Theodore Steriotis

Liquid‐Phase Exfoliation of Graphite Towards Solubilized Graphenes

Following the astonishing discoveries of fullerenes and carbon nanotubes in earlier decades, the rise of graphene has recently triggered an exciting new area in the field of carbon nanoscience with continuously growing academic and technological impetus. Currently, several methods have been proposed to prepare graphenes, such as micromechanical cleavage, thermal annealing of SiC, chemical reduction of graphite oxide, intercalative expansion of graphite, bottom-up growth, chemical vapor deposition, and liquid-phase exfoliation. Especially this latter top-down approach is very appealing from a chemist’s point of view for the following reasons: i) it is direct, simple, and benign producing graphenes just by solvent treatment of graphite powders, and ii) the as-obtained sheets form colloidal dispersions in the solvents used for the exfoliation, thereby enabling their manipulation into various processes, like mixing, blending, casting, impregnation, spin-coating, or functionalization. The key parameter for suitable solvents is that the solvent–graphene interactions must be at least comparable to those existing between the stacked graphenes in graphite. To that end, Coleman and coworkers have successfully demonstrated this concept using N-methylpyrrolidone, N,N-dimethylacetamide, g-butyrolactone, 1,3-dimethyl-2-imidazolidinone, and benzyl benzoate as

Graphene Fluoride: A Stable Stoichiometric Graphene Derivative and its Chemical Conversion to Graphene

Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.

Enhanced hydrogen storage by spillover on metal-doped carbon foam: an experimental and computational study

A lightweight, oxygen-rich carbon foam was prepared and doped with Pd/Hg alloy nanoparticles. The composite revealed high H2 sorption capacity (5 wt%) at room temperature and moderate pressure (2 MPa). The results were explained on the basis of the H2 spillover mechanism using Density Functional Theory.

Merging high doxorubicin loading with pronounced magnetic response and bio-repellent properties in hybrid drug nanocarriers.

Hybrid magnetic drug nanocarriers are prepared via a self-assembly process of poly(methacrylic acid)-graft-poly(ethyleneglycol methacrylate) (p(MAA-g-EGMA)) on growing iron oxide nanocrystallites. The nanocarriers successfully merge together bio-repellent properties, pronounced magnetic response, and high loading capacity for the potent anticancer drug doxorubicin (adriamicin), in a manner not observed before in such hybrid colloids. High magnetic responses are accomplished by engineering the size of the magnetic nanocrystallites (∼13.5 nm) following an aqueous single-ferrous precursor route, and through adjustment of the number of cores in each colloidal assembly. Complementing conventional magnetometry, the magnetic response of the nanocarriers is evaluated by magnetophoretic experiments providing insight into their internal organization and on their response to magnetic manipulation. The structural organization of the graft-copolymer, locked on the surface of the nanocrystallites, is further probed by small-angle neutron scattering on single-core colloids. Analysis showed that the MAA segments selectively populate the area around the magnetic nanocrystallites, while the poly(ethylene glycol)-grafted chains are arranged as protrusions, pointing towards the aqueous environment. These nanocarriers are screened at various pHs and in highly salted media by light scattering and electrokinetic measurements. According to the results, their stability is dramatically enhanced, as compared to uncoated nanocrystallites, owing to the presence of the external protective PEG canopy. The nanocarriers are also endowed with bio-repellent properties, as evidenced by stability assays using human blood plasma as the medium.

Development of new drug delivery system based on ordered mesoporous carbons: characterisation and cytocompatibility studies

Ordered mesoporous carbons that encapsulate the poorly soluble compounds ibuprofen and indomethacin were systematically studied by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and X-ray photon electron spectroscopy (XPS). The results showed marked differences in the release profiles of the two drug molecules in simulated gastric fluids. In vitro toxicity profiles appear to be compatible with potential therapeutic applications bringing them to the forefront as carriers of poorly water soluble drugs.

