Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: a short review

A review on approaches for hazardous organics removal from Bayer liquors

Alumina is a valuable raw material for the production of adsorbents, abrasives, polishing agents, refractory materials, and aluminum. It is generally produced from bauxites through the Bayer process. Several organic compounds such as humic matters and oxalates are introduced into the Bayer liquor during the digestion process, resulting in significant hazards to precipitation of aluminum hydroxide. Therefore, it is crucial to remove these organic compounds from Bayer liquor to enhance the production of alumina. It is difficult to remove these organic compounds. Various approaches for organics removal from Bayer liquors have been developed in the past few decades, including thermal treatment, chemical precipitation, membrane technology, photocatalytic degradation, biodegradation, and wet oxidation. This paper reviews the technologies for organics removal from Bayer liquor and the relative mechanisms proposed in the literature to identify its essential parameters. Chemicals dosage, temperature, pH value, reaction time, and solution concentration are essential factors in the process. Removal efficiency, green principle, and economic viability of various methods are discussed, and potential technologies are suggested. Wet oxidation appears to be a promising method for removing organic matters in Bayer liquors. Moreover, the combination of wet oxidation and electrooxidation shows excellent potential in organics removal. Various approaches for removing organic compounds and perspectives for further investigation are proposed.

Novel Visible Light-Driven Photocatalytic Chlorine Activation Process for Carbamazepine Degradation in Drinking Water

Photolysis of free chlorine (HOCl/ClO^-) is an advanced oxidation process (AOP) to produce hydroxyl (HO^•) and other radicals for refractory micropollutant degradation. However, HOCl/ClO^- is only conducive to activation and production of radicals by ultraviolet (UV) light. For the first time, we show the use of visible light (>400 nm) to produce HO^• and ClO^•, through use of graphitic carbon nitride (g-C₃N₄) and photogenerated h_vb⁺, e_cb^-, and O₂^•- in the presence of HOCl/ClO^-, which was termed visible light g-C₃N₄-enabled chlorine AOP (VgC-AOP). The VgC-AOP increased the pseudo first-order degradation rate constant of a model micropollutant, carbamazepine, by 16 and 7 times higher than that without g-C₃N₄ and HOCl/ClO^-, respectively, and remained active over multiple use cycles. Effects of water quality [pH, alkalinity, Cu(II), and natural organic matter (NOM)] and the operational conditions (g-C₃N₄ and HOCl/ClO^- concentrations, irradiation wavelength, and dose) were investigated. Of particular significance is its superior performance in the presence of NOM, which absorbs less light at visible light wavelengths and scavenges less surface-bonded reactive species, compared against UV/TiO₂ or UV/chlorine AOPs. The VgC-AOP is practically relevant, feasible, and easily implementable and it expands the potential types of light sources (e.g., LEDs and solar light).

Selenide-chitosan as High-performance Nanophotocatalyst for Accelerated Degradation of Pollutants

Water pollution is one of the major global challenges today. Water bodies are contaminated by the heavy release of waste effluents of textile industries, which includes intensively colored dye pollutants. Herein, a ternary nanocomposite of bismuth copper selenide with small particle size and ternary metal selenide (TMS)-chitosan microspheres (TMS-CM) of the spherical porous surface were successfully synthesized. SEM, XRD, EDX, FTIR, and UV/Vis spectrophotometry analysis revealed the structural and morphological characteristics of the newly synthesized nanocomposites. SEM imaging showed the average diameter of TMS nanoparticle to be 33 nm. The crystal size was calculated as 6.33 nm and crystalline structure as orthorhombic using XRD findings. EDX confirmed the presence of Bi, Cu, and Se in the ternary nanocomposite. The bandgap of 1.8 eV was calculated from Tauc's plot for the TMS nanocomposite. SEM confirmed the successful synthesis of spherical TMS-CM microspheres of porous surface morphology with an average size of 885.6 μm. The presence of chitosan microspheres in the synthesis of TMS nanocomposite was identified by FTIR spectral analysis. Furthermore, highly efficient photocatalytic degradation (up to 95.4%) of ARS was achieved within 180 min at pH 4.0 using 0.5 g of TMS-CM in sunlight. The first-order kinetic model fitted well to the photocatalytic decontamination of ARS using TMS-CM with a rate constant of 6.1x10-2  min-1 . The TMS-CM gave attractive results and high efficiency in photocatalytic degradation of ARS dye after reusing and regeneration of up to seven successive cycles. The newly synthesized nanophotocatalyst could be efficiently used for the decontamination of dye polluted water from textile industries.

