Efficient photocatalytic oxidative deamination of imine and amine to aldehyde over nitrogen-doped KTi3NbO9under purple light

Article abstract of DOI:10.1039/d0cy01338b

KTi3NbO9 nanoparticles were fabricated via a simple hydrothermal method with a post-calcination treatment. The nitrogen doping (N-KTi3NbO9) leads to a narrow band gap, which in turn facilitates efficiently catalysis of imine deamination under purple light that matches its absorption spectra. Furthermore, N-KTi3NbO9 exhibits excellent performance in the tandem reaction of photocatalytic imine formation and deamination from various amines. The conversion of benzylamine was up to 100% with >85% benzaldehyde selectivity. This journal is

Full text of DOI:10.1039/d0cy01338b

Catalysis
Science &
Technology
View Article Online
View Journal
PAPER
Efficient photocatalytic oxidative deamination of
imine and amine to aldehyde over nitrogen-doped
KTi3NbO9 under purple light†
Cite this: DOI: 10.1039/d0cy01338b
ab
ac
ac
ac
Jian Zhao,d
*
Zhuobin Yu,
LinJuan Pei
Xianmo Gu,
Ruiyi Wang,
Jie Wang,
ac
ac
*
and Zhanfeng Zheng
KTi3NbO9 nanoparticles were fabricated via a simple hydrothermal method with a post-calcination
treatment. The nitrogen doping (N-KTi3NbO9) leads to a narrow band gap, which in turn facilitates
efficiently catalysis of imine deamination under purple light that matches its absorption spectra.
Furthermore, N-KTi3NbO9 exhibits excellent performance in the tandem reaction of photocatalytic imine
formation and deamination from various amines. The conversion of benzylamine was up to 100% with
>85% benzaldehyde selectivity.
Received 3rd July 2020,
Accepted 11th August 2020
DOI: 10.1039/d0cy01338b
rsc.li/catalysis
NbO9, shown in Fig. S1,† is considered as a promising
1 Introduction
photocatalyst due to its unique tunnel structure.14–16
The oxidative deamination reactions are widely applied for
the generation of diverse reactive intermediates in organic
syntheses.1 For example, the deamination of aromatic amines
is an important method for the conversion of imino groups to
aldehydes or ketones, which are critical intermediates in the
synthesis of amino acids, adenine, guanine, cytosine, and
their derivatives, as shown in Scheme 1.2,3 At present, the
deamination of aromatic amines is mainly achieved via an
indirect pathway involving aryl diazonium salt intermediates
(Sandmeyer reaction or Meerwein reaction), which requires
harsh experimental conditions.4,5 Therefore, the selective
transformation of aromatic amines under mild conditions
has attracted considerable attention.6,7 The utilization of solar
energy to drive this chemical transformation is a promising
approach in the context of green and sustainable chemistry.8
Numerous catalysts, such as TiO2 and Nb2O5, have been
explored during the past few years for such a photocatalytic
chemical transformation. These works mainly focus on the
oxidative coupling of amines.9–13 There are few reports on
photocatalytic amine deamination, a tandem reaction of
amine oxidative coupling, and deamination of imines. KTi3-
Moreover, nitrogen-doped KTi3NbO9 (N-KTi3NbO9) showed
significantly improved optical properties (electronic
structure), endowing it with advantageous electrical
conductivity and thermal stability.17,18 In this study, KTi3-
NbO9 nanoparticles were obtained via
method, followed by post-calcination.
a
hydrothermal
N-KTi3NbO9
photocatalysts were then fabricated by annealing KTi3NbO9
under ammonia gas (NH3). The doped catalyst showed
excellent performance in photocatalytic imine deamination
and the tandem reaction of amine oxidative coupling and
imine deamination under purple light irradiation. We also
found that the high conversion of amines with high
deamination efficiency was achieved when the light source
matched with the light absorption properties of N-KTi3NbO9.
2 Experimental
2.1 Photocatalysts preparation
All chemicals were purchased from Sinopharm Chemical
Reagent Co., Ltd., and used without further purification.
