Degradation of N,N-diethyl-m-toluamid (DEET) on lead dioxide electrodes in different environmental aqueous matrixes.

This study investigates the electrochemical degradation of N,N-diethyl-m-toluamide (DEET) on PbO2 and Bi-PbO2 anodes. The difference in electrode crystalline structure was responsible for the better DEET degradation and TOC removal on PbO2 than on Bi-PbO2. In 1 M Na2SO4, the degradation efficiency and apparent rate constant (kapp) of DEET oxidation on PbO2 increased with the increase in current density or temperature (activation energy=24.4 kJ mol(-1)). The kapp values in DEET-spiked environmental matrixes (municipal wastewater treatment plant secondary effluent (MWTPSE), groundwater (GW), and river water (RW)) were the same (6.05×10(-4) s(-1)), but significantly smaller than that in 1 M Na2SO4 (2.23×10(-3) s(-1)). The TOC removal efficiency was better in MWTPSE than in RW and GW; however, the mineralization current efficiencies in MWTPSE and RW were similar but higher than that in GW. During electrolysis, the aromaticity was lower in GW than in RW.

Electro-regeneration of Ce(IV) in real spent Cr-etching solutions.

This paper presents the electro-regeneration of Ce(IV) in real (hazardous) spent thin-film transistor liquid-crystal display (TFT-LCD) Cr-etching solutions. In addition to Ce(III)>Ce(IV) in diffusivity, a quasi-reversible behavior of Ce(III)/Ce(IV) was observed at both boron-doped diamond (BDD) and Pt disk electrodes. The Ce(IV) yield on Pt increased with increasing current density, and the best current efficiency (CE) was obtained at 2A/2.25 cm(2). The performance in terms of Ce(IV) yield and CE of tested anodes was in order BDD>Pt>dimensional stable anode (DSA). At 2A/2.25 cm(2) on Pt and 40 °C for 90 min, the Ce(IV) yield, CE and apparent rate constant (k) for Ce(III) oxidation were 81.4%, 21.8% and 3.17 × 10(-4) s(-1), respectively. With the increase of temperature, the Ce(IV) yield, CE, and k increased (activation energy = 10.7 kJ/mol), but the specific electricity consumption decreased. The Neosepta CMX membrane was more suitable than Nafion-117 and Nafion-212 to be used as the separator of the Ce(IV) regeneration process. The obtained parameters are useful to design divided batch reactors for the Ce(IV) electro-regeneration in real spent Cr-etching solutions.

An electrochemical approach to simultaneous determination of acetaminophen and ofloxacin.

This study presents a simple electrochemical approach for preparing a poly(L-serine) film-modified glassy carbon electrode, which responds quickly and sensitively during the simultaneous determination of acetaminophen and ofloxacin in prepared, environmental, and pharmaceutical samples. The prepared electrode exhibited catalytic activities and promoted the oxidation of acetaminophen and ofloxacin. Acetaminophen and ofloxacin showed linear responses between 1.0 × 10(-5) and 1.0 × 10(-4) mol/L and their limits of detection were 1.2 × 10(-7) and 1.6 × 10(-7) mol/L, respectively. The average recoveries (± relative standard deviations) of acetaminophen and ofloxacin were 96.8 ± 3.5 % and 97.6 ± 3.2 %, respectively, indicating that the prepared electrode and detection method are very accurate and reproducible for the simultaneous determination of acetaminophen and ofloxacin.

Effects of NH4⁺ on Ce(IV) electro-regeneration in simulated and real spent TFT-LCD Cr-etching solutions.

This investigation studies the electro-regeneration of Ce(IV) from Ce(III) in 4 M HNO(3) in the presence/absence of NH(4)(+) and real spent thin-film transistor liquid-crystal display (TFT-LCD) Cr-etching solutions. On Pt, at 2 A and 70 °C for 100 min, the Ce(IV) yield and apparent rate constant of Ce(III) oxidation in 4 M HNO(3) without NH(4)(+) were 100% and 5.54 × 10(-4) s(-1), respectively (and the activation energy was 13.1 kJ mol(-1)). Cyclic voltammetric and electrolytic measurements consistently support the noticeable inhibition by NH(4)(+) of Ce(III) oxidation and lowering of the Ce(IV) yield, respectively. The apparent diffusion coefficients for 0.2 and 0.02 M Ce(III) oxidation in 4 M HNO(3) that contained 0-0.6 M NH(4)(+) were (0.38-0.25) × 10(-5) and (1.6-0.9) × 10(-5) cm(2) s(-1), respectively. Because of combined effects of NH(4)(+) and anion impurities, the 100 min Ce(IV) yield of a real spent TFT-LCD Cr-etching solution (with [NH(4)(+)]/[Ce(III)] = 0.74 M/0.39 M) was 82%, lower than that of 4 M HNO(3) without NH(4)(+), but higher than those of 4 M HNO(3) that contained anion impurities with/without 0.4 M NH(4)(+).

High estrogen concentrations in receiving river discharge from a concentrated livestock feedlot.

