Computational insight in the impact of cooperative phenomena and correlated spatial disorder on the macroscopic behaviour of metal-organic frameworks (MOFs) is essential to consciously engineer these phenomena for targeted applications. However, the spatial extent of these effects, ranging over hundreds of nanometres, limits the applicability of current state-of-the-art computational tools in this field. To obtain a fundamental understanding on these long-range effects, the micromechanical model is introduced here. This model overcomes the challenges associated with conventional coarse-graining techniques by exploiting the natural partitioning of a MOF material into unit cells. By adopting the elastic deformation energy as the central quantity, the micromechanical model hierarchically builds on experimentally accessible input parameters that are obtained from atomistic quantum mechanical or force field simulations. As a result, the here derived micromechanical equations of motion can be adopted to shed light on the effect of long-range cooperative phenomena and correlated spatial disorder on the performance of mesoscale MOF materials.

The functionalisation of silicon nanoparticles with a terminal thiocyanate group, producing isothiocyanate-capped silicon nanoparticles (ITC-capped SiNPs) has been successfully attained. The procedure for synthesis is a two-step process that occurs via thermally induced hydrosilylation of hydrogen terminated silicon nanoparticle (H-SiNPs) and further reaction with potassium thiocyanate (KSCN). The synthesis was confirmed by Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Photoelectron Spectroscopy (XPS). At the same time, the internalisation and the cytotoxicity of ITC-capped SiNPs in vitro was assessed in two cell lines: Caco-2, human colorectal cancer cells and CCD-841, human colon “normal” cells. The results showed that above concentrations of 15 μg/ml, the cell viability of both cell lines depleted significantly when treated with ITC SiNPs, particularly over a 48 hour period, to approximately 20% cell viability at the highest treatment concentration (70 μg/ml). Flow cytometry was employed to determine cellular uptake, in Caco-2 cells treated with ITC SiNPs and it was observed that at lower SiNP concentration, uptake efficiency was significantly improved at a time period under 12 hours; overall it was noted that cellular uptake was positively dependent on the period of incubation and the temperature of incubation. As such, it was concluded that the mechanism of uptake of ITC SiNP was through endocytosis. Synchrotron FTIR spectroscopy, by means of line spectral analysis and IR imaging, provided further evidence to suggest the internalisation of ITC SiNPs displays a strong localisation, with an affinity for the nucleus of treated Caco-2 cells.

The relationship between crystallization process and opto-electronic properties of silicon quantum dots (Si QDs) synthesized by atmospheric pressure plasmas (APPs) is studied in this work. The synthesis of Si QDs is carried out flowing silane as gas precursor in a plasma confined to a submillimeter space. Experimental conditions are adjusted to propitiate the crystallization of the Si QDs and produce QDs with both an amorphous and a crystalline character. In all the cases, Si QDs present a well-defined particle mean size in the range of 1.5-5.5 nm. Si QDs present optical bandgaps between 2.3 eV and 2.5 eV, which are affected by quantum confinement. Plasma parameters evaluated using optical emission spectroscopy are then used as inputs for a collisional plasma model, whose calculations yield the surface temperature of the Si QDs within the plasma, justifying the crystallization behavior for certain experimental conditions. We measure the ultraviolet-visible optical properties and electronic properties through various techniques, build an energy level diagram for the valence electrons region as a function of the crystallinity of the QDs and finally discuss the integration of these as active layers of all-inorganic solar cells.

