A Theoretical Study of the Interaction of Hydrogen and Oxygen with Palladium or Gold Adsorbed on Pyridine‐Like Nitrogen‐Doped Graphene

The interaction of H₂ and O₂ molecules in the presence of nitrogen‐doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley–Rideal mechanism and then through a Langmuir–Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.     

WO3 Quantum Dots Decorated GO/Mg‐doped ZnO Composites for Enhanced Photocatalytic Activity under Nature Sunlight

Graphene oxide/Mg‐doped ZnO/tungsten oxide quantum dots composites (WQGOMZ) were prepared through co‐precipitation method, and were studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Fluorescence spectra (FL), and UV–vis diffuse reflection spectra. Furthermore, the photocatalytic activity of resultant WQGOMZ was evaluated under nature sunlight. Experimental results showed that WO₃QDs can remarkably heighten the photocatalytic activity of GOMZ composite, in which is nearly 6.58 times higher than that of GOMZ composite. Simultaneously, WQGOMZ composites possess optical memory ability and maintain high photocatalytic stability for more than 40 days. The enhanced photocatalytic activity and optical memory ability are attributed to the effective synergistic effect between ZnO and WO₃QDs.     

Fe2O3–TiO2 Nanocomposites for Enhanced Charge Separation and Photocatalytic Activity

Photocatalysis provides a cost effective method for both renewable energy synthesis and environmental purification. Photocatalytic activity is dominated by the material design strategy and synthesis methods. Here, for the first time, we report very mild and effective photo‐deposition procedures for the synthesis of novel Fe₂O₃–TiO₂ nanocomposites. Their photocatalytic activities have been found to be dramatically enhanced for both contaminant decomposition and photoelectrochemical water splitting. When used to decompose a model contaminant herbicide, 2,4‐dichlorophenoxyacetic acid (2,4‐D), monitored by both UV/Vis and total organic carbon (TOC) analysis, 10 % Fe–TiO₂–H₂O displayed a remarkable enhancement of more than 200 % in the kinetics of complete mineralisation in comparison to the commercial material P25 TiO₂ photocatalyst. Furthermore, the photocurrent is nearly double that of P25. The mechanism for this improvement in activity was determined using density functional theory (DFT) and photoluminescence. These approaches ultimately reveal that the photoelectron transfer is from TiO₂ to Fe₂O₃. This favours O₂ reduction which is the rate‐determining step in photocatalytic environmental purification. This in situ charge separation also allows for facile migration of holes from the valence band of TiO₂ to the surface for the expected oxidation reactions, leading to higher photocurrent and better photocatalytic activity.     

Hierarchical Nitrogen‐Doped Flowerlike ZnO Nanostructure and Its Multifunctional Environmental Applications

Hierarchical nitrogen‐doped ZnO flowerlike nanostructures were synthesized on a large scale. These nanostructures were characterized by FESEM, HRTEM, XRD, FTIR, XPS, and TGA, and their suitability for multifunctional environmental applications was investigated. The experimental results demonstrated that the hierarchical N‐doped ZnO flowerlike nanostructure enhances the photodegradation of methyl blue (MB) and acid orange 7 (AO7) by presenting a large specific surface area and high light utilization rate, inhibits the growth of bacteria without light irradiation, and increases the permeate flux when used in a membrane filtration system. These advantages of the hierarchical N‐doped ZnO flowerlike nanostructure brings benefits to the environmental application fields.     

Reactivity of Graphene and Hexagonal Boron Nitride In‐Plane Heterostructures with Oxygen: A DFT Study

A density‐functional study has been undertaken to investigate the chemical properties of in‐plane heterostructures of graphene and hexagonal boron nitride. The interactions of armchair and zigzag linking edges with oxygen are looked at in detail. The results of the calculations indicate that the linking edges are highly reactive to oxygen atoms and predict that oxygen molecules can accordingly be adsorbed dissociatively. Furthermore, because oxygen atoms cooperatively interact with the heterostructures, the process can lead to opening of the linking edges, thus splitting the two materials.     

