Intermediate Toxicity Research Articles

A novel magnetic CuFeAl-LDO catalyst for efficient degradation of tetrabromobisphenol a in water

• CuFeAl-LDO catalyst showed higher catalytic activity and better stability. • The co-existence of metal species enhanced the synergistic degradation property. • SO 4 •– , •OH and 1 O 2 were the main active species in CuFeAl-LDO/PMS system. • Response surface optimization could predict degradation performance effectively. • The degradation mechanism and toxicity of intermediates was investigated. Layered double hydroxide (LDHs) precursors were successfully prepared by co-precipitation method, and then the magnetic Cu 1 Fe 0.5 Al 0.5 -LDO catalyst was constructed and characterized after high-temperature calcination. In the Cu 1 Fe 0.5 Al 0.5 -LDO catalyst activated peroxymonosulfate (PMS) to degrade tetrabromobisphenol A (TBBPA) system, the effects of different reaction parameters, including catalyst dosage, PMS concentration, initial pH, common anion and natural water organic matter on the degradation of TBBPA were investigated. The results showed that the degradation rate of TBBPA (15 mg/L) by 0.1 g/L Cu 1 Fe 0.5 Al 0.5 -LDO catalyst and 0.5 mM PMS reached 99.91% within 60 min under the conditions of weak alkaline (pH = 8.5), and the reaction conditions were further optimized by response surface methodology. In addition, the magnetic Cu 1 Fe 0.5 Al 0.5 -LDO catalyst showed certain stability and reproducibility after 5 consecutive repeated reactions. The excellent degradation of TBBPA was mainly attributed to the existence of a large amount of SO 4 •– , •OH and 1 O 2 active species in the Cu 1 Fe 0.5 Al 0.5 -LDO/PMS system. The activation mechanism of PMS and the degradation pathway of TBBPA were proposed. Toxicity Assessment Software Tool (TEST) indicated that the Cu 1 Fe 0.5 Al 0.5 -LDO/PMS system can effectively reduce the harm and risk of TBBPA to the overall environment. This work provided a possible novel idea for the application of Cu 1 Fe 0.5 Al 0.5 -LDO/PMS system in the degradation of brominated phenolic organic pollutants in actual water.

Biofilm response and removal via the coupling of visible-light-driven photocatalysis and biodegradation in an environment of sulfamethoxazole and Cr(VI)

The widespread contamination of water systems with antibiotics and heavy metals has gained much attention. Intimately coupled visible -light-responsive photocatalysis and biodegradation (ICPB) provides a novel approach for removing such mixed pollutants. In ICPB, the photocatalysis products are biodegraded by a protected biofilm, leading to the mineralization of refractory organics. In the present study, the ICPB approach exhibited excellent photocatalytic activity and biodegradation, providing up to ∼1.27 times the degradation rate of sulfamethoxazole (SMX) and 1.16 times the Cr(VI) reduction rate of visible-light-induced photocatalysis . Three-dimensional fluorescence analysis demonstrated the synergistic ICPB effects of photocatalysis and biodegradation for removing SMX and reducing Cr(VI). In addition, the toxicity of the SMX intermediates and Cr(VI) in the ICPB process significantly decreased. The use of MoS2/CoS2 photocatalyst accelerated the separation of electrons and holes, with•O2– and h+ attacking SMX and e– reducing Cr(VI), providing an effective means for enhancing the removal and mineralization of these mixed pollutants via the ICPB technique. The microbial community results demonstrate that bacteria that are conducive to pollutant removal are were enriched by the acclimation and ICPB operation processes, thus significantly improving the performance of the ICPB system.

Degradation of norfloxacin by MOF-derived lamellar carbon nanocomposites based on microwave-driven Fenton reaction: Improved Fe(III)/Fe(II) cycle

