Radical defects modulate the photocatalytic response in 2D-graphitic carbon nitride

Graphitic carbon nitride (gCN) is an important heterogeneous metal-free catalytic material. Thermally induced post-synthetic modifications, such as amorphization and/or reduction, were recently used to enhance the photocatalytic response of these materials for certain classes of organic transformations, with structural defects possibly playing an important role. The knowledge of how these surface modifications modulate the photocatalytic response of gCN is therefore not only interesting from a fundamental point of view, but also necessary for the development and/or tuning of metal-free gCN systems with superior photo-catalytic properties. Herein, employing density functional theory calculations and combining both the periodic and molecular approaches, in conjunction with experimental EPR measurements, we demonstrate that different structural defects on the gCN surface generate distinctive radical defect states localized within the electronic bandgap, with only those correlated with amorphous and reduced gCN structures being photo-active. To this end, we (i) model defective gCN surfaces containing radical defect states; (ii) assess the interactions of these defects with the radical precursors involved in the photo-driven alkylation of electron-rich aromatic compounds (namely perfluoroalkyl iodides); and (iii) describe the photo-chemical processes triggering the initial step of that reaction at the gCN surface. We provide a coherent structure/photo-catalytic property relationship on defective gCN surfaces, elaborating how only specific defect types act as binding sites for the perfluoroalkyl iodide reagent and can favor a photo-induced charge transfer from the gCN surface to the molecule, thus triggering the perfluoroalkylation reaction.

The nature of radical defects governs the photocatalytic activity of graphitic carbon nitride.     

Zero-dimensional subschemes of ruled varieties

Here we study zero-dimensional subschemes of ruled varieties, mainly Hirzebruch surfaces and rational normal scrolls, by applying the Horace method and the Terracini method This research is part of the T.A.S.C.A. project of I.N.d.A.M., supported by P.A.T. (Trento) and M.I.U.R. (Italy)     

Role of the dispersion route on the phase transformation of a nano-crystalline transition alumina

De-agglomeration of a nanocrystalline transition alumina powder was performed in distilled water at its natural pH under magnetic stirring for 170 h or by ball milling for 3 h. Gibbsite appeared near transition aluminas in the magnetic stirred sample. In addition, a relevant lowering of the α-Al₂O₃ crystallization temperature was observed in the dispersed materials with respect to the as-received powder. However, the activation energy of the above transformation, determined by the Kissinger method, was in any case about 480–500 kJ/mol and unaffected by the dispersion route. On the contrary, it was reduced of about 10% in α-alumina seeded samples, obtained by flash plunging the powders at 1,290 °C for 10 min.     

On Singular Curves in the Case of Positive Characteristic

Nuclear convergence spaces are studied. It is shown that an L_e-embedded convergence vector space E is L_eL_M-embedded if it is Schwartz and satisfies a certain countability condition which expresses that the set of filters converging to zero is essentially countable. Further it is shown that if E is L_eL_M-embedded and nuclear, then the identity E → E can be approximated with finite operators in the equable continuous convergence structure on L(E, E). This result is used in the study of the spectrum Hom_cH_e(U) of the convergence algebra H_e(U) of holomorphic functions on a circled convex open set to prove sufficient conditions for the validity of the formula Hom_cH_e(U) ～ U.     

Charged particle multiplicity distributions for fixed number of jets inZ0 hadronic decays

The multiplicity distributions of charged particles in full phase space and in restricted rapidity intervals for events with a fixed number of jets measured by the DELPHI detector are presented. The data are well reproduced by the Lund Parton Shower model and can also be well described by fitted negative binomial distributions. The properties of these distributions in terms of the clan model are discussed. In symmetric 3-jet events the candidate gluon jet is found not to be significantly different in average multiplicity than the mean of the other two jets, thus supporting previous results of the HRS and OPAL experiments. Similar results hold for events generated according to the LUND PS and to the HERWIG models, when the jets are defined by the JADE jet finding algorithm. The method seems to be insensitive for measuring the color charge ratio between gluons and quarks.     

