Fabrication Of Hollow Silica Nanomaterials Using Nanocrystalline Cellulose As Templates

Hollow nanomaterials have important applications in biochemistry andmaterials fields such as drug release, catalytic, fuel, enzyme carrier, due to they havelarge specific surface area and the hollow internal structure. ParticuLarly, hollowsilica nanomaterials have attracted great interest because of its high melting point,non-toxic, high stability, and other special properties. Templating is the most usedmethod to fabricate hollow silica nanomaterials. In most of cases, the shape of theprepared hollow silica is spherical. Other shapes are rarely reported. CelluLose isthe most abundant and biodegradable natural polymer material on the planet.Compared with other templates, using celluLose as templates have a lot ofadvantages, since the plant cells are actually a system composed of nanomaterials.Rod-like nanocrystalline celluLose (NCC) can be obtained as template materials forfabrication of hollow silica though inorganic acid hydrolysis. NanocrystallinecelluLose was reported using as templates to fabricate hollow silica material in theliterature. In their procedures, nanocrystalline celluLose must be chemicallymodified, and then coated with a layer of silica gel. The process is too complicated.In this article, we report a simple approach to fabricate hollow silica nanomaterialsusing negatively charged NCC which obtained through suLfuric acid hydrolysis.In this investigation, we took advantage of the negatively charged property ofNCC and employed cationic surfactant cetyltrimethylammonium bromide (CTAB) toconvert the surface charge of NCC into positive to promote deposition of silicic acidsol. Then, the polycondensation reaction of TEOS exclusively took place at theparticles surface in the presence of ammonia following the so-called sol-gel process.As a consequence, silica-coated NCC particles were successfuLly prepared. Hollowsilica nanomaterials were finally obtained after calcination of the obtainedcomposite of silica/NCC to remove the organic template. The resuLts showed that:NCC with the length of ca.100-150nm and a diameter of ca.10-15nm wereprepared by hydrolysis of microcrystalline celluLose (MCC) in64%suLfuric acid at45°C after30min. Then NCC was used as template to prepare core-shell compositeof silica and NCC. The sol-gel reaction of TEOS was employed to coat NCC thoughelectrostatic attraction by adding CTAB in alkaline conditions. This paper mainlyinvestigated the influence of the dosage of CTAB, ammonia, TEOS, the ratio ofwater and ethanol on the formation of core-shell materials, and finally got the optimum experimental conditions:4mL of NCC dispersion (0.5%w/v),0.03g CTABwas dissolved in a mixture of40mL of H2O,20mL of EtOH,0.4mL of aqueousammonia, then the complex of silica/NCC was obtained well. The powder ofsilica/NCC composite was calcined at600℃for6hours to remove the organic NCCcore. The TEM image showed that: hollow silica particles are very uniform (rod-like)as NCC, with the length of around100-150nm, with the outer diameter in the rangeof30-40nm, and with the thickness of shell about10-15nm.FTIR spectra, TG, XRD, and BET were employed to characterize theintermediate and final products. From FTIR spectra it can be seen that strong IRabsorption bands appear at1100cm^-1,800cm^-1and470cm^-1.These are thecharacteristic absorption peaks of silica absorption peaks. TG showed that the heatstability of hollow silica has improved. XRD showed that both of them exhibited abread peak near20°, the characteristic peak of silica. All above data confirmed thatsilica has successfuL coated onto the surface of NCC. BET resuLts showed that thespecific surface area of silica-coated NCC was only36.42m²/g, while aftercalcination it increased up to1499.73m²/g. The increment of specific surface areawas caused not only by the exposure of interior surface, but also caused by theaddition of CTAB, which rendered the wall of mesoporous. So hollow silica obtainedin our experiment gave rise to a huge surface area, which is suitable for a number ofpromising applications.Innovations of this paper are:(1) Put forward a novel and simple method tofabricate hollow silica nanomaterials: using negatively charged NCC through thesuLfuric acid hydrolysis as templates, employing positively charged CTAB as bridgeto adsorb silica gel and for mesoporous wall structure to prepare high specificsurface area of the hollow silica nanomaterials.(2) Systematically investigated theinfluence factors of forming hollow silica to get the optimal control process.