Paramagnetic Radical Research Articles

Heat-activated peracetic acid for degradation of diclofenac: kinetics, influencing factors and mechanism

ABSTRACT Heat-activated peracetic acid (PAA) was used to degrade diclofenac (DCF) in this study. Electron paramagnetic resonance and radical scavenging experiments proved that organic radicals (i.e. CH3C(=O)O• and CH3C(=O)OO•) were the primary active species for DCF removal in the heat/PAA process. The degradation efficiency of DCF increased with the increase of temperature or initial PAA concentration in the heat/PAA process, and the optimal reaction pH for DCF removal was neutral. The presence of NO3 − or SO4 2− insignificantly affected DCF degradation, while Cl− was favourable for DCF removal in this process. In contrast, an obvious inhibition on the removal of DCF was observed with the addition of natural organic matter, which might be responsible for the lower DCF removal in real waters. Finally, dechlorination, formylation, dehydrogenation and hydroxylation were proposed to be four degradation pathways of DCF in the heat/PAA system based on the five detected transformation products.

Bicarbonate-enhanced generation of hydroxyl radical by visible light-induced photocatalysis of H2O2 over WO3: Alteration of electron transfer mechanism

The generation of hydroxyl radical (•OH) by visible light-illuminated tungsten oxide (WO3) was found to be significantly improved in the presence of hydrogen peroxide (H2O2) and bicarbonate ion (HCO3−). A ternary system of hν/WO3/H2O2/HCO3− showed synergistic enhancement in oxidation of benzoic acid (BA, a •OH probe compound) into hydroxybenzoic acids (HBAs), exhibiting even less consumption of H2O2 than hν/WO3/H2O2. Analyses of HBAs from BA oxidation (three HBA isomers and 18O-labelled HBA from H218O2) suggested that hν/WO3/H2O2/HCO3−, contrary to hν/WO3/H2O2, generated •OH mainly via one-electron transfer from the conduction band of WO3 to H2O2. The dominant one-electron reduction of H2O2 over HCO3−-treated WO3 was further evidenced by Koutecký–Levich plots obtained with a rotating disk electrode setup. Based on different experiments using electron paramagnetic resonance spectroscopy, radical scavengers and probes, (photo-)electrochemical measurements, and density functional theory calculations, the mechanisms underlying the enhanced generation of •OH by hν/WO3/H2O2/HCO3− were discussed.

Construction of H6PW9V3O40@rht‐MOF‐1 for deep oxidative desulfurization of fuel oil

AbstractDeep desulfurization is impending for environmental conservation by way of reducing supplied emissions from fuel oil. Developing new and effective catalysts on deep desulfurization is still a great changeling. In this piece of work, a series of three H3+nPW(12‐n)VnO40@rht‐MOF‐1 have been synthesized by one‐pot self‐assembly hydrothermal reaction of CuCl2·2H2O and 5‐tetrazolyl isophthalic acid (H3TZI) with three H3+nPW(12‐n)VnO40 (polyoxometalates [POMs]), respectively. X‐ray crystallographic analysis reveals that the POMs have been successfully encapsulated in the cages of rht‐MOF‐1. The affording complex 3, as heterogeneous catalyst, is able to effectively catalyze the extraction catalytic oxidation desulfurization system (ECODS) of model oil and real fuel oil under mild reaction conditions. The remarkable encapsulation of POMs in rht‐MOF‐1 resulted in the heterogeneous catalysis, enabling it to be recycled in the system. The reaction kinetics has been investigated, and the redial reaction mechanism has been verified by electron paramagnetic resonance (EPR) analysis and radical quenching experiments. This approach provides an easy and effective route on developing heterogeneous catalysts that could be applied in the deep ECODS of fuel oil.

Carbon nanotube filter functionalized with MIL-101(Fe) for enhanced flow-through electro-Fenton.

Herein, an electrochemical carbon nanotubes (CNT) filter modified with MIL-101(Fe) has been designed for the electro-Fenton applications by serving as a functional flow-through electrode. Under an electric field, the hybrid filter enabled the in situ generation of H2O2via the two-electron oxygen reduction reaction, which promoted the production of HO by the accelerated Fe2+/Fe3+ cycling of MIL-101(Fe). It was observed that 93.2±1.2% tetracycline and 69.0±0.8% total organic carbon (TOC) were removed in 2h under the optimized conditions. The electron paramagnetic resonance (EPR) analysis and radical scavenging experiments revealed that HO predominated the tetracycline degradation. As compared to the batch reactor, the performance of the proposed system was improved by 5.6 times owing to the convection-enhanced mass transport. The plausible working mechanism and degradation pathway were also subsequently proposed. The findings reported in this study provide a promising insight for the environmental remediation by integrating nanotechnology and Fenton chemistry.

