Exploring the Different Photocatalytic Performance for Dye Degradations over Hexagonal ZnIn2S4 Microspheres and Cubic ZnIn2S4 Nanoparticles

Different pathways for the degradation of rhodamine (RhB) as well as different activity order for the degradation of RhB and methyl orange (MO) were observed over hexagonal ZnIn2S4 microspheres and cubic ZnIn2S4 nanoparticles. A detailed study of the physicochemical and surface properties of these two ZnIn2S4 polymorphs has been carried out to elucidate these phenomena. The results reveal that hexagonal ZnIn2S4 microspheres are composed of nanolamella petals growing in the ab plane, i.e., the negative (0001) S plane. This negative (0001) S plane not only is favorable for the adsorption of the cationic dye RhB via N(Et)2 groups but also can accumulate the photogenerated holes. These make the hole-directed photocatalytic de-ethylation of RhB more expedient over hexagonal ZnIn2S4 microspheres. This negative (0001) S plane of hexagonal ZnIn2S4 microspheres also shows promoting effect for the degradation of cationic dye like MB, but not for the degradation of anionic dye like MO. Our result provides some new insights in how the surface facet can take effect on influencing the performance of a photocatalyst and why different polymorphs can exhibit different photocatalytic performance.