The effect of both the Fe:Ni ratio (5 to 1:1) and the relative Lewis acidity of a metal oxide support on catalytic activity, selectivity and stability was investigated in the CO2 mediated oxidative dehydrogenation of ethane (CO2-ODH). To avoid effects of varying pore sizes, shapes and volumes of the supports, chromia and zirconia overlayers were coated onto a common γ-Al2O3 carrier (CrOx@Al2O3 and ZrOx@Al2O3). Separately, oxidic FexNiy alloy precursor nanoparticles were prepared using a nonaqueous surfactant-free method and deposited by sonication onto the carrier. In comparison to previous studies in the field, this synthesis technique yields closely associated iron and nickel increasing the chances for alloy formation. During reduction, a mixture of a bcc and a fcc alloy phase was formed, with the content of bcc increasing with increasing iron content as predicted by the bulk phase diagram. Upon exposure to carbon dioxide at elevated temperatures, the bcc metallic phase is selectively oxidised to an inverse spinel structure via the dissociation of CO2. When exposed to CO2-ODH conditions, the bare ZrOx@Al2O3 support shows no activity. The presence of FeNi phases increases the conversion of ethane and CO2 marginally (< 2 %) but forms ethylene at high selectivity (SC2H4 > 80 %). The CrOx@Al2O3 support shows some initial activity (XC2H6 < 5 %) at very high ethylene selectivity (SC2H4 > 90 %) but deactivates with time on stream. Comparison of the ethane and carbon dioxide conversions suggest that direct dehydrogenation rather than the oxidative pathway is taking place. When FeNi particles with the highest Fe content are added, the ethane conversion behavior hardly changes, but the CO2 conversion is increased now supporting the stochiometric CO2-ODH reaction (SC2H4 > 95%). It is therefore evident that a tandem catalyst system between a reducible oxide carrier and the FeNi species is required. Increasing the Ni content results in an increase in activity and stability while changing the dominant reaction pathway to a combination of dry reforming, CO2-ODH and possibly the reverse Boudouard reactions, with the latter countering catalyst deactivation through carbon deposition.

The synthesis in water of silicon nanoparticles has recently attracted a lot of attention. However many scientists have expressed concerns on the nanomaterials obtained. We decided to explore two different routes to obtain silicon nanoparticles starting from a silane precursor. We report our findings regarding the preparation of nanomaterials under microwave irradiation and hydrothermal conditions starting from aqueous mixtures of (3-aminopropyl) triethoxysilane and sodium citrate. The microwave process, in particular, has been reported to yield silicon quantum dots bearing a surface layer of 3-aminopropyl moieties, allowing for the preparation of luminescent substrates amenable to biological-friendly amide chemistry. However, rigorous experimental design and thorough characterization of the products definetely rule out the formation of silicon nanoparticles. By highlighting the main issues linked to the proper characterization of these materials, we prove that the nanoparticles produced under both microwave and hydrothermal conditions, are a mixture of silica and carbon quantum dots.

In this work, we explore the effect of ligand binding groups on the visible and NIR photoluminescent properties within phophorus-boron co-doped silicon nanocrystals (PB:Si NCs) by exploiting both the X-type (covalent) and L-type (Lewis donor molecule) bonding interactions. We find that the cooperative nature of both X- and L-type bonding from alkoxide/alcohol, alkylamide/alkylamine, and alkylthiolate/alkylthiol on PB:Si NCs results in photoluminescence (PL) energy blue shifts from the as-synthesized, hydride-terminated NCs (PB:Si–H) in excess of 0.4 eV, depending on the surface termination. These PL blue shifts appear greatest in the most strongly confined samples with diameters <4 nm where the surface-to-volume ratio is high and, therefore, the ligand effects are most pronounced. A correlation between the donor group strength (either X-type or L-type) and the degree of D–A state modulation is found, and the proportion of the PL blue shift from the X- and L-type interactions is quantified. Raman spectroscopy is used to provide additional evidence of the strength of the L-type donor groups. Additionally, we probe how the nature of the ligand chemistry affects the radiative lifetime and PL efficiency and find that the ligands do not significantly change the D–A emission dynamics, and all samples retain the long 50–130 μs lifetimes characteristic of these transitions. Finally, we describe three mechanisms that operate to effect the D–A recombination energies: (1) X-type ligands that modulate the PB:Si–X NC wavefunction; (2) L-type ligands that perturb the donor and acceptor states via a molecular orbital theory picture; and (3) X- and L-type ligands that cause a dielectric increase around the PB:Si NC core, which provides Coulomb screening and modulates the donor and acceptor states even further