Graphene Oxide Hybridised TiO2 for Visible Light Photocatalytic Degradation of Phenol

In industrial pollutants, phenol is a kind of degradation-resistant hazardous compound. It is generated during industrial processes in factories and treatment at sewage plants. In this study, we analyse the photocatalytic activity of TiO2 and rGO as a composite for the degradation of phenol. Hybridised titanium dioxide/reduced graphene oxide (TiO2/rGO) nanocomposites were synthesised by a simple hydrothermal method using flake graphite and tetrabutyl titanate as raw materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) specific area analysis, Fourier transform infrared spectroscopy (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), photoelectrochemical analysis, and UV–vis diffuse reflectance spectra (DRS) were employed to characterise the physicochemical properties of the as-prepared nanocomposites. The results showed the TiO2/rGO nanocomposites’ significant anatase phase and a small fraction of the rutile phase the same as that of the as-prepared TiO2 nanoparticles. The spherical TiO2 nanoparticles (diameter 20–50 nm) were agglomerated slightly and the agglomerates were anchored on the rGO sheets and dispersed symmetrically. The specific surface area of TiO2/rGO-4% nanocomposites was 156.4 m2/g, revealing a high specific surface area. Oxygen-containing functional groups that existed in TiO2/rGO-4% nanocomposites were almost removed during hydrothermal processing. The photocurrent response of TiO2/rGO-4% was strongest among the TiO2/rGO nanocomposites, and the bandgap of TiO2/rGO-4% was 2.91 eV, showing a redshift of absorption into the visible region, which was in favour of the high photocatalytic activity of TiO2/rGO nanocomposites under visible light (λ > 420 nm). Moreover, the samples were employed to photodegrade phenol solution under visible light irradiation. TiO2/rGO-4% nanocomposite degraded the phenol solution up to 97.9%, and its degradation rate constant was 0.0190 h−1, which had higher degradation activity than that of other TiO2/rGO nanocomposites. This is a promising candidate catalyst material for organic wastewater treatment.

Potential of TiO2 with Various Au Nanoparticles for Catalyzing Mesotrione Removal from Wastewaters under Sunlight

Nowadays, great focus is given to the contamination of surface and groundwater because of the extensive usage of pesticides in agriculture. The improvements of commercial catalyst TiO₂ activity using different Au nanoparticles were investigated for mesotrione photocatalytic degradation under simulated sunlight. The selected system was 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy. It was found that TiO₂ particles size was ~20 nm and ~50 nm, respectively. The Au nanoparticles were below 10 nm and were well distributed within the framework of TiO₂. For 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L), band gap energy was 2.45 eV. In comparison to the pure TiO₂, addition of Au nanoparticles generally enhanced photocatalytic removal of mesotrione. By examining the degree of mineralization, it was found that 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates. The effect of tert-butanol, NaF and ethylenediaminetetraacetic acid disodium salt on the transformation rate suggested that the relative contribution of various reactive species changed in following order: h⁺ > ^●OH_ads > ^●OH_bulk. Finally, several intermediates that were formed during the photocatalytic treatment of mesotrione were identified.

Biomedical Waste Management by Using Nanophotocatalysts: The Need for New Options

Biomedical waste management is getting significant consideration among treatment technologies, since insufficient management can cause danger to medicinal service specialists, patients, and their environmental conditions. The improvement of waste administration protocols, plans, and policies are surveyed, despite setting up training programs on legitimate waste administration for all healthcare service staff. Most biomedical waste substances do not degrade in the environment, and may also not be thoroughly removed through treatment processes. Therefore, the long-lasting persistence of biomedical waste can effectively have adverse impact on wildlife and human beings, as well. Hence, photocatalysis is gaining increasing attention for eradication of pollutants and for improving the safety and clearness of the environment due to its great potential as a green and eco-friendly process. In this regard, nanostructured photocatalysts, in contrast to their regular counterparts, exhibit significant attributes such as non-toxicity, low cost and higher absorption efficiency in a wider range of the solar spectrum, making them the best candidate to employ for photodegradation. Due to these unique properties of nanophotocatalysts for biomedical waste management, we aim to critically evaluate various aspects of these materials in the present review and highlight their importance in healthcare service settings.

Historical development and prospects of photocatalysts for pollutant removal in water

Photocatalysis, as a low-cost and environment friendly technology, has demonstrated a significant potential for water pollution purification; it has received extensive attention in recent decades. The key is the photocatalyst; a large number of photocatalysts have been developed. To better understand and further develop the photocatalysis technology for water treatment, this review summarizes its development over time. The development period is divided into four stages (1960s-1993, 1994-2000, 2001-2010, and 2011-present) to provide readers with a better understanding of the development characteristics, and causes and consequences of each historical stage. This review expounds the origin and development of photocatalysis and the obstacles encountered and overcome. It describes the development of mechanisms and methods to solve these problems in each time period. Moreover, it reviews the recent development of new photocatalysts, the concept of designing photocatalysts, and photocatalytic-coupling systems. Finally, it enumerates the problems that continue to exist in the application of photocatalysis technology, and highlights the key issues that must be addressed in future research. The review is aimed at providing the researchers with a deeper understanding of photocatalysis technology and encourage further development of the application of photocatalysis to water treatment.

