Ahsanulhaq Qurashi

Ultra-fast Microwave Synthesis of ZnO Nanowires and their Dynamic Response Toward Hydrogen Gas

Ultra-fast and large-quantity (grams) synthesis of one-dimensional ZnO nanowires has been carried out by a novel microwave-assisted method. High purity Zinc (Zn) metal was used as source material and placed on microwave absorber. The evaporation/oxidation process occurs under exposure to microwave in less than 100 s. Field effect scanning electron microscopy analysis reveals the formation of high aspect-ratio and high density ZnO nanowires with diameter ranging from 70 to 80 nm. Comprehensive structural analysis showed that these ZnO nanowires are single crystal in nature with excellent crystal quality. The gas sensor made of these ZnO nanowires exhibited excellent sensitivity, fast response, and good reproducibility. Furthermore, the method can be extended for the synthesis of other oxide nanowires that will be the building block of future nanoscale devices.

Fabrication and gas sensing properties of In2O3 nanopushpins

The growth of nanopushpin-like In2O3 nanostructures was demonstrated on the silicon substrate by catalyst-free chemical vapor deposition method. Structural analysis revealed single-crystalline nature of the In2O3 nanopushpins with a cubic crystal structure. The hydrogen sensor made from the In2O3 nanopushpins showed swift response and excellent stability. The influence of operation temperature on the hydrogen gas sensing property of In2O3 nanostructures was also investigated. Our results reveal that the sensor response of In2O3 nanopushpins increases with increasing the operation temperature.

Sonochemical assisted hydrothermal synthesis of pseudo-flower shaped Bismuth vanadate (BiVO4) and their solar-driven water splitting application

Bismuth vanadate (BiVO4) is a well-known photocatalyst due to its lower bandgap (Eg) and visible electromagnetic light absorption capacity. Herein, we reported the pulse ultra-sonochemical assisted hydrothermal approach to synthesize S-BiVO4. For the comparison purpose, H-BiVO4 is also synthesized via conventional hydrothermal approach. The surface morphology of S-BiVO4 through scanning electron microscope (SEM) indicates condensed microarrays (MAs) having pseudo-flower shapes. The energy dispersive X-rays (EDX) spectrum also confirmed the elemental percent composition of Bi, V and O in BiVO4. X-rays diffraction (XRD) pattern further confirmed the monoclinic scheelite phase of S-BiVO4. Fourier transformed infrared (FTIR) spectrum showed Bi-O and Bi-V-O vibrational bands at 1382 and 1630cm-1, respectively. The diffuse reflectance spectroscopy (DRS) indicated absorption edge at ∼515nm, corresponds to bandgap value (Eg) of 2.41eV, which is suitable range for water splitting applications. The photocurrent density from water splitting under artificial 1 SUN visible light source found at 60 and 50μA/cm2 for S-BiVO4 and H-BiVO4, respectively. The stability test through chronoamperometry showed that S-BiVO4 was more stable than H-BiVO4. It can be depicted from the growth mechanism that ultrasonication played a definite role in the overall synthesis of pseudo-flower shaped S-BiVO4 MAs.

Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties

Synthesis of SnO2 nanoparticles have been successfully accomplished moderately at lower temperature by facile, rapid, efficient and mild ultrasonic irradiation method. The as-grown SnO2 nanoparticles are investigated by various characterization techniques in terms of structural, optical, electrical and gas sensing properties. XRD investigation has shown that the SnO2 nanoparticles materials exhibit single rutile crystal phase with high crystallinity. FESEM studies showed uniform and monodisperse morphology of SnO2 nanoparticles. The chemical composition of SnO2 was systematically studied by EDX measurements. Additional confirmation of three Raman shifts (432, 630, 772cm-1) indicated the characteristic properties of the rutile phase of the as-grown SnO2 nanoparticles. The optical properties of SnO2 nanoparticles were examined by DRS, and the electronic band gap of SnO2 nanoparticles were around 3.6eV. Electrical properties of the SnO2 nanoparticles measured at various temperatures have shown the semiconducting properties. Surface area and pore size of synthesized nanoparticles were analyzed from BET. It has been revealed that SnO2 nanoparticles have surface area is 47.8574m2/g and the pore size is 10.5nm. Moreover, hydrogen gas sensor made of SnO2 nanoparticles showed good sensitivity and faster response for the hydrogen gas. This method is template-less and surfactant-free which circumvents rigorous reaction work-up for the former removal, reaction temperature and reaction time compared to hydrothermal synthesis and pertinent to many other oxide materials.

Sonochemical assisted synthesis of RGO/ZnO nanowire arrays for photoelectrochemical water splitting

This article presented the synthesis of a hybrid nanoarchitecture material composed of reduced graphene oxide (RGO) multiple sheets and ZnO nanowire arrays (NWAs) formed on an arbitrary ZnO coated fluorine doped tin oxide (FTO) substrates via pulse sonication and hydrothermal approach. The NWAs have high aspect-ratio, high density, apt positioning and well-ordered formation. FESEM images demonstrated that RGO layers have been effectively intercalated between and on the accessible surfaces of the ZnO NWAs. The diameter of ZnO nanowires is 80-150nm and length about 1-2μm. Raman spectrum of hybrid material exhibited characteristic D and suppressed G peaks for graphene and E2 mode at 437cm-1 for ZnO NWAs. UV-visible spectrum indicated slight red shift towards visible range after formation of RGO/ZnO NWAs heterostructure. The Photoelectrochemical results indicated higher current densities for RGO/ZnO NWAs heterostructure due to water oxidation reaction at the working electrode compared to pristine ZnO NWAs.

