Rapid and high-performance adsorptive removal of hazardous acridine orange from aqueous environment using Abelmoschus...

In this research, the performance of naturally abundant lignocellulosic by-product, Abelmoschus esculentus, and its processed seed powder referred as AESP, as a potential biosorbent for the removal of acridine orange (AO) from the aqueous environment was examined. The AESP biosorbent was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) analysis, diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FTIR) and pH_ZPC analyses. The average size of the biosorbent according to particle size distribution analysis was found to be ∼132 μm. The batch adsorption experiments were conducted by altering the parameters such as contact time, solution pH, biosorbent dosage, initial dye concentration, stirring speed and temperature. Sorption of cationic AO dye onto AESP was found to be rapid, and the equilibrium condition reached within 30 min. The isotherms (Langmuir, Freundlich, Redlich-Peterson and Sips), kinetic models (pseudo-first order, pseudo-second order, Elovich, intra-particle diffusion, Bangham and modified-Freundlich models) and thermodynamic parameters were also evaluated. High values of determination coefficients (R²) and minimal values of non-linear error functions (i.e. HYBRD, RMSE, MPSD, ARE, APE and χ²) indicated that experimental data were best fitted with Sips isotherm and pseudo-second order kinetic model. Accordingly, the maximum loading capacity of AESP was found to be 259.4, 284.3 and 346.5 mg/g for the temperatures of 15, 30 and 45 °C, respectively. The thermodynamic parameters showed that the adsorption of AO onto the AESP surface was an endothermic and spontaneous process. Besides these, the central composite experimental design (CCD) superimposed with response surface methodology (RSM) modeling was also employed to investigate the effect of four significant parameters (solution pH, contact time, initial AO concentration and AESP dosage) and their interaction-term effects on the adsorption capacity of AESP and to formulate the mathematical model for the experimental data using multi-variate statistical analysis. Maximum dye uptake capacity under the optimum conditions of variables (pH 8.96, contact time 32.06 min, initial dye concentration 867.71 mg/L and AESP dosage 1.89 g/L) was 312.1 mg/g at temperature 30 °C, and it was found to be very close to the experimentally determined values (313.4 ± 0.057 mg/g). The promising reusability potential of AESP using 0.1 M HCl, implied that, the lignocellulosic biosorbent AESP might be helpful for the appropriate designing of the environmental-friendly purification systems.