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. 2015 Aug 27:5:13515.
doi: 10.1038/srep13515.

Microbial synthesis of Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites for catalytic reduction of nitroaromatic compounds

Ya Tuo  1 , Guangfei Liu  1 , Bin Dong  1 , Jiti Zhou  1 , Aijie Wang  2 , Jing Wang  1 , Ruofei Jin  1 , Hong Lv  1 , Zeou Dou  1 , Wenyu Huang  1
Affiliations

Microbial synthesis of Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites for catalytic reduction of nitroaromatic compounds

Ya Tuo et al. Sci Rep. .

Abstract

Magnetically recoverable noble metal nanoparticles are promising catalysts for chemical reactions. However, the chemical synthesis of these nanocatalysts generally causes environmental concern due to usage of toxic chemicals under extreme conditions. Here, Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites are biosynthesized under ambient and physiological conditions by Shewanella oneidensis MR-1. Microbial cells firstly transform akaganeite into magnetite, which then serves as support for the further synthesis of Pd, Au and PdAu nanoparticles from respective precursor salts. Surface-bound cellular components and exopolysaccharides not only function as shape-directing agent to convert some Fe3O4 nanoparticles to nanorods, but also participate in the formation of PdAu alloy nanoparticles on magnetite. All these three kinds of magnetic nanocomposites can catalyze the reduction of 4-nitrophenol and some other nitroaromatic compounds by NaBH4. PdAu/Fe3O4 demonstrates higher catalytic activity than Pd/Fe3O4 and Au/Fe3O4. Moreover, the magnetic nanocomposites can be easily recovered through magnetic decantation after catalysis reaction. PdAu/Fe3O4 can be reused in at least eight successive cycles of 4-nitrophenol reduction. The biosynthesis approach presented here does not require harmful agents or rigorous conditions and thus provides facile and environmentally benign choice for the preparation of magnetic noble metal nanocatalysts.

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Figures

Figure 1
Figure 1. Morphology and element analyses.
TEM and HRTEM images (insert) of (a) Pd/Fe3O4, (c) Au/Fe3O4 and (e) PdAu/Fe3O4 obtained through the addition of Pd(II) or/and Au(III) precursor salt solutions to the biogenic Fe3O4 suspension. The EDX spectra in (b,d,f) correspond to samples of (a,c,e), respectively.
Figure 2
Figure 2. Crystalline structure.
(a) XRD patterns of (i) Pd/Fe3O4, (ii) Au/Fe3O4 and (iii) PdAu/Fe3O4. (b) Magnification of the peaks (111) and (200) in the 2θ range of 36–48°.
Figure 3
Figure 3. XPS spectra of PdAu/Fe3O4.
(a) survey scan, (b) Fe 2p, (c) Pd 3d and (d) Au 4f.
Figure 4
Figure 4. Magnetic properties.
Magnetic hysteresis loops of (a) Fe3O4, (b) Pd/Fe3O4, (c) Au/Fe3O4 and (d) PdAu/Fe3O4. The insert pattern showed the magnetic separation of Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 after catalysis reaction.
Figure 5
Figure 5. Characterization of the organic components on the surface of different biogenic nanomaterials.
(a) FTIR spectra. (b–g) CLSM images. (b,e) bright-field microscopy, (c,f) green fluorescence (SYTO9) representing nucleic acids, and (d,g) orange fluorescence (lectin PHA-L conjugates) representing exopolysaccharides on (b–d) biogenic Fe3O4 and (e–g) PdAu/Fe3O4. (h) fluorescence intensity curves corresponding to CLSM images. (i) TAG analyses of Fe3O4 and PdAu/Fe3O4.
Figure 6
Figure 6. Catalytic performances.
(a) Plots of ln(Ct/C0) versus time for the reduction of 4-NP by NaBH4 in the presence of Pd/Fe3O4, Au/Fe3O4, Pd/Fe3O4 + Au/Fe3O4 or PdAu/Fe3O4. (b) The reusability of PdAu/Fe3O4 as catalyst for reduction of 4-NP by NaBH4. (c,d) TEM image and size distribution of PdAu/Fe3O4 after reusing for eight runs. Error bars represented standard deviation (n = 3). Significant differences based on the one-way ANOVA (p < 0.05).
Figure 7
Figure 7. Scheme for synthesis and application of Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanoparticles.
The biogenic Fe3O4 nanoparticles were firstly produced by S. oneidensis MR-1 from akaganeite, and then served as support for the further synthesis of Pd, Au and PdAu nanoparticles from respective precursor salts. Microbially originated organic substances like surface-bound cellular components and exopolysaccharides not only function as shape-directing agent to convert some Fe3O4 nanoparticles to nanorods, but also participate in the formation of PdAu alloy nanoparticles on magnetite. The catalytic capabilities of the resultant nanocomposites were tested with the reduction of 4-NP by NaBH4.
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