1：Experimental Design and Method Selection:

The study employed a sol-gel synthesis method to prepare pure and Fe-doped TiO2 nanoparticles. The rationale was to create nanostructured materials with enhanced photocatalytic properties under visible light. Theoretical models included the Debye-Scherrer formula for crystallite size calculation, Kubelka-Munk function for optical bandgap determination, and first-order kinetic models for photocatalytic degradation analysis.

2：Sample Selection and Data Sources:

Samples included pure TiO2, 3 at% Fe-doped TiO2, and 7 at% Fe-doped TiO2 nanoparticles. Selection criteria were based on doping concentrations to study the effect of Fe on structural, optical, and photocatalytic properties. Data were acquired from synthesized samples using various characterization techniques.

3：List of Experimental Equipment and Materials:

Equipment: Powder X-ray diffractometer (Phillips, PANanalytical Xpert pro), SEM (ZEISS, EVO-18), HR-TEM (JEM-2100), FT-IR spectrometer (Shimadzu IRPrestige-21), Confocal Raman spectrometer (Alpha300RA Raman, WITec GmbH), UV-VIS-NIR spectrophotometer (Shimadzu UV-3600), Fluorescence spectrometer (Horiba Jobin Yvon Fluorlog-3, TCSPC), UV-VIS-Spectrophotometer (UV-3092). Materials: Titanium tetra-isopropoxide (TTIP, Sigma Aldrich), Iron (III) nitrate non-hydrate (Fe(NO3)3.9H2O, Sigma Aldrich), Hydrochloric acid, Ethanol, Ammonia, Methylene blue (MB), BaSO4 reference, KBr discs.

4：2). Materials:

4. Experimental Procedures and Operational Workflow: Synthesis: TTIP dissolved in ethanol, stirred, HCl added, pH adjusted with ammonia, precipitate filtered and dried at 150°C, powders annealed at 500°C for 2h. Characterization: XRD (2θ 20° to 80°), SEM/EDX for morphology and composition, HR-TEM for particle size and structure, FTIR (300–4000 cm?1), Raman (50–800 cm?1), UV-Vis DRS with BaSO4 reference, PL with xenon lamp excitation. Photocatalytic Test: 15 mg catalyst in 30 mL MB solution (1.6×10-5M) under 200W tungsten bulb, samples taken every 30 min, centrifuged, absorption measured at 666 nm.

5：9H2O, Sigma Aldrich), Hydrochloric acid, Ethanol, Ammonia, Methylene blue (MB), BaSO4 reference, KBr discs. Experimental Procedures and Operational Workflow:

5. Data Analysis Methods: XRD data analyzed with Debye-Scherrer formula for crystallite size, lattice parameters calculated, strain and dislocation density evaluated. Optical data processed using Kubelka-Munk function for bandgap. Photocatalytic efficiency calculated from absorption spectra, first-order kinetics applied for rate constants. Statistical and software tools included Gaussian fitting for FWHM and linear regression for kinetic plots.