Electron Spin Resonance Tests Research Articles

Photocatalyst for Antibiotics Degradation by In Situ Growth of Direct Z-Type Bi2S3/Bi4Ti3O12 Heterojunction.

Effective removal of antibiotics from aqueous solutions has emerged as a hot research topic in wastewater treatment. Photocatalytic degradation of antibiotics is one of the most effective methods to reduce ecological damage and environmental pollution. In this work, a novel photocatalyst consisting of Z-type heterojunction Bi2S3/Bi4Ti3O12 (BS/BTO) with visible light responses was prepared by an in situ growth method, and the obtained material was used for the degradation of tetracycline hydrochloride (TC). The best performing photocatalyst was BS/BTO-2, which exhibited high photocatalytic activity. The rates of TC degradation reached 97.9% within 40 min of illumination. The photocatalyst demonstrated a high stability and reproducibility even after 5 cycles. Electron spin resonance (EPR) tests and quenching experiments established that ·O2- and h+ were the main species responsible for the elimination of TC. On the basis of theoretical calculations and experimental data, a possible mechanism for the photocatalytic degradation of TC has been proposed. The heterojunction structure, which effectively increases the visible light absorption range and decreases the compounding efficiency of photogenerated electrons and holes, is principally responsible for the photocatalytic performance of BS/BTO. Additionally, liquid chromatography-mass spectrometry (LC-MS) was utilized to investigate the formation and degradation of reaction intermediates. The nontoxicity of the solution after tetracycline degradation was verified by cultivating wheat seeds. This work offers guidance for bismuth-based photocatalysts in the field of sustainable wastewater treatments.

Salt template-assisted polymer tethering strategy to achieve high dispersed cobalt single atoms/clusters on porous carbon catalysts for effective Fenton-like reactions

The exploration of the synthesis of porous carbon-supported metal nanocatalysts with high metal loading and dispersion for the development of heterogenous catalysts is important. However, this remains a challenging subject. In this paper, a salt template-assisted polymer tethering strategy was proposed to prepare Co single atom and ultrafine cluster anchored on porous carbon (Co-NPC) with a high-loading of 16.9wt%, thereby exposing high density of reaction sites. The obtained Co-NPC catalyst exhibited excellent catalytic performance for almost 100% degradation of bisphenol A (BPA) within 20min, which is much faster than the CoSA-NPC catalyst with only single atom sites and Co-NC without salt template added. Radical quenching experiments and electron paramagnetic resonance tests verified that both the nonradical oxidation pathway by 1O2, the electron transfer and radical oxidation pathway by •OH, SO4•- appeared during the degradation process. After 3 cycles, the removal rate of BPA did not decrease significantly. The fixed bed experiment revealed that Co-NPC could realize the continuous degradation of methylene blue (MB) with almost 100% degradation efficiency. This research indicated that the strategy by pyrolyzing metal coordinated polymer is a potential method for the synthesis of high metal loading catalyst at gram scale, meeting the requirement of practical applications.

Phosphate-Induced Acidic Microenvironment for Improved Contaminant Removal during FeS Oxygenation.

The coexistence of mackinawite (FeS) and phosphate is widely observed in natural systems. However, the underlying mechanism regarding how phosphate influences the environmental behavior of FeS, especially during the FeS oxygenation in aquatic systems, remains in its fancy. This study for the first time reported that the presence of phosphate, even at a low concentration of 0.3 mM, significantly promoted the FeS-mediated O2 activation and thus the pollutant degradation. The enhancement was attributed to a substantial increase in the generation of •OH, as evidenced by the electron paramagnetic resonance tests and the identification of the probing products. A combination of experiments and theoretical calculations revealed that phosphate adsorbed onto the FeS surface via a monodentate mononuclear configuration, establishing an acidic microenvironment on the FeS surface. Such acidic microenvironment not only increased the utilization efficiency of Fe(II) toward H2O2 generation (i.e., ), but also prevented the subsequent side reaction of H2O2 self-decomposition (i.e., ). The results highlight the beneficial role of commonly encountered phosphate in FeS-based systems, which has profound implications for the degradation of waterborne contaminants.

