Preparation Of Magnetic Cobalt-based Nanomaterials And Their Removal For Organic Dyes From Water

The organic dye was a kind of widely existing pollution in water.Its structure was complicated,with the characteristics of non-biodegradable and toxic carcinogenesis,which have great potential risks to human beings and ecosystems,so the development of effective technologies to remove the organic dyes in water is essential.Adsorption and photo-Fenton catalysis methods have been the research focus due to their advantages such as mild reaction conditions,easy operation and small secondary pollution.Therefore,we designed a series of magnetic cobalt-based nanomaterials and explored their performance and related mechanisms for the highly efficient removal of organic dyes from water in this paper.The main points are as follows:（1）Magnetically recyclable cobalt nanoparticles（Co-PC）embedded on hierarchically porous carbon were successfully fabricated using a simple“one pot”method,in which the initial concentration,adsorption time,adsorbent dosage,temperature,and Cl^-concentration of organic dye were systematically investigated.The results show that Co-PC exhibits superior adsorption properties for the anionic dye Congo Red compared to the cationic dye Methylene Blue.For Congo Red and Methylene Blue with an initial concentration of 120 mg L^-1,the removal efficiency of Congo Red（97.3%）at 5 min was 3.66 times higher than that of Methylene Blue removal（26.6%）.The Langmuir isotherm model calculated the maximum adsorption amount of Co-PC for Congo Red as high as 1209.86 mg g^-1,which was 3.75 times higher than that of Methylene Blue.From the thermodynamic correlation parameters,it is known that the adsorption of Co-PC on Congo Red and Methylene Blue is a spontaneous endothermic process dominated by physical adsorption.Moreover,the adsorption efficiency of Co-PC for Congo Red remained more than 80%after five reuses.（2）A series of metal organic framework derived multi antennary nitrogen-doped carbon-based cobalt iron bimetallic nanomaterials(Co_xFe_1-xN-NC)were successfully prepared by simple self-assembly and subsequent thermal treatment.Research has found that the introduction of an appropriate amount of metallic iron can accelerate the electron transfer between cobalt iron bimetallic,thereby promoting the process of the photo-Fenton reaction.Among them,the Co_0.8Fe_0.2N-NC catalyst exhibits the best adsorption and photo-Fenton catalytic degradation performance.The catalytic experiments on non azo dyes（Methylene Blue,Rhodamine B,Malachite Green,Neutral Red）and azo dyes（Congo Red,Methyl Orange）found that they had obvious catalytic degradation on non azo dyes,for example,the degradation rate of Methylene Blue was 9.7 times that of Methyl Orange.Free radical capture experiment and electron paramagnetic resonance test showed that·OH and h⁺played a significant role in the degradation process.In addition,the catalysts had superior cycled performance,and no obvious degradation performance occurred after being cycled four times.（3）Nitrogen-doped carbon-based cobalt iron bimetallic nanomaterials and porous sheet carbon nitride were successfully composite（CoFeN-g-C₃N₄,named CFN-CN）to construct Z-type heterostructures using simple mechanical stirring.Systematic exploration of the effect of different catalysts,dye concentration,catalyst dosage,hydrogen peroxide concentration,pH and coexisting inorganic anions on the adsorption and photo-Fenton degradation of azo dyes was carried out.The experimental results showed that CFN-CN1 exhibited the best degradation rate for azo dye Methyl Orange,reaching 96.8%at 40 min,meanwhile,the degradation rate constant is 11.8 and 2.81 times that of g-C₃N₄ and CoFeN.The introduction of inorganic anion HCO₃^-could significantly promote the degradation of Methyl Orange,and the degradation rate constant of Methyl Orange after the addition of 20 mM HCO₃^-was 6.58 times higher than that of the blank group.Radical trapping experiments and electron paramagnetic resonance tests found that·OH and·O₂^-were the major active species.In addition,the degradation performance of the catalyst decreased by only about 7.3%after being reused four times,indicating excellent cycling performance.