The presence of antibiotics as micro-contaminants in the water and aqueous environments is a health concern to humans and the ecosystem. Therefore, their elimination by adsorption to available and cheap materials in water treatment plants is a research topic of high relevance. The present paper reports on the adsorption behavior of oxytetracycline on a bio-adsorbent prepared from Posidonia oceanica; an abundant Mediterranean biomass. Characterization of the pretreated Posidonia biomaterial was achieved using several analyses such as Boehm acid–base titration method, pH_PZC determination, and analysis techniques (FTIR, ¹³C CP-MAS NMR, optical microscopy, and TGA). The pH_PZC occurred around pH 2.11. Posidonia biomaterial showed a fast and high uptake rate throughout the adsorption process, which is a definite advantage for analytical applications such as water decontamination. The experimental kinetic data fitted very rightly the pseudo-second-order kinetic model and the equilibrium uptake can adopt the bi-Langmuir isotherm model for all studied pH values which assumes adsorptions at the two localized sites. Maximum adsorption capacities of 11.8 mg∙g⁻¹ and 4.4 mg∙g⁻¹ for the two adsorption sites are reached at pH 6. The oxytetracycline adsorption process onto Posidonia bio-adsorbent is spontaneous (Δ_adsG⁰ < 0), exothermic (Δ_adsH⁰ < 0), and entropically favorable (Δ_adsS⁰ > 0). The effect of pH on adsorption behavior and the thermodynamic parameters of adsorption are consistent with a possible origin of adsorption of oxytetracycline by means of hydrogen bonding interactions between surface hydroxyl and phenolic groups of the biomaterial and oxytetracycline. The proposed green and environmentally friendly biomaterial offers potential benefits as a bio-adsorbent in the remediation of aquatic environments contaminated by various organic materials. Graphical abstract

The choice of the functional monomer is addressed in the present study. It is not only dictated by its ability to interact with the template molecule. Its reactivity towards the cross-linker in the radical polymerization reaction is also to be considered in order to yield a suitable distribution of the monomer bearing binding groups within the material and also to adjust the cross-linking degree which provides rigidity to MIP network. MIPs prepared using two functional monomers of very different reactivity in radical polymerization allowed to investigate the criteria for the optimum choice of the functional monomer. MIPs were made of cross-linked poly(methacrylic acid) or poly(maleic acid) bound as thin films to a silica solid support. Ethylene glycol dimethacrylate was the cross-linker. Calculations of the composition drift of the copolymer material from monomers reactivity ratios give new insights into the control of MIP properties by the choice of the functional monomer. As a consequence of the lower reactivity of maleic acid than methacrylic acid for copolymerization with methacrylic esters, the incorporation of maleic acid is low, the cross-linking density is very high, the polymer coating is very thin, and the specific area is high. The final structure of the MIP network with a predominance of isolated functional units closely surrounded by cross-links yields a rigid material capable of preserving the memory of the model molecule of patulin in molecular imprints. Low reactivity of the functional monomer has beneficial effects regarding the binding selectivity for the target molecule compared to materials prepared from the more reactive methacrylic acid which lead to the formation of flexible polymer formed of short poly(methacrylic acid) sequences.