Graphene oxide (GO) with an extraordinary atomic and electronic structure has germinated into an attractive building block for the design and fabrication of new chiral nanomaterials. Herein, we have synthesized a GO-humic acid (HA) sandwich-type complex that can selfassemble into a twisted, long-range-ordered nanostructure in aqueous media.

The content of oxygen-containing functional groups in GO-HA complex was analyzed by SRXPS. The atomic ratio of O/C in GO-HA (0.41) is markedly higher than in GO (0.23), demonstrating an increase of oxygen-containing groups in GO-HA due to HA adsorption and good hydrophilicity.

Chirality of GO-HA was investigated by SRCD, the intensity of the CD peak significantly increased at the GO/HA mass ratio of 1:2, indicating that HA provided apparent chirality amplification (Figure 1). Furthermore, it can be observed that the CD signal of each enantiomeric nanostructure in GO-HA was apparently enhanced with the increase of pH. With the increase of pH from 4.1 to 10.5, the CD signal of GO-HA, increased at high pH. The VT-CD analysis showed that the CD intensity at 220 nm of GO and GO-HA decreased with the increase of temperature from 5 to 45 °C. Importantly, the VT-CD spectra of GO was irreversible after a 5-45-5 °C cycle, while the GO-HA presented reversible behavior, demonstrating that the structure of GO-HA was more stable and ordered than that of GO.

Figure 1 Synchrotron radiation CD study of circular dichroism of GO-HA complex.

The orientation and average size of the GO-HA assembly nanostructure was investigated by using SAXS. The SAXS 2D patterns of GO nanosheets exhibited circular shape, while the GO-HA presented an elliptical shape at GO/HA mass ratios of 1:1 and 1:2, suggesting the formation of orientational order. Furthermore, the profiles of scattering intensity showed a weak and wide scattering peak in GO sheets, while a strong and narrow scattering peak appeared for GO？HA complex and it dramatically increased at 1:1 and 1:2, indicating the increase of orientational order in the assembly nanostructure. Subsequently, a one-dimensional electron density correlation function was used to analyze the size of the assembly domain. The data showed that at the 1:1 and 1:2 GO/HA mass ratios, GO-HA sheets formed a long-range lamellar structure with a mean length of 162.9 and 164.6 nm, respectively (Figure 2).

Figure 2 SAXS 2D patterns of GO and GO-HA aqueous dispersions.

This work has been published in J. Phys. Chem. C 2016, 120, 25789-25795.

Article: Xiaoyan Zhou, Bing Wang, Tu Lan, Hanqing Chen, Hailong Wang, Ye Tao, Zhihong Li, Kurash Ibrahim, Dongqi Wang*, Weiyue Feng*, Chirality of Graphene Oxide Humic Acid Sandwich Complex Induced by a Twisted, Long-Range-Ordered Nanostructure. J. Phys. Chem. C, 2016, 120: 25789-25795