Open dumping and disposal of waste iron ore in freshwater and landfills are increasing environmental concerns. Therefore, following the environmental sustainability and circular economy approach, this study recovered iron-based coagulants from waste laterite ore (WLO) and assessed their performance in water treatment. Chemical leaching of WLO was performed using HCl with varying acid concentrations, temperatures, and treatment times. The optimum iron solubilization efficiency of 86% was achieved at an optimized HCl concentration of 13 mol/L, a reaction temperature of 90 °C, a mixing speed of 500 rpm, and a treatment time of 240 min. The recovered WLO-based iron coagulant exhibited a greenish color and showed promising performance in treating water from the River Indus Canal, particularly in removing turbidity and heavy metals. This performance of the WLO-based iron coagulant was nearly identical to that of conventional ferric chloride. Overall, recovering iron-based coagulants from WLO may reduce the cost of coagulating drinking water or wastewater. Furthermore, the present study's findings will be useful in protecting the environment by either not discharging the WLO into freshwater bodies or by dry stacking.

This study investigated the bioconversion of textile wastewater plant sludge (TWS) and cattle manure (CM) into biogas through co-anaerobic digestion (CAND), focusing on detailed characteristics analyses and ratio optimization. The lab-scale biochemical methane potential experiments were conducted to optimize the ratio of TWS and CM. An optimum TWS: CM ratio of 3:2 was further evaluated in a pilot-scale anaerobic digester with a 1 m³ capacity, undergoing continuous monitoring and operation for six months to validate system upscaling and process optimization. The biological analyses of the resultant digestate confirmed the presence of different methanogens and provided insight into co-digestion mechanisms. The elemental analysis revealed the stabilization of the inorganic contaminants of the TWS due to the addition of CM. The critical parameters of the digestion process were also analyzed, i.e., changes in volatile solids, pH, and COD. The comparative Life Cycle Assessment demonstrated that the CAND of TWS outperformed incineration with energy recovery and landfilling with biogas recovery, yielding net-negative impacts for climate change (–57.8 kg CO₂-Eq) and fossil energy use (–12 kg oil-Eq). Pilot-scale digestion achieved a biogas yield of 492 NmL/g VS, confirming the feasibility of scale-up despite a reduction relative to batch-scale BMP results.

In this study, LaFeO3/g-C3N4 (LFO/g-CN) hybrid materials with mass ratios of LFO and g-CN of 1/0.5, 1/1, and 1/1.5 were synthesized and evaluated for the visible light photocatalytic degradation of the azo-dye Orange G (OG). The composite materials were characterized to determine their textural, morphological, and optical properties. Preliminary photocatalytic results highlighted a significant synergistic interaction between LFO and g-CN. The LFO/g-CN (1/1.5) composite exhibits the highest activity, achieving 50% OG removal, representing a 2.7-fold improvement over pristine g-CN, with a rate constant of 0.0048 min-1 (3.7 times higher than bare g-CN). The degradation kinetics follow a pseudo-first-order model. The influence of key operational parameters, including catalyst loading, initial pH, pollutant concentration, and visible-light intensity, was systematically investigated using the optimized LFO/g-CN (1/1.5) composite. Optimal OG conditions (0.5 g L-1 catalyst, pH 2.0, 10 mg L-1 OG concentration, 0.95 W cm-2 visible light intensity) yielded a maximum rate constant of 0.0119 min-1 and 82% OG decolorization after 135 min. At higher catalyst or dye concentrations, the photocatalytic activity declined due to light scattering and surface saturation. Enhanced OG degradation under acidic conditions was attributed to favourable electrostatic attraction between the positively charged catalyst surface and anionic OG moieties. The composite also demonstrated excellent stability, retaining over 77% of its initial activity after four reuse cycles. These findings highlight the potential of LFO/g-CN heterojunctions as efficient visible-light photocatalysts for sustainable water remediation.

