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There is no agreement regarding which solvent is more suitable to obtain sol–gel–derived titania (TiO2) samples with an enhanced photocatalytic behavior. Furthermore, the solvent effect on the preparation of TiO2-RGO (reduced graphene oxide) nanocomposites has not been published yet and could be an attractive experimental strategy to modulate structure and properties. On the basis of these observations, TiO2-RGO nanocomposites were fabricated in this study. It was evaluated for the influence of using either isopropyl (IsoprOH) or ethyl (EtOH) alcohol on the textural and photocatalytic properties of the prepared materials. The use of IsoprOH led to samples with smaller crystallite size, narrower apparent band gap, smaller isoelectric point, larger adsorption capacity, and higher photocatalytic activity. In addition, the incorporation of RGO into TiO2 greatly improved the adsorption capacity and photocatalytic activity of the latter. However, the optimal loading of RGO to prepare composites with enhanced photocatalytic activities was 1 wt%. This finding can be related to the stacking of RGO sheets when concentrations above 1 wt% are used, which could prevent UV light to reach the TiO2 particles and also decrease the photocatalytic capacity of the composites. Moreover, materials with RGO concentration above 1 wt% could exhibit a highly negatively charged surface, which may decrease the separation of the generated electron–hole pairs and lead to faster recombination rates of charge carriers.
Recent studies of subaerial volcano carbon flux have challenged previous assumptions about carbon recycling in the mantle and the ratio of ingassing to outgassing. This chapter reviews the current state of knowledge of the flux of carbon from subaerial volcanoes at subduction zones and intraplate locations, as well as through diffuse degassing away from volcanic vents. It also reviews the importance of crustal carbonate assimilation and carbonate platforms on these fluxes. The chapter presents an overview of how these fluxes are estimated – including descriptions of new technologies and recent field campaigns – and the timescales of flux measurements. It also summarizes what is currently known about the flux of carbon versus other volatile elements in these various settings. Supplemental online material is available for this chapter at www.cambridge.org/9781108477499#resources.
The Earth is a powerful organic chemist, transforming vast quantities of carbon through complex processes, leading to diverse suites of products that include the fossil fuels upon which modern societies depend. When exploring how the Earth operates as an organic chemist, it is tempting to turn to how organic reactions are traditionally studied in chemistry labs. While highly informative, especially in terms of insights gained into reaction mechanisms, this approach can also be a source of frustration, as many of the reactants and conditions employed in chemistry labs have few or no parallels to geologic processes. The primary goal of this chapter is to provide examples of predicting thermodynamic influences and using the predictions to design experiments that reveal the mechanisms of how reactions occur at the elevated temperatures and pressures encountered in the Earth. This work is ongoing, and we hope this chapter will inspire numerous and diverse experimental and theoretical advances in hydrothermal organic geochemistry.
Iron sulfides have attracted much interests for their potential as anode materials in energy storage devices in view of their low costs, and environmentally benign and high theoretical capacities. Among them, Fe1−xS is relatively rarely investigated. In this work, Fe1−xS@rGO has been synthesized using a facile in situ hydrothermal method. After wrapped by rGO, the morphology of Fe1−xS particles changes from hexagonal flakes to irregular particles with much smaller sizes. As the anode material for lithium ion batteries, Fe1−xS@rGO exhibits excellent lithium storage ability. It can deliver an initial discharge capacity of 1575.5 mA h/g in the potential window of 0.005–3 V, and a reversible capacity of 907.8 mA h/g can be maintained after 200 cycles at 100 mA/g. Its improved electrochemical performance can be attributed to the effect of enhanced contact area and shortened Li+ ion transport distance because of rGO’s contribution.
The hierarchical Au-loaded SnO2 nanoflowers were synthesized using a new developed self-reductive hydrothermal method, of which the gas-sensing properties were enhanced significantly. The SnO2 hierarchical nanoflowers were composed of well-defined nanosheets with a specific surface area of around 84 m2/g. Gas sensors made of pure and Au-doped SnO2 were fabricated, and their gas-sensing properties were characterized. The 1.0 at.% Au-loaded SnO2 sensor prepared by the new developed self-reductive method showed much more excellent selectivity toward ethanol at 200 °C than the one prepared with the conventional hydrothermal method. Its response to ethanol was around 3 times higher than that of the pure SnO2 sensor. A very wide detection range of 1–500 ppm for ethanol, good repeatability, and long-term stability were also approved.
