Frontier Electron Density Research Articles

Insight into the photodegradation of methylisothiazolinone and benzoisothiazolinone in aquatic environments

Methylisothiazolinone (MIT) and Benzisothiazolinone (BIT) are two widely used non-oxidizing biocides of isothiazolinones. Their production and usage volume have sharply increased since the pandemic of COVID-19, inevitably leading to more release into water environment. However, their photochemical behaviors in water environment are still unclear. Therefore, this study investigated photodegradation properties of MIT and BIT in natural water under simulated sunlight. The results demonstrated that direct photolysis was mainly responsible for their photodegradation which occurred through their excited singlet states rather than triplet states. The quantum yields of MIT and BIT photodegradation were 11 - 13.6 × 10−4 and 2.43 - 5.79 × 10−4, respectively. pH had almost no effect on the photodegradation of MIT, while the photodegradation of BIT was significantly promoted under alkaline condition due to abundance of BIT in its deprotonated form (BIT-N−). Cl−, NO3− and dissolved organic matter (DOM) in natural water inhibited the photodegradation of both MIT and BIT, with the light screening effect of DOM being the most significantly inhibitory factor. The addition of other isothiazolinones, which possibly coexisted with MIT and BIT in actual condition, slightly inhibited the photodegradation of MIT and BIT. The estimated half-life under natural sunlight at a 30°N latitude was estimated to be approximately 1.1 days. The photodegradation pathways of MIT and BIT are similar, primarily initiated from the ring-opening at the N-S bond, with Frontier electron densities (FED) calculations suggesting the likelihood of oxidation and ·OH addition reactions at the O, N, and S sites. While the photodegradation products exhibited significantly reduced acute toxicity compared to their parent compounds, they nonetheless posed substantial chronic toxicity. These insights are vital for assessing the ecological impacts of MIT and BIT in aquatic environments.

Corrosion resistance of aluminum against acid activation in 1.0 M HCl by symmetrical ball − type zinc phthalocyanine

The inhibition effect of symmetrical Ball − type Zinc Phthalocyanine on Aluminum in 1mol/L hydrochloric acid was analyzed by electrochemical techniques. A novel ball-type zinc phthalocyanine (Zn-Pc) inhibitor has been synthesized and verified utilizing FTIR, nuclear magnetic resonance (1H NMR and 13C NMR), MALDI-TOF MS, and absorption spectroscopy (UV-Vis). In addition, laser-induced breakdown and photoluminescence spectroscopy were employed for additional study. Weight loss technique was employed to investigate the corrosion inhibition effectiveness of the synthesized Zn-Pc on Aluminum in 1mol/L hydrochloric acid at the range of variation temperatures (293–333 K). The inhibition efficiency of Zn-Pc increased with higher concentrations of Zn-Pc and decreased as the temperature increased. Furthermore, Zn-Pc demonstrated outstanding outcomes, achieving 72.9% at a very low inhibitor concentration (0.4 mmol/L) at 298 K. The experimental data for Zn-Pc Aluminum in 1mol/L hydrochloric acid obeys the Langmuir adsorption isotherm. Moreover, the corrosion system’s thermodynamic parameters and activation energy were determined. Quantum chemical calculations applying the (DFT) Density Functional Theory method was conducted and applied in this study. These calculations played a pivotal role in elucidating molecular structures and reactivity patterns. Through DFT, numerous reactivity indicators were computed, providing valuable insights into the chemical behavior of the studied compounds. These indicators, such as frontier molecular orbitals, electron density, and molecular electrostatic potential, were subsequently correlated with experimental data.

