Photocatalysis has been widely applied in various areas, such as solar cells, water splitting, and pollutant degradation. Therefore, the photochemical mechanisms and basic principles of ...photocatalysis, especially TiO2 photocatalysis, have been extensively investigated by various surface science methods in the last decade, aiming to provide important information for TiO2 photocatalysis under real environmental conditions. Recent progress that provides fundamental insights into TiO2 photocatalysis at a molecular level is highlighted. Insights into the structures of TiO2 and the basic principles of TiO2 photocatalysis are discussed first, which provides the basic concepts of TiO2 photocatalysis. Following this, details of the photochemistry of three important molecules (oxygen, water, methanol) on the model TiO2 surfaces are presented, in an attempt to unravel the relationship between charge/energy transfer and bond breaking/forming in TiO2 photocatalysis. Lastly, challenges and opportunities of the mechanistic studies of TiO2 photocatalysis at the molecular level are discussed briefly, as well as possible photocatalysis models.
The basic principles and fundamental processes of TiO2 photocatalysis are highlighted. Recent progress made on the studies of the nature of TiO2 photocatalysis, in particular whether photocatalytic reactions are driven by separated charges or by energy produced via nonadiabatic exciton decay or nonadiabatic charge recombination, is summarized and discussed in detail.
Thermally stable Au single-atoms supported by monolayered CuO grown at Cu(110) have been successfully prepared. The charge transfer from the CuO support to single Au atoms is confirmed to play a key ...role in tuning the activity for CO oxidation. Initially, the negatively charged Au single-atom is active for CO oxidation with its adjacent lattice O atom depleted to generate an O vacancy in the CuO monolayer. Afterward, the Au single-atom is neutralized, preventing further CO reaction. The produced O vacancy can be healed by exposure to O2 at 400 K and accordingly the reaction activity is restored.
This note extends the topic of the performance of ashing soil samples and then using spectral subtraction of diffuse reflectance Fourier transform mid-IR spectroscopy (DRIFTS) of original and ashed ...samples in highlighting the significance of the organic fraction. It was found that accurately interpreting the ash subtracted spectra (mid-infrared range from 4000cm−1 to 400cm−1) is nearly impossible not only because soil minerals undergo extreme spectral changes from the ashing process but also because inorganic residues from burning soil organic matter (mainly humic substances) also confound the spectra of the mineral fraction. Removing soil organic matter using wet ashing methods with H2O2, NaOCl, or Na2S2O8 is associated with inaccuracies in spectra interpretation from organic remains (uncompleted organic matter removal) and spectral changes of minerals from wet ashing processes. Accordingly, with the current techniques of dry and wet ashing it is impossible to accurately interpret the ash subtracted spectra of soil samples.
•Dry and wet ashing effects on soil spectra interpretation were examined.•Soil minerals undergo extreme spectral changes from both dry and wet ashing processes.•Inorganic residues from burning organic matter confound the spectra of soil mineral.•It is impossible to accurately interpret the ash subtracted spectra of soil samples.
We have investigated the photocatalysis of partially deuterated methanol (CD3OH) and H2O on TiO2(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical ...calculations. Photocatalyzed products, CD2O on Ti5c sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD3OH have been clearly detected, while no evidence of H2O photocatalysis was found. The experimental results show that dissociation of CD3OH on TiO2(110) occurs in a stepwise manner in which the O–H dissociation proceeds first and is then followed by C–D dissociation. Theoretical calculations indicate that the high reverse barrier to C–D recombination and the facile desorption of CD2O make photocatalytic methanol dissociation on TiO2(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O–H recombination after H2O photocatalytic dissociation on TiO2(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.
