Preparation of Au nanoparticles on a magnetically responsive support via pyrolysis of a Prussian blue composite

Journal of Colloid and Interface Science 540 (2019) 563–571

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Preparation of Au nanoparticles on a magnetically responsive support via pyrolysis of a Prussian blue composite Baiyu Ren a, Ahmad Esmaielzadeh Kandjani a, Miao Chen a,b, Matthew R. Field c, Daniel K. Oppedisano a, Suresh K. Bhargava a,⇑, Lathe A. Jones a,⇑ a b c

Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Science, RMIT University, GPO Box 2476, Melbourne, VIC 3001, Australia CSIRO Mineral Resources, Clayton, VIC 3169, Australia RMIT Microscopy & Microanalysis Facility, RMIT University, Melbourne, VIC 3001, Australia

g r a p h i c a l a b s t r a c t Au nanoparticles on an Fe-based support.

a r t i c l e

i n f o

Article history: Received 22 October 2018 Revised 24 December 2018 Accepted 7 January 2019 Available online 8 January 2019 Keywords: Metal organic framework Prussian blue Porous carbon Arsenic detection

a b s t r a c t A strategy is described for the direct preparation of Au nanoparticles (AuNPs) on a Fe-based support, coated with porous carbon (PC), via pyrolysis of an AuCN functionalised Prussian Blue (PB) metal organic framework (MOF). The composite starting material was prepared with an even distribution of AuCN on the surface via galvanic exchange of PB with a gold salt in solution. The resulting structures after pyrolysis were shown to be active Au-based nanomaterials for model applications including catalysis (4nitrophenol reduction) and electroanalysis (arsenic (III) detection), suggesting broad application where Au nanoparticles are required at a liquid-solid interface. The Fe based support was seen to consist of Fe, Fe3C and Fe4C phases, and the carbon coating increased the stability and improved the conductivity of the materials. The temperature of pyrolysis was seen to affect the activity of the supported nanoparticles, with an increased Au surface area obtained at the higher pyrolysis temperature (650 °C) tested. A general strategy is thus confirmed for preparation of noble metal nanoparticles evenly distributed on a magnetic support, allowing easy separation of catalysts from products in heterogeneous applications. Crown Copyright Ó 2019 Published by Elsevier Inc. All rights reserved.

1. Introduction ⇑ Corresponding author. E-mail addresses: [email protected] (S.K. Bhargava), lathe.jones@ rmit.edu.au (L.A. Jones). https://doi.org/10.1016/j.jcis.2019.01.027 0021-9797/Crown Copyright Ó 2019 Published by Elsevier Inc. All rights reserved.

Gold nanoparticles (AuNPs) have been extensively studied due to their application in a broad range of fields including catalysis,

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sensing, biomedicine, energy and environmental chemistry [1–7]. Methods to prepare gold nanoparticles on an appropriate support for direct use in these fields is an area of research that continues to attract attention. The common methods used are based on wet-chemistry via chemical reduction of Au3+ with reducing reagents in solution [8–10]. The high surface energy of AuNP surfaces means that they are susceptible to aggregation during either synthesis or application, leading to a change in activity [11]. To solve this problem, capping agents are usually applied during preparation procedures to prevent aggregation, and the AuNPs are cleaned afterwards to avoid blocking of the gold surface with the capping agent. A support is required to immobilise and stabilize AuNPs for use in applications, with common supports being metal oxides, mesoporous silica, or carbon-based materials including graphene, graphene oxides, carbon nanotubes, conducting polymers, organic-inorganic hybrids, or metal organic frameworks (MOFs) [12–17]. The combination of AuNPs with their support leads to heterogeneous materials which can exhibit improved activity and performance due to synergistic effects [12–20], and the stability of AuNPs on the support is critical, as leaching may occur during use [21]. MOFs have emerged as a class of multifunctional materials with applications in catalysis, gas storage and separation [22,23]. Because of the spatial orientation of metal ions and organic linkers, MOFs have large specific surface areas and high pore volumes. Furthermore, their unique three-dimensional framework leads to the potential for rational design, architectural control and functionalization of pores [23,24]. The emergence of MOFs has provided promising routes to fabricate Au-MOF composite materials by embedding AuNPs into the pores of MOFs, which can be used as catalysts in either liquid or gas phase heterogeneous catalytic reactions [24–30]. Furthermore, the utilization of MOFs as precursor materials or templates for the production of carbon-based materials has attracted interest for applications such as drug delivery, magnetic resonance, catalysis, energy storage and conversion, gas sensing and wastewater remediation [31–35]. For example, MOF derived Fe/FexC/C nanostructures have shown promising catalytic performance for the oxygen reduction reaction (ORR), where candidates are sought to replace commercial Pt/C catalysts, which display some of the stability problems common to nanoparticle/ support materials mentioned previously [36,37]. We have recently reported on the incorporation of gold in a stable form onto the surface of Prussian blue (PB) as AuCN, via a one-step direct galvanic replacement reaction involving PB in Au (III) solution [38]. This allows the dispersion of Au-based nanostructures onto PB without the use of any capping reagents or additional reducing reagents. There have been recent reports on the pyrolytic treatment of MOFs to obtain mixed carbon/metal materials with promising catalytic properties [39,40]. Direct pyrolysis of MOFs have thus been explored to prepare active and stable nanomaterials without, the need to embed nanoparticles onto support materials in a separate step [39,41]. Furthermore, the use of Febased MOFs as self-sacrificing complexes can lead to the production of magnetically-responsive materials, which are capable of being recovered and recycled with a magnet [42]. In order to improve surface stability, carbon coating of MOF-derived materials has been used with materials such as Vulcan XC-72, graphene, and carbon nanotubes being most common, which improves the conductivity, and protect nanoparticles from harsh alkaline and acidic environments [36,43,44]. There are also some recent reports on insitu formation of carbon layers through pyrolysis based procedures using precursors such as formaldehyde, polydopamine (PDA) or polyphenol tannic acid (TA), including the formation of metal nanoparticles protected by the porous carbon layer formed [43,45,46]. TA is a well-known non-toxic carbon source which

can coordinate to Fe (III) ions spontaneously and be deposited on a range of substrates [47,48]. A layer of porous carbon (PC) can thus obtained by pyrolysis of materials containing TA layers. Based upon the above perspectives, and the continued need for supported Au nanoparticles for multiple applications, here we describe the pyrolysis of AuCN/PB composites coated with TA layers, which leads to the reduction of Au (I) to gold nanoparticles, and simultaneous conversion of PB to a Fe-based composite support, to obtain active and stable PC coated composites of AuNPs supported on iron-based nanocubes (labelled as Au/Fe/FexC/PC-t, where t denotes the pyrolysis temperature). The supported AuNPs are free of blocking capping reagents and uniformly decorate the cubic supports. We have tested the resulting nanomaterials with model applications in catalysis and sensing, namely the chemical reduction of 4-nitrophenol by NaBH4 and electrochemical detection of As (III), to confirm the activity and stability of the structures. Controlled functionalization of a redox active MOF via galvanic replacement, followed by pyrolysis, is thus presented as a viable method for the synthesis of nanoparticles evenly distributed on a support for a broad range of applications.