Heterogeneous activation of H2O2/Na2S2O8 with iron ore from water distribution networks for pollutant removal.

In this study, we investigated using the main composition of pipe deposits from water distribution networks as catalyst to activate dual-oxidant H2O2/Na2S2O8 system to produce radicals for perchloroethylene and chloramphenicol removal. According to the results, the degradation efficiency of perchloroethylene by H2O2/Na2S2O8 system was 92.05% within 8 h. Due to the slow conversion between ≡Fe3+ and ≡Fe2+, the hydroxylamine was introduced to reduce reaction time. As for the results, the degradation efficiency of chloramphenicol in the H2O2/Na2S2O8 system with hydroxylamine assistance was 73.31% within 100 min. Meanwhile, several key affecting factors and the kinetic models were investigated. The primary radicals were identified by electron paramagnetic resonance and radical scavenging tests. Eleven degradation products were confirmed by high-resolution liquid chromatography-mass spectrometry. The result of this study provided the theoretical basis for resource utilization of pipe deposits in water treatment in case of emerging contamination events.

Sulfamethoxazole degradation by alpha-MnO2/periodate oxidative system: Role of MnO2 crystalline and reactive oxygen species.

Pollutant degradation via periodate ([Formula: see text]) and transitional metal oxides provides an economical, energy-efficient way for chemical oxidation process in environmental remediation. However, catalytic activation of periodate by manganese dioxide and the associated mechanism were barely investigated. In this study, four MnO2 polymorphs (α-, β-, γ- and δ-MnO2) were synthesized and tested to activate [Formula: see text] for the degradation of sulfamethoxazole (SMX). The reactivity of different MnO2 structures followed the order of α-MnO2 > β-MnO2 > γ-MnO2 > δ-MnO2, suggesting that the particular crystalline structure in α-MnO2 would exhibit higher activities via [Formula: see text] activation. Herein, in α-MnO2/[Formula: see text] system, 91.1% of SMX was eliminated within 30min with degradation rate constant of 0.0649min-1, and the neutral pH exhibited higher efficiency in SMX degradation compared with acidic and alkaline conditions. Singlet oxygen (1O2) was unveiled to be the dominant ROS according to the results of electron paramagnetic resonance, chemical probes and radical quenching experiments, whereas [Formula: see text] and •OH were mainly acted as a free-radical precursor. Six oxidation products were identified by LC-MS, and the elimination of sulfonamide bond, hydroxylation and direct oxidation were found to be the important oxidation pathways. The study dedicates to the mechanistic study into periodate activation over alpha-MnO2 and provides a novel catalytic activation for selective removal in aqueous contaminants.

Peroxymonosulfate activation by sponge-based FeS material for efficient degradation of tetracycline: The critical role of sponge

The effective control of antibiotic pollution in water has become an important issue in the field of environmental protection. In this study, the composite of iron sulfide and melamine sponge (FeS@MS) was successfully synthesized by in-situ synthesis method and applied to the oxidative removal of tetracycline (TC) in the presence of peroxymonosulfate (PMS). Under optimal conditions ([FeS@MS] = 0.1 g/L and [PMS] = 0.2 mM), 95.7% of TC was degraded in 5 min. The presence of NO3−, SO42−, and Cl− slightly inhibited TC removal, whereas HPO4− had a certain promotion effect in activating PMS to degrade TC. The primary reactive oxygen species (ROS), including SO4−, OH, 1O2, and O2− were identified through electron paramagnetic resonance (EPR) spectroscopy and radical quenching experiments. In addition, Fe3+ in solution could react with FeS to produce Fe2+, which continuously activates PMS to generate radicals for TC degradation. The presence of MS reduced the agglomeration of FeS and played a protective role in the slow release of Fe2+. The degradation performance was further validated in real water matrices. This study provided new insight into fabricating functional material for the remediation of antibiotic wastewater.

