Experimental Study On The Degradation Of Methylene Blue By A Heterogeneous Fenton-like System With Iron Nanoparticles Coated By Calcium Alginate

Methylene blue（MB）is widely used in the printing and dyeing industry and is also one of the important components of this type of wastewater.The wastewater containing MB has strong biological toxicity and stable chemical properties,which is difficult to be effectively degraded by general wastewater treatment processes.The Fe NPs-Fenton oxidation which can destroy persistent organic matter efficiently and improve biodegradation potential to realize high mineralization,has become an important technology for removing dyes from aquatic environment.Nevertheless,the inherent drawbacks are still a restricted factor for extensive actual applications such as stringent requirements for rigorous solution p H,secondary pollution owing to the production of iron-containing sludge.Moreover,the chemosynthetic Fe NPs still suffer from easily oxidation and agglomeration,and the traditional synthesis technology are toxic and costly.In this paper,GT-Fe NPs@CA was synthesized using calcium alginate（CA）and green tee extract,and were used to degrade MB in aqueous phase as a Fenton-like catalyst.The composites were characterized by SEM,EDS,XPS and FTIR.An attempt to reveal the degradation performance and mechanism was also done.The main conclusions were shown as follows:1.Green tea extracts were used as reducing and stabilizing agent.The SEM,EDS,XPS and FTIR images shown that the prepared Fe NPs had an even distribution with an average particle size of 10～50 nm.Moreover,Fe NPs could be well immobilized in calcium alginate microspheres.2.Compared with the traditional and Fe NPs-Fenton system,there was no iron-containing sludge in the reaction of the GT-Fe NPs@CA Fenton system.After 240 min,the highest removal efficiency（99%）of MB(100 mg·L^-1)was achieved at the optimal conditions(p H=3.0,GT-Fe NPs@CA=5.0 g·L^-1,H₂O₂=10 mmol·L^-1).Furthermore,the results indicated that GT-Fe NPs@CA/H₂O₂ was effective in MB removal more than 70%in a range of p H from 3.0 to 9.0.The degradation process is endothermic,entropy-increasing and spontaneous.After reaction,catalyst was easy to separate solid and liquid.3.The pseudo-second-order model showed that the chemical reaction on the surface is possible adsorption mechanisms,e.g.,chemical adsorption by surface functional groups（i.e.,CA）.The GT-Fe NPs@CA adsorption fitted to Langmuir model and was valid for single-layer adsorption.4.The MB was first adsorbed on the active site of GT-Fe NPs@CA.Subsequently,Fe²⁺/Fe³⁺leaching from iron oxides and ZVI played an important role in catalysis of H₂O₂,and the·OH radicals formed in the Fenton system,which could destroy MB efficiently and improve biodegradation potential to realize high mineralization.The experimental conditions could also affect the decomposition of hydrogen peroxide.The synthesis of GT-Fe NPs@CA was environmental and low-cost.The GT-Fe NPs@CA/H₂O₂ system overcomed the disadvantages,such as narrow p H reaction range and easy to produce iron-containing sludge,which had great practical value,and provided experimental basis for the application of green and efficient heterogeneous Fenton technology.