Electron Spin Resonance Tests Research Articles

Highlight the plasma-generated reactive oxygen species（ROSs）dominant to degradation of emerging contaminants based on experiment and density functional theory

This paper aims to deeply analyze the degradation mechanism of emerging contaminants by dielectric barrier discharge (DBD) plasma through experiments and simulations. It was confirmed that DBD plasma exhibits a high degradation effect on three emerging contaminants by the generated reactive oxygen species (ROSs). Increasing the output power leads to higher ROSs production and higher degradation rates of emerging contaminants. At an input power of 94.6 W, the degradation rates of sulfamethoxazole (SMX), bisphenol A (BPA) and ciprofloxacin (CIP) reach 94.5 %, 92.9 %, and 98.6 %, respectively. Trapping agent experiments were conducted to investigate the role of ROSs (·OH, ·O2–, and 1O2) in emerging contaminants degradation. Notably, capturing of 1O2 led to a decrease of up to 31 % in the degradation rate of BPA. Electron spin resonance (ESR) tests confirmed the involvement of various ROSs, especially 1O2, in the degradation process. Density functional theory (DFT) was employed to further explore the action mechanism of ROSs in the DBD plasma system. For SMX and BPA, the degradation is initiated by the dissociation of annular structures, while for CIP, annular structures are directly opened by ROSs. These findings highlight the importance of 1O2 and ·OH in the degradation process. Finally, the toxicity of intermediates produced by ROSs-dominate to degradation was declined. This work can provide new insights and unique guidance on the plasma degradation mechanism of emerging contaminants.

Improved aquaculture wastewater treatment and concomitant power generation in a photoelectrocatalytic fuel cell equipped with S-scheme Fe2WO6/ZnO nanorod arrays photoanode and NiFe2O4 cathode

The treatment of aquaculture wastewater involved the elimination of refractory organics and total nitrogen (TN) concurrently was one of the towering challenges in wastewater treatment. In this work, aquaculture wastewater comprised of tetracycline (TC) and TN as well as its energy recovery was recuperated in a visible light responsive photocatalytic fuel cell (PFC) system. The S-scheme Fe2WO6 nanoparticle-anchored on ZnO nanorod array (Fe2WO6/ZNA) photoanode and NiFe2O4 nanoflower-loaded on carbon felt (NiFe2O4/CF) cathode spanned photoelectrocatalysis and catalytic chlorination, conducing both contaminant removal and power production. In the presence of optimized conditions (0.5 M Cl−, dual constructed electrodes, solution pH 7), the system exhibited a maximum power density of 1.820 mW cm−2 and removed 100 % and 88.4 % of TC and TN in 120 min, respectively. The yielded small amount of NH4+ and NO3– can also destroy by NiFe2O4/CF cathode because of its large surface area and rapid charge carrier transport. Moreover, the toxicity results testified that the treated aquaculture organic seemed to have no harmful impact on zebrafish model after PFC-chlorine treatment. The mechanism involving S-scheme Fe2WO6/ZNA-NiFe2O4/CF electrodes and PFC-chlorination enabled the core species Cl and OH partook in the photoelectrocatalytic reaction. Based on the trapping agent, electron spin resonance and liquid chromatography mass spectrometry test outcomes, the degradation pathway of TC and its by-product was also postulated.

Unraveling the contribution of Co(IV) and free radicals in Co2+-activated Peroxymonosulfate process: Reaction mechanism, degradation pathway, and DFT calculation

