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 (ΔEb) 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.
Uranium is one of the most commonly detected radionuclides in the environment. Of the two most predominant oxidation states, U(VI) is much more soluble, mobile and toxic than U(IV). Consequently, converting U(VI) to U(IV) can facilitate the removal of U from water and reduce its mobility and biological exposure. In this work, stabilized zero-valent iron (ZVI) nanoparticles were prepared using starch or carboxymethyl cellulose (CMC) as stabilizers and then tested for reductive removal of U(VI) from simulated groundwater. Nearly 100% removal of U(VI) (initial U = 25 mg/L) was achieved using CMC-stabilized ZVI (Fe = 35 mg/L) at pH 6. In pH range of 6–9, the lower pH favored the reaction. CMC-ZVI nanoparticles presented better deliverability than starch-ZVI, while bare ZVI nanoparticles was almost trapped in the soil column. CMC-ZVI worked effectively in the presence of a model humic acid (up to 10 mg/L as TOC) and bicarbonate (1 mM), though higher dosages of the ligands inhibited U(VI) removal. After treatment, no re-mobilization of U was detected when aged for 6 months under anoxic conditions and the addition of strong ligands only remobilized U(VI). When exposed to oxic conditions, the immobilized U will be partially oxidized and remobilized due to the ingress of atmospheric O2 and CO2. In terms of toxicity reduction, the ZVI treated U had almost no inhibition for natural bacteria activity, while dissolved U(VI) showed significant inhibitive effects. The CMC-ZVI nanoparticles may serve as effective reactive materials to facilitate immobilization of U(VI) in groundwater, which in turn can greatly mitigate the human exposure and toxic effects of U on biota.
Interactions between graphene oxide (GO) and cell membranes play a crucial role in the nanotoxicity of GO toward organisms. However, little is known about interactions of GO with lipid membranes in the presence of heavy metals. This study investigated the attachment of GO and adsorption of heavy metals onto simulated cell membranes (spherical supported lipid bilayers, SSLBs) formed by cationic, neutral and anionic lipids, i.e., SSLB(+), SSLB(0) and SSLB(−), using batch experiments, density functional theory (DFT) calculations, and spectroscopic analyses. In the binary systems, the SSLBs bind with GO through hydrogen binding and with heavy metals via complexation. The attachment of GO or adsorption of heavy metals onto SSLBs decreased in the order SSLB(−) > SSLB(0) > SSLB(+), largely controlled by the type and number of functional groups in the SSLBs. Evidence from batch experiments, DFT calculations and spectroscopic analyses confirmed that in the ternary system GO first binds with metals, and then the GO–metal complexes attach to SSLBs via hydrogen bonding through GO rather than cation bridging through metals. Moreover, metal adsorption onto GO strengthens hydrogen bonding by withdrawing electrons from the GO surface. Therefore, in the ternary system, heavy metals promoted the GO attachment to SSLBs. However, GO suppressed the adsorption of heavy metals onto SSLBs by blocking the adsorption sites via steric hindrance. This study highlighted the importance of molecular interactions on assessing the nanotoxicity of GO to cells in the coexistence of heavy metals.
Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi5O7Br nanostructures were synthesized via a facile, low-temperature thermal treatment procedure, and their photocatalytic activity toward nitrogen fixation was evaluated and compared. Spectroscopic measurements showed that the tubular Bi5O7Br sample prepared at 40 °C (Bi5O7Br-40) exhibited the highest electron-transfer rate among the series, producing a large number of O2.– radicals and oxygen vacancies under visible-light photoirradiation and reaching a rate of photocatalytic nitrogen fixation of 12.72 mM·g–1·h–1 after 30 min of photoirradiation. The reaction dynamics was also monitored by in situ infrared measurements with a synchrotron radiation light source, where the transient difference between signals in the dark and under photoirradiation was analyzed and the reaction pathway of nitrogen fixation was identified. This was further supported by results from density functional theory calculations. The reaction energy of nitrogen fixation was quantitatively estimated and compared by building oxygen-enriched and anoxic models, where the change in the oxygen vacancy concentration was found to play a critical role in determining the nitrogen fixation performance. Results from this study suggest that Bi5O7Br with rich oxygen vacancies can be used as a high-performance photocatalyst for nitrogen fixation.
