Study On Thermodynamics、Kinetics And Mechanism Of The Direct Bonding Reaction Of Nano Bi₂S₃with Gelatin

Bionanocomposite is a new type of ecological material that combining theunique optical, electronic, or catalytic properties of the nanoelements with therecognition or biocatalytic functions of biomolecules, and represents a rapidlygrowing field of research. So far, the research on bionanocomposites mostlyfocused on the materials’ preparation, characterization and the development of itsnovel functional, while the thermodynamics, kinetics and mechanism of theformation reaction were rarely reported. What is more, the research on directbonding reaction were even less. So we studied the direct bonding reactionbetween nano Bi2S3and gelatin in detail by a series of testing methods in thisarticle, the research mainly include the following four parts.1. The formation of Bi2S3/gelatin bionanocomposites. The water-solubleBi2S3/gelatin bionanocomposites were synthesized at different pH, temperaturesand concentration of Bi3+. The solution of composite can be stable for33and38days at pH7.40and12.0respectively. The bionanocomposites were characterizedby XRD、TEM and DLS, and the results showed they were gelatin coated nanorods.The optical property of the bionanocomposites was studied by UV-vis spectra, theresults showed the Eg decreased as Bi2S3concentration and temperature increased.2. The thermodynamic of the direct bonding reaction of nano Bi2S3withgelatin. The thermodynamic of the direct bonding reaction of nano Bi2S3withgelatin was studied according to the formation of composites and the intrinsicfluorescence quenching of gelatin respectively. The binding constant, the bindingpoint number, fluorescence quenching rate constant, bond constant andthermodynamic parameters (entropy change ΔrSm, enthalpy change ΔrHm, Gibbsfree energy change ΔrGm) of the reaction were calculated. The results showed thatelectrostatic force and hydrophobic force existed between nano Bi2S3with gelatin,the quenching mechanism of gelatin fluorescence was static, resonance energy transfer occured between them.3. The kinetics of the direct bonding reaction of nano Bi2S3withgelatin. Thekinetics of the direct bonding reaction of nano Bi2S3with gelatin was studied byusing UV-vis spectrum spectrum method and fluorescent spectrometry according tothe formation of composites and the intrinsic fluorescence quenching of gelatinrespectively. The reaction order of each reagent, pre-exponential factor, activationenergy was calculated and reaction rate equation was get, the kinetic parameters atdifferent pH (activation entropy, activation enthalpy, activaton Gibbs free energy)was calculated, too.4. The mechanism of the direct bonding reaction of nano Bi2S3with gelatin.The conformation change of gelatin in the direct bonding reaction wascharacterized by IR, UV–vis, synchronous fluorescence spectrometry,three-dimensional spectrometry and viscosity. The results showed that themolecular chains of gelatin were more stretching, the secondary structure of gelatinand the micro environment of fluorescent groups in gelatin was changed afterbonding with Bi2S3. The fluorescence of gelatin almost quenched completely at acertain concentration, the structure of gelatin was damaged severely. Theinformation of IR indicated the carboxylate radical of the side chain in gelatin wasthe bond site of nano Bi2S3and gelatin. The mechanism of the direct bondingreaction was proposed by integrating the information above, that is,Bi3+coordinated with carboxylate radical of the side chain in gelatinmacromolecule to form Bi3+/gelatin complex, then S2combined with Bi3+cooperated by gelatin to form Bi2S3particles. At the same time the particleswerecoated by gelatin, which may enhanced its stability in aqueous phase.