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The reason that some molecules, but not others, are easily adsorbed was not fully understood. In order to spotlight the effect of morphological structure and surface functional composition of adsorbate rather than focusing only on the nature of adsorbent as in most of literature reports, this work reports the biosorption of two dyes (anionic Orange G and cationic malachite green) and two pharmaceuticals (Ibuprofen and ampicillin) as target representative contaminants onto plasma-modified cocoa shell (CPHP) used as alternative low-cost adsorbent. As results, when molecules were mixed in solution and then exposed to a substrate, the factors that affect adsorption include the relative solvation of the adsorbates, the ability of each molecule to adhere to the surface, and the degree of interaction between the molecules once they were adsorbed. The maximum adsorbed amounts at 298 K of OG, MG, IBP, and AMP were 23.96, 14.65, 13.99, and 06.66 mg/g, respectively. The most solvated molecules may not adsorb rapidly to the surface, while comparatively, the less soluble molecules will aggregate, so as to maximize self-interactions via Van der Waals, hydrogen bonds or other interactions. This work demonstrated that the adsorbate intrinsic properties could play a significant role in the adsorption process. Hence, properties such as functional active groups, dimensions, and hydrophobicity were the determining parameters in the adsorption process mechanism. Accordingly, the pharmaceuticals biosorption mechanism involved π-π bonding, hydrophobic effect, electrostatic interaction, and van der Waals forces whereas the dye biosorption mechanism was dominated as well known by electrostatic attraction and hydrogen bonding phenomenon. Experimental parameters such as initial pH of solution and contact time were optimized. The optimum pH values were 2.0 for ibuprofen (IBP) and 7.0 for ampicillin (AMP). The kinetics of adsorption and the experimental isotherms data were analyzed using non-linear models. Results indicated that Avrami fractional order was the most successfully fitted model for pharmaceutical biosorption and based on the statistical values of SD and R2adj parameters, Liu isotherm was the most successfully fitted model.

This study reports the tailoring of surface chemistry of palm fibers via plasma for the adsorption of sodium diclofenac from aqueous solution. Surface functionalization of palm fibers was carried out with three feeding gases: humid air, air saturated with hydrogen peroxide and air saturated with sodium hydroxide. Functionalized palm fibers were physicochemical characterized and their diclofenac adsorption properties were compared. Diclofenac adsorption tests were performed at different operating conditions (initial concentration, particle size, pH and temperature). Kinetics and isotherms of the diclofenac adsorption on raw and plasma-based functionalized fibers were quantified and modeled with different equations. Thermodynamic parameters of diclofenac adsorption were estimated and statistical physics calculations were carried out to characterize the adsorption orientation of diclofenac molecules on biomass surface. Overall, the palm fibers functionalized with plasma and hydrogen peroxide showed the best adsorption properties for the removal of this pharmaceutical. Results showed that diclofenac adsorption was a multi-molecular exothermic process with an inclined adsorption orientation on the fiber surface. The experimental maximum adsorption capacities decreased from 33.12 to 24.71 mg/g at 25–50 °C. Liu model provided the best correlation of experimental data for all adsorption temperatures. Solution pH played a relevant role in the diclofenac adsorption mechanism where hydrogen bonding, van der Waals forces and electrostatic interactions were involved. This paper contributes to the valorization of biomasses for implementing low-cost and effective adsorption processes to face the water pollution caused by pharmaceuticals.

Removal of cationic dye, Azur II, and anionic dye, Reactive Red 2 (RR-2) from aqueous solutions, has been successfully achieved by using a modified agricultural biomaterial waste: cocoa shell husk (Theobroma cacao) treated by gliding arc plasma (CPHP). The biomass in its natural form CPHN and modified form CPHP was characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and point of zero charge (pHpzc). Experimental variables such as initial pH, contact time, and temperature were optimized for adsorptive characteristics of CPHN and CPHP. The results show that the removal of the Azur II dye was favorable in the basic pH region (pH 10) while the Reactive Red 2 dye was favorable in the acidic pH region (pH 2). The minimum equilibrium time for Azur II and RR-2 dye was obtained after 40 and 240 min, respectively. The adsorption kinetics and isotherm data obtained were best described by a pseudo-second-order kinetic rate model and a combination of Langmuir-Freundlich isotherm models. This work indicates that the plasma-treated raw materials are good alternative multi-purpose sorbents for the removal of many coexisting pollutants from aqueous solutions.