Mechanism of Molecular Oxygen Activation Mediated by Hydroxyl Groups on the Surface of Red Clay
The activation mechanism of molecular oxygen(O2)by surface hydroxyl groups(Me-OH,Me=Al,Si,Fe)of natural clay minerals is still unclear.In this study,red clay(R-Clay)was heat-treated at varying temperatures in N2 to adjust the number and shape of Me-OH sites on its surface,thus activating O2 to different degrees for tetracy-cline(TC)degradation in water.As the temperature increased,the kaolin structure in R-Clay was gradually destroyed,and the Fe2O3 structure became more prominent.Among them,Me-OH on the surface of red clay(R-Clay400)exists in the form of Al-Al-OH and Al-Si-OH,which efficiently degraded(86.36％)and mineralized TC(40％,6 h).Under visible light irradiation,both oxygen atoms and TC molecules on R-Clay400 Si-O-Al can be used as electron donors to transfer photogenerated electrons(e-)to O2 adsorbed on the surface of R-Clay400 to form superoxide radical(·O2-)and singlet oxygen(1O2),thus achieving efficient degradation of TC.Here,the surface Me-OH,used as the Br(o)nsted site,adsorbs O2 by hydrogen bond,which promotes electron transfer rather than traditional electron donor.This study further clarified the activation mechanism of clay minerals to O2 and promoted the development of related research fields of mineral-based materials.
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