For the first time, using a chemical pollutant (an antibiotic) as a photosensitizer to improve the elimination of a microbiological contaminant of emerging concern (antibiotic-resistant bacteria) is presented. The effect of ciprofloxacin (CIP) on the inactivation of three light-promoted antibiotic-resistant bacteria (ARB) was evaluated. Ciprofloxacin-resistant Escherichia coli, ciprofloxacin-resistant Staphylococcus aureus, and carbapenem-resistant Klebsiella pneumoniae. Firstly, the photosensitizing effect of CIP on E. coli inactivation was studied. Irradiated CIP (1 ppm) induced superoxide anion radical formation (confirmed through EPR analyses), and the combination of these reactive oxygen species (ROS) with ongoing solar radiation exposure enhanced bacterial inactivation. CIP enhanced the disinfection of antibiotic-resistant E. coli (by 1.84 log units at 120 min of irradiation) and improved the inactivation of K. pneumoniae (by 3.48 log units at 135 min)—both Gram-negative bacteria. Conversely, the photo-inactivation of the Gram-positive bacteria S. aureus did not significantly change (just a slight reduction of 0.42 log units at 120 min) by the presence of CIP. Showing the bacterial structure influences the disinfection process. Another critical factor was antibiotic concentration. A high CIP concentration (10 ppm) induced an interfering screen effect, while a low concentration promoted bacteria inactivation via photosensitization (in Gram-negative bacteria). Interestingly, no photosensitizing effect was observed when CIP was replaced by levofloxacin (LEV, another fluoroquinolone antibiotic), indicating a strong dependence on antibiotic structure. Additionally, the effect of the light source on photosensitized inactivation was evaluated, substituting sunlight with UVC irradiation. Under UVC light, CIP worsened ARB photo-inactivation, suggesting disinfection was mainly due to direct light action on microorganisms rather than photosensitization. Finally, the influence of water components on sunlight-photosensitized disinfection was examined using simulated urine and freshwater. The ARB inactivation decreased as matrix complexity increased. Thus, the effectiveness order was Milli-Q water > freshwater > urine.

Commercial TiO2 P25 was modified with iron species using simple, mild and cost-effective synthesis conditions. The novel TiO2-Fe material exhibits both high disinfectant activity and long stability under visible light irradiation. The bactericidal activity of the synthesized catalyst was assessed by its capability to inactivate Escherichia coli under both simulated solar and LED-visible light. XRD confirmed the structural integrity of the material, while diffuse reflectance spectroscopy evidenced its absorption in the visible region. Mössbauer and FTIR analysis of the TiO2-Fe catalyst indicate that iron exists predominantly in the Fe3+ state in a Ti-O-Fe bond. Electrochemical studies allowed to correlate the reactivity with the conduction and valence band positions, providing insights into the production of reactive oxygen species (ROS) responsible for bacterial inactivation. A first noteworthy aspect of this study is the identified Ti-O-Fe bond in the TiO2-Fe material, a feature that has not been previously reported in the literature. Another innovative aspect is the simplicity of the synthesis method, which employs a thermally mild and time-efficient process, thereby providing an efficient and accessible approach for enhancing photocatalytic properties. Our findings suggest that the prepared TiO2-Fe photocatalyst holds potential for future applications in antimicrobial paint coatings designed for hospital environments, aiming to enhance infection control under indoor lighting conditions.

In this study, the synergistic and antagonistic effects of Fe species and coexisting natural organic matter (NOM) on the efficacy of solar light disinfection of water are investigated. Different initial iron species (Fe2+/Fe3+) and naturalorganic matter types (Suwannee River-SRNOM, Nordic Reservoir NOM-NDNOM, SR Humic Acid-SRHA, and SR Fulvic Acid-SRFA) were selected. The bactericidal actions of Fe and NOM, alone or in conjunction, were evaluated at various initial iron dosing concentrations, NOM concentrations, irradiation intensities, and pH values. We show that when an appropriate iron (1 ppm Fe2+ or 0.25 ppm Fe3+) and NOM concentration (2 ppm SRNOM or 5 ppm NDNOM) coexisted, synergistic inactivation was observed in the pH range 5.0-8.0. A plausible explanation is that the presence of Fe+NOM significantly promoted the generation of hydroxyl radicals (center dot OH) and singlet oxygen (1O2), which led to enhanced disinfection rates. These results elucidate the previously understudied effects of ubiquitous elements in natural waters and their impact on solar-mediated bacterial inactivation.

