Developing economical and efficient electrocatalysts toward hydrogen evolution reaction (HER) plays a crucial role in promoting the utilization of hydrogen energy. Herein, a bottom-up strategy is ...exploited to synthesize ultrafine molybdenum carbide (Mo2C) nanocrystals assembling in boron, nitrogen co-doped carbon matrix (BNC). The BNC framework not only increases the dispersibility of carbide particles, but also provides additional active sites to intensify HER performance. Moreover, in comparison with mono-heteroatom modification, the catalyst decorating with B and N simultaneously is demonstrated to be a generalist which can efficaciously catalyze HER in both acidic and alkaline electrolyte. In-depth studies show that N-doping is conductive to capturing protons in acid while B-doping facilitates the adsorption and dissociation of water in alkali. This work may shed some light on the rational design and manufacture of HER electrocatalysts with high compatibility to distinct electrolytic environments.
Mo2C@BCN as an efficient electrocatalyst for hydrogen evolution. Display omitted
Searching for high-efficiency and earth-abundant electrocatalysts towards hydrogen evolution reaction (HER) is one of the most promising pathways to ameliorate environmental contamination. In this ...work, we report a facile protocol to achieve the synthesis of the coupled molybdenum carbide and molybdenum nitride (Mo2C/Mo2N), in which ammonium heptamolybdate (AHM) serves as molybdenum source and hexamethylenetetramine (HMT) is chosen as a N-containing carbon source. By virtue of adjusting the ratios of precursors and carbonization temperatures, a variety of products with different structural features and HER performance can be obtained. Compared to single component of carbide or nitride, the Mo2C/Mo2N hybrid prepared with AHM/HMT ratio of 1:2 at 700 °C shows superior catalytic activity, with an overpotential of 205 mV required to drive 10 mA cm−2 of current density and a Tafel slope of 71.8 mV dec−1. The boosted HER performance is attributed to the synergistic effect between Mo2C and Mo2N, and the electronic modulation of active sites due to N-doping.
•Facile synthesis of coupled Mo2C/Mo2N hybrid is demonstrated.•The precursors composition and temperatures cause the change of phase structure.•The structure-performance correlation is investigated.•The heteroatom N doping could modulate the electronic structure of active sites.•The optimized catalyst presents favorable HER activity and excellent stability.
Zinc-substituted tricalcium phosphate/fluoridated hydroxyapatite (ZnTCP/FHA) biphasic composite coatings and Zinc containing fluoridated hydroxyapatite (ZnFHA) coating were prepared on Ti6Al4V ...substrates through a modified sol–gel method. The release of zinc ions from these coatings was characterized through a designed cycled immersion test: the coatings were soaked in the TRIS solution with pH of 7.25 at 37
°C for 96
h (one cycle). This process was repeated twice with the solution refreshed at the end of the each cycle. The Zn concentrations were measured at a 24-hour interval during the first cycle and at the end of each cycle. The results indicated that ZnTCP/FHA coatings released Zn at a rather slow and sustained rate while ZnFHA coatings released Zn at a rapid and therefore unsustained rate. This Zn release behavior difference is attributed to the different chemical states of Zn in the coatings. The current results demonstrated that the designed biphasic composite approach could potentially be a good way to tailor the release of Zn through combinations of different Zn chemical states, with the durability of the coatings not impaired.
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•Six low-index surface atomic structures were completely built.•Surface energies were calculated via first-principles density functional theory (DFT).•An equilibrium rutile TiO2 model ...was constructed based on Wullf principles.•The established model is in the consistence with typical morphology of fully-developed rutile TiO2 particles.
Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.
Agriculture is one of humankind’s most significant sources of biomass; it also places tremendous pressure on ecosystems through its increasing demand for agricultural products. However, few studies ...have assessed human pressures on ecosystems from agricultural production and consumption based on a whole-supply-chain perspective. Based on the concept of human appropriation of net primary productivity (HANPP), we evaluate trends of agricultural HANPP embodied in consumption from a global perspective and trace the pressure from agriculture production that is exerted on the environment using an environmentally extended multiregional input–output (MRIO) model. The results show that agricultural HANPP embodied in consumption accounted for over two-thirds of total HANPP but brought about less than 7% of global value added. India, Brazil, and China were found to have the highest level of agricultural HANPP embodied in consumption. Agricultural net exporters were found to usually be low- and lower-income countries, while net importers are found to be high-income countries. According to the driving factor analysis, high-income and low-income countries should cooperate by adjusting consumption patterns and sharing agricultural technology to alleviate the pressure from agricultural production. Our study highlights the importance of agrarian expertise sharing and the need to develop sustainable and green agricultural production.