The Co2+ and Peroxymonosulfate (PMS) reaction is a highly regarded advanced oxidation process (AOP) that has been extensively researched. The consensus regarding the relative contribution of reactive species in the Co2+/PMS system under different pH conditions has not been established. In this study, quenching experiments and electron spin resonance (ESR) tests demonstrated the coexistence of Co(IV), sulfate radical (SO4•-), hydroxyl radical (•OH), and singlet oxygen (1O2), and there fell to CBZ degradation were Co(IV) > SO4•->•OH ≈ 1O2 in the optimal conditions, where almost 100% of CBZ was degraded in the Co2+/PMS system within 30 min. Furthermore, Cl− would suppress the formation of Co(IV), SO4•-, and •OH but enhance the yield of 1O2, thereby showing a trend of inhibiting CBZ degradation. The probe compound used in this study was Methyl Phenyl Sulfoxide (PMSO), while methyl phenyl sulfone (PMSO2) as the indicator of Co(IV), the generation efficiency of PMSO2 (η'[PMSO2]) increased with reaction time and reached 70%–98% at 40 min at all set pH values (3, 4, 6, and 8). These results suggest that Co(IV) played a significant role in the Co2+/PMS system and its importance became more pronounced as the reaction progressed. PMSO probe and SO4•- quantification experiments jointly revealed that Co(IV) had the greatest performance at pH 4, and compared to other pH values, SO4•- had the largest contribution in the initial stage of the reaction at pH 6. The Ecological Structure Activity Relationships (ECOSAR) software was utilized to predict the toxicity of the degradation by-products. Additionally, luminescent bacteria experiments were conducted to assess the acute toxicity of the reaction solution. The results of these experiments demonstrated that the Co2+/PMS process exhibited a remarkable ability to detoxify the solution.

Dual-plasma enhanced 2D/2D/2D g-C3N4/Pd/MoO3-x S-scheme heterojunction for high-selectivity photocatalytic CO2 reduction

The localized surface plasmon resonance (LSPR) effect has shown significant progress in enhancing the efficiency of light absorption and separating photogenerated carriers. Herein, the dual-plasma enhanced 2D/2D/2D g-C3N4/Pd/MoO3-x (CPM) S-scheme heterojunction photocatalysts were synthesized using the method of hydrothermal and electrostatic self-assembly for high-selectivity photocatalytic reduction of CO2 to produce CO. The dual LSPR effect of MoO3-x and ultrathin Pd nanosheets synergistically broadened the optical response range of the CPM composites and successfully improved the photocatalytic activity and near-infrared (NIR) performance. The optimized CPM-30 photocatalysts exhibited CO yields of 18.55 μmol g−1 with a selectivity of 96.3%. In addition, the CO yield reached 3.92 μmol g−1 after 4 h of NIR light photoirradiation. The electron spin resonance (ESR) and ultraviolet photoelectron spectroscopy (UPS) tests showed that the S-scheme heterojunctions were constructed by coupling g-C3N4/Pd nanosheets and MoO3-x. This work will provide a reference for improving product selectivity through the design of two-dimensional composites and the utilization of plasma materials.

Yeast-biotemplate-assisted fabrication of self-phosphorus doped Co3O4@C hollow architecture for ciprofloxacin degradation via peroxymonosulfate activation: Performance, mechanism and toxicity evaluation

Sustainable development of highly active catalysts for peroxomonosulfate (PMS) activation to destruct organic pollutants in wastewater has irreplaceable significance, but remains a challenge. Herein, we report the successful preparation of P-doped Co3O4 integrated porous carbon hollow architecture (Co3O4@PC-HM) using spherical yeast as a natural biological template and cobalt nitrate as a cobalt source. The unique hollow microspherical structure endows Co3O4@PC-HM with large specific surface area for providing copious surface-exposed active sites, and the self-P doping facilitates the electron transfer rate, which concomitantly contribute to boosting the PMS activation for ciprofloxacin (CIP) degradation. Specifically, the Co3O4@PC-HM exhibits an excellent performance for activating PMS to degrade CIP with a removal efficiency of 95% in 20 min. Quenching experiments and electron paramagnetic resonance tests indicate the coexistence of radical and non-radical pathways in the Co3O4@PC-HM/PMS system, among which 1O2 and SO4•− play the dominant roles in CIP degradation. Simultaneously, four possible pathways of CIP degradation with the Co3O4@PC-HM/PMS system are proposed. Toxicity evaluation based on ECOSAR procedure and the growth status of mung bean roots reveal that the degradation process catalyzed by the Co3O4@PC-HM/PMS system efficiently decreases the toxicity of CIP. The natural biological template strategy has guiding significance for the synthesis of other hollow structure for versatile applications.

