A Dual Catalyst with SERS Activity for Probing Stepwise Reduction and Oxidation Reactions

Abstract

Aromatic azo compounds are high‐value chemicals extensively used as pigments, drugs, and food additives, but their production typically requires stoichiometric amounts of environmentally unfriendly metals or nitrites. There is an urgent need to develop a dual catalytic system capable of reducing nitroaromatics to aromatic amines, followed by their oxidation to azo compounds. Here we report such a dual catalyst based on Ag@Pd‐Ag core‐frame nanocubes for the stepwise conversion of 4‐nitrothiophenol to trans‐4,4′‐dimercaptoazobenzene under ambient conditions. Our in situ surface‐enhanced Raman spectroscopy study reveals three sequential processes that include the Pd‐catalyzed reduction of 4‐nitrothiophenol to 4‐aminothiophenol by hydrogen, a period during which the 4‐aminothiophenol remain unchanged until all hydrogen has depleted, and the Ag‐catalyzed oxidation of 4‐aminothiophenol to trans‐4,4′‐dimercaptoazobenzene by the O2 from air. This work will lead to an environmentally friendly and sustainable approach to the production of aromatic azo compounds.

Addressing the Effects of Size‐dependent Absorption, Scattering, and Near‐field Enhancements in Plasmonic Catalysis

“…It allows the utilization of metal nanoparticles (NPs), such as gold (Au) and silver (Ag), as catalysts and visible light as an eco‐friendly and abundant energy input to drive chemical reactions ,,. As the LSPR excitation in Ag and Au NPs is strongly dependent on size, shape,, structure, composition,, and the dielectric constant of the environment, a systematic understanding of how these parameters govern LSPR‐mediated catalytic processes is imperative for the design of catalysts with desired performances.…”

Bifunctional Ag@SiO2/Au Nanoparticles for Probing Sequential Catalytic Reactions by Surface‐Enhanced Raman Spectroscopy

“…Taken together, we believe that the Au islands could serve as a catalyst to facilitate the reduction of 4‐NTP by NaBH 4 . Once NaBH 4 was completely consumed in the reaction solution, the Ag atoms in the outmost surface could activate O 2 in the aqueous solution for the oxidation of 4‐ATP to trans ‐DMAB …”

“…On the other hand, we observed as mall peak at 1594 cm À1 ,w hich can be assigned to the n CC of 4-ATP.B ased on our previous findings, the intensity of n CC for 4-ATP could become one order of magnitude weakert han that of the band for 4-NTP after the reduction of 4-NTP to 4-ATP by NaBH 4 . [39][40][41] From the presence of n CS band at 1082cm À1 ,w eargued that some of the 4-ATP molecules were adsorbed on the Au surface. From 22 to 66 min, the SERS spectra remained essentially unaltered.…”

“…[39] Once NaBH 4 wasc ompletely consumed in the reaction solution, the Ag atoms in the outmost surface could activate O 2 in the aqueous solution for the oxidation of 4-ATP to trans-DMAB. [41] To gain ab etter mechanistic insight into the oxidation of 4-ATPt otrans-DMAB on the surface of the Ag@SiO 2 /Au nanoparticles, we directly functionalized the surface of the nanoparticles (obtained at at itration volumeo f0 .4 mL) with 4-ATP and then recorded the SERS spectra. As shown in Figure S7 we also observed the four peaks of trans-DMAB at 1142 cm À1 , 1390 cm À1 ,1 430cm À1 ,a nd 1576 cm À1 ,t ogether with two peaks of 4-ATP peaks at 1595a nd 1489 cm À1 ,s uggesting that some of the immobilized 4-ATP could be oxidized by the O 2 from air to generate trans-DMAB.T his observation is consistent with previous findings.…”

Bifunctional Metal Nanocrystals for Catalyzing and Reporting on Chemical Reactions

“…We demonstrated the use of Ag@Pd-Ag nanocubes as a dual catalyst for in situ SERS monitoring the Pd-catalyzed reduction of 4-NTP by NaBH 4 and the Ag-catalyzed oxidation of 4-ATP to trans-DMAB by the O 2 from air. [21,32] In a typical experiment, the as-prepared bimetallic nanocubes were incubated with a 4-NTP solution in ethanol at room temperature for 1 h prior to the SERS measurements in liquid phase under the excitation of a 532 nm laser. Figure 6 A shows the time-dependent SERS spectra collected from the 4-NTPfunctionalized Ag@Pd-Ag nanocubes containing 2.2 wt % of Pd.…”