A novel pyrazole-hydrazone modified silica gel as an adsorbent for efficient and selective removal of Pb(II) from aquatic media: kinetic, isotherm, thermodynamic, and functional theory studies

Today, water pollution is one of the most important strategic issues. Furthermore, water contaminated with heavy metals represents a major challenge for human health and the environment in many countries. To reduce the threat of water pollution to humans and the environment, it is imperative to develop water treatment technology. In this study, a novel SiPz adsorbent was developed using a functional organic ligand of 5-methyl-1H-pyrazole-3-carbohydrazide immobilization onto the surface silica and employed as effective and selective adsorption of Pb(II) from aqueous solutions. The obtained material was systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, and Brunauer-Emmett-Teller, which confirmed that the pyrazole-hydrazone was successfully functionalized on the silica surface. Parameters influencing adsorption performance, such as pH, time, initial concentration, and temperature, were studied in the batch method. The results show that the hybrid material exhibits rapid Pb(II) adsorption, with a maximum adsorption capacity of 200.34 mg/g at a pH = 6. The kinetics and isotherms of Pb(II) adsorption onto SiPz were characterized, revealing that the adsorption mechanism adheres to pseudo-second-order kinetics and aligns with the Langmuir models. The thermodynamic analysis suggested that the adsorption process is endothermic and spontaneous. The outcomes from competitive experiments involving Pb(II), Cd(II), Cu(II), and Zn(II) demonstrated that SiPz exhibits a pronounced selectivity for Pb(II) alongside exceptional regenerative capabilities. In addition, a theoretical study using DFT and QTAIM methods shows that nitrogen and oxygen atoms have great potential in the field of Pb(II) decontamination due to their good coordination. Therefore, the SiPz adsorbent can be considered a potential candidate for the purification of Pb(II) from contaminated water sources.