Single and binary adsorption of paracetamol and diclofenac onto biochar produced from pepper stem: Which adsorption properties change in the binary system?

Abstract

The importance of combating the contamination of water resources with emerging pollutants must be kept all the more in view by scientists, since such pollutants are harmful and pose challenges for traditional water treatment methods. The current study was designed to scrutinize the adsorption properties of a low-cost biochar for two pharmaceuticals in both single and binary systems. The work was focused on understanding how paracetamol (PARA) and diclofenac (DIC) co-adsorb, and it can serve as a beacon for similar studies, especially in modeling the adsorption processes of such systems. Using a low-cost biochar from pepper stem (PS) with a high surface area = 727.5 m2/g as adsorbent, experiments were carried out in both the single and binary systems to investigate the adsorption behavior of the mentioned pharmaceuticals. Results showed that, in the single system, the PS biochar demonstrates a slightly greater adsorption capability for both PARA and DIC, with a capacity of 354.66 and 256.10 mg/g, respectively, compared to its capacity for each pharmaceutical in the presence of the other in the solution. Interestingly, the effect of the presence of one of the pharmaceuticals on the thermodynamic parameters (ΔGº, ΔSº, and ΔHº) of the other was ignorable, and interactions such as hydrogen bonding, π-π, n-π, and anion-π interactions were at work for the adsorption processes, with different extends in each pharmaceutical-biochar case. On the other hand, the presence of one of the pharmaceuticals was effective on the kinetics of the adsorption process of the other and caused a decrease in its adsorption rate, especially in the initial stage of the process. Overall, in addition to the suitability of pepper stem biochar for PARA and DIC, results showed that the presence of one pharmaceutical is not influential on all the adsorption properties of the other, and the results can be exploited for studding similar systems.