In this paper, a new type of iron-based magnetic nanoparticle material embedding mesoporous carbon (Fe@C700) was prepared by simple pyrolysis of a MIL-101-Fe precursor and employed in the microwave-catalyzed degradation of norfloxacin (NOR) with the presence of H2O2. Characterization results showed successful anchoring of Fe0 nanoparticles in the carbon matrix. Under optimal treatment conditions (Calcination temperature = 700 °C, H2O2 dosage = 40 mM, MW power = 500 W, NOR dosage = 50 mg L−1 and initial pH = 4), the degradation efficiency of NOR reached 95.22%. The catalyst showed exceptional degradation properties over a relatively wide pH range. The mesoporous carbon in the catalyst promoted electron transfer, enhanced the Fe(III)/Fe(II) cycle, increased contact between Fe0 and Fe2+ with H2O2, and accelerated the production of ·OH. Furthermore, density functional theory (DFT) calculations were used to predict the fragile active sites in NOR and to analyze the degradation pathway of NOR in combination with intermediates. Fe@C700 retained good activity after 5 cycles. Reduced toxicity of intermediates predicted by T.E.S.T. compared to NOR. This study presented a new avenue for the rational design of Fe0-carbon composites as microwave-assisted Fenton-like catalysts for potential applications in wastewater treatment.

Removal of chlorhexidine digluconate from aqueous solution by heterogenous photocatalysis using sunlight-driven Ni-doped TiO2 material

Photoactive Ni-TiO2 was synthesized through green hydrothermal method with preferential photocatalytic performance in visible and solar light for synthetic and formulated wastewater treatment. Incorporation of this transition metal into TiO2 was examined by XRD, FTIR, UV–visible DRS, XPS, SEM-EDS and HRTEM analysis. According to the Langmuir–Hinshelwood model, the photodegradation of the chlorhexidine digluconate under solar (R2=0.986) and simulated visible light (R2=0.982), follows a pseudo-first-order kinetics. The interaction of operational fractions, such as S/C ratio, irradiation time, and pH of the reaction mixture, were evaluated using the RSM. Although complete mineralization of CHD was not achieved using Ni-TiO2 under visible light, but the parent compound was mineralized to some extent, as demonstrated by TOC reduction (85.71%-synthetic wastewater and 61.17%-formulated wastewater), UV254 (89.91% synthetic wastewater and 55.39%-formulated wastewater) and UV280 (68.23%-synthetic wastewater and 68.23%-formulated wastewater) absorbance variations. Based on the identified transformed products, the possible degradation pathway was proposed and bacterial susceptibility test on Bacillus cereus DPAML065 was performed to evaluate the toxicity of oxidation intermediates. Comparative studies about energy consumption and removal efficiency during simulated visible light/Ni-TiO2 and sunlight/ Ni-TiO2 mediated treatment system for formulated wastewater revealed that sunlight/ Ni-TiO2 mediated treatment system was high energy efficient (1.67 kWhKg-1) system.

Photocatalytic removal of tetracycline by a Z-scheme heterojunction of bismuth oxyiodide/exfoliated g-C3N4: performance, mechanism, and degradation pathway

Antibiotics, once being released into the environment, become recalcitrant organic pollutants, which pose a potential risk to ecological balance and human health. In this study, a Z-scheme heterojunction of bismuth oxyiodide (BiOI)/exfoliated g-C3N4 (BiOI/ECN hereafter) was synthesized by the combination of thermal exfoliation of g-C3N4 and chemical precipitation of BiOI for efficient photocatalytic degradation of tetracycline in aqueous solutions under visible light irradiation. The optimized BiOI/ECN delivered an outstanding degradation rate at circa 0.0705 min−1, which was 10 times higher than that of the bulk g-C3N4. The photocatalytic degradation efficiency of tetracycline remained almost unchanged in a pH range of 3–11, and the BiOI/ECN displayed an excellent photostability upon recycled usage. The photocatalytic mechanism of tetracycline was ascribed to the main reactive oxidation species of photogenerated holes and superoxide radicals. In addition, the possible degradation pathways of tetracycline were investigated by HPLC-MS to identify intermediates. The toxicity of photocatalytic-generated intermediates of tetracycline was found significantly alleviated according to the calculation of quantitative structure–activity relationship prediction. This work not only provides an attractive photocatalyst for the removal of tetracycline but also opens a new avenue for rational design of Z-scheme heterojunction composites for tetracycline degradation.