High 1T phase and sulfur vacancies in C-MoS2@Fe induced by ascorbic acid for synergistically enhanced contaminants degradation

Applicating co-catalyst into Fenton-like advanced oxidation processes to improve the performance for wastewater remediation has attracted widespread attention. Among them, developing highly active and green heterogeneous catalyst integrating homogeneous ferrous ions and inorganic co-catalyst is a great challenge. Herein, ascorbic acid additive was creatively introduced into the precursor composed of thiourea, sodium molybdate and ferric chloride to synthesize carbon intercalated molybdenum disulfide anchoring iron (C-MoS2@Fe) by a simple one-step hydrothermal method. C-MoS2@Fe exhibited an amazing apparent first-order constant as high as 0.739 min−1 about 10 times higher than that of the homogeneous Fe2+/MoS2 system for the sulfamethoxazole (SMX) removal and achieved 68.7% removal of TOC in 6 min, which was attribute to the synergistic enhancement of high 1T phase (82.0%) and sulfur vacancies induced by the introduction of ascorbic acid. Notably, the C-MoS2@Fe was also capable of efficiently degrading multiple organic contaminants such as pharmaceuticals, phenolic compounds, and organic dyes. Compared with the homogeneous Fe2+/PMS system, the C-MoS2@Fe/PMS system expanded the effective pH range (2.0 ∼ 9.0) and the ultralow iron ions leaching (0.204 mg L-1) avoided the formation of iron containing sludge. The results of electron paramagnetic resonance (EPR), radical quenching and probe experiments indicated that •OH was the main active species with the contribution rate about 60.3%. Furthermore, possible degradation pathways were proposed based on the intermediate products of SMX investigated by LC-MS. This study provides novel insights for the development of highly active and green catalysts for wastewater remediation.

Activation of peroxymonosulfate by magnetic CuFe2O4@ZIF-67 composite catalyst for the study on the degradation of methylene blue

In this research, a novel magnetically recoverable composite catalyst, CuFe2O4 @ZIF-67, was synthesized. CuFe2O4 @ZIF-67 composite catalyst was applied to degrade methylene blue (MB) in water by activating peroxymonosulfate (PMS). The results showed that the degradation rate of MB (20 mg/L) reached 98.9% in 30 min in the 0.2-CuFe2O4 @ZIF-67 (75 mg/L) + PMS (125 mg/L) system. Both electron paramagnetic resonance (EPR) studies and radical quenching experiments revealed that SO4−•, •OH, 1O2 and •O2− were involved in the degradation of MB. We proposed a catalytic mechanism of PMS activation by CuFe2O4 @ZIF-67. With the synergistic effect of Co3+/Co2+, Fe3+/Fe2+ and Cu2+/Cu+ redox cycles, it can keep its outstanding catalytic activity. Recycling tests showed that the removal rate of MB can still be maintained above 85%, indicating that CuFe2O4 @ZIF-67 has good reusability. In general, owing to its reusability and excellent catalytic activity, the CuFe2O4 @ZIF-67 composite catalyst has a good application prospect in water pollution control.

PELDOR Measurements on Nitroxide-Labeled Oligonucleotides.

In the past decades, pulsed dipolar electron paramagnetic resonance spectroscopy (PDS) has emerged as a powerful tool in biophysical chemistry to study the structure, dynamics, and function of biomolecules like oligonucleotides and proteins. Structural information is obtained from PDS methods in form of a distribution of distances between spin centers. Such spin centers can either be intrinsically present paramagnetic metal ions and organic radicals or may be attached to the biomolecule by means of site-directed spin labeling. The most common PDS experiment for probing interspin distances in the nanometer range is pulsed electron-electron double resonance (PELDOR or DEER). In the protocol presented here, we provide a step-by-step workflow on how to set up a PELDOR experiment on a commercially available pulsed EPR spectrometer, outline the data analysis, and highlight potential pitfalls. We suggest PELDOR measurements on nitroxide-labeled oligonucleotides to study the structure of either RNA-cleaving DNAzymes in complex with their RNA targets or modified DNAzymes with different functions and targets, in which deoxynucleotides are substituted by nitroxide-labeled nucleotides.

