Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.V. B. thanks the Australian Research Council (ARC) for a Future Fellowship (FT140101285) and funding support through an ARC Discovery (DP170103477). ARC is also acknowledged for DECRA Fellowships to E. D. G. (DE170100164) and J. v. E. (DE150100427) and a Future Fellowship to N. C. (FT1401000834). M. S. acknowledges RMIT University for an Australian Postgraduate Award (APA). A. E. K., E. D. G., P. R. and R. R. acknowledge RMIT University for Vice Chancellor Fellowships. V. B. recognizes the generous support of the Ian Potter Foundation toward establishing an Ian Potter NanoBioSensing Facility at RMIT University. The authors acknowledge the support from the RMIT Microscopy and Microanalysis Facility (RMMF) for technical assistance and providing access to characterization facilities. This work was also supported by the ARC Centre of Excellence for Nanoscale BioPhotonics (CE140100003)

Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance

Silicon-based contaminants are ubiquitous in natural graphite, and they are thus expected to be present in exfoliated graphene. Here, the authors show that such impurities play a non-negligible role in graphene-based devices, and use high-purity parent graphite to boost the performance of graphene sensors and supercapacitor microelectrodes

Candle-soot derived photoactive and superamphiphobic fractal titania electrode

Carbon soot is one of the oldest materials known for its hydrophobic properties, robustness, and availability, making it an ideal material for use in various applications. The drawbacks, however, are the loose structural binding between constructing carbon nanoparticles and the amorphous nature of soot itself. In this paper, we present a facile chemical vapor deposition (CVD) method that maintains the soot template structural integrity and enables its modification into a highly photoactive, self-cleaning titania fractal network. The results show that the small air pockets available on the surface combined with the salinization process produces a TiO2 fractal network with superamphiphobic properties. Given the high surface area of the fractal network structure and titania's well-known photocatalytic activity, the designed surfaces were assessed for their photocatalytic decoloration activities. The results showed that the soot template derived TiO2 films can offer enormous potential in many different applications where self-cleaning and/or high surface area and photoactive properties are required

Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices

Straddled Band Aligned CuO/BaTiO₃ Heterostructures: Role of Energetics at Nanointerface in Improving Photocatalytic and CO₂ Sensing Performance

This work details novel insights on the role of energetics, that is, energy band bending and built-in potential at the nanointerface of CuO/BaTiO₃ forming type I <i>p</i>/<i>n</i> heterostructures, evaluated by correlating X-ray photoelectron spectroscopy and ultraviolet diffuse reflectance spectroscopy studies. Cetyltrimethyl­ammonium bromide (CTAB) assisted hydrothermal route was used to synthesize BaTiO₃ cuboids with six active {100} facets, and its CuO based heterostructures were tested for bifunctional applications in environmental nanoremediation. Straddled CuO/BaTiO₃ heterostructures reported herein showcased exceptional flexibility as a ultraviolet (UV) active photocatalyst for methyl orange (MO) degradation and chemo-resistive CO₂ gas sensor. CuO/BaTiO₃ heterostructures in equimole ratio could degrade 99% MO in 50 min with rate constant (κ) of a first-order reaction observed to be 10 and 100-fold greater in comparison with BaTiO₃ and CuO samples, respectively. Subsequently, in a parallel application, trials were carried out on CuO/BaTiO₃ heterostructures for their sensitivity and stability toward CO₂ gas below 5000 ppm. Upon Ag decoration, the sensor response improved compared to CuO/BaTiO₃ heterostructures at 160 °C, with enhanced response/recovery times (<i>t</i>₉₀) of 300 and 320 s, respectively towards 100 ppm CO₂ gas. Improved photoactivity was rationalized in terms of effective charge severance of photogenerated e–h pairs owing to favorable band alignment, while the optimum CO₂ sensor response was attributed to efficient nanointerfaces configured in large numbers and Ag⁰/Ag⁺ acting as redox couple

A Nanoengineered Conductometric Device for Accurate Analysis of Elemental Mercury Vapor