This study aimed to enhance solar disinfection (SODIS) by the photo-Fenton process, operated at natural pH, through the re-utilization of fruit wastes. For this purpose, pure organic acids present in fruits and alimentary wastes were tested and compared with synthetic complexing agents. Owing to solar light, complexes between iron and artificial or natural chelators can be regenerated through ligand-to-metal charge transfer (LMCT) during disinfection. The target complexes were photoactive under solar light, and the Fe:Ligand ratios for ex situ prepared iron complexes were assessed, achieving a balance between iron solubilization and competition with bacteria as a target for oxidizing species. In addition, waste extracts containing natural acidic ligands were an excellent raw material for our disinfection enhancement purposes. Indeed, lemon and orange juice or their peel infusions turned out to be more efficient than commercially available organic acids, leading to complete inactivation in less than 1 h by this novel "fruto-Fenton" process, i.e. in the presence of a fruit-derived ligand, Fe(II) and H2O2. Finally, its application in Lake Leman water and in situ complex generation led to effective bacterial inactivation, even in mildly alkaline surface waters. This work proposes interesting SODIS and fruit-mediated photo-Fenton enhancements for bacterial inactivation in resource-poor contexts and/or under the prism of circular economy.

In this study, MS2 bacteriophage was inactivated by homogeneous and heterogeneous photo-Fenton processes in an alkaline matrix (pH 8) using low concentrations of H2O2 and iron forms (1 mg/L), including Fe(II), Fe(III), and Fe (hydr)oxides. As a reference, it has been demonstrated that excellent efficiency towards MS2 inactivation was achieved within 2 min with Fe(II) and 10 min with Fe(III) in the homogeneous photo-Fenton process. Mined iron and five naturally occurring iron (hydr)oxides, including wustite, goethite, hematite, magnetite, and maghemite, were used to assess the virus removal in the heterogeneous photo-Fenton process. Total (5-logU) inactivation of the MS2 bacteriophage was observed within 15-40 min by iron (hydr)oxides in the presence of light and H2O2. Photosensitization of natural organic matter had a significant impact on virus inactivation in both homogeneous and heterogeneous photo-Fenton processes, but dually; it enhanced the formation of complexes between organic matter and iron species, facilitating the homogeneous process at alkaline pH, but hindering the heterogeneous photo-Fenton reaction. Nevertheless, the heterogeneous photo-Fenton process may serve as an efficient method for the inactivation of enteric viruses in water, even at a slightly basic pH, despite the scavenging action of natural organic matter. The low-concentration requirements of this process and the availability of iron oxides in nature contribute to the sustainability of the process, which can be suitable for use in resource-poor environments.

The present study aimed to fill the knowledge gap between the implications of intracellular and extracellular antibiotic resistance mechanisms may inflict on the inactivation pathways of the photo-Fenton process under mild conditions. It was thus designed as a cross-comparison of the effect of homogeneous and heterogeneous photo-Fenton (near-neutral pH, [Fe]=1 mg/L, and [H2O2]=10 mg/L) on seven strains of Staphylococcus aureus exhibiting different mechanisms of antibiotic resistance, or susceptibility. Additionally, variations in antibiotic tolerance (MIC test) and relative changes in the presence of antibiotic resistance genes were qualitatively monitored during treatment using PCR. The results suggest that resistance to antibiotics does not confer enhanced resistance to photo-Fenton, as it attained a 4-logU reduction within 50-100 min for all strains, regardless of resistance status. Strains that express intracellular resistance mechanisms do not pose a risk; however, strains that express external mechanisms for their defense against antibiotics occasionally interfere with the inactivation process. This phenomenon was mainly linked to the cell wall thickening of some of the externally resistant strains as compared to their susceptible homologues. Eventually, by conferring resistance to antibiotics, this cell wall alteration may reduce susceptibility to Fenton-related reagents by either reducing their intracellular diffusion or rendering cell walls less prone to leaching upon extracellular attacks. In addition, the photo-Fenton process either remained unchanged or lowered the antibiotic resistance threshold. Moreover, the homogeneous photo-Fenton system considerably lowered the detection of antibiotic resistance genes within 90 min with respect to hv, hv/H2O2, or heterogeneous photo-Fenton. In conclusion, the results suggest that the homogeneous photo-Fenton system could be an effective treatment for hindering the spread of antibiotic resistance, but treatment conditions should aim to maximize the degradation of ARG, as their concentration decreases more slowly than that of bacteria.