Microfluidic-integrated DNA nanobiosensors.

Over the last few decades, an increased demand has emerged for integrating biosensors with microfluidic- and nanofluidic-based lab-on-chip (LOC) devices for point-of-care (POC) diagnostics, in the medical industry and environmental monitoring of pathogenic threat agents. Such a merger of microfluidics with biosensing technologies allows for the precise control of volumes, as low as one nanolitre and the integration of various types of bioassays on a single miniaturized platform. This integration offers several favorable advantages, such as low reagent consumption, automation of sample preparation, reduction in processing time, low cost analysis, minimal handling of hazardous materials, high detection accuracy, portability and disposability. This review provides a synopsis of the most recent developments in the microfluidic-integrated biosensing field by delineating the fundamental theory of microfluidics, fabrication techniques and a detailed account of the various transduction methods that are employed. Lastly, the review discusses state-of-the-art DNA biosensors with a focus on optical DNA biosensors.

Synthesis of Gd2O3:Eu nanoplatelets for MRI and fluorescence imaging.

We synthesized Gd2O3 and Gd2O3 doped by europium (Eu) (2% to 10%) nanoplatelets using the polyol chemical method. The synthesized nanoplatelets were characterized by X-ray diffraction (XRD), FESEM, TEM, and EDX techniques. The optical properties of the synthesized nanoplatelets were investigated by photoluminescence spectroscopy. We also studied the magnetic resonance imaging (MRI) contrast enhancement of T1 relaxivity using 3 T MRI. The XRD for Gd2O3 revealed a cubic crystalline structure. The XRD of Gd2O3:Eu3+ nanoplatelets were highly consistent with Gd2O3 indicating the total incorporation of the Eu3+ ions in the Gd2O3 matrix. The Eu doping of Gd2O3 produced red luminescence around 612 nm corresponding to the radiative transitions from the Eu-excited state 5D0 to the 7F2. The photoluminescence was maximal at 5% Eu doping concentration. The stimulated CIE chromaticity coordinates were also calculated. Judd-Ofelt analysis was used to obtain the radiative properties of the sample from the emission spectra. The MRI contrast enhancement due to Gd2O3 was compared to DOTAREM commercial contrast agent at similar concentration of gadolinium oxide and provided similar contrast enhancement. The incorporation of Eu, however, decreased the MRI contrast due to replacement of gadolinium by Eu.

Hierarchical ZnO/zeolite nanostructures: synthesis, growth mechanism and hydrogen detection†

An improved hydrothermal method has been contrived for the synthesis of highly uniform, ordered, and monodispersed zeolite nanocrystals. An efficient impregnation of zinc on the outer surface of zeolite was carried out using aqueous solution at room temperature followed by high temperature calcination to form an interpenetrating network of hierarchical ZnO/zeolite-nanostructured assembly. The hierarchical structures offer high surface area, a porous structural network, a stimulated surface for catalytic and redox reactions, and better electron transport properties. Morphological and comprehensive structural analysis was carried out by advanced techniques including XRD, FESEM, TEM, STEM-EDS, BET and XPS, respectively. A plausible growth mechanism has been proposed for the formation of zeolite and ZnO/zeolite hierarchical nanocrystals. The hydrogen gas sensor made with these ZnO/zeolite hierarchical nanocrystals exhibited a very fast response of ∼10 s with slow recovery.

Nanofiller graphene–ZnO hybrid nanoarchitecture: optical, electrical and optoelectronic investigation

We report the sonochemical synthesis of a hybrid nanoarchitecture composed of vertically aligned arrays of ZnO nanorods (diameter ∼80 nm and length ∼1 μm) and a few atomic layers of arc discharge prepared graphene. High resolution FESEM images demonstrated that graphene layers have successfully been embedded in between the ZnO nanorod arrays (NRAs). Raman spectra of the hybrid nanomaterial exhibited D, G and 2D Raman fingerprints of graphene and ZnO (E2) modes at 437 cm−1 which confirmed the formation of a ZnO–graphene hybrid nanomaterial. The ZnO–graphene hybrid nanomaterial exhibits intense broad room temperature photoluminescence. Using graphene as a nanofiller considerably enhanced the electrical conductivity of the ZnO NRAs and the hybrid material exhibits a semi-metallic behaviour. Photoconductivity of the hybrid nanosystem has also been investigated which strengthens its candidature as a potential hybrid nanomaterial with optoelectronic synergy between its components.

Rapid microwave synthesis of high aspect-ratio ZnO nanotetrapods for swift bisphenol A detection.

Highly crystalline and high aspect-ratio ZnO nanotetrapods were grown by a novel and swift microwave synthesis. FESEM analysis revealed that each tetrapod has four thin arms and are derived from the midst of the crystal. The diameter of each arm is larger at the base and smaller at the tip. Structural analysis revealed that these nanotetrapods are single crystalline and have a wurtzite hexagonal crystal structure. These ZnO nanotetrapods were used for the detection of BPA. The electrochemical sensor based on the ZnO nanotetrapods modified electrode showed electrocatalytic activity in terms of significant improvement of the anodic current of BPA and lowering of the detection limit. Under optimized conditions, the squarewave oxidation peak current of BPA was linear over the concentration range of 12.4 nM to 1.2 μM with the detection limit of 1.7 nM and sensitivity of 5.0 μA nM(-1) cm(-2). This sensor showed high sensitivity and response compared with other electrochemical sensors reported for the detection of BPA.