Facile synthesis of bimetallic ACF/CC@FeOCl–Cu composite cathode for efficient degradation of sulfamethoxazole at neutral pH by a flow-through heterogeneous electro-Fenton process

Flow-through heterogeneous electro-Fenton (FHEF) process shows a broad prospect for refractory organic pollutants removal. However, maintaining a long-term service life of higher catalytic cathode is crucial for the development of cathode materials, especially for iron-functionalized cathode operated under harsh conditions. In this study, a novel bimetallic CC@FeOCl–Cu composite was synthesized through one-step calcination, coupled with a series of microstructure characterization methodology, including XRD, SEM-EDS, XPS, and FTIR. The superior catalytic activity of CC@FeOCl–Cu could be ascribed to Fe–Cu synergy and better dispersion of FeOCl nanosheets. With the optimal Cu:Fe ratio of 1:60, the bifunctional ACF/CC@FeOCl–Cu cathode was employed in FHEF process, exhibiting an outstanding performance for sulfamethoxazole (SMX) removal over a wide pH range (3.0–9.0). Comparison of experimental results indicated that the ACF/CC@FeOCl–Cu-FHEF process showed higher performance than ACF/CC@FeOCl-FHEF and homogeneous EF processes. The average SMX removal efficiency was 98% and TOC removal efficiency was more than 57% even after 10 cycles. Radical quenching experiments and electron spin resonance test confirmed that •OH was the primary active species. More •OH was generated in the ACF/CC@FeOCl–Cu-FHEF process because the doping of Cu could enhance catalytic activity of cathode. In addition, the satisfactory performance could be observed in the ACF/CC@FeOCl–Cu-FHEF process for the treatment of real landfill leachate, indicating its potential for practical application in wastewater treatment.

Three-dimensional rGO/CNT/g-C3N4 macro discs as an efficient peroxymonosulfate activator for catalytic degradation of sulfamethoxazole

Over the past few years, advanced oxidation processes (AOPs) have shown promising efficiencies for wastewater remediation. Carbocatalysis, in particular, has been exploited widely thanks to its sustainable and economical properties but has an issue of recovery and reusability of the catalysts. To address this, three-dimensional (3D) binary and ternary graphene-based composites in the form of macro discs were created to activate peroxymonosulfate (PMS) for catalytic oxidation of sulfamethoxazole (SMX). Graphene oxide served as the base, while graphitic carbon nitride (g-C3N4) and/or single-walled carbon nanotubes (SWCNTs) were added. Among the various discs synthesized, rGNTCN discs (ternary composite) were proven to be the most efficient by completely degrading SMX in 60 min owing to their large surface area and nitrogen loading. The catalytic system was further optimized by varying the reaction parameters, and selective radical quenching and electron paramagnetic resonance tests were performed to identify the active radical, revealing the synergistic role of both radical and non-radical pathways. This led to the development of possible SMX degradation pathways. This research not only provides insights into ternary carbocatalysis but also gives a novel breakthrough in catalyst recovery and reusability by transforming nanocatalysts into macro catalysts.

Boosting Nd3+ emission in Nd/Al/Y co-doped silica glass by mid-range localized environmental manipulation

Improving the repetition frequency of high-energy lasers is vital to promote the development and application of high-energy lasers, and its key lies in finding the laser gain media with excellent thermal shock resistance and high emission cross-section. Rare-earth ion (RE3+)-doped silica glass, whose thermal shock parameter is 1.5 times higher than that of yttrium aluminum garnet (YAG) crystals, is expected to satisfy this criterion after enhancing the emission intensity of RE3+. Nevertheless, modulating the spectral properties of RE3+ in rigid silica glass networks poses a significant challenge. Herein, we propose a mid-range localized environmental manipulation approach, which dramatically changes the microscopic symmetry of RE3+ from amorphous to the desired crystal structures for emission enhancement. As a representative, Nd/Y/Al co-doped silica glasses were prepared and heat-treated for different durations to form different mid-range localized environments, which were demonstrated by transmission electron microscopy, electron paramagnetic resonance tests, and Judd-Ofelt theory analysis. The results show that Nd3+ enters the YAG structure in favor of its emission enhancement. After optimizing the mid-range local environment of Nd3+ to balance fluorescence enhancement with fluorescence quenching and Rayleigh scattering, the emission intensity increases by 300%. Our work suggests that the mid-range localized environmental manipulation approach is extremely promising for promoting the development of high-energy and high-repetition-rate lasers. Furthermore, this approach can be generalized to adjust the emission characteristics of other RE3+-doped glasses and fibers.

