Results

Activity report 2024

Outcomes

A3.1. Testing and validating the demonstrator technology with VIS-/Solar-active composite beads

Continuing the activity that started in 2023, the protocol for depositing the optimized composite thin films based on TiO2 and gC3N4 at larger scale was confirmed to be efficient, through Raman spectroscopy results. The following results were obtained while testing and validating the technology with VIS-/Solar-active composite beads:

  • The mass of the beads that was inserted in the photocatalytic demonstrator reactor has been optimized to ensure the treatment of one liter of pollutant (methylene blue). It has been observed that a mass of 3 grams for each tray (6 grams in total in the reactor) is optimal, as at higher quantities a shielding of the beads has occurred.

  • Tests using the photocatalytic demonstrator reactor were performed, under simulated solar radiation belonging to the UV-VIS and UV domains, as well as in darkness, using two pollutants: methylene blue and imidacloprid. It has been observed that the samples are photoactive under irradiation, registering a higher photocatalytic efficiency under UV-VIS radiation (47% versus 38% for MB and 64% versus 54% for IMD respectively). This confirms the embedding of the graphitate carbon nitrate filling in the matrix TiO2;

  • Test to assess the stability of the samples have been conducted in order to see their reusability. This has been done by subjecting the same samples to 3 consecutive photocatalytic tests under UV-VIS irradiation. The efficiency remains constant for all 3 testing cycles in the case of IMD, however it decreases after the first testing cycle in the case of MB;

  • A complex characterization of the layers before and after photocatalysis as well as before and after regeneration consisting in thermal treatment at 450oC was performed;

  • It was observed that a slight restructuring of the layer surface takes place after the photocatalytic tests, as well as a possible partial washing of the layers, according to SEM;

  • The sample regeneration is efficient in removing the secondary degradation products of the pollutants, which still remained on the surface after photocatalysis, as evidenced by the Raman spectroscopy, XRF and ellipsometry;

  • The crystallinity degree increases following the regeneration treatment, as confirmed by XRD analyses;

  • Photocatalytic tests under natural solar radiation were done, with a promising photocatalytic efficiency (approximatively 50% for both pollutants). The differences from the corresponding tests carried out using the solar simulator can be attributed to the lower irradiance of the natural radiation.

A3.2. Design and testing of the regeneration operation modes

To increase the reusability of the photocatalytic beads, a regeneration stage between two consecutive testing periods is required. In the frame of the project:

  • A regeneration protocol of the photocatalytic beads has been developed and implemented, based on rinsing the photoreactor loaded with beads in distilled water (in two stages), as well as the drying and annealing of the beads in an oven at 450oC.

A3.3. Dissemination

 The main results of the project were disseminated towards (a) the general public through the updated project website, (b) the academic community through the publishing of 1 article in ISI journals, while another is under review, as well as through 4 poster communications at national and international scientific conferences.

A. Published papers

• S. Simeonov, A. Szekeres, M. Covei, H. Stroescu, M. Nicolescu, P. Chesler, C. Hornoiu, M. Gartner, Sol-Gel Multilayered Niobium (Vanadium)-Doped TiO2 for CO Sensing and Photocatalytic Degradation of Methylene Blue, Materials 2024, 17, 1923. https://doi.org/10.3390/ma17081923 FI=3.748.

B. Communications at national / international conferences

• C. Bogatu, M. Covei, I. Tismanar, A. Duta, H. Stroescu, M. Nicolescu, J.M. Calderon-Moreno, I. Atkinson, M. Gartner, TiO2-g-C3N4 „Photocatalytic Composite Beads for Advanced Wastewater Treatment”, SPASEC27-AOT28, 10-14 iun 2024, Limassol, Cyprus;

• M. Covei, I. Tismanar, C. Bogatu, A. Duta, H. Stroescu, M. Nicolescu, J.M. Calderon-Moreno, I. Atkinson, M. Gartner, „Stability of Solar-active Photocatalytic Composite Beads”, SPASEC27-AOT28, 10-14 jun 2024, Limassol, Cyprus;

• M. Covei, C. Bogatu, D. Perniu, I. Tismanar, A. Duta, H. Stroescu, M. Nicolescu, J.M. Calderon Moreno, I. Atkinson, M. Gartner, „VIS-active Photocatalytic Thin Film Beads for Wastewater Treatment”, CHIMIA 2024, 30 may – 1 jun 2024, Constanta, Romania

Activity report 2022

Outcomes

A1.1. Design, development, characterization and testing of the TiO2-GO VIS-/Solar-active composite photocatalytic beads

  •  Considering the application of the TiO2-GO VIS-/Solar-active composite photocatalytic beads in the advanced wastewater treatment, the stability in water of 4 types of silica gel and quartz beads was tested. The quartz type substrate (beads diameter: 2…3 mm) showed good stability for a period of more than 48 h of immersion in water and it was selected for deposition of the photocatalytic composite thin films.