Growth Mechanism and Chemical Bonding in Scandium‐Doped Copper Clusters: Experimental and Theoretical Study in Concert

Size matters! The electronic structure and size‐dependent stability of neutral and cationic scandium‐doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank–Kasper‐shaped Cu₁₆Sc⁺ cluster (shown here), which could be the germ of a new crystallization process.

     

cis–trans Isomerisation of Substituted Aromatic Imines: A Comparative Experimental and Theoretical Study

The cis–trans isomerisation of N‐benzylideneaniline (NBA) and derivatives containing a central C?N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans${{\mathop \rightarrow \limits ^{h\nu }_{}}}$ cis isomerisation and the kinetics of the thermal backreaction cis${{\mathop \rightarrow \limits ^{\Delta }_{}}}$ trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition‐state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time‐dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify “optimal switches” with good photochromicity and reasonable thermal stability.     

Magnetically Recoverable Core–Shell Nanocomposites with Enhanced Photocatalytic Activity

Core–shell structured Fe₃O₄/SiO₂/TiO₂ nanocomposites with enhanced photocatalytic activity that are capable of fast magnetic separation have been successfully synthesized by combining two steps of a sol–gel process with calcination. The as‐obtained core–shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO₂, and an outer layer of TiO₂ nanocrystals with a tunable average size. The convenient control over the size and crystallinity of the TiO₂ nanocatalysts makes it possible to achieve higher photocatalytic efficiency than that of commercial photocatalyst Degussa P25. The photocatalytic activity increases as the thickness of the TiO₂ nanocrystal shell decreases. The presence of SiO₂ interlayer helps to enhance the photocatalytic efficiency of the TiO₂ nanocrystal shell as well as the chemical and thermal stability of Fe₃O₄ core. In addition, the TiO₂ nanocrystals strongly adhere to the magnetic supports through covalent bonds. We demonstrate that this photocatalyst can be easily recycled by applying an external magnetic field while maintaining their photocatalytic activity during at least eighteen cycles of use.     

On the Origin of the Visible‐Light Activity of Titanium Dioxide Doped with Carbonate Species

Plane‐wave‐based pseudopotential density functional theory (DFT) calculations are used to elucidate the origin of the high photocatalytic efficiency of carbonate‐doped TiO₂. Two geometrically possible doping positions are considered, including interstitial and substitutional carbon atoms on Ti sites. From the optical absorption properties calculations, we believe that the formation of carbonates after doping with interstitial carbon atoms is crucial, whereas the contribution from the cationic doping on Ti sites is negligible. The carbonate species doped TiO₂ exhibits excellent absorption in the visible‐light region of 400–800 nm, in good agreement with experimental observations. Electronic structure analysis shows that the carbonate species introduce an impurity state from Ti 3d below the conduction band. Excitations from the impurity state to the conduction band may be responsible for the high visible‐light activity of the carbon doped TiO₂ materials.     

PdO/TiO2 and Pd/TiO2 Heterostructured Nanobelts with Enhanced Photocatalytic Activity

Heterostructures play an important role not only in the manufacture of semiconductor devices, but also in the field of catalysis. Herein, we report the synthesis of PdO/TiO₂ and Pd/TiO₂ heterostructured nanobelts by means of a simple co‐precipitation method, followed by a reduction process using surface‐modified TiO₂ nanobelts as templates. The as‐obtained heterostructures were characterized by transmission electron microscopy, X‐ray photoelectron spectroscopy, and UV/Vis diffuse reflectance spectroscopy. PdO and Pd nanoparticles with a size of about 1.3 and 1.6 nm were assembled uniformly on the surface of TiO₂ nanobelts, respectively. Compared with TiO₂ nanobelts, PdO/TiO₂ and Pd/TiO₂ hybrid nanobelts exhibit enhanced photocatalytic activity upon UV and visible‐light irradiation. Photoelectrochemical technology was used to study the heterostructure effect on enhanced photocatalytic activity. Our mechanistic investigation revealed that energy‐band matching is the major factor in the observed enhancement of photocatalytic activity.     

