1：Experimental Design and Method Selection:

The study employed a sol-gel method using citric acid as a gelling agent to synthesize Ni1-xCuxAl2O4 nanoparticles. This method was chosen for its cost-effectiveness and ability to produce homogeneous nanoparticles at lower temperatures.

2：Sample Selection and Data Sources:

Pigments with compositions x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 were prepared. Chemicals included nickel nitrate, aluminum nitrate, copper nitrate, and citric acid from S. d. fine.

3：02, 04, 06, 08, and 1 were prepared. Chemicals included nickel nitrate, aluminum nitrate, copper nitrate, and citric acid from S. d. fine. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a muffle furnace for calcination, magnetic stirrer, XRD (BRUKER D8 Advanced), FT-IR (JASCO FT-IR 4100), UV-DRS (JASCO-V670 spectrophotometer), SEM-EDX (ZESIS EVO18), TEM, XPS (Prevac with VG Scienta mono-chromator), and materials were metal nitrates and citric acid.

4：Experimental Procedures and Operational Workflow:

Metal nitrates were dissolved in water, mixed with citric acid, stirred and heated to form a sol, which was gelated, dried, and calcined at 800°C for 3 hours. Characterization involved XRD, FT-IR, UV-DRS, SEM-EDX, TEM, XPS, and colorimetric analysis using CIE-LAB coordinates. Chemical resistance tests used 10% H2SO4 and 10% NaOH solutions.

5：Data Analysis Methods:

Data were analyzed using Debye-Scherrer's formula for crystalline size, Tauc plot for band gap calculation, and standard techniques for spectroscopic and morphological analysis.