Doping of biogenic Pd catalysts with Au enables dechlorination of diclofenac at environmental conditions

By using the metal reducing capacities of bacteria, Pd nanoparticles can be produced in a sustainable way (‘bio-Pd’). These bio-Pd nanoparticles can be used as a catalyst in, for example, dehalogenation reactions. However, some halogenated compounds are not efficiently degraded using a bio-Pd catalyst. This study shows that the activity of bio-Pd can be improved by doping with Au(0) (‘bio-Pd/Au’). In contrast with bio-Pd, bio-Pd/Au could perform the removal of the model pharmaceutical compound diclofenac from an aqueous medium in batch experiments at neutral pH and with H₂ as the hydrogen donor (first order decay constant of 0.078 ± 0.009 h⁻¹). Dehalogenation was for both catalysts the only observed reaction. For bio-Pd/Au, a disproportional increase of catalytic activity was observed with increasing Pd-content of the catalyst. In contrast, when varying the Au-content of the catalyst, a Pd/Au mass ratio of 50/1 showed the highest catalytic activity (first order decay value of 0.52 ± 0.02 h⁻¹). The removal of 6.40 μg L⁻¹ diclofenac from a wastewater treatment plant effluent using bio-Pd was not possible even after prolonged reaction time. However, by using the most active bio-Pd/Au catalyst, 43.8 ± 0.5% of the initially present diclofenac could be removed after 24 h. This study shows that doping of bio-Pd nanoparticles with Au(0) can be a promising approach for the reductive treatment of wastewaters containing halogenated contaminants.