Low power consumption, fast response and quick recovery times are important parameters for gas sensors performance. Herein, we report the experimental and theoretical studies of ZnO and Cr doped ZnO ...nanostructures used in low temperature (50 °C) sensors for the detection of CO. The synthesized films were characterized by XRD, UV-Vis, FE-SEM and EDX. The XRD patterns for the ZnO and 0.5 wt% Cr/ZnO films confirm the formation of a single-phase hexagonal wurtzite structure. The reduction of the ZnO optical band gap from 3.12 eV to 2.80 eV upon 0.5 wt% Cr doping is well correlated with the simulation data. The FE-SEM images of the films show spherical morphology with the estimated particle sizes of about ~40 nm and ~ 25 nm were recorded for the ZnO and 0.5 wt% Cr/ZnO films, respectively. Enhanced gas sensing performance is achieved with Cr doping and the sensitivity of ZnO increases from 9.65% to 65.45%, and simultaneously decreasing the response and recovery times from 334.5 s to 172.3 s and from 219 s to 37.2 s, respectively. These improvements in gas sensing performance are due to the reduction in particle size and optical band gap, and an increase in specific surface area.
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•Layered co-sensitization was evaluated in order to achieve high DSSC performance.•Natural pigments from Ixora and Canarium odontophyllum were extracted.•Adsorption studies were ...carried out for each extracted dyes.•Individual dyes, the mixture and layered co-sensitized were tested in DSSCs.•The layered co-sensitization gave the highest conversion efficiency among all.
This paper describes a double layered co-sensitization in dye sensitized solar cells (DSSCs) by using natural pigments from Ixora flower (Ixora sp. (Rubiaceae)) and the outer dark purple skin of ‘Kembayau’ (Canarium odontophyllum) fruit. UV–vis absorption data revealed that both dyes were anthocyanins. Co-sensitization was done by first adsorbing the dye from C. odontophyllum into TiO2 electrode by dipping, and then by removing adsorbed dye of the top layer of TiO2 using a de-sorption solution before the Ixora sp. dye was allowed to adsorb. Power conversion efficiency of the co-sensitized solar cell was 1.55%. The conversion efficiencies of DSSCs sensitized with Ixora sp. , C. odontophyllum and the mixture of both dyes (1:1) were 0.96%, 0.59% and 1.13% respectively. The superior conversion efficiency achieved by layered co-sensitization is attributed to the high adsorption capacities of Ixora sp. and C. odontophyllum, and the homogeneous monolayer adsorption of Ixora sp. as revealed by Freundlich and Langmuir adsorption isotherms.
An ultra-high plasmonic refractive index sensing structure composed of a metal–insulator–metal (MIM) waveguide coupled to a T-shape cavity and several metal nanorod defects is proposed and ...investigated by using finite element method. The designed plasmonic MIM waveguide can constitute a cavity resonance zone and the metal nanorod defects can effectively trap the light in the T-shape cavity. The results reveal that both the size of defects in wider rectangular cavity and the length of narrower rectangular cavity are primary factors increasing the sensitivity performance. The sensitivity can achieve as high as 8280 nm/RIU (RIU denotes the refractive index unit), which is the highest sensitivity reported in plasmonic MIM waveguide-based sensors to our knowledge. In addition, the proposed structure can also serve as a temperature sensor with temperature sensitivity as high as 3.30 nm/°C. The designed structure with simplicity and ease of fabrication can be applied in sensitivity nanometer scale refractive index sensor and may potentially be used in optical on-chip nanosensor.
A plasmonic nanostructure (PNS) which integrates metallic and dielectric media within a single structure has been shown to exhibit specific plasmonic properties which are considered useful in ...refractive index (RI) sensor applications. In this paper, the simultaneous realization of sensitivity and tunability of the optical properties of PNSs consisting of alternative Ag and dielectric of nanosphere/nanorod array have been proposed and compared by using three-dimensional finite element method. The proposed system can support plasmonic hybrid modes and the localized surface plasmonic resonances and cavity plasmonic resonances within the individual PNS can be excited by the incident light. The proposed PNSs can be operated as RI sensor with a sensitivity of 500 nm/RIU (RIU = refractive index unit) ranging from UV to the near-infrared. In addition, a narrow bandwidth and nearly zero transmittance along with a high absorptance can be achieved by a denser PNSs configuration in the unit cell of PNS arrays. We have demonstrated the number of modes sustained in the PNS system, as well as, the near-field distribution can be tailored by the dielectric media in PNSs.
Although efficiency of Dye Sensitized Solar Cell (DSSC) is still below the performance level of the market dominance silicon solar cells, in the last two decades DSSC has gathered sufficient ...interests because of the simplicity in device fabrication and low material cost, and therefore, DSSC is providing a possibility of solar cells production at a low entry cost. This review presents the research progress made in the implementation of natural pigments in DSSC. These pigments function as dye sensitizers and they play a major role in DSSC by absorbing light, and supplying electrons to the semiconductor matrixes in the cell. The common choices of dyes are the metal complexes, organic and/or natural dyes. A better efficiency with higher durability is observed for DSSC using metal complexes and organic dyes, however, the process of synthesizing these dyes is laborious, costly, and involves the use of toxic materials. As an alternative, natural pigments (dyes) found in plants such as anthocyanin, carotenoid, aurone, chlorophyll, tannin, betalain and many others are accepted as dyes in DSSCs. These natural pigments are easily obtained from fruits, flowers, leaves, seeds, barks and various parts of plants. Despite the limited performance of natural dyes, the prevailing advantages of natural dyes include high absorption coefficients, high light harvesting efficiency, low cost extraction and low toxicity. This review provides insight into the usage of the various natural pigments as sensitizers, the techniques to improve the pigments performance in DSSC, an outlook on the developmental work on the application of natural pigments in DSSC and their limitation. Additionally, the paper discusses the overall operation principle and the recent developments of each component of DSSC, as well as, comparing the material cost between natural dye and synthetic dye DSSC.
