Yu et al. Nanoscale Research Letters 2012, 7:234 http://www.nanoscalereslett.com/content/7/1/234 Page 3 of 4 Figure 2 FT-IR spectra. (a) GO, (b) GO after glow discharge treatment and (c) Pd/GO. still tiny decreases in the absorption bands at 1,725, 1,221 and 1,056 cm-1. We can assume that the decreases were caused by the modification of the functional groups (C = O, C-OH and C-O) by the Pd nanoparticles. TEM analysis was applied to determine the morphol- ogy of the Pd/GO sample. Figure 3 shows that Pd nano- particles were uniformly dispersed on GO with an average particle diameter of 1.6 nm and a narrow distri- bution (standard deviation, SD = 0.37 nm). High-resolu- tion TEM imaging (Figure 3b) of Pd NPs clearly showed the existence of lattice fringes with d = 0.224 nm, which could be attributed to the (111) planes of Pd. This result was consistent with the aforementioned AFM characterizations. The pH effect of the Pd deposition process can be explained by the deposition-precipitation mechanism. GO sheets are highly negatively charged between pH 4 and 10, which can be attributed to the de-protonation of surface hydroxy and carboxy groups at the surface of GO [3-5]. Higher pH resulted in lower zeta potential and more de-protonation of surface groups. For palla- dium precursors in the solvent, with the addition of NaOH, palladium chloride would hydrolyze into poly- nuclear palladium (II) hydroxocomplexes (PHCs) with a diameter of 2 nm [14,15]. The PHC has a positively charged core by Na+ cations and, thus, can be absorbed onto GO by electrostatic forces. In lower pH (4 and 5) (Figure 1a,b), PHCs were not formed, and electrostatic repulsion between GO substrate and PdCl42- complexes kept the palladium off the substrate. Conclusions Pd nanoparticles with an average size of 1.6 nm are deposited on graphene oxide following a deposition-pre- cipitation method and glow discharge plasma reduction at room temperature. The pH value has a significant effect on the fabrication of Pd/GO composites. The glow discharge plasma can efficiently reduce Pd precur- sors while maintaining GO unreduced. Pd/GO compo- site is successfully fabricated with high dispersion of metal nanoparticles. Abbreviations GO: Graphene oxide; AFM: Atomic force microscopy; FT-IR: Fourier transform infrared; TEM: Transmission electron microscopy; PHC: Palladium (II) hydroxocomplex. Acknowledgements The financial support from the National Natural Science Foundation of China (#20990223) is greatly appreciated. We appreciate Dr. Mingdong Dong at Aarhus University, Denmark for his help in the operation of the AFM. Authors’ contributions YY synthesized and characterized the Pd/GO samples and wrote the manuscript. YZL prepared the raw GO material, YXP conceived and designed the experiments, and CJL coordinated the study. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Figure 3 TEM image. (a) and (b) Pd/GO and (c) size distribution of Pd nanoparticles on GO.