1：Experimental Design and Method Selection:

The study used a precipitation technique to synthesize ZnO nanoparticles from ZnCl2 salt with different precipitants (ammonium hydroxide and oxalic acid) to form precursors (Zn(OH)2 and ZnC2O4), followed by calcination at 500 and 700°C. Characterization methods included XRD for crystallite size and phase analysis, TEM for particle size, UV-Vis spectroscopy for band gap determination, ESR for defect analysis, luminescence spectroscopy for defect identification, and photocatalytic activity testing for phenol degradation under UV irradiation.

2：Sample Selection and Data Sources:

ZnO nanopowders were synthesized from ZnCl2 using ammonium hydroxide or oxalic acid as precipitants. All chemicals were of chemical purity. Samples were calcined at 500 and 700°C.

3：List of Experimental Equipment and Materials:

Equipment included a vacuum pump for filtration, microwave furnace for drying, resistive furnace for calcination, XRD with Cu-Kα radiation, TEM (JEM 200, Jeol, Japan), UV-Vis-NIR spectrometer (Cary 5000, Agilent Technologies, USA), ESR spectrometer (CMS-8400, Adani, Belarus), fluorescence spectrometer (LUMINA, Thermo Scientific, USA), TimeHarp 260 NANO system with PMA 182 detector (PicoQuant, Germany), Nd:YAG pulsed laser (NL202 model, EKSPLA, Lithuania), UV reactor (Heraeus Noblelight Peschl Ultraviolet Reactor LRS1 with TQ 150 lamp), and HPLC (Agilent 1260). Materials included ZnCl2, ammonium hydroxide, oxalic acid, distilled water, and phenol.

4：0). Materials included ZnCl2, ammonium hydroxide, oxalic acid, distilled water, and phenol. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Precipitates were formed by adding ZnCl2 solution to precipitant solutions with stirring, filtered, washed, dried in microwave furnace, and calcined. Characterization involved XRD, TEM, UV-Vis, ESR, luminescence measurements, and photocatalytic tests where photocatalyst was dispersed in phenol solution, irradiated with UV light, and analyzed by HPLC.

5：Data Analysis Methods:

Crystallite size calculated using Debye Scherrer's equation, band gap determined using Tauc plot, luminescence decay analyzed using time-correlated single photon counting, ESR spectra interpreted for defect types, and photocatalytic activity assessed by phenol concentration change over time.