Sang Moon Lee

Influence of visible-light irradiation on physicochemical and photocatalytic properties of nitrogen-doped three-dimensional (3D) titanium dioxide.

We report highly active visible-light driven nitrogen-doped three-dimensional polycrystalline anatase TiO2 photocatalysts (N-3D TiO2) for environmental and biomedical applications. N-3D TiO2 is synthesized at a low temperature (<90°C) without thermal treatment via a modified hydrothermal process (HP) and ultrasound irradiation (UI). The N-3D TiO2 is additionally irradiated with visible-light to improve the hydroxylation of its surface. Under visible-light irradiation, the photocatalytic activity of visible-light irradiated N-3D TiO2 (*N-3D TiO2; [k]=1.435 h(-1)) is 26.1 times higher than that of 3D TiO2 ([k]=0.055 h(-1)). The *N-3D TiO2 is highly recyclable and retained 91.8% of the initial decolorization rate after fifteen cycles. Interestingly, the *N-3D TiO2 shows very strong antibacterial properties against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) after exposure to visible-light for 3h. The antibacterial properties of *N-3D TiO2 are more effective than those of TiO2, 3D TiO2, and N-3D TiO2. More than 91.3% of the E. coli is sterilized after ten cycles. There are a large increase in the photocatalytic and antibacterial activity of *N-3D TiO2 relative to that of N-3D TiO2 owing to the hydroxylation of the N-3D TiO2 surface as a result of the visible-light irradiation. These results indicate that *N-3D TiO2 might have utility in several promising applications such as highly efficient water/air treatment, inactivation of pathogenic microorganisms, and solar-energy conversion.

Sea-urchin-like iron oxide nanostructures for water treatment

To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe2O3/Fe3O4 phase) nanostructures (called u-MFN) with large surface areas (94.1m(2) g(-1)) and strong magnetic properties (57.9 emu g(-1)) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g(-1)) and Cr(VI) (35.0 mg g(-1)) and the organic pollutant Congo red (109.2 mg g(-1)). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions.

Hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide and its application in heavy metal removal and solar-induced photocatalytic degradation

In this study, hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide nanostructures (3D-Fe2O3) were synthesized by a facile and rapid ultrasound irradiation method. Additives, templates, inert gas atmosphere, pH regulation, and other complicated procedures were not required. Dense 3D-Fe2O3 with a relatively large Brunauer-Emmett-Teller (BET) surface area of 129.4 m2/g was synthesized within 23 min, and the BET surface area was further improved to 282.7 m2/g by a post heat-treatment process. In addition, this post processing led to phase changes from maghemite (γ phase) to hematite (α phase) Fe2O3. Subsequent characterization suggested that the growth mechanism of the 3D-Fe2O3 follows self-assembly and oriented attachment. The prepared 3D-Fe2O3 was applied to wastewater purification. Ultrasound-irradiated 3D-Fe2O3 can eliminate a As(V) and Cr(VI) from water with 25 times faster removal rate by using a one third smaller amount than commercial α-Fe2O3. This was attributed to the inter-particle pores and relatively positively charged surface of the nanostructure. In addition, post heat treatment on ultrasound-irradiated 3D-Fe2O3 significantly influenced the photocatalytic degradation of methylene blue and phenol, with a 25 times higher removal efficiency than that of commercial α-Fe2O3, because of both high BET surface area and good crystallization of the prepared samples.