Catalytic reduction with Pd has emerged as a promising technology to remove a suite of contaminants from drinking water, such as oxyanions, disinfection byproducts, and halogenated pollutants, but low activity is a major challenge for application. To address this challenge, we synthesized a set of shape- and size-controlled Pd nanoparticles and evaluated the activity of three probe contaminants (i.e., nitrite, N-nitrosodimethylamine (NDMA), and diatrizoate) as a function of facet type (e.g., (100), (110), (111)), ratios of low- to high-coordination sites, and ratios of surface sites to total Pd (i.e., dispersion). Reduction results for an initial contaminant concentration of 100 μM show that initial turnover frequency (TOF0) for nitrite increases 4.7-fold with increasing percent of (100) surface Pd sites (from 0% to 95.3%), whereas the TOF0 for NDMA and for diatrizoate increases 4.5- and 3.6-fold, respectively, with an increasing percent of terrace surface Pd sites (from 79.8% to 95.3%). Results for an initial nitrite concentration of 2 mM show that TOF0 is the same for all shape- and size-controlled Pd nanoparticles. Trends for TOF0 were supported by results showing that all catalysts but one were stable in shape and size up to 12 days; for the exception, iodide liberation in diatrizoate reduction appeared to be responsible for a shape change of 4 nm octahedral Pd nanoparticles. Density functional theory (DFT) simulations for the free energy change of hydrogen (H2), nitrite, and nitric oxide (NO) adsorption and a two-site model based on the Langmuir-Hinshelwood mechanism suggest that competition of adsorbates for different Pd sites can explain the TOF0 results. Our study shows for the first time that catalytic reduction activity for waterborne contaminant removal varies with the Pd shape and size, and it suggests that Pd catalysts can be tailored for optimal performance to treat a variety of contaminants for drinking water. © 2013 American Chemical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was primarily supported by Water CAMPWS, a Science and Technology Center program of the National Science Foundation under Agreement No. CTS-0120978, and in part by King Abdullah University of Science and Technology. This work was performed in part at the Nano Research Facility (NRF), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under Grant No. ECS-0335765. TEM analysis was carried out in part at the Frederick Seitz Materials Research Laboratory Central Facilities (MRL), University of Illinois. We thank Professor Yujie Xiong at University of Science and Technology in China for training for shape- and size- controlled Pd nanoparticle synthesis when he was on the staff of the NRF at Washington University in St. Louis. We thank Dr. Danielle Gray of the School of Chemical Sciences 3M Materials Science Laboratory for performing XRD analyses. We thank Dr. Rick Haasch of MRL for performing XPS analyses. We thank Rudiger Laufhutte of the School of Chemical Sciences Microanalytical Laboratory for performing ICP-MS analyses. We thank Jian Li at the Department of Civil and Environmental Engineering for assisting in solving the two-site model. We thank Professor Michael Janik of Penn State University for consultation regarding computation of ion adsorption and for the use of his Statistical Thermodynamics spreadsheets.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.