KTi3NbO9 (abbreviated as KTNO) was prepared via
a
hydrothermal process with post-sintering. Briefly, niobium
oxalate [Nb(HC2O4)5, 1.61 g] and titanium oxysulfate
(TiOSO4·xH2O, 1.72 g) were added to an aqueous KOH
a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese
Academy of Sciences, Taiyuan 030001, Shanxi, China. E-mail: zfzheng@sxicc.ac.cn,
guxm@sxicc.ac.cn
b Taiyuan University of Technology, Taiyuan 030024, China
c Center of Materials Science and Optoelectronics Engineering, University of
Chinese Academy of Sciences, Beijing, 100049, China
d Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion,
School of Chemistry and Chemical Engineering, Tianjin University of Technology,
Tianjin, 300384, China
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0cy01338b
Scheme 1 An example of oxidative deamination reactions available.3
This journal is © The Royal Society of Chemistry 2020
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
solution (1 m, 50 mL), and the mixture was stirred for 1 h. 3 Results and discussions
This solution was then transferred to a PTFE-lined autoclave
3.1 Physicochemical properties of KTNO and N-KTNO
(100 mL in volume) and kept at 180 °C for 24 h. After the
The powder XRD patterns of the prepared KTNO and
hydrothermal process, the white precipitate was separated
N-KTNO are presented in Fig. 1a, and are in agreement with
those of orthorhombic KTi3NbO9 (space group C2/m, lattice
parameters a = 6.392 Å, b = 3.785 Å, c = 14.865 Å) (JCPDS No.
17-0312). Notably, the XRD pattern of KTNO is similar to that
of N-KTNO, which demonstrates that nitrogen doping does
not change lattice nor phase structure. Fig. 1b shows TEM
images and HR-TEM analysis of the prepared KTNO and
N-KTNO. The mean diameter of the KTNO nanoparticles is
80 nm. Lattice distance was 0.32 and 0.30 nm, corresponding
to the (200) and (112) planes of KTi3NbO9. Similar mean
particle diameter and lattice distance were also observed for
N-KTNO. The specific surface areas for KTNO and N-KTNO
are small at 2.08 and 6.20 m2 g−1, respectively (Fig. S4†).
via centrifugation, washed with deionized water, and dried
in air for 12 h at 80 °C, respectively. The final KTNO
nanoparticles were obtained by calcining the dried
precipitate for
Similarly, N-KTi3NbO9
2
h
at 900 °C under air atmosphere.
(abbreviated as N-KTNO)
nanoparticles were obtained by calcining the dried
precipitate for 2 h at 900 °C under an NH3 atmosphere,
followed by treatment in air at 500 °C. The optimized
calcination time for N-KTNO in air was determined by the
photocatalytic activity (Fig. S2†). For comparison, g-C3N4
was prepared according to literature.19
2.2 Characterization
X-ray diffraction (XRD) patterns were acquired using a
MiniFlex II diffractometer employing Cu Kα radiation (λ =
1.5418 Å).
A 2100F transmission electron microscope
operated at 200 kV was used, with an attachment for energy-
dispersive spectroscopy (EDS). Nitrogen sorption isotherms
were recorded on an automatic adsorption instrument
(Micromeritics, TriStar II 3020 analyzer), operating at the
liquid nitrogen temperature (77 K). UV-vis diffuse-reflectance
(UV-vis-DR) spectra were recorded on a Shimadzu UV-3600
spectrophotometer. X-ray photoelectron spectra (XPS) were
recorded on a Thermo ESCALAB 250 spectrometer, employing
an Al Kα X-ray source (hν = 1486.6 eV). Binding energies were
calibrated with respect to the C1s peak at 284.6 eV.
Photoluminescence (PL) spectra were recorded on a Hitachi
F-7000 FL spectrophotometer. The photoelectrochemical
measurements were studied on an electrochemical station
(CHI660E, Chenhua, China). The electron paramagnetic
resonance (EPR) spectra were recorded using
a Bruker
EMXPLUS10/12 EPR electron paramagnetic resonance
spectrometer.
