No abstract

Electrocatalytic reduction has recently received increasing attention as a method of converting waste nitrate into value-added ammonia, but most studies have focused on complex strategies of catalyst preparation and little has been done in the way of large-scale demonstrations. Herein, we report that in situ activation of a pristine Ni electrode, either on a lab scale or a pilot scale, is effective in facilitating nitrate reduction to ammonia, exhibiting extraordinarily high activity, selectivity, and stability. The self-activated Ni cathode has a robust capacity to reduce nitrate over a wide range of concentrations and achieves great conversion yield, NH4 +–N selectivity, and Faradaic efficiency, respectively, 95.3, 95.5, and 64.4% at 200 mg L–1 NO3 ––N and 97.8, 97.1, and 90.4% at 2000 mg L–1 NO3 ––N, for example. Fundamental research indicates that Ni­(OH)2 nanoparticles are formed on the Ni electrode surface upon self-activation, which play crucial roles in governing nitrate reduction reaction (NO3RR) through the atomic H*-mediated pathway and accordingly suppressing hydrogen evolution reaction. More importantly, the self-activated Ni­(OH)2@Ni cathode can be easily scaled up to allow large volumes of real industrial wastewater to be processed, successfully transferring nitrate into ammonia with high yields and Faradaic efficiency. This study demonstrates a new, mild, and promising method of cleaning nitrate-laden wastewater that produces ammonia as a valuable byproduct.

Inorganic constituents in real wastewater, such as halides and carbonates/bicarbonates, may have negative effects on the performance of electrochemical systems because of their capability of quenching HO • . However, we discovered that the presence of Cl − and HCO 3 − in an electrochemical system is conducive to the formation of ClO • , which plays an important role in promoting the simultaneous elimination of biorefractory organics and nitrogen in secondary coking wastewater effluent. The 6-h operation of the coupled electrochemical system (an undivided electrolytic cell with a PbO 2 /Ti anode and a Cu/Zn cathode) at a current density of 37.5 mA cm −2 allowed the removal of 87.8% of chemical oxygen demand (COD) and 86.5% of total nitrogen. The electron paramagnetic resonance results suggested the formation of ClO • in the system, and the probe experiments confirmed the predominance of ClO • , whose steady-state concentrations (8.08 × 10 −13 M) were 16.4, 26.5, and 1609.5 times those of Cl 2•− (4.92 × 10 −14 M), HO • (3.05 × 10 −14 M), and Cl • (5.02 × 10 −16 M), respectively. The rate constant of COD removal and the Faradaic efficiency of anodic oxidation obtained with Cl − and HCO 3 − was linearly proportional to the natural logarithm of the ClO • concentration, and the specific energy consumption was inversely correlated to it, demonstrating the crucial role of ClO • in pollutant removal.

No abstract

N,S dual-doped graphene-like carbons synthesized from coke wastewater sludge flocs exhibit ultrahigh capacitance and outstanding oxygen reduction performance.