Kohn-Sham Density Functional Theory: Predicting and Understanding Chemistry

Solar-powered water evaporation — the extraction of vapour from liquid water using solar energy — provides the basis for the development of eco-friendly and cost-effective freshwater production. Liquid water consumes and carries energy, and, thus, plays an essential role in this process. As such, extensive experimental and theoretical studies have been focused on water management to achieve efficient solar vapour generation. Many innovative materials have been proposed to enable highly controllable and efficient solar-to-thermal energy conversion to address the challenges in the energy–water nexus from the microscale to the molecular level. In this Review, we summarize the fundamental principles of materials design for efficient solar-to-thermal energy conversion and vapour generation. We discuss how to integrate photothermal materials, nanostructures/microstructures and water–material interactions to improve the performance of the evaporation system via in situ utilization of solar energy. Focusing on materials science and engineering, we overview the key challenges and opportunities for nanostructured and microstructured materials in both fundamental research and practical water-purification applications. Materials engineering enables the control of water–material interactions in solar vapour generators, which aim to efficiently utilize solar energy for the cost-effective production of clean water. This Review discusses material-design principles for solar evaporators, spanning from macrostructures to molecular configurations.

Materials for solar-powered water evaporation

Recent years have seen a large increase of the research effort focused on framework materials, including the nowadays-ubiquitous metal–organic frameworks but also dense coordination polymers, covalent organic frameworks, and molecular frameworks. With the quickly increasing number of structures synthesized and characterized, one pattern emerging is the common occurrence of flexibility. More specifically, an important number of framework materials are stimuli-responsive: their structure can undergo changes of large amplitude in response to physical or chemical stimulation. They can display transformations induced by temperature, mechanical pressure, guest adsorption or evacuation, light absorption, etc. and are sometimes referred to as smart materials, soft crystals, or dynamic materials. This Perspective highlights recent progress in this field, showcasing some of the most novel and unusual responses to stimuli, as well as advances in the fundamental understanding of flexible framework materials.

https://hal.archives-ouvertes.fr/hal-02269625/document

Responsive Metal–Organic Frameworks and Framework Materials: Under Pressure, Taking the Heat, in the Spotlight, with Friends

Strengthening behavior of few-layered graphene/aluminum composites

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics

Study of hydrogen bonding in ethanol-water binary solutions by Raman spectroscopy.

Raman spectra of ice VII and X were investigated using strong plasma shockwave generated by laser-induced breakdown (LIB) in liquid water. Simultaneously, the occurrence of the hydrogen emission lines of 656 nm (Hα), 486 nm (Hβ), 434 nm (Hγ) and 410 nm (Hδ) was observed. At 5 × 1012 W/cm2 optical power density, the O-H symmetric stretching, translational and librational modes of ice VII and a single peak at 785 cm−1 appeared in the spectra. The band was assigned to the Raman-active O-O mode of the monomolecular phase, which was the symmetric hydrogen bond of cuprite ice X. The spectra indicated that ice VII and X structure were formed, as the trajectory of the strong plasma shockwave passes through the stable Pressure-Temperature range of ice VII and X. The shockwave temperature and pressure were calculated by the Gruneisen model.

/pdf/raman-spectra-from-symmetric-hydrogen-bonds-in-water-by-high-2ghfjd0cia.pdf

Raman spectra from symmetric hydrogen bonds in water by high-intensity laser-induced breakdown.

B3LYP and CCSD(T) (single-point) calculations are performed on structures and interconversion transition states for five C2N2 isomers, i.e., the linear structures NCCN 1, CNCN 2, CNNC 3, and CCNN 4, and the NNC three-membered ring structure with exocyclic C–C bonding 5. A schematic potential-energy surface of the five C2N2 isomers is established. It is shown that the elusive and long searched for isomer 3 lies in a deep potential well against isomerization to the well-studied isomers 1 and 2, while the two transition states, which have been predicted to connect the isomers 1 and 3, are actually associated with the interexchange of the two cyano groups in isomer 2. It is also shown that the experimentally unknown but expectedly important isomer 4 may take an isomerization pathway to the isomer 1 via the intermediate 5, and the isomer 4 also lies in a deep potential well. Both the isomers 3 and 4 may be thermally as stable as the isomer 2. The results presented in this paper may provide useful information f...

Theoretical study on potential-energy surface of C2N2

Stimulated Raman scattering (SRS) from ice-VIII was investigated using shock-induced compression (SIC) generated by laser-induced breakdown in liquid water. Three backward SRS peaks of OH stretching vibrations and one backward SRS characteristic peak of lattice translation were observed. The SRS spectra indicated that the ice-VIII structure is formed by SIC, as the trajectory of the SIC passes through the stable pressure-temperature range of ice-VIII. The static electric field generated by electron jets protects proton-ordered structure. The laser-induced shock wave mechanism is also discussed.

Stimulated Raman scattering from ice-VIII by shock-induced compression in liquid water

Based on the 4,4′-bipyridine organic linker, metal–organic frameworks of Co2(4,4′-bpy)3(NO3)4·xH2O (CB-MOF) have been prepared. The pressure-dependent structure evolution of CB-MOF has been investigated up to 11 GPa. An isostructural phase transition was observed at about 6 GPa followed by negative compressibility along the b axis.

Chenglin Sun

Papers

Study of hydrogen bonding in ethanol-water binary solutions by Raman spectroscopy.

Raman spectra from symmetric hydrogen bonds in water by high-intensity laser-induced breakdown.

Theoretical study on potential-energy surface of C2N2

Stimulated Raman scattering from ice-VIII by shock-induced compression in liquid water

Pressure-induced isostructural phase transition of a metal–organic framework Co2(4,4′-bpy)3(NO3)4·xH2O