Enhanced activation of sulfite by CoFe2O4-loaded with WS2 nanosheet with smooth surface for elimination and detoxification of metronidazole

In this study, cobalt ferrite-loaded tungsten disulfide (CoFe2O4@WS2) with different loading ratios was prepared by coprecipitation as a catalyst for activating sulfite in the degradation of metronidazole (MNZ) for the first time. Characterization analysis revealed that the heterogeneous catalyst possesses favorable surface properties and catalytic stability. The CoFe2O4@WS2/Na2SO3 (2:1) system exhibited the best catalytic performance under optimal conditions, achieving an impressive MNZ degradation efficiency of up to 95 % within 20 min. Quenching experiments and electron paramagnetic resonance tests indicated that oxysulfur radicals (SO3•−, SO4•− and SO5•−),1O2, •O2− and •OH generated during Na2SO3 activation and participates in the degradation of MNZ to varying degrees, while the redox cycles of Co2+/Co3+ and Fe2+/Fe3+ on the catalyst surface facilitated electron transfer, thereby promoting radical generation. Importantly, the synergistic effect between highly active W (Ⅳ) sites and unsaturated S on the catalyst surface effectively enhanced ion valence state recycling among various metal ions, ensuring continuous decomposition of sulfite, thereby facilitating sustained generation of ROS and the degradation of MNZ, confirming that WS2 played an excellent co-catalysis role. MNZ was degraded into various intermediates through three distinct pathways before ultimately mineralizing into inorganic small molecules. Toxicity analysis results indicated that the intermediate toxicity diminished with the reaction, reducing potential risks to aquatic ecosystem. Furthermore, findings demonstrated that the catalyst has excellent anti-interference ability, recyclability and low ion leaching rate. This study provides a novel approach for the efficient degradation of multiple organic pollutants using sulfites with promising application in practical water treatment.

Effective periodate activation by the ball-milled bimetallic zero-valent iron/manganese oxides catalyst for sulfamethoxazole degradation

Developing a green and efficient catalyst for oxidant activation to tackle refractory organics pollution is challenging for water purification. In this study, we prepared a zero-valent iron-based bimetallic catalyst (ZVI/Mn3O4) for periodate (PI) activation using a simple and convenient ball-milling method. Electrochemical characterization and theoretical calculations confirm that the synergy between Fe and Mn enables the ZVI/Mn3O4 system to exhibit higher electron transfer efficiency compared to its individual components. Consequently, the ZVI/Mn3O4/PI system demonstrated enhanced PI activation and significantly improved removal of sulfamethoxazole (SMX), with reaction rates being 18.61 to 57.01 times higher than the comparison systems. The influence of various physicochemical parameters on SMX removal was investigated, confirming the wide tolerance ZVI/Mn3O4/PI system towards multiple aqueous matrices. Furthermore, the scalability of this system for industrial applications was validated through the preparation of larger batches of catalysts (4.21 g per batch) and testing in a custom-designed magnetic plate continuous-flow reactor. Quenching experiments and electron spin resonance tests confirmed that •O2– and 1O2 were the primary reactive species responsible for SMX degradation, with no toxic iodine byproducts detected, attributed to the carefully designed catalyst, which optimized the interaction between PI and the catalyst. Based on these findings, a potential catalytic mechanism and degradation pathway were proposed, highlighting ZVI's role as an electron pump to enhance Mn3O4's activation of PI. Additionally, toxicity assessments via prediction, zebrafish cultivation, wheat germination, and E. coli culture confirmed the excellent detoxification capability of ZVI/Mn3O4/PI system for SMX degradation. Overall, this work provides a new research paradigm for the convenient manufacture of ZVI-based catalysts and the development of advanced techniques for PI activation in water purification.

