Stability of Palladium-Polypyrrole-Foam Nickel Electrode and Its

Palladium-polypyrrole-foam nickel composite electrode (Pd/PPY(PTS)/Ni) was prepared through electrodeposited of palladium nanoparticles onto preformed...
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Stability of Palladium-Polypyrrole-Foam Nickel Electrode and Its Electrocatalytic Hydrodechlorination for Dichlorophenol Isomers Junjing Li,†,‡ Huiling Liu,*,†,‡ Xiuwen Cheng,†,‡ Yanjun Xin,†,‡,§ Wenxian Xu,†,‡ Zhenpeng Ma,§ Jun Ma,†,‡ Nanqi Ren,†,‡ and Qing Li∇,⊥ †

Department of Environmental Science and Engineering and ‡State Key Laboratory of Urban Water Resources and Environment (SKLUWRE), Department of Environmental Science and Engineering, Harbin Institute of Technology, Huanghe Road 73, Nangang District, Harbin 150090, P. R. China § School of Resource and Environment, Qingdao Agricultural University, Qingdao 266109, P. R. China ∇ Department of Pathology and Cell Biology, Columbia University, Broadway, New York 10027, United States ABSTRACT: Palladium-polypyrrole-foam nickel composite electrode (Pd/PPY(PTS)/Ni) was prepared through electrodeposited of palladium nanoparticles onto preformed electrodes (surface of electrodes was coated with potentiostatic electropolymerized polypyrrole). The stability of the fresh and used composite electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that the surface state, morphology, and crystalline structure of the composite electrode were stable after 5 recycle uses. Electrocatalytic activity of the composite electrode was evaluated for the hydrodechlorination (ECH) of six kinds of dichlorophenols (DCPs). Results indicated that 2,4DCP showed higher hydrodechlorination rate. Further, the pathway of electrochemical hydrodechlorination of six kinds of dichlorophenol isomers was investigated.

1. INTRODUCTION Chlorophenols have been listed as a significant priority contaminants with great potential risk to human beings in many countries.1−4 The destruction of chlorophenols in wastewater is a very critical issue which has attracted wide attention and interest of researchers. Several physical, chemical, and biological methods have been developed in the treatment of wastewater and remediation of polluted groundwater, such as adsorption, advanced oxidation processes,5 biological degradation, hydrodehalogenation, etc. It has been proved that some more toxic byproducts could be generated in some treament processes. Munoz et al. investigated the generation of chlorinated byproducts upon Fenton-like oxidation of chlorophenols at different conditions and found that some virulent byproducts such as polychlorinated biphenyls (PCBs), dioxins, and dichlorodiphenyl ethers produced.6 In recent years, the hydrodechlorination method, in which chlorines in organic compounds are replaced by hydrogen, has received attention as one of the most promising innovative technologies.7,8 The hydrodechlorination method includes catalytic hydrodechlorination technology and electrocatalytic hydrodechlorination technology. The source and nature of hydrogen used in hydrodechlorination concluding hydrogen molecule and more effective reductive atomic hydrogen ([H]) is very important to the dechlorination efficiencies. For catalytic hydrodechlorination technology, high pressure or temperature is needed with commonly used Pd/C, Pd/Al2O3 as catalysts. The bimetallic microsized particles, such as Pd−Fe, can be efficient for improving dechlorination with [H] adsorbed on a Pd catalyst.9 However, the mass of [H] decreased in the reaction process with the consumption of zerovalent metal and the performance of catalyst was affected.10 © 2012 American Chemical Society