The construction of Z-scheme heterojunction ZnIn2S4@CuO with enhanced charge transfer capability and its mechanism study for the visible light degradation of tetracycline

In this study, copper oxide (CuO) was prepared by the microwave-assisted hydrothermal technique subsequently, CuO was grown in situ onto different rare metal compounds to prepare Z-scheme heterojunctions to improve the degradation efficiency of tetracycline (TC) in water environments. Various characterization proved the successful synthesis of all composite materials, and the formation of tight heterojunction interfaces, among which, the core–shell structure ZnIn2S4@CuO exhibited excellent photocatalytic degradation capability. Research results indicated that the degradation efficiency of ZnIn2S4@CuO for TC (50 mg/L) in the water environment reached 95.8 %, and the degradation rate is 2.41 times and 12.93 times that of CuO and ZnIn2S4 alone, respectively, the reason is because of the introduction of ZnIn2S4, Z-scheme heterojunction structures and internal electric field (IEF) is constructed and formed to extend the visible light response range of photocatalysts to improve electron-hole separation efficiency, and enhance charge transfer. In addition, ZnIn2S4@CuO-2 exhibited good stability and reproducibility, with no significant loss of activity after five cycles. Finally, the precise locations of free radical attack on TC were investigated by the combined use of high-resolution mass spectrometry (HR-MC) and frontier electron densities (FEDs), and a reasonable degradation pathway was provided. The results of this research provide a new and viable approach to overcome the limitations of conventional photocatalytic materials in terms of limited visible light absorption range and fast carrier recombination rates, which offers promising prospects for a wide range of applications in the field of wastewater purification.

Magnetic CoFe alloy@N-CNTs as fenton-like activator for the efficient abatement of imidacloprid: Kinetics, transformation mechanisms, and toxicity assessment

A magnetic bimetal-carbon nanohybrid, CoFe alloy@N-CNTs was designed to activate peroxydisulfate (PDS) for the degradation of imidacloprid (IMI). Under optimal conditions, 5 mg/L of IMI were completely removed within 6 h with a mineralization degree of 42.9 %. Moreover, a high rate of IMI removal was observed over a wide pH range and in the presence of different anions and humic acids. Stability tests conducted over five cycles and material characterizations confirmed the stability of CoFe alloy@N-CNTs. Furthermore, radical and non-radical oxidation contributed to the degradation process based on the results of quenching experiments, electron paramagnetic resonance (EPR), radical quantification and X-ray photoelectron spectroscopy (XPS). Hydroxylation was identified as the main degradation pathway through mass spectrometry observation, frontier electron densities (FEDs) theory calculations, fluorescence intensities and mineralization degree. Additionally, the predicted ecotoxicity of IMI and its intermediates towards three aquatic organisms using ECOSAR software was not harmful or low toxic, verifying the potential application of this technique from an ecological risk perspective. This study provides valuable insights for designing metal–carbon nanohybrids as efficient Fenton-like catalyst in water treatment.

Symmetry and reactivity of π-systems in electric and magnetic fields: a perspective from conceptual DFT.

The extension of conceptual density-functional theory (conceptual DFT) to include external electromagnetic fields in chemical systems is utilised to investigate the effects of strong magnetic fields on the electronic charge distribution and its consequences on the reactivity of π-systems. Formaldehyde, H2CO, is considered as a prototypical example and current-density-functional theory (current-DFT) calculations are used to evaluate the electric dipole moment together with two principal local conceptual DFT descriptors, the electron density and the Fukui functions, which provide insight into how H2CO behaves chemically in a magnetic field. In particular, the symmetry properties of these quantities are analysed on the basis of group, representation, and corepresentation theories using a recently developed automatic program for symbolic symmetry analysis, QSYM2. This allows us to leverage the simple symmetry constraints on the macroscopic electric dipole moment components to make profound predictions on the more nuanced symmetry transformation properties of the microscopic frontier molecular orbitals (MOs), electron densities, and Fukui functions. This is especially useful for complex-valued MOs in magnetic fields whose detailed symmetry analyses lead us to define the new concepts of modular and phasal symmetry breaking. Through these concepts, the deep connection between the vanishing constraints on the electric dipole moment components and the symmetry of electron densities and Fukui functions can be formalised, and the inability of the magnetic field in all three principal orientations considered to induce asymmetry with respect to the molecular plane of H2CO can be understood from a molecular perspective. Furthermore, the detailed forms of the Fukui functions reveal a remarkable reversal in the direction of the dipole moment along the CO bond in the presence of a parallel or perpendicular magnetic field, the origin of which can be attributed to the mixing between the frontier MOs due to their subduced symmetries in magnetic fields. The findings in this work are also discussed in the wider context of a long-standing debate on the possibility to create enantioselectivity by external fields.

