1：Experimental Design and Method Selection:

The study used a microwave-hydrothermal method to synthesize composites of Mg(OH)2, CuO, and Cu2O for CO2 capture and photocatalytic reduction. The rationale was to combine the high CO2 adsorption of Mg(OH)2 with the photocatalytic properties of copper oxides. Theoretical models included characterization techniques to correlate physical properties with activity.

2：Sample Selection and Data Sources:

Composites were synthesized with varying weight percentages of copper oxides (0.5%, 5%, 10%, 15%, 20%) using magnesium nitrate and copper acetate precursors. Data sources included experimental measurements from characterization and photocatalytic tests.

3：5%, 5%, 10%, 15%, 20%) using magnesium nitrate and copper acetate precursors. Data sources included experimental measurements from characterization and photocatalytic tests. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a programmable microwave (MARS-6, CEM), X-ray diffractometer (Bruker D8 Advance), UV-Vis NIR spectrophotometer (Cary 5000), surface area analyzer (Bel-Japan Minisorp II), SEM (JEOL 6490 LV), FTIR (Perkin Elmer FTIR/FIR Frontier), HRTEM (FEI Titan G2 80-300), XPS (K-Alpha-X-ray photoelectron spectrometer), potentiostat (AUTOLAB PGSTAT 302N), gas chromatographs (Thermo Scientific and Agilent Technologies 7820 A), and solar simulator with Xe lamp. Materials included magnesium nitrate hexahydrate (Aldrich, 99%), copper acetate monohydrate (Aldrich, 99%), NaOH, deionized water, ethanol, NaSO4 electrolyte, Ag/AgCl reference electrode, Pt counter electrode, ITO glass, and chromotropic acid for formaldehyde detection.

4：Experimental Procedures and Operational Workflow:

Synthesis involved dissolving precursors, adding NaOH, microwave treatment at 600 W and 100°C for 30 min, washing, and drying. Characterization included XRD, XPS, UV-Vis DRS, SEM, HRTEM, N2 physisorption, and photoelectrochemical measurements. CO2 capture experiments were done in a batch reactor at 20°C and 2 psi, monitoring with gas chromatography. Photocatalytic tests in liquid phase used halogen lamps (300-900 nm), purging with CO2, and analyzing products with GC and UV-Vis. Gas phase tests used a solar simulator (150 W Xe lamp, AM 1.5 G), purging with N2 and CO2, and analyzing with GC.

5：5 G), purging with N2 and CO2, and analyzing with GC. Data Analysis Methods:

5. Data Analysis Methods: Data analysis included using Debye-Scherrer equation for crystallite size, lattice strain calculations, BET surface area analysis, band gap estimation from UV-Vis, XPS deconvolution, Mott-Schottky plots for flat band potentials, Nyquist plots for charge transfer resistance, and quantification of reaction products.