2. Experimental section 2.1. Chemicals All chemicals were purchased from Sigma Aldrich, except 4nitrophenol (BDH) and NaBH4 (BDH), and were used as received. All solutions were prepared with Milli-Q water. To prepare stock solution, 0.132 g of As2O3 was dissolved in concentrated NaOH, adjusted to pH 3.0 with H2SO4 and diluted to 100 mL with MilliQ water to obtain As (III) stock solution. As (III) solutions of other concentrations were prepared from this stock solution daily.

2.2. Materials synthesis 2.2.1. Synthesis of precursors PB and AuCN/PB cubes were synthesized via procedures outlined in our previous report [38]. Briefly, 3.8 g polyvinylpyrrolidone (PVP) and 0.11 g K4Fe(CN)6 were dissolved in 50 mL HCl (0.1 M), followed by thermal treatment at 80 °C for 24 h in an electric oven. The obtained PB cubes were collected by centrifuge and dried at 120 °C. PB cubes were re-dispersed in water, and then HAuCl4 was added dropwise at 80 °C under constant stirring until the final concentration of PB and HAuCl4 was 1.125 g/L and 1.33 mM, respectively. After reaction for 1 h, the AuCN/PB cubes were isolated by several centrifuge-wash cycles with Milli-Q water. To synthesise AuCN/PB coated by TA (AuCN/PB@TA), the AuCN/ PB nanocubes were added to a solution of TA until the final concentration of AuCN/PB and TA was 2.07 g/L and 2.27 g/L, respectively. The pH of the solution was then adjusted to 8 with KOH. The obtained blue-black material was collected by several centrifugewash cycles and dried at room temperature. PB coated by TA (PB@TA) was prepared in the same way, using PB instead of AuCN/PB.

2.2.2. Pyrolysis of precursors AuCN/PB@TA cubes were heated at either 550 °C or 650 °C for 5 h under argon to obtain Au/Fe/FexC/PC-550 and Au/Fe/FexC/PC650, respectively. PB@TA cubes were heat-treated in the same way to obtain Fe/Fe3C/PC-550 and Fe/Fe3C/PC-650, respectively. AuCN/PB and PB cubes were heated at 550 °C for 2 h under Ar to obtain Au/Fe/FexC and Fe/Fe3C, respectively.

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2.3. Characterization Scanning electron microscopy was performed using an FEI Verios 460L SEM. This SEM was equipped with a retractable concentric backscatter electron (CBS) detector for backscatter imaging and an Oxford X-MaxN20 for energy dispersive X-ray spectroscopy (EDS). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) images were collected on JEOL 1010 and JEOL 2010 TEM microscopes, respectively. X-ray diffraction (XRD) patterns were collected on a Bruker D4 Endeavor X-ray diffractometer with Cu Ka radiation (k = 1.5406 Å). Fourier transform infrared (FTIR) spectra were collected on a Perkin-Elmer frontier FTIR spectrometer. Raman measurements were recorded on Perkin-Elmer Raman Station 400F Raman spectrometer with a 785 nm excitation wavelength. X-ray photoelectron spectroscopy (XPS) analysis was performed on Thermo Scientific K-Alpha X-ray photoelectron spectrometer using an Al Ka X-ray source (Ephoton = 1486.7 eV) using the C 1s peak at 284.6 eV as an internal standard. Thermogravimetric analysis (TGA) was undertaken from 30 °C to 850 °C under a nitrogen flow of 20 mL/min with a temperature increase rate of 10 °C/min. Nitrogen sorption measurements were carried out at 77 K on a Micromeritics (ASAP 2400) analyser. Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods were used to calculate surface area, pore volume and pore size distribution based on the nitrogen desorption branch. 2.4. Reduction of 4-nitrophenol The reduction of 4-nitrophenol by NaBH4 in the presence of the catalysts was performed in a 1 cm path length quartz cuvette. 0.3 mL of 4-nitrophenol (1 mM) was added to 2.7 mL of Milli-Q water, followed by the injection of 0.3 mL of freshly prepared NaBH4 aqueous solution (0.2 M). The solution colour changed to yellow immediately. Designated amounts of catalyst were then added to the above solution. The initial concentration of 4nitrophenol and concentration at time t is denoted as C0 and Ct, respectively, and the ratio of Ct and C0 is evaluated from the relative intensity of the absorbance (At/A0). Since excess NaBH4 was used, the concentration of NaBH4 remained essentially constant throughout the reaction, and the reaction can be regarded as a pseudo-first-order [49]. The time-dependent absorption spectra were recorded on the Cary 500 Scan UV–Vis-NIR spectrophotometer in the range 200–500 nm. The absorbance of the solution at 400 nm was taken to calculate the rate constant. To study the reusability of the catalysts, a magnet was used to separate solid catalysts from solution and the recycled catalysts were washed with Milli-Q water twice before re-use. All measurements were conducted at 18 °C. 2.5. Electrochemical detection of As (III) Electrochemical measurements were performed on a CH Instruments (CHI 760C) electrochemical workstation with a standard three-electrode system, where a rotating glassy carbon (GC) disk electrode modified with Au/Fe/FexC/PC-550 or Au/Fe/FexC/PC-650 was used as the working electrode, and a platinum wire and a Ag/AgCl (3 M NaCl, 0.21 V vs SHE) electrode as counter and reference electrode respectively. To prepare the working electrode, the rotating glassy carbon (GC) disk electrode was first polished with 0.05 mm alumina paste, followed by a rinse with Milli-Q water. 10 mL of sample slurry (1.5 mg/mL) was dropped on the GC electrode. After drying, the samples were covered by 10 mL of Nafion polymer solution (0.5 wt%). For comparison, a rotating glassy carbon (GC) disk electrode without modification was also covered by the same amount of Nafion solution, which was labelled as GC electrode. Cyclic voltammetry (CV) was conducted

