Study On The Effects Of Molecular Sieves With Different Structures On The Adsorption,Controlled Release And Bacteriostatic Performance Of Citral

Litsea cubeba oil and its main component citral are widely used in perfumery and antibacterial fields due to their fresh lemon aroma and strong antibacterial activity.However,its volatile loss and deterioration due to the influence of light,heat,acid and alkali greatly limit its application performance.How to overcome the above problems is one of the research hotspots for today’s scientists.Volatile and poorly soluble citral was used as the research object.Non-volatile and poorly soluble ibuprofen was used as a comparison.Mesoporous molecular sieves SBA-15,MCM-41 and supermicroporous molecular sieve S（with functionalization of amino groups which were labeled as N-SBA-15,N-MCM-41 and N-S）as carriers.The effects of molecular sieve pore size and amination on the adsorption performance of target compounds were systematically explored.In-depth studies of controlled release performance of different molecular sieves on target compounds in three different pH buffer solutions were conducted,and the results obtained are as follows:By studying the citral/molecular sieve adsorption curve and the thermogravimetric chart of ibuprofen/molecular sieve,it was found that the smaller the pore size of the molecular sieve,the stronger the adsorption capacity of the target compound.Amino-functionalized molecular sieves have greatly improved the adsorption of citral because the-OH on the surface of the molecular sieve is replaced with-NH₂,and its contacting with the carbonyl group in citral through hydrogen bond is beneficial to the adsorption of citral.However,due to the relatively smaller pore sizes of MCM-41 and S,the degree of blockage of the channels of these two molecular sieves is relatively larger due to the introduction of amino groups.The adsorption capacity of three molecular sieves for citral is changed to:N-SBA-15（7.696%）>N-MCM-41（4.019%）>N-S（3.381%）.The above rules also basically apply to the adsorption of ibuprofen,but the adsorption of ibuprofen for functionalized supermicroporous molecular sieve is weaker than the unfunctionalized one,which may be related to the fact that the molecular size of ibuprofen is larger than citral.Through in-depth study of the release system,the effect of the pore size of molecular sieves on the release of volatile and insoluble citral and non-volatile and insoluble ibuprofen in three different pH buffer solutions was proposed:molecular sieve can increase citral in the buffer solution.The smaller the pore size of the molecular sieve,the higher the release rate.The release rate of citral/molecular sieve in the buffer is:SIF（pH7.4）>DW（pH5）>SGJ（pH1.2）,and the release rate of citral/N-molecular sieve in the buffer is:SGJ（pH1.2）>DW（pH5）>SIF（pH7.4）,this is probably because that the amino group is alkaline,which affects the internal environment of the molecular sieve in an acidic environment and protects the citral,which slows down the cyclization of citral in an acidic environment,making the citral/N-molecular sieve reach the highest sustained release rate in an acidic environment.After functionalization,the release rate of the target compound is slowed down,and the purpose of long-term controlled release is achieved.The release rate of ibuprofen/molecular sieve in the buffer is:SIF（pH7.4）>DW（pH5）>SGJ（pH1.2）,while the release rate of ibuprofen/N-molecular sieve in alkaline environment is still the highest.With the release of volatile citral to the air during the releasing in the buffer solution,the concentration of citral slowly decreases when the release curve reaches the highest point,which the non-volatile ibuprofen keeps the ibuprofen content basically unchanged when the highest point is reached.The bacteriostatic performance of molecular sieve with adsorption of citral was studied by the plate bacteriostatic method.Considering that the daily bacteriostatic process mostly occurred in a non-closed environment,the plate was seted without sealing.The results showed that the inhibitory effect on the Colletotrichumgloeosporioides was:citral/N-molecular sieves(The EC₅₀ of citral/N-S is 222.5760mg/L)>citral/molecular sieves(The EC₅₀ of citral/S is 931.0682mg/L)>pure citral(The EC₅₀ is 1538.2311mg/L).It shows that the adsorption and controlled release of citral through molecular sieve is helpful to enhance the bacteriostasis,and the stronger the adsorption and controlled release performance of molecular sieve,the better the bacteriostatic performance.