2.3 Photocatalytic activity test
Typically, the photocatalytic activity for selective amine or
imine oxidation was conducted under the irradiation of a
100 W COB LED lamp at 80 °C in an air-tight flask sealed
with 1 atm of O2 (flushed with 0.35 mL s−1 of O2 flow for 1
min prior to use). The reaction mixture consists of
benzylamine (0.08 mmol) or N-benzylidenebenzylamine
(0.04 mmol), photocatalyst (20 mg), and acetonitrile (2 mL)
as the solvent. The obtained product was analyzed via GC
(Shimadzu 2014C GC; WondaCap 5 column) and GC-MS
(Bruker SCION SQ 456). The output spectra of various
colored LEDs, namely a purple LED (375–430 nm, maximum
at 400 nm), a blue LED (425–510 nm, maximum at 455
nm), green LED (475–600 nm, maximum at 525 nm), are
presented in Fig. S3.†
Fig. 1 (a) XRD patterns of KTNO and N-KTNO, (b) TEM images and
HRTEM analysis of KTNO (b-1 and b-2), and N-KTNO (b-3 and b-4).
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Catalysis Science & Technology
Paper
The XPS spectra of KTNO and N-KTNO are shown in Fig.
S5.† K 2p3/2 and K 2p1/2 peaks at 292.2 and 294.8 eV can be
assigned to K+ in the titanate.20 Ti 2p3/2 and Ti 2p1/2 peaks at
458.0 and 464.0 eV are ascribed to Ti4+, and Nb 3d5/2 and Nb
3d3/2 peaks at 206.3 and 209.0 eV can be ascribed to
Nb5+.21,22 O 1s peaks at 529.5 and 532.0 eV are attributed to
O–M and O–H species, respectively.23 The K 2p, Ti 2p, Nb 3d,
photocatalysts are 2.88 and 2.45 eV, respectively.22 In Fig. 2b,
both KTNO and N-KTNO are n-type semiconductors, and the
flat band potentials (namely Fermi energy level, Ef) are 0.43
eV (KTNO) and 0.47 eV (N-KTNO) vs. Ag/AgCl, which are
respectively 0.17 eV and 0.13 eV vs. RHE for KTNO and
N-KTNO according to literature.27,28 Moreover, as shown in
Fig. 2c, the relative potential of the valance band (VB) vs. the
Fermi energy level was 1.39 eV for KTNO and 0.96 eV for N-
KTNO, respectively. Consequently, we plotted their band
alignment in Fig. 2d. The change in the bandgap structure
was caused by a new N 2p orbital formed above the O 2p VB
after N-doping.29 Fig. S6† shows the PL spectra of KTNO and
N-KTNO. The peaks at 540 and 630 nm are ascribed to TiO6
units and the defect-related energy, respectively.30,31
Compared with KTNO, the PL intensity of N-KTNO decreased
significantly. In Fig. S7(a),† it can be observed that the
photocurrent response of N-KTNO is remarkedly improved.
Furthermore, in Fig. S7(b),† it is apparently found that the
arc radius of N-KTNO is obviously smaller than that of KTNO,
indicating that N-KTNO can efficiently promote the
transportation of photo-generated charge carriers at the
and
O 1s peaks of N-KTNO are the same as KTNO.
Additionally, characteristic N 1s peaks are observed at 395.7
and 399.7 eV for N–M (M = Ti or Nb) or molecularly
chemisorbed nitrogen,24,25 which indicates that N is doped
into KTNO successfully. The N content in N-KTNO was
estimated to be 0.84 at%.
The colour of KTNO changes from white to greyish-green
after N-doping (Fig. 2a), resulting in extended absorption in
the visible-light range.26 The extended absorption is
confirmed by the UV-vis-DR spectra in Fig. 2a. The
absorption edge of KTNO was approx. at 430 nm, while it
obviously red-shifted to approx. 500 nm after N-doping.