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at 100 mV s 1 in 0.5 M H2SO4 between different potential ranges with and without the addition of arsenic (III). Square wave anodic stripping voltammetry (SWASV) measurements were performed at different concentrations of As (III) in 0.5 M H2SO4. Arsenic (III) was first pre-deposited at 0.15 V for 150 s, followed by a scan from 0.3 to 0.7 V with a frequency of 15 Hz, an amplitude of 25 mV and a potential increment of 4 mV. SWASV analyses were also undertaken in 0.1 M sodium acetic buffer solution (pH 5) in the presence of 0.01 M ethylenediaminetetraacetic acid (EDTA). Experimental conditions: preconditioning potential, 0.5 V; preconditioning time, 60 s; initial potential, 0.5 V; final potential, 0.7 V; frequency, 15 Hz; amplitude, 25 mV; potential increment, 4 mV. The rotating rate of the working electrode was kept at 1000 rpm during all measurements. 3. Results and discussion Scheme 1 illustrates the synthetic procedure to make the series of iron-based composites derived from PB described in this study. Route B represents the synthesis of the main material described in this paper, Au/Fe/FexC/PC-650, where PB was first treated with Au3+ and then a layer of TA was applied, followed by pyrolysis at 650 °C. For direct comparison, pyrolysis at 550 °C was undertaken in the same way to obtain Au/Fe/FexC/PC-550. These two temperatures were found to be the most effective for generating materials that maintained structural integrity, and reduced the Au(I) to Au(0). For comparison purposes, products without any Au were also obtained through Route A, leading to formation of Fe/Fe3C with a porous carbon coating (Fe/Fe3C/PC). Route C in the lower line illustrates the preparation of the products without the carbon coating derived from TA. The experimental conditions are depicted in Table 1 for each of the materials. The abbreviations shown in Table 1 are used throughout the paper for simplicity. 3.1. Characterization of the products Characterisation was undertaken to determine the composition, morphology and surface chemistry of the materials obtained. SEM images of Au/Fe/FexC/PC-650 are shown in Fig. 1b, which indicate that spherical gold nanoparticles (AuNPs) in the size range of 50– 70 nm are well-dispersed onto the surface of Fe-based boxes, which also contain a coating of porous carbon (PC) on their exterior. The product from the pyrolysis of AuCN/PB cubes (Au/Fe/FexC) shows no such carbon encapsulation due to the lack of a TA coating prior to pyrolysis, and a rougher surface is observed in Fig. 1a where there is no porous carbon (PC) [46]. Fig. 2a shows the XRD patterns of the AuCN/PB@TA precursor and Au/Fe/FexC/PC-650 generated by pyrolysis. The XRD pattern of AuCN/PB@TA shows two distinguishable peaks at 30.6° and 47.4°, which can be assigned to AuCN (JCPDS 11-0307), with the rest of the peaks matching well with the standard pattern of PB (JCPDS 73-0687). Au/Fe/FexC/PC-650 reveals diffraction patterns for Fe4C (JCPDS 65-3286), a-Fe (JCPDS 06-0696) and Fe3C (JCPDS 77-0255), indicating the existence of multiple Fe based phases in Au/Fe/FexC/PC-650 as a consequence of the heat treatment, though the Au nanoparticle diffraction peaks are too small to show with this instrumentation, and are characterised by XPS. Fig. 2b compares the FTIR spectra of AuCN/PB@TA and Au/Fe/FexC/PC-650. AuCN/PB@TA shows a similar FTIR spectrum to PB with an absorption band at 2070 cm 1 that can be ascribed to the stretching vibration mode of ACN functional group, which is a characteristic peak of PB [50]. Another peak at 495 cm 1 reveals the bending mode of FeACANAFe and the stretching mode of FeACAN is shown at 603 cm 1 [50,51]. The absorption band at 1414 cm 1 is due to the CAN bending vibration in PB [52]. The small peak at

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Scheme 1. Schematic illustration of synthetic procedures used in this manuscript.

Table 1 Experimental variables for preparing MOF-derived composites.

*

Abbreviations*

Compositions*

Au

TA Coating

Pyrolysis temperature/°C

Au/Fe/FexC/PC-550 Au/Fe/FexC/PC-650 Fe/Fe3C/PC-550 Fe/Fe3C/PC-650 Au/Fe/FexC Fe/Fe3C

Au/Fe/Fe4C/Fe3C@C/PC Au/Fe/Fe4C/Fe3C@C/PC Fe/Fe3C@C/PC Fe/Fe3C@C/PC Au/Fe/Fe4C/Fe3C@C Fe/Fe3C@C

Yes Yes No No Yes No

Yes Yes Yes Yes No No

550 650 550 650 550 550

PC: porous carbon layers; @C/PC: composites coated by a graphite layer and a layer of porous carbon; TA: tannic acid.

Fig. 1. Backscattered (top) electron and secondary electron (bottom) SEM images of (a) Au/Fe/FexC and (b) Au/Fe/FexC/PC-650. Bright spots on the backscatter images are Au nanoparticles.

431 cm 1 indicates the stretching vibration of AuAC [53]. The FTIR spectrum of Au/Fe/FexC/PC-650 reveals that the characteristic features of PB have vanished after pyrolysis, confirming the decomposition of PB MOF framework to form the new Fe based phases [54].

Fig. 2c shows the Raman spectra of AuCN/PB@TA and Au/Fe/ FexC/PC-650. For AuCN/PB@TA, the characteristic feature of PB presents at 2148 cm 1, which is attributed to ACN functional group [55], and another peak at 270 cm 1 indicates the presence

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Fig. 2. (a) XRD patterns, (b) FTIR, and (c) Raman spectra of AuCN/PB@TA and Au/Fe/FexC/PC-650, showing the effect of pyrolysis on the TA coated starting material.

