Nanoscale Palladium Catalyst Synthesis And Its Application In Chromium Detoxification And Hydrogen Production

Metal nanomaterials have been used to deal with a variety of water pollutions,such as heavy metal pollution and organic materials.The methods and the affecting factors of the production of the metal nanomaterials affect the morphology and the catalytic capacity.Therefore,finding the most appropriate methods and the affecting factors is important to environmental protection.We firstly used Shewanella loihica PV-4 to produce the palladium nanoparticles with smaller size and higher catalytic capacity.Pd(II)reduction occurred inside and outside the Shewanella loihica PV-4 and the particle size fell into 4-10 nm,which was smaller than the palladium nanoparticles generated without Shewanella loihica PV-4(50-100 nm).Results showed that higher Pd(II)concentration,weaker acidic condition,and higher electron donor concentration could accelerate the procedure.These results proved the feasibility of the biosynthesis of palladium nanoparticles by Shewanella loihica PV-4 and the fact that smaller size palladium nanoparticles could be produced in the presence of Shewanella loihica PV-4.Biosynthesized palladium nanoparticles were used to catalytically reduce the chromium(VI)(Cr(VI))in the groundwater,which was compared to the palladium nanoparticles generated without the Shewanella loihica PV-4.The results showed that the biosynthesized palladium nanoparticles got faster Cr(VI)removal efficiency(100%in 3 h)than the one with chemical palladium(34.2±2.8%),which proved the smaller size biosynthesized palladium nanoparticles possessed higher catalytic capacity.These results provided key factors to heavy metal disposal.To deal with the loss of palladium catalysts,biosynthesis of palladium nanoparticles was placed in the cathodic chamber of the microbial electrolysis cell,which realized in situ electrodeposition of palladium on the electrode and the hydrogen production.By calculating the electrochemical active areas of the two electrodes,we found that the biosynthesized palladium electrode got higher electrochemical active area(40.5±3.5 m2 g-1)than the palladium electrode without MR-1(16.8±2.8 m2 g-1),and electrochemical activity than the electrode produced without Shewanella oneidensis MR-1.At the same time,the electrodes were used to catalyze the hydrogen production,of which the hydrogen production rate of the biosynthesized electrode was 61.8±2.0 L-H2 m-3 d-1,while the one with the chemical electrode was 38.5±2.0 L-H2 m-3 d-1.These results proved the feasibility of in situ palladium electrode production and hydrogen production in the microbial electrolysis cells and dealt with the loss of catalysts problem.