The Synergistic Effect of Photoelectrochemical (PEC) Reactions Exemplified by Concurrent Perfluorooctanoic acid (PFOA) Degradation and Hydrogen Generation over Carbon and Nitrogen codoped TiO2 Nanotube Arrays (C-N-TNTAs) photoelectrode

•C, N codoped TiO2 nanotube arrays exhibited high visible-light photoreactivity.•Synergistic effect of PEC system was quantified in terms of photocurrent.•PEC exhibited effective separation of electrons and holes.•PFOA was readily degraded in PEC system over C-N-NTNA electrode.

We studied the synergistic effect of photoelectrochemical reactions exemplified by concurrent oxidization of perfluorooctanoic acid (PFOA) and hydrogen generation over carbon and nitrogen codoped TiO2 nanotube arrays (C-N-TNTAs) photoanode. The synthesized C-N-TNTAs were characterized by extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) and results confirmed the successful doping of carbon and nitrogen into the TNTAs framework without altering its crystalline structure. Mott-Schottky analysis yielded a donor density of 3.547 × 1018/cm3 and 1.159 × 1018/cm3 for TNTA and C-N-TNTA, respectively. The photogenerated electrons had a lifetime (τel) of 2.52, 4.01, and 6.34 ms under biased potential of 0, 0.5, and 1.0 V (vs. Ag/AgCl), respectively, indicating the increase in lifetime of phtogenerated electrons in photoelectrochemical (PEC) process. The synergetic effect was further quantified in terms of current/time profile at bias potential of 0 V at 1.1 mA and 1 V at 3.1 mA, individually. Results showed an increase in synergetic efficiency of 56 and 65% at a biased potential of 0.5 and 1.0 V, respectively. PEC effectively separated the photogenerated electron-hole pairs and enhanced the oxidation and reduction capability of the system. PFOA removal reached 56.1% in 180 min (initial concentration = 40 mg/L) over the C-N-TNTA photoanode in PEC mode. Results showed that perfluorooctanate, C7F15COO−, was first adsorbed on the C-N-TNTA anode surface followed by formation of C6F13COO− after losing CF2 units. Results of electron spin resonance (ESR) further confirmed that reactive species such as OH and CH3 were responsible for the decomposition of PFOA during PEC reactions.

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