Adsorption of acid red 14 from aqueous solutions by ZnO-tyre: kinetics, isotherms, and mechanisms

This research evaluated the effectiveness of using zinc oxide-waste tyre (ZnO-WT) for the adsorptive removal of the harmful acid red 14 azo dye (AR14 AzD) from polluted water. The synthesised materials were characterised using FT-IR, XRD, FESEM, EDX-map, and pHpzc analyses. Examination of key operational factors confirmed that the adsorptive removal rate of AzD reached 90.09% under the conditions of pH= 3, ZnO-WT= 1 g L− 1, [AR14]₀= 20 mg L− 1, and T= 298 K within 2 hours. The pseudo-second-order (PSO) (R2= 0.9981) and Langmuir (R2= 0.9984) kinetic and isotherm models fitted well with all AzD adsorption data. Notably, the maximum adsorption capacity (qm) of ZnO-WT towards AR14 was found to be 204.082 mg g− 1 at T= 298 K. Moreover, adsorption thermodynamics revealed that the AR14 uptake process was both endothermic (+ΔH ∘) and spontaneous (−ΔG ∘). Reusability tests demonstrated that the nanocomposites (NCs) were sufficiently stable and reusable. The production cost of the ZnO-WT NCs on a laboratory scale was 0.0886 USD per 8 g, while the cost associated with AR14 adsorptive removal was 0.0576 USD, making it an economical option for large-scale industrial use. These results suggest that waste tyres could be repurposed to produce a new class of carbon materials, with ZnO-WT effectively serving as a low-cost and environmentally friendly adsorbent for removing AR14 dye from aqueous solutions.