Electrochimica Acta 60 (2012) 147–153 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Electrochemical oxidation of lignin at lead dioxide nanoparticles photoelectrodeposited on TiO 2 nanotube arrays Ke Pan a , Min Tian a , Zi-Hua Jiang a , Bruce Kjartanson b , Aicheng Chen a,∗,1 a Department of Chemistry, Lakehead University, Thunder Bay, 955 Oliver Road, Ontario P7B 5E1, Canada b Department of Civil Engineering, Lakehead University, Thunder Bay, 955 Oliver Road, Ontario P7B 5E1, Canada a r t i c l e i n f o Article history: Received 19 August 2011 Received in revised form 6 November 2011 Accepted 6 November 2011 Available online 15 November 2011 Keywords: TiO2 nanotubes PbO2 nanoparticles Photoelectrochemical deposition Lignin Electrochemical oxidation a b s t r a c t In this study, we have successfully fabricated lead dioxide (PbO 2 ) nanoparticles supported on TiO 2 nano- tubes (TiO 2 NT/PbO 2 ) for the treatment of kraft lignin. The TiO 2 nanotubes were grown directly on Ti substrates by electrochemical anodization and the PbO 2 nanoparticles were formed by the combination of photochemical and electrochemical deposition. Scanning electron microscopy (SEM) and energy dis- persive X-ray spectrometry (EDS) were employed to study the surface morphology and composition of the fabricated Ti/TiO 2 NT/PbO 2 electrodes. The resulting electrode was utilized as a novel approach for the oxidation and modification of lignin. UV–vis spectroscopy was employed to monitor the lignin oxidation process in situ. The effects of concentration, current and temperature on the oxidation of lignin have been investigated, as well as post-oxidation changes in the chemical oxygen demand (COD) of the lignin solution. Fourier transform Infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) were used to characterize the oxidized lignin as well as the resulting products. Our study shows that the electrochemical oxidation of lignin via the fabricated Ti/TiO 2 NT/PbO 2 electrode is a promising approach for the remediation of lignin wastewater and the generation of lignin-derived value-added products. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Electrochemical oxidation has been described as a promis- ing approach for the treatment of wastewater due to its ease of operation, wide range of treatment conditions and environmental compatibility [1–6]. Organic pollutants in industrial wastewater can be oxidized by OH radicals and chemisorbed active oxygen species that are produced during electrochemical oxidation reac- tions. Lignin is one of the most significant organic contaminants found in pulp and paper industrial wastewater, causing a high COD and color of effluent. However, the degradation of lignin in industrial effluent is relatively complex due to its inherent, highly biorefractory structure. On the other hand, lignin is one of the most abundant biopolymers on earth, constituting approximately 30% of the dry weight of softwoods and 20% of hardwoods. It is a renewable, non-toxic, commercially available and low cost natural resource that has significant potential for being utilized as a basic raw material for the polymer industry. To date, lignin has primar- ily been used as a low-grade fuel for the pulp and paper industry because of the lack of effective modification and depolymerization ∗ Corresponding author. Tel.: +1 807 343 8318; fax: +1 807 346 7775. E-mail address: aicheng.chen@lakeheadu.ca (A. Chen). 1 ISE member. methods [7]. Electrochemical oxidation has been explored for the degradation and modification of lignin [8–15]. However, the low efficiency of the process and the high cost of the electrode materials have hampered the wide application of this technique. Therefore, it will be of significant benefit to develop a low cost electrode with high efficacy for the oxidation of lignin. Among the most commonly used anodes for the oxidation of organic pollutants; boron-doped diamond (BBD) and lead dioxide (PbO 2 ) exhibit the highest oxidative power [16–21]. In comparison with BBD, PbO 2 is a cheaper and more easily prepared electrode with stable performance with a wide range of electrolytes [22,23]. In addition, PbO 2 electrodes are promising for environmental appli- cations due to their high corrosion resistance in acidic solutions. Nevertheless, the fragile PbO 2 coating may easily flake from the surface of the substrate because of its relatively high interfacial resistance [24]. One remedy for addressing this issue is to increase the loading capacity of PbO 2 on a flat substrate surface to enhance its electrochemical properties. It has been reported that the useable surface area of the electrode may be greatly increased when verti- cally aligned TiO 2 nanotubes (NTs) are prepared on a Ti substrate via the application of an anodic current [25–27]. Thus, the loading capacity of PbO 2 might be enhanced when using a TiO 2 NT sub- strate. However, as TiO 2 is a semiconducting material, it is difficult to deposit PbO 2 onto the TiO 2 surface using standard electrochem- ical deposition techniques [28,29]. In contrast, metallic oxides such 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.11.025