of FeACN/AuACN [56]. The peak at 517 cm 1 is due to the FeAC stretching mode [57,58]. The Raman spectrum of Au/Fe/FexC/PC650 displays characteristic peaks of graphitic-like materials, showing a D band at 1327 cm 1 and a G band at around 1583 cm 1, due to the generation of the carbon shell during pyrolysis. Since the D band corresponds to the A1g symmetry breathing mode involving phonons near the K zone boundary, it is used to denote the disorder of graphitic carbon [59]. The presence of point defects and disordered graphene triggers strong Raman features in D band [60]. The E2g stretching vibration mode of CAC bond gives rise to the Raman G band, which can be produced in all sp2 carbon systems. XPS spectra of AuCN/PB@TA and Au/Fe/FexC/PC-650 are shown in Fig. 3. The binding states of iron are presented in Fig. 3a. For AuCN/PB@TA, the signal at 708.4 eV can be attributed to Fe2+, while another satellite peak at 711.4 eV is the characteristic peak of Fe3+ [36,61]. After pyrolysis, the signals appearing at 707.0 eV in the Fe 2p3/2 spectra are due to zero-valence Fe, which could originate from metallic iron or iron carbide [62]. The blue-shift of the Fe 2p XPS peak after pyrolysis indicates the reduction of Fe2+ and Fe3+ to Fe (0). The Au 4f XPS spectrum of Au/Fe/FexC/PC-650 in Fig. 3b shows two distinct peaks at 84.3 and 88.0 eV, respectively. Both signals show a blue-shift of 0.8 eV compared with AuCN/ PB@TA, due to the reduction of Au (I) to Au (0) [63,64]. This result confirms the presence of metallic gold after pyrolysis, and the bright spots observed in the backscatter SEM images are thus confirmed as metallic gold nanoparticles (Fig. 1b). Fig. 3c shows the N 1s XPS spectrum of Au/Fe/FexC/PC-650. It can be deconvoluted into three peaks, revealing the presence of pyridinic N, pyrrolic N and graphitic N [36]. The first two kinds of nitrogen can coordinate with iron to generate FeANx [37]. These results indicate some N doping in the porous carbon layers. The characterisation data has thus confirmed that the AuCN/PB composite has decomposed under pyrolytic conditions to form metallic gold nanoparticles supported on a mixed phase Fe-based support, and that the use of TA has led to a carbon layer on the surface to assist in conductivity and stability for catalytic or analytical

applications, which will be tested in the following sections. Further characterisation data of all of the materials studied is included in supporting information. 3.2. Reduction of 4-nitrophenol Model applications were chosen to probe the activity and stability of the materials, and confirm that they may have a general use for applications requiring supported Au nanoparticles. Catalytic reduction of 4-nitrophenol by NaBH4 was undertaken. Fig. S12 in the Supporting Information shows the spectral profile of 4nitrophenol, with an absorption maximum at 317 nm that shifts to 400 nm after NaBH4 addition [65]. We confirmed that 4nitrophenol reduction would not occur without a catalyst as the peak at 400 nm maintained intensity even after 18 h under the conditions used. Fig. 4b shows the evolution of the UV–vis spectra with time after adding 1 mg of Au/Fe/FexC/PC-650. The reduction of 4-nitrophenol occurs through a constant decrease in the 400 nm peak intensity, and the appearance of new peaks at 300 nm and 230 nm confirm the generation of 4-aminophenol. It is also visually observed that the yellow colour of the solution fades (Fig. 4a). The linear relationship between ln(Ct/C0) and time for Au/Fe/FexC/PC-650 is shown in Fig. 4c, along with the material produced at the lower pyrolysis temperature, Au/Fe/FexC/PC-550, and without the carbon coating Au/Fe/FexC. The rate constants were estimated using these slopes and are listed in Table 2. Au/ Fe/FexC/PC-650 obtained a higher rate constant (0.301 min 1) than the other samples, revealing the product prepared at the higher temperature to be the better catalyst. The two materials without any Au exhibited significantly lower rate constants, indicating that the Au nanoparticles are acting as the active surface for the heterogeneous catalysis. The dosage of Au/Fe/FexC/PC-650 was investigated and is shown in Table 2 and Fig. S16. Three amounts (1, 3, 5 mg) were chosen, with the reaction rate increasing with the amount of catalyst, giving the highest rate constant of 0.725 min 1 at a 5 mg dose.

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Fig. 3. (a) Fe 2p, (b) Au 4f and (c) N 1s XPS spectra of AuCN/PB@TA and Au/Fe/FexC/PC-650, showing the effect of pyrolysis on the TA coated starting material.

Fig. 4. (a) Image of the magnetic separation of the catalyst from the reaction mixture; The reduction of 4-nitrophenol with 1 mg of Au/Fe/FexC/PC-650 (b) absorption spectra (c) plot of ln(Ct/C0) vs reaction time.

Fig. 4a shows that Au/Fe/FexC/PC-650 could be easily separated with a magnet due to the magnetic properties of mixed phase Fe-based nanobox that supports the Au nanoparticles, allowing the catalysts to be recovered from the reaction solution. The recovered Au/Fe/FexC/PC-650 sample was then investigated for reusability. The results in Table 2 and Fig. S17 confirm reasonable stability of Au/Fe/FexC/PC-650 for re-use, as the conversion efficiency of 4nitrophenol was quite stable from 2 to 5 recycles, though there was some activity lost after the first cycle [66].

3.3. Electrochemical detection of As (III) Electroanalysis was used to test the stability and conductivity of the supported Au nanoparticles on the Fe-based supports. Voltammograms of the Au/Fe/FexC/PC samples in 0.5 M H2SO4 (Fig. S18) show similar CVs, where the dominant anodic features at 0.55 V and corresponding broad cathodic peaks at 0.3 V are assigned to Fe2+/Fe3+ processes [67], and a broad peak starting from 1.1 V is typical of an Au oxidation feature coupled to a small Au

B. Ren et al. / Journal of Colloid and Interface Science 540 (2019) 563–571 Table 2 Summary of rate constants for the reduction of 4-nitrophenol catalyzed by all samples. Catalysts

Recycle steps

Dosage/mg

Rate constant/min

Fe/Fe3C Fe/Fe3C/PC-650 Au/Fe/FexC Au/Fe/FexC/PC-550 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650 Au/Fe/FexC/PC-650

