Kinetics of Photoelectrocatalytic Degradation of Nitrophenols on Nanostructured TiO₂ Electrodes

Abstract

In the present work, titanium oxide (TiO2) nanotubes were directly grown by the electrochemical oxidation of titanium substrates at 20 V in a nonaqueous electrolyte (DMSO/HF). The morphology and microstructure of the synthesized TiO2 photocatalysts were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The kinetically photoelectrochemical degradation of 2-nitrophenol (2-NPh) and 4-nitrophenol (4-NPh) at the TiO2 nanotubes was examined, individually and when they were mixed together. It was found that the photoelectrochemical degradation of 2-NPh is faster than that of 4-NPh. In order to determine the kinetic behavior of 2-NPh and 4-NPh in the course of the photoelectrocatalytic oxidation of their mixtures, an experimental design with 36 samples and a test set with 6 samples were used to build up a partial least-squares (PLS) model. The degradation of both 4-NPh and 2-NPh became slower in the binary mixture compared with the individual degradation rates of the 4-NPh and 2-NPh. The present work has demonstrated that UV−vis spectroscopy coupled with PLS calibration can be used to in situ monitor the concentration changes, providing a novel approach to determine the competitive effects of different organic pollutants during water purification and wastewater treatment.

Unraveling Kinetic Effects during Photoelectrochemical Mineralization of Phenols. Rutile:Anatase TiO2 Nanotube Photoanodes under Thin-Layer Conditions

“…In order to compare the kinetic performance of these systems, the maximum values for the heterogeneous rate constants, k h = k obs max ( V / A ) = kK ( V / A ), were estimated and are also reported in Table . The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 –2 cm s –1 ) with the values reported for similar systems such as o -nitrophenol (1.39 × 10 –2 cm s –1 ) and PNP (0.79 × 10 –2 cm s –1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm –2 . In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 –2 cm s –1 and 3.02 × 10 –2 cm s –1 , respectively.…”

“…The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 −2 cm s −1 ) with the values reported for similar systems such as o-nitrophenol (1.39 × 10 −2 cm s −1 ) and PNP (0.79 × 10 −2 cm s −1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm −2 . 34 In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 −2 cm s −1 and 3.02 × 10 −2 cm s −1 , respectively. In any case, the maximum observed kinetic constants k obs = kK and the k h values for the oxidation of the two phenols on the three electrodes are also shown in Table 2.…”

Unraveling Kinetic Effects during Photoelectrochemical Mineralization of Phenols. Rutile:Anatase TiO2 Nanotube Photoanodes under Thin-Layer Conditions

“…In order to compare the kinetic performance of these systems, the maximum values for the heterogeneous rate constants, k h = k obs max ( V / A ) = kK ( V / A ), were estimated and are also reported in Table . The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 –2 cm s –1 ) with the values reported for similar systems such as o -nitrophenol (1.39 × 10 –2 cm s –1 ) and PNP (0.79 × 10 –2 cm s –1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm –2 . In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 –2 cm s –1 and 3.02 × 10 –2 cm s –1 , respectively.…”

“…The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 −2 cm s −1 ) with the values reported for similar systems such as o-nitrophenol (1.39 × 10 −2 cm s −1 ) and PNP (0.79 × 10 −2 cm s −1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm −2 . 34 In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 −2 cm s −1 and 3.02 × 10 −2 cm s −1 , respectively. In any case, the maximum observed kinetic constants k obs = kK and the k h values for the oxidation of the two phenols on the three electrodes are also shown in Table 2.…”

Characterization and Mechanism of the Photoelectrocatalytic Oxidation of Organic Pollutants in a Thin-Layer Reactor

“…exponential fitting parameters and t represents the reaction time. We found that for all concentrations of BPA, I net -t fits a first-order exponential decay model with correlation coefficients ranging from 0.9629 to 0.9935, which is in good agreement with the concentration decay kinetics obtained using the traditional method [28]. These results confirm the validity of Eq.…”

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams

“…Interestingly, the electrochemical performances of gCN air towards KHP degradation were preserved upon repeating the same experiment after three months, highlighting a good material stability. The experimental trend in Figure 6 b, in agreement with a pseudo-first order kinetics [ 56 ], could be fitted with either a single or a double exponential function. The obtainment of a better match with experimental results in the latter case (see the corresponding χ 2 value in Figure 6 b) indicates that two distinct processes, i.e., adsorption and decomposition, take place simultaneously on the material surface.…”

