Alexandros P. Katsoulidis

Compression and Aggregation-Resistant Particles of Crumpled Soft Sheets

Unlike flat sheets, crumpled paper balls have both high free volume and high compressive strength, and can tightly pack without significantly reducing the area of accessible surface. Such properties would be highly desirable for sheet-like materials such as graphene, since they tend to aggregate in solution and restack in the solid state, making their properties highly dependent on the material processing history. Here we report the synthesis of crumpled graphene balls by capillary compression in rapidly evaporating aerosol droplets. The crumpled particles are stabilized by locally folded, π-π stacked ridges as a result of plastic deformation, and do not unfold or collapse during common processing steps. In addition, they are remarkably aggregation-resistant in either solution or solid state, and remain largely intact and redispersible after chemical treatments, wet processing, annealing, and even pelletizing at high pressure. For example, upon compression at 55 MPa, the regular flat graphene sheets turn into nondispersible chunks with drastically reduced surface area by 84%, while the crumpled graphene particles can still maintain 45% of their original surface area and remain readily dispersible in common solvents. Therefore, crumpled particles could help to standardize graphene-based materials by delivering more stable properties such as high surface area and solution processability regardless of material processing history. This should greatly benefit applications using bulk quantities of graphene, such as in energy storage or conversion devices. As a proof of concept, we demonstrate that microbial fuel electrodes modified by the crumpled particles indeed outperform those modified with their flat counterparts.

Extraordinary Selectivity of CoMo3S13 Chalcogel for C2H6 and CO2 Adsorption

or metals, [ 5 ] has recently been expanded to include the emerging new chalcogenide materials called chalcogels. [ 6–10 ] Unlike the nanocrystalline chalcogenide aerogels reported by Brock et al., [ 6 , 11 , 12 ] the chalcogels feature random amorphous networks similar to those of silica. Because of the “soft” nature of electron-rich chalcogen atoms, the polarizability of the internal surface of chalcogels is much higher than those of metal oxides, porous carbons, and organic polymers and therefore provides an entirely new medium through which to study the diffusion and separation of gases. [ 13 ] Photocatalysis, catalysis, gas separation, and removal of heavy metals with chalcogels are just some of the proposed applications that make use of the unique electronic properties (tunable bandgaps and high surface polarizability) of such high surface area materials. [ 8 ]

Synthesis and acidic catalytic properties of ordered mesoporous alumina–tungstophosphoric acid composites

A series of well-ordered mesoporous alumina–tungstophosphoric (HPW) acid composite frameworks has been prepared by a sol–gel copolymerization route in the presence of non-ionic surfactants. The resulting materials feature a high loading of HPW acids (up to ∼53 wt%) in composite framework and possess hexagonal p6mm pore structure with uniform large pores. The mesoscopic order of these structures was evidenced by SAXS analysis, TEM images and N2 physisorption measurements. The composite materials exhibited BET surface areas in the range of 54–71 m2 g−1, total pore volumes in the range of 0.11–0.14 cm3 g−1 and quite narrow pore size distributions with peak maxima in the 7.1–8.3 nm range. The Keggin clusters were incorporated in mesoporous alumina walls by strong chemical bonds according to the FT-IR and UV/vis spectroscopy analysis. This chemical linkage of HPW to the alumina matrix is responsible for the outstanding stability of these materials against water-leaching. The mesoporous surfaces exhibited exceptional acidity that arises from the unique alumina–HPW composite structure. As the loading of HPW increases, the surface acidic character of the composites enhanced, and this is reflected in the higher catalytic activity towards isopropanol conversion.

