Response Surface Methodology Was Used To Optimize The Adsorption Of Azo Dye DR80 In Water By Magnetic Fe 3 O 4 /chitosan Nanoparticles

In recent years, with the rapid development of dyeing industry, there is a strong desire for dye in the market. Only in the domestic market, the annual output of dye soared to 1.15 million tons in 2015. However, the amount of dyeing wastewater producing in the process of dye's production and usage account for about 2% of the total wasterwater discharges. The massive discharge of dyeing wastewater, especially persistence azo dyeing wastewater, causes serious pollution to water system. Therefore, in order to realize the efficient adsorption of direct red 80(DR80) in simulation wastewater and rapid saparation after adsorption, we prepared a super paramagnetic Fe3O4/chitosan nano-particles by a chelation-coprecipitation method between Fe3+ and chitosan-HCl solutions. Response surface methodology (RSM) was employed to optimize the variables of DR80 asorption process; a central composite design was applied to arrange the optimization experiment. We established an adsorption prediction model with the adsorbing capacity as its response variable, and process parameters as its independent variable. And the statistical analysis shows that the adsorption model is reliable and accurate. Then, on the basis of RSM, we researched the main effects, quadratic effects and interactions of process variables. The results showed that the adsorption temperature and adsorption time have the maximum and minimum contribution to the azo dye DR80 removal on magnetic Fe3O4/chitosan, respectively, at the same time also found that the interaction between dye concentration and the adsorption time almost can be ignored. In addition, we combined RSM with expectation function to search the maximum response value within the whole scope of the variables, and under composite desirability value D=0.9999, maximum adsorption capacity is 4757.97 mg-g-1 obtained at T= 75?, CDR80= 525 mg-L-1, and t= 188.3 min which was the corresponding optimal conditions for DR80 adsorption onto magnetic Fe3O4/chitosan.In this paper, we employed five different models to study the adsorption kinetics. The result shows that pseudo-second order fit the experimental data very well, and the intraparticle diffusion was the rate-controlled step of the adsorption processes. Then, we applied eight two-parameter and three-parameter's isotherm model to fit the experimental data, and the adsorption equilibrium result indicate that the adsorption process was monolayer chemisorption. Thermodynamic research indicate that the endothermic nature of the dye adsorption process and an increase in the degrees of random at the solid-liquid interface during the dye adsorption on the active site of magnetic Fe3O4/chitosan, respectively. To sum up, the adsorption of azo dye DR80 onto magnetic Fe3O4/chitosan was efficient and effective. And the rapid magnetic response has very important economic and realistic significance for the practical application of azo dyes wastewater treatment.