Direct synthesis of carbon nanosheets by the solid-state pyrolysis of betaine

Carbon sheets of a few nanometers thick (nanosheets) define a peculiar class of carbon materials with unique surface-to-volume ratio, smooth surface morphologies and thin edges, flexibility and elasticity, high thermal and chemical stability, and lightness [1, 2]. In this respect, carbon nanosheets are promising candidates for hydrogen storage materials, sensors, catalyst supports, fillers, templates, and substrates for further functionalization and single graphene production [3–16]. In early studies, the particular carbon nanomaterials have been synthesized via radio-frequency or microwave plasma-enhanced chemical vapor deposition (CVD), expansion of graphite, chemical reduction of exfoliated graphite oxide, a solvothermal route, or catalytic growth [1–16]. However, these preparative methods suffer (depending on the case) from the following drawbacks: (i) low yield or/and concurrent formation of other carbon morphologies, which limits extensive studies and development; (ii) the thickness of the sheets rarely falls below 10 nm; (iii) from a technical standpoint, they often require a sophisticated apparatus, controlled atmosphere, high temperature, flammable gaseous mixtures, gas flow adjustments, time-consuming steps, catalysts, or highly corrosive and potentially explosive chemicals; and (iv) poor surface functionality, which restricts further derivatization. Unambiguously, the direct formation of customized carbon nanosheets at fairly good yields using simple and safe methods would be highly recommended from the viewpoint of commercial usage and applications. Betaine, (CH3)3N CH2COO , is an important zwitterionic organic compound widely distributed in nature. Although the thermal decomposition of betaine has been studied in detail [17, 18], nonetheless, there is no information available on the structure and morphology of the residual carbon after pyrolysis. To that end, herein we report the pyrolytic formation of ultrathin carbon nanosheets in air using betaine as a molecular precursor. This alternative yet paradox approach towards sheet-like carbons exhibits the following advantages: (i) it produces powder carbon nanosheets at fairly good yields; (ii) the thickness of the sheets is far less than 10 nm; (iii) the method is simple, safe, and inexpensive proceeding under normal conditions; and (iv) it directly introduces oxygen-containing functional groups in the solid, thus providing active sites to the surface for further modification. Overall, the present method offers new possibilities for the cost-efficient production and processing of this kind of materials. Typically, 1 g of anhydrous betaine (Sigma) was calcined in air at 400 C for 2 h at a heating rate of 10 C min to afford a lightweight, black-brown powder at 2% yield [17, 18] (Fig. 1). This sample, thereafter denoted as BET400, contains exclusively carbon nanosheets. The reported yield is sufficient enough for the preparation of bulk quantities of powder nanosheets (Fig. 1). Also note that calcination takes A. B. Bourlinos (&) V. Georgakilas Institute of Materials Science, NCSR ‘‘Demokritos’’, Ag. Paraskevi Attikis, Athens 15310, Greece e-mail: bourlinos@ims.demokritos.gr

Electrosprayed mesoporous particles for improved aqueous solubility of a poorly water soluble anticancer agent: in vitro and ex vivo evaluation

ABSTRACT Encapsulation of poorly water‐soluble drugs into mesoporous materials (e.g. silica) has evolved as a favorable strategy to improve drug solubility and bioavailability. Several techniques (e.g. spray drying, solvent evaporation, microwave irradiation) have been utilized for the encapsulation of active pharmaceutical ingredients (APIs) into inorganic porous matrices. In the present work, a novel chalcone (KAZ3) with anticancer properties was successfully synthesized by Claisen‐Schmidt condensation. KAZ3 was loaded into mesoporous (SBA‐15 and MCM‐41) and non‐porous (fumed silica, FS) materials via two techniques; electrohydrodynamic atomization (EHDA) and solvent impregnation. The effect of both loading methods on the physicochemical properties of the particles (e.g. size, charge, entrapment efficiency, crystallinity, dissolution and permeability) was investigated. Results indicated that EHDA technique can load the active in a complete amorphous form within the pores of the silica particles. In contrast, reduced crystallinity (˜79%) was obtained for the solvent impregnated formulations. EHDA engineered formulations significantly improved drug dissolution up to 30‐fold, compared to the crystalline drug. Ex vivo studies showed EHDA formulations to exhibit higher permeability across rat intestine than their solvent impregnated counterparts. Cytocompatibility studies on Caco‐2 cells demonstrated moderate toxicity at high concentrations of the anticancer agent. The findings of the present study clearly show the immense potential of EHDA as a loading technique for mesoporous materials to produce poorly water‐soluble API carriers of high payload at ambient conditions. Furthermore, the scale up potential in EHDA technologies indicate a viable route to enhance drug encapsulation and dissolution rate of loaded porous inorganic materials.

