Anomalous Depletion of Pore-Confined Carbon Dioxide upon Cooling below the Bulk Triple Point: An In Situ Neutron Diffraction Study.

The phase behavior of sorbed CO{2} in an ordered mesoporous silica sample (SBA-15) was studied by neutron diffraction. Surprisingly, upon cooling our sample below the bulk critical point, confined CO{2} molecules neither freeze nor remain liquid as expected, but escape from the pores. The phenomenon has additionally been confirmed gravimetrically. The process is reversible and during heating CO{2} refills the pores, albeit with hysteresis. This depletion was for the first time observed in an ordered mesoporous molecular sieve and provides new insight on the phase behavior of nanoconfined fluids.

In situ growth of capping-free magnetic iron oxide nanoparticles on liquid-phase exfoliated graphene.

We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature.

Tailor-made graphite oxide-DAB poly(propylene imine) dendrimer intercalated hybrids and their potential for efficient CO2 adsorption.

We report the rational design and synthesis of DAB poly(propylene imine) dendrimer (DAB) intercalated graphite oxide (GO) hybrids with tailorable interlayer distances. The amine groups originating from the intercalated dendrimer molecules cross-link adjacent GO sheets and strongly favour CO2 adsorption under wet flue gas conditions.

Alginate fibers as photocatalyst immobilizing agents applied in hybrid photocatalytic/ultrafiltration water treatment processes.

Ca alginate polymer fibers were developed to effectively disperse and stabilize an efficient photocatalyst such as AEROXIDE(®) TiO(2) P25 in their matrix. The biopolymer/TiO(2) fibers were prepared and tested either in the hydrogel non-porous form or in the highly porous aerogel form prepared by sc-CO(2) drying. Batch photocatalytic experiments showed that the porous, Ca alginate/TiO(2) fibers, exhibited high efficiency for the removal of methyl orange (MO) from polluted water. In addition, their high porosity and surface area led to high MO degradation rate which was faster than that observed not only for their non-porous analogs but also of the bulk P25 TiO(2) powder. Specifically, 90% removal for 20 µM MO was achieved within 220 min for the porous sc-CO(2) dried fibers while for their non-porous analogs at 325 min. The corresponding value (at 60 µM MO) for the porous sc-CO(2) dried fibers was 140 min over 240 min for the AEROXIDE(®) TiO(2) P25 as documented in the literature. Furthermore the composite alginate/photocatalyst porous fibers were combined with TiO(2) membranes in a continuous flow, hybrid photocatalytic/ultrafiltration water treatment process that led to a three fold enhancement of the MO removal efficiency at 400 ml of 20 µM MO total treated volume and to dilution rather than condensation in the membrane retentate as commonly observed in filtration processes. Furthermore the permeability of the photocatalytic membrane was enhanced in the presence of the fibers by almost 20%. This performance is achieved with 26 cm(2) and 31 cm(2) of membrane and stabilized photocatalyst surfaces respectively and in this context there is plenty of room for the up-scaling of both membranes and fibers and the achievement of much higher water yields since the methods applied for the development of the involved materials (CVD and dry-wet phase inversion in a spinning set-up) are easily up-scalable and are not expected to add significant cost to the proposed water treatment process.

Double-side active TiO2-modified nanofiltration membranes in continuous flow photocatalytic reactors for effective water purification.

A chemical vapour deposition (CVD) based innovative approach was applied with the purpose to develop composite TiO(2) photocatalytic nanofiltration (NF) membranes. The method involved pyrolytic decomposition of titanium tetraisopropoxide (TTIP) vapor and formation of TiO(2) nanoparticles through homogeneous gas phase reactions and aggregation of the produced intermediate species. The grown nanoparticles diffused and deposited on the surface of γ-alumina NF membrane tubes. The CVD reactor allowed for online monitoring of the carrier gas permeability during the treatment, providing a first insight on the pore efficiency and thickness of the formed photocatalytic layers. In addition, the thin TiO(2) deposits were developed on both membrane sides without sacrificing the high yield rates. Important innovation was also introduced in what concerns the photocatalytic performance evaluation. The membrane efficiency to photo degrade typical water pollutants, was evaluated in a continuous flow water purification device, applying UV irradiation on both membrane sides. The developed composite NF membranes were highly efficient in the decomposition of methyl orange exhibiting low adsorption-fouling tendency and high water permeability.

Hydrogen storage in polymer-functionalized Pd-decorated single wall carbon nanotubes.

Palladium is usually supported on porous materials in the form of nanoparticles. The hydrogen storage capacity of such a system is usually much higher than the separated capacity of the metal (approximately 0.7 H/Pd) and the support. Pd nanoparticles provide a source of hydrogen atoms by dissociation. The atomic hydrogen spills over from the Pd structure to the support via surface diffusion and this phenomenon is known as hydrogen spillover. In this study commercial SWNTs were dispersed in PEG 200 solution. Then the precursor PdCl2 in PEG 200 was added and the whole left to react under stirring with reflux at 200 degrees C for 1 h. Succeeding washings with ethanol and centrifugation followed for several times and finally the sample was dried at 60 degrees C. Through this procedure a 3 wt% Pd loading was achieved whereas the TEM derived nanoparticle size distribution indicated a 50% percentage of Pd nanoparticles with diameter less than 8 nm. Hydrogen isotherms up to 2 MPa were carried out with the gravimetric method. The defined storage capacity of 1.2 wt% at 0.2 MPa was quite satisfactory. However, a 0.2 wt% portion of this storage capacity was attributed to the formation of water molecules through reaction of H atoms with the dissociatively adsorbed oxygen atoms on the Pd nanoparticles. This conclusion was educed from a series of thermal desorption experiments following the H2 adsorption/desorption cycles and regeneration. Through this set of experiments several other important parameters were defined as the temperature for complete hydrogen desorption and the optimum conditions for PEG removal.

Prediction of binary adsorption isotherms of Cu(2+), Cd(2+) and Pb(2+) on calcium alginate beads from single adsorption data.

The binary adsorption of Cu(2+)-Cd(2+), Pb(2+)-Cd(2+) and Pb(2+)-Cu(2+) mixtures onto Ca-Alginate beads, prepared from Laminaria digitata, was studied using batch experiments. Competitive sorption models including extended Sips, extended Langmuir, Jain and Snoeyink modified Langmuir (JS modified) as well as Ideal Adsorpted Solution Theory (IAST) models were applied to predict the binary adsorption using single component adsorption parameters. The extended and the JS modified Langmuir approaches provide excellent prediction of the binary adsorption, while the extended Sips fails to predict the experimental data, giving only fair results in the case on Pb(2+)-Cu(2+) mixtures. On the contrary, the IAST models, though they are more complicated, provide less accurate estimation of sorption in binary metal ion solutions. In general, single component adsorption parameters can be effectively used for the prediction of a materials adsorption performance in binary metal ion solutions.