Per- and polyfluoroalkyl substances (PFAS) have emerged as a major concern in aquatic systems worldwide due to their widespread applications and health concerns. Perfluorooctanoic acid (PFOA) is one of the most-detected PFAS. Yet, a cost-effective technology has been lacking for the degradation of PFAS due to their resistance to conventional treatment processes. To address this challenge, we prepared a novel adsorptive photocatalyst, referred to Fe/TNTs@AC, based on low-cost commercial activated carbon (AC) and TiO2. The composite material exhibited synergistic adsorption and photocatalytic activity and enabled a novel “concentrate-&-destroy” strategy for rapid and complete degradation of PFOA in water. Fe/TNTs@AC was able to adsorb PFOA within a few minutes, thereby effectively concentrating the target contaminant on the photoactive sites. Subsequently, Fe/TNTs@AC was able to degrade >90% of PFOA that was preconcentrated on the solid in 4 h under UV irradiation (254 nm, 21 mW cm‒2), of which 62% was completely mineralized to F−. The efficient photodegradation also regenerated Fe/TNTs@AC, eliminating the need for expensive chemical regenerants, and after six cycles of adsorption/photodegradation, the material showed no significant drop in adsorption capacity or photocatalytic activity. Simulations based on the density functional theory (DFT) revealed that Fe/TNTs@AC adsorbs PFOA in the side-on parallel mode, facilitating the subsequent photocatalytic degradation of PFOA. According to the DFT analysis, scavenger tests, and analysis of degradation intermediates, PFOA decomposition is initiated by direct hole oxidation, which activates the molecule and leads to a series of decarboxylation, C–F bond cleavage, and chain shortening reactions. The innovative “concentrate-&-destroy” strategy may significantly advance conventional adsorption or photochemical treatment of PFAS-contaminated water and holds the potential to degrade PFOA, and potentially other PFAS, more cost-effectively.
In this work, a novel strategy for building single-atom silver-induced amorphous graphitic carbon nitride (g-C3N4) with a hollow tubular morphology is developed. By forming a tubular supramolecular gel, silver is successfully isolated by the nitrogen atoms in both melamine and nitrate anions, impeding agglomeration in the subsequent thermal polymerization. The high density of single-atom-dispersed silver (atomic ratio up to 11.6%) selectively breaks the hydrogen bonds in layered g-C3N4, leading to a fully amorphous structure. Silver-induced full amorphization not only enhances the visible light absorption of g-C3N4 but also accelerates charge transfer, endowing the as-prepared photocatalyst having the optimal silver content with 52 times higher surface area specific naproxen (NPX) removal activity than pure g-C3N4. Both density functional theory (DFT) calculations and steric effects are applied to explain the degradation pathway of NPX. The toxicity of NPX is reduced by sufficient irradiation. This work provides useful insights into the design and morphology control of single metal ion-dispersed g-C3N4 for environmental applications.
Graphitic carbon nitride (g-C3N4) is widely used as a visible-light-driven photocatalyst but limited by the rapid photoexcited electron-hole pairs recombination rate. To promote the photocatalytic activity of g-C3N4, a class of heterojunction photocatalysts, perovskite-type sodium niobate (NaNbO3) nanorods modified g-C3N4 (SNCN), was fabricated through a two-step hydrothermal and thermal polymerization method in this study. X-ray powder diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) demonstrated the successful decoration of NaNbO3 onto g-C3N4, as well as the formation of material interface with high reactivity. The optimal material (SNCN-3) exhibited an extremely high degradation efficiency of ofloxacin (OFL) under simulated solar light, as the kinetic rate constant (k) was 29.6 and 10.4 times of that for the neat g-C3N4 and NaNbO3, respectively. Energy band structure analysis indicated that SNCN-3 was a type II heterojunction. Moreover, surface photovoltage (SPV), photoluminescence (PL) and transient photocurrent response measurements confirmed SNCN-3 had the highest electron-hole separation efficiency compared with NaNbO3, g-C3N4 and the other SNCN composites. Quenching tests indicated that O2– and holes were the primary reactive species for OFL degradation. Density functional theory (DFT) calculation on further revealed the atoms of OFL with high Fukui index (f 0) preferred to be attacked by the produced radicals. Cleavage of piperazine moiety and substitution of F were the key OFL degradation pathways. In addition, the reduced toxicity of transformation products after photocatalysis verified the proposed technique was a green method. This work provided the promising application of g-C3N4/NaNbO3 heterojunction photocatalysts for degradation of antibiotic pollutants in water.