Molybdenum disulfide as excellent Co-catalyst boosting catalytic degradation of sulfamethoxazole by nZVI/PDS process

Nanoscale zero valent iron (nZVI) is environmentally friendly Fe-based materials that can effectively activate peroxydisulfate (PDS). However, the slow conversion of Fe3+ to Fe2+ limits its large-scale practical application. In this work, molybdenum disulfide (MoS2) was firstly used as a co-catalyst to facilitate the degradation performance of nZVI/PDS process for sulfamethoxazole (SMX), a typical sulfonamide antibiotic. Compared with nZVI/PDS process, the SMX degradation efficiency obtained by MoS2/nZVI/PDS system was increased by 37.2%. The addition of MoS2 could significantly accelerate the Fe2+/Fe3+ cycle, resulting in the enhanced decomposition of PDS and thus boosting catalytic degradation of SMX. Up to 98.6% degradation efficiency of SMX and 29.6% removal of total organic carbon (TOC) could be achieved under the optimal conditions within 30 min.The stability of MoS2/nZVI/PDS process for SMX removal were also certified based on five consecutive runs. Besides, electron Paramagnetic Resonance spectroscope (EPR) and radical quenching experiments identified that both sulfate radical (SO4·-) and hydroxyl radical (·OH) were responsible for SMX degradation.Based on the intermediates detected by high-resolution accurate mass quadrupole time-of-flight liquid chromatography/mass spectrometer (UPLC-QTOF-MS), possible degradation pathway of SMX was proposed. Overall, this study provides a new perspective for enhancing iron-based advanced oxidation processes with co-catalyst to achieve rapid and efficient degradation of organic pollutants in the aquatic environment.

Ultrafast photodegradation of nitenpyram by Ag/Ag3PO4/Zn–Al LDH composites activated by persulfate system: Removal efficiency, degradation pathway and reaction mechanism

In this study, an investigation is conducted into the degradation of nitenpyram (NTP) using highly efficient APMMO/PDS/Vis system. As photocatalysts, silver phosphate (AP) and calcined Zn–Al layered double hydroxides (MMO) exhibit high efficiency in achieving charge separation. Besides, the injection of electrons into peroxydisulfate (PDS) from the APMMO can contribute to obtaining the species in the active state with higher efficiency. Based on the APMMO/PDS/Vis system, 50 mg/L of nitenpyram (NTP, 50 mL) can be completely removed in 60 min using 0.8 g/L photocatalyst and 0.2 g/L PDS under the optimum condition and visible light (780 nm > λ > 420 nm). Meanwhile, as demonstrated under visible light within 30 min, an ultrahigh degradation efficiency can be achieved by NTP based on APMMO1/PDS/Vis system. Besides, the electron paramagnetic resonance (EPR) technique and radical quenching experiments suggested 1O2, h+, SO4−•, •O2−, and •OH are all contributory to the removal of pollutants. Given the outcomes achieved by LC/MS system and mass spectrometry, the primary degradation intermediates of NTP end up being converted into photodegradation products (such as 2-Chloropyridine, 6-Chloropurine Riboside and dl-Leucine). Additionally, there are three potential photodegradation pathways to NTP degradation have been deployed. Moreover, the NTP light degradation occurring in APMMO1/PDS/Vis system is competent under the three types of real water sample. Accordingly, the high-efficiency APMMO1/PDS/Vis system is fit for use in water pollution control for agricultural productions.

Efficient degradation of bisphenol A with MoS2/BiVO4 hetero-nanoflower as a heterogenous peroxymonosulfate activator under visible-light irradiation

Photocatalyst activated peroxymonosulfate (PMS) under visible-light irradiation to construct a photo-Fenton system has shown great application prospect for environmental remediation. In this study, MoS2/BiVO4 heterojunction nanoflowers were successfully synthesized by hydrothermal method and used to activate PMS under visible-light to achieve highly efficient degradation of bisphenol A (BPA). The constructed heterojunction showed excellent catalytic activity, which was attributed to the synergistic effect of effective separation of charge carriers and PMS activation. In the MoS2/BiVO4/PMS/vis system, 2-MoS2/BiVO4 (2-MB) exhibited the highest degradation rate constant for BPA (0.1747 min−1), which was 91.9 times of pure MoS2 and 38.0 times of pure BiVO4, respectively. The electron paramagnetic resonance (EPR) and radical quenching experiments demonstrated that the oxidative degradation of BPA was mainly participated by SO4−, OH, 1O2 and h+ active species. Through the analysis of energy band structure and element valence state of photocatalyst and the identification of reaction intermediates, the degradation mechanism and degradation pathways were proposed. In addition, MoS2/BiVO4 heterojunction showed high catalytic ability for various organic pollutants (herbicides, pesticide intermediates, antibiotics and dyes), and common anions (Cl−, SO42− and NO3−) and humic acid (HA) had little effect on its degradation efficiency. This study has provided a new solution for the use of heterojunction photocatalysts for visible-light assisted PMS activation to achieve highly efficient degradation of organic pollutants.

