Study On The Modification Of Activated Carbon Fiber And Its NO Adsorption Characteristics

In recent years,air pollution has attracted more and more attention.Among them,nitrogen oxides have a great impact on the ecological environment,and they also directly affect human health.The effective removal of nitrogen oxide pollution is an important research topic.NO accounts for the majority of the total amount of nitrogen oxide,and the most important thing of removing nitrogen oxide is the purification treatment of NO.Activated Carbon Fiber(ACF)contains a lot of micropores and surface functional groups,and it has a broad-spectrum adsorption effect on pollutants in gases and liquids.It is of the great significance to use ACF to adsorb and catalyze NO in tail gas.In the process of adsorption,both physical adsor:ption and chemical adsorption occur on ACF.In order to further improve its adsorption catalytic performance,three methods are generally used:change the pore distribution structure,surface functional group modification and loading catalyst.The first method mainly changes the physical structure of ACF,while the latter two methods mainly change its chemical structure.In this paper,four kinds of activated carbon fibers that are easy to be purchased in the market were tested on the NO adsorption property,and the cheapest Viscose based activated carbon fiber(VACF)with relatively good NO adsorption performance was selected as the research object.VACF was modified by three different methods to improve its adsorption performance.NO removal performance at different temperatures of VACF was tested,and the VACF adsorption performance decreased with increasing temperature and almost lost adsorption at temperature 343 K,resulting in a regeneration temperature of at least 343 K.This article uses the re-activation process to change the pore structure and content of oxygen containing functional groups of VACF.The surface nitrogen modification of VACF was carried out by grafting treatment of urea and NH4Cl.Different catalysts were loaded on VACF by constant volume impregnation and coprecipitation method.The pore structure,surface structure and crystal structure of different modified VACF samples were tested and characterized,as well as their catalytic purification performance for NO.The VACF was modified by activators(NaOH,Na2HPO4 and H2O2)in the re-activation process.The best ultrasonic impregnation condition for preparing VACF with good NO adsorption was determined by orthogonal test.The results show that at the right concentration,Na2HPO4,NaOH and H2O2 as activators,the specific surface area,micropore volume,as well as the total pore volume data of VACF have a certain increase.Among them,10%H2O2 as activator has the most obvious effect of improving the NO adsorption performance of VACF.The ultrasonic impregnation process for VACF with high specific surface area and excellent NO adsorption performance was obtained by orthogonal test:impregnate VACF at 353 K for 5 h in 10 wt%H2O2 solution.The adsorption capacity of VACF after re-activation modification was significantly improved.The order of iodine adsorption capacity of the ten samples was:sample 4>sample 10>sample 8>sample 9>sample 5>sample 1>sample 3>sample 7>sample 6>sample 2.When NO gas with a concentration of 600ppm was treated,the order of NO adsorption capacity was:sample 10>sample 4>sample 8>sample 1>sample 7>sample 9>sample 5>sample 2>sample 3>sample 6.The modification method of VACF with high adsorption capacity for NO at room temperature was obtained by re-activation processVACF was grafted with surface nitrogen at different concentrations of urea soultion and NH4Cl solution.The grafting mechanism was obtained by analysing the infrared spectrum and X-ray photoelectron spectrum.The main reaction in the grafting process of NH4Cl is:NH4Cl hydrolyzes to produce NH3·H2O,and then NH3·H2O reacts with the surface carboxyl of VACF to form an amide group.The main reaction in the grafting process of urea is:Amino reacts with surface carboxyl of VACF and forms amide groups.The adsorption mechanism of VACFN on NO was obtained by studying the adsorption property of NO:The NO gas adsorbs at the active site on VACF surface and becomes NOad(adsorption state),then oxidized to NO2ad(adsorption state)by O2 and oxygen-containing functional groups(C=O)on the surface of VACF,and then reacts with amide and amino to reduce to N2.The catalyst of CuO,CeO2,CuO-CeO2 and MnO2 prepared by constant volume impregnation method and coprecipitation method on VACF and VACFN improves the NO adsorption performance of VACF at temperature 373 K-523 K,and the NO adsorption performance increases first and then decreases with the increase of the catalyst loading rate.The adsorption properties of CuO-CeO2/VACF and CuO-CeO2/VACFN were all better than those of monometal-supported samples.This is due to the synergistic effect of VACF adsorption and the catalysis of CeO2 and CuO,the presence of CeO2 makes CuO more evenly dispersed on VACF surfaceIn this paper,various modified VACF samples were made by three different kinds of modification methods.The samples were characterized by BET,XPS,FTIR,SEM,XRD and other analytical testing methods.The mechanism of catalytic oxidation of NO adsorbed by VACF and the effect of crystal structure and chemical properties of VACF on NO adsorption were discussed.The results of NO adsorption test showed that;at temperature 473 K,20%CuO-30%CeO2/VACFN has the best NO adsorption,and the adsorption rate of NO was up to 94.31%at 800 ppm.,thus,it can be combined with ternary catalytic converter to provide a secondary catalytic purification scheme for NO in automobile exhaust in the future.At room temperature,the dynamic adsorption rate of the sample prepared by the optimized re-activation process(impregnate VACF at 353 K for 5 h in 10 wt%H2O2 solution)to 600 ppm NO was 40.63%,and its adsorption capacity is 38.66 mg/g in 1 h.It can be used as a filter element of protective mask or air purification material to remove NO effectively in the atmosphere.