Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation

Environmental Science and Pollution Research, Mar 2017

Cobalt-impregnated activated carbon (GAC/Co) was used to produce sulfate radical (SO4 ·−) from peroxymonosulfate (PMS) in aqueous solution (hereafter called PMS activation). We evaluated its effectiveness by examining the degradation of orange acid 7 (AO7). GAC/Co exhibited high activity to activate PMS to degrade AO7. The degradation efficiency of AO7 increased with increasing dosage of GAC/Co or PMS and elevated temperatures. pH 8 was most favorable for the degradation of AO7 by GAC/Co-activated PMS. The radical quenching experiments indicated that the reactions most likely took place both in the bulk solution and on the surface of GAC/Co. We found that SO4 ·− played a dominant role in AO7 degradation. Sodium chloride (NaCl) which presents in most dye wastewater had a significant impact on AO7 degradation. Low dosages (<0.4 M) of NaCl showed a slight inhibitory effect, whereas high dosages (0.8 M) increased the reaction rate. HOCl was confirmed as the main contributor for accelerating AO7 degradation with high concentration of NaCl. In a continuous-flow reaction with an empty-bed contact time of 1.35 min, AO7 was not detected in the effluent for 0 to 18.72 L of treated influent volume (156 h) and 85% removal efficiency was still observed after 40.32 L of treated volume (336 h). Finally, the azo bond and the naphthalene structure in AO7 were destroyed and the degradation pathway was proposed.

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Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation

Environ Sci Pollut Res Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation Tianyin Huang 0 1 2 Jiabin Chen 0 1 2 Zhongming Wang 0 1 2 Xin Guo 0 1 2 John C. Crittenden 0 1 2 0 Brook Byers Institute for Sustainable Systems and the School of Civil and Environmental Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA 1 School of Environmental Science and Engineering, Suzhou University of Science and Technology , Suzhou 215001 , People's Republic of China 2 Responsible editor: Vítor Pais Vilar 3 John C. Crittenden Cobalt-impregnated activated carbon (GAC/Co) was used to produce sulfate radical (SO4·−) from peroxymonosulfate (PMS) in aqueous solution (hereafter called PMS activation). We evaluated its effectiveness by examining the degradation of orange acid 7 (AO7). GAC/Co exhibited high activity to activate PMS to degrade AO7. The degradation efficiency of AO7 increased with increasing dosage of GAC/Co or PMS and elevated temperatures. pH 8 was most favorable for the degradation of AO7 by GAC/Co-activated PMS. The radical quenching experiments indicated that the reactions most likely took place both in the bulk solution and on the surface of GAC/Co. We found that SO4·− played a dominant role in AO7 degradation. Sodium chloride (NaCl) which presents in most dye wastewater had a significant impact on AO7 degradation. Low dosages (<0.4 M) of NaCl showed a slight inhibitory effect, whereas high dosages (0.8 M) increased the reaction rate. HOCl was confirmed as the main contributor for accelerating AO7 degradation with high concentration of NaCl. In a continuous-flow reaction with an empty-bed contact time of 1.35 min, AO7 was not detected in the effluent for 0 to 18.72 L of treated influent volume (156 h) and 85% removal efficiency was still observed after 40.32 L of treated volume (336 h). Finally, the azo bond and the naphthalene structure in AO7 were destroyed and the degradation pathway was proposed. Peroxymonosulfate; Orange acid 7; Activated carbon; Cobalt; Chloride Introduction Recently, dye wastewater generated from textile, printing, leather, food, and pharmaceutical industries have attracted worldwide concern due to their large concentrations in wastewaters and their environmental risk (Bakheet et al. 2013; Yang et al. 2011) . Azo dyes, characterized by azo bonds (−N=N–), are the most widely utilized colorants, accounting for 50% of all commercial dyes (Azam and Hamid 2006; Garcia-Segura et al. 2013) . Azo dyes are extremely stable because they are designed to be resistant to water, weather, detergent, and biodegradation during the production (Cai et al. 2014b) . The occurrence of azo dyes in the environment is undesirable not only because of their color but also because they are persistent, toxic, and carcinogenic (Cai et al. 2014a; Peng et al. 2008) . Thus, it is imperative to treat the azo dye wastewater before discharge into the receiving waters. However, the conventional wastewater treatment methods are inefficient to degrade the azo dyes (Cai et al. 2014b; Grčić et al. 2012) . Alternative treatment methods for azo dyes include electrochemical treatment (Brillas and Martinez-Huitle 2015) , ozonation (Szpyrkowicz et al. 2001) , photo-catalysis (Han et al. 2009) , and Fenton or Fenton-like reactions (Szpyrkowicz et al. 2001; Zhang et al. 2013a) . Currently, sulfate radical (SO4·−)-based advanced oxidation processes (SR-AOPs) have demonstrated great promise in the degradation of the recalcitrant pollutants (Qian et al. 2016; Zhang et al. 2015a, b) . SO4·− is known as a strong oxidant possessing a high redox potential (2.5–3.1 V) but more selective than hydroxyl radical (HO·) over a wide pH range (Chen et al. 2016a; Qian et al. 2015) . SO4·− can be generated from the peroxymonosulfate (PMS) when activated by UV (Guan et al. 2011; He et al. 2014; Zhang et al. 2015b) , heat (Antoniou et al. 2010; Chen et al. 2016b; Gao et al. 2016; Yang et al. 2010) , or transition metal ions (Anipsitakis and Dioniou 2004; Chan and Chu 2009) . UV irradiation and thermal activation are not cost efficient due to the high-energy input. By contrast, transition metal ions are cost-effective activators for PMS due to their natural abundance and low-energy input. Among the transition metal ions, cobalt (Co) is considered the most effective activator for PMS (Anipsitakis and Dioniou 2004; Nfodzo and Choi 2011) . Co(II)-activated PMS has been widely used to degrade phenolic compounds (Zhang et al. 2009) , dyes (Wang et al. 2011) , and other recalcitrant contaminants (Mahdi Ahmed et al. 2012). Nonetheless, Co is regarded as a priority contaminant in water, because Co has a potential health risk (e.g., asthma, pneumonia, and other lung problems) (Shukla et al. 2010) . To restrict the discharge of Co(II) into the water, heterogeneous activation of PMS with Co was preferred because when Co(II) is impregn (...truncated)


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Tianyin Huang, Jiabin Chen, Zhongming Wang, Xin Guo, John C. Crittenden. Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation, Environmental Science and Pollution Research, 2017, pp. 9651-9661, Volume 24, Issue 10, DOI: 10.1007/s11356-017-8648-7