Development of Ti4O7 reactive electrochemical membrane and electrochemical oxidation of naphthols in aqueous solution

Naphthols (NAPs), commonly used phenolic compounds, have significant impact on environmental risk and human health, necessitating advanced treatment methods for their degradation. In this study, a Ti4O7 reactive electrochemical membrane (REM) was developed for the electrochemical oxidation of NAPs. The Ti4O7 REM presented a porosity of 42.18 ± 2.3% and a median pore diameter of 1.21 µm. High permeability (846 LMH bar−1) was achieved at relatively low transmembrane pressure and resulted in a convection-enhanced rate constant for Fe (CN)64- oxidation of 1.7 × 10−4 m/s. The increase in current density and decrease in plate spacing had a positive influence on NAPs degradation. The TOC removal efficiencies of 1-naphthol (1-NAP) and 2-naphthol (2-NAP) were 68.6% and 63.5%, respectively at the current density of 6 mA/cm2 and plate spacing of 10 mm. Additionally, quantum chemical calculation using density functional theory (DFT) was employed to identify the active sites of NAPs through atom charge and frontier electron density (FED) calculations. Results showed that C14 and C10 were identified as the active sites for 1-NAP, while C9 and C13 were the active sites for 2-NAP. Hydroxyl radical and sulfate radical produced on the electrode surface were the main oxidants for NAPs degradation during the electro-oxidation process. The degradation pathway included hydroxylation, oxygenation, decarbonylation, and ring-open processes, which was in agreement with the theoretical calculations. Furthermore, the quantitative structure-activity relationship (QSAR) predictive model was used to assess the toxicity changes during the electrochemical oxidation process of NAPs, suggesting that the toxicity of intermediates increased at the beginning and significantly reduced at the end. This comprehensive study provides practical and theoretical insights into the application of electrochemical oxidation technique for the reduction of refractory compounds in wastewater.

A Spectroscopic Approach on Permanganate Oxidation of 1-[(4-Chlorophenyl)methyl]piperidin-4-amine in Presence of Ruthenium(III) Catalyst with DFT Analysis on Reaction Mechanism Pathway

The kinetic oxidation of 1-[(4-chlorophenyl)methyl]piperidin-4-amine (CMP) using alkaline potassium permanganate in presence of Ru(III) as catalyst was conducted spectrophotometrically at 303 K. The Pseudo first-order reaction was maintained with regard to oxidant and substrate during the reaction at an ionic strength of 0.01 mol dm-3. The first-order kinetics has been depicted with respect to catalyst Ru(III) chloride and less than unit order with substrate and medium. For the slow step, different activation parameters including ΔH# (kJ mol-1), Ea (kJ mol-1), ΔG# (kJ mol-1) and ΔS# (J K-1 mol-1) were calculated. The effect of temperature, variation of substrate concentration, oxidant, ionic strength were studied. The stoichiometry ratio of the reaction to the substrate and oxidizing agent was found to be 1:4. The products of reaction were isolated and identified as chlorobenzene and L-alanine, N-(2-aminomethylethyl)-carboxylic acid by LC-MS spectra, a suitable mechanism has been proposed and the rate laws are derived. The frontier molecular orbital (FMO) and frontier electron density (FED) of piperidiamine and the oxidative products were studied using density functional theory (DFT). The results of the theoretical calculations supported the suggested reaction pathways.

