The Controllable Construction Of Nanochannel In Two-Dimensional Lamellar Membrane For High Permeance

As the development of global economy,the water pollution and absence of abundant water source is an urgent problem for human beings.Thus,it is significant to develop efficient and energy-saving water processing technology.Due to many advantages,i.e.environmental-friendly,membrane separation technology has become the focus of water treatment.Two-dimensional?2D?lamellar separation membrane is one of the most often studied as its unique membrane structure in recent years.Now,there are many kinds of 2D nanosheets for lamellar membrane,including graphene oxide?GO?,transition metal dichalcogenide and carbide,layered double hydroxides?LDHs?,etc.This 2D separation membrane prepared by the stacking of two-dimensional nanosheets,shows fast and selective transport for molecular.The manipulation of nanochannel including channel structure and microenvironment in lamellar membrane is conducted in order to achieve membrane performance with high permeance and rejection.In this research,rigid MXene nanosheets are prepared and used as the building blocks for lamellar membrane.Due to the self-stacking feature of rigidity nanosheet,the controllable construction of nanochannel and the intensification of transportation process are achieved.The details and conclusions are as following:?1?Via soft-etching low-power sonication procedure,double-layered Ti₃C₂T_x MXene was produced and filtrated for preparing MXene lamellar membrane.Compared with GO membrane,the MXene membrane with unique channel structure showed improved membrane performance.The rigid sheets can stack into regular and straight interlayer channels by a direct self-stacking procedure,rather than irregular ones presented usually in the existing lamellar membranes.This novel membrane exhibited precise molecular rejection for molecules larger than² nm and,importantly,unparalleled molecular permeation.Specifically,the permeance values for water and organics were²300 and 5000 L m^-2 h^-1 bar^-1,respectively;2 and 20times greater than the highest reported values under identical rejection conditions.More significantly,using these channels we explored molecular transfer mechanism,and established the corresponding transport rate equation.?2?Considering different rigidity between MXene and GO nanosheet,MXene was used as spacers to manipulate the channel structure and improve the molecular transport in GO lamellar membrane.Compared with GO membrane,GO/MXene composite membrane had increased water permeance,which was 6 times higher than that of GO membrane.Another spacers,PGO was also detailedly studied in our experiment.The results showed that the spacing of PGO increased the width of interlayer channel and improved molecular permeance,while resulting in the deterioration of sieving property of composite membrane.This suggested the superiority of rigid MXene nanosheets for improving performance of GO membrane.The rejection for different organic dyes demonstrated that the prepared GO/MXene composite membrane had interlayer width of above 1.5 nm.The transmembrane pressure during test also had important influence on membrane separation.