Electronic and Band Structure Tuning of Ternary Semiconductor Photocatalysts by Self Doping: The Case of BiOI

Foreign nonmetal or metal element doping has been widely used to tailor the electronic and band structures of wide band gap binary oxide semiconductor photocatalysts, extending their absorption edges into the visible light range for better utilization of solar light. Besides doping with foreign elements, self-doping can also tune the electronic and band structures of semiconductor photocatalysts but only limited to binary metal oxides, such as oxygen-deficient TiOx (x < 2). In this study, we demonstrate that self-doping is able to tune the electronic and band structures of ternary semiconductor photocatalysts and thus significantly enhance their photocatalytic activities by utilizing BiOI as the example. Density functional theory calculations revealed that iodine self-doping could effectively tune the electronic structures of BiOI. Motivated by the calculations, iodine self-doped bismuth oxyiodide photocatalysts were synthesized with a soft chemical method to illustrate this band structure tailoring approach. Experimental results confirmed that self-doping could change the electronic structures to intrinsically improve the optical absorption property and charge transfer ability, thus enhancing the photocatalytic activity of ternary semiconductors. Meanwhile, the intense absorption with a steep absorption edge of self-doped ternary semiconductors is different from that of foreign elements doped TiO2 with discrete bands, confirming this is a novel electronic and band structure tuning method. This successful band structure tailoring example of ternary semiconductors suggests the self-doping strategy could be general to develop novel visible light driven ternary photocatalysts with enhanced performances.