A generalized predictive model for TiO2-Catalyzed photo-degradation rate constants of water contaminants through artificial neural network

Titanium dioxide (TiO₂) is a well-known photocatalyst in the applications of water contaminant treatment. Traditionally, the kinetics of photo-degradation rates are obtained from experiments, which consumes enormous labor and experimental investments. Here, a generalized predictive model was developed for prediction of the photo-degradation rate constants of organic contaminants in the presence of TiO₂ nanoparticles and ultraviolet irradiation in aqueous solution. This model combines an artificial neural network (ANN) with a variety of factors that affect the photo-degradation performance, i.e., ultraviolet intensity, TiO₂ dosage, organic contaminant type and initial concentration in water, and initial pH of the solution. The molecular fingerprints (MF) were used to interpret the organic contaminants as binary vectors, a format that is machine-readable in computational linguistics. A dataset of 446 data points for training and testing was collected from the literature. This predictive model shows a good accuracy with a root mean square error (RMSE) of 0.173.

Preparation and characterization of a copper phosphotungstate/titanium dioxide (Cu-H3PW12O40/TiO2) composite and the photocatalytic oxidation of high-concentration ammonia nitrogen

Currently, the majority of wastewater with a high concentration of ammonia nitrogen (NH₄⁺/NH₃) is treated using biological methods, which have poor biodegradability and low removal efficiency. In this paper, a composite photocatalyst of copper phosphotungstate/titanium dioxide (Cu-H₃PW₁₂O₄₀/TiO₂) was prepared by sol-gel hydrothermal synthesis, and the composite catalyst was characterized by X-ray diffraction (XRD), UV-vis-diffuse reflectance spectroscopy (UV-VIS-DRS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS)、scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The photocatalytic oxidation of a high-concentration NH₄⁺/NH₃ solution was carried out under ultraviolet (UV) light to explore the effects of different influencing factors on the photocatalytic effect and to optimize the reaction conditions. The prepared composite catalyst exhibited higher photocatalytic activity than that of TiO₂. When the initial concentration of the solution was 300 mg·L^-1, the initial pH was 11, the catalyst concentration was 1.5 g·L^-1, the loading level of Cu-H₃PW₁₂O₄₀ was 40%, and the aeration rate was 1.5 L·min^-1, the removal rate of NH₄⁺/NH₃ by the composite photocatalyst could reach >80%. Very little NO₂^- and NO₃^- were produced, and N₂ was the main product.

Reclamation of agro-wastewater polluted with thirteen pesticides by solar photocatalysis to reuse in irrigation of greenhouse lettuce grown

In Mediterranean countries, reuse of reclaimed water is essential for crop irrigation. The occurrence of pesticides in agro-wastewater may represent a risk for human health and environment owing to their release in soil and translocation to plants. The novelty of this work relies on the reuse of reclaimed agro-wastewater polluted with thirteen pesticides for lettuce irrigation. Removing of pesticide residues in agro-wastewater was carried out using natural sunlight and TiO2/Na2S2O8 in a pilot facility located in Murcia (SE of Spain). The studied pesticides were azoxystrobin, boscalid, chlorpropham, flutolanil, flutriafol, isoxaben, methoxyfenozide, myclobutanil, napropamide, prochloraz, propamocarb, propyzamide and triadimenol, which are commonly used in southeast Spain to treat lettuces grown. Different heterogeneous and homogeneous processes were studied and compared. Previously, the optimization of the process for the selection of the best catalytic system was performed at lab-scale. TiO2+ S2O82- was selected due to the greater effectiveness, achieving almost complete disappearance after about 400 kJ m-2 of cumulative UVA exposure. No significant differences were observed in quality parameters of lettuce grown using treated and non-treated agro-wastewater.