Based on the UV-vis-DR spectra and Eg = 1240/λ (λ, the cut-off
wavelength), the band gap Eg of KTNO and N-KTNO
Fig. 2 (a) Electronic photographs and UV-vis-DR spectra, (b) Mott–Schottky curves, (c) valence-band XPS spectra and (d) the schematic diagram
of the DOS of KTNO and N-KTNO.
This journal is © The Royal Society of Chemistry 2020
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
material surface/interface. Consequently, in combination
with the above results, this implies that N-doping enhances
the charge separation and photocatalytic performance of
KTNO.
3.2 Photocatalytic activity for imine
(N-benzylidenebenzylamine) deamination over N-KTNO
under purple light
The photocatalytic performances of N-KTNO for imine
deamination
(selective
aerobic
oxidation
of
N-benzylidenebenzylamine) (Scheme 2) under white and
single-colored (purple, blue, and green) LED illumination are
shown in Fig. 3a. The activity does not change much when
the catalyst amount is more than 20 mg (Fig. S8†). Therefore,
20 mg of catalyst was applied in this study to eliminate the
surface area difference. The conversion rate of imine was
respectively 25.1% and 18.8% with a high benzaldehyde
selectivity (87.0% and 93.1%) for white and blue light,
whereas it decreases to 3.5% under green light. Under purple
light irradiation, the conversion rate exceeds 95% with >80%
selectivity for benzaldehyde, accompanied by a trace of
PhCHNH, as identified by GC-MS (Fig. S9†). Then, the
time-course of imine conversion and benzaldehyde generated
under purple light irradiation was studied, as given in
Fig. 3b. The imine conversion rate increases linearly from
35.2% to 97.0% with a high benzaldehyde selectivity as
prolonging the reaction time. The rest of the products
contained benzamide (3.8%), N-formylbenzylamine (6.8%)
and other impurities with trace amounts.
For comparison, traditional photocatalysts P25 and g-C3N4
were also utilized in N-benzylidenebenzylamine deamination
under purple light irradiation. In Fig. 3c, N-KTNO, P25 and g-
C3N4 showed excellent imine conversion, superior to KTNO.
However, the benzaldehyde selectivity for P25 and g-C3N4 was
much lower than that for N-KTNO. The benzaldehyde yield was
in the order of N-KTNO > P25 > g-C3N4 > KTNO. These results
demonstrated that N-KTNO exhibits excellent performance in
photocatalytic imine deamination.32 The stability of the
N-KTNO photocatalyst for imine deamination is presented in
Fig. S10,† where N-KTNO seems to be a highly efficient and
robust photocatalyst for the described process in terms of the
conversion rate of imine and the selectivity for benzaldehyde.
Fig. 3 (a) Imine conversion, benzaldehyde selectivity under white and
single-colored
LED
lights,
(b)
the
time
profile
for
N-benzylidenebenzylamine deamination under purple light, (c) imine
conversion and benzaldehyde selectivity over different samples under
purple light. Light intensity 200 mW cm−2, 80 °C, 12 h.
3.3 Proposed photocatalytic imine
(N-benzylidenebenzylamine) deamination mechanism
The mechanism of the photocatalytic imine deamination
under purple light was investigated. The absorption edge of
N-KTNO before and after N-benzylidenebenzylamine
adsorption was located at 500 and 530 nm, respectively. The
absorption difference also led to the formation of a new band
centered at 410 (Fig. S11†). These results imply that a new
surface complex is probably formed between the adsorbed
N-benzylidenebenzylamine and N-KTNO. The absorption
band of this surface complex matches well with the light
spectrum of purple LED lights (inset, Fig. 4). Moreover, as
stated above, the highest photocatalytic activity was achieved
Scheme
2 The reaction formula for imine deamination (selective
aerobic oxidation imine).
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Catalysis Science & Technology
Paper
be the NH3 desorption from the catalyst surface. Then, the
active sites return to the original state for another reaction
cycle.
3.4 Photocatalytic activity for the tandem reaction of imine
formation and deamination over N-KTNO under purple light
As mentioned in the introduction, great efforts have been
made towards the development of photocatalysts for the
oxidative coupling of amines to imines, such as Nb2O5 (ref.
