Waheed S. Khan

Hollow core–shell η-Fe2O3 microspheres with excellent lithium-storage and gas-sensing properties

Hollow core-shell eta-Fe(2)O(3) microspheres exhibit not only superior electrochemical performance as lithium storage electrodes but also excellent sensitivities to trace levels of gases.

Synthesis of novel ZnV2O4 hierarchical nanospheres and their applications as electrochemical supercapacitor and hydrogen storage material

Hierarchical nanostructures (Hs) have recently garnered enormous attention due to their remarkable performances in catalysis, electronic devices, energy storage and conversion. Considering the advantage of hierarchical nanostructures, we have formulated a facile and template free method to synthesize novel hierarchical nanospheres (NHNs) of ZnV2O4. Both zinc and vanadium are earth abundant, relatively economical and can offer several oxidation states, which can render a broad range of redox reactions favorable for electrochemical energy storage applications. Keeping these points in mind, we investigated for the first time the electrochemical supercapacitor performance of NHNs. The electrochemical measurements were performed in 2 M KOH solution. The measured specific capacitance of ZnV2O4 electrode is 360 F/g at 1 A/g with good stability and retention capacity of 89% after 1000 cycles. Moreover, the hydrogen storage properties of NHNs were measured at 473, 573, and 623 K with an absorption of 1.76, 2.03, and 2.49 wt %. respectively. These studies pave the way to consider ZnV2O4 as prospective material for energy storage applications.

Template free synthesis of CuS nanosheet-based hierarchical microspheres: an efficient natural light driven photocatalyst

Well controlled nanosheets-based hierarchical microspheres (NSHMS) of pure covellite phase CuS were synthesized using a facile PVP assisted solvothermal process. The reaction conditions were optimized using various amounts of PVP to develop unique hierarchical structured hollow microspheres. CuS hollow structures have a bandgap of ~1.97 eV. These mesoporous structures exhibit excellent photocatalytic activity in degradation of organic dyes (Methylene Blue) under natural light in comparison to other structures of copper sulphide. These photocatalysts show extraordinary reusability with over 96.5% degradation of organic dye after 6th cycle. A “bottom-up” assembly was successfully developed to synthesize hollow microspheres with unique and well defined architectures at large scale, which offer a good opportunity to understand the fundamental significance of unusual and complex hierarchical structures for their potential applications.

A novel Z-scheme WO3/CdWO4 photocatalyst with enhanced visible-light photocatalytic activity for the degradation of organic pollutants

A novel Z-scheme WO3/CdWO4 photocatalyst has been fabricated with sheet-like tungsten trioxide (WO3) hybridized by rod-like cadmium tungstate (CdWO4) via a hydrothermal and chemisorption method. The as-synthesized WO3/CdWO4 photocatalyst exhibited enhanced photocatalytic efficiency for the degradation of different organic dyes under visible light irradiation. It was found that the photocatalytic performance of the composite WO3/CdWO4 was much higher than that of either WO3 or CdWO4 for the degradation of each organic dye. The highest activity of the composite was recorded for the degradation of MB which was about 7 times greater than pure CdWO4 and 2.3 times that of pure WO3. The enhanced performance of the photocatalyst was mainly attributed to the increased surface area and introduction of WO3 into the composite sample, which can induce higher adsorption activity for organic dyes and increased electron–hole separation at the interface between two semiconductors by establishing an inner electric field.

Synthesis of CuS flowers exhibiting versatile photo-catalyst response

Hierarchically structured covellite copper sulfide (CuS) microflowers composed of nanosheets have been successfully fabricated via a one-pot sonochemical process, using copper sulfate and thiourea aqueous solution as precursors in the presence of citric acid, without any prefabricated template. Large-scaled architectures are homogeneous and quite separately displaced and assembled by pure hexagonal single-crystalline CuS nanosheets, having thickness within 20 nm. The as obtained hierarchical CuS structures possess rather high surface area and unique double pore size distributions measured from N2 adsorption isotherms. Moreover, a possible growth mechanism for the CuS hierarchical architectures is proposed on the basis of temporal evolution controlled experiments. Most importantly, these hierarchically structured CuS catalysts showed highly efficient and versatile photo-catalytic activities as well as excellent recyclability in degrading highly concentrated dye aqueous solutions of methylene blue (MB), rhodamine B (RhB) and their mixed solution (MB + RhB) with the help of hydrogen peroxide (H2O2) under natural light irradiation, suggesting a promising application in wastewater purification.

