A composite FeOOH@microalgae for heavy metals and Congo red removal from aqueous solution

A microalgae-oxide complex (FeOOH@Microalgae) was successfully synthesized; it showed a high adsorption ability for removal of Cr(VI), Cu(II), Pb(II), Cd(II), and Congo red from contaminated aqueous solution. The product was characterized using X-ray diffraction, scanning electron microscopy (SEM), transmission electron micrography (TEM), X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The SEM and TEM images showed that the complex formed using nano-sized FeOOH, which covered micron-sized microalgae, and the degree of product aggregation was related to the synthetic temperature. The aggregation degree increased with a decrease in the synthesis temperature, thus, micron-sized microalgae can be immobilized. The adsorption experimental results of pH effect, sorption kinetics, and the isotherm indicated that FeOOH@Microalgae showed a reasonable adsorption effect on four metal ions, and the adsorption ability of Pb(II) was substantially higher than that of the other three ions. Kinetic data showed agreement with a pseudo-second-order equation, and the Langmuir model fit the isotherm data of four heavy metal ions. The adsorption mechanism indicated that the adsorption process was related to the surface hydroxyl (or carboxyl) groups of the adsorbent that interacted with metal ions. Hence, FeOOH@Microalgae, as an efficient adsorbent, can be extensively applied for the treatment of heavy metal contaminated wastewater.