Unraveling Kinetic Effects during Photoelectrochemical Mineralization of Phenols. Rutile:Anatase TiO2 Nanotube Photoanodes under Thin-Layer Conditions

“…In order to compare the kinetic performance of these systems, the maximum values for the heterogeneous rate constants, k h = k obs max ( V / A ) = kK ( V / A ), were estimated and are also reported in Table . The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 –2 cm s –1 ) with the values reported for similar systems such as o -nitrophenol (1.39 × 10 –2 cm s –1 ) and PNP (0.79 × 10 –2 cm s –1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm –2 . In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 –2 cm s –1 and 3.02 × 10 –2 cm s –1 , respectively.…”

“…The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 −2 cm s −1 ) with the values reported for similar systems such as o-nitrophenol (1.39 × 10 −2 cm s −1 ) and PNP (0.79 × 10 −2 cm s −1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm −2 . 34 In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 −2 cm s −1 and 3.02 × 10 −2 cm s −1 , respectively. In any case, the maximum observed kinetic constants k obs = kK and the k h values for the oxidation of the two phenols on the three electrodes are also shown in Table 2.…”

Characterization and Mechanism of the Photoelectrocatalytic Oxidation of Organic Pollutants in a Thin-Layer Reactor

“…exponential fitting parameters and t represents the reaction time. We found that for all concentrations of BPA, I net -t fits a first-order exponential decay model with correlation coefficients ranging from 0.9629 to 0.9935, which is in good agreement with the concentration decay kinetics obtained using the traditional method [28]. These results confirm the validity of Eq.…”

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams

“…Interestingly, the electrochemical performances of gCN air towards KHP degradation were preserved upon repeating the same experiment after three months, highlighting a good material stability. The experimental trend in Figure 6 b, in agreement with a pseudo-first order kinetics [ 56 ], could be fitted with either a single or a double exponential function. The obtainment of a better match with experimental results in the latter case (see the corresponding χ 2 value in Figure 6 b) indicates that two distinct processes, i.e., adsorption and decomposition, take place simultaneously on the material surface.…”

Unraveling Kinetic Effects during Photoelectrochemical Mineralization of Phenols. Rutile:Anatase TiO2 Nanotube Photoanodes under Thin-Layer Conditions

“…In order to compare the kinetic performance of these systems, the maximum values for the heterogeneous rate constants, k h = k obs max ( V / A ) = kK ( V / A ), were estimated and are also reported in Table . The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 –2 cm s –1 ) with the values reported for similar systems such as o -nitrophenol (1.39 × 10 –2 cm s –1 ) and PNP (0.79 × 10 –2 cm s –1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm –2 . In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 –2 cm s –1 and 3.02 × 10 –2 cm s –1 , respectively.…”

“…The k h value obtained for the degradation of PNP in the anatase electrode is consistent (0.48 × 10 −2 cm s −1 ) with the values reported for similar systems such as o-nitrophenol (1.39 × 10 −2 cm s −1 ) and PNP (0.79 × 10 −2 cm s −1 ), which were previously oxidized in anatase TiO 2 nanotube electrodes and linearly corrected to a UV photon flux of 30 mW cm −2 . 34 In addition, the maximum k h values for the oxidation of PNP and PMP were obtained with the 20% rutile electrode, 10.6 × 10 −2 cm s −1 and 3.02 × 10 −2 cm s −1 , respectively. In any case, the maximum observed kinetic constants k obs = kK and the k h values for the oxidation of the two phenols on the three electrodes are also shown in Table 2.…”

Characterization and Mechanism of the Photoelectrocatalytic Oxidation of Organic Pollutants in a Thin-Layer Reactor

“…exponential fitting parameters and t represents the reaction time. We found that for all concentrations of BPA, I net -t fits a first-order exponential decay model with correlation coefficients ranging from 0.9629 to 0.9935, which is in good agreement with the concentration decay kinetics obtained using the traditional method [28]. These results confirm the validity of Eq.…”

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams

“…Interestingly, the electrochemical performances of gCN air towards KHP degradation were preserved upon repeating the same experiment after three months, highlighting a good material stability. The experimental trend in Figure 6 b, in agreement with a pseudo-first order kinetics [ 56 ], could be fitted with either a single or a double exponential function. The obtainment of a better match with experimental results in the latter case (see the corresponding χ 2 value in Figure 6 b) indicates that two distinct processes, i.e., adsorption and decomposition, take place simultaneously on the material surface.…”