Preparation And Properties Of Three-dimensional Network Structured SiO₂ And TiO₂ Nanomaterials Templated By Bacterial Cellulose

Bacterial cellulose（BC） possesses three-dimentional nanofibrous network structure which is similar to natural extracellular matrix. There are plenty of unique and uniform hydroxyl groups on BC fiber surface, which can be modified and composited. A new research area in inorganic mineralization of BC to form three-dimensional network nanomaterials, will be widely used in fields of catalysis, photoluminescence, magnetic property, wave-absorbing, solar cell, tissue engineering scaffold, and so on. In the process of inorganic formation, BC acts as the nucleation sites, sterichindrance and three-dimentional scaffold, which could decreases effectively the size of inorganic products to nanoscale. However, in previous researches, the acids or alkalis were used as catalyzers in the process of inorganics formation templated by BC, moreover, the inorganic particles were zero-dimensional. In this paper, a facile method using fewer raw materials with less steps was applied in the preparation of SiO₂ nanotubes, TiO₂ nanowires and TiO₂ nanotubes with three-dimensional network structure, during which the BC served as the mineralizing template, as well as the reactant and catalyzer.In this paper, the BC aerogel treated by ethanol was firstly immersed into 1M TEOS/ethanol solution at room temperature（RT） or-30 °C for 24 h, and then into ethanol/water（9 ml:1 ml） solution for 48 h to promote the reaction of hydrolysis and polymerization, finally the amorphous SiO₂-RT and SiO₂-30 nanotubes with three-dimensional network structure were obtained after freeze-drying and removing the BC template by calcined at 500 oC. The average diameter of SiO₂-RT and SiO₂-30 nanotubes was 63.1 nm and 43.7 nm, respectively, and the average nanotubal wall thickness was 18.6 nm and 9.0 nm, respectively. The characteristic peak of Si-O-C was found in Fourier transform infrared spectrum of SiO₂/BC-RT hybrid composite, shown that the combination between SiO₂ and BC fiber was chemical combination. TG/DSC results showed that the content of SiO₂ in SiO₂/BC-RT was 50.8 wt%, which was more than 34.8 wt% in SiO₂/BC-30, and the existence of SiO₂ reduced the pyrolysis temperature of BC template. The calculated results from nitrogen adsoption-desorption curves indicated the specific surface area of SiO₂-RT and SiO₂-30 was 177.1 m2·g-1 and 451.0 m2·g-1, respectively, and the mesopores size was 3.819 nm and 3.81 nm, respectively. The photoluminescence intensity in SiO₂-30 nanotube was higher than that in SiO₂-RT, because there was larger specific surface area, lower nanotubal density, and more defects in SiO₂-30 nanotube. The compressive stress of SiO₂-RT nanotube which acts as the potential tissue engineering scaffold, was 9.18 kPa when the strain is 60%. Mouse fibroblasts cells（L929） and human osteosarcoma cells（MG-63） were selected to estimate the biocompatibility of SiO₂-RT nanotubes. The growth state of cells on the edge of nanotubal scaffolds was observed via optical microscope, the cells growth state on nanotubal scaffolds was observed by SEM, and the influence of SiO₂ on cells growth was quantitaive tested by CCK-8. All those results indicated that the biocompatibility of SiO₂ were excellent.In order to obtain TiO₂ nanowires, the BC aerogel treated by isopropanol was firstly immersed into isopropanol solution of acetylacetonate and tetrabutyl titanium with the concentration of 0.1M and 0.3 M at RT for 24 h, and then into isopropanol/water（9 ml:1 ml） solution for the reaction of hydrolysis and polymerization for 48 h, the anatase TiO₂-01 nanowires with three-dimensional network structure were finally obtained after freeze-drying and calcined at 500 oC. The TiO₂ became anatase mixed with rutile after calcined at 600 oC, 700 oC or 800 oC. TG/DSC advised the 19.8 wt% and 52.4 wt% of TiO₂ content in TiO₂/BC-01-AcAc and TiO₂/BC-03-AcAc, and TiO₂ decreased the pyrolysis temperature of BC template. The photo degradation of methyl orange showed that higher calcination temperature lead to weaker photocatalysis ability of TiO₂ nanowires.The anatase TiO₂ nanotubes were prepared on the basis of the preparation of TiO₂ nanowires, by removing acetylacetone and calcinated at 500 oC. The TiO₂ was anatase after calcined at 600 oC, and anatase mixed with rutile after calcined at 700 oC or 800 oC. The characteristic peak of Ti-O-C was found in Fourier transform infrared spectrum of TiO₂/BC-01 hybrid composite, shown that it was chemical combination between TiO₂ and BC fiber. TG/DSC results showed that the TiO₂ content in TiO₂/BC-01 was 11.6 wt%, and TiO₂ decreased the pyrolysis temperature of BC template. The calculated results from nitrogen adsoption-desorption curves provided the special surface area and mesopores size of TiO₂-01 were 1629 m2·g-1 and 3.4 nm, respectively. The photodegradation results of methyl orange revealed that the photodegradation rate of TiO₂ nanomaterial calcined at 500 oC, 600 oC and 700 oC were close to 100% within 40 min. The compressive stress of TiO₂-01 nanotube, the potential tissue engineering scaffold, was 1.80 kPa at the strain of 60%. The L929 cells and the MG-63 cells were selected to estimate the biocompatibility of TiO₂-01 nanotubes. The growth state of cells on the edge of nanotubal scaffolds was observed via optical microscope, the cells growth state on nanotubal scaffolds was observed by SEM, and the influence of TiO₂ on cells growth was quantitaive tested by CCK-8. All those results indicated that the biocompatibility of TiO₂ were excellent.In summary, this paper studied and achieved a new approach to prepare SiO₂ nanotubes, TiO₂ nanowires and TiO₂ nanotubes with three-dimensional network structure, and carried on preliminary applications of photoluminescence, photocatalysis and biocompatibility.