•Natural pigments have a promising future as sensitizers in DSSCs.•Anthocyanin, carotenoid, aurone, chlorophyll, tannin and betalain are among the natural pigments used as sensitizers.•Low-cost extraction, vast availability and eco-friendliness are major attractions of natural pigments.•The total fabrication cost for DSSC sensitized with chlorophyll is less than ~€ 2 per Watt peak.
We numerically and theoretically investigate a highly sensitive and tunable plasmonic refractive index sensor that is composed of a metal-insulator-metal waveguide with a side-coupled nanoring, ...containing silver nanorods using the finite element method. Results reveal that the presence of silver nanorods in the nanoring has a significant impact on sensitivity and tunability performance. It gives a flexible way to tune the system response in the proposed structure. Our designed sensor has a sensitivity of 2080 nm/RIU (RIU is the refractive index unit) along with a figure of merit and a quality factor of 29.92 and 29.67, respectively. The adequate refractive index sensitivity can increase by adding the silver nanorods in a nanoring, which can induce new surface plasmon polaritons (SPPs) modes that cannot be found by a regular nanoring. For a practical application, a valid introduction of silver nanorods in the nanoring can dramatically reduce the dimension of the proposed structure without sacrificing performance.
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•Cr doped cerium oxide nanostructures utilised for potential water treatment process.•Methylene blue dye degradation used as model study.•Catalysts were tested under UV- and H2O2- ...assisted Advanced Oxidation Process.•High Cr doping results in higher degradation efficiency for both AOP’s.•Attributed to lower band gap, oxygen vacancy and inhibition of exciton recombination.
Optimization of Advanced Oxidation Processes (AOPs) is key for the demand in green and sustainable method for degradation of organic contaminants in aqueous solution. In this study, the effect of Cr doping on CeO2 nanostructure was investigated to evaluate the catalytic performances of the Cr doped CeO2 nanocomposites with Methylene Blue (MB) used as model contaminant. Two types of AOPs were also explored; photocatalysis and H2O2 assisted. The Cr-doped CeO2 samples were prepared by deposition precipitation method and characterized with XRD, FE-SEM-EDX, UV–vis Spectroscopy and TPR. Generally, increase in Cr doping improved the catalytic activity in MB degradation efficiency for photocatalysis and H2O2-assisted methods, where with 3% weight of Cr-doping achieved 41 % and 59 % of MB degradation across 100 min respectively. The improvement of catalytic activity was attributed to the effects on Cr doping, which lowers the CeO2 band gap and also the Cr species serving as electron trapping centers to slow down the recombination of the charge carriers. The MB degradation results also showed that for Cr-doped CeO2 system, H2O2-assisted was the more effective catalytic method compared to photocatalysis. Isopropanol has been found explicitly feasible to demonstrate a plausible scavenging properties toward hydroxyl radical by suppressing the MB degradation in the reaction media, thus, suggesting that, the MB degradation mechanism proceeds via hydroxyl radical species.
In this paper, a periodic metallic-dielectric nanorod array which consists of Si nanorods coated with 30 nm Ag thin film set in a hexagonal configuration is fabricated and characterized. The ...fabrication procedure is performed by using nanosphere lithography with reactive ion etching, followed by Ag thin-film deposition. The mechanism of the surface and gap plasmon modes supported by the fabricated structure is numerically demonstrated by the three-dimensional finite element method. The measured and simulated absorptance spectra are observed to have a same trend and a qualitative fit. Our fabricated plasmonic sensor shows an average sensitivity of 340.0 nm/RIU when applied to a refractive index sensor ranging from 1.0 to 1.6. The proposed substrates provide a practical plasmonic nanorod-based sensing platform, and the fabrication methods used are technically effective and low-cost.
Plasmonic effect using a cross-hair can convey strongly localized surface plasmon modes among the separated composite nanostructures. Compared to its counterpart without the cross-hair, this ...characteristic has the remarkable merit of enhancing absorptance at resonance and can make the structure carry out a dual-band plasmonic perfect absorber (PPA). In this paper, we propose and design a novel dual-band PPA with a gathering of four metal-shell nanorods using a cross-hair operating at visible and near-infrared regions. Two absorptance peaks at 1050 nm and 750 nm with maximal absorptance of 99.59% and 99.89% for modes 1 and 2, respectively, are detected. High sensitivity of 1200 nm refractive unit (1/RIU), figure of merit of 26.67 and Q factor of 23.33 are acquired, which are very remarkable compared with the other PPAs. In addition, the absorptance in mode 1 is about nine times compared to its counterpart without the cross-hair. The proposed structure gives a novel inspiration for the design of a tunable dual-band PPA, which can be exploited for plasmonic sensor and other nanophotonic devices.
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•Natural dye was extracted from Canarium odontophyllum.•Dye constituents were separated by column chromatography.•DSSCs were sensitized with the constituents.•Improved performances of ...DSSCs using constituents.
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.
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