| Layered materials are important function materials, and have a broad application prospect in many fields such as catalysis, adsorptions etc. In this research work, a series of layered materials, including titania-pillared layered niobic acid, CrOx-pillared layered niobic acid, hybrid materials of CdS with layered niobic acid, were prepared. The photo-degradation performances of rhodamine B by using these layered products as catalyst were investigated. The structures of the intercalated layered intermediates and the final layered product were characterized in detail by means of powder XRD, Fourier transformation infrared spectra(FT-IR), UV-Vis diffuse reflectance(DR-UVVis) and scanning electron micrographs(SEM) techniques.(1) Preparation and photocatalytic property of titania-pillared layered niobic acidBy employing layered niobic acid(HNb3O8) as the host, tetra-n-butyl titanate((C4H9O)4Ti, abbreviated as TBT) as the titanium source, Ti(IV) polycationsintercalated layered niobic acid were synthesized with a stepwise ions-exchange way. Upon calcination in air environment, titania-pillared layered niobic acid(abbreviated as TiO2-HNb3O8) was obtained. To obtain the pillared layered product with a high thermal stability and a well-ordered layered structure, a series of titanium-pillaring solutions with various Ti(IV)-polycation concentrations were used. The Ti(IV) polycations-intercalated layered intermediate produced by the exchange reaction between n-decylamine-pre-swelled layered niobic acid and a dilute titanium-pillaring solutions(V(TBT) : V(CH3COOH) : V(H2O) = 1 : 16 : 40) showed a bad layered structure and a relatively-low thermal stability, though its interlayer distance was rather large. The Ti(IV) polycations-intercalated layered intermediate prepared by using the titanium-pillaring solutions obtained with V(TBT) : V(CH3COOH) : V(H2O) = 1 : 16 : 20 ratio had good thermal stability as well as the layered structure not only, but also its interlayer distance is relatively large. Compared with un-pillared layered HNb3O8, the titania-pillared layered HNb3O8(TiO2-HNb3O8) had a high photocatalytic activity. When the TiO2-HNb3O8 sample prepared based on V(TBT) : V(CH3COOH) : V(H2O) = 1 : 16 : 20 was employed as the catalyst, 92% of rhodamine B(50 mL, 10 mg?L-1 solution) was degraded after irradiation 2 h with an UV-light, and 20% of that was degraded after 2 h under visible light.(2) Preparation of CrOx-pillared layered niobic acid by exfoliating-reassembling technique and catalytic property of the pillared layered productsIn this part, the exfoliating-reassembling technique was used. The nanosheets constituting the layered frame Nb3O8- was generated firstly, then the dispersed nanosheets was mixed with chromium(III) acetate(Cr(OAc)3) aqueous solution. Upon refluxing, the Cr(III)-polycations gradually produced, and the dispersed nanosheets aggregated with change of p H at the same time. Thus, the as-produced Cr(III)-polycations could be intercalated into the interlayer regions of the aggregated layered niobic acid, giving rise to Cr(III)-polycations-intercalated layered intermediate. Upon calcination, the CrOx-pillared layered niobic acid(abbreviated as CrOx-HNb3O8) could be obtained. It was found that the concentration of chromium(III) acetate aqueous solution had no significant effect for the intercalation performance. The as-prepared CrOx-HNb3O8 was active for photo-degradation reaction of rhodamine B under both UV and visible light. For example, when using the CrOx-pillared layered niobic acid with 9.35 wt% chromium as catalyst, we found that 35% rhodamine B(50 m L, 10 mg?L-1 solution) was degraded after irradiation 2 h with an Uv-light; when the CrOxHNb3O8 sample with chromium content of 9.07 wt% was employed as catalyst, about 32% of rhodamine B was degraded after 2 h under visible-light irradiation. For the CrOx-HNb3O8 sample with relatively-high chromium content, the catalytic performance could be effectively improved by doping the layered sample with nitrogen.(3) Hybridization of CdS with niobic-acid nanosheets, and catalytic property of the hybrid materialsBy employing tetrabutyl ammonium hydroxide as the exfoliating agent, the layered niobic acid(HNb3O8) was exfoliated firstly, generating highly-dispersed nanosheets. Then by using cadmium nitrate(Cd(NO3)2) as a cadmium source, and thiourea as a precipitance, CdS was produced in the supernatant solution containing highly-dispered nanosheets. At the same time, the nanosheets aggregated quickly by changing pH value of the system. Thus, the hybridization of CdS with niobic-acid nanosheets could be achieved. Compared CdS or HNb3O8, under visible-light irradiation, the hybrid materials(Abbreviated as CdS-eHNb3O8) showed a high catalytic active for photo-degradation reaction of rhodamine B, indicating that there was a synergy between CdS and layered HNb3O8. It was also found that the band-gap energy of the hybrid materials decreased with increasing Cd content. The hybrid materials with 44.96 wt% Cd showed the best catalytic activity. Its band-gap energy was 2.04 eV. When this hybrid material was employed as the catalyst, after 2 h with visible-light irradiation, about 91% of rhodamine B was degraded. Upon nitrogendoping, the photocatalytic activity of the hybrid materials decreased significantly, indicating that nitrogen-doping could restrain seriously the synergy between CdS and layered HNb3O8. |
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