17β-Estradiol Degradation Photoinduced By Iron Complex, Clay And Iron Oxide Minerals: Effect Of The Iron Complexing Agent Ethylenediamine-N, N’-Disuccinic Acid

Light-induced transformation in aqueous solutions or suspensions/on soil surface is an important degradation pathway for many pollutants and may result in efficiency losses. It is well known that polycarboxylate-iron complexes are high photoactivity species, which could undergo rapid photochemical reactions under sunlight irradiation leading to the formation of oxidative species and degradation of pollutants. Several polycarboxylate-iron complexes such as Fe(Ⅲ)-oxalate, Fe(Ⅲ)-citrate as photocatalyst are well studied. Recently, because of the widely used in the various area and high concentration detected existing in the environment, aminopolycarboxylic acids (APCAs) has aroused the scientists much interests. APCAs may present behavior similar to that of polycarboxylic acid. The photolysis of Fe-EDTA/NTA is studied by several authors. EDDS is one of natural occurring APCAs, which has been proposed as a safe and environmentally benign replacement for EDTA for environmental remediation products. EDDS could form strong complex with iron, and the physicochemcial properties of Fe(Ⅲ)-EDDS have been reported. However, the photochemical process of Fe(Ⅲ)-EDDS is poor understood.Clay and iron oxide minerals are widespread in nature and possess particular structural and surface charge characteristics. Clay and iron oxide minerals play an important role in the earth-chemical transformation and cycles of pollutants, involving in the adsorption, hydrolysis, auto-oxidation and photocatalytical redox processes in the environment. The clay and iron oxides minerals, either as active catalysts or supports, have been widely used as heterogeneous catalysts for the oxidation of organic pollutants. Iron is one of the elements commonly found in the clay minerals and the main component in iron oxides. Carboxylate could not only form complexes with soluble iron in the clay and iron oxides mineral suspensions, but also form surface complexes with the structure iron in the minerals, promoting the dissolution of the iron oxide in minerals under irradiation. In the same time, the surface properties of minerals will be changed due to the carboxylate-minerals complex formation. In this work, we first introduce EDDS into the clay (Natural Montmorillonite and Montmorillonite KSF) and iron oxides mineral (Goethite) and studied the photoactivity of the EDDS-clay/iron oxides mineral system using 17β-Estradiol (E2) as the model pollutant.E2 is one of the endocrine-disrupting chemicals (EDCs) and is well-known to exhibit very potent estrogenic activity even at a very low concentration (～10-9 M, in vitro). Due to the harmful effect of E2 and the widespread occurrence in the aquatic environment, people pay more and more attention to the removal of E2 in the wastewater. Several advanced oxidation processes (AOPs) have been applied succesufully for oxidation and mineralization of E2, such as TiO2-mediated photocatalysis, photo-Fenton catalytic reactions, O3/UV process, ozonation, electrochemical oxidation process. However, no reference reported using EDDS-Fe(III)/clay/iron oxides to degradation of E2 under irradiation.The objective of this work is to understand the photochemical process and the reaction mechanism of E2 degradation in the presence of light and Fe(III)/clay/iron oxides-EDDS complexes, which can produce basic knowledge that could be used to predict the fate of organic pollutant in natural environments and also expand the view of wastewater treatment. Main experiment contents and conclusions of this dissertation are as follows.(1) In the first part of this work, the properties of Fe(III)-EDDS was studied and the model minerals (Montmorillonite KSF, natural Montmorillonite, Goethite) were characterized with X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Transform infrared (FT-IR) and Transmission electron microscopy (TEM), etc. The experimental results indicated that pH was an important parameter for the speciation of Fe(III)-EDDS. Under 365 nm irradiation, the Fe(III)-EDDS complexes at different pH were easily photolyzed. During the irradiation, the absorbance of Fe(III)-EDDS at X= 240 nm decreases faster at lower pH, but it seems that at higher pH, there are more new species formed in the solution. The iron contents in the form of Fe2O3 existing in the KSF, NM, Goethite are 4.76%,4.28%,100% respectively. But the amount of free iron ions in the minerals was in the order:KSF> Goethite>NM. The BET surface area of the minerals were Goethite (71 m2 g-1)> NM (32 m2 g-1)> KSF (5 m2 g-1). The isoelectric points (PI) of KSF, NM, Goethite is about 5,2 and 4 respectively. The acido-basic properties of the surface of the three solids are rather different. Indeed, once in suspension the solid modified the solution pH. Values of 7.7,9.0 and 3.7 are respectively measured for Goethite, NM and KSF. The quite different properties of the minerals help understand the photochemical process of the EDDS-minerals systerm.