Mixed-phase TiO₂ systems offer unique opportunities for enhancing photocatalytic performance via interpolymorph junctions (homojunctions). While anatase/rutile interfaces have been extensively studied, anatase/brookite junctions remain comparatively underexplored. Here, we demonstrate that homojunctions between anatase and brookite, formed via a template-free, pH-controlled synthesis and low-temperature calcination (200 °C), significantly enhance photocatalytic activity under simulated solar light. High-resolution TEM reveals direct anatase/brookite junctions without isolated brookite crystallites. At the same time, IR spectroscopy detects the formation of CO2.− radical ions, suggesting that the homojunctions act as active defect sites, potentially contributing to visible light absorption or increasing photocatalytic performance. Notably, the surface generation of CO2.− under mild conditions could open new perspectives for CO₂ activation and solar fuel production, while also positioning this species as a valuable intermediate in organic synthesis for the formation of carboxylic acids. Compared to an anatase/brookite/rutile system obtained through calcination at 600 °C, the sample calcined at low temperature exhibits superior performance in degrading paracetamol, a model emerging contaminant in city water. Importantly, Surface-Enhanced Raman Spectroscopy (SERS) enables direct identification of paracetamol degradation intermediates, revealing a mechanistic pathway similar to that promoted by a commercial anatase/rutile TiO2. These findings underscore the potential of anatase/brookite homojunctions as efficient charge-separating interfaces, as further supported by electrochemical impedance spectroscopy.

Bacterial contamination in drinking water systems poses a serious health risk due to poor hygiene, human activities, and cross-contamination within the water supply. This study examines the potential of iron-doped titanium oxide nanometric powder (Fe-TiO2) for the photocatalytic disinfection of Gram-negative E. coli and Gram-positive S. aureus under visible light. The Fe-TiO2 photocatalyst, with an optimal nominal content of 2.5 wt % Fe, was synthesized using a surfactant-assisted sol-gel method, resulting in a mesoporous nanomaterial composed of anatase nanoparticles with a specific surface area of 123 m2/g. A sample of undoped anatase TiO2, obtained using the same sol-gel method and exhibiting a specific surface area of 116 m2/g, was utilized to confirm the role of Fe-doping in disinfection. The nanopowders were characterized using X-ray diffraction, N2 sorption at -196 °C, diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy, electrophoretic mobility measurements, high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, and field emission scanning electron microscopy. Photocatalytic disinfection tests were conducted using 1 and 0.5 g/L Fe-TiO2 with varying initial bacterial concentrations, with 1 g/L yielding the most promising results under the experimental conditions employed. After 240 min of treatment with 1 g/L Fe-TiO2, a 99.9% removal of both E. coli and S. aureus was achieved starting from a bacterial concentration of 1 × 106 CFU/mL. A 99.9% removal of E. coli and a 99.8% removal of S. aureus were achieved starting from 1 × 104 CFU/mL. The Fe-TiO2 nanomaterial was effective against high concentrations of both bacteria under visible light. Reusability was studied by recovering the Fe-TiO2 nanoparticles and assessing their performance over three cycles. The photocatalytic disinfection effectiveness of Fe-TiO2 nanoparticles under visible light was validated using an actual tap water sample containing 167 CFU/mL total coliforms and 8 CFU/mL E. coli . The bacteria were photocatalytically inactivated within 30 min.

Nanocrystal (NC) sensitizers enable triplet–triplet annihilation photon upconversion (TTA-UC), converting NIR or visible light into higher-energy photons and offering promising potential for applications, especially in solar-driven reactions.

This study investigated the adsorption performance of LaFeO3/g-C3N4 (LFO/g-CN) composite material for the removal of Orange G (OG) dye from aqueous solutions. The LFO/g-CN composite, prepared by wet impregnation method from LFO phase and g-CN compound, was characterized using various techniques including Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Brunauer–Emmett–Teller (BET) surface area analysis. BET results revealed a significant increase in surface area from 3.7 m2 g−1 for LFO to 51 m2 g−1 for the LFO/g-CN composite. The adsorption efficiency was optimized by examining different factors affecting the adsorption process including adsorbent amount, initial pH, solution temperature, contact time and initial OG dye concentration. The maximum removal percentage of OG onto LFO/g-CN material was found to be 72 ΔG^∘ < 0) and endothermic ( Δ H^∘ > 0). This information contributes to a better understanding of LFO/g-CN as an efficient adsorbent for dye removal, offering potential applications in wastewater treatment at elevated temperatures.

In this study, we explored the effect of Cr3+ substitution by partially and fully replacing Fe3+ in the normal spinel ZnFe2O4 crystal structure at electrochemical interfaces. The resulting ZnCrxFe2-xO4 nanomaterials exhibited an average particle size between 20 and 50 nm with a spherical morphology. The materials also demonstrated energy band gaps ranging from 2.1 to 3.1 eV X-ray diffraction (XRD) analysis confirmed that all the synthesized materials maintained a normal spinel structure, attributed to the octahedral site preference energy (OSPE) of Zn2+, Fe3+, and Cr3+ ions. Electrochemical performance assessments revealed that the ZnFe2O4-based sensor achieved a sensitivity of (37.8 f 0.2) mu A/mM with a kinetic rate constant of (13.1 f 2.8) ms-1, while the ZnCr2O4-based sensor exhibited a sensitivity of (32.4 f 0.5) mu A/mM and a kinetic rate constant of (3.73 f 0.55) ms-1 in the detection of paracetamol, whereas ZnCrFeO4 sensor has produced the second-best sensitivity (35.7 f 0.1 mu A/mM) and the rate constant (4.53 f 0.54 ms-1) with the lowest limit of detection (1.94 f 0.01 mu M). These differences in electrochemical performance were correlated with the variations in the energy band gaps caused by the restructuring of the normal spinel structure. Our findings indicate that the ZnFe2O4 sensor has a higher potential for direct electron transfer, whereas the other sensors are more likely to facilitate surface-mediated electron transfer.

