Theoretical Studies On Environmental Behaviour Of Three Typical Aromatic Pollutants:Sorption On Clays And Deoxidization By Supported Pd Catalysts In Aqueous Environments

The increasing trace organic pollutants in aquatic environment have detrimental effects on aquatic ecosystem and human health.Among the huge mumber of organic pollutants,the compounds with aromatic ring are difficult to be biodegraded due to their aromatic structures.Through the migration,transformation and enrichment,concentration of the organic pollutants with aromatic ring in water environment can be increased several to hundreds of times.In recent years,aromatic organic pollutants can be detected in all kinds of waters in China and the concentration showed an upward trend.Meanwhile,the composition is becoming more and more complex,which poses a grave threat to human health and ecological safety.So the study about the fate of the organic pollutants with aromatic rings in water is imperative.Here,aflatoxin B1,phenanthrene and 1,4-Dinitrobenzene are chosen as the typical pollutants,we studied the sorption on clays and deoxidization by supported Pd catalysts of aromatic organic pollutants in aqueous environments.The molecular structure of these three chemicals share a common feature,which is the benzene rings act as the core of the molecular structure.Here,we discriminated the bonding types of aflatoxin B1?AFB1?and phenanthrene to clay minerals by combined batch experiment with model computation,expounded their bonding mechanisms which have been not quantitatively described by researchers.Meanwhile,a supported Pd Catalysts was prepared to explore the laws and mechanism of reduction of Nitro-aromatic compounds by some reductant such as sodium formate,which exists widely in nature environments.1.Here,we discriminated the bonding types of aflatoxin B1?AFB1?contaminant to different clays by combined batch experiment with model computation,expounded their bonding mechanisms.The observed adsorbent-to-solution distribution coefficients?Kd?of AFB1 presented in increasing order of 18.5-37.1,141.6-158.3,and 354.6-484.7 L/kg for kaolinite,illite,and smectite,respectively.Normalization of adsorbent-specific surface areas showed that adsorption affinity of AFB1 is mainly dependent on the outside surfaces of clay aggregates.The model computation and test of ionic effect further suggested that weakly electrostatic attractions?C=O··Si-O and C··O-Si?are responsible for AFB1-kaolinite adsorption?Kd,18.5-37.1 L/kg?;a weak electron-donor-acceptor attraction??C=O?2··K+··?O-Al?3?is related to AFB1-illite adsorption?Kd,141.6-158.3 L/kg?;a strong calcium-bridging linkage(?C=O?2··Ca²⁺··?O-Si?4)is involved in AFB1-smectite adsorption?Kd,354.6-484.7 L/kg?.Changes in Gibbs free energy??Go?suggested that the computed result is reliable,providing a sound reproduction of AFB1-clay interaction.2.By combined batch experiment with model computation,we discriminated the bonding types of phenanthrene to clays especially smectite,giving further details about their bonding mechanisms.Ca/Na-smectite was obtained by purification of MX-80 using high concentration solution of Ca²⁺ and Na+ respectively.The adsorbent-to-solution distribution coefficients?Kd?of adsorption of phenanthrene on Na-smectite is in a increasing order of 14.22-16.29 L/kg,and 5.36-7.48 L/kg on Ca-smectite.The model computation and test of ionic effect further suggested that a weak electron-donor-acceptor attraction(aromatic··Ca²⁺··?O-Si?4)is related to phenanthrene-smectite adsorption?Kd,141.6-158.3 L/kg?.Metal cations can also affect the adsorption of phenanthrene by changing the structure of smectite.Normally,the diffusion layer in electric double layer structure gets thiner as the concentration of metal cations gets higher.Meanwhile,thickening of the diffusion layer leads to less adsorption capacitiy to phenanthrene by a molecular basis of contact inhibition between clay crystal surface and phenanthrene.Accordingly,Ca²⁺ with higher valence plays a leading role in soption of phenanthrene to smectite.3.A supported Pd Catalysts was prepared to explore the laws and mechanism of reduction of 1,4-Dinitrobenzene by sodium formate,which exists widely in nature environments.By the observation that the most reduced compound is 4-nitroaniline,and 4-hydroxylaminonitrobenzene is one of the intermediate products that could be detected.Graphene can effectively prevent the Pd particles loaded on the graphene sheet from agglomerating owing to its high specific surface.The activity of graphene supported Pd for deoxidized of 1,4-Dinitrobenzene was tested,the pseudo-first-order rate kinetic constant?kobs?is 1.98×10-2min-1?R²=0.987?.