Oxidation Process Research Articles

Activation mechanism of CoFe2O4 nanocatalysts on different oxidants and degradation efficiency of butyl xanthate

Owing to the technological limitations associated with beneficiation technology, large amounts of flotation reagents remain in mineral processing wastewater, which is extremely detrimental to humans and the environment. In addition, direct reuse of mineral processing wastewater will adversely affect the entire mine water system. Efficient treatment of residual butyl xanthate from tailing wastewater has recently attracted increasing interest. In this study, we compared the degradation efficiencies of cobalt iron oxide (CoFe2O4) nanoparticles assisted by sulfite-activated advanced processes and persulfate (PDS) and peroxymonosulfate (PMS) advanced oxidation processes on butyl xanthate (BX) for the first time and explored possible reaction mechanisms in various systems. We conducted comprehensive experiments on the acid/alkali washed catalysts using oxidizing agents, obtaining catalysts best adapted to three degradation systems. Results of batch experiments indicated that the BX degradation rate for all the three systems exceeded 95 % within 60 min under their respective optimal conditions and that the best total organic carbon content (TOC) removal rate for these systems was 85.79 %. The effects of key factors, such as catalyst dosage, oxidant dosage, solution pH, and coexisting ions, on BX degradation were investigated. Furthermore, the active free radicals that played a major role in each system were detected via electron paramagnetic resonance (EPR). EPR results indicated that SO3·− and ·O2− were the main active species of the CoFe2O4/sodium sulfite system, ·OH and ·O2− participated in the degradation of BX in the CoFe2O4/PDS system, and ·O2− was present in the CoFe2O4/PMS system. Thus, this study promotes the application of CoFe2O4 with magnetism as a catalyst in wastewater treatment and provides new insights into the effective treatment of organic pollutants in tailing wastewater.

Integration of single-atom photothermal catalysts with surface-localized high temperature in peroxymonosulfate-based Fenton-like systems for enhanced antibiotics degradation

This study delves into integrating single-atom catalysts with photothermal effect in peroxymonosulfate (PMS)-based Fenton-like systems for enhanced pollutant degradation. A single-atom photothermal catalyst (Co/PMCNs) was designed using mesoporous carbon spheres as both a single-atom support and a photothermal material. Near-infrared (NIR) light was employed due to its superior thermal effect and penetration capacity in water. It was found that Co/PMCNs could generate surface-localized high temperatures for accelerating PMS activation and reducing energy gap of activation reactions, leading to improved degradation performance. Surface-localized high temperatures were demonstrated as key in distinguishing photothermal heating from external heat sources for PMS activation. Moreover, this system performed well across various operating conditions and water matrices, with Co/PMCNs showing promising recyclability. This study highlights the impact of surface-localized high temperatures on heterogeneous catalysis under NIR irradiation, and underscores the potential of integrating single-atom catalysts with photothermal effects into advanced oxidation processes for effective water pollution control.

Artificial Neural Network-driven Optimization of Fe3O4 Nanoparticles/PVDF Macrospheres in Fenton-like System for Methylene Blue Degradation

Efficient degradation of industrial dyes remains a critical challenge in environmental engineering. This study introduces a novel Fe3O4 nanoparticles/PVDF macrospheres in a Fenton-like system, optimized using an Artificial Neural Network (ANN) for the degradation of Methylene Blue (MB). A feedforward backpropagation neural network model to optimize and predict the performance of this advanced oxidation process under various operational conditions. The model was trained, validated, and tested with robust datasets, demonstrating high predictive accuracy and generalization capability. The Mean Square Error (MSE) and Root Mean Square Error (RMSE) during testing were 0.0200 and 0.1414, respectively, indicating precise predictions. The coefficient of determination (R²) and correlation coefficient (R) were exceptionally high at 0.9744 and 0.9871, affirming the model's ability to capture the underlying dynamics of the degradation process effectively. The ANN-driven approach not only enhanced the efficiency of the MB degradation process but also provided significant insights into the scalability and applicability of the Fe3O4/PVDF system for practical water treatment solutions. This study underscores the potential of integrating advanced machine learning techniques with chemical engineering processes to achieve sustainable and efficient environmental management solutions, particularly for the treatment of recalcitrant wastewater contaminants.

