Zeta potentials were measured with NICOMP 380 ZLS Zeta Potential/Particle Size Analyzer. The XPS measurements were performed

on an Axis Ultra DLD XPS (Kratos Analytical, Manchester, UK) using a monochromated Al Kα (1,486.6 eV) source at 15 AZD1208 kV. Scanning electron microscopy (SEM) images were taken on a ZEISS-ULTRA 55 SEM (Oberkochen, Germany) equipped with an X-ray energy-dispersive spectroscope (EDS) at an accelerating voltage of 20 kV (provided in Additional file 1). In addition, the conductive properties of the nanoscale GO film coated on the mica surface were tested using a conductive AFM. The detailed process and results have been given in Additional file 1. Results and discussion Tailoring large-area GO by different metal ions Graphene oxide is very widely generated using natural graphite powder through the Hummers method. The chemically derived GO is soluble in pure water due to hydrophilic functional groups, e.g., carboxyl, hydroxyl, and epoxide groups on the surface [16, 21]. Figure 1a shows the AFM image of GO with atom-level smoothness and the sizes in the range of 1 to 10 μm. The height profile of the AFM image in Figure 1e is approximately 1 nm, which is consistent with the data reported in the literature, indicating the formation of a single-layered GO. Figure 1b,c,d depicts that the nanoscale GO pieces with buy HM781-36B different sizes were tailored utilizing three kinds of

metal ions (Ag+, Ni2+, Co2+), respectively. Corresponding profile analysis of these AFM height images (Figure 1f,g,h) has given heights of approximately 1 nm, which were elementally consistent

with the thickness of GO. Similarly, in the addition of Ag+ ion system, some nanoparticles have been found to be dispersed in the solution or attached on the GO surfaces similar to what we have reported previously [22]. In our previous work, we mainly focused on the synthesis of silver-GO composites. When testing the samples Loperamide by AFM, some little pieces were occasionally detected in the high-resolution images, which were neglected as contamination before [22]. Thereafter, in order to investigate the tailoring mechanism, we selected the other weak oxidation of metal ions, such as Ni2+ and Co2+, and obtained results similar to the information given previously. In addition, XPS data have been provided in Additional file 1: Figure S1. Figure 1 Tapping-mode AFM images of GO and nanoscale GO pieces. (a) GO, (b) Ag+, (c) Co2+, and (d) Ni2+ and corresponding profile analysis: (e) GO, (f) Ag+, (g) Co2+, and (h) Ni2+. Tailoring large-area GO by silver ions For silver ions, a series of systematic experiments have been carried out. In a typical experiment, 0.50 mg/mL of an aqueous GO dispersion (10 mL) was added to 10 mM aqueous AgNO3 solution (10 mL). As shown in Figure 2a, the large-area GO has been tailored into small fragments after the reaction was kept for approximately 12 h. TEM image and EDS data were given in Additional file 1: Figure S2.