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This research investigated the effects of surface fluorination on both rates of organic compound oxidation (phenol and terephthalic acid (TA)) and ClO4–formation at boron-doped diamond (BDD) film anodes at 22 °C. Different fluorination methods (i.e., electrochemical oxidation with perfluorooctanoic acid (PFOA), radio frequency plasma, and silanization) were used to incorporate fluorinated moieties on the BDD surface, which was confirmed by X-ray photoelectron spectroscopy (XPS). The silanization method was found to be the most effective fluorination method using a 1H,1H,2H,2H-perfluorodecyltrichlorosilane precursor to form a self-assembled monolayer (SAM) on the oxygenated BDD surface. The ClO4–formation decreased from rates of 0.45 ± 0.03 mmol m–2min–1during 1 mM NaClO3oxidation and 0.28 ± 0.01 mmol m–2min–1during 10 mM NaCl oxidation on the BDD electrode to below detectable levels (<0.12 μmoles m–2min–1) for the BDD electrode functionalized by a 1H,1H,2H,2H-perfluorodecyltrichlorosilane SAM. These decreases in rates corresponded to 99.94 and 99.85% decreases in selectivity for ClO4–formation during the electrolysis of 10 mM NaCl and 1 mM NaClO3electrolytes, respectively. By contrast, the oxidation rates of phenol were reduced by only 16.3% in the NaCl electrolyte and 61% in a nonreactive 0.1 M KH2PO4electrolyte. Cyclic voltammetry with Fe(CN)63–/4–and Fe3+/2+redox couples indicated that the long fluorinated chains created a blocking layer on the BDD surface that inhibited charge transfer via steric hindrance and hydrophobic effects. The surface coverages and thicknesses of the fluorinated films controlled the charge transfer rates, which was confirmed by estimates of film thicknesses using XPS and density functional theory simulations. The aliphatic silanized electrode also showed very high stability during OH•production. Perchlorate formation rates were below the detection limit (<0.12 μmoles m–2min–1) for up to 10 consecutive NaClO3oxidation experiments.

This research focused on improving mineralization rates during the advanced electrochemical oxidation treatment of agricultural water contaminants. For the first time, bismuth-doped tin oxide (BDTO) catalysts were deposited on Magnéli phase (TinO2n–1, n= 4–6) reactive electrochemical membranes (REMs). Terephthalic acid (TA) was used as a OH•probe, whereas atrazine (ATZ) and clothianidin (CDN) were chosen as model agricultural water contaminants. The BDTO-deposited REMs (REM/BDTO) showed higher compound removal than the REM, due to enhanced OH•production. At 3.5 V/SHE, complete mineralization of TA, ATZ, and CDN was achieved for the REM/BDTO upon a single pass in the reactor (residence time ∼3.6 s). Energy consumption for REM/BDTO was as much as 31-fold lower than the REM, with minimal values per log removal of <0.53 kWh m–3for TA (3.5 V/SHE), <0.42 kWh m–3for ATZ (3.0 V/SHE), and 0.83 kWh m–3for CDN (3.0 V/SHE). Density functional theory simulations provided potential dependent activation energy profiles for ATZ, CDN, and various oxidation products. Efficient mass transfer and a reaction mechanism involving direct electron transfer and reaction with OH•were responsible for the rapid and complete mineralization of ATZ and CDN at very short residence times.

This research focused on synthesis, characterization, and application of point-of-use catalytic reactive electrochemical membranes (REMs) for electrocatalytic NO3–reduction. Deposition of Pd–Cu and Pd–In catalysts to the REMs produced catalytic REMs (i.e., Pd–Cu/REM and Pd–In/REM) that were active for NO3–reduction. Optimal performance was achieved with a Pd–Cu/REM and upstream counter electrode, which reduced NO3–from 1.0 mM to below the EPAs regulatory MCL (700 μM) in a single pass through the REM (residence time ∼2 s), obtaining product selectivity of <2% toward NO2–/NH3. Nitrate reduction was not affected by dissolved oxygen and carbonate species and only slightly decreased in a surface water sample due to Ca2+and Mg2+scaling. Energy consumption to treat surface water was 1.1 to 1.3 kWh mol–1for 1 mM NO3–concentrations, and decreased to 0.19 and 0.12 kWh mol–1for 10 and 100 mM NaNO3solutions, respectively. Electrocatalytic reduction kinetics were shown to be an order of magnitude higher than catalytic NO3–reduction kinetics. Conversion of up to 67% of NO3–, with low NO2–(0.7—11 μM) and NH3formation (<10 μM), and low energy consumption obtained in this study suggest that Pd–Cu/REMs are a promising technology for distributed water treatment.

The low average Martian (left to right) figure 2B and 2c. The Martian brine electrolyser: (b) the assembled lab-scale electrolyser with 5 cm 2 active area; and (c) components of the electrolyser MEMBRANE ELECTRODE ASSEMBLY (MEA) TITANIUM FLOW FIELD END PLATE CURRENT COLLECTOR POWER LEADS FLOW INLET/ OUTLET GRAPHITE FLOW FIELD figure 2A: The Martian brine electrolyser. Feature chemeng on mars MARCH 2021 | The Chemical Engineer | page 22 Shrihari Sankarasubramanian, Pralay Gayen and Vijay K Ramani discuss work on methods to make fuel and oxygen on the red planet M ARS, the fourth planet from the Sun, has been an object of fascination for millennia. Schematic and electrochemical reactions at both electrodes E 0,cell = 1.23V H 2 + 2OH - <=> 2H 2 O+2e E 0,cathode = 0.83V vs SHE 1/2O 2 + H 2 O+2e <=> 2OH E 0,anode = 0.40V vs SHE CATHODE FLOW FIELD OH - OH OH OH OH OH OH OH H 2 O H 2 O H 2 O H 2 O OH OH OH 2e 2e ANODE SEPARATOR mars DGv2.indd 24 18/02/2021 15:28 MARCH 2021 | The Chemical Engineer | page 25 feature chemeng on mars terrestrial temperatures (-36ºC) were achieved and maintained by immersing a vessel with 2.8 M Mg(ClO 4) 2 solution (simulated Martian regolithic brine, SMRB, in a dry-ice bath with an ethylene glycol and ethanol mixture. [Extracted from the article]