Synthesis and characterisation of superior AC/ZnO NPs biocomposite for hexavalent chromium Cr(VI) adsorption

This study aims to synthesize biocomposite by combining banana stem activated carbon (AC) and ZnO Nanoparticles (NPs) to evaluate their adsorption potential towards hexavalent chromium (Cr (VI)) (20 mg/L). The AC used was successfully synthesized by an impregnation method using phosphoric acid (H3PO4) for 24 h, followed by a carbonization method. ZnO NPs were synthesized using the direct precipitation method using zinc acetate dihydrate (0.2 M) and KOH (0.4 M) as precursors. The AC/ZnO NPs biocomposite was fabricated using the mechanical alloying method at a frequency of 10 Hz for 30 min. The FTIR results show that both adsorbents, namely pure AC and AC/ZnO NPs have abundant functional groups. XRD results show the adsorbent is amorphous with pure AC at 89.95% and AC/ZnO NPs biocomosite at 56.49%. SEM results showed that the morphology of AC resembled crushed bovine bone marrow, and the morphology of ZnO NPs showed a marshmallow-like shape. The UV-vis spectrometer test results show that at the absorption peak of 350 nm the Cr (VI) removal efficiency slowly decreases and disappears at a dose variation of 1.5 g pure AC, 2 g biocomposite AC/ZnO NPs, and 2 g pure AC with Cr (VI) removal efficiency of 99.61%, 99.64%, and 99.83% respectively. Finally, we can report that the high degradation ability for Cr (VI) can be related to thesharp peak of -C=O group, reduced Delta LO-TO, and smaller average crystallite size in AC/ZnO NPs biocomposite.