Protective coatings on iron by anodic oxidation of phenols in oxalic acid medium

Crossflow electrochemical filtration for elimination of ibuprofen and bisphenol a from pure and competing electrolytic solution conditions

For the first time, a crossflow electrochemical filtration system containing multiwalled carbon nanotubes (MWNTs) blended with buckypaper as a flat sheet dual membrane electrode was investigated for the removal of two contaminants of emerging concern, Ibuprofen and Bisphenol A. Breakthrough experiments revealed that a crossflow configuration could be highly efficient in eliminating both contaminants at applied DC potentials of 2 and 3 V over an extended period, from pure salt electrolyte as well as from synthetic secondary wastewater effluent. The shear flow provided consistent surface coverage resulting in excellent sorption performance. The long residence time of the two contaminants within the membrane (18.3 s) was sufficient enough to allow for almost complete degradation of phenolic aromatic products and quinoid rings and the resulting formation of aliphatic carboxylic acids, which was more evident at a higher applied potential (3 V). The formation of the non-toxic aliphatic carboxylic acids is a clear indication of the superior electrochemical performance of the crossflow mode over the dead-end flow-through system. Moreover, this study provides an in-depth understanding of different factors such as filter surface area and residence time that can greatly affect the removal of the contaminants considered.

Doped carbon nanotube networks for electrochemical filtration of aqueous phenol: electrolyte precipitation and phenol polymerization

Electrochemical filtration with anodic carbon nanotube (CNT) networks is reported to be effective for chemical and microbiological water treatment. Here, we investigate how CNT doping affects the electrochemical filtration performance toward the remediation of aromatic wastewaters. Purified and well-characterized undoped (C-CNT), boron-doped (B-CNT), and nitrogen-doped (N-CNT) anodic carbon nanotube networks are challenged with aqueous phenol in a sodium sulfate electrolyte. Steady-state current and effluent total organic carbon (TOC) measurements are utilized to evaluate the oxidative performance as a function of voltage and electrolysis time. In terms of steady-state TOC removal, at an applied voltage of 3 V all three anodic CNT networks are able to remove approximately 7 to 8 mgC L(-1) of the influent TOC within the ~1 s liquid residence time of the electrochemical filter. The anodic CNT networks are partially passivated over the 5 h electrolysis time with the B-CNT network displaying the least passivation. The extent of passivation was observed to be inversely correlated to the CNT work function. SEM, XPS, and TGA of the electrolyzed CNT networks are used to identify the two primary passivation mechanisms of electrochemical phenols polymerization and electrochemical electrolyte precipitation. In agreement with chronoamperometry results, the B-CNT network has the lowest extent of passivating polymer and precipitate formation. The precipitant is determined to likely be sodium persulfate or carbonate and is removed with a simple acidic water wash. The polymer is determined to likely be polyphenylene oxide and is partially removed with the wash. All three anodic CNT networks display potential for energy efficient electrochemical filtration of aromatic wastewaters and the B-CNT are determined to be the most resistant to passivation.

Reaction pathways and mechanisms of the electrochemical degradation of phenol on different electrodes

Laboratory experiments were carried out on the kinetics and pathways of the electrochemical (EC) degradation of phenol at three different types of anodes, Ti/SnO2-Sb, Ti/RuO2, and Pt. Although phenol was oxidised by all of the anodes at a current density of 20 mA/cm2 or a cell voltage of 4.6 V, there was a considerable difference between the three anode types in the effectiveness and performance of EC organic degradation. Phenol was readily mineralized at the Ti/SnO2-Sb anode, but its degradation was much slower at the Ti/RuO2 and Pt anodes. The analytical results of high-performance liquid chromatography (HPLC) and gas chromatography coupled with mass spectrometry (GC/MS) indicated that the intermediate products of EC phenol degradation, including benzoquinone and organic acids, were subsequently oxidised rapidly by the Ti/SnO2-Sb anode, but accumulated in the cells of Ti/RuO2 and Pt. There was also a formation of dark-coloured polymeric compounds and precipitates in the solutions electrolyzed by the Ti/RuO2 and Pt anodes, which was not observed for the Ti/SnO2-Sb cells. It is argued that anodic property not only affects the reaction kinetics of various steps of EC organic oxidation, but also alters the pathway of phenol electrolysis. Favourable surface treatment, such as the SnO2-Sb coating, provides the anode with an apparent catalytic function for rapid organic oxidation that is probably brought about by hydroxyl radicals generated from anodic water electrolysis.

Electrochemically mediated electrodeposition/electropolymerization to yield a glucose microbiosensor with improved characteristics

A procedure is described that provides for electrochemically mediated deposition of enzyme and a polymer layer permselective for endogenous electroactive species. Electrodeposition was first employed for the direct immobilization of glucose oxidase to produce a uniform, thin, and compact film on a Pt electrode. Electropolymerization of phenol was then employed to form an anti-interference and protective polyphenol film within the enzyme layer. In addition, a stability-reinforcing membrane derived from (3-aminopropyl)trimethoxysilane was constructed by electrochemically assisted cross-linking. This hybrid film outside the enzyme layer contributed to the improved stability and permselectivity. The resulting glucose sensor was characterized by a short response time (<4 s), high sensitivity (1200 nA/mM x cm2), low interference from endogenous electroactive species, and working lifetime of more than 50 days.