Photocatalysts are useful for various applications, including
the
conservation and storage of energy, wastewater treatment, air purification,
semiconductors, and production of high-value-added products. Herein,
Zn
x
Cd1–x
S nanoparticle (NP) photocatalysts with different concentrations
of Zn2+ ions (x = 0.0, 0.3, 0.5, or 0.7)
were successfully synthesized. The photocatalytic activities of Zn
x
Cd1–x
S
NPs varied with the irradiation wavelength. X-ray diffraction, high-resolution
transmission electron microscopy, energy-dispersive X-ray spectroscopy,
and ultraviolet–visible spectroscopy were used to characterize
the surface morphology and electronic properties of the Zn
x
Cd1–x
S NPs. In
addition, in situ X-ray photoelectron spectroscopy was performed to
investigate the effect of the concentration of Zn2+ ions
on the irradiation wavelength for photocatalytic activity. Furthermore,
wavelength-dependent photocatalytic degradation (PCD) activity of
the Zn
x
Cd1–x
S NPs was investigated using biomass-derived 2,5-hydroxymethylfurfural
(HMF). We observed that the selective oxidation of HMF using Zn
x
Cd1–x
S
NPs resulted in the formation of 2,5-furandicarboxylic acid via 5-hydroxymethyl-2-furancarboxylic
acid or 2,5-diformylfuran. The selective oxidation of HMF was dependent
on the irradiation wavelength for PCD. Moreover, the irradiation wavelength
for the PCD depended on the concentration of Zn2+ ions
in the Zn
x
Cd1–x
S NPs.
Modulating
the oxygen vacancy (V
0)
in nanostructures has opened a new avenue for efficient catalyst design,
facilitating biomass oxidation reactions and electrocatalytic properties.
In this study, we have investigated the properties of NiO-based catalysts
with varying degrees of V
0 achieved through
ion doping of the catalyst with cations of different oxidation states
(TM3+) or the same valence state (TM2+) as Ni2+ in the NiO matrix. By introducing charge-mismatched dopants,
we enhanced the concentration of V
0 in
the NiO catalyst, resulting in remarkable selectivity (∼50%)
for the conversion of 2,5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic
acid (FDCA), as well as a lower overpotential in the oxygen evolution
reaction (OER). We believe that charge-mismatched doping offers a
novel avenue for optimizing defect engineering in oxide-based catalysts,
which can enable more efficient biomass conversion and water splitting.
These findings have made a significant contribution to the field of
multipurpose catalysis and hold the potential to inspire new catalyst
designs that would usher in a more sustainable future.
Existing methods for the photocatalytic transformation of aromatic alcohols to value-added products via C−C cross-coupling are inefficient and insufficiently selective. Herein, a series of cadmium sulfide nanowires (CdS NWs) loaded with Ag 2 S (denoted as Ag 2 S@CdS NWs) are constructed via a simple Ag + exchange protocol for the photocatalytic transformation of benzyl alcohol. We successfully demonstrated that the selectivity toward specific products in the photocatalytic transformation of benzyl alcohol over Ag +exchanged CdS NWs is controlled by varying the amount of exchanged Ag + ions. Notably, the product of the photocatalytic reaction was dependent on the amount of Ag + ions exchanged: with a Ag + exchange of <5 mol %, the C−C coupling product was obtained with >90% selectivity and >95% transformation yield owing to photoinduced electron transfer from the conduction band of CdS to Ag 2 S. Conversely, with a Ag + exchange of >7 mol %, a cocatalyst in which Ag 2 S and Ag are mixed was produced, and benzaldehyde was obtained with >90% selectivity and >90% transformation yield because of photoinduced hole transfer from the valence band of CdS to Ag 2 S/Ag. This study proves that Ag 2 S@CdS NWs can be used as a basis for the development of heterojunction photocatalysts for the conversion of aromatic alcohols into value-added products via C− C cross-coupling reactions or photooxidation toward aromatic aldehyde.
A charge
mismatch between transition-metal-ion dopants and metal
oxide nanoparticles (MO NPs) within an engineered complex engenders
a significant number of oxygen vacancies (VO) on the surface
of the MO NP construct. To elucidate in-depth the mechanism of this
tendency, Co ions with different charge states (Co3+ and
Co2+) were doped into ZnO NPs, and their atomic structural
changes were correlated with their photocatalytic efficiency. We ascertained
that the increase of the Zn–O bond distances was distinctly
affected by Co3+-ion doping, and, subsequently, the number
of VO was noticeably increased. We further investigated
the mechanistic pathways of the photocatalytic oxidation of 2,5-hydroxymethylfurfural
(HMF), which have been widely investigated as biomass derivatives
because of their potential use as precursors for the synthesis of
sustainable alternatives to petrochemical substances. To identify
the reaction products in each oxidation step, selective oxidation
products obtained from HMF in the presence of pristine ZnO NPs, Co3+- and Co2+-ion-doped ZnO NPs were evaluated. We
confirmed that Co3+-ion-doped ZnO NPs can efficiently and
selectively oxidize HMF with a good conversion rate (∼40%)
by converting HMF to 2,5-furandicarboxylic acid (FDCA). The present
study demonstrates the feasibility of improving the production efficiency
of FDCA (an alternative energy material) by using enhanced photocatalytic
MO NPs with the help of the charge mismatch between MO and metal-ion
dopants.
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