Magnetic Nanocarbon Adsorbents with Enhanced Hexavalent Chromium Removal: Morphology Dependence of Fibrillar vs Particulate Structures

Fibrillar and particulate structure magnetic carbons (MCFs and MCPs) were prepared from the same precursor (polyacrylonitrile and Fe(NO3)(3)center dot 9H(2)O) by using a different method, displaying a significant morphology dependence on wastewater treatment. TEM, SEM, XPS, TGA, etc. were systematically carried out to characterize the carbon samples to verify the morphology difference between these two kinds of carbon adsorbents. The results demonstrated that, along with the increase of the Fe(NO3)(3)center dot 9H(2)O loading in the precursor from 10 to 40 wt %, the fibrillar nanoadsorbents displayed an improved activity from 12.6% to 51.4% Cr(VI) removal percentage with the initial Cr(VI) concentration at 4 mg/L. For the maximum removal capacity, the fibrillar sample (MCFs-40) demonstrated 3 times higher removing capacity (43.17 mg/g) than that of particulate nanoadsorbents (MCPs-40, 15.88 mg/g) for the Cr(VI) removal with pH at 1, demonstrating that the fibrillar sample was more favorable for the wastewater treatment than particulate sample. This enhanced removal was mainly attributed to higher specific surface area of the fibrillar sample, leading to more active sites for the adsorption of Cr(VI) and produced Cr(III) ions. The chemical adsorption of Cr(VI) ions over two kinds of adsorbents were disclosed in this removal process. There was a good stability of 5 recycles for the Cr(VI) removal in the neutral solution over MCFs-40 (about 1.4 mg/g) and MCPs-40 (about 0.41 mg/g) with initial Cr(VI) concentration at 4 mg/L. This work can provide an understanding for the rational design of adsorbent in wastewater treatment.