Highly exposed active
facets and surface oxygen vacancies (OVs)
are beneficial for the photocatalytic removal of various harmful organic
compounds. In this study, uniform Zn2+-doped BiOI microspheres,
assembled by ultrathin nanosheets with highly exposed {001} facets,
with OVs were successfully synthesized for NO removal under visible
light irradiation. The phase structure and chemical states are analyzed
by means of X-ray diffraction and X-ray photoelectron spectroscopy,
respectively. The transmission electron microscopy observations reveal
that replacing Bi3+ with Zn2+ can lead to the
increased exposure of the {001} facets. X-ray photoelectron and electron paramagnetic
resonance spectroscopy results confirm that low-state Zn2+ increases the number of OVs, indicating that an increased number
of OVs and a reduced thickness of the nanosheets can enhance the photocatalytic
activity for the removal of NO. The photo-oxidative removal efficiency
of NO over 3%Zn-BiOI reaches 53.6% and remains highly stable (52.9%)
for up to 210 min under visible light irradiation. The calculation
of interface adsorption confirms that OVs and Zn2+ can
not only offer a donor energy level to extend the solar response range
but also act as adsorption sites for low concentration of NO and O2 to optimize the transmission capacity of surface charge carriers.
Moreover, this work systematically explains the function of OVs and
Zn2+ in the adsorption process of NO. The in situ Fourier
transform infrared spectroscopy supports understanding of the photo-oxidative
removal mechanisms of NO over Zn-BiOI: (i) the byproducts were bidentate
nitrites (bi-NO2
–), chelate nitrites
(ch-NO2
–), and bridging nitrites (br-NO3
–) in the dark condition and (ii) the final
products were bridging nitrites and bidentate nitrites (bi-NO3
–) under visible light irradiation. OVs
are found to play an important role both in the dark adsorption and
photo-oxidative removal of NO by the 3%Zn-BiOI sample.
Constructing
oxygen vacancies (OVs) in metal-oxide semiconductors
is an effective and simple way to enhance the photocatalytic performance
via promoting the utilization of solar light and boosting the formation
of surface reactive oxygen species (ROS). The presence of different
oxygen atoms in the same crystal structure can possibly lead to the
formation of different types of OVs with distinct physicochemical
and optoelectronic properties. Particularly, the two different crystallographic
positions of oxygen atoms in the [BiO]2
2+ layer
of (BiO)2CO3 (BOC) allow the construction of
two types of OVs (OVs1 and OVs2). In this work, OVs1-BOC and OVs2-BOC
are synthesized via introducing the OVs1 and OVs2 on the surface of
the BOC. The influence of OVs1 and OVs2 on the generation of ROS in
the BOC is demonstrated based on theoretical and experimental studies
by analyzing the separation and redox potentials of photogenerated
charge carriers, absorption surface adsorbates (H2O and
O2), and reaction active energy. The photocatalytic performance
is evaluated by photo-oxidative nitric oxide (NO) removal efficiency
under visible light irradiation. The OVs1-BOC and OVs2-BOC exhibit
50.0 and 41.6% photo-oxidative NO removal efficiencies, while generating
15.6 and 16.54 ppb NO2, respectively. The in situ Fourier
transform infrared spectroscopy and estimated NO conversion pathway
reveal the photo-oxidative NO removal mechanism and suppression of
NO2 formation on the surfaces of OVs1-BOC and OVs2-BOC.
This work demonstrates a straightforward approach for enhancing the
photo-oxidative NO removal via manipulating the OV defect position
in semiconductors.
Sphere-like Bi 5 O 7 I (BOI) doped with La (L-BOI) samples were prepared by a solvothermal method followed by calcination at 450 °C for 2 h. Au nanoparticles were loaded on 6% La-doped Bi 5 O 7 I (2%A− 6%L-BOI) microspheres by a room-temperature chemical reduction method. The UV−vis absorption spectra show that the L-BOI and 2%A− 6%L-BOI samples have a strong visible-light absorption in comparison with the pure BOI. The electron paramagnetic resonance results indicate that the number of oxygen vacancies in L-BOI samples is increased with an increasing amount of the La dopant. The band structure of the prepared photocatalysts is investigated by confirming the positions of the valence band (VB) measured by XPS-VB and the Fermi level computed by density functional theory, respectively. NO is selected as a target gaseous pollutant to confirm the influence of La doping and the plasmonic effect of Au nanoparticles on the photocatalytic activity of BOI microspheres. The 2%A−6%L-BOI sample exhibits an enhanced photocatalytic performance compared to BOI, L-BOI, and A-BOI photocatalysts under visible-light irradiation. Interestingly, the 2%A−6%L-BOI sample also can reduce the amount of intermediate NO 2 during the NO removal process. The enhanced photocatalytic efficiency of the 2%A−6%L-BOI photocatalyst is profited from the synergy of La-ion doping, oxygen vacancy, and the surface plasmon resonance effect of Au nanoparticles. Based on the results of trapping experiments and electron spin resonance spectroscopy tests, h + , e − , and • O 2 − were involved in the NO oxidative removal.
aOutdoor bamboo-fiber-reinforced composites (OBFRCs) with four different densities were prepared, and the microstructure and physicomechanical properties of pristine samples were evaluated. In addition, the surface color, glossiness, roughness, water absorption, and wettability of the samples were tested to investigate the effects of panel density on the extent of surface weathering due to ultraviolet radiation. The results showed that the OBFRCs exhibited excellent physical and mechanical properties, which improved with increasing density. However, increases in the density led to decreases in the hygroscopicity and dimensional stability of the OBFRCs. After weathering, the surface contact angle and surface roughness increased, and the dimensional stability improved. The surface glossiness, water absorption, and surface free energy decreased. A higher density resulted in improved color stability, which suggested that density played an important role in determining surface photodegradation properties. Thus, densityincreasing treatments had positive effects on the physical and mechanical properties as well as the color stability and wettability of the OBFRCs, but they may negatively affect the roughness and dimensional stability. Based on service-performance and cost-minimization considerations, 1.1 g/cm 3 was determined as the most appropriate density for general applications.
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