Aqueous Adsorption And Predictive Model Of Typical Organic Contaminants By Carbon Nanotubes

Knowledge of adsorption of organic contaminants by carbon nanotubes (CNTs) and their predictive models are essential not only for the application of CNTs as superior sorbents, but also for the assessment of environmental and ecologic risks of both CNTs and organic contaminants. Adsorption of organic contaminants by CNTs are mainly influenced by the properties of aqueous solution, organic contaminants and CNTs. Frequently, different kinds of organic contaminants exist concurrently in the real environment. Competition between them will change their adsorption on CNTs. Desorption of organic contaminants from CNTs into water is the reverse process of adsorption, which can be used to regenerate CNTs. The desorption prosess could also influence the transport, transform and fate of both CNTs and organic contaminants. In this dissertation, influences of properties of aqueous solution, organic contaminants and CNTs on the adsorption, competition and desorption behaviors of organic contaminants on CNTs were investigated, and the predictive model of adsorption was also studied. The mainly conclusions of this dissertation are as follows:(1) Influence of pH on the adsorption of organic compounds by CNTs was mainly dependent on the dissociation of organic compounds, but not on the surface oxidation of CNTs. Adsorption of nonionizable organic compounds on CNTs can not be altered by pH. While adsorption of ionizable organic compounds on CNTs decreased rapidly after dissociation. Transformation and oxidization loss of 1-naphthol occurred in the alkaline solution. Surface oxygen-containing groups on CNTs can interact with 1-naphthol in a way similar to polymerization and enhance the adsorption of 1-nappthol on CNTs.(2) Surface oxidation of CNTs reduced the surface area-normalized adsorption capacity of organic compounds significantly because of the competition of water molecules, but not altered their adsorption affinity. The decrease of surface area-normalized adsorption capacity of the organic compound with more polarity and higher adsorption affinity by surface oxidation was less. Because organic compound with more polarity and higher adsorption affinity can occupy more adsorption sites on CNTs surface.(3) Adsorption capacity (QO) of organic compounds on CNTs showed a significant multiple linear relationship with the surface area (Asurf) and oxygen-containing group amounts (Nacidic groups) of CNTs, QO=0.591 (±0.023)×Asurf-77.7 (±17.7)×Nacidic groups-9.98 (±5.53). Linear solvation energy relationships were observed between adsorption affinity (E, b) and solvatochromic parameters (αm,π*) of organic compounds, E(b)= β1×αm+π1×π*+C. Adsorption affinity of organic compounds on CNTs is independent of the tube lengths and surface oxygen-containing group amounts. However, adsorption affinity of a given compound is bigger for CNTs with bigger micropore surface area. Predictive model of adsorption, based on the physiochemical properties of both organic compounds and CNTs and with clearly physical significance, was obtained in this study.(4) Competition of naphthalene decreased the adsorption affinity of neutral 2,4-dichlorophenol(DCP)/4-chloroaniline(PCAN), but not their adsorption capacity. For dissociated DCP/PCAN, naphthalene not only decreased their adsorption affinity but also their adsorption capacity. Neutral DCP/PCAN also decreased the adsorption affinity and capacity of naphthalene. But dissociated DCP/PCAN did not change both the adsorption affinity and capacity of naphthalene. The formation of bi-layer competition adsorption on CNTs was proposed for naphthalene and neutral DCP/PCAN, while mono-layer competition adsorption on CNTs for naphthalene and dissociated DCP/PCAN.(5) Desorption hysteresis was not observed for nitrobenzenes and phenols from all CNTs. Significant desorption hysteresis was observed for aniline and 4-methylaniline from surface oxidated CNTs. Endothermic and irreversible amidation reaction of amino group of anilines with oxygen-containing groups (i.e., carboxyl or lactonic groups) on CNTs was observed and responsible for the observed desorption hysteresis. Electron-withdrawing functional group (e.g,-NO2 and -Cl) could weak the amidation reaction and thus the desorption hysteresis. Inversely, electron-donating functional group (e.g,-CH3) could enhance the amidation reaction and thus the desorption hysteresis.