Integrating photocatalytic reduction of CO2 with selective oxidation of tetrahydroisoquinoline over InP–In2O3 Z-scheme p-n junction

Article abstract of DOI:10.1007/s11426-019-9620-1

The development of a facile strategy to construct stable hierarchal porous heterogeneous photocatalysts remains a great challenge for efficient CO₂ reduction. Additionally, hole-trapping sacrificial agents (e.g., triethanolamine, triethylamine, and methanol) are mostly necessary, which produce useless chemicals, and thus cause costs/environmental concerns. Therefore, utilizing oxidation ability of holes to develop an alternative photooxidation reaction to produce value-added chemicals, especially coupled with CO₂ photoreduction, is highly desirable. Here, an in situ partial phosphating method of In₂O₃ is reported for synthesizing InP–In₂O₃ p-n junction. A highly selective photooxidation of tetrahydroisoquinoline (THIQ) into value-added dihydroisoquinoline (DHIQ) is to replace the hole driven oxidation of typical sacrificial agents. Meanwhile, the photoelectrons of InP–In₂O₃ p-n junction can induce the efficient photoreduction of CO₂ to CO with high selectivity and stability. The evolution rates of DHIQ and CO are 2 and 3.8 times higher than those of the corresponding In₂O₃ n-type precursor, respectively. In situ irradiated X-ray photoelectron spectroscopy and electron spin resonance are utilized to confirm that the direct Z-scheme mechanism of InP–In₂O₃ p-n junction accelerate the efficient separation of photocarriers.

Full text of DOI:10.1007/s11426-019-9620-1

SCIENCE CHINA
Chemistry
•ARTICLES•
https://doi.org/10.1007/s11426-019-9620-1
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Integrating photocatalytic reduction of CO2 with selective
oxidation of tetrahydroisoquinoline over InP–In2O3 Z-scheme p-n
junction
Bohang Zhao1, Yi Huang1, Dali Liu1, Yifu Yu1,2 & Bin Zhang1,3*
1Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Science, Tianjin University,
Tianjin 300072, China;
2Institute of Molecular Plus, Tianjin University, Tianjin 300072, China;
3Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
Received July 15, 2019; accepted September 20, 2019; published online November 18, 2019
The development of a facile strategy to construct stable hierarchal porous heterogeneous photocatalysts remains a great chal-
lenge for efficient CO2 reduction. Additionally, hole-trapping sacrificial agents (e.g., triethanolamine, triethylamine, and me-
thanol) are mostly necessary, which produce useless chemicals, and thus cause costs/environmental concerns. Therefore,
utilizing oxidation ability of holes to develop an alternative photooxidation reaction to produce value-added chemicals, espe-
cially coupled with CO2 photoreduction, is highly desirable. Here, an in situ partial phosphating method of In2O3 is reported for
synthesizing InP–In2O3 p-n junction. A highly selective photooxidation of tetrahydroisoquinoline (THIQ) into value-added
dihydroisoquinoline (DHIQ) is to replace the hole driven oxidation of typical sacrificial agents. Meanwhile, the photoelectrons
of InP–In2O3 p-n junction can induce the efficient photoreduction of CO2 to CO with high selectivity and stability. The evolution
rates of DHIQ and CO are 2 and 3.8 times higher than those of the corresponding In2O3 n-type precursor, respectively. In situ
irradiated X-ray photoelectron spectroscopy and electron spin resonance are utilized to confirm that the direct Z-scheme
mechanism of InP–In2O3 p-n junction accelerate the efficient separation of photocarriers.
CO2 reduction, dehydrogenation, photocatalysis, Z-scheme, tetrahydroisoquinoline
Citation:
Zhao B, Huang Y, Liu D, Yu Y, Zhang B. Integrating photocatalytic reduction of CO2 with selective oxidation of tetrahydroisoquinoline over InP–
In2O3 Z-scheme p-n junction. Sci China Chem, 2019, 62, https://doi.org/10.1007/s11426-019-9620-1
1 Introduction
instance, porous and hierarchal features are engineered into
photocatalytic nanomaterials for enhancing photoadsorption
and accelerating photocarrier separation [23–26]. Growing
another appropriate material on pure semiconductors to
produce Type I, Type II and Z-scheme hybrid photocatalysts
is effective for promoting the charge separation efficiency
[27–30]. However, the rational design of heterostructured
photocatalysts endowing porous and hierarchal character-
istics is still challenging [31]. In addition, for most typical
methods, the lattice mismatches between heterostructures
often lead to weak interface stability and interfacial in-
activation [32]. Thus, it is highly desirable to develop a facile
Photocatalytic reduction of CO2 (PRC) is a promising way to
convert greenhouse gas into fuels and useful chemical ma-
terials [1–7], and thus provides a possible way to solve the
global energy crisis and environmental problems [8–12].