(2) The quantum yield of·OH and the degradation of E2 in homogeneous irradiated Fe(III)-EDDS system was investigated. For the first time, the quantum yield of·OH was detected by photolysis of Fe(III)-EDDS. The quantum yield of’OH was independent of the concentration of Fe(III)-EDDS. Lower wavelength and higher concentration of O2 favored the quantum yields of’OH. The quantum yield of·OH radical formation was higher at higher pHs between 3.0 and 9.0. This result is particularly interesting in terms of the natural environment. Correspondingly, E2 could be photodegraded by the photolysis of Fe(III)-EDDS, which is influenced by the concentration of Fe(III)-EDDS, pH, O2 and the concentration of Fe(III). The Fe(III)-EDDS complex would be of importance for the transformation of organic compounds in the environment due to its higher photoactivity at pHs more relevant to the environment. The reaction rate constants with·OH of E2 and EDDS were also measured to be 6.7×109 M-1s-1 and 2.0×108 M-1s-1 respectively. Although the reaction rate constant of kE2,.oH is about ten times higher than the KEDDSs,·OH, due to the ten times higher concentration of EDDS used than that of E2 in our experiments, the competition between EDDS and E2 reacting with·OH should not be ignored. Several photoproductions was detected by LC-MS. The photodegradation mechanism was deduced in this work. Attacking by Hydroxyl radical was thought to be the main degradation pathway of E2.(3) The quantitative determination of·OH radicals in the Montmorillonite suspensions under irradiation of a 250 W metal halide lamp (λ≥365 nm) was investigated for the first time. Low pH value facilitated the formation of hydroxyl radicals in the pH range of 2.0 to 10.0. The·OH concentration increased with increasing the concentration of Montmorillonite in aqueous solutions in the range of 0 to 20.0 g L-1. Higher concentration like 25.0 g L"1 of Montmorillonite inhibited the·OH production. Iron, predominantly free iron in the clays, is believed to be one of the most important factors determining·OH formation. Structural irons in Montmorillonite have also contributions to·OH formation but especially in the presence of carboxylate ions. The formation of·OH from Montmorillonite under irradiation of near UV and visible light indicates that clays might play important role not only in transfer through adsorption but also in transformation through oxidation of organic compounds on the surface of clay particles in air, water, soil or even top sediments.(4) The adsorption and photocatalytic degradation process of E2 in the suspension of Montmorillonite KSF, Natural Montmorillonite (NM) and Goethite were studied. The adsorption of E2 on the minerals is fast and weak. The results followed the Langmuir equation in the KSF and Goethite suspensions, and the Freundlich equation in NM suspensions. EDDS influence slightly the E2 adsorption on the minerals. However, the influence of E2 adsorption on the degradation process was not found. The E2 degradation rate was influenced by the concentration of minerals and pH. The degradation of E2 was decreased with increasing the pH and in the basic pH there was almost no E2 degradation. The optimal pH for the E2 degradation was around 3.0 in all the three minerals. The results indicated that the iron in the minerals was involved in the photocatalytic process.(5) The photocatalytic degradation process of E2 in the suspension of Montmorillonite KSF, Natural Montmorillonite and Goethite in the presence of EDDS were studied. In these three minerals-EDDS suspensions, the degradation of E2 significantly increased at near-neutral pH and basic pH (pH 5.0 to 9.0). On the contrary without EDDS, the optimal pH is limited in the acid pH (3.0 to 4.0). The degradation kinetics of E2 follows the Langmuir-Hinshelwood rate law in all the three minerals-EDDS system. Small amount of minerals is enough to get good degradation efficiency in the presence of EDDS, i.e. KSF 0.1 g L-1,NM 0.1 g L-1 and Goethite 0.1 g L-1. The concentration of EDDS is a very important factor influencing the efficiency of E2 degradation. EDDS plays an important role for keeping ferrous iron soluble at cirumneutral pH and the photochemical process of the minerals-EDDS can continue. During the E2 degradation, EDDS also is degraded. Oxygen is a very important factor that affects the photodegradation of E2. Oxygen takes part in the photochemical process in such system. Without oxygen, the hydroxyl radicals barely could be formed. After adding 2-propanol into the suspension, there was almost no E2 degradation, indicating that the main degradation pathway of E2 was the reaction with·OH. Thus all these results show that the concentration of minerals and EDDS, solution pH and oxygen must be taken into account as major parameters to improve the efficiency of the mineral-EDDS photochemical process.Based on the above results, EDDS-Fe(III)/mineral systems are effective photocatalysis system for the removal of the organic pollutants. The most specialties of the EDDS-Fe(III)/mineral photochemical system are their high photocatalysis efficiency in the neutral pH range, even in the basic pH. And iron, the minerals and EDDS widely exist in the nature environment. Thus, they are promising ways for the removal of the contaminations in the nature aqueous environment.