Emerging contaminants (EC) and environmental pollutants are a class of natural or synthetic chemical compounds of extreme importance to the pharmaceutical and agricultural industries that contaminate Earth's atmosphere, lithosphere, and hydrosphere, thus affecting the terrestrial ecosystem and human health. Among these compounds and their derivatives, we can highlight pesticides, surfactants, pharmaceutical products, fertilizers, heavy metals, etc [1–3] Therefore, developing electroanalytical techniques capable of removing the ECs is extremely important for achieving the sixth goal of the United Nations Sustainable Development Goals, which guarantees clean water and sanitation for all[4–6]
It’s a fact that water is an indispensable natural resource for maintaining the conditions of existence and environmental equilibrium of all species of living beings on our planet. Starting from this principle, it’s imperative to maintain the global hydric resources with the minimum conditions of potability and human and industrial use to secure one of the basic conditions for life on planet Earth [2][4, 6].
Ofloxacin (OFL) is a highly prescribed synthetic antibiotic for treating respiratory and urinary infections in humans and animals [7]. As a contaminant, it not only persists in the environment due to the difficulty of biological degradation but can also contribute to developing bacteria resistance to the antibiotic [7, 8]. Aiming to reduce the impact of ofloxacin on the environment, it has developed works investigating the antibiotic's capture by adsorption [7–9]. For example, Cu-BTC@Fe3O4 nanoparticles presented an adsorption capacity of 11.14 mg g− 1 for ofloxacin, with an efficiency of 62.31% within a 3-hour contact time [9]. Additionally, calcined Verde-lodo (CVL) clay effectively adsorbed ofloxacin and presented potential for electrochemical-based regeneration after adsorption [10].
Computational methodologies based on Density Functional Theory (DFT) [11–13] were utilized to investigate the adsorption mechanism of emerging contaminants [14–17]. According to [16], compared to other contaminants, ofloxacin was found to be most reactive, as indicated by its lower hardness value, obtained from the HOMO/LUMO energy gap, considering that molecules with larger gaps are more stable and less reactive. This result suggests that ofloxacin has higher removals. Electronic properties, e.g., the density of states and charge density, of the interaction between paracetamol and different adsorbents were obtained using DFT calculations, showing a good correlation with experiments performed [17].
Due to the environmental problems related to the EC, this work pursues an alternative to detect and remove the drug ofloxacin (OFL) in a simple, fast, and inexpensive way using of two adsorbents, zinc stannate (Zn2SnO4) and reduced graphene oxide (rGO), because both the surfaces possess numerous applications in adsorptive process [18–21]. To better understand the stability and spontaneity of the adsorption process of OFL in both compounds (zinc stannate and reduced graphene oxide), theoretical calculations involving adsorption energy were performed [19, 22, 23]. Furthermore, electronic properties calculations such as band structures and total density of states were performed to understand better the energy band gap for the adsorbents (Zn2SnO4 and rGO) without the adsorbate and with the adsorbate (OFL), as well as analyze the conduction and valence bands of the species.