Currently, increasing efforts have been devoted to the ex-
ploration of suitable semiconductors (e.g., metal oxides [13–
16], oxynitrides [17], phosphides [4,18], sulphides [19] and
metal complexes [20–22]) as photocatalysts for PRC. For
*Corresponding author (email: bzhang@tju.edu.cn)
© Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
chem.scichina.com link.springer.com

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Zhao et al. Sci China Chem
strategy to synthesize heterogeneous materials with porous
and hierarchical architectures for PRC.
Sacrificial agents are often adopted to trap photo-
generated holes during PRC measurements because of the
high oxidation potential of water [33,34]. Although the
addition of sacrificial agents (e.g., triethanolamine, trie-
thylamine, and methanol) can boost the performance of
PRC, this process inevitably increase costs and cause en-
vironmental concerns. Thus, effective utilization of photo-
induced holes for catalytic oxidation synthesis of value-
added chemicals to replace useless sacrificial agents is of
vital importance [35–38].
Figure 1 Schematic diagram illustrating the synthesis and energy band
diagram of of InP–In2O3 p-n junction nanosheet-based porous microspheres
(color online).
Dihydroisoquinoline (DHIQ) and its derivatives, ones of
important intermediates in pharmaceuticals and fine chemi-
cals [39,40], are typically synthesized by the well-designed
multi-component multistep process [41] or noble metal cat-
2.2 Synthesis of InP–In2O3
InS-TETA inorganic-organic hybrids were synthesized ac-
cording to our previously work [44]. In a typical procedure,
tartaric acid (2 mmol), InCl3 (1 mmol) and L-cysteine
(6 mmol) were added into a mixture solvent of DIW and
TETA with a total volume of 18 mL (VDIW/VTETA=2:1) in a
50 mL Teflon-lined stainless-steel autoclave. After stirring to
form a homogeneous solution, the autoclave was sealed and
treated at 160 °C for 24 h. Then, it was cooled down natu-
rally to room temperature. The white precipitate was washed
by DIW and absolute ethanol, respectively, and dried in a
vacuum oven to produce InS-TETA.
A 10 mg as-prepared InS-TETA was put into a solvent of
12 mL DIW in a 20 mL Teflon-lined stainless-steel autoclave
under stirring to form a homogeneous solution. The auto-
clave was sealed and kept at 180 °C for 10 h. The yellow
precipitate was washed by DIW and absolute ethanol, re-
spectively, and dried in a vacuum oven to produce hier-
archical porous In2S3 microsphere.
alyzed
dehydrogenation
of
corresponding
tetra-
hydroisoquinoline (THIQ) precursors [42,43]. However, the
complex process or the use of noble metal restricts their
practical applications. Impressively, THIQ owns a lower
oxidation potential than water, providing rich possibility for
using THIQ to replace conventional sacrificial agents during
PRC. Therefore, a selective photooxidation of cheap THIQ
to value-added DHIQ, especially integrated with efficient
PRC, is economically desirable.
Here, by using n-type In2O3 nanosheet-based porous
hierarchical spheres as the starting materials, we report an in
situ partial phosphating method to synthesize InP–In2O3 p-n
junction (Figure 1). By coupling PRC with the dehy-
drogenation of THIQ, the conversion efficiency of PRC into
CO can be boosted, meanwhile, the DHIQ with an out-
standing selectivity can be obtained. Moreover, DHIQ deri-
vatives can be accessible by integrating with PRC.
Furthermore, the Z-scheme mechanism of InP–In2O3 p-n
junction is found to be important for accelerating the se-
paration of electrons and holes, making their performance
much higher than those of starting In2O3.
A 50 mg as-prepared hierarchical porous In2S3 micro-
sphere was put into a tube furnace. Then, the sample was
heated to 500 °C with a rate of 1 °C/min, and kept at 500 °C
for 3 h under flowing air atmosphere. Finally, it was cooled
down naturally to room temperature to produce hierarchical
porous In2O3 microsphere.