The synergistic effect between WO3 and g-C3N4 towards efficient visible-light-driven photocatalytic performance

We have developed a facile, scaled up, efficient and morphology-based novel WO3–g-C3N4 photocatalyst with different mass ratios of WO3 and g-C3N4. It was used for the photodegradation of rhodamine B (RhB) under visible light irradiation and it showed excellent enhanced photocatalytic efficiency as compared to pure g-C3N4 and WO3. The apparent performance of the composite/hybrid was 3.65 times greater than pure WO3 and 3.72 times greater than pure g-C3N4 respectively, and it was also found to be much higher than the previously reported ones. Furthermore, the optical properties of composite samples were evaluated. The bandgap of composite samples lies in the range of 2.3–2.5 eV, which was favourable for photodegradation. The possible mechanism for enhanced catalytic efficiency of the WO3–g-C3N4 photocatalyst is discussed in detail. It was found that the enhanced performance is due to the synergistic effect between the WO3 and g-C3N4 interface, improved optical absorption in the visible region and suitable band positions of WO3–g-C3N4 composites.

Effect of the morphology of CuS upon the photocatalytic degradation of organic dyes

A variety of well defined, highly symmetrical, super complex and hierarchical architectures of covellite copper sulfide have been successfully prepared by a simple solvothermal approach. The effects of various influencing parameters on the formation of CuS hierarchical architectures were precisely investigated and a possible formation mechanism has been elucidated. The reaction time was found to be a critical factor in controlling the CuS architecture and highly complex structures were obtained with elongated reaction times. The as-synthesized architectures exhibited excellent photocatalytic activities in the visible region for the degradation of individual dyes (methylene blue and rhodamine B) and their mixed solutions in the presence of H2O2. The efficient photocatalytic activity can be attributed to the carefully controlled hierarchical CuS structures. Overall, this study is of great importance in the “bottom-up” assembly of copper sulfide nanoplates to obtain highly complex structures which offer a good opportunity to understand the fundamental significance of atypical structures for their potential applications.

Synthesis of novel ZnV2O4 spinel oxide nanosheets and their hydrogen storage properties

We report the synthesis of ZnV2O4 spinel oxide novel nanosheets via a template free route to explore its potential hydrogen storage properties for the first time. 2D layered nanostructures are excellent candidates for storage applications. This attracted our interest to synthesize novel spinel oxide nanosheets (NSNs) of ZnV2O4. The maximum value for hydrogen absorption in ZnV2O4 nanosheets at 473 K is 1.36 wt.% and 1.74 wt.% at 573 K, respectively. Our hydrogen storage measurements along ZnV2O4 reveal its superiority over previous reports on hydrogen absorption values concerning oxides, nitrides and chalcogenides. To understand the rate-limiting mechanism, various kinetics models are applied. The calculations show that kinetics is governed by 3D growth with constant interface velocity. The measurements point to ZnV2O4 spinel oxide as a promising hydrogen storage material. PL measurements demonstrate the potential for violet/blue optoelectronic devices.

Electrical and optical properties of single zigzag SnO2 nanobelts

We report here on investigations of electrical and optical properties of single zigzag SnO2 nanobelts. Large scale zigzag nanobelts were obtained on a silicon substrate by a Chemical Vapor Deposition (CVD) approach. The average value of carrier concentrations (Nd) and electron mobility (μ) were calculated to be 1.39 × 1018 cm−3 and 70.76 cm2 V−1 s−1, respectively. Room temperature PL exhibits a broad emission peak centred at 600 nm. Three Raman active modes at 474.8, 633.8, 775.8 cm−1 were observed. Electron paramagnetic resonance measurements suggest the presence of many singly ionized states.

solid and liquid lipid-based binary solid lipid nanoparticles of diacerein: in vitro evaluation of sustained release, simultaneous loading of gold nanoparticles, and potential thermoresponsive behavior

Binary fatty acid mixture-based solid lipid nanoparticles (SLNs) were prepared for delivery of diacerein, a novel disease-modifying osteoarthritis drug, with and without simultaneously loaded gold nanoparticles (GNPs). In order to optimize SLNs for temperature-responsive release, lipid mixtures were prepared using different ratios of solid (stearic acid or lauric acid) and liquid (oleic acid) fatty acids. SLNs were prepared by microemulsification (53 nm), hot melt encapsulation (10.4 nm), and a solvent emulsification-evaporation technique (7.8 nm). The physicochemical characteristics of SLNs were studied by Zetasizer, Fourier transform infrared, and X-ray diffraction analysis. High encapsulation of diacerein was achieved with diacerein-loaded and simultaneously GNP-diacerein-loaded SLNs. In vitro dissolution studies revealed a sustained release pattern for diacerein over 72 hours for diacerein-loaded SLNs and 12 hours for GNP-diacerein-loaded SLNs. An increase in diacerein payload increased the release time of diacerein while GNPs decreased it. In addition, rapid release of diacerein over 4 hours was observed at 40°C (melting point of optimized fatty acid mixture), demonstrating that these binary SLNs could be used for thermoresponsive drug delivery. Kinetic modeling indicated that drug release followed zero order and Higuchi diffusion models (R10>0.9), while the Korsmeyer-Peppas model predicted a diffusion release mechanism (n<0.5).