Controllable Growth Of CaCO₃ Induced By Lignin Monomer Model Compounds And Its Mechanism

Calcium carbonate（CaCO₃）is the most abundant biological mineral in nature.Although the crystallization process of CaCO₃has been investigated for nearly hundred years,the understanding of the formation mechanism of crystals in organic matter solutions is still limited,which greatly restricts the industrial application of CaCO₃.Lignin abundant in nature and is one of the three major components of plants.However,in the industrial applications,lignin is mainly burned and discharged as waste in the paper pulping process,which results in a great waste of biomass resources.There are rich active functional groups in lignin,such as hydroxyl,carboxyl and methoxy groups,which can regulate the mineralization growth of CaCO₃crystals.Due to complicated structure of lignin,its monomer model compounds（cinnamic acid,p-coumaric acid,ferulic acid and erucic acid）were first used as precursors to explore the effect of lignin on the growth of CaCO₃crystals and its mechanism.This thesis investigated the mechanism of CaCO₃crystal growth by biomineralization,especially the growth of CaCO₃crystals induced by lignin monomer model compounds as organic matter.Based on the lignin monomer model compounds and mixed lignin monomer model compound solution growth system,the effects of various factors(including effect of the type and concentration of lignin monomer model compounds,Ca²⁺concentration,pH and reaction temperature,etc.)on the nucleation of CaCO₃mineral phase,phase transition process,product morphology and assembly rules were explored.The growth mechanism of CaCO₃crystals in the lignin monomer system also was revealed.This thesis is mainly divided into the following three parts:（1）Growth process and mechanism of CaCO₃crystals in the cinnamic acid solutionCinnamic acid（CA）is one of the lignin monomer model compounds.It has a simple structure and only contains one carboxyl group,which is suitable for the initial research.Then under the influence of cinnamic acid,two relatively pure CaCO₃crystal forms were synthesized,namely cinnamic acid&aragonite（CAAs）and cinnamic acid and vaterite crystals（CAVs）.Also the polymorph states are more likely to appear in the growth process of CaCO₃.The results showed that CAAs and CAVs have the characteristics of aragonite and vaterite,respectively.The polymorph state conforms with the structural properties of polycrystalline.In addition,in the CA system,the crystal form of CaCO₃follows the growth rule that from calcite to calcite&aragonite to polymorph state to aragonite&vaterite polymorph state to vaterite.Detailed growth process of CaCO₃crystals in the CA system was also revealed.（2）Growth process and mechanism of CaCO₃crystals in p-coumaric acid,ferulic acid and sinapic acid solutionsp-Coumaric acid（PCA）,ferulic acid（FA）and sinapic acid（SA）each has one more hydroxyl group,one hydroxyl group and methoxy group,one hydroxyl group and two methoxy groups than CA,which are suitable for in-depth research of the CaCO₃formation induced by lignin.Under effect of that three monomers,PCA&CaCO₃crystals（PC-ACCs）,FA&CaCO₃crystals（F-ACCs）and SA&CaCO₃composite crystals（S-ACCs）were synthesized.The results showed that different monomer concentrations have little effect on the crystal form of CaCO₃crystals.With the increase of pH,the ratio of vaterite decreases,and when the pH is 10,it basically turns into calcite.The temperature has a great influence on the morphology of the CaCO₃crystal.As increasing in temperature,the CaCO₃crystal growth into a more complex pinecone-like vaterite crystal.Through the calculation of the crystal form ratio,it is found that the number of methoxy groups on monomer would affect the stability on vaterite.FA with one methoxy group has the greatest stability on vaterite,followed by PCA,and SA has the worst stability on vaterite.（3）Growth process and mechanism of CaCO₃crystals in the mixed lignin monomer model compound solutionsPlants are mainly divided into softwood（SD）,hardwood（HD）and grass（GS）.Therefore,constructing growth systems based on the lignin monomer model compound ratio of these plant species is helpful to the research of lignin-induced CaCO₃crystal growth mechanism.Under the effect of that three lignin ratios,SD&CaCO₃crystals（SD-LCCs）,HD&CaCO₃crystals（HD-LCCs）and GS&CaCO₃crystals（GS-LCCs）were synthesized.Combined with previous work,it is found that the organic matter concentration and temperature have little effect on the crystal form of CaCO_3.Pinecone vaterite is formed at 55℃.The effect of pH on the system of different ratios are different.With the increase of pH,the proportion of calcite gradually increases.When the pH is higher than 10,most of the SD-LCCs is calcite,while the HD and GS proportions are still the main crystal form of vaterite even pH=11.However,due to the complex system,the specific mechanism needs to be further explored.The discovery of these growth mechanisms will help to have an in-depth understanding of the biomineralization mechanism,and provide guidance for the resource utilization of lignin monomer and the synthesis of diverse CaCO₃crystals by inducing of lignin.