1：Experimental Design and Method Selection:

A hydrothermal method was used to synthesize α-Fe2O3 nanoparticles by varying the volume ratio of ethylene glycol (EG) and water in the solvent, with FeCl3·6H2O and urea as precursors. The method was chosen for its ability to control crystal growth and facet exposure.

2：Sample Selection and Data Sources:

Nanoparticles were synthesized under different conditions (e.g., 0 mL EG, 1 mL EG, 5 mL EG with water) to produce three types: op-hexahedral NPs, cop-hexahedral NPs, and octadecahedral NPs.

3：List of Experimental Equipment and Materials:

Materials included FeCl3·6H2O, urea, ethylene glycol, distilled water, and absolute ethanol. Equipment included a Teflon-lined autoclave, electronic oven, centrifuge, Bruker D8 ADVANCE diffractometer (XRD), FEI NOVA Nano SEM 230 (SEM), Tecnai G2 F20 (TEM), 3FLEX 3500 Multi-Port High-Throughput Gas Adsorption Analyzer (BET surface area), ESCALAB 250xi spectrometer (XPS), and WS-30A sensor measurement system.

4：Experimental Procedures and Operational Workflow:

Precursors were dissolved in solvent, heated in an autoclave at 180°C for 6 hours, cooled, centrifuged, washed, and dried. Characterization involved XRD, SEM, TEM, BET, XPS, and gas-sensing tests at various temperatures and gas concentrations.

5：Data Analysis Methods:

XRD patterns were indexed to α-Fe2O3; SEM and TEM images analyzed morphology; BET theory calculated specific surface area; XPS spectra deconvoluted for oxygen species; gas sensitivity defined as Ra/Rg.