Saeed M. Alhassan

Graphene Foam Developed with a Novel Two-Step Technique for Low and High Strains and Pressure-Sensing Applications

Freestanding, mechanically stable, and highly electrically conductive graphene foam (GF) is formed with a two-step facile, adaptable, and scalable technique. This work also demonstrates the formation of graphene foam with tunable densities and its use as strain/pressure sensor for both high and low strains and pressures.

Novel graphene foam composite with adjustable sensitivity for sensor applications.

In this study, free-standing graphene foam (GF) was developed by a three-step method: (1) vacuum-assisted dip-coating of nickel foam (Ni-F) with graphene oxide (GO), (2) reduction of GO to reduced graphene oxide (rGO), and then (3) etching out the nickel scaffold. Pure GF samples were tested for their morphology, chemistry, and mechanical integrity. GF mimics the microstructure of Ni-F while individual bones of GF were hollow, because of the complete removal of nickel. The GF-PDMS composites were tested for their ability to sense both compressive and bending strains in the form of change in electrical resistance. The composite showed different sensitivity to bending and compression. Upon applying a 30% compressive strain on the GF-PDMS composite, its resistance increased to ∼120% of its original value. Similarly, bending a sample to a radius of 1 mm caused the composite to change its resistance to ∼52% of its original resistance value. The relative change in resistance of the composite by an applied pressure/strain can be tuned to considerably different values by heat-treating the GF at different temperatures prior to infusing PDMS into its scaffold. Upon heat treating the GF at 800 °C prior to PDMS infusion, the GF-PDMS demonstrated ∼10 times better sensitivity than the untreated sample for a compressive strain of 20%. The composite was also tested for its ability to retain a change in electrical resistance when a brief load/strain is applied. The GF-PDMS composite was tested for at least 500 cycles under compressive cyclic loading and showed good electromechanical durability. Finally, it was demonstrated that the composite can be used to measure human blood pressure when attached to human skin.

Self‐Pillared, Single‐Unit‐Cell Sn‐MFI Zeolite Nanosheets and Their Use for Glucose and Lactose Isomerization

Single-unit-cell Sn-MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single-step, synthesis is based on repetitive branching caused by rotational intergrowths of single-unit-cell lamellae. The self-pillared, meso- and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated.

Highly electrically conductive nanocomposites based on polymer-infused graphene sponges.

Conductive polymer composites require a threedimensional 3D network to impart electrical conductivity. A general method that is applicable to most polymers for achieving a desirable graphene 3D network is still a challenge. We have developed a facile technique to fabricate highly electrical conductive composite using vacuumassisted infusion of epoxy into graphene sponge GS scaffold. Macroscopic GSs were synthesized from graphene oxide solution by a hydrothermal method combined with freeze drying. The GSepoxy composites prepared display consistent isotropic electrical conductivity around 1Sm, and it is found to be close to that of the pristine GS. Compared with neat epoxy, GSepoxy has a 12ordersofmagnitude increase in electrical conductivity, attributed to the compactly interconnected graphene network constructed in the polymer matrix. This method can be extended to other materials to fabricate highly conductive composites for practical applications such as electronic devices, sensors, actuators, and electromagnetic shielding.

Influence of electrolyte and polymer loadings on mechanical properties of clay aerogels.

The effects of electrolyte and polymer loadings on formation, density, and mechanical properties of clay aerogels have been investigated. Coherent aerogels were formed at all tested concentrations except at a combination of low electrolyte (<0.04 M) and polymer (<1% w/v) concentrations because of partial clay flocculation. The compressive modulus and yield strength of the aerogels containing poly(vinyl alcohol) are sensitive to electrolyte loading at low polymer concentration but are otherwise insensitive. Mechanical properties show power law dependence on aerogel density, which depends mainly on polymer loading. The power law exponent for the compressive modulus is 3.74 when the relative density is used in the model and 5.7 when the measured bulk density is used instead. These high exponent values are attributed to the layered microstructure of these aerogels.

