Preparation Of Ferric Biochar Materials Via In-situ Enriched In Typha Cattails And The Removal Of Toxic Organic Dyes Pollutants

The treatment of organic dye pollutants has caused a difficult problem in environment due to the characteristics of large volume,difficulty in biodegradation and high pollution intensity.The total amount of wastewater produced by the printing and dyeing industry each year accounts for 35%of the total industrial wastewater in the country.40～300 m³industrial wastewater will be produced every 1 ton product in printing and dyeing industry,most of which are complex and difficult to biodegrade.The green and effective method or technology for removal of this wastewater has become a hot issue in the world.Due to the large surface area,abundant surface functional groups,high ion exchange capacity,biochar was widely studied and used as the adsorbent and energy material.At present,there are lots of researches on the pyrolysis condition exploration and surface modification of biochar for enhanced adsorption ability.More importantly,it was reported that the catalytic performance of biochar would be improved when load iron on biochar surface using mechanical mixing or composition.Hence,there is few report about loading iron on biochar by plant in situ enrichment.In this thesis,Fe was successfully enriched in the root of Typha by water culture first,and the preparation conditions of cattail roots iron（CRI）were optimized.The adsorption model of organic dyes on CRI biochar was established.The two photocatalytic systems including like-Fenton and Bi OBr were constructed for the removal of organic dyes.This study provides the experimental basis for new type iron-biochar material prepared by plant in situ enrichment,and the new method for the adsorption and degradation of organic dye pollutants in environment.The main contents and conclusions are as follows:1.Water culture experiment was used to enrich iron elements in the root of Typha root.By adding different concentrations of Fe SO₄aqueous solution,the biochar was labeled as CRI-0,CRI-50,CRI-100,CRI-150,respectively.It was found that the iron content on CRI biochar was increased with the applied iron concentration increased.When the concentration of iron solution was more than 150 mg/L,the plant could stop the enrichment of iron in terms of its self-regulation.The distribution of iron scattered in and out of the root cells was observed in plant sections.SEM showed that the surface of CRI biochar formed large patches or agglomeration particles when the iron ion concentration was more than 100 mg/L during the cultivated process.XRD and EDS results showed that iron was in the form of Fe₂O₃on the surface of biochar.The optimum preparation conditions were as follows:the pyrolysis temperature was 700°C,and the heating rate was17°C/min.The CRI-100 biochar material gained the largest species surface ares.2.Baed on the above chapter,the adsorption characteristics of CRI-0 and CRI-100 on organic dye Rh B were studied.The adsorption capacity of CRI-100 was 33.73 mg/g,which is twice than that of blank CRI-0（15.39 mg/g）.The kinetic adsorption equations of both two are in accordance with the first-order kinetic model,and the isothermal adsorption equations are all in accordance with the Langmuir isothermal adsorption model.The thermodynamic△G,△S and△H are all less than zero,which indicates that the adsorption process is a self-releasing heat process.And the degree of confusion of the system is reduced.The measurement of Zeta potential shows that the adsorption mechanism of Rh B adsorbent with negative charge on the surface of the adsorbent（p H≈6.2）CRI-100 is mainly the charge attraction between the two adsorbents.Therefore,the adsorption capacity in acidic and neutral conditions is larger than that in alkaline condition.The addition of positive ion Al³⁺can strongly inhibit the adsorption amount of Rh B by CRI-100.The experimental results further confirm the adsorption mechanism.3.Catalytic properties of CRI-100-1M（1 month）and CRI-100-2M（1 month）in Typha aqua were compared,SEM showed that CRI-100-2M biochar exhibited a clear iron membrane structure in plant root.The iron content of CRI-100-2M was 2.5 times higher than that of CRI-100-1M biochar.The larger the specific surface area and the better the adsorption effect of cationic CV.It was found that the adsorption ability of iron biochar prepared by artificial mechanical mixing was much lower than that of CRI-100-2M biochar.The adsorption of cationic dyes is mainly achieved by charge adsorption of CRI-100-2M.By adjusting the ratio of N₂and O₂and adding Na F to the adsorption system,the adsorption performance of CV was significantly affected by the addition of oxygen due to the activation of molecular oxygen by iron on the surface of CRI-100-2M,where oxygen molecules competing with the substrate CV and resulting adsorption amount of CV decreased.4.Under visible light irradiation,like Fenton system was constructed by hydrogen peroxide and CRI-100 catalyst.Compared with the traditional homogeneous Fenton system,it can effectively degrade organic dyes under neutral and alkaline conditions.It was found that hydroxyl radical was the main active species in the reaction system through the free radical capture experiment,and the iron ion shedding was not detected in the photocatalytic degradation experiment of CRI-100 biochar catalyst,and the rate of degradation could be maintained at a high rate after repeated recycling.It showed that this kind of Fenton catalyst is very stable and could be used repeatedly.5.It is found that biological carbon（BC）with a large specific surface area of 341.27m²/g,which was made from the stem of cattail.The bio carbon powder is used as the carrier,and the biocarbon@bromine（BC@Bi OBr）photocatalyst with biological carbon as the kernel is prepared under the water and heat condition by the mass ratio of 2:3.Agent.The physical structure and properties of the catalyst were preliminarily characterized by means of SEM,XRD,Zeta potential analyzer,UV-Vis DRS and fluorescence spectroscopy.The results showed that the positive charge bismuth hydroxide flocculating precipitate was adsorbed by electrostatic force and negatively charged biochar during the preparation process,and finally formed the Bi OBr cluster catalyst coated with biochar as the core surface.Therefore,the surface crystalline phase,specific surface area and charge amount of BC@Bi OBr catalyst are basically consistent with those of pure Bi OBr,and no BC are found on the surface.BC as a good conductive material,the cluster structure can not only improve the response of BC@Bi OBr to visible light,but also reduce the recombination probability of holes and electrons.With rhodamine B as substrate probe,the catalytic degradation ability of two catalysts under visible light irradiation was tested.The results showed that BC@Bi OBr had higher photocatalytic activity than pure Bi OBr,which could be related to the generation of more oxygen free radicals.