Ball milling of pyrolytic residue from oil sands with MnO2 and reuse as PMS activator: Measurement of ROS exposure and mechanism insights

Pyrolysis is an important process to recover petroleum from oil sands, while the pyrolytic residue of oil sands (PROS) is commonly treated as solid waste. In this study, PROS was treated by ball milling with manganese dioxide and converted into Mn-loaded carbon sand (MnBMCS), which was reused as a peroxymonosulfate (PMS) activator to degrade aniline (AN) in wastewater. The AN (100 mg/L) was almost completely removed by 2 g/L MnBMCS and 1 g/L PMS. Electron paramagnetic resonance tests confirmed the existence of three reactive oxygen species (ROS) including sulfate radical (SO4∙−), hydroxyl radical (∙OH) and singlet oxygen (O21) in MnBMCS/PMS system. A probe-based kinetics model was constructed to measure the ROS exposure. The O21 exposure was 6.73 and 22.95 times of SO4∙− and ∙OH exposure, respectively. But the contribution of SO4∙− to AN degradation was much greater than that of O21 due to its higher oxidation capacity. Characterization analysis showed that Mn(Ⅳ)/Mn(Ⅲ) redox electrons could activate PMS to produce SO4∙− and ∙OH, CO activated PMS to produce O21, and π-π* was also beneficial to generate SO4∙− and ∙OH. This study proposes an innovative integrated process to promote the governance mode of PROS from harmless disposal to high-value resource utilization.

Inhibition of inorganic chlorinated byproducts formation during electrooxidation treatment of saline phenolic wastewater via synergistic cathodic generation of H2O2

The electrochemical treatment of saline wastewater is prone to the formation of inorganic chlorinated byproducts, being a significant challenge for this technology. In this study, we introduce an electrooxidation system utilizing a self-supporting nitrogen-doped carbon-based cathode embedded in carbon cloth (N@C-CC), designed to generate H₂O₂. This system aims to rapidly neutralize free chlorine produced at the anode, a precursor to inorganic chlorinated byproducts, thereby reducing their formation. Our results demonstrate that using the N@C-CC cathode in saline wastewater treatment yielded considerably lower concentrations of ClO₃⁻ and ClO₄⁻ (0.08 mM and 0.024 mM, respectively), which were only 20.5% and 22.7% of the levels produced using a Pt cathode without H₂O₂ generation. Moreover, the presence of cathodically generated H₂O₂ that quenches free chlorine did not significantly impact the degradation performance of phenol. Electron paramagnetic resonance tests and quenching experiments indicated that 1O₂ was primarily responsible for phenol removal. Validation with real wastewater demonstrated reductions of 68.6% and 56.3% in ClO3− and ClO4− concentrations, respectively, while effectively removing other pollutants. This study thus offers a compelling method for mitigating the formation of inorganic chlorinated byproducts during the electrooxidation of saline wastewater.

Ternary photocatalyst Bi5O7I/Bi2O2CO3/Ag2CO3 with double Z-scheme heterojunction for the degradation of levofloxacin under visible light: Practical application and DFT calculation

A novel double Z-scheme heterojunction Bi5O7I/Bi2O2CO3/Ag2CO3 was constructed by a simple hydrothermal calcination and one-step in-situ growth technique, demonstrating efficient levofloxacin degradation (86.9 % in 60 min). The degradation rates of the system are 1.5, 4.1, 1.3 and 1.4 times faster than those of pure Bi5O7I, Bi2O2CO3, Ag2CO3 and binary Bi5O7I/Bi2O2CO3, respectively. The method enhances the photocatalyst performance through improving the separation efficiency of electron-hole pairs (e-/h+) and the production of various free radicals in the double Z-scheme system. The generation of hydroxyl radicals (•OH), superoxide radicals (•O2–) and holes (h+) species were directly confirmed by Electron Spin Resonance test, and their contributions on the degradation of Levofloxacin follow the order of h+ > •OH > •O2–. The band structure, density of states, work function and potential sites of contaminant vulnerability in the material were determined by Density Functional Theory (DFT), which provides additional evidence for the formation of double Z-scheme heterojunction. Besides, the degradation experiment was conducted with four real surface water bodies, including lake water, river water, tap water and effluent of sewage treatment plant. The results show that the degradation rate for Levofloxacin reaches 60∼80 %. Moreover, Levofloxacin and its intermediate products were identified and their toxicity was predicted with Quantitative Structure-Activity Relationship (QSAR) modelling, which can be useful in the future for the actual design of a double Z-scheme heterojunction photocatalyst to efficiently remove pollutants under visible light irradiation.

