Humin Cheng

The preparation, characterization, photoelectrochemical and photocatalytic properties of lanthanide metal-ion-doped TiO2 nanoparticles

Lanthanide metal-ion-doped TiO2 nanoparticles were prepared with hydrothermal method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP) and fluorescence spectrum. The results showed that a small part of metal ions entered into the lattice of TiO2 and others adsorbed on the surface of TiO2. The photoelectrochemical and photocatalytic properties of these lanthanide metal-ion-doped TiO2 nanoparticles were investigated and the results showed that the photoresponse of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 electrodes were much larger and that of Sm3+-doped TiO2 electrode was a little larger than that of undoped TiO2 electrode, indicating that the photogenerated carriers were separated more efficiently in Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than in undoped TiO2 nanoparticles. The photocatalytic degradation of rhodamine B (RB) was conducted in the suspension of lanthanide metal-ion-doped TiO2 nanoparticles, and its first-order reaction rate constant (k) and average initial rate (rini) were significantly higher in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than those in the presence of undoped TiO2 nanoparticles. The enhanced photocatalytic degradation rate of RB in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles is attributed to increased charge separation in these systems. The effect of the content of La3+ on the reaction parameters (k and rini) was also investigated and the result showed that there was an optimal value (ca. 0.5%) of the content of La3+ to make the rate constant (k) and average initial rate (rini) reach the maxima.

The photoelectrochemistry of transition metal-ion-doped TiO2 nanocrystalline electrodes and higher solar cell conversion efficiency based on Zn2+-doped TiO2 electrode

Metal-ion-doped TiO2 nanoparticles were prepared with hydrothermal method. The change of photocurrents at different electrode potentials and wavelengths of incident light showed two different characteristics for various transition metal-ion-doped TiO2 electrodes. In Zn2+ and Cd2+-doped TiO2 electrodes, a characteristic of n-type semiconductor was observed and the incident photon to conversion efficiency (IPCE) were larger than that of pure TiO2 electrode at the thickness of electrode film of 0.5 μm when the content of doped metal ion was less than 0.5%. The effect of the thickness of films on IPCE was also investigated. The IPCE of pure TiO2 electrode was strongly dependent on the thickness of films. The change tendency of the IPCE for Zn2+-doped TiO2 (0.5% Zn2+) electrodes with its thickness was different from that of pure TiO2. In Fe3+, Co2+, Ni2+, Cr3+ and V5+-doped TiO2 electrodes, a phenomenon of p-n conversion was observed. The difference of photoresponse and the value of photocurrents are dependent on the doping method and concentration of the doped metal ions. The maximum conversion efficiency of RuL2(SCN)2-sensitized Zn2+-doped TiO2 solar cell (1.01%) was larger than that of RuL2(SCN)2-sensitized pure TiO2 solar cell (0.82%) at the same conditions when 0.5 mol · l−1 (CH3)4N · I + 0.05 mol · l−1 I2 in propylene carbonate solution was used as electrolyte.

Formation of crystalline nanosized titania in reverse micelles at room temperature

Shuttle-like crystalline TiO2 nanoparticles were synthesized by hydrolysis of titanium tetrabutoxide in the presence of acids in NP-5 (Igepal CO-520)–cyclohexane reverse micelle at room temperature. Pure rutile nanoparticles were obtained at appropriate acid concentrations. The influences of various reaction conditions, such as concentration and type of acid, water content, H2O/Ti molar ratio, and reaction time, on the formation, crystal phase, morphology, and size of the TiO2 particles were investigated.

Preparation of BaSO4 nanoparticles in non-ionic w/o microemulsions

Abstract Spherical and cubic BaSO 4 nanoparticles with barite structure were synthesized in Triton X-100/ n -hexanol/cyclohexane/water water-in-oil microemulsions by mixing two separately prepared microemulsions containing (NH 4 ) 2 SO 4 and Ba(OAc) 2 , respectively. The effects of water content and the presence of (NH 4 ) 2 SO 4 on the size of the microemulsion droplets were investigated by dynamic light scattering. Particle characterization was accomplished by transmission electron microscopy and the effects of water content, holding time, surfactant content and reactant concentration on the particle characteristics were studied. Due to the cage-like nature of the microemulsion droplets, the size of the microemulsion droplets has a controlling effect upon the size of the particles prepared. As the water-to-surfactant molar ratio increases, both the particle size and its polydispersity increase in general. The particle shape was found to convert from spherical to cubic as the water content in the microemulsions increases. It has been shown that monodisperse cubic BaSO 4 nanoparticles can be produced inside spherical microemulsion droplets under suitable conditions.

