Ultrasensitive NOX Detection in Simulated Exhaled Air: Enhanced Sensing via Alumina Modification of In-Situ Grown WO3 Nanoblocks.

Seedless growth of vertically aligned nanostructures, which can induce smoother transport and minimize Ohmic contact between substrate and semiconductor, can be fabricated by in situ growth utilizing modified hydrothermal methods. Such devices can be useful in designing non-invasive ultrasensitive hand-held sensors for diagnostic identification of volatile organic compounds (VOCs) in exhaled air, offering pain-free and easier detection of long-term diseases such as asthma. In the present work, WO3 nanoblocks, with a high surface area and porosity, have been grown directly over transparent conducting oxide to minimize Ohmic resistance, facilitating smoother electron transfer and enhanced current response. Further modification with porous alumina (γ-Al2 O3 ), by electrodeposition, resulted in the selective and ultrasensitive detection of NOX in simulated exhaled air. Crystal phase purity of as-fabricated pristine as well modified samples is validated with X-ray diffraction analysis. Morphological and microstructural analyses reveal the successful deposition of porous alumina over the surface of WO3 . Improved surface area and porosity is presented by porous alumina in the modified WO3 device, suggesting more active sites for the gas molecules to get adsorbed and diffuse through the pores. Oxygen vacancies, which are detrimental in the transport phenomenon in the presented sensors, have been studied using X-ray photoelectron spectroscopic (XPS) analysis. Gas sensing studies have been performed by fabricating chemiresistor devices based on bare WO3 and Al2 O3 -modified WO3 . The higher sensitivity for NOX gas in case of γ-Al2 O3 -modified WO3 based devices, as compared to bare WO3 -based devices, is attributed to the better surface area and charge transport kinetics. The presented device strategy offers crucial understanding in the design and development of non-invasive, hand-held devices for NO gas present in the human breath, with potential application in medical diagnostics.

Effect of surface overlayer in enhancing the photoelectrochemical water oxidation of in situ grown one-dimensional spinel zinc ferrite nanorods directly onto the substrate.

Overlayer passivation minimizes surface defects and arrests the back transfer of electrons for an enhanced charge extraction. Surface passivation of ZnFe2O4 using alumina yields enhanced charge carrier density from 8.43 × 1020 cm-3 to 18.83 × 1020 cm-3 giving a record efficiency in this class of compounds.

Efficient Energy Harvesting in SnO2-Based Dye-Sensitized Solar Cells Utilizing Nano-Amassed Mesoporous Zinc Oxide Hollow Microspheres as Synergy Boosters.

Finding the material characteristics satisfying most of the photovoltaic conditions is difficult. In contrast, utilization of foreign materials that can contribute to light harvesting and charge transfers in the devices is now desirable/thought-provoking. Herein, a binary hybrid photoanode utilizing nano-amassed micron-sized mesoporous zinc oxide hollow spheres (meso-ZnO HS) in conjunction with SnO2 nanoparticles (NPs), i.e., SnO2 NP_ZnO HS (for an optimized weight ratio (8:2)), displayed a nearly ∼4-fold increase in the efficiency (η) compared to that of bare SnO2 nanoparticle device. Enhanced device efficacy in the composite photoanode-based device can be accredited to the dual function of nano-amassed meso-ZnO HS. Nano-amassed micron-sized ZnO HS embedded in the photoanode can increase the light-harnessing capability without sacrificing the surface area as well as optical confinement of light by multiple reflections within its cavity and enhanced light-scattering effects. Electrochemical impedance spectroscopy analysis revealed an extended lifetime of electron (τe) and a higher value of R ct2 at the working electrode/dye/redox mediator interface, indicating a minimum photoinduced electron interception. The open-circuit voltage decay reveals a slower recombination kinetics of photogenerated electrons, supporting our claim that the nano-ammased meso-ZnO HS can serve as an energy barrier to the photoinjected electrons to retard the back-transfer to the electrolyte. Moreover, the improvement in the fill factors of the composite-based devices is endorsed to the facile penetration of the electrolyte through the pores of nano-amassed meso-ZnO HS, which increases the regeneration probability of oxidized dyes.

Cs -Symmetric Triphenylamine-Linked Bisthiazole-Based Metal-Free Donor-Acceptor Organic Dye for Efficient ZnO Nanoparticles-Based Dye-Sensitized Solar Cells: Synthesis, Theoretical Studies, and Photovoltaic Properties.

Herein, we have designed a metal-free donor-acceptor dye by incorporating an electron deficient bisthiazole moiety as a linker in between the electron donor triphenylamine and cyanoacetic acid acceptor. The bisthiazole-based organic dye D1 was synthesized using the Pd-catalyzed Suzuki cross-coupling and Knoevenagel condensation reactions. On the basis of the optical, electrochemical, and computational studies, dye D1 showed a better electronic interaction between the donor and acceptor moieties. As-synthesized C 2 symmetric triphenylamine-linked bisthiazole-based organic dye D1 has four anchoring groups, which play a significant role for better adsorption on the ZnO surface along with the enhanced kinetics of photoexcited electron injection. Consequently, photovoltaic properties of the organic dye D1 has been carried out by fabricating the ZnO nanoparticles (ZnO NPs)-based solar device. We obtained the maximum incident photon-to-current conversion efficiency of about 56.20%, with a short-circuit photocurrent density (J sc) of 13.60 mA cm-2, which results in a power conversion efficiency (PCE) of 4.94% under AM 1.5 irradiation (100 mW cm-2). The high PCE value is the result of proficient electron injection from E LUMO of dye D1 to the conduction band of ZnO NPs, as suggested by the computational calculations. Electrochemical impedance spectroscopy measurement is carried out to calculate the electron lifetime and also reveals the insight to the reduced charge recombinations at the various active interfaces of the photovoltaic device.