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Nowadays, water pollution by industrial waste water that contains heavy metal elements, such as Cd, has become an urgent concern to be solved. In this work, magnetic γ-Fe2O3/Fe-doped ...hydroxyapatite (HAP) nanostructures are realized as Cd(II) adsorbents with outstanding adsorption performance. The Vibrating Sample Magnetometer (VSM) analysis and magnetic separation experiments reveal that γ-Fe2O3/Fe-doped HAP nanostructures can be effectively separated by external magnet. Compared with pure HAP, the γ-Fe2O3/Fe-doped HAP nanostructures show higher adsorbed concentration and adsorption rate. The maximum adsorbed concentration at the equilibrium is 258 mg g−1 (under initial concentration of 500 mg L−1, temperature = 25 °C and pH = 5.0), which is higher than values reported for most of HAP-based adsorbents. The adsorption data could be well fitted by the Freundlich model, and the adsorption kinetic follows the pseudo-second-order model. Furthermore, the study of adsorption mechanism reveals that both ion-exchange and electrostatic interaction are involved in process of Cd(II) adsorption.
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The storage and landfill of spent V2O5–WO3/TiO2 selective catalytic reduction (SCR) catalysts can pose environmental hazards, and the valuable tungsten, vanadium and titanium ...resources are wasted due to the lack of appropriate recycling technology. In this study, we explore an effective and low-cost method to simultaneously recycle tungsten, vanadium and titanium from spent SCR catalysts. We extract tungsten and vanadium are from spent SCR catalysts by a Na2CO3–NaCl molten salt roasting-leaching method, then obtain enriched tungsten, vanadium solution through an ion-exchange and NaOH elution process, and separate tungsten and vanadium via an ammonium salt precipitation method. By optimizing the experimental conditions, 95.5% of tungsten and 94.9% vanadium are leached from the spent SCR catalysts, among which 93.4% of vanadium and 96.2% of tungsten can be precipitated. The leached residue mainly consists of nano-sized TiO2 and sodium titanate nanorods, which is used as adsorbent for heavy metal ions (Pb(Ⅱ), Cd(Ⅱ) and Cr(Ⅲ)). The maximum adsorption capacities are 338.503 mg g−1 for Pb(Ⅱ), 227.675 mg g−1 for Cd(Ⅱ) and 97.262 mg g−1 for Cr(Ⅲ) at pH 6.0. Competitive adsorption among the three metal ions follows the sequence of Pb(Ⅱ) > Cd(Ⅱ) > Cr(Ⅲ). The adsorption data can be well fitted by the Langmuir model, and the adsorption kinetic follows the pseudo-second-order model. Furthermore, the X-ray photoelectron spectroscopy (XPS) analysis shows that the adsorption of Pb(Ⅱ), Cd(Ⅱ) and Cr(Ⅲ) by our adsorbent can be ascribed to the ion exchange of heavy metal ions with Na ions.
Different crystal phases of TiO2 were produced by calcinations of metatitanic acid at various temperatures. H2TiO3-lithium adsorbent was obtained from the acid-modified adsorbent precursor Li2TiO3 ...which was synthesized by a solid-phase reaction between TiO2 and LiOH·H2O. Effects of crystal phases of TiO2 on the pull-out rate of Li+ from Li2TiO3 and adsorption properties of lithium adsorbent were studied. The results indicate that anatase structure rather than rutile reacted with LiOH·H2O aids the extraction of Li+ and the adsorption performance of lithium adsorbent. The maximum Li+ drawn out ratio from Li2TiO3 reaches 98.69%, and the maximum saturated adsorptive capacity comes up to 39.2mgg−1.
H2TiO3-lithium adsorbent is obtained from the acid-modified Li2TiO3.The maximum saturated adsorptive capacity of adsorbent comes up to 39.2mgg−1.Anatase rather than rutile aids the adsorption performance of lithium adsorbent.Refinement is done by the Rietveld method using Materials Studio 5.5.Bond distances and angles in TiO6 octahedrons are used to explain the phenomenon.
Large quantities of titanium white waste acid (TWWA) are generated during TiO2 production by the sulfate process. Recycling by concentration is the most widely used method to treat TWWA. However, ...serious fouling occurs during this process. The chemical composition of fouling obtained from a commercial plant was analyzed. The phase equilibria of CaSO4-FeSO4-H2SO4-H2O at 373.15 and 378.15 K were studied to elucidate the fouling mechanism. The fouling was mainly composed of CaSO4 (anhydrite) (74.97 wt %) and TiO(OH)2 (anatase) (24.48 wt %). The mass fractions of CaSO4 and FeSO4 in the equilibrium liquid phase of the CaSO4-FeSO4-H2SO4-H2O system increased with an increase in temperature and a decrease in H2SO4 concentration. The Pitzer method was successfully employed to describe the equilibrium behavior. During the mixing of the recycled acid and the initial TWWA, some CaSO4 (anhydrite) precipitated from the liquid phase, while some FeSO4·H2O dissolved in the liquid phase during the mixing and heating process. In the heating process, CaSO4 (anhydrite) did not precipitate out from the liquid phase. It was thus concluded that CaSO4 (anhydrite) precipitation during the mixing process is the key factor for the fouling on the heat exchanger surface during the primary evaporation process.
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