Isotope fractionation between different phases is a subtle but very important phenomenon that is related to the quantum nature of light nuclei, and that has important consequences for geochemistry, hydrology, and biology. Here we present a joint experimental/theoretical investigation of the differential segregation of hydrogen and deuterium at the liquid/vapor interface of mixtures of light and heavy water. We use both vibrational sum-frequency spectroscopy and path integral molecular dynamics simulations to quantitatively assess this phenomenon. The experimental and theoretical results indicate that the last layer of water molecules at the liquid/vapor interface is enriched in hydrogen. We discuss in detail the extent, the physical origin, and the implications of this surface-specific isotope effect.

This paper reports the effects of substrate roughness on the odd-even effect in n-alkanethiolate self-assembled monolayers (SAMs) probed by vibrational sum frequency generation (SFG) spectroscopy. By fabricating SAMs on surfaces across the so-called odd-even limit, we demonstrate that differentiation of the vibrational frequencies of CH from SAMs derived from alkyl thiols with either odd (SAM) or even (SAM) numbers of carbons depends on the roughness of the substrate on which they are formed. Odd-even oscillation in SFG susceptibility amplitudes was observed for spectra derived from SAM and SAM fabricated on flat surfaces (RMS roughness = 0.4 nm) but not on rougher surfaces (RMS roughness = 2.38 nm). In addition, we discovered that local chemical environments for the terminal CH group have a chain-length dependence. There seems to be a transition at around C, beyond which SAMs become "solid-like".

Objectives This review considers the state of occupational injury surveillance and prevention among migrant workers in China and suggests areas of focus for future research on the topic. Methods Bibliographic databases were searched for qualitative and quantitative studies on surveillance of and interventions to prevent occupational injury among migrant workers in mainland China. Additional abstracts were identified from the citations of relevant articles from the database search. Studies fitting the inclusion criteria were evaluated, and findings were extracted and summarised. Results The search uncovered 726 studies in the English-language databases searched, and 3109 in the Chinese database. This article analyses a total of 19 research articles that fit the inclusion criteria with qualitative or quantitative data on occupational injury surveillance and prevention of migrant workers in China. Despite evidence of the vulnerability of migrant workers in the workplace, there is little systematic surveillance of occupational injury and few evaluated interventions. Conclusions Migrant workers account for a disproportionate burden of occupational injury morbidity and mortality in China. However, data are inconsistent and inadequate to detail injury incidence or to evaluate interventions. The following are suggestions to decrease injury incidence among migrants: strengthen the national system of occupational injury surveillance; focus surveillance and interventions on high-risk occupations employing migrants such as construction, manufacturing and small mining operations; improve occupational safety training and access to appropriate safety equipment; evaluate recent changes in occupational health and safety and evaluate outcome of multi-party interventions to reduce occupational injury among migrant workers.

In an effort to enhance the thermoelectric performance in Si nanowires, we have explored the thermoelectric figure of merit (ZT) of the Ge/Si core−shell structured nanowires by using ab initio electronic structure calculations in the framework of Boltzmann transport theory. Our results show that the ZT value of the Ge/Si core−shell nanowire with p-type doping can reach 0.85 at 300 K, significantly larger than the observed ZT value of 0.36 in pure Si nanowires. The underlying mechanism for this enhanced ZT is mainly attributed to the reduced lattice thermal conductivity in the Ge/Si core−shell structure. Moreover, we suggest that appropriate Ge content in the Ge/Si core−shell nanowire may further optimize its ZT value. The current research proposed a way to design high-performance thermoelectric materials through a proper construct of heterostructured materials.