Understanding the role of silica nanospheres with their light scattering and energy barrier properties in enhancing the photovoltaic performance of ZnO based solar cells.

The present study discusses the design and development of a dye sensitized solar cell (DSSC) using a hybrid composite of ZnO nanoparticles (ZnO NP) and silica nanospheres (SiO2 NS). A ≈22% enhancement in the overall power conversion efficiency (PCE, η) was observed for the device fabricated with a binary hybrid composite of 1 wt% SiO2 NS and ZnO NP compared to the pristine ZnO NP device. A systematic investigation revealed the dual function of the silica nanospheres in enhancing the device efficacy compared to the bare ZnO NP based device. Sub-micron sized SiO2 NS can boost the light harvesting efficiency of the photoanode by optical confinement, resulting in increased propagation length of the incident light by multiple internal reflections, which was confirmed by UV-Vis diffused reflectance spectroscopy. Electrochemical impedance spectroscopic (EIS) analysis showed a reduced recombination of photo-generated electrons to the I-/I3- redox shuttle in the case of the composite photoanode. The higher recombination resistance (Rct) in the case of a 1 wt% composite indicates that the SiO2 NS serves as a partial energy barrier layer to retard the interfacial recombination (back transfer) of photo-generated electrons at the working electrode/electrolyte interface, increasing the device efficiency.

Rational design of hierarchical ZnO superstructures for efficient charge transfer: mechanistic and photovoltaic studies of hollow, mesoporous, cage-like nanostructures with compacted 1D building blocks.

Mesoporous and hollow zinc oxide (ZnO) hierarchical superstructures assembled with compact 1D building blocks that provide an efficient and faster transport pathway for photo-generated charge carriers have been synthesized using a biomass derived polysaccharide "alginic acid". To understand the interactions between the organic bio-template and inorganic growth units of ZnO in aqueous medium, the effects of additives such as the alginate ion (ALGI) and ammonium hydroxide (NH4OH), along with the controlled reaction conditions, are investigated using Field Emission Scanning Electron Microscopy (FESEM) and powder X-ray diffraction. Dynamic and steady-state photoluminescence measurements are carried out to understand the charge transfer processes in the compact 1D superstructures. Experimental analyses reveal that the alginate ions, under hydrothermal reaction conditions, act as a structure directing agent and assemble 1D ZnO nanorods (NRs) hierarchically while NH4OH assists the formation of ZnO growth units. A plausible mechanism for ZnO cage formation is proposed based on the experimental observations. Morphology dependent photovoltaic properties of ZnO heterostructures, i.e., for ZnO cages, ZnO NRs and ZnO PNPs, have been studied along with electrochemical impedance spectroscopy (EIS). Enhancement of ∼ 60% and ∼ 35% in power conversion efficiency (PCE) is observed in ZnO cage based devices as compared to ZnO NR- and ZnO PNP-based devices, respectively.

Ethyl Cellulose and Cetrimonium Bromide Assisted Synthesis of Mesoporous, Hexagon Shaped ZnO Nanodisks with Exposed ±{0001} Polar Facets for Enhanced Photovoltaic Performance in Quantum Dot Sensitized Solar Cells.

Hexagon shaped mesoporous zinc oxide nanodisks (ZnO NDs) with exposed ±{0001} polar facets have been synthesized by using ethyl cellulose (EC) and cetrimonium bromide (CTAB) as the capping and structure directing agents. We have characterized ZnO NDs using analytical techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area analysis and proposed a plausible mechanism for the formation of ZnO NDs. EC molecules form a colloidal solution in a 1-butanol:water (3:1) solvent system having a negative zeta potential (ζ ≈ -32 mV) value which can inhibit CTAB assisted c-axis growth of ZnO crystal and encourage the formation of ZnO NDs. In the control reactions carried out in presence of only CTAB and only EC, formation of hexagonal ZnO nanorods (NRs) and ZnO nanosheets (NSs) composed of numerous ZnO nanoparticles are observed, respectively. Photovoltaic properties of ZnO NDs as compared to ZnO NRs, ZnO NSs, and conventional ZnO nanoparticles (NPs) are investigated by co-sensitizing with CdS/CdSe quantum dots (QDs). An ∼35% increase in power conversion efficiency (PCE, η) is observed in ZnO NDs (η ≈ 4.86%) as compared to ZnO NPs (η ≈ 3.14%) while the values of PCE for ZnO NR and ZnO NS based devices are found to be ∼2.52% and ∼1.64%, respectively. Enhanced photovoltaic performance of the ZnO NDs based solar cell is attributed to an efficient charge separation and collection, boosted by the exposed ±(0001) facets apart from the single crystalline nature, better light-scattering effects, and high BET surface area for sensitizer particle adsorption. Electrochemical impedance spectroscopy (EIS) analysis further reveals that the charge recombination resistance and photoinduced electron lifetime are substantially higher in the ZnO ND based device than in ZnO NR, ZnO NP, and ZnO NS based devices, which demonstrates a slower electron-hole (e(-)-h(+)) recombination rate and faster charge migration through the single crystalline ZnO NDs.