Novel Ketone Derivatives Involving Triphenylamine Electron‐Donating Group as Low Migration Photoinitiators for Visible Light Radical Polymerization and 3D Printing

AbstractGiven the ongoing advancements in photopolymerization technology, there is an imperative need to develop novel free radical photoinitiators (PIs) with long‐wavelength absorbance and low migration. To meet the demand for visible light photopolymerization, four novel ketone derivatives photoinitiators (PHMOs) were synthesized in this study via a one‐step reaction. By constructing the push‐pull structure, the maximum absorption wavelength of the new PIs was red‐shifted to the vicinity of 400 nm, satisfying the requirement of visible excitation. The one‐component photoinitiation effect of PHMOs under visible light was comparable to that of Irgacure 1173, among which the photopolymerisation performance of PHMO‐2 was significantly superior to that of 1173. The photopolymerization effect of the two‐component photoinitiaton system composed by the addition of hydrogen donor was significantly improved. PHMO‐1 was successfully used in 3D printing to produce well‐defined printed products. The photolysis mechanism of PHMOs was investigated by steady‐state photolysis and electron spin resonance test. In addition, PHMOs had good solubility, thermal stability and good biosafety. Attributed to the presence of double bonds, PHMOs had low migration. These excellent properties indicated that PHMOs had desirable potential applications in the field of visible light polymerization.

In situ treatment of contaminated soil using persulfate activated by sulfidated zero-valent iron

Soil contamination with hazardous substances like phenol poses significant environmental and health risks. In situ soil mixing can be a promising technological solution to this challenge. A persulfate and sulfidated zero-valent iron (S-ZVIbm) system for remediating contaminated soil was developed and tested to be suited to in situ soil mixing. S-ZVIbm was synthesized using a ball mill process, and the optimal sulfur to iron molar ratio for effectively removing phenol from soil removal without pyrophoric risks was 0.12. Soil slurry experiments were performed, and the best phenol oxidation results (high stoichiometric efficiency and sustained oxidation after mixing) were achieved at a persulfate to S-ZVIbm molar ratio of 2:1 and a persulfate to phenol molar ratio of 8:1. A high organic matter content of the silty clay fraction of the soil strongly suppressed persulfate activation, so suppressed phenol removal and increased persulfate consumption. Electron spin resonance and radical scavenging tests confirmed that hydroxyl and sulfate radicals were present during the degradation of phenol. While sulfate radicals predominantly facilitated degradation in the soil, both sulfate and hydroxyl radicals were crucial in the aqueous phase in the absence of soil organic matter. In situ soil mixing simulation tests indicated that the persulfate and S-ZVIbm doses and the mixing rate and duration strongly affected the efficacy of the system, and the optimal conditions for phenol removal were determined. The results indicated that the persulfate/S-ZVIbm system could be tuned to achieve sustained persulfate activation and to remediate contaminated soil employing in situ soil mixing technique.

Simulated sunlight-driven photocatalytic activation of peroxydisulfate by core–shell Ag@SiO2/TiO2 nanocomposite for efficient methyl orange degradation

