| Along with the increasing seriousness of indoor air pollution, simple and efficient adsorption technology of activated carbon has attracted widespread attention. Due to the process was only pure physical adsorption, the removal capacities of activated carbon on formaldehyde and ammonia was limited. This study was performed to investigate the formaldehyde capacities of several different activated carbons, and select the activated carbon with optimal type and size for the removal of formaldehyde. The modification of the selected activated carbon was by the use of nitric acid and metals. Both the isothermal adsorption model and the adsorption kinetics model were used to describe the formaldehyde and ammonia adsorption behaviors, and the removal mechanisms of modified activated carbon to formaldehyde and ammonia were analyzed. The primary conclusions are listed as follows:Investigation on the removal ability of formaldehyde was performed by the three kinds of activated carbons. The results showed that relationships of specific surface area among the three kinds of samples are as follows:coconut shell activated carbon> coal activated carbon> larch starch activated carbon. The specific surface area, the number of oxygen containing functional group and particle size of the activated carbons show great influences on adsorption of formaldehyde. The activated carbon with higher specific surface area and higher microporous proportion shows stronger adsorption capacity on formaldehyde. Coconut shell activated carbonhas the largest formaldehyde adsorption capacity of 1.38 mg·g-1. The more the surface oxygen containing functional groups is, the stronger the adsorption capacity; the smaller the particle size is, the better adsorption ability is. The best effect of the formaldehyde removal is the coconut shell activated carbon with the particle size of 20-40 mesh.The coconut shell activated carbon was modified via nitric acid impregnation. The changes of the pore structure and surface functional groups of the samples before and after the modification were analyzed. Studied the adsorption behavior of the samples under the static and dynamic conditions. Analyzed the adsoiption reaction process with combinations of the isothermal adsorption model and the adsorption dynamics. The mechanism of adsorption reaction were expounded. The results showed that the specific surface area of the activated carbon modified by nitric acid was reduced and the mesoporous proportion was increased after modification by nitric acid. With the increase of the concentration of nitric acid, the specific surface area of the samples were reduced gradually, while the mesoporous ratio was in the opposite trends, increased from 23.00% to 29.79%. The total acid functional group of the activated carbon after modification was increased, and the activated carbon(AC-N5) modified by the nitric acid with the concentration of 5 mol·L-1 increased 0.393 mmol·g-1. The ability to formaldehyde of the modified samples became bigger, increased from 1.38 mg·g-1 to 3.45 mg·g-1. The saturated adsorption amount of the samples to formaldehyde changed in the following order:AC-N5>AC-N7>AC-N3>AC-N1>ACraw. It showed that when concentration of the nitric acid was less than 5 mol·L-1, the formaldehyde adsorption capacity of the samples increased as the concentration of nitric acid increased. Both the Langmuir equation and the Freundlich equation could be well describe the adsorption behavior of the formaldehyde on the 5 kinds of samples. The kinetics study showed that the adsorption dynamics process of formaldehyde conforms to the Quasi second order kinetics mode. The adsorption process of the formaldehyde on the activated carbon of before and after modification was the physical and chemical adsorption.Activated carbon for efficient formaldehyde removal was prepared via CuCl2 impregnation of coconut shell based activated carbon. Nitrogen adsorption isotherm was employed for pore structure analysis. Scanning electron microscopy (SEM) was used for morphology structure observation. The surface elements of activated carbon were tested by XPS. XRD was used for analyzing the crystal forms of cupric salt. Dynamic formaldehyde adsorption at room temperature was used for adsorption performance test. Results showed that cupric salt existed in three forms of Cu0, CuCl and CuCl2. Cu loading can cause the surface area and pore volume of activated carbon decreased, together with average pore diameter increased as the concentration of the cupric salt increased. After modification, surface oxygen containing groups on the surface of activated carbon increased. When CuCl2 concentration is 0.5 mol·L-1, formaldehyde adsorption capacity of the modified activated carbon is 3.1 times of the original one. Adsorption behavior of formaldehyde on modified activated carbons fitted Freundlich adsorption isotherm well. The kinetics study showed that the adsorption dynamics process of formaldehyde conforms to the Quasi second order kinetics mode, and all of the correlation coefficient R2 were higher than 0.99. The adsoiption process of the formaldehyde on the activated carbon of before and after modification was the physical and chemical adsorption.Activated carbon for efficient ammonia removal was prepared via ZnCl2 impregnation of coconut shell based activated carbon. Nitrogen adsorption isotherm(BET), scanning electron microscopy(SEM), Boehm titration, X-ray diffraction (XRD) and thermogravimetric(TG) were used to characterize the surface structures and surface oxygen containing functional groups of the activated carbon before and after modification. Dynamic ammonia adsorption at room temperature was used for adsorption performance test. The adsorption kinetics and adsorption removal mechanism of the activated carbons on ammonia were also studied. Results showed that after modification by ZnCl2, the surface area and pore volume of activated carbon decreased, together with average pore diameter increased as the concentration of the ZnCh increased. After modification, surface oxygen containing groups on the surface of activated carbon increased. The most one was the activated carbon modified with 11% ZnCl2 which increased 0.259 mmol·g-1. The ZnCl2 modification was conducive to the adsorption of activated carbon on ammonia. Ammonia adsorption capacity of the modified activated carbon(75.58 mg·g-1) is 3.1 times of the original one(12.5 mg·g-1). The kinetics study showed that the adsorption dynamics process of ammonia conforms to the Quasi second order kinetics mode. The adsorption process of the ammonia on the activated carbon of before and after modification was the physical and chemical adsorption. |
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