The effect of humic acid on the stability and aggregation kinetics of WO3 nanoparticles

The physicochemical properties including size, hydrodynamic diameter, agglomeration rate, surface area, crystal structure, and surface charge were determined for WO3 using x-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), UV-Vis spectrometer (DRS), and Zetasizer Nano ZS. The stability and aggregation behavior of WO3 were investigated using dynamic light scattering (DLS) to monitor the hydrodynamic size and zeta potential. The effect of ionic strength was further studied using NaCl, MgCl2. and CaCl2 electrolytes at pH 5 as well as the effect of humic acid. WO3 nanoparticles behaved similarly in deionized water suspensions and in the presence of NaCl electrolytes. The stability of nanoparticles was notable at low concentration (1 ppm) of humic acid particularly with NaCl electrolytes. Divalent cations enhanced agglomeration of nanoparticles even at the highest concentration of humic acid due to the formation of cation-humic acid bridges. The Derjaguin-Landau-Verwey-Overbeek theory was used to investigate the interaction energies, and it was found that van der Waals attraction forces are dominant in the presence of divalent cations.