Herein, core–shell Ag@SiO2/TiO2 nanocomposites were synthesized and applied to activate peroxydisulfate (PDS) for wastewater purification. The Ag core and Ag-doped TiO2 shell were obtained by stober method and calcination method. The dispersion degree and size of Ag in TiO2 would influence the oxygen vacancy. Ag enhanced the visible absorption of TiO2 and activated PDS. Improved degradation performance was attributed to enhanced PDS activation by photogenerated e−, which separated h+and thus promoted methyl orange(MO) degradation. Reactive oxidative species were verified under dark and light conditions via quenching experiments and electron paramagnetic resonance tests, demonstrating SO4•–, h+, O2•–, and1O2were formed in light,whereasSO4•–, •OH, O2•–, and 1O2were responsible for MO degradation under dark conditions. The Ag@SiO2/TiO2/PDS/light system showed selectivity for removal of cationic dyes (e.g., methylene blue and malachite green) through adsorption and photocatalysis, whereas anionic dyes (e.g., MO) were degraded by photocatalysis alone. Besides, we found excess adsorption of micropollutant onto catalyst may be adverse to the activation of PDS. Therefore, the adsorption of oxidant (such as PDS) onto the catalyst surface would be beneficial for catalytic activation and micropollutant degradation, especially onto active sites. This work aims to provide a new avenue for core-shell structure catalyst synthesis in wastewater purification.

High performance long-afterglow phosphor-based ZnIn2S4/Sr2MgSi2O7:Eu2+,Dy3+ photocatalyst capable of dark state long-term application for photocatalytic sterilization

Eco-friendly photocatalytic sterilization utilizing solar energy via the generation of reactive radicals excited by light irradiation devastating bacterial cells and mineralizing organic pollutants effectively exhibits vast application potential in marine biofouling prevention due to the abundant solar energy available in the ocean. Focusing on the issue of the cessation of photocatalytic processes in the absence of light, in this study, we selected the long afterglow material Sr2MgSi2O7:Eu2+,Dy3+ (SMSO), which exhibits persistent sky-blue luminescence after brief illumination, as the substrate for in situ compositing with the visible-light-responsive ZnIn2S4 (ZIS). The emission spectrum of SMSO partially overlaps with the absorption spectrum of ZIS, and their energy bands were well-matched. Consequently, the ZIS/SMSO=1:0.5 (mass ratio) exhibited the synergistic degradation and bactericidal performance under both light and dark conditions. ZIS/SMSO=1:0.5 exhibited the degradation rate of methyl orange (MO) of 72.4 % when exposed to 5 minutes of simulated sunlight, 2.6-fold increase compared to ZIS, and especially, it exhibited the sustained degradation rate of 38.7 % after 5 h in darkness. Besides, ZIS/SMSO=1:0.5 exhibited the bactericidal rate of 28.9 % under simulated visible light of 1 h, which was 2.9 and 2.5 times the bactericidal rate of ZIS and SMSO, respectively; and especially, after 6 h in darkness, it reached 64.4 %, which was 2.8 and 1.9 times the bactericidal rate of ZIS and SMSO, respectively. The Electron Spin Resonance (ESR) test validated the notably higher ·OH and ·O2- signals of the ZIS/SMSO=1:0.5 complex than those of individual components when exposed to light, and the sustained existence of ·OH signal even in darkness, revealing that the continuously generation of active free radicals even in the absence of light due to that the SMSO can continuously excite the ZIS. Combining with the in situ XPS analysis and the density functional theory calculations, an S-scheme heterojunction between ZIS and SMSO is formed which contribute to the higher yield of ·OH for ZIS/SMSO=1:0.5 under both light and dark conditions. And the calculation of the adsorption energies of ZIS and SMSO for O2 and OH- in the composite revealed that the ZIS component is more favorable for adsorbing O2, while the SMSO component is more favorable for adsorbing OH-. These analyses manifested the S-scheme electron transfer of the system. Finally, the ZIS/SMSO=1:0.5 composite of environmentally friendly broad-spectral-responsive ternary metal sulfides with the long afterglow materials is capable of a sustained degradation and bactericidal effect, not only under light irradiation but also in the subsequent darkness. It offers valuable insights into photocatalytic materials that overcome light availability limitations for preventing marine biofouling.