2 Experimental
InP–In2O3 was synthesized by gas-solid reaction using
sodium hypophosphite as phosphorus source [45]. First,
10 mg as-prepared In2O3 and 5 mg NaH2PO2•H2O were put
in two separate quartz boats with NaH2PO2•H2O at the up-
stream side for the furnace. Subsequently, the samples were
heated to 300 °C for 1, 2 and 3 h, respectively (see details in
Table S1 and Figure S6, Supporting Information online) in a
closed Ar atmosphere at a rate of 2 °C/min (take the 2 h
sample as example of InP–In2O3 mentioned in the text). After
cooling down to room temperature, the sample was washed
with DIW and absolute ethanol several times, respectively,
and finally dried in a vacuum oven overnight.
2.1 Chemicals
Indium chloride (InCl3), L-cysteine, triethylenetetramine
(TETA) were purchased from Aladdin Ltd. (China). Sodium
hypophosphite, anhydrous magnesium sulfate and trietha-
nolamine (TEOA) were purchased from JK Chemical Ltd.
(China). Tetrahydroisoquinoline derivatives was purchased
from Bide Pharmatech Ltd. (China). The carbon dioxide
(CO2) gas was bought from Air Liquide (Tianjin) Co., Ltd.
(China). Deionized water (DIW) was used in all the ex-
perimental processes. All chemicals were of analytical grade
and used without further purification.

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Zhao et al. Sci China Chem
2.3 Materials characterizations
was characterized and quantified by GC-2010 Plus with BID
using the following equation. The measurement of the THIQ
conversion was discussed later.
Powder X-ray diffraction (XRD) was performed on a Bruker
D8 Focus Diffraction System (Germany) using a Cu Kα
source (λ=0.154178 nm) and the in-situ and ex-situ X-ray
photoelectron spectroscopy (XPS) measurements were per-
formed on a photoelectron spectrometer using Al Kα radia-
tion as the excitation source (PHI 5000 VersaProbe) with or
without illumination. All the peaks were calibrated with C 1s
spectrum at binding energy of 284.8 eV. Scanning electron
microscopy (SEM) and energy disperse spectroscopy (EDS)
analysis were taken with a Hitachi S-4800 scanning electron
microscope (Japan) equipped with the Thermo Scientific
energy-dispersion X-ray fluorescence analyser (USA).
Transmission electron microscopy (TEM), high resolution
TEM (HRTEM) and scanning transmission electron mi-
croscope EDS (STEM-EDS) element mapping images were
obtained with Tecnai G2 F20 system equipped with EDAX.
UV-Vis diffuse reflectance absorbance spectrum was tested
on Shimadzu UV3600 (Japan). The gas chromatograph-
mass spectrometer (GC-MS) was carried out with TRACE
DSQ. The liquid phase product was measured on Aglient
7890A (USA) with thermal conductivity (TCD) and flame
ionization detector (FID). Nuclear magnetic resonance
(NMR) spectra were recorded on Varian Mercury Plus 400
instruments (USA) at 400 MHz (1H NMR) and 100 MHz
(13C NMR). Chemical shifts were reported in parts per
million (ppm) down field from internal tetramethysilane.
Multiplicity was indicated as follows: s (singlet), d (doub-
let), t (triplet), q (quartet), mm (multiplet), dd (doublet of
doublet), br (broad). Coupling constants were reported in
Hz. The injection temperature was set at 280 °C. Nitrogen
was used as the carrier gas at 1.5 mL/min. The gas phase
product was measured on Shimadzu GC-2010 Plus (Japan)
with barrier discharge ionization detector (BID). The
electron spin resonance (ESR) analysis was obtained with
Bruker A300 and 300 W Xe lamp (Germany) with the light
intensity of 500 mW/cm2 in the wavelength region of
320–780 nm.
The evolution rate of CO were calculated using the
equation of
Evolution rate (µmol/(g h))
Peak area of CO×C
Peak area of standard gas ×t ×m
=
× V
(1)
where C is the concentration of CO in standard gas, t is the
illumination time, m is the mass of used catalyst, and V is the
volume of used Sneaker bottle.