Catalytic degradation of sulfamethoxazole by peroxymonosulfate activation system composed of nitrogen-doped biochar from pomelo peel: Important roles of defects and nitrogen, and detoxification of intermediates

Nitrogen doping could improve the catalytic performance of carbon materials, in which the nitrogen configuration could be used as active sites for peroxymonosulfate (PMS) activation. Herein, this paper studied how to turn waste to “treasure” by agriculture waste pomelo peel to prepare nitrogen-doped biochar and successfully applied it to advanced oxidation field. The effects of the sodium bicarbonate (NaHCO3), melamine, and pyrolysis temperature on the catalytic activity of biochar for the removal of sulfamethoxazole (SMX) were investigated. The optimized nitrogen-doped biochar (C−N−M 1:3:4) possessed high specific surface area (SSA, 738 m2/g) and high level of nitrogen doping (nitrogen content 13.54 at%). Accordingly, it exhibited great catalytic performance for PMS activation to remove SMX antibiotic, and 95% of SMX was removed within 30 min. High catalytic activity of C−N−M 1:3:4 was attributed to rich defects, carbonyl group, high content of graphitic N and pyrrolic N, and large SSA, in which non-radical oxidation process based on singlet oxygen (1O2) and electron transfer contributed to the SMX degradation. The prepared nitrogen-doped biochar possessed high stability and reusability and the removal efficiency of SMX still reached 80% after four cycles. Additionally, the phytotoxicity assay indicated that the toxicity of degradation intermediates was obviously decreased in the PMS/ C−N−M 1:3:4 system.

Designing Oxygen Vacancy Mediated Bi2moo6/C3n5 S-Scheme Heterojunctions for Boosted Photocatalytic Removal of Tetracycline Antibiotic and Cr(Vi): Intermediate Toxicity and Mechanism Insight

Designing Oxygen Vacancy Mediated Bi2moo6/C3n5 S-Scheme Heterojunctions for Boosted Photocatalytic Removal of Tetracycline Antibiotic and Cr(Vi): Intermediate Toxicity and Mechanism Insight

Valuable cobalt/biochar with enriched surface oxygen-containing groups prepared from bio-waste shrimp shell for efficient peroxymonosulfate activation

Converting bio-waste shrimp shell into valuable cobalt-based biochar with enriched surface oxygen-containing groups for high-efficiency ciprofloxacin degradation via advanced oxidation technology is achieved. • The synergy of in-situ formed CoSiO x and biochar in the designed composites. • As-fabricated composites can efficiently activate PMS for CIP degradation. • Activation mechanism followed by multi-reaction pathways. • Degradation pathways and toxicity assessment were systematically researched. Efficient activation of peroxymonosulfate using cobalt-based heterogeneous catalytic composites to produce highly reactive oxygen species for the degradation of toxic organic pollutants has been paid increased attention nowadays; however, the concept of transforming bio-waste into valuable cobalt-based catalysts remains much room to undertake. Herein, the natural marine bio-waste shrimp shell with a high total silicon content was firstly utilized as functional matrix for cobalt species to activate peroxymonosulfate for environmental remediation is reported. Remarkably, benefiting from the cooperative synergistic effect between in-situ formed CoSiO x and biochar, onto which is enriched in abundant surface functional groups, the resultant Co-SSP-700 with high specific surface area and outstanding stability exhibited prominent activity for ciprofloxacin degradation, namely nearly 90% of ciprofloxacin could be achieved within 40 min. EPR spectroscopy and scavenger tests were conducted out to investigate oxygen species, illustrating that the possible activation mechanism of PMS mainly ran through the multi-reaction pathways, whereas the radical mechanism induced by SO 4 •− and O 2 •− was a determining factor. More importantly, the intermediates of ciprofloxacin degradation were identified by LC-MS analyses to propose the possible degradation pathways and the aquatic toxicity of intermediates was explored by constructing a QSAR model.

Acute toxicity of Galium odoratum to the freshwater cladoceran Moina macrocopa

Galium odoratum (L.) is a medicinal plant with a number of health benefits, used in traditional and modern medicine. The toxicity of the coumarin in Galium odoratum is classified as high, however, no experimental data or data on toxic effects in humans following intake of Galium odoratum are available. The potential toxic effect can be estimated based on the content of coumarin and knowledge of its toxicity. The aim of the current study is to evaluate the acute toxicity effects of a range of concentrations of Galium odoratum water extract on Moina macrocopa and calculate the LC50 within 24 hours. In order to compare the toxicity with those of other, well-known and widely used medicinal plants, extracts of Matricaria chamomilla and Tribulus terrestris are also tested.  The results show that LC50 value of Galium odoratum is comparable with those of Matricaria chamomilla and Tribulus terrestris, and Galium odoratum has intermediate toxicity between the two other studied species. 