Infrared spectroscopic study of neutral water clusters is crucial to understanding of the hydrogen-bonding networks in liquid water and ice. Here we report infrared spectra of size-selected neutral ...water clusters, (H₂O)n (n = 3–6), in the OH stretching vibration region, based on threshold photoionization using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals observed in the 3,500–3,600-cm−1 region of (H₂O)₅ provide unique spectral signatures for the formation of a noncyclic pentamer, which coexists with the global-minimum cyclic structure previously identified in the gas phase. The main features of infrared spectra of the pentamer and hexamer, (H₂O)n (n = 5 and 6), span the entire OH stretching band of liquid water, suggesting that they start to exhibit the richness and diversity of hydrogenbonding networks in bulk water.
This paper proposes a modified particle swarm optimization algorithm with dynamic adaptation. In this algorithm, a modified velocity updating formula of the particle is used, where the randomness in ...the course of updating particle velocity is relatively decreased and the inertia weight of each particle is different. Moreover, this algorithm introduces two parameter describing the evolving state of the algorithm, the evolution speed factor and aggregation degree factor. By analyzing the influence of two parameters on the PSO search ability, a new strategy is presented that the inertia weight dynamically changes based on the run and evolution state. In the strategy the inertia weight is given by a function of evolution speed factor and aggregation degree factor, and the value of inertia weight is dynamically adjusted according to the evolution speed and aggregation degree. The feature of the proposed algorithm is analyzed and several testing functions are performed in simulation study. Experimental results show that, the proposed algorithm remarkably improves the ability of PSO to jump out of the local optima and significantly enhance the convergence precision.
Despite significant progress made in the past decades, it remains extremely challenging to investigate the dissociative chemisorption dynamics of molecular species on surfaces at a full-dimensional ...quantum mechanical level, in particular for polyatomic-surface reactions. Here we report, to the best of our knowledge, the first full-dimensional quantum dynamics study for the dissociative chemisorption of H2O on rigid Cu(111) with all the nine molecular degrees of freedom fully coupled, based on an accurate full-dimensional potential energy surface. The full-dimensional quantum mechanical reactivity provides the dynamics features with the highest accuracy, revealing that the excitations in vibrational modes of H2O are more efficacious than increasing the translational energy in promoting the reaction. The enhancement of the excitation in asymmetric stretch is the largest, but that of symmetric stretch becomes comparable at very low energies. The full-dimensional characterization also allows the investigation of the validity of previous reduced-dimensional and approximate dynamical models.
Simultaneously enhancing the thermal conductivity, insulation, and mechanical properties of high-density polyethylene (HDPE) composites is highly desired for electronic and electrical applications. ...In this research, HDPE/boron nitride (BN)/coconut shell charcoal (CSC) composites were prepared. Benefit from the synergistic effect between the multi-dimensional hybrid fillers, the prepared HDPE/BN/CSC composites exhibited enhanced comprehensive properties compared to the HDPE/BN composites and pure HDPE. In particular, as for HDPE/25BN/3CSC (25 wt% BN, 3 wt% CSC) nanocomposites compared to the pure HDPE, enhancements in in-plane thermal conductivity of 980.89%, normal thermal conductivity of 138%, and tensile strength of 18.91% were obtained, while higher volume resistivity and decomposition temperature were achieved. This work provides a simple but effective way for improving the thermal conductivity and comprehensive physical properties of HDPE composites.
•HDPE/BN/CSC composites were prepared.•High thermal conductivity of the HDPE/BN/CSC composites were achieved.•Thermal stability, mechanical properties, and insulation properties were all enhanced at appropriate CSC contents.
Pinpointing the role of geometric phaseDuring chemical reactions, electrons usually rearrange more quickly than nuclei. Thus, theorists often adopt an adiabatic framework that considers vibrational ...and rotational dynamics within single electronic states. Near the regime where two electronic states intersect, the dynamics get more complicated, and a geometric phase factor is introduced to maintain the simplifying power of the adiabatic treatment. Yuan et al. conducted precise experimental measurements that validate this approach. They studied the elementary H + HD reaction at energies just above the intersection of electronic states and observed angular oscillations in the product-state cross sections that are well reproduced by simulations that include the geometric phase.Science, this issue p. 1289Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD → H2 + D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H2 products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.
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