For photocatalysts with a hydrophilic surface, such as graphene oxide, TiO2, ZnO or selected C3N4 materials, well dispersed samples can usually be obtained by simple stirring or vortexing, as demonstrated in Figure . In contrast, hydrophobic photocatalysts require more specialized techniques for dispersion due to their water-repelling nature, and in this case ultrasonic treatment is especially useful. Figure and 2C show a photocatalyst with intermediate hydrophobicity. In this case, short (10 s) treatment in a regular ultrasonic bath is sufficient to achieve adequate dispersion.