|
Project
title |
In depth study of the
structure photocatalytic activity relationship of lanthanide metal doped titania photocatalysts (PHOTOLANTI) |
|
Project
Code and number |
PN-III-P1-1.1-TE-2016-0562; No. 10/2018 |
|
Contracting
Authority |
UEFISCDI |
|
Project
Host Institution |
University
of Bucharest |
|
Run
period |
02.05.2018-30.04.2020 |
|
Total
funding |
450.000,00
lei |
Research
Team:
1.
Bogdan Cojocaru - director
2.
Octavian Pavel - young researcher
3.
Daniel Avram - PhD student
4.
SAbina Ion - PhD student
Project Summary
Doping of TiO2 with rare earth metals emerged as a very
efficient method to improve the photocatalytic performances. In addition, the upconversion effect representing the combination of
multiple low energy photons to one high energy photon has been assumed to
increase the number of UV/Vis photons required for a desired photochemical
transformation. However, in this stage there is a series of questions at which
the answers are missing or not clear:
i)
it is not clear where the catalytic behavior is attributed to the
defects of titania or of the lanthanide guest dopant,
ii)
there is not a systematic control of doping of titania
by lanthanide species in order to answer to this question,
iii)
it is not clear where the photocataltic
activity is related or not to the upconversion,
iv)
there is no coherent literature information about the
solubility of lanthanides in the titania matrix.
To answer these questions a correlation of a rigorous control of
the preparation of these materials providing well homogeneous substituted Ln
species and lanthanide oxide domains with characterization and catalytic
evaluation in a representative reaction is necessary. The project will
focus the efforts with the aim to find answers to these questions by:
1. Synthesis of well homogeneous and egg-shell distributed Ln-TiO2
substituted Ti4+ photocatalysts;
2. Discrimination of the effect of the Ln location (as either
substitutional dopant or segregated phase) and of the type of the metal species
where the defects responsible for the photocatalytic activity are associated,
using various in-situ and ex-situ techniques;
3. Photoluminescence exhaustive investigations in order to
elucidate to what extent the upconversion contributes
to the enhancement of the photocatalytic performances;
4. Correlation of the results of these measurements with the
photocatalytic results in the selective aerobic oxidative condensation of benzylamine under both batch and continuous flow
experiments.
The implementation degree of the project:
Phase I/2018 (02.05.2018
31.12.2018): Synthesis of photocatalysts by
controlled doping of TiO2 with various lanthanides (Budget 138000 lei)
In order to achieve this phase, the following activities are
carried out:
Activity 1.1. - Synthesis of
Ln-TiO2 photocatalysts by inverse microemulsion method;
Activity 1.2. - Synthesis
of Ln-TiO2 photocatalysts by ethoxyde-lanthanide reaction;
Activity 1.3. - Synthesis
of Ln-TiO2 photocatalysts by impregnation
method;
Activity 1.4. - Physico-chemical characterization of the prepared catalusts
(XRD, Raman, photoluminescence);
Summary of the research report (Phase I):
A
series of TiO2 catalysts containing 1%Er, 1%Yb, 1%Dy, 1%, Nd,
1%Pr, 1%Tm or 1%Tb were prepared by doping via-sol gel or wet impregnation
methods. 1%Er, 1%Yb, 1%Dy, 1%, Nd, 1%Pr and 1%Tb
doped TiO2 were also prepared by microemulsion method
using a n-hexanol : CTAB :water mixture. To study the effect of the doppant amount a series of samples containing 0.1, 0.3, 1
and 1.5% Eu was prepared by sol-gel method. To study
the upconversion effect TiO2 containing 1%Er-1%Yb
were prepared bay sol-gel and microemulsion. In the
same time, to study the effect of the dopant location, 1%Er-1%Yb doped,
1%Er-1%Yb impregnated, 1%Er doped and 1% Yb
impregnated, 1% Er impregnated and 1% Yb doped were prepared.
Samples
were calcined at 500, 750, 1000C.
Selected
samples were characterized by X-Ray diffraction (phase content, anatase/rutile ratio, particle
size), Raman spectroscopy, DR-UV-Vis spectroscopy.
XRD
analysis shows that doping TiO2 modifies the anatase-rutile
content. Literature shows that lanatinde doping
extends the anatase-rutile transformation above 700C.
The sample containing 1% Eu exhibits also a Eu2Ti2O7
phase at high calcination temperatures. Particle size depends on the dopant
nature and it is smaller than for the undoped TiO2.