Degradation of gemfibrozil in aqueous solutions by gas–liquid dielectric barrier discharge plasma combined with CNTs/γFe2O3

AbstractThe degradation effects and mechanism on gemfibrozil (GEM) in aqueous solution by dielectric barrier discharge (DBD) plasma combined with the catalyst CNTs/γFe2O3 are investigated. The concentrations of plasma‐generated reactive species, including H2O2, O3, , and OH, are measured with spectrophotometric and fluorescent probes. The effects of the plasma treatment period, discharge power, initial GEM concentration, solution pH value, conductivity, and the catalytic property are studied on the degradation rate and energy efficiency. Compared with the sole plasma treatment, CNTs/γFe2O3 could maximally improve the GEM degradation rate and energy efficiency to 99.7% ± 0.2% and 76.5 ± 5.2 mg·kW−1·h−1, respectively. The solution's total organic carbon removal efficiency has been increased to 47.2% ± 2.7%. Meanwhile, the possible degradation pathways of the plasma‐treated GEM solution and overall biological toxicity of GEM degradation intermediates and residual catalyst in solution are investigated.

Boosting the activation of Peroxymonosulfate and the degradation of metronidazole over FeCo2O4 quantum dots anchored on β-FeOOH Nanosheets: Inspired from octahedral Co(II) with missing angle

Peroxymonosulfate (PMS) activation by bimetallic Co/Fe oxides, especially spinel FeCo2O4, is a promising way in decontaminating organic pollutants in wastewaters. However, it suffers from low efficiency and the intrinsic catalytic mechanisms are still poorly understood. Therefore, we applied lattice VOs (oxygen vacancies) adjustment strategy to construct a octahedral Co(II)–enriched FeCo2O4 quantum dots anchored on β-FeOOH nanosheets composite (Co(II)-FCQDs/FNS) for boosting PMS activation during the degradation of Metronidazole (MNZ), and pure FeCo2O4 quantum dots (FCQDs) was studied as a comparison. As a result, in PMS/Co(II)-FCQDs/FNS system, 5–30 mg·L−1 MNZ could be completely degraded within 5 min with the usage of 0.05 g·L−1 catalyst, and the degradation efficiency of 100 mg·L−1 MNZ reached 99.92% within 40 min with the PMS utilization of 62.90% at the same condition, whose degradation rate constant was 6.45 times than that of the FCQDs/PMS system. The electron paramagnetic resonance (EPR) and quenching experiments indicated that PMS /Co(II)-FCQDs/FNS system was a pure radical-based (sulfate radicals (SO4•−), hydroxyl radicals (•OH) and superoxide radical (O2•−) oxidation process. Density functional theory (DFT) calculation revealed that the generation of octahedral Co(II) derived from oxygen vacancies, improved the charge transfer in the spinel lattice while providing a new electron transfer channel from lattice Co(II)/Fe(II) to the surface of FeCo2O4. Simultaneously, strengthened the surface adsorption of HSO5− and increased the number of unpaired electrons, thus boosting the PMS activation performance. In addition, the influence of reaction parameters and water matrix were investigated. Finally, the degradation pathway of MNZ was proposed and the toxicity of intermediates was also assessed. This work is expected to facilitate the design and application of PMS/Co(II)-FCQDs/FNS system for decontaminating organic pollutants from wastewater.

Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies.

