Facile synthesis of Mn-doped MoS2 nanosheets on carbon nanotubes as efficient electrocatalyst for hydrogen evolution reaction.

As a substitute of Pt-based catalysts, MoS2-based catalysts have been widely used in hydrogen evolution reaction, but the inherent low conductivity, limited active edges, self-stacking and agglomeration still hinder their activities. In this work, Mn-doped MoS2 nanosheets were vertically anchored on carbon nanotubes (CNTs) by the one-step hydrothermal reaction, in which Mn-O-C/Mo-O-C was considered as a bridge between Mn-MoS2 and CNTs. The doping of the Mn element enables the spreading of MoS2 on CNTs and the rapid escape of hydrogen bubbles from the electrode, while conductive CNTs with hydrophilicity can accelerate the electron transport process between the electrolyte and the material. With an overpotential of 150 mV at a current density of -10 mA cm-2 and a Tafel slope of 39 mV dec-1, this material exhibited excellent catalytic hydrogen evolution activity, which could open the path for designing commercial electrocatalysts.

Synergistic Effects on the Co-pyrolysis of Agricultural Wastes and Sewage Sludge at Various Ratios.

This study investigated the co-pyrolysis of blends of sewage sludge (SS) with rice husk (RH) and with hemp straw (HS) at different ratios by using thermogravimetry (TG) and its rate (DTG, derivative TG) analysis at heating rates of 10, 20, and 30 K/min. The resulting kinetic parameters of activation energy (E a) were calculated by both Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose models, followed by comparison of experimental values with calculated values to reveal the synergistic effects of SS/RH and SS/HS. With increasing additions of RH or HS to SS, a gradual decreasing trend in the experimental pyrolysis temperature range was evident, ranging from 144.5 to 95.2 °C for SS/RH and from 144.5 to 88.8 °C for SS/RH. Moreover, such temperature ranges were 6.7-20.4 °C less than the calculated values at the same blending ratio. The fitting results of the two kinetic models showed that with the same SS mass ratio, the experimental E a * (average activation energy) of both SS/RH and SS/HS were less than the calculated E a *. Especially, the experimental E a * of 7SS-3RH was lower around 43.8% than the calculated E a *, whereas the experimental E a * of 3SS-7HS was lower by about 39.4% than the calculated E a *. Synergistic analysis demonstrated that the co-pyrolysis of RH or HS with SS at various mass ratios presented obvious synergistic effects and then the decrease of E a. The mechanism experiment showed that the co-pyrolysis of SS/HS may promote the decrease of E a by changing the co-pyrolysis gas products or by increasing the overflow of volatile matter and then forming intermediate transition products, while SS/RH may accelerate the decrease of the E a by using an appropriate K addition ratio from RH as a metal catalyst.

Influence of Synthesis Methods on the High-Efficiency Removal of Cr(VI) from Aqueous Solution by Fe-Modified Magnetic Biochars.

Fe-modified biochars have been widely used in removal of Cr(VI) from water due to the resulting modified surface functional groups and magnetization property. However, few studies have synthetically investigated modification methods and synthesis parameters on the improvement of the removal efficiency of Cr(VI) by Fe-modified biochars. Herein, 10 types of corn straw-based magnetic biochars were produced using pre-modification and post-modification methods with various modifier ratios, and the highest heating temperature (HHT). Cr(VI) removal results suggest that the removal efficiency of pre-modified biochars ranged from 50.7 to 98.6%, which was much higher than that of post-modified (6.6-21.6%) and unmodified biochars (0.4-7.6%). The effect of synthesis methods on Cr(VI) adsorption was in the following order: Fe-modification method > modifier ratio > HHT. The adsorption kinetics and isotherm results of three types of pre-modified biochars were well fitted with the pseudo-second-order model (R 2 > 0.99) and the Langmuir adsorption model (R 2 > 0.99), respectively, indicating the surface homogeneity of the pre-modified biochars and unilayer chemisorptions of Cr(VI). Characterization results show that iron oxides or zerovalent iron particles were successfully deposited onto the surface of biochars and magnetism was introduced. A good Pearson correlation (r = -0.9694) between the removal efficiency and pH value in modified biochar suggests that the lower pH value may offer more positive charges and promote electrostatic attraction. Therefore, the dominant mechanism for enhanced Cr(VI) adsorption on pre-modified biochar was electrostatic attraction, resulting from its distinguished acidity nature. Our findings provide new insights into the high-efficiency removal of Cr(VI) onto Fe-modified magnetic biochars and will benefit future design of more efficient magnetic biochars.