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

Chlorine dioxide (ClO₂) degradation of the organophosphorus pesticides azamethiphos (AZA) and dimethoate (DM) (10 mg/L) in deionized water and in Sava River water was investigated for the first time. Pesticide degradation was studied in terms of ClO₂ level (5 and 10 mg/L), degradation duration (0.5, 1, 2, 3, 6, and 24 h), pH (3.00, 7.00, and 9.00), and under light/dark conditions in deionized water. Degradation was monitored using high-performance liquid chromatography. Gas chromatography coupled with triple quadrupole mass detector was used to identify degradation products of pesticides. Total organic carbon was measured to determine the extent of mineralization after pesticide degradation. Real river water was used under recommended conditions to study the influence of organic matter on pesticide degradation. High degradation efficiency (88-100% for AZA and 85-98% for DM) was achieved in deionized water under various conditions, proving the flexibility of ClO₂ degradation for the examined organophosphorus pesticides. In Sava River water, however, extended treatment duration achieved lower degradation efficiency, so ClO₂ oxidized both the pesticides and dissolved organic matter in parallel. After degradation, AZA produced four identified products (6-chlorooxazolo[4,5-b]pyridin-2(3H)-one; O,O,S-trimethyl phosphorothioate; 6-chloro-3-(hydroxymethyl)oxazolo[4,5-b]pyridin-2(3H)-one; O,O-dimethyl S-hydrogen phosphorothioate) and DM produced three (O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) phosphorothioate; e.g., omethoate; S-(2-(methylamino)-2-oxoethyl) O,O-dihydrogen phosphorothioate; O,O,S-trimethyl phosphorodithioate). Simple pesticide degradation mechanisms were deduced. Daphnia magna toxicity tests showed degradation products were less toxic than parent compounds. These results contribute to our understanding of the multiple influences that organophosphorus pesticides and their degradation products have on environmental ecosystems and to improving pesticide removal processes from water.

Photocatalytic Degradation of Aqueous Rhodamine 6G Using Supported TiO2 Catalysts. A Model for the Removal of Organic Contaminants From Aqueous Samples

As a model for the removal of complex organic contaminants from industrial water effluents, the heterogeneous photocatalytic degradation of Rhodamin 6G was studied using TiO₂-derived catalysts, incorporated in water as suspension as well as supported in raschig rings. UV and Visible light were tested for the photo-degradation process. TiO₂ catalysts were synthesized following acid synthesis methodology and compared against commercial TiO₂ catalyst samples (Degussa P25 and Anatase). The bandgap (E_g) of the TiO₂ catalysts was determined, were values of 2.97 and 2.98 eV were obtained for the material obtained using acid and basic conditions, respectively, and 3.02 eV for Degussa P25 and 3.18 eV for anatase commercial TiO₂ samples. Raschig rings-supported TiO₂ catalysts display a good photocatalytic performance when compared to equivalent amounts of TiO₂ in aqueous suspension, even though a large surface area of TiO₂ material is lost upon support. This is particularly evident by taking into account that the characteristics (XRD, RD, Eg) and observed photodegradative performance of the synthesized catalysts are in good agreement with the commercial TiO₂ samples, and that the RH6G photodegradation differences observed with the light sources considered are minimal in the presence of TiO₂ catalysts. The presence of additives induce changes in the kinetics and efficiency of the TiO₂-catalyzed photodegradation of Rh6G, particularly when white light is used in the process, pointing toward a complex phenomenon, however the stability of the supported photocatalytic systems is acceptable in the presence of the studied additives. In line with this, the magnitude of the chemical oxygen demand, indicates that, besides the different complex photophysical processes taking place, the endproducts of the considered photocatalytic systems appears to be similar.

Organocatalytic vs. Ru-based electrochemical hydrogenation of nitrobenzene in competition with the hydrogen evolution reaction

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities. Although PhNO2 hydrogenation is the favoured reaction, the hydrogen evolution reaction (HER) competes in both systems under catalytic conditions. H2 formation occurs in larger amounts when using the Ru nanoparticle based catalyst. While similar reaction outputs were observed for both catalytic systems, DFT calculations revealed some significant differences related to distinct interactions between the catalytic material and the organic substrates or products, which could pave the way for the design of new catalytic materials.

Synthesis of Magnetic Fe3O4/ZnWO4 and Fe3O4/ZnWO4/CeVO4 Nanoparticles: The Photocatalytic Effects on Organic Pollutants upon Irradiation with UV-Vis Light

Magnetic Fe3O4/ZnWO4 and Fe3O4/ZnWO4/CeVO4 nanoparticles with different molar ratios of CeVO4 to other inorganic components were synthesized through co-precipitation with a sonochemical-assisted method. X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, vibrating sample magnetometry, and scanning electron microscopy (SEM) methods were used for the physico–chemical characterization of the obtained nanoparticles. As shown in the SEM images, the average sizes of the Fe3O4/ZnWO4 and Fe3O4/ZnWO4/CeVO4 nanoparticles that formed aggregates were approximately 50–70 nm and 80–100 nm, respectively. The photocatalytic performance of these nanoparticles was examined by measuring methylene blue degradation under visible light (assisted by H2O2). The sample with a mass ratio of 1:2:1 (Fe3O4/ZnWO4/CeVO4, S4) exhibited optimal photocatalytic performance, and thus this sample was subsequently used for the photodegradation of different organic pollutants upon irradiation with ultraviolet (UV) and visible light. Approximately 90% and 70% degradation of methyl violet and methylene blue, respectively, was observed after visible light irradiation. Additionally, the mechanism of the photocatalytic reaction was investigated by measuring ˙OH release under UV light in a system with terephthalic acid and by measuring the release of ˙O2−, ˙OH, and hole scavengers.