The impregnated sol-gel samples show a more evident effect: samples calcined at
750C have a high amount of anatse (~90%), higher than
for the doped samples (<50%) or the undoped TiO2
(0%), behaviour very simmilar
with that of the samples prepared by micoremulsion
method.
Raman
analysis show the evolution from anatase to rutile
with the calcination temperature.
Modification
of TiO2 by doping or impregnation did not lead to an important change of the
band-gap values, But the absorption bands
characteristic to the lanthanides can be useful for absorption in the visible
spectrum.
For
Dy, Tb and Pr in TiO2 a
large and short-lived emission was observed, corresponding to the lanthanide
ions on the surface of the nanoparticles. The only samples presenting emission
with excitation in the TiO2 emission band are 1%Nd(i/d)-TiO2 and 1%Er, 1%Yb(i)-TiO2
as result of substitution of tetravalent Ti from TiO2
with Nd and Er/Yb.
Dissemination
Oral Communications:
.
Phase II/2019 (01.01.2019-31.12.2019): Corelation of the physisco-chemical
properties of the prepared catalysts with their catalytic activity (Budget
255075 lei)
In order to achieve this phase, the following activities are
carried out:
Activity 2.1. - Physico-chemical
characterization of the prepared catalysts (XRD, Raman,
photoluminescence, DR-UV-Vis, DLS)
Activity 2.2. Testing the activity of the prepared catalysts
in the partial photo-oxidation and coupling of amines
Activity 2.3. Correlation of the
activity with the physico-chemical characterization
data
Summary of the
research report (Phase II):
The research team
continued to prepare a series of catalysts by doping via-sol gel (%Gd, 1%Yb, 1%Er). 1%Tm doped TiO2 was also
prepared by microemulsion method using a n-hexanol : CTAB
:water mixture. Samples were calcined at 500, 750, 1000oC.
Selected samples
were characterized by X-Ray diffraction (phase content, anatase/rutile ratio, particle size),
Raman spectroscopy, DR-UV-Vis spectroscopy, DLS particle size distribution.
XRD analysis shows
that doping TiO2 modifies the anatase-rutile
content. Literature shows that lanatinde doping
extends the anatase-rutile transformation above
700oC. Particle size and anatas/rutile
ratio depends on the dopant nature and it is smaller than for the undoped TiO2.
Raman analysis
shows the evolution from anatase to rutile
with the calcination temperature.
Modification of
TiO2 by doping or impregnation did not lead to an important
change of the band-gap values, however the absorption bands characteristic to
the lanthanides can be useful for absorption in the visible spectrum.
DLS analysis
showed a difference in the particle sizes depending on the preparation
method. Micoremulsion preparation resulted
in smaller particles and with a narrow size distribution.
Photoluminescence
studies showed a similar behavior for Nd and Er doped samples both as shape and dynamic of
emission.
The catalytic
activity of the prepared samples wast tested in the
selective aerobic oxidation of benzylamine. The
activity of the samples and the selectivity to benzonitrile
or imine (coupling product) varied function of dopant nature, calcination
temperature and preparation method. These parameters influenced the anatase/rutile ratio and the concentration of defects (generaly oxygen vacancies) on the surface of the particles.
Dissemination
Book Chapters
Research articles
Participation to
international conferences
Phase III/2020 (01.01.2020-30.04.2020): Corelation of the physisco-chemical
properties of the prepared catalysts with their catalytic activity (Budget 56925
lei)
In order to achieve this phase, the following activities are
carried out:
Activity 3.1. - Testing the activity of the prepared catalysts in
the partial photo-oxidation and coupling of amines and correlation of the activity with the physico-chemical
characterization data
Activity 3.2. Additional preparation and testing if
necessary
The activity of the photocatalytic systems under Vis irradiation
was insignificant even in the systems where upconversion
was expected to play a role. The activity of the prepared systems in
photo-oxidation of benzylamine was lower than that of
other optimized photocatalytic systems reported in literature mainly because of
the selected solvent (chloroform). Literature reports this behavior in organic
solvents as consequence of water in the reaction environment. However, the
absence of water led the reaction toward the formation of benzonitrile
instead of imine, in most cases this being the main product. The formation of
imine (coupling product between benzylic anhydride and benzylamine)
starts after water is formed as co-product in formation of benzonitrile.
Dissemination
Research articles