Morphology‐Dependent Gas‐Sensing Properties of ZnO Nanostructures for Chlorophenol

The crystal‐plane effect of ZnO nanostructures on the toxic 2‐chlorophenol gas‐sensing properties was examined. Three kinds of single‐crystalline ZnO nanostructures including nanoawls, nanorods, and nanodisks were synthesized by using different capping agents via simple hydrothermal routes. Different crystal surfaces were expected for these ZnO nanostructures. The sensing tests results showed that ZnO nanodisks exhibited the greatest sensitivity for the detection of toxic 2‐chlorophenol. The results revealed that the sensitivity of these ZnO samples was heavily dependent on their exposed surfaces. The polar (0001) planes were most reactive and could be considered as the critical factor for the gas‐sensing performance. In addition, calculations using density functional theory were employed to simulate the gas‐sensing reaction involving surface reconstruction and charge transfer both of which result in the change of electronic conductance of ZnO.     

Small‐Sized and Contacting Pt–WC Nanostructures on Graphene as Highly Efficient Anode Catalysts for Direct Methanol Fuel Cells

The synergistic effect between Pt and WC is beneficial for methanol electro‐oxidation, and makes Pt–WC catalyst a promising anode candidate for the direct methanol fuel cell. This paper reports on the design and synthesis of small‐sized and contacting Pt–WC nanostructures on graphene that bring the synergistic effect into full play. Firstly, DFT calculations show the existence of a strong covalent interaction between WC and graphene, which suggests great potential for anchoring WC on graphene with formation of small‐sized, well‐dispersed WC particles. The calculations also reveal that, when Pt attaches to the pre‐existing WC/graphene hybrid, Pt particles preferentially grow on WC rather than graphene. Our experiments confirmed that highly disperse WC nanoparticles (ca. 5 nm) can indeed be anchored on graphene. Also, Pt particles 2–3 nm in size are well dispersed on WC/graphene hybrid and preferentially grow on WC grains, forming contacting Pt–WC nanostructures. These results are consistent with the theoretical findings. X‐ray absorption fine structure spectroscopy further confirms the intimate contact between Pt and WC, and demonstrates that the presence of WC can facilitate the crystallinity of Pt particles. This new Pt–WC/graphene catalyst exhibits a high catalytic efficiency toward methanol oxidation, with a mass activity 1.98 and 4.52 times those of commercial PtRu/C and Pt/C catalysts, respectively.     

Neutral and Oxidized Triisopropylsilyl End‐Capped Oligothienoacenes: A Combined Electrochemical,Spectroscopic, and Theoretical Study

This work presents an analysis of the structural, electrochemical, and optical properties of a family of triisopropylsilyl end‐capped oligothienoacenes (TIPS‐ Tn ‐TIPS, n=4–8) by combining cyclic voltammetry, spectroscopic techniques, and quantum‐chemical calculations. TIPS‐ Tn ‐TIPS compounds form stable radical cations, and dications are only obtained for the longest oligomers (n=7 and 8). Oxidation leads to the quinoidization of the conjugated backbone, from which electrons are mainly extracted. The absorption and fluorescence spectra show partially resolved vibronic structures even at room temperature, due to the rigid molecular geometry. Two well‐resolved vibronic progressions are observed at low temperatures due to the vibronic coupling, with normal modes showing wavenumbers of ≈1525 and ≈480 cm^?1. Optical absorption bands display remarkable bathochromic dispersion with the oligomer length, indicative of the extent of π conjugation. The optical properties of the oxidized compounds are characterized by in situ UV/Vis/NIR spectroelectrochemistry. The radical cation species show two intense absorption bands emerging at energies lower than in the neutral compounds. The formation of the dication is only detected for the heptamer and the octamer, and shows a new band at intermediate energies. Optical data are interpreted with the help of density functional theory calculations performed at the B3LYP/6‐31G** level, both for the neutral and the oxidized compounds.     

