Theoretical insight into the degradation of p-nitrophenol by OH radicals synergized with other active oxidants in aqueous solution

Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

Effect of pH on the ozonolysis degradation of p-nitrophenol in aquatic environment and the synergistic effect of hydroxy radical

Density functional theory (DFT) was employed to elucidate the mechanisms for ozonolysis reaction of p-nitrophenol (PNP) and its anion form aPNP. Thermodynamic data, coupled with Average Local Ionization Energies (ALIE) analysis, reveal that the ortho-positions of the OH/O- groups are the most favorable reaction sites. Moreover, rate constant calculations demonstrate that the O3 attack on the C2-C3 bond is the predominant process in the reaction between neutral PNP and O3. For the aPNP + O3 reaction, the most favorable pathways involve O3 attacking the C1-C2 and C6-C1 bonds. The rate constant for PNP ozonolysis positively correlates with pH, ranging from 5.47 × 108 to 2.86 × 109 M-1 s-1 in the natural aquatic environment. In addition, the formation of hydroxyl radicals in the ozonation process of PNP and the mechanisms of its synergistic reaction of PNP with ozone were investigated. Furthermore, the ozonation and hydroxylation processes involving the intermediate OH-derivatives were both thermodynamically and kinetic analyzed, which illustrate that OH radicals could promote the elimination of PNP. Finally, the toxic of PNP and the main products for fish, daphnia, green algae and rat were assessed. The findings reveal that certain intermediates possess greater toxicity than the original reactant. Consequently, the potential health risks these compounds pose to organisms warrant serious consideration.

New insights into the degradation mechanism of ibuprofen in the UV/H2O2 process: role of natural dissolved matter in hydrogen transfer reactions

Ibuprofen (IBU), a widely used antipyretic and analgesic, has been frequently detected in various natural water systems. Advanced oxidation processes (AOPs) are effective ways to remove pollutants from water. The degradation of IBU under UV/H2O2 conditions in the presence of various kinds of natural dissolved matter was investigated using density functional theory (DFT). The eco-toxicological properties were predicted based on a quantitative structure-activity relationship (QSAR) model. The calculated results showed that two H-abstraction reactions occurring at the side chain are predominant pathways in the initial reaction. H2O, NH3, CH3OH, C2H5OH, HCOOH and CH3COOH can catalyze the H transfer in the degradation process through decreasing the energy barriers and the catalysis effects follow the order of NH3 > alcohols > acids > H2O. The catalysis effects differ under acid or alkaline conditions. The overall rate coefficient of the reaction of IBU with ˙OH is calculated to be 5.04 × 109 M-1 s-1 at 298 K. IBU has harmful effects on aquatic organisms and human beings and the degradation process cannot significantly reduce its toxicity. Among all products, 2-(4-formylphenyl)propanoic acid, which is more toxic than IBU, is the most toxic with acute and chronic toxicity, developmental toxicity, mutagenicity, genotoxic carcinogenicity and irritation/corrosivity to skin. The findings in this work provide new insights into the degradation of IBU and can help to assess its environmental risks.

Role of Hydroxyl Radical in Degradation of NTO: DFT Study

Hydroxyl radicals are important reactive oxygen species produced in the aquatic environment under sunlight irradiation. Many organic pollutants may be decomposed as they encounter hydroxyl radicals, due to their high oxidative ability. NTO (5-nitro-1,2,4-triazol-3-one), an energetic material used in military applications, may be released to the environment and dissolved in surface water and groundwater due to its good water solubility. A detailed investigation of the possible mechanism for NTO decomposition in water induced by hydroxyl radical as one of the pathways for NTO environmental degradation was performed by computational study at the PCM/M06-2X/6-311++G(d,p) level. Decomposition of NTO was found to be a multistep process that may begin with an addition of hydroxyl radical to the carbon atom of C═N double bond and consequent release of a nitrite radical. The formed intermediate undergoes a series of chemical transformations that include the attachments of hydroxyl radical to carbon atoms, the transfer of hydrogen to hydroxyl radical, isomerization, and bond cleavage, leading to low-weight inorganic compounds, such as ammonia, nitrogen gas, nitrous acid, nitric acid, and carbon(IV) oxide. The anionic form of NTO is more reactive toward interaction with the hydroxyl radical as compared with its neutral form. Calculated activation energies and high exergonicity of the studied process support the significant contribution of the hydroxyl radical to NTO mineralization in environment.

Theoretical insights into the degradation mechanisms, kinetics and eco-toxicity of oxcarbazepine initiated by OH radicals in aqueous environments

As an anticonvulsant, oxcarbazepine (OXC) has attracted considerable attention for its potential threat to aquatic organisms. Density functional theory has been used to study the mechanisms and kinetics of OXC degradation initiated by OH radicals in aqueous environment. A total of fourteen OH-addition pathways were investigated, and the addition to the C8 position of the right benzene ring was the most vulnerable pathway, resulting in the intermediate IM8. The H-abstraction reactions initiated by OH radicals were also explored, where the extraction site of the methylene group (C14) on the seven-member carbon heterocyclic ring was found to be the optimal path. The calculations show that the total rate constant of OXC with OH radicals is 9.47 × 10⁹ (mol/L)^-1sec^-1, and the half-life time is 7.32 s at 298 K with the [·OH] of 10^-11 mol/L. Moreover, the branch ratio values revealed that OH-addition (89.58%) shows more advantageous than H-abstraction (10.42%). To further understand the potential eco-toxicity of OXC and its transformation products to aquatic organisms, acute toxicity and chronic toxicity were evaluated using ECOSAR software. The toxicity assessment revealed that most degradation products such as OXC-2OH, OXC-4OH, OXC-1O-1OOH, and OXC-1OH' are innoxious to fish and daphnia. Conversely, green algae are more sensitive to these compounds. This study can provide an extensive investigation into the degradation of OXC by OH radicals and enrich the understanding of the aquatic oxidation processes of pharmaceuticals and personal care products (PPCPs).

