Shervin Kabiri

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 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.

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.

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.

Functionalized three-dimensional (3D) graphene composite for high efficiency removal of mercury

The synthesis of a thiol-functionalized graphene composite with a unique three-dimensional porous structure composed of graphene nanosheets decorated with αFeOOH and porous silica microparticles (diatomaceous earth) is presented. The performance of this material for the removal of mercury ions (Hg2+) from water is evaluated using a batch adsorption and membrane separation approach. An outstanding adsorption performance of >800 mg g−1 (at 400 mg L−1 Hg2+) was demonstrated significantly exceeding currently available benchmark adsorbents. An excellent adsorption performance was confirmed for the efficient (~100%) removal of a low (4 mg L−1) and high (120 mg L−1) concentration of Hg in real water samples using this composite in the form of membranes. The results indicate the versatility of the developed composite to be used in different forms for several water purification scenarios (batch, column, membranes) relevant for both drinking and wastewater treatments. Based on their outstanding performance, low cost, and simple and scalable preparation, the presented 3D graphene composites have a considerable potential for the development of efficient and cost-competitive adsorbents and membranes for environmental applications.

Study of iron oxide nanoparticle phases in graphene aerogels for oxygen reduction reaction

Iron oxide nanoparticles have been extensively used for energy production in fuel cells; however, the different phases of iron oxide have not been adequately investigated for their effect on the oxygen reduction reaction (ORR). The low temperature synthesis of four kinds of iron oxide nanoparticles with different phases was incorporated inside 3D reduced graphene oxide (rGO) aerogels and their electrochemical, catalytic and electron transfer properties were determined for ORR. The results showed that, at low potentials (0.20 V), rGO composites containing magnetite, maghemite and goethite catalyse ORR via four-electron transfer kinetics while hematite facilitated two-electron transfer kinetics. At higher potentials (0.70 V), all four catalysts proceeded via a two-electron pathway.

Graphene Oxide: A New Carrier for Slow Release of Plant Micronutrients

The environmental problems and low efficiency associated with conventional fertilizers provides an impetus to develop advanced fertilizers with slower release and better performances. Here, we report of development of a new carrier platform based on graphene oxide (GO) sheets that can provide a high loading of plant micronutrients with controllable slow release. To prove this concept, two micronutrients, zinc (Zn) and copper (Cu), were used to load on GO sheets and hence formulate GO-based micronutrients fertilizer. The chemical composition and successful loading of both nutrients on GO sheets were confirmed by X-ray photoelectron spectroscopy, thermogravimetric analysis, and X-ray diffraction (XRD). The prepared Zn-graphene oxide (Zn-GO) and Cu-graphene oxide (Cu-GO) fertilizers showed a biphasic dissolution behavior compared to that of commercial zinc sulfate and copper sulfate fertilizer granules, displaying desirable fast and slow micronutrient release. A visualization method and chemical analysis were used to assess the release and diffusion of Cu and Zn in soil from GO-based fertilizers compared with commercial soluble fertilizers to demonstrate the advantages of GO carriers and show their capability to be used as a generic platform for macro- and micronutrients delivery. A pot trial demonstrated that Zn and Cu uptake by wheat was higher when using GO-based fertilizers compared to that when using standard zinc or copper salts. This is the first report on the agronomic performance of GO-based slow-release fertilizer.