Design of a novel multifunctional soil conditioner based on Fe-modified hydroxyapatite/polydopamine/amino carbon nanotubes

Abstract

A composite soil conditioner based on Fe-doped hydroxyapatite/polydopamine/amino carbon nanotubes (Fe-HAP@PDA@CNT-NH2) was prepared for controlling release of flavic acid (FA) fertilizers and for the treatment of soil contaminants methylene blue (MB). Firstly, Fe-doped hydroxyapatite (Fe-HAP) was prepared by hydrothermal method. Then, Fe-doped hydroxyapatite/polydopamine/aminocarbon nanotube (Fe-HAP@PDA@CNT-NH2) composite was prepared by in situ polymerization of dopamine (DA) with amino carbon nanotubes (CNT-NH2) on the Fe-HAP surface. Finally, Fe-HAP@PDA@CNT-NH2@FA composite soil conditioner was obtained by loading with FA. Scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were applied to analyze the composition and morphology of the composites. The loading and slow release experiments showed that Fe-HAP@PDA@CNT-NH2 owned good loading efficiency on FA and had a wide applicability with different fertilizer slow release effects in different pH environments. Adsorption experiment revealed that Fe-HAP@PDA@CNT-NH2 possessed high adsorption capacity for MB under different pH conditions. The pseudo-second order and Langmuir models discussed above can be utilized to describe the adsorption mechanism utilizing kinetic and isothermal adsorption models. In addition, the plant experiment also proved the effect of the composite soil conditioner on soil and plants. Hence, the new composite soil conditioner has a great promoting effect on soil improvement and crop growth.