Theoretical investigation of electronic, energetic, and mechanical properties of polyvinyl alcohol/cellulose composite hydrogel electrolyte

Hydrogels are a new class of electrolytic materials employed in zinc-air batteries due to their significant on the battery's performance. However, the effectiveness of electrolytic hydrogel is affected by factors such as water content, temperature, additives, etc. Using DMol3 and molecular dynamics modeling techniques, this research aimed at investigating the electronic properties, effect of water content, and temperature on the binding energy, cohesive energy, and the mechanical properties of polyvinyl alcohol/cellulose-based composite hydrogel at the molecular level. The electronic optimized structures of the polymeric materials and parameters such as frontier molecular orbitals, band gap and electron density were analyzed. The results revealed that the binding energies of hydrogel polymer composite increased as the number of water molecules in the composite increased up to 60 % after which the binding energy decreased. In addition, the temperature increase led to a decrease in the binding energy of the composite. The cohesive energy density of the composite was highest at 40 % water content while higher temperatures decreased the cohesive energy density of the hydrogel. As the number of water molecules increased from 29 to 256, the tensile modulus increased from 0.707 × 10−3 to 2.821 × 10−3 Gpa; while the bulk modulus (K) increased in the order of K 40 > 50 > 30 > 20 > 10 respectively. These results serve as a theoretical enlightenment and a guide for experimental works in the field of energy conversion and storage devices.

Electrooxidation of chlorophene and dichlorophen by reactive electrochemical membrane: Key determining factors of removal efficiency

This study systematically investigated the variable main electrooxidation mechanism of chlorophene (CP) and dichlorophen (DCP) with the change of reaction conditions at Ti4O7 anode operated in batch and reactive electrochemical membrane (REM) modes. Significant degradation of CP and DCP was observed, that is, CP exhibited greater removal efficiency in batch mode at 0.5–3.5 mA cm−2 and REM operation (0.5 mA cm−2) with a permeate flow rate of 0.85 cm min−1 under the same reaction conditions, while DCP exhibited a faster degradation rate with the increase of current density in REM operation. Density functional theory (DFT) simulation and electrochemical performance tests indicated that the electrooxidation efficiency of CP and DCP in batch mode was primarily affected by the mass transfer rates. And the removal efficiency when anodic potentials were less than 1.7 V vs SHE in REM operation was determined by the activation energy for direct electron transfer (DET) reaction, however, the adsorption function of CP and DCP on the Ti4O7 anode became a dominant factor in determining the degradation efficiency with the further increase of anodic potential due to the disappeared activation barrier. In addition, the degradation pathways of CP and DCP were proposed according to intermediate products identification and frontier electron densities (FEDs) calculation, the acute toxicity of CP and DCP were also effectively decreased during both batch and REM operations.

Degradation of iohexol in the Co(II)/peracetic acid system under neutral conditions: Influencing factors, degradation pathways and toxicity

Advanced oxidation processes based on peracetic acid (PAA) activation have received more attention in water treatment recently. In this study, the degradation of iohexol (IOH, a classical iodinated X-ray contrast media) in the Co(II)/PAA system under neutral conditions, which mainly produced carbon-centric radicals, was investigated. Results showed that IOH decomposition follows the pseudo-first-order kinetic with a rate constant of 0.283 min−1. Appropriately increasing concentrations of PAA or Co(II) could promote the removal of IOH, while elevating the dosage of H2O2 inhibits the elimination of IOH in the Co(II)/PAA system. The IOH elimination was affected by pH, with the best response in pH between 5 and 7 in the Co(II)/PAA system. Additionally, low Cl− doses have negligible effects whereas high Cl− impeded the breakdown of IOH. Br−, I−, HCO3−, H2PO4− and humic acid suppressed the degradation of IOH. Removal of IOH was significantly inhibited in three selected real water samples. Furthermore, six IOH degradation pathways, including H-abstraction, amide hydrolysis, amino oxidation, deiodination reaction, hydroxylate and elimination reaction, were proposed on the basis of the liquid chromatography-tandem mass spectrometry, ion chromatography and DFT theoretical calculations (Frontier electron densities and fukui functions) results. Finally, the ECOSAR assessment showed that some degradation byproducts were much more toxic than IOH parent, but were much more biodegradable. Overall, this study indicates a potential risk when applying the carbon-centric radicals involved in PAA-based AOPs to remediate halogenated organic pollutants in water.