CeO2 for Water Remediation: Comparison of Various Advanced Oxidation Processes

Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO2, employed as a non-conventional photocatalyst/Fenton-like material. The first one has been prepared by chemical precipitation with KOH, while the second one has been obtained by exposing the as-synthetized CeO2 to solar irradiation in H2 stream. This latter treatment led to obtain a more defective CeO2 (coded as “grey CeO2”) with the formation of Ce3+ sites on the surface of CeO2, as determined by Raman and X-ray Photoelectron Spectroscopy (XPS) characterizations. This peculiar feature has been demonstrated as beneficial for the solar photo–Fenton reaction, with the best performance exhibited by the grey CeO2. On the contrary, the bare CeO2 showed a photocatalytic activity higher with respect to the grey CeO2, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO2 reported here, allows to tune and modify the physico-chemical properties of CeO2, allowing a choice of different CeO2 samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity.

All-solid-state Z-scheme WO3 nanorod/ZnIn2S4 composite photocatalysts for the effective degradation of nitenpyram under visible light irradiation

A Z-scheme WO₃/ZnIn₂S₄ photocatalyst was synthesized via a simple solvothermal method. Compared with pure WO₃ and ZnIn₂S₄, photocatalytic experiments showed that these Z-scheme photocatalysts exhibited enhanced activity for the degradation of nitenpyram (NTP). The apparent rate constant (k) of NTP degradation on 50WZ (WO₃/ 50 wt% Znln₂S₄) was 0.042 min^-1 (∼3.8 times higher than WO₃ and ∼2.5 times higher than ZnIn₂S₄). Photoluminescence (PL), photocurrent (PC), and electrochemical impedance spectroscopy (EIS) showed that the separation and transfer efficiency of photogenerated carriers in 50WZ was markedly enhanced, which was favorable for improving its photocatalytic activity. Active species capture experiments and electron spin resonance (ESR) measurements showed that superoxide radicals and holes were the main active species for NTP degradation, and they confirmed the formation of the Z-scheme structure. Furthermore, a possible NTP degradation pathway was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS).

Comparative study of atrazine degradation by magnetic clay activated persulfate and H2O2

To effectively remove the endocrine disrupting chemicals (EDCs) in water, Fe3O4 was loaded on the surface of modified sepiolite clay by the method of co-precipitation to catalyze potassium persulfate (K2S2O8) and hydrogen peroxide (H2O2) respectively to generate SO4˙- and ·OH for atrazine (ATZ) removal. The magnetic clay catalyst was characterized by XRD, SEM, N2 adsorption-desorption and isoelectric point. The degradation efficiency of ATZ in the two systems was systematically compared in terms of initial pH, oxidant dosage and oxidant utilization rate. The results revealed that, after 90 minutes, systems with K2S2O8 and H2O2 can remove 65.7% and 57.8% of the ATZ under the given conditions (30 °C, catalyst load: 1 g L-1, initial pH: 5, [ATZ]0: 10 mg L-1, [H2O2]0: 46 mmol L-1, [PDS]0: 46 mmol L-1). The magnetic clay catalyst still maintained good catalytic activity and stability during the four consecutive runs. Based on the quenching experiments, it was demonstrated that the dominant radical species in the two systems were SO4˙-/·OH and ·OH, respectively. However, the degradation efficiency of the two systems presented different responses toward the condition variations; the system with K2S2O8 was relatively more sensitive to solution pH, the oxidant efficiency was generally higher than that of the H2O2 system (except 184 mmol L-1).

Ultrasound and heterogeneous photocatalysis for the treatment of vinasse from pisco production

Production of the distilled alcohol pisco results in vinasse, dark brown wastewater with high polyphenols contents and chemical oxygen demand (COD). No prior research exists on the efficiency of advanced oxidations processes (AOPs) in treating pisco vinasse. Therefore, the purpose of this study was to assess the efficiency of ultraviolet (UV), ultrasound (US), US + UV, heterogeneous photocatalysis (HP), and HP + US treatments. Polyphenols, COD, and color removal, as well as oxidation-reduction potential, were monitored over a 60-minute treatment period. Energy consumption levels and synergies were also calculated. The HP + US treatment achieved the best removal ratios for polyphenols (68%), COD (70%), and color (48%). While the HP treatment was the second most efficient in terms of polyphenols (62%), COD (58%), and color (40%) removal, this AOP comparatively required the least amount of energy. Considering the energy efficiency and relatively high pollutant-removal rates of the HP treatment, this AOP is recommended as a practical alternative for treating pisco vinasse.