13, 33 and 34) and TiO2.35,36 If the same process could be
driven by N-KTNO, it is possible to photocatalyze the selective
one-pot oxidation of primary amines to aldehydes via imine
intermediates, thereby succeeding in the photocatalytic
tandem reaction of imine formation and imine deamination
under mild conditions.7 As shown in Fig. 5, the conversion
rate of benzylamine to corresponding imine (>85%
selectivity) increases as the reaction time prolongs to 5 h. A
trace amount of benzaldehyde was detected as an
intermediate during the formation of the imine, which is
consistent with previous reports.33,35–38 After
5 h, the
selectivity for benzaldehyde products rapidly increases,
accompanied by a dramatic decrease of imine selectivity. The
final benzaldehyde product selectivity was up to 90% with
100% benzylamine conversion. These results indicate that
the tandem reaction of benzylamine oxidative coupling and
imine deamination could be successfully driven by N-KTNO
in one-pot photocatalytic reactions.
Photocatalytic of the tandem reaction of benzylamine
oxidative coupling and imine deamination over various
photocatalysts are summarized in Table S1.† The conversion
of benzylamine over N-KTNO far exceeds KTNO, which can
be attributed to two aspects: (1) the narrow bandgap of
N-KTNO (Fig. 2), which efficiently improve light utilization,
and (2) abundant oxygen vacancies, which facilitate the
adsorption of water (Scheme 2) and the formation of
Fig.
4 (a) Schematic of adsorbed N-benzylidenebenzylamine and
N-KTNO photocatalyst; (inset) the light spectrum of purple LED lights and
surface complex; (b) proposed mechanism for imine deamination (selective
aerobic oxidation of N-benzylidenebenzylamine to benzaldehyde) over the
N-KTNO photocatalyst under purple light irradiation.
for the purple light. Thus, we proposed that the surface
complex could absorb light and participate in a direct
electron transfer from a donor level, which consists of N 2p
orbitals from both the adsorbed amine species and CB of
N-KTNO (Fig. 4a). A plausible mechanism is shown in
Fig. 4b.
In step 1, the surface complex (amide species) was formed
between the N-benzylidenebenzylamine reactant and N-KTNO
photocatalyst. Under purple light irradiation, the surface
complex absorbs light and initiate the reaction by generating
holes and electrons (Fig. 4a). Photo-generated electrons could
be captured by O2 forming O2−. The resulting radicals will
react with the amide species to produce compound A. In step
2, the deamination product benzaldehyde and PhCHNH
intermediate were obtained by the C–N bond cleavage of
compound A. The PhCHNH intermediate adsorb on the
surface of N-KTNO (compound B). In step 3, the adsorbed
PhCHNH intermediate is attacked by H2O forming another
benzaldehyde product via compound C. The final step would
Fig.
5 The time profile for the tandem reaction of benzylamine
deamination. Reaction conditions: N-KTNO catalyst (20 mg),
benzylamine (0.08 mmol), acetonitrile (2 mL), purple light 200 mW
cm−2, 80 °C.
This journal is © The Royal Society of Chemistry 2020
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
benzaldehyde.39 The analysis for the number of oxygen
2 B. Chen, L. Wang and S. Gao, Recent advances in aerobic
oxidation of alcohols and amines to imines, ACS Catal.,
2015, 5(10), 5851–5876.
vacancies is provided in Fig. S12.† Moreover, the yield of the
−1
benzaldehyde product over N-KTNO (1210 mmol molcatalyst
)
is also much higher than those over TiO2 (197 mmol
molcatalyst−1) and Nb2O5 (430 mmol molcatalyst−1). In addition,
N-KTNO achieves a much higher catalytic activity than other
thermal catalysts reported in terms of benzaldehyde yield,
reaction time and temperature (Table S2†).7,39,40
To further demonstrate the extensive application of
N-KTNO in this tandem reaction, various amines were
examined (Table S3†). The high conversion of different
amines with high efficiency of imines deamination to
aldehyde products is achieved (Table S3,† entries 1–5). The
results in Table S3† also confirm that aldehyde formation is
via the deamination of corresponding imine intermediates.