Simple SummaryNeonicotinoids are the most widely used insecticides in North America and many studies document the negative effects of neonicotinoids on bees. Monarch butterflies are famous for their long-distance migrations, and for their ability to sequester toxins from their milkweed host plants. The neonicotinoids imidacloprid and clothianidin were suggested to correlate with declines in North American monarchs. We examined how monarch development, survival, and flight were affected by exposure to neonicotinoids, and how these effects depend on milkweed host plant species that differ in their cardenolide toxins. Monarch survival and flight were unaffected by low and intermediate neonicotinoid doses. At the highest dose, neonicotinoids negatively affected monarch pupation and survival, for caterpillars that fed on the least toxic milkweed. Monarchs fed milkweed of intermediate toxicity experienced moderate negative effects of high insecticide doses. Monarchs fed the most toxic milkweed species had no negative consequences associated with neonicotinoid treatment. Our work shows that monarchs tolerate low neonicotinoid doses, but experience detrimental effects at higher doses, depending on milkweed species. To our knowledge, this is the first study to show that host plant species potentially reduce the residue of neonicotinoid insecticides on the leaf surface, and this phenomenon warrants further investigation.Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development, survival, and flight of monarch butterflies, and how these chemicals interact with the monarch’s milkweed host plant. We first fed caterpillars field-relevant low doses (0.075 and 0.225 ng/g) of neonicotinoids applied to milkweed leaves (Asclepias incarnata), and found no significant reductions in larval development rate, pre-adult survival, or adult flight performance. We next fed larvae higher neonicotinoid doses (4–70 ng/g) and reared them on milkweed species known to produce low, moderate, or high levels of secondary toxins (cardenolides). Monarchs exposed to the highest dose of clothianidin (51–70 ng/g) experienced pupal deformity, low survival to eclosion, smaller body size, and weaker adult grip strength. This effect was most evident for monarchs reared on the lowest cardenolide milkweed (A. incarnata), whereas monarchs reared on the high-cardenolide A. curassavica showed no significant reductions in any variable measured. Our results indicate that monarchs are tolerant to low doses of neonicotinoid, and that negative impacts of neonicotinoids depend on host plant type. Plant toxins may confer protective effects or leaf physical properties may affect chemical retention. Although neonicotinoid residues are ubiquitous on milkweeds in agricultural and ornamental settings, commonly encountered doses below 50 ng/g are unlikely to cause substantial declines in monarch survival or migratory performance.

Transformation of Reactive Blue 19 by a recombinant peroxidase DyP.

Wastewater containing recalcitrant dyes causes environmental problems. A new superfamily of heme-containing peroxidases, dye-decolorizing peroxidases (DyPs), has been found to decolorize different kinds of dyes, especial anthraquinone dyes efficiently. However, the mechanism of dyes degradation by DyPs has not been fully understood and the toxicity of dye degradation intermediates by DyPs catalysis to microbes is unclear. In this study, a purified recombinant Thermobifida fusca DyP (TfuDyP) in E. coli BL21(DE3) was used to treat Reactive Blue 19 (RB19), an anthraquinone dye. The reaction intermediates analyzed by ultra performance liquid chromatography/mass spectroscopy (UPLC-MS) indicated the initial site of TfuDyP attack on RB19. In addition, it was found that both RB19 and its incomplete degradation products inhibited the growth of Bacillus subtilis. These findings provided a novel understanding of DyPs catalysis to anthraquinone dyes.

Unveiling the visible–light–driven photodegradation pathway and products toxicity of tetracycline in the system of Pt/BiVO4 nanosheets

The antibiotics pollution has currently captured increasing concerns due to its potential hazards to the environment and human health. The development of efficient and viable techniques for the removal of antibiotics is one of the research hotspots in fields of wastewater treatment and pharmaceutical industry. Although the photodegradation of antibiotics is widely studied, the evolution and toxicity of degradation intermediates have been rarely documented. Herein, Pt nanoparticles (NPs) decorated BiVO4 nanosheets (Pt/BiVO4 NSs) that exhibit excellent tetracycline (TC) photodegradation activity and stability have been prepared. Especially, the TC degradation efficiency reaches ca. 88.5% after 60 min under visible light irradiation, which is superior to most of the metal loaded two–dimensional photocatalysts reported hitherto. The excellent photocatalytic activity is attributable to the enhanced light absorption capacity and charge separation efficiency in Pt/BiVO4 NSs. h+, •O2− and •OH are the main active species for TC degradation, resulting in three possible degradation pathways. Furthermore, we first verify that TC solutions treated by Pt/BiVO4 NSs are harmless to Escherichia coli K–12 and various bacteria in natural rivers, which would not stimulate Escherichia coli to produce antibiotics resistance genes (ARGs). This work develops an environmentally friendly photodegradation strategy using Pt/BiVO4 NSs with potentials for efficient remediation of antibiotics pollution in wastewater.