  • Bead substrate etching in concentrated acid (nitric acid, sulphuric acid) was done for up to 48h to increase the porosity and specific surface area, thus ensuring the deposition of a uniform photocatalytic film. The optimal conditions for the quartz-type beads’ etching were selected: 2h of immersion in concentrated sulphuric acid.

  • Photocatalytic thin films based on TiO2 were deposited on the spherical substrate (beads) by using the sol-gel method, a low-cost, versatile technique that allows the fine control of the process parameters. The etched beads were obtained by immersion under orbital mixing (30 min) of in undiluted /diluted TiO2 sol (obtained from the titanium tetraisopropoxide precursor), followed by thermal treatment up to 450oC to remove the continuous medium, the volatile compounds and to increase the film crystallinity. The influence of the number of deposition layers and of the sol to ethanol dilution ratio (v/v) on the structure (XRD), morphology (SEM, AFM), surface composition (EDX, XRF) and on the photocatalytic activity (methylene blue photodegradation efficiency) and stability of the thin films was investigated. This allowed the selection of the etched beads with sulphuric acid and coated with a single TiO2 layer deposited from the undiluted TiO2 sol to be further used as reference and as intermediary layer for the TiO2-GO (graphene oxide) composite beads.

  • The TiO2-GO composite thin films were deposited on the previously optimized substrate, from a TiO2-GO composite sol (by using the TiO2 sol precursors and commercial GO aqueous dispersion added to obtain 5% of GO in the film). The films were thermally treated at 150oC to prevent GO degradation. This led to a low crystallinity degree for the composite TiO2-GO films. The influence of the following parameters on the structural, morphological, chemical composition, optical and photocatalytic properties of the layers was investigated: the dilution ratio of the sol with ethanol (2:1 and 1:1) and the influence of an intermediate, previously optimized, TiO2 layer. It was proved that the TiO2 intermediate layer is advantageous, especially from the point of view of the photocatalytic efficiency and the stability of the samples during 3 cycles of photocatalysis (both in MB and IMD solutions).

  • The samples obtained from the diluted sol (sol:EtOH = 1:1), promoted the best film uniformity and showed promising results: photodegradation efficiency of ~40% for MB and ~20% for IMD after 8h of UV+VIS irradiation (G=55W/m2) and good stability after 3 successive cycles of photocatalysis. Therefore, they are recommended for future testing in the laboratory demonstrator reactor with photocatalytic beads, that will be designed and developed within the project in 2023.

A1.2. Design, development, characterization and testing of the TiO2-gC3N4 VIS-/Solar-active composite photocatalytic beads

 The main advantage of using gC3N4, compared to GO, is its good stability at temperatures higher than 450oC, which allows the thermal treatment of the TiO2-gC3N4 composites and the increase in the degree of crystallinity of the composite structure, leading to a higher photocatalytic efficiency.

  • Crystalline powders of gC3N4 were obtained from urea or melamine. The influence of the precursor type and of the calcination temperature (550oC and 600oC) on the structural, morphological and chemical composition properties of the samples was investigated. Based on the XRD, SEM and Raman results, the powder obtained from urea at 550oC was selected as optimal (with high crystallinity degree and fine morphology). This powder was further added as ethanolic dispersion in the TiO2-gC3N4 sol-gel synthesis.
  • The composite TiO2-gC3N4 thin layers (with 5% gC3N4) were obtained following a similar procedure as that used for the TiO2-GO composite beads. The influence of the dilution ratio of the sol (undiluted sol or diluted sol with ethanol, sol:EtOH=1:1), and of the presence of an intermediate layer of TiO2 (previously optimized) on the structural (XRD, Raman), morphological (SEM), chemical composition (EDX, XRF), optical (Eg –DR UV- VIS) and photocatalytic properties (MB and IMD photodegradation efficiency) of the layers was investigated.
  • The VIS-activation of the TiO2-gC3N4 thin films is more significant as compared to the composite TiO2-GO beads, in agreement with the higher crystallinity degree (corelated with the higher annealing temperature) of these layers. The results showed that the samples obtained from diluted sol had a higher degree of uniformity. The intermediate layer of TiO2 improve the photodegradation efficiency of both the pollutants (with ~.15%) for the standard dye (MB) and the pesticide (IMD).
  • These samples o showed good pollutant photo-degradation efficiencies: ~65% for MB and 45% for IMD, after 8h of UV-VIS irradiation (G=55W/m2) and are recommended for further testing, to establish their stability during successive cycles of photocatalysis (at least 3 cycles) – during the 2023 stage of the 1.2. Activity (also known as Activity 2.1).
  • The influence of the percentage of gC3N4 in the layer on the properties of interest will also be included during the 2023 stage of the 1.2. Activity (also known as Activity 2.1).