High Selectivity Fuel from Efficient CO2 Conversion by Zn-Modified rGO and Amine-Functionalized CuO as a Photocatalyst

Reduced graphene oxide (rGO) has been used in copper (II) oxide (CuO)-based photocatalysts as an additive material. An application of this CuO-based photocatalyst is in the CO₂ reduction process. The preparation of rGO by a Zn-modified Hummers' method has resulted in a high quality of rGO in terms of excellent crystallinity and morphology. However, implementing Zn-modified rGO in CuO-based photocatalysts for the CO₂ reduction process has yet to be studied. Therefore, this study explores the potential of combining Zn-modified rGO with CuO photocatalysts and performing these rGO/CuO composite photocatalysts to convert CO₂ into valuable chemical products. The rGO was synthesized by using a Zn-modified Hummers' method and covalently grafted with CuO by amine functionalization with three different compositions (1:10, 1:20, and 1:30) of rGO/CuO photocatalyst. XRD, FTIR, and SEM were used to investigate the crystallinity, chemical bonds, and morphology of the prepared rGO and rGO/CuO composites. The performance of rGO/CuO photocatalysts for the CO₂ reduction process was quantitively measured by GC-MS. We found that the rGO showed successful reduction using a Zn reducing agent. The rGO sheet could be grafted with CuO particles and resulted in a good morphology of rGO/CuO, as shown from the XRD, FTIR, and SEM results. The rGO/CuO material showed photocatalytic performance due to the advantages of synergistic components and resulted in methanol, ethanolamine, and aldehyde as fuel with amounts of 37.12, 8730, and 17.1 mmol/g catalyst, respectively. Meanwhile, adding CO₂ flow time increases the resulting quantity of the product. In conclusion, the rGO/CuO composite could have potential for large-scale CO₂ conversion and storage applications.

Mechanistic insight into the degradation of 1H-benzotriazole and 4-methyl-1H-benzotriazole by •OH-based advanced oxidation process and toxicity assessment

Benzotriazoles (BTs) are highly produced chemicals that are commonly used in the manufacture of aircraft de-icing/antifreeze fluids (ADAFs), coolants, etc. BTs have been detected in a variety of water environments, causing health hazards to aquatic species and humans. In this study, 1H-benzotriazole (BTri) and 4-methyl-1H-benzotriazole (4-TTri) were selected to investigate their degradation mechanisms in the aqueous phase initiated by ·OH using a theoretical calculation method. Addition reactions are the main type of reactions of ·OH with BTri and 4-TTri. The total rate constants for the reactions of BTri and 4-TTri with ·OH at 298 K are 8.26 × 10⁹ M^-1 s^-1 and 1.81 × 10¹⁰ M^-1 s^-1, respectively. The reaction rate constants increase as the temperature rises, indicating that rising temperatures promote the degradation of BTri and 4-TTri. 7-hydroxy-1H-benzotriazole (1-P1) and 4-hydroxy-benzotriazoles (1-P2) produced via multiple reaction pathways are important transformation products of BTri. After successive reactions with ·OH, 1-P1 and 1-P2 can be successively converted to 4,7-dihydroxy-1H-benzotriazole (1-P7), 4,7-dione-1H-benzotriazole (1-P8), and 1,2,3-triazole-4,5-dicarboxylic acid (1-P9), which is consistent with the product compositions detected in the experiments. The toxicity assessment indicated that the acute toxicity and chronic toxicity of the resulting transformation products are significantly reduced compared to BTri as the degradation process progressed, and ultimately showed no harm to all three aquatic organisms (fish, daphnia, and green algae). Hence, advanced oxidation processes (AOPs) can not only effectively remove BTs from water, but also reduce their toxic effects on aquatic organisms.

In-situ Electrochemical Synthesis of H2O2 for p-nitrophenol Degradation Utilizing a Flow-through Three-dimensional Activated Carbon Cathode with Regeneration Capabilities

The growing ubiquity of recalcitrant organic contaminants in the aqueous environment poses risks to effective and efficient water treatment and reuse. A novel three-dimensional (3D) electrochemical flow-through reactor employing activated carbon (AC) encased in a stainless-steel (SS) mesh as a cathode is proposed for the removal and degradation of a model recalcitrant contaminant p-nitrophenol (PNP), a toxic compound that is not easily biodegradable or naturally photolyzed, can accumulate and lead to adverse environmental health outcomes, and is one of the more frequently detected pollutants in the environment. As a stable 3D electrode, granular AC supported by a SS mesh frame as a cathode is hypothesized to 1) electrogenerate H2O2 via a 2-electron oxygen reduction reaction on the AC surface, 2) initiate decomposition of this electrogenerated H2O2 to form hydroxyl radicals on catalytic sites of the AC surface 3) remove PNP molecules from the waste stream via adsorption, and 4) co-locate the PNP contaminant on the carbon surface to allow for oxidation by formed hydroxyl radicals. Additionally, this design is utilized to electrochemically regenerate the AC within the cathode that is significantly saturated with PNP to allow for environmentally friendly and economic reuse of this material. Under flow conditions with optimized parameters, the 3D AC electrode is nearly 20% more effective than traditional adsorption in removing PNP. 30 grams of AC within the 3D electrode can remove 100% of the PNP compound and 92% of TOC under flow. The carbon within the 3D cathode can be electrochemically regenerated in the proposed flow system and design thereby increasing the adsorptive capacity by 60%. Moreover, in combination with continuous electrochemical treatment, the total PNP removal is enhanced by 115% over adsorption. It is anticipated this platform holds great promises to eliminate analogous contaminants as well as mixtures.

