Dan Liu

Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks and could coexist with sulfate-reducing bacteria (SRB) in anoxic environments, however, the interactions of clay minerals and SRB are not well understood. The objective of this study was to understand the reduction rate and capacity of structural Fe(III) in dioctahedral clay minerals by a mesophilic SRB, Desulfovibrio vulgaris and the potential role in catalyzing smectite illitization. Bioreduction experiments were performed in batch systems, where four different clay minerals (nontronite NAu-2, mixed-layer illite-smectite RAr-1 and ISCz-1, and illite IMt-1) were exposed to D. vulgaris in a non-growth medium with and without anthraquinone-2,6-disulfonate (AQDS) and sulfate. Our results demonstrated that D. vulgaris was able to reduce structural Fe(III) in these clay minerals, and AQDS enhanced the reduction rate and extent. In the presence of AQDS, sulfate had little effect on Fe(III) bioreduction. In the absence of AQDS, sulfate increased the reduction rate and capacity, suggesting that sulfide produced during sulfate reduction reacted with the phyllosilicate Fe(III). The extent of bioreduction of structural Fe(III) in the clay minerals was positively correlated with the percentage of smectite and mineral surface area of these minerals. X-ray diffraction, and scanning and transmission electron microscopy results confirmed formation of illite after bioreduction. These data collectively showed that D. vulgaris could promote smectite illitization through reduction of structural Fe(III) in clay minerals.

Abstract Organic photodetectors with UV‐sensitivity are of great potential for various optoelectronic applications. Integration of high charge carrier mobility, long exciton diffusion length as well as unique UV‐sensitivity for active materials is crucial for construction of UV‐sensitive devices with high performance, however, very few organic semiconductors can integrate these properties simultaneously. Herein, two novel organic semiconductors containing large steric hindrance triphenylamine groups, 1,6‐distriphenylamineethynylpyrene (1,6‐DTEP) and 2,7‐distriphenylamineethynylpyrene (2,7‐DTEP) are designed and synthesized. It demonstrates that the single crystals of both 1,6‐DTEP and 2,7‐DTEP exhibit superior integrated optoelectronic properties of high charge carrier mobility, unique UV absorption, high photoluminescence quantum yields as well as small exciton binding energies. Organic phototransistors constructed using 1,6‐DTEP and 2,7‐DTEP single crystals show ultrasensitive performance with ultra‐high photoresponsivity of 2.86 × 10 6 and 1.04 × 10 5 A W −1 , detectivity ( D *) of above 1.49 × 10 18 and 5.28 × 10 16 Jones under 370 nm light illumination, respectively. It indicates the great potential of 1,6‐DTEP and 2,7‐DTEP‐based phototransistors for organic UV‐photodetector applications and also provides a new design strategy to develop series of better performance UV photoelectric organic materials for related research in organic optoelectronics.

Abstract Brucite, Mg (OH) 2 , is an important analog for studying the thermodynamics of hydrous silicate minerals in the deep Earth, as well as H/D isotope fractionation between minerals and water. In this study, we measured in situ Raman and Fourier transform infrared spectra for the natural and deuterated brucite samples, at high temperatures to 650 K, just before the dehydration of brucite at ambient pressure. All of the optical modes systematically shift to lower frequencies at elevated temperature, while deuterium substitution reduces the magnitudes of the temperature dependence. The isobaric mode Grüneisen parameters ( γ iP ), as well as the intrinsic anharmonic parameters ( a i ), have been evaluated for the vibrational modes between Mg (OH) 2 and Mg (OD) 2 . The anharmonic contribution to the thermodynamic properties (such as internal energy, isochoric and isothermal heat capacities, and entropy) is positive and severe at high temperature. The difference in the heat capacity is up to ~7% at 700 K due to the anharmonic effect. The deuterium isotopic effect on the thermodynamics is positive, and the magnitude of the isotopic effect is comparable to that from the anharmonic effect. On the other hand, the anharmonicity significantly decreases the magnitude of the positive pressure dependence of the D/H fractionation β factor for brucite, and this correction could be more important at elevated temperature. At the temperature of 800 K, 10 3 ·(∂ln β /∂ P ) T decreases from +0.23 GPa −1 (for quasi‐harmonic approximation) to approaching zero, due to the anharmonic correction.

Clinohumite is a potentially abundant silicate mineral with high water concentration (2~3 wt% H2O) that is generated from dehydration of serpentine-group minerals in subduction zones. Previous studies show that fluorine substitution (OH- = F-) can stabilize clinohumite to significantly higher temperature in subduction zones, although temperatures within the slabs are thought to be well within the stability field of both F-bearing and OH-clinohumite. We collected in-situ high-temperature Raman and Fourier transform infrared (FTIR) spectra for both the synthetic [Mg9Si4O16(OH)2] and natural [Mg7.84Fe0.58Mn0.01Ti0.25(SiO4)4O0.5(OH)1.30F0.20] clinohumite samples up to 1243 K. Three OH bands above 3450 cm–1 are detected for both the natural and synthetic samples with negative temperature dependence, due to neighboring H-H repulsion in the crystal structure. Additional OH peaks are detected for the natural sample below 3450 cm–1 with positive temperature dependence, which could be explained by non-polar F- substitution in the OH site. Hence, F- substitution significantly changes the high-temperature behavior of hydrogen bonds in the humite-group minerals. On the other hand, we evaluated the mode Grüneisen parameters (γiP, γiT), as well as the intrinsic anharmonic parameters (ai) for clinohumite, chondrodite, and phase A, the dense hydrous magnesium silicate (DHMS) phases along the brucite–forsterite join. The estimated averaged anharmonic parameters (ai_avg) for these DHMS phases are systematically smaller than those of olivine. To model the thermodynamic properties of minerals (such as heat capacity) at the high-temperature conditions of the mantle, the DeBye model, which simply approximates the lattice vibrations as harmonic oscillators, is commonly used. In contrast to forsterite, such quasi-harmonic approximations are valid for clinohumite at subduction zone temperatures, as the anharmonic contribution is no more than 2% when extrapolated to 2000 K. Hence, the classic DeBye model can reasonably simulate the thermodynamic properties of these DHMS phases in subduction zones.