An advanced sol-gel strategy for enhancing interfacial reactivity of iron oxide nanoparticles on rosin biochar substrate to remove Cr(VI)

Abstract

The application of iron oxide nanoparticles (IONs) is often limited by agglomeration and low loading. Here, we presented a facile phase change material (PCM) -based sol-gel strategy for the fabrication of α-Fe₂O₃ nanoparticles. Rosin was used as the PCM in the sol-gel process and the carbon-based substrate of α-Fe₂O₃ nanoparticles in the thermal process. The α-Fe₂O₃ nanoparticle embedded rosin-derived biochar(α-Fe₂O₃@HrBc)were highly dispersed. The dispersity of α-Fe₂O₃ nanoparticle could be regulated by the weight ratios of rosin to FeCl₃·6H₂O during the preparation, as evidenced by the scanning electron microscope (SEM) spectrum and the sorption capacity results. Among a series of α-Fe₂O₃@HrBc nanocomposites, the one with the weight ratios of 1/1.5 rosin/FeCl₃·6H₂O had the highest capacity for hexavalent chromium (Cr(VI)) sorption. This phenomenon can be ascribed to a remarkably enhanced interfacial reactivity due to an increase in the dispersity of α-Fe₂O₃ nanoparticle. In addition, SEM showed that the majority of α-Fe₂O₃ nanoparticles was dispersed on and inside the biochar substrate. Batch adsorption experiments revealed that the α-Fe₂O₃@HrBc adsorbed 90% Cr(VI) within one minute, and the maximum capacity was up to 166 mg·g^-1 based on the Langmuir model. The FTIR and XPS spectra revealed that the adsorbed Cr(VI) species were partially reduced to less toxic Cr(III). Considering that α-Fe₂O₃ nanoparticles provided important sorption sites, the newly formed Cr(III) and the remaining Cr(VI) ions could be adsorbed on α-Fe₂O₃@HrBc via the formation of FeCr coprecipitation.

Keywords: Abundant active sites; High dispersion; Iron oxide nanoparticles; Monodispersed; Phase change material; Rosin.