Oxide
semiconductors like bismuth-based oxide or layered-double-hydroxide
accompanied by many surface oxygen vacancies (OVs) are emerging as
highly promising photocatalysts for artificial N2 fixation.
However, their band edge reduction potentials actually do not meet
nitrogen fixation requirements at all. The mechanism that triggers
the photocatalytic NH3 synthesis reaction still remains
unclear. Herein, taking BiOBr as a prototypical photocatalyst, we
reveal a photoexcitation-assisted N2 activation mechanism,
which can perfectly address the abovementioned problem. Specifically,
the OV defect states serve as a springboard that offers the photogenerated
electrons the reduction potential that is much higher than conduction
band edge under visible light. The physically adsorbed *N2 can trap the electron to form the *N2
•– transient state and collapse
into the *N2 vibrational excited state. This process deposits
a high amount of energy into *N2 and sharply lowers the
π* orbital of *N2 below the band edge, thereby allowing
*N2 to capture photogenerated electrons at band edge and
trigger the following NH3 synthesis. This study advances
the fundamental understanding of photocatalytic N2 fixation
and may provide an alternative way for the design of efficient ammonia
photocatalysts.
Photochromic systems with an ultrahigh rate of thermal relaxation are highly desirable for the development of new efficient photochromic oscillators. Based on DFT calculations, we designed a series of 5‐phenylazopyrimidines with strong push–pull character in silico and observed very low energy barriers for the thermal (Z)‐to‐(E) isomerization. The structure of the (Z)‐isomer of the slowest isomerizing derivative in the series was confirmed by NMR analysis with in situ irradiation at low temperature. The substituents can tune the lifetime of thermal back isomerization from hundreds of microseconds to several nanoseconds (8 orders of magnitude). The photoswitching parameters were extracted from transient absorption techniques and a dominant rotation mechanism of the (Z)‐to‐(E) thermal fading was proposed based on DFT calculations.
The direct Z-scheme photocatalytic heterojunction, possessing
type
II band alignments but simultaneously realizing the spatial separation
of photogenerated electrons and holes (PEHs) and the well-preserved
strong redox ability, is a promising strategy for solving energy and
environmental issues. However, the conventional method of solely relying
on the direction of interfacial electric field (IEF) to determine
the Z-scheme is often different with experiments. Properly evaluating
and constructing the direct Z-scheme remain limited. Herein, combining
hybrid density functional theory and excited state ultrafast dynamics
simulation, we find that the formative factor of the Z-scheme path
comes from two aspects by systematically exploring a series of prototypical
heterojunctions taking X2Y3 ferroelectrics (X:
Al, Ga, In. Y: S, Se, Te) and BCN semiconductors. On the one hand,
the interlayer recombination of PEHs with weak redox ability can be
significantly promoted by the IEF. On the other hand, for PEHs with
strong redox ability, the weak nonadiabatic coupling of interface
transfer channel plays a key role in preserving the high activity
of PEHs, which can extend the reacting time of PEHs from femtosecond
to hundreds of nanosecond scale. This study deepens the understanding
of Z-scheme formation and can accelerate the design of direct Z-scheme
photocatalysts.
N2 fixation under mild condition using renewable electricity or solar energy is a promising alternative to the century-old Haber-Bosch process, whereas it is generally impeded by initial hydrogenation and competitive...
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