1：Experimental Design and Method Selection:

The study involves a one-step thermal oxidation process to fabricate coaxial core-shell structures from iron microwires, with controlled parameters such as temperature and gas atmosphere to achieve desired morphologies and phases. Methods include XRD, SEM, XPS, Raman spectroscopy, magnetization measurements, AFM, photodegradation tests, and photoelectrochemical measurements.

2：Sample Selection and Data Sources:

High purity (99.99%) iron metal microwires with a diameter of 75 μm were used as precursors. Samples were prepared at oxidation temperatures of 500°C for 3 hours and 750°C for 1 hour, with a gas mixture of 10% oxygen and 90% argon. Additional post-annealing in nitrogen at 750°C for 30 minutes was performed for some samples.

3：99%) iron metal microwires with a diameter of 75 μm were used as precursors. Samples were prepared at oxidation temperatures of 500°C for 3 hours and 750°C for 1 hour, with a gas mixture of 10% oxygen and 90% argon. Additional post-annealing in nitrogen at 750°C for 30 minutes was performed for some samples. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes a horizontal quartz tube furnace, STADI-P X-ray diffractometer with MoKα1 radiation, JEOL FEG-SEM JSM 6701F scanning electron microscope, K-alpha+ ThermoFisher Scientific XPS spectrometer, T64000 HORIBA Jobin-Yvon triple Raman spectrometer, MPMS/SQUID from Quantum Design for magnetization, AFM/SPM Series 5500 atomic force microscope, 450 W Xe lamp with AM 1.5 G filter for simulated sunlight, UV-Vis spectrophotometer, and a three-electrode photoelectrochemical cell with Ag/AgCl reference and platinum counter electrodes. Materials include iron microwires, methylene blue dye, NaOH electrolyte.

4：5 G filter for simulated sunlight, UV-Vis spectrophotometer, and a three-electrode photoelectrochemical cell with Ag/AgCl reference and platinum counter electrodes. Materials include iron microwires, methylene blue dye, NaOH electrolyte. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Microwires were oxidized in the furnace at specified temperatures and times. Structural and morphological characterizations were conducted using XRD, SEM, XPS, Raman, AFM, and magnetization measurements. Photocatalytic activity was assessed by degrading methylene blue under simulated sunlight, monitoring absorption at 664 nm. Photoelectrochemical performance was evaluated using linear sweep voltammetry and chronoamperometry in a three-electrode setup.

5：Data Analysis Methods:

XRD patterns were refined using Rietveld method with GSAS software. Surface roughness was calculated using WSxM software. Photodegradation efficiency was monitored via UV-Vis absorption. Photocurrent and stability were analyzed from voltammetry and amperometry data.