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:

  1. New pathway to artificial lignocellulosic material in one-pot enzymatic approach, I. Sabina, C. Opris, B. Cojocaru, M. Tudorache, I. Zgura, A. Galca, M. Enache, G. Maria, V. Parvulescu, 14th Pannonian International Symposium on Catalysis, 03.09.2018 – 09.09.2018, Stary Smokovec, Slovacia.
.

 

 

 

Phase II/2019 (01.01.2019-31.12.2019): Corelation of the physisco-chemical properties of the prepared catalysts with their catalytic activity

In order to achieve this phase, the following activities are carried out:

 

Activity 2.1. -  Physico-chemical characterization of the prepared catalusts (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

 

 

Phase III/2020 (01.01.2020-30.04.2020): Corelation of the physisco-chemical properties of the prepared catalysts with their catalytic activity

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