Remediation of 17-α-ethinylestradiol aqueous solution by photocatalysis and electrochemically-assisted photocatalysis using TiO2 and TiO2/WO3 electrodes irradiated by a solar simulator

Estrogen toxicity reduction of industrial biochemical tailwater by electrolysis biofilters with ceramsite‑sulfur-siderite fillers

Biochemical tailwater of the industrial park wastewater treatment plant is facing the growing demand of advanced treatment and toxicity reduction. However, existing information on toxicity reduction of real industrial biochemical tailwater is still limited so far. Herein, the water quality of biochemical tailwater from an integrated industrial park in Taihu Lake Basin, China, was systematically investigated, and typical endocrine disrupting chemicals (EDCs) and estrogen toxicity were detected. Estrogen toxicity reduction by previously proposed electrolysis biofilters with ceramsite‑sulfur-siderite fillers was further verified. Results showed that total nitrogen (TN) and estrogen toxicity removal increased by 41.0 % and 30.3 % respectively under the optimal voltage of 4 V and electric loading of 24 h/d, and significantly positive correlation between estrogen toxicity reduction and TN removal (p < 0.05) was observed. The lowest effluent estrogen toxicity was 0.79-0.95 ng_E2/L (in estradiol equivalent concentration) by the biofilter with ceramsite‑sulfur-siderite fillers, which was lower than the estrogen disruption effects mass concentration threshold of 1 ng/L. Electrical stimulation promoted the increase of the abundance of denitrifying bacteria Thauera and electroactive bacteria Hydrogenophaga, thus enhancing the removal of TN, furthermore, the abundance of Thiobacillus and Sulfuritalea were significantly correlated with the reduction of estrogen toxicity. The study highlights the potential of electrolysis biofilter in realizing the synergy of estrogen toxicity reduction and autotrophic denitrification of industrial biochemical tailwater, and paves the way for the application of electrolysis biofilter in the advanced purification of industrial biochemical tailwater.

Bioinorganic Nanoparticles for the Remediation of Environmental Pollution: Critical Appraisal and Potential Avenues

Nowadays, environmental pollution has become a critical issue for both developed and developing countries. Because of excessive industrialization, burning of fossil fuels, mining and exploration, extensive agricultural activities, and plastics, the environment is being contaminated rapidly through soil, air, and water. There are a variety of approaches for treating environmental toxins, but each has its own set of restrictions. As a result, various therapies are accessible, and approaches that are effective, long-lasting, less harmful, and have a superior outcome are extensively demanded. Modern research advances focus more on polymer-based nanoparticles, which are frequently used in drug design, drug delivery systems, environmental remediation, power storage, transformations, and other fields. Bioinorganic nanomaterials could be a better candidate to control contaminants in the environment. In this article, we focused on their synthesis, characterization, photocatalytic process, and contributions to environmental remediation against numerous ecological hazards. In this review article, we also tried to explore their recent advancements and futuristic contributions to control and prevent various pollutants in the environment.

Solar-driven photoelectrocatalytic degradation of anticancer drugs using TiO2 nanotubes decorated with SnS quantum dots

In recent years, the growing interest in applying photoelectrocatalysis (PEC) to decompose organic pollutants has resulted in the need to search for new photoelectrode materials with high activity under visible light radiation. The presented research showed an increased photoelectrocatalytic activity under sunlight of Ti/TiO₂ sensitized with SnS quantum dots, obtained by the successive ionic layer adsorption and reaction (SILAR) method. The presence of SnS caused the enhanced absorption of visible irradiation and the reduction of recombination of generated charges by a p-n heterojunction created with the TiO₂. The highest efficiency of photoelectrocatalytic degradation of anticancer drugs (ifosfamide, 5-fluorouracil, imatinib) was achieved for the SnS-Ti/TiO₂ photoelectrode with a SnS quantum dot size from 4 to 10 nm. In addition, a decrease of IF PEC degradation efficiency was observed with increasing pH and with the presence of Cl^-, NO₃^-, HCO₃^- and organic matter in the treated solution. Studies of the PEC mechanism have shown that drug degradation occurs mainly as a result of the direct and indirect action of photogenerated holes on the SnS-Ti/TiO₂ photoelectrode, and the identified degradation products allowed for the presentation of the degradation pathway of IF, 5-FU and IMB. Duckweed (Lemna minor) growth inhibition tests showed no toxicity of the drug solutions after treatment.

