Adsorption Of Organic Pollutants In Aqueous Solution On Mesoporous Materials MCM-48

Due to their large surface areas, high pore volumes, relatively even distributions of pore sizes, surfaces enriched with unsaturated groups and orderly long-range structures, the mesoporous materials have been widely applied in industries such as chemical, biomedical, environmental protection and functional materials. In recent years, many scientists have demonstrated that the mesoporous molecular sieves have better adsorption of organic contaminants in wastewater. This paper reviews the applications of different types of mesoporous adsorbents for removal of dyes and phenolic compounds in aqueous solution.As a kind of M41S series of mesoporous materials. MCM-48with two independent three-dimensional pore systems and excellent transmission performance, is easy to transmit the molecule obstacles. Therefore it is a kind of very good separation and enrichment material. MCM-48has large specific surface area, surface easily modified by organic group, uniform pore size distribution and good thermal stability. It has been successfully used for adsorption several kinds of organic pollutants in effluents by researchers. In order to improve the adsorption capacity of goal pollutant, scholars have studied improvement of the preparation method or introducing silane coupling agent to mesoporous materials for surface modification. We mainly studied MCM-48and aminopropyl modified MCM-48for adsorption of several typical organic targets in aqueous solution, and it contains three parts.1. Mesoporous MCM-48was synthesized using hexadecyltrimethyl ammonium bromide(CTAB) and triblock poly(ethylene oxide)-poly(propylene oxide)-poly (ethylene oxide)(P123) as co-template, tetraethoxysilane as silica source at40℃, and employed as an effective adsorbent for the adsorption of methyl violet and methyiene blue from water. The prepared MCM-48was characterized by X-ray diffraction (XRD), N2adsorption/desorption, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and transmission electron microscope (TEM). Using Uv-vis spectrophotometry studied the MCM-48adsorption of methyl violet and methylene blue in aqueous solution. The effects of the experimental parameters, including sample solution initial pH, initial concentration, MCM-48amount, adsorbed time and temperature have been investigated. Results showed that the lower temperature and higher initial pH value were beneficial to the dyes adsorption. The experiment data could be well described by the Langmuir equations and pseudo-second-order kinetic model. Thermodynamic parameters ΔG0, Δ S0and Δ H0values were negative, indicating that the MCM-48adsorption of two dyes was spontaneous and exothermic.2. Aminopropyl modified MCM-48(NH2-MCM-48) was prepared by co-condensation method using CTAB and P123as the co-template. The synthesized material was characterized by XRD, N2adsorption/desorption, FT-IR, SEM, TEM, and Thermogravimetric analysis (TGA), and compared with the characterizations of MCM-48. Aminopropyl modified MCM-48still has good orderly mesoporous structure. Meanwhile’we compared MCM-48and NH2-MCM-48adsorption properties for phenol. After modification of MCM-48, NH2-MCM-48has a obvious increase in phenol adsorption capacity. The experiment data revealed adsorption isotherms and adsorption kinetics could be well fit by Langmuir model and pseudo-second-order kinetics respectively. Adsorption process of phenol was spontaneous and exothermic.3. The adsorption of o-nitrophenol, m-nitrophenol and p-nitrophenol in aqueous solution by aminopropyl modified MCM-48(NH2-MCM-48) was studied. Investigations were focused on the factors such as the effect of pH, dosage of sorbent, initial concentrations of nitrophenols, temperature and adsorption time on the adsorption of nitrophenols. Adsorption isotherms were determined for the nitrophenols and the data fit well with the Langmuir equation. The pseudo-first-order and pseudo-second-order models were applied to investigate the kinetics of the adsorption and the results showed that it well followed the pseudo-second-order model. Similarly the adsorption process was spontaneous and exothermic. Competitive adsorption experiments showed that in the ternery system NH2-MCM-48preferentially adsorbed o-nitrophenol, followed by the p-nitrophenol, finally the m-nitrophenol.