Preparation Of Carbon Nanotube-Stainless Steel Microfibrous Composite And Its Application In Wastewater Treatment

With the fast development of modern industry,people’s material and cultural requirements are also on the rise,making the production of various chemical products increase gradually.As a kind of basic organic synthetic materials,the extensive use of m-cresol also brings corresponding environmental problems.Among the treatment methods of m-cresol waste water,catalytic wet oxidation is attracting more and more attention,especially heterogeneous catalytic wet oxidation,in which a good catalyst support plays an important role.Carbon nanotube（CNT）is a kind of ideal support,but it cannot be used in fixed bed reaction due to the small size which will cause large bed resistance and leakage of CNT.To solve these problems,we combine CNT with microfibrous composite to prepare a series of materials owning both the advantages of CNT and microfibrous composite and further investigate their preparation process.Besides,we also load the metal active component on them to prepare a series of catalysts for catalytic wet oxidation and test their degradation ability of m-cresol.In this study,we optimize the operation condition of the fixed bed catalytic wet oxidation and study the reaction and deactivation mechanisms of the catalysts.Phosphate wastewater is also an important source of aquatic ecological pollution in recent years.Researchers have developed many methods to treat the phosphate wastewater,among which adsorption is most widely used due to its low cost,simple design and operation and no sludge requiring secondary treatment.Lanthanum species can form strong chemical bond with phosphate and thus have high adsorption rate,capacity and efficiency,making them ideal adsorbents.However,complicate synthesis steps,high cost,easy agglomeration and strong leakage limit their application.In this study,we combine lanthanum carbonate and microfibrous composite to enlarge the adsorbent service life.The network structure of microfibrous composite can avoid adsorbent agglomerate and improve adsorption efficiency.In this paper,we optimize the preparation process of lanthanum carbonate-microfibrous composite（LC-MF）and then apply it in the adsorption of phosphate.The adsorption conditions are optimized and the kinetic is studied.Finally the adsorption mechanism is also investigated.Firstly,iron loaded microfibrous composite entrapped CNT（Fe-CNT/MF）is prepared through a combined wet paper making,sintering and metal organic chemical vapor deposition（MOCVD）method and applied to the fixed bed degradation of m-cresol.Results show that catalyst prepared by MOCVD method performs higher efficiency than by impregnation method.Higher loading,temperature,bed height and lower feed flow rate are beneficial to m-cresol degradation,with more than 99%m-cresol romoval and 45%TOC removal and good regeneration ability of the catalyst.The reaction mechanisms of m-cresol degradation over fixed bed reactor include two pathways,changing into methylhydroquinone first or Methylcatechol first.In both pathways the final products are CO₂ and H₂O.Secondly,we use chemical vapor deposition（CVD）method to synthesize CNT directly on the surface of microfibrous composite（CNT-MF）through acetylene.Results show that CNT-MF prepared without additional catalyst has a better quality.The best preparation conditions of CNT-MF are 700℃,500 m L/min N₂,10%C₂H₂ and 80 min deposition time.Then the prepared CNT-MF is applied to the fixed bed adsorption of m-cresol.Results show that though the adsorption capacity of structure fixed bed is smaller than particle fixed bed,the bed resistance and pressure drop are significantly decreased,which enhance the mass and heat transfer and are beneficial to the adsorption of m-cresol.Thirdly,MOCVD method is applied to load metal active component on CNT-MF to prepare a novel iron loaded CNT-microfibrous composite（Fe-CNT-MF）catalyst and its catalytic ability is tested in fixed bed degradation of m-cresol.Results show that higher temperature,bed height,H₂O₂ concentration and lower flow rate,p H are beneficial to the degradation of m-cresol,with over 99%m-cresol 53%TOC removal.However,in low p H,the leakage of active component is severe.After 24 h,the catalyst still exhibits high activity and stability,with only 10%and 7%decrease in m-cresol and TOC removal,respectively,and no iron leakage is detected.The degradation mechanism shows that under acid conditions,the degradation of m-cresol goes through the first pathway.In basic condition,some m-cresol will be degraded through the second pathway.Deactivation study indicates that the deactivation of Fe-CNT-MF is caused by carbon deposition,surface properties change and additional oxygen functionalities.Finally,we combine the microfibrous composite with lanthanum carbonate to prepare a novel kind of lanthanum carbonate fabricated microfibrous composite（LC-MF）.The preparation process is optimized and the adsorbent is tested in phosphate adsorption.The results indicate that the best p H for phosphate adsorption over LC-MF is 6-9,ionic strength and co-existing anions have little effect on the performance of LC-MF.The adsorption isotherm can be described by Freundlich model and adsorption kinetic can be fitted by pseudo second order model,indicating that it is a chemical adsorption process,and the equilibrium time is 300 min.Intra-particle model indicates that the adsorption process can be divided into three parts,including external surface adsorption,inner surface adsorption and equilibrium.After 5 recycling runs,the capacity of LC-MF can still remain 80%of the fresh one,indicating a good regeneration ability of LC-MF.The adsorption mechanism is also investigated,proving that the adsorption process includes electrostatic attraction and ligand exchange.