The oxidation state of Cu nanoparticles
during CO oxidation in
CO + O2 gas mixtures was sensitively monitored via localized
surface plasmon resonances. A microreactor, equipped with in situ
UV–vis and mass spectrometry, was developed and used for the
measurements. Cu nanoparticles of ∼30 nm average diameter were
supported on optically transparent, planar quartz wafers. The aim
of the study is 2-fold: (i) to demonstrate the performance and usefulness
of the setup and (ii) to use the combined strength of model catalysts
and in situ measurements to investigate the correlation between the
catalyst oxidation state and its reactivity. Metallic Cu is significantly
more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase
is only maintained under conditions where close to full oxygen conversion
is achieved. This implies that kinetic measurements, aimed at determining
the apparent activation energy for metallic Cu under realistic steady-state
conditions, are difficult or impossible to perform.
Constructing heterojunctions with face-to-face interface is a new avenue for accelerating the charge separation in semiconductor photocatalysts toward highly efficient solar water splitting systems. Here, a novel SnS 2 / TiO 2 2D−2D ultrathin nanosheet heterostructure was fabricated via a hydrothermal route in two steps. The obtained 2D−2D SnS 2 /TiO 2 nanojunction has not only provided large contact areas but also shortened the charge transport distance, resulting in significantly enhanced photocatalytic H 2 evolution property. The H 2 generation rate obtained for the optimized sample reaches 652.4 μmol h −1 g −1 , far exceeding (∼8 times) that of pristine TiO 2 and SnS 2 ultrathin nanosheets under simulated solar irradiation. Moreover, further analysis reveals a photoinduced carrier transfer from TiO 2 to SnS 2 at the interface junction, which causes a partial reduction of the SnS 2 cocatalyst to SnS in the nanocomposite during the photocatalytic reactions. These results not only demonstrate that the construction of 2D−2D heterojunction is a promising approach to improve the photocatalytic H 2 production activity of nanostructured semiconductor photocatalysts but also provide new understanding into the role and evolution of SnS 2 nanosheets during the photocatalytic reaction process in heterogeneous photocatalyst systems.
Flat
model and powder Cu, ZnO/Cu, and CeO
x
/Cu
catalysts were studied by focusing on the role of the oxide
phase as a promoter in the water gas shift (WGS) and its reverse reaction
(RWGS). Activity measurements of the powder catalysts showed that
both oxides enhance Cu reactivity, with CeO
x
/Cu being more active than ZnO/Cu in the WGS reaction. In situ
ultraviolet–visible spectroscopy, exploiting the localized
surface plasmon resonances of metallic Cu nanoparticles, together
with X-ray photoelectron spectroscopy was then used to elucidate the
origin of the enhanced reactivity on flat model catalysts. These experiments
showed that ZnO and CeO
x
promote H2O and CO2 dissociation, leading to oxidation of
the Cu nanoparticles. CeO
x
performs better
in this respect than ZnO. This is important because the reactivity
in the WGS and RWGS reactions is related to the ability to activate
H2O and CO2. The Ce3+ ions are identified
as the most efficient sites for H2O and CO2 dissociation,
while Cu0 keeps Ce3+ stable by promoting reduction
of Ce4+ during the dissociation process. In this sense,
the CeO
x
/Cu catalyst forms a bifunctional
catalyst, which is more active in the (R)WGS than CeO
x
and Cu catalysts separately.
Although tellurite is highly toxic to organisms, elemental tellurium nanomaterials (TeNMs) have many uses. The microbe-mediated reduction of tellurite to Te(0) has been shown to be a green and cost-effective approach for turning waste into wealth. However, it is difficult to tune the morphology of biogenic nanomaterials. In this study, a series of experiments was conducted to investigate the factors influencing tellurite reduction by the tellurite-reducing bacterium Lysinibacillus sp. ZYM-1, including pH, tellurite concentration, temperature, and heavy metal ions. The optimal removal efficiency of tellurite was respectively achieved at pH 8, 0.5 mM tellurite, and 40 °C. All of the tested metal ions retarded the reduction of tellurite, especially Cd and Co, which completely inhibited its reduction. Further characterization of the biogenic TeNMs indicated that their morphology could be tuned by the tellurite concentration, pH, temperature, and organic solvents used. Regular Te nanosheets were produced using 5 mM tellurite. The TeNMs were primarily synthesized in the cell membrane. Hexagonal Te nanoplates, nanorods, nanoflowers, and nanobranches were synthesized when combining membrane fractions with tellurite and NADH. The diverse morphologies are assumed to be induced by the synergy between the reduction kinetics and the protein structure. Therefore, this study confirmed that the bacterium can tune the morphology of TeNMs, broadening the potential application of biogenic TeNMs.
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