PdCu alloy prepared by ultrasonic method catalyzes the degradation of p-nitrophenol

PdCu alloy nanocatalysts supported on NiFe layered double hydroxide (PdCu-LDHs) were prepared by a green ultrasound-assisted reduction method. The cavitation effect of ultrasound made part of CO₃^2- decompose to CO₂, and NO₃^- and Cl^- replace intercalation, which anchor the PdCu between layers. The action of ultrasound dissociated hydroxyl groups (-OH) on surface of LDHs to H· to reduce Cu²⁺ and Pd²⁺ to Cu⁰ and Pd⁰ and Cu promote the synergy between Pd alloy and LDHs. The electronic effects between Cu and Pd improved the catalytic performance for the reduction reaction of 4-NP and the stability of PdCu-LDHs. The PdCu-LDHs prepared at 400 W, 25 kHz, 1 h, can completely degrade p-nitrophenol (4-NP) within 5 min with n(4-NP)/n(Pd) = 50 and n(4-NP)/n(NaBH₄) = 0.15. The TOF value is 988.20 h^-1, which is 27.7 times that of Pd/C catalyst (commercial).

Degradation of UV-P mediated by hydroxyl radical, sulfate radical and singlet oxygen in aquatic solution: DFT and experimental studies

2-(2'-hydroxy-5'-methylphenyl) benzotriazole (UV-P) is a type of emerging persistent organic pollutant that is reported harmful to organisms. However, its degradation mechanisms and transformation behaviors in aquatic environments are not yet clear, which are significant for better understanding its environmental fate and potential toxicological impacts. In present work, the degradation mechanisms, kinetics, half-life times and eco-toxicity assessment of UV-P initiated by hydroxyl radical (•OH), sulfate radical (SO₄•^‾), and singlet oxygen (¹O₂) are systematically studied using density functional theory (DFT) and experimental methods. The initiated reaction results show that benzene ring of UV-P is vulnerable to attack by •OH, while benzotriazole is easily attacked by SO₄•^‾. The kinetic calculations indicate that •OH-addition reaction R15 is dominant initial pathway. And the half-life (t_1/2) of UV-P is calculated according to rate constants, t_1/2 decreases rapidly with [ROS] increasing. UV-P exhibits environmental persistence when [•OH] ≤ 10^-17 M. The subsequent degradation mechanisms of hydroxylated UV-P react with •OH and O₂ are also calculated. A novel ring-opening reaction channel is proposed that O₂-addition intermediate combines with hydroperoxyl radical (HO₂•) to cleave aromatic ring. The rate-determining step is intramolecular dehydration reaction with the energy barrier of 32.98 kcal mol^-1 and 41.13 kcal mol^-1 to cleave benzene ring and benzotriazole ring, respectively. The degradation experiments of UV-P are conducted in Co₃O₄ activated potassium peroxymonosulfate (PMS) system, and liquid chromatograph-mass spectrometer (LC-MS) results identified that dihydroxylated species are main intermediates, which is consistent with theoretical calculation results. Furthermore, the eco-toxicity assessment shows that the acute and chronic toxicities of most degradation products are reduced compared with UV-P, however, their toxicity levels still keep at toxic and harmful. The environmental risk of UV-P deserves more attention.

Chemical Overview of Gel Dosimetry Systems: A Comprehensive Review

Advances in radiotherapy technology during the last 25 years have significantly improved both dose conformation to tumors and the preservation of healthy tissues, achieving almost real-time feedback by means of high-precision treatments and theranostics. Owing to this, developing high-performance systems capable of coping with the challenging requirements of modern ionizing radiation is a key issue to overcome the limitations of traditional dosimeters. In this regard, a deep understanding of the physicochemical basis of gel dosimetry, as one of the most promising tools for the evaluation of 3D high-spatial-resolution dose distributions, represents the starting point for developing new and innovative systems. This review aims to contribute thorough descriptions of the chemical processes and interactions that condition gel dosimetry outputs, often phenomenologically addressed, and particularly formulations reported since 2017.

Influence of Synthesis Conditions on Physicochemical and Photocatalytic Properties of Ag Containing Nanomaterials

Silver (Ag) containing nanomaterials were successfully prepared by varying synthesis conditions to understand the influence of preparation conditions on the physicochemical and photocatalytic properties of these materials. Different analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Diffuse reflectance UV-vis spectra (DR UV-vis), X-ray photoelectron spectroscopy (XPS) measurements, and N2-physisorption were used to investigate the physicochemical properties of synthesized Ag containing nanomaterials. The samples (Ag-1 and Ag-2) prepared using AgNO3, NaHCO3, and polyvinylpyrrolidone (PVP) template exhibited pure Ag metal nanorods and nanoparticles; the morphology of Ag metal is influenced by the hydrothermal treatment. The Ag-3 sample prepared without PVP template and calcined at 250 °C showed the presence of a pure Ag2O phase. However, the same sample dried at 50 °C (Ag-4) showed the presence of a pure Ag2CO3 phase. Interestingly, subjecting the sample to hydrothermal treatment (Ag-5) has not resulted in any change in crystal structure, but particle size was increased. All the synthesized Ag containing nanomaterials were used as photocatalysts for p-nitrophenol (p-NP) degradation under visible light irradiation. The Ag-4 sample (pure Ag2CO3 with small crystallite size) exhibited high photocatalytic activity (86% efficiency at pH 10, p-NP concentration of 16 mg L−1, 120 min and catalyst mass of 100 mg) compared to the other synthesized Ag containing nanomaterials. The high photocatalytic activity of the Ag-4 sample is possibly due to the presence of a pure Ag2CO3 crystal structure with nanorod morphology with a low band gap energy of 1.96 eV and relative high surface area.

Electron structure modulation and bicarbonate surrounding enhance Fenton-like reactions performance of Co-Co PBA

Although several strategies have been developed to improve the efficiency of heterogeneous Fenton-like reactions, investigating the relationship among the electronic properties of the catalyst surface, the complex water matrix and catalytic activity remains challenges. Herein, the electron density of the active site Co(II) in Co Prussian blue analogs (Co-PBAs) is proved to be modulated by the anion source method. The elevated electron density of Co(II) and the higher metallicity of the catalyst lead to an increase in electron transport efficiency as revealed by X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and density functional theory (DFT) calculations. Furthermore, the negative shift of the D-band center of Co(II) can effectively release intermediates to avoid catalyst poisoning. Bicarbonate has been demonstrated to activate peroxymonosulfate (PMS) by weakening the peroxide bond. Its activation mechanism involves free radical mechanism and non-radical mechanism: the first step is the generation of HCO₄^-, then it is further hydrolyzed to generate •OH and ¹O₂, and the other is HCO₄^- interact with Co(III) to form Co(IV)=O. In addition, the degradation pathways of target contaminants p-nitrophenol and toxicity verification of intermediate products have been investigated. This study provides guidance for the research of Fenton-like reactions.

Theoretical evidence for the formation of perfluorocarboxylic acids form atmospheric oxidation degradation of fluorotelomer acrylates

The atmospheric oxidation degradation of fluorotelomer acrylates (FTAcs) has been proposed as a potential source of perfluorocarboxylic acids (PFCAs) in remote locations. In this paper, detailed reactions of the main oxidant OH radicals with 4:2 FTAc in the atmosphere have been investigated by using density functional theory (DFT) calculation. All possible pathways involved in the oxidation process were presented and discussed. Based on the mechanism, transition state theory (TST) was used to predict the rate constants of the key elementary steps including the initial reactions of OH radical with n:2 FTAcs and the subsequent reactions of the main intermediates. Studies show that the reaction processes of OH radical addition to C = C bond are dominant and the fluorotelomer glyoxylate and formaldehyde are the major products. At 296 K, the calculated overall rate constant of 4:2 FTAc with OH radical is 1.19 × 10^-11 cm³ molecule^-1 s^-1 with an atmospheric lifetime of 23.3 h. In the atmosphere, fluorotelomer glyoxylate will continue to be oxidized, which will lead to the formation of PFCAs ultimately. In addition, atmospheric reactions of more carbons FTAc (C_nF_2n+1CH₂CH₂OC(O)CH = CH₂, n = 6, 8, 10) are also discussed in the presence of O₂/NO_x.

Degradation of 4-Tert-Butylphenol in Water Using Mono-Doped (M1: Mo, W) and Co-Doped (M2-M1: Cu, Co, Zn) Titania Catalysts

Mono-doped (Mo-TiO₂ and W-TiO₂) and co-doped TiO₂ (Co-Mo-TiO₂, Co-W-TiO₂, Cu-Mo-TiO₂, Cu-W-TiO₂, Zn-Mo-TiO₂, and Zn-W-TiO₂) catalysts were synthesized by simple impregnation methods and tested for the photocatalytic degradation of 4-tert-butylphenol in water under UV (365 nm) light irradiation. The catalysts were characterized with various analytical methods. X-ray diffraction (XRD), Raman, Diffuse reflectance (DR) spectroscopies, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Energy dispersive spectroscopy (EDS) were applied to investigate the structure, optical properties, morphology, and elemental composition of the prepared catalysts. The XRD patterns revealed the presence of peaks corresponding to the WO₃ in W-TiO₂, Co-W-TiO₂, Cu-W-TiO₂, and Zn-W-TiO₂. The co-doping of Cu and Mo to the TiO₂ lattice was evidenced by the shift of XRD planes towards higher 2θ values, confirming the lattice distortion. Elemental mapping images confirmed the successful impregnation and uniform distribution of metal particles on the TiO₂ surface. Compared to undoped TiO₂, Mo-TiO₂ and W-TiO₂ exhibited a lower energy gap. Further incorporation of Mo-TiO₂ with Co or Cu introduced slight changes in energy gap and light absorption characteristics, particularly visible light absorption. In addition, photoluminescence (PL) showed that Cu-Mo-TiO₂ has a weaker PL intensity than undoped TiO₂. Thus, Cu-Mo-TiO₂ showed better catalytic activity than pure TiO₂, achieving complete degradation of 4-tert-butylphenol under UV light irradiation after 60 min. The application of Cu-Mo-TiO₂ under solar light conditions was also tested, and 70% of 4-tert-butylphenol degradation was achieved within 150 min.

Optimization of PNP Degradation by UV-Activated Granular Activated Carbon Supported Nano-Zero-Valent-Iron-Cobalt Activated Persulfate by Response Surface Method

Nitrophenols are toxic substances that present humans and animals with the risk of deformities, mutations, or cancer when ingested or inhaled. Traditional water treatment technologies have high costs and low p-nitrophenol (PNP) removal efficiency. Therefore, an ultraviolet (UV)-activated granular activated carbon supported nano-zero-valent-iron-cobalt (Co-nZVI/GAC) activated persulfate (PS) system was constructed to efficiently degrade PNP with Co-nZVI/GAC dosage, PS concentration, UV power, and pH as dependent variables and PNP removal rate as response values. A mathematical model between the factors and response values was developed using a central composite design (CCD) model. The model-fitting results showed that the PNP degradation rate was 96.7%, close to the predicted value of 98.05 when validation tests were performed under Co-nZVI/GAC injection conditions of 0.827 g/L, PS concentration of 3.811 mmol/L, UV power of 39.496 W, and pH of 2.838. This study demonstrates the feasibility of the response surface methodology for optimizing the UV-activated Co-nZVI/GAC-activated PS degradation of PNP.

DFT insights into the degradation mechanism of carbendazim by hydroxyl radicals in aqueous solution

Advanced oxidation of carbendazim by OH radicals is a central step in its wastewater remediation. However, the understanding of the degradation mechanism of carbendazim has always been a challenge. In this paper, the degradation mechanism of carbendazim by •OH in aqueous solution has been explored using density functional theory (DFT) calculations. On account of the structural and electronic characteristics analysis, the nucleophilic aromatic substitution, dehydrogenation oxidation, and decarboxylation degradation pathways were mainly investigated. These degradation reactions may produce hydroxyl substitution products, oxidized aldehyde and carboxyl products, and decarboxylated carbamic acid products. Computational studies demonstrated that these possible degradation reactions are facile to take place kinetically and have large thermodynamic driving forces, indicating the feasibility of the relevant degradation pathways. Additionally, the ecological risk of carbendazim and its possible degradation products was evaluated, showing that the acute toxicity of degradation products decreases in varying degrees compared with that of carbendazim. The comprehensive mechanistic studies open an avenue for the understanding on the degradation of organic pollutants such as benzimidazole pollutants on molecular level.

Recent developments in photocatalysis of industrial effluents ։ A review and example of phenolic compounds degradation

Industrial expansion and increased water consumption have created water scarcity concerns. Meanwhile, conventional wastewater purification methods have failed to degrade recalcitrant pollutants efficiently. The present review paper discusses the recent advances and challenges in photocatalytic processes applied for industrial effluents treatment, with respect to phenolic compounds degradation. Key operational parameters including the catalyst loading, light intensity, initial pollutants concentration, pH, and type and concentrations of oxidants are evaluated and discussed. Compared to the other examined controlling parameters, pH has the highest effect on the photo-oxidation of contaminants by means of the photocatalyst ionization degree and surface charge. Furthermore, major phenolic compounds derived from industrial sources are comprehensively presented and the applicability of photocatalytic processes and the barriers in practical applications, including high energy demand, technical challenges, photocatalyst stability, and recyclability have been explored. The importance of energy consumption and operational costs for realistic large-scale processes are also discussed. Finally, research gaps in this area and the suggested direction for improving degradation efficiencies in industrial applications are presented. In the light of these premises, selective degradation processes in real water matrices such as untreated sewage are proposed.

A Flower-like In2O3 Catalyst Derived via Metal-Organic Frameworks for Photocatalytic Applications

The most pressing concerns in environmental remediation are the design and development of catalysts with benign, low-cost, and efficient photocatalytic activity. The present study effectively generated a flower-like indium oxide (In₂O₃-MF) catalyst employing a convenient MOF-based solvothermal self-assembly technique. The In₂O₃-MF photocatalyst exhibits a flower-like structure, according to morphology and structural analysis. The enhanced photocatalytic activity of the In₂O₃-MF catalyst for 4-nitrophenol (4-NP) and methylene blue (MB) is likely due to its unique 3D structure, which includes a large surface area (486.95 m² g^-1), a wide spectrum response, and the prevention of electron-hole recombination compared to In₂O₃-MR (indium oxide-micro rod) and In₂O₃-MD (indium oxide-micro disc). In the presence of NaBH₄ and visible light, the catalytic performances of the In₂O₃-MF, In₂O₃-MR, and In₂O₃-MD catalysts for the reduction of 4-NP and MB degradation were investigated. Using In₂O₃-MF as a catalyst, we were able to achieve a 99.32 percent reduction of 4-NP in 20 min and 99.2 percent degradation of MB in 3 min. Interestingly, the conversion rates of catalytic 4-NP and MB were still larger than 95 and 96 percent after five consecutive cycles of catalytic tests, suggesting that the In₂O₃-MF catalyst has outstanding catalytic performance and a high reutilization rate.

Facile synthesis of ZnMoO4/AlPO4-5 nanorod composites as visible-light-driven photocatalysts and high-performance energy storage materials

The present article describes the facile one-step hydrothermal synthesis of single-crystalline ZnMoO4/AlPO4-5 nanorod composites. The physicochemical properties of the synthesized materials, such as structure, morphology, and bandgap, were determined using techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption-desorption isotherms, X-ray photoelectron (XPS), ultraviolet-visible (UV-vis), and photoluminescence (PL). The XRD pattern of synthesized ZnMoO4/AlPO4-5 verifies the synthesis of nanocomposites. Diffuse UV-vis spectra reveal that ZnMoO4/AlPO4-5 nanorod composites exhibit an indirect semiconductor with an optical bandgap between 3.15 and 3.7 eV depending on Mo : Zn ratio. In comparison to pure AlPO4-5, ZnMoO4/AlPO4-5 nanocrystal composites showed significantly higher photocatalytic activity for the degradation of para-nitrophenol (PNP, 0.04 g l-1), with 14, 99, 70, and 54% for AlPO4-5, Mo : Zn (2)/AlPO4-5, Mo : Zn (4)/AlPO4-5, and Mo : Zn (6)/AlPO4-5, respectively. This result might be attributed to the composite's efficient charge transfer and optimized electron-hole pair recombination. The supercapacitive ability of ZnMoO4/AlPO4-5 nanorod composites was also investigated in this work. For the prepared electrodes using AlPO4-5, Mo : Zn (2)/AlPO4-5, Mo : Zn (4)/AlPO4-5, and Mo : Zn (6)/AlPO4-5, the capacitance values were 400, 725, 450, and 481.25 F g-1, respectively, at a current density of 0.5 A g-1. This study shows that ZnMoO4/AlPO4-5 nanorod composites are a potential visible-light-responsive photocatalyst. The electrochemical results further demonstrate the high capacitance of ZnMoO4/AlPO4-5 nanorod composites toward energy-storage applications.

Bicarbonate-enhanced iron-based Prussian blue analogs catalyze the Fenton-like degradation of p-nitrophenol

P-nitrophenol (PNP), a widely used compound, is harmful to the environment and human health. In this study, four iron-based Prussian blue analogs (PBAs) were prepared by coprecipitation (Co-Fe PBA, Mn-Fe PBA, Cu-Fe PBA and Fe-Fe PBA). The Co-Fe PBA exhibited high peroxymonosulfate (PMS) activation performance for PNP degradation, removing over 90% of PNP in 60 min at an optimal pH of 7, temperature at 30 ℃, initial concentration of 20 mg/L, PBA dose of 0.2 g/L and PMS dose of 1 g/L. The physicochemical properties of the Co-Fe PBA were investigated by various characterization methods. The catalytic activity of PBA and the influence of various process parameters and water quality on the catalytic reaction were investigated to elucidate the mechanism of p-nitrophenol degradation by PBA-activated persulfate. Moreover, the mechanism of accelerated degradation of PNP under HCO₃^- conditions and the role of major reactive oxides were determined by EPR measurement methods and free radical trapping experiments. HCO₃^- was found to directly activate PMS to produce reactive oxygen species, and ¹O₂, ∙OH and SO₄^∙- were all greatly increased. This work presents a promising green heterogeneous catalyst for the degradation of emerging contaminants (ECs) in real wastewater with natural organic matter and coexisting anions by PMS activation.

Theoretical investigation on the mechanisms and kinetics of OH/NO3-initiated atmospheric oxidation of vanillin and vanillic acid

Vanillin and vanillic acid are two kinds of lignin pyrolysis products that are generated by biomass combustion. The gas-phase oxidation mechanisms of vanillin and vanillic acid initiated by OH/NO₃ radicals were investigated by using density functional theory (DFT) at M06-2X/6-311+G(3df,2p)//M06-2X/6-311+G(d,p) level. The initial reactions of vanillin and vanillic acid with OH/NO₃ radicals can be divided into two patterns: OH/NO₃ addition and H-atom abstraction. For vanillin reacted with OH radical, the OH addition mainly occurs at C2-position to produce highly chemically activated intermediate (IM2). The oxidation products 3,4-dihydroxy benzaldehyde, malealdehyde, methyl hydrogen oxalate, methylenemalonaldehyde, carbonyl and carbonyl compounds are formed by the subsequent reactions of IM2. H-atom abstracting from aldehyde group occurs more easily than from the other positions. In addition, vanillin reacting with NO₃ radicals principally proceeds via NO₃-addition at C1 sites and H-atom abstracting from OH group (C1) to generate HNO₃. The primary reaction mechanisms of vanillic acid with OH/NO₃ radicals were similar to vanillin. The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was performed to calculate the rate constants of the significant elementary reactions. The total rate constants for OH-initiated oxidation of vanillin and vanillic acid are 5.72 × 10^-12 and 5.40 × 10^-12 cm³ molecule^-1 s^-1 at 298 K and 1 atm. The atmospheric lifetimes were predicted to be 48.56 h and 51.44 h, respectively. As a supplement, the kinetic calculations of NO₃ radicals with two reactants were also discussed. This work investigates the atmospheric oxidation processes of vanillin and vanillic acid, and hopes to provide useful information for further experimental research.

p-nitrophenol degradation by hybrid advanced oxidation process of heterogeneous Fenton assisted hydrodynamic cavitation: Discernment of synergistic interactions and chemical mechanism

The present study has investigated p-nitrophenol (PNP) degradation by hybrid advanced oxidation process (AOP) of hydrodynamic cavitation with heterogenous Fe₃O₄ nanoparticles. 78.8 ± 1.2% of PNP degradation was obtained at optimum operational conditions: inlet pressure = 8 atm, pH = 3, initial concentration of PNP = 20 mg L^-1, Fe₃O₄:H₂O₂ = 1:100. PNP degradation profiles were analyzed using a kinetic model based on the reaction network. The closest match between the simulated and experimental degradation profiles was obtained for the initial concertation of [H₂O₂] = 0.6 M, which was far higher than concentration of externally added H₂O₂. This was attributed to in-situ generation of H₂O₂ through transient cavitation. Intense shear and turbulence generated in cavitating flow caused surface leaching of Fe₃O₄ particles that released Fe²⁺/Fe³⁺ ions. The synergy in the hybrid AOP was in-situ Fenton reactions between leached Fe²⁺/Fe³⁺ ions and H₂O₂ present in the reaction mixture. The mechanism in ^•OH mediated oxidative degradation of PNP was further explored with Density Functional Theory (DFT) simulations. Both ^•OH addition on benzene ring and H-abstraction reactions were simulated to identify the possible pathways for the degradation. On the basis of activation free energy analysis, degradation pathways initiating with both ^•OH addition and H abstraction were determined to be feasible. The ortho-C of benzene ring was the most favourable site for ^•OH addition, while H atom of phenolic hydroxyl group was more susceptible (or more reactive) for H-atom abstraction route.

Activation of persulfate by green nano-zero-valent iron-loaded biochar for the removal of p-nitrophenol: Performance, mechanism and variables effects

In this study, with the green tea extraction solution as a reducing agent and green tea residues as a raw material of biochar, green nano zero-valent iron biochar (G-nZVI-BC) was prepared with the green synthesis method and then combined with potassium persulfate to degrade p-nitrophenol in water. Compared with zero-valent iron-loaded biochar (C-nZVI-BC) prepared by the traditional chemical liquid phase synthesis method, G-nZVI-BC containing tea polyphenols further improved dispersibility of Fe⁰ on biochar, prevented nZVI agglomeration on BC, and promoted PNP degradation. The system constructed by G-nZVI-BC/PDS showed the high oxidation resistance than the C-nZVI-BC/PDS system, thus endowing the synthesis material with long-term reactivity. Both the radical pathway and non-radical pathways contributed to catalytic degradation and free radicals played a key role. The G-nZVI-BC/PDS system realized the good removal effect on PNP in the pH range of 3.06-9.23. The reusability of G-nZVI-BC and the PNP removal effect in water body conditions indicated that G-nZVI-BC had a good application prospect in the field of water treatment.

Acetaminophen degradation by hydroxyl and organic radicals in the peracetic acid-based advanced oxidation processes: Theoretical calculation and toxicity assessment

The research on the mechanisms and kinetics of radical oxidation in peracetic acid-based advanced oxidation processes was relatively limited. In this work, HO^• and organic radicals mediated reactions of acetaminophen (ACT) were investigated, and the reactivities of important organic radicals (CH₃COO^• and CH₃COOO^•) were calculated. The results showed that initiated reaction rate constants of ACT are in the order: CH₃COO^• (5.44 × 10¹⁰ M^-1 s^-1) > HO^• (7.07 × 10⁹ M^-1 s^-1) > CH₃O^{• (}1.57 × 10⁷ M^-1 s^-1) > CH₃COOO^• (3.65 × 10⁵ M^-1 s^-1) >> ^•CH₃ (5.17 × 10² M^-1 s^-1) > CH₃C^•O (1.17 × 10² M^-1 s^-1) > CH₃OO^• (11.80 M^-1 s^-1). HO^•, CH₃COO^• and CH₃COOO^• play important roles in ACT degradation. CH₃COO^• is another important radical in the hydroxylation of aromatic compounds in addition to HO^•. Reaction rate constants of CH₃COO^• and aromatic compounds are 1.40 × 10⁶ - 6.25 × 10¹⁰ M^-1 s^-1 with addition as the dominant pathway. CH₃COOO^• has high reactivity to phenolate and aniline only among the studied aromatic compounds, and it was more selective than CH₃COO^•. CH₃COO^•-mediated hydroxylation of aromatic compounds could produce their hydroxylated products with higher toxicity.

A microwave atmospheric plasma strategy for fast and efficient degradation of aqueous p-nitrophenol

Plasma technology has received intensive research interest in pollutants degradation. However, conventional plasma generator suffers from erosion of electrodes and consequent short life time and pollution. In this work, an electrodeless high-flow microwave atmospheric plasma jet is developed for fast degradation of p-nitrophenol. With the assistance of injection locking technology, stable plasma is managed to be generated by low-cost magnetron. 100% removal of 100 mg/L PNP is achieved after 12 min, with a TOC removal efficiency of 57.6%. The fast degradation is probably due to the high cross section (around 153 mm²) of plasma gas. Change in the removal efficiency are less than 4% and 5% as the pH of the solution changes from 2.02 to 12.07 and conductivity varies between 5^.38 × 10^-2 and 43.6 mS/cm, respectively. Moreover, optical emission spectroscopy spectra of the microwave plasma and a hydroxyl radical scavenger (t-butanol) are employed to identify the generated oxidizing species, which indicates that ^•OH is the key factor during the degradation process. The hydroxylated intermediates and organic acid transformed from PNP were revealed. Based on the examined intermediate products, the possible degradation mechanism and pathway are analyzed.

Insight into the degradation of p-nitrophenol by visible-light-induced activation of peroxymonosulfate over Ag/ZnO heterojunction

In this report, the peroxymonosulfate activation over Ag/ZnO heterojunction under visible light (Ag/ZnO/PMS/Vis) for p-nitrophenol (p-NP) contaminant degradation was conducted in detail. Herein, the catalyst dosage was decreased, and the results showed that a dosage of 0.5 g L^-1 Ag/ZnO and 4 mM PMS almost completely degraded 30 mg L^-1 p-NP after 90 min of irradiation. In addition, the PMS activation mechanism of Ag/ZnO/PMS/Vis system was proposed by investigations of the influence of PMS concentration, the FTIR spectra, UV-Vis spectroscopy, and electrochemical analyses. Additionally, the role of SO₄^•- in the photocatalytic reaction is determined by a combination of a trapping test using isopropanol and tert-butanol as probe compounds and electron spin resonance (ESR) spectroscopy. This report provides a potential alternative to remove persistent organic contaminants in sewage using PMS incorporated with Ag/ZnO under visible light irradiation.

Mechanistic insight into the degradation of ibuprofen in UV/H2O2 process via a combined experimental and DFT study

The study investigated the degradation kinetic and transformation mechanism of ibuprofen (IBP) in UV/H₂O₂ process from both experimental and theoretical aspects. Impacts of H₂O₂ dosage, solution pH, quenching agent, and concentration of nitrite (NO₂^-) on IBP degradation in UV/H₂O₂ process were evaluated. Both experimental results and theoretical calculations indicated that ^•OH played an important role in the degradation of IBP and its transformation products. The second-order rate constants of ^•OH and ^•NO₂ with IBP were calculated as 3.93 × 10⁹ M^-1 s^-1 and 5.59 × 10^-3 M^-1 s^-1, based on the transition state theory, which explained the phenomenon that addition of NO₂^- inhibited IBP degradation. Further, according to the results of ultra-high-resolution mass and density functional theory calculations, mechanisms of a detailed degradation pathway for IBP were clarified. Namely, the detailed mechanistic formation pathways for hydroxylated and keto-based products were proposed. Then, possible active sites of the keto-based products, as well as the corresponding subsequent products were predicted by Condensed Fukui Function. Our study can broaden the knowledge of the reactions of emerging contaminants with ^•OH, and provide theoretical foundation for the optimization of UV/H₂O₂ process.

Full insights into the roles of pH on hydroxylation of aromatic acids/bases and toxicity evaluation

Advanced oxidation processes (AOPs) based on hydroxyl radicals (•OH) are the most important technologies for the removal of bio-recalcitrant organic pollutants in industrial wastewater. The pH is one of the crucial environmental parameters that affect the removal efficiency of pollutants in AOPs. In this work, the mechanistic and kinetic insights into the roles of pH on the hydroxylation of five aromatic acids and bases in UV/H₂O₂ process have been investigated using theoretical calculation methods. Results show that the reactivity of •OH towards the twelve ionic/neutral species is positively correlated with electron-donating effect of substituents, which contributes to the positively pH-dependent reactivity of aromatic acids and bases towards •OH. The hydroxylation apparent rate constants (k_app, M^-1 s^-1) (at 298 K) increase as the pH values increase from about 1 to 10, but they decrease as the pH values increase from about 10 to 14. However, the best pH values for degradation are not around 10 because the [•OH] decreases continuously with the increasing pH values from 3 to 9.5. Combining the factors of k_app and [•OH], the best degradation pH values are around 5.5~7.5 for p-hydroxybenzoic acid, p-aminophenol, aniline and benzoic acid, 3.0~7.5 for phenol and 5.5~7.5 for mixed pollutants of these aromatic acids/bases in UV/H₂O₂ process. Moreover, a significant number of hydroxylation by-products are more toxic or harmful to aquatic organisms and rat (oral) than their parental pollutants. Altogether, this work provides comprehensive understanding of the roles of pH on •OH-initiated degradation behavior of aromatic acids and bases.

Reactivity of aromatic contaminants towards nitrate radical in tropospheric gas and aqueous phase

Aromatic compounds (ACs) give a substantial contribution to the anthropogenic emissions of volatile organic compounds. Nitrate radicals (NO₃) are significant oxidants in the lower troposphere during nighttime, with concentrations of (2-20) × 10⁸ molecules cm^-3. In this study, the tropospheric gas and liquid phase reactions of ACs with nitrate radical are investigated using theoretical computational methods, which can give a deep insight into the reaction mechanisms and kinetics. Results show that the reactivity of ACs with nitrate radicals decreases as the electron donating characteristics of the functional group on the ACs decrease, as ΔG^≠ of the reaction with NO₃ increasing from -1.17 to 17.84 kcal mol^-1. The reaction of NO₃ towards ACs in the aqueous phase is more preferable, with the atmospheric lifetime 0.07-1281 min. An assessment of the aquatic toxicity of ACs and their degradation products indicated that the risk of their degradation products remains and should be given more attention.

Theoretical investigation on the contribution of HO, SO4- and CO3- radicals to the degradation of phenacetin in water: Mechanisms, kinetics, and toxicity evaluation

Indirect oxidation induced by reactive free radicals, such as hydroxyl radical (HO), sulfate radical (SO₄^-) and carbonate radical (CO₃^-), plays an important or even crucial role in the degradation of micropollutants. Thus, the coadjutant degradation of phenacetin (PNT) by HO, SO₄^- and CO₃^-, as well as the synergistic effect of O₂ on HO and HO₂ were studied through mechanism, kinetics and toxicity evaluation. The results showed that the degradation of PNT was mainly caused by radical adduct formation (RAF) reaction (69% for Г, the same as below) and H atom transfer (HAT) reaction (31%) of HO. For the two inorganic anionic radicals, SO₄^- initiated PNT degradation by sequential radical addition-elimination (SRAE; 55%), HAT (28%) and single electron transfer (SET; 17%) reactions, while only by HAT reaction for CO₃^-. The total initial reaction rate constants of PNT by three radicals were in the order: SO₄^- > HO > CO₃^-. The kinetics of PNT degradation simulated by Kintecus program showed that UV/persulfate could degrade target compound more effectively than UV/H₂O₂ in ultrapure water. In the subsequent reaction of PNT with O₂, HO and HO₂, the formation of mono/di/tri-hydroxyl substitutions and unsaturated aldehydes/ketones/alcohols were confirmed. The results of toxicity assessment showed that the acute and chronic toxicity of most products to fish increased and to daphnia decreased, and acute toxicity to green algae decreased while chronic toxicity increased.

Photocatalytic transformation fate and toxicity of ciprofloxacin related to dissociation species: Experimental and theoretical evidences

Chemical speciation of ionizable antibiotics greatly affects its photochemical kinetics and mechanisms; however, the mechanistic impact of chemical speciation is not well understood. For the first time, the impact of different dissociation species (cationic, zwitterionic and anionic forms) of ciprofloxacin (CIP) on its photocatalytic transformation fate was systematically studied in a UVA/LED/TiO₂ system. The dissociation forms of CIP at different pH affected the photocatalytic degradation kinetics, transformation products (TPs) formation as well as degradation pathways. Zwitterionic form of CIP exhibited the highest degradation rate constant (0.2217 ± 0.0179 min^-1), removal efficiency of total organic carbon (TOC) and release of fluoride ion (F^-). Time-dependent evolution profiles on TPs revealed that the cationic and anionic forms of CIP mainly underwent piperazine ring dealkylation, while zwitterionic CIP primarily proceeded through defluorination and piperazine ring oxidation. Moreover, density functional theory (DFT) calculation based on Fukui index well interpreted the active sites of different CIP species. Potential energy surface (PES) analysis further elucidated the reaction transition state (TS) evolution and energy barrier (ΔE_b) for CIP with different dissociation species after radical attack. This study provides deep insights into degradation mechanisms of emerging organic contaminants in advanced oxidation processes associated to their chemical speciation.

Scale-Up of Cluster Beam Deposition to the Gram Scale with the Matrix Assembly Cluster Source for Heterogeneous Catalysis (Catalytic Ozonation of Nitrophenol in Aqueous Solution)

The deposition of precisely controlled clusters from the beam onto suitable supports represents a novel method to prepare advanced cluster-based catalysts. In principle, cluster size, composition, and morphology can be tuned or selected prior to deposition. The newly invented matrix assembly cluster source (MACS) offers one solution to the long-standing problem of low cluster deposition rate. Demonstrations of the cluster activities under realistic reaction conditions are now needed. We deposited elemental silver (Ag) and gold (Au) clusters onto gram-scale powders of commercial titanium dioxide (TiO₂) to investigate the catalytic oxidation of nitrophenol (a representative pollutant in water) by ozone in aqueous solution, as relevant to the removal of waste drugs from the water supply. A range of techniques, including scanning transmission electron microscopy (STEM), Brunauer-Emmett-Teller (BET) surface area test, and X-ray photoelectron spectroscopy (XPS), were employed to reveal the catalyst size, morphology, surface area, and oxidation state. Both the Ag and Au cluster catalysts proved active for the nitrophenol ozonation. The cluster catalysts showed activities at least comparable to those of catalysts made by traditional chemical methods in the literature, demonstrating the potential applications of the cluster beam deposition method for practical heterogeneous catalysis in solution.