Interface structure plays an extremely
important role in the charge-transfer
and photocatalytic performances in plasmonic metal/semiconductor systems.
Defect engineering by introducing an oxygen vacancy (Ovac) is an effective way to modulate the interface structure. Here,
a representative photocatalyst system including TiO2, TiO2–x
, Au-TiO2 and Au-TiO2–x
as designed delicately to reveal
the detailed mechanism of the plasmon-resonance-induced charge separation
in interfacial defect structure from the nanoscale. The local charge
transfer via a conducting amorphous-like interface layer is visualized
as the arched valence change from Ti3+ to Ti4+ at the Au-TiO2–x
interface after
Schottky contact. This phenomenon eventually leads to the enhancement
of localized surface plasmon resonance (LSPR) at 2.3 eV, and the introduction
of Ovac reduces the Schottky barrier height of Au-TiO2–x
by 5 mV compared with that of Au-TiO2. Under visible light, Au-TiO2–x
excites the most photogenerated carriers to the surface, which
is larger than that of TiO2–x
and
Au-TiO2. It can be concluded that the changes in electronic
structure eventually promote charge transfer in visible light and
explain the original reason that the coupling of Ovac and
Au could improve the photocatalytic performance.
Hybrid nanoparticles have intrinsic advantages to achieve better activity in photocatalysis compared to single-component materials, as it can synergistically combine functional components, which promote light absorption, charge transportation, surface reaction, and catalyst regeneration. Through functional modular assembly, a rational and stepwise approach has been developed to construct FeO-CdS-Au trimer nanoparticles and its derivatives as magnetically separable catalysts for photothermo-catalytic hydrogen evolution from water. In a typical step-by-step synthetic process, FeO-Ag dimers, FeO-AgS dimers, FeO-CdS dimers, and FeO-CdS-Au trimers were synthesized by seeding growth, sulfuration, ion exchange, and in situ reduction consequently. Following the same reaction route, a series of derivative trimer nanoparticles with alternative semiconductor and metal were obtained for water-reduction reaction. The experimental results show that the semiconductor acts as an active component for photocatalysis, the metal nanoparticle acts as a cocatalyst for enhancement of charge separation, and the FeO component helps in the convenient separation of catalysts in magnetic field and improves photocatalytic activity under near-infrared illumination due to photothermic effect.
Monodisperse ZnO particles with adjustable size have been produced on a large scale by two-step seeding-growth polyol reactions. Through spin coating of supersaturated ZnO/diethylene glycol solution and evaporation of solvent, opaline ZnO photonic crystal (PC) film with good crystallinity and uniform photonic structures can be prepared from these ZnO particles. Compared with a disorderly stacked ZnO film, the ZnO PC film shows a higher activity in photocatalytic reduction of CO 2 due to the generated slow photons at the edge of the photonic band gap and their promotion to the light absorption. When the electronic band gap of ZnO matches the red edge of the photonic band gap of ZnO PC, the enhancement factor of photocatalytic activity represented by CO evolution can be maximized to 2.64-fold in the current experiment. Compared to the traditional inverse opal photocatalysts, the opaline ZnO photocatalysts are prepared by simplified and scalable procedures, and they still possess the same enhancement in activity compared to ZnO without the photonic structure, which might be broadly used in solar energy utilization, environment protection, and many other green chemical processes in the future.
In
the industry, designing synergetic functional nanocatalysts
is a desirable strategy to achieve both high activity and selectivity
for CO2 hydrogenation. Herein, we fabricate the bicomponent
tandem catalysts ZnZrO
x
/SAPO-34@UIO-n (n = 66, 66-NH2, and 67)
to catalyze CO2 conversion into light olefins. Monodispersed
SAPO-34 zeolites are used as the core for the growth of the UIO-n shell to obtain its membrane-encapsulated nanocrystal,
SAPO-34@UIO-n, which is mixed by grinding with ZnZrO
x
to obtain the ZnZrO
x
/SAPO-34@UIO-n catalyst. CO2 hydrogenation
yielded highly selective C2–C4 olefins
(80%) for the catalyst ZnZrO
x
/SAPO-34@UIO-66,
whereas 57% C2–C4 paraffins were obtained
for the catalyst ZnZrO
x
/SAPO-34 without
a UIO-n membrane. The stable UIO-n membrane in the bifunctional catalyst ZnZrO
x
/SAPO-34@UIO-n adjusted the conversion of
CO2 hydrogenation products from paraffins to olefins.
Photocatalytic reduction of CO 2 has been a challenge for some time because this complex reaction produces multiple products, some of which require a high electron density around the active sites to drive the multi-electron reduction. Herein, a Pd-NiO/TiO 2 catalyst was prepared by hydrothermal production of anatase TiO 2 nanosheets, followed by chemical deposition of NiO and photoreduction of Pd. The introduction of NiO to TiO 2 formed a p−n junction, whose internal electric field drives the migration of holes to NiO. Meanwhile, the introduction of Pd to TiO 2 formed a Schottky junction, which facilitated the photo-generated electron transfer from TiO 2 to Pd. The directional migration of electrons and holes significantly enhanced the charge separation and generated high electron density on Pd, which efficiently and selectively reduced CO 2 to CH 4 .
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