– – – – – – 1 2 3 4 5

1 1 1 1 1 3 5 5 5 5 5

0.009 0.015 0.161 0.209 0.301 0.348 0.725 0.368 0.313 0.314 0.311

1

reduction peak at 0.88 V, though the voltammograms are not as clean as pure Au materials due to the mixed phase support material, which precludes the determination of a reliable electrochemical surface area [68]. However, the higher Au reduction peak of Au/Fe/FexC/PC-650 does suggest that a comparatively higher surface area of Au is created at the higher pyrolysis temperature. Both samples (two pyrolysis temperatures) were then used for the electrochemical detection of As (III). Voltammograms in 0.5 M H2SO4 at 10 ppm As (III) are shown in Fig. S19, where both GC and Fe/Fe3C/ PC-650 electrodes, acting as controls, show no arsenic redox peaks in the range of 0.2 V to 0.7 V (vs. Ag / AgCl), due to their lack of Au which is a well-studied material for As(III) electroanalysis. For both Au/Fe/FexC/PC samples (Fig. S19b and S19c), a broad reduction feature starting from 0 V is assigned to the reduction of As (III) to As (0). On the reverse scan, an anodic stripping peak at 0.2 V occurs, which is assigned to the re-oxidation of As (0) to As (III) from the Au surface [71]. Square Wave Anodic Stripping Voltammetry (SWASV) was used to study the electroanalytical performance of the Au/Fe/FexC/PC650 sample for comparison to other Au nanostructures in the literature, and the stripping peaks at different As (III) concentrations are shown in Fig. 5a. Pre-deposition at 0.15 V has been used for 150 s to reduce As (III) to As (0) on the surface before anodic stripping. Au/Fe/FexC/PC-650 shows a linear increase of the stripping current with As (III) concentration (Fig. 5b). Similarly, The SWASV response of Au/Fe/FexC/PC-550 and corresponding calibration curve is shown in Fig. S20. Au/Fe/FexC/PC-650 shows a higher sensitivity of 0.03 mA ppb 1 compared to Au/Fe/FexC/PC-550 with 0.01 mA ppb 1. The limit of detection (LoD, S/N = 3) was calculated to be 0.40 ppb and 0.19 ppb for Au/Fe/FexC/PC-550 and Au/Fe/FexC/PC-650, respectively. The result indicates Au/Fe/FexC/PC-650 has superior electroanalytical performance for As (III) detection, with a higher sensitivity and lower LoD, which may derive from the larger

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Au electrochemical surface area generated at the higher pyrolysis temperature. Interference studies were conducted to evaluate the practical feasibility of Au/Fe/FexC/PC-650 for arsenic (III) determination and probe the stability of the materials under a broader range of conditions. Cu (II) is considered to be a major interfering ion as it can form a metal alloy or amalgam with arsenic during the preconditioning period on Au [69,70], and arsenic and copper have similar stripping potentials. Fig. S21 shows the SWASV responses of Au/Fe/ FexC/PC-650 with the addition of Cu (II) at 1010 ppb As (III) in 0.5 M H2SO4. The corresponding calibration curves in Fig. S21b indicate interference of Cu (II) at higher concentrations, as the stripping current of As (III) decreased with the addition of Cu (II). Therefore, a chelating agent (EDTA) was used to eliminate the interference of Cu (II) [69,70]. A 0.1 M sodium acetic buffer solution (pH 5) was used as the electrolyte for the interference experiments. Interference studies of Cu (II) in the absence and presence of 0.01 M EDTA at 100 ppb As (III) are shown in Fig. S22a and Fig. S22c. In the absence of EDTA, the stripping signal of Cu (II) increased causing interference with the As (III) determination, as shown in Fig. S22b. However, there is no obvious Cu (II) stripping current to cause interference even at high concentrations of Cu (II) (up to 1 ppm) in the presence of 0.01 M EDTA in this potential window (Fig. S22c). The As (III) stripping peaks in Fig. S22d are constant at all concentrations of Cu (II). The SWASV responses of Au/Fe/FexC/PC-650 at different concentrations of As (III) at 100 ppb Cu (II) in 0.1 M sodium acetic buffer solution (pH 5) with 0.01 M EDTA are shown in Fig. S22e. The corresponding calibration curves (Fig. S22f) show good linearity at lower concentrations of As (III) but levelled off at higher concentration due to the saturation effect of arsenic on the surface. Au/Fe/FexC/PC-650 modified Glassy Carbon Electrode (GCE) thus has a sensitivity of 0.04 mA ppb 1 and a LoD of 0.15 ppb (S/N = 3) in 0.1 M sodium acetic buffer solution (pH 5) with 0.01 M EDTA. The stability and reproducibility of the materials in any application is important, and so was tested for this quite demanding application of As analysis in H2SO4. Analyses were performed over a series of weeks, and also with 3 different electrodes (Fig. S23). There was no obvious change on the SWASV responses of 1 ppm As (III) after two weeks. The high stability of Au/Fe/FexC/PC-650, even under highly acidic conditions (0.5 M H2SO4) may be due to the protection afforded by the outer carbon shell on the inner iron and iron carbide composite, which enhances the stability of the materials compared to bare, Fe-based supports. SWASV responses of three different electrodes with the same preparation procedures at 1 ppm As (III) also show good reproducibility, providing a further measure of repeatability and stability of the these materials, and the reliability of the synthetic technique used to obtain them.

Fig. 5. (a) SWASV responses of Au/Fe/FexC/PC-650 for As (III) at different concentrations in 0.5 M H2SO4. The dash line refers to the baseline. (b) Calibration curves of current density vs. As (III) concentrations for Au/Fe/FexC/PC-650. SWASV conditions: preconditioning potential, 0.15 V; preconditioning time, 150 s; initial potential, 0.3 V; final potential, 0.7 V; frequency, 15 Hz; amplitude, 25 mV; potential increment, 4 mV.

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4. Conclusions Our key finding is that a composite formed via galvanic exchange of a redox active MOF with a noble metal, followed by pyrolysis, is a versatile preparation method for nanomaterials in which AuNPs are well-dispersed on an Fe-based support. The use of the Au based PB hybrid as the precursor ensures a homogenous distribution of the Au on the surface of the final material, and generation of the Au nanoparticles via direct pyrolysis can be considered a convenient alternative to methods such as impregnation and immobilization of separately synthesized nanoparticles on a support. A particular highlight is the that the stability of the materials is enhanced with the porous carbon shell, and the magnetic properties of the Fe based support allows efficient magnetic recycling of the catalyst. Supported Au nanoparticles have thus been directly prepared on their support, without the need to isolate them first followed by impregnation. This is a key improvement over traditional methods of nanoparticle synthesis which may not lead to such a homogeneous distribution of the active metal nanoparticles over the support [72]. It is also an advance over recent work where PB has been treated by pyrolysis, as the galvanic replacement step ensures a homogeneous distribution of the Au over the surface of the cubes, which has previously only been possible with far more complex synthetic procedures based on MOFs [73]. Model, well-known applications of 4-nitrophenol reduction and As (III) analysis suggest the performance of the Au nanoparticles in this configuration to be comparable to other Au nanomaterials, confirming possible applicability in a broader range of applications where Au nanomaterials find utility. These results thus suggest that future work using this strategy could be extended to the synthesis of a broader range of nanomaterials, where noble metal salts have the required standard reduction potential to functionalise the surface of a redox active MOF, followed by pyrolytic decomposition to obtain noble metal nanoparticles on a range of supports. Acknowledgements The authors acknowledge the facilities and technical support of the Australian Microscopy & Microanalysis Research Facility at the RMIT Microscopy & Microanalysis Facility (RMMF). B. R. thanks RMIT University for RMIT postgraduate Research International Scholarship (RPIS). A. K. thanks RMIT University for a Vice Chancellor’s Postdoctoral Fellowship. Appendix A. Supplementary material Supporting Information contains extensive characterisation data of all materials and starting materials, as well as analysis and extended catalytic results from the materials studies to support the conclusions of the paper. Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcis.2019.01. 027. References [1] C.M. Cobley, J. Chen, E.C. Cho, L.V. Wang, Y. Xia, Gold nanostructures: a class of multifunctional materials for biomedical applications, Chem. Soc. Rev. 40 (1) (2011) 44–56. [2] M. Haruta, Gold as a novel catalyst in the 21st century: preparation, working mechanism and applications, Gold bull. 37 (1) (2004) 27–36. [3] N. Khlebtsov, L. Dykman, Biodistribution and toxicity of engineered gold nanoparticles: a review of in vitro and in vivo studies, Chem. Soc. Rev. 40 (3) (2011) 1647–1671. [4] K.-S. Lee, M.A. El-Sayed, Gold and silver nanoparticles in sensing and imaging: sensitivity of plasmon response to size, shape, and metal composition, J. Phys. Chem. B 110 (39) (2006) 19220–19225.

