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

Abstract 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 BixOyIz/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.