We developed a novel conductometric device with nanostructured gold (Au) sensitive layer which showed high-performance for elemental mercury (Hg⁰) vapor detection under simulated conditions that resemble harsh industrial environments. That is, the Hg⁰ vapor sensing performance of the developed sensor was investigated under different operating temperatures (30–130 °C) and working conditions (i.e., humid) as well as in the presence of various interfering gas species, including ammonia (NH₃), hydrogen sulfide (H₂S), nitric oxide (NO), carbon mono-oxide (CO), carbon dioxide (CO₂), sulfur dioxide (SO₂), hydrogen (H₂), methane (CH₄), and volatile organic compounds (VOCs) such as ethylmercaptan (EM), acetaldehyde (MeCHO) and methyl ethyl ketone (MEK) among others. The results indicate that the introduction of Au nanostructures (referred to as nanospikes) on the sensor’s surface enhanced the sensitivity toward Hg⁰ vapor by up-to 450%. The newly developed sensor exhibited a limit of detection (LoD) (∼35 μg/m³), repeatability (∼94%), desorption efficiency (100%) and selectivity (∼93%) when exposed to different concentrations of Hg⁰ vapor (0.5 to 9.1 mg/m³) and interfering gas species at a chosen operating temperature of 105 °C. Furthermore, the sensor was also found to show 91% average selectivity when exposed toward harsher industrial gases such as NO, CO, CO₂, and SO₂ along with same concentrations of Hg⁰ vapor in similar operating conditions. In fact, this is the first time a conductometric sensor is shown to have high selectivity toward Hg⁰ vapor even in the presence of H₂S. Overall results indicate that the developed sensor has immense potential to be used as accurate online Hg⁰ vapor monitoring technology within industrial processes

Zinc Titanate Nanoarrays with Superior Optoelectrochemical Properties for Chemical Sensing

In this report, the gas sensing performance of zinc titanate (ZnTiO3) nanoarrays (NAs) synthesized by coating hydrothermally formed zinc oxide (ZnO) NAs with TiO2 using low-temperature chemical vapor deposition is presented. By controlling the annealing temperature, diffusion of ZnO into TiO2 forms a mixed oxide of ZnTiO3 NAs. The uniformity and the electrical properties of ZnTiO3 NAs made them ideal for light-activated acetone gas sensing applications for which such materials are not well studied. The acetone sensing performance of the ZnTiO3 NAs is tested by biasing the sensor with voltages from 0.1 to 9 V dc in an amperometric mode. An increase in the applied bias was found to increase the sensitivity of the device toward acetone under photoinduced and nonphotoinduced (dark) conditions. When illuminated with 365 nm UV light, the sensitivity was observed to increase by 3.4 times toward 12.5 ppm acetone at 350 °C with an applied bias of 9 V, as compared to dark conditions. The sensor was also observed to have significantly reduced the adsorption time, desorption time, and limit of detection (LoD) when excited by the light source. For example, LoD of the sensor in the dark and under UV light at 350 °C with a 9 V bias is found to be 80 and 10 ppb, respectively. The described approach also enabled acetone sensing at an operating temperature down to 45 °C with a repeatability of >99% and a LoD of 90 ppb when operated under light, thus indicating that the ZnTiO3 NAs are a promising material for low concentration acetone gas sensing applications.The support from the Australian Research Council through Discovery Project DP150101939 is gratefully acknowledged. R.K.C.B. acknowledges the financial assistance of the RMIT University HDR publication grant. A.E.K. acknowledges the RMIT Vice Chancellor fellowship scheme

1,4-Dihydropyrrolo[3,2‑<i>b</i>]pyrroles as a Single Component Photoactive Layer: A New Paradigm for Broadband Detection

Single component organic photodetectors capable of broadband light sensing represent a paradigm shift for designing flexible and inexpensive optoelectronic devices. The present study demonstrates the application of a new quadrupolar 1,4-dihydropyrrolo­[3,2-<i>b</i>]­pyrrole derivative with spectral sensitivity across 350–830 nm as a potential broadband organic photodetector (OPD) material. The amphoteric redox characteristics evinced from the electrochemical studies are exploited to conceptualize a single component OPD with ITO and Al as active electrodes. The photodiode showed impressive broadband photoresponse to monochromatic light sources of 365, 470, 525, 589, 623, and 830 nm. Current density–voltage (<i>J</i>–<i>V</i>) and transient photoresponse studies showed stable and reproducible performance under continuous on/off modulations. The devices operating in reverse bias at 6 V displayed broad spectral responsivity (<i>R</i>) and very good detectivity (<i>D</i>*) peaking a maximum 0.9 mA W^–1 and 1.9 × 10¹⁰ Jones (at 623 nm and 500 μW cm^–2) with a fast rise and decay times of 75 and 140 ms, respectively. Low dark current densities ranging from 1.8 × 10^–10 Acm^–2 at 1 V to 7.2 × 10^–9 A cm^–2 at 6 V renders an operating range to amplify the photocurrent signal, spectral responsivity, and detectivity. Interestingly, the fabricated OPDs display a self-operational mode which is rarely reported for single component organic systems