Elsevier

Applied Surface Science

Volume 434, 15 March 2018, Pages 522-533
Applied Surface Science

Full Length Article
Enhanced catalytic activity of Ag nanoparticles supported on polyacrylamide/polypyrrole/graphene oxide nanosheets for the reduction of 4-nitrophenol

https://doi.org/10.1016/j.apsusc.2017.10.209Get rights and content

Highlights

  • Ag/PAM/PPy/GO composite nanosheets were successfully synthesized.

  • They exhibited an excellent catalytic activity for the reduction of 4-NP by NaBH4.

  • The corresponding catalytic mechanism has been revealed.

  • The effect of different components on the catalytic performance were detailedly investigated.

  • The composite nanosheets can act as excellent recyclable catalysts for the reduction of 4-NP.

Abstract

High-density and well-dispersed Ag nanoparticles (Ag NPs) with a mean size of 20 nm have been successfully supported on the surface of polyacrylamide functionalized polypyrrole/graphene oxide (PAM/PPy/GO) nanosheets. The obtained Ag/PAM/PPy/GO composite nanosheets exhibited an excellent catalytic activity for reduction of 4-nitrophenol by NaBH4 with the kinetic reaction rate constant of 3.38 × 10−2 s−1 due to the synergistic effect of all the components of the composite nanosheets. The corresponding catalytic mechanism has been revealed by investigating the effect of different components of Ag/PAM/PPy/GO composite nanosheets on the catalytic performance: GO with the excellent two-dimensional structures offered large surface area for the immobilization of more Ag NPs; PPy with a high electric conductivity promoted the electron transport in the reduction of 4-NP; PAM did not only act as a good linker between Ag NPs and PPy/GO nanosheets for the synthesis of Ag/PAM/PPy/GO composite nanosheets, but also could facilitate the efficient contact between 4-NP and Ag NPs; Ag NPs were the catalytic active site for the reduction of 4-NP, respectively.

Graphical abstract

Ag/PAM/PPy/GO composite nanosheets were successfully synthesized, which exhibited an excellent catalytic activity for the reduction of 4-NP by NaBH4, and the corresponding catalytic mechanism has been revealed by investigating the effect of different components of Ag/PAM/PPy/GO composite nanosheets on the catalytic performance.

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Introduction

Along with the impressive and continuous developments of science and technology in the modern society, new nanocomposite materials with the integration of structure functions and devisable comprehensive performance based on nano effects, have become a new research focus. Noble metal nanoparticles, such as Au, Pd, Pt, Ag, have attracted great attentions because of their unusual properties that are markedly different from their respective bulk metals in electronic devices [1], optical materials [2], waste water treatment [3], medicine [4], catalytic processes [5], [6] and so on. Due to the much low cost and the characteristics of high reactivity and selectivity [7], silver nanoparticles (Ag NPs) have been exploited as a kind of efficient catalyst for a variety of catalytic reactions, such as oxidative conversion of methanol into formaldehyde [8], selective butadiene epoxidation [9] and the oxidation of D-glucose [10], especially for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) [11], which is not only a commercially important intermediate for the manufacture of analgesic and antipyretic drugs [12], [13], [14], such as paracetamol and phenacetin, but also used enormously as a photographic developer, corrosion inhibitor, anticorrosion-lubricant and hair-dyeing agent [15]. Therefore, the reduction of 4-NP to 4-AP catalyzed by Ag NPs has been intensively investigated as an alternative effective and eco-friendly route for the efficient production of 4-AP in industry [16].

