Microscopic solvation and femtochemistry of charge-transfer reactions: the problem of benzene(s)-iodine binary complexes and their solvent structures

Construction of a novel ursolic acid-based supramolecular gel for efficient removal of iodine from solution

Pentacyclic triterpenes is a natural amphipathic product which possess a rigid backbone and several polar functional groups such as hydroxyl, carbonyl and carboxyl groups. The amphipathic character makes it easy to realize self-assemble into complex nano structure and therefore attract extensive attention due to the simple synthetic processes and renewable raw materials. Hence, a novel Ursolic acid-based hydrogel was prepared successfully via a simple self-assembly of triterpenoid derivative in methanol by capture water molecule in air. The resulting hydrogel show a porous morphology and good elasticity including strong heat resistance. Based on the characteristic above, the hydrogel showed a good iodine adsorption capacity and can removal 75.0% of the iodine from cyclohexane solution and 66.3% from aqueous solution within 36 h. Data analysis indicate that all the iodine adsorption process are dominated by chemisorption and belongs to the multi-site adsorption on heterogenous surfaces. In addition, the obtained hydrogel also possesses a good recyclability which can maintain more than 82% of its capacity after 5 cycles. The simple preparation method and easily available raw materials endow it a great potential in future pollutant treatment.

An Economical Modification Method for MIL-101 to Capture Radioiodine Gaseous: Adsorption Properties and Enhancement Mechanism

Radioactive iodine is one of the inevitable by-products of nuclear energy application. However, it is a great threat to public health and the adsorbent needs to be adopted for removing the radioactive iodine. The iodine adsorbent needs to have some advantages, such as simple preparation method, low cost, high absorption capacity, and recyclable utilization. In order to meet the above requirements, the etched material of institute Lavoisier 101 (MIL-101) was prepared to absorb the gaseous iodine. After the MIL-101 is etched, the iodine adsorption performance has been greatly improved. The iodine adsorption experiment of etched MIL-101 with different etching time (1 h, 3 h, 4 h, and 6 h) was completed, the results show that the optimal etching time is 4 hours and the capture capacity of the etched MIL-101 is 371 wt%, which is about 22% higher than that of original MIL-101. The experiment results of XRD, FT-IR, and XPS prove that the components and structure of etched MIL-101 are accordable with those of MIL-101. The surface roughness is introduced in this work. The pore roughness is also an important factor to the adsorption capacity, and the related research also supports this conclusion. Furthermore, after iodine is absorbed, etched MIL-101 can be treated by ethanol for iodine release, and the etched MIL-101 has satisfied recyclability within three cycles. Compared with MIL-101, etched MIL-101 not only had good reversible adsorption of iodine but also can adsorb low-concentration iodine. The etched MIL-101 has a broad application prospect in nuclear emergency response and radiation detection.

Simulated adsorption of iodine by an amino-metal-organic framework modified with covalent bonds

Radioactive iodine in nuclear waste is increasingly harmful to the human body and the environment because of its strong radioactivity, high fluidity, easy solubility in water, and long half-life. It is very important to find clean and economical materials to recover and fix radioactive iodine. In this paper, the amino-metal-organic framework was covalently modified to obtain composite materials to improve the recycling of iodine in the environment. These adsorbents are used to adsorb iodine in water, showing outstanding adsorption performance. The adsorption data are in good agreement with the Langmuir isothermal adsorption model and pseudo-second-order kinetic model, indicating that the adsorption process is mainly monolayer adsorption and chemical adsorption. The two materials showed selective adsorption capacity for iodine in the solution containing multiple competing ions. The adsorption capacity of the covalently modified composite increased from 949.52 to 2157.44 mg/g. Compared with the amino-metal-organic framework, the modified composite contains more electron-rich groups as active sites, and forms charge transfer compounds with iodine to realize chemical adsorption. Through the simulated adsorption of ultra-high-pressure micro-jet, the material has certain working ability under high pressure, which provides a theoretical basis for the future recovery and utilization of iodine under high pressure.

Lignin-based electrospinning nanofibers for reversible iodine capture and potential applications

The capture of radioactive iodine has recently attracted much attention due to the release of radioactive iodine during nuclear waste disposal and disasters. Exploring highly efficient, sustainable, and eco-friendly materials for capturing radioactive iodine has great significance in developing safe nuclear energy. We reported highly efficient, natural, lignin-based, electrospun nanofibers (LNFs) for reversible radioiodine capture. Abundant iodine adsorption sites, such as functional groups and the interaction between the intermolecular forces exist in LNFs. The capacity of the LNFs for the saturated adsorption of iodine was found to be 220 mg·g^-1, which is higher than that of the majority of bio-based adsorbents studied. Moreover, the LNFs exhibited an excellent recycling behavior, and their absorption capacity remained at 84.72% after 10 recycles. Therefore, the results imply that the lignin-based nanofibers can act as a natural, sustainable and eco-friendly packed material for the purification columns in industrial applications. The results demonstrate that the novel, nanostructured, natural biomass, as an ideal candidate has the potential for practical nuclear wastewater purification.

