Tailoring the morphology and optical properties of alumina nanostructures by carbon quantum dot modification for enhanced heavy metal adsorption

In this study, alumina/CQD (carbon quantum dot) nanostructures are synthesized using varying concentrations of CQD solution to systematically investigate their structural, morphological, and optical characteristics. X-ray diffraction (XRD) analysis shows a gradual transition from a crystalline to an amorphous structure with increasing CQD content used through the synthesis process. For the samples with lower values of CQD content (AQD-1 and AQD-7), the calculated crystallite sizes by the Scherrer equation are 2.93 and 2.77 nm. In comparison, they cannot be calculated for the samples synthesized using higher values of CQDs (AQD-9 and AQD-13). The results indicate that the volume of the CQD solution notably influenced the nanostructure morphology and the distribution of CQDs in the produced nanostructures. Also, a notable dependence of the samples' optical properties on CQD concentration is observed. The indirect band gap energy of the nanostructures, in particular, demonstrates a systematic increase by increasing the CQD content, suggesting the tunability of the nanostructure's optical properties by adjusting the carbon concentration used in the synthesis process. The nanocomposites' specific surface area (SSA) decreased with increasing CQD concentration from 247.2 to 97.7 m²/g, suggesting partial pore blockage or aggregation induced by CQD incorporation. The synthesized nanocomposites exhibited high efficiency in the water treatment even in water containing high concentrations of copper ions (184 ppm), underscoring their potential as effective adsorbents for heavy metal remediation. These findings suggest promising prospects for developing multifunctional nanomaterials suitable for optical and environmental applications.