We all recognize the importance of photochemistry and photocatalysis in daily life [...]

Arsenic (As) contamination is a severe problem in drinking-water sources. This study designed and investigated a novel combined electrocoagulation–filtration (ECF) system to investigate As treatment and filtration in drinking water in collaboration with HANDS-Pakistan and Medico International, Germany. Two separate pilot-scale ECF systems were designed and developed with an electrocoagulation (EC) unit and a commercially available PAUL® filter configured with vertical flat-sheet ultra-low-pressure membranes of 0.04 µm pore size for the combined treatment and filtration of different As concentrations. Real drinking water at different As concentrations, i.e., 100, 200, and 300 μg/L were tested on one ECF system with EC electrodes of iron (Fe) and another system with aluminum (Al), at different treatment times (0, 5, 10, 20, 45, 60, 120, 180 min), at a fixed current density (12 mA/cm2) and water flow rate of 1 L/min. The initial results showed 99% As removal within 5 min with the combined ECF treatment for both electrodes of Fe and Al. In addition, the effect of ECF on different water-quality parameters and the ionic interference on ECF performance and As filtration were analyzed. The results showed the promising potential of combined ECF treatment and filtration for treating and purifying As.

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A salicylic-acid (SA)-modified samarium-doped TiO2 complex (Sm-TiO2/SA) was synthesized via a sol-gel method followed by impregnation. A Raman Fourier transform IR and X-ray photoelectron spectroscopic study showed that SA (as an electron donor) forms a surface complex on the Sm-TiO2 surface through its phenolic/carboxylic functional groups. In the Sm-TiO2/SA complex, a ligand-to-metal charge transfer (LMCT) is active, inducing a marked red-shift in the absorption spectrum of TiO2, which extends to 550-600 nm. The synergetic effect between the LMCT process and the luminescent properties of the lanthanide ions (Sm3+) is discussed and supported by the photoluminescence spectra. Further photocatalytic experiments (under sunlight) and the study of the effect of different scavengers show the presence of competitive reactions between de-ethylation and cleavage of Rhodamine B (RhB) during its degradation. With the Sm-TiO2/SA complexes, the superoxide radical ion (O-2(center dot-)) is the main active species responsible for the N-de-ethylation pathway under sunlight irradiation. The cleavage of RhB by the hydroxyl radical ((OH)-O-center dot) appears, instead, to dominate with the Sm-TiO2 photocatalysts.

This work investigates the effect of the inclusion of Bi3+ ions in ZnFe2O4 nanoparticles on electron transfer at the electrochemical interface. ZnBixFe2-xO4 (x = 0, 0.5, 1, 2) nanomaterials are synthesized and the impact of Bi3+ ions on the chemical features of ZnFe2O4 nanoparticles is studied by using different materials' characterization techniques. The effect of the change in the chemical composition of ZnFe2O4 nanoparticles on the electrochemical sensing performance is extensively studied and correlated with the electrochemical sensitivity and kinetic rate constant. Screen-printed electrodes functionalized with ZnBixFe2-xO4 nanomaterials have an excellent enhancement of electrochemical sensing performance towards paracetamol, as a test molecule, compared to the carbon electrodes. The highest sensitivity (37.8 f 0.2 mu A/mM) and the best kinetic rate constant (13.1 f 2.8 ms-1) are achieved by the ZnFe2O4 sensor, while the ZnBi2O4 sensor achieved a sensitivity of (23.5 f 0.6) mu A/ mM with a kinetic rate constant of (0.45 f 0.16) ms- 1. The ZnFe2O4 sensor is found to have a direct electron transfer, whereas the other sensors participate in a surface state-mediated electron transfer at the electrochemical interface. This research shows a clear path to the potential applications of spinel oxide-based electrochemical sensors for specific drugs or molecules detection.

