Study Of The Decoloration Of Cationic Dyes By Zero-valent Iron Nanoparticles

The removal of dyes is of great concern because many kinds of dys and their degradation products cause serious environmental problems due to their high stability and complex aromatic structures. Their presence in water could directly affect the photosynthesis phenomenon of aquatic life due to their color. Dyes can disturb the aquatic ecosystem and food chain because of their toxicity and carcinogenicity, they have been demonstrated to have harmful effects on human health during short periods of exposure. Domestic and foreign scholars have used different kinds of techniques to change the structure of refractory compounds, in order to enhance the biodegradability of the compounds and make them easily be treated in the subsequent conventional biochemical treatment. Recently, nanoscale zero valent iron (nZVI) has attracted much attention because of its larger specific surface area which can provide more reactive sites per unit mass for the efficient removal of a wide range of contaminants.Therefore, in this study, two cationic dyes, malachite green (MG) and methylene blue (MB), were selected to study the decolorization performance of the modified NZVI and Fe NPs synthesized using green methods based on green tea extracts. The specific research contents and results are as follows:1. Nano zerovalent iron (NZVI) technology has aroused tremendous interests for degradating number of environmental contaminants both in surface water and underground water. However, these nanoscale particles are prone to aggregate, which may result in the decrease of its reactivity in liquid phase. Modified Fe NPs with polyacrylic acid (PAA-Fe) has enhanced the dispersion of NZVI and reduced its agglomeration. And for the first time, PAA modified NPs (PAA-Fe) were used for degradation of methylene blue in water phase. The prepared PAA-Fe NPs characterized in terms of Transmission electron microscope (TEM), Scanning electron microscope (SEM), X-ray diffraction (XRD) and specific surface area. The results indicate that compared with unmodified pristine zero-valent iron NPs, the surface area of PAA-Fe NPs is increase. PAA-Fe NPs are smoother with smaller particle size.2. With 0.1% of PAA, the decolorization efficiencies of methylene blue by using PAA-Fe NPs are 98.84%,27.32% higher than that of pristine Fe NPs in 60min. Decolorization efficiencies were also affected by initial pH value, initial concentration of methylene blue, dosage of PAA-Fe NPs and degradation temperature. Kinetic analyses based on the experimental data illustrate that the decolorization reaction of methylene blue fitted well to the pseudo first-order kinetics model with more than 26.53 kJ/mol activation energy.3. Green tea extract was used to synthesize iron nanoparticles (G-Fe NPs) and degrade malachite green (MG) in aqueous solution at room temperature. Green tea extracts that act as both reducing and capping agents in the synthesis of Fe NPs contain a high concentration of caffeine/polyphenols. Compared with iron nanoparticles produced by borohydride reduction (K-Fe NPs), scanning electron microscopy (SEM) and Transmission electron microscope (TEM) confirmed that G-Fe NPs increased their reactivity and a decrease occurred in the aggregation of iron nanoparticles for the Fe NPs. Fourier Transform Infrared spectrometer (FTIR) indicated that some polyphenols are bound to the surfaces of G-Fe NPs as a capping/stabilizing agent.4. The decolorization efficiencies of methylene blue by using G-Fe NPs are 90.70%%, 27.44% higher than that of pristine K-Fe NPs in 60min. Experimental variables, such as G-Fe NPs dosage, initial malachite green concentration, solution pH and the reaction temperature, were investigated. Batch experiments suggest that the decolorization efficiency was enhanced with the increase of G-Fe NPs dosage and reaction temperature, but decreased with increasing initial malachite green concentration and initial solution pH. Furthermore, kinetics for the degradation of MG using these G-Fe NPs fitted well to a first-order exponential decay kinetics model.