Grape bunches of novel conjugated chain bonded fullerene oligomers: design of a potential electron trap carbonaceous molecular material.

Developing π electron conjugated groups as covalent bonded bridges between fullerenes in their oligomers is key to optimizing and maximizing functions of the fullerene-based materials. In this work, a series of novel conjugated chain bonded fullerene C60 oligomers (CBFOs) with a well-defined nano-architecture and "grape bunches" shapes are rationally designed and viably constructed based on fullerene-carbenes by means of DFT calculations. The results show that the presently designed CBFOs present a much better electron-accepting ability together with a much lower reorganization energy than the isolated fullerene C60, and characterized as the potential ideal candidate for electron acceptors. The frontier molecular orbital and electron density analysis can well support the results of diabatic electron affinity (EAa) and vertical electron affinity (EAv) calculations. Moreover, these CBFOs exhibit strong absorption in the visible region but no obvious absorption in the ultraviolet region. In addition, the optical properties of the CBFOs and two dimensional structure are also simulated and explored theoretically. We hope that the present study would be helpful for developing covalent-bonded-fullerene based electron trap molecular materials, building blocks of nano-devices and nano-machinery applications.

Interfacial charge transfer effects of α-Fe2O3/Cu2O heterojunction and enhancement mechanism of its photocatalytic oxidation

In order to construct Cu2O based heterostructures with high efficiency of interfacial charge transfer and clarify the enhancing mechanism of its photocatalytic performance for degrading antibiotics, and reveal the characteristics of band reconstruction and the photocatalytic reaction path, the α-Fe2O3/Cu2O heterojunction was established based on hydrothermal method. The crystal plane structure, morphological state, photoelectric conversion properties and photocatalytic degradation kinetics of α-Fe2O3/Cu2O heterojunction were revealed by XRD, XPS, UV-Vis, BET, SEM, TEM and RSM, and the reconstruction principles of bandgap formations of heterojunction were analyzed by the density function theory. The reaction intermediates of levofloxacin were distinguished with HPLC-MS/Ms, and the reactive sites and photocatalytic oxidation paths of levofloxacin were clarified from the frontier electron density calculation. It turned out that the constructed α-Fe2O3/Cu2O heterojunction emerged high energy (111) preferred crystal plane orientation and significantly enhanced the specific surface area and visible spectral excitation efficiency. The micromorphologies of Cu2O, M1-Cu2O, M2-Cu2O and M3-Cu2O crystals were cube, irregular polyhedron and approximate sphere, respectively. The introduction of Fe 3d hybrid orbital in α-Fe2O3/Cu2O heterojunction widened the band gap of Cu2O microcrystals, resulting in the migration of spectral absorption edging to high energy level and causing blueshift. Photogenerated superoxide radicals and hydroxyl radicals were the dominant active species for photocatalytic oxidation of levofloxacin. The removal rate of levofloxacin by α-Fe2O3/Cu2O heterojunction could still reach more than 70% after eight cycles and show high material durability. The ring opening reaction process and decarboxylic reaction of quinolone group and piperazine side chain were the main pathways for photocatalytic oxidation of levofloxacin. This study systematically revealed the interfacial charge transfer characteristics and photocatalytic reaction mechanism of α-Fe2O3/Cu2O heterojunction.

