Green Synthesis of Cu-Doped Aluminium Hydroxide Sludge Using Lavender for Adsorption of Reactive Azo Dye: A Waste-to-Resource Approach

As waste management becomes a competitive sector, it is evident that international guidelines will further encourage the reuse of waste materials. While aluminium hydroxide sludge (AHS) is a problematic waste associated with health and environmental impacts, it is also a valuable material in terms of treating textile wastewater. This paper focuses on the green synthesis of Cu-doped AHS using lavender extract for the adsorption of a reactive azo dye, Remazol Red (RR)239. Results of SEM and FT-IR analyses show that AHS is in the form of aluminium hydroxide and its chemical structure comprises approximately 9.88±0.56% C, 63.39±0.63% O, 21.94±0.10% Al, and 4.04±0.14% S content by weight. Adsorption studies demonstrated that the lowest RR239 uptake was 18.7% at pH 11, while it increased as the pH value decreased to 7. It was also determined that RR239 dye adsorption with Cu-AHS is more suited to pseudo 2nd-order kinetics. The comparison of the RR239 dye uptake capacities of Cu-AHS and AHS adsorbent exhibited that there is a great reduction in RR239 dye removal of Cu-AHS and AHS adsorbents after 75 mg/L RR239 dye concentration. However, across all concentrations, Cu-AHS exhibited a higher RR239 dye uptake capacity than that of AHS. Adsorption isotherms also presented that the dye adsorption of AHS and Cu-AHS is more suitable for the Langmuir isotherm. The environmental advantages of the green synthesis method used in this study and the outstanding capacity of AHS in RR239 dye removal are vital in terms of guiding other studies in waste management.