Characterization And Mechanism Analysis Of Activated Car Bon Fiber Stabilized Nanoscale Zero-valent Iron For The Removal Of Cr (Ⅵ) From Aqueous Solution

Water is the most important source for human beings, and play an important role in human’s daily life and industrial production. Due to its high toxicity and carcinogenicity, Cr(Ⅵ) has become a focus of environmental pollutants. In recent years, because of its high reactivity and be able to repair various pollutants, NZVI has become a very important means of environmental remediation technology. However, there are still some problems need to be solved in the application of NZVI, such as the particles were easy to be oxidized and aggregation.To solve above problems, this study selected activated carbon fiber as supported material to prepared stabilized NZVI, and the sodium borohydride was used to reduce ferrous iron to zero-valent iron. The physicochemical properties of these activated carbons were characterized by X-ray diffraction(XRD),atomic force microscope (AFM), scanning electron microscopy (SEM),N2 adsorption/desorption isotherms and Fourier transform infrared spectroscopy (FTIR). Batched experiments was carried out to compare the Cr(Ⅵ) removals efficiencies by ACF、NZVI and ACF-NZVI. The effect of solution pH and ultrasonic to removals efficiencies were investigated. X-ray photoelectron spectroscopy (XPS) was used to analyze the removal mechanisms.The characterization results showed that NZVI particles were hemispherical and distributed on ACF surface as a single form. As support material, ACF was effectively prevented the aggregation of NZVI particles.The distribution of particle size of ACF-NZVI was widespread ranging from 10.4 to 115.9 nm with a mean diameter of 68.2 nm and 93.5% particles have the diameter less than 100 nm.The specific surface area of ACF-NZVI was 935.1m2/g, which was much higher the specific surface area of NZVI and less than the ACF’s. The FTIR analyze showed that there were few functional groups of ACF-NZVI, the broad bands appeared at 3442cm-1 could be attributed to the vibration of O-H and N-H groups.The weak peak appeared at 1634cm-1 could be attributed to the deformation vibration of N-H.The results of batched experiments showed that 67.0% Cr(Ⅵ) was removed by ACF-NZVI from 70mg/L solution and higher than ACF (52.6%) and NZVI (59.4%). 7.8mg Cr were removed by per gram ACF-NZVI. The removal of Cr(Ⅵ) was strong pH dependent and decreased with the increasing solution pH. The ions form of Cr(Ⅵ) and the activity of NZVI in the different pH conditions may be the main factors of different removal rate. Ultrasonic can clear the deposits in time, prevent the formation of the passivation layer and keep the activity of NZVI, resulted in the Cr(Ⅵ) removal efficiencies increased from67.0% to 80.2%. The fitting parameters of Fe 2p, Cr 2p, C 1s high resolution XPS spectra showed that 56.6% Cr(Ⅵ) was reduced to Cr(Ⅲ) by NZVI, the adsorption of ACF and the reduction of NZVI leaded to the removal of Cr(Ⅵ) and prat of functional groups were transformed into others in the Cr(Ⅵ) removal processes.