Preparation And Photocatalytic Performance Of Functionalized MIL-101(Cr) Composites

With the rapid development of pharmaceuticals and industries,antibiotics and fossil energy are becoming more and more widely used in daily life.Most antibiotics and volatile organic compounds（VOCs）are difficult to remove effectively due to their stable structures and low environmental concentrations.Conventional wastewater and waste gas treatment technologies such as physical adsorption,biodegradation and chemical oxidation cannot effectively remove antibiotics and VOCs.Photocatalysis technology,which is mainly based on semiconductor materials,provides us with a more ideal method of energy utilization and pollution control.Metal organic framework materials（MOFs）have many advantages as photocatalysts.MIL-101（Cr）,which has a large specific surface area,rich pore structure,adsorption/catalytic selectivity and quite good chemical stability,is ideal for the study of photocatalysts,but the visible light utilization of MIL-101（Cr）is too poor,resulting in a less than ideal photocatalytic activity.In order to fully utilize the advantages of MIL-101（Cr）,the construction of binary heterojunctions by combining MIL-101（Cr）with Ag₃PO₄ and defective black TiO₂ which have good visible light utilization,respectively,is an effective and feasible solution.The main contents of this paper are as follows:1.Z-type Ag/Ag₃PO₄/MIL-101（Cr）heterojunction photocatalysts（referred to as AAM-x）were successfully prepared by a simple in situ precipitation method.The photocatalytic activity of the AAM-x samples was evaluated using a common tetracycline（TC）antibiotic.All AAM-x materials were more effective in removing TC than Ag₃PO₄ and MIL-101（Cr）.among them,AAM-3 exhibited efficient photodegradation efficiency and good structural stability,with 97.9%removal of TC（20 mg/L）by AAM-3（0.5 g/L）under 60 min of visible light.The effects of photocatalyst dosage,pH value and inorganic anions were also systematically investigated.According to the X-ray photoelectron spectroscopy analysis,metallic silver particles appeared on the surface of the Ag₃PO₄/MIL-101（Cr）mixture during the catalyst synthesis.The results of photoluminescence spectra,photocurrent response,electrochemical impedance and fluorescence lifetime indicated that AAM-3 had high efficiency of photocatalytic charge separation.An all-solid Z-type heterojunction mechanism including metal Ag,Ag₃PO₄ and MIL-101（Cr）is proposed to rationalize the excellent photocatalytic performance and photostability of the AAM-x composites and to explain the role of metal Ag as a charge transfer bridge.The intermediates of TC were identified using high performance liquid chromatography-mass spectrometry,and possible pathways for TC degradation were also discussed.This work provides a viable idea for removing antibiotics by Ag₃PO₄/MOF-based heterogeneous structured photocatalyst.2.TiO₂@MIL-101（Cr）composites were successfully prepared by a two-step hydrothermal method and used for the photocatalytic degradation of formaldehyde（HCHO）gas under visible light.the introduction of MIL-101（Cr）promoted charge transport and enhanced the contact between the active site and the contaminant,while the defective black TiO₂ had the advantage of a relatively wide range of photo sorption and effective separation of photogenerated charges due to oxygen vacancies.We constructed a novel system consisting of Z-type heterojunction and oxygen vacancies synergistically,and TiO₂@MIL-101（Cr）exhibited excellent photocatalytic performance for HCHO,with the best material TM-20 achieving 92.1%removal of HCHO,which was 2.2 and 1.7 times higher than MIL-101（Cr）and TiO₂,respectively.The effect of catalyst dosage was investigated and the TiO₂@MIL-101（Cr）composite had excellent recovery stability.This strategy is coordinated composite of MIL-101（Cr）and defective black TiO₂ for the efficient degradation of the gaseous pollutant HCHO driven by visible light,and can provide a theoretical basis for the development of a Z-type heterojunction photocatalytic system with coordinated interaction with MOF.