Controllable Synthesis of Hierarchical Porous Fe<sub>3</sub>O<sub>4</sub> Particles Mediated by Poly(diallyldimethylammonium chloride) and Their Application in Arsenic Removal

Hierarchical porous Fe<sub>3</sub>O<sub>4</sub> particles with tunable grain size were synthesized based on a facile poly (diallyldimethylammonium chloride) (PDDA)-modulated solvothermal method. The products were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), N<sub>2</sub> adsorption–desorption technique, vibrating sample magnetometer (VSM), and dynamic light scattering (DLS). The results show that increasing the PDDA dosage decrease the grain size and particle size, which increased the particle porosity and enhanced the surface area from 7.05 to 32.75 m<sup>2</sup> g<sup>–1</sup>. Possible mechanism can be ascribed to the PDDA function on capping the crystal surface and promoting the viscosity of reaction medium to mediate the growth and assembly of grain. Furthermore, the arsenic adsorption application of the as-obtained Fe<sub>3</sub>O<sub>4</sub> samples was investigated and the adsorption mechanism was proposed. High magnetic Fe<sub>3</sub>O<sub>4</sub> particles with increased surface area display improved arsenic adsorption performance, superior efficiency in low-level arsenic removal, high desorption efficiency, and satisfactory magnetic recyclability, which are very promising compared with commercial Fe<sub>3</sub>O<sub>4</sub> particles.