Novel MIL-88B(Fe)/ZnTi-LDH high-low junctions for adsorption and photodegradation of tetracycline: Characteristics, performance, and mechanisms

In this paper, a high-efficient MIL-88B(Fe)/ZnTi-LDH high-low junction photocatalyst was successfully prepared by a simple method for the photodegradation of tetracycline (TC). The combination of MIL-88B(Fe) and ZnTi-LDH created an internal electric field and high-low junction, facilitated the separation of carriers, and thus enhanced photocatalytic activity. The optimized MZ-30% sample showed the highest photocatalytic degradation of TC about 93.51%. The photocatalytic kinetic removal rate of MZ-30% reached 0.0941 min−1, 31.36 times of MIL-88B(Fe) (0.003 min−1) and 1.7 times of ZnTi-LDH (0.0550 min−1). Furthermore, MZ-30% possessed the highest adsorption capacity for TC (543.89 mg/L). The effects of co-existing ions, initial pH, water source, and humic acid (HA) on TC degradation were examined. The main active substances of MIL-88B(Fe)/ZnTi-LDH in photocatalytic reaction were 1O2, h+, and ·O2- confirming by reactive species elimination experiment and electron spin resonance (ESR) tests. The molecular structure and toxicity of intermediates were investigated by a high-performance liquid chromatography-mass spectrometer (HPLC-MS) and Toxicity Estimation Software Tool (T.E.S.T), and the possible degradation pathway of TC was revealed. The results highlight that MIL-88B(Fe)/ZnTi-LDH high-low junction composite is a desirable photocatalyst for removing antibiotics and other emerging contaminants in water.

Constructing C-doped TiO2/β-Bi2O3 hybrids Z-scheme heterojunction for enhanced CO2 photoreduction

Rational fabricating advanced photocatalysts to recycle CO2 into solar fuel is one of the most promising approaches to simultaneously address energy shortages and global warming. TiO2 has been widely used in photocatalytic CO2 reduction due to its abundant reserves, non-toxicity and harmlessness etc. However, it remains significantly challenging for practical applications due to the fast electron-hole recombination. Herein, we design a direct TiO2 based Z-Scheme heterojunction by self-assembly of C-doped TiO2 nanoparticles on 3D hierarchical petal of flower-like β-Bi2O3 (C-TiO2/β-Bi2O3). In situ electron paramagnetic resonance tests, in situ X-ray photoelectron spectroscopy and theoretical calculations reveal that electrons are transferred from β-Bi2O3 to C-TiO2 due to the formation of Z-Scheme heterojunction, which greatly accelerates the separation of photogenerated carriers to promote efficient CO2 photoreduction. Ultimately, the optimal heterojunction shows significantly enhanced photocatalytic activity for CO2 reduction to CO (31.07 μmol g–1 h−1) compared to the pure TiO2 (3.28 μmol g–1 h−1) without using any photosensitizers and sacrificial agents. This work provides a unique insight to design direct Z-Scheme heterojunctions and delivers a promising photocatalyst for overcoming global warming and energy-supply issues.

Efficient degradation of antibiotics by heterojunction photocatalysts driving peroxydisulfate activation under visible light irradiation

Heterogeneous iron materials show potential for activating peroxydisulfate (PDS). However, these systems may be constrained by low efficiency and secondary pollution. The visible-light-assisted activation has been demonstrated as a feasible and effective approach to enhance PDS activation by iron-based materials. In this study, a visible-light-responsive Bi2WO6/Fe2O3 heterojunction photocatalyst was synthesized to improve the ability of Fe2O3 for PDS activation through an effective Fe(III)/Fe(II) cycle. Rapid tetracycline (TC, a common antibiotic) removal (91.7% within 60 min at a concentration of 20 mg·L-1) was achieved in the constructed Bi2WO6/Fe2O3/PDS/vis system under conditions of 0.3 g·L-1 PDS and 0.3 g·L-1 catalyst. The corresponding pseudo-first-order rate constant reached 4.16 × 10-2 min-1, which was 8.42 and 16.38 times higher than those of Bi2WO6/Fe2O3/vis and Bi2WO6/Fe2O3/PDS systems, respectively. Moreover, the Bi2WO6/Fe2O3 exhibited favorable stability and reusability even after five cycles. Lastly, a catalytic mechanism for TC removal and PDS activation was proposed based on quenching experiments and electron spin resonance (ESR) tests. The SO4•- and •OH played a major role in TC removal, while •O2– and 1O2 contributed as auxiliary factors. This study presents a promising strategy for activating PDS using cost-effective and stable Fe(III)-based heterojunctions, and such an idea can be used to design catalysts for other high-value reactions.

