Preparation And Properties Of Al₂O₃ Ceramic Membrane For Water Treatment

Al₂O₃ceramic nanofiltration membrane have broad application prospects in the field of water treatment due to its advantages.However,there are problems such as complicated technical route and difficult control of membrane integrity in the preparation process of Al₂O₃ceramic nanofiltration membrane.In addition,there are many types of water pollutants to be treated,and the molecular weights are different,which puts forward stricter requirements on the pore size distribution of ceramic membranes used for treating different water pollutants.In this study,Al OOH sol was prepared by using aluminum isopropoxide as raw material and nitric acid as peptizer by sol-gel method,and Al OOH gel layer was directly coated on Al₂O₃support by dip-coating method.The pore size of the ceramic membrane is regulated by adjusting the solid content of the sol,and a high water flux Al₂O₃ceramic nanofiltration membrane with controllable membrane thickness and pore size is obtained after heat treatment.Rotational rheometer,zeta potentiometer,FESEM,energy spectrometer,specific surface area and pore size analyzer and filtration test device was used to analyze the influence of preparation process on the structure and filtration performance of Al₂O₃nanofiltration membrane.Then the difference in filtration performance of Al₂O₃nanofiltration membranes with different pore sizes was tested with organic dye solutions.In this study,Al OOH sols with a solid content of 3wt%,4wt%,5wt%,and 6wt%were coated on a support and heat-treated to obtain the corresponding Al₂O₃nanofiltration membranes with a thickness of 6μm.With the solid content increased from 3wt%to6wt%,the pore size of Al₂O₃nanofiltration membrane decreased from 3.16 nm to 2.24 nm,and the pure water flux decreased from 267.2 L·m^-2bar^-1h^-1to 190.1 L·m^-2bar^-1h^-1.During the preparation process of Al OOH sol,Al OOH sol with similar rheological properties but different solid content can be obtained by controlling the process parameters such as the amount of nitric acid added and the standing time.The flow viscosity of the Al OOH sol should be controlled in the range of 0.0025～0.005 Pa·s,so that the thickness of the Al OOH gel film after dip-coating is about 6～12μm;the storage modulus of the Al OOH gel layer increases with the aging time increase.When the storage modulus of the Al OOH gel layer is greater than the saturated vapor pressure of the solvent under normal pressure,it will not crack due to the evaporation of the solvent during the heat treatment process.The research results show that by controlling the process parameters,Al OOH sol with controllable solid content and rheological properties can be obtained.After further heat treatment,an Al₂O₃ceramic membrane with a smooth surface without cracks and controllable film thickness and pore size can be obtained,which has nanofiltration performance.The prepared Al₂O₃nanofiltration membranes were used to filter Congo red,crystal violet,methylene blue,and rhodamine B dye wastewater to study its filtration effect,and the rejection rate was all above 99%.It is also found that there is a certain correspondence between the molecular weight of the dye to be filtered and the pore size of the Al₂O₃nanofiltration membrane.Cleaning the Al₂O₃nanofiltration membrane after dye solution filtration can restore the pure water flux to 75.8%of the initial value.After 3cycles of filtration,the Al₂O₃nanofiltration membrane still has a high pure water flux of71.5%,that has a strong regeneration ability.