1. Adelina Stănoiu (former Tomescu), U-1700-038M-8092
2. Cristian Eugen Simion, U-1700-030F-9765
3. Corneliu Ghica, U-1700-029U-5827
4. Ioana Dorina Vlaicu, U-1700-037A-2366
5. Andrei Cristian Kuncser, U-1700-032N-6988
6. Cătălina Gabriela Mihalcea, U-1900-062F-0766
7. Ionel Florinel Mercioniu, U-1700-039E-8823
8. Daniela Ghica, U-1700-035Y-0481
9. Mariana Ștefan, U-1700-034N-5930
10. Ion Viorel Dinu, U-1700-030A-3912
11. Ovidiu Gabriel Florea, U-1700-032D-4435

Stage 1/2022 – Quantitative and qualitative Gd doping level effects.

In the case of chemo-resistive gas sensors, the main requirements are related to sensitivity and selectivity, along with a good stability over time of the material parameters. Therefore, at this stage we proceeded to a material selection based on the synthesis route, the exhaustive morpho-structural evaluations and the preliminary sensing investigations.

Activity 1.1. Synthesis of nanostructured powders: SnO₂, Gd₂O_3, and SnO₂ doped with 1-20 at. % Gd.

A premise of any fundamental study or any commercial application is the reproducibility and control of each step in the technological process. Therefore, the optimization of the material synthesis in accordance with the experiment and the final application, was taken into consideration at this stage. Pure and Gd-doped SnO2 powders, with the general formula Sn1-xGdxO(4-x)/2 (where x = 0.01; 0.05; 0.1; 0.2, corresponding to nominal concentrations of 1, 5, 10, 20 at. %) , and of Gd2O3 were synthesized by two alternative methods, co-precipitation and hydrothermal.

Activity 1.2. Studies on the morphology, grain size, crystal structure, crystallinity phase purity as well as pore structure by microstructural investigations of the obtained nanopowders: SnO₂, Gd₂O_3, and SnO₂ doped with 1-20 at. % Gd.

X-ray diffraction (XRD) was performed with a Bruker D8 Advance X-ray diffractometer. The Rietveld analysis indicates the formation of a SnO2 - Gd2O3 nanocomposite even for the SnO2 sample doped with 5%, considering the presence of Gd2O3 as a secondary phase with poor crystallization. TEM/HRTEM analytical results were obtained with JEOL JEM-2100 and JEOL ARM 200F transmission electron microscopes, equipped with X-ray detectors used for EDS type investigations. The results of the distribution of nanoparticles, the electron diffractogram and the HRTEM images obtained at different magnifications reveal the shape of the nanoparticles, the uniformity of the crystallite sizes and highlight the crystallographic planes. The STEM-EDS maps highlight the presence and distribution of the constituent elements, confirm the presence of Gd in the sample and the uniformity of its distribution. The two morphologies of nanoparticles, quasi-spheres and sticks, provide distinct EDS signals corresponding to tetragonal SnO2 and cubic Gd2O3. The average specific surface areas for the pure SnO2 systems and for the SnO2 systems doped with 1%, 3%, 5%, 10%, 20%Gd were estimated theoretically using the size distributions obtained by TEM. The textural properties were determined with the BET method (Brunauer, Emmett, Teller), using the Micromeritics ASAP 2020 instrument, by measuring the amount of gas (N2) adsorbed/desorbed from the surface of the powders in order to determine the specific surface area and porosity of the materials indicated by TEM/HRTEM as being porous. Electron spin resonance (RES) measurements were made in the X (9.87 GHz) and Q (34.16 GHz) microwave frequency bands. The RES spectra of all measured samples present signals characteristic of Gd3+ ions located in isolated positions in the network and respectively agglomerated. The CO2 detection properties for the sensors obtained based on the studied materials were evaluated under dynamic conditions similar to those in the field. The preliminary selection highlights the hydrothermally prepared Gd2O3 whose nano-sticks present a strong diffraction contrast typical of single-crystal micro-objects, in contrast to the mild contrast of the weakly crystallized Gd2O3 nano-sticks obtained by coprecipitation.