However, the photocatalytic activity is low when utilizing
phenylethylamine as a reactant (Table S2,† entry 6). These
results imply that the presence of an N-benzyl group plays a
crucial role in imine deamination, which may be responsible
for stabilizing the adjacent –C.35
3 T. Nagakubo, T. Kumano, T. Ohta, Y. Hashimoto and M.
Kobayashi, Copper amine oxidases catalyze the oxidative
deamination and hydrolysis of cyclic imines, Nat. Commun.,
2019, 10(1), 413–424.
4 L. Liu and J. Zhang, Gold-catalyzed transformations of
alpha-diazocarbonyl compounds: selectivity and diversity,
Chem. Soc. Rev., 2016, 45(3), 506–516.
5 B. Ma, Z. Wu, B. Huang, L. Liu and J. Zhang, Gold-catalysed
facile access to indene scaffolds via sequential C-H
functionalization and 5-endo-dig carbocyclization, Chem.
Commun., 2016, 52(60), 9351–9354.
6 Q. Xiao, T. Connell, J. Cadusch, A. Roberts, A. Chesman and
D. Gomez, Hot-carrier organic synthesis via the near-perfect
absorption of light, ACS Catal., 2018, 8(11), 10331–10339.
7 G. Golime, G. Bogonda, H. Kim and K. Oh, Biomimetic
oxidative deamination catalysis via ortho-naphthoquinone-
catalyzed aerobic oxidation strategy, ACS Catal., 2018, 8(6),
4986–4990.
8 D. Cambie, C. Bottecchia, N. Straathof, V. Hessel and T.
Noel, Applications of continuous-flow photochemistry in
organic synthesis, material science, and water treatment,
Chem. Rev., 2016, 116(17), 10276–10341.
9 Z. Yu, E. Waclawik, Z. Wang, X. Gu, Y. Yuan and Z. Zheng,
Dual modification of TiNb2O7 with nitrogen dopants and
oxygen vacancies for selective aerobic oxidation of
benzylamine to imine under green light, J. Mater. Chem. A,
2017, 5(9), 4607–4615.
10 X. Lang, H. Ji, C. Chen, W. Ma and J. Zhao, Selective
formation of imines by aerobic photocatalytic oxidation of
amines on TiO2, Angew. Chem., Int. Ed., 2011, 50(17),
3934–3937.
11 X. Lang, W. Ma, Y. Zhao, C. Chen, H. Ji and J. Zhao, Visible-
light-induced selective photocatalytic aerobic oxidation of
amines into imines on TiO2, Chem. – Eur. J., 2012, 18(9),
2624–2631.
4 Conclusions
In summary, N-KTi3NbO9 nanoparticles are obtained via a
simple hydrothermal method, followed by a post-calcination
treatment. The N-KTi3NbO9 photocatalyst was fabricated by
annealing KTNO under NH3 and air atmosphere in sequence.
N-KTi3NbO9 achieves excellent photocatalytic activity in imine
deamination under the light matched with its absorption
properties. Moreover, N-KTi3NbO9 shows outstanding
photocatalytic performance for the selective aerobic oxidation
of amines to aldehydes via imine intermediates, and this may
give crucial insights for the mechanism investigation in amines
oxidative coupling reactions. In this study, the tandem reaction
of imine formation and deamination, or the transformation
from aromatic amine to aromatic imine, and then to aromatic
aldehyde under mild conditions in one-pot was successfully
achieved. We believe that this synthetic strategy is practicable
and can be extended to diverse photocatalytic reactions.
12 S. Furukawa, Y. Ohno, T. Shishido, K. Teramura and T.
Tanaka, Selective amine oxidation using Nb2O5 photocatalyst
and O2, ACS Catal., 2011, 1(10), 1150–1153.