Solar-driven photocatalytic treatment as sustainable strategy to remove pesticide residues from leaching water

We have demonstrated the potential leaching of eight compounds, one insecticide (flonicamid) and seven fungicides (myclobutanil, penconazole, boscalid, difenoconazole, trifloxystrobin, pyraclostrobin and fenpyroximate) trough a typical Mediterranean soil (Calcaric regosol). The concentrations found in leaching water were in all cases above the limit set by the EU in groundwater (0.1 μg L^-1). For this, the efficiency of different homogeneous (photo-Fenton and photo-Fenton-like) and heterogeneous (ZnO and TiO₂) photocatalytic systems was tested in deionized water to choose the most appropriate treatment to remove pesticide residues from leaching water. The efficiency was in the order: ZnO + S₂O₈^2- (pH 7) > TiO₂+ S₂O₈^2- (pH 7) > ZnO (pH 7) > TiO₂ (pH 7) > Fe³⁺ (pH 3) > Fe³⁺ (pH 5) > Fe²⁺ (pH 3) > Fe²⁺ (pH 5). Thus, in the subsequent experiment we focus on the efficacy of solar heterogeneous photocatalysis (ZnO/Na₂S₂O₈ and TiO₂/ Na₂S₂O₈) on their removal from leaching water. A fast removal was observed for all pesticides at the end of the photoperiod, noticeably higher in the case of ZnO system, with the exception of flonicamid, a recalcitrant pesticide where the degradation rate only reached about 20% after 240 min of solar exposure. Although the mineralisation of the initial dissolved organic carbon was not complete due to the presence of interfering substances in the leaching water, the conversion rate under ZnO/Na₂S₂O₈ treatment was about 1.3 times higher than using TiO₂/Na₂S₂O₈.

Trends in sensitive detection and rapid removal of sulfonamides: A review

Sulfonamides in environmental water, food, and feed are a major concern for both aquatic ecosystems and public health, because they may lead to the health risk of drug resistance. Thus, numerous sensitive detection and rapid removal methodologies have been established. This review summarizes the sample preparation techniques and instrumental methods used for sensitive detection of sulfonamides. Additionally, adsorption and photocatalysis for the rapid removal of sulfonamides are also discussed. This review provides a comprehensive perspective on future sulfonamide analyses that have good performance, and on the basic methods for the rapid removal of sulfonamides.

Scaling up the electrokinetic-assisted phytoremediation of atrazine-polluted soils using reversal of electrode polarity: A mesocosm study

Electrokinetic-assisted phytoremediation (EKPR) has been recently proposed for the removal of pesticides from polluted soils. In this work, we report the results from an EKPR experiment that was carried out in a mesocosm mock-up of 0.386 m³ using ryegrass (Lolium perenne L.) and a low permeability soil spiked with atrazine. Plants were initially grown for 35 days; then, the soil was spiked with atrazine at a dose of 2 mg kg^-1 soil. A DC electrical field of 0.6 V cm^-1 was applied 24 h every day, switching polarity daily. Another identical mock-up with the same experimental conditions but without plants was used for comparison purposes. The duration of the EKPR test was 19 days during which some operational parameters were registered (electric current intensity, soil pH and temperature) and soil porewater samples were taken and analysed. Plant tissues and soil samples from the different sections in which the mock-ups were divided, were also collected and analysed at the end of the experiment. 3-D profiles of soil pH, water content and atrazine residues concentration in plants and soil were obtained and discussed. The results of this experiment were compared with others previously reported by us from a similar EKPR pot test. In spite of the difficulties to get an adequate geometric and operational similarity between setups of different scale, the main output parameters of the EKPR process (electric current, specific current charge, overall atrazine removal, specific atrazine removal efficiency, root biomass:soil weight ratio) were discussed. It was shown that, although the processes carried out are essentially the same in both scales, their extent may be quite different; it highlights the limitations of small-scale experiments to predict the results at field conditions.

