Preparation Of Chitosan-stabilized Fe~0 Nanoparticles For Cr(?) Removal

Chromium is an important industrial material,and it can not be substituted in many areas.The wide utilization of chromium as well as irrational emissions cause serious water pollution.Due to its carcinogenicity,hypertoxicity and stong movability,Cr?VI?is stipulated as priority pollutant.Therefore,much concern has been paid on the technology for remediating Cr?VI?contamination by environmental researchers.Recently,due to its large specific surface area,high reactivity and suitting for a variety of water pollutants,nanoscale zero-valent iron?NZVI?is considered as a new technology for remediating Cr?VI?contamination.However,the spontaneous combustion,agglomeration and oxidized by oxygen when exposed to air are the major challenges for NZVI using in practical application process.These problems have seriously hampered the preparation and application of NZVI.To solve these problems,this research preparied NZVI with chitosan as stabilizer by the solution method and optimized the preparation conditions.Cr?VI?removal effectiveness with the prepared chitosan-Fe⁰ nanoparticles was investigated by batch experiments.The main contents are as follows:The conditions for preparating chitosan-Fe⁰ nanoparticles are optimized:chitosan is dissolved in 0.05 mol/L HNO₃ to make the mass concentration of 0.5%.30 mL of chitosan solution is mixed with 120 mL of solution containing 2.978 g of FeSO₄·7H₂O,adjusting the pH=6.The solution is stirred over 30 min under nitrogen gas in a three-necked flask.Then,100 mL of freshly prepared solution contianing 2.434 g of NaBH₄ is dropped in the three-necked flask by 1 drop per second.Again,the solution is stirred for another 90 min under room temperature,and then the chitosan-Fe⁰ nanoparticles are obtained.The results of characterization demonstrate that the size of chitosan-Fe⁰ nanoparticles is about 100-150 nm and the chitosan-Fe⁰ nanoparticles have good oxidation resistance.The ability of chitosan-Fe⁰ nanoparticles to remove Cr?VI?is better than the common NZVI and iron powder under the same experimental conditions.The effect of the initial concentration of Cr?VI?,the dose of the chitosan-Fe⁰ nanoparticles,pH and temperature on removal efficiency of Cr?VI?are examined by batch experiments.The experimental results show that the reaction rate constant decrease with the increase of initial concentration of Cr?VI?and pH but increase with the increase of the dose of the chitosan-Fe⁰ nanoparticles and temperature.The rate of reduction of Cr?VI?can be expressed by pseudo-first-order.Organic acids can hardly reduce Cr?VI?,but they can accelerate the rate of reduction of Cr?VI?by the chitosan-Fe⁰ nanoparticles without light.In the light conditions,organic acids can weakly reduce Cr?VI?,and they can obviously accelerate the rate of reduction of Cr?VI?by the chitosan-Fe⁰ nanoparticles.