Exploiting the Potential of Supported Magnetic Nanomaterials as Fenton-Like Catalysts for Environmental Applications

In recent years, the application of magnetic nanoparticles as alternative catalysts to conventional Fenton processes has been investigated for the removal of emerging pollutants in wastewater. While this type of catalyst reduces the release of iron hydroxides with the treated effluent, it also presents certain disadvantages, such as slower reaction kinetics associated with the availability of iron and mass transfer limitations. To overcome these drawbacks, the functionalization of the nanocatalyst surface through the addition of coatings such as polyacrylic acid (PAA) and their immobilization on a mesoporous silica matrix (SBA15) can be factors that improve the dispersion and stability of the nanoparticles. Under these premises, the performance of the nanoparticle coating and nanoparticle-mesoporous matrix binomials in the degradation of dyes as examples of recalcitrant compounds were evaluated. Based on the outcomes of dye degradation by the different functionalized nanocatalysts and nanocomposites, the nanoparticles embedded in a mesoporous matrix were applied for the removal of estrogens (E1, E2, EE2), accomplishing high removal percentages (above 90%) after the optimization of the operational variables. With the feasibility of their recovery in mind, the nanostructured materials represented a significant advantage as their magnetic character allows their separation for reuse in different successive sequential batch cycles.

Complete solar-driven dual-photoelectrode fuel cell for water purification and power generation in the presence of peroxymonosulfate

This study reports the development of complete solar-driven dual-photoelectrode fuel cell (PFC) based on WO₃ photoanode and Cu₂O photocathode with peroxymonosulfate (PMS) serving as cathodic electron acceptor. As indicated by photoelectrochemical measurements, the PMS was able to improve thermodynamic properties of photocathode, achieving an increased open circuit potential from 0.42 V to 0.65 V vs standard hydrogen electrode (SHE). Under simulated sunlight irradiation (~100 mW cm^-2), the maximum power density of 0.12 mW cm^-2 could be obtained at current density of 0.34 mA cm^-2, which was 8.57 times of that produced by PFC without PMS (0.014 mW cm^-2). Correspondingly, adding PMS (1.0 mM) increased overall removal efficiency of 4-chlorophenol (4-CP) from 39.8% to 96.8%, accounting for the first-order kinetic constant (k=0.056 min^-1) being 6.67 times of that in the absence of PMS (k=0.0084 min^-1). Radical quenching and electron spin-resonance (ESR) results suggested the contribution of free radicals (•OH and SO₄^•-) and non-radical pathway associated with direct activation of PMS by Cu₂O photocathode. Fourier transformed infrared (FTIR) analysis confirmed the strong non-radical interaction between Cu₂O photocathode and PMS, resulting in 4-CP removal via activation of PMS by surface complex on Cu₂O. The proof-in-concept complete solar-driven dual-photoelectrode fuel cell may offer an effective manner to realize water purification and power generation, making wastewater treatment more economical and more sustainable.

Treatment of real wastewater by photoelectrochemical methods: An overview

An inadequate and inefficient performance ability of conventional methods to remove persistent organic pollutants urges the need of alternative or complementary advanced wastewater treatments methods to ensure the safer reuse of reclaimed water. Photoelectrochemical methods are emerging as promising options among other advanced oxidation processes because of the higher treatment efficiency achieved due to the synergistic effects of combined photochemical and electrolysis reactions. Synergistic effects of integrated photochemical, electrochemical and photoelectrochemical processes not only increase the hydroxyl radical production; an enhancement on the mineralization ability through various side reactions is also achieved. In this review, fundamental reaction mechanisms of different photoelectrochemical methods including photoelectrocatalysis, photo/solar electro-Fenton, photo anodic oxidation, photoelectroperoxone and photocatalytic fuel cell are discussed. Various integrated photochemical, electrochemical and photoelectrochemical processes and their synergistic effects are elaborated. Different reactor configurations along with the positioning of electrodes, photocatalysts and light source of the individual/combined photoelectrochemical treatment systems are discussed. Modified photoanode and cathode materials used in the photoelectrochemical reactors and their performance ability is presented. Photoelectrochemical treatment of real wastewater such as landfill leachate, oil mill, pharmaceutical, textile, and tannery wastewater are reviewed. Hydrogen production efficiency in the photoelectrochemical process is further elaborated. Cost and energy involved in these processes are briefed, but the applicability of photocatalytic fuel cells to reduce the electrical dependence is also summarised. Finally, the use of photoelectrochemical approaches as an alternative for treating soil washing effluents is currently discussed.

