Our recents findings

In our recent articles published by the American Chemical Society and the Royal Society of Chemistry, we have discovered the versatility of MXenes, a new generationof 2D nanomaterials, in AOPs for wastewaters treatment. Indeed, MXenes are known as co-catalyst but we have proved they can be used as material precursors for the design of efficient catalysts.

In the first work, we have used for the first time Nb-substituted binary Ti-based MXenes to prepare an innovative oxide nanoheterostructures (TiNbOx). Their photocatalytic performance in the degradation of sulfamethoxazole (SMX) under UVA light has shown high efficiency in the degradation of thi spharmaceutical. The complex interplay between the structural, morphological, and electronic properties of TiNbOx suggested that a higher Ti:Nb ratio, smaller particle size, and larger specific surface area were the key factors contributing to its superior photocatalytic performance. The proposed degradation mechanism involved •OH as the primary ROS. The primary conclusion of this first work illustrates that MXenes can be used as material precursors from which the resulting oxide nanoheterostructures can be further explored in wastewaters treatment.

Therefore, in the second work, we have used TiNbOx as a catalyst for the activation of peroxymonosulfate (PMS) in the degradation of both SMX and caffeine (CAF) in effluents collected at WWTP in Bratislava to highlight their potential applicability. TiNbOx displayed promising performance in WW with more than 80% of SMX and CAF removed. By using advanced spectroscopic techniques (XPS and EPR), we have also elucidated the activation mechanism of PMS where the formation of a surface complex on TiNbOx is considered. Such a surface complex can undergo a reductive conversion to generate SO4•‾ and •OH. 

These findings open the doors in the research and development of a new generation of catalysts that might be integrated to WWTP technology!

Link to our articles in ACS Applied Nanomaterials & Nanoscale: 

doi.org/10.1021/acsanm.4c02523: MXene-Derived Oxide Nanoheterostructures for Photocatalytic Sulfamethoxazole Degradation

doi.org/10.1039/D4NR02819H: Tailored MXene-derived Nano-Heterostructure Oxide for Peroxymonosulfate Activation in the Treatment of Municipal Wastewaters

In our article entitled "Unravelling the activation mechanism of oxidants using copper ferrite nanopowder and its application in the treatment of real waters contaminated by phenolic compounds" which is published in Chemical Engineering Journal, we have clarified the activation mechanism of different persulfate oxidants into radical species since there is some contradictory results in the literature.

Copper ferrites (CuFe2O4) nanopowder was prepared by hydrothermal method and comprehensively characterized by XRD, SEM, XPS and UPS. CuFe2O4 was tested for the degradation of bisphenol A (BPA) in the dark and under UVA light, both in the presence of peroxymonosulfate (PMS) or peroxydisulfate (PDS). By combining CuFe2O4 and UVA light with either PMS or PDS a significant synergy effect was observed and the complete degradation of BPA was achieved within less than 20 min. The activation mechanism of PMS and PDS using CuFe2O4 was elucidated, revealing sulfate radicals as the primary reactive species in PMS-containing systems, whereas a predominantly non-radical pathway was observed in the presence of PDS. Indeed, advanced spectroscopic techniques indicated that surface copper played an important role where an electron transfer from the pollutant to PDS via CuFe2O4 was suggested. Furthermore, the CuFe2O4/PMS/UVA system was tested in effluents from wastewaters treatment plant and conlusion about their postential application was highlithed.  

These findings highlight the complexity of the wastewaters treatment problematic but also the feasibility in achieving promising degradation efficiency using a "simple" nanomaterial! 

Link to our article in Chemical Engineering Journal: doi.org/10.1016/j.cej.2024.148623 

In our feature article entitled "Controversial mechanism of simultaneous photocatalysis and Fenton-based processes: additional effect or synergy?" which is published in Chemical Communications, we have highlighted the controversial synergistic mechanism of photochemically versatile nanomaterials. Indeed, many published articles have reported the advantages of coupling photocatalysis and Fenton-based processes for environmental remediation purposes, especially wastewaters treatment, but without providing detailed discussion on how and why the resulting process is better, thus leading to misconception about their synergy. 

In this feature article, the simultaneous triggering of these two advanced oxidation processes is critically discussed from both performance and mechanism sides since additional effect and synergy are often misunderstood in the literature. The aim of this feature article is to inform scientists about the complexity of simultaneously triggered photocatalysis and Fenton-based processes but also to highlight the potential development of a new generation of catalysts that might be integrated to current wastewater treatment technology to achieve higher efficiency and their implications in the circular economy of water.  