In this manuscript, the improvement of solar disinfection (SODIS) for water treatment through the photo-Fenton reaction using iron replacements, namely calcined herbs and spices (thyme, cumin, cinnamon, ginger, and cocoa), naturally containing high content of metals. The bactericidal performance of SODIS, H2O2/light and solar photo-Fenton (light/H2O2/Fe2+) were assessed in pure and Lake Leman water. Sodium percarbonate (SPC) and ashes were successfully employed as substitutes of H2O2 and Fe2+, respectively. Low spices‘/herbs’ addition improved the H2O2/light process, especially when ginger, cumin, thyme, or cocoa were used, inducing effective heterogeneous photo-Fenton process even at alkaline pH. In ultrapure water, solar photo-Fenton with ashes was only slightly slower than the corresponding Fe2+-driven reaction, while in lake water total bacterial inactivation was achieved by cumin, thyme or ginger ashes. SPC enhanced SODIS performance, while the addition of ashes resulted in faster kinetics than light/SPC only. Overall, this work succeeded in converting the classic photo-Fenton process into a low-cost variant, the “phyto-Fenton” process, driven by the metals contained in the organic-free ashes and the H2O2 content of SPC.

For fifty years, heterogeneous photocatalysis has been considered as having potential to remove organic and microbiological pollutants from water under either artificial UV light or sunlight irradiation. However, after tens of thousands of published research papers, this system has been unable to move from laboratory bench scale to application mainly due to intrinsic thermodynamic limitations as well as kinetical and engineering drawbacks inherent to the heterogenous nature of the process undergoing to much longer treatment times when compared with other well-established water treatment options. Based on recent literature evidence, this critical review aims to describe and discuss the most significant drawbacks and limitations of TiO2-based photocatalytic processes to eliminate biological and chemical pollutants from water at a convenient degradation rate and in a noncomplex operational way. The properties and mechanistic action mode of TiO2 and similar semiconductors and their inherent engineering limitations for water treatment are highlighted. Moreover, the most common strategies unsuccessfully explored in the literature to overcome these drawbacks are described. Even if this analysis is specially focused on TiO2-based photocatalysis, most of the assertions and conclusions herein can be extrapolated to all the other semiconductors when the purpose is to reach water disinfection and detoxification. As 50 years ago, the main challenge remains to develop a new, modified (i.e., doped), or combined (i.e., junctions) photocatalyst generating high oxidative species at enough rates to significantly decrease the treatment time of this type of process (hours) in contrast with the tens of seconds or minutes observed for other systems.

Clean water is essential for human survival, but access to safe drinking water remains a challenge in resource -limited regions. Herein, we explored a low-cost but effective solution for water potabilization using natural iron sources from soils along with sunlight to remove coliforms from water. We evaluated 30 soil samples from tropical regions and among them, we found that soils from Colombia and Cameroon with high clay content and low carbon levels were the most effective catalysts. Their combination with H2O2 enhanced the solar disinfection (SODIS) yield and induced a heterogeneous photo-Fenton process with secondary homogeneous contribution and/or photocatalytic action. We also found that storing soils in acidic conditions increased the concentration of soluble iron species, leading to enhanced E. coli removal due to homogeneous Fenton and Fenton-like processes. The addition of citrate as a ligand further improved the performance of the system, by facilitating the regen-eration of dissolved iron, through metal chelation, thanks to the formation of photo-active complexes. Moreover, we explored the possibility of using sodium percarbonate as a substitute for H2O2 and found it to be a successful alternative, even over alkaline lake water samples. We discuss the mechanism behind the improved activity of sodium percarbonate and suggest that ferruginous soils, when combined with any form of H2O2, can induce the photo-Fenton process over a wide pH range and at low mg/L concentrations. Our study provides valuable in-sights into the potential of using natural iron sources to enhance solar disinfection, making clean water more accessible to communities in need.

Data of the experimental and predicted E. coli inactivation and H2O2 profiles under different conditions of UV radiation, water temperature and initial H2O2 concentration.

