pH-Sensitive Highly Dispersed Reduced Graphene Oxide Solution Using Lysozyme via an in Situ Reduction Method

Well-dispersed, high-quality reduced graphene oxide (RGO) solutions were prepared using an in situ reduction process with lysozyme (lys) as the dispersant. The lys-RGO reaches a concentration as high as 0.22 mg/mL and can remain stable for over six months. Atomic force microscopy indicates that the lys-RGO is effectively exfoliated with an average thickness of about 1 nm. Furthermore, XPS and Raman spectra demonstrate that the presence of lysozyme promotes the chemical reduction of GO and restores the sp(2) hybridization in the obtained RGO. The dispersibility effect of lys-RGO solution is pH-sensitive. Zeta potential and UV-vis spectrum analysis indicate that the RGO sheets will aggregate in the pH range of 2.5-7.5 and disperse well at pH 8-12.5. It is found that the dispersibility of the lys-RGO is reversible, and over 80% of the aggregates can be redissolved after pH regulation. This reversible dispersing was attributed to the strong adsorption affinity of lysozyme onto RGO, resulting from the hydrophobic and pi-pi stacking. This highly dispersed lys-RGO solution has great potential for application in composite materials and biochemical fields.