Synergistic photocatalysis and fenton-like process driven by a biochar-supported biochar/iron hydroxide oxide/bismuth molybdate S-type heterojunction for tetracycline degradation: Mechanistic insights and degradation pathways

Photocatalysis-Fenton system, based on S-type iron hydroxide oxide/bismuth molybdate supported on biochar, was fabricated for efficient tetracycline removal. Biochar/iron hydroxide oxide/bismuth molybdate catalyst not only exhibits exceptional photocatalytic performance but also accelerates the Fenton reaction cycle in the presence of hydrogen peroxide. Within 40 min, the biochar/iron hydroxide oxide/bismuth molybdate achieved a remarkable degradation efficiency of 97% for tetracycline, surpassing that of biochar/iron hydroxide oxide (65%) and biochar/bismuth molybdate (59%). Experimental analysis and density functional theory calculations confirmed the charge migration mechanism of S-type iron hydroxide oxide/bismuth molybdate. Moreover, the excellent degradation ability of biochar/iron hydroxide oxide/bismuth molybdate was demonstrated across a wide pH range (3–11), overcoming the limitations associated with traditional Fenton systems that operate efficiently only within a narrow pH range. Quenching experiments and electron paramagnetic resonance tests identified primary active species including •O2–, h+, and •OH. Additionally, we elucidated the potential degradation pathway of tetracycline in this study, supplying novel perceptions into synthesizing bifunctional photocatalysts in photocatalysis-Fenton-like systems.

Interfacial photothermal-enhanced FeCo@BC nanocomposites activating peroxymonosulfate for efficient tetracycline degradation

This study explores leveraging the exceptional photothermal properties of carbon-based catalysts for enhanced tetracycline degradation via PMS activation. To minimize the impact of the high heat capacity of bulk water, we engineered a siphon-driven interfacial reactor that utilizes the photothermal effect to significantly enhance the efficiency of PMS activation. The increased temperature accelerates catalytic reactions, enabling the effective activation of peroxymonosulfate (PMS) to degrade pollutants through this thermal advantage. The photothermal-enhanced FeCo@BC demonstrates nearly 100% degradation efficiency of tetracycline within 15 min in differential batch mode. Further investigations, including quenching experiments and electron paramagnetic resonance tests, confirm that singlet oxygen (1O2) is the principal active species in the FeCo@BC/PMS system. This system also benefits from oxygen vacancies (Ov) that improve the adsorption and binding of PMS on FeCo@BC surfaces, aiding in the conversion of PMS into 1O2 and other radicals. In continuous operation mode, the interface photothermal reactor (IPR) achieved continuous tetracycline degradation, maintaining over 94% activity for 60 min.

Regulating iron center by defective MoS2 for superior Fenton-like catalysis in water purification: The key role of surface interaction and superoxide radical in accelerating metal redox-cycling

Transition metals exhibit high reactivity for Fenton-like catalysis in environmental remediation, but how to save consumption and reduce pollution is of great interest. In this study, rationally designed defect-engineered Fe@MoS2 (Fe@D-MoS2) was prepared by incorporating reactive iron onto structural defects generated from the chemical acid-etching, aiming to improve the energetic consumption of the catalyst in Fenton-like applications. Morphological and structural properties were elucidated in details, the Fenton-like reactivity was evaluated with five phenolic contaminants for oxidant activation, radical generation and environmental remediation. Compared to Fe@MoS2, Fe@D-MoS2 exhibited a 18.9-fold increase in phenol degradation (0.09 versus 1.79 min−1). Quenching experiments, electron paramagnetic resonance tests and electrochemical measurements revealed the dominant sulfate and superoxide radicals. Rendered by strong metal-substrate surface and electronic interactions from regulated chemical environment and coordination structure, the inert ≡ Fe(III) was reduced to the reactive ≡ Fe(II) accompanied by the ≡ Mo(IV) oxidation to ≡ Mo(V) in MoS2 lattice, with adjacent sulfur serving as the key electron transfer bridge. Therefore, this work shows that the incorporation of reactive centers is able to boost two-dimensional sulfide materials for environmental catalysis applications.

