Palladium nanoparticles encapsulated in core-shell silica: A structured hydrogenation catalyst with enhanced activity for reduction of oxyanion water pollutants
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Water Desalination and Reuse Research Center (WDRC)
Environmental Science and Engineering Program
Environmental Nanotechnology Lab
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AbstractNoble metal nanoparticles have been applied to mediate catalytic removal of toxic oxyanions and halogenated hydrocarbons in contaminated water using H2 as a clean and sustainable reductant. However, activity loss by nanoparticle aggregation and difficulty of nanoparticle recovery are two major challenges to widespread technology adoption. Herein, we report the synthesis of a core-shell-structured catalyst with encapsulated Pd nanoparticles and its enhanced catalytic activity in reduction of bromate (BrO3-), a regulated carcinogenic oxyanion produced during drinking water disinfection process, using 1 atm H2 at room temperature. The catalyst material consists of a nonporous silica core decorated with preformed octahedral Pd nanoparticles that were further encapsulated within an ordered mesoporous silica shell (i.e., SiO2@Pd@mSiO2). Well-defined mesopores (2.3 nm) provide a physical barrier to prevent Pd nanoparticle (6 nm) movement, aggregation, and detachment from the support into water. Compared to freely suspended Pd nanoparticles and SiO2@Pd, encapsulation in the mesoporous silica shell significantly enhanced Pd catalytic activity (by a factor of 10) under circumneutral pH conditions that are most relevant to water purification applications. Mechanistic investigation of material surface properties combined with Langmuir-Hinshelwood modeling of kinetic data suggest that mesoporous silica shell enhances activity by promoting BrO3- adsorption near the Pd active sites. The dual function of the mesoporous shell, enhancing Pd catalyst activity and preventing aggregation of active nanoparticles, suggests a promising general strategy of using metal nanoparticle catalysts for water purification and related aqueous-phase applications.
SponsorsThis work was financially supported by the Academic Excellence Alliance (AEA) program at King Abdullah University of Science and Technology (KAUST) and NSF Chemical, Bioengineering, Environmental, and Transport Systems (No. CBET-0746453). We thank Jeffery Bertke and Rudiger Laufhutte (Department of Chemistry at the University of Illinois at Urbana-Champaign (UIUC)) for helping to acquire the XRD patterns and elemental analysis, respectively. We appreciate the help from Ruiqing Lu (UIUC) with obtaining the zeta potential measurements, and Dr. Shaoying Qi (UIUC) for gas adsorption experiments. Technical Assistance at KAUST was provided by Dr. Hongnan Zhang, Dr. Zhonghai Zhang, Mr. Rubal Dua and Mr. Guoying Chen. Four anonymous reviewers provided insightful comments to help improve the presentation of the results in this paper.
PublisherAmerican Chemical Society (ACS)