Recently, electrocatalytic hydrodechlorination (ECH) has successfully been applied to the destruction of chlorinated organic compounds. Bonin et al. proposed that ECH has advantages over catalytic hydrodechlorination due to the continuous adsorbed nascent [H] produced during the electrochemical reduction of H+ or H2O.11 Electrochemical hydrodechlorination (ECH) as a powerful reductive degradation method has received much attention due to its simple operations, promise of high-energy efficiency, and mild reaction conditions,12,13 while palladium was considered to be the most effective catalyst for hydrodechlorination of chlorinated organic compounds due to its great ability to absorb hydrogen.14,15 Thus, the electrodeposition of palladium micro/nanoparticles onto preformed electrodes (the surface of electrodes was coated with a conductive film) for ECH attracted many researchers.16−18 It was found that conductive film on the electrode substrate was beneficial to disperse the catalytic particles and modify the electronic nature of the electrode, with the improvement of catalytic performance.16 Polypyrrole (PPY), polyaniline (PANI), and polythiophene (PTh) are three well-known π-conjugated conducting polymers. PPY and PANI can be electropolymerized in aqueous solution, and electropolymerization potential of the former was lower than that of the later. PTh films are usually electropolymerized in organic solvents, most of which are toxic, because the presence of water is bad to this system and results in a low conductivity film. Therefore, PPY has been attractive because of its ease of Received: Revised: Accepted: Published: 15557

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preparation, excellent stability, high electronic conductivity, and nontoxic properties.19 So far, many researchers have been carrying out investigations on the dechlorination of 2,4-DCP (dichlorophenol),20 but little research focuses on the electrochemical hydrodechlorination of the six DCP isomers. Up to now, the systematic investigations about the ECH of all the DCP isomers have not yet been reported. Therefore, the pathway of ECH processes of these DCPs is not fully understood. In this study, palladium-polypyrrole-foam nickel composite electrode (Pd/PPY(PTS)/Ni) was prepared through electrodeposited of palladium nanoparticles onto preformed electrodes (surface of electrodes was coated with potentiostatically electropolymerized polypyrrole). The stability of the fresh and used composite electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Xray photoelectron spectroscopy (XPS). Further, the pathway of ECH for six DCP isomers was discussed in detail.

2. EXPERIMENTAL SECTION 2.1. Materials. Dichlorophenols were purchased from Sinopharm Chemical Reagent Co. Ltd. The monomer pyrrole was purified by distillation under reduced pressure. It was distilled to give a product boiling at 65 °C, then stored at about 4 °C and protected from light with tin foils. All the other chemicals were ACS reagent grade and used without any further purification. Proton exchange membrane used was Nafion-117. Millipore-Q water was used throughout all the experiments. 2.2. Preparation of Composite Electrode. Ni foam was pretreated as follows: It was placed in 0.5 mol·L−1 dilute sulfuric acid solution for 2 min. Then, it was placed in acetone to remove ion on the surface for 30 min. And then it was cleaned in Millipore-Q water (18.2 MΩ) for 30 min. All the processes were under ultrasonic conditions according to our previous study.21 Prior to the electrolytic deposition of palladium nanoparticles onto preformed electrodes, polypyrrole was electropolymerized on foam nickel (with constant effective electrode surface 30 mm × 10 mm × 1 mm, which was shown in Figure 1a) with the constant potential of 0.6 V for 20 min at 0 °C in pyrrole solution containing 0.1 mol·L−1 pyrrole and 0.2 mol·L−1 p-toluene sulfonic acid (PTS). After being cleaned with MQ-water, the PPY film was obtained. Subsequently, the resulting film was immersed into 1 mmol·L−1 of PdCl2 aqueous solution containing of 3 mmol·L−1 of NaCl solution. Finally, Pd nanoparticles were electrodeposited onto the polypyrrole film at the constant current of 6 mA with the temperature of 40 °C until the solution became colorless, which was consistent with the previous research of our groups.21 2.3. Characterization of Electrode. Scanning electron microscopy (SEM) was performed with a FEI Quanta 200F. Xray diffraction (XRD) patterns were collected on Model D/ MAX-IIIB diffractometer equipped with Cu Kα radiation source (λ = 0.15406 nm). An accelerating voltage of 40 kV and an emission current of 30 mA with a scanning rate of 5°·min−1 were employed, respectively. X-ray photoelectron spectroscopy (XPS) was performed on a Model PHI-5700 ESCA apparatus with Al Kα X-ray source. All the binding energies (BE) were referenced with the adventitious carbon (binding energy = 284.6 eV). Inductively coupled plasma spectrometer (Optima ICP 5300DV, Perkin-Elmer) was used to analyze the drop of Pd particles. It should be clarified that