Member of the doctoral committee of Drd. Cătălina G. Mihalcea, research assistant in Laboratory 70 - Atomic Structures and Defects in Advanced Materials (LASDAM), INCDFM. Dr. Cătălina G. Mihalcea carries out her activity in the research topic of the group in which she is included, of the CERIC-ERIC and PN-III-P4-PCE-2021-0384 projects. The topic of the doctoral thesis is "Nanostructured materials for gas sensing: correlations between functional, electronic and microstructural properties" and it is carried out under the guidance of the supervisor Prof. C. M. Teodorescu, at the Doctoral School of Physics, University of Bucharest.

ISI papers:

1. Corneliu Ghica, Catalina G. Mihalcea, Cristian E. Simion, Ioana D. Vlaicu, Daniela Ghica, Ion V. Dinu, Ovidiu G. Florea, Adelina Stanoiu*, Influence of relative humidity on CO₂ interaction mechanism for Gd-doped SnO₂ with respect to pure SnO₂ and Gd₂O₃, Sens. Actuators B. Chem. 368, 1 October 2022, 132130, https://doi.org/10.1016/j.snb.2022.132130
2. Andrei C. Kuncser, Ioana D. Vlaicu, Ion V. Dinu, Cristian E. Simion, Alexandra C. Iacoban, Ovidiu G. Florea, Adelina Stanoiu*, The impact of the synthesis temperature on SnO₂ morphology and sensitivity to CO₂ under in-field conditions, Materials Letters 325, 15 October 2022, 132855, https://doi.org/10.1016/j.matlet.2022.132855
3. Adelina Stanoiu, Corneliu Ghica, Catalina Gabriela Mihalcea, Daniela Ghica and Cristian Eugen Simion*, The Role of the Synthesis Routes on the CO-Sensing Mechanism of NiO-Based Gas Sensors, Chemosensors 10 (11), 9 November 2022, 466, https://doi.org/10.3390/chemosensors10110466
4. Cristian E. Simion, Ioana D. Vlaicu, Alexandra C. Iacoban, Catalina G. Mihalcea, Corneliu Ghica and Adelina Stanoiu*, The influence of the synthesis method on Gd₂O₃ morpho-structural properties and sensitivity to CO₂ under in-field conditions, Materials Chemistry and Physics 296, 15 February 2023, 127354, https://doi.org/10.1016/j.matchemphys.2023.127354

Papers presented at conferences:

1. Catalina G. Mihalcea*, Corneliu Ghica, Cristian E. Simion, Ioana D. Vlaicu, Daniela Ghica, Ion V. Dinu, Ovidiu G. Florea, Adelina Stanoiu, The structure and morphology of pure SnO₂, Gd-doped SnO₂ and pure Gd₂O₃ nanoparticles for applications in chemoresistive gas sensors, oral presentation at the 19th International conference on Advanced Nanomaterials ANM 2022, July 27-29, University of Aveiro, Aveiro – Portugal
2. Catalina G. Mihalcea*, Corneliu Ghica, Cristian E. Simion, Ioana D. Vlaicu, Daniela Ghica, Ion V. Dinu, Ovidiu G. Florea, Adelina Stanoiu, Structural and morphological properties of Gd-doped SnO₂ nanopowders and their role in the gas sensing mechanism, poster session 2 at the 9th International Conference on Optical, Optoelectronic and Photonic Materials and Applications & 14th Europhysical Conference on Defects in Insulating Materials ICOOPMA-EURODIM 2022, July 3–8, Ghent, Belgium

Papers under review at ISI journals:

Experimental methods for investigating gas-sensing properties under in-field conditions - NIMP facilities:

https://infim.ro/wp-content/uploads/2022/11/Gas-Mixing-Station-scaled.jpg

Dr. Adelina Stănoiu

adelina.stanoiu@infim.ro

stanoiu.adelina@yahoo.com