High-efficiency carbamazepine degradation using a Ni/Co-LDH as the peroxymonosulfate activator: Performance, mechanism and degradation pathway

In this study, Ni/Co layered double hydroxide (Ni/Co-LDH) with uniform flake structure was synthesized successfully as an effective activator in the carbamazepine (CBZ) degradation by peroxymonosulfate (PMS). Our results indicated that Ni/Co-LDH possessed a high specific surface area (72.9942 m2/g) and exhibited great activation performance, in which 100% CBZ removal could be achieved within 300 s under neutral conditions with 5 mg/L Ni/Co-LDH and 0.3 mmol/L PMS. In addition, the crystal structure and morphology of the prepared Ni/Co-LDH kept unchanged during degradation cycles. X-ray photoelectron spectroscopy (XPS) analysis and free radical identification experiment speculated that the cycle of Ni2+/Ni3+ and Co2+/Co3+ on Ni/Co-LDH surface were responsible for efficient HO•/SO4•− generation from PMS. Based on identified products through high resolution mass spectrometry (HR-MS), it was proposed that the degradation pathway of CBZ was a heterozygous process involving deamidation, hydroxylation and electron transfer. The ECOSAR calculation results indicated the toxicity of some products was still at very toxic level, thus certain attention should be paid to the toxicity of intermediates in the process of treating pollutants in water.

A new UV source activates ozone for water treatment: Wavelength-dependent ultraviolet light-emitting diode (UV-LED)

The newly emerged ultraviolet light-emitting diode (UV-LED) as a new UV source may replace the conventional UV lamps for water treatment in the foreseeable future. In this study, UV-LED with four wavelengths (i.e., 255, 265, 280, and 310 nm) was used to investigate the wavelength-dependency of UV-LED/O3 process on the radical/non-radical formation and hexazinone degradation. The degradation of hexazinone in UV-LED/O3 process with different wavelengths (31.1–97.4%) was higher than that of O3 oxidation process alone (20.0%), and the hexazinone removal rate at 280 nm was the highest (97.4%). The fluence-based rate constant of hexazinone degradation in UV-LED/O3 process (0.19–2.97 × 10−5 m2·J−1) was higher than that in low-pressure UV/O3 (LPUV/O3) process (0.15 × 10−5 m2·J−1). Hydroxyl radical (·OH) and superoxide radicals (O2−) were the dominant active species in UV-LED/O3 process, and the single oxygen (1O2) was also beneficial to the degradation of hexazinone. The possible degradation pathways were proposed based on high resolution mass spectrum (MS). The reaction sites of free radicals were further predicted by density functional theory (DFT) calculations. Besides, the Toxicity Estimation Software Tool (T.E.S.T.) and Vibrio fischeri were used to estimate the potential toxicity of hexazinone and intermediates and it was suggested that alkaline environment and sufficient oxidation time were conductive to reducing the toxicity of wastewater.

Synergistically boosting sulfamerazine degradation via activation of peroxydisulfate by photocatalysis of Bi2O3-TiO2/PAC under visible light irradiation

Photocatalysis-activated sulfate-radical advanced oxidation process (SR-AOP) is an effective approach to remove organic micropollutants from water. Here, we tested a photocatalysis-activated SR-AOP in which peroxydisulfate (PDS) was activated by composites of Bi2O3-TiO2 photocatalyst supported onto commercial powdered activated carbon (Bi2O3-TiO2/PAC) under visible light irradiation. This “Vis-Cata-PDS” treatment exhibited outstanding degradation performance (97.96% removal) towards sulfamerazine (SMZ) following optimized reaction conditions of 0.1 g/L Bi2O3-TiO2/PAC and 0.1 g/L PDS at pH of 7. Synergistic effects were observed between the visible-light photocatalytic activation of PDS via direct electron transfer and nonradical PDS activation over pristine PAC within Bi2O3-TiO2/PAC. Both active radicals (SO4·−, h+, ·O2−) and nonradical singlet oxygen (1O2) and the mediated electron transfer of pristine PAC within Bi2O3-TiO2/PAC were contributed to SMZ degradation. Based on intermediates identified by Liquid Chromatograph-Mass Spectrometer (LC-MS) combined with density functional theory (DFT) calculations, three degradation pathways were proposed and that were mostly attributed to SO2 extrusion/Smiles-type rearrangement and S-N bond cleavage, and toxicity of intermediates were effectively alleviated. An inhibitory effect on SMZ degradation was observed for presence of HCO3−, whereas presence of SO42− was less inhibitory and Cl− had no effect. The Bi2O3-TiO2/PAC composite displayed excellent reusability and stability, and it was effective towards a number of tested micropollutants (sulfadiazine, sulfamethoxazole, ciprofloxacin, bisphenol A and methyl orange) and in real water matrixes. This work offers deep insights into the nonradical oxidation mechanism and application of Vis-Cata-PDS over a Bi2O3-TiO2/PAC composite for removal of organic micropollutants.

