Effect of fluid shear stress on catalytic activity of biopalladium nanoparticles produced by Klebsiella Pneumoniae ECU-15 on Cr(VI) reduction reaction

Abstract Background Biopalladium (bioPd(0)) nanoparticles onKlebsiella PneumoniaeECU-15 were synthesized mainly on the microorganism's surface. Data suggest that the resistance of mass transfer around the cell surface region plays a critical role in bioPd(0) synthesis process. However, the mechanisms for its role remains elusive. Results The experimental results indicated that 1) diffusion resistance existed around the microorganism's cell in reaction vessel and 2) fluid shear stress affected the mass transfer rates differently according to its strength and thus had varying effects on the bioPd(0) synthesis. More than 97.9 ± 1.5% Chromium(VI)(Cr(VI)) (384 μM) was reduced to Cr(III) within 20 min with 5% Pd/bioPd(0) as catalyst, which was generated by theK. PneumoniaeECU-15, and the catalytic performance of Pd/bioPd(0) was stable over 6 months. The optimal condition of bioreduction of Pd(II) to Pd(0) was determined at the Kolmogorov eddy length of 7.33 ± 0.5 μm and lasted for 1 h in the extended reduction process after the usual adsorption and reduction process. Conclusions It is concluded that a high bioPd(0) catalytic activity can be achieved by controlling the fluid shear stress intensity in an extended reduction process in the bioreactor.