Investigating The Diffusion Process Of Solvent Molecules In Nanochannels By FTIR Spectroscopy

Recently,two-dimensional(2D)nanochannels have shown to be a promising platform for energy conversion and molecular separation devices.The transport and diffusion behaviours of molecules in the nanochannels have attracted growing attention because they determine the performance of these nanodevices.However,the existing research methods usually focus on the macroscopic results,such as the concentration changes and the diffusion rates of the diffusates in the upstream and downstream of the devices.It is challenging to detect the diffusion behaviour of the molecules inside the nanochannels and the interaction between the diffusates and the wall of nanochannels during the diffusion process.In order to address these difficulties,in this thesis,attenuated total reflection infrared(ATR-FTIR)spectroscopy was applied to in situ investigate the diffusion behaviour of solvent molecules in the 2D nanochannels of graphene oxide(GO)film.The main progress we achieved is listed as follows:1.Based on time-dependent ATR-FTIR spectroscopy,a real-time method was established to in situ monitor the diffusion process of solvent molecules in the nanochannels of GO films.Taking the diffusion process of ethylene glycol in GO film as an example,this method was verified by comparing with the traditional “pat and weigh” method.The diffusion coefficient obtained by our method is consistent with that measured by the traditional “pat and weigh” method and the results obtained by timedependent ATR-FTIR method are quite reproducible.In the meanwhile,the interaction between the GO nanosheets and the organic solvents was in situ monitored constantly.It is indicated that this method is feasible and reliable to investigate the diffusion behaviour of solvent molecules in the 2D nanochannels of GO films.2.The diffusion process of four organic solvents,N,N-Dimethylformamide(DMF),Dimethyl sulfoxide(DMSO),ethylene glycol and cyclohexane,in the 2D nanochannels was in situ investigated by time-dependent ATR-FTIR.The order of the diffusion coefficient goes in DMF > DMSO > EG > c-hexane.The diffusion coefficient of the organic solvent in GO film decreases as the interaction between the solvent molecules and the GO nanosheets increases.In the meanwhile,by comparing the spectra of the solvents in the diffusion process and in their bulk status,we found that the aggregation states of solvent molecules in the confined 2D nanochannels were different from those in the bulk phase.For example,the dimers in bulk DMSO disassociated when they diffused into GO film.3.Time-dependent ATR-FTIR spectroscopy was also used to explore the diffusion process of DMF and ethylene glycol mixtures(with various DMF/ethylene glycol molar ratios)in the 2D nanochannels of GO films at the same time.Significant delay time was observed in the diffusion process of DMF.A special “overshoot” phenomenon occurred in the diffusion process of the ethylene glycol.The addition of DMF will significantly increase the diffusion coefficient of ethylene glycol.However,the addition of a small amount of ethylene glycol(molar percentage ?50%)increases the diffusion coefficient of DMF,while the addition of a large amount of ethylene glycol(molar percentage >67%)decreases the diffusion coefficient of DMF in the nanochannels.These phenomena can be explained as follows: the interaction between the wall of the 2D nanochannels and glycol is much stronger than the interaction between the wall of the 2D nanochannels and DMF;the addition of DMF can inhibit the aggregation of ethylene glycol molecules.