Sol-gel preparation and characterization of Co_3O_4 nanocrystals

A new citrate acid-hydrazine sol-gel route for preparation of Co3O4 nanoparticles has been developed. Co3O4 nanoparticles with different particle-sizes and morphology were prepared at different heat-treatment temperatures and the pure cubic nanocrystals of Co3O4 were obtained at 600℃. The synthesis process was monitored by infrared spectroscopy (IR), thermal gravimetric and differential thermal analysis (TG-DTA). The structure and morphology of Co3O4 nanocrystals were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The infrared absorption bands blue-shifted with particle size decreasing, which could be attributed to increasing surface effect. XPS results showed that predominant species at surface layers of Co3O4 nanocrystals are octahedral Co (Ⅲ).

Surface Microstructure Characterization of Sol-gel Derived Porous TiO_2 Thin Films

Porous TiO2 thin films were prepared from alkoxide solutions with and without polyethylene glycol (PEG) by sol-get route on soda lime glass, and were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that TiO2 film prepared from precursor solution without PEG is composed of spherical particles of about 100 nm and several nanometer mesoporous pores. With the increase of the amount of PEG added to the precursor solution, the diameter and the depth of the pores in the resultant films increas on the decomposition of PEG during heat-treatment, which lead to them increase of the surface roughness of the films. XRD and TEM results show that the single anatase phase is precipitated and there are some orientation effects in (101) direction.

Sol-gel derived bioactive hydroxyapatite/titania composite films on Ti6Al4V

The composite films consisting of the titania gel impregnated with hydroxyapatite （HAP） submicron particles were prepared on commercial Ti6A14V plates processed by a sol-gel route. HAP powders were synthesized based on wet chemical precipitation method with Ca（NO3）2.4H2O and （NH4）2HPO4 as starting reagents. After being calcined at 900℃, HAP powders were ultrasonically scattered in ethanol to produce HAP sol. The titania sol was prepared using titanium （IV） isopropoxide {Ti[OCH（CH3）2]4} as precursor. Both the titania sol and the HAP/titania mixture were sequentially spin-coated on the substrates and calcined at various temperatures. The characteristics and mechanical adhesion of the composite films were investigated. The results show that the as-prepared films are dense, homogeneous, well-crystallized, and there is a good interfacial adhesion between the film and the substrate. The in vitro bioactivities of these films were discussed based on the analysis of the variations of Ca and P concentrations in the simulated body fluid and their surface morphologies against immersion time.

Low-temperature catalytic methane deep oxidation over sol-gel derived mesoporous hausmannite (Mn_(3)O_(4)) spherical particles

In this study,Mn_(3)O_(4) spherical particles(SPs)were synthesized by the sol-gel process,after which they were thermally annealed at 400℃,and comprehensively characterized.X-ray Diffraction(XRD)revealed that Mn_(3)O_(4) exhibited a tetragonal spinel structure,and Fourier transformed infrared(FTIR)spectroscopy identified surfaceadsorbed functional groups.Scanning electron microscopy(SEM)and the specific surface area analyses by Brunauer−Emmett−Teller(BET)revealed a porous,homogeneous surface composed of strongly agglomerated spherical grains with an estimated average particle size of∼35 nm,which corresponded to a large specific surface area of∼81.5 m^(2)/g.X-ray photoelectron spectroscopy(XPS)analysis indicated that Mn_(3)O_(4) was composed of metallic cations(Mn^(4+),Mn_(3)+,and Mn^(2+))and oxygen species(O_(2)−,OH−and CO_(3)2−).The optical bandgap energy is∼2.55 eV.Assessment of the catalytic performance of the Mn_(3)O_(4) SPs indicated T90 conversion of CH4 to CO_(2) and H2O at 398℃ for gas hourly space velocity(GHSV)of 72000 mL^(3) g^(−1) h^(−1).This observed performance can be attributed to the cooperative effects of the smallest spherical grain size with a mesoporous structure,which is responsible for the larger specific surface area and available surface-active oxygenated species.The cooperative effect of the good reducibility,higher ratio of active species(OLat/OAds),and results of density functional theory(DFT)calculations suggested that the total oxidation of CH4 over the mesoporous Mn_(3)O_(4) SPs might take place via a two-term process in which both the Langmuir−Hinshelwood and Mars−van Krevelen mechanisms are cooperatively involved.