Mechanistic study of electrooxidation of coexisting chloramphenicol and natural organic matter: Performance, DFT calculation and removal route

The electrooxidation performance of coexisting chloramphenicol (CAP) and natural organic matter (NOM) by Ti4O7 anode was systematically investigated in this study. Intrinsic reaction kinetics showed that the removal of CAP followed pseudo-first-order kinetics, 72.42 ± 0.20 % removal with 40.79 ± 0.41 % mineralization rate of CAP was achieved in 60 min using 5 mA cm−2. The oxidation mechanisms of CAP were elucidated by density functional theory (DFT) simulations and experiments involving hydroxyl free radical (•OH) scavenger, which indicated that the efficient degradation of CAP was attributed to the combined action of •OH attack and direct electron transfer (DET) reaction. The degradation pathway of CAP was proposed based on frontier electron densities (FEDs) calculation and intermediate products identification, and less ecological risks of CAP degradation solution were also proved by acute toxicity test. Humic acid (HA), selected as the typical NOM, could inhibit the degradation of CAP to a certain extent by competitive action for electrooxidation with effective removal and mineralization of HA, which was further confirmed based on real wastewater treatment experiments. Specifically, the degree of humification and aromaticity of HA was weakened, and some complex small molecular organic matters such as aromatic proteins were generated. These findings proved the feasibility of Ti4O7 anode electrooxidation to remove CAP antibiotics and organic matter from water, in consideration of the potential negative role of CAP and organic matter for ecological environment and human health.

Prediction of the photofading of 1‐H or 1‐ethyl derivatives of 3‐cyano‐6‐hydroxy‐4‐methyl‐5‐(p‐X‐phenylazo)‐2‐pyridone dyes and their azo‐hydrazone tautomerism: A theoretical study

AbstractThe lightfastness calculations for photofading of monoazo pyridone dyes were performed. For this purpose, all‐valence molecular orbital method PM3 was applied. Frontier electron density distribution on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was examined. The obtained parameters seem to reflect the tendency for an electrophilic attack with a singlet oxygen (1O2) atom or a nucleophilic attack with superoxide anion (O2●─) on a particular atom in a molecule. Reactivity indicators for superdelocalisability () and electron density distribution in ground and excited state were calculated. Superdelocalisabilities enable the fastness values to be explained in different chemical molecules depending on tautomeric forms in which they may occur.

Theoretical investigation on interactions between N-methylpyrrolidone-FeCl3 and components in model oil: The role of S-Fe coordination in thiophene removal

Metal-based coordinated ionic liquids (ILs) have drawn wide attention due to their high sulfide selectivity and desulfurization rate on extractive desulfurization (EDS). Here, a systematical investigation on the interactions between N-methylpyrrolidone-FeCl3 (NMP-FeCl3) and thiophene (TH) in the presence of model oil consisting of 1-octene (OCT), toluene (TOL), cyclohexane (CHA) and cyclohexene (CHE) was carried out using density functional theory (DFT). Three stable structures of NMP-FeCl3-TH complexes at room temperature (298 K) were taken into consideration to compare different interactions between NMP-FeCl3 and TH. The interactions were analyzed using natural bond orbital, atoms in molecules theory, independent gradient model based on Hirshfeld partition, frontier molecular orbital theory and electron density difference. Results show that π-π stacking interactions, hydrogen bonds, CH···π interactions and S-Fe coordination exist in the complexes of NMP-FeCl3 and TH/OCT/TOL/CHA/CHE. The coordination of lone-pair electrons in S atom and empty orbital in Fe atom is the strongest interactions among all complexes, and thus is demonstrated as the predominant desulfurization mechanism of NMP-FeCl3 IL extracting TH from fuel oils.

N/B co-doped polymeric carbon nitride with boosted charge transfer property and enhanced photocatalytic degradation of tetracycline

