Muhammad Shahid

A stable and highly efficient visible-light photocatalyst of TiO2 and heterogeneous carbon core–shell nanofibers

A novel core–shell heterostructure of TiO2 nanofibers with carbon quantum dots embedded in an amorphous carbon shell has been successfully prepared via a simple electrospinning and impregnation process. Here, carbon quantum dots (CQDs) are designed as sensitizers for the visible-light response and amorphous carbon ensures intimate contact with TiO2. The photocatalytic performance is evaluated by the degradation of rhodamine-B under visible light irradiation. It is found that the composite nanofibers with an appropriate thickness of carbon shell exhibit a stable and highly efficient photocatalytic activity, and the apparent quantum efficiency can reach as high as 52%, which is about 10 times that of pure TiO2 nanofibers. Structural analyses show that the enhanced photocatalytic activity is attributed to the synergistic effect of TiO2, the amorphous carbon thin shell and the CQDs embedded inside. Due to the intimate contact between TiO2 and the carbon shell, the photogenerated electrons can be easily transferred from the CQDs to TiO2 resulting in a longer lifetime of the photogenerated electron–hole pairs and a higher photocatalytic activity. In addition, the unique upconversion properties of the CQDs enables the nanofibers to utilize more solar energy and increase the photocatalytic activity. Also, the carbon shell can induce more oxygen vacancies on the surface of the nanofibers, which can further enhance the photocatalytic activity. The results in this work may be beneficial to the future study of exploring new carbon-based heterostructured materials for visible-light-driven photocatalysts.

A high-performance TiO2 nanowire UV detector assembled by electrospinning

Here, a transparent, flexible and nanoscale TiO2 ultraviolet (UV) photodetector has been fabricated by electrospinning. Well aligned TiO2 nanowires were collected on a flexible mica substrate. Then, the nano-device was simply assembled by depositing interdigitated platinum electrodes on the surface. Upon UV illumination, the photosensitivity of this device is up to over three orders of magnitude with relatively fast and stable response speed under 254 nm and 365 nm UV light. This nanosensor retains a high photo-dark current ratio, fast response time and stable durability during bending tests, indicating an excellent reversibility and stability of the flexible TiO2 nanowires. The highly flexible photosensor demonstrates a good potential candidate for wearable optoelectronic applications.

Electrospun assembly: a nondestructive nanofabrication for transparent photosensors

Transparent electrodes based on a metal nanotrough network show superior electrical and optical properties. However, most metal networks fabricated by electrospinning are formed as film electrodes and are hard to pattern for the geometry shape of the device without any loss. Herein, we fabricate a highly transparent and flexible photodetector (PD) via a simple controlled electrospinning method. Owing to the trough- and belt-like geometry of Pt network electrodes, up to 83% transmittance can be obtained when the sheet resistances is 16 Ω sq-1, which may be the best performance for Pt-based transparent electrodes at present. The benefit of this advantage, is that a wearable UV PD could be obtained by a facile electrospun assembly. This all-transparent device achieves an extraordinary transparency of 90% at 550 nm and an even superior response sensitivity compared with that of a Pt film-based sensor (14 Ω sq-1 at 50% transparency). More importantly, this assembly approach has the versatility to enable us to fabricate highly transparent and flexible electronics in wearable applications, especially for the integration of oxide semiconductors and adhesive photoelectric hybrids.

Stretchable Platinum Network‐Based Transparent Electrodes for Highly Sensitive Wearable Electronics

A platinum network-based transparent electrode has been fabricated by electrospinning. The unique nanobelt structured electrode demonstrates low sheet resistance (about 16 Ω sq-1 ) and high transparency of 80% and excellent flexibility. One of the most interesting demonstrations of this Pt nanobelt electrode is its excellent reversibly resilient characteristic. The electric conductivity of the flexible Pt electrode can recover to its initial value after 160% extending and this performance is repeatable and stable. The good linear relationship between the resistance and strain of the unique structured Pt electrode makes it possible to assemble a wearable high sensitive strain sensor. Present reported Pt nanobelt electrode also reveals potential applications in electrode for flexible fuel cells and highly transparent ultraviolet (UV) sensors.

Indium-doped SnO2 nanobelts for high-performance transparent and flexible photosensors by a facile assembly

Flexible and transparent electronics is the emerging future technology for optoelectronic devices. Recently, it has attracted considerable attention from the research community due to its prodigious commercial applications. Herein, we report highly flexible and transparent ultraviolet photosensors based on indium-doped tin oxide nanobelts with enhanced simultaneous photosensitivity and recovery speed, compared to pure SnO2 nanobelts. Optoelectronic properties of the nanobelt photosensors have been found to be strongly related to the indium doping concentration and grain size of the nanobelts. A facile assembly method has been used to prepare the well-aligned nanobelt device for UV photosensors. Excellent flexible properties of the nanobelts have been explored, which show a superior response during bending tests and almost maintain their properties after 300 bending cycles. The enhanced photosensitivity of about 70 times that of undoped SnO2 nanobelts along with a highly enhanced recovery speed of less than 1.75 s have been achieved by the precise doping of In3+ into SnO2 lattice nanobelts. All these results show that our prepared photosensors demonstrate superior mechanical, electrical, and optical properties for their use in flexible and transparent electronics.