Molecular characterization of a hyperbranched polyester. I. Dilute solution properties

A hyperbranched polyester was fractionated by precipitation to produce 10 fractions with molecular weights between 20 × 10³ and 520 × 10³ g mol^?1. Each of these fractions was examined by size exclusion chromatography, dilute‐solution viscometry, intensity, and quasi‐elastic light scattering in chloroform solution at 298 K. High‐resolution solution‐state ¹³C NMR was used to determine the degree of branching; for all fractions this factor was 0.5 ± 0.1. Viscometric contraction factors, g′, decreased with increasing molecular weight, and the relation of this parameter to the configurational contraction factor, g, calculated from a theoretical relation suggested a very strong dependence on the universal viscosity constant, Φ, on the contraction factor. A modified Stockmayer–Fixman plot was used to determine the value of (〈r²〉_o/M_w)^1/2, which was much larger than the value for the analogous linear polymer. The scaling relations of the various characteristic radii (R_g, R_h, R_T, and R_η) with molecular weight all had exponents less than 0.5 that agreed with the theoretical predictions for hyperbranched polymers. The exponent for R_g was interpreted as fractal dimension and had a value of 2.38 ± 0.25, a value that is of the same order as that anticipated by theory for branched polymers in theta conditions and certainly not approaching the value of 3 that would be associated with the spherical morphology and uniform segment density distribution of dendrimers. Second virial coefficients from light scattering are positive, but the variation of the interpenetration function, ψ, with molecular weight and the friction coefficient, k_o, obtained from the concentration dependence of the diffusion coefficient suggests that chloroform is not a particularly good solvent for the hyperbranched polyester and that the molecules are soft and penetrable with little spherical nature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1339–1351, 2003     

Rank 2 stable vector bundles on Fano 3-folds of index 2

Let X be a Fano 3-fold of the first kind with index 2. In this paper, we characterize the chern classes of rank 2 stable vector bundles on X and we find a bound for the least twist of a rank 2 reflexive sheaf on X which has a global section.     

Measurements with a small (M=24.4 kg) cryogenic gravitational-wave antenna atT=1.5 K

Summary New measurements obtained at the University of Rome by means of a cryogenic gravitational-wave antenna of massM=24.4 kg operated atT=4.5 and 1.5 K are reported. The operation was interrupted after 90 hours of data taking, mainly during successive nights, although the antenna could continue to function very satisfactorily for a much longer time. The rate of disturbances is so small that it can be easily eliminated by coincidences with other antennas. The overall effective temperature obtained with an appropriate data analysis algorithm atT=1.5 K isT _eff∼=0.79 K. This value is mostly due to the noise temperature of the FET preamplifier which constitutes the main limiting factor to the sensitivity of present gravitational-wave resonant antennas.

---

Riassunto Si presentano i risultati di nuove misure eseguite all'Università di Roma con un'antenna gravitazionale criogenica di massaM=24.4 kg funzionante aT=4.5 e 1.5 K. Le misure sono state interrotte dopo 90 ore di raccolta di dati, fatte prevalentemente durante la notte, nonostante che l'antenna potesse continuare a funzionare molto soddisfacentemente per tempi assai più lunghi. La frequenza statistica dei disturbi è tale da poterli facilmente eliminare a mezzo di coincidenze con altre antenne. La temperatura efficace dell'antenna funzionante aT=1.5 K, ottenuta impiegando nell'analisi dei dati un opportuno algoritmo, èT _eff=0.79 K. Questo valore è dovuto prevalentemente alla temperatura di rumore di fondo del FET del preamplificatore che costituisce il principale fattore limitante la sensibilità delle attuali antenne risonanti.

---

Резюме Приводятся результаты новых измерений, проведенных в Римском Университете с помощью антенны гравитационных волн с массойМ=24.4 кг, работающей при низких температурахТ=4.5 и 1.5 К. Действие антенны было прервано после 90 часов работы, хотя антенна могла продолжать фынкционировть очень удовлетворительно более продолжительное время. Интенсивность возмущений является настолько малой, что их влияние может Быть легко исключено посредством совпадений с другими антеннами. Полная эффективная температура, полученная с помощью анализа соответствующих данных приТ=1.5 К, составляетТ _эфф=0.79 К. Эта величина, главным образом, обусловлена шумовой температурой FET предусилителя, который представляет основой ограничивающий фактор для чувствитеительности резонансных антенн гравитационных волн.

---

---

Research supported by the Faculty of Natural Sciences of the University of Rome and by the C.N.R.