Adsorption of malachite green dye from aqueous solutions using mesoporous chitosan–zinc oxide composite material

Abstract

Chitosan–zinc oxide composite with an average size of 33 nm was synthesized by facile chemical precipitation technique for application in the removal of water contaminants such as dyes. Malachite green (MG) was the model colorant for the sorption process. Material characterization was achieved using selected spectroscopic techniques. Elemental analysis results revealed that the material had high concentration levels of Zn (965,000 ± 53.2 mg/kg) compared to Fe (756.5 ± 45.3 mg/kg) and P (166 ± 26.6 mg/kg). Batch adsorption experiments of the dye onto chitosan–ZnO (CS–ZnO) composite was investigated with a UV–Visible photometer. The rate of dye removal was greatly influenced by pH, dye strength, amount of adsorbent and contact time. High removal capacity of 98.5% was achieved with reducing dye strength of 2.3 mg/L, dosage of 0.6 g and pH 8 within 180 min equilibration time. Langmuir model depicted the results perfectly with a r2 coefficient of 0.998 and a sorption capacity of 11 mg/g. The separation factor (RL) was 0.49, which is smaller than unity, signifying a favorable removal for the MG dye onto CS–ZnO material. Further, the sorption of the dye followed pseudo-second-order model indicating that chemisorption was the rate-limiting process. The rapid removal of MG on this novel adsorbent within a short time makes it a promising candidate for wastewater treatment applications.