were used to determine anthocyanin content and stability based on the impacts of storage temperature. Melastoma malabathricum fruit pulp exhibited the highest anthocyanin content (8.43 mg/L) followed by H. rosa-sinensis and C. variegatum. Significantly greater stability of extracted anthocyanin pigment was shown when all three were stored at 4°C. The highest half-life periods for anthocyanin in M. malabathricum, H. rosa-sinensis, and C. variegatum were 541, 571, and 353 days at 4°C. These were rapidly decreased to 111, 220, and 254 days when stored at 25°C. The photovoltaic efficiency of M. malabathricum was1.16%, while the values for H. rosa-sinensis and C. variegatum were 0.16% and 1.08%, respectively. Hence, M. malabathricum fruit pulp extracts can be further evaluated as an alternative natural sensitizer for DSSCs.

Plasmonic spectrum on 1D and 2D periodic arrays of rod-shape metal nanoparticle pairs with different core patterns for biosensor and solar cell applications

Simulations of surface plasmon resonance (SPR) on the near field intensity and absorption spectra of one-dimensional (1D) and two-dimensional (2D) periodic arrays of rod-shape metal nanoparticle (MNP) pairs using the finite element method (FEM) and taking into account the different core patterns for biosensor and solar cell applications are investigated. A tunable optical spectrum corresponding to the transverse SPR modes is observed. The peak resonance wavelength (λ res) can be shifted to red as the core patterns in rod-shape MNPs have been changed. We find that the 2D periodic array of core–shell MNP pairs (case 2) exhibit a red shifted SPR that can be tuned the gap enhancement and absorption efficiency simultaneously over an extended wavelength range. The tunable optical performances give us a qualitative idea of the geometrical properties of the periodic array of rod-shape MNP pairs on SPRs that can be as a promising candidate for plasmonic biosensor and solar cell applications.

Dynamic Light Scattering and Zeta Potential Studies of Ceria Nanoparticles

A Cerium (IV) oxide nanoparticle (nanoceria) is widely used in different applications such as biomedicine and catalysis due to its unique structural, morphological and catalytic properties. In this report, the dispersion of nanoceria in both aqueous and non-aqueous (methanol and ethanol) media were studied. Adsorption-desorption processes were observed upon addition of different classes of surfactants such as citric acid (CA), cetrimonium bromide (CTAB) and diethanolamine (DEA). Stable dispersions were obtained in both aqueous, non-aqueous and electrolyte assisted media with the overall mechanism being hydrolysis, dissolution and adsorption. XRD, FE-SEM, FTIR and DLS have been used in the present study to characterize the nanoceria and to quantitatively analyze their average particle size distributions in a unique electrolyte mixture of (0.1 M NaOH/ 65% HNO3:H2O, 1:1 v/v) which has not been reported previously. The surface charge study was carried out across a wide pH range between 1.4 – 9.6 and the isoelectric points (IEP) with respect to 15 ml H2O and 50 ml H2O dispersed phases occurred at a pH of about 6.5 and 6.7 respectively. The present study could be useful in a wide range of applications including nanoparticle synthesis, stabilization, and adsorption of toxic materials, biomedical and pharmaceutical.

Ruthenium Dye (N3) Removal from Simulated Wastewater Using Bamboo Charcoal and Activated Bamboo Charcoal

The presence of heavy metals such as mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (T1) and ruthenium (Ru) in wastewater, even in trace quantities, could cause a negative impact on our health. The adsorption method has been proven to be the most effective and low-cost method for removing of heavy metals from wastewater. In this study, biomass waste was used as a low-cost precursor for the production of cost-effective charcoal and activated carbon. Solid waste from a common local bamboo species (Gigantochloa sp.) was used to produce charcoal and activated carbon. The simulated wastewater was made with Ruthenium complex (N3) dye solution as the adsorbate. The bamboo charcoal was prepared by carbonization, and activated carbon was prepared by NaOH activation after carbonization. The morphological characteristics, chemical compositions, and the lattice structures of the prepared adsorbents were analyzed using SEM, EDX, and XRD. The adsorption performance of the prepared adsorbents toward N3 dye was evaluated, and the highest adsorption capacity of 1.50 mg/g was obtained from activated carbon. The results showed that the activated bamboo-based charcoal has a better adsorption efficiency when compared to the bamboo charcoal for the treatment of N3 dye in wastewater.