Polymeric carbon nitride (PCN) is an excellent metal-free photocatalyst. Nevertheless, its application has been seriously limited due to its inherent shortcomings such as the rapid recombination of charge carriers, insufficient light absorption capacity and slow reaction kinetics. The hetero/homo-atom doping was believed as an effective method to improve the photocatalytic performance of PCN. Herein, N/B co-doped PCN (NBCN) was synthesized by a facile one-step thermal condensation method with the assistant of recrystallization. The characterization results of XPS and NMR verified that N and B were successfully doped into the tri-s-triazine units of PCN. According to the calculation of density functional theory, N/B co-doping significantly varied the electronic structure of PCN and resulted in the spatial split of HOMO and LUMO in NBCN. This facilitated the transfer and separation of charge carriers, consequently, leading to a better photocatalytic performance. The photocatalytic degradation rate of tetracycline over NBCN was 2.5 times that over PCN. Additionally, the vulnerably attacked sites in the tetracycline molecular were predicted by Frontier Electron Densities. The possible degradation intermediates and pathways were proposed with the help of HPLC-MS analysis. Furthermore, the acute toxicity testing revealed that the global toxicity of the treated solution decreased gradually during photocatalysis.

Energy band reconstruction mechanism of Cl-doped Cu2O and photocatalytic degradation pathway for levofloxacin

Cl-doped Cu 2 O microparticles were prepared by hydrothermal synthesis . XRD, BET, SEM, TEM, UV–Vis and RSM were used to reveal the microstructure, optical properties and degradation regularity of the Cl-doped Cu 2 O microparticles. The band gap structures and state densities of Cl-doped Cu 2 O microparticles were computed based on density functional theory . The major intermediate degradation products and potential photocatalytic degradation pathways of levofloxacin were identified by HPLC–MS/MS. The photocatalytic active sites of levofloxacin and its intermediate products were calculated based on the frontier electron densities. The results showed that the prepared Cl-doped Cu 2 O microparticles increased the specific surface area and absorption efficiency of visible light compared with undoped pure Cu 2 O. The doping of Cl introduced hybrid orbitals and oxygen vacancy defects in the Cu 2 O crystal cell and decreased the forbidden bandwidth of Cu 2 O crystal microparticles, leading to a redshift of the absorption edge . Cl doping could form a shallow donor impurity energy level composed of Cl 3 p orbital in the energy gap of Cu 2 O and make the energy band denser and move to a lower energy, which could promote the electron leap to the conduction band through the impurity level . The doping of Cl can make the density of states curve of the Cu 2 O crystal shift to low-energy and the Cl-doped Cu 2 O rendered to half-metallic behavior and characteristic behavior of an n type semiconductor. The photocatalytic degradation of levofloxacin was attributed to attack of photogenerated holes and hydroxyl radicals , and the ring opening of the piperazine ring by oxidation and decarboxylation reactions from the quinolone ring might be two photocatalytic degradation pathways. This study revealed the mechanism of oxygen vacancy formation and the change rules of the band structure by doping of the nonmetal chlorine into Cu 2 O crystallites . • Migration laws of band structure and state density of Cl-doped Cu 2 O were revealed. • Doping of Cl introduced hybrid orbitals and oxygen vacancies in the Cu 2 O crystal. • Doping of Cl decreased band gap of Cu 2 O and led to red shift of absorption edge. • Holes and hydroxyl radicals are the main photocatalytic active species. • Degradation paths of levofloxacin were piperazine ring opening and decarboxylation.

Reutilization of waste self-heating pad by loading cobalt: A magnetic and green peroxymonosulfate activator for naphthalene degradation

The disposal and recovery of solid wastes and the remediation of polycyclic aromatic hydrocarbons (PAHs) are the key issues of environmental pollution control. In this study, micro cobalt loaded on iron-carbon-vermiculite composite (Co-ICV) was prepared for the first time by the reutilization of waste self-heating pad as a carrier of cobalt catalyst, which exhibited better performance than bulk cobalt catalyst in peroxymonosulfate (PMS) activation for the degradation of naphthalene (NAP) in water. Above 98% of NAP (2.0 mg/L) was effectively eliminated within 15 min by the Co-ICV (0.2 g/L) activated PMS (0.5 mmol/L) in a pH range of 5.0–9.0. High magnetism and very limited cobalt leaching realized the convenient separation and stable reusability of Co-ICV. Mechanism investigation indicated that Co(II) species were the main active sites to activate PMS decomposition for the generation of SO4•− and •OH, contributing to the rapid degradation of NAP. Meanwhile, the NAP degradation pathways were deduced via combining the identification of intermediates and the calculation of frontier electron densities (FEDs). Furthermore, the ability of the Co-ICV/PMS system for the NAP degradation in actual lake water and the removal of other refractory pollutants demonstrated that the combination of Co-ICV and PMS was a prospective method for the removal of PAHs. Overall, Co-ICV is a green and promising activator of PMS, and the future development will provide more insights into the comprehensive utilization of solid wastes for the remediation of wastewater containing PAHs.