3 Results and discussion
3.1 Morphology and structural characterization
Nanosheet-based porous hierarchical In2O3 spheres were
synthesized by air oxidation of the corresponding In2S3
precursors [45]. Then, the partial phosphating process was
carried out by gas-solid reaction using sodium hypopho-
sphite as the phosphorus source (see the details in the Sup-
porting Information online). The SEM images (Figures S1–
S3) show the successful preparation of nanosheet-based
porous hierarchical In2O3 spheres. After phosphating, the
hierarchical porous morphology of In2O3 can be maintained
(Figure 2(a)). The TEM image (Figure 2(b)) indicates the
nanosheet-based morphology of as-prepared materials. In the
HRTEM image (Figure 2(c)), the fringe spacing of 0.42 nm
matches well with the (211) lattice plane of In2O3, and some
amorphous parts can be clearly seen (the red circle in Figure
2(c)). The amorphous region may be caused by phosphati-
zation. After crystallization at elevated temperature in Ar
atmosphere, all the fringe spacings can be attributed to the
mixture of In2O3 and InP (Figure 2(d)), revealing the het-
erogeneous components of In2O3 and InP rather than P-
doping structure. Such hybrid InP–In2O3 structure is con-
firmed later by its Z-scheme photocatalytic mechanism.
Although the exact reason for the formation of hetero-
geneous materials is still unclear, the InP–In2O3 hybrids may
be associated with the InP–In2O3 interface energy and the
elastic repulsion between neighboring In2O3, as discussed in
the initial randomly distributed Ag2S small islands on CdS
during the partial cation exchange reaction of CdS nanorods
with Ag+ cations [46]. The high-angle annular dark field
(HAADF) image and the associated STEM-EDS element
mapping images (Figure 2(e)) suggest the existence of
phosphorus element in the samples. All the XRD peaks are
found to originate from cubic In2O3 (JCPDS NO.06-0416)
(Figure 2(f)). After crystallization, some weak peaks indexed
to cubic InP (JCPDS NO.32-0452) can be seen (Figure S4),
confirming the compositions of InP and In2O3 in the samples.
XPS is introduced to verify the element valence state of as-
converted samples (Figure 2(g) and Figure S5). For InP–
2.4 Photocatalytic CO2 reduction
The CO2 photocatalytic reduction is performed in a non-
proton environment using Sneaker bottle, which could avoid
the competition hydrogen evolution reaction and improve the
energy conversion efficiency for CO2 reduction. In a typical
procedure of photocatalytic CO2 reduction, 25 mg photo-
catalyst was well-dispersed in CO2 purged mixture solution
of 25 mL acetonitrile and 0.02 mmol THIQ. 300 W Xe lamp
with the light intensity of 500 mW/cm2 in the wavelength
region of 320–780 nm was used as the light source. To
eliminate the thermal effect, condensate water (25 °C) was
introduced to cooling down the system. The generated CO

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Zhao et al. Sci China Chem
Figure 3 (a) Cartoon integrating the photocatalytic reduction reaction of
CO2 with the oxidative dehydrogenation of tetrahydroisoquinoline over
InP–In2O3; (b) time-dependent THIQ conversion rates and (c) the evolving
amount of CO over In2O3 and InP–In2O3; (d) cycle tests of InP–In2O3 for
both CO2 reduction and THIQ conversion; (e) mass spectra of GC-MS
analysis in 13CO2 isotope experiment; (f) performance comparisons of
THIQ and its derivatives measured after 10 h (color online).
Figure 2 (a) SEM and (b) TEM images of InP–In2O3; (c, d) HRTEM
images of InP–In2O3 before and after crystallization; (e) HAADF and
STEM-EDS elemental mapping images of InP–In2O3; (f) XRD patterns of
InP–In2O3 before and after crystallization; (g) P 2p XPS spectra of InP and
InP–In2O3 (color online).
which is determined by NMR spectrum and GC spectro-
metry and the selectivity of DHIQ is up to 97% (Figures S11
and S12). Meanwhile, the amount of CO over In2O3 and InP–
In2O3 shows nearly linear growth to 178 and 663 μmol/g,
respectively (Figure 3(c)). In addition, the ratio of reduction
product/oxidation product is 0.93, which is slightly deviated
from 1 due to the deviation of manual injection. Besides, no
obvious CO can be detected without THIQ (Figure 3(f)),
illustrating the boosted CO2-to-CO conversion reaction in
the presence of THIQ. Furthermore, the photocatalytic ac-
tivity of InP–In2O3 is retained after five runs (Figure 3(d)),
suggesting a good stability of the as-pyepared catalyst
(Figures S14 and S15). The rates of CO production and
conversion of THIQ are kept at about 62 μmol/(g h) and
92%, respectively, suggesting the robust durability of InP–
In2O3. To verify the carbon source of CO formation, 13CO2
isotope experiment was carried out. The results of mass
spectrometry show that 13CO (m/z=29) is detected once CO2
is replaced by 13CO2, indicating the carbon atom of evolved
CO originates from CO2 feedstock (Figure 3(e)). In addition,
when using Ar as the reaction gas, CO cannot be detected,
further confirming that CO product stems from PRC.
