Biosorption Of Two Basic Dye By Three Marine Macroalga

Dye wastewater has the characteristics of large discharge,high chorma,and complicated components.The discharged wastewater is leading to increasingly serious environmental problems.At present,there are lots of methods to remove dyes from dye wastewater all around the world,but these methods have some disadvantages.As a new type of biosorbent,macroalgae have advantages of low costs,high removal efficiency,which indicates a great application prospect in wastewater treatment,but there are few reports focusing on the removal of dyes by using macroalgae.In this study,the Sargassum hemiphyllum,Ulva lactuca and Gracilaria lemaneiformis were investigated as biosorbent to remove the methylene blue(MB)and malachite green(MG).The factors including initial pH,adsorption time,biomass dosage and initial dye concentration were investigated.The adsorption isotherm,kinetics and thermodynamics were used to analyse the experimental data and Scanning Electron Micriscopy(SEM),moreover,Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)analysis were applied to characterize the changes of algae biosorbent after adsorption and clarify the biosorption mechanism.This study can provide the theoretical basis for the development and utilization of using algae biosorbent as the environmental materials.The results are as follows:1.The optimum pH value for three kinds of algae to adsorbe MB was 4~7.In addition,the optimum pH value for U.lactuca and G.lemaneiformis to adsorbe MG was 6~7,and for the adsorption of MG by S.hemiphyllum,the optimum pH value was 5~7.The adsorption time for S.hemiphyllum,U.lactuca and G.lemaneiformis to adsorbe MB and MG to reach equilibrium were in 60 min and 20~30 min,respectively.Increasing the biomass dosage led to an increase in adsorption efficiency and an decrease of the adsorption capacity.The adsorption capacity increased with the increase in initial dye concentration and then reached constant.2.Langmuir,Freundlich and Dubinin-Radushkevich models were applied to fit Isotherm data,and the result suggested that the Langmuir model matched the data much better.The maximum biosorption capacity of MB were 729.93 mg/g,709.22 mg/g,231.48 mg/g,and of MG were 961.54 mg/g,1552.39 mg/g,182.15 mg/g,respectively.The biosorption proceeds mainly through physical mechanism.The kinetics results indicated that the pseudo-second order model described the kinetic of three kinds algae adsorption of two kinds of dyes successfully,which showed that adsorption involving valency forces through sharing or exchange of electrons between sorbent and sorbate.The intraparticle diffusion inferred that the intraparticle diffusion was not the only rate control step.Thermodynamics results showed the reaction of U.lactuca and G.lemaneiformis to adsorbe MB were spontaneous exothermic,while the reaction of S.hemiphyllum was spontaneous endothermic.The reaction of S.hemiphyllum and G.lemaneiformis to adsorbe MG were spontaneous endothermic,while the reaction of U.lactuca was spontaneous exothermic.3.The SEM observation has shown that the surface structure of the algae had been changed sommth and full.FTIR analysis indicated that the adsorption of two kinds of dyes were related to the hydroxyl,amino and carboxyl of the algae.XPS analysis suggested that ion exchange took place in the adsorption process and the ratio of hydroxyl,carboxyl on the algae reduced after adsorption.In conclusion,the experimental results showed that S.hemiphyllum,U.lactuca and G.lemaneiformis had different absorption capicity on MB and MG,respectively,moreover,compared with other absorption materials,the three kinds of algae can absorb MB and MG more effectively,which indicated the bright prospect of them to be applied in the treatment of dye wastewater.