Photocatalytic Performance of Electrospun Silk Fibroin/ZnO Mats to Remove Pesticide Residues from Water under Natural Sunlight

We have evaluated the efficiency of silk fibroin (SF) coated with ZnO nanoparticles in the photocatalytic disappearance of one acaricide (etoxazole) and three fungicides (difenoconazole, myclobutanil and penconazole) in water exposed to sunlight irradiation. Electrospun SF/ZnO mats were successfully synthesized by electrospinning technique and characterized by XRD, FE-SEM, XPS, XDS, FTIR, and BET. The influence of catalyst loading on the degradation kinetics of the different pesticides was examined in order to gain knowledge of maximum degradation efficiency. A significant increment in degradation rates was observed with the addition of ZnO. SF mats with 25 mg of ZnO were finally selected since no significant differences (p < 0.05) were detected when the loading was enlarged from 25 to 50 mg for the majority of the compounds. In the experimental conditions, the half-lives ranged from 33 min to 93 min for etoxazole and myclobutanil, respectively. The comparison of SF materials coated with similar amount of TiO2 and ZnO showed that the later was slightly more efficient to remove pesticide residues. Hence, the use of electrospun SF/ZnO nanostructures would provide an environmentally friendly approach with photocatalytic activity to be applied in the reclamation of water polluted by pesticides.

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

Electrospun silk fibroin/TiO2 mats. Preparation, characterization and efficiency for the photocatalytic solar treatment of pesticide polluted water

The photocatalytic properties of silk fibroin (SF) incorporating TiO₂ nanoparticles using an electrospinning technique were examined. Electrospun SF/TiO₂ mats were successfully prepared and characterized by different techniques (XRD, FE-SEM, XPS, XDS, FTIR and BET). The photocatalytic efficiency of these materials were assessed by their ability to degrade four pesticides (boscalid, hexythiazox, pyraclostrobin and trifloxystrobin) in water exposed to solar irradiation. The effect of catalyst loading on the disappearance kinetics of the different pesticides was studied in order to determine the maximum degradation efficiency. The degradation rate significantly increases upon adding the TiO₂. However, no significant differences (p < 0.05) were observed when the TiO₂ loading was increased from 25 to 50 mg for most compounds. Thus, SF mats with 25 mg of TiO₂ were selected. Therefore, a new and simple approach to produce materials with photocatalytic activity, safety and potential application in the purification of water contaminated by pesticides has been developed.

The photocatalytic properties of silk fibroin (SF) incorporating TiO₂ nanoparticles using an electrospinning technique were examined.

Improved photoelectrocatalytic degradation of tetrabromobisphenol A with silver and reduced graphene oxide-modified TiO2 nanotube arrays under simulated sunlight

In present study, reductive graphene oxide and silver nanoparticles co-comodified TiO₂ nanotube arrays were prepared, and which was investigated to degrade tetrabromobisphenol A. The arrays co-modified with silver nanoparticles and reductive graphene oxide prepared by electrodeposition method exhibited good photoelectrocatalytic degradative activity for tetrabromobisphenol A, and the degradation efficiency reached 99.6% within 80 min. The synergistic effect of high photoresponse of Ag nanoparticles with their high capture ability for photogenerated electrons and the extended wavelength absorption range of reductive graphene oxide resulted in the highest degradation efficiencies. Degradation is postulated to follow a stepwise reductive debromination mechanism.

Heterogeneous Catalytic Performance and Stability of Iron-Loaded ZSM-5, Zeolite-A, and Silica for Phenol Degradation: A Microscopic and Spectroscopic Approach

In this study, we compared the performances of three iron-containing crystalline and amorphous catalysts, that is, Fe-Zeo-A, Fe-ZSM-5, and Fe-silica, respectively, for the degradation of phenol in an aqueous solution. Catalytic activity for the degradation of phenol was assessed by heterogeneous photolysis, Fenton, and photo-Fenton oxidation. All catalysts exhibited higher activity in the photo-Fenton process. In addition, the catalyst stability was evaluated by the estimation of the iron loss and structural variations after the oxidation processes. Results revealed that Fe-silica and Fe-ZSM-5 exhibit higher catalytic activity (~100% phenol removal), while only 64% of phenol removal over Fe-Zeo-A was observed. Moreover, among all catalysts, Fe-ZSM-5 exhibited higher stability with low iron leaching, attributed to the uniform distribution of bonded Fe in the crystalline framework and narrow channels. On the contrary, amorphous Fe-silica exhibited higher iron leaching due to the presence of isolated iron species in the structure, leading to the partial involvement of a homogeneous reaction during the degradation of phenol. The structural stability of Fe-based catalysts was examined using microscopic and spectroscopic techniques.

