Citric acid-functionalized Acacia pods as a robust biosorbent for decontamination of wastewater containing crystal violet dye: Experimental study combined with statistical optimization

Abstract

This study reports the chemical modification of Acacia pods (AP) by citric acid and its application for crystal violet (CV) dye removal from water. The raw and modified AP (AP@CA) were characterized using scanning electron microscope, energy-dispersive X-ray spectrometer, Fourier-transform infrared spectrometer, X-ray diffractometer and N2 adsorption-desorption. The characterization findings confirm that the AP was successfully modified by citric acid with an increase in the surface area from 29.69 to 51.12 m2.g−1. The CV adsorption data reasonably agreed with pseudo-second-order kinetics and Langmuir isotherm models. The maximum uptake capacity of AP for CV dye increased from 267.67 to 300.92 mg.g−1 after citric acid modification. The CV adsorption mechanism mainly occurred through electrostatic forces, n-π interactions and H-bonds. The response surface methodology was employed to assess the effect of key parameters including pH (4.0–8.0), contact time (10–110 min) and absorbent dose (0.2–1.2 g.L−1) on the CV removal performance. The highest CV removal efficiency of 98.82% was obtained at pH 8, AP@CA dose 1 g.L−1 and contact time 90 min. The CV removal efficiency of AP@CA is still above 89.31% after five regeneration times. Overall, AP@CA material can be utilized as a promising reusable adsorbent for treating dye-containing effluents.