Figure 1. Schematic diagram of the effectively used electrode (a) and the reaction system used for ECH on the Pd/PPY(PTS)/Ni electrode (b): (1) Pt foil, (2) foam nickel, (3) constant temperature water bath kettle with magnetic stir, (4) stirrer, (5) potentiostat, and (6) Hshaped electrolyzer.

the used sample for characterization was the electrode which has been applied to ECH for five consecutive times. The conditions were similar to the ECH of 2,4-dichlorophenol measurement. 2.4. Electrocatalytic Activity. Electrochemical hydrodechlorination activity and stability of the fresh and used composite electrode was evaluated for dechlorination of six kinds of dichlorophenols (DCPs), which was carried out on an H-shaped electrolyzer, as shown in Figure 1b. Pt foil was served as anode, which was positioned vertically and parallel to composite electrode prepared, separated by a distance of 1 cm. Anolyte and catholyte were 50 mL of 0.05 mol·L−1 Na2SO4 solution and 50 mL of 0.05 mol·L−1 Na2SO4 solution containing 0.5 mmol·L−1 dichlorophenol, respectively. Further, the reaction current and temperature were constanted at 5 mA and 40 °C, respectively. At time intervals, the analyzed samples were collected and examined by high performance liquid chromatography (HPLC, Shimadzu LC-10A) equipped with a UV detector. Aliquots of 10 μL were injected automatically into the HPLC to determine the concentration of DCPs and products. The separation was performed using a Kromasil KR100-5 C18 column (5 μm, mobile phase of methanol/water (70%/30% V/V) at the flow rate of 1.0 mL·min−1. The wavelength of the UV detector was set at 270 nm. In addition, it should be indicated that the mobile phase was sonicated for 2 min before the analysis to remove dissolved gas. 15558

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Figure 2. SEM images and EDAX elemental analysis of fresh (a, b) and used Pd/PPY(PTS)/Ni electrodes (c, d).

Figure 3. XPS Pd 3d, N 1s core-level spectra (a−d) of as-prepared Pd/PPY(PTS)/Ni and Pd/PPY(PTS)/Ni (used five times) electrodes.

3. RESULTS AND DISCUSSION 3.1. Morphology Analysis. In order to investigate the morphology of the fresh and used Pd/PPY(PTS)/Ni composite electrode, SEM micrographs were conducted, as shown in Figure 2. As seen from Figure 2a, palladium particles were dispersed on the surface of electrode, exhibiting irregular morphology. Further, slightly aggregation phenomenon had occurred. By comparing with Figures 2a and c, it is noticed that there are some substances, which may be 2,4-DCP and the

decomposed products, adsorbed on the surface of electrode. In order to identify the elements on the electrode surface, EDAX elemental analysis of the corresponding electrodes was performed. The results of EDAX (in Figures 2b and d) confirmed that the existence of palladium, nickel, nitrogen, and sulfur elements. No carbon element and chlorine element were detected in Figure 2d, perhaps because, the amount of substances adsorbed was too low to be detected. 15559

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be attributed to the (111) and (220) faces of Pd0 (JCPDS File No. 05-0681). Pd nanoparticles were electrodeposited onto the PPYs. Under the external electrical field, the positive valence Pd(II) was transferred to the negative electrode and then was reduced to Pd(0). Pd species with lower charge density were not detected with XRD, which can be explained by the fact that the concentration of Pd(II) was too low to be checked out. The reason should be the sensitivity of XRD is much lower than that of XPS. The content of Pd(II) was so little that they cannot be detected by XRD. Additionally, the metal crystallite size could be calculated by using the Scherrer formula:25