The electrochemical exfoliation of graphite is one of the cheapest and most tunable industrial techniques to produce graphene nanosheets with tunable degree of oxidation and solubility. Anodic oxidation allows high-yield production of electrochemically exfoliated graphene oxide (EGO) in either acids or salt solutions, with the key role played by ions electrochemically driven in between the graphene sheets. This chemical intercalation is followed by a mesoscale mechanical exfoliation process, which is key for the high yield of the process, but which is still poorly understood. In this work, we use Raman spectroscopy to simultaneously monitor the intercalation and oxidation processes taking place on the surface of highly ordered pyrolytic graphite (HOPG) during electrochemical exfoliation. The mechanism of EGO formation in either acidic (0.5 M H2SO4) or neutral (0.5 M Li2SO4) electrolytes through blistering and cracking steps is discussed and described. This process is compared also to non-destructive intercalation of graphite in an organic electrolyte (1 M NaClO4 in acetonitrile). The results obtained show how high exfoliation yield and low defectivity shall be achieved by the combination of efficient, non-destructive intercalation followed by chemical decomposition of the intercalants and gas production.

2-dimensional metal oxides have many potential industrial applications including heterogeneous catalysis, water splitting, renewable energy conversion, supercapacitor applications, biomaterials, gas separation and gas storage. Herein we report a simple and scalable method for preparation of 2-dimensional TiO2 nanostructures by reaction of titanium isopropoxide with acetic acid at 333 K in isopropanol, followed by calcination at 673 K to remove the organic ligands. Both the products and reaction intermediates have been studied using electron microscopy, X-ray diffraction, N2 physisorption, NMR, thermogravimetric analysis, X-ray photoelectron, Raman, and infrared spectroscopies. The anisotropic condensation of the planar Ti6O4(OiPr)8(OAc)8 complex is believed to be responsible for the formation of the 2D structure. This research demonstrates that the metal complexes are promising building blocks for desired architectures, and the self-assembly of an acetate bidentate ligand is a versatile tool for manipulating the shape of final products.

In the realm of two-dimensional materials framework, single-element graphene-like lattices, known as Xenes, pose several issues concerning their environmental stability with implication in their use for technology transfer to a device layout. In this Discussion, we scrutinize the chemical reactivity of epitaxial silicene, taken as a case in point, in oxygen-rich environments. Oxidation of silicene is detailed by means of a photoemission spectroscopy study upon carefully dosing molecular oxygen in vacuum and subsequent exposure to ambient conditions, showing different chemical reactivity. We therefore propose a sequential Al2O3 encapsulation of silicene as a solution to face degradation proving effectiveness by virtue of the interaction between silicene and silver substrate. Based on this direction, we generalize our encapsulation scheme to a large number of metal-suported Xenes by taking the case of epitaxial phosphorene-on-gold into account.

Photoelectrochemical (PEC) splitting of water to make hydrogen is a promising clean-energy technology. Oxygen evolution reaction (OER) largely determines the energy efficiency in PEC water-splitting. Hematite, which is a cheap and sustainable semiconductor material with excellent chemical properties, a favourable band gap (2.1 eV) and composed of earth abundant elements is a suitable model photoanode material for studying OER. To understand the design of energy efficient anodes, it is highly desirable to have mechanistic insight in OER at an atomistic level which can be directly connected to experimentally measured quantities. We present a multiscale computational model of OER which connects the thermodynamics and kinetics of elementary charge transfer reactions in OER to kinetics of OER at laboratory length and time scales. We couple density functional theory (DFT) and DFT based molecular dynamics (DFT-MD) simulations with solvent effects at an atomistic level with kinetic Monte Carlo (kMC) simulations at a coarse-grained level in our multiscale model. The time and applied bias potential dependent surface coverage, which are experimentally not known, and the O2 evolution rate during OER at the hematite-water interface are calculated by the multiscale model. Furthermore, the multiscale model demonstrates the effect of explicitly modelling the interaction of water with the electrode surface via direct adsorption.