In2O3, the peak located at 129.5 eV can be ascribed to P3−.
The slightly shift toward higher binding energy of InP–In2O3
than InP, which was caused by the surrounding O atoms with
stronger electronegativity [47], and the weak peak intensity
compared with the pure InP indicated the partial phosphating
of the initial In2O3. All the aforementioned results demon-
strate the successful preparation of InP–In2O3.
3.2 Photocatalytic performance
The PRC was performed under the illumination of 300 W Xe
lamp (see Supporting Information online for details). As
shown in Figure 3(a), the photogenerated electrons and holes
from exited InP–In2O3 are used to reduce CO2 and oxidize
THIQ, respectively. During the irradiation, the evolving
amount of CO, and the conversion of THIQ and its oxidative
product were monitored by gas chromatography. For com-
parison, the performance of In2O3 was also evaluated (see
details in Table S1 and Figure S9(a–c)). As displayed in
Figure 3(b), 0.02 mmol THIQ can be alomost completely
converted after 10 h illumination over InP–In2O3, superior to
that of pure In2O3. The oxidation product of THIQ is DHIQ,
To investigate the substrate tolerance, 6-Br- and 6,7-di-
methoxy-THIQ were selected as the representative electro-

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Zhao et al. Sci China Chem
withdrawing and -donating groups, respectively. Im-
pressively, THIQ with electro-withdrawing or -donating
groups can either be facilely oxidized and show an extremely
acceptable conversion and high selectivity, simultaneously.
And the CO yield can reach 170 μmol/(g h) for 6,7-di-
methoxy-THIQ, suggesting the evolution rate of CO2-to-CO
can be accelerated by suitable THIQ derivatives (Figure 3
(f)).
3.3 Electron transfer and mechanism
Figure 4 (a, b) In situ irradiated XPS spectra of O 1s (a) and P 2p (b) in
InP–In2O3. (c, d) DMPO spin-trapping ESR spectra recorded for •O2 and
•OH under UV-Vis light for InP, In2O3, InP-In2O3; (e, f) schematic illus-
tration of the electron tranfer mode of Type-II and Z-scheme heterojunction
for InP–In2O3 (color online).
A series of characterizations were adopted to elucidate the
enhanced PRC performance of InP–In2O3 in the presence of
THIQ. First, UV-Vis diffuse reflectance absorbance spectra
(Figure S13) shows that InP–In2O3 owns stronger absor-
bance of visibile light than In2O3. Then, transient photo-
current response curves indicate that InP–In2O3 shows
enhanced photocurrent than In2O3, indicating higher se-
paration efficiency of photogenerated electron-hole pairs in
InP–In2O3 (Figure S9(d)). In addtion, oxygen vacancies can
be observed for both In2O3 and InP–In2O3 samples (Figures
S6 and S7), indicating that the improved performance of the
InP–In2O3 p-n junction do not originate from the presence of
oxygen vacancies. The positions of conduction or valance
band (CB or VB) of In2O3 and InP were measured using
Mott-Schottky plots (Figures S8 and S10) [48,49]. Next,
some control experiments are carried out to show the pho-
tocatalytic mechanism of p-n junction. Firstly, in situ irra-
diated XPS [50] was carried out. After illumination, O 1s
peak does positively shift from 531.7 to 531.8 eV (Figure 4
(a)), indicating the decrease of electron density of In2O3. At
the same time, the characteristic peak of P3− corresponding to
InP experience a slightly negative shift of 0.1 eV after illu-
mination, indicating an increase in the electron density of
InP. These in situ irradiated XPS results provide a solid proof
for the In2O3-to-InP tranfer of photoelectrons, which is in
good agreement with the Z-scheme mechanism. To further
verify the interfacial electron tranfer mode, the ESR analysis
−
−
However, for InP–In2O3, the intensities of •O2 and •OH
were both detected. These characteristics suggested that our
photocatalytic process follows a Z-scheme mechanism
(Figure 4(f)), which is in accordance with in situ irradiated
XPS observations. Moreover, the signals of both DMPO-
−
•OH and DMPO-•O2 that motivated by InP–In2O3 were
much stronger than the signal of InP and In2O3, which in-
dicated that the Z-scheme system exists much higher sepa-
rate and tranfer efficiency. Therefore, the fabrication of a Z-
scheme system in InP–In2O3 p-n junction, rather than type-II
heterojunction, is a rational reason for boosting the CO2-to-
CO reaction by coupling with THIQ oxidation.