Preparation of BiVO4/CO32−-Bi2O2CO3 heterojunctions for enhanced photocatalytic activity in the degradation of levofloxacin under visible light

The issue of levofloxacin elimination from wastewater has become significant. In this study, a series of BiVO4/CO32−-Bi2O2CO3 composite photocatalysts were constructed by the hydrothermal method for the photocatalytic degradation of levofloxacin. Various methods were used to investigate the morphology, composition, functional groups, optical, and photoelectrochemical properties of BiVO4/CO32−-Bi2O2CO3. In the photocatalytic degradation experiment, the best photocatalytic activity was exhibited when the molar ratio of BiVO4 to CO32−-Bi2O2CO3 was 0.8 (0.8VCBOC). The photocatalytic degradation efficiency of levofloxacin is 78% within 90 min under 300 W Xenon lamp (λ ≥ 420 nm), which is 1.24 times that of CO32−-Bi2O2CO3 (63%). The free radical capture experiment and electron spin resonance tests indicated that·O2- is the active species in the photocatalytic degradation of levofloxacin, and the Z-scheme heterojunction model was subsequently proposed. The photocatalytic activity of BiVO4/CO32−-Bi2O2CO3 was improved through the formation of the heterojunction and the expansion of the absorption rang. Based on LC–MS analysis, possible degradation pathways of levofloxacin in the 0.8VCBOC system were proposed. Moreover, excellent cyclic stability was demonstrated by the 0.8VCBOC catalyst in the cyclic stability experiment. This work presents a method for the simple and feasible construction of visible-light-induced photocatalysts based on CO32− self-doped Bi2O2CO3 for the degradation of levofloxacin.

Oxidative pretreatment of refractory gold ore using persulfate under ultrasound for efficient leaching of gold by a novel eco-friendly lixiviant: Demonstration of the effect of particle size and economic benefits

A novel pretreatment method for refractory gold ore using ultrasound-activated persulfate was developed to overcome the low extraction efficiency of gold in the leaching process. The feasibility of the pretreatment method was verified primarily by EPR (Electron paramagnetic resonance) and pre-oxidation tests. The free radicals generated by ultrasound-activated persulfate effectively promoted the oxidation of sulfide in the gold ore. The pretreatment efficiency of this process was higher than that of traditional heat activation, and the oxidation efficiency was two times higher. Furthermore, the gold leaching efficiency was higher under ultrasound activation conditions when using a novel eco-friendly lixiviant (Jinchan-its main effective component is Na3CN3C3H3N6O3, i.e., carbonized sodium cyanurate). Morphology analysis indicated that the synergistic effect of persulfate and ultrasound effectively reduced the particle size of the refractory gold ore, improved the specific surface area, and facilitated the oxidation of the enclosures, which benefited the subsequent leaching process. The maximum leaching efficiency of gold reached 86.9% after ultrasonic activated persulfate pretreatment for 3 h. This study provides a promising refractory gold ore pretreatment to improve gold leaching through persulfate oxidation using ultrasound activation.

Mechanochemical remediation of lindane-contaminated soils assisted by CaO: Performance, mechanism and overall assessment

Soil contamination caused by persistent organic pollutants (POPs) has been a worldwide concern for decades. With lindane-contaminated soil as the target, a mechanochemical method assisted by CaO was comprehensively evaluated in terms of its remediation performance, degradation mechanism and overall assessment. The mechanochemical degradation performance of lindane in cinnamon soil or kaolin was determined under different additives, lindane concentrations and milling conditions. 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazinyl free radical (DPPH•) and electron spin resonance (ESR) tests evidenced that the degradation of lindane in soil was caused mainly by the mechanical activation of CaO to produce free electrons (e-) and the alkalinity of the generated Ca(OH)2. Dehydrochlorination or dechlorination by elimination, alkaline hydrolysis, hydrogenolysis and the subsequent carbonization were the main degradation pathways of lindane in soil. The main final products included monochlorobenzene, carbon substances and methane. The mechanochemical method with CaO was proved to also efficiently degrade lindane in three other soils and other hexachlorocyclohexane isomers and POPs in soil. The soil properties and soil toxicity after remediation were assessed. This work presents a relatively clear discussion of various aspects of the mechanochemical remediation of lindane-contaminated soil assisted by CaO.