3.2. XPS Analysis. In order to investigate the surface state of the fresh and used Pd/PPY(PTS)/Ni composite electrode, a typical XPS survey spectrum was performed, as displayed in Figure 3. The Pd 3d spectrum presented that the existence of a main contribution together with a minor component at higher binding energy (BE) values. From the curve-fitting analysis (Figure 3b and 3d), it was found that Pd 3d spectra of fresh and used electrodes resulted from two pairs of spin−orbit components. The binding energy of the major spin−orbit split doublet (Pd 3d5/2 and Pd 3d3/2) for the fresh and used Pd/ PPY(PTS)/Ni electrodes appeared at about 335.3 and 340.7 eV, respectively, which were attributed to the presence of metallic palladium Pd(0), which is the dominant component.22 In Chen’s study,17 the binding energy of Pd 3d is 337.3 and 342.5 eV, higher than the results in this study. The probable reason is the strength between the Pd and polypyrrole polymer is different, which could arise from the different preparation conditions. The second pair of Pd signals appeared at higher BE values (BE = 336.8 for Pd 3d5/2 and BE = 342.0 for Pd 3d3/2) and are attributed to Pd atoms with lower charge density (Pd(II)). This phenomenon is similar with the report by Evangelisti.23 Evangelisti et al proposed a hypothesis that perturbation occurred during the dispersion process of Pd clusters in polyvinylpyridine matrix. Figure 3a and 3c also showed the N 1s core-level XPS spectrum of as-prepared and used Pd/PPY(PTS)/Ni composite electrodes. The prominent peak at about 339.5 eV was associated with neutral pyrrolylium nitrogen with an amine-like structure,24 while the lower and higher binding energy (BE) peaks at about 397.2 and 400.7 eV were assigned to N− and N+,22 respectively. Additionally, the evolution of N− indicated that the little deprotonation of the PPY(PTS) occurred at the beginning of preparation for the Pd film. From the XPS data, the atomic concentration of palladium on as-prepared electrode and used for five times were obtained, which were 1.21% and 1.20%, respectively. In addition, the content of palladium in the aqueous phase after dechlorination for 120 min in each use cycle was examined by ICP in order to study the Pd losses. The results showed that there is nearly no drop of elemental composition of the Pd/PPY(PTS)/Ni electrode. Therefore, the stability of the electrode is good. 3.3. XRD Analysis. Figure 4 showed the XRD patterns of the fresh and used composite electrode. Notably, with the deposition of PdCl2, Pd0 was detected, since characteristic diffraction peaks at 39.82° and 67.80° were detected, which can

D=

Kλ β cos θ

(1)

where D is crystallite size of particle, K is a constant (in this study, K = 0.94), λ = 0.15406 nm, β is the full width at halfheight of angle of diffraction in radians after corrected, and θ is the diffraction angle. After calculating, the Pd crystallites sizes of fresh and used composite electrode were about 10.65 and 10.01 nm, respectively. Further, the d value could be calculated by using the Bragg equation, 2d sin θ = nλ, and for palladium, the lattice constant was obtained by the following formula: a = d h2 + l 2 + k 2

(2)