Attribution of runoff change in the alpine basin: a case study of the Heihe Upstream Basin, China

ABSTRACT Quantifying the relative contributions of different factors to runoff change is helpful for basin management, especially in the context of climate change and anthropogenic activities. The effect of snow change on runoff is seldom evaluated. We attribute the runoff change in the Heihe Upstream Basin (HUB), an alpine basin in China, using two approaches: a snowmelt-based water balance model and the Budyko framework. Results from these approaches show good consistency. Precipitation accounts for 58% of the increasing runoff. The contribution of land-cover change seems unremarkable for the HUB as a whole, where land-cover change has a major effect on runoff in each sub-basin, but its positive effect on increasing runoff in sub-basins 1 and 3 is offset by the negative effect in sub-basin 2. Snow change plays an essential role in each sub-basin, with a contribution rate of around 30%. The impact of potential evapotranspiration is almost negligible. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR S. Huang

High photodetectivity of low-voltage flexible photodetectors assembled with hybrid aligned nanowire arrays

One-dimensional (1-D) hybrid nanostructures with high opto-electronic performance, flexible features, and a rationally designed device assembly have an exponentially growing demand for their use in transparent and flexible photodetectors. To meet these requirements, a cost effective and facile processing route is mandatory for their fabrication and integration into the device assembly. Herein, we have successfully assembled photodetectors from high quality well-oriented uniaxially aligned hybrid ZnO–ZnGa2O4 nanofibers. Our prepared flexible devices demonstrate outstanding performance in terms of large responsivity (1.73 × 102 A W−1), high photodetectivity (∼1.02 × 1012 Jones), and external quantum efficiency (7.10 × 104%) along with fast rise and recovery times of less than 400 and 500 ms, respectively. In addition, the prepared photodetectors have shown outstanding flexibility and stability with more than 70% retention in photosensitivity at a very small bending radius of 2 mm. The synthesized hybrid nanofibers have also shown more than 80% transparency in the visible range (400–700 nm). The assembled hybrid photodetectors indicate that ZnO–ZnGa2O4 nanofibers are highly valuable for optoelectronic devices. It is also worth emphasizing that our assembled flexible photodetectors based on hybrid nanofibers with high surface-to-volume ratio have promising applications in soft electronics and invisible optoelectronic devices.

Understanding the impacts of climate change and human activities on streamflow: a case study of the Soan River basin, Pakistan

Climate change and land use change are the two main factors that can alter the catchment hydrological process. The objective of this study is to evaluate the relative contribution of climate change and land use change to runoff change of the Soan River basin. The Mann-Kendal and the Pettit tests are used to find out the trends and change point in hydroclimatic variables during the period 1983–2012. Two different approaches including the abcd hydrological model and the Budyko framework are then used to quantify the impact of climate change and land use change on streamflow. The results from both methods are consistent and show that annual runoff has significantly decreased with a change point around 1997. The decrease in precipitation and increases in potential evapotranspiration contribute 68% of the detected change while the rest of the detected change is due to land use change. The land use change acquired from Landsat shows that during post-change period, the agriculture has increased in the Soan basin, which is in line with the positive contribution of land use change to runoff decrease. This study concludes that aforementioned methods performed well in quantifying the relative contribution of land use change and climate change to runoff change.

Transparent Ultraviolet Photodetectors Based on Ga2O3 Electrospun Nanowires

Ultraviolet photodetectors (PDs) based on low-dimensional (LD) gallium oxide nanofibers were synthesized and assembled by a low cost and scalable electrospinning method. Highly uniaxially aligned nanofibers were used to assemble photodetectors. Photoconductive investigations indicate that the prepared photodetectors (PDs) are highly sensitive to ultraviolet (UV) light. The prepared photodetectors have shown a high photosensitivity (103), fast photoresponse, excellent stability, and reproducibility under the illumination of UV light 254 nm. These electrospun nanofibers have also shown a high transparency (<85%) in the visible light 400-700 nm range. The high transparency of these nanobelts demonstrates their use for invisible UV photosensors.

Anisotropy of mechanical and thermal properties of perovskite LaYbO3: first-principles calculations

ABSTRACT LaYbO3 ceramic material with a perovskite structure has the advantages of a high melting point, sintering resistance and high-temperature phase stability. It is a promising candidate for a structurally and functionally integrated material. However, the anisotropy of physical properties of LaYbO3 has rarely been studied. Herein, the anisotropy of the mechanical and thermal properties of LaYbO3 was studied by first-principles calculations. The elastic coefficients, Young’s modulus, Poisson’s ratio and minimum thermal conductivity of LaYbO3 were found to exhibit anisotropic characteristics. In particular, the sound velocity of the longitudinal wave was nearly twice that of the transverse wave. Especially, the minimum thermal conductivity of LaYbO3 at high temperature was found to be as low as 0.88u2005W/mu2005K, indicating that the compound has potential for use in thermal insulation applications.