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Reduced graphene oxide (rGO) composite aerogels were synthesized by the radiation reduction of graphene oxide (GO) with the assistance of Eu3+, which demonstrated excellent adsorption performance for diverse organic pollutants. Eu3+ promoted the formation of the gel by inducing the pre-assembly of GO so that the required pH range for synthesizing the rGO aerogel by radiation reduction was broadened and the minimum absorbed dose was also reduced. At pH 2, the Eu3+-induced pre-assembly fabricated more mesopores and enlarged the specific surface area of the obtained hierarchically porous rGO-Eu composite aerogel, which enabled the high-capacity (81–395 g g−1) and ultrafast removal of organic solvents. The different effects of organic solvents on the unique fluorescence emission of Eu(III) also allowed the in situ detection of certain organic solvents such as pyridine. At pH 6, Eu3+ enhanced the reduction of GO by capturing more hydrated electrons, the most reductive species produced by water radiolysis, and synergistically reduced GO. The obtained rGO-Eu composite aerogel with a high reduction degree, demonstrated outstanding adsorption capacities for various anionic organic dyes (40.5–1572.5 mg g−1) owing to the strong π–π interaction and electrostatic attraction. Benefitting from high reduction, it demonstrated adsorption capacity for cationic dyes (97.3–1367.6 mg g−1) comparable to other reported graphene-based aerogels. The rGO-Eu aerogel prepared by radiation reduction might be suitable as a broad-spectrum adsorbent for organic pollutants. [ABSTRACT FROM AUTHOR]

The efficient exfoliation of hexagonal boron nitride (h-BN) to fabricate boron nitride nanosheets (BNNS) is a challenging task in the popular field of two-dimensional material preparation. In this paper, a new radiation-induced reduction-exfoliation method is introduced to achieve the one-step exfoliation of h-BN to form Ni-nanoparticle-(NiNP)-bound BNNS (Ni/BNNS) in a binary isopropanol/water medium using gamma-ray radiation at ambient temperature and pressure. The process involves the effective intercalation of Ni2+ ions into h-BN interlayers dispersed in the isopropanol/water medium, followed by the in situ growth of NiNPs under gamma-ray irradiation. Taking advantage of the volume expansion effect generated by the growth of the NiNPs and with help from a cationic surfactant, such as hexadecyltrimethylammonium chloride (CTAC), sheet-like Ni/BNNS in 200 nm squares and with an average BNNS thickness of less than 5 nm can be peeled from h-BN and stably dispersed in water. The prepared magnetic Ni/BNNS exhibits good catalytic performance, excellent structural stability, and reusability toward the reduction of 2-nitroaniline (2-NA). After 5 cycles, the conversion of 2-NA still reaches 95.9% within 500 s. More interestingly, when Ni/BNNS was dispersed in water/methanol solution at a content of 0.17 mg mL−1 followed by exposure to simulated sunlight irradiation, H2 evolution of 8404.3 μmol gNi−1 within 2 h can be detected. This work not only provides a new idea for realizing the exfoliation of layers of nanoscale sheets from h-BN, but it also opens a new route to the one-step preparation of two-dimensional-material-supported nanometal catalysts by taking advantage of gamma-ray radiation. [ABSTRACT FROM AUTHOR]

In the spirit of the radiation chemical "spur model", the lifetime of a spur (τ(s)) is an important indicator of overlapping spurs and the establishment of homogeneity in the distribution of reactive species created by the action of low linear energy transfer (LET) radiation (such as fast electrons or γ irradiation). In fact, τ(s) gives the time required for the changeover from nonhomogeneous spur kinetics to homogeneous kinetics in the bulk solution, thus defining the so-called primary (or "escape") radical and molecular yields of radiolysis, which are obviously basic to the quantitative understanding of any irradiated chemical system. In this work, τ(s) and its temperature dependence have been determined for the low-LET radiolysis of deaerated 0.4 M aqueous solutions of H(2)SO(4) and pure liquid water up to 350 °C using a simple model of energy deposition initially in spurs, followed by random diffusion of the species of the spur during track expansion until spur overlap is complete. Unlike our previous τ(s) calculations, based on irradiated Fricke dosimeter simulations, the current model is free from any effects due to the presence of oxygen or the use of scavengers. In acidic solutions, the spur lifetime values thus obtained are in very good agreement with our previous calculations (after making appropriate corrections, however, to account for the possibility of competition between oxygen and Fe(2+) ions for H˙ atoms in the Fricke dosimeter, an effect which was not included in our original simulations). In this way, we confirm the validity of our previous approach. As expected, in the case of pure, oxygen-free water, our calculated times required to reach complete spur overlap are essentially the same (within uncertainty limits) as those found in acidic solutions. This explicitly reflects the fact that the diffusion coefficients for the hydrated electron and the H˙ atom that are involved in the overall calculation of the lifetime of spurs in neutral or acidic media, respectively, are of similar magnitude over the 25-350 °C temperature range studied.

