Diana N. H. Tran

Graphene-Diatom Silica Aerogels for Efficient Removal of Mercury Ions from Water

A simple synthetic approach for the preparation of graphene-diatom silica composites in the form of self-assembled aerogels with three-dimensional networks from natural graphite and diatomite rocks is demonstrated for the first time. Their adsorption performance for the removal of mercury from water was studied as a function of contact time, solution pH, and mercury concentration to optimize the reaction conditions. The adsorption isotherm of mercury fitted well with the Langmuir model, representing a very high adsorption capacity of >500 mg of mercury/g of adsorbent. The prepared aerogels exhibited outstanding adsorption performance for the removal of mercury from water, which is significant for environmental applications.

Graphene: a multipurpose material for protective coatings

Graphene based materials have attracted great interest in the development of new and advanced protective coatings due to their excellent chemical resistance, impermeability to gases, adsorption capacity, anti-bacterial properties, mechanical strength, lubricity and thermal stability. This review presents current progress and discusses the major challenges and future potential of graphene in the field of protective coatings. This review specifically focuses on the most recent advances in the application of graphene for corrosion resistant coatings, flame retardant coatings, wear/scratch resistant coatings, anti-fouling coatings, pollutant adsorption coatings and anti-septic coatings.

Graphene Aerogels Decorated with α-FeOOH Nanoparticles for Efficient Adsorption of Arsenic from Contaminated Waters

Arsenic (As) is the worlds most hazardous chemical found in drinking water of many countries; therefore, there is an urgent need for the development of low-cost adsorbents for its removal. Here, we report a highly versatile and synthetic route for the preparation of a three-dimensional (3D) graphene-iron oxide nanoparticle aerogel composite for the efficient removal of As from contaminated water. This unique three-dimensional (3D) interconnected network was prepared from natural graphite rocks with a simple reaction, without the use of harsh chemicals, which combines with the exfoliation of graphene oxide (GO) sheets via the reduction of ferrous ion to form a graphene aerogel composite decorated with iron oxide nanoparticles. The prepared adsorbent showed outstanding absorption performance for the removal of As from contaminated water, because of its high surface-to-volume ratio and characteristic pore network in the 3D architecture. The performed case study using real drinking water contaminated with As under batch conditions showed successful removal of arsenic to the concentration recommended by the World Health Organisation (WHO).

Selective adsorption of oil–water mixtures using polydimethylsiloxane (PDMS)–graphene sponges

We report a porous and green three dimensional (3-D) polydimethylsiloxane (PDMS)–graphene sponge with hydrophobic and oleophilic properties using the sugar templating method. The prepared sponge exhibited high adsorption performance for the removal of petroleum products, organic solvents and emulsified oil–water mixtures, especially under a continuous vacuum regime achieving an adsorption capacity of 4.5 L of hexane in 30 min. The proposed synthetic method is simple and economical for the scalable production of porous 3-D graphene sponges, which can be successfully used for efficient and cost-effective oil spill clean-ups and water purification for environmental applications.

Morphology-controlled MnO2 modified silicon diatoms for high-performance asymmetric supercapacitors

Successful conversion of diatomites (SiO2) into silicon diatoms was achieved via the magnesiothermic reduction method followed by deposition of MnO2 nanosheets to fabricate unique 3D silicon-diatom@MnO2 electrodes and demonstrate their application for high-performance supercapacitors. The synergy between the microporous diatom structure and layered MnO2 nanosheets was found to produce excellent electrochemical performance evidenced by high specific capacitance (341.5 F g−1 at a current density of 0.5 A g−1), good rate capability (47.7% retention with current increases around 20 times) and steady cycling performance (84.8% remained after 2000 cycles). The prepared asymmetric supercapacitor based on silicon diatom@MnO2 nanosheets as a positive electrode and active graphene oxide (AGO) as a negative electrode delivered a maximum power density of 2.22 kW kg−1 and an energy density of 23.2 W h kg−1, which is superior to many other silicon-based and MnO2-based materials. These outstanding performances are attributed to the unique 3D microstructures, good conductivity of silicon diatoms and the highly porous surface formed by interconnection of MnO2 nanosheets. Considering the low cost of initial materials and simplicity of the fabrication process, these silicon diatom@MnO2 nanosheet electrodes have significant potential to be used as an electrode material for inexpensive and high-performance supercapacitors.

Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors

Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (ID/IG ∼ 0.12), and high conductivity (6.2 × 10(4) S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags.