Conflicts of interest
13 Y. Zhang, L. Pei, Z. Zheng, Y. Yuan, T. Xie and J. Yang, et al.,
Heterojunctions between amorphous and crystalline
niobium oxide with enhanced photoactivity for selective
aerobic oxidation of benzylamine to imine under visible
light, J. Mater. Chem. A, 2015, 3(35), 18045–18052.
14 A. Wadsley, Alkali titanoniobates - crystal structures of
KTiNbO5 + KTi3NbO9, Acta Crystallogr., 1964, 17(6), 623–625.
15 K. Teshima, S. Lee, A. Yamaguchi, S. Suzuki, K. Yubuta and T.
Ishizaki, et al., The growth of highly crystalline, idiomorphic
potassium titanoniobate crystals by the cooling of a potassium
chloride flux, CrystEngComm, 2011, 13(4), 1190–1196.
16 J. Colin, V. Pralong, M. Hervieu, V. Caignaert and B. Raveau,
Lithium insertion in an oriented nanoporous oxide with a
tunnel structure: Ti2Nb2O9, Chem. Mater., 2008, 20(4),
1534–1540.
There are no conflicts to declare.
Acknowledgements
We appreciate the financial support from the National
Natural Science Foundation of China (No. 21773284) and the
Hundred Talents Program of the Chinese Academy of
Sciences and Shanxi Province.
Notes and references
1 S. Ghosh and C. Jana, Metal free biomimetic deaminative
direct C-C coupling of unprotected primary amines with
active methylene compounds, Org. Biomol. Chem.,
2019, 17(48), 10153–10157.
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Catalysis Science & Technology
Paper
17 M. Yang, A. VanWassen, R. Guarecuco, H. Abruna and F.
DiSalvo, Nano-structured ternary niobium titanium nitrides
as durable non-carbon supports for oxygen reduction
reaction, Chem. Commun., 2013, 49(92), 10853–10855.
18 S. Dong, X. Chen, X. Zhang and G. Cui, Nanostructured
transition metal nitrides for energy storage and fuel cells,
Coord. Chem. Rev., 2013, 257(13–14), 1946–1956.
29 H. Park, T. Song and U. Paik, Porous TiNb2O7 nanofibers
decorated with conductive Ti1−xNbxN bumps as a high power
anode material for Li-ion batteries, J. Mater. Chem. A,
2015, 3(16), 8590–8596.
30 A. Kudo and E. Kaneko, Photoluminescent properties of ion-
exchangeable layered oxides, Microporous Mesoporous Mater.,
1998, 21(4–6), 615–620.
19 L. Ge, C. Han, X. Xiao and L. Guo, In situ synthesis of
cobalt-phosphate (Co-Pi) modified g-C3N4 photocatalysts
with enhanced photocatalytic activities, Appl. Catal., B,
2013, 142, 414–422.
31 Q. Ma, Y. Zhou, M. Lu, A. Zhang and G. Zhou, Synthesis and
luminescence of pure and Eu3+-activated Aurivillius-type Bi3-
TiNbO9 nanophosphors, Mater. Chem. Phys., 2009, 116(2–3),
315–318.
20 D. Salinas, S. Guerrero, A. Cross, P. Araya and E. Wolf,
Potassium titanate for the production of biodiesel, Fuel,
2016, 166, 237–244.
32 G. Liu, L. Wang, C. Sun, X. Yan, X. Wang and Z. Chen, et al.,
Band-to-band
visible-light
photon
excitation
and
photoactivity induced by homogeneous nitrogen doping in
layered titanates, Chem. Mater., 2009, 21(7), 1266–1274.
33 S. Furukawa, Y. Ohno, T. Shishido, K. Teramura and T.
Tanaka, Selective amine oxidation using Nb2O5 photocatalyst
and O2, ACS Catal., 2011, 1(10), 1150–1153.
34 S. Furukawa, Y. Ohno, T. Shishido, K. Teramura and T.
Tanaka, Reaction mechanism of selective photooxidation of
amines over Niobium Oxide: visible-light-induced electron
transfer between adsorbed amine and Nb2O5, J. Phys. Chem.
