| Summary: | In this study, the waste neem leaves (Azadirachta indica) gained visible attraction for neem leaf–activated carbon (NLAC) preparation in the thermal process by using ammonium carbonate as an activating agent. Using NLAC, a nanocomposite of NLAC/Fe2O3 was synthesized by hydrothermal techniques for Cr(VI) elimination from the aqueous solution. The formation of NLAC/Fe2O3 composite was additionally confirmed by the use of various powerful investigative techniques such as FE-SEM, VSM, TEM, EDX, FT-IR, XRD, and BET. The NLAC/Fe2O3 has a saturation magnetization of 1.18 emu/g and surface area and pore volume of 245.2 m2/g and 0.038 cm3/g, respectively. The composite has crystalline structure and the average particle size of Fe2O3 present on the activated carbon surface was about 14–17 nm. The BBD (Box-Behnken design) model was used for Cr(VI) removal and the obtained R 2 and adj-R 2 values for the model were very high about 0.9805 and 0.9555. The ANOVA data indicated that the Cr(VI) model was a statistically significant one with the F and p values of 39.17 and 0.0001. About 91.4% of Cr(VI) was removed by NLAC/Fe2O3 composite in the optimized condition of 0.05 g of adsorbent dose, solution pH 3.58, and initial Cr(VI) solution of 10.42 mg/L respectively. The adsorption of Cr(VI) on NLAC/Fe2O3 composite was imitated by the Langmuir isotherm model (R 2 = 0.98), proceeded with the pseudo-second-order kinetics model (R 2 = 0.99), and the maximum uptake capacity as calculated from the isotherm was 188.71 mg/g. The adsorption process was endothermic and adsorbent can be used for up to four cycles. This study showed that NLAC/Fe2O3 composite could be employed as an effective, affordable cost adsorbent to remove pollutants from wastewater. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
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