Dithiol-mediated immobilization of CdS nanoparticles from reverse micellar system onto Zn-doped silica particles and their high photocatalytic activity

Cds nanoparticles, prepared in a reverse micellar system, were immobilized directly onto alkanedithiol-modified Zn-doped silica particles, which were themselves prepared via hydrolysis of tetraethylorthosilicate in the presence of Zn(NO(3))(2) followed by contact with dithiol molecules. The resulting CdS-Zn-SiO(2) composite was then used as a photocatalyst for the generation of H(2) from 2-propanol aqueous solution. Under UV irradiation (lambda>300 nm), a high photocatalytic activity was observed for the CdS-Zn-SiO(2) composite material. This is effected by electron transfer from the photoexcited ZnS (dithiol-bonded Zn on SiO(2)) to CdS nanoparticles. The photocatalytic activity is increased with a decrease in the number of methylene groups in the dithiol molecules, according to the rank order 1,10-decanedithiol <1,6-hexanedithiol <1,2-ethanedithiol.     

Incorporation of CdS Nanoparticles Formed in Reverse Micelles into Mesoporous Silica

The incorporation of CdS nanoparticles, prepared in reverse micellar systems, into thiol-modified mesoporous silica, such as FM41 (functionalized MCM-41) and FM48 (functionalized MCM-48), has been investigated. The nanoparticles were immobilized in the mesopores via the incorporation of water droplets of the reverse micelles. A particle-sieving effect for FM41 having large (L-FM41, 3.8 nm) and medium (M-FM41, 3.6 nm) pore size was observed, in that the incorporation of the CdS nanoparticles was decreased with increasing particle size and with decreasing pore size of the FM41. Chemical vapor deposition treatment employed to narrow the mesopores of the CdS-FM41 enhanced the stability of CdS nanoparticles against heat treatment. The CdS-FM41 composites demonstrated photocatalytic activity for H(2) generation from 2-propanol aqueous solution, the better photocatalytic activity being obtained with the larger pore size for CdS-L-FM41. Copyright 2001 Academic Press.     

Preparation of Gd(2)O(3) : Eu(3+) and Gd(2)O(2)S : Eu(3+) phosphor fine particles using an emulsion liquid membrane system

Size- (submicrometer-sized) and morphology- (spherical) controlled composite Gd-Eu oxalate particles were prepared in an emulsion liquid membrane (water-in-oil-in-water emulsion) system. The oxalate particles thus prepared were calcined in air to obtain Gd(2)O(3) : Eu(3+) phosphor particles and in sulfur atmosphere to obtain Gd(2)O(2)S : Eu(3+) phosphor particles. These submicrometer-sized spherical phosphor particles showed photoluminescence properties with emission peak at 614 nm for Gd(2)O(3) : Eu(3+) and 628 nm for Gd(2)O(2)S : Eu(3+).     

Immobilization of RuS2 Nanoparticles Prepared in Reverse Micellar System onto Thiol-Modified Polystyrene Particles and their Photocatalytic Properties

RuS₂ nanoparticles, smaller than 3 nm in diameter, were prepared by H₂S gas injection into the AOT/isooctane reverse micellar solution containing RuCl₃ aqueous solution. The nanoparticle size was found to be independent of the W_o (water content) value of the reverse micellar system, as shown by TEM observation. The recovery and immobilization of the RuS₂ nanoparticles from reverse micelles onto thiol-modified polystyrene particles (PSt-SH) were successfully carried out, by the addition of PSt-SH into the reverse micellar solution under conditions of mild stirring. The resulting composites, PSt-RuS₂, showed photocatalytic activity for H₂ generation form aqueous solution containing 2-propanol and Na₂SO₃ as sacrificial electron donors.     

