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 ( \(\to \) $\to$ d \(\leftarrow \) $\leftarrow$ ) for ZnO/Mg/AC (0.5 g) and ( \(\leftarrow \) $\leftarrow$ d \(\to \) $\to$ ) 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 \(D\%\) $D\%$ : 86.15% as a consequence of reduced crystallite size: 22.67 nm, decreased skin depth: 0.002 cm, widening of optical phonon vibration ( \(\Delta (\text{LO}-\text{TO})\) $\mathrm{\Delta }(\text{LO}-\text{TO})$ ): 252 cm⁻¹ and increased \({E}_{\text{g}}\) $E_{\text{g}}$ : 4.6 eV as a function AC variation. Moreover, the finding of high photocatalytic performance \(\ge \) $\ge$  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.