Photocatalytic Cellulose-Paper: Deepening in the Sustainable and Synergic Combination of Sorption and Photodegradation

Clean water is one of the sustainable development goals set by the United Nations for 2030. The development of effective but worldwide affordable strategies is essential to guarantee this achievement. Photocatalysis technology fulfills these criteria whenever the photocatalyst is sustainable and nontoxic. In this article, a cellulose-paper modified with a polyamide-titanium dioxide (TiO₂) nanocomposite by dip-coating is evaluated to degrade estrogens efficiently under solar light. The study deepens on the synergic combination of the sorptive capacity of the polyamide and the activity of TiO₂. The photocatalytic performance was studied under artificial and sunlight in a miniaturized experimental setup (batch of six reactors). Also, the effects of the dispersed/immobilized catalyst, irradiation time, and adsorption evaluation were studied under kinetic conditions. The photocatalyst composition, considering the polyamide (nylon-6) and TiO₂ amounts and the dipping cycles, was studied by a response surface methodology, and the reusability of the photocatalytic cellulose-paper was investigated. The LED source provided removal efficiencies of 65, 62, and 52% (for estrone, 17β-estradiol, and estriol, respectively) after 420 min of light exposure. Under sunlight, the efficiency increased up to 99.5% for estrone and 17β-estradiol and 98.5% for estriol after 180 min of irradiation. The sustainable character of the cellulosic substrate, the low toxicity of the nanocomposite ingredients, and its performance under sunlight make the material attractive for in-field application.

Environmental aspects of hormones estriol, 17β-estradiol and 17α-ethinylestradiol: Electrochemical processes as next-generation technologies for their removal in water matrices

Hormones as a group of emerging contaminants have been increasingly used worldwide, which has increased their concern at the environmental level in various matrices, as they reach the water bodies through effluents due to the ineffectiveness of conventional treatments. Here we review the environmental scenario of hormones estriol (E3), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2), explicitly their origins, their characteristics, interactions, how they reach the environment, and, above all, the severe pathological and toxicological damage to animals and humans they produce. Furthermore, studies for the treatment of these endocrine disruptors (EDCs) are deepened using electrochemical processes as the remediation methods of the respective hormones. In the reported studies, these micropollutants were detected in samples of surface water, underground, soil, and sediment at concentrations that varied from ng L^-1 to μg L^-1 and are capable of causing changes in the endocrine system of various organisms. However, although there are studies on the ecotoxicological effects concerning E3, E2, and EE2 hormones, little is known about their environmental dispersion and damage in quantitative terms. Moreover, biodegradation becomes the primary mechanism of removal of steroid estrogens removal by sewage treatment plants, but it is still inefficient, which shows the importance of studying electrochemically-driven processes such as the Electrochemical Advanced Oxidation Processes (EAOP) and electrocoagulation for the removal of emerging micropollutants. Thus, this review covers information on the occurrence of these hormones in various environmental matrices, their respective treatment, and effects on exposed organisms for ecotoxicology purposes.

