Polystyrene-templated hollow mesoporous magnetite as a bifunctional adsorbent for the removal of rhodamine B via simultaneous adsorption and degradation

Rhodamine B (RhB) is classified as one of the most hazardous pollutants due to its toxic and carcinogenic nature. This study uses a new class of adsorbent, polystyrene-templated hollow mesoporous magnetite (HMM), to remove RhB from the aqueous solution via simultaneous adsorption and degradation. The obtained HMM is spherical with a 320-350 nm particle size. The particle is integrated with a hollow core at ca. 230 nm in diameter. HMM possesses a porous interior, with the respective specific surface area and pore volume of 132.0 m2/g and 0.63 cm3/g. Its adsorption/desorption isotherm exhibits the typical type-IV IUPAC classification with the H4-type hysteresis profile, indicating the presence of mesoporous wedged-shaped pores. The influences of three independent variables on the RhB removal rate are studied, including pH, adsorbent loading mc, and temperature T. The highest removal rate of RhB is obtained at 99.7% when pH = 6, mc = 0.8 wt%, T = 50 °C, and time = 240 min. The study suggests that the whole removal process of RhB follows the pseudo-second-order law and multilayer mechanism and is generally favorable, spontaneous, and endothermic. Further elaboration using the multi-linear IPD shows that surface diffusion plays a major role in removing RhB. At the same time, the modified Langmuir also considers the Fenton degradation reaction as one of the factors that promote the dye removal, particularly in higher T. Based on the study, HMM exhibits excellent performance in removing RhB by facilitating both adsorption and Fenton reaction in a one-step process.