Comprehensive analysis of laminar burning velocity in DEK/NH3-air premixed flames under varied pressure conditions

3-pentanone (DEK) is a biomass oxygenated fuel with high energy density and low emissions. It shows promising potential in increasing the combustion of NH3. This study examines the laminar burning velocity (LBV) of a fuel mixture composed of DEK/NH3-air. The LBV of DEK/NH3-air was determined with a constant-volume combustion bomb under the following conditions: initial temperature (T) of 448 K, pressure (P) of 1 to 3 atm, equivalence ratio (ϕ) between 0.7 and 1.3, and NH3 mole fraction (XNH3) varying from 0 % to 90 %. A combustion kinetic model for DEK/NH3 mixed fuel was developed and verified using experimental results. Overall, the model can capture the trend of LBV well. Subsequently, a comprehensive kinetic analysis was conducted utilizing this mechanism to elucidate the effect of NH3 mixing on DEK/NH3-air mixed fuel. The results indicate that LBV of DEK/NH3-air mixture declines as XNH3 increases, primarily attributed to the reduction in radical pool concentration. Conversely, the effect of the decrease in flame temperature is relatively minor. Furthermore, as XNH3 mole fraction decrease, there is a slight alteration in the consumption pathway of NH3. The elevation in DEK mole fraction leads to an increased production of radicals, thereby amplifying the oxidation process of NH3. The proportion of the oxidation of NHi pathway also increases. Finally, the change of NO content in DEK/NH3-air flame was observed. The rise in XNH3 leads to a gradual increase in the content of NO until it reaches a peak, after which it starts to decline. This phenomenon is dependent on the presence of O, OH, and NHi radicals. In addition, it has been discovered that augmenting ϕ can significantly reduce the concentration of NO in DEK/NH3-air mixture.

Hollow TiO2/Bi2MoO6 Janus-nanofibers for photo-reforming of antibiotics into carbon monoxide

Photo-reforming is an environmentally friendly technology for converting organic wastewater into carbon monoxide (CO), a potential energy source and an important industrial material. Achieving efficient photo-reforming of CO production remains a challenge due to the limitation on fast photogenerated carrier recombination. Here, the TiO2/Bi2MoO6 hetero-nanofibers are well-designed to possess unique Janus interface and ingenious hollow structure. The photo-deposition experiments demonstrated that the Janus binary interface can realize the directional migration of interfacial charges and the spatial separation of redox sites. Moreover, the hollow framework allows full exposure of the bicomponent to reactants and provides excellent optical absorption through multiple light scattering inside the tube, as evidenced by theoretical simulations via COMSOL Multiphysics. The photo-reforming yield of CO from 6000 ppm tetracycline hydrochloride (TCH) solution reaches 2.69 μmol∙g−1∙h−1 (corresponding degradation rate of 44.55 % after 5 h), about 1.44-fold superior to that of the TiO2/Bi2MoO6 core-shell hetero-nanofibers. 13C isotope tracing experiments showed that the efficiency of CO production in the photocatalytic TCH oxidation process is superior to that in carbon dioxide reduction process. Furthermore, when oxygen was introduced into the photocatalytic system, the photo-reforming CO yield from the TCH solution was significantly increased to 60.45 μmol∙g−1∙h−1, which was 22.47 and 5.12 times higher than in carbon dioxide and air atmosphere, respectively. This work provides a promising interfacial engineering to design efficient photo-reforming catalysts for energy production and environmental remediation.

Simple incorporation and calcination of Zn-Al LDH during PEO processing in near-neutral pH solutions

Plasma electrolytic oxidation (PEO) process was employed for preparing oxide coatings on AA2024 aluminum alloy in solutions containing Zn-Al layered double hydroxide (LDH) particles. Sodium hexametaphosphate aqueous solution was selected as the standard solution, based on its almost neutral pH value considered as important for the LDH stability. Different additives to the standard solution were examined including 2-mecaptobenzothiazole (MBT) and different Zn-Al LDH compounds. The formed coatings underwent characterization regarding their morphology, chemical and phase composition, as well as assessment of their photocatalytic and corrosion protection efficiency. Coating thickening and compactness evolution were noted for all coatings with LDH additions to the standard solution. Obtained coatings are well-crystallized featuring γ-Al2O3 and two Zn-containing crystalline phases, namely ZnO and NaZnPO4, originating mainly from the LDH addition to the solution. PEO coatings obtained in this study demonstrated very reasonable photocatalytic activity for immobilized photocatalyst, reaching 51 % after 6 h under UV irradiation. The inclusion of Zn-Al LDH substantially boosted the impedance modules at low frequencies by two orders of magnitude compared to bare AA2024 alloy when exposed to a 3.5 % NaCl solution.

