Biomimetically Synthesis Of Micro-and Nanostructured Titania With Induced By Polyamines And Related Molecules At Room Temperature

It is well known that nature possesses the ability to produce biominerals withexquisite nanostructures under inherently benign conditions (low temperature,ambient pressure, and near-neutral pH). Hence, the development of biomimeticsynthetic pathways to widely used inorganic materials, such as titanium dioxide, is ofgreat importance in the context of green-chemistry principles, and for potential scaleup in energy efficient ways (biomimetic titanification). However, it is difficult toreveal the mechanism of interaction between the organic molecules, titaniumprecursors, and titanium dioxide, which caused that the tailoring of size, morphology,and polymorphs of titanium dioxide in this method is far less sophisticated than thatof traditional synthesis; and the technological application of final products has beenstrongly hindered.In this paper, the polyamines and related molecules were employed to mediate theformation of titanium dioxide with different sizes, morphologies, and polymorphs,which might provide new insights into in vitro bio-enabled titanium dioxide formationand pave the way for further controllable biomimetic synthesis of titania through theuse of tailor-made organic molecules; and the obtained TiO2showed excellentperformance in applications. The details in this study were summarized as follows:Firstly, we demonstrated the glucan polymers mediated syntheses of titania atroom temperature, which is a energy-conserving and environmentally benignsynthetic pathway. Wormhole-like particles (both rutile and anatase) with high surfaceareas and quasi-sphere shaped particles (anatase) were obtained for chitosan, sodiumalginate and cellulose, respectively; particularly, we observed the phasetransformation from anatase to rutile in the chitosan mediated titania process;experimental results revealed a distinct dependence of the phase transformation on theprotonation level of amino groups in chitosan. The obtained results suggest thatdifferent charged groups of glucan polymers strongly impacted on the size, shapes andpolymorphs of the obtained titania particles.Secondly, poly(allylamine hydrochloride)(PAH), a mimic of biopolyamines, wasused as catalytic template for fabricating a novel nanostructure of titanium dioxide atroom temperature, for the first time, hollow spheres with mixed phases (anatase andrutile) were obtained through a biomimetic synthetic route, and the tiny anatase andrutile nanocrystals were observed mixing at sub-10nm scale on the hollow spheres.The structural information about the precipitated titanium dioxide gained bytransmission electron microscopy, X-ray diffraction and X-ray photoelectronspectroscopy revealed a distinct dependence of the polymorph and morphology of the titanium dioxide precipitates on the molecular structure of the polyamines andtitanium precursors. Moreover, we observed the phase transformation from anatase torutile in the formation process of hollow spheres, and it was suggested that theprotonated amino groups on PAH played a key role in the transformation of bothpolymorphs and morphologies of titanium dioxide. The PAH-mediated titaniumdioxide hollow spheres showed high photocatalytic performance in the degradation ofrhodamine B, which could be largely attributed to its unique nanostructure.Additionally, poly(diallyldimethylammonium chloride)(PDDA), a long chainquaternary amine polymer, was used as another catalytic template for biomimeticsynthesis of titanium dioxide, which also led to a hollow structure with a mixture ofanatase and β-TiO2.Lastly, we reported that the graphene oxides (GO) with better electronegative areformed by using solvent green (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt,SG) adsorption on GO surface through π-π stack interaction; and these negativelycharged GO are exposed in a lysine solution to prepare GO-SG-Ly hybrid templates.Then, the positively charged lysine layers induced the hydrolysis and condensation ofTi precursor, to form the GO-TiO2hybrid nanosheets. More importantly, the amountof TiO2can be controlled by varying the polymerization of lysine.