Mansoor Sarfraz

Synthesis of hierarchical porous spinel nickel cobaltite nanoflakes for high performance electrochemical energy storage supercapacitors

Hierarchical porous spinel nickel cobaltite (NiCo2O4) nanoflakes synthesized through a cost-effective and scalable chemical precipitation method exhibited high specific capacitance (1270 F g−1), excellent rate capability (81% capacity retention at 10 A g−1) and cycling stability (only 4.8% loss after 5000 cycles).

Influence of surfactant type on the dispersion state and properties of graphene nanoplatelets reinforced Aluminium matrix nanocomposites

ABSTRACT Graphene dispersion in aluminium matrix is a critical concern for the attainment of composite improved mechanical and tribological properties which hinders broad applications of Al nanocomposites. Herein, graphene nanoplatelets (GNPs) dispersion in Al matrix achieved by colloidal processing, i.e., combining sonication and surfactant dispersing aid. In this work, the performance of the two types of surfactant (anionic, sodium dodecyl benzene sulfonate (SDBS), and nonionic polymeric, ethyl cellulose (EC)) were evaluated for effective GNPs dispersion in a solvent and Al matrix. Surfactant assisted GNPs solvent dispersion characterized through sedimentation test and UV-vis spectroscopy to optimize surfactant concentration. Density, hardness, wear properties and microstructural characterizations of GNPs/Al powder and sintered discs were performed to gauge the effect of surfactant type. It was found that surfactant addition enhances dispersion ability of GNPs than neat GNPs but at low GNPs fractions. The results show that EC assisted GNPs/Al nanocomposites of 0.5 wt% GNPs concentration has shown an increase in hardness (31%) and reduce wear rate (98%). Whereas, 0.3 wt% SDBS assisted GNPs/Al nanocomposites shown maximal increases in hardness (18%) and reduce wear rate (98%) as compared to pure aluminium, respectively. Conclusively, it has been revealed that polymeric EC based surfactant GNPs owing to steric repulsion shows better dispersion effect resulting in high density and improved wear resistance and performed better than SDBS based surfactant GNPs in Al matrix.

A three-dimensional graphene framework-enabled high-performance stretchable asymmetric supercapacitor

The construction of flexible and stretchable supercapacitors with high energy density and superior stability is critical for modern wearable electronics but still remains considerably challenging. Herein we develop an ultrahigh-performance stretchable asymmetric supercapacitor (SASC) by using electrically and mechanically robust three-dimensional graphene frameworks as electrodes for the first time, in which three-dimensional graphene and a deliberately designed three-dimensional graphene/polyaniline composite are employed as the anode and cathode, respectively. The newly developed SASCs show the highest energy density of 77.8 W h kg−1 among all reported stretchable supercapacitors, and also deliver exceptional cycling stability with 95.6% capacitance retention after 10 000 charge–discharge cycles and excellent electrochemical durability with 91.2% capacitance retention after 100 stretching cycles at a large strain of 100%. The practicability of our SASC has been further demonstrated by efficiently powering a light-emitting diode indicator (1.8 V, 10 mA) under repeated stretching of a SASC mounted on a finger. Moreover, by connecting three SASCs in series, the tandem device can even drive an STC89C51RC microcontroller-based complex circuit (5.0 V) to light a liquid crystal display.

Reversible 3D self-assembly of graphene oxide and stimuli-responsive polymers for high-performance graphene-based supercapacitors

The assembly of graphene into functional macrostructures has attracted intense interest in recent years. Herein we report the first reversible 3D self-assembly of graphene oxide/reduced graphene oxide with stimuli-responsive polymers poly(N-isopropylacrylamide) (PNIPAM) or poly(propylene oxide) (PPO), which results in a photo/thermal reversible supramolecular graphene/polymer composite hydrogel with adjustable sol–gel transition temperature. The assembly method is extremely convenient and straightforward based on a new assembly mechanism, i.e., PNIPAM or PPO chains with temperature-responsive hydrophilicity/hydrophobicity can reversibly adsorb onto and cross-link the graphene sheets via noncovalent interactions. Utilizing the reversibility of the 3D assembly, we further develop a new strategy to prepare a graphene macrostructure with minimum re-stacking of graphene sheets and an ultrahigh specific surface area (∼1410 m2 g−1), based on which we successfully fabricate a supercapacitor electrode and a flexible/foldable all-solid-state supercapacitor with remarkable electrochemical performance (292 F g−1 at 1 A g−1 and 215 F g−1 at 100 A g−1).

