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

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-FeO nanoparticles. Rosin was used as the PCM in the sol-gel process and the carbon-based substrate of α-FeO nanoparticles in the thermal process. The α-FeO nanoparticle embedded rosin-derived biochar(α-FeO@HrBc)were highly dispersed. The dispersity of α-FeO nanoparticle could be regulated by the weight ratios of rosin to FeCl·6HO during the preparation, as evidenced by the scanning electron microscope (SEM) spectrum and the sorption capacity results. Among a series of α-FeO@HrBc nanocomposites, the one with the weight ratios of 1/1.5 rosin/FeCl·6HO 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-FeO nanoparticle. In addition, SEM showed that the majority of α-FeO nanoparticles was dispersed on and inside the biochar substrate. Batch adsorption experiments revealed that the α-FeO@HrBc adsorbed 90% Cr(VI) within one minute, and the maximum capacity was up to 166 mg·g 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-FeO nanoparticles provided important sorption sites, the newly formed Cr(III) and the remaining Cr(VI) ions could be adsorbed on α-FeO@HrBc via the formation of FeCr coprecipitation.