Lignocellulosic biomass derived N-doped and CoO-loaded carbocatalyst used as highly efficient peroxymonosulfate activator for ciprofloxacin degradation

Burning lignocellulosic biomass wastes in an outdoor atmosphere has placed heavy burden on ecological environment and increased risk on human health. Converting solid agricultural wastes into functional materials is a research hotspot. In this study, N-doped and CoO-loaded carbocatalyst (CoO-N/BC) was successfully synthesized from the cotton stalk biomass via a simple synthesis process of impregnation and carbonization. Compared with cotton stalk biomass derived pristine biochar, the CoO-N/BC possessed a higher specific surface area (466.631 m2 g−1vs 286.684 m2 g−1) as well as a better catalytic performance in the activation of peroxymonosulfate (PMS) for CIP degradation. The superior catalytic efficiency was ascribed to the directional flow of electrons on the well-organized carbon network of CoO-N/BC, which accelerated electron migration and improved electron conduction ability. Based on the results of radical quenching experiment and electron paramagnetic resonance (EPR), both radical and non-radical process conjointly led to the stepwise decomposition of CIP, and singlet oxygen (1O2) mediated non-radical pathway was discovered to play a dominant role. Besides, the carbon-bridge mediated non-radical pathway was proved to accelerate this degradation process through the experiments of prolong the time of adding CIP at different time intervals. Nitrogen doped sites and CoO active sites as well as defects formed in sp2-hybridized carbon network were supposed to be the active sites for PMS. Furthermore, EIS and LSV were employed to confirm the electron transfer mediated non-radical process of reaction system. This work provides a modified strategy for the disposition of lignocellulosic biomass wastes and illuminates the underlying mechanism of heterogeneous catalysis by CoO-N/BC.

Synthesis of nitrogen and sulfur Co-doped carbon with special hollow sphere structure for enhanced catalytic oxidation

• Nano-CaCO 3 is used as template for carbon sphere synthesis by CVD. • The N and S doping percentage of the carbon sphere can be easily regulated. • The N and S co-doping can achieve enhanced activity than single doped carbons. • The incorporation of secondary S atoms could enhance the O 2 •− generation in the PMS activation. In this study, a facile atmospheric pressure chemical vapor deposition (CVD) method is used for the synthesis of nitrogen and sulfur co-doped hollow carbon sphere (NSC). Nano-CaCO 3 is used as template for the formation of hollow and highly hierarchical porous carbon structure. The doped percentages of N and S can be easily regulated by changing the ratio of N and S precursors and the deposition temperature. The obtained NSC is highly active for the catalytic oxidation of organic pollutants with peroxymonosulfate (PMS) as oxidant, and the reaction rate constant is 4.5 and 32.7 times faster than the single N or S doped samples, respectively. The PMS activation mechanism is comprehensively investigated by electron paramagnetic resonance (EPR) and radical quenching tests. Superoxide intermediate (O 2 •− ) and singlet oxygen ( 1 O 2 ) play the dominant role for phenol degradation. Moreover, with the introduction of secondary doped S atoms, more O 2 •− are generated for organics degradation. The excellent catalytic activity of NSC should be resulted from the optimized N and S doping percentages and large specific surface area (SSA). The synthesis strategy in this study provides a facile and low-cost synthetic method for heteroatom doped carbon materials and would expand the application of metal-free materials in the environmental remediation field.

Enhancing Fenton-like catalytic efficiency of Bi2WO6 by iodine doping for pollutant degradation

Introducing reductive species into heterogeneous catalysts can improve their catalytic efficiency in Fenton-like processes. Iodide ions (I−), a typical reductive species with good reducibility, might enhance the catalytic performance of H2O2 activation when doped in heterogeneous catalysts. In this study, the iodine-doped Bi2WO6 (IX-Bi2WO6) nanosheets were synthesized with a facile hydrothermal method and used to activate H2O2 to degrade bisphenol A (BPA). Compared with Bi2WO6, which was almost inactive, the IX-Bi2WO6 exhibited great improvement for BPA degradation. Among the fabricated catalysts, the I0.50-Bi2WO6 with an iodine content of 0.50 mmol was found to be most effective and could work efficiently in a wide pH range from 4.0 to 10.0. Moreover, with a low consumption of H2O2 (H2O2 : pollutant molar ratio = 10:1), 78% BPA was degraded within 10 min at initial pH 7.0. Unlike the conventional H2O2 activation mechanism, the direct electron transfer was verified to be the main mechanism for the BPA degradation based on the results of electron paramagnetic resonance (EPR) analysis, radical quenching, and electrochemical experiments in this work. Furthermore, the activation of H2O2 by iodine-doped BiVO4 and Bi2MoO6 was also conducted to validate the applicability of such an iodine doping approach. These results indicate that the introduction of reductive species I− is a promising and effective method to develop highly efficient Bi-based catalysts for H2O2 activation.