Atomic Force Microscopy Study of Ultrafine Particles Prepared in Reverse Micelles

The imaging of ultrafine Au, Pd, CdS, and ZnS particles prepared in reverse micelles has been studied by atomic force microscopy (AFM). Mica substrates, derivatized with a monolayer of amine or thiol-terminated silanes, were used to immobilize the particles. The substrates were exposed to reverse micellar solutions containing the particles and were then immersed in appropriate solvent media to remove surfactants. This resulted in a partial coating of the surfaces by the particles. The particle size was estimated as the height of protrusion, shown on the AFM images. The size values for the Pd and CdS particles, thus obtained, were found to be almost identical to those obtained by transmission electron microscopy (TEM), whereas those for the Au and ZnS particles were larger than those obtained by TEM. Scanning electron microscopy showed that the Au particles tended to aggregate on the surfaces, while Pd particles were isolated from one another. Copyright 2000 Academic Press.     

Preparation of Y2O3 nanoparticulate thin films using an emulsion liquid membrane system

Y2O3 nanoparticulate thin films have been prepared using an emulsion liquid membrane (water-in-oil-in-water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as a surfactant and VA-10 (2-methyl-2-ethylheptanoic acid) as an extractant (cation carrier). Yttrium ions were extracted from the external water phase and stripped into the internal water phase to make precursor oxalate nanoparticles. Y2O3 nanoparticulate thin film was prepared by casting the W/O emulsion, separated from the external phase and containing the Y oxalate nanoparticles, on a Si substrate, followed by calcination in air. Well-arranged thin-layer nanoparticulate film, consisting of Y2O3 nanoparticles smaller than 20 nm, was obtained via spin coating of the W/O emulsion. A multilayer nanoparticulate thin film was also fabricated via a simple procedure of repeated coating and subsequent calcination.     

Dithiol-mediated incorporation of CdS nanoparticles from reverse micellar system into Zn-doped SBA-15 mesoporous silica and their photocatalytic properties

CdS nanoparticles, as prepared in reverse micellar systems, were incorporated into alkanedithiol-modified Zn-doped SBA-15 mesoporous silica (dtz.sbnd;ZnSBA-15; pore diameter, ca. 4 nm), which were themselves prepared via hydrolysis of tetraethylorthosilicate (TEOS) in the presence of Zn(NO(3))(2) and triblock copolymer, as a nonsurfactant template and pore-forming agent, followed by contact with dithiol molecules. A particle-sieving effect for the dtz.sbnd;ZnSBA-15 was observed, in that the incorporation of the nanoparticles was remarkably decreased with increasing the nanoparticle size. The resulting CdSz.sbnd;ZnSBA-15 composite was then used as photocatalysts for the generation of H(2) from 2-propanol aqueous solution. Under UV irradiation (lambda>300 nm), a high photocatalytic activity was observed for this composite material. This is effected by electron transfer from the photoexcited ZnS (dithiol-bonded Zn on SBA-15) to CdS nanoparticles. The photocatalytic activity is increased with a decrease in the number of methylene groups in the dithiol molecules, according to the rank order 1,10-decanedithiol < 1,6-hexanedithiol < 1,2-ethanedithiol.     

Preparation of Y2O3:Eu3+ nanoparticles in reverse micellar systems and their photoluminescence properties

Y2O3:Eu3+ phosphor nanoparticles (4-8 nm in size) with spherical morphology and narrow size distribution were obtained by calcination of composite Y-Eu hydroxide nanoparticles, which were prepared in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane or polyethylene glycol mono-4-nonylphenyl ether (NP-5)/cyclohexane reverse micellar systems. This was achieved by the incorporation of the Y-Eu hydroxide nanoparticles into polyurea (PUA) via in situ polymerization of hexamethylene diisocyanate (HDI) in the reverse micellar solution and subsequent calcination of the resulting PUA materials. The emission intensity of the Y2O3:Eu3+ nanoparticles, prepared in the AOT/isooctane system, was significantly lower than that of the micrometer-size particles prepared in a homogeneous aqueous solution, since the calcined nanoparticles contained Na2SO4 impurity derived from the remaining AOT surfactant. The nanoparticles prepared in the NP-5/cyclohexane system, in contrast, showed higher emission intensity compared to the nanoparticles prepared in the AOT/isooctane system and longer luminescence lifetime compared to the micrometer-size particles prepared in the homogeneous aqueous solution. The photoluminescence intensity of Y2O3:Eu3+, prepared via the proposed process was found to decrease with decreasing the particle size.