“Memory catalysis”: Extending the photocatalytic antibacterial performance of a palladium-modified ZnO nanocomposite

In this study, Pd-ZnO nanocomposite was synthesized via the facile solvothermal method. Then, PdO-ZnO was obtained by continuing calcination of the synthesized Pd-ZnO. X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), and X-ray Photoelectron Spectroscopy (XPS) tests showed that Pd was converted to PdO in the process of calcination. The photocatalytic sterilization experiment showed that in the 3 % Pd-ZnO system, 2 × 107 CFU/mL of E. coli was completely killed within 3 h, while 3 % PdO-ZnO took 1.5 h. In electron spin resonance (ESR) tests on PdO-ZnO, The ·OH and ·O2− signals can be detected under light and within 20 min after the end of light. 1 × 105 CFU/mL of E. coli were killed within 1 h by the optical “memory” effect of PdO-ZnO. PdO-ZnO inactivates E. coli by disrupting the membrane structure of bacteria as demonstrated by scanning electron microscopy (SEM) test. PdO-ZnO is non-toxic and can be demonstrated through cytotoxicity experiments on HTT2.

Bi2MoO6 nanoflower-like microsphere photocatalyst modified by boron doped carbon quantum dots: Improving the photocatalytic degradation performance of BPA in all directions

Bi-based semiconductor photocatalyst represented by Bi2MoO6 (BMO) has obvious advantages in the degradation of bisphenol A (BPA), but three prominent problems that restrict the improvement of photocatalytic performance, namely, insufficient solar absorption, less active sites and serious photogenerated carrier recombination, need to be solved urgently. For this reason, we specially designed a simple structure of B-doped carbon quantum dots (BCQDs) modified BMO nanoflower-like microsphere composite to improve the photocatalytic performance of the system from the above three dimensions. The optimized BCQDs/BMO sample completely degraded BPA within 120 min under simulated sunlight, corresponding to an apparent constant of 0.03453 min−1, while the control sample of CQDs/BMO without B doping only degraded about 84 % of BPA within 160 min, with an apparent coefficient of 0.01138 min−1. Even after filtering out UV components below 400 nm, the degradation performance of the optimal composite catalyst did not decrease. The improved catalytic performance comes from the excellent up-conversion luminescence performance and good electron storage capacity of CQDs on the one hand, and the introduction of B on the other hand can adjust the surface structure of CQDs to generate more active sites and functional interfaces to further promote the catalytic reaction. Free radical trapping and electron spin resonance (ESR) tests have shown that·OH and·O2- are the main active substances in the degradation of BPA. The current BCQDs/BMO catalysts, despite their simple structure, can simultaneously improve the catalytic performance from the three important aspects mentioned above, which will guide the design of others semiconductor based photocatalysts.

Natural coal gangue activated persulfate for tetracycline hydrochloride degradation: Mechanisms, theoretical calculations, and comparative study

The development of catalysts with low-cost and high-efficiency for advanced oxidation process is the key issue to remove organic pollutants. In this work, natural coal gangue (CG) was used to activate potassium monopersulfate (PMS) for the removal of tetracycline hydrochloride (TC). For comparison, sodium persulfate (PS), potassium persulfate (PDS), and hydrogen peroxide (H2O2) were also activated by CG to remove TC. The active species in the TC degradation processes in PMS/CG, PS/CG, PDS/CG, and H2O2/CG systems were investigated by capture experiments and electron spin resonance (ESR) tests. DFT calculation indicated that PMS was more easily adsorbed by CG in comparison with PS, PDS, and H2O2. In addition, Fukui function was adopted to determine how electrophilic, nucleophilic and free-radical attacks occurred on sites of TC molecules in detail. Mechanism investigation showed that the surface-bonded and structural hydroxyl groups of natural CG were favorable for the adsorption of PMS molecules onto the CG surface and thus facilitated the generation of active species, which were crucial in the TC degradation process. This paper sheds new light for natural minerals or solid wastes to participate in advanced oxidation process (AOPs) for wastewater treatment.

