The role of ball milled h-BN in the enhanced photocatalytic activity: A study based on the model of ZnO

h-BN/ZnO composite photocatalysts were prepared by ball milling of ZnO with hexagonal BN (h-BN). The photocatalytic activity of ZnO for the degradation of cationic dyes could be significantly enhanced by coupling with ball milled h-BN and the stability of ZnO benefited from the presence of h-BN as well. However, for the degradation of anionic dyes, no apparent enhancement was observed. The optimal amount of h-BN and the ball milling time were found to be 1.0 wt.% and 20 min, respectively. Through various characterization techniques (XRD, UV–vis DRS, SEM, TEM, and terephthalic acid photoluminescence probing) and the compared photocatalytic degradation experiments, the observed photocatalytic behaviors could be attributed to the negatively charged h-BN created by the ball milling process. The role of the milled h-BN was discussed to serve as (1) holes-transfer promoter and (2) attractive or repulsive sites for the adsorption of the charged dyes via electrostatic forces. The study confirms that the ball milled h-BN could be used as a holes transfer promoter for ZnO. However, the finial photocatalytic performance of h-BN/ZnO is determined by the superposition of the two effects for a specific degradation process. This is the reason why the enhancement of ball milled h-BN is only effective for cationic dyes.