Protecting celtuce (Lactuca sativa L. var. augustana) slices against storage-induced oxidative stress and discoloration by using diode laser exposure

Diode laser irradiation is a novel approach applied to preserve the quality of fresh commodities and minimise oxidative processes, including browning in fresh-cut products. The objective of this study was to investigate the efficacy of diode laser treatment in enhancing the quality of celtuce slices during refrigerated storage at 4 °C. The celtuce slices were subjected to a 660 or 450 nm diode laser for 5 min and then stored for 10 d. Both laser treatments hindered the progression of weight loss and firmness increase in the celtuce slices. The use of a 450 nm diode laser effectively prevented the development of browning and preserved the surface colour by inhibiting the increase in a* and overall colour difference values, as compared to other treatments, during storage for 10 d. The diode laser treatment suppressed the increase in oxidative stress by lowering the levels of MDA, H2O2, and O-2 while retaining a high level of DPPH scavenging activity, AsA, and antioxdant enzyme activities, including SOD, CAT, APX, and GR, in comparison to the untreated slices. The treatment enhanced chlorophylls content due to the up-regulation of LsHEMA1 gene and down-regulation of LsNYC1 gene. The treatment also inhibited factors involving enzymatic browning reaction by suppressing PAL activity, total phenols content, PPO activity and LsPPO gene expression. These suggest that the blue diode laser exposure at 450 nm for 5 min is an effective approach hindering oxidative stress and discoloration of celtuce slices during storage.

Novel catalytic membrane based on γ-FeOOH@PVDF/peroxymonosulfate for efficient ammonia recovery: Self-cleaning mechanism and emerging organic contaminant degradation performance

The resolution of membrane fouling issues is crucial for the commercial application of membrane distillation (MD) ammonia recovery. The peroxymonosulfate-based advanced oxidation process (PMS-AOP) exhibited conspicuous degradation of organic pollutants, and in-situ coupling with the MD process could probably achieve desirable antifouling performance. In this research, a novel γ-FeOOH@PVDF catalytic membrane was fabricated by gas–liquid self-deposition method and fluorination treatment. The γ-FeOOH nanosheets arrayed on the substrate membrane endowed the catalytic membrane with superhydrophobicity. The MD ammonia recovery of the digestate achieved a high recovery rate (97.3%), and no membrane fouling or wetting phenomena were detected by real-time monitoring by optical coherence tomography (OCT). The batch degradation experiments of thiamphenicol (TAP) validated the γ-FeOOH@PVDF/PMS system with superior degradation performance and stability. The electron paramagnetic resonance (EPR) coordinated free radical quenching experiment determined the active substance (SO4•-, 1O2, O2•- and •OH) in the degradation process. In addition, the potential self-cleaning mechanism of the radical and non-radical pathways of γ-FeOOH@PVDF was elucidated via density functionaltheory (DFT) calculation. The quinone groups in the organic pollutants facilitated the redox of Fe(Ⅲ)/Fe(Ⅱ) and accelerated the activation of PMS. Hence, the catalytic membrane developed in this research provided a novel instructive strategy for membrane fouling control and also exhibited significant potential of coupling catalysis and membrane technology for water treatment.

