Aspects of superior photocatalytic dye degradation and adsorption efficiency of reduced graphene oxide multiwalled carbon nanotubes with modified ZnO-Al₂O₃ nanocomposites

Due to the poor effectiveness of nanomaterials, the elimination of hazardous textile dyes from wastewater is quite challenging. A wide range of low-cost, hybrid, and highly effective nanomaterials have attracted much research for their potential in wastewater treatment. Herein, ZnO-Al₂O₃ nanoparticles were successfully grafted on reduced graphene oxide/multiwalled carbon nanotubes (ZnO-Al₂O₃-rGO/MWCNT) via the hydrothermal process. This nanohybrid material has been characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunner Emmet Teller (BET) analysis. ZnO-Al₂O₃-rGO/MWCNT has degraded 30 ppm Congo red dye to 90% within 1 h, while 20 ppm rose Bengal dye to 80% within 1.5 h. The kinetics of degradation for both these dyes is followed well by the pseudo-first-order model. Furthermore, ZnO-Al₂O₃-rGO/MWCNT was explored for the adsorption of Sudan III and displayed an outstanding removal capacity (220 mg g⁻¹) compared with bare catalyst ZnO−Al₂O₃ (72 mg g⁻¹). The sorption of Sudan III dye onto the adsorbent is spontaneous endothermic and follows pseudo−second−order kinetics and Langmuir isotherm models. Experiments using radical trapping have shown that hydroxyl radicals are the principal reactive intermediates in the photoexcitation process. The desorption and regeneration of as−prepared nanocomposite are also assessed.