Nanobiocatalytic Degradation of Acid Orange 7

Abstract

The catalytic properties of various metal nanoparticles have led to their use in environmental remediation applications. However, these remediation strategies are limited by their ability to deliver catalytic nanoparticles and a suitable electron donor to large treatment zones. Clostridium pasteurianum BC1 cells, loaded with bio‐Pd nanoparticles, were used to effectively catalyze the reductive degradation and removal of Acid Orange 7 (AO7), a model azo compound. Hydrogen produced fermentatively by the C. pasteurianum BC1 acted as the electron donor for the process. Pd‐free bacterial cultures or control experiments conducted with heat‐killed cells showed limited reduction of AO7. Experiments also showed that the in situ biological production of H2 by C. pasteurianum BC1 was essential for the degradation of AO7, which suggests a novel process where the in situ microbial production of hydrogen is directly coupled to the catalytic bio‐Pd mediated reduction of AO7. The differences in initial degradation rate for experiments conducted using catalyst concentrations of 1ppm Pd and 5ppm Pd and an azo dye concentration of 100ppm AO7 was 0.39hr‐1 and 1.94hr‐1 respectively, demonstrating the importance of higher concentrations of active Pd(0). The degradation of AO7 was quick as demonstrated by complete reductive degradation of 50ppm AO7 in 2 hours in experiments conducted using a catalyst concentration of 5ppm Pd. Dye degradation products were analyzed via Gas Chromatograph‐Mass Spectrometer (GCMS), High Performance Liquid Chromatography (HPLC), UltraViolet‐Visible spectrophotometer (UV‐Vis) and Matrix‐Assisted Laser Desorption/Ionization (MALDI) spectrometry. The presence of 1‐amino 2‐naphthol, one of the hypothesized degradation products, was confirmed using mass spectrometry.