Non-radical mechanism and toxicity analysis of β-cyclodextrin functionalized biochar catalyzing the degradation of bisphenol A and its analogs by peroxydisulfate

Bisphenols (BPs) are distributed in worldwide as typical environmental hormones, which potentially harm the ecological environment and human health. In this study, four BPs, i.e., bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, were used as prototypes to identify the intrinsic differences in degradation mechanisms correlated with the molecular structures in peroxydisulfate (PDS)-based advanced oxidation processes (AOPs). Electron transfer was the main way of modified biochar to trigger the heterogenous catalysis of PDS, which can cause the degradation of BPs. Phenolic hydroxyl groups on bisphenol pollutants were considered as possible active sites, and the existence of substituents was the main reason for the differentiation in the degradation efficiency of various bisphenols. Results of ecotoxicity prediction showed that most intermediates produced by the degradation of BPs in the β-SB/PDS system, which was dominated by the electron transfer pathway, had a lower toxicity than the parent molecules, while the toxicity of several ring cleavage intermediates was higher. This study presents a simple modification scheme for the conversion of biochar into functional catalysts and provides insights into the mechanism of heterogeneous catalytic degradation mediated by modified biochar as well as the degradation differences of bisphenol pollutants and their potential ecotoxicity.

Photocatalytic degradation of tetracycline antibiotic by a novel Bi2Sn2O7/Bi2MoO6 S-scheme heterojunction: Performance, mechanism insight and toxicity assessment

The fabrication of step-scheme (S-scheme) heterojunction with superior redox capability has been emerging as a prospective strategy for environmental remediation. Herein, novel Bi2Sn2O7/Bi2MoO6 S-scheme heterojunctions have been fabricated via in-situ anchoring Bi2Sn2O7 nanoparticles on Bi2MoO6 microspheres. The optimized Bi2Sn2O7/Bi2MoO6 (BSO/BMO-6%) attains the highest reaction rate constant (k) in the degradation of tetracycline hydrochloride (TC, k = 0.0397 min−1), which is 3.62 folds higher than that of pristine Bi2MoO6. Such an improvement is originated from more exposed active sites, higher photo-excited charge separation efficiency, superior redox ability, and efficient production of reactive h+, •OH and •O2–. Besides, Bi2Sn2O7/Bi2MoO6 could efficiently degrade the TC antibiotic in actual water matrix. Significantly, the toxicity evaluation verifies the nontoxicity of Bi2Sn2O7/Bi2MoO6. Moreover, the degradation pathways of TC are determined and the toxicity of degradation intermediates is appraised by using HPLC-MS spectra and QSAR prediction. A possible photocatalytic mechanism over S-scheme Bi2Sn2O7/Bi2MoO6 has been elucidated based on experimental studies combined with density functional theory (DFT) calculations. This work offers new insights for the design of high-performance S-scheme heterojunctions for environmental remediation.

Intermediate accumulation and toxicity reduction during the selective photoelectrochemical process of atrazine in complex water bodies

Selective removal of atrazine (ATZ) in wastewater and clarification of the degradation intermediate-toxicity correlation are of great importance. A newly molecularly imprinted, {001} facets-exposed TiO2 (MI-TiO2,001) photoanode with strong catalytic and selective ability was designed. ATZ was selectively removed from pesticide wastewater, reaching 1.9 µg L−1, approximately 1/10 of the concentration achieved with nonselective treatment. This selective removal originated from the preferential adsorption and enrichment of ATZ onto MI-TiO2,001. The highly specific recognition relied on the halogen bond and strong hydrogen bond formed between the Cl atom and triazine ring π orbital of ATZ and the surface -OH group of MI-TiO2,001 as well as the recognition of MI-TiO2,001 to the shape and size of ATZ. The specific interaction leads to different accumulations of intermediates. The correlation of intermediate and toxicity was also discussed. Aquatic toxicity was rapidly reduced through the direct dealkylation path, and due to the accumulation of highly toxic 2‑hydroxy-4-ethylamino-6-isopropylamino-s-triazine, there will be transient fluctuations via the dechlorination-hydroxylation path first. The final product was identified as nearly nontoxic cyanuric acid, the selective accumulation of which indicated that there was almost 100% removal of aquatic toxicity and cytotoxicity with only 9.8% removal of total organic carbon. This work provides new insight into the correlation of pollutant degradation intermediates and changes in toxicity.