 

A1.3. Dissemination 2022

A general presentation of the project was given at the Networking and Brokerage event, in the framework of the FIT-4-NMP (part of the International Conference for Semiconductors, CAS), October 13th, 2022.

Activity report 2023

Outcomes

A2.1. Design, development, characterization and testing of the TiO2-gC3N4 VIS-/Solar-active composite photocatalytic beads

Continuing the activity that started in 2022, the influence of the percentage of graphitized carbon nitride (gC3N4) of the thin composite layer on the photocatalytic properties of layers was tested.

  • Thin films with the composition QAS/TiO2-gC3N4(x%) and QAS/TiO2/TiO2-gC3N4(x%), where x is a value of 1, 2, 5 or 10 were obtained. A superior photocatalytic efficiency of the samples that contain an intermediary layer of TiO2 was observed. Also, the most promising results (under UV, UV-VIS radiation, as well as in darkness) were obtained for the sample which contains 5% gC3N4.
  • Stability tests for all 8 samples mentioned above were performed, by submitting them to 3 photocatalytic cycles each, under UV-VIS radiation. In the case of methylene blue (MB), as well as imidacloprid (IMD), the sample QAS/TiO2/TiO2-gC3N4(5%) showed the highest stability.
  • Thin films (composites with GO and gC3N4 filler) deposited on planar substrate, using the same protocol as the films on beaded substrate were analyzed by ellipsometry and Raman.
  • The Raman analysis could point out the presence of GO in the composite thin film, but not that of gC3N4, due to the overlapping structural vibrations of C-N and C-C.
  • The ellipsometric analysis confirmed the small thickness of the layers (approximately 100 nm for the composite layer based on TiO2-GO and 130 nm for the one based on TiO2-gC3N4); bandgap energy values are 3.22 eV and 3.33 eV, respectively.

 

A2.2. Modelling the photocatalytic demonstrator reactor with VIS-/Solar-active composite beads

The demonstrator photoreactor includes:

  • A central device which consists of a vertical quartz tube, perforated lids at the upper and lower sides of the tube, perforated trays that hold the photocatalytic beads and rods that hold everything in place;
  • An aluminum profile support structure;
  • A recirculation vessel for the MB and IMD solutions;
  • A pump and a flow meter, with the electric control panel for both;
  • Hoses for the solution circulation.

The most important (and novel) aspect of the photoreactor is the central device. This was carefully considered and the radiation transmittance through it was modelled using both VIS and UV-A radiation, from a vertical solar simulator.

Three different quartz tubes were considered, with variable interior diameters, wall thickness and quartz crystallinity degree. It was demonstrated that the wall thickness of these tubes can affect their transmittance (which is lost in up to 5% by increasing the wall thickness with just 0.5 mm). However, the quartz crystallinity degree is the deciding factor. Accordingly, a quartz tube with the inner diameter of 66 mm and a wall thickness of 2.5 mm was selected for the photocatalytic demonstrator reactor.

 

A2.3. Design and development of the photocatalytic demonstrator reactor with VIS-/Solar-active composite beads

  • The central device was designed using the CATIA software;
  • The central device was constructed to include the quartz tube previously optimized (transmittance of >90% under UV-A and VIS radiation), 3D printed lids with water canals (made from Acrylonitrile Styrene Acrylate), perforated trays to hold the photocatalytic beads (3D printed, also from Acrylonitrile Styrene Acrylate) and rods (galvanized steel) to hold everything in place.
  • The device was integrated in the photoreactor by positioning it on an aluminum frame. It has been connected using hoses to a recirculating vessel which contains the pollutant solution. The device also requires two pumps which offer a flow of 1 to 2.5 L/min, a flowmeter and an electric control panel.

 

Reactor Components

1 – central device

2 – recirculation vessel

3 – pumps and flow meter

4 – control panel
Tray Beads
The demonstrator photoreactor with photocatalytic beads

 

A2.4. Testing and validating the demonstrator technology with VIS-/Solar-active composite beads

  • The demonstrator photoreactor was tested using distilled water and is in a workable condition.
  • The chemical stability (in darkness, as well as under UV-VIS irradiation, with high irradiation of 1000 W/m2) of all the components was confirmed by comparing conductivity and pH values of the inlet and outlet water;
  • The flow influences the movement of the beads on the surface of the trays, with higher flow leading to overlap of the beads.
  • The process of obtaining the thin composite layers was re-optimized in order to obtain a higher quantity of photocatalytic beads simultaneous.
  • The 2.4 activity will continue in 2024 by testing the photocatalytic technology using MB and IMD, under UV, UV-VIS and no irradiation (controlled irradiance of 200-1000 W/m2), using the solar simulator. The bead amount will be varied between 10 and 40 g for the treatment of 1 to 3 L of pollutant solution. The number and position of the beads trays will also be varied to see the effect on the photocatalytic efficiency.

