Metal–Organic Frameworks for Separations

Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be produced on a large scale at low cost. Thus, it has been regarded as an important component for making various functional composite materials. Especially, graphene-based semiconductor photocatalysts have attracted extensive attention because of their usefulness in environmental and energy applications. This critical review summarizes the recent progress in the design and fabrication of graphene-based semiconductor photocatalysts via various strategies including in situ growth, solution mixing, hydrothermal and/or solvothermal methods. Furthermore, the photocatalytic properties of the resulting graphene-based composite systems are also discussed in relation to the environmental and energy applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation and photocatalytic disinfection. This critical review ends with a summary and some perspectives on the challenges and new directions in this emerging area of research (158 references).

Graphene-based semiconductor photocatalysts

On the Controllable Soft-Templating Approach to Mesoporous Silicates

Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

In order to clarify the origin of the hysteresis between freezing and melting of pore water, we performed x-ray diffraction measurements of water confined inside the cylindrical pores of seven kinds of siliceous MCM-41 (a member of ordered mesoporous materials denoted by Mobil Oil researchers) with different pore radii (1.2–2.9 nm) and the interconnected pores of Vycor glass as a function of temperature. The hysteresis effect depends markedly on the size of the cylindrical pores: the hysteresis is negligibly small in smaller pores and becomes remarkable in larger pores. This strongly suggests that the hysteresis is arisen from size-dependent supercooling of water confined to the mesopores. For the water confined to the mesopores with pore radius of 1.2 nm, a continuous transition between a liquid and a solid precedes the first-order freezing transition of the pore water which would occur by the same mechanism as in bulk water.

Freezing and melting of water in a single cylindrical pore: The pore-size dependence of freezing and melting behavior

The effect of temperature on adsorption isotherms of Ar, N2, O2, C2H4, and CO2 on mesoporous MCM-41 molecular sieves with different pore sizes (pore radius rp = 1.2, 1.4, 1.8, 2.1 nm) has been measured. The occurrence of adsorption hysteresis upon capillary condensation of these molecules in mesopores depends on their capillary critical temperatures (Tcc), which are far below the corresponding bulk critical temperatures (Tc). In accord with theoretical predictions of confined geometry effects on the criticality of fluids in narrow pores, a plot of (Tc − Tcc)/Tc against d/rp for Ar, N2, O2, and C2H4 seems to form a single straight line passing through the origin, where d is the molecular diameter. The data for CO2 deviates from this relationship. These results are compared with critical point shifts of fluids in conventional mesoporous adsorbents with an interconnected network of pores available in the literature.

Capillary Critical Point of Argon, Nitrogen, Oxygen, Ethylene, and Carbon Dioxide in MCM-41

The thermal desorption spectra of ammonia, amines and pyridines chemisorbed on Cr2O3 as well as the infrared absorption spectra have been measured in order to elucidate the acidic properties of the surface. The adsorption of ammonia on the bare Cr2O3 surface at room temperature leads to the formation of two kinds of coordination species giving rise to desorption peaks at 443 and 543 K, and the bonding of the latter species to the surface is strengthened to cause a shift in the peak to 593 K when the adsorption temperature is raised to 473 K. Dimethylamine bonded to Lewis-acid sites on Cr2O3 causes the N—H bond-cleavage reaction when the sample is heated at 473 K. Pyridine is strongly held on the surface: half the pyridine molecules absorbed on Cr2O3 at room temperature remain on the surface even after evacuation at 773 K. The infrared study of these molecules suggests the formation of an α-pyridone-like complex.

Thermal desorption and infrared studies of ammonia, amines and pyridines chemisorbed on chromic oxide

We performed measurements of a series of adsorption–desorption isotherms of nitrogen into MCM-41 and SBA-15 mesoporous molecular sieves with different pore sizes in a wide temperature range between a bulk triple point (Tt) and a bulk critical point (Tc). The hysteresis loop shrinks with increasing temperature and eventually disappears at the hysteresis critical temperature (Tch), in accord with the appearance of metastable states in a single pore. We estimated the exact pore sizes of our samples from comparing the experimental equilibrium pressure at 77 K with the NLDFT isotherms, where the condensation pressures at 77 K were determined by extrapolating a plot of the equilibrium pressure versus temperature measured above Tch. The pore critical temperature (Tcp) was also determined from the inflection point in a plot of the inverse slope of the adsorption step against temperature. Tch is always lower than Tcp. Both plots of (Tc−Tch)/Tc versus d/rp and (Tc−Tcp)/Tc versus d/rp form straight lines passing thr...

Capillary condensation of nitrogen in MCM-41 and SBA-15

To examine the nature of the adsorption and desorption branches in hysteretic adsorption isotherms of gases on mesoporous materials, we measured the temperature dependence of the adsorption and desorption isotherms of argon, oxygen, and carbon dioxide onto MCM-41 with a pore diameter of 4.4 nm. The results clearly show that in the open-ended cylindrical pores of MCM-41, capillary condensation rather than evaporation takes place near a thermodynamical equilibrium transition, as opposed to the general statement that capillary evaporation can occur via a meniscus formed at the pore mouth, and, thus, takes place at equilibrium.

Kunimitsu Morishige

Papers

Freezing and melting of water in a single cylindrical pore: The pore-size dependence of freezing and melting behavior

Capillary Critical Point of Argon, Nitrogen, Oxygen, Ethylene, and Carbon Dioxide in MCM-41

Thermal desorption and infrared studies of ammonia, amines and pyridines chemisorbed on chromic oxide

Capillary condensation of nitrogen in MCM-41 and SBA-15

Nature of adsorption and desorption branches in cylindrical pores.