Role of primary reaction initiated by 254 nm UV light in the degradation of p-nitrophenol attacked by hydroxyl radicals.
The degradation kinetics of p-nitrophenol (p-NP) exposed to 254/185 nm UV light were studied in two modes, i.e., 254 nm UV light intensity enhanced mode and normal mode. It was observed that the extra 254 nm UV light source accelerated the degradation process both in the presence and the absence of oxygen. Considering that hydroxyl radical (*OH) is the dominant factor that causes the degradation of p-NP, the enhanced degradation that occurred in the presence of the extra light source was attributed to the synergistic effect between *OH attack and the primary reactions initiated by 254 nm UV light. The synergistic effect has been confirmed by 266 nm laser flash photolysis (LFP) experiments. It is demonstrated that the phenoxy radical generated from the photoionization of p-NP is capable of reacting with *OH. On the basis of these results, it should be noted that UV light could cause more severe damage to p-NP attacked by *OH in aqueous solution.
Enhanced photocatalytic performances of TiO2-graphene hybrids on nitro-aromatics reduction to amino-aromatics
Graphene sheets have been considered as acceptors and transporters of photoinduced electrons generated from illuminated photocatalysts. Herein, we utilize these electrons with the help of graphene sheets in photocatalytic selective reduction. First, graphene-modified TiO2 hybrids are prepared by electrostatic assembly and in situ photocatalytic reduction processes using P25 and graphene oxide as precursors and then the photocatalytic reduction of nitro-aromatics to the corresponding amino-aromatics with these hybrids is examined under UV light irradiation. Results indicate that the addition of graphene sheets can effectively minimize the recombination of photogenerated charge carriers derived from the irradiated TiO2 and better encourage these separated electrons to participate in the reactions, which effectively improves the reduction ability of these TiO2-graphene hybrids in the presence of oxalic acid as hole scavengers. Besides the enhanced conversion rate, higher yields of amino-aromatics are achieved when using the graphene-modified TiO2 as a photocatalyst compared with those for pure TiO2.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.