Stéphanie Lambert

Improving effect of metal and oxide nanoparticles encapsulated in porous silica on fermentative biohydrogen production by Clostridium butyricum.

This paper investigated the enhancement effect of nanometre-sized metallic (Pd, Ag and Cu) or metallic oxide (FexOy) nanoparticles on fermentative hydrogen production from glucose by a Clostridium butyricum strain. These nanoparticles (NP) of about 2-3 nm were encapsulated in porous silica (SiO2) and were added at very low concentration (10(-6) mol L(-1)) in batch hydrogen production test. The cultures containing iron oxide NP produced 38% more hydrogen with a higher maximum H2 production rate (HPR) of 58% than those without NP or with silica particles only. The iron oxide NP were used in a 2.5L sequencing-batch reactor and showed no significant effect on the yields (established at 2.2 mol(hydrogen) mol(glucose)(-1)) but an improvement of the HPR (+113%, reaching a maximum HPR of 86 mL(hydrogen) L(-1) h(-1)). These results suggest an improvement of the electron transfers trough some combinations between enzymatic activity and inorganic materials.

Effect of metal ions and metal nanoparticles encapsulated in porous silica on biphenyl biodegradation by Rhodococcus erythropolis T902.1

Biodegradation of biphenyl was carried out by Rhodococcus erythropolis T902.1 in presence of nanometer-sized metallic (Co, Pd, Ag and Cu) nanoparticles (NPS) synthesized by the sol–gel process. In order to prevent their agglomeration, the metallic NPs (1–2xa0nm diameter) were anchored inside microporous silica crystallites and named Co/SiO2, Pd/SiO2, Ag/SiO2 and Cu/SiO2 samples, respectively. They were added at low concentrations of 10−6, 10−5 and 10−4xa0M of metal in the culture medium, and their impact was compared with that of the simple metal ions added as cobalt, palladium, silver or copper salts. The cultures containing Pd/SiO2 or Co/SiO2 samples at 10−4xa0M of metal achieved a 50xa0% higher biphenyl degradation yield after 18xa0days of incubation and improved R. erythropolis T902.1 growth compared with those without (positive control) or with silica particles only. The highest biodegradation performance, i.e., 107xa0±xa03xa0ppm/day, which was about 85xa0% higher than in control conditions without NPs, was recorded in 250-mL baffled flasks stirred at 150xa0rpm with Co/SiO2 sample at 10−4xa0M Co. Furthermore, the stimulating effect of NPs on biphenyl biodegradation seems to also depend on the thermal treatment conditions applied to NPs since the experimental results indicated that, after calcination, the cobalt oxide NPs at a concentration of 10−4xa0M were more effective than the reduced cobalt NPs with a degradation yield of 81xa0±xa01 and 77xa0±xa02xa0%, respectively, after 18xa0days. On the other hand, the results showed that the addition of 10−4xa0M of Cu2+ or Ag+ ions or the addition of Cu/SiO2 or Ag/SiO2 samples at 10−4xa0M of metal have an inhibitory effect on biphenyl biodegradation. However, Cu2+ and Ag+ ions were more toxic to the R. erythropolis T902.1 bacteria than the respective Cu or Ag NPS anchored inside silica particles. Moreover, this work showed that in these conditions, the activity of catechol 1,2-dioxygenase (a critical enzyme in aromatic biodegradation pathway) was severely inhibited, whereas the presence of 10−4xa0M of Co2+ ions or Co/SiO2 sample stimulated the enzyme activity compared to the conditions without NPs.Graphical Abstract