A Theoretical and Experimental Investigation of the Spectroscopic Properties of a DNA‐Intercalator Salphen‐Type ZnII Complex

The photophysical and DNA‐binding properties of the cationic zinc(II) complex of 5‐triethylammonium methyl salicylidene ortho‐phenylenediiminato (ZnL²⁺) were investigated by a combination of experimental and theoretical methods. DFT calculations were performed on both the ground and the first excited states of ZnL²⁺ and on its possible mono‐ and dioxidation products, both in vacuo and in selected solvents mimicked by the polarizable continuum model. Comparison of the calculated absorption and fluorescence transitions with the corresponding experimental data led to the conclusion that visible light induces a two‐electron photooxidation process located on the phenylenediiminato ligand. Kinetic measurements, performed by monitoring absorbance changes over time in several solvents, are in agreement with a slow unimolecular photooxidation process, which is faster in water and slower in less polar solvents. Moreover, structural details of ZnL–DNA binding were obtained by DFT calculations on the intercalation complexes between ZnL and the d(ApT)₂ and d(GpC)₂ dinucleoside monophosphate duplexes. Two main complementary binding interactions are proposed: 1) intercalation of the central phenyl ring of the ligand between the stacked DNA base pairs; 2) external electrostatic attraction between the negatively charged phosphate groups and the two cationic triethylammonium groups of the Schiff‐base ligand. Such suggestions are supported by fluorescence titrations performed on the ZnL/DNA system at different ionic strengths and temperatures. In particular, the values of the DNA‐binding constants obtained at different temperatures provided the enthalpic and entropic contributions to the binding and confirmed that two competitive mechanisms, namely, intercalation and external interaction, are involved. The two mechanisms are coexistent at room temperature under physiological conditions.     

Oxadiazole‐2‐thiol Adsorption on Gold Nanorods: A Joint Theoretical and Experimental Study by Using SERS,XPS, and DFT

The chemisorption of 1,3,4‐oxadiazole‐2‐thiol (ODT) on gold nanorods has been investigated by using surface‐enhanced Raman spectroscopy (SERS) and density functional theory (DFT). Although most of the SERS spectra have remarkable similarity to the normal Raman spectra of the pure analyte, the adsorption of ODT on a gold surface leads to a drastic change in its Raman spectrum and distinct vibrational features are obtained with gold nanorods and spherical nanoparticles. Simulated Raman spectra for hybrid systems that consist of an oxadiazole moiety coordinated to a Au₂₀ gold cluster provided valuable information about the coordination mode and enabled us to assign vibration modes.     

A Theoretical DFT‐Based and Experimental Study of the Transmetalation Step in Au/Pd‐Mediated Cross‐Coupling Reactions

In this work a combined theoretical and experimental investigation of the cross‐coupling reaction involving two metallic reaction centers, namely gold and palladium, is described. One metal center (Au) hereby is rather inert towards change in its oxidation state, whereas Pd undergoes oxidative insertion and reductive elimination steps. Detailed mechanistic and energetic studies of each individual step, with the focus on the key transmetalation step are presented and compared for different substrates and ligands on the catalytic Pd center. Different aryl halides (Cl, Br, I) and aryl triflates were investigated. Hereby the nature of the counteranion X turned out to be crucial. In the case of X=Cl and L=PMe₃ the oxidative addition is rate‐determining, whereas in the case of X=I the transmetalation step becomes rate‐determining in the Au/Pd‐cross‐coupling mechanism. A variety of Au–Pd transmetalation reaction scenarios are discussed in detail, favoring a transition state with short intermetallic Au–Pd contacts. Furthermore, without a halide counteranion the transmetalation from gold(I) to palladium(II) is highly endothermic, which confirms our experimental findings that the coupling does not occur with aryl triflates and similar weakly coordinating counteranions—a conclusion that is essential in designing new Au–Pd catalytic cycles. In combination with experimental work, this corrects a previous report in the literature claiming a successful coupling potentially catalytic in both metals with weakly coordinating counteranions.     

Cycloaddition of Nitrile Oxides to Graphene: a Theoretical and Experimental Approach

Density functional theory (DFT) studies of the interaction between graphene sheets and nitrile oxides have proved the feasibility of the reaction through 1,3-dipolar cycloaddition. The viability of the approach has been also confirmed experimentally through the cycloaddition of few-layer exfoliated graphene and nitrile oxides containing functional organic groups with different electronic nature. The cycloaddition reaction has been successfully achieved in one-pot from the corresponding oximes under microwave (MW) irradiation. The successful formation of the isoxazoline ring has been confirmed by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS).