Sustainable electro-Fenton simultaneous reduction of Cr (VI) and degradation of organic pollutants via dual-site porous carbon cathode driving uncoordinated molybdenum sites conversion.

Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable "iron-free" EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS2 nanoarray promoter (MoS2 NA). The NPC-D/MoS2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis.

Integrating anodic sulfate activation with cathodic H2O2 production/activation to generate the sulfate and hydroxyl radicals for the degradation of emerging organic contaminants.

Conventional electrocatalytic degradation of pollutants involves either cathodic reduction or anodic oxidation process, which caused the low energy utilization efficiency. In this study, we successfully couple the anodic activation of sulfates with the cathodic H2O2 production/activation to boost the generation of sulfate radical (SO4·-) and hydroxyl radical (·OH) for the efficient degradation of emerging contaminants. The electrocatalysis reactor is composed of a modified-graphite-felt (GF) cathode, in-situ prepared by the carbonization of polyaniline (PANI) electrodeposited on a GF substrate, and a boron-doped diamond (BDD) anode. In the presence of sulfates, the electrocatalysis system shows superior activities towards the degradation of pharmaceutical and personal care products (PPCPs), with the optimal performance of completely degrading the representative pollutant carbamazepine (CBZ, 0.2 mg L-1) within 150 s. Radicals quenching experiments indicated that ·OH and SO4·- act as the main reactive oxygen species for CBZ decomposition. Results from the electron paramagnetic resonance (EPR) and chronoamperometry studies verified that the sulfate ions were oxidized to SO4·-radicals at the anode, while the dissolve oxygen molecules were reduced to H2O2 molecules which were further activated to produce ·OH radicals at the cathode. It was also found that during the catalytic reactions SO4·-radicals could spontaneously convert into peroxydisulfate (PDS) which were subsequently reduced back to SO4·-at the cathodes. The quasi-steady-state concentrations of ·OH and SO4·-were estimated to be 0.51×10-12 M and 0.56×10-12 M, respectively. This study provides insight into the synergistic generation of ·OH/SO4·- from the integrated electrochemical anode oxidation of sulfate and cathode reduction of dissolved oxygen, which indicates a potential practical approach to efficiently degrade the emerging organic water contaminants.

A three-dimensional Cu nanobelt cathode for highly efficient electrocatalytic nitrate reduction.

Water treatment techniques for destructive removal of nitrates by reducing them to harmless N2 have recently begun to emerge. In this study, we present a novel three-dimensional (3D) Cu nanobelt cathode for efficient electrochemical nitrate reduction. Upon an applied potential of -1.4 V vs. Ag/AgCl, the removal efficiency of nitrates by the 3D Cu nanobelt electrode reaches 100% at 60 min, compared to 2.6% for the Cu foam electrode under the same conditions. Based on the mass balance on nitrogen atoms, the major product is determined to be ammonia. In the simulated wastewater containing NaCl, the as-generated ammonia ions are simultaneously oxidized into harmless N2 by the in situ generated ClO- ions from the Pt anode, resulting in the complete removal of inorganic nitrogen (nitrate, nitride and ammonia) from wastewater. The mechanism for the improvement of electrocatalytic activity is systematically investigated. Firstly, the large surface area of the 3D Cu nanobelt electrode facilitates the mass transfer of nitrates, resulting in accelerated electrochemical kinetics. Secondly, linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) measurements confirm that the 3D Cu nanobelt electrode exhibits improved charge transfer ability. Also, further investigations demonstrate that the 3D Cu nanobelt electrode preferentially reacts with nitrates, compared to the pristine Cu foam electrode readily reacting with the dissolved oxygen (DO) to generate H2O2. This study might expand the prospects of electrocatalytic techniques towards the destructive removal of inorganic nitrogen pollutants in wastewater.