Three-dimensional nano-mulberries consisting of SnO2 nanoparticles have been successfully anchored onto the surfaces of reduced graphene oxide (RGO) to construct hierarchical hybrids—SnO2@RGO with a one-pot approach. The SnO2 nano-mulberries with different amounts of RGO have been produced for optimizing their composition effect on Li storage performance. Specifically, SnO2@RGO hybrids incorporated with optimized amount of RGO nanosheets (∼20.8%) exhibit highly enhanced capacity of ∼1025 mA h/g at 0.1 A/g and a reversible capacity of 750 mA h/g over 100 cycles at 0.2 A/g. The materials also deliver much better rate performance with average specific capacity of ∼498 mA h/g at 2 A/g in comparison with that of SnO2 nano-mulberries. After cycling for 600 times at 1 A/g, the SnO2@RGO electrodes still maintain high reversible capacity of ∼602 mA h/g, corresponding to 35% of the second cycle and 133% of the 70th discharge capacity.
The ‘deep sea’ encompasses a broad range of habitats that differ greatly in their assemblages and ecosystem functioning. Habitats may be described by a combination of environmental factors (e.g., depth, slope) and biotic factors (e.g., source of primary productivity). We review recent attempts to define deep-sea biogeographic provinces based on spatial and temporal variations in oceanographic conditions, and consider potential boundaries to distributional ranges, in particular habitats based on recent phylogeographic studies. We briefly discuss abiotic interactions in various habitats, noting the particular influence of local hydrodynamics. We consider competition and predation at whale falls and hydrothermal vents, discuss symbiotic interactions particularly with respect to deep-sea corals, which are particularly prevalent in submarine canyons and seamounts, and consider the difficulties of inferring processes from patterns.
Regular WO3 nanocubes have been prepared on a large scale through a convenient hydrothermal route at the temperature of 200 °C. The products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A crystal growth process for WO3 nanocubes was simply proposed based on the comparative experiments. The band gap energy (Eg) was determined to be 2.58 eV based on the UV-vis DRS analysis, and the PL spectrum exhibited a strong blue light emission band centered at 469 nm. The as-prepared WO3 nanocubes showed higher visible light photocatalytic performance for degrading rhodamine B compared with WO3·H2O and WO3·0.33H2O/WO3 which were obtained at 80 °C and 140 °C, respectively, suggesting potential application in the region of wastewater purification.
The research of high-performance flexible supercapacitors is urgent due to the rapid development of wearable and portable electronics. The key challenge is the preparation of flexible electrodes with high areal capacitance since electrodes are the most important part of supercapacitors. Compared to those conventional electrodes loading with typical flexible substrates such as textile, PET, paper et al, free-standing electrodes have many advantages such as more efficient capacity contribution, solidly embedded active materials and thinner thickness. Herein, we have successfully fabricated a novel sandwich-like structure free-standing MoO3-rGO (reduced graphene oxide) composite film electrode for flexible supercapacitors using simple vacuum filtration method followed by HI reduction process. The obtained MoO3-rGO composite film electrode shows excellent electrochemical performance, whose areal specific capacitance reaches 8972 mF·cm-2 (1.5 mA·cm-2). Here, MoO3 provides pseudocapacitance and rGO provides double-layer capacitance. After cycling for 2000 cycles, the capacity retention is 86.7%, showing good cycle stability. Besides, the as-prepared composite film has good flexibility and will not break easily during following bending, rolling, folding or twisting steps. This study has been approved to be an important step for the high-performance electrode design for free-standing flexible supercapacitors.
Controlled reaction conditions in simple, template-free hydrothermal processes yield Tm-Lu2O3 and Tm-GdVO4 nanocrystals with well-defined specific morphologies and sizes. In both oxide families, nanocrystals prepared at pH 7 reaction media exhibit photoluminescence in ∼1.95 μm similar to bulk single crystals. For the lowest Tm3+ concentration (0.2 % mol) in GdVO4 measured 3H4 and 3F4 fluorescence lifetimes τ are very near to τrad.