Mesoporous WO3/TiO2 spheres with tailored surface properties for concurrent solar photocatalysis and membrane filtration

The strategical integration of membrane water filtration with semiconductor photocatalysis presents a frontier in deep purification with a self-cleaning capability. However, the membrane fouling caused by the cake layer of the reclaimed TiO₂ nanoparticles is a key obstacle. Herein, mesoporous WO₃/TiO₂ spheres (∼450 nm in diameter) consisting of numerous self-assembled WO₃-decoated anatase TiO₂ nanocrystallites are successfully prepared via a facile wet-chemistry route. The decoration of monolayered WO₃ significantly affects the surface, photocatalytic, and optical properties of original mesoporous TiO₂ spheres. XRD and Raman analyses show the presence of monolayered WO₃ suppresses the crystal growth of TiO₂ during the calcination process, significantly improves the surface acidity, and causes an obvious red shift in absorption edge. These favorable textural properties, coupling the enhanced interfacial charge carrier separation, render mesoporous WO₃/TiO₂ spheres with a superior photocatalytic activity in degradation of methylene blue under UV, visible, and solar light irradiations. The optimal molar ratio of W/Ti is examined to 6%. The synthesized mesoporous WO₃/TiO₂ spheres also show much higher flux during membrane filtration in both dead-end and cross-flow modes, suggesting a promising photocatalyst for concurrent membrane filtration and solar photocatalysis.

Photocurrent Response and Progesterone Degradation by Employing WO3 Films Modified with Platinum and Silver Nanoparticles

The effect of silver (Ag⁰ ) and platinum (Pt⁰ ) metallic nanoparticles (NPs) on WO₃ film was investigated by studying the photocurrent response under polychromatic irradiation. The structural phase revealed by X-ray diffraction analysis indicates a monoclinic crystal nanostructure. WO_3, Ag⁰ /WO_3, and Pt⁰ /WO₃ electrodes were used to degrade 0.35 mg L^-1 progesterone hormone in aqueous solution under polychromatic irradiation for 3h. The studies on degradation were investigated under electrochemically assisted heterogeneous photocatalysis (EHP) conditions. For photodegradation of progesterone, higher performance was achieved when WO₃ was functionalized and when the EHP configuration was adopted with bias at +0.7 V vs Ag/AgCl. This study reveals that incorporation of metallic NPs onto a semiconductor increases its efficiency, thereby preventing electron-hole recombination in the photocatalyst and photoelectrochemical limitations of WO₃ due to surface plasmon resonance and the trapping state. Therefore, efficient advances in the degradation of organic contaminants during water treatment can be realized.

Evaluation of advanced oxidation processes for water and wastewater treatment - A critical review

This study provides an overview of established processes as well as recent progress in emerging technologies for advanced oxidation processes (AOPs). In addition to a discussion of major reaction mechanisms and formation of by-products, data on energy efficiency were collected in an extensive analysis of studies reported in the peer-reviewed literature enabling a critical comparison of various established and emerging AOPs based on electrical energy per order (E_EO) values. Despite strong variations within reviewed E_EO values, significant differences could be observed between three groups of AOPs: (1) O₃ (often considered as AOP-like process), O₃/H₂O₂, O₃/UV, UV/H₂O₂, UV/persulfate, UV/chlorine, and electron beam represent median E_EO values of <1 kWh/m³, while median energy consumption by (2) photo-Fenton, plasma, and electrolytic AOPs were significantly higher (E_EO values in the range of 1-100 kWh/m³). (3) UV-based photocatalysis, ultrasound, and microwave-based AOPs are characterized by median values of >100 kWh/m³ and were therefore considered as not (yet) energy efficient AOPs. Specific evaluation of 147 data points for the UV/H₂O₂ process revealed strong effects of operational conditions on reported E_EO values. Besides water type and quality, a major influence was observed for process capacity (lab-vs. pilot-vs. full-scale applications) and, in case of UV-based processes, of the lamp type. However, due to the contribution of other factors, correlation of E_EO values with specific water quality parameters such as UV absorbance and dissolved organic carbon were not substantial. Also, correlations between E_EO and compound reactivity with OH-radicals were not significant (photolytically active compounds were not considered). Based on these findings, recommendations regarding the use of the E_EO concept, including the upscaling of laboratory results, were derived.

