1：Experimental Design and Method Selection:

The study involved synthesizing core–shell metal@ZnO nanoparticles (Au@ZnO, Pd@ZnO, Pt@ZnO) via a facile hydrothermal reaction and subsequent sintering treatment. Various characterization techniques (XRD, TEM, UV-Vis, XPS, BET) were used to analyze structural and compositional properties. Gas sensing measurements were conducted using a homemade tube-furnace sensor test system.

2：Sample Selection and Data Sources:

Nanoparticles were synthesized from chemicals obtained from suppliers (e.g., Aladdin, Sigma-Aldrich). Standard target gases (benzene, toluene, ethanol, formaldehyde, NO2) in synthetic air were used for sensing tests.

3：List of Experimental Equipment and Materials:

Equipment included PANalytical X’Pert PRO XRD system, JEOL JEM-2010F TEM, SHIMADZU UV-3600 spectrophotometer, VG Scientific XLESCALAB 250Xi XPS, SSA-7300 BET analyzer, Keithley 2601 source meter, digital mass flow controllers, Teflon autoclave, muffle furnace. Materials included chloroplatinic acid hexahydrate, chloroauric acid, palladium chloride, L-ascorbic acid, hexamethylenetetramine, trisodium citrate dihydrate, CTAB, zinc nitrate hexahydrate, silver paste, ethanol.

4：Experimental Procedures and Operational Workflow:

Synthesis involved preparing metal nanoparticles (Au, Pd, Pt seeds), then hydrothermal reaction with CTAB, AA, HMT, Zn(NO3)2·6H2O at 85°C for 8h, followed by sintering at 500°C. Sensor fabrication involved drop-coating nanoparticles on alumina substrates with Pt wires, sintering at 400°C for 20h. Gas sensing tests were done at 200-450°C with target gases, measuring resistance changes.

5：0h. Gas sensing tests were done at 200-450°C with target gases, measuring resistance changes. Data Analysis Methods:

5. Data Analysis Methods: Sensor response defined as Rair/Rgas - 1 for reducing gases. Data analyzed for response, sensitivity, response time, recovery time using Keithley source meter and statistical methods.