Preparation Of Hydrophobic Metal-Organic Framework And Its Adsorption-Photocatalytic Performance For Toluene Oxidation

The problem of indoor environmental pollution still affects the life and work of human.VOCs,particulates,nitrogen oxides,sulfur oxides and other harmful substances released into the indoor environment from decoration,furniture,and industrial production can cause humans to suffer from respiratory tract infections,cancers,and leukemias.Toluene,as the most representative and most toxic indoor organic pollutant,is often used as the target of experimental research.At present,the methods for indoor environmental treatment on the market mainly include ventilation and adsorption methods.Although these methods are simple,they can only achieve the effect of transferring and enriching pollutants,and they still need to carry out the follow-up treatment.Photocatalytic technology can deeply degrade pollutants into CO₂ and H₂O under the light irradiation.It has the advantages of high efficiency and no secondary pollution,and has attracted the attention of researchers.As an efficient,non-toxic,and low-cost photocatalyst,TiO₂ has become the commonly used material in photocatalytic technology.However,as a semiconductor,TiO₂ also faces the problem of high photogenerated electron-hole recombination rate.The combination of metal organic framework materials MIL-101 and TiO₂ can effectively accelerate electrons-holes transfer,and the porous and large specific surface area of MIL-101 is conducive to the high exposure of TiO₂ active sites and the improvement of the material’s adsorption performance for pollutants.However,the inability of this type of composite material to adapt to the actual complex environment still hinders its development.The high hydrophilicity of MIL-101 and TiO₂ makes it easy to be covered by water vapor in a high-humidity environment,which is not conducive to the progress of the photocatalytic reaction.The porous and stable polymeric organic material polydivinylbenzene forms a hydrophobic protective layer on the surface of the composite material to block part of the water vapor,which increased the chance of contact between pollutants and the material,thereby improving the photocatalytic activity.Several commonly used hydrophobic materials were loaded on MIL-101 by thermal deposition to form a tight hydrophobic layer.The successful preparation of the composite material was proved by XRD,SEM and FT-IR,and the hydrophobicity of the material was confirmed by the hydrophobic angle measurement.The results showed that the PDVB-modified MIL-101 had the strongest hydrophobicity,with a hydrophobic angle of135.74°.In the toluene adsorption experiment,PDVB showed the most excellent adsorption capacity in the absence of water vapor,and at the same time,the strong hydrophobic performance in the presence of water vapor kept the toluene adsorption capacity stable.The tightly bonded MIL-101@TiO₂ composite was prepared by in-situ hydrothermal method,and PDVB was loaded on the surface of the composites by thermal deposition to form a hydrophobic layer.The morphology,structure and element composition of the material were characterized by XRD,SEM and FT-IR,which proved the successful preparation of the composite material,and confirmed the hydrophobicity of the material by the water contact angle.The results showed that MIL-101@TiO₂@PDVB had excellent hydrophobic property with a hydrophobic angle of 142.5°.The results have showed that humidity is one of the important factors affecting the photocatalytic reaction under different humidity.At RH=60%,MIL-101@TiO₂@PDVB exhibited remarkable photocatalytic degradation of toluene.When the humidity increased to 90%,the activity of MIL-101@TiO₂ decreased and gradually deactivated,while the toluene degradation rate of MIL-101@TiO₂@PDVB stabilized at63.33%,which was mainly due to the hydrophobic layer preventing water molecules and toluene The competitive adsorption ensured the effective contact between the material and the toluene molecules.In addition,MIL-101@TiO₂@PDVB also showed outstanding adsorption-photocatalytic performance in the degradation of liquid phase organics,and can maintain stability in long-term alkali resistance experiments and cycle experiments.