Nitrate reduction to nitrogen in wastewater using mesoporous carbon encapsulated Pd-Cu nanoparticles combined with in-situ electrochemical hydrogen evolution.

ABSTRACT

The conversion of NO3--N to N2 is of great significance for zero discharge of industrial wastewater. Pd-Cu hydrogenation catalysis has high application prospects for the reduction of NO3--N to N2, but the existing form of Pd-Cu, the Pd-Cu mass ratio and the H2 evolution rate can affect the coverage of active hydrogen (*H) on the surface of Pd, thereby affecting N2 selectivity. In this work, mesoporous carbon (MC) is used as support to disperse Pd-Cu catalyst and is applied in an in-situ electrocatalytic H2 evolution system for NO3--N removal. The Pd-Cu particles with the average size of 6 nm are uniformly encapsulated in the mesopores of MC. Electrochemical in-situ H2 evolution can not only reduce the amount of H2 used, but the H2 bubbles can also be efficiently dispersed when PPy coated nickel foam (PPy/NF) is used as cathode. Moreover, the mesoporous structure of MC can further split H2 bubbles, reducing the coverage of *H on Pd. The highest 77% N2 selectivity and a relatively faster NO3--N removal rate constant (0.10362 min-1) can be achieved under the optimal conditions, which is superior to most reported Pd-Cu catalytic systems. The prepared catalyst is further applied to the denitrification of actual deplating wastewater. NO3--N with the initial concentration of 650 mg L-1 can be completely removed after 180 min of treatment, and the TN removal can be maintained at 72%.