Amino polycarboxylic acid complex agent modified Fe0 enhanced activation of H2O2 double decomposition pathways for tetracycline removal under neutral condition

The summary of this study explores the modification of Fe0 with amino polycarboxylic acid complex agents (APCAs) to enhance H2O2 catalysis for tetracycline (TC) removal under neutral conditions. The ethylenediaminetetraacetic acid-modified Fe0/H2O2 system (EDTA-Fe0/H2O2) achieved a removal efficiency of 90.2 % for 50 mg/L TC, significantly higher than the 23.9 % efficiency of the traditional Fe0/H2O2 system. The removal rate of various pollutants by the EDTA- Fe0/H2O2 process is 2.9 to 8.4 times higher than that of the Fe0/H2O2 process. After four cycles of use, the removal rate of TC by the EDTA-Fe0/H2O2 system can still reach 76.3 %. Additionally, the effect of treating TC in natural freshwater can also achieve 80.1 %. Characterization revealed that EDTA-Fe0 had a larger Fe(II) proportion, better hydrophobicity, and lower corrosion potential than Fe0, indicating higher activity. Quenching experiments and electron paramagnetic resonance tests confirmed that •OH was the major reactive species. Shell-isolated nanoparticle-enhanced Raman spectroscopy indicated the presence of *OOH species, suggesting the involvement of a dioxygen coordination reaction. Density functional theory calculations showed that both dioxygen and single oxygen coordination H2O2 decomposition pathways played significant roles, and EDTA-Fe0 exhibited high catalysis ability for H2O2 in both pathways. Analysis of the relationship between APCAs’ group structure and APCAs-Fe0 properties indicated that the number of carboxyl groups was crucial for enhancing catalytic activity, while the number of amino groups also impacted antibiotic removal efficiency. Overall, this study provides a solid theoretical foundation for further Fe0 applications and suggests a new method to improve TC removal.

Phase–activity relationship of MnO2 nanomaterials in periodate oxidation for organic pollutant degradation

Manganese dioxide (MnO2), renowned for its abundant natural crystal phases, emerges as a leading catalyst candidate for the degradation of pollutants. The relationship between its crystal phase and catalytic activity, particularly for periodate activation, has remained both ambiguous and contentious. This study delineates the influence of various synthetic MnO2 phase structures on their capabilities in catalyzing periodate-assisted pollutant oxidation. Five distinct MnO2 phase structures (α-, β-, γ-, δ-, and ε-MnO₂) were prepared and evaluated to activate periodate and degrade pollutants, following the sequence: α-MnO₂ > γ-MnO₂ > β-MnO₂ > ε-MnO₂ > δ-MnO₂. Through quenching experiments, electron paramagnetic resonance tests, and in situ electrochemical studies, we found an electron transfer-mediated process drive pollutant degradation, facilitated by a highly reactive metastable intermediate complex (MnO₂/PI*). Quantitative structure-activity relationship analysis further indicated that degradation efficiency is strongly associated with both the crystal phase and the Mn (IV) content, highlighting it as a key active site. Moreover, the α-MnO₂ phase demonstrated exceptional recycling stability, enabling an effective pollutant removal in a continuous flow packed-bed reactor for 168 h. Thus, α-MnO₂/PI proved highly effective in mineralizing organic pollutants and reducing their toxicities, highlighting its significant potential for environmental remediation.

Chemically bonded CdBiO2Br/BiOI heterojunction with strong interfacial electric field for enhanced photocatalysis

Semiconductor-based photocatalysis shows a large potential for contaminant purification, however, a single semiconductor photocatalyst suffers from low utilization efficiency of photogenerated carriers, leading to inferior photocatalytic activity. Herein, CdBiO2Br@BiOI (CBOB@BiOI) heterojunction with a close interface interaction is prepared by a facile precipitation method at the ambient atmosphere. X-ray photoelectron spectroscopy and Density Functional Theory calculations on work function consistently disclose that the formation of CdBiI bonds at the interface induces the electron migration from BiOI to CdBiO2Br, which allows CBOB@BiOI heterojunction to have a strong interfacial electric field (IEF) for efficiently separating photocharges. In-situ Kelvin-probe Force Microscopy measurement demonstrates that CBOB@BiOI heterojunction shows a larger surface potential than CdBiO2Br and BiOI in dark and a potential decrease under illumination, which can be ascribed to the photoinduced electron migration within heterojunction driven by the IEF. Thus, the CBOB@BiOI heterojunction shows a much more efficient photocatalytic activity for the breakdown of tetracycline hydrochloride (TC), which is 2.44 and 3.99 times higher than CdBiO2Br and BiOI, respectively. Electron Paramagnetic Resonance test also confirms that the CBOB@BiOI heterojunction produces much more superoxide radicals and holes as reactive species than CdBiO2Br and BiOI. Furthermore, the latent degradation pathways of TC are investigated by Liquid Chromatograph Mass Spectrometer. This work may provide new ideas for constructing intimately bonded heterojunction photocatalysts with a strong IEF for efficient photocatalytic activity.