Pharmaceuticals and personal care products (PPCPs) have been widely detected in ecosystems. However, effective water purification technologies for PPCPs degradation are lacking. In this work, an active activated carbon fiber supported titanate nanotubes (TNTs@ACF) composite was synthesized via one-step hydrothermal process, which was applied for adsorption and photocatalytic degradation of PPCPs under simulated solar light. Characterizations indicated that the successful grafting of TNTs onto ACF was achieved and surface modification occurred. Diclofenac (DCF, a model PPCPs) was rapidly adsorbed onto TNTs@ACF, and subsequently photodegraded (98.8 %) under solar light within 2 h. TNTs@ACF also performed well over a wide range of pH, and was resistant to humic acid. The good adsorption and photocatalytic activity of TNTs@ACF was attributed to the well-defined hybrid structure, enabling corporative adsorption of DCF by TNTs and ACF, and extending the light absorbance to visible region. Furthermore, the description of degradation pathway and evaluation of ecotoxicity for DCF and its intermediates/byproduct were proposed based on experimental analysis, density functional theory (DFT) calculation and quantitative structure–activity relationship (QSAR) analysis, respectively, indicating the photocatalytic degradation of DCF can offer the step-by-step de-toxicity. Our study is expected to offer new strategy as “pre-accumulation and in-situ destruction” for environmental application.
Electrokinetic remediation is an effective technology for soil contaminated with heavy metals. However, little is known about the fate of antibiotic resistance in the process under heavy metal stress, since antibiotic resistance genes (ARGs) are widely distributed and can be co-selected with heavy metals. This study focused on antibiotic resistant bacteria and ARGs over different remediation periods (1, 2, and 5 days), voltages (0.4 and 0.8 V cm−1), and initial concentrations (250–1,000 mg kg−1 for Cu, and 1,000–3,000 mg kg−1 for Zn). The application of polarity-reversal maintained a suitable pH, eliminating possible negative effects on soil quality. In addition to a decrease in total metals, the speciation was modified as residual forms decreased while reactive forms increased. Compared with anti-oxytetracycline bacteria, anti-sulfamethoxazole bacteria were more resistant to the electric field, which might be ascribed to greater constraints on their resistance enzymes. The presence of heavy metals accelerated the spread of ARGs, with a 2.67-fold increase for tetG, and a 3.86-fold increase for sul1. Among the ARGs studied, tetM and tetW, as well as sul genes were more easily removed than tetC and tetG genes. Finally, a significant correlation was found between ARGs and Cu, consistent with the relatively stronger toxicity of Cu and its high potential to induce the SOS response. This study advances the understanding of how electrokinetics influences antibiotic resistance in soil with heavy metals, which has important implications for the simultaneous control of these pollutants in soil.
Organic Matter (OM) with different molecular weight and functional groups can impact the adsorptive removal of metal ions, and the influence trend can be facilitated, inhibited or unchanged. However, the association capabilities of different ligands were superficially expounded. Based on the sorption behavior of Cr(III) onto titanate nanotubes (TNTs) with coexisting citric acid (CA), humic acid (HA) and fulvic acid (FA), this study highlighted differential absorbance and DFT simulations to quantitatively detect the mutual effect. As results, adsorption capacities of Cr(III) obviously enhanced from ca. 60 mg/g to 85 mg/g with CA or FA; while HA can slightly promote Cr(III) adsorption. UV spectra scanning proved that FA and HA led to the remarkable red shift of peak A1 (232 nm), A2 (262 nm), A3 (295 nm), A4 (431 nm) of Cr(III), and the area ratio of A2/A3 followed the order Cr-HA > Cr-FA > Cr-CA ≈ Cr. DFT calculations further confirmed that the simultaneous formation of ligand-metal-adsorbents complex and electrostatic effect promoted Cr(III) adsorption, with binding energies of −202.9 −420.8 kJ/mol and − 3958 kJ/mol, respectively. Meanwhile, the bridge connection of OM mainly appeared in the outer sphere of TNTs, as the larger molecular scale prevented their insertion into the inner spacing of TNTs, especially for HA and FA. Therefore, the adsorption mechanism was the combined actions of electrostatic attraction, bridge connection of OM and steric effect. This study can give insights into OM effects on metal adsorption, and quantificationally describe the junction state of ternary complex.