Investigation of tip sonication effects on structural quality of graphene nanoplatelets (GNPs) for superior solvent dispersion

The exceptional properties of graphene and its structural uniqueness can improve the performance of nanocomposites if it can attain the uniform dispersion. Tip sonication assisted graphene solvent dispersion has been emerged as an efficient approach but it can cause significant degradation of graphene structure. This study aimed to evaluate the parametric influence of tip sonication on the characteristics of sp2 carbon structure in graphene nanoplatelets by varying the sonication time and respective energy at three different amplitudes (60%, 80% and 100%). The study is essential to identify appropriate parameters so as to achieve high-quality and defect-free graphene with a highly desirable aspect ratio after solvent dispersion for composite reinforcement. Quantitative approach via Raman spectroscopy is used to find the defect ratio and lateral size of graphene evolved under the effect of tip sonication parameters. Results imply that the defect ratio is steady and increases continually with GNPs, along with the transformation to the nano-crystalline stage I up to 60 min sonication at all amplitudes. Exfoliation was clearly observed at all amplitudes together with sheet re-stacking due to considerable size reduction of sheets with large quantity. Finally, considerable GNPs fragmentation occurred during sonication with increased amplitude and time as confirmed by the reduction of sp2 domain (La) and flake size. This also validates the formation of edge-type defect in graphene. Convincingly, lower amplitude and time (up to 60 min) produce better results for a low defect content and larger particle size as quantified by Raman analysis.

Characterization and analysis of nanostructured CdO thin film using LIBS technique

Nanostructured thin films of cadmium oxide (CdO) have been synthesized using sol-gel technique on slide glass substrates. Thickness of the film is about 250 nm with average grain sizes of CdO in the range of 93-250 nm. Laser induced breakdown spectroscopy (LIBS) is used to investigate the synthesized CdO thin film. We have investigated LIBS spectrum of CdO thin film in air atmosphere using Spectrolaser-7000 system with 100 mJ fundamental laser beam from Nd:YaG laser and varied delay times from 200 ns to 2 microseconds. Many atomic and ionic lines of Cd were resolved and the variation with the delay time was studied. The plasma parameters have also been studied for Cd 508.58 nm. It is found that plasma cooled very fast after 500 ns as compared to the bulk material. The later showed that the recombination processes are growing very fast with time for nanostructured CdO thin film.

Surfactant-decorated graphite nanoplatelets (GNPs) reinforced aluminum nanocomposites: sintering effects on hardness and wear

The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets (GNPs) using two types of surfactant: anionic (sodium dodecyl benzene sulfate (SDBS)) and non-ionic polymeric (ethyl cellulose (EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures (550 and 620°C). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.

Analysis of allyl diglycol carbonate by laser induced-breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used to identify the impurities in the allyl diglycol carbonate, which is used as a charged particle track recording material in solid-state nuclear track detectors. Impurities of magnesium, calcium, sodium and silicon are detected. Plasma parameters such as temperature and electron density are also calculated at optimized conditions in air and argon atmosphere using the silicon lines. The temperature of the LIBS plasma produced in argon atmosphere was higher than the temperature of the LIBS plasma produced in air. Variation in the emission intensity of the carbon I line (247.8561 nm) with respect to acquisition delay and laser power is also studied. It is found that the intensities of Ca and Na lines from LIBS spectra were enhanced 30–40 times in an argon atmosphere as compared to air. Hence LIBS in an argon atmosphere can be used for better identification of impurities in plastics.