Crystallization Of Calcium Carbonate On L-Cysteine Self-Assembled Monolayers

Calcium carbonate is a kind of crystal with great research values. The huge reserve and wide distribution in nature, cheap acquired price, and the specific physics and physicochemistry charactors make Ca CO3 popular in industries like rubber, papermaking, medical treatment and medcine, coating, biomineralization and etc. Therefore, it is of great value to carry out researches on the crystal growth mechanism, polymorph and morphology control, and growth orientation of Ca CO3. In this paper, we employed the widely ultilized gas diffusion method to achieve the supersaturation, chose the unique natural amino acid-L-cysteine to make the self-assembled monolayer and to induce the nucleation and growth of Ca CO3. The results showed that the L-cysteine self-assembled monolayer could succesfully control the crystal phase, morphologies and nuleating orientations. We also further discussed the inducing mechanism of L-cysteine self-assembled monolayer and the growth mechanism of Ca CO3 crystals. The main conclusions are as follows:1. Via the gas diffusion method, it was firstly found that different polymorphs and morphologies of Ca CO3 nucleated at different solution depths: at the upper area there were calcite crystals, at the lower area there were vaterite, interestingly is that in the mid part there were calcite and vaterite phases. Differ from the previous conclusion that the multiple crystallization of Ca CO3 is resluted of the experiment setups, in this paper we believe that the concentrion gradients of NH4+, NH3, p H, and the ratio of CO32- to Ca2+ is the inner elements.2. The L-cysteine self-assembled monolayer could avoid the influence of the concentrion gradients of solution, and effectively control the crystal phase of Ca CO3. Under the mild and near neutral p H environment, the uniform calcite rhombohedrons were obtained.3. By altering the diffusion time of solid ammunium carbonate and the initial solution p H, we succesfully achieved the control of nucleating orientations of calcite. With the near neutral solution p H, the self-assembled monolayer perfered the(001) crystal face to nucleate first; at relative higher p H, there prefered the(104) face. The fractions of(001) and(104) orientation cloud reach approximately 95% and 98%.4. L-cysteine molecule is a kind of amphoteric compound, whith could exibit amphoteric or neutral charactors in different p H environments. Basing on this property, calcite morphologies were controlled succesfully via a simple method. Between p H of 6.0~9.0, the self-assembled monolayer mainly induced the standard calcite rhombohedrons; by enhancing the solution alkalinty above 12.0, calcite crystals exhibit brand new morphologies with the pinecone shape and the polycrystalline sphere shape.5. By controlling of the aging temprature and pressure, we obtained a kind of calcite crystals with a novel morphology with the porous sponge-liked shape. This material greatly improved the hydrophobicity of the normal self-assembled monolayer. The simple synthetic process and good reproducibility of this experiment, the high stability and environmental friendly characters of the porous calcite crystals may have a broad application prospect in the future.