From rust to robust disinfectants: How do iron oxides and inorganic oxidants synergize with UVA light towards bacterial inactivation?

Pathogens in drinking water remain a challenge for human health, photo-Fenton process is a promising technique for pathogen inactivation, herein, two common iron oxides, hematite and magnetite mediate persulfate (peroxymonosulfate-PMS - and peroxydisulfate-PDS) involved photo-Fenton-like processes were constructed for E. coli inactivation, and the inactivation performance was investigated and compared with the photo-Fenton process under a low intensity UVA irradiation. Results indicated that with a low dose of iron oxides (1 mg/L) and inorganic peroxides (10 mg/L), PMS-involved photo-Fenton-like process is the best substitute for the photo-Fenton one over pH range of 5-8. In addition, humic acid (HA, one of the important components of natural organic matter) incorporated iron oxide-mediated photo-Fenton-like processes for bacteria inactivation was also studied, and facilitating effect was found in UVA/hematite/PMS and UVA/magnetite/PDS systems. Reactive oxygen species (ROS) exploration experiments revealed that ·OH was the predominant radical in H2O2- and PDS-containing systems, whereas 1O2 was one of the principal reactive species in the PMS systems. In addition to the semiconductor photocatalysis of iron oxides and UVA-activated oxidants, iron-complexes (iron-oxidant complexes and iron-bacteria complexes) mediated ligand-to-metal charge transfer (LMCT) processes also made contribution to bacterial inactivation. Overall, this study demonstrates that it is feasible to replace H2O2 with PMS in a photo-Fenton-like process for water disinfection using a low dose of reagents, mediated by cheap catalysts, such as hematite and magnetite, it is also hoped to provide some insights to practical water treatment.

Corrigendum: Colloidal nanomaterials for water quality improvement and monitoring.

[This corrects the article DOI: 10.3389/fchem.2022.1011186.].

Colloidal nanomaterials for water quality improvement and monitoring.

Water is the most important resource for all kind forms of live. It is a vital resource distributed unequally across different regions of the globe, with populations already living with water scarcity, a situation that is spreading due to the impact of climate change. The reversal of this tendency and the mitigation of its disastrous consequences is a global challenge posed to Humanity, with the scientific community assuming a major obligation for providing solutions based on scientific knowledge. This article reviews literature concerning the development of nanomaterials for water purification technologies, including collaborative scientific research carried out in our laboratory (nanoLAB@UA) framed by the general activities carried out at the CICECO-Aveiro Institute of Materials. Our research carried out in this specific context has been mainly focused on the synthesis and surface chemical modification of nanomaterials, typically of a colloidal nature, as well as on the evaluation of the relevant properties that arise from the envisaged applications of the materials. As such, the research reviewed here has been guided along three thematic lines: 1) magnetic nanosorbents for water treatment technologies, namely by using biocomposites and graphite-like nanoplatelets; 2) nanocomposites for photocatalysis (e.g., TiO2/Fe3O4 and POM supported graphene oxide photocatalysts; photoactive membranes) and 3) nanostructured substrates for contaminant detection using surface enhanced Raman scattering (SERS), namely polymers loaded with Ag/Au colloids and magneto-plasmonic nanostructures. This research is motivated by the firm believe that these nanomaterials have potential for contributing to the solution of environmental problems and, conversely, will not be part of the problem. Therefore, assessment of the impact of nanoengineered materials on eco-systems is important and research in this area has also been developed by collaborative projects involving experts in nanotoxicity. The above topics are reviewed here by presenting a brief conceptual framework together with illustrative case studies, in some cases with original research results, mainly focusing on the chemistry of the nanomaterials investigated for target applications. Finally, near-future developments in this research area are put in perspective, forecasting realistic solutions for the application of colloidal nanoparticles in water cleaning technologies.

Unraveling the Pivotal Role of Atropisomerism for Cellular Internalization.

The intrinsic challenge of large molecules to cross the cell membrane and reach intracellular targets is a major obstacle for the development of new medicines. We report how rotation along a single C-C bond, between atropisomers of a drug in clinical trials, improves cell uptake and therapeutic efficacy. The atropisomers of redaporfin (a fluorinated sulfonamide bacteriochlorin photosensitizer of 1135 Da) are separable and display orders of magnitude differences in photodynamic efficacy that are directly related to their differential cellular uptake. We show that redaporfin atropisomer uptake is passive and only marginally affected by ATP depletion, plasma proteins, or formulation in micelles. The α4 atropisomer, where meso-phenyl sulfonamide substituents are on the same side of the tetrapyrrole macrocycle, exhibits the highest cellular uptake and phototoxicity. This is the most amphipathic atropisomer with a conformation that optimizes hydrogen bonding (H-bonding) with polar head groups of membrane phospholipids. Consequently, α4 binds to the phospholipids on the surface of the membrane, flips into the membrane to adopt the orientation of a surfactant, and eventually diffuses to the interior of the cell (bind-flip mechanism). We observed increased α4 internalization by cells of the tumor microenvironment in vivo and correlated this to the response of photodynamic therapy when tumor illumination was performed 24 h after α4 administration. These results show that properly orientated aryl sulfonamide groups can be incorporated into drug design as efficient cell-penetrating motifs in vivo and reveal the unexpected biological consequences of atropisomerism.

Natural solar activation of modified zinc oxides with rare earth elements (Ce, Yb) and Fe for the simultaneous disinfection and decontamination of urban wastewater.

