Mechanism of p-substituted phenol oxidation at a Ti4O7 reactive electrochemical membrane.
This research investigated the removal mechanisms of p-nitrophenol, p-methoxyphenol, and p-benzoquinone at a porous Ti4O7 reactive electrochemical membrane (REM) under anodic polarization. Cross-flow filtration experiments and density functional theory (DFT) calculations indicated that p-benzoquinone removal was primarily due to reaction with electrochemically formed OH(•), while the dominant removal mechanism of p-nitrophenol and p-methoxyphenol was a function of the anodic potential. At low anodic potentials (1.7-1.8 V/SHE), p-nitrophenol and p-methoxyphenol were removed primarily by an electrochemical adsorption/polymerization mechanism on the REM. Increasing anodic potentials (1.9-3.2 V/SHE) resulted in the electroassisted adsorption mechanism contributing far less to p-methoxyphenol removal compared to p-nitrophenol. DFT calculations indicated that an increase in anodic potential resulted in a shift in p-methoxyphenol removal from a 1e(-) direct electron transfer (DET) reaction that resulted in radical formation and significant adsorption/polymerization, to a 2e(-) DET reaction that formed nonadsorbing products (i.e., p-benzoquinone). However, the anodic potentials were too low for the 2e(-) DET reaction to be thermodynamically favorable for p-nitrophenol. The decreased COD adsorption for p-nitrophenol at higher anodic potentials was attributed to reaction of soluble/adsorbed organics with OH(•). These results provide the first mechanistic explanation for p-substituted phenolic compound removal during advanced electrochemical oxidation processes.
Department of Chemical Engineering, University of Illinois at Chicago , 810 South Clinton Avenue, Chicago, Illinois 60607, United States.
Amr M
AM
Zaky
Brian P
BP
Chaplin
D000327:Adsorption; D000840:Anisoles / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry; D057919:Biological Oxygen Demand Analysis; D004563:Electrochemistry; D008567:Membranes, Artificial; D008956:Models, Chemical; D008968:Molecular Conformation; D009596:Nitrophenols / Q000737:chemistry; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D016062:Porosity; D011789:Quantum Theory; D013816:Thermodynamics; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*
D000840:Anisoles; D016227:Benzoquinones; D008567:Membranes, Artificial; D009596:Nitrophenols; D010636:Phenols; C004532:quinone; C009760:mequinol; D014025:Titanium; C024836:4-nitrophenol