Herein we demonstrate that adding single-atoms of selected transition metals to graphitic carbon nitrides allow the tailoring of their electronic and chemical properties of these 2D nanomaterials, directly impacting their usage in photocatalysis. These single-atoms photocatalysts were successfully prepared with Ni2+, Pt2+ or Ru3+ by cation exchange, using poly(heptazine imides) (PHI) as the 2D layered platform. Differences in photocatalytic performance for these metals were assessed using rhodamine-B (RhB) and methyl orange (MO) as model compounds for degradation. We have demonstrated that single-atoms may either improve or impair the degradation of RhB and MO depending on the proper matching of the net charge of these molecules and the surface potential of the catalyst, which in turn is responsive to the metal incorporated into the PHI nanostructures. Computer simulations demonstrated that even one transition metal cation causes dramatic changes in the electronic structure of PHI, especially regarding light absorption, which was extended all along the visible up to the near IR region. Besides introducing new quantum states, the metal atoms strongly polarized the molecular orbitals across the PHI and electrostatic fields arising from the electronic transitions have become at least tenfold stronger. This simple proof of concept demonstrates that these new materials hold promise as tools for many important photocatalytic reactions, which are strongly dependent on our ability to control surface charge and it polarization under illumination, such as H2 evolution, CO2 reduction and photooxidations in general.

The involvement of water in the selective oxidation of MAL to MAA over a pure Keggin-type H3PMoO12O40 catalyst was investigated using an in-situ DRIFTS reactor coupled with a mass spectrometer for the first time to elucidate the reaction pathway associated with water. By comparing the spectra and activity data using D2O instead of H2O during transient switching experiments has allowed us to evaluate the possible active sites where D2O is activated. It has been found that, during the cycling switches of D2O in and out of MAL+O2 gas feed at 320 C, the formation of MAA-OD product is increased and decreased when D2O is added and removed, respectively. This suggests that the deuterium from D2O is involved in the production of gas phase MAA-OD. In addition, the in-situ DRIFTS-MS results obtained from the isotopic switches between D2O and H2O reveal changes in the characteristic infrared bands of Keggin unit between 1200 and 600 cm-1. It is found that the isotopic exchange possibly occurs on the bridging oxygen of MoOMo unit, where water is activated for the formation of MAA. Based on the in-situ DRIFTS-MS analysis from the transient switching experiments, the reaction mechanism associated with the effect of water on the selective oxidation of MAL to MAA over Keggin-type H3PMoO12O40 catalyst is proposed.

Aromatic self-assembled monolayers (SAMs) can be cross-linked into molecular nanosheets  carbon nanomembranes (CNMs)  via low-energy electron irradiation. Due to their favorable mechanical stability and tunable functional properties, they possess a high potential for various applications including nanosensors, separation membrane for osmosis or energy conversion devices. Despite this potential, the mechanistic details of the electron irradiation induced cross-linking process still need to be understood in more detail. Here we studied the cross-linking of 4'-nitro-1,1´-biphenyl-4-thiol SAM on gold. The SAM samples were irradiated with different electron energies ranging from 2.5 to 100 eV in ultra-high vacuum and subsequently analysed by complementary techniques. We present results obtained via spectroscopy and microscopy characterization by high-resolution X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction with micrometre sized electron beams (LEED) and low-energy electron microscopy (LEEM). To demostrate the formation of CNMs, the formed two-dimensional molecular materials were transferred onto grids and oxidized wafer and analyzed by optical, scanning electron (SEM) and atomic force microscopy (AFM). We found a strong energy dependence for the cross section for the cross-linking process, which rates decrease exponentially towards lower electron energies by about four orders of magnitude. We conduct a comparative analysis of the cross sections for the C-H bond scission via electron impact ionization and dissociative electron attachment and find out that these different ionization mechnisms are responsible for the variation of the cross-linking cross section with electron energy.