Contrasting mechanisms for photodissociation of methyl halides adsorbed on thin films of C6H6 and C6F6

The mechanisms for photodissociation of methyl halides (CH3X, X = Cl, Br, I) have been studied for these molecules when adsorbed on thin films of C6H6 or C6F6 on copper single crystals, using time-of-flight spectroscopy with 248 nm and 193 nm light. For CH3Cl and CH3Br monolayers adsorbed on C6H6, two photodissociation pathways can be identified - neutral photodissociation similar to the gas-phase, and a dissociative electron attachment (DEA) pathway due to photoelectrons from the metal. The same methyl halides adsorbed on a C6F6 thin film display only neutral photodissociation, with the DEA pathway entirely absent due to intermolecular quenching via a LUMO-derived electronic band in the C6F6 thin film. For CH3I adsorbed on a C6F6 thin film, illumination with 248 nm light results in CH3 photofragments departing due to neutral photodissociation via the A-band absorption. When CH3I monolayers on C6H6 thin films are illuminated at the same wavelength, additional new photodissociation pathways are observed that are due to absorption in the molecular film with energy transfer leading to dissociation of the CH3I molecules adsorbed on top. The proposed mechanism for this photodissociation is via a charge-transfer complex for the C6H6 layer and adsorbed CH3I.

From structure to structural dynamics: Ahmed Zewail's legacy

In this brief tribute to Ahmed Zewail, we highlight and place in the historical context, several of the major achievements that he and his colleagues have made in Femtochemistry (of which he was the principal instigator) and his introduction of ultrafast electron scattering, diffraction, microscopy and spectroscopy. By achieving a sub-picosecond temporal resolution, coupled with a picometer spatial resolution, he revolutionised our understanding of the corpus of chemical, physical, biological and materials science systems.

Photoinduced electron transfer in donor-acceptor complexes of ethylene with molecular and atomic iodine

Building upon our recent studies of radical addition pathways following excitation of the I2 chromophore in the donor-acceptor complex of ethylene and I2 (C2H4···I2), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (λmax = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene-I radical complex on the basis of our prior work. The formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I-I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, anti- and gauche-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C2H4···Br2 complex, where CT excitation led to only one product, anti-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I2 complex, the breakup of the photolytically generated I2(-•) anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin-orbit coupling.

Dynamics of clusters: from elementary to biological structures

Between isolated atoms or molecules and bulk materials there lies a class of unique structures, known as clusters, that consist of a few to hundreds of atoms or molecules. Within this range of "nanophase," many physical and chemical properties of the materials evolve as a function of cluster size, and materials may exhibit novel properties due to quantum confinement effects. Understanding these phenomena is in its own rights fundamental, but clusters have the additional advantage of being controllable model systems for unraveling the complexity of condensed-phase and biological structures, not to mention their vanguard role in defining nanoscience and nanotechnology. Over the last two decades, much progress has been made, and this short overview highlights our own involvement in developing cluster dynamics, from the first experiments on elementary systems to model systems in the condensed phase, and on to biological structures.

Resonance Raman Investigation of the Short-Time Photodissociation Dynamics of the Charge-Transfer Absorption of the I2−Benzene Complex in Benzene Solution

Resonance Raman spectra were obtained for the I2-benzene complex in benzene solvent with excitation wavelengths in resonance with the CT-band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal I-I stretch mode nu(18), the nominal symmetric benzene ring stretch mode nu5, and the nominal symmetric CCH bending nu7. There is also a small contribution from the nominal out-of-plane CH oop wag nu15. A preliminary resonance Raman intensity analysis was done, and the results for the I2-benzene complex were compared to results previously reported for the 1-hexene-I2 complex. We briefly discuss the differences and similarities in the CT-band absorption excitation of an I2-benzene complex relative to those of an I2-alkene complex.

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

The photodissociation dynamics of the acetone S2 (n, 3s) Rydberg state excited at 195 nm has been studied by using femtosecond pump-probe mass-selected multiphoton ionization spectroscopy. For the first time, the temporal evolutions of the initial state, intermediates, and methyl products were simultaneously measured and analyzed for this reaction to elucidate the complex dynamics. Two mechanisms were considered: (1) the commonly accepted mechanism in which the primary dissociation occurs on the first triplet-state surface, and (2) the recently proposed mechanism in which the primary dissociation takes place on the first singlet-excited-state surface. Our results and analyses supported the validity of the new mechanism. On the other hand, the conventional mechanism was found to be inadequate to describe the observed dynamics. The temporal evolution of methyl products arising from the secondary dissociation of hot acetyl intermediates exhibited a very complex behavior that can be ascribed to the combination of a nonuniform initial vibrational distribution and the competition between dissociation and slow intramolecular vibrational redistribution.

Effect of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of donor-acceptor complexes: Stochastic simulations and experiments

The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes has been explored both theoretically and experimentally. The theoretical description involves the explicit treatment of both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The wave packet motion and the electronic transition are described within the framework of the stochastic point-transition approach. It is shown that the variation of the pulse carrier frequency within the absorption band can significantly change the effective charge recombination dynamics. The mechanism of this phenomenon is analyzed and a semiquantitative interpretation is suggested. The role of the vibrational coherence in the recombination dynamics is discussed. An experimental investigation of the ultrafast charge recombination dynamics of two donor-acceptor complexes in valeronitrile also is presented. The decays of the excited state population were found to be highly nonexponential, the degree of non-exponentiality depending on the excitation frequency. For one complex, the charge recombination dynamics was found to slow down upon increasing the excitation frequency, while the opposite behavior was observed with the other complex. These experimental observations follow qualitatively the predictions of the simulations.