Nickel ion removal from aqueous media using polyaniline-macadamia nutshells and its reuse for photodegradation of orange dye

The present study describes the adsorption of nickel(II) ion onto an agrowaste-polymeric nanocomposite, polyaniline-macadamia nutshells. The pre-synthesized nanocomposite was characterized via scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry and Fourier transform infrared spectroscopy analyses. The adsorption process was studied as a function of the initial pH (2-8) of simulated nickel ion solution, initial nickel ion concentration (25-100 mg/L), contact time (5-300 min), adsorbent dosage (0.5-4 g/L), temperature (25-45 degrees C) and agitation speed (180 rpm). The optimum pH was found to be pH 7 and the ideal adsorbent dosage was 2 g/L. The best fit for the kinetics data (R-2=0.99) was recorded using the pseudo-second order. The maximum adsorption capacity (238.1 mg/g) was obtained via the Langmuir isotherm model at 45 degrees C. The values recorded for the changes in Gibbs free energy (-2.30, -2.94 and -3.44 kJ/mol) were found to be below 20 kJ/mol. Similarly, the value recorded for the enthalpy change (14.52 kJ/mol) was also below 20 kJ/mol. Both instances are indicative of the existence of physisorption. Surface complexation and cation-pi interaction are possibly involved in the adsorption process. In order to elucidate on the reusability of the nanocomposite, the spent adsorbent was reused for the photodegradation of another contaminant, orange 2 dye. The complete degradation (99.7%) of the dye was achieved within 25 min. Overall, the results show that polyaniline-macadamia nutshells have the potential to remove nickel ions from aqueous media. [GRAPHICS] .

Automated summary

The present study successfully adsorbed nickel ions using a polyaniline-macadamia nutshells nanocomposite. The optimal conditions were found to be pH 7 and an adsorbent dosage of 2 g/L. The results indicate that surface complexation and cation-pi interaction may be involved in the adsorption process, and physical adsorption is present.