Visible light-active sub-5 nm anatase TiO2 for photocatalytic organic pollutant degradation in water and air, and for bacterial disinfection

Biodegradable Polylactide/TiO2 Composite Fiber Scaffolds with Superhydrophobic and Superadhesive Porous Surfaces for Water Immobilization, Antibacterial Performance, and Deodorization

In this short communication, TiO₂-nanoparticle-functionalized biodegradable polylactide (PLA) nonwoven scaffolds with a superhydrophobic and superadhesive surface are reported regarding their water immobilization, antibacterial performance, and deodorization. With numerous regular oriented pores on their surface, the as-fabricated electrospun porous PLA/TiO₂ composite fibers possessed diameters in the range from 5 µm down to 400 nm, and the lengths were even found to be up to the meters range. The PLA/TiO₂ composite fiber surface was demonstrated to be both superhydrophobic and superadhesive. The size of the pores on the fiber surface was observed to have a length of 200 ± 100 nm and a width of 150 ± 50 nm using field-emission scanning electron microscopy and transmission electron microscopy. The powerful adhesive force of the PLA/TiO₂ composite fibers toward water droplets was likely a result of van der Waals forces and accumulated negative pressure forces. Such a fascinating porous surface (functionalized with TiO₂ nanoparticles) of the PLA/TiO₂ composite fiber scaffold endowed it with multiple useful functions, including water immobilization, antibacterial performance, and deodorization.

Research progress of photocatalytic sterilization over semiconductors

With increasingly serious environmental issues, practical applications of semiconductor photocatalysts for environmental purification have attracted broad attention. Semiconductor photocatalysts for the disinfection of soil surfaces, air and water are of great interest.

Effects of bulk and surface defects on the photocatalytic performance of size-controlled TiO2 nanoparticles

Defects are one of the crucial factors influencing the photocatalytic activities of TiO₂ nanoparticles (NPs), as they directly affect the charge separation efficiencies. However, we found that the effect of bulk or surface defects on the photocatalytic performance of TiO₂ is totally different. Here, we controllably synthesized four kinds of uniform TiO₂ NPs, which were used to investigate how the bulk and surface defects influenced the photoactivities of samples with different particle sizes. Through XPS and EPR analysis, bulk and surface defects were observed in all the TiO₂ samples and their amounts had been reduced after the calcination process. The reduction of bulk and surface defects enhanced the photoactivities of TiO₂ NPs with diameters >10 nm, but the situation was inverse for those samples with diameters <10 nm. Therefore, we demonstrated that bulk defects play a dominate role in the change in photoactivity in particles larger than 10 nm, while surface defects are more important than bulk defects for particles less than 10 nm.

Improving Visible Light-Absorptivity and Photoelectric Conversion Efficiency of a TiO₂ Nanotube Anode Film by Sensitization with Bi₂O₃ Nanoparticles

This study presents a novel visible light-active TiO₂ nanotube anode film by sensitization with Bi₂O₃ nanoparticles. The uniform incorporation of Bi₂O₃ contributes to largely enhancing the solar light absorption and photoelectric conversion efficiency of TiO₂ nanotubes. Due to the energy level difference between Bi₂O₃ and TiO₂, the built-in electric field is suggested to be formed in the Bi₂O₃ sensitized TiO₂ hybrid, which effectively separates the photo-generated electron-hole pairs and hence improves the photocatalytic activity. It is also found that the photoelectric conversion efficiency of Bi₂O₃ sensitized TiO₂ nanotubes is not in direct proportion with the content of the sensitizer, Bi₂O₃, which should be carefully controlled to realize excellent photoelectrical properties. With a narrower energy band gap relative to TiO₂, the sensitizer Bi₂O₃ can efficiently harvest the solar energy to generate electrons and holes, while TiO₂ collects and transports the charge carriers. The new-type visible light-sensitive photocatalyst presented in this paper will shed light on sensitizing many other wide-band-gap semiconductors for improving solar photocatalysis, and on understanding the visible light-driven photocatalysis through narrow-band-gap semiconductor coupling.

Graphene oxide-enhanced sol-gel transition sensitivity and drug release performance of an amphiphilic copolymer-based nanocomposite

We report the fabrication of a highly sensitive amphiphilic copolymer-based nanocomposite incorporating with graphene oxide (GO), which exhibited a low-intensity UV light-triggered sol-gel transition. Non-cytotoxicity was observed for the composite gels after the GO incorporation. Of particular interest were the microchannels that were formed spontaneously within the GO-incorporated UV-gel, which expedited sustained drug release. Therefore, the present highly UV-sensitive, non-cytotoxic amphiphilic copolymer-based composites is expected to provide enhanced photothermal therapy and chemotherapy by means of GO's unique photothermal properties, as well as through efficient passive targeting resulting from the sol-gel transition characteristic of the copolymer-based system with improved sensitivity, which thus promises the enhanced treatment of patients with cancer and other diseases.

Antibacterial modification of an injectable, biodegradable, non-cytotoxic block copolymer-based physical gel with body temperature-stimulated sol-gel transition and controlled drug release

Biomaterials are being extensively used in various biomedical fields; however, they are readily infected with microorganisms, thus posing a serious threat to the public health care. We herein presented a facile route to the antibacterial modification of an important A-B-A type biomaterial using poly (ethylene glycol) methyl ether (mPEG)- poly(ε-caprolactone) (PCL)-mPEG as a typical model. Inexpensive, commercial bis(2-hydroxyethyl) methylammonium chloride (DMA) was adopted as an antibacterial unit. The effective synthesis of the antibacterial copolymer mPEG-PCL-∼∼∼-PCL-mPEG (where ∼∼∼ denotes the segment with DMA units) was well confirmed by FTIR and (1)H NMR spectra. At an appropriate modification extent, the DMA unit could render the copolymer mPEG-PCL-∼∼∼-PCL-mPEG highly antibacterial, but did not largely alter its fascinating intrinsic properties including the thermosensitivity (e.g., the body temperature-induced sol-gel transition), non-cytotoxicity, and controlled drug release. A detailed study on the sol-gel-sol transition behavior of different copolymers showed that an appropriate extent of modification with DMA retained a sol-gel-sol transition, despite the fact that a too high extent caused a loss of sol-gel-sol transition. The hydrophilic and hydrophobic balance between mPEG and PCL was most likely broken upon a high extent of quaternization due to a large disturbance effect of DMA units at a large quantity (as evidenced by the heavily depressed PCL segment crystallinity), and thus the micelle aggregation mechanism for the gel formation could not work anymore, along with the loss of the thermosensitivity. The work presented here is highly expected to be generalized for synthesis of various block copolymers with immunity to microorganisms. Light may also be shed on understanding the phase transition behavior of various multiblock copolymers.