Acceleration of Fe3+/Fe2+ cycle in garland-like MIL-101(Fe)/MoS2 nanosheets to promote peroxymonosulfate activation for sulfamethoxazole degradation

Iron-based molybdenum disulfide (Fe-MoS2) has emerged as a Fenton-like catalyst for the highly efficient degradation of antibiotics, but the structure–activity relationship remains elusive. Herein, garland-like MIL-101(Fe)/MoS2 nanosheets (MMS) with dual metal active sites (Fe and Mo) and rich sulfur vacancies were fabricated to directly activate peroxymonosulfate (PMS) for fast degradation of different organic pollutants (phenols, dyes and drugs), even in real water bodies. The MMS exhibited extremely fast catalytic rate constant of 0.289 min−1 in the degradation of sulfamethoxazole (SMX), which was about 36 and 29 times that of single MoS2 (0.008 min−1) and MIL-101(Fe) (0.01 min−1). Moreover, MMS with good stability and reusability could reach 92% degradation of SMX after 5 cycles. Quenching experiments and electron spin resonance (ESR) tests revealed that hydroxyl radicals (.OH) and singlet oxygen (1O2) were the dominant reactive oxygen species (ROS) for SMX degradation. The integration of experimental works, characterization techniques and density functional theory (DFT) calculations unraveled that the formation of sulfur vacancies in MMS catalyst could expose more Mo sites, improve the charge density and boost the electron transfer, which was conducive to accelerating the Fe3+/Fe2+ cycle for enhancing the activation of PMS. Finally, the C-N, N-O, S-N, C-O and C-S bonds of SMX were easily attacked by ROS to generate the nontoxic intermediates in the MMS/PMS/SMX system. This study offers a new approach to designing high-performance Fe-MoS2 catalysts for the removal of organic pollutants.

Phosphorus doping to enhance the peroxymonosulfate activation efficiency of carbon nitride for degrading tetracycline

Herein, a new type of peroxymonosulfate (PMS) activator—phosphorus-doped carbon nitride (P-C3N4)—was prepared using a one-step thermal shrinkage method. Material characterisation confirmed the successful doping of phosphorus in graphite-phase carbon nitride (g-C3N4) by replacing the carbon atoms in its triazine ring structure to form PN bonds. Phosphorus doping can regulate and re-organise the surface electronic structure of g-C3N4 without changing its structure. Moreover, phosphorus doping promotes varying degrees of optimisation of the g-C3N4 pore structure and electronic transport between the g-C3N4 sites. Batch experiments on tetracycline (TC) degradation revealed that 0.2 P-C3N4 showed the best physicochemical properties, the constructed P-C3N4/PMS system exhibited high TC removal efficiency and P-C3N4 exhibited good reusability and structural stability. Quenching experiments and electron paramagnetic resonance tests revealed that singlet oxygen was the primary active species in the P-C3N4/PMS system. The mechanism of PMS activation using P-C3N4 was then proposed. The analysis of TC and its intermediate products using liquid chromatography–mass spectroscopy demonstrated that TC was primarily degraded via ring-opening, hydroxylation, deamination and dealkylation reactions. Analysis using the toxicity estimation software tool demonstrated that most intermediate products were less toxic than TC. Thus, this study provides a feasible method for removing TC from aquatic environments.

Efficient degradation of tetracycline residues in pharmaceutical wastewater by Ni/Fe bimetallic atomic cluster composite catalysts with enhanced electron transfer pathway

Metal cluster catalysts have large atomic load, interaction between atomic sites, and wide application of catalysis. In this study, a Ni/Fe bimetallic cluster material was prepared by a simple hydrothermal method and used as an efficient catalyst to activate the degradation system of peroxymonosulfate (PMS), which showed nearly 100% tetracycline (TC) degradation performance over a wide pH range (pH = 3–11). The results of electron paramagnetic resonance test, quenching experiment and density functional theory (DFT) calculation show that the non-free radical pathway electron transfer efficiency of the catalytic system is effectively improved, and a large number of PMS are captured and activated by high density Ni atomic clusters in Ni/Fe bimetallic clusters. The degradation intermediates identified by LC/MS showed that TC was efficiently degraded into small molecules. In addition, the Ni/Fe bimetallic cluster/PMS system has excellent efficiency for degrading various organic pollutants and practical pharmaceutical wastewater. This work opens up a new way for metal atom cluster catalysts to efficiently catalyze the degradation of organic pollutants in PMS systems.