Preliminary treatment of landfill leachate by hydrodynamic cavitation supported by Fenton process

Hydrodynamic cavitation as an effective and environmentally friendly method of treating wastewater. Massive amounts of energy may be released into the surrounding liquid during hydrodynamic cavitation, resulting in mechanical , chemical and thermal impacts. Bacteria and organic materials in sewage can be broken down by these circumstances. Furthermore, a coupling effect may be created by combining hydrodynamic cavitation with other water treatment techniques. In this study it is aim to investigate and improve the hydrodynamic cavitation (HDC) process supported by Fenton process for the pretreatment of landfill leachate. In the second phase of the study, the effectiveness of the hydrodynamic cavitation process was investigated in conjunction with the Fenton process. The parameters such as the number of cavitation events, pH, and temperature were evaluated. The effluent was characterized and monitored for COD measurements. The consequences of operational variables such H2O2, Fe+2 , and pH values were investigated to determine the optimal Fenton oxidation process parameters. The findings of the experiment showed that pH values were ideal for Fenton oxidation of 3.5-4.5, 30 mM H2O2, and 5 mM Fe+2. A combined treatment process of Fe+2+H2O2, HDC + Fenton, and Cavitation alone were conducted for the treatment of landfill leachate. The results showed that the removal rates of chemical oxygen demand (COD) for the combined processes were 32.85%, 44.28%, and 7%, respectively. Temperature, pH, and the number of cavitation events were among the parameters that were assessed. The effluent was measured for COD and was characterized.

Theoretical-experimental study of Fe–ZrO2 and Co–ZrO2. Oxidative degradation of methyl orange azo dye

In recent years, advanced oxidation processes (AOPs) based on the generation of sulfate radicals (SO4●-) (SR-AOPs) have emerged as an innovative method for the decontamination of water and wastewater. In this study, Fe(II) and Co(II) catalysts supported on ZrO₂ were synthesized and employed as an activator for PMS and PS for the degradation of methyl orange. The general objective is to gain detailed insight into the interaction between oxidants and supported metal catalysts at the molecular level. Experimental results and density functional theory (DFT) calculations were employed to analyze the potential activation mechanism of the oxidants. The support was prepared via coprecipitation, and metal ion deposition was achieved through incipient wetness impregnation. The characterization of the catalysts was conducted through atomic absorption spectrometry, X-ray diffraction and Fourier-transform infrared spectroscopy. The findings indicated that PMS was the most efficient oxidant, with Co–ZrO2 emerging as the most effective catalyst (77% MO mineralization), compared to Fe–ZrO2, which exhibited a lower degree of mineralization (37.6%) under the specified experimental conditions. The use of PS as an oxidant resulted in low levels of degradation for both catalysts. The remarkable catalytic efficacy of the Co–ZrO₂/PMS system was elucidated through the application of density functional theory (DFT) calculations. These revealed that the adsorption energy of the oxidants on Co–ZrO₂ is lower than that on Fe–ZrO₂, which could facilitate the subsequent release of radicals to the reaction medium.

Reinvestigation on the UV/sulfite oxidation of organic pollutants: The overlooked role of excited states and bromate control

In recent years, the UV/sulfite (S(IV)) has been proposed as a promising advanced oxidation process for water treatment in the presence of oxygen. However, the mechanism of S(IV) activation is not fully understood, as the interaction between S(IV) and photo-excited pollutants has been underexplored. In this work, an aerated UV/S(IV) system was established, and propranolol (PRO) was selected as a target pollutant. Under the irradiation at 254 nm, this system could degrade 95.6 % of PRO with 2 mM S(IV) in 60 min. The removal of PRO was positively related to the S(IV) dose, while an increasing pH exhibited a negative effect. Direct photolysis, SO4•−, and HO• collaboratively contributed to PRO removal, with SO4•− playing a primary role. Laser flash photolysis reveals that both radical cation of PRO (product of biphotonic process) and the triplet state (T1PRO) can react with HSO3− at rate constants of 5.2 × 108 M−1 s−1 and 2.1 × 107 M−1 s−1, accordingly. These reactions may offset the deficient photoactivation of S(IV) under acidic conditions. Apart from PRO, other organic pollutants could also be effectively degraded. Furthermore, this system has a great advantage over UV/persulfate due to the absence of transformation of background bromide ions to hazardous bromate. Our study significantly updates the decontaminating mechanism of organic pollutants in the aerated UV/sulfite system.