From biomass to high performance solar–thermal and electric–thermal energy conversion and storage materials

We demonstrate that lightweight, highly electrically conductive, and three-dimensional (3D) carbon aerogels (CAs) can be produced via a hydrothermal carbonization and post pyrolysis process using various melons as raw materials. This two-step process is a totally green synthetic method with cheap and ubiquitous biomass as the only raw material. These black-colored, highly electrically conductive and 3D structured CAs are ideal materials for energy conversion and storage. Paraffin wax was impregnated into the CA scaffold by vacuum infusion. The obtained CA–wax composites show excellent form-stable phase change behavior, with a high melting enthalpy of 115.2 J g−1. The CA–wax composites exhibit very high solar radiation absorption over the whole UV-vis-NIR range, and 96% of light can be absorbed by the phase-change composite and stored as thermal energy. With an electrical conductivity of 3.4 S m−1, the CA–wax composite can be triggered by low electric potential to perform energy storage and release, with an estimated electric–heat conversion efficiency of 71.4%. Furthermore, the CA–wax composites have excellent thermal stability with stable melting–freezing enthalpy and excellent reversibility. With a combination of low-cost biomass as the raw materials, a green preparation process, low density, and excellent electrical conductivity, the 3D CAs are believed to have promising potential applications in many energy-related devices.

Graphene Arrested in Laponite–Water Colloidal Glass

Graphene production in water from graphite sources is an important technological route toward harvesting the unique properties of this material. Graphene forms thermodynamically unstable dispersions in water, limiting the use of this solvent due to aggregation. We show that graphene-water dispersions can be controlled kinetically to produce graphene by using laponite clay. Laponite exhibits rapid gelation kinetics when dispersed in water above its gelation concentration, allowing graphene aggregation to be halted after exfoliation in water at ambient conditions. The transparency of laponite colloidal glass and films is important in examining the extent of graphene exfoliation.

Effect of solvent on the uncatalyzed synthesis of aminosilane-functionalized graphene

Uncatalyzed functionalization of thermally reduced graphene (TRG) with 3-aminopropyltriethoxy silane (APTS) is reported and the effect of the solvent on selective functionalization is discussed. The chemical, morphological and thermal properties of the functionalized TRG (f-TRG) have been studied using FTIR, XPS, EELS, Raman spectroscopy, TEM, and TGA. Our results indicate that the use of organic solvent during the silylation reaction not only increases grafting yield from 7 to 8 atomic% of Si attachment but also directs APTS groups to the edges of TRG as revealed using energy filtered TEM elemental mapping. A reaction mechanism based on attachment of the silane groups on the TRG surface through residual, surface bound phenolic and carbonyl groups is proposed and discussed. The present approach provides an economical route for mass production of APTS-f-TRG and sheds light on the role of organic solvents in silane functionalization of graphene.

Non-destroyable graphene cladding on a range of textile and other fibers and fiber mats

Electrically insulating textile and synthetic fibers were cladded with chemically modified graphene via a three-step technique to induce electrical conductivity. Electrical conductivities of 13 and 4.5 S cm−1 were obtained for aramid and nylon fibers, respectively. The graphene cladding is non-destroyable when washed in detergent or sonicated.

Interactions, morphology and thermal stability of graphene-oxide reinforced polymer aerogels derived from star-like telechelic aldehyde-terminal benzoxazine resin

Graphene oxide (GO)-reinforced nanocomposite aerogels of polybenzoxazine prepared via freeze-drying of GO suspensions in benzoxazine precursor solutions have been studied. The synthesis of GO is confirmed using Raman and Fourier transform infrared (FT-IR) spectroscopy. The benzoxazine monomer (SLTB(4HBA-t403)) has been synthesized using 4-hydroxybenzaldehyde as a phenolic component, paraformaldehyde, and tri-functional polyetheramine (Jeffamine T-403) as an amine source. The chemical structure of the benzoxazine monomer is confirmed by nuclear magnetic resonance (1H-NMR) spectroscopy and FT-IR. The interactions of GO and SLTB(4HBA-t403) have been investigated using FT-IR. The morphological and thermal stability of nanocomposite aerogels are examined and compared with the neat polybenzoxazine aerogel. The structures of the aerogels and the effect of GO on the morphology of the aerogels are studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of GO on the ring-opening polymerization of benzoxazine is also evaluated using differential scanning calorimetry (DSC) whereas the thermal stability of the nanocomposite aerogels is characterized by thermogravimetric analysis (TGA).