The ability to efficiently utilize solar thermal energy to enable liquid-to-vapor phase transition has great technological implications for a wide variety of applications, such as water treatment and chemical fractionation. Here, we demonstrate that functionalizing graphene using hydrophilic groups can greatly enhance the solar thermal steam generation efficiency. Our results show that specially functionalized graphene can improve the overall solar-to-vapor efficiency from 38% to 48% at one sun conditions compared to chemically reduced graphene oxide. Our experiments show that such an improvement is a surface effect mainly attributed to the more hydrophilic feature of functionalized graphene, which influences the water meniscus profile at the vapor-liquid interface due to capillary effect. This will lead to thinner water films close to the three-phase contact line, where the water surface temperature is higher since the resistance of thinner water film is smaller, leading to more efficient evaporation. This strategy of functionalizing graphene to make it more hydrophilic can be potentially integrated with the existing macroscopic heat isolation strategies to further improve the overall solar-to-vapor conversion efficiency.
Sharp peaks in the dissociative electron attachment ͑DEA͒ cross sections of uracil and thymine at energies below 3 eV are assigned to vibrational Feshbach resonances ͑VFRs͒ arising from coupling between the dipole bound state and the temporary anion state associated with occupation of the lowest * orbital. Three distinct vibrational modes are identified, and their presence as VFRs is consistent with the amplitudes and bonding characteristics of the * orbital wave function. A deconvolution method is also employed to yield higher effective energy resolution in the DEA spectra. The site dependence of DEA cross sections is evaluated using methyl substituted uracil and thymine to block H atom loss selectively. Implications for the broader issue of DNA damage are briefly discussed.
We present a detailed study on dissociative electron attachment (DEA) to isolated gas-phase cytosine (C) and thymine (T). The experimental setup used for these measurements is a crossed electron/neutral beam instrument combined with a quadrupole mass spectrometer. Electron attachment to these biomolecules leads to dissociation into various fragments without a hint of any measurable amount of stable C or T parent anions. The fragment anions with highest abundance are (C-H)and (T-H) -, respectively. Quantum chemical calculations were performed to calculate the electron affinities and binding energies of the different isomers of the (T-H) fragment. Besides (C-H)and (T-H) -, we observed five other fragment anions formed by DEA to cytosine and eight additional product anions were detected in the case of thymine. Ion efficiency curves were measured for all fragment anions in the electron energy range from about 0 to 14 eV. For mixtures of T or C with SF 6 or CCl 4 in the collision chamber, additional resonances close to 0 eV were observed, resulting from ion molecule reactions of SF 6or Clwith the respective biomolecule.
Excess charge deposited on gas-phase thymine (T) and uracil (U) by resonant attachment of low-energy (0-3 eV) electrons induces the loss of hydrogen, which exclusively takes place from the N positions. This bond selectivity can be made site selective by properly adjusting the electron energy. While electrons at 1 eV result in loss of hydrogen from N1, the reaction can be switched to loss of hydrogen from N3 by tuning the electron energy to 1.8 eV. We find that any energy (and charge) transfer is completely blocked when the NÀH bond is replaced by NÀCH 3 . The present results have significant consequences for the exploration of the initial molecular processes leading to DNA damage, specifically in relation to recent observations of strand breaks in plasmid DNA induced by very low energy (0-4 eV) electrons.[1]Recent gas-phase experiments on the isolated nucleobases (NBs) thymine (T), cytosine (C), adenine (A), guanine (G), and uracil (U) have demonstrated that they all effectively capture low-energy electrons in the range below 3 eV . [2][3][4][5][6] The generated transient negative ion (TNI) subsequently decomposes by the loss of a neutral hydrogen atom. The overall dissociative electron attachment (DEA) reaction can be expressed as Equation (1), in which NB À# is the TNI of thecorresponding nucleobase and (NBÀH) À is the closed-shell anion formed by the ejection of a neutral hydrogen radical whereby the excess charge remains on the nucleobase. The reaction is effective already at energies below the threshold for electronic excitation (at subexcitation energies) and driven by the appreciable electron affinity of the (NBÀH) radicals, which is in the range between 3 and 4 eV, dependent on the site from which the hydrogen atom is ejected [2,6] (see below). Experiments with partly deuterated thymine [5] demonstrated that hydrogen abstraction occurs exclusively from the N sites, although H loss from the C sites is energetically accessible within that energy range. In the present contribution we demonstrate by means of methylated thymine and uracil that by properly adjusting the electron energy, the loss of hydrogen can be made even site selective with respect to the N1 and N3 positions. In light of strong efforts to induce cleavage of particular bonds by coherent laser control using tailored ultrafast pulses [7] the present result is very remarkable.In addition to these basic aspects, our findings have direct implications for the molecular description of radiation damage in biological systems, more specifically, for DNA in living cells. It is well accepted that the main biological effect is usually not produced by the primary interaction of the highenergy quanta with the complex molecular network within a living cell, but rather by the action of the secondary species generated along the ionization track.[8] The interaction of these secondary species (ions, electrons, radicals) with DNA and its surrounding can cause mutagenic, genotoxic, and other potentially lethal DNA lesions such as single-strand breaks (SSBs) and do...
We have investigated experimentally the formation of anions and cations of deoxyribose sugar (C(5)H(10)O(4)) via inelastic electron interaction (attachment/ionization) using a monochromatic electron beam in combination with a quadrupole mass spectrometer. The ion yields were measured as a function of the incident electron energy between about 0 and 20 eV. As in the case of other biomolecules (nucleobases and amino acids), low energy electron attachment leads to destruction of the molecule via dissociative electron attachment reactions. In contrast to the previously investigated biomolecules dehydrogenation is not the predominant reaction channel for deoxyribose; the anion with the highest dissociative electron attachment (DEA) cross section of deoxyribose is formed by the release of neutral particles equal to two water molecules. Moreover, several of the DEA reactions proceed already with "zero energy" incident electrons. In addition, the fragmentation pattern of positively charged ions of deoxyribose also indicates strong decomposition of the molecule by incident electrons. For sugar the relative amount of fragment ions compared to that of the parent cation is about an order of magnitude larger than in the case of nucleobases. We determined an ionization energy value for C(5)H(10)O(4) (+) of 10.51+/-0.11 eV, which is in good agreement with ab initio calculations. For the fragment ion C(5)H(6)O(2) (+) we obtained a threshold energy lower than the ionization energy of the parent molecular ion. All of these results have important bearing for the question of what happens in exposure of living tissue to ionizing radiation. Energy deposition into irradiated cells produces electrons as the dominant secondary species. At an early time after irradiation these electrons exist as ballistic electrons with an initial energy distribution up to several tens of electron volts. It is just this energy regime for which we find in the present study rather characteristic differences in the outcome of electron interaction with the deoxyribose molecule compared to other nucleobases (studied earlier). Therefore, damage induced by these electrons to the DNA or RNA strands may start preferentially at the ribose backbone. In turn, damaged deoxyribose is known as a key intermediate in producing strand breaks, which are the most severe form of lesion in radiation damage to DNA and lead subsequently to cell death.
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