Porous Electrospun Fibers Embedding TiO2 for Adsorption and Photocatalytic Degradation of Water Pollutants

Using a bipolymer system consisting of polyvinylpyrrolidone (PVP) and poly(vinylidene fluoride) (PVDF), P25-TiO₂ was immobilized into thin film mats of porous electrospun fibers. Pores were introduced by dissolving sacrificial PVP to increase surface area and enhance access to TiO₂. The highest photocatalytic activity was achieved using a PVDF:PVP weight ratio of 2:1. Methylene blue (MB) was used to visualize contaminant removal, assess the sorption capacity (5.93 ± 0.23 mg/g) and demonstrate stable removal kinetics ( k_MB > 0.045 min^-1) under UVA irradiation (3.64 × 10^-9 einstein/cm²/s) over 10 cycles. Treatment was also accomplished via sequential MB sorption in the dark and subsequent photocatalytic degradation under UVA irradiation, to illustrate that these processes could be uncoupled to overcome limited light penetration. The photocatalytic mat degraded bisphenol A and 17α-ethynylestradiol in secondary wastewater effluent (17 mg TOC/L), and (relative to TiO₂ slurry) immobilization of TiO₂ in the mat mitigated performance inhibition by co-occurring organics that scavenge oxidation capacity. This significantly lowered the electrical energy-per-order of reaction (EEO) needed to remove such endocrine disruptors in the presence of oxidant scavenging/inhibitory organics. Thus, effective TiO₂ immobilization into polymers with affinity toward specific priority pollutants could both increase the efficiency and reduce energy requirements of photocatalytic water treatment.

Advances in antimicrobial photodynamic inactivation at the nanoscale

The alarming worldwide increase in antibiotic resistance amongst microbial pathogens necessitates a search for new antimicrobial techniques, which will not be affected by, or indeed cause resistance themselves. Light-mediated photoinactivation is one such technique that takes advantage of the whole spectrum of light to destroy a broad spectrum of pathogens. Many of these photoinactivation techniques rely on the participation of a diverse range of nanoparticles and nanostructures that have dimensions very similar to the wavelength of light. Photodynamic inactivation relies on the photochemical production of singlet oxygen from photosensitizing dyes (type II pathway) that can benefit remarkably from formulation in nanoparticle-based drug delivery vehicles. Fullerenes are a closed-cage carbon allotrope nanoparticle with a high absorption coefficient and triplet yield. Their photochemistry is highly dependent on microenvironment, and can be type II in organic solvents and type I (hydroxyl radicals) in a biological milieu. Titanium dioxide nanoparticles act as a large band-gap semiconductor that can carry out photo-induced electron transfer under ultraviolet A light and can also produce reactive oxygen species that kill microbial cells. We discuss some recent studies in which quite remarkable potentiation of microbial killing (up to six logs) can be obtained by the addition of simple inorganic salts such as the non-toxic sodium/potassium iodide, bromide, nitrite, and even the toxic sodium azide. Interesting mechanistic insights were obtained to explain this increased killing.

Photoelectrocatalytic degradation of oxalic acid using WO3 and stratified WO3/TiO2 photocatalysts under sunlight illumination

The WO₃ and stratified WO₃/TiO₂ thin films are successfully prepared by the spray pyrolysis method. The structural, morphological, compositional and photoelectrocatalytic properties of WO₃ and stratified WO₃/TiO₂ thin films are studied. XRD analysis confirms that films are polycrystalline with monoclinic and tetragonal crystal structures for WO₃ and TiO₂ respectively. The SEM images clearly show 3D sheeted porous structure of the as-prepared TiO₂ forms on WO₃ in stratified WO₃/TiO₂ samples. The synthesized photoelectrodes was used as catalyst for photoelectrocatalytic degradation of oxalic acid in aqueous medium. The rate constant (k) was evaluated as a function of the initial concentration of species. A significant decrease in concentrations of organic species was observed from COD analysis. The photoelectrocatalytic degradation effect is relatively higher in the case of the stratified WO₃/TiO₂ than WO₃ thin film photoelectrode in the degradation of oxalic acid and 83% removal efficiency of oxalic acid is obtained after 180min. Based on the obtained experimental data, the possible photoelectrocatalytic reaction mechanism was proposed. The photoelectrocatalytic experimental results indicate that stratified WO₃/TiO₂ photoelectrode is the promising material for removing of water pollutants.

