Micro-Structure And Surface Hydrophilicity/Hydrophobicity Modification Of Zeolite-Based Composites For Toluene Adsorption

Volatile organic compounds?VOCs?posed a serious threat to human health and atmospheric environment due to their large variety and complex components.Particularly,the benzene series?represented by toluene?emitted from printing industry exhibit higher toxicity and has attracted increasing attention.Due to the low concentration of toluene emitted by printing industry,adsorption method is considered as one of the most convenient and effective technology for its control.Zeolite is widely used in the adsorption field due to their excellent thermal stability and adsorption performance.However,the hydrophilicity of zeolite restricts their application in practical industry.In order to improve the hydrophobicity and adsorption properties,zeolite was modified from two aspects:surface microstructure and hydrophilic group,respectively.On the basis of this,zeolite@layered double hydroxide?LDH?and microporous zeolite/mesoporous zeolite composite were synthesized to impro the adsorption performance under wet conditions.Firstly,three kinds of mesoporous zeolites MCM-41,MCM-48 and SBA-15 and three microporous zeolites Y,ZSM-5 and TS-1 were successfully prepared by hydrothermal method.All samples were characterized carefully.The results showed that the toluene breakthrough time of microporous zeolites?24.4-36.2 min?were longer than that of mesoporous zeolites?9.7-22.7 min?under dry condition.The toluene adsorption performance of pure zeolites decreased under humid condition,especially for microporous zeolites which breakthrough time was significant decreased by 60%-82%.The breakthrough time of the mesoporous zeolites and microporous zeolites was only7.4-18.9 min and 6.4-9.8 min,respectively.And the pore structure and surface hydrophobicity were the main factors affecting the adsorption performance of pure zeolite.Zeolite@LDH composite were prepared by coprecipitation method in order to improve its hydrophobicity and adsorption.The results indicated that adsorption performance of all zeolite@LDH composite was better than that of pure zeolite.The breakthrough time of mesoporous-zeolite@LDH and microporous-zeolite@LDH was increased to 27.3-32.5 min and 35.2-42.1 min,respectively under dry condition.Under humid condition,their breakthrough time was increased to14.3-22.8 min and 13.2-14.8 min,respectively.It was also determined that the main reason for the improvement of the adsorption property was that the generation of multiple pore structure increased the number of toluene adsorption sites and adsorption strength.At the same time,the vertical growth of LDH on the surface of zeolite increased the surface hydrophobicity of the composite,thereby increasing its adsorption performance under wet conditions.In order to further reduce the cations and silicon hydroxyl hydrophilic groups on the surface of zeolite,and improve the adsorption properties,all silicon zeolite was loaded on microporous zeolite to prepare ZSM-5/MCM-41 and ZSM-5/silicalite-1 composites.It was found that the toluene adsorption performance of the above composites was significantly improved under humid condition compared with pure zeolite,ZSM-5/MCM-41?75%?exhibited the best adsorption performance with a breakthrough time of 18.5 min.In addition,ZSM-5/SBA-15 coated composites with different morphology were prepared.The adsorption properties of all ZSM-5/SBA-15 composites were significantly improved.Under dry condition,the breakthrough time of ZSM-5/SBA-15 composite was as high as 37.2-49.4 min while under humid condition,the breakthrough time of the composite was also increased to 14.9-27.4 min.²⁹Si-NMR and FT-IR results indicated that the increase of?Si O?₄Si and the decrease of?Si O?₃Si?OH?resulted in the advantage of toluene adsorption in the in the competitive adsorption process between toluene and water,thereby reducing the effect of water vapor on adsorption performance under humid condition.