Water dispersed multi-walled carbon nanotubes modified by tannin acid

• Tannin acid modified MWCNTs have been prepared by a two-step process.
• The modified MWCNTs showed sufficient dispersion and stability in water.
• Sufficient dispersion was due to the adsorption of tannin acid on MWCNTs surface.
• The structure of modified MWCNTs was not damaged.
• The water contact angle of tannin acid modified MWCNTs decreased greatly.

In order to achieve sufficient dispersion and highly stabilized multi-walled carbon nanotubes (MWCNTs) in water, a convenient, economical and environment friendly surface modification process without any inorganic corrosive acid or elevated temperature has been developed. The MWCNTs were first treated with a mixed solution of NaOH and H2O2 for 12 h at room temperature. Then the MWCNTs were blended with a tannin acid aqueous solution in an ultrasonic cleaner for 2 h. The results consistently confirmed the adsorption of tannin acid onto the MWCNTs surface, while the structure of MWCNTs was not damaged. The modified MWCNTs showed much better dispersion and stability in water than those of the pristine MWCNTs.