ZnCl₂-doped mesoporous silica nanoparticles prepared via a simple one-pot method for highly efficient nitrate removal

Nitrate is a crucial nutrient in the natural nitrogen cycle. However, human activities have elevated nitrate levels in aquatic ecosystems beyond natural thresholds, posing risks to human health and the environment. In this work, ZnCl₂-doped mesoporous silica nanoparticles (ZnCl₂@MSN) were synthesized using a one-pot preparation method, leading to a streamlined process with reduced time and energy consumption. The homogeneous mesoporous ZnCl₂@MSN exhibited efficient nitrate removal from water, primarily through ion exchange mechanisms (70.97%), with additional support from electrostatic attraction (29.03%). A removal efficiency of 85.11% ± 4.96% was achieved, with a maximum removal capacity of 22.37 mg g^-1 within 15 min in synthetic water (0.75 g ZnCl₂@MSN; 100 mL of 100 mg L^-1 nitrate solution, without pH adjustment, at room temperature (25 °C)). Furthermore, batch adsorption demonstrated a removal efficiency of up to 99.05% ± 5.88% for real water samples. The experimental data fitted best to the Langmuir isotherm model (R² = 0.9966) and the pseudo-second-order model (R² = 0.9985). Thermodynamic studies revealed a spontaneous and exothermic adsorption process. Nitrate exhibited tolerance to coexisting ions using ZnCl₂@MSN in the order of PO₄^3- > CO₃^2- > F^- > Cl^- > SO₄^2- > Br^-, and the material could be reused up to three times. This research highlights the significant advantages of ZnCl₂@MSN, which is synthesized through a simpler and more energy-efficient procedure compared to similar materials reported previously. Despite its streamlined preparation, ZnCl₂@MSN achieves a superior adsorption capacity, requiring less adsorbent for effective treatment. This not only minimizes waste generation but also reduces operational costs. Furthermore, its excellent reusability enhances cost-efficiency, making it a highly practical solution. Importantly, the evaluation of treated water confirmed that the zinc concentration remained well below the EPA discharge limit. These findings underscore the potential of ZnCl₂@MSN as an advanced, sustainable, and economical material for nitrate removal.