Ball milling boosted the activation of peroxymonosulfate by biochar for tetracycline removal

Biochar materials have been commonly applied in advanced oxidation processes, and various strategies were explored to enhance the practical performance of biochar. In this study, ball milling, a simple grinding method, were used to treat biochar, and the ball-milled biochar materials were used to activate peroxymonosulfate (PMS) for tetracycline (TC) removal. It was demonstrated that the ball-milled biochar materials using different ball mass ratios and ball milling time benefited the generation of oxygen-functional groups and defects on the surface, thereby enhanced the catalytic performance of biochar to degrade TC. Besides, the different experimental conditions (initial pH, catalyst dosage, PMS dosage, and TC dosage) and coexisting substances all affected the degradation efficiency of TC. Electron paramagnetic resonance and radicals quenching experiments showed that the radicals attached to the biochar contributed greatly to the degradation of TC, and both free radicals and non-free radicals participated in the TC degradation process.

Peroxymonosulfate activation by algal carbocatalyst for organic dye oxidation: Insights into experimental and theoretical

Preparation of nitrogen-doped algal carbocatalyst (NC) for peroxymonosulfate (PMS) activation to oxidative degrade methylene blue (MB), and the mechanism of radical and nonradical pathway in N-C/PMS system are investigated. Firstly, a series of N-doped carbonaceous materials (NC) were prepared using nitrogen-rich Taihu blue algae biomass as precursor at different annealing temperatures. It was found that the NC prepared by annealing at 800 °C (N-C-8) showed an optimal MB degradation performance of over 99% after 60 min. Confirmed by electron paramagnetic resonance (EPR) analyses and radical quenching experiments, radical and nonradical pathway (1O2 oxidation and electron-transfer) are both involved in MB degraded process. Moreover, both graphitic N derived from the intrinsic Taihu blue algae, and nitrogen vacancy evolved from nitrogen dopants decomposition exhibited high correlation with the MB removal rate in the N-C/PMS system. Finally, three possible degradation pathways of MB were proposed based on the Density Functional Theory (DFT) calculation and identified intermediates. Overall, this work provides a new insight into the intrinsic roles of nitrogen-dopants and nitrogen vacancies on the as-prepared carbocatalyst for PMS activation, and advances the understanding of the resource utilization of algal biomass.

Manipulating Grain Boundary Defects in π‐Conjugated Covalent Organic Frameworks Enabling Intrinsic Radical Generation for Photothermal Conversion

Defects are prevalent in covalent organic frameworks (COFs) constructed based on reversible covalent chemistries. However, manipulating defects in COFs to achieve functionalities remains a significant challenge. Herein, a facial method is provided to regulate the boundary unreacted defects in π‐conjugated COFs to generate distinct and stable paramagnetic radicals, which endow the COFs with a bulk ferromagnetic transition behavior at low temperature, and the efficient photothermal conversion with application in solar vapor generation and seawater desalination. This work not only provides new insights to tailor and control the physicochemical properties of COFs by defect engineering but also enriches the applications of COFs in solar energy utilization.

Constructing Pd/ferroelectric Bi4Ti3O12 nanoflake interfaces for O2 activation and boosting NO photo-oxidation

Photo-oxidative NOx removal often encountered with sluggish charge carrier separation kinetics and poor selectivity. Herein, Pd/ferroelectric Bi4Ti3O12 nanoflakes (Pd/BTO NF) were constructed to investigate the photo-excited charge separation, O2 activation and the generated reactive oxygen species (ROS) in dictating NO removal. Results showed that the depolarization field of ferroelectric BTO NF significantly promoted bulk charge separation, leading to boosted NO removal reaction kinetics (10 times higher) for Pd/BTO NF comparing with Pd/TiO2. Revealed by electronic paramagnetic resonance and radical scavenging tests, it is observed that the primary O2 activation species differed among Pd, Ag and Pt supported BTO NF photocatalysts, which resulted in different selectivity. The underlying mechanism of NO photo-oxidative conversion pathway was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy. This work illustrate that metal/ferroelectric interfaces can be tuned to obtain differing O2 activation species, and notable selectivity changes in photocatalysis mediated environmental remediation reactions.