Ordered mesoporous Cr2O3 frameworks incorporating Keggin-type 12-phosphotungstic acids as efficient catalysts for oxidation of benzyl alcohols

Ordered mesoporous chromium(III) oxide–phosphotungstic acid (PWA) nanocomposite structures with controllable composition (∼17 to 49 wt% in PWA) have been successfully prepared via an ultrasound-assisted nanocasting route, using mesoporous SBA-15 silica as a rigid mold. These materials possess 3D hexagonal mesostructure, large internal BET surface areas of ∼67 to 80 m2 g−1, and uniform pores of ∼3 to 4 nm size according to small-angle X-ray scattering, high resolution transmission electron microscopy and N2 physisorption. The Keggin-type structure of [PW12O40]3− anions is preserved intact into the Cr2O3 framework, as confirmed by total X-ray diffuse scattering and pair distribution function analysis and infrared and diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy. The integration of regular porosity, large internal surface area, and Cr2O3–PWA composition makes these materials highly promising for applications in oxidation catalysis. Although pure mesoporous Cr2O3 and PWA compounds exhibit low catalytic activity, the mesoporous Cr2O3–PWA composites showed superior activity and selectivity for the oxidation of selected secondary benzyl alcohols, giving good-to-high yields within a short reaction time. Furthermore, the Cr2O3–PWA composite frameworks demonstrated remarkable durability and reusability upon multiple usages without leaching or decomposition of the incorporated PWA clusters. This enhancement is attributed to the synergistic interactions between the PWA and Cr2O3 components as well as the well-ordered open-pore structure and large catalytically active surface area.

Extraordinary selectivity of CoMo 3 S 13 chalcogel for C 2 H 6 and CO 2 adsorption

or metals, [ 5 ] has recently been expanded to include the emerging new chalcogenide materials called chalcogels. [ 6–10 ] Unlike the nanocrystalline chalcogenide aerogels reported by Brock et al., [ 6 , 11 , 12 ] the chalcogels feature random amorphous networks similar to those of silica. Because of the “soft” nature of electron-rich chalcogen atoms, the polarizability of the internal surface of chalcogels is much higher than those of metal oxides, porous carbons, and organic polymers and therefore provides an entirely new medium through which to study the diffusion and separation of gases. [ 13 ] Photocatalysis, catalysis, gas separation, and removal of heavy metals with chalcogels are just some of the proposed applications that make use of the unique electronic properties (tunable bandgaps and high surface polarizability) of such high surface area materials. [ 8 ]

Extraordinary Selectivity of CoMo[subscript 3]S[subscript 13] Chalcogel for C[subscript 2]H[subscript 6] and CO[subscript 2] Adsorption

or metals, [ 5 ] has recently been expanded to include the emerging new chalcogenide materials called chalcogels. [ 6–10 ] Unlike the nanocrystalline chalcogenide aerogels reported by Brock et al., [ 6 , 11 , 12 ] the chalcogels feature random amorphous networks similar to those of silica. Because of the “soft” nature of electron-rich chalcogen atoms, the polarizability of the internal surface of chalcogels is much higher than those of metal oxides, porous carbons, and organic polymers and therefore provides an entirely new medium through which to study the diffusion and separation of gases. [ 13 ] Photocatalysis, catalysis, gas separation, and removal of heavy metals with chalcogels are just some of the proposed applications that make use of the unique electronic properties (tunable bandgaps and high surface polarizability) of such high surface area materials. [ 8 ]

Extraordinary Selectivity of CoMo3S13Chalcogel for C2H6and CO2Adsorption

or metals, [ 5 ] has recently been expanded to include the emerging new chalcogenide materials called chalcogels. [ 6–10 ] Unlike the nanocrystalline chalcogenide aerogels reported by Brock et al., [ 6 , 11 , 12 ] the chalcogels feature random amorphous networks similar to those of silica. Because of the “soft” nature of electron-rich chalcogen atoms, the polarizability of the internal surface of chalcogels is much higher than those of metal oxides, porous carbons, and organic polymers and therefore provides an entirely new medium through which to study the diffusion and separation of gases. [ 13 ] Photocatalysis, catalysis, gas separation, and removal of heavy metals with chalcogels are just some of the proposed applications that make use of the unique electronic properties (tunable bandgaps and high surface polarizability) of such high surface area materials. [ 8 ]