This work aims to examine the application of ZnO/Curcumin nanocomposite materials, in which curcumin (natural dye) is used as a photosensitizer in the photocatalytic degradation of methylene blue (MB) under visible light irradiation. The ZnO/x t_1/2 ) of 0.0423 min−1 and 16 min. The significant improvement in the photocatalytic properties of ZnO under visible light irradiation induced by the addition of curcumin as a photosensitizer could be due to the increase in the concentration of reactive radical species in the solution, such as superoxide ( O_2^· - ) and hydroxyles ( OH^· ).

By ionic exchange of preformed methylimogolite nanotubes (chemical formula (OH)3Al2O3SiCH3), nanotubes with the chemical formula (OH)3Al2-xFexO3SiCH3 were obtained, with x values of 0.05 and 0.1, corresponding to a nominal Fe content of 1.4 and 2.8 wt%, respectively. The nanotubes were characterized using low angles X-ray powder diffraction; N2 sorption at -196 degrees C; Diffuse Reflectance UV-Vis spectroscopy and High-Resolution Transmission Electron Microscopy coupled to Energy Dispersive X-Ray Analysis. Their electrochemical behaviour was investigated by Cyclic Voltammetry: a redox behaviour was observed only with a Fe content of 2.8 wt%, likely due to Fe-oxyhydroxide clusters (FeOOH) at the nanotubes' outer surface. Based on the electrochemical and physicochemical characterizations, nanocomposites of Fe-doped methylimogolite and reduced Graphene Oxide (rGO) were obtained for the first time through a simple method, previously developed by some of us to disperse electrochemically active nanomaterials onto carbon supports. In the micro/mesoporous nanocomposites (specific surface area in the 370-284 m2 g-1 range) the NTs were highly dispersed within the 3D rGO matrix. Cyclic Voltammetry showed that the capacitive behaviour of the Fe-doped NTs alone were enhanced when they were embedded in the 3D rGO matrix.

The photocatalytic degradation of the emerging contaminant paracetamol in aqueous solution has been studied under 1 SUN (~1000 W m−2) in the presence of four commercial TiO2 powders, namely sub-micrometric anatase and rutile, and nanometric brookite and P25 (the popular anatase/rutile mixture used as a benchmark in most papers). The rutile powder showed low activity, whereas, interestingly, the anatase and the brookite powders outperformed P25 in terms of total paracetamol conversion to carboxylic acids, which, according to the literature, are the final products of its degradation. To explain such results, the physicochemical properties of the powders were studied by applying a multi-technique approach. Among the physicochemical properties usually affecting the photocatalytic performance of TiO2, the presence of some surface impurities likely deriving from K3PO4 (used as crystallization agent) was found to significantly affect the percentage of paracetamol degradation obtained with the sub-micrometric anatase powder. To confirm the role of phosphate, a sample of anatase, obtained by a lab synthesis procedure and having a “clean” surface, was used as a control, though characterized by nanometric particles and higher surface area. The sample was less active than the commercial anatase, but it was more active after impregnation with K3PO4. Conversely, the presence of Cl at the surface of the rutile did not sizably affect the (overall poor) photocatalytic activity of the powder. The remarkable photocatalytic activity of the brookite nanometric powder was ascribed to a combination of several physicochemical properties, including its band structure and nanoparticles size.

In this work, 3D-structured clay filters were prepared and coated with iron-doped titanium dioxide (Fe-TiO2) using 3D printing and sol–gel soaking and calcination techniques. Three-dimensional printing was employed to mold and shape the clay filters before annealing. The coated and uncoated filters were characterized for different properties, i.e., morphology, optical properties, and crystalline structure, using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), UV/Vis diffused reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The FESEM images show uniform coatings of round-shaped Fe-TiO2 on the tiny pore of the clay filter. The optical energy band gap of the obtained coating was around 2.8 eV, estimated by Tauc’s plot, compared with 3.2 eV of pristine anatase TiO2. The XRD spectra data processed through XRD software revealed the coatings of TiO2 on the filter surface with the obtained phase of anatase. The photocatalytic performance of bare and coated filters was initially tested for the degradation of indigo carmine (IC) dye and the obtained results suggested the photocatalytic degradation of IC dye by the Fe-TiO2 clay filter compared with the bare filter. Afterward, the denitrification of nitrate NO3 at various concentrations was performed using Fe-TiO2-coated clay filters and analyzing the total nitrogen (TN) analysis and reduction of NO3 to nitrite (NO2−), nitrogen monoxide (NO), and nitrogen gas (N2). The TN analysis revealed up to 81% denitrification efficiency of the 30 ppm NO3 solution with the photocatalytic response of the Fe-TiO2-coated filter. The results revealed that the Fe-TiO2-coated clay filter has a high potential for denitrification applications under natural sunlight.