Engineered graphene–nanoparticle aerogel composites for efficient removal of phosphate from water

The contamination of aqueous systems with phosphates has considerable environmental concerns and here, we present a new method for phosphate removal based on graphene aerogel composites. 3-Dimensional graphene aerogels decorated with goethite (αFeOOH) and magnetite (Fe3O4) nanoparticles were synthesised and their application in capturing phosphates in water was successfully demonstrated. The prepared aerogels showed superior capacity to remove up to 350 mg g−1 at an initial phosphate concentration of 200 mg L−1 from water. The Freundlich model was suitable to describe the adsorption mechanism of phosphate removal by the graphene–iron nanoparticle aerogels through both mononuclear and polynuclear adsorption onto the nanosized αFeOOH and Fe3O4 nanoparticles. These new phosphate adsorbents can be produced in different forms and dimensions, using a simple, green and scalable process, and have the potential to be applied for practical applications in phosphate management of waste and storm water.

Engineering of graphene/epoxy nanocomposites with improved distribution of graphene nanosheets for advanced piezo-resistive mechanical sensing

Conductive nanostructured composites combining an epoxy polymer and graphene have been explored for applications such as electrostatic-dissipative, anti-corrosive, and electromagnetic interference (EMI) shielding, stealth composite coating and specifically for sensors. For many of these applications, the limits of dispersion of graphene nanosheets and the interface between fillers and matrices have affected their electrical, structural and mechanical properties. To address these problems, we present the use of a dimethylbenzamide (DMBA)-based hardener to modify the surface of reduced graphene oxide (RGO) and create a 3D architecture with a micro-porous structure. DMBA is applied to provide two functions: one is to act as a stabilizer to avoid restacking of graphene sheets during the reduction process, and the second is to provide a linkage between RGO and epoxy for the formation of homogeneous nanocomposites. Thin films of conductive polymer graphene composites (CPCs) were prepared using a simple doctor blade method, while piezoresistive sensors were prepared by spraying to demonstrate their application for mechanical strain sensing. The electrical properties of the composites as a function of graphene fillers were shown to significantly increase from 1012 Ω sq−1 for neat epoxy to 106 Ω sq−1 for 2 wt% RGO in epoxy composites, while the modulus calculated using nanoindentation exhibited a 43.3% enhancement from 3.56 GPa for epoxy to 6.28 GPa for the composites containing 2 wt% graphene. The results of piezo-resistive performance for mechanical strain sensing under both static and dynamic strain modes showed good sensitivity with a gauge factor (GF) of 12.8 and a fast response time of 20 milliseconds. A minor loading/unloading hysteresis loop after 1000 cycles indicated good reversibility and reproducibility of the sensors. Excellent reproducibility, long-term stability and reliability of the sensing devices are confirmed working without decay of sensitivity after a 6-month exposure to ambient atmosphere. The results obtained suggest that these types of piezo-resistive sensors based on RGO/epoxy CPCs due to their simple, scalable and low cost production could lead to the development of high-performance mechanical strain sensors for a broad range of applications including real-time monitoring, wearable electronics, and structural health monitoring (SHM).

Graphene-Borate as an Efficient Fire Retardant for Cellulosic Materials with Multiple and Synergetic Modes of Action

To address high fire risks of flamable cellulosic materials, that can trigger easy combustion, flame propagation, and release of toxic gases, we report a new fire-retardant approach using synergetic actions combining unique properties of reduced graphene oxide (rGO) and hydrated-sodium metaborates (SMB). The single-step treatment of cellulosic materials by a composite suspension of rGO/SMB was developed to create a barrier layer on sawdust surface providing highly effective fire retardant protection with multiple modes of action. These performances are designed considering synergy between properties of hydrated-SMB crystals working as chemical heat-sink to slow down the thermal degradation of the cellulosic particles and gas impermeable rGO layers that prevents access of oxygen and the release of toxic volatiles. The rGO outer layer also creates a thermal and physical barrier by donating carbon between the flame and unburnt wood particles. The fire-retardant performance of developed graphene-borate composite and mechanism of fire protection are demonstrated by testing of different forms of cellulosic materials such as pine sawdust, particle-board, and fiber-based structures. Results revealed their outstanding self-extinguishing behavior with significant resistance to release of toxic and flammable volatiles suggesting rGO/SMB to be suitable alternative to the conventional toxic halogenated flame-retardant materials.

Molecular interactions behind the synergistic effect in mixed monolayers of 1-octadecanol and ethylene glycol monooctadecyl ether.

Mixed monolayers of 1-octadecanol (C18OH) and ethylene glycol monooctadecyl ether (C18E1) were studied to assess their evaporation suppressing performance. An unexpected increase in performance and stability was found around the 0.5:0.5 bicomponent mixture and has been ascribed to a synergistic effect of the monolayers. Molecular dynamics simulations have attributed this to an additional hydrogen bonding interaction between the monolayer and water, due to the exposed ether oxygen of C18E1 in the mixed system compared to the same ether oxygen in the pure C18E1 system. This interaction is maximized around the 0.5:0.5 ratio due to the particular interfacial geometry associated with this mixture.