PhotoCatBead

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 450^oC 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 TiO_2-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 150^oC 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 450^oC, 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 (550^oC and 600^oC) 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 550^oC 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 13^th, 2022.