Kinetic and isotherm studies of bisphenol A adsorption onto orange albedo(Citrus sinensis): Sorption mechanisms based on the main albedo components vitamin C, flavones glycosides and carotenoids

Orange albedo and its adsorption capacity towards bisphenol A (BPA) were studied. Adsorption experiments were conducted in batch mode at 25–55°C. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer−Emmett−Teller (BET) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the biosorbent. The effects of various parameters including adsorption time, equilibrium pH, adsorbent dosage and initial adsorbate concentration were investigated. The optimum contact time and pH for the removal of BPA were 60 min and 2, respectively. It was found that the adsorption isotherms best matched the Freundlich model, the adsorption of BPA being multilayer and that of the albedo surface heterogeneous. From the kinetic studies, it was found that the removal of BPA best matched the pseudo-second order kinetic model. An adsorption mechanism based on the albedo surface molecules is proposed and gives a good account of π–π interactions and hydrogen bonding. Orange albedo, with a maximum BPA loading capacity of 82.36 mg g−1 (significantly higher than that of most agricultural residues), is a good candidate for BPA adsorption in aqueous media.