3D hierarchically porous NiO/NF electrode for the removal of chromium(VI) from wastewater by electrocoagulation

3D hierarchically porous NiO/NF (Ni foam) was synthesized by a facile hydrothermal method and a subsequent annealing process in different atmospheres for the simultaneous Cr(VI) removal and hydrogen generation from wastewater by the electrocoagulation method. O-2 atmosphere for annealing increased the Ni3+ content in NiO, thus led to an enhanced electrostatic interaction with Cr(VI)/OH- anions and subsequently increased the Cr(VI) adsorption and Ni hydroxide flocculant production. Thus, the NiO-O-2/NF electrode exhibited the best Cr(VI) removal performance of 99.5% within 20 min at the applied potential of 0.97 V vs. RHE, along with a hydrogen generation rate of 1.1 mmol g(-1) h(-1). The removal mechanism was suggested, including the reduction of Cr(VI) to Cr(III), direct complexation reactions with the freshly produced amorphous Ni hydroxides, and adsorption on NiO-X/NF electrodes.