Fast kinetics and time-dependent yields of the hydrated electron (e(-)(aq)) in pure water under conditions of high temperature and pressure up to the supercritical region were investigated by picosecond and nanosecond pulse radiolysis experiments. More significant decays at short times followed by plateau components at longer times were observed with increasing temperature, suggesting faster spur reaction processes. In supercritical water, it was also found that the e(-)(aq) yields strongly depend on the pressure (density). Comparison of these measurements with Monte-Carlo computer simulations allowed us to identify spur reactions of e(-)(aq) that occur predominantly at high temperatures and also to provide new key information on certain spur model parameters. In particular, the experimental time-dependent e(-)(aq) yields were best reproduced if the electron thermalization distance decreases with increasing temperature. This "shrinkage" of spur sizes at high temperatures was attributed to an increase in the scattering cross sections of subexcitation electrons, likely originating from a decrease in the degree of structural order of water molecules as the temperature is increased.

Monte-Carlo simulations of the radiolysis of the ferrous sulfate (Fricke) dosimeter with low-linear energy transfer (LET) radiation (such as (60)Co γ-rays or fast electrons) have been performed as a function of temperature from 25 to 350 °C. The predicted yields of Fe(2+) oxidation are found to increase with increasing temperature up to ∼100-150 °C, and then tend to remain essentially constant at higher temperatures, in very good agreement with experiment. By using a simple method based on the direct application of the stoichiometric relationship that exists between the ferric ion yields so obtained G(Fe(3+)) and the sum {3 [g(e(-)(aq) + H˙) + g(HO(2)˙)] + g(˙OH) + 2 g(H(2)O(2))}, where g(e(-)(aq) + H˙), g(HO(2)˙), g(˙OH), and g(H(2)O(2)) are the primary radical and molecular yields of the radiolysis of deaerated 0.4 M H(2)SO(4) aqueous solutions, the lifetime (τ(s)) of the spur and its temperature dependence have been determined. In the spirit of the spur model, τ(s) is an important indicator for overlapping spurs, giving the time required for the changeover from nonhomogeneous spur kinetics to homogeneous kinetics in the bulk solution. The calculations show that τ(s) decreases by about an order of magnitude over the 25-350 °C temperature range, going from ∼4.2 × 10(-7) s at 25 °C to ∼5.7 × 10(-8) s at 350 °C. This decrease in τ(s) with increasing temperature mainly originates from the quicker diffusion of the individual species involved. Moreover, the observed dependence of G(Fe(3+)) on temperature largely reflects the influence of temperature upon the primary free-radical product yields of the radiolysis, especially the yield of H˙ atoms. Above ∼200-250 °C, the more and more pronounced intervention of the reaction of H˙ atoms with water also contributes to the variation of G(Fe(3+)), which may decrease or increase slightly, depending on the choice made for the rate constant of this reaction. All calculations reported herein use the radiolysis database of Elliot (Atomic Energy of Canada Limited) and Bartels (University of Notre Dame) that contains all the best currently available information on the rate constants, reaction mechanisms, and g-values in the range 20 to 350 °C., (This journal is © the Owner Societies 2011)

The photolysis of melatonin in aqueous solution has been studied spectrometrically with a 248 nm laser. The formation of hydrated electrons in a monophotonic process has been confirmed in neutral solution with a quantum yield of 0.22. Two main absorption bands at 340 and 460 nm plus an absorption shoulder resulted from the counterpart of the ejected electron, a melatonin radical, in solution. The big difference for the relative intensity of the absorption peaks under various pH conditions reveals that the melatonin radical exists in the solution through an acid-base equilibrium. In support from the pH dependence of the spectrum of the intermediate, the pKa1 for the doubly-protonated melatonin radical against the mono-protonated melatonin cation radical was estimated to be -0.95 and the pKa2 for the mono-protonated melatonin cation and melatonin neutral radical was 4.5 +/- 0.5. This work will benefit the basic understanding about melatonin as a UV-light protector, as a light receptor and the antioxidation functions of melatonin.