Solar disinfection (SODIS) was probed for its underlying mechanism. When Escherichia coli was exposed to UVA irradiation, the dominant solar fraction acting in SODIS process, cells exhibited a shoulder before death ensued. This profile resembles cell killing by hydrogen peroxide (H2O2). Indeed, the use of specialized strains revealed that UVA exposure triggers intracellular H2O2 formation. The resultant H2O2 stress was especially impactful because UVA also inactivated the processes that degrade H2O2-peroxidases through the suppression of metabolism, and catalases through direct enzyme damage. Cell killing was enhanced when water was replaced with D2O, suggesting that singlet oxygen plays a role, possibly as a precursor to H2O2 and/or as the mediator of catalase damage. UVA was especially toxic to mutants lacking miniferritin (dps) or recombinational DNA repair (recA) enzymes, indicating that reactions between ferrous iron and UVA-generated H2O2 lead to lethal DNA damage. Importantly, experiments showed that the intracellular accumulation of H2O2 alone is insufficient to kill cells; therefore, UVA must do something more to enable death. A possibility is that UVA stimulates the reduction of intracellular ferric iron to its ferrous form, either by stimulating O-2(center dot-) formation or by generating photoexcited electron donors. These observations and methods open the door to follow-up experiments that can probe the mechanisms of H2O2 formation, catalase inactivation, and iron reduction. Of immediate utility, the data highlight the intracellular pathways formed under UVA light during SODIS, and that the presence of micromolar iron accelerates the rate at which radiation disinfects water.

Data of the experimental and predicted E. coli inactivation and H2O2 profiles under dark conditions to study the effect of rising water temperature.

Succinic acid was used as a spacer to bind titanium dioxide onto nylon as a new approach to develop self-cleaning fibers. Photoinduced decomposition of stains was achieved within acceptable times under ultraviolet A irradiation, a component of both solar light and indoor lamps spectrum. The surface properties of this innovative film were determined by scanning electron microscopy, electron-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The self-cleaning process was evaluated by analyzing the discoloration of coffee and palm oil stains by ultraviolet/visible diffuse reflection spectroscopy and mineralization via CO2 evolution, recorded using an infrared sensor. The results indicate that grafting TiO2 onto nylon, a synthetic fiber, using succinic acid is a successful chemical binding method, leading to a new self-cleaning material for stain discoloration. This new material is a promising solution to save water and reduce wastewater generated by the use of conventional substances used in textile cleaning.

In this study, the possibility of predicting the efficacy of Solar water disinfection (SODIS) for the removal of bacterial pathogens was assessed by the development of a three-level plan: firstly, systematic E. coli inactivation was performed (in vitro) in Lake Geneva water, under otherwise controlled conditions of water temperature (20-50 degrees C), sunlight intensity (0-1200 W/m2), presence of natural dissolved organic matter (DOM, 0-6 mg/L) and turbidity (0-50 NTU). As a second step a kinetic evaluation led to the selection of the most relevant parameters to be included in a novel static and dynamic model theoretical formulation. The static and dynamic models reliably described the experimental findings (bacterial inactivation under various climatic conditions) and were considered as equally eligible candidates for disinfection modeling. The final step considered ambient temperature, incident radiation and cloud-cover data to forecast (in silico) SODIS efficacy in Africa as a case study. The simulation results were compared with the experimental data and indicated that most African regions are suitable for SODIS processes, but there are areas of risk correlated with climatological conditions (cloudcover and temperature). The results of this study could be applied for regional in decision-making strategies for application of SODIS or in the search for viable alternatives to SODIS in cases where it is deemed unsuitable.

Bi2WO6 is considered an effective photocatalyst, even under the visible part of the solar spectrum, and recent advances in the modification of its structure leave promise for harnessing its enhanced effectiveness. Our experimental E. coli disinfection results have shown that the flower-like morphology brought considerable enhancement to the overall performance over the nanoparticle form. To clarify the photocatalytic mechanism of Bi2WO6, a combination of experimental and computational methods has been employed to investigate the surface properties of Bi2WO6 nanosheets self-assembly flower-like architecture. Although experimental evidence has determined the band edge positions of the as-synthesized samples, so as to address the photocatalytic properties, the mechanistic basis of this concept remains unclear. The calculation results demonstrated here deepen our understanding and indicate the potential of surface configuration to considerably alter the electronic structure and related photocatalytic properties of Bi2WO6 nanosheets. Firstly, we consider a range of surface slab models of Bi2WO6 (010) facet and calculate their surface Gibbs free energies. Having determined that the bi-termination is energetically more favorable by ab initio atomistic thermodynamics, hydrogen passivated termination was proved to be most stable. Through the analysis of the electronic band structure within the DFT-1/2 scheme and work function of the most stable termination, excellent agreement of experimental and theoretical predictions provided a meaningful understanding on the kinetic dependence of photocatalytic bacterial inactivation.

