The relationship between microstructure and photocatalytic behavior in lanthanum-modified 2D TiO2 nanosheets upon annealing of a freeze-cast precursor

Effect of Multiply Twinned Ag(0) Nanoparticles on Photocatalytic Properties of TiO2 Nanosheets and TiO2 Nanostructured Thin Films

Ag-decorated TiO₂ nanostructured materials are promising photocatalysts. We used non-standard cryo-lyophilization and ArF laser ablation methods to produce TiO₂ nanosheets and TiO₂ nanostructured thin films decorated with Ag nanoparticles. Both methods have a common advantage in that they provide a single multiply twinned Ag⁽⁰⁾ characterized by {111} twin boundaries. Advanced microscopy techniques and electron diffraction patterns revealed the formation of multiply twinned Ag⁽⁰⁾ structures at elevated temperatures (500 °C and 800 °C). The photocatalytic activity was demonstrated by the efficient degradation of 4-chlorophenol and Total Organic Carbon removal using Ag-TiO₂ nanosheets, because the multiply twinned Ag⁽⁰⁾ served as an immobilized photocatalytically active center. Ag-TiO₂ nanostructured thin films decorated with multiply twinned Ag⁽⁰⁾ achieved improved photoelectrochemical water splitting due to the additional induction of a plasmonic effect. The photocatalytic properties of TiO₂ nanosheets and TiO₂ nanostructured thin films were correlated with the presence of defect-twinned structures formed from Ag⁽⁰⁾ nanoparticles with a narrow size distribution, tuned to between 10 and 20 nm. This work opens up new possibilities for understanding the defects generated in Ag-TiO₂ nanostructured materials and paves the way for connecting their morphology with their photocatalytic activity.

Surface Properties of 1DTiO2 Microrods Modified with Copper (Cu) and Nanocavities

This work deals with Cu-modified 1DTiO2 microrods (MRs) and their surface properties. The pristine lyophilized precursor Cu_1DTiO2, prepared by an environmentally friendly cryo-lyophilization method, was further annealed in the temperature interval from 500 to 950 °C. The microstructure of all samples was characterized by electron microscopy (SEM/EDS and HRTEM/SAED), X-ray powder diffraction (XRD), infrared spectroscopy, simultaneous DTA/TGA thermoanalytical measurement, and mass spectroscopy (MS). Special attention was paid to the surface structure and porosity. The 1D morphology of all annealed samples was preserved, but their surface roughness varied due to anatase-rutile phase transformation and the change of the nanocrystals habits due to nanocavities formation after releasing of confined ice-water. The introduction of 2 wt.% Cu as electronically active second species significantly reduced the direct bandgap of 1DTiO2 in comparison with undoped TiO2 and the standard Degussa TiO2_P25. All samples were tested for their UV absorption properties and H2 generation by PEC water splitting. We presented a detailed study on the surface characteristics of Cu doped 1DTiO2 MRs due to gain a better idea of their photocatalytic activity.

Photocatalytic production of dihydroxyacetone from glycerol on TiO2 in acetonitrile

In this paper, photocatalytic production of dihydroxyacetone (DHA) from glycerol in acetonitrile on TiO₂ was investigated. HPLC-MS analysis showed that glycerol was converted to DHA, glyceraldehyde (GAD), glyceric acid and several other chemicals. Using acetonitrile as the reaction medium instead of water not only provided a more selective process for production of DHA but also increased the glycerol conversion. After 300 min, with 1 g L⁻¹ catalyst loading and 4 mM initial glycerol concentration, glycerol conversion and DHA selectivity were 96.8% and 17.8% in acetonitrile compared to 36.1% and 14.7% in water, respectively. The half-life of glycerol decreased by a factor of 6.2, from 467 min to 75 min, by changing the solvent from water to acetonitrile. Experiments using biodiesel-derived crude glycerol verified the effectiveness of the proposed process for the photocatalytic production of DHA from crude glycerol. A mechanism was proposed to explain the higher selectivity towards DHA over GAD in this process.

Photocatalytic conversion of glycerol and selectivity for dihydroxyacetone production was increased by using acetonitrile as the reaction medium.