A microporous Cu2+ MOF based on a pyridyl isophthalic acid Schiff base ligand with high CO2 uptake

A new Cu2+ complex that was isolated from the initial use of 5-((pyridin-4-ylmethylene)amino)isophthalic acid (PEIPH2) in 3d metal–organic framework (MOF) chemistry is reported. Complex {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞ denoted as Cu-PEIP·7DMF was isolated from the reaction of Cu(NO3)2·2.5H2O with PEIPH2 in N,N-dimethylformamide (DMF) at 100 °C and contains both the PEIP2− ligand and its 5-NH2-mBDC2− fragment. After the structure and properties of Cu-PEIP were known an analogous complex was prepared by a rational synthetic method that involved the reaction of Cu(NO3)2·2.5H2O, 5-((pyridin-4-ylmethyl)amino)isophthalic acid (PIPH2 – the reduced analogue of PEIPH2) and 5-NH2-mBDCH2 in DMF at 100 °C. Cu-PEIP comprises two paddle-wheel [Cu2(COO)4] units and exhibits a 3D-framework with a unique trinodal underlying network and point symbol (4.52)4(42·54·64·83·92)2(52·84). This network consists of pillared kgm-a layers containing a hexagonal shaped cavity with a relatively large diameter of ∼8–9 A surrounded by six trigonal shaped ones with a smaller diameter of ∼4–5 A and thus resembles the structure of HKUST-1. Gas sorption studies revealed that Cu-PEIP exhibits a 1785 m2 g−1 BET area as well as high CO2 sorption capacity (4.75 mmol g−1 at 273 K) and CO2/CH4 selectivity (8.5 at zero coverage and 273 K).

Development and evaluation of materials for thermochemical heat storage based on the CaO/CaCO3 reaction couple

The current work relates to the development of synthetic calcium oxide (CaO) based compositions as candidate materials for energy storage under a cyclic carbonation/decarbonation reaction scheme. Although under such a cyclic scheme the energy density of natural lime based CaO is high (∼ 3MJ/kg), the particular materials suffer from notable cycle-to-cycle deactivation. To this direction, pure CaO and CaO/Al2O3 composites have been prepared and preliminarily evaluated under the suggested cyclic carbonation/decarbonation scheme in the temperature range of 600-800°C. For the composite materials, Ca/Al molar ratios were in the range between 95/5 and 52/48 and upon calcination the formation of mixed Ca/Al phases was verified. The preliminary evaluation of materials studied was conducted under 3 carbonation/decarbonation cycles and the loss of activity for the case of natural CaO was obvious. Synthetic materials with superior stability/capture c.f. natural CaO were further subjected to multi-cyclic carbonation/d...

Nanoporous carbon — metal composites for hydrogen storage

AbstractMetal-carbon composites have shown considerable hydrogen storage potential at room temperature. In the present work the behaviour of two different Pd amalgam doped carbon substrates, namely a carbogenic foam and a mildly oxidised ordered mesoporous carbon, are compared on the basis of their hydrogen sorption properties at 77 and 298 K and low pressures, aiming to investigate the effect of surface on the storage capacity. In both cases, the introduction of alloy nanoparticles leads to an improvement of the hydrogen uptake with respect to pure carbons. This effect is significant for the carbogenic foam however small for the ordered carbon.