As calculated, the Pd lattice constant (3.912 Å) of the fresh and used composite electrode did not vary obviously, suggesting the as-prepared composite Pd/PPY(PTS)/Ni electrodes were stable. 3.4. Electrochemical Hydrodechlorination of Dichlorophenol Isomers. The ECH of 0.5 mmol·L−1 solution of six kinds of dichlorophenol isomers in 0.05 mol·L−1 Na2SO4 was studied and shown in Figure 5. Clearly, the as-prepared composite electrode showed higher electrochemical hydrodechlorination for 2,4-DCP, for which 91.1% of dichlorophenol can be degraded after 2 h of electrochemical reaction. The lowest removal rate of dichlorophenol for 3,5-DCP was only 68%. Further, the decrease of the removal rates of dichlorophenol isomers fitted in the following order: 2,4DCP >2,3-DCP > 3,4-DCP > 2,5-DCP > 2,6-DCP > 3,5-DCP. Moreover, the reaction rates and kinetic data were investigated. As seen from Figure 5b, the removal of dichlorophenols versus reaction time fitted well with the pseudofirst order kinetic formula. The corresponding rate constant k followed the following order: 2,4-DCP (0.02282 min−1) > 2,3-DCP (0.01939 min−1) > 3,4-DCP (0.01372 min−1) > 2,5-DCP (0.01288 min−1) > 2,6-DCP (0.01010 min−1) > 3,5-DCP (0.00996 min−1), which was consistent with the ECH. The concentrations of reactant and product as a function of reaction time for six kinds of DCP isomers were plotted in Figure 6. For all the DCP isomers, phenol was the main product and concentrations of generated monochlorophenols were very low (lower than 0.04 mmol·L−1). The position of both chlorines on the benzene ring relative to the hydroxyl group has a great effect on product distribution. As shown in Figure 6, each DCP isomer possessed chlorine ortho to the hydroxyl group generated ortho-CP as the primary monochlorophenol product. One probable reason was that the chlorines positioned meta or para to hydroxyl group in dichlorophenol with a chlorine ortho to the hydroxyl group were more susceptible to be attacked by active hydrogen adsorbed on the surface of the electrode than ortho-chlorine. Another probable reason was that the generated monochlor-

Figure 4. X-ray diffraction patterns of the fresh electrode and used electrode for five times. 15560

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attacked because of the presence of intramolecular hydrogen bonding resulting from the interaction between the hydroxyl group and the ortho-substituted chlorine. Meanwhile, orthochlorophenol was harder to dechlorinated than other monochlorophenols, meaning that the steric hindrance effect was obvious. For 2,6-DCP and 3,5-DCP, 2-CP and 3-CP formed, respectively. The ECH of 3,4-DCP should, from resonance stabilization considerations, result in the preferential formation of 3-CP. Nevertheless, the formation amount of 3-CP and 4-CP is similar in this study. Resonance stabilization was not the major effect under this situation. The removal rates of 2,3-DCP and 3,4-DCP were high (higher than 80%), probably indicating that chlorine substitutions at adjacent positions would destabilize the isomers and make isomers easy to be attacked. The result was similar with that of catalytic hydrodechlorination of DCP isomers using a nickel/silica catalyst in Shin’s study.27 The low removal rate of 2,6-DCP may be attributed to the obvious steric effects for this very sterically constrained system resulting the suppression of the reaction. Ma et al. reported the pKa values of DCP isomers.28 It is interesting to note that the known pKa values of six kinds of DCP isomers have some relation with the difficult degree of electrochemical dechlorination of DCP isomers. For example, pKa values of syn conformer DCP isomers decreased in following order: 2,4-DCP (7.9) > 2,3DCP (7.71) > 2,5-DCP (7.51) > 2,6-DCP (6.78) for the orthodichlorophenols and 3,4-DCP (8.62) > 3,5-DCP (8.25). The further study of the relationship between the pKa and ECH of DCPs will be carried out in our research. 3.5. Stability of Composite Electrode. Generally speaking, stability is very important for recycling of catalysts in practical applications. To confirm the possibility of recycle utilization of the as-prepared Pd/PPY(PTS)/Ni composite electrode, several cycles experiments for the electrocatalytic hydrodechlorination of 2,4-DCP were conducted. Meanwhile, ICP was carried out to detect the drop of the Pd nanoparticles. It was found that slightly drop phenomenon occurred, suggesting that our electrode was stable. As seen from Figure 7, the removal rate of 2,4-DCP for the as-prepared electrode

Figure 5. Removal rate as a function of time (a) and kinetics (b) during the ECH of 0.5m mol·L−1 DCP isomers (the corresponding degradation rate constants are listed in the parentheses).

Figure 6. Concentration of reactant and product as a function of time during the ECH of 0.5 mmol·L−1 DCP isomers with the same electrochemical condition (current 5 mA, at 40 °C): DCP (■), phenol (●), 2-CP (▲), 3-CP (▼), 4-CP (○).