[5] A. Morozan, S. Donck, V. Artero, E. Gravel, E. Doris, Carbon nanotubes-gold nanohybrid as potent electrocatalyst for oxygen reduction in alkaline media, Nanoscale 7 (41) (2015) 17274–17277. [6] K. Saha, S.S. Agasti, C. Kim, X. Li, V.M. Rotello, Gold nanoparticles in chemical and biological sensing, Chem. Rev. 112 (5) (2012) 2739–2779. [7] Y. Zhang, X. Cui, F. Shi, Y. Deng, Nano-gold catalysis in fine chemical synthesis, Chem. Rev. 112 (4) (2012) 2467–2505. [8] T.K. Sau, C.J. Murphy, Room temperature, high-yield synthesis of multiple shapes of gold nanoparticles in aqueous solution, J. Am. Chem. Soc. 126 (28) (2004) 8648–8649. [9] M.L. Personick, M.R. Langille, J. Zhang, N. Harris, G.C. Schatz, C.A. Mirkin, Synthesis and isolation of {110}-faceted gold bipyramids and rhombic dodecahedra, J. Am. Chem. Soc. 133 (16) (2011) 6170–6173. [10] P. Pachfule, S. Kandambeth, D.D. Díaz, R. Banerjee, Highly stable covalent organic framework–Au nanoparticles hybrids for enhanced activity for nitrophenol reduction, ChemComm 50 (24) (2014) 3169–3172. [11] Y. Lin, Y. Qiao, Y. Wang, Y. Yan, J. Huang, Self-assembled laminated nanoribbon-directed synthesis of noble metallic nanoparticle-decorated silica nanotubes and their catalytic applications, J. Mater. Chem. 22 (35) (2012) 18314–18320. [12] A. Dey, A. Kaushik, S.K. Arya, S. Bhansali, Mediator free highly sensitive polyaniline–gold hybrid nanocomposite based immunosensor for prostatespecific antigen (PSA) detection, J. Mater. Chem. 22 (29) (2012) 14763–14772. [13] C. Minelli, S.B. Lowe, M.M. Stevens, Engineering nanocomposite materials for cancer therapy, Small 6 (21) (2010) 2336–2357. [14] C. Wang, X. Tan, S. Chen, R. Yuan, F. Hu, D. Yuan, Y. Xiang, Highly-sensitive cholesterol biosensor based on platinum–gold hybrid functionalized ZnO nanorods, Talanta 94 (2012) 263–270. [15] C. Li, S. Bolisetty, R. Mezzenga, Hybrid nanocomposites of gold single-crystal platelets and amyloid fibrils with tunable fluorescence, conductivity, and sensing properties, Adv. Mater. 25 (27) (2013) 3694–3700. [16] S.K. Maji, S. Sreejith, A.K. Mandal, X. Ma, Y. Zhao, Immobilizing gold nanoparticles in mesoporous silica covered reduced graphene oxide: a hybrid material for cancer cell detection through hydrogen peroxide sensing, ACS Appl. Mater. Interfaces 6 (16) (2014) 13648–13656. [17] X. Xiao, H. Li, P. Si, One-step fabrication of bio-functionalized nanoporous gold/ poly (3, 4-ethylenedioxythiophene) hybrid electrodes for amperometric glucose sensing, Talanta 116 (2013) 1054–1059. [18] M.M. Schubert, S. Hackenberg, A.C. Van Veen, M. Muhler, V. Plzak, R.J. Behm, CO oxidation over supported gold catalysts—‘‘Inert” and ‘‘active” support materials and their role for the oxygen supply during reaction, J. Catal. 197 (1) (2001) 113–122. [19] G.C. Bond, D.T. Thompson, Gold-catalysed oxidation of carbon monoxide, Gold Bull. 33 (2) (2000) 41–50. [20] M. Haruta, Novel catalysis of gold deposited on metal oxides, Catal. Surv. Jpn. 1 (1) (1997) 61–73. [21] Z. Dong, X. Le, Y. Liu, C. Dong, J. Ma, Metal organic framework derived magnetic porous carbon composite supported gold and palladium nanoparticles as highly efficient and recyclable catalysts for reduction of 4-nitrophenol and hydrodechlorination of 4-chlorophenol, J. Mater. Chem. A 2 (44) (2014) 18775–18785. [22] O.M. Yaghi, G. Li, H. Li, Selective binding and removal of guests in a microporous metal-organic framework, Nature 378 (6558) (1995) 703. [23] H. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Design and synthesis of an exceptionally stable and highly porous metal-organic framework, Nature 402 (6759) (1999) 276. [24] H. Liu, Y. Liu, Y. Li, Z. Tang, H. Jiang, Metal-organic framework supported gold nanoparticles as a highly active heterogeneous catalyst for aerobic oxidation of alcohols, J. Phys. Chem. C 114 (31) (2010) 13362–13369. [25] Y. Liu, X. Chen, M. Zhu, U. Jameel, Recent progress of synthesis and application in Au@ MOFs hybrid materials, Catal. Surv. Asia 21 (3) (2017) 130–142. [26] H.-L. Jiang, B. Liu, T. Akita, M. Haruta, H. Sakurai, Q. Xu, Au@ ZIF-8: CO oxidation over gold nanoparticles deposited to metal-organic framework, J. Am. Chem. Soc. 131 (32) (2009) 11302–11303. [27] S. Hermes, M.K. Schröter, R. Schmid, L. Khodeir, M. Muhler, A. Tissler, R.W. Fischer, R.A. Fischer, Metal@ MOF: loading of highly porous coordination polymers host lattices by metal organic chemical vapor deposition, Angew. Chem. Int. Ed. 44 (38) (2005) 6237–6241. [28] Y. Li, X. Luo, Z.-L. Xu, J. Ge, Monodispersed gold nanoparticles supported on a Zirconium-based porous metal-organic framework and its high catalytic ability for the reverse water-gas shift reaction, ChemComm (2017). [29] K. Sugikawa, Y. Furukawa, K. Sada, SERS-active metal–organic frameworks embedding gold nanorods, Chem. Mater. 23 (13) (2011) 3132–3134. [30] L. He, Y. Liu, J. Liu, Y. Xiong, J. Zheng, Y. Liu, Z. Tang, Core-shell noble-metal@ metal-organic-framework nanoparticles with highly selective sensing property, Angew. Chem. Int. Ed. 52 (13) (2013) 3741–3745. [31] X. Cai, W. Gao, M. Ma, M. Wu, L. Zhang, Y. Zheng, H. Chen, J. Shi, A Prussian blue-based core-shell hollow-structured mesoporous nanoparticle as a smart theranostic agent with ultrahigh pH-responsive longitudinal relaxivity, Adv. Mater. 27 (41) (2015) 6382–6389. [32] L. Zhang, H.B. Wu, S. Madhavi, H.H. Hng, X.W. Lou, Formation of Fe2O3 microboxes with hierarchical shell structures from metal–organic frameworks and their lithium storage properties, J. Am. Chem. Soc. 134 (42) (2012) 17388– 17391.