 

A2.5. Dissemination

The main results of the project were disseminated towards (a) the general public through the update of the project website, (b) the academic community through the publishing of 2 articles in ISI journals, as well as through 9 oral and 1 poster communications at international scientific conferences, (c) interested parties by organizing of 2 workshops.

A. Published papers

• Covei, M.; Bogatu, C.; Gheorghita, S.; Duta, A.; Stroescu, H.; Nicolescu, M.; Calderon-Moreno, J.M.; Atkinson, I.; Bratan, V.; Gartner, M., “Influence of the deposition parameters on the properties of TiO2 thin films on spherical substrates”, Materials (Basel), 2023, 16, 4899. doi:10.3390/ma16144899 (IF=3.748).

• Gartner M., Szekeres A., Stroescu H., Mitrea D., Covei M., “Advanced Nanostructured Coatings Based on Doped TiO2 for Various Applications”, Molecules, 2023, 28 (23), 7828. doi:10.3390/molecules28237828 (IF=4.927).

B. Communications at international conferences

• Covei M., Bogatu C., Perniu D., Gheorghita S., Duta A., Stroescu H., Nicolescu M., Calderon-Moreno J.M., Atkinson I., Bratan V., Gartner M., "Composite TiO₂-gC₃N₄ thin film beads for advanced wastewater treatment", 18th International Conference on Chemistry and the Environment (ICCE 2023), 11-15 June 2023, Venice, Italy;

• Covei M., Bogatu C., Gheorghita S., Duta A., Stroescu H., Nicolescu M., Calderon-Moreno J.M., Atkinson I., Bratan V., Gartner M., "Comparative assessment of TiO2-GO and TiO2-gC3N4 photocatalytic thin films on spherical substrate", 12th International Conference on Environmental Engineering and Management (ICCEM), 13-16 September 2023, Iasi, Romania;

• Bratan V., Covei M., Stroescu H., Carata M., Gartner M., “The use of UV Visible spectroscopy for the characterization of semiconductor oxides”, RomPhysChem, 25-26 September 2023, Bucharest, Romania;

• Covei M., Bogatu C., Gheorghita S., Tismanar I., Duta A., Stroescu H., Nicolescu M., Calderon-Moreno J.M., Atkinson I., Bratan V., Gartner M., “Composite photocatalytic beads based on TiO2 and carbon derivates for wastewater treatment”, RomPhysChem, 25-26 September 2023, Bucharest, Romania;

• Szekeres A., Simeonov S., Gartner M., Covei M., “Influence of sol-gel technological conditions on thin TiO2 films properties”, RomPhysChem, 25-26 September 2023, Bucharest, Romania;

• Stroescu H., Gartner M., Calderon Moreno J.M., Atkinson I., Bratan V., Covei M., Gheorghita S., Bogatu C., Perniu D., Duta A., “Substrate influence on the properties of TiO2 photocatalytic surfaces”, Conference for Sustainable Energy, 26-28 October 2023, Brasov, Romania;

• Gartner M., Stroescu H., Calderon Moreno J.M., Atkinson I., Bratan V., Covei M., Gheorghita S., Bogatu C., Perniu D., Duta A., “VIS-solar active composites based on TiO2 and carbon derivatives (GO and gC3N4)”, Conference for Sustainable Energy, 26-28 October 2023, Brasov, Romania;

• Covei M., „Photocatalytic beads for advanced wastewater treatment”, Conference for Sustainable Energy, 26-28 October 2023, Brasov, Romania;

• Bogatu C., Gheorghita S., Covei M., Duta A., „Photocatalytic thin films based on TiO2-g-C3N4 composites for advanced wastewater treatment”, Conference for Sustainable Energy, 26-28 October 2023, Brasov, Romania;

• Tismanar I., Duta A., „In situ prepared photocatalytic composite of TiO2-gC3N4”, Conference for Sustainable Energy, 26-28 October 2023, Brasov, Romania.

C. Workshops

• A dedicated workshop in the frame of the RomPhysChem-17, International Conference of Physical Chemistry, Bucharest, 26 September 2023. The workshop brought together around 40 participants from universities and research institutes from Romania and abroad, working in the field of advanced materials.

• The “Photocatalytic systems for advanced wastewater treatment” workshop, that took place on the 26th of October 2023, with 32 participants form academic institutions, intercommunity associations and the extended public, which expressed an interest in the results of the PED598/2022 project.