Degradation of neonicotinoids with different molecular structures in heterogeneous peroxymonosulfate activation system through different oxidation pathways

The elimination of neonicotinoids(NEOs)from water has been a research priority due to their threats to human health and ecosystems.In this study,we established the heterogeneous peroxymonosulfate(PMS)activation system using manganese catalyst(Mn NC)and cobalt catalyst(Co NC)to trigger the nonradical oxidation and synergistic oxidation pathway,respectively to remove NEOs.The results showed that the nonradical oxidation system exhibited superior NEOs degradation capability.The composition of organic pollutants in wastewater significantly impacted subsequent degradation processes.The charge distribution and reaction sites of various NEOs were analyzed using density functional theory(DFT)calculations,and it demonstrated the electron distribution and activity of NEOs were significantly influenced by the type and number of substituents.Nitro group(–NO_(2))and cyanide group(–C≡N)were identified as strong electron-withdrawing groups and prone to be attacked by negatively charged radicals.The transformation of NEOs was analyzed,and result showed that the C and N sites adjacent to the nitro group and cyanide group were more susceptible to oxidation attacks.S and N atoms,which possess strong electronegativity and high electron cloud density,were identified as key active sites in the degradation pathway.The outcomes of this study provide valuable guidance for the oriented regulation of oxidation pathways towards efficient removal of NEOs in water.

A nonradical oxidation process initiated by Ti-peroxo complex showed high specificity toward the degradation of tetracycline antibiotics

Nonradical oxidation has received wide attention in advanced oxidation processes for environmental remediation.Understanding the relationship between material characteristics and their ability to initiate nonradical oxidation processes is the key to better material design and performance.Herein,a novel titanium-based metal-organic framework MIL-125-Ti/H_(2)O_(2) system was established to show a highly selective degradation efficacy toward tetracycline antibiotics.MIL-125-Ti with the abundance of TiO6 octahedra units was found to effectively activate H_(2)O_(2) under dark conditions by forming an oxidative Ti-peroxo complex.The presence of the Ti-peroxo complex,confirmed by UV-visible spectrophotometer,fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy characterizations,showed superior degradation(>95%removal rate)of oxytetracycline hydrochloride(OTC),doxycycline hydrochloride,chlortetracycline hydrochloride,and tetracycline.Density functional theory calculations were performed to assist the elucidation on the mechanism of H_(2)O_(2) activation and antibiotics degradation.The MIL-125-Ti/H_(2)O_(2) system was highly resistant to halogens and background organics,and could well maintain its original catalytic activity in actual water matrices.It retained the ability to degrade 75%of OTC within ten test cycles.This study provides new insight into the nonradical oxidation process initiated by the unique Ti-peroxo complex of Ti-based MOF.

Three-Dimensional Welded Mn_(1) Site Catalysts with nearly 100% Singlet Oxygen Fabrication for Contaminant Elimination

Reactive oxygen species(ROS)have a significant part in the elimination of recalcitrant organic pollutants and commonly coexist in one advanced oxidation system.It is difficult for us to make clear the effect of the co-instantaneous generation of radicals and nonradicals,which would cover and obscure the transformation pathway.Herein,a coordinate welding process is presented for fabricating accessible Mn1 site catalysts(Mn SSCs)in order to clarify the nonradical(singlet oxygen/^(1)O_(2))generated pathway and transformation in oxidative removal of contaminants.The Mn SSCs achieve nearly 100%^(1)O_(2) fabrication by activating peroxymonosulfate,which displays an excellent sulfamethoxazole elimination performance,super anti-anion interference,and extraordinary stability.As revealed by density functional theory calculations,the Mn SSCs with a special welded three-dimensional nanostructure could significantly boost the activation process by oxidizing the peroxymonosulfate at the interlayer of Mn SSCs and reducing dissolved oxygen on the surface of Mn SSCs.This design of Mn SSCs with a three-dimensional welded nanostructure might offer a potential approach for employing single site catalysts for environmental remediation.

