Photocatalytic oxidation of diuron using nickel organic xerogel under simulated solar irradiation

The Fabrication and Property Characterization of a Ho2YSbO7/Bi2MoO6 Heterojunction Photocatalyst and the Application of the Photodegradation of Diuron under Visible Light Irradiation

A novel photocatalytic nanomaterial, Ho2YSbO7, was successfully synthesized for the first time using the solvothermal synthesis technique. In addition, a Ho2YSbO7/Bi2MoO6 heterojunction photocatalyst (HBHP) was prepared via the hydrothermal fabrication technique. Extensive characterizations of the synthesized samples were conducted using various instruments, such as an X-ray diffractometer, a Fourier transform infrared spectrometer, a Raman spectrometer, a UV-visible spectrophotometer, an X-ray photoelectron spectrometer, and a transmission electron microscope, as well as X-ray energy dispersive spectroscopy, photoluminescence spectroscopy, a photocurrent test, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. The photocatalytic activity of the HBHP was evaluated for the degradation of diuron (DRN) and the mineralization of total organic carbon (TOC) under visible light exposure for 152 min. Remarkable removal efficiencies were achieved, with 99.78% for DRN and 97.19% for TOC. Comparative analysis demonstrated that the HBHP exhibited markedly higher removal efficiencies for DRN compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.13 times, 1.21 times, or 2.95 times higher, respectively. Similarly, the HBHP demonstrated significantly higher removal efficiencies for TOC compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.17 times, 1.25 times, or 3.39 times higher, respectively. Furthermore, the HBHP demonstrated excellent stability and reusability. The mechanisms which could enhance the photocatalytic activity remarkably and the involvement of the major active species were comprehensively discussed, with superoxide radicals identified as the primary active species, followed by hydroxyl radicals and holes. The results of this study contribute to the advancement of efficient heterostructural materials and offer valuable insights into the development of sustainable remediation strategies for addressing DRN contamination.

Photo-electrochemical oxidation herbicides removal in stormwater: Degradation mechanism and pathway investigation

Although advanced oxidation processes (AOPs) such as photoelectrochemical oxidation (PECO), electrochemical oxidation (ECO) and photocatalytic oxidation (PCO), have shown potential for wastewater treatment, their application in urban stormwater has rarely been studied. This paper explored their major degradation mechanisms and possible degradation pathways of herbicides for stormwater applications (with treatment difficulty compared with wastewater). PECO and ECO showed excellent removal performance for diuron (100 %) and moderate for atrazine (around 35 %) under a relatively low potential (2 V). Superoxide radical (·O₂^-) has been found to be the dominant reactive species. Besides, there is evidence to indicate that hydroxyl radical (·OH) and free chlorine (·Cl) also support the degradation reactions. Up to 11 possible intermediate products have been identified during both diuron and atrazine degradation processes under PECO operation. Based on the proposed possible degradation pathways, the intermediates presented during PECO are species with further oxidation. As evidenced by the undetected species of more oxidized intermediates for ECO and PCO, some further degradation steps are missing, which demonstrate their lower oxidation capacity leading to incomplete decomposition of stormwater herbicides. Thus, PECO has a great potential to be developed into a passive stormwater degradation system due to its strong oxidation potential.

Effect of operational parameters on photocatalytic degradation of ethylparaben using rGO/TiO2 composite under UV radiation

The objective of this study was to analyze the influence of different operational variables (catalyst loading, initial EtP concentration, medium pH, the presence of anions and radical scavengers) on the performance of ethylparaben (EtP) photodegradation catalyzed with an rGO/TiO₂ composite. EtP was selected for study after analyzing the effect of paraben chain length on its catalytic photodegradation, finding that the photodegradation rate constant values of methyl-, ethyl-, and butyl-paraben are 0.050, 0.096, and 0.136 min^-1, respectively. This indicates that the photodegradation rate constant of parabens is higher with longer alkyl chain, which augments its oxidation capacity. The percentage removal of EtP at 40 min increases from 66.3 to 98.6 % when the composite dose rises from 100 to 700 mg/L; however, an additional increase in the composite dose to 1000 mg/L does not substantively improve the photodegradation rate or percentage EtP removal (98.9 %). A rise in the initial EtP concentration from 15 to 100 mg/L reduces the percentage of degradation from 100 to 76.4 %. The percentage EtP degradation is lower with higher solution pH. The presence of HCO₃^- or Cl^- anions in the medium reduces the degradation performance. Results obtained using positive hole and hydroxyl radical scavengers demonstrate that positive holes play an important role in EtP degradation. No degradation product evidences toxicity against the cultured human embryonic kidney cell line HEK-293.

Characteristics and Behavior of Different Catalysts Used for Water Decontamination in Photooxidation and Ozonation Processes

The objective of this study was to summarize the results obtained in a wide research project carried out for more than 15 years on the catalytic activity of different catalysts (activated carbon, metal–carbon xerogels/aerogels, iron-doped silica xerogels, ruthenium metal complexes, reduced graphene oxide-metal oxide composites, and zeolites) in the photooxidation (by using UV or solar radiation) and ozonation of water pollutants, including herbicides, naphthalenesulfonic acids, sodium para-chlorobenzoate, nitroimidazoles, tetracyclines, parabens, sulfamethazine, sodium diatrizoate, cytarabine, and surfactants. All catalysts were synthesized and then texturally, chemically, and electronically characterized using numerous experimental techniques, including N2 and CO2 adsorption, mercury porosimetry, thermogravimetric analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–vis spectroscopy, photoluminescence analysis, and transmission electron microscopy. The behavior of these materials as photocatalysts and ozonation catalysts was related to their characteristics, and the catalytic mechanisms in these advanced oxidation processes were explored. Investigations were conducted into the effects on pollutant degradation, total organic carbon reduction, and water toxicity of operational variables and the presence of different chemical species in ultrapure, surface, ground, and wastewaters. Finally, a review is provided of the most recent and relevant published studies on photocatalysis and catalyzed ozonation in water treatments using similar catalysts to those examined in our project.

Fungal bioremediation of diuron-contaminated waters: Evaluation of its degradation and the effect of amendable factors on its removal in a trickle-bed reactor under non-sterile conditions

The occurrence of the extensively used herbicide diuron in the environment poses a severe threat to the ecosystem and human health. Four different ligninolytic fungi were studied as biodegradation candidates for the removal of diuron. Among them, T. versicolor was the most effective species, degrading rapidly not only diuron (83%) but also the major metabolite 3,4-dichloroaniline (100%), after 7-day incubation. During diuron degradation, five transformation products (TPs) were found to be formed and the structures for three of them are tentatively proposed. According to the identified TPs, a hydroxylated intermediate 3-(3,4-dichlorophenyl)-1-hydroxymethyl-1-methylurea (DCPHMU) was further metabolized into the N-dealkylated compounds 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichlorophenylurea (DCPU). The discovery of DCPHMU suggests a relevant role of hydroxylation for subsequent N-demethylation, helping to better understand the main reaction mechanisms of diuron detoxification. Experiments also evidenced that degradation reactions may occur intracellularly and be catalyzed by the cytochrome P450 system. A response surface method, established by central composite design, assisted in evaluating the effect of operational variables in a trickle-bed bioreactor immobilized with T. versicolor on diuron removal. The best performance was obtained at low recycling ratios and influent flow rates. Furthermore, results indicate that the contact time between the contaminant and immobilized fungi plays a crucial role in diuron removal. This study represents a pioneering step forward amid techniques for bioremediation of pesticides-contaminated waters using fungal reactors at a real scale.

Design of Experiment for the Optimization of Pesticide Removal from Wastewater by Photo-Electrochemical Oxidation with TiO2 Nanotubes

The Design of Experiment (DoE) technique has been used to investigate the photo-electrochemical removal of diuron (DRN) from wastewater. The process is carried out in a photo-electrochemical flow reactor, in which titania nanotubular electrode is irradiated with a simulated solar light. Different operative conditions have been investigated, in a planned 23 full factorial design in which imposed current density, flow rate and initial concentration have been varied at two levels. The removal process of DRN was investigated in terms of specific removal rate (K) and cell voltage (E), which were assumed as objective functions: the results show that the applied current has a paramount effect on both of the objective functions. From the analyses of the intermediates, it appears that the investigated parameters may exert different effects on the distribution of the reaction products: the initial concentration of diuron and the electrode potential seem to play a more important role, in this case.

Nanocellulose–organic montmorillonite nanocomposite adsorbent for diuron removal from aqueous solution: optimization using response surface methodology

Herbicides have been ubiquitous in water environments in recent years, and so it is an appealing proposition to develop an efficient adsorbent for the adsorption of diuron. Therefore, the present study investigated a cellulose nanocrystal/organic montmorillonite nanocomposite adsorbent (CNC/CTM) and its adsorption properties towards diuron present in water. The structure and characteristics of the adsorbent used in this study were characterized by various characterization methods. The optimal diuron adsorption conditions for the CNC/CTM nanocomposite were analyzed based on the response surface methodology (RSM). The adsorption isotherms and kinetics of diuron adsorption were investigated. The results indicated that the adsorption process is the result of hydrogen bonding and the hydrophobicity of the alkyl chain. Under the optimal adsorption conditions, 0.07 g L⁻¹ CNC/CTM adsorbed 5.86 mg L⁻¹ diuron in less than 318.68 min and an efficiency of 82.32% could be achieved. The simulation results showed that the adsorption capacity of CNC/CTM for diuron removal followed the Sips model most closely. The maximum adsorption capacity was approximately 69.04 mg g⁻¹ at 288 K. The experimental data was described best by a pseudo-second-order kinetic equation, signifying a chemical adsorption process. The adsorbent can be reused at least five times after simple solvent washing. This study provides a theoretical basis for understanding the adsorption process of diuron present in water.

CNCs and CTM were combined to obtain a nanocomposite used to remove diuron in water. The adsorption of the nanocomposite was analyzed using response surface methodology, isothermal adsorption model and adsorption kinetics.