Preparation Of MOF-titanium-based Nanomaterial Composites And Their Photocatalytic Performance For Removal Of Pollutants In Water

Nowadays,the rapid development of industry is often accompanied by the production of heavy metal ions and organic pollutants.These pollutants are generally more toxic and threats to the environment and organisms.Therefore,it is urgent to take effective and environmentally friendly methods to remove these pollutants.Among the many treatment methods,the photocatalytic method is widely used because of its mild working environment,green pollution-free and low price.Metal-organic framework materials?MOFs?are a kind of porous materials with periodic network framework formed by coordination self-assembly of metal ions/cluster and organic ligands.Such materials have various synthetic methods and adjustable active sites as well as are easy to cultivate single crystals.They are widely used in the fields of adsorption,sensing,gas separation and storage and catalysis.Titanium-based nanomaterials such as TiO₂ and its derivatives,titanates and their derivatives have been widely used in the environmental field due to their non-toxic and low-cost characteristics.In this paper,a two-dimensional MOF material with Zn²⁺as the center metal ion independently synthesized by our research group is selected to compound with titanate nanotubes?TNTs?,nitrogen-doped potassium tetratitanate?N-K₂Ti₄O₉?and nitrogen-sensitized titanium dioxide?NHPI-TiO₂?.These composites have been characterized and the photocatalytic removal performance of pollutants have been investigated under ultraviolet light,white light and visible light.The corresponding mechanism has been explored.The main works of this paper are as follows:1.BUC-21 was synthesized by a simple hydrothermal method and TNTs using TiO₂?P25?asthe raw material.BUC-21/TNTs?BT-X?composites were prepared by simple ball milling.The composites were characterized by means of PXRD,FTIR,XPS,TEM,HRTEM,UV-Vis DR and Zeta potential.The photocatalytic performance of BUC-21/TNTs forsimultaneous removal of Cr?VI?and Cr?III?under ultraviolet light was investigated.Theeffects of initial pH and inorganic co-existing ions on the performance of BUC-21/TNTswere also clarified.The experimental results showed that since TNTs could rapidly adsorbthe Cr?III?reduced by BUC-21,and accelerate the release of the active site of BUC-21.This synergistic effect of photocatalytic reduction and adsorption not only achieved thesimultaneous removal of Cr?VI?and Cr?III?,but also accelerated the reaction rate.Theoptimal pH value of this reaction was weakly acidic,which was beneficial to the practicalapplication of BT-1?the mass ratio of BUC-21 to TNTs is 1:1?.Through cyclicexperiments and PXRD as well as TEM characterization after the reaction,it had beenconfirmed that BT-1 had excellent cycling and stability.Finally,the mechanism wasinvestigated using XPS and Zeta potentials.2.Series composites of BUC-21 and N-K₂Ti₄O₉?B1NX?were prepared by ball milling,andthe composites were characterized by PXRD,FTIR,TEM,HRTEM,XPS,UV-Vis DR,and PL.The photocatalytic properties of the composites under ultraviolet and white lightwere explored,and the effects of the initial pH of the solution,small molecule organicacids,and real water bodies?lake water and tap water?on their performance were alsostudied.The results revealed that the introduction of N-K₂Ti₄O₉ improved the separationand transfer rate of photogenerated electrons under ultraviolet light irradiation,therebyimproving the photocatalytic efficiency.The optimal ratio B1N0.5?the mass ratio ofBUC-21 to N-K₂Ti₄O₉ is 1:0.5?could completely reduce Cr?VI?on 40 min.Upon whitelight irradiation,BUC-21 and N-K₂Ti₄O₉,which had no catalytic performance,couldcompletely reduce Cr?VI?on 90 min after being compounded.Photoluminescence spectra,time-resolved photoluminescence analysis and instant photocurrent testing had verifiedthat fast photo-generated electron-hole separation efficiency.Cycle experiment and theinorganic co-existing ion experiments also showed that the BUC-21/N-K₂Ti₄O₉composites had good reusability and stability.Finally,the mechanism was investigatedusing VB-XPS,active material capture,and ESR tests.3.Series of composites?B1NTX?were prepared by simple ball milling usingN-hydroxyphthalimide-sensitized titanium dioxide?anatase??NHPI-TiO₂?and BUC-21.The PXRD,TEM,HRTEM,XPS and UV-Vis DR were used to characterize.In addition,the photocatalytic degradation of bisphenol A by the composite was investigated underlow power visible light,and it was confirmed that the composites showed betterphotocatalytic degradation effect than BUC-21 and NHPI-TiO₂ alone.The effect of pH onits photocatalytic process was also researched.It was found that the degradation efficiencyof the composites could be kept at around 92%between pH 5-9,indicating that thecomposites has a wide application range of acid and alkali.Finally,ESR were used tocapture the active material in the photocatalytic process and the mechanism of thephotocatalytic process was explored.