Preparation of Al2O3-coated expanded graphite with enhanced hydrophilicity and oxidation resistance

Expanded graphite (EG), as a new kind of functional carbon-based material, is a vital supporting material and heat transfer enhancer for preparing highly conductive form-stable composite phase change materials (PCMs). However, the hydrophobic nature of EG makes it difficult to incorporate with inorganic PCMs. In this work, we intended to solve this drawback and a modified EG named Al2O3-coated EG which was characterized by enhanced hydrophilicity was developed via a heterogeneous nucleation technique and subsequent heat treatment. Experiments found that the Al2O3 layer on the surface of EG was uniform and essentially amorphous, and was well-bonded to EG via chemical interactions between oxygen atoms from Al2O3 and carbon atoms from EG. The hydrophilicity and oxidation resistance of Al2O3-coated EG could be enhanced by increasing the amount of Al2O3. Most importantly, compared with EG, the water contact angle of Al2O3-coated EG dropped from 90.7° to 33.9° when only 4.4 wt% Al2O3 was used, indicating that the hydrophilicity of EG could be greatly enhanced by low cost. Moreover, molecular dynamics (MD) simulation of the hydrophilicity of EG and Al2O3-coated EG proved that the preparation of Al2O3-coated EG was an efficient and feasible method to improve the hydrophilicity of EG.