Over the past two decades, the vibrational Stark effect has become an important tool to measure and analyze the in situ electric field strength in various chemical environments with infrared spectroscopy. The underlying assumption of this effect is that the normal stretching mode of a target bond such as CO or CN of a reporter molecule (termed vibrational Stark effect probe) is localized and free from mass-coupling from other internal coordinates, so that its frequency shift directly reflects the influence of the vicinal electric field. However, the validity of this essential assumption has never been assessed. Given the fact that normal modes are generally delocalized because of mass-coupling, this analysis was overdue. Therefore, we carried out a comprehensive evaluation of 68 vibrational Stark effect probes and candidates to quantify the degree to which their target normal vibration of probe bond stretching is decoupled from local vibrations driven by other internal coordinates. The unique tool we used is the local mode analysis originally introduced by Konkoli and Cremer, in particular the decomposition of normal modes into local mode contributions. Based on our results, we recommend 31 polyatomic molecules with localized target bonds as ideal vibrational Stark effect probe candidates.

such as global warming and climate changes. [1][2][3][4] Solar energy is clean and abundant, for example, nearly four million exajoules (4 × 10 18 J) of solar energy reaches the earth annually. [1,5] Conversion of solar energy into chemical energy through photocatalytic decomposition of water to produce hydrogen is one of the suitable approaches to utilize solar energy. [6][7][8][9][10] The different types of fundamental photocatalytic reactions include i) semiconductor-based photocatalysis, ii) dye-sensitized semiconductor-based photo catalysis, iii) quantum dot-based photocatalysis, iv) 2D layered materials-based photocatalysts, and v) plasmonic photocatalysts. [11] Photocatalytic hydrogen evolution reaction (HER) are mainly based on inorganic semiconductor and poly merbased organic semiconductors, for exampl, in a conventional dye-sensitized semiconductor photocatalytic hydrogen production system, the dye molecules are excited to inject electrons into the conduction band of a semiconductor or polymer (inorganic semiconductor TiO 2 or g-C 3 N 4 is usually chosen), then the electrons are quickly captured by the co-catalyst (such as precious metals Efficient photocatalytic hydrogen evolution reaction (HER) in the visibleto-near infrared region at a low cost remains a challenging issue. This work demonstrates the fabrication of organic-inorganic composites by deposition of supramolecular aggregates of a chlorophyll derivative, namely, zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide a (Chl) on the surface of Ti 3 C 2 T x MXene with 2D accordion-like morphology. This composite material isemployed as noble metal-free catalyst in photocatalytic HER under the white light illumination, where Chl serves as a small molecule organic semiconductor component instead of ordinary inorganic and polymer organic semiconductors such as TiO 2 and g-C 3 N 4 , and Ti 3 C 2 T x serves as a co-catalyst. Different composition ratios of Chl/Ti 3 C 2 T x are compared for their light-harvesting ability, morphology, charge transfer efficiency, and photocatalytic performance. The best HER performance is found to be as high as 52 ± 5 µmol h −1 g cat −1 after optimization. Such a large HER activity is attributed to the efficient light harvesting followed by exciton transfer in Chl aggregates and the resultant charge separation at the interface of Chl/Ti 3 C 2 T x .

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Vibrational sum-frequency generation (SFG) spectroscopy is used to determine the surface pK a of p-methyl benzoic acid (pMBA) at the air–water interface by monitoring the carbonyl and carboxylate stretching modes over the pH range of 2 to 12. The SFG intensities of pMBA and its conjugate base, p-methyl benzoate (pMBA−), exhibit an anomalously large enhancement over a narrow pH range (∼0.5) centered at pH 6.3 near the SFG-determined surface pK a, 5.9 ± 0.1. The increase in the surface pK a relative to the bulk value of 4.34 is consistent with the trend previously observed for long chain carboxylic acids in which the surface pK a is higher than the bulk solution pK a. SFG polarization studies help distinguish the orientation and number density contributions to this observed anomalous surface phenomenon. The large SFG intensity increase is attributed to an increase in the pMBA and pMBA− surface concentrations in this narrow pH range due to a cooperative adsorption effect between pMBA and pMBA−. This cooperativity is manifested only on the 2D air–water interface, where the interactions between the acid and base are not as dielectrically screened as in the aqueous bulk phase. Surface effects are critical to understanding and controlling the reactivity, solubility, and behavior of organic acids at interfaces and can have an impact on biomedical applications.