For the first time, Fe-doping (0.05, 1.0, and 2.5 wt.% Fe) was performed on a high-surface-area anatase/brookite TiO2 by adopting a simple template-free sol-gel synthesis followed by calcination at a mild temperature. The powders’ textural and surface properties were characterized by following a multi-technique approach. XRD analysis showed that the anatase/brookite ratio slightly varied in the Fe-doped TiO2 (from 76.9/23.1 to 79.3/22.7); Fe doping noticeably affected the cell volume of the brookite phase, which decreased, likely due to Fe3+ ions occupying interstitial positions, and retarded the crystallite growth. N2 sorption at −196 °C showed the occurrence of samples with disordered interparticle mesopores, with an increase in the specific surface area from 236 m2 g−1 (undoped TiO2) to 263 m2 g−1 (2.5 wt.% Fe). Diffuse Reflectance UV-Vis spectroscopy showed a progressive decrease in the bandgap energy from 3.10 eV (undoped TiO2) to 2.85 eV (2.5 wt.% Fe). XPS analysis showed the presence of some surface Fe species only at 2.5 wt.% Fe, and accordingly, the ζ-potential measurements showed small changes in the pH at the isoelectric point. The photocatalytic degradation of simazine (a persistent water contaminant) both under UV and simulated solar light was performed as a probe reaction. Under UV light, Fe-doping improved simazine degradation in the sample at 0.05 wt.% Fe, capable of degrading ca. 77% simazine. Interestingly, the undoped TiO2 was also active both under UV and 1 SUN. This is likely due to the occurrence of anatase/brookite heterojunctions, which help stabilize the photogenerated electrons/holes.

Biofilms in water distribution lines strongly affect water safety as they are the main carriers of pathogens. The current study investigated the biofilm formation and identification of selected pathogens in different distribution pipeline materials and their disinfection method in an annular reactor (AR). Initially, the quality of the flowing water from each pipeline material was analyzed, i.e., pH, TDS, EC, turbidity, and salinity; then, the biofilm formation was monitored for each material, i.e., ABS, PC, PVC, PP, and HDPE. Further, the disinfection kinetics of biofilm at different chlorine doses, i.e., 0.5, 1.0, 1.5, and 2.0 mg/L, was investigated. The selected pathogens, i.e., E. coli, Pseudomonas, Shigella, Salmonella sp., and Vibrio sp. were identified in biofilms formed in different pipeline materials. The disinfection kinetics results showed that a chlorine dose of 2.0 mg/L was the most effective in disinfecting selected pathogens. Following the disinfection kinetics, it was observed that Salmonella sp. was disinfected within 7 days, whereas other pathogenic biofilms were disinfected within 14 days. The efficacy of chlorine disinfection was affected by the types of pipeline materials. The study outcomes could provide insights into biofilms’ disinfection method and the selection of suitable pipeline materials to ensure drinking water safety.

A reverse-micelle sol–gel method was chosen for the preparation of Fe-doped TiO2 samples that were employed in the photodegradation of the crystal violet dye under visible light irradiation in a batch reactor. The dopant amount was varied to assess the optimal photocatalyst composition towards the target dye degradation. The photocatalysts were characterized through a multi-technique approach, envisaging XRPD and QPA as obtained by Rietveld refinement, FE-SEM analysis, DR UV−vis spectroscopy, N2 adsorption/desorption isotherms measurement at −196 °C, ζ-potential measurement, and XPS analysis. The physical-chemical characterization showed that the adopted synthesis method allows obtaining NPs with uniform shape and size and promotes the introduction of Fe into the titania matrix, finally affecting the relative amounts of the three occurring polymorphs of TiO2 (anatase, rutile and brookite). By increasing the Fe content, the band gap energy decreases from 3.13 eV (with undoped TiO2) to 2.65 eV (with both 2.5 and 3.5 wt.% nominal Fe contents). At higher Fe content, surface Fe oxo-hydroxide species occur, as shown by DR UV-vis and XP spectroscopies. All the Fe-doped TiO2 photocatalysts were active in the degradation and mineralization of the target dye, showing a TOC removal higher than the undoped sample. The photoactivity under visible light was ascribed both to the band-gap reduction (as confirmed by phenol photodegradation) and to dye sensitization of the photocatalyst surface (as confirmed by photocatalytic tests carried out using different visible-emission spectra LEDs). The main reactive species involved in the dye degradation were determined to be positive holes.