Comparative degradation of amido black 10B and Bismarck brown by electro-Fenton process. Comprehensive electrochemical study and degradation pathway of amido black 10B

Abstract

This study has two important objectives: first, to comprehensively investigate the electrochemical behavior of AMB and second, to evaluate the performance of the electro-Fenton/electrocoagulation (EF-EC) process for the removal of AMB and Bismarck brown (BIS) dyes from the environment. The complex electrochemical behavior of AMB has made researchers reluctant to investigate it. Therefore, examined the cyclic voltammetric behavior of AMB over a wide pH range and reported important data on the highly diverse redox processes of this extraordinary molecule that had not been previously reported in any database. Briefly, AMB is reduced in three steps, two of which involve the reduction of the azo groups and the third step involves the reduction of the nitro group. We also reported a three-component Pourbaix diagram for AMB reduction with all its details. AMB is oxidized in a two-electron step at pHs 〈 10 and in two one-electron steps at pHs 〉 10. At all pHs, the oxidized molecule is highly reactive and decomposes rapidly. The degradation of AMB and BIS was carried out through the EF-EC process and an efficient, green, and economical method for the almost complete removal of AMB and BIS dyes was proposed. Central composite design (CCD) was used to optimize variables such as current density, initial dye concentration, and initial hydrogen peroxide concentration. The results show that this method can remove AMB and BIS in aqueous solutions up to 99.3 % and 99.5 %, respectively. We also presented a very comprehensive mechanism for AMB degradation. In AMB degradation, due to the presence of many functional groups in the AMB structure, a large number of intermediates are formed, which we have identified using voltammetric data as well as LC-MS results.