| The interaction between mineral surface and organic small molecule plays an important scientific basis for understanding mineral processing,surface modification,etc.However,the theoretical study of self-assembled monolayers on natural mineral surface is still lacking.In this thesis,eight alkyl bisphosphonic acid compounds were first synthesized in two steps;then,three kinds of natural mineral were used as the substrate,such as muscovite mica,calcite and bone mineral powders in which main component is hydroxyapatite,and the self-assembled monolayers of alkyl bisphosphonic acid were prepared on the corresponding mneral surface through a wet adsorption reaction and a subsequent heat treatment process under low vacuum.Finally,the surface properties of the corresponding mineral and its anchored mechanism were studied in detail.In this paper,the main research work and major achievements are illustrated as follows:First,under the relatively mild reaction conditions,eight alkyl bisphosphonic acid compounds(the number of carbon atoms is from 9 to 23)were synthesized using commercially available reagents,and the structure of the title product was confirmed by FT-IR,HRMS and NMR.Experimental results showed that the proton signal of bisphosphonic acid 1H NMR shifted to the high field,while the asymmetric stretching vibration absorption peak of the alkyl chain methylene group red shifted,the solubility of the compound in the polar solvent was significantly reduced,and the tendency of this series of alkyl bisphosphonic acids exhibited a stronger lipophilicity and a more ordered crystal structure with the increasing of alkyl chain length.Then,by the method of a wet adsorption reaction and a subsequent heat treatment under low vacuum,self-assembled monolayers of alkyl bisphosphonate were prepared on the atomically flat mica surface,and the height of cetylbisphosphonate,heptadecylbisphosphonate,and nonadecylbisphosphonate monolayer corresponds to 2.4 nm,2.37 nm/2.70 nm,and 2.80 nm,respectively.Compared to the same chain length alkylphosphonate monolayers self-assembled on mica surface,the smaller inclined angle indicated that the alkylbisphosphonate monolayer "stands" straighter and steadier than alkylphosphonate monolayer on the mica surface.TOF-SIMS and XPS show that the head group P-OH of alkyl bisphosphonic acid and the Si+ on the surface of mica form a strong P-O-Si bond by covalent bonding,and the long chain alkyl group faces the outer side of the mica surface.The anchored mechanism of the alkylbisphosphonate SAMs to the the mica surface is as follows:In Stage I,where the hydroxyl group takes part in the adsorption process,and partial hydroxyl groups of bisphosphonic acid are bound to the mica surface by hydrogen-bonding interaction,long-chain alkyl tails self-assembled on the outer side of the mica surface promoted by van der Waals force between the side chains,thus a physisorption interaction between bisphosphonic acid and the mica surface is achieved.Stage ?,under low vacuum,interactions between the bisphosphonic acid headgroups of C16-BPA and the mica surface developed further by heating for several hours at 105?,and a chemisorption interaction is ultimately facilitated to form stable P-O-M bonds.Secondly,ordered alkylbisphosphonate monolayers were self-assembled on a flat calcite surface.TOF-SIMS analysis showed that the alkyl bisphosphonic acid monolayer was anchored onto the calcite surface,and the P-OH of head group and the calcium ion on the surface of the calcite reacted covalently to form a stable P-O-Ca bond,and the long alkyl chains faced the outer side of the calcite surface and self-assembled to form a monolayer of calcium bisphosphonate.The mechanism is as follows:in the first stage of the adsorption reaction,the surface hydroxyl group of the calcite and the P-OH group in the bisphosphonic acid molecule interact through hydrogen bonding,which participate and promote the adsorption reaction process,whileas,H+is released by the bisphosphonic acid in the aqueous solution,thus the acid-salt reaction between calcium carbonate and H+ is occurred on the surface of CaCO3,by releasing CO2 and promoting the shifting of the chemical equilibrium,to be the formation a relatively stable alkyl bisphosphonate salt.In the second stage,heating at 105? under the low vacuum,one molecule of water is removed by condensation reaction,and a stable P-O-Ca bond is formed between the phosphonic acid head group and Ca+ surface of calcite.Thirdly,in the ethanol-water solution system,the surface of the ground CaCO3 was modified by the alkyl bisphosphonic acid,and the surface of CaCO3 powders was full activated coating by hydrophobic alkylbisphosphonate monolayers.The surface P content of ground CaCO3 powders modified by alkylbisphosphonate monolayers was analyzed by ICP-AES,TG and EDS mapping mode,independently.The result of three independent method have good consistency,confirming the monolayer modification of ground CaCO3 powders surface.Finally,the surface of bone minerals was modified by tridecyl bisphosphonate monolayers in an ethanol-water solution system.The main component of the obtained inorganic salt product in the reaction is Ca(H2PO4)·2H2O.FT-IR,31P CP-MAS NMR and 13C CP-MAS NMR spectra of alkylbisphosphonate-modified bone minerals indicated that that one phosphonic acid group in the alkyl bisphosphonic acid replaced one PO43-group of bone mineral phase.Thus,the entire alybisphosphonate molecule is chemically adsorbed to the surface of the bone mineral,and the alkyl chain was oriented toward the outside of the surface to render the modified bovine bone powder to be hydrophobic.In conclusion,it has been shown in this thesis that the method of alkyl bisphosphonate monolayer,based on solution adsorption-heating treatment under low vacuum,can be applied to the surface modification of various substrates with different chemical compositions.It is believed and expected that further studies focused on both theoretical and practical research should be achieved.This method will provide a simple and practical interface modification method for the construction of organic phosphonate monolayers on the surface of a wide range of oxide solids,which is not only suitable for relatively flat surfaces,also applicable for granular materials with complex microtopography. |
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