Nano-porous palladium (Pd) thin films could potentially be applied to hydrogen gas sensing materials with high sensitivity and selectivity. In our previous study, a nano-porous Pd film was fabricated with a three-dimensional network structure from an AlPd mother alloy film by a dealloying method using the chelating ability of an organic acid. This process was simple and environmentally friendly because it only required organic acid in a ppm concentration, and did not exhaust a strong acid waste solution, including heavy metal ions. This method was modified to improve the Pd purity of the dealloyed specimen, reaction rate, and morphology control. In this study, the existence of a composition undulation pattern was shown in the AlPd mother alloy film, and its effects on the morphology of the dealloyed specimen were evaluated. Furthermore, this pattern could be controlled by N2 gas addition to the Ar sputtering gas during the preparation of the AlPd mother alloy film.
Oriented ZnO seed layers were deposited by three different techniques, namely, simple drop casting (DC), sol-gel derived dip coating (DPC) and spin coating of ball-milled ZnO powder solution(BMD) for the subsequent growth of vertically aligned ZnO nanorods along the substrate normal. X-ray diffraction (XRD) analyses revealed that ZnO(DC) seed layer exhibit the highest preferential c-axis texturing among the ZnO seed layers synthesized by different techniques. The Scanning Electron Microscopy (SEM) analysis evident that the morphology of ZnO seed layer surface is compact and coherently carpets the underlying substrate. ZnO nanorods(NRs) were then grown by hydrothermal method atop the ZnO seeded and non-seeded substrates grown by different techniques to elucidate the best ZnO seed layer promoting well-aligned ZnO Nanorods. The presence of c-axis oriented ZnO(DC) seeding layers was found to significantly affect the surface morphology and crystallographic orientation of the resultant ZnO NRs films. The optical band gap of ZnO(DC) seed and ZnO NRs were estimated to be 3.30 eV and in the range of 3.18 – 3.25 eV respectively by using UV-VIS-NIR diffuse reflection spectroscopy. The room temperature photoluminescence analyses revealed that nanostructured ZnO films exhibit a sharp near-band-edge luminescence peak at ∼380 nm consistent with the estimated optical band gap and the ZnO nanorod arrays are notably free from defect-related green-yellow emission peaks.
Monoclinic VO2 is a known polymorph of vanadium dioxide that has received much attention due to its oxidative capabilities, geometric configuration, and promising applications in functional windows. VO2 can usually be obtained through a hydrothermal method under high pressure. In this work we report a synthesis of VO2 doped with Manganese using a rapid single-step hydrothermal process with V2O5, manganese (II) acetate and citric acid as precursors. Different syntheses were carried out in which the concentration of V2O5 and citric acid remained constant whereas the concentration of manganese (II) acetate was varied. The reactants underwent a stirring phase for 30 minutes before being loaded into a hydrothermal reactor for 2.5 hours at 200°C. The resultant was washed three times to remove the residual precursors. Imaging and spectroscopy characterizations such as TEM, SEM and UV-VIS-NIR have been performed on different doping concentration and the results display a dependence on doping concentrations.
We presented a green and simple method to synthesize carbon nanodots (C-dots) from millets using hydrothermal synthesis route for the first time. The obtained C-dots have average diameter ranging from 6 to 10 nm. Optical measurements showed the insight into the formation of functional groups on the particle surfaces, resulting in their good water solubility and bioconjugation. After treatment with C-dots, small subpopulation of the human cervical tumor cells became bright and exhibited multicolor fluorescence under different excitation wavelength. The achievement demonstrated potential applications of fluorescent C-dots in the field of biomedical application.
