Effect of crystallite size reduction and widening of optical phonon vibration due to AC variation on ZnO/Mg composites in implementation of methylene blue degradation.

The fashion industry's reliance on dyes contributes significantly to environmental pollution, which disturbs the ecological balance. To address this issue, we used ZnO/Mg combined with activated carbon (AC) at various concentrations (0.1 g, 0.5 g, and 1 g), which were synthesized via sol-gel and mechanical alloying processes. The analysis of X-ray diffraction shows reduced crystallite size, with d-spacing change ( $\to$ d $\leftarrow$ ) for ZnO/Mg/AC (0.5 g) and ( $\leftarrow$ d $\to$ ) for ZnO/Mg/AC (1 g), respectively. The results of the IR spectrum indicated the main vibrations is MgO and Zn-O bonds at wave numbers 673 cm^-1 and 467 cm^-1. It was found that ZnO/Mg/AC (1 g) shows high degradation performance $D\%$ : 86.15% as a consequence of reduced crystallite size: 22.67 nm, decreased skin depth: 0.002 cm, widening of optical phonon vibration ( $\Delta (\text{LO}-\text{TO})$ ): 252 cm^-1 and increased $E_{\text{g}}$ : 4.6 eV as a function AC variation. Moreover, the finding of high photocatalytic performance $\ge$  80% for 0.25 mL MB dissolved in 250 mL distilled water is obtained from all composites. Based on these results, ZnO/Mg/AC shows potential as a photocatalyst to solve the MB waste problem.