The high salinity and coexistence of scaling ions (Ca2+, Mg2+, HCO3-) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl- poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L - 1) with Ca2+ (80.0 mg L - 1), Mg2+ (30.0 mg L - 1) and HCO3- (180.0 mg L - 1), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl- poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl- at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pdδ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.
Keywords: Catalyst poisoning; Chlorinated organic pollutant; Electrocatalysis; Hydrodechlorination; Scaling.
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