Visible-Light Photocatalytic Degradation Efficiency of Tetracycline and Rhodamine B Using a Double Z-Scheme Heterojunction Catalyst of UiO-66-NH2/BiOCl/Bi2S3.

BiOCl is a promising photocatalyst, but due to its weak visible light absorption capacity and low photogenerated electron-hole pair separation rate, its practical application is limited to a certain extent. In this study, a novel double Z-scheme heterojunction UiO-66-NH2/BiOCl/Bi2S3 catalyst was constructed to broaden the visible light response range and promote high photogenerated hole-electron separation of BiOCl. Its photocatalytic performance is evaluated by dissociating tetracycline (TC) and rhodamine B (RhB) in visible light. The optimal proportion of UiO-66-NH2/BiOCl/Bi2S3 hybrids exhibits the best degradation efficiency of visible light illumination (∼93% in 120 min for TC and ∼98% in 60 min for RhB). The synergistic effect of a large visible light response range and the Z-scheme charge transfer mechanism ensure the excellent visible photocatalytic activity of UiO-66-NH2/BiOCl/Bi2S3. It is proven that h+ and •O2- are the main active substances in the photocatalysis process by active substance capture experiments and electron spin resonance tests. The intermediates and degradation processes are analyzed by high-performance liquid chromatography-mass spectrometry. This study proves that the new UiO-66-NH2/BiOCl/Bi2S3 photocatalyst has great application potential in the field of water pollution degradation and will provide a new idea for the optimization of BiOCl.

Roles of soil minerals in the degradation of chlorpyrifos and its intermediate by microwave activated peroxymonosulfate

Soil mineral is one of the important factors that affecting oxidant decomposition and pollutants degradation in soil remediation. In this study, the effects of iron minerals, manganese minerals and clay minerals on the degradation of chlorpyrifos (CPF) and its intermediate product 3,5,6-trichloro-2-pyridinol (TCP) by microwave (MW) activated peroxymonosulfate (PMS) were investigated. As a result, the addition of minerals had slight inhibitory effect on the degradation efficiency of CPF by MW/PMS, but the degradation efficiency of TCP was improved by the addition of some specific minerals, including ferrihydrite, birnessite, and random symbiotic mineral of pyrolusite and ramsdellite (Pyr-Ram). The stronger MW absorption ability of minerals is beneficial for PMS decomposition, but the MW absorption ability of minerals cannot be fully utilized because of the weaker MW radiation intensity under constant temperature conditions. Through electron spin resonance test, quenching experiment and electrochemical experiment, electron transfer, SO4− and OH, SO4− dominated TCP degradation by MW/PMS with the addition of birnessite, Pyr-Ram and ferrihydrite, respectively. Besides, the adsorption effect of ferrihydrite also enhanced the removal of TCP. The redox of Mn (III)/Mn (IV) or Fe (II)/Fe (III) in manganese/iron minerals participated in the generation of reactive species. In addition, the addition of minerals not only increased the variety of alkyl hydroxylation products of CPF, causing different degradation pathways from CPF to TCP, but also further degraded TCP to dechlorination or hydroxylation products. This study demonstrated the synergistic effect of minerals and MW for PMS activation, provided new insights for the effects of soil properties on soil remediation by MW activated PMS technology.