Mechanistic Investigation of Rapid Catalytic Degradation of Acetaminophen Using Electrochemical-Induced CoFe2O4 by Activation of Peroxymonosulfate

Advanced oxidation technology based on PeroxyMonoSulfate (PMS) has become a research hotspot in the field of water treatment. To improve the activation efficiency of PMS, electrochemically assisted spinel type catalyst CoFe2O4 was used to activate PMS and achieve effective degradation of acetaminophen. The influence of single factor on degradation was explored to determine the best degradation process parameters of E/CoFe2O4/PMS system. Results show that under the optimum reaction conditions (DC voltage is 6[Formula: see text]V, the initial mass concentration of acetaminophen is 10[Formula: see text]mg[Formula: see text]L[Formula: see text], the dosage of CoFe2O4 is 0.3[Formula: see text]g[Formula: see text]L[Formula: see text], and the mass concentration of PMS is 1.5[Formula: see text]g[Formula: see text]L[Formula: see text]), the degradation rate of acetaminophen reaches up to 95% within 20[Formula: see text]min. CoFe2O4 catalyst showed a good stability, with only a 12% decrease in acetaminophen degradation after three cycles. Radical quenching tests show that [Formula: see text] and [Formula: see text] played predominant roles in the advanced oxidation process. This work provides a new strategy for more efficiency in PMS activation.

Periodate activation via metals and metal-based complexes: progress in degradation properties and mechanisms

ABSTRACT Residuals of refractory organics in water create a deep hazard to the water environment and human health, hence it is urgent to develop efficient approaches to remove refractory organics. Being a novel oxidizer, periodate (PI, IO4-) is considered to be stable and efficient in advanced oxidation processes for degrading refractory organics, such as antibiotics, dyes, pesticides, etc. Since the activity of PI alone is low, it is necessary to activate the PI to form active species in effectively removing organics. The studies of PI activation via monometallic, bimetallic, metal oxides, metal complexes, etc., have obtained more concerns owing to the high efficiency in decomposing organics. However, no reviews related to these studies have been published in recent years. This review summarized the properties and uses of PI, analyzed degradation properties and mechanisms of various metals and metal-based complexes in activating PI to remove refractory organics, and highlighted the limitations of these processes as well as the future research directions.

NH3/C2H6 and NH3/C2H5OH oxidation in a shock tube: Multi-speciation measurement, uncertainty analysis, and kinetic modeling

This study examines NH3, NO, and CO profiles during NH3/C2H6 and NH3/C2H5OH oxidation in a shock tube using laser absorption spectroscopy at 1317–1957 K and ∼2.8 bar, with 5–20% C2H6 or C2H5OH, equivalence ratios of 0.5/1.0/1.5, and a 0.9 argon dilution ratio. Metrological uncertainty analysis on mole fractions have been performed. A novel dynamic uncertainty methodology is proposed to time-resolved speciation profiles. From the experimental measurements, the promotional effect on ammonia ignition by C2H6 or C2H5OH is identical under investigated conditions. The multi-speciation profiles demonstrate reasonable relations among the consumption of NH3 and the formation of NO and CO, which show strong temperature and equivalence ratio dependence. An updated PTB-NH3/C2 1.1 mechanism accurately predicts ignition delay times and speciation profiles. Sensitivity analysis reveals NH3 chemistry’s significant control, with NH3+O2/H/OH and N2H2+M reactions being critical at >1300 K, and HO2 interactions being pivotal at 800–1200 K. The reactions related to N2H2 and N-C chemistries dominate for fuel-rich mixtures at high temperatures, resulting in a reverse equivalence ratio dependence on IDTs, namely fuel-rich mixtures exhibit the lowest reactivity. The N-C chemistries, particularly the pronounced reaction pathway of HCN→CN→NCO→HNCO→CO play a crucial role in maintaining the CO level constant after reaching its peak position under fuel-rich conditions·NH3 consumption pathways shift from NH2→H2NO→HNO→NO→NO2→N2O→N2 at intermediate temperatures to NH3→NH2→NH→N(HNO)→NO→(N2O)N2 at high temperatures. The C2-additives participate in the oxidation process by introducing additional OH/H/CH3 radicals, thereby facilitating the reactive radical pool and developing the N-C intersystem-crossing pathways. In summary, the extensive multi-speciation data, metrological uncertainty analysis, mechanism validation and development, together with comprehensive kinetic modelling can be valuable resources for further studies of ammonia combustion.

