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A facile synthesis of high efficiency semiconductor photocatalyst hybrids is of great importance in making the photocatalytic systems more viable and applicable. This study presents that simply reversing chemical precipitation order of CdS results in significantly different photocatalytic activity in terms of hydrogen production from water under visible light when hybridized with platinized TiO2 particles (Pt-TiO2). It has been found that CdS obtained via dropping an aqueous cadmium cation in aqueous sulfide solution (i.e., Pt-TiO2 suspension with S2−) with equal molar ratios (hereafter CdSR) has a maximum >10-fold greater amount of hydrogen than that obtained by simply reversing the dropping order (i.e., dropping S2− to Pt-TiO2 suspension with Cd2+; hereafter CdRS). Such a high activity of CdSR, however, is very sensitive to photocatalytic running conditions, in particular, kind and concentration of electron donor (Na2S and/or Na2SO3) which largely changes the hydrogen production ratio (R H) of CdSR to CdRS. Detailed surface analyses indicate that physicochemical properties of CdSR are very different from those of CdRS including larger and red-shifted onset light absorption and altered photoluminescence, S/Cd atomic ratios >1, and hexagonal crystallinity (vs cubic-CdRS), the differences of which were attributed to the primary reasons for higher activity of CdSR. Finally, the photocatalytic hydrogen production mechanism was proposed based on the experimental results.

We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner-and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner-and outer-halo populations, with peaks at [Fe/H] = −1.5 and −2.2, respectively. From consideration of the absolute carbon abundances for our sample, A(C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP-s stars (those with strong overabundances of elements associated with the s-process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP-s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP-s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner-and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.

Highly fluorescent and amphiphilic carbon quantum dots (CQDs) were prepared by microwave-assisted pyrolysis of citric acid and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), which functioned as an A and B polyamidation type monomer set. Gram quantities of fluorescent CQDs were easily obtained within 5 min of microwave heating using a household microwave oven. Because of the dual role of TTDDA, both as a constituting monomer and as a surface passivation agent, TTDDA-based CQDs showed a high fluorescence quantum yield of 29% and amphiphilic solubility in various polar and nonpolar solvents. These properties enable the wide application of TTDDA-based CQDs as nontoxic bioimaging agents, nanofillers for polymer composites, and down-converting layers for enhancing the efficiency of Si solar cells.

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