Abstract
The increasing use of pharmaceuticals is causing serious environmental pollution because of their improper disposal, leading to water contamination. Of particular concern are benzodiazepines (BDZs) given their low removal efficiencies by conventional treatment processes. This concern warrants the development of alternative or complementary treatment technologies with high removal efficiencies. Toward this end, we have developed a facile one-step hydrothermal method to synthesize a nanohybrid of manganese sulfide (MnS2) and reduced graphene oxide for the efficient adsorptive removal of the most commonly detected BDZ, that is, alprazolam (ALP). The as-prepared samples were thoroughly characterized using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, and photoluminescence spectroscopy. Removal of ALP from aqueous solutions was investigated at different temperatures, pH values, and adsorbent dosages. Both high pH and temperature favored ALP removal. The experimental equilibrium data could be accurately described by the Langmuir isotherm model, whereas the adsorption kinetic data were well-represented by the pseudo-second- order model. Relevant thermodynamic parameters, such as Gibbs free energy (Delta G degrees), enthalpy change (Delta H degrees), and entropy change (Delta S degrees), were also calculated from the experimental equilibrium data. The positive value of Delta H degrees and the negative value of Delta G degrees indicated the endothermic and spontaneous nature of ALP adsorption by the synthesized adsorbent. Multiple adsorption-desorption cycles indicated that the present adsorbent can be efficiently regenerated several times without significant degradation in its performance.