Enhanced activation of peroxymonosulfate with cobalt-doped manganese-iron oxides for contaminant degradation: Regulation of oxygen vacancy defects

Peroxymonosulfate (PMS) based on heterogeneous catalytic reaction was a promising advanced oxidation process (AOP) to remove refractory contaminants. However, the contaminant degradation efficiency was challenged by the limited number of catalytic active site and low capacity for durable electron transfer. In this study, cobalt-doped manganese-iron oxides (CoxMn1-xFe2O4) rich in oxygen vacancy (Ov) were synthesized using a microwaved hydrothermal method and applied to activate PMS for bisphenol A (BPA) degradation, which achieved the complete removal of BPA within 30 min. In all samples, Co0.5Mn0.5Fe2O4 exhibited good catalytic activity for PMS, which was approximately 21.10 times higher than that of MnFe2O4. The results of density functional theory calculations and in-situ characterization demonstrated that the enhanced performance was ascribed to the generation of Ov and the enrichment of active site, which significantly accelerated the cycling of redox pairs and improved the PMS adsorption, which was more favorable to the formation of active specie in the electron transport process. The oxidation process involved both free radical and non-radical mechanisms, with main reactive species of O2−, and 1O2 being responsible for BPA degradation. In addition, the effects of different aqueous matrices, the results of reusability experiments, and ecotoxicity assessment experiments demonstrated the viability of the Co0.5Mn0.5Fe2O4/PMS system for real sewage purification. This research revealed a structural regulation method to enhance the catalytic activity of the material and offered new perspectives on the engineering of rich Ov.

Exploring the intensified catalytic role of biochar in facilitating advanced oxidation of tebuconazole

Biochar (pyrolyzed organic material) has been increasingly recognized for its catalytic role in facilitating the advanced oxidation of emerging organic pollutants. However, the inherent catalytic capacity remains highly uncontrollable, leading to considerable uncertainty when scaling up for real-world applications. This study explores the intensified catalytic role of biochar coated with CaO2 in generating hydroxyl radicals (OH·) and facilitating advanced oxidation of tebuconazole, a prevalent fungicide, tebuconazole was selected as a representative pesticide in agricultural drainage. In addition to evaluating the potential for degradation by advanced oxidation processes (AOPs), the adsorption capabilities of two commercially available biochars, one derived from agricultural waste (ABC) and the other from spruce chips (SBC), as well as their CaO2-coated derivatives (ABC/CaO2 and SBC/CaO2), were also assessed. By taking advantage of the strong adsorption capacity of biochar, and activating AOPs at the adsorption sites by CaO2, this material enables more efficient and targeted removal of tebuconazole. The results indicate that CaO2 coating on biochar promoted over tenfold increase in the generation of OH·, resulting in 99% tebuconazole removal within 10 min. Despite a decrease in adsorption capacity of 40–50% resulted by CaO2 coating, the 10-minutes overall pesticide removal performance was significantly enhanced. The catalytic potential of biochar is closely related to its surface chemical properties, particularly the presence of persistent free radicals which can be regenerated. This research paves a new way for employing CaO2-enhanced intensified biochar in agricultural mitigation measures.

Application of antioxidants in cold plasma treatment of fish oil

As a mild non-thermal treatment technology, cold plasma can lead to lipid oxidation when applied to products with high lipid content. This study focuses on the physical and chemical properties of fish oil with cold plasma treatment and to explore the potential of Curcumin, Tea polyphenols, Vitamin E and β-Carotene in inhibit the oxidation process. Following treatment, the peroxide value and malondialdehyde value of the fish oil significantly increased, while the content of unsaturated fatty acids decreased and the singlet oxygen content rose (p < 0.0 5). However, the introduction of antioxidants during treatment yielded diminished peroxide and malondialdehyde values in the fish oil, thereby effectively curbing the presence of singlet oxygen. Notably, fish oil enriched with vitamin E exhibited the most robust antioxidant activity among the tested compounds. This study offers insights into strategies for enhancing the stability of high-fat foods subjected to cold plasma treatment. Industrial relevanceFish oil has long been essential in the processing of food, pharmaceuticals, and animal feed, making its quality crucial. This study revealed that cold plasma treatment accelerated the oxidation of fish oil; however, the addition of antioxidants effectively mitigated this effect. In industrial settings, cold plasma technology is favored in the food industry for its low-temperature operation and high efficiency in microbial inactivation. Despite these advantages, the reactive species produced during the process can cause lipid peroxidation and alter amino acids in proteins. This research offered critical insights into optimizing process parameters to minimize lipid oxidation. It also lays the groundwork for developing more efficient and safer food processing technologies and offers new approaches to extending the shelf life of fish oil and other lipid-rich foods during cold plasma treatment.