Ultraviolet oxidative degradation of typical antidepressants: Pathway, product toxicity, and DFT theoretical calculation

The ubiquity of antidepressants in the environment has posed a potential threat to eco-systematic safety. In this study, six kinds of antidepressants including fluoxetine (FLU), paroxetine (PAR), sertraline (SER), fluvoxamine (FLX), citalopram (CTP), and venlafaxine (VEN) were selected to explore their degrading kinetics, transformation pathways, and the acute toxicity of the reaction solution during UV oxidation. The results showed that the order of the photodegradation rate was FLU > PAR > SER > CTP > FLX > VEN. The calculation results of density functional theory (DFT) and molecular orbital theory showed that it was positively correlated with the frontier electron density of drugs and negatively correlated with the HOMO-LUMO gap, respectively. Intermediates were identified with UHPLC-Q-TOF/MS/MS to propose the possible degradation pathways of the drugs and the most likely directions of the reactions were determined by the single point energy calculation. The results of toxicity tests indicated that the acute toxicity of the reaction solution of PAR did not change significantly. The photolysates toxicity of FLU, SER, and FLX decreased at the end of the reaction, while that of CTP and VEN was increased by 1.5 and 1.3 times compared with the parent compound, respectively. Toxicity predictions by the quantitative structure activity relationship (QSAR) model showed that except FLU-162, FLX-174, and VEN-230, other degradation products have developmental toxicity. The results revealed the transformation pathways of these drugs under the UV disinfection process in wastewater treatment plants, especially the formation of toxic by-products during the disinfection process.

Effect of pH and Cl- concentration on the electrochemical oxidation of pyridine in low-salinity reverse osmosis concentrate: Kinetics, mechanism, and toxicity assessment

To reduce the pressure of salt separation crystallization and contaminants removal, we systematically investigated the electrochemical oxidation of pyridine (Pyr) in low-salinity reverse osmosis concentrate (ROC) using a Ti/RuO2-IrO2 anode with a high-performance chlorine evolution reaction. We mainly focused on the pH- and Cl- concentration-dependent reaction kinetics, degradation mechanisms, and toxicity assessment. Specifically, the Pyr degradation followed a pseudo-first-order kinetic model. A pH-dependent reaction kinetics study showed that reactive chlorine species (RCS) and ·OH were the dominant species that reacted with Pyr. Furthermore, the degradation efficiency of Pyr reached its maximum value at pH 2, owing to the formation of more RCS. Additionally, Pyr degradation depends on the contribution of RCS in the presence of Cl-. Under low and high Cl- concentrations, the secondary effects were free available chlorine (FAC) and ·OH, respectively. The concentration of trichloromethane (TCM) increased to 9.96 μM first and then decreased to 5.42 μM within 90 min. The variation trend in its concentration is consistent with that of the RCS contribution under different pH and Cl- concentration. The active sites of Pyr were calculated using frontier electron density (FED) and Laplacian bond order (LBO) calculations. The degradation performance and mechanisms of Pyr, wherein ring cleavage on the 6 N atom of Pyr was the main mechanism by electrochemical treatment, were explored through theoretical calculations and gas chromatography-mass spectrometry (GC–MS) analysis. The generation of transformation products (TPs) increased the toxicity of the Pyr water after electrochemical treatment. The overall findings provide new insights into the treatment of ROC, offering significant reference information for improving water utilization and near-zero liquid discharge (near-ZLD) of real wastewater.