Improvements relating to nanomaterials

A process for preparing a product comprising one or more graphene layers is disclosed which comprises: producing hydrodynamic cavitation in a liquid medium comprising a diaromatic component to synthesise the one or more graphene layers from the diaromatic component. The diaromatic component may be naphthalene, methylnaphthalene or ethylnaphthalene. The liquid medium may also comprise a stabilizer such as N-methyl-2-pyrrolidone (NMP). The grapheme layers may be formed on substrate particles such as carbon or silicon. The hydrodynamic cavitation may be generated by flowing the liquid medium through a constriction. A process using ultrasonic cavitation is also disclosed.