1：Experimental Design and Method Selection:

A MOF route using ZIF-8 templates was developed to fabricate Ag–ZnO hollow nanocages. The strategy involved synthesis of Ag–ZIF-8 precursor by reducing Ag ions into Ag NPs within ZIF-8 cavities, followed by calcination in air to form Ag–ZnO hollow NCs via the Kirkendall effect.

2：Sample Selection and Data Sources:

ZIF-8 was synthesized via chemical precipitation using zinc acetate and 2-methylimidazole in methanol. Ag–ZIF-8 composites were prepared by adding different volumes of AgNO3 solution to ZIF-8, reduced with NaBH

3：Pure ZnO NPs, ZnO NCs, and Ag–ZnO NCs were obtained by calcination at specific temperatures and heating rates. List of Experimental Equipment and Materials:

Materials included 2-methylimidazole, silver nitrate, zinc acetate, methanol, ethanol, sodium borohydride from Aldrich and Sinopharm Chemical Reagent Co., Ltd. Equipment included XRD (D8 Advance, Bruker), SEM (Nova NanoSEM 450, FEI), TEM (Tecnai G2 F20, FEI), XPS (ESCALAB MKII, VG Scientific), TGA/DSC (STA 449 F5, Netzsch), UV–Vis spectrophotometer (Lambda 950, Perkin-Elmer), BET analyzer (ASAP 2020, Micromeritics), UPS (VG Scienta R4000), and gas sensing analysis system (CGS-4TP, Elite Tech Co., Ltd).

4：Experimental Procedures and Operational Workflow:

ZIF-8 synthesis involved mixing solutions A and B under stirring. Ag–ZIF-8 was prepared by adding AgNO3 solutions to ZIF-8, reduced with NaBH

5：Calcination was done at 600°C (1°C/min) for ZnO NPs and 500°C (10°C/min) for ZnO and Ag–ZnO NCs. Sensors were fabricated by coating paste onto Ag-Pd electrodes and tested in a chamber with ethanol injection. Data Analysis Methods:

XRD for crystal structure, SEM/TEM for morphology, XPS for chemical states, BET for surface area, UPS for work function, and gas response defined as Ra/Rg. Response and recovery times measured at 90% change. Detection limits calculated from log(Sg-1)–log(Cg) plots.