As well known, smaller Ag NPs with narrow distribution usually shows higher activity for the reduction reactions due to its higher surface-to-volume ratio and more negative redox potential, which are beneficial to the electrons transfer from Ag surface to reactants [17], [18]. However, Ag NPs with smaller size can easily aggregate together due to its higher surface energies, resulting in the decrease of the surface area of catalysts and a remarkable reduction in its original catalytic activities [19], [20]. The immobilization of Ag NPs on an appropriate supporter surface is considiered as one of the effective way to solve its aggregation, and the electrons transfer performance of the supporter as well as the concentration of reactants on the supporter surface, which should be achieved by introducing some functional groups having affinity to the reactants on the surface, are also important affect factors on the catalytic performance of Ag NPs. Up to now, various supporters, such as silica [21], zeolite [22], alumina [23], ceria [24], titania [25], [26], carbon materials (including activated carbon [27], carbon spheres [16], carbon nanotubes [28], carbon nanofibers [7], graphene oxide [29]) and polymeric materials [30], have been used for the immobilization of Ag NPs in order to prevent the nanoparticles from aggregation and serve as carriers for the electrons transfer from Ag surface to reactants. However, these supporters are all one-component material,in which the three functions, i.e. the excellent electric conductivity, the uniform distribution of Ag NPs and the concentration of reagents on its surface, could be hardly intergrated simultaneously. However, the multi-functionization should be achieved out of nanocomposites through a synergistic effect of each composition in the nanocomposites.

Recently, our group has developed the technology of surface functionalization for polypyrrole/graphene oxide (PPy/GO) nanosheets by covalent interaction, which possesses the large surface area as well as high electric conductivity at room temperature. Some novel functionalized PPy/GO nanocomposites modified by imidazolium-type poly(ionic liquids) [31], [32] or hydrophilic polymers [33] have been synthesized, which could be used as good electrode materials for detecting dopamine and ascorbic acid. Herein, a novel kind of nanocomposites composed of Ag NPs and polyacrylamide (PAM) modified PPy/GO nanosheets (PAM/PPy/GO), Ag/PAM/PPy/GO composite nanosheets, were successfully prepared, where Ag NPs with appropriate sizes were uniformly and stably distributed on the surface of PAM/PPy/GO nanosheets due to the strong coordination interaction between Ag+ ions and amide groups during the in-situ reduction of Ag NPs [34]. The catalytic activity of the obtained Ag/PAM/PPy/GO composite nanosheets for the reduction of 4-NP by NaBH4 was investigated, and the corresponding catalytic mechanism was discussed. The research results indicate that the Ag/PAM/PPy/GO composite nanosheets have an excellent catalytic activity for the reduction of 4-NP due to the synergistic effect of GO, PPy, PAM, and Ag NPs.

Section snippets

Materials

Pyrrole (Py) (≥98.0%), high-purity graphite powder (≥99.85%), allyl chloride (≥98.0%) and acrylamide (AM) (≥98.5%) purchased from Sinopharm Chemical Reagent Co. Ltd. are chemical grade. All the other reagents were analytical grade, and used without further purification, including KMnO4 (Tianjin Baishi Chemical Co. Ltd, ≥99.5%), FeCl3·6H2O (≥99.0%), H2SO4 (≥98.3%), KOH (≥85.0%) and NaCl (≥99.5%) (Sinopharm Chemical Reagent Co. Ltd.), 2,2-azobisisobutyronitrile (AIBN) (≥98.0%) (Aladdin reagent

Morphology and characterizations of Ag/PAM/PPy/GO composite nanosheets

Fig. 1 presents SEM and TEM images of PAM/PPy/GO nanosheets (S0) and Ag/PAM/PPy/GO composite nanosheets (S1) synthesized after the procedure as Scheme 1. S0 shows a flaky texture with wrinkled forms in Fig. 1(a), which is similar to our previous report [33]. S1 exhibits a rough surface with many spots in Fig. 1(b), born of Ag NPs. The existence of Ag NPs in S1 with a typical laminated structure can be well confirmed by TEM images. Compared with S0 in Fig. 1(c), Ag NPs can be clearly observed

Conclusions

In summary, high-density and well-dispersed Ag NPs with a mean size of 20 nm have been successfully deposited on the surface of PAM/PPy/GO nanosheets due to the presence of PAM, which were applied as a good linker between Ag NPs and PPy/GO nanosheets. The obtained Ag/PAM/PPy/GO composite nanosheets exhibited an excellent catalytic activity for the reduction of 4-NP by NaBH4 arising from the synergistic effect of GO, PPy, PAM, as well as Ag NPs, and the corresponding catalytic mechanism have been

Acknowledgements

The financial supports from the National Natural Science Foundation of China (No. 51203072, 51273087 and 21203082) are greatly appreciated.

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