B. Ren et al. / Journal of Colloid and Interface Science 540 (2019) 563–571 [33] L. Zhang, H.B. Wu, X.W. Lou, Metal–organic-frameworks-derived general formation of hollow structures with high complexity, J. Am. Chem. Soc. 135 (29) (2013) 10664–10672. [34] B. Kong, C. Selomulya, G.F. Zheng, D.Y. Zhao, New faces of porous Prussian blue: interfacial assembly of integrated hetero-structures for sensing applications, Chem. Soc. Rev. 44 (22) (2015) 7997–8018. [35] T. Wen, X. Wang, J. Wang, Z. Chen, J. Li, J. Hu, T. Hayat, A. Alsaedi, B. Grambow, X. Wang, A strategically designed porous magnetic N-doped Fe/Fe3C@C matrix and its highly efficient uranium(vi) remediation, Inorg. Chem. Front. (2016). [36] Y. Hou, T. Huang, Z. Wen, S. Mao, S. Cui, J. Chen, Metal-organic frameworkderived nitrogen-doped core-shell-structured porous Fe/Fe3C@ C nanoboxes supported on graphene sheets for efficient oxygen reduction reactions, Adv. Energy Mater. 4 (11) (2014). [37] J. Wei, Y. Liang, Y. Hu, B. Kong, G.P. Simon, J. Zhang, S.P. Jiang, H. Wang, A versatile iron–tannin-framework ink coating strategy to fabricate biomassderived iron carbide/Fe-N-carbon catalysts for efficient oxygen reduction, Angew. Chem. Int. Ed. 128 (4) (2016) 1377–1381. [38] B. Ren, L.A. Jones, D.K. Oppedisano, A.E. Kandjani, M. Chen, F. Antolasic, S.J. Ippolito, S.K. Bhargava, The preparation of a AuCN/prussian blue nanocube composite through galvanic replacement enhances stability for electrocatalysis, ChemistrySelect 2 (19) (2017) 5333–5340. [39] R.V. Jagadeesh, K. Murugesan, A.S. Alshammari, H. Neumann, M.-M. Pohl, J. Radnik, M. Beller, MOF-derived cobalt nanoparticles catalyze a general synthesis of amines, Science 358 (6361) (2017) 326–332. [40] R.V. Jagadeesh, A.-E. Surkus, H. Junge, M.-M. Pohl, J. Radnik, J. Rabeah, H. Huan, V. Schünemann, A. Brückner, M. Beller, Nanoscale Fe2O3-based catalysts for selective hydrogenation of nitroarenes to anilines, Science 342 (6162) (2013) 1073–1076. [41] P. Pachfule, D. Shinde, M. Majumder, Q. Xu, Fabrication of carbon nanorods and graphene nanoribbons from a metal–organic framework, Nat. Chem. 8 (7) (2016) 718–724. [42] Z. Dong, G. Yu, X. Le, Gold nanoparticle modified magnetic fibrous silica microspheres as a highly efficient and recyclable catalyst for the reduction of 4-nitrophenol, New J. Chem. 39 (11) (2015) 8623–8629. [43] J. Xi, Y. Xia, Y. Xu, J. Xiao, S. Wang, (Fe, Co)@nitrogen-doped graphitic carbon nanocubes derived from polydopamine-encapsulated metal-organic frameworks as a highly stable and selective non-precious oxygen reduction electrocatalyst, ChemComm 51 (52) (2015) 10479–10482. [44] D. Deng, L. Yu, X. Chen, G. Wang, L. Jin, X. Pan, J. Deng, G. Sun, X. Bao, Iron encapsulated within pod-like carbon nanotubes for oxygen reduction reaction, Angew. Chem. Int. Ed. 52 (1) (2013) 371–375. [45] N.P. Wickramaratne, V.S. Perera, B.-W. Park, M. Gao, G.W. McGimpsey, S.D. Huang, M. Jaroniec, Graphitic mesoporous carbons with embedded prussian blue-derived iron oxide nanoparticles synthesized by soft templating and lowtemperature graphitization, Chem. Mater. 25 (14) (2013) 2803–2811. [46] H. Yang, S.J. Bradley, A. Chan, G.I.N. Waterhouse, T. Nann, P.E. Kruger, S.G. Telfer, Catalytically active bimetallic nanoparticles supported on porous carbon capsules derived from metal-organic framework composites, J. Am. Chem Soc. (2016). [47] H. Ejima, J.J. Richardson, F. Caruso, Phenolic film engineering for templatemediated microcapsule preparation, Polym. J. 46 (8) (2014) 452–459. [48] H. Ejima, J.J. Richardson, K. Liang, J.P. Best, M.P. van Koeverden, G.K. Such, J. Cui, F. Caruso, One-step assembly of coordination complexes for versatile film and particle engineering, Science 341 (6142) (2013) 154–157. [49] J. Lee, J.C. Park, H. Song, A nanoreactor framework of a Au@SiO2 Yolk/Shell structure for catalytic reduction of p-nitrophenol, Adv. Mater. 20 (8) (2008) 1523–1528. [50] P.J. Kulesza, M.A. Malik, A. Denca, J. Strojek, In situ FT-IR/ATR spectroelectrochemistry of Prussian Blue in the solid state, Anal. Chem. 68 (14) (1996) 2442–2446. [51] X.-Q. Zhang, S.-W. Gong, Y. Zhang, T. Yang, C.-Y. Wang, N. Gu, Prussian blue modified iron oxide magnetic nanoparticles and their high peroxidase-like activity, J. Mater. Chem. 20 (24) (2010) 5110–5116. [52] X. Zhang, C. Sui, J. Gong, R. Yang, Y. Luo, L. Qu, Preparation, characterization, and property of polyaniline/Prussian blue micro-composites in a lowtemperature hydrothermal process, Appl. Surf. Sci. 253 (22) (2007) 9030– 9034.

