Synthesis Of Hierarchical Carbonate Superstructures,Investigation Of Their Growth Mechanism And Treatment Of Chromium Pollution

As important bio-or geological minerals,carbonates are ubiquitous in nature.Biologically,carbonate biominerals usually display delicate morphology and remarkable microstructures,which exhibit self-assemblies of building blocks in the various scales.They are widely utilized by the organism as protective shells,supportive skeletons,and light-sensitive or gravity sensor organs.Geologically,deposition of carbonates can be put to beneficial use as a means of sequestering carbon dioxide.Meanwhile,carbonates are cheap,good biocompatibility and biodegradability and easy synthesis to hierarchical superstructures,which can be applied as industrial fillers,drug carriers and pollutant treatment reagents.In this dissertation,we report a new reactive system to produce worm-like,helical superstructures and 3D periodic motifs with a cationic polyelectrolyte was applied to effectively induce liquid precursor in the mineral solution.Moreover,nanosheet-structured Ba CO3 controlled by free phosphate anions were also reported.From the studies above,the regulatory mechanism of various inorganic additives and the formation mechanism of nonequilibrium architectures were analyzed and explained by the growth process of nonequilibrium mineral morphologies.The main results and conclusions were summarized as follows:1.Pure carbonate “biomorphs” with sinuous off-equilibrium morphologies including hinge-like,spiral and worm-like architectures have been synthesized for the first time in a cationic polyelectrolyte-induced liquid precursor process.During the formation of these superstructures,the process-directing reagent of poly(allylamine hydrochloride)and the synergetic doping ions(Mg2+,Sr2+ and Ba2+)will fine-tune the properties of liquid mineral phases,the polymorph switch and resultant morphologies.Use of the liquid precursor in which various species and amount of doping ions are employed offers excellent intermediates to build a variety of biomorphic superstructures.The conclusion is drawn that local microenvironments,intricate changes of mineral solution,growth fronts and preformed structure could direct the evolution of biomorphs.The corresponding work includes(a)wormlike and helical superstructures of vaterite and wheat-like superstructures of calcite obtained by Ca-Mg systems;(b)In Ca-Ba systems,low barium fractions(χBa<4.7%)will result into vaterite fibers composed of nanosheets,minerals composed of nanosheets are confirmed that they are vaterite phase.At 25% <χBa <47%,these minerals can develop into helicoidal structures;(c)In Ca-Sr systems,at 4.7% < χSr<23%,vaterite phase took up a major proportion where globules,worms and helices can be observed.Our research corroborates that abundant biomimetic structures can be achieved in the PILP process with the combination of the doping ions,and this study may provide a universal approach.2.Remarkable self-organized spatial patterns with concentric bands or rings were demonstrated here in the poly(allylamine hydrochloride)(PAH)controlled nonclassical crystallization process,with the combination of various doping strontium ions.These periodically dynamic patterns were composed of aragonite nanoparticles,which were arranged vertical to the interface of bands.Experiments showed that higher strontium content in bulk solution were advantageous to the growth of patterns.Growth of these self-assembled motifs was determined by the two alternating proceses: formation of new liqud mineral phase and crystallization process around the above intermediates.3.A feasible strategy was reported for the first time to synthesize nanosheet-structured Ba CO3 microspheres(NSBCs)under the controlling of phosphate,which could be used as effective adsorbents for the removal of Cr(VI)ions.The possible formation mechanism of NSBCs has been thoroughly explored by the time-resolved experiments.Evidences revealed that NSBCs were developed from the initial amorphous aggregates,and then gradually crystallized into plate-shaped particles,and finally to NSBCs composd of intersectional nanosheets.NSBCs showed an excellent adsorption capacity of Cr(VI)(max=227 mg g-1)and rapid removal effiency within 60 min.The kinetic and isotherm processes of adsorption could fit well with a pseudo-second-order model and Langmuir adsorption model,respectively.The superior behavior of NSBCs for Cr(VI)removal from an aqueous solution should be amenable to the potential application in water treatment and cleaning in consideration of low-cost investment,the favorable adsorption process as well as as well as the recovery of chromium resource.