3 research outputs found
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
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 <i>Escherichia coli</i> K-12 as the model microorganism. The bacterial cells were found
to be inactivated and decomposed primarily due to attack from photogenerated
H<sub>2</sub>O<sub>2</sub>. Extracellular reactive oxygen species
(ROSs), such as H<sub>2</sub>O<sub>2</sub>, 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
A Recyclable Mineral Catalyst for Visible-Light-Driven Photocatalytic Inactivation of Bacteria: Natural Magnetic Sphalerite
Motivated
by recent studies that well-documented mineral photocatalyst
for bacterial inactivation, a novel natural magnetic sphalerite (NMS)
in lead–zinc deposit was first discovered and evaluated for
its visible-light-driven (VLD) photocatalytic bactericidal properties.
Superior to the reference natural sphalerite (NS), vibrating sampling
magnetometeric (VSM) analysis revealed the ferromagnetic property
of NMS, indicating its potential for easy separation after use. Under
the irradiation of fluorescence tubes, NMS could inactivate 7 log<sub>10</sub> Gram-negative <i>Escherichia coli</i> K-12 without
any regrowth and metal ions leached out from NMS show no toxicity
to cells. The cell destruction process starting from cell wall to
intracellular components was verified by TEM. Some products from damaged
cells such as aldehydes, ketones and carboxylic acids were identified
by FTIR with a decrease of cell wall functional groups. The relative
amounts of potassium ion leakage from damaged cells gradually increased
from initial 0 to approximately constant concentration of 1000 ppb
with increasing reaction time. Superoxide radical (•O<sub>2</sub><sup>–</sup>) rather than hydroxyl radical (•OH) was
proposed to be the primary reactive oxidative species (ROSs) responsible
for <i>E. coli</i> inactivation by use of probes and electron
spin resonance (ESR). H<sub>2</sub>O<sub>2</sub> determined by fluorescence
method is greatly involved in bacterial inactivation in both nonpartition
and partition system. Multiple cycle runs revealed excellent stability
of recycled NMS without any significant loss of activity. This study
provides a promising natural magnetic photocatalyst for large-scale
bacterial inactivation, as NMS is abundant, easily recycled and possessed
an excellent VLD bacterial inactivation ability