Up to now, titanium dioxide (TiO2) is the most established semiconductor photocatalyst, which is used to achieve photocatalytic H2 evolution, pollutants degradation, CO2 reduction, and N2 reduction under UV light irradiation. TiO2 as photocatalyst is always under the spotlight due to its unique properties like outstanding thermal/chemical stability, wide bandgap with suitable band edge, low cost, non-toxicity, and corrosion resistance. To further improve the photocatalytic activity of TiO2, the versatile and porous metal-organic frameworks (MOFs) can be introduced to constructionTiO2/MOF composites, which can accomplish the enhanced light absorption performance and improved electron-hole pair separation. With this review, the fabrication strategies, characterizations techniques, photocatalytic activities and the mechanisms of some selected TiO2/MOF composites were reviewed and highlighted. The last but not the least, the outlooks and challenges of TiO2/MOF composites as photocatalysts for energy conversion and environment remediation are proposed.
Covalent organic frameworks (COFs) have recently been demonstrated to have great application potentials in water treatment. Their photocatalytic performance towards bacterial disinfection and organic pollutant degradation yet has seldom been investigated. In this study, AgI modified COFs (using 2,5-diaminopyridine and 1,3,5-triformylphloroglucinol as precursors) (COF-PD/AgI) were fabricated and their applications to photocatalytically disinfect bacteria and degrade organic pollutants were investigated. COF-PD/AgI exhibited effective photocatalytic performance towards Escherichia coli disinfection and organic pollutant (Rhodamine B and acetaminophen) degradation. SEM images were employed to investigate cell disinfection process, while theoretical density functional theory (DFT) calculation and intermediates determination were used to elucidate organic pollutant degradation processes. Scavenger experiments, ESR spectra and chemical probes experiments confirmed O2−, h+ and OH played important roles in the photocatalytic process. The formation of dual-band Z-scheme heterojunction improved photocatalytic performance. COF-PD/AgI remained high photocatalytic activity in the four consecutive cycles and could serve as a promising photocatalyst for water purification.
In this study, natural chalcopyrite (NCP) was employed in the activation of peroxymonosulfate (PMS) for bisphenol S (BPS) degradation. Firstly, the NCP catalyst was characterized via X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) techniques. Then, several key parameters such as catalyst dosage, PMS dosage and initial pH were investigated in NCP/PMS system. Furthermore, the transformation of various free radicals (SO4•−, •OH and O2•−) with the changes of initial pH were investigated by quenching experiments and electron spin resonance (ESR) study. Also, sulfur species cycling of copper and iron species were investigated via exogenous Cu2+ and Fe3+ addition experiments and X-ray photoelectron spectroscopy (XPS) analysis, the result indicated that sulfur species promoted Fe3+/Fe2+ and Cu2+/Cu+ cycles on the NCP surface. Furthermore, thirteen major degradation intermediates of BPS were detected by UPLC-QTOF-MS/MS and density functional theory (DFT) method was used to illustrate possible reaction pathways of BPS. Finally, a reasonable reaction mechanism of NCP/PMS system for BPS degradation was proposed on the basis of the comprehensive analysis. In brief, this work helps to provide useful information for the application of natural metallic sulfide minerals in treatment of contaminated waters.
A series of CuCo2O4 composite spinels with an interconnected meso-macroporous nanosheet morphology were synthesized using the hydrothermal method and subsequent calcination treatment to activate peroxymonosulfate (PMS) for benzophenone-4 (BP-4) degradation. As-prepared CuCo2O4 composite spinels, especially CuCo-H3 prepared by adding cetyltrimethylammonium bromide, showed superior reactivity for PMS activation. In a typical reaction, BP-4 (10.0 mg/L) was almost completely degraded in 15 min by the activation of PMS (200.0 mg/L) using CuCo-H3 (100.0 mg/L), with only 9.2 μg/L cobalt leaching detected. Even after being used six times, the performance was not influenced by the lower leaching of ions and surface-absorbed intermediates. The possible interface mechanism of PMS activation by CuCo-H3 was proposed, wherein a unique interconnected meso-macroporous nanosheet structure, strong interactions between copper and cobalt, and cycling of Co(II)/Co(III) and Cu(I)/Cu(II) effectively facilitated PMS activation to generate SO4•– and •OH, which contributed to BP-4 degradation. Furthermore, combined with intermediates detected by liquid chromatography quadrupole time-of-flight mass spectrometry and density functional theory calculation results, the degradation pathway of BP-4 involving hydroxylation and C–C bond cleavage was proposed.
