Effect of Hydrogen Addition on Soot Formation and Emission in Acetylene Laminar Diffusion Flame.

Hydrogen (H2) has been regarded as a highly competitive alternative fuel that does not produce CO2 and soot during combustion. There are few studies of cofiring H2 with hydrocarbons. Meanwhile, the effect of hydrogen addition on soot formation and emission is questionable. In this study, the effect of H2 addition with varying ratios (between 0 and 50% by molar fraction while the remainder is nitrogen) on soot formation in acetylene (50% by molar fraction) laminar diffusion flames was experimentally and numerically investigated. Results show that with H2 addition, the flame height increases and the temperature decreases. The total soot emission and the primary particle size both increase with H2 addition. The addition of H2 promotes soot formation. In addition, the soot oxidation is weakened due to the lower flame temperature. Chemical kinetic analysis shows that the concentrations of A1, H, and H2O increase with H2 addition, which is consistent with the experimental results. According to the HACA reaction, the increase of the molar fraction of A1 and H radicals could promote PAH growth and soot formation.

Long-term effects of phytoextraction by a poplar clone on the concentration, fractionation, and transportation of heavy metals in mine tailings.

Mine tailings are one of main causes of diffused heavy metal pollution since the heavy metals in there may acquire mobility. The current knowledge of the processes at work in long-term phytoremediation by woody species remains insufficient. Through a 4-year field study, we evaluated the phytoextraction efficiency of Populus deltoides CL. 'Xianglin 90' grown on a mine tailing co-polluted by Cd, Cu, Cr, Ni, Pb, and Zn. The concentrations of Cd, Cu, Ni, Pb, and Zn in the rhizospheric soil were reduced by amounts ranging from 12.86 to 42.19% during the study period. Bioconcentration factors and translocation factors showed that the accumulation of Cd and Zn occurring in the shoots was the most effective. Combined with the considerable biomass produced by poplar, the extracted amounts of Cd and Zn could reach 0.61 g and 10.66 g plant-1, respectively, in which the shoots account for 77.3% (Cd) and 89.0% (Zn) of the overall extraction amounts. Acid-soluble Cd and Zn increased by 5.49% and 4.29%, respectively, in the rhizosphere compared to the bulk soil, indicating that poplar enhanced the mobility of Cd and Zn in the rhizosphere, which explained its ability for bioaccumulation and root-shoot translocation. Moreover, calculated time required to address the issue of Cd and Zn pollution was theoretically shortened by more than half from 2015 to 2019. This study brings new insights into the long-term effects of phytoextraction on the concentration, fractionation, and transportation of heavy metals and confirms the potential of poplar as a Cd and Zn remediation species.

Electrochemical exfoliation of ultrathin ternary molybdenum sulfoselenide nanosheets to boost the energy-efficient hydrogen evolution reaction.

Developing low-cost and highly efficient transition metal dichalcogenides as alternative electrocatalysts has become an urgent need for the hydrogen evolution reaction (HER). However, the inert basal planes of transition metal dichalcogenides severely suppress their practical applications. Herein, we developed ultrathin ternary molybdenum sulfoselenide (MoSexS2-x) nanosheets by using the cathodic electrochemical exfoliation approach in non-aqueous electrolytes. The exfoliated MoSexS2-x nanosheets demonstrated high structural integrity with lateral dimensions up to ∼1.5 µm and an average thickness of about 3 nm. Owing to the unique ultrathin structure and immensely exposed active sites, the ternary MoSexS2-x nanosheets supported on Ni foam demonstrated a greatly enhanced electrocatalytic activity for the HER in 1.0 M KOH with an overpotential of 123 mV at a current density of 10 mA cm-2 and high stability, superior to majority of the previously published MoS2-based electrocatalysts. Furthermore, the ternary MoSexS2-x nanosheets as a highly active bifunctional electrocatalyst contributed to enhanced energy-efficient hydrogen production and electrocatalytic synthesis of ammonia.

Scalable Production of Few-Layer Niobium Disulfide Nanosheets via Electrochemical Exfoliation for Energy-Efficient Hydrogen Evolution Reaction.

Two-dimensional (2D) niobium disulfide (NbS2) materials feature unique physical and chemical properties leading to highly promising energy conversion applications. Herein, we developed a robust synthesis technique consisting of electrochemical exfoliation under alternating currents and subsequent liquid-phase exfoliation to prepare highly uniform few-layer NbS2 nanosheets. The obtained few-layer NbS2 material has a 2D nanosheet structure with an ultrathin thickness of ∼3 nm and a lateral size of ∼2 µm. Benefiting from their unique 2D structure and highly exposed active sites, the few-layer NbS2 nanosheets drop-casted on carbon paper exhibited excellent catalytic activity for the hydrogen evolution reaction (HER) in acid with an overpotential of 90 mV at a current density of 10 mA cm-2 and a low Tafel slope of 83 mV dec-1, which are superior to those reported for other NbS2-based HER electrocatalysts. Furthermore, few-layer NbS2 nanosheets are effective as bifunctional electrocatalysts for hydrogen production by overall water splitting, where the urea and hydrazine oxidation reactions replace the oxygen evolution reaction.