Magnetic porous carbon nanocomposites derived from cactus (Opuntia stricta Haw.) for the removal of toxic dyes: optimization of synthesis conditions using response surface methodology.

Abstract

BACKGROUND: Water purification of industrial effluents containing toxic organic dyes by low-cost biomass-based adsorbents is not only in accordance with environmental remediation policies, but also reduces total treatment costs. The conversion of Opuntia stricta Haw. biowaste, one of the most harmful invasive plants, into absorbents can lessen the ecological problems caused by this plant species as well as create more value-added products for water decontamination. We report on the fabrication conditions of O. stricta zinc ferrite (ZnFe2O4)-loaded activated carbon (ZnFe2O4@AC) for the elimination of two types of dyes including Rhodamine B (RhB), methyl orange (MO) and acid yellow17 (AY), with process optimization based on response surface methodology combined with Box–Behnken design. The optimized ZnFe2O4@AC was structurally characterized by scanning electron microscopy and X-ray diffraction. RESULTS: The optimal ZnFe2O4@AC was attained at a 1.5 ZnFe2O4:OBC ratio, 5 h carbonization time and 519 °C pyrolysis temperature. In removing RhB, MO and AY by optimized ZnFe2O4@AC, remarkable adsorption capacities (53.34–82.8 mg g−1) were achieved via confirmation tests with very low errors (<2%) and high desirability (>95%). Moreover, kinetic results suggested that the Elovich model was the best description for RhB and AY dye adsorption, whereas MO adsorption by ZnFe2O4@AC followed the pseudo-second-order model. The maximum adsorption capacities calculated from the Langmuir equation were determined in the order: AY (82.73 mg g−1) < RhB (125.13 mg g−1) < MO (180.51 mg g−1). CONCLUSION: ZnFe2O4@AC derived from O. stricta could be recommended as a high-efficiency bioadsorbent for the elimination of cationic, anionic and neutral dyes.