Radioactive wastewater containing high concentration of radionuclides poses severe threats to ecosystem and human health, so efficient removal of these toxic heavy metals is urgently needed. Titanate nanomaterials have been demonstrated good adsorbents for heavy metals due to ion exchange property. In this study, titanate nanorings (TNRs) were synthesized using the facile hydrothermal-cooling method. The TNRs were composed of sodium trititanate, with a chemical formula of Na0.66H1.34Ti3O7•0.27H2O and a Na content of 2.38 mmol/g. The TNRs demonstrated sufficient adsorption performance to radionuclides europium (Eu) and uranium (U) ions. Specifically, even at a high initial concentration of 50 mg/L, 86.5% and 92.6% of the two metal ions can be rapidly adsorbed by the TNRs within 5 min, and equilibrium was reached within 60 min at pH 5. The maximum adsorption capacity (Qmax) obtained by the Langmuir isotherm model was 115.3 mg/g for Eu(III) and 282.5 mg/g for uranium U(VI) at pH 5, respectively. The adsorption capacities of the two metals under various water chemical conditions were highly related to their species. Ion exchange between metal cations and Na+ in the TNR interlayers was the dominant adsorption mechanism, and adsorption of U(VI) was more complicated because of the co-existence of various uranyl (UO22+) and uranyl-hydroxyl species. The spent TNRs were effectively regenerated through an acid-base or ethylenediamine tetraacetic acid (EDTA) treatment and reused. Considering the large adsorption capacity and quick kinetic, TNRs are promising materials to remove radionuclides in environmental purification applications, especially emergent treatment of leaked radionuclides.
Sulfachloropyridazine (SCP) was commonly used as a broad-spectrum sulfonamide antibiotic and hard to be removed through traditional sewage treatment process. In this study, we developed a simple and controllable strategy to realize in-situ construction of Co(OH)2 nanoparticles decorated urchin-like WO3 (Co(OH)2/WO3), which could efficiently remove SCP through peroxymonosulfate (PMS) activation. Some tiny nanoparticles of Co(OH)2 decorated on the spines/nanorods or surfaces of urchin-like WO3 by transmission electron microscopy (TEM) analysis. The obtained 10 wt% Co(OH)2/WO3 realized completely removal of SCP (degradation efficiency 100%) with a high reaction rate constant (k1) of 0.88 min−1 within 3 min at optimal pH 7. That was because the urchin-like WO3 with numerous adsorption functional groups on its surface (e.g., W = O and –OH bonds) could adsorb the Co2+ easily to form CoOH+, which was perceived the rate-limiting step for PMS activation and generating radicals. Radical quenching experiments indicated that SO4•− played a more significant role than HO• radicals. Density functional theory (DFT) calculation revealed that the atoms of SCP with high Fukui index (f−) were active sites, which preferred to be attacked by the electrophilic SO4•− and HO• radicals. The toxicity of the intermediates by SCP degradation was evaluated by quantitative structure–activity relationship (QSAR) prediction through Toxicity Estimation Software Tool (T.E.S.T.). The possible degradation pathway and catalytic mechanism for SCP removal were proposed. Considering the good catalytic properties of Co(OH)2/WO3-PMS, the material will show great application potential in the removal of emerging contaminants in water.
Arsenic contamination has attracted worldwide concerns, owing to its toxicity and severe threat to human and environment. It is urgent to develop efficient adsorbents to remove arsenic pollutants. Within this paper, both pristine MIL-88A(Fe) and MIL-88A(Fe) decorated on cotton fibers were successfully fabricated using an eco-friendly method. The pristine MIL-88A(Fe) displayed outstanding adsorption performances towards four selected arsenic pollutants, in which the adsorption capacities toward As(III), As(V), ROX and ASA were 126.5, 164.0, 261.4 and 427.5 mg g−1, respectively. Additionally, MIL-88A(Fe) exhibited excellent removal efficiencies in a wide pH range and with the presence of different co-existing ions. It was proposed that the coordinative interactions of As–O–Fe between arsenic pollutants and MIL-88A(Fe) contributed to the superior adsorption performances. Furthermore, two MIL-88A(Fe)/cotton fibers composites were synthesized by both post synthesis (MC-1) and in-situ synthesis (MC-2), which demonstrated identically outstanding adsorption activities toward four selected arsenic pollutants. MC-1 and MC-2 enhanced the stability and reusability of MIL-88A(Fe), which was challenging issues of pristine MIL-88A(Fe) powder. Additionally, the fixed-bed column packed by MC-1 or MC-2 can continuously eliminate arsenic pollutants from the water flow. This work provided a new possibility of metal-organic frameworks to accomplish potentially large-scale application to purify the arsenic-contaminated water.