Piezocatalytic techniques and materials for degradation of organic pollutants from aqueous solution

With the rapid development of industry, agriculture, and urbanization, various organic pollutants have accumulated in natural water, posing a potential threat to both the ecological environment and human beings, and removing organic pollutants from water is an urgent priority. Piezoelectric techniques, with the advantages of green, simple operation, and high efficiency, are highly sought after in the degradation of environmental organic pollutants. Moreover, combining piezoelectric techniques with advanced oxidation processes (AOPs), photocatalysis, or electrocatalysis can further effectively promote the efficient degradation of target pollutants. Therefore, a perspective is presented on the recent progress of piezoelectric techniques for the degradation of various organic pollutants from aqueous solutions. The classification of various piezoelectric materials, as well as modification strategies for improving piezocatalysis, are first systematically summarized. Furthermore, the latest research on piezocatalysis and its combination with other technologies, such as AOPs, photocatalysis, and electrocatalysis, in the degradation of environmental pollutants is discussed. The potential mechanisms of piezocatalysis are also analyzed in depth. Finally, the urgent challenges and future opportunities for piezoelectric techniques in the degradation of organic pollutants are provided.

Activation of periodate by C2N3 loaded with metal single-atoms for ultrafast removal of micropollutants: Electron transfer outperforms reactive oxygen species

Different transition metal single-atoms may lead to a variety of reaction mechanisms in advanced oxidation processes (AOPs). The transition metal (Fe, Ni and Mn) single-atom C2N3 catalysts were used to degrade acetaminophen (AP) by activating periodate (PI). Mn-CN+PI system can completely remove AP in 2 min, and its rate constant (5.7550 min−1) was 9.37 and 22.69 times higher than that of Ni-CN+PI and Fe-CN+PI. The system showed excellent performance in different influencing factors and micropollutant removal experiments. The recyclable Mn-CN sponge sheet showed good practical application performance in microreactor experiments. Electron paramagnetic resonance, radical quenching, electrochemical experiments, combined with theoretical simulation certified that Mn-CN+PI system was dominated by electron transfer mechanism, which was superior to reactive oxygen species that dominated Ni-CN+PI and Fe-CN+PI systems. The electron transfer-mediated pollutant degradation provides insights into PI-based AOPs, and offers a feasible pathway for micropollutant degradation.

Effect of cyclic oxidation temperature on compressive strength of Cu-based brake pad for high-speed train

The cyclic oxidation tests of Cu-based brake pads at temperatures of 25, 300, 400, 500, 550, 600, 650 and 700 °C were conducted to simulate the oxidation of the friction surface under different braking speeds. Furthermore, the effect of cyclic oxidation temperature on the compressive strength was investigated. The results show that the cyclic oxidation process of Cu-based brake pads can be divided into three stages: mild oxidation (≤400 °C), moderate oxidation (500–600 °C) and severe oxidation (≥650 °C). Mild oxidation results in the formation of spherical Cu2O particles. The surface is covered by Cu2O and Fe2O3 nanosheets for moderate oxidation. Severe oxidation is characterized by a continuous thick CuO film, Fe2O3 nanosheets, and eroded graphite particles. The compressive strength and toughness of Cu-based brake pads show a declining trend as the cyclic oxidation temperature rises. The compressive strength of the Cu-based brake pad after oxidized at 700 °C, recorded at 30.56 MPa, is considerably lower than that of the original samples, which was 132.2 MPa. This reduction in compressive strength is attributed to the embrittlement of the metallic matrix and the formation of pores from graphite oxidation.