Investigation on the conductivity and microstructure of AOT/non-ionic surfactants/water/n-heptane mixed reverse micelles

Abstract Properties and microstructures of mixed reverse micelles of anionic surfactant AOT and non-ionic surfactants in n -heptane were investigated using conductivity and dynamic light scattering. As in the reverse micelle formed with AOT alone, a conductivity maximum was also observed in conductivity- W 0 (molar ratio of water to surfactants) curves for mixed reverse micelles, and W 0,max (the W 0 where the conductivity reaches its maximum) moved to a smaller W 0 value with increasing non-ionic surfactant content and EO chain length. When NaCl solutions were solubilized by the mixed reverse micelles, the W 0,max moved to a larger W 0 value with increased concentration of NaCl solutions. These phenomena were interpreted in terms of the proposed physical meaning of W 0,max and the results of dynamic light scattering. The relationship between the conductivity of reverse micelles and their microstructures was discussed.

Synthesis and characterization of mixed CdSZnS nanoparticles in reverse micelles

Abstract Three different types of mixed CdSZnS semiconductor nanoparticles were synthesized in reverse micelles and were characterized by optical absorption and photoluminescence (PL) spectroscopy. The coprecipitated ZnxCd1−xS nanoparticles, comprised of homogeneously mixed crystals, show a continuously tunable energy gap from single CdS nanoparticles to ZnS nanoparticles. Coating the CdS core particles with a layer of ZnS in reverse micelles leads to ZnS-coated CdS (CdS/ZnS) nanoparticles with a core-shell structure, which show absorption and PL characteristics which differ considerably to those of either the coprecipitated particles or the sum of the separate particles. The intensity of the PL band centered at 630 nm, which arises from the coated CdS/ZnS nanoparticles, shows a maximum at a Zn/Cd molar ratio of about 1:1 on increasing the Zn/Cd ratio when the total concentration of CdS and ZnS is kept constant. CdS-coated ZnS (ZnS/CdS) nanoparticles synthesized in reverse micelles have absorption spectra similar to those of the coated ZnS/CdS nanoparticles but show no significant luminescence activation.

Solubilization behavior of mixed reverse micelles: effect of surfactant component, electrolyte concentration and solvent

Abstract Solubilization of water and aqueous NaCl solution in mixed reverse micellar systems formed with anionic surfactant AOT and nonionic surfactants in cyclohexane, n-hexane, n-heptane, n-octane and isooctane was studied. It was found that, for mixed reverse micelles, a maximum solubilization capacity of water occurred in the presence of a certain concentration of NaCl electrolyte which is indicated as Cmax. Cmax increased with increasing the content and EO chain length of the nonionic surfactant, and was significantly influenced by the solvent used. The physical meaning of Cmax was studied using dye-solubilization and percolation conductivity measurements. The solubilization capacity of water in reverse micellar systems was determined by two factors, the stability of the microdroplet interfacial film and the size of the microdroplet. For a reverse micellar system at constant temperature, a maximum solubilization capacity of water can be obtained by regulating the surfactant composition, the electrolyte content and the solvent.

Fluorescence probing of mixed reverse micelles formed with AOT and nonionic surfactants in n-heptane

Abstract The nature of the aqueous core of mixed reverse micelles formed with AOT and nonionic surfactants in n-heptane was investigated by fluorescence techniques. The emission properties of 1,8-anilinonaphthalenesulfonic acid (ANS) and tris(2,2′-bipyridine)ruthenium dichloride hexahydrate (Ru(bpy)32+) were found to be extremely sensitive to the solubilized water content. The fluorescence intensity decreases with increasing water content while the position of the emission maximum λmax shifts to longer wavelengths. The λmax of the fluorescence probe also depends on the added nonionic surfactant content and their EO chain length. The microstructure of the waterpool and the effect of added nonionic surfactants were studied by the fluorescence analysis of the two fluorescence probes from the viewpoint of their different location in mixed reverse micelles.

Conducting properties of mixed reverse micelles

Abstract The conducting properties of mixed reverse micelles formed with AOT and other surfactants have been investigated, with the emphasis on the effect of solvents and surfactant composition. The phenomena observed were interpreted according to the formerly proposed physical meaning of W0,max, which stands for the molar ratio of water to surfactants at the conductivity maximum of reverse micellar systems, and the results obtained from dynamic light scattering.

STUDY ON PERCOLATION OF MIXED REVERSE MICELLES

Abstract The temperature-induced percolation behaviors of AOT reverse micelles in the presence of nonionic surfactants have been studied. The effects of water content, solvent and concentration of electrolyte in solubilized water have also been investigated. It was found that the percolation temperature of AOT reverse micelles was decreased by adding nonionic surfactants, and more pronounced effects were observed with the increase of EO chain length and content of nonionic surfactants. The increase of molecular volume of the solvent and the increase of concentration of the added NaCl electrolyte have shown assisting and resisting effects on the process, respectively. The apparent hydrodynamic diameter of droplets of different mixed reverse micelles has been measured using dynamic light scattering, by which the percolating mechanism of mixed reverse micelles was discussed in combination with the results obtained from conductivity measurements.