Ozone-based technologies are used for micro-pollutants removal in wastewater treatment. However, the generation of the toxic by-product bromate (BrO3−) is of a great concern. LaCoO3 (LCO) catalytic ozonation has been used to overcome this significant drawback in the sole ozonation, achieving better BrO3− elimination efficiency. However, a key challenge is how to enhance micro-pollutant (benzotriazole, BZA) degradation efficiency and to eliminate formed BrO3− synchronously under various water qualities in drinking water or wastewater treatment. Therefore, the objective of this study is to propose a practical strategy of BZA removal and BrO3− reduction synchronously in water or wastewater treatment. In this study, important factors influencing BZA removal and BrO3− reduction were investigated, including [catalyst], [BZA], initial pH solution, [NH4+-N] and [(bi)carbonate alkalinity]. Based on the performance and mechanism of these effects, a practical strategy for BZA degradation and BrO3− elimination with and without Br− in the influent was developed. Additionally, the density functional theory (DFT) calculation successfully predicted the attack site on BZA by molecular ozone and formed hydroxyl radical (HO·) during LCO catalytic ozonation. Fukui indexes of f+ and f0 were calculated to forecast direct ozone molecule and HO· attack, respectively. Combination of DFT calculation with intermediates that identified through liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS), BZA degradation pathway was established more accurately. Additionally, four new intermediates were identified in this study. Overall, this study proposes a useful strategy for synchronous micro-pollutants degradation and BrO3− elimination, while also suggesting the feasibility of LCO catalytic ozonation for water or wastewater purification.
Peracetic acid (PAA) is increasingly used as an alternative disinfectant and its advanced oxidation processes (AOPs) could be useful for pollutant degradation. Co(II) or Co(III) can activate PAA to produce acetyloxyl (CH3C(O)O•) and acetylperoxyl (CH3C(O)OO•) radicals with little •OH radical formation, and Co(II)/Co(III) is cycled. For the first time, this study determined the reaction rates of PAA with Co(II) (kPAA,Co(II) = 1.70 × 101 to 6.67 × 102 M–1·s–1) and Co(III) (kPAA,Co(III) = 3.91 × 100 to 4.57 × 102 M–1·s–1) ions over the initial pH 3.0–8.2 and evaluated 30 different aromatic organic compounds for degradation by Co/PAA. In-depth investigation confirmed that CH3C(O)OO• is the key reactive species under Co/PAA for compound degradation. Assessing the structure–activity relationship between compounds’ molecular descriptors and pseudo-first-order degradation rate constants (k′PAA• in s–1) by Co/PAA showed the number of ring atoms, EHOMO, softness, and ionization potential to be the most influential, strongly suggesting the electron transfer mechanism from aromatic compounds to the acetylperoxyl radical. The radical production and compound degradation in Co/PAA are most efficient in the intermediate pH range and can be influenced by water matrix constituents of bicarbonate, phosphate, and humic acids. These results significantly improve the knowledge regarding the acetylperoxyl radical from PAA and will be useful for further development and applications of PAA-based AOPs.
It is quite important and challenging for efficient activating the molecular oxygen (O2) to reactive oxygen species (ROS), especially in environmental remediation. Herein, the CuS4 atomic clusters are constructed on the surface of ZnInS4 nanosheet (CuS4-ZIS), which shows much better ability for activating O2 to ROS than pristine ZnInS4 nanosheet (ZIS) and the CuS3.6 atomic clusters counterpart (CuS3.6-ZIS). Results display that CuS4-ZIS can energetic favorably adsorb the O2 and more electrons could transfer from the CuS4-ZIS to O2 than ZIS and CuS3.6-ZIS. Besides, a better charge separation and transfer is observed on CuS4-ZIS. Thus, higher concentration of superoxide radicals (·O2−, partially transformed into ·OH) can be generated over Cu-S4 atomic clusters under light illumination. Therefore, CuS4-ZIS exhibits higher degradation efficiency of tetracycline (TC) than pristine ZIS and CuS3.6-ZIS. Moreover, the degradation pathway of TC is proposed based on the results of HPLC-MS and the theoretical calculations.