Figure 7. Effect of repeat use of Pd/PPY(PTS)/Ni on the removal of 2,4-DCP.

ophenols were attacked by active hydrogen and the difficult degrees of monochlorophenols to be attacked were different. In Han’s work, theoretical study of molecular structures and properties of the complete series of chlorophenols was done.26 Relative energy calculated showed that ortho-chlorophenol was the most stable in monochlorophenols and harder to be

was remained approximately constant even after ten cycles. The reason for a slightly decrease of the activity for 10 uses may be that substances adsorbed on the electrode surface increased with consecutive usage cycles, thus the surface active site of catalyst decreased with the increase of adsorbate. On the whole, the composite electrode was stable. Therefore, the recycle 15561

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(5) Aquino Neto, S.; Andrade, A. R. Electrooxidation of glyphosate herbicide at different DSA compositions: pH, concentration and supporting electrolyte effect. Electrochim. Acta 2009, 54, 2039. (6) Munoz, M.; Pedro, Z. M.; Casas, J. A.; Rodriguez, J. J. Assessment of the generation of chlorinated byproducts upon Fenton-like oxidation of chlorophenols at different conditions. J. Hazard. Mater. 2011, 190, 993. (7) Zhu, K. R; Baig, S. A.; Xu, J.; Sheng, T. T.; Xu, X. H. Electrochemical reductive dechlorination of 2,4-dichlorophenoxyacetic acid using a palladium/nickel foam electrode. Electrochim. Acta 2012, 69, 389. (8) Yuan, G.; Keane, M. A. Aqueous-phase hydrodechlorination of 2,4-dichlorophenol over Pd/Al2O3: reaction under controlled pH. Ind. Eng. Chem. Res. 2007, 46, 705. (9) Jovanovic, G. N.; Plazl, P. Z.; Sakrittichai, P.; Al-Khaldi, K. Dechlorination of p-chlorophenol in a microreactor with bimetallic Pd/Fe catalyst. Ind. Eng. Chem. Res. 2005, 44, 5099. (10) Yang, B.; Yu, G.; Huang, J. Electrocatalytic hydrodechlorination of 2,4,5-trichlorobiphenyl on a palladium-modified nickel foam cathode. Environ. Sci. Technol. 2007, 41, 7503. (11) Bonin, P. M. L.; Edwards, P.; Bejan, D.; Lo, C. C.; Bunce, N. J.; Konstantinov, A. D. Catalytic and electrocatalytic hydrogenolysis of brominated diphenyl ethers. Chemosphere 2005, 58, 961. (12) Hoshi, N.; Sasaki, K.; Hashimoto, S.; Hori, Y. Electrochemical dechlorination of chlorobenzene with a mediator on various metal electrodes. J. Electroanal. Chem. 2004, 568, 267. (13) Jalil, A. A.; Panjang, N. F. A.; Akhbar, S.; Sundang, M.; Tajuddin, N.; Triwahyono, S. Complete electrochemical dechlorination of chlorobenzenes in the presence of naphthalene mediator. J. Hazard. Mater. 2007, 148, 1. (14) Cheng, I. F.; Fernando, Q.; Korte, N. Electrochemical dechlorination of 4-chlorophenol to phenol. Environ. Sci. Technol. 1997, 31, 1074. (15) Dabo, P.; Cyr, A.; Laplante, F.; Jean, F.; Menard, H.; Lessard, J. Electrocatalytic dehydrochlorination of pentachlorophenol to phenol or cyclohexanol. Environ. Sci. Technol. 2000, 34, 1265. (16) Chen, G.; Wang, Z. Y.; Xia, D. G. Electrochemically reductive dechlorination of micro amounts of 2,4,6-trichlorophenol in aqueous medium on molybdenum oxide containing supported palladium. Electrochim. Acta 2004, 50, 933. (17) Chen, G.; Wang, Z. Y.; Yang, T.; Huang, D. D.; Xia, D. G. Electrocatalytic hydrogenation of 4-chlorophenol on the glassy carbon electrode modified by composite polypyrrole/palladium film. J. Phys. Chem. B 2006, 110, 4863. (18) Wang, Y.; Fachini, E. R.; Cruz, G.; Zhu, Y.; Ishikawa, Y.; Colucci, J. A.; Cabrera, C. R. Effect of surface composition of electrochemically codeposited platinum/molybdenum oxide on methanol oxidation. J. Electrochem. Soc. 2001, 148, C222. (19) Dejeu, J.; Taouil, A. E.; Rougeot, P.; Lakard, S.; Lallemand, F.; Lakard, B. Morphological and adhesive properties of polypyrrole films synthesized by sonoelectrochemical technique. Synth. Met. 2010, 160, 2540. (20) Gomez-Quero, S.; Cardenas-Lizana, F.; Keane, M. A. Effect of metal dispersion on the liquid-phase hydrodechlorination of 2,4dichlorophenol over Pd/Al2O3. Ind. Eng. Chem. Res. 2008, 47, 6841. (21) Li, J. J.; Liu, H. L.; Wang, Z. W. Electrocatalytic Hydrodehalogenation of 2,4-dichlorophenol on palladium coated foam nickel cathode. Presented at the 5th International Conference on Bioinformatics and Biomedical Engineering, Wuhan, PRC, May 2011. (22) Lim, V. W. L; Kang, E. T.; Neoh, K. G. Electroless plating of palladium and copper on polypyrrole films. Synth. Met. 2001, 123, 107−115. (23) Evangelisti, C.; Panziera, N.; Pertici, P.; Vitulli, G.; Salvadori, P.; Battocchio, C.; Polzonetti, G. Palladium nanoparticles supported on polyvinylpyridine:Catalytic activity in Heck-type reactions and XPS structural studies. J. Catal. 2009, 262, 287. (24) Seo, M. H.; Lim, E. J.; Choi, S. M.; Nam, S. H.; Kim, H. J.; Kim, W. B. Synthesis, characterization, and electrocatalytic properties of a