C, 2013, 117(1), 442–450.
35 X. Lang, W. Ma, Y. Zhao, C. Chen, H. Ji and J. Zhao, Visible-
light-induced selective photocatalytic aerobic oxidation of
amines into imines on TiO2, Chemistry, 2012, 18(9),
2624–2631.
36 X. Lang, H. Ji, C. Chen, W. Ma and J. Zhao, Selective
formation of imines by aerobic photocatalytic oxidation of
amines on TiO2, Angew. Chem., Int. Ed., 2011, 50(17),
3934–3937.
21 L. Kong, Z. Jiang, C. Wang, F. Wan, Y. Li and L. Wu, et al.,
Simple ethanol impregnation treatment can enhance
photocatalytic activity of TiO2 nanoparticles under visible-light
irradiation, ACS Appl. Mater. Interfaces, 2015, 7(14), 7752–7758.
22 H. Huang, C. Wang, J. Huang, X. Wang, Y. Du and P. Yang,
Structure inherited synthesis of N-doped highly ordered
mesoporous Nb2O5 as robust catalysts for improved visible
light photoactivity, Nanoscale, 2014, 6(13), 7274–7280.
23 S. Lou, Y. Ma, X. Cheng, J. Gao, Y. Gao and P. Zuo, et al.,
Facile synthesis of nanostructured TiNb2O7 anode materials
with superior performance for high-rate lithium ion
batteries, Chem. Commun., 2015, 51(97), 17293–17296.
24 J. Yuan, M. Chen, J. Shi and W. Shangguan, Preparations
and photocatalytic hydrogen evolution of N-doped TiO2 from
urea and titanium tetrachloride, Int. J. Hydrogen Energy,
2006, 31(10), 1326–1331.
25 Z. Zhai, Y. Huang, L. Xu, X. Yang, C. Hu and L. Zhang, et al.,
Thermostable nitrogen-doped HTiNbO5 nanosheets with a
high visible-light photocatalytic activity, Nano Res.,
2011, 4(7), 635–647.
26 H. Park, H. Wu, T. Song, X. David Lou and U. Paik, Porosity-
Controlled TiNb2O7 microspheres with partial nitridation as
a practical negative electrode for high-power Lithium-Ion
batteries, Adv. Energy Mater., 2015, 5(8), 1401945.
37 L. Aschwanden, T. Mallat, M. Maciejewski, F. Krumeich and
A. Baiker, Development of a new generation of gold catalysts
for amine oxidation, ChemCatChem, 2010, 2(6), 666–673.
38 B. Zhu, M. Lazar, B. Trewyn and R. Angelici, Aerobic
oxidation of amines to imines catalyzed by bulk gold
powder and by alumina-supported gold, J. Catal.,
2008, 260(1), 1–6.
27 C. Yao, R. Wang, Z. Wang, H. Lei, X. Dong and C. He, Highly
dispersive and stable Fe3+ active sites on 2D graphitic
carbon nitride nanosheets for efficient visible-light
photocatalytic nitrogen fixation, J. Mater. Chem. A,
2019, 7(48), 27547–27559.
39 L. Al-Hmoud and C. Jones, Reaction pathways over copper
and cerium oxide catalysts for direct synthesis of imines
from amines under aerobic conditions, J. Catal., 2013, 301,
116–124.
40 L. Gong, L. Xing, T. Xu, X. Zhu, W. Zhou and N. Kang, et al.,
Metal-free oxidative olefination of primary amines with
benzylic C-H bonds through direct deamination and C-H
bond activation, Org. Biomol. Chem., 2014, 12(34),
6557–6560.
28 C. Yao, A. Yuan, Z. Wang, H. Lei, L. Zhang and L. Guo, et al.,
Amphiphilic two-dimensional graphitic carbon nitride
nanosheets
for
visible-light-driven
phase-boundary
photocatalysis, J. Mater. Chem. A, 2019, 7(21), 13071–13079.
This journal is © The Royal Society of Chemistry 2020
Catal. Sci. Technol.