Mesoporous titania photocatalyst: effect of relative humidity and aging on the preparation of mesoporous titania and on its photocatalytic activity performance

Mesoporous TiO₂ has been synthesized by the sol–gel method, using a nonionic triblock copolymer P123 as surfactant template under acidic conditions. The as-prepared samples were characterized by thermogravimetry–differential thermal analysis (TG–DTA), nitrogen absorption–desorption (BET), field emission scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of the mesoporous TiO₂ was evaluated by degradation of methylene blue under high-intensity UV light irradiation; the amount of methylene blue was measured by UV–visible spectroscopy. TG–DTA analysis revealed that the surfactant had been removed partly in as-synthesized samples. BET analysis proved that all the samples retained mesoporosity with a narrow pore-size distribution (4.5–6.3 nm) and high surface area (103–200 m²/g). All calcined mesoporous TiO₂ had high photocatalytic activity in the photodegradation of methylene blue.     

Triethylphosphate/Phosphorus Pentoxide as an Efficient Reagent for the Phosphorylation of Phenols

Abstract

A simple, efficient, and novel method has been developed for the phosphorylation of phenols. Treatment of phenols with a mixture of triethylphosphate/phosphorus pentoxide gives the corresponding phosphate derivatives in good yields. This method is easy, rapid, and offers good yields for the phosphorylation of phenols. The reaction of triethylphosphate with phosphorus pentoxide was also studied by variable-temperature ³¹P-NMR spectroscopy.     

Thermodynamic ground states of platinum metal nitrides

The thermodynamic stabilities of various phases of the nitrides of the platinum-metal elements are systematically studied using density functional theory. It is shown that for the nitrides of Rh, Pd, Ir, and Pt two new crystal structures, in which the metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. The region of stability with respect to those structures extends to 17 GPa for PtN2. Calculations show that the PtN2 simple tetragonal structures at this pressure are thermodynamically stable also with respect to phase separation. The fact that the local density and generalized gradient approximations predict different values of the absolute formation enthalpies as well different relative stabilities between simple tetragonal and the pyrite or marcasite structures are further discussed.     

Dilute magnetic semiconductor and half-metal behaviors in C-codoped BeO nanotubes: A first principles simulations

The geometric, electronic and magnetic properties of C-codoped single walled BeO nanotubes (SWBeONTs) are systematically explored by using ab-initio density functional theory calculations. We performed our calculations for C codoping BeO nanotube in two different chiralities: (8,0) and (5,5). In each case, two different configurations are considered, first the two oxygen atoms replaced by two carbon atoms are on first nearest neighbor sites in the plane of codoping and second they are far from each other. We found when C atoms are at the nearest-neighboring positions; the antiferromagnetism (AFM) phase is stable while increasing the distance between the two C atoms, the ferromagnetism stability increases. In the AFM phase the structures are nonmagnetic semiconductors, but in the FM phase all these systems are half-metallic systems with high magnetic moment and 100% spin polarization which can be used as magnetic nanostructure and possible future applications in permanent magnetism, magnetic recording, and spintronics.     

Killing vector fields on Riemannian and Lorentzian 3-manifolds

We give a complete local classification of all Riemannian 3-manifolds $(M,g)$ admitting a nonvanishing Killing vector field T. We then extend this classification to timelike Killing vector fields on Lorentzian 3-manifolds, which are automatically nonvanishing. The two key ingredients needed in our classification are the scalar curvature S of g and the function $\text{Ric}(T,T)$, where Ric is the Ricci tensor; in fact their sum appears as the Gaussian curvature of the quotient metric obtained from the action of T. Our classification generalizes that of Sasakian structures, which is the special case when $\text{Ric}(T,T)=2$. We also give necessary, and separately, sufficient conditions, both expressed in terms of $\text{Ric}(T,T)$, for g to be locally conformally flat. We then move from the local to the global setting, and prove two results: in the event that T has unit length and the coordinates derived in our classification are globally defined on ${\mathbb{R}}^3$, we give conditions under which S completely determines when the metric will be geodesically complete. In the event that the 3-manifold M is compact, we give a condition stating when it admits a metric of constant positive sectional curvature.     

Novel swelling/shrinking behaviors of glucose-binding hydrogels and their potential use in a microfluidic insulin delivery system

Hydrogels based on lightly crosslinked poly(methacrylamidophenylboronic acid-co-acylamide) swell monototically at pH 7.4 with exposure to increasing concentrations of glucose. At pH 10 these hydrogels first shrink and then reswell with increasing glucose concentration. A mechanism for these disctinct behaviors is proposed and preliminary results validating this mechanism are presented. A simple microfabricated glucose-sensitive valve based on this hydrogel is described.