utilization of the as-prepared Pd/PPY(PTS)/Ni composite electrode was possible and its stability in treating organic wastewater was satisfactory.

4. CONCLUSIONS In this study, Pd-PPY-Ni composite electrode has been successfully prepared through electrodeposited of palladium nanoparticles onto preformed electrodes (surface of electrodes was coated with potentiostatically electropolymerized polypyrrole). The fresh and used composite electrode was characterized by SEM, XPS, and XRD. It was found that Pd0 was the dominant component dispersed on the surface of the electrode. Moreover, the surface state of the composite electrode was stable after the recycle utilization. The electrocatalytic activity of the as-prepared composite electrode was evaluated by the electrocatalytic hydrodechlorination (ECH) of dichlorophenols. Results indicated that the electrocatalytic hydrodechlorination (ECH) for dichlorophenols fitted well with pseudo-first-order kinetic formula and the following order: 2,4-DCP > 2,3-DCP > 3,4-DCP > 2,5 DCP → 2,6-DCP > 3,5DCP. Further, the product was mainly phenol. Each DCP isomer possessed chlorine ortho to the hydroxyl group generated ortho-CP as the primary monochlorophenol product.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86-451 53625118. Fax: +86-451 53625118. E-mail address: [email protected]. Present Address ⊥

Currently with State Key Laboratory of Urban Water Resources and Environment (SKLUWRE), Department of Environmental Science and Engineering, Harbin Institute of Technology, Huanghe Road 73, Nangang District, Harbin 150090, PRC.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (No. 50978066, No. 51178138), National Creative Research Groups of National Natural Science Foundation of China (No. 51121062), and State Key Laboratory of Urban Water Resources and Environment (No. 2010DX03). The authors acknowledge the contribution of Qinghua Chen toward this work.

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REFERENCES

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