S. Xu, Hua-Jian Lin, X. Lin et al.
Journal of Catalysis 399 (2021) 150–161
of simplicity, universality and effectiveness compared with con-
ventional routes, by which diverse building blocks can be flexibly
and readily combined via molecular interactions with interface
configuration elaborately tailored.[28-33]
2.3. Preparation of SC and SPC nanocomposites
(1)Preparation of SPC nanocomposites with different percent-
age of CdSe QDs
Polyelectrolytes (PEs), as a peculiar category of polymers, are
generally harnessed as the ‘‘molecular glues” to access the electro-
static self-assembly of multilayered heterostructures or films.[34-
200 mg SnO
(20 mL, 10 mg mL ). After stirring for 1 h, the mixture was cen-
trifuged and washed with DI H O. After drying at 60 ℃ for 4 h,
2
NSs was added into the PDDA aqueous solution
ꢀ1
2
3
7] In these cases, PEs are generally utilized as the surface charge
100 mg as-synthesized product was then added into CdSe@MAA
QDs ethanol solution and stirred vigorously for 1 h to trigger the
electrostatic self-assembly. The weight percentage of CdSe QDs is
controlled as 4.8, 9.1, 16.7, 28.6, 37.5, and 44.4%, resulting in the
SPC-x (x = 4.8, 9.1, 16.7, 28.6, 37.5, 44.4%) nanocomposites. Finally,
the samples were separated by centrifugation and washed with
absolute ethanol for three times, and dried at 333 K overnight.
(2)Preparation of SPC nanocomposites with different concentra-
tion of PDDA
modifying agent to afford the positively or negatively charged sur-
face which is in favor of integrating with the oppositely charged
counterparts for constructing composite heterostructures.[38,39]
Apart from the intrinsic surface charge modifying capability, we
wonder that whether PEs can directly participate in the charge
transfer process, and to what extent do PEs influence the photore-
dox catalysis efficiency, which has so far not yet been unleashed.
Virtually, non-conjugated PEs as non-conductive polymers have
been deemed as detrimental to the photoactivities of self-
assembled photosystems since conventional opinion believes that
they markedly retard the interfacial charge transfer by cutting off
the charge flow pathway as a result of their insulating properties.
Consequently, calcination is normally mandatory in previous
works to completely remove the PEs for attaining sufficiently inti-
mate interfacial contact of building blocks and reduced charge
transport resistance.[33] Noteworthily, PEs are featured by various
polar functional groups grafted on the molecular backbone, which
are distinct from conventional conductive polymers with typical
conjugated structure.[40-42] We reason that utilization of non-
conjugated insulating PEs as interfacial charge transfer mediator
is far beyond researchers’ cognition, and it would unlock unex-
pected charge transfer potential of non-conjugated PEs as well as
significantly diversify the insulating polymers-based photosystems
for photoredox catalysis without involving co-catalysts.
200 mg SnO
(10 mL) with concentration of 10, 20, 40, and 60 mg mL , and vig-
orously stirred for 1 h. After that, PDDA-modified SnO NSs (SP)
was sufficiently rinsed with DI H O and dried in vacuum at 60 °C
2
NSs was added into PDDA aqueous solution
ꢀ1
2
2
for 4 h. Subsequently, 100 mg as-synthesized product was added
into CdSe@MAA QDs ethanol solution and vigorously stirred for
1 h to access the electrostatic self-assembly, wherein weight per-
centage of CdSe QDs is controlled to be 37.5%. The samples were
rinsed with absolute ethanol and then dried in vacuum at 60 °C
for 4 h. The obtained samples were denoted as SPC-x (10, 20, 40,
ꢀ1
60 mg mL ), in which ꢁ refers to the PDDA concentration. As a
control, SnO NSs without PDDA modification was directly added
into the CdSe with the same percentage of 37.5%. The obtained
samples are denoted as SnO NSs@CdSe QDs (SC) nanocomposites.
The sample obtained by replacing CdSe QDs with CdS QDs with
other synthetic conditions unchanged is called SnO NSs @CdS
QDs and SnO NSs @PDDA-40@CdS QDs.
2
2
2
Herein, with these guidelines as inspiration, we conceptually
unleash the charge transport capability of solid-state non-
2
conductive PEs to rationally design the multilayered MOs {SnO
nanosheets (SnO NSs), TiO }@PDDA@TMCs QDs (CdSe QDs, CdS
2
2.4. Characterization
2
2
QDs) heterostructured photosystems for photocatalytic selective
organic transformation. The results reveal that ultra-thin non-
conjugated PDDA intermediate layer intercalated at the interface
Zeta potentials are probed by dynamic light-scattering analysis
(ZetasizerNano ZS-90). Crystal structure was determined by X-ray
diffraction (XRD, X’Pert Pro MPD, Philips, Holland) using Cu Ka as
of MOs (SnO
2
NSs, TiO
2
NSs) and TMCs QDs (CdSe QDs, CdS QDs)
the radiation source under 40 kV and 40 mA. UV–vis diffuse reflec-
functions as an efficient charge transfer mediator to engender the
cascade electron transport channel with electrons directionally
transferring from TMCs QDs to MOs, resulting in the significantly
enhanced charge separation and photoactivities toward selective
reduction of aromatic nitro compounds to amino derivatives under
visible light irradiation. Moreover, essential role of the ultrathin
PDDA interim layer as charge mediator has been evidenced to be
universal. Our work would open a new vista to explore non-
conductive polymers-based photosystems for substantial solar-
to-chemical conversion.
tance spectra (DRS) (Varian Cary 500 UV–vis spectrophotometer,
Varian, America) were obtained using BaSO as the reflectance
4
background ranging from 250 to 800 nm. Brunauer-Emmett-
Teller (BET) specific surface areas were determined on a Quan-
tachrome Autosorb-1-C-TCD automated gas sorption analyzer.
Photoluminescence (PL) spectra were collected on a Varian Cary
Eclipse spectrometer. Morphologies of the samples were probed
by field-emission scanning electron microscopy equipped with
energy-dispersive spectroscopy (FESEM, EDX, Philips XL-30, Phi-
lips, Holland). Transmission electron microscopy (TEM) and high-
resolution (HR) TEM, EDX images were collected on a JEOL-2010
with an accelerating voltage of 200 kV. Fourier transforms infrared
(
FTIR) spectra were recorded on a TJ270-30A infrared spectropho-
2
. Experimental section
tometer (Tianjin, China). X-ray photoelectron spectroscopy (XPS)
spectra were recorded on a photoelectron spectrometer (ESCALAB
250, Thermo Scientific, America), for which binding energy (B.E.) of
the elements was calibrated by the B.E. of carbon (284.60 eV).
2.1. Preparation of SnO NSs
2
SnO
2
NSs were prepared by a modified hydrothermal method
and detailed information is provided in SI.[43]
2.5. Photocatalytic performances
In a typical photocatalytic reaction, a 300 W Xe arc lamp (PLS-
SXE 300, Beijing Perfect Light Co., Ltd.) with a UV-CUT filter to cut
off light with a wavelength k < 420 nm was used as the irradiation
source. 10 mg catalysts and 40 mg sodium sulfite as a quencher for
2.2. Preparation of CdSe QDs
CdSe QDs were prepared by an aqueous method and the
detailed information is provided in SI.[44]
holes were added into a 30 mL solution of nitroaromatic com-
pounds (5 mg L- , Solvent: H
1
bubbling.
2
O) in a quartz vial under N
2
151