Link to our article in Chemical Communications: doi.org/10.1039/D3CC03992G  

In our article entitled "New insights into the mechanism of coupled photocatalysis and Fenton-based processes using Fe surface-modified TiO2 nanotube layers: The case study of caffeine degradation" which is published in Catalysis Today, we have highlighted for the first time a potential synergy between the two involved AOPs.

The iron-surface modified TiO2 nanotube (Fe-TNT) layers were prepared by electrochemical anodization of Ti foil and impregnation of Fe(III) precursor solution followed by annealing at 450 °C for 2 h in air. After a comprehensive characterization of the nanomaterial, the degradation of caffeine was investigated both in the dark and under UVA with and without the presence of 500 µM H2O2. It has been found that in the presence of H2O2 under UVA, Fe-TNT can degrade 67 % of caffeine after 3 h, of which 4 % is from photolysis, 23.5 % from photocatalysis and 39.5 % from Fenton-based processes. It is important to note that Fenton-based reactions are due to the iron leaching. In addition, the main degradation by-products are identified by LC-MS and IC-MS techniques, thus leading to the proposal of different degradation pathways of caffeine.  

These findings introduced for the first time the concept of the photochemical versatility where a single nanomaterials can trigger several AOPs simultaneously and in synergy! Of course, further work is required to provide solid proofs of our findings! 

Link to our article in Catalysis Today: doi.org/10.1016/j.cattod.2023.02.004 

In our article entitled "Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V" which is published in Dalton Transactions, we have discussed the simultaneous combination of different photo-induced oxidation processes that enhanced the degradation of caffeine in water using TiO2 photocatalyst modified by Fenton active elements.

Concerning the photochemical properties, V- and Ce-surface modified TiO2 nanotube layers (V-TNT and Ce-TNT) exhibit the same (Eg ≈ 3.3 eV) with the valence band situated at 3.3 V (vs. SHE), thus the main reactive oxygen species that have been identified during caffeine degradation are hydroxyl radicals (HO•). However, although Ce-TNT produces more HO• than V-TNT, it is the latter that exhibit the highest performance with a degradation extent of 45% after 2h UVA irradiation at pH = 3 in the presence of H2O2. Therefore, we highlight that adsorption properties are also a crucial paramater since photocatalysis is a surface-dependent process. Indeed, at pH = 3, the surface of V-TNT is negative (while that of Ce-TNT is positive), thus interacting better with caffeine. In addition, the TEM analysis shows that our materials are composed of nanotwin structured nanotubes. Such a structure improves the transport of charge carriers, thus exhibiting higher photocatalytic degradation efficiencies compared to the literature. 

Finally, we have evaluated the contribution of both photocatalysis and Fenton-based processes and we show that, along photocatalysis and H2O2 photolysis, Fenton-based processes account to 10% of the total degradation extent of caffeine. This work highlights that the role of Fenton-based processes is overlooked when photocatalysts containing Fenton-active elements are employed (like Fe, V, Ce, etc.) Currently, we are carrying out further work using Fe-TNT in order to propose new insights into the so-called "photochemically versatile materials", an innovative concept that requires further development to reach efficient photoactive materials! 

Link to our article in Dalton Transactions: doi.org/10.1039/D2DT00829G

In our article entitled "Ce ions surface-modified TiO2 aerogel powders: a comprehensive study of their excellent photocatalytic efficiency in organic pollutants removal" which is published in New Journal of Chemistry, we have discussed the how Ce has improved the photo-induced degradation of caffeine (a psychoactive drug) in water in the presence of TiO2 photocatalyst.

Concerning the photochemical properties, although the energy bandgap of pure TiO2 and Ce modified TiO2 remains the same (Eg ≈ 3.2 eV) similar, the valence band of the surface-modified material was shifted toward negative value, thus improving the generation of reactive oxygen species. Indeed, higher concentration of HO• was measured. In addition, the photocurrent generated by Ce modified TiO2 has been improved compared to pure TiO2, thus indirectly highlighting a better e-/h+ pair separation. 

Finally, since this system involved a photocatalytic material (TiO2) which was modified on its surface by an element active in Fenton reactions (Ce), it might be also assumed that combined photocatalytic and Fenton processes occured. Such hypothesis is actually under intense investigation and an article will be published soon on this topic! 

Link to our article in New Journal of Chemistry: doi.org/10.1039/D0NJ05976E