One-pot, green, rapid synthesis of flower-like gold. nanoparticles/reduced graphene oxide with. regenerated silk fibroin as efficient oxygen reduction

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1 Supporting Information One-pot, green, rapid synthesis of flower-like gold nanoparticles/reduced graphene oxide with regenerated silk fibroin as efficient oxygen reduction electrocatalysts Shengjie Xu, Yong Liu, Peiyi Wu* 8 Laboratory of Advanced Materials, State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai, 00, P. R. China 9 EXPERIMENTAL SECTION 0 Preparation of other shapes Au NPs/RGO composites Spherical I: mg GO was sonicated and dispersed in 8 ml water to prepare mg/ml GO solution, then 0 ml wt% RSF and ml 0 mm HAuCl were added with raising ph to by the addition of.0 M NaOH. The mixture was sonicated for another 0 min, and heated to 0-0 o C for 0 h. Cooled the solution rapidly and then removed excessive RSF and smaller Au NPs which were not absorbed on graphene by a 0 min centrifugation at 000 rpm for several times and the resulting black precipitates were redispersed in water for further characterization.

2 Spherical II: mg GO was sonicated and dispersed in 8 ml water, and 0 ml wt% RSF was added. The ph of the mixture was raised to around by the addition of.0 M NaOH. The mixture was heated to 0-0 o C for -h after 0 min sonication. Then ml 0 mm HAuCl was added with adjusting the ph to by.0 M HCl, and heated to 0 o C for another h. Cooled the solution rapidly and then removed excessive RSF and smaller Au NPs which were not absorbed on graphene by a 0 min centrifugation at 000 rpm for several times and the resulting black precipitates were redispersed in water for further characterization Branched: mg GO was sonicated and dispersed in 8 ml water, and 0 ml wt% RSF was added. The solution was sonicated for another 0 min, and heated to 0-0 o C for h. Then M NaOH was added to raise ph to, and heated for another h. After that,.ml mm HAuCl was added with adjusting the ph to by.0 M HCl, and heated to o C for min. Cooled the solution rapidly and then removed excessive RSF and smaller Au NPs which were not absorbed on graphene by a 0 min centrifugation at 000 rpm for several times and the resulting black precipitates were redispersed in water for further characterization. Figure S. (a) FTIR spectra of RSF reduced RGO and flower-like Au NPs/RGO

3 composite. (b) TGA curves of GO, RSF reduced RGO and flower-like Au NPs/RGO composite. FTIR spectra (Figure Sa) indicate that the flower-like Au NPs/RGO composite has the functional groups of RSF, as revealed by the obvious peaks at 0, 00, 0 and 0 cm -, which are assigned to N-H stretching, C-H stretching in aromatic ring, amide I and amide II, respectively. 8 In TGA curves, The weight loss within the range from 00 to 0 o C is attributed to the decomposition of oxygenic functional groups of GO, and the weight loss section from 0 to 0 o C is ascribed to the RSF weight loss, suggesting RSF chains are still absorbed on RGO sheets after Au NPs reduction. Figure S. XRD patterns of flower-like Au NPs/RGO composite, branched Au NPs/RGO composite and spherical Au (I), (II) NPs/RGO composite. 9 0 XRD patterns show all of the Au NPs with different morphologies have the same crystal faces (), (00), (0) and (). The peaks of branched Au NPs/RGO composite and flower-like

4 Au NPs/RGO composite are broader than that of spherical Au NPs/RGO composite, which can be ascribed to the edge effect of their secondary branches. Figure S. UV-vis spectra of Au NPs/RGO composites prepared with different ratio of HAuCl : RGO, (a) :, (b) :, (c) 8: (V: V). UV spectra show that the main absorbance peak is red shifted with increasing the ratio of HAuCl : RGO. The peaks (with ratio of HAuCl : RGO about : and 8:) are ranged from 00 to 80 nm, which is also resulted from the edge effect of their secondary branches. Figure S. CV curve of RGO reduced by RSF

5 Figure S. EDS of spherical Au (I), (II) NPs composite (a), (b), branched Au NPs/RGO composite (c) and flower-like Au NPs/RGO composite (d). The insets are the corresponding TEM images. TEM images show the morphologies of Au NPs prepared under different reaction conditions. The size of these Au are 0 nm (spherical I), 80 nm (spherical II), 00 nm (length) (branched) and 00 nm (flower-like), respectively. Au contents in these composites can be calculated in EDS patterns, the mass fraction is. (spherical I),.8 (spherical II),.(branched) and. wt% (flower-like), respectively.

6 Figure S. The dependence of n value for flower-like Au NPs/RGO composite on the potential. The experimental data were obtained from Figure b.