Graphene in Water is Hardly Ever Neutral

Area of Science:

• Materials Science
• Physical Chemistry
• Surface Science

Background:

• Graphene's unique properties make it suitable for various applications.
• Stable colloidal dispersions of graphene in water are crucial for its use in aqueous systems.
• Understanding the surface charge of nanomaterials in water is key to controlling their behavior.

Purpose of the Study:

• To investigate the origin and nature of the electrical charge on graphene in water.
• To determine if this charge can stabilize graphene colloidal dispersions without additional agents.
• To explore methods for tuning the graphene surface charge.

Main Methods:

• Potentiometric titration
• Isothermal titration calorimetry
• Electrokinetic measurements (e.g., zeta potential)
• Density Functional Theory (DFT) calculations
• Raman Spectroscopy
• Atomic Force Microscopy (AFM) for direct force measurements

Main Results:

• Graphene exhibits a significant electrical charge in aqueous environments.
• This intrinsic charge effectively stabilizes single- and few-layer graphene colloidal dispersions.
• The charge arises from the interaction of graphene with water's hydroxide and hydronium ions.
• The magnitude and sign of the charge are controllable by altering the solution pH.

Conclusions:

• The inherent charge on graphene, driven by water ion interactions, enables stable colloidal dispersions.
• pH-dependent surface charge control offers a versatile method for manipulating graphene's behavior in water.
• These findings are crucial for advancing graphene-based applications in aqueous media.