Bifunctional Au−Fe₃O₄ Heterostructures for Magnetically Recyclable Catalysis of Nitrophenol Reduction

Abstract

The dumbbell- and flower-like Au−Fe3O4 heterostructures by thermal decomposition of the iron−oleate complex in the presence of Au nanoparticles (NPs) have been successfully fabricated using different sizes of Au NPs as the seeds for magnetically recyclable catalysis of p-nitrophenol and 2,4-dinitrophenol reduction. The heterostructures exhibit bifunctional properties with high magnetization and excellent catalytic activity toward nitrophenol reduction. The epitaxial linkages in dumbbell- and flower-like heterostructures are different, leading to the change in magnetic and catalytic properties of the heterostructured nanocatalysts. The pseudo-first-order rate constants for nitrophenol reduction are 0.63−0.72 min−1 and 0.38−0.46 min−1 for dumbbell- and flower-like Au−Fe3O4 heterostructures, respectively. In addition, the heterostructured nanocatalysts show good separation ability and reusability which can be repeatedly applied for nearly complete reduction of nitrophenols for at least six successive cycles. The reaction mechanism for nitrophenol reduction by Au−Fe3O4 nanocatalysts is also proposed and confirmed by XPS and FTIR analyses. These unique properties make Au−Fe3O4 heterostructures an ideal platform to study various heterogeneous catalytic processes which can be potentially applied in a wide variety of fields in purification, catalysis, sensing devices, and green chemistry.

Nickel nanoparticles decorated on electrospun polycaprolactone/chitosan nanofibers as flexible, highly active and reusable nanocatalyst in the reduction of nitrophenols under mild conditions

“…The initial TOF values provided by Ni-NP/ENF catalyst at the 3rd reuse were calculated as 39.7 mol 2-nitrophenol/mol Ni min, 40.0 mol 2,4-dinitrophenol/mol Ni min, 54.0 mol 2,4,6-trinitrophenol/mol Ni min at 298 K. These results are revealing that Ni-NP/ENF catalyst retains 86, 83 and 82% of its inherent activity even at 3rd catalytic reuse in the reduction of 2-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol, respectively. The reusability performance of Ni/ENF catalyst is higher than that of obtained by Au@SiO 2 [70], polygonal shaped Au [71] and citrate stabilized Au nanoparticles [72] used as catalyst in the reduction of nitrophenols.…”

Single Metal of Silver Nanoparticles in the Microemulsion for Recyclable Catalysis of 4-Nitrophenol Reduction

“…Herein, BH 4 -was adsorbed onto the surface of Ag NPs to react and transfer electrons to Ag NPs [30]. And then the bare Ag NPs serve as catalyst to transfer electrons from BH 4 -to nitrophenols, leading to the production of amino derivatives, 2-amion-4-nitrophenol and p-aminophenol [49]. …”

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

“…In addition, while a metal or semiconductor domain can enable optical detection (e.g., via excitonic or LSPR absorption, or photoluminescence), a magnetic module can be utilized for complementary purposes, such as for magnetic resonance imaging (MRI), optical imaging, and magnetic separation (Choi et al, , 2008Jun et al, 2007;Jiang et al, 2008;Xu et al, 2008;Gao et al, 2009;Schladt et al, 2010;Bigall et al, 2012;Lim and Majetich, 2013). The existence of bonding heterointerfaces through which dissimilar materials can electronically communicate has clearly been recognized to impact on the magnetic (Xu et al, 2008;Lee et al, 2010a;Umut et al, 2012;Pineider et al, 2013;Kim and Song, 2014;Schick et al, 2014;López-Ortega et al, 2015;Velasco et al, 2015), optical (Levin et al, 2009;Korobchevskaya et al, 2011;Comin et al, 2012), transport (Lee et al, 2010a), magneto-optical Armelles et al, 2013), (electro)catalytic (Yin et al, 2008;Wang et al, 2009aWu et al, 2009;Lee et al, 2010b;George et al, 2011aGeorge et al, , 2013Jang et al, 2011b;Lin and Doong, 2011;Chen et al, 2012;Sun et al, 2012), and energy-storing properties of appropriately engineered MHNCs . Examples of MHNCs derived from heterogeneous deposition pathways are collected in Figures 2B-Q.…”

“…Examples of MHNCs derived from heterogeneous deposition pathways are collected in Figures 2B-Q. Thermal decomposition of metallorganic precursors in the presence of preformed noble metal, Fe 3 O 4 , FePt, or UO 2 seeds in non-coordinating solvents, such as octadecene (ODE) or phenyl ether containing oleic acid (OLAC), oleyl amine (OLAM), and/or tri-n-octyl phosphine (TOP) surfactants at 200-300°C has enabled access to hetero-dimer HNCs made of two nearly spherical and/or cubic-shaped domains epitaxially interconnected, such as of Me-Fe 3 O 4 (Me = Au, AuAg, PtPd, AuPd, AuPt, Pt, Pd, Ni, Cu) (Yu et al, 2005;Shi et al, 2006b;Choi et al, 2008;Wei et al, 2008;Wang et al, 2009aGeorge et al, 2011aGeorge et al, , 2013Jang et al, 2011a;Lin and Doong, 2011;Nakhjavan et al, 2011;Zhai et al, 2011;Leung et al, 2012;Sun et al, 2012;Kim and Song, 2014;Victor et al, 2015), Fe 3 O 4 -MnO , Au-MnO (Choi et al, 2008;Schladt et al, 2010) (He et al, 2009;Lee et al, 2010a;Wu et al, 2011a;Schladt et al, 2012;Liu et al, 2014;Yang et al, 2015), respectively. Depending on the geometric features of the two-component domains, these heterostructures exhibit various morphological profiles, spanning from peanut-, dumbbell-, brick-to flower-like (Figures 2B-D).…”

“…In all cases, the formed concave region or void was exactly commensurate to the volume that was originally occupied by the Au domain; in addition, in the particular case of AuPt-Fe 3 O 4 , I 2 -driven oxidation of the AuPt domain led to a nanocontainer section that encased a residual Pt domain (George et al, 2011a). The formation of such exotic nanostructures with concave surfaces or extended cavities indirectly discredited the earlier assumption that the metal (hemi)domain of these hetero-dimer MHNCs was totally "naked, " that is, in direct contact with the external environment; in contrast, the metaletching experiments unveiled that the portion of the metal, which was not nested in the Fe 3 O 4 domain, could accommodate a thin, porous (hence, permeable), or discontinuous Fe 3 O 4 shell that guaranteed its chemical accessibility, a feature that should be taken into account to explain their (electro)catalytic performance (Yin et al, 2008;Wang et al, 2009aWu et al, 2009;Lee et al, 2010b;George et al, 2011aGeorge et al, , 2013Lin and Doong, 2011;Chen et al, 2012;Sun et al, 2012).…”