Ultrafine Pd nanoparticles@g-C3N4 for highly efficient dehalogenation of chlorinated environmental pollutant: Structure, efficacy and mechanisms

Abstract

Catalytic hydrodechlorination represents one of the most promising strategies for the remediation of chlorinated environmental pollutants. However, the wide application of this approach in the practical settings is hampered by the efficiency and stability of catalysts as well as the danger of using molecular hydrogen as hydrogen source. By combining the advantages of both palladium nanocatalyst and graphitic carbon nitride (g-C3N4) as support, here we report the preparation of a hybrid material with ultrafine Pd nanoparticles (NPs, ca. 2 nm) finely embedded inside the well-ordered geometric structure of g-C3N4 by making use of the unique interaction between metal and nitrogen functional groups, and for the first time apply this catalyst for the remediation of chlorinated environmental pollutant. This catalyst (Pd NPs@g-C3N4) exhibited significantly better catalytic performance than any catalysts reported previously with catalytic activity as high as ca. 101 mmol•g−1Pd•min−1 and the ability to achieve rapid complete dechlorination of 1.0 mM 4-chlorophenol (4-CP) within 2 min by using a very low dosage of NaBH4 (2 equivalent) as hydrogen source. The distinctive catalytic dehalogenation property of Pd NPs@g-C3N4 was attributed to i) the ultrafine Pd NPs that activated molecular hydrogen into numerous reactive species (e.g., atomic hydrogen) and ii) the electron-deficient nature of Pd nanocatalyst due to the presence of g-C3N4 support that greatly facilitated the electron transfer on the catalyst surface. This hybrid Pd NPs@g-C3N4 catalyst displayed a rapid dechlorination ability, wide pH applicability, good stability and recyclability. This study provides a promising alternative catalyst for highly efficient dehalogenation of chlorinated environmental pollutants and can shed light onto developing other powerful catalysts for the remediation of these recalcitrant contaminants in water. This work provides new insights into the preparation of ultrafine metal catalyst by using nitrogen functional groups and the possible effect of support to the electronic structure of Pd nanocatalyst.