| Four ionic liquids([Bmim][BF4],[Bmim][TFSI],[P8883][BF4]and[P8883][TFSI])were synthesized and characterized via FTIR and TG and analyzed for their toluene and xylene absorption properties.On the basis of the theory of quantum chemistry,the interaction between phosphonium-based ionic liquids and toluene was calculated using Materials Studio software Dmol3 module by selecting toluene as a model compound and the comparison was made with the imidazole.The microscopic parameters of ion-pairs and toluene-ionic liquids such as bond length,bond angle,hydrogen bonding,C/H??interaction,electric charge distribution,molecular orbital were analyzed in detail.The main conclusions are as follows:1.The absorption performance of quaternary phosphonium ionic liquids on toluene is much greater than that of imidazoles,and the order of absorption capacity of anion for toluene is[BF4]->[TFSI]-in the case of the same cation.Therefore,Ionic liquids have better absorption of toluene,and[P8883][BF4]has the best absorption capacity of 2.840 g/g for toluene at 298 K.The absorption capacity for o-xylene,m-xylene,and p-xylene was 1.462 g/g,0.936 g/g and 0.678 g/g,respectively.The absorption order of[P8883][TFSI]is:toluene>o-xylene>p-xylene>m-xylene.2.The ion pairs of[Bmim][BF4]and[Bmim][TFSI]mainly depend on hydrogen bonding,and there are five hydrogen bonds between the anions and cations in two ionic liquids respectively.The absorption of toluene by[Bmim][BF4]and[Bmim][TFSI]belongs to physical absorption.Toluene can form three C/H??bonds with[Bmim]+cations and two hydrogen bonds with[BF4]-to make the absorption system more stable.The frontier molecular orbitals of the[Bmim][BF4]·C7H8 system show a stronger interaction between toluene and[BF4]-,and it can be seen from Eabs?[Bmim][BF4]?C7H8?>Eabs?[Bmim][TFSI]·C7H8?that[Bmim][BF4]has better absorption of toluene.3.The ion pairs of[P1114][BF4]and[P1114][TFSI]mainly depend on hydrogen bonding,and there are seven and five hydrogen bonds between the cations and anions of the above ionic liquids.The absorption of toluene by[P1114][BF4]and[P1114][TFSI]belongs to physical absorption.Toluene can form three C/H??bonds with[P1114]+cations,and a hydrogen bond with[BF4]-and[TFSI]-respectively to make the absorption system more stable.The frontier molecular orbitals of[P1114][BF4]·C7H8 and[P1114][TFSI]·C7H8 indicate that there is a strong interaction between toluene and[P1114]+and[BF4]-,and it can be seen from Eabs([P1114][BF4]·C7H8)>Eabs([P1114][TFSI]·C7H8)that the toluene absorption capacity is[BF4]->[TFSI]-when the cation is constant.4.The ionic liquid[P4443][BF4]mainly depend on hydrogen bonding between the anions and cations,and there are six hydrogen bonds between them.The absorption of one and two toluene by[P4443][BF4]all belongs to physical absorption.Toluene can form three C/H??bonds with the[P4443]+and two hydrogen bonds with the[BF4]-,both of which play an important role in the stabilization of[P4443][BF4]·C7H8 when[P4443][BF4]absorbs a toluene.The newly added toluene will form four C/H??bonds with the[P4443]+,and the four C/H??bonds act together to make the[P4443][BF4]·2C7H8 system balanced and stable when the second toluene is absorbed.The frontier molecular orbitals of the[P4443][BF4]·C7H8 and[P4443][BF4]·2C7H8 systems indicate that there is a strong interaction between toluene and[P4443]+and[BF4]-,and the two toluene molecules can still be stably absorbed.It can be seen that[P4443][BF4]absorbs two toluene molecules more favorably than a single from Eabs([P4443][BF4]·2C7H8)>Eabs([P4443][BF4]·C7H8),and the Eabs([P4443][BF4]·C7H8)>Eabs([P1114][BF4]·C7H8)shows that the toluene absorption capacity increases with the increase of the quaternary cation side carbon chain when the anion is constant.Compared to[Bmim][BF4],[P4443][BF4]has better absorption performance for single toluene,and the advantage of[P4443][BF4]·2C7H8 is even more pronounced from the micro-characteristics of absorption energy,structural parameters,frontier molecular orbital distribution and so on. |
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