Simultaneous bacterial inactivation and degradation of an emerging pollutant under visible light by ZnFe2O4co-modified with Ag and rGO

Simultaneous photo-inactivation ofE. coliand degradation of EE2 was achieved in the presence of ZnFe₂O₄-Ag/rGO. H₂O₂was mainly responsible for bacterial inactivation whereas, OH˙ was found to have more influence in EE2 degradation.

Broad-spectrum antimicrobial photocatalysis mediated by titanium dioxide and UVA is potentiated by addition of bromide ion via formation of hypobromite

Antimicrobial photocatalysis involves the UVA excitation of titanium dioxide (TiO2) nanoparticles (particularly the anatase form) to produce reactive oxygen species (ROS) that kill microbial cells. For the first time we report that the addition of sodium bromide to photoactivated TiO2 (P25) potentiates the killing of Gram-positive, Gram-negative bacteria and fungi by up to three logs. The potentiation increased with increasing bromide concentration in the range of 0-10mM. The mechanism of potentiation is probably due to generation of both short and long-lived oxidized bromine species including hypobromite as shown by the following observations. There is some antimicrobial activity remaining in solution after switching off the light, that lasts for 30min but not 2h, and oxidizes 3,3',5,5'-tetramethylbenzidine. N-acetyl tyrosine ethyl ester was brominated in a light dose-dependent manner, however no bromine or tribromide ion could be detected by spectrophotometry or LC-MS. The mechanism appears to have elements in common with the antimicrobial system (myeloperoxidase+hydrogen peroxide+bromide).

Photodegradation of estrogenic endocrine disrupting steroidal hormones in aqueous systems: Progress and future challenges

This article reviews different photodegradation technologies used for the removal of four endocrine disrupting chemicals (EDCs): estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2). The degradation efficiency is greater under UV than visible light; and increases with light intensity up to when mass transfer becomes the rate limiting step. Substantial rates are observed in the environmentally relevant range of pH7-8, though higher rates are obtained for pH above the pKa (~10.4) of the EDCs. The effects of dissolved organic matter (DOM) on EDC photodegradation are complex with both positive and negative impacts being reported. TiO2 remains the best catalyst due to its superior activity, chemical and photo stability, cheap commercial availability, capacity to function at ambient conditions and low toxicity. The optimum TiO2 loading is 0.05-1gl(-1), while higher loadings have negative impact on EDC removal. The suspended catalysts prove to be more efficient in photocatalysis compared to the immobilised catalysts, while the latter are considered more suitable for commercial scale applications. Photodegradation mostly follows 1st or pseudo 1st order kinetics. Photodegradation typically eradicates or moderates estrogenic activity, though some intermediates are found to exhibit higher estrogenicity than the parent EDCs; the persistence of estrogenic activity is mainly attributed to the presence of the phenolic moiety in intermediates.

Adsorption of the harmful hormone ethinyl estradiol inside hydrophobic cavities of CTA(+) intercalated montmorillonite

Hydrophobic cavities produced by cetyltrimethylammonium cation (CTA(+)) exchanged and trapped in the interlayer space of montmorillonite were used to remove the harmful hormone contaminant ethinyl estradiol (EE2) from water. X-ray diffraction, thermogravimetry/derivative thermogravimetry, elemental analysis (carbon, hydrogen, nitrogen), Fourier transform infrared, scanning electron microscopy/energy dispersive spectroscopy, Brunauer-Emmett-Teller and contact angle analyses showed that the intercalation of 9, 16 and 34 wt% CTA(+) in the montmorillonite resulted in the d001 expansion from 1.37 to 1.58, 2.09 and 2.18 nm, respectively. EE2 adsorption experiments showed that the original clay montmorillonite does not remove EE2 from water whereas the intercalated composites showed high efficiency with adsorption capacities of 4.3, 8.8 and 7.3 mg g(-1) for M9CTA(+), M16CTA(+) and M34CTA(+), respectively. Moreover, experiments with montmorillonite simply impregnated with cetyltrimethylammonium bromide showed that the intercalation of CTA(+) to form the hydrophobic cavity is very important for the adsorption properties. Simple solvent extraction can be used to remove the adsorbed EE2 without significant loss of CTA(+), which allows the recovery and reuse of the adsorbent for at least five times.