Self-sacrifice transformation for fabrication of type-I and type-II heterojunctions in hierarchical BixOyIz/g-C₃N₄ for efficient visible-light photocatalysis

Construction of semiconductor heterojunction with hierarchical architectures is highly effective for improving photocatalytic performance. Different heterojunction types with distinct mechanisms lead to different photocatalytic activity enhancement level, and thus the control on heterojunction type is meaningful. Herein, we achieve the fabrication of a series of different types of hierarchical heterojunctions in Bi_xO_yI_z/g-C₃N₄, namely, g-C₃N₄/BiOI, g-C₃N₄/Bi₄O₅I₂, and g-C₃N₄/Bi₅O₇I. g-C₃N₄/BiOI is prepared by a direct precipitation method, and g-C₃N₄/Bi₄O₅I₂ and g-C₃N₄/Bi₅O₇I are obtained by in situ calcination transformation of g-C₃N₄/BiOI at different temperature. Among them, g-C₃N₄/BiOI and g-C₃N₄/Bi₄O5I₂ are type-I heterojunction, and g-C₃N₄/Bi₅O₇I belongs to type-II heterojunction. The photocatalyitc activity is surveyed by decomposition of diverse industrial contaminants, including methyl orange, bisphenol A and tetracycline hydrochloride under visible light irradiation (λ > 420 nm). It is found that g-C₃N₄/Bi₅O₇I shows largely enhanced photodegradation performance compared to g-C₃N₄/BiOI and g-C₃N₄/Bi₄O5I₂. The much higher photocatalytic activity of g-C₃N₄/Bi₅O₇I is attributed to the enhanced specific surface area, more efficient charge separation and surface transfer efficiency and increased density of charge carriers owing to the formation of type-II heterojunction. The study provides a reference for in situ fabrication of hierarchical photocatalysts with diverse heterojunction types for optimizing photocatalytic activity.