About 400 subglacial lakes are known from Antarctica. The question of whether life unique of subglacial lakes exists has been paramount since their discovery. Despite frequent evidence of microbial life mostly from accretion ice, subglacial lakes are characterized by physiologically hostile conditions to metazoan life, as we know it. Pure water (salinity ≤0.4–1.2%), extreme cold (−3°C), high hydrostatic pressure, areas of limited or no oxygen availability and permanent darkness altogether require physiological adaptations to these harsh conditions. The record of gene sequences including some associated with hydrothermal vents does foster the idea of metazoan life in Lake Vostok. Here, we synthesize the physico-chemical environment surrounding sub-glacial lakes and potential sites of hydrothermal activity and advocate that the physico-chemical stability found at these sites may be the most likely sites for metazoan life to exist. The unique conditions presented by Lake Vostok may also offer an outlook on life to be expected in extra-terrestrial subglacial environments, such as on Jupiter's moon Europa or Saturn's moon Enceladus.
In this study, we report developments towards the application of large zeolite particles, with diameter ca. 40 μm, as tracers in Positron Emission Particle Tracking (PEPT) imaging using 68Ga. The influence of intrapore Na+ and TEA+ (tetraethylammonium) cation concentrations and framework Si/Al ratio on the morphology of mordenite particles has been investigated, advancing understanding of the relationship between these factors. Moreover, the influence of ethanol concentration in the gel during aging on intrapore cation concentration, Si/Al ratio and particle morphology has also been investigated. Additionally, facile ion-exchange between aqueous Ga3+ and intrapore H+ in mordenite has been demonstrated. The influence of pH and gallium speciation on ion-exchange has been investigated to determine favourable conditions for 68Ga3+ uptake by the zeolite.
We report the synthesis and optical properties of pure ZnS and Ag doped ZnS nanostructures. ZnS(Ag) was synthesized by using the hydrothermal technique and later annealed at different temperatures under vacuum conditions. It was observed that the photoluminescence (PL) emission from the ZnS(Ag) nanostructures can be easily tuned from the blue (445 nm) to green (530 nm) region of visible light by varying the annealing temperature. This tunability has been attributed to the introduction of excess sulfur vacancy states, which is evident from the PL excitation spectra. This observed change in the PL emission wavelength can be highly beneficial in the imaging screens where ZnS is regularly used and can be easily interfaced with the silicon photodiodes showing maximum sensitivity at 550 nm.
An unusual occurrence of asbestiform sepiolite, filling veins in the antigorite serpentinites of the Voltri Unit exposed in a borrow pit (now reclaimed) in the Deiva forest, near Sassello, NW Italy, was investigated with an in-depth analytical approach aimed at studying its crystal-chemistry and structure and evaluating its possible hazards for human health. Optical microscopy and scanning electron microscopy (energy-dispersive spectroscopy mode) proved that these sepiolite fibres, apparently up to several cm long, are made up of bundles of thinner fibrils (or laths: average length > 100 µm; thickness ≈ 80 nm), with a composition consistent to that reported in the literature. The dehydration process was monitored through thermo-gravimetric analyses and Fourier-transform infrared spectroscopy, performed at increasing T; the latter, in particular, showed the presence of moderate amounts of aliphatic hydrocarbons – not yet identified thoroughly – associated with the sample. The crystal structure refinement with the Rietveld method showed no relevant difference from the literature models, although a peculiar distribution of zeolitic H2O molecules was observed. The geological context suggests that the Sassello sepiolite precipitated from hydrothermal fluids, which were saturated in Mg and silica by the interaction of the host serpentinites. The same setting favoured formation of abiotic hydrocarbons, by means of the Fischer–Tropsch reaction. The extremely long and flexible fibrils (length/width aspect ratio >> 3) of this sepiolite specimen could represent a serious hazard for human health if air dispersed and inhaled; also, its atypical association with hydrocarbons (only reported once previously) might even favour further fragmentation in thinner units.
A new trimetallic compound with formula (NH4)H2Co2O(OH)(MoO4)1.6(WO4)0.4•H2O and lamellar structure was prepared by hydrothermal synthesis. The solid was characterized using X-ray diffraction (XRD), thermogravimetric (TGA) and differential thermal (DTA) analyses, Fourier-transform infrared spectroscopy (FT–IR), laser Raman spectroscopy (LRS), and atomic absorption spectroscopy (AA). Crystallographic studies showed that the solid crystallizes with hexagonal symmetry in space group R-3 m with a = 6.0807 and c = 21.7591 Å.