Carbapenem-resistant Klebsiella pneumoniae is a critical priority pathogen according to the World Health Organization's classification. Effluents of municipal wastewater treatment plants (EWWTP) may be a route for K. pneumoniae dissemination. Herein, the inactivation of this microorganism in simulated EWWTP by the photo-electro-oxidation (PEO) and photo-electro-Fenton (PEF) processes was evaluated. Firstly, the disinfecting ability and action pathways of these processes were established. PEO achieved faster K. pneumoniae inactivation (6 log units in 75 min of treatment) than the PEF process (6 log units in 105 min of treatment). PEO completely inactivated K. pneumoniae due to the simultaneous action of UVA light, electrogenerated H2O2, and anodic oxidation pathways. The slower inactivation of K. pneumoniae when using PEF was related to interfering screen effects of iron oxides on light penetration and the diffusion of the bacteria to the anode. However, both PEO and PEF avoided the recovery and regrowth of treated bacteria (with no detectable increase in the bacteria concentration after 24 h of incubation). In addition to the bacteria evolution, the effect of treatment processes on the resistance gene was examined. Despite inactivation of K. pneumoniae by PEF was slower than by PEO, the former process induced a stronger degrading action on the gene, conferring the resistance to carbapenems (PEF had a Ct value of 24.92 cycles after 105 min of treatment, while PEO presented a Ct of 19.97 cycles after 75 min). The results of this research indicate that electrochemical processes such as PEO and PEF are highly effective at dealing with resistant K. pneumoniae in the EWWTP matrix.

In this work, Ag nanoparticles were loaded on ZIF-67 covered by graphene oxide (Ag/ZIF-67@GO), and its catalytic performance was studied for the heterogeneous activation of peroxymonosulfate (PMS) under visible-light. The catalyst surface morphology and structure were analyzed by FT-IR, XRD, XPS, DRS, FE-SEM, EDX, TEM, BET, ICP-AES and TGA analysis. The efficacy of PMS activation by the Ag/ZIF-67@GO under visible light was assessed by phenol degradation and E. coli inactivation. Phenol was completely degraded within 30 min by HO•, SO4•- and O2•- generated through the photocatalytic PMS activation. In addition, total E. coli inactivation was attained in 15 min that confirmed the highly efficient catalytic activation of PMS by the as-made nanocomposite under visible light. The reaction mechanism was elucidated and the importance of the generated reactive species followed the order of: HO• > SO4•- > O2•- > h+, implying a radical-pathway dominated process.

Intensive research has been focused on the synthesis of N-modified TiO2 materials having visible light absorption in order to get higher solar photocatalytic degradation rates of pollutants in water. However, an exhaustive revision of the topic underlines several controversial issues related to N-modified TiO2 materials; these issues concern (a) the methodology used for preparation, (b) the assessment of the structural characteristics, (c) the mechanistic action modes and (d) the raisons argued to explain the limited performances of the prepared materials for organic and biological targets photodegradation in water. Taking advantage of last year's progress in analytical chemistry and in material characterization methods, the authors show, for example, that some works in the literature controversially attribute the term nitrogen doping without enough analytical evidence. Additionally, some papers describe N-modified TiO2 photocatalysts as being able to generate holes with enough oxidative potential to form hydroxyl radicals under visible light. This last assertion often derives from a no pertinent use of illumination sources, light filters, or targets or a limited understanding of the thermodynamic aspects of the studied systems. None of N-containing materials prepared by herein presented methods leads, under solar light, to a significant enhancement in pollutants degradation and microorganism's inactivation kinetics.

This paper studies the worldwide applicability of solar water disinfection (SODIS) technology through a novel parameter: the SODIS potential. This parameter is defined as the inverse ratio between the required exposure time to achieve a four log disinfection of E. coli and the six hours recommended by the standard SODIS protocol. The E. coli inactivation kinetics was predicted by fitting the results under different temperature and incident radiation to a semi-empirical inactivation model, including a synergy term between bacterial stress sources (light/heat). To estimate the SODIS potential, a solar calculator was developed based on the Sun's position, atmospheric extinction, cloud-cover, and elevation. The time-varying total incident radiation available at any location worldwide was estimated for each day along the year during sunlight hours. The time-varying temperature was also estimated from minimum and maximum values, introducing its dynamic variation along with the solar exposure of the water. Both incident radiation and temperature values are input into the kinetic model to estimate the disinfection rate. Based on these values, the number of batch disinfections that can reach the goal of 99.99% bacterial elimination in 1 day and the minimum daily time required to achieve this goal is computed; the latter is finally transformed to the SODIS potential. The results of the study, illustrated as contours indicating the SODIS potential and other relevant indicators overlayed on a world map, confirm that latitude has a significant contribution to the SODIS potential, with the highest values close to the equator. However, the results also highlight the importance of temperature and cloud-cover, with critical differences between equal latitude regions.