Photocatalytic mineralization of hard-degradable morphine by visible light-driven Ag@g-C3N4 nanostructures

The entrance of some hard-degradable pharmaceutical contaminants can cause irreparable damage to humans and other organisms; therefore, removing these pollutants from water is one of the most important activities in water purification field. In this work, the mineralization of morphine was performed using photocatalytic degradation method. Graphitic carbon nitride (g-C₃N₄) nanosheets, due to their promising tunable characteristics, were chosen as visible-light-driven nanostructured heterogeneous photocatalyst. To enhance the photocatalytic activity, g-C₃N₄ was doped with Ag noble metal due to its surface plasmon resonance effect and acting as an electron sink. The photodegradation of morphine was evaluated under different pH values, the dosage of the photocatalyst, initial concentration of morphine, and Ag% loading under sunlight as green energy. The maximum efficiency was obtained in the very low concentration of Ag@g-C₃N₄ photocatalyst with the superior low value of 0.17 g L^-1. Near complete mineralization of morphine was achieved by Ag@g-C₃N₄ with metal content percentage equal to 5 in 180 min and pH = 2. Also, using various active species scavengers, superoxide anion radical was identified as the main responsible species in the photocatalysis reaction of morphine degradation.

Reclamation of grey water for non-potable purposes using pilot-scale solar photocatalytic tubular reactors

Application of pilot-scale slurry-type tubular photocatalytic reactor was tested for the decentralized treatment of actual grey water. The reactors were fabricated by reusing the locally available materials at low cost, operated in batch recycle mode with 25 L of grey water. The influence of operational parameters such as catalysts' concentration, initial slurry pH and addition of H₂O₂ on COD abatement were optimized. The results show that Ag-decorated TiO₂ showed a two-fold increase in COD abatement than did pure TiO₂. Better COD abatement was observed under acidic conditions, and addition of H₂O₂ significantly increases the rate of COD abatement. Within 2 h, 99% COD abatement was observed when the reactor was operated with optimum operational conditions. Silver ion lixiviate was also monitored during the experiment and is five times less than the permissible limits. The catalyst shows good stability even after five cycles without much loss in its photocatalytic activity. The results clearly reveal that pilot-scale slurry tubular solar photocatalytic reactors could be used as a cost-effective method to treat grey water and the resulting clean water could be reused for various non-potable purposes, thus conserving precious water resource. This study favours decentralized grey water treatment and possible scaling up of solar photocatalytic reactor using locally available materials for the potential reuse of treated water.

Adsorptive removal and photocatalytic degradation of organic pollutants using metal oxides and their composites: A comprehensive review

Metal oxide nanomaterials and their composites are comprehensively reviewed for water remediation. The controlled morphological and textural features, variable surface chemistry, high surface area, specific crystalline nature, and abundant availability make the nanostructured metal oxides and their composites highly selective materials for efficient removal of organic pollutants based on adsorption and photocatalytic degradation. A wide range of metal oxides like iron oxides, magnesium oxide, titanium oxides, zinc oxides, tungsten oxides, copper oxides, metal oxides composites, and graphene-metal oxides composites having variable structural, crystalline and morphological features are reviewed emphasizing the recent development, challenges, and opportunities for adsorptive removal and photocatalytic degradation of organic pollutants viz. dyes, pesticides, phenolic compounds, and so on. It also covers the deep discussion on the photocatalytic mechanism of metal oxides and their composites along with the properties relevant to photocatalysis. High photodegradation efficiency, economically-viable approaches for the preparation of photocatalytic materials, and controlled band-gap engineering make metal oxides highly efficient photocatalysts for degradation of organic pollutants. The review would be an excellent resource for researchers who are currently focusing on metal oxides-based materials for water remediation as well as for those who are interested in adsorptive and photocatalytic applications of metal oxides and their composites.

Atrazine degradation using Fe3O4-sepiolite catalyzed persulfate: Reactivity, mechanism and stability

In this study, with sepiolite as a support, a novel magnetic Fe₃O₄-sepiolite composite was fabricated by coprecipitation method. The characterization results reveal that the sepiolite support could anchor Fe₃O₄ nanoparticles with good dispersion. The composite was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. 71.6% of ATZ and 20.9% of solution TOC could be removed after 60 min with 92 mmol/L of PS ([ATZ]₀ = 10 mmol/L). Due to the good adsorption capacity of Fe₃O₄-sepiolite composite toward ATZ, the degradation was considered to be facilitated by an adsorption process, since the adsorbed ATZ can be more easily transported to the active sites and be degraded in situ. Operation factors, including PS dose and solution pH, were investigated and found to be influential for the ATZ removal. The Fe₃O₄-sepiolite composite maintained its catalytic activity and structural stability with negligible Fe leaching during the recycling batch experiments. The intermediate products were further identified and the possible transformation pathway was then proposed based on the results. The findings of this research promote the application of Fe₃O₄-sepiolite composite as efficient and recyclable heterogeneous catalyst for organic degradation, and provide insights into the development of alternative catalysts with good adsorptive properties.