Multi-structured Prussian Blue-Yeast Based Hybrid Microspheres:Synergistic Treatment Of Dye Wastewater By Adsorption And Fenton Catalysis

Due to the characteristics of bright color and lasting stability,synthetic dyes have rapidly developed in various fields such as textile dyeing,plastics,leather,prints and cosmetics.However,while people enjoy the brilliant colors of synthetic dyes,they also suffer from serious harm to the natural environment and human health.Considering the variety and structural stability of synthetic dyes,typical biological treatment is hard to meet a satisfactory effect.By contrast,adsorption and Fenton catalytic strategy,based on physical and chemical treatment method,have been recognized by many researchers because of their simple operation,quick response and high processing efficiency.Nevertheless,some limitations still existed when the single adsorption or Fenton degradation of dye pollutants is operated.Such as difficult recovery and regeneration of adsorbent;high cost and secondary pollution in the process of Fenton catalytic oxidation,etc.In this case,integrating the two to form a hybrid treatment method with adsorption+Fenton catalysis synergetic effect seems to be an effective way to treat refractory dye wastewater.Nanomaterial has brought a new dawn in review of hybrid treatment process of dye waste water.By adjusting nanoparticles with unique microstructure,modifying the surface or assembling molecules,a series of hybrid functional materials with double or multiple functions can be formed,which can not only reduce the mass transfer resistance between the pollutant molecules and active substances,improve the catalytic efficiency,but also promote the regeneration of adsorbent,ensuring the continuous and effective adsorption and catalytic reaction on the same substrate.It can be sure that multi-functional micro/nano composites have gained great potential in the hybrid treatment of dye wastewater.However,some key issues still need to be further explored and studied.For example,the controllable synthesis of the microstructure and its compatibility in environment,the synergistic mechanism in organic dye wastewater treatment,etc.To this end,multi-structured hybrid microspheres based on Prussian blue-yeast were controllably prepared in this paper,where simple and easy obtained Prussian Blue nanoparticles?PB NPs?were used as the basic unit,and the resource-rich and environment-friendly brewing yeasts were selected as the biological carrier.In order to arouse the adsorption activity and Fe^II/Fe^III Fenton catalytic activity in the structure of PB@yeast NPs microspheres and their derivatives,the adsorption and Fenton catalytic performence of core-shell Prussian blue@yeast,hollow porous Prussian blue@yeast and N-doped Fe₃O₄@yeast-based carbon hybrid microspheres on various dyes were systematically investigated by static or dynamic response system.Main research contents include:?1?Preparation of core-shell Prussian blue@yeast and its Fenton catalytic performance.Core-shell PB@yeast hybrid microspheres were prepared by liquid phase precipitation,in which PB NPs were assembled on the surface of yeast cells.Fenton catalytic experimental results showed that the fluorescent dye CXT removal efficiency under the condition of dark reaction was similar to pure yeast,and the removal efficiency increased rapidly with assistance of H₂O₂ and UV light,which is much higher than that of yeast and PB NPs?6.9times than PB NPs?,indicating that core-shell PB@yeast microspheres combined with biological adsorption of yeast and Fenton catalytic properties of PB NPs,and those two functions have a synergistic effect.?2?Preparation of hollow porous Prussian blue@yeast and its adsorption coupled catalytic mechanism.PB NPs was in situ grown on the inner and outer surface of inactive yeast cells by means of mild hydrothermal method,and the hollow and porous structured PB@yeast hybrid microspheres were formed.From FE-SEM images,the distribution of PB NPs on the yeast cell wall surface was more even than core-shell PB@yeast prepared before,which is mainly due to PB NPs directly anchored on the abundant surface functional groups of internal/external yeast cell wall.This unique hollow porous structure can provide more active adsorption and catalytic sites for the attachment of dye molecules,thus significantly improving the adsorption and Fenton catalytic degradation capacity of PB@yeast in the process of dye pollutants removal.Adsorption coupled Fenton catalytic experimental results indicated that PB@yeast microspheres could completely