In-situ constructing Bi2S3 nanocrystals-modified Bi12O17Cl2 nanosheets with features of rich oxygen vacancies and reinforced photocatalytic performance

•Bi2S3 nanocrystals-modified Bi12O17Cl2 2D nanosheets were fabricated using pure CS2.•Such in-situ anion exchange synthesis produced composites with oxygen vacancies.•These composites showed enhanced photocatalytic performance because of microstructural merits.•A photocatalysis mechanism was prospected basing analytical and experimental results.