Vol.:(0123456789) 1 3 Chemical Papers https://doi.org/10.1007/s11696-020-01243-w ORIGINAL PAPER Nifedipine degradation by an electro‑oxidation process using titanium‑based RuO 2 –IrO 2 –TiO 2 mixed metal oxide electrode Mohd Dzul Hakim Wirzal 1,2  · Palanivel Sathishkumar 3  · Lina Abdullah Alshahrani 3  · Abdull Rahim Mohd Yusof 2  · Feng Long Gu 3  · Munawar Saeed Qureshi 4,5  · Muhammad Khalid 4  · Faiz Muhammad Khokhar 6 Received: 23 November 2019 / Accepted: 4 June 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020 Abstract The interest in new emerging pollutants (NEPs) does not only focus on the main compounds but also the degradation or intermediate products. It is important to have an efective primary treatment for the removal/degradation of NEPs from hospital and clinical wastewater to protect the environment. In this study, nifedipine degradation was performed by an electro-oxidation method using titanium-based mixed metal oxide (MMO) electrode. The determination of nifedipine was carried out by diferential pulse voltammetry at hanging mercury drop electrode using Britton–Robinson bufer (BRB). The nifedipine oxidation peak was observed at + 0.7 V at a scan rate of 20 mV s −1 in BRB pH 8. Titanium-based electrodes with diferent metal oxide compositions were assessed as an anode material for nifedipine degradation as follows: TiO 2 / Ti, IrO 2 –TiO 2 /Ti, RuO 2 –TiO 2 /Ti, and IrO 2 –RuO 2 –TiO 2 /Ti. The electro-oxidation of nifedipine was monitored using cyclic voltammetric techniques, and the degradation intermediates were confrmed using LC–MS. Approximately 65–83% of nifedipine degradation was achieved using RuO 2 –TiO 2 /Ti and IrO 2 –TiO 2 /Ti electrodes. Interestingly, RuO 2 –IrO 2 –TiO 2 electrode showed complete (100%) electro-oxidation of nifedipine at 30 min. Two nifedipine degradation intermediates were identifed, namely 5-methoxycarbonyl-2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3-carboxylic acid (compound I) and 2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicarbaldehyde (compound II) during the electro-oxidation process using RuO 2 –IrO 2 –TiO 2 electrode. Finally, the degradation pathway of nifedipine by MMO electrode was proposed. This is the frst report on the nifedipine degradation using MMO titanium electrode by the electro-oxidation process. Keywords Degradation · Electro-oxidation · Mixed metal oxide · Nifedipine · Titanium anode Introduction Pharmaceutical active compounds (PhACs) contamination in the water resources has received a considerable atten- tion due to their negative impact on ecological systems (Esmaili et al. 2017; Maryskova et al. 2016; Sathishkumar et al. 2014; Wirzal et al. 2013). Nifedipine (3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-di- carboxylate) is a frequently used calcium uptake inhibitor to treat hypertension and cardiovascular diseases (Stone et al. 1980). This cardiac drug has been considered as a common pharmaceutical pollutant in surface water. The interactive efect of nifedipine and its metabolites with environmental contaminants may cause a serious threat to aquatic organ- isms (Falfushynska et al. 2017). Generally, it is highly pho- tosensitive and its pharmacological activity can lose due to the formation of nitro-pyridine derivative by photo-degra- dation process during the pharmaceutical utilization (Waller * Abdull Rahim Mohd Yusof rahim@kimia.fs.utm.my * Munawar Saeed Qureshi saeed.munawar9@gmail.com 1 Chemical Engineering Department, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia 2 Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia 3 Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education; School of Chemistry and Environment, South China Normal University, Guangzhou 510006, People’s Republic of China 4 Department of Chemistry, Khwaja Fareed University of Engineering and Information Technology, Rahimyar Khan 64200, Pakistan 5 Department of Chemistry, Government Degree College, Jungle Shah, Keamari, Karachi, Karachi 75620, Pakistan 6 Institute of Advanced Research Studies in Chemical Sciences, University of Sindh, Jamshoro 76090, Pakistan