Remarkable Facet Selective Reduction of 4-Nitrophenol by Morphologically Tailored (111) Faceted Cu₂O Nanocatalyst

Abstract

In this work, we have disclosed the facile syntheses of morphologically diverse Cu 2 O nanoparticles using our laboratory designed modified hydrothermal reactor employing low-cost copper (II) acetate precursor compounds. The reaction conditions dovetail the effect of ethylene glycol (EG) and glucose to exclusively evolve the morphology tuned Cu 2 O nanomaterial at different pHs. The morphology tuning produces octahedron (Oh), dwarf hexapod (DHP), and elongated hexapod (EHP) Cu 2 O structures only with the optimized reagent concentrations. Interestingly, all of them were bestowed with a (111) facet, a superlative facet for facile nitroarene reduction. Thus, the morphology reliant catalytic reaction becomes evident. However, when used individually, EG and glucose evolve ill-defined CuO/Cu 2 O and Cu 2 O structures, respectively. We have observed that a change in pH of the medium at the onset of the reaction is obligatory for the evolution of tailor-made morphologically diverse Cu 2 O nanoparticles. However, preformed Cu 2 O particles do not suffer further structure/morphology changes under deliberate pH (6.0–9.0) change. With the as-obtained Oh, DHP, and EHP Cu 2 O structures, we further delve into the realm of catalysis to understand the splendor of the nanocatalyst, morphology and surface area dependence, facet selective reactivity, and other factors affecting the catalytic efficiency. The remarkable rate of catalysis of 4-nitrophenol (4-NP), evident from the catalyst activity parameter ( k a = 123.6 g –1 s –1 ), to produce 4-aminophenol in the presence of a reducing agent like sodium borohydride (NaBH 4 ) of the as-prepared catalysts is evidence of the collaborative effects of the effective surface area, surface positive charge, and active (111) facet of the Cu 2 O nanocatalyst. We have also studied the effect of other common anions, namely, Cl – , NO 2 – , NO 3 – , CO 3 2– , and SO 4 2– on the reduction process. To obtain a general consensus about facets, we compared (100) and (111) faceted Cu 2 O nanocatalysts not only for 4-NP reduction but also for the reduction of toxic chromium Cr(VI) in the presence of formic acid to further emphasize the importance of facet selectivity in catalysis and the versatility of the morphology tuned as-prepared Cu 2 O.

Synthesis of Au, Ag, and Au–Ag Bimetallic Nanoparticles Using Pulicaria undulata Extract and Their Catalytic Activity for the Reduction of 4-Nitrophenol

“…Figure 6 c) when Au–Ag alloy NPs prepared at low concentrations of PE were used. Typically, one of the most important factor which governs the efficiency of nanocatalysts during the reduction of 4-NPh is the morphology of the nanocatalyst, since a well-tuned morphology with defined facets tends to increase the surface area of a nanocatalyst, which in turn enhances the active site of the catalyst in the reaction medium, and thus has a direct effect on its catalytic activity [ 50 ]. Therefore, in this case, Au–Ag alloy NPs obtained at higher concentrations of PE demonstrated higher catalytic activity towards the reduction of 4-NPh due to the well-defined spherical shaped morphology and smaller size ( Figure 5 ) of the nanocatalyst as compared to Au–Ag bimetallic NPs synthesized using low concentrations of PE ( Figure 4 ).…”

Glycerol: An Optimal Hydrogen Source for Microwave-Promoted Cu-Catalyzed Transfer Hydrogenation of Nitrobenzene to Aniline

“…Although several applications for copper catalysis in transfer hydrogenation have already been reported in the literature (Štefane and Požgan, 2014;Fan et al, 2018;Zhang and Li, 2019), the use of CuNPs for nitrobenzene reduction via transfer hydrogenation has not received much attention, to the best of our knowledge (Feng et al, 2014). In fact, the common approach to nitro benzene reduction by Cu catalysis is performed in the presence of NaBH 4 , which is used as a hydride donor (Wu et al, 2013;Aditya et al, 2017;de Souza et al, 2017). Herein, glycerol has been exploited as an efficient capping agent in the production of CuNPs, and as a solvent and hydrogen donor in the Cu-catalyzed reduction of nitrobenzene derivatives.…”

Benzophenone assisted UV-activated synthesis of unique Pd-nanodendrite embedded reduced graphene oxide nanocomposite: a catalyst for C–C coupling reaction and fuel cell

“…Different morphologies and facets exhibit different physical and chemical properties, as in the case of Pd. [5][6][7][8]32 The fcc crystal structure of Pd has various exposed facets depending on morphology. In the case of PRGO-nt we observed triangles, pentagons and hexagons with exposed (111) and (100) facets.…”

“…Nanoparticles (NPs) containing a small percentage of noble metals that act as catalytically active sites when distributed on a support for maximum utilization of size, shape and crystal facets, are a current focus due their low cost syntheses. [5][6][7] Palladium (Pd) NPs are a unique class of heterogeneous catalyst and are used in a wide range of research elds as sensors, devices, energy storage materials 5,7 and catalysts of organic synthesis reactions, including the Suzuki-Miyaura, Sonogashira, Stille and Heck carbon-carbon coupling and carbon-oxygen bond formation reactions. 9,10 Pd NPs as heterogeneous catalysts for the synthesis of chemical compounds have advantages over homogeneous catalysts with respect to stability, selectivity, cost-effectiveness, reusability and the presence of multiple active sites.…”