remove selected fluorescent CXT,cationic methylene blue?MB?and anionic methyl orange?MO?in a relatively short time,showing excellent cooperative processing ability and general applicability of dye po llutants.The adsorption coupled catalytic mechanism follows three steps:bio-adsorption-Fenton catalytic degradation-adsorption site regeneration.These three behaviors are mainly controlled and regulated by adsorption during the reaction process,and their synergistic actions enhanced the removal efficiency of target pollutants by PB@yeast.?3?Preparation of cage-like N-doped Fe₃O₄@yeast-carbon and its adsorption and regeneration behavior.PB@yeast microspheres were used as templates to obtain 3D cage-like N-doped Fe₃O₄@yeast-carbon?donated as Fe₃O₄@C?hybrid microspheres by pyrolysis at low temperature.Adsorption experiments showed that Fe₃O₄@C had a good adsorption capacity for rhodamine B?RhB?removal.At room temperature,the maximum adsorption capacity could be to 257.06 mg?g^-1,which was obviously superior to other PB-based adsorbent.This is mainly attributed to the unique porous cage-like structure and N doping synergy of Fe₃O₄@C,in which the cage-like microspheres created a favorable condition for the rapid diffusion of RhB molecules,reducing the diffusion resistance,while the presence of N increased the electron density on the surface of the carbon layer and enhanced the interaction between dye molecules and the adsorbent,thus leading to fast and efficient adsorption properties.Regeneration experiments showed that Fe₃O₄@C could react with Persulfate?PS?to generate strong SO₄·^-and effectively realize in situ regeneration of adsorbent.In addition,the regenerated Fe₃O₄@C could be separated from the water by a simple applied magnetic field.After 5 cycles,its adsorption capacity did not decrease significantly,showing good reusability.?4?Design of Fe₃O₄@yeast-carbon fixed bed reactor and its dynamic adsorption performance.Fe₃O₄@yeast-carbon was used as the packed adsorbent,and a lab-scale fixed bed reactor was independently designed to investigate the continuous and dynamic adsorption capacity of RhB dye wastewater removal.The penetration curve of RhB adsorption by Fe₃O₄@C under different conditions were analyzed and modeled to establish the dynamic adsorption models.The results showed that BDST model could predict the penetration time at t_0.5,while Yoon-Nelson model was more suitable to describe and predict the process of RhB adsorption by Fe₃O₄@C in the fixed bed?correlation coefficient R²?29?0.97?.The Fenton-like regeneration experiments showed that Fe^III in the structure of Fe₃O₄@C could be used as the main active site to active potassium bisulfate?PMS?to produce a large number of strong oxidative?OH and SO₄^-?,both of which could attack RhB adsorbed on the surface and pore of the adsorbent and receive rapid regeneration of the active sites.Moreover,yeast-based carbon in Fe₃O₄@C structure could also participate in PMS activation reaction through electron transfer process,improving the regeneration rate of adsorbent.?5?Design of Fe₃O₄@yeast-carbon fluidized bed reactor and its Fenton-like catalytic performance.Using Fe₃O₄@yeast-carbon as packed catalyst,a lab-scale circulating fluidized bed reactor?FBR?was independently designed to analyze the degradation of flowing RhB dye wastewater by Fe₃O₄@C activated PMS reaction.By calculating the hydrodynamic characteristics,it is found that the ideal decentralized fluidized bed state could be achieved with a very small fluid velocity,which was lower in energy consumption than most liquid-solid fluidized bed catalytic reaction systems reported in literature.The Fenton-like experimental results showed that the actual consumption of PMS oxidant in this system was far less than the theoretical consumption,and it could effectively remove RhB under the condition of low PMS dosage,which was mainly attributed to the high mixing degree and good mass transfer effect of FBR.Through single-factor and response surface analysis and optimization about the Fe₃O₄@C catalyst amount,the initial concentration of RhB solution,PMS oxidant dosage and reaction time,the optimal experimental conditions were obtained as follows:0.11 g of Fe₃O₄@C catalyst,0.29 mM of PMS,22.34 mg?L^-11 of RhB concentration and 49 min of reaction time.The relative error between the verification experiment and the predicted value is only 1.1%,indicating the mathematical model is reliable and correct,which provides the necessary scientific basis and theoretical guidance for the magnification experimental study of RhB degradation.