Environmental estrogenic chemicals interrupt endocrine systems and generate reproductive abnormalities in wildlife, especially natural and synthetic estrogenic steroid hormones such as 17beta-estradiol (E2), estrone (E1), estriol (E3), 17alpha-ethynylestradiol (EE2), and diethylstilbestrol (DES). Concentrated animal feedlot operations (CAFOs) are of particular concern since large amounts of naturally excreted estrogens are discharged into aquatic environments. This study investigated E2, E1, E3, EE2, and DES with high performance liquid chromatography/tandem mass (HPLC-MS/MS) analyses along Wulo Creek in southern Taiwan, near a concentrated livestock feedlot containing 1,030,000 broiler chickens, 934,000 laying hens, 85,000 pigs, and 1500 cattle. Sampling was performed from December 2008 to May 2009, in which 54 samples were collected. Experimental results indicate that concentrations of EE2 were lower than the limit of detection (LOD), and concentrations of DES were only detected twice. Concentrations ranged from 7.4 to 1267 ng/L for E1, from not detected (ND) to 313.6 ng/L for E2, and from ND to 210 ng/L for E3. E1 had the highest average mass fraction (72.2 + or - 3.6%), which was significantly higher than E3 (16.2 + or - 1.7%) and E2 (11.5 + or - 2.6%). Additionally, the mean E2 equivalent quotient (EEQ) ranged from 17.3 to 137.9 ng-E2/L. Despite having a markedly lower concentration than E1, E2 more significantly contributed (52.4 + or - 6.0%) EEQ than E1 (19.7 + or - 3.5%). Moreover, the concentrations of E2, E1, and E3 upstream were significantly higher than concentrations downstream, suggesting a high attenuation effect and fast degradation in the study water. Most concentrations in winter season were higher than those of spring season due to the low dilution effect and low microbial activity in the winter season. Based on the results of this study, we recommend further treatment of the wastewater discharge from the feedlot.

Regeneration of Ce(IV) in simulated spent Cr-etching solutions using an undivided cell.

This study investigated regeneration of Ce(IV) from Ce(III) oxidation at 0.05-0.5Acm(-2) in 4M HNO(3) with/without anion impurities (SO(4)(2-) (0.01-0.2M), Cl(-) (0.01-0.08M), and/or Cr(2)O(7)(2-) (0.005-0.016M)) in an undivided cell. Both Ce(IV) yield and current efficiency (CE) were significantly lower in 0.1M than in 1-4M HNO(3) and different on anode materials (in order Pt>IrO(2)/Ti>glassy carbon). The apparent rate constants for Ce(III) oxidation on the Pt anode (k(1)) and for Ce(IV) reduction on a stainless steel cathode (k(2)) were (0.40-1.80)x10(-4) and (0.08-1.01)x10(-4)s(-1), respectively, corresponding to the apparent mass transfer coefficients of (2.0-9.0)x10(-3) and (0.4-5.1)x10(-3)cms(-1), respectively. For Ce(III) oxidation at 0.3Acm(-2) in 4M HNO(3) containing multi-impurity (0.025M SO(4)(2-)+0.08M Cl(-)+0.016M Cr(2)O(7)(2-)), the k(1) was lowered by one order of magnitude although the k(2) remained unchanged, and both Ce(IV) yield and CE were reduced by approximately 89%. The decrease of Ce(IV) yield and CE by the uni-impurity was in order Cl(-)>Cr(2)O(7)(2-)>SO(4)(2-). The obtained parameters are useful to design undivided batch reactors for the Ce(IV) electro-regeneration in spent Cr-etching solutions.

Anion effects on the electrochemical regeneration of Ce(IV) in nitric acid used for etching chromium.

The anion impurities such as SO4(2-), Cl(-), and Cr2O7(2-) commonly present in the spent (hazardous) Cr-etch solutions from color filter manufacturing processes may influence the solutions' regeneration by the electrooxidation of Ce(III) to Ce(IV). This study, therefore, investigated the effects of these anions on Ce(III)/Ce(IV) redox reactions at glassy carbon in HNO3. In cyclic voltammetric tests, the presence of SO4(2-) decreased the formal potential but increased the peak potential separation (Delta Ep) of Ce(III)/Ce(IV) couple, and lowered the peak current for Ce(IV) reduction whereas Cl(-) did not change the formal potential and Delta Ep, but the peaks for Cl(-) and Ce(III) oxidation partially overlapped. Cr2O7(2-) slightly lowered the peak current for Ce(III) oxidation but significantly decreased that for Ce(IV) reduction. The Tafel slope for Ce(III) oxidation was approximately 65mVdecade(-1) in the absence of anion impurities. Increasing SO4(2-), Cl(-), or Cr2O7(2-) in solution raised the Tafel slope. The Ce(III)/Ce(IV) equilibrium potential decreased with the increase of SO4(2-) or Cl(-) but was hardly influenced by Cr2O7(2-) addition. These observations from individual anion species together well explained the anions' co-effect (kinetic hindrance) on the Ce(III) oxidation in HNO3, revealing that these anions are unfavorable for the electrooxidation of Ce(III) in the spent Cr-etch solutions.