571

[53] H. Niu, B. Volesky, Characteristics of gold biosorption from cyanide solution, J. Chem. Technol. Biotechnol. 74 (8) (1999) 778–784. [54] Z. Wen, S. Ci, F. Zhang, X. Feng, S. Cui, S. Mao, S. Luo, Z. He, J. Chen, Nitrogenenriched core-shell structured Fe/Fe3C-C nanorods as advanced electrocatalysts for oxygen reduction reaction, Adv. Mater. 24 (11) (2012) 1399–1404. [55] E. Imperio, G. Giancane, L. Valli, Spectral characterization of postage stamp printing inks by means of Raman spectroscopy, Analyst 140 (5) (2015) 1702– 1710. [56] R. Mazˇeikiene˙, G. Niaura, A. Malinauskas, Electrocatalytic reduction of hydrogen peroxide at Prussian blue modified electrode: an in situ Raman spectroelectrochemical study, J. Electroanal. Chem. 660 (1) (2011) 140–146. [57] L. Fan, Y. Ma, Y. Su, R. Zhang, Y. Liu, Q. Zhang, Z. Jiang, Green coating by coordination of tannic acid and iron ions for antioxidant nanofiltration membranes, RSC Adv. 5 (130) (2015) 107777–107784. [58] I. Michaud-Soret, K.K. Andersson, L. Que Jr, J. Haavik, Resonance Raman studies of catecholate and phenolate complexes of recombinant human tyrosine hydroxylase, Biochemistry 34 (16) (1995) 5504–5510. [59] R. Qiang, Y. Du, H. Zhao, Y. Wang, C. Tian, Z. Li, X. Han, P. Xu, Metal organic framework-derived Fe/C nanocubes toward efficient microwave absorption, J. Mater. Chem. A 3 (25) (2015) 13426–13434. [60] M.S. Dresselhaus, A. Jorio, M. Hofmann, G. Dresselhaus, R. Saito, Perspectives on carbon nanotubes and graphene Raman spectroscopy, Nano Lett. 10 (3) (2010) 751–758. [61] D. Jampaiah, T.S. Reddy, A.E. Kandjani, P. Selvakannan, Y.M. Sabri, V.E. Coyle, R. Shukla, S.K. Bhargava, Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection, J. Mater. Chem. B 4 (22) (2016) 3874–3885. [62] W.-J. Jiang, L. Gu, L. Li, Y. Zhang, X. Zhang, L.-J. Zhang, J.-Q. Wang, J.-S. Hu, Z. Wei, L.-J. Wan, Understanding the high activity of Fe–N–C electrocatalysts in oxygen reduction: Fe/Fe3C nanoparticles boost the activity of Fe–Nx, J. Am. Chem. Soc. 138 (10) (2016) 3570–3578. [63] R.H. Li, H. Kobayashi, J.W. Tong, X.Q. Yan, Y. Tang, S.H. Zou, J.B. Jin, W.Z. Yi, J. Fan, Radical-involved photosynthesis of AuCN oligomers from Au nanoparticles and acetonitrile, J. Am. Chem. Soc. 134 (44) (2012) 18286– 18294. [64] W.Z. Yi, X.Q. Yan, R.H. Li, J.Q. Wang, S.H. Zou, L.P. Xiao, H. Kobayashi, J. Fan, A new application of the traditional Fenton process to gold cyanide synthesis using acetonitrile as a cyanide source, Rsc Adv. 6 (20) (2016) 16448–16451. [65] Z.F. Jiang, D.L. Jiang, A.M.S. Hossain, K. Qian, J.M. Xie, In situ synthesis of silver supported nanoporous iron oxide microbox hybrids from metal-organic frameworks and their catalytic application in p-nitrophenol reduction, Phys. Chem. Chem. Phys. 17 (4) (2015) 2550–2559. [66] F.-H. Lin, R.-A. Doong, Bifunctional Au Fe3O4 heterostructures for magnetically recyclable catalysis of nitrophenol reduction, J. Phys. Chem. C 115 (14) (2011) 6591–6598. [67] L.-J. Wan, T. Moriyama, M. Ito, H. Uchida, M. Watanabe, In situ STM imaging of surface dissolution and rearrangement of a Pt–Fe alloy electrocatalyst in electrolyte solution, ChemComm (1) (2002) 58–59. [68] X. Dai, O. Nekrassova, M.E. Hyde, R.G. Compton, Anodic stripping voltammetry of arsenic (III) using gold nanoparticle-modified electrodes, Anal. Chem. 76 (19) (2004) 5924–5929. [69] H.-H. Chen, J.-F. Huang, EDTA assisted highly selective detection of As3+ on Au nanoparticle modified glassy carbon electrodes: facile in situ electrochemical characterization of Au nanoparticles, Anal. Chem. 86 (24) (2014) 12406– 12413. [70] J.-F. Huang, H.-H. Chen, Gold-nanoparticle-embedded nafion composite modified on glassy carbon electrode for highly selective detection of arsenic (III), Talanta 116 (2013) 852–859. [71] B. Ren, L.A. Jones, M. Chen, D.K. Oppedisano, D. Qiu, S.J. Ipolito, S.K. Bhargava, The effect of electrodeposition parameters and morphology on the perfomace of Au nanostructures for the detection of As(III), J. Electrochem. Soc., 164 (14), H1121. [72] B. Hvolbaek, T.V.W. Jansses, B.S. Clausen, H. Falsig, C.H. Christensen, J.K. Norskov, Catalytic activity of Au nanopartricles, Nano Today 2 (4) (2007) 14. [73] A. DHakshinamoorthy, A.M. Asiri, H. Garcia, Metal Organic frameworks as versatile hosts of Au nanoparticles in heterogeneous catalysis, ACS Catal. 7 (4) (2017) 2896.