Preparation Of Fly Ash Cenospheres @ Carbon Nanotubes And Their Adsorption Properties For Pb(?)

The unique tubular structure of carbon nanotubes and high specific surface area make it have good adsorption properties.However,due to the agglomeration of carbon nanotubes in aqueous solution,its use in wastewater treatment is limited.In addition,recovery of free carbon nanotubes from solution after adsorption remains a major problem.Therefore,it is common to use carbon nanotubes on the surface of the carrier material to solve this problem.In this thesis,chemical vapor deposition(CVD)was used to study the growth of carbon nanotubes on the surface of fly ash cenospheres,and carbon nanotubes with high density defects(Fly Ash Cenospheres@Carbon Nanotubes)were obtained.Firstly,the physical and chemical properties of fly ash cenospheres were studied.Secondly,the influence of preparation parameters on the microstructure of fly ash cenospheres@carbon nanotubes was studied,and its growth mechanism was discussed.Finally,Pb(II)was used in powder.Adsorption of fly ash cenospheres@carbon nanotubes on the adsorption of fly ash cenospheres@carbon nanotubes.The main findings of this paper are as follows:(1)Fly ash cenospheres have a unique spherical structure and aluminosilicate glass phase surface.Fly ash cenospheres O,Si,Al,Na,Mg,K,Ca,Ti,Fe elements,of which O,Si,Al accounted for about 95%by weight of the total weight.The content of Fe in fly ash cenospheres varies from 0.52 to 2.09 wt%,and the content of Fe in surface and bulk elements is consistent.XRD and XPS analysis showed that the aluminosilicate glass phase encapsulated the crystal phase of mullite,sillimanite and cristobalite to form the whole structure of the cenospheres,and Fe exists in the form of amorphous oxide in the aluminosilicate glass.In the middle.(2)In the process of growing carbon nanotubes on the surface of fly ash cenospheres,the preparation parameters affect the microstructure of carbon nanotubes.The temperature increased from 710°C to 770°C.The carbon product on the surface of fly ash changed from carbon fiber to carbon nanotube and the diameter of the tube became smaller.The I_D/I_G in Raman spectrum increased from 1.91 to 2.34,indicating an increase in disordered structure.When the growth time increased from 5 min to 60 min,the growth density of carbon nanotubes on the surface of fly ash cenospheres increased and the tube diameter became thicker,while the amorphous carbon deposited on the surface of carbon nanotubes increased;the ethylene flow rate increased from 60 sccm to at 150 sccm,the growth density of carbon nanotubes on the surface of fly ash hollow microspheres increased,and when the ethylene flow rate was 150 sccm,carbon fibers appeared on the surface of the fly ash hollow microspheres.When the growth temperature is 750°C,the growth time is 30 min,and the ethylene flow rate is 120 sccm,the surface of the fly ash cenospheres is uniformly covered with a layer of carbon nanotubes.SEM analysis showed that the diameter of carbon nanotubes grown on the surface of fly ash hollow microspheres was 20-50 nm,showing a three-dimensional network structure.TEM analysis showed that the carbon nanotubes grown on the surface of fly ash void microbeads had closed compartments.The structure has a multi-layered tube wall with a wall thickness of about 6 nm,which belongs to a bamboo-shaped multi-walled carbon nanotube.The I_D/I_G value in the Raman spectrum is 2.04,indicating that the fly ash fly ash cenospheres@carbon nanotubes have high defects;FT-IR and XPS analysis indicate that hydroxyl groups,carboxyl groups and lactones are introduced into the surface of carbon nanotubes during growth.Hydrophilic oxygen-containing functional groups.(3)Fly ash cenospheres@carbon nanotubes adsorption of Pb(II)shows high adsorption capacity.At 25°C,the p H was 7,the adsorption capacity was 34.69 mg/g when the lead ion concentration was 100 mg/L;the adsorption capacity of Pb(II)was about 275.19 mg/g.When the p H increased from 3 to 11,the surface potential of the fly ash cenospheres@carbon nanotubes increased from 8.1827 m V to-36.7174 m V,which made it have a good adsorption effect on Pb(II).The adsorption isotherm fitting is in accordance with the Freundlich equation,and the adsorption kinetics fit is in accordance with the quasi-second-order kinetic equation.After the long-range adsorption,the intraparticle diffusion model is Pb(II)adsorbed on the fly ash cenospheres@carbon nanotubes.The main quick control steps.Adsorption thermodynamics studies show that the adsorption process is a spontaneous endothermic reaction,and the process is reversible and the adsorption driving force is strong.The adsorption mechanism of ly ash cenospheres@carbon nanotubes on Pb(II)is the electrostatic attraction between the carboxyl group,hydroxyl group and lactone functional group and Pb(II)on the surface.