Gan Zhang

I am a chemist from China. I joined the Prof. Juan Manuel García Ruiz’s group in 2010 when I started the master and PhD study in Crystallization and Crystallography, and received the PhD title in 2015. My research in the group towards the polymorphic and morphological control of the crystallization of calcium carbonate as well as the hydrate forms in alkaline silica-rich media, to explore the morphogenetic mechanism of silica biomorphs. My work is strongly related to silica carbonate biomorphs, the purely inorganic materials but exhibited a wide range of biomimetic behaviors which are reminiscent of living organisms. This work is part of the research of Project PROMETHEUS, which leads to the further understanding of the early geological and biological history of Earth.

Silica-carbonate biomorphs are self-assembled crystalline materials exhibit a wide range of biomimetic morphologies without the constraints of crystallographic symmetry. These materials are composed of carbonate nanocrystals in well-defined orientations displaying complex structure from macro to nanoscale. Compared to the biominerals in living organisms as well as most of the biomimetic materials under the guideline of organic compound, silica-carbonate biomorphs are totally abiotic and occur in moderately alkaline silica-rich environment (pH range from 11 to 8.5). So far this abiotic “life-like” phenomenon has been discovered and studied through barium carbonate and strontium carbonate.

My PhD thesis was titled “Morphogenesis of self-assembled crystalline materials of calcium carbonate and silica”, and it mainly focused on the crystallization and growth behaviors of polymorphic calcium carbonate and the hydrated form (monohydrocalcite, CaCO3·H2O) in silica-rich alkaline environments, to discover the mechanism of the morphogenesis of calcium carbonate minerals structures in alkaline silica-rich media. In addition, this thesis also included the study on the crystallization of barium carbonate under the similar conditions, to explore the relation between biomorphic calcium carbonate and biomorphic barium carbonate, aiming to elucidate the key factor of the formation of silica-carbonate biomorphs.

In this thesis, I reported the concomitant growth of aragonite and calcite under the same chemical environment, but adopted different growth processes and displayed different morphologies: calcite adopted rhombohedral and preserved the crystallographic continuity and symmetry in shapes, while aragonite broke crystallographic symmetry and exhibited complex biomimetic shapes with typical features of biomorphs. This dramatic difference between the crystallization behaviours of the two minerals phases was explained by the difference in the growth mechanisms at nanoscale. Besides, I have also reported a new pathway to produce stable monohydroalcite in alkaline silica-rich solution, and silica was proved to play a key factor on the morphogenesis of monohydrocalcite. Under certain temperatures, this kind of monohydrocalcite also exhibited biomorphic morphology and texture. This finding was first time to present biomorphic behaviours for carbonate minerals with crystalline structures other than orthorhombic, and it clearly indicates that the crystal lattice is not the key factor in the formation of biomorphs. In addition, I also developed a novel fluorescence microscopy technique which allowed measuring the local pH in microenvironment in alkaline aqueous solution. An oscillatory behavior of pH at the growth front of biomorphs was discovered by this technique, and it first time experimentally demonstrated the chemical coupling of carbonate and silica versus the variation of pH during the growth of biomorphs, and provided further understanding of the mechanism behind the morphogenesis of biomorphs.

Parts of the results in this thesis have been published in the journals listed below:

  1. Zhang, G.; Delgado-Lopez, J. M.; Choquesillo-Lazarte, D.; Garcia-Ruiz, J. M., Crystallization of monohydrocalcite in a silica-rich alkaline solution. CrystEngComm 2013, 15, (33), 6526-6532.
  2. Zhang, G.; Delgado-López, J. M.; Choquesillo-Lazarte, D.; García-Ruiz, J. M., Growth Behavior of Monohydrocalcite (CaCO3·H2O) in Silica-Rich Alkaline Solution. Crystal Growth & Design 2015, 15, (2), 564-572.
  3. Zhang, G.; Morales, J.; Garcia-Ruiz, J. M., Growth behaviour of silica/carbonate nanocrystalline composites of calcite and aragonite. Journal of Materials Chemistry B 2017, 5, (8), 1658-1663.
  4. Montalti, M.; Zhang, G.; Genovese, D.; Morales, J.; Kellermeier, M.; García-Ruiz, J. M., Local pH oscillations witness autocatalytic self-organization of biomorphic nanostructures. Nature Communications 2017, 8, 14427.
  5. Zhang. G.; Morales, J.; Verdugo-Escamilla, C.; García-Ruiz, J. M., Crystallization of biomorphic monohydrocalcite in silica-rich alkaline solutions. (On submission).

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