Photoactivity testing: The degradation of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) dye, a stable free-radical molecule that can scavenge other free radicals, was used to monitor photoactivity following the procedure described by Dransfield et al. [9]. In two separate jars (plastic lid and sides covered with aluminium foil), DPPH (0.0052 g) and ZnO (0.031 g) were mixed with a 62.5 ml suspension medium (MOTG) containing mineral oil and caprylic capric triglyceride (mass ratio 1:1). The mixture in each jar was magnetically stirred for 1.5 h before being combined together and poured into a crystallising dish (135 mm inner diameter×23 mm inner height, all sides covered with aluminium foil) which was again magnetically stirred for 5 min.