A Systematic Investigation of p-Nitrophenol Reduction by Bimetallic Dendrimer Encapsulated Nanoparticles

Abstract

We demonstrate that the reduction of p-nitrophenol to p-aminophenol by NaBH4 is catalyzed by both monometallic and bimetallic nanoparticles (NPs). We also demonstrate a straightforward and precise method for the synthesis of bimetallic nanoparticles using poly(amido)amine dendrimers. The resulting dendrimer encapsulated nanoparticles (DENs) are monodisperse, and the size distribution does not vary with different elemental combinations. Random alloys of Pt/Cu, Pd/Cu, Pd/Au, Pt/Au, and Au/Cu DENs were synthesized and evaluated as catalysts for p-nitrophenol reduction. These combinations are chosen in order to selectively tune the binding energy of the p-nitrophenol adsorbate to the nanoparticle surface. Following the Brønsted–Evans–Polanyi (BEP) relation, we show that the binding energy can reasonably predict the reaction rates of p-nitrophenol reduction. We demonstrate that the measured reaction rate constants of the bimetallic DENs is not always a simple average of the properties of the constituent metals. In particular, DENs containing metals with similar lattice constants produce a binding energy close to the average of the two constituents, whereas DENs containing metals with a lattice mismatch show a bimodal distribution of binding energies. Overall, in this work we present a uniform method for synthesizing pure and bimetallic DENs and demonstrate that their catalytic properties are dependent on the adsorbate’s binding energy.

Catalytic Activity of Mono- and Bi-Metallic Nanoparticles Synthesized via Microemulsions

“…The reduction of 4-nitrophenol via NaBH 4 can be catalyzed not only by monometallic Pt nanoparticles, but also by the bimetallic PtBi and PtPb nanoparticles. However, the reduction via the three different catalysts does not follow pseudo first-order kinetics, even with a 200-times excess of the reducing agent, which is the common approach in the literature [28,29,[31][32][33]. Our results strongly indicate: (1) the presence of first-order kinetics only for the first step of the reduction mechanism, i.e., the hydrogenation of 4-nitrophenol to 4-nitrosophenol; and (2) a strong influence of the temperature on the kinetics of the reaction, which cannot be described with the Arrhenius equation.…”

“…As reported in [27], the reaction follows the Langmuir-Hinshelwood mechanism. However, if a large enough amount of NaBH 4 is used (at least >100-times more than 4-nitrophenol), the kinetics simplify to a pseudo first-order reaction [28][29][30][31][32]. Thus, to test the catalytic activity of the synthesized nanoparticles, we used an excess of NaBH 4 and treated the reaction as a pseudo first-order reaction.…”

Atomic‐Level‐Designed Catalytically Active Palladium Atoms on Ultrathin Gold Nanowires

“…This provides a reasonable explanation for the superior activity of isolated Pd atoms in Au@Ag ML @Pd NWs over that of ensemble Pd in Au@Pd NWs (Figure 4a,b). Since the binding energy of 4-NP on reactive center depends on its composition (electronic effect), [27] and noble metals, e.g., Au or Ag, are capable of activating nitro group, while Pd atom facilitates the storage of hydrogen radical intermediates (synergy effect). [28] Both of which indicates that the high activity observed for the isolated Pd atoms is a result of electronic and synergy effects.…”

Catalytic activity of Ni complexed aminoclay towards the reduction of Cr(V), p-nitrophenol and fluorescein dye

“…Polyacrylonitrilesupported Ag nanoparticle was used for the catalytic reduction of NiP . Other catalysts like Pd/ Fe 3 O 4 @ dextran (Lara et al 2015), Ag (Naraginti and Sivakumar 2014), fly ash@polypyrrole/Au composite (Sun et al 2016), Cu-supported graphite carbon material (Morales et al 2017), Pt nanoparticles , bimetallic dendrimer (Pozun et al 2013) and hydroxyapatite (Sowmiya et al 2015) were used for the catalytic reduction of NiP. After thorough literature survey, the catalytic reduction of NiP by AC-Ni catalyst system was not found.…”