Removal Of Typical Pollutants From Wastewater By Green Synthesized Manganese Nanomaterials

Manganese oxide nanoparticles have been shown to be used for the remediation of various types of pollutants in water bodies.In addition,the synthesis of manganese nanoparticles using plant extracts is gradually attracting the attention of scholars because of its economic and environmental advantages.In this study,manganese oxide nanoparticles(Mn NPs)were prepared from green tea extracts and applied to remove mitoxantrone(MTX),As(V),and Cu(II)contaminants in the aqueous environment and the related removal mechanisms were further investigated by physicochemical characterization.The main findings are as follows.Firstly,The green tea extract was used as a reducing agent to reduce potassium permanganate to produce manganese oxide nanoparticles.To confirm the superiority of green synthesized manganese oxide nanoparticles,the properties of the materials before and after calcination were compared,and three calcination modification temperatures and atmospheres were set.The experimental results showed that with the increase of calcination temperature,the surface organic functional groups carbonized and decomposed to form different manganese oxides.The uncalcined Mn NPs showed the highest removal rates of MTX and Cu(II)complex pollutants,reaching 95.2%and 99.9%,respectively,indicating that the organic macromolecules on the surface of the materials provide abundant adsorption sites,thus making the removal efficiency of the pollutants better than that of the calcined materials.Secondly,to further investigate the mechanism of organic pollutant removal by Mn NPs,MTX,a representative antibiotic pollutant,was selected as the study object to investigate the removal mechanism by Mn NPs.The maximum removal efficiency of MTX by Mn NPs reached 97.4%(adsorption capacity of 97.40 mg g^-1)under laboratory conditions and 77.3%for MTX in actual wastewater.The SEM and FTIR analysis showed that MTX was uniformly adsorbed on the surface of Mn NPs,and MTX was attached to the negatively charged Mn NPs surface in the form of chemisorption through its intramolecular-NH group.Isothermal adsorption modeling and kinetic studies showed that the adsorption of MTX proceeded through the Langmuir and pseudo-secondary models,further confirming that chemisorption occurred between the two.As a result,the adsorption mechanism of Mn NPs on MTX is proposed,which mainly involves a combination of valence bonding adsorption,hydrogen bonding,electrostatic interactions,and pore filling.Finally,the removal of typical heavy metal pollutants As(V)and Cu(II)from water bodies by Mn NPs was investigated and the removal mechanisms were explored based on the results of the previous studies.The results showed that Mn NPs have a certain removal capacity for both As(V)and Cu(II),and the removal rates of Mn NPs reached 87.0%(2.8mg g^-1)and 91.5%(12.2 mg g^-1)for As(V)and Cu(II),respectively,under the optimal conditions.The adsorption of Mn NPs on As(V)and Cu(II)The adsorption processes of Mn NPs on As(V)and Cu(II)were in accordance with the Langmuir-type isothermal adsorption model,and the adsorption processes on As(V)were in accordance with the pseudo primary kinetics and dominated by physical adsorption.The adsorption process for Cu(II)followed pseudo-secondary kinetics and was dominated by chemisorption.Overall,the Mn NPs materials synthesized using green tea extracts have good removal effects on MTX,As(V),and Cu(II)pollutants in the aqueous environment and have great potential for practical applications,which are expected to be used for the removal of typical organic and heavy metal pollutants from wastewater.