Kinetics and thermodynamics of the bioreduction of potassium tetrachloroaurate using inactivated oat and wheat tissues

The reduction kinetics of gold(III) to gold(0), the growth of gold nanoparticles with time, and the activation energy of the nanoparticle formation were investigated using oat and wheat biomasses at pH 4. Both the gold reduction and the nanoparticle growth were found to follow first-order kinetics with nanoscale size ranges in the growth period of 1–6 h of 4.54–19 nm for oat biomass and 8.0–51.8 nm for wheat biomass. The formation of gold(0) on oat and wheat biomasses was determined to occur at rates of 0.040 and 0.049 mM/min, respectively. The rate of nanoparticles growth was determined to be 0.0052 and 0.0035 nm/min for wheat and oat, respectively, whereas the activation energy for the reduction of gold(III) on oat and wheat biomasses was 4.8 ± 0.5 and 0.66 ± 0.07 kJ/mol, respectively. However, the activation energy for the growth of the produced nanoparticles was determined to be 12.0 ± 1.2 and 17.0 ± 1.7 kJ/mol for oat and wheat, respectively. The lower activation energy for the wheat indicates that the reduction process is much more favorable on the wheat biomass.