This study investigates the capability of modified zinc oxides (ZnO) with Ce, Yb and Fe towards the simultaneous inactivation of pathogenic bacteria (Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa) and Contaminants of Emerging Concern (CECs, Diclofenac, Sulfamethoxazole and Trimethoprim) under natural sunlight. Several catalyst loads (from 0 to 500 mg/L) were assessed as proof-of principle in isotonic solution followed by the evaluation of organic matter effect in simulated and actual urban wastewater (UWW), using bare TiO2-P25 as reference. The order of photocatalysts efficiency for both bacterial and CECs removal was: ZnO-Ce â‰… TiO2-P25 > ZnO-Yb > ZnO-Fe > photolysis > darkness in all water matrices. The best photocatalytic performance for water disinfection and decontamination was obtained with 500 mg/L of ZnO-Ce: 80% of ∑CECs removal after 45 min (4.4 kJ/L of accumulated solar UV-A energy (QUV)) and the total inactivation of bacteria (Detection Limit of 2 CFU/mL) after 120 min (14 kJ/L of QUV) in UWW. The microbial and CECs abatement mechanism was described based on the generation of hydroxyl radicals, which was experimentally demonstrated for ZnO-Ce. Additionally, no significant release of Zn2+ and Ce was detected after the solar exposure. These results point out for the first time the capability of ZnO-Ce for the simultaneous UWW disinfection and decontamination under natural sunlight.

Attenuation of toxicity and occurrence of degradation products of the fungicide tebuconazole after combined vacuum UV and UVC treatment of drinking water.

Antifungal azoles are the most frequently used fungicides worldwide and occur as active ingredients in many antifungal pharmaceuticals, biocides, and pesticides. Azole fungicides are frequent environmental contaminants and can affect the quality of surface waters, groundwater, and drinking water. This study examined the potential of combined vacuum UV (185 nm) and UVC (254 nm) irradiation (VUV/UVC) of the azole fungicide tebuconazole and the transformation product 1,2,4-trizole on degradation and changes in ecotoxicity. In vivo ecotoxicity was examined before and after UV treatment using bioassays with test organisms from different trophic levels to integrate changes in biological effect of the parent compound and the degradation products. The test battery included the luminescent bacterium Aliivibrio fischeri, the Gram-positive bacterium Bacillus subtilis, the fungus Fusarium graminearum, the green microalga Raphidocelis subcapitata, and the crustacean Daphnia magna. The combined VUV/UVC treatment of tebuconazole in drinking water efficiently degraded the parent compound at the µg/L-mg/L level and resulted in transformation products with lower toxicity than the parent compound. A direct positive correlation was observed between the applied UV dose (fluence, J/cm2), the disappearance of tebuconazole, and the decrease in ecotoxicity. The combined VUV/UVC process does not require addition of supplementary oxidants or catalysts and our study suggests that VUV/UVC-mediated photolysis of azole fungicides in water can decrease the overall toxicity and represent a potentially environmentally friendly treatment method.

Elucidation of the photoinduced transformations of Aliskiren in river water using liquid chromatography high-resolution mass spectrometry.

Aliskiren was selected as a compound of potential concern among a suspect screening list of more than 40,000 substances on a basis of high occurrence, potential risk and the absence of information about its environmental fate. This study investigated the photoinduced degradation of aliskiren in river water samples spiked at trace levels exposed to simulated sunlight. A half-life time of 24 h was observed with both direct and indirect photolysis playing a role on pollutant degradation. Its photo-induced transformation involved the formation of six transformation products (TPs), elucidated by LC-HRMS - resulted from the drug hydroxylation, oxidation and moieties loss with subsequent cyclization structurally. The retrospective suspected analysis performed on a total of 754 environmental matrices evidenced the environmental occurrence of aliskiren and two TPs in surface waters (river and seawater), fresh water, sediments and biota. In silico bioassays suggested that aliskiren degradation undergoes thought the formation of TPs with distinct toxicity comparing with the parent compound.

Study of the photoinduced transformations of maprotiline in river water using liquid chromatography high-resolution mass spectrometry.

Maprotiline was identified as a compound of potential interest further to a suspect screening test carried out for a list of more than 40,000 substances based on specific occurrence, hazard and risk indicators. Despite the high frequency of appearance of this drug in wastewater treatment stations, his environmental fate is still unknown. Herein, we investigated for the first time the maprotiline degradation pathways in river water spiked with the drug at a concentration close to those detected in natural waters. Preliminary photocatalytic experiments in ultrapure water produced 32 transformation products (TPs) resulted mainly from the multiple hydroxylation/oxidation in different positions of the drug molecule. From the river water experiments, 12 TPs were formed by photolysis matching with those observed in ultrapure water experiments, and 2 were also formed resulted from biotic degradation. Employing HPLC-HRMS, we were able to elucidate the chemical structures of TPs and assess the overall degradation mechanism. Preliminary bioassays suggested lower toxicity of TPs relatively to the parent compound.

Ultrafast Dynamics of Manganese(III), Manganese(II), and Free-Base Bacteriochlorin: Is There Time for Photochemistry?

Manganese(III) and manganese(II) complexes of halogenated sulfonamide tetraphenylbacteriochlorins were prepared for the first time via a transmetalation reaction and shown to be stable at room temperature. The behavior of the electronic states of the paramagnetic complexes is remarkably different from those of the metal-free bacteriochlorins or diamagnetic metallobacteriochlorins. The Mn3+ complex exhibits eight electronic transitions between different states from 300 to 1100 nm, with a very prominent band (molar absorption coefficient of ca. 50000 M-1 cm-1) at 829 nm. Ultrafast transient absorption showed the formation of an excited singquintet state that decays to a tripquintet state with a femtosecond lifetime. The tripquintet state decays in 5 ps, yielding a tripseptet state with a 570 ps lifetime. The electronic absorption of the Mn2+ complex more closely resembles those of diamagnetic metallobacteriochlorins, but the longest decay lifetime is only ca. 8 ps. The intense photoacoustic waves generated with near-infrared excitation suggest the use of these complexes in photoacoustic tomography.