Syntheses And Pollutants Elimination Activities Of Metal-organic Frameworks Containing Polyoxometalate Clusters

With rapid economic development,water pollution has become a serious problem in developing countries.Many water treatment methods have been widely studied and applied.The application of adsorption and photocatalysis has a long history.Metal-organic frameworks can form complex network structures by self-assembly through the coordination of organic ligands and metal ions.MOFs are considered to have more advantages than traditional porous materials and have great potential in environmental applications.In this paper,several metalorganic frameworks were synthesized by hydrothermal method.The morphology of classical metal-organic frameworks,MIL-88 A was adjusted by room temperature stirring method,and their characterization and analysis were carried out to delve their performance in fluorescence sensing,adsorption and photocatalytic.Finally,we discuss the mechanism of removing pollutants in water.The experimental results are as follows:1.Two polymolybdate hybrid materials [β-Mo8O26](11bca)(NH4)2·2H2O(BUC-76)and [δ-Mo8O26](11bca)2·2H2O(BUC-77)with different isomeric were synthesized by hydrothermal method.The characterization of these two materials were analyzed.The results showed that BUC-76 and BUC-77 were stable in common solvents and p H from 1 to 12.The two materials can be used as adsorbents to adsorb and remove heavy metal Pb2+ in water.And they can be regenerated by being washed with dilute inorganic acids like HNO3 after adsorption of Pb2+.Methylene blue of cationic dye was selectively adsorbed and can be used in solid phase extraction column.In addition,BUC-77 can be used as a fluorescent probe to identify Pb2+ ions in water.A good linearity was observed between the fluorescence quenching percentage of BUC-77 and the Pb2+ concentration,along with the detection limit being 6.91 ppb.The results revealed that BUC-77 could be potentially used to achieve both detection and removal of Pb2+ in wastewater.2.As a metal-organic framework,Cu2Mo4O14(11pbc)·2H2O(BUC-74)with bimetal,copper and molybdenum was synthesized by hydrothermal method.The adsorption properties of BUC-74 were investigated by removing promethazine hydrochloride in water.The maximum adsorption capacity of BUC-74 to promethazine hydrochloride reached 602 mg/g at 303 K.The kinetic process of adsorption conforms to pseudo-second-order kinetic equation,and the thermodynamic process of adsorption conforms to Langmuir isotherm model.Meanwhile,the standard Gibbs free energy(ΔG0<0),endothermic change(ΔH0>0)and entropy change(ΔS0>0)of the adsorption process were calculated by Langmuir isotherm model.It indicated that this process was a spontaneous and endothermic adsorption process and the degree of freedom is gradually increasing.It is presumed that electrostatic adsorption acts out a major role in the adsorption process.According to the characterization of BUC-74,which responds with the visible light.The photocatalytic activity of catalytic were explored by reduction of Cr(Ⅵ)and the reduction efficiency affected by p H value.The results showed that BUC-74 can completely reduce 10 mg/L Cr(Ⅵ)to Cr(Ⅲ)with 90 minutes.The reduction efficiency is decreasing with the increase of p H.There is no collapse of the structure and little effect on the photocatalytic efficiency of BUC-74 after it has been recycled of five times.It is proved that BUC-74 is a new material with dual functions of adsorption and photocatalysis.3.MIL-88A-1 and MIL-88A-2 were powder ferrous MOF material,prepared by optimizing the synthesis method.SEM characterization showed that the particle sizes of MIL-88A-1 is bigger than MIL-88A-2.Rhodamine B of dyes and bisphenol A of emerging pollutants were used to study the photocatalytic activity of degrading organic pollutants.The experimental results showed that these samples have good photocatalytic activity,especially MIL-88A-2.It is shown that photocatalytic degradation efficiency was enhanced by photoFenton reaction with H2O2,and the photocatalytic mechanism was validated by the experiment on capturing active substances and experiment on PL of capturing · OH.Comparing the characterization of MIL-88A-2 before and after recycling,it can be seen that MIL-88A-2 shows superior stability and reusability.It proves that MIL-88A-2 has broad application prospects as photocatalyst.