Developing therapeutic nanoparticles that actively target disease cells or tissues by exploiting the binding specificity of receptors presented on the cell surface have extensively opened up biomedical applications for drug delivery and imaging. An ideal nanoparticle for biomedical applications is required to report confirmation of relevant targeting and the ultimate fate in physiological environment for further verification, e.g. to adapt dosing or predict response. Herein, we demonstrate tracking of silicon nanoparticles through intrinsic photoluminescence (PL) during the course of cellular targeting and uptake. Time-resolved analysis of PL characteristics under cellular microenvironment provides dynamic information of physiological condition where the silicon nanoparticles exposed. In particular, the PL lifetime of the silicon nanoparticles is on the order of microseconds, significantly longer than the nanosecond lifetimes exhibited by fluorescent molecules naturally presented in cells, thus allows discrimination of the nanoparticles from the cellular background autofluorescence in time-gated imaging. The PL lifetime is a physically intensive property that reports the inherent characteristics of the nanoparticles regardless of surrounding noise. Furthermore, we investigate a unique means to inform the lifespan of the biodegradable silicon nanoparticles responsive to local microenvironment in the course of endocytosis. Multivalent strategy of nanoparticles for enhanced cell targeting is also demonstrated with complementary analysis of time-resolved PL emission imaging and fluorescence correlation spectroscopy. The result presents a promising potential of the photoluminescent silicon nanoparticles toward advanced cell targeting systems that simultaneously enable tracking the cellular trafficking and the tissue microenvironment monitoring.

he mechanism of nitrobenzene hydrogenation on non-noble metals such as Ni is different from that previously reported on noble metals like Pt. The newly proposed pathway involves the initial dissociation of the two N-O bonds of nitrobenzene (Ph-NO2 → Ph-NO → Ph-N), leading to a partial oxidation of the catalyst surface, followed by two successive hydrogenation steps (Ph-N → Ph-NH → Ph-NH2) that finally produce the functionalized aniline. Due to the oxophylic nature of non-noble metals like Ni, Co or Cu, the hydrogenation of the Ph-N intermediate and the removal of O in the form of water become the most energy demanding steps of the process. The strength of the interaction of O, H and N with different metals, and the preferential mode of adsorption of nitroarenes on clean and partially oxidized systems obtained from DFT calculations, is used now to propose an efficient non-noble metal catalyst that optimizes activity and selectivity.

Flexible electrodes with robust mechanical properties and high electrochemical performance are of significance for practical implementation of flexible batteries. Here we demonstrate a general and straightforward co-assembly approach to prepare flexible electrodes, where electrochemically exfoliated graphene (EG) is exploited as the film former/conducting matrix and different binary metal oxides (Li4Ti5O12, LiCoO2, Li2MnO4, LiFePO4) are incorporated. The resultant EG-metal oxide hybrids exhibit a unique layer-interlocked structure, where metal oxide is conformably wrapped by the highly flexible graphene. Due to numerous contact interphases generated between EG and intercalated material, the hybrid films show high flexibility, which can endure rolling, bending, folding and even twisting. When serving as the anode for Li-ion batteries, the freestanding EG-Li4Ti5O12 hybrid presents a characteristic flat discharge plateau at 1.55 V (vs Li/Li+), indicating transformation of Li4Ti5O12 to Li7Ti5O12. Small polarization, high rate capability and excellent cycling stability against mechanical bending are also demonstrated for the prepared EG-Li4Ti5O12 hybrid. Finally, full cells composing of EG-Li4Ti5O12 and EG-LiFePO4 hybrids show impressive cycling (98% capacity retention after 100 cycles at 1C) and rate performance (84% capacity retained at 2.5C). The straightforward co-assembly approach based on EG can be extended to other two-dimensional layered materials for constructing high-efficient flexible energy storage devices.