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Simultaneous Adsorption and Electrochemical Reduction of N-Nitrosodimethylamine Using Carbon-Ti₄O₇ Composite Reactive Electrochemical Membranes

Almassi, Soroush, Li, Zhao, Xu, Wenqing, Pu, Changcheng, Zeng, Teng, Chaplin, Brian P.
Environmental science & technology 2018 v.53 no.2 pp. 928-937
N-nitrosodimethylamine, adsorption, carbon, carbon nanotubes, density functional theory, electrochemistry, electron transfer, liquids, reaction mechanisms, surface water
This study focused on synthesis and characterization of Ti₄O₇ reactive electrochemical membranes (REMs) amended with powder-activated carbon (PAC) or multiwalled carbon nanotubes (MWCNTs). These composite REMs were evaluated for simultaneous adsorption and electrochemical reduction of N-nitrosodimethylamine (NDMA). The carbon-Ti₄O₇ composite REMs had high electrical conductivities (1832 to 2991 S m–¹), where carbon and Ti₄O₇ were in direct electrical contact. Addition of carbonaceous materials increased the residence times of NDMA in the REMs by a factor of 3.8 to 5.4 and therefore allowed for significant electrochemical NDMA reduction. The treatment of synthetic solutions containing 10 μM NDMA achieved >4-log NDMA removal in a single pass (liquid residence time of 11 to 22 s) through the PAC-REM and MWCNT-REM with the application of a −1.1 V/SHE cathodic potential, with permeate concentrations between 18 and 80 ng L–¹. The treatment of a 6.7 nM NDMA-spiked surface water sample, under similar operating conditions (liquid residence time of 22 s), achieved 92 to 97% removal with permeate concentrations between 16 and 40 ng L–¹. Density functional theory calculations determined a probable reaction mechanism for NDMA reduction, where the rate-limiting step was a direct electron transfer reaction.