Huixian Shi

Synthesis and Characterization of Novel Plasmonic Ag/AgX-CNTs (X = Cl, Br, I) Nanocomposite Photocatalysts and Synergetic Degradation of Organic Pollutant under Visible Light

A series of novel well-defined Ag/AgX (X = Cl, Br, I) loaded carbon nanotubes (CNTs) composite photocatalysts (Ag/AgX-CNTs) were fabricated for the first time via a facile ultrasonic assistant deposition-precipitation method at the room temperature (25 ± 1 °C). X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption analysis, scanning electron microscopy, and ultraviolet-visible light absorption spectra analysis were used to characterize the structure, morphology, and optical properties of the as-prepared photocatalysts. Results confirmed the existence of the direct interfacial contact between Ag/AgX nanoparticles and CNTs, and Ag/AgX-CNTs nanocomposites exhibit superior absorbance in the visible light (VL) region owing to the surface plasmon resonance (SPR) of Ag nanoparticles. The fabricated composite photocatalysts were employed to remove 2,4,6-tribromophenol (TBP) in aqueous phase. A remarkably enhanced VL photocatalytic degradation efficiency of Ag/AgX-CNTs nanocomposites was observed when compared to that of pure AgX or CNTs. The photocatalytic activity enhancement of Ag/AgX-CNTs was due to the effective electron transfer from photoexcited AgX and plasmon-excited Ag(0) nanoparticles to CNTs. This can effectively decrease the recombination of electron-hole pairs, lead to a prolonged lifetime of the photoholes that promotes the degradation efficiency.

Enhancement of photocatalytic activity of nano-scale TiO2 particles co-doped by rare earth elements and heteropolyacids

Nano-scale TiO(2) photocatalysts co-doped by rare earth ions (La(3+), Ce(3+)) and heteropolyacids were designed and prepared by sol-gel method to probe synergistic effect on photocatalytic elimination of organic compounds, and their physicochemical properties were characterized by X-ray diffraction (XRD), specific surface area and porosity (BET and BJH), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS) as well as Raman spectroscopy. The photocatalytic activity of prepared catalysts was evaluated by the degradation of methylene blue (MB) in water under UV-light irradiation. The results showed that the co-doping of the rare earth ions and heteropolyacids can significantly improve the photocatalytic activity of prepared composite photocatalysts due to the efficient inhibition of the recombination of photogenerated electron-hole pairs. The enhancement mechanism of co-doping of the rare earth ions and heteropolyacids on TiO(2) is also discussed.

Systematic approach to in-depth understanding of photoelectrocatalytic bacterial inactivation mechanisms by tracking the decomposed building blocks.

A systematic approach was developed to understand, in-depth, the mechanisms involved during the inactivation of bacterial cells using photoelectrocatalytic (PEC) processes with Escherichia coli K-12 as the model microorganism. The bacterial cells were found to be inactivated and decomposed primarily due to attack from photogenerated H2O2. Extracellular reactive oxygen species (ROSs), such as H2O2, may penetrate into the bacterial cell and cause dramatically elevated intracellular ROSs levels, which would overwhelm the antioxidative capacity of bacterial protective enzymes such as superoxide dismutase and catalase. The activities of these two enzymes were found to decrease due to the ROSs attacks during PEC inactivation. Bacterial cell wall damage was then observed, including loss of cell membrane integrity and increased permeability, followed by the decomposition of cell envelope (demonstrated by scanning electronic microscope images). One of the bacterial building blocks, protein, was found to be oxidatively damaged due to the ROSs attacks, as well. Leakage of cytoplasm and biomolecules (bacterial building blocks such as proteins and nucleic acids) were evident during prolonged PEC inactivation process. The leaked cytoplasmic substances and cell debris could be further degraded and, ultimately, mineralized with prolonged PEC treatment.

Role of in Situ Resultant H2O2 in the Visible-Light-Driven Photocatalytic Inactivation of E. coli Using Natural Sphalerite: A Genetic Study

This study investigated how a natural sphalerite (NS) photocatalyst, under visible light irradiation, supports photocatalytic bacterial inactivation. This was done by comparing parent E. coli BW25113, and its two isogenic single-gene knock-out mutants, E. coli JW0797-1 (dps(-) mutant) and JW1721-1 (katE(-) mutant), where both dps and KatE genes are likely related to H2O2 production. NS could inactivate approximately 5-, 7- and 7-log of E. coli BW25113, JW0797-1, and JW1721-1 within 6 h irradiation, respectively. The two isogenic mutants were more susceptible to photocatalysis than the parental strain because of their lack of a defense system against H2O2 oxidative stress. The ability of in situ resultant H2O2 to serve as a defense against photocatalytic inactivation was also confirmed using scavenging experiments and partition system experiments. Studying catalase activity further revealed that in situ H2O2 played an important role in these inactivation processes. The destruction of bacterial cells from the cell envelope to the intracellular components was also observed using field emission-scanning electron microscopy. Moreover, FT-IR was used to monitor bacterial cell decomposition, key functional group evolution, and bacterial cell structures. This is the first study to investigate the photocatalytic inactivation mechanism of E. coli using single-gene deletion mutants under visible light irradiation.