In situ generation of hydroxyl radical by cobalt oxide supported porous carbon enhance removal of refractory organics in tannery dyeing wastewater S. Karthikeyan, R. Boopathy, G. Sekaran ⇑ Environmental Technology Division, Council of Scientific and Industrial Research (CSIR) – Central Leather Research Institute (CLRI), Adyar, Chennai 600 020, Tamil Nadu, India graphical abstract article info Article history: Received 13 October 2014 Accepted 26 January 2015 Available online 4 February 2015 Keywords: Nanoporous activated carbon Heterogeneous Fenton like system Tannery dyeing wastewater Hydroxyl radical Organic dyes abstract In this study, cobalt oxide doped nanoporous activated carbon (Co-NPAC) was synthesized and used as a heterogeneous catalyst for the Fenton oxidation of organic dye chemicals used in tannery process. The nanoporous activated carbon (NPAC) was prepared from rice husk by precarbonization followed by chemical activation at elevated temperature (600 °C). The cobalt oxide was impregnated onto NPAC and characterized for UV–visible, Fluorescence spectroscopy, FT-IR, HR-TEM, XRD, BET surface area and XPS analyses. The hydroxyl radical generation potential of Co-NPAC from hydrogen peroxide decompo- sition was identified (k exi , 320 nm; k emi , 450 nm) by Excitation Emission Spectra (EES) analysis. The conditions for the degradation of tannery dyeing wastewater such as, Co-NPAC dose, concentration of H 2 O 2 , and temperature were optimized in heterogeneous Fenton oxidation process and the maximum percentage of COD removal was found to be 77%. The treatment of dyes in wastewater was confirmed through UV–Visible spectra, EES and FT-IR spectra analyses. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction In India, there are more than 3000 tanneries classified under small scale to medium scale sectors. Leather industries generate about 25–30 m 3 of wastewater per tonne of raw hides/skins pro- cessing, which are natural and synthetic organic dyes, syntans, organic nitrogen, ammoniacal nitrogen, sulfates, sulfides and heavy metals [1]. In India, the present annual leather processing capacity generates nearly 30–40 billion m 3 volume of leather wastewater. Globally, the volume of wastewater was found to be 300–500 billion m 3 volume. Wastewater generated from leather industry contains significant concentration of refractory organic compounds and hazardous pollutants [2]. The conventional http://dx.doi.org/10.1016/j.jcis.2015.01.066 0021-9797/Ó 2015 Elsevier Inc. All rights reserved. Abbreviations: APHA, American Public Health Association; AOP, advanced oxidation process; NPAC, nanoporous activated carbon; Co-NPAC, cobalt oxide on nanoporous activated carbon; BET, Brunauer–Emmett–Teller; HK, Horvath Kawa- zoe; XPS, X-ray photoelectron spectroscopy; EES, Excitation Emission Spectra; TA, terephthalic acid; HTA, 2-hydroxyterephthalic acid; ZSM-5, Zeolite Socony Mobil-5; FT-IR, Fourier Transform Infrared Spectroscopy; FTA, Fe-doped TiO 2 coated on activated carbon; HR-TEM, high resolution-Transmission Electron Microscopy; HR- SEM, high resolution-Scanning Electron Microscopy; XRD, X-ray diffraction; EPR, Electron Paramagnetic Resonance; EDX, Energy-Dispersive X-ray spectroscopy; ROS, reactive oxygen species; COD, chemical oxygen demand; TOC, total organic carbon; TKN, total Kjeldahl nitrogen; BOD 5 , biological oxygen demand; VFA, volatile fatty acids; CBC, carbon black composites; FAS, ferrous ammonium sulfate. ⇑ Corresponding author at: Environmental Technology Division, Central Leather Research Institute, Adyar, Chennai 600 020, Tamil Nadu, India. Fax: +91 44 24452941. E-mail addresses: karthik.keyan02@gmail.com (S. Karthikeyan), ganesansekaran@ gmail.com (G. Sekaran). Journal of Colloid and Interface Science 448 (2015) 163–174 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis