1：Experimental Design and Method Selection:

The study involved the rational fabrication of direct Z-scheme heterostructure photocatalysts composed of ultrathin Bi3O4Cl and BiOCl nanosheets via alkaline chemical etching and solvent exfoliation. Theoretical models and algorithms, including Density Functional Theory (DFT) calculations, were employed to predict band structures and internal electric fields. Detailed procedures included hydrothermal treatment, sonication, and exfoliation methods.

2：Sample Selection and Data Sources:

Samples included pure BiOCl, nanocrystal Bi3O4Cl/BiOCl heterostructures, and ultrathin Bi3O4Cl/BiOCl nanosheets. Selection criteria involved using precursors like Bi(NO3)3·5H2O and KCl, with synthesis conditions optimized for heterostructure formation. Data sources included experimental characterizations and theoretical computations.

3：List of Experimental Equipment and Materials:

Equipment included X-ray diffractometer (D8 Advanced, Bruker), transmission electron microscopy (Tecnai G2 F30, FEI), scanning electron microscopy (MERLIN Compact, ZEISS), X-ray photoelectron spectroscopy (Escalab 250Xi, Thermo Scientific), UV–Vis diffuse reflectance spectra (PerkinElmer Lambda 950), atomic force microscope (Agilent 5500), spin-trapping ESR measurement (Bruker model A 300), electrochemical workstation (ZENNIUM, Zahner), and gas chromatograph (Fuli, GC-8A). Materials included Bi(NO3)3·5H2O, KCl, PVP, NaOH, IPA, AgNO3, FeCl3, and DMPO.

4：Experimental Procedures and Operational Workflow:

Synthesis involved hydrothermal treatment at 120°C for 10 h, followed by exfoliation via sonication in IPA and centrifugation. Characterization steps included XRD, TEM, SEM, XPS, UV–Vis DRS, AFM, PL, photocurrent, EIS, and ESR measurements. Photocatalytic tests were conducted in a batch reactor under visible light irradiation with sacrificial reagents, and O2 evolution was measured using gas chromatography.

5：Data Analysis Methods:

Data analysis included bandgap estimation from UV–Vis DRS, charge carrier dynamics from PL and time-resolved PL, electrochemical properties from photocurrent and EIS, and radical detection from ESR. Theoretical computations used DFT to model band structures and adsorption energies.