Based on above results, a plausible photocatalytic me-
chanism for coupling the CO2-to-CO reaction with the THIQ
photooxidation over InP–In2O3 is proposed in Scheme 1. The
transfer of charge carriers in Z-scheme InP–In2O3 is shown
in Figure 1, which is endowed the prolonged lifetime of
photogenerated carriers to boost surface chemical reaction.
For details, the photogenerated holes from In2O3 oxidize the
THIQ to the associated cation radical A, which is subse-
quently deprotonated to form intermediate B (a radical an-
ion). After taking off another proton and releasing one
electron, the target product (DHIQ) is acquired. As reported
in previous work [35], the released protons can be reduced by
the electron from InP to generate H2. However, only little
amount of H2 was detected in our system. It is well known
that a single electron transfer process is undergone to form
−
was implemented to disclose the spin reactive •OH and •O2
species motivated by the photocatalysts in water/methanol
by using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a
spin trap [51,52]. It can be seen the DMPO-•OH character-
istic peaks generated under UV-Visible light in Figure 4(d).
The ESR spectra with relative intensities of 1:2:2:1 in-
dentified to DMPO-•OH addition compound were distinctly
detected for both In2O3 and InP–In2O3, nevertheless, no
clearly signal could be observed for InP. Similarly, as shown
in Figure 4(c), the DMPO-•O2− signals were also tested under
UV-Vis irradiation and six characteristic peaks with similar
strength were only detected for InP and InP–In2O3. Con-
sidering the way of electron tranfer, the formation of both
•−
surface adsorbed CO2 in the first step of CO2 reduction
reaction [16], which will abide further reaction with elec-
trons and protons [31]. According to the aforementioned
information and our experimental results, we make a rea-
sonable inference that the released protons from THIQ and
•−
photogenerated electrons will attack the CO2 to form CO
and H2O. The Z-scheme system fabricated by InP–In2O3 and
the presence of THIQ are responsible for boosting CO2-to-
CO conversion reaction, and simultaneously yielding value-
added DHIQ with high selectivity.
−
•O2 and •OH on InP–In2O3 should be forbidden if the het-
erojunction follows the type-II rules as shown in Figure 4(e).

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In summary, a facile in situ partial phosphating method has
been developed to synthesize InP–In2O3 p-n junction for
photocatalytic conversion CO2 to CO with 92% selectivity.
The CO evolution rate can be boosted after integrating with
the dehydrogenation of THIQ derivatives. Such photo-
oxidation reaction of THIQ can lead to the highly selective
formation of DHIQ. After decorated with electron-donating
groups, the evolution rates of both CO and dehydrogenation
product can be increased, and reach to 170 and
200 μmol/(g h) for CO and the dehydrogenation product of
6,7-dimethoxy-1,2,3,4-THIQ, respectively. Such excellent
performances are attributed to the efficient separation/
transfer caused by the Z-scheme mechanism of nanosheet-
based InP–In2O3 p-n junction. Our work may not only pro-
vide new opportunities for both CO2 conversion and DHIQ
derivatives with excellent selectivity and high economic
value, but also open up a promising method of THIQ deri-
vatives to replace oxygen evolution reaction or sacificant
agents during CO2 conversion reaction.
Acknowledgements This work was supported by the National Natural
Science Foundation of China (21422104), and the Natural Science Foun-
dation of Tianjin City (17JCJQJC44700, 16JCZDJC30600).
Conflict of interest The authors declare that they have no conflict of
interest.
Supporting information The supporting information is available online at
http://chem.scichina.com and http://link.springer.com/journal/11426. The
supporting materials are published as submitted, without typesetting or
editing. The responsibility for scientific accuracy and content remains en-
tirely with the authors.
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