Sol–gel derived coating applied to long-period gratings for enhanced refractive index sensing properties

Long-period fibre gratings (LPGs) have previously been used to detect quantities such as temperature, strain, and refractive index (RI). We report here, to the best of our knowledge, the first investigation on refractive index sensing properties of LPGs with sol–gel derived titanium and silicon oxide coatings. It is revealed that the RI sensitivity of an LPG is affected by both the thickness and the index value of the coating; a coating with higher index and thickness will enhance the LPG RI sensitivity significantly. The surrounding refractive index induced LPG resonance shift has been evaluated over the LPGs' most sensitive RI region from 1.42 to 1.44. We have identified that, in this region, the uncoated LPG has an RI sensitivity of (-673.0 ± 0.4) nm/uri (unit of refractive index) while the LPG coated with titanium oxide exhibits a sensitivity as high as (-1067.15 ± 0.04) nm/uri. The experimental results also reveal that, even in the RI insensitive region around 1.33, there still is a marked enhancement in RI sensitivity of the sol–gel coated LPG compared to the uncoated one. This is potentially significant as coated LPGs may be extended to low RI gas and semi-liquidized based sensing applications.

Novel sol–gel preparation of (P2O5)0.4–(CaO)0.25–(Na2O)X–(TiO2)(0.35−X) bioresorbable glasses (X = 0.05, 0.1, and 0.15)

Quaternary phosphate-based glasses in the P2O5–CaO–Na2O–TiO2 system with a fixed P2O5 and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), 31P nuclear magnetic resonance (31P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The 31P NMR and FTIR results revealed that the glass structure consist of mainly Q1 and Q2 phosphate units and the Ti4+ cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing Na2O content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO2 content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed.

Spatially orthogonal chemical functionalization of a hierarchical pore network for catalytic cascade reactions

The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol–gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous–mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions.

Influence of La-doping on phase transformation and photocatalytic properties of ZnTiO3 nanoparticles synthesized via modified sol-gel method

Non-doped and La-doped ZnTiO3 nanoparticles were successfully synthesized via a modified sol–gel method. The synthesized nanoparticles were structurally characterized by PXRD, UV-vis DRS, FT-IR, SEM-EDS, TEM, Raman and photoluminescence spectroscopy. The results show that doping of La into the framework of ZnTiO3 has a strong influence on the physico-chemical properties of the synthesized nanoparticles. XRD results clearly show that the non-doped ZnTiO3 exhibits a hexagonal phase at 800 °C, whereas the La-doped ZnTiO3 exhibits a cubic phase under similar experimental conditions. In spite of the fact that it has a large ionic radius, the La is efficiently involved in the evolution process by blocking the crystal growth and the cubic to hexagonal transformation in ZnTiO3. Interestingly the absorption edge of the La-doped ZnTiO3 nanoparticles shifted from the UV region to the visible region. The photocatalytic activity of the La-doped ZnTiO3 nanoparticles was evaluated for the degradation of Rhodamine B under sunlight irradiation. The optimum photocatalytic activity was obtained for 2 atom% La-doped ZnTiO3, which is much higher than that of the non-doped ZnTiO3 as well as commercial N-TiO2. A possible mechanism for the degradation of Rhodamine B over La-doped ZnTiO3 was also discussed by trapping experiments. More importantly, the reusability of these nanoparticles is high. Hence La-doped ZnTiO3 nanoparticles can be used as efficient photocatalysts for environmental applications.

On the impact of Cu dispersion on CO2 photoreduction over Cu/TiO2

A family of Cu/TiO2 catalysts was prepared using a refined sol–gel method, and tested in the photocatalytic reduction of CO2 by H2O to CH4 using a stirred batch, annular reactor. The resulting photoactivity was benchmarked against pure TiO2 nanoparticles (synthesised by an identical sol–gel route). CO2 photoreduction exhibited a strong volcano dependence on Cu loading, reflecting the transition from 2-dimensional CuOx nanostructures to 3-dimensional crystallites, with optimum CH4 production observed for 0.03 wt.% Cu/TiO2.