Nonradical-dominated peroxymonosulfate activation through bimetallic Fe/Mn-loaded hydroxyl-rich biochar for efficient degradation of tetracycline

Biochar-based transition metal catalysts have been identified as excellent peroxymonosulfate(PMS)activators for producing radicals used to degrade organic pollutants.However,the radical-dominated pathways for PMS activation severely limit their practical applications in the degradation of organic pollutants from wastewater due to side reactions between radicals and the coexisting anions.Herein,bimetallic Fe/Mn-loaded hydroxyl-rich biochar(FeMn-OH-BC)is synthesized to activate PMS through nonradical-dominated pathways.The as-prepared FeMn-OH-BC exhibits excellent catalytic activity for degrading tetracycline at broad pH conditions ranging from 5 to 9,and about 85.0%of tetracycline is removed in 40 min.Experiments on studying the influences of various anions(HCO_(3)^(−),NO_(3)^(−),and H_(2)PO_(4)^(−))show that the inhibiting effect is negligible,suggesting that the FeMn-OHBC based PMS activation is dominated by nonradical pathways.Electron paramagnetic resonance measurements and quenching tests provide direct evidence to confirm that 1O2 is the major reactive oxygen species generated from FeMn-OH-BC based PMS activation.Theoretical calculations further reveal that the FeMn-OH sites in FeMn-OH-BC are dominant active sites for PMS activation,which have higher adsorption energy and stronger oxidative activity towards PMS than OH-BC sites.This work provides a new route for driving PMS activation by biochar-based transition metal catalysts through nonradical pathways.

Fe_(3)O_(4)/MoO_(x)S_(y)表面缺陷实现自由基与非自由基类芬顿反应历程的切换

自由基与非自由反应历程共同主导的高级氧化技术,无法实现对有机污染物的高效且高选择性降解,难以满足不同废水的降解需求.本研究通过引入缺陷和调节Mo^(4+)/Mo^(6+)比例,在Fe_(3)O_(4)/MoO_(x)S_(y)活化过一硫酸氢盐(PMS)体系中实现了自由基与非自由基分别主导的类芬顿反应历程的切换.通过表面包硅修饰破坏了Fe_(3)O_(4)和MoO_(x)S_(y)的晶格结构,引入了表面缺陷.丰富的缺陷电子使得催化剂表面暴露更多的Mo^(4+),进一步促进了PMS活化分解产生自由基,最大反应k值可达1.530 min^(-1),自由基反应历程主导降解有机污染物的贡献率则达到了81.33%.Fe含量的改变也会影响催化剂表面暴露Mo^(4+)/Mo^(6+)的比例.Mo^(6+)有助于产生^(1)O_(2),因此,随着Mo^(6+)占比的提高可实现从自由基向非自由基反应历程的切换,且非自由基反应历程主导的降解污染物的贡献率最高可达68.26%.自由基反应历程主导的类芬顿体系可实现对实际有机废水化学需氧量(COD)的高效去除;而非自由基反应历程主导的类芬顿体系则可显著提高废水的可生化性(BOD/COD=0.997).Fe_(3)O_(4)/MoO_(x)S_(y)/PMS类芬顿体系中自由基与非自由基反应历程的切换,拓展了高级氧化技术在废水处理中的靶向应用.

Diatomic Fe-Fe catalyst enhances the ability to degrade organic contaminants by nonradical peroxymonosulfate activation system

Atomically dispersed catalysts have been widely studied due to their high catalytic activity and atom utilization.Single-atom catalysts have achieved breakthrough progress in the degradation of emerging organic contaminants(EOCs)by activating peroxymonosulfate(PMS).However,the construction of atomically dispersed catalysts with diatomic/multiatomic metal active sites by activating PMS to degrade pollutants is still seldom reported,despite the unique merits of atom-pair in synergistic electronic modulation and breaking stubborn restriction of scaling relations on catalytic activity.We have synthesized Fe1-N-C,Fe_(2)-N-C,and Fe_(3)-N-C catalysts with monoatomic iron,diatomic iron,and triatomic iron active center,respectively.The results show that the catalytic degradation activity of Fe_(2)-N-C is twice that of Fe1-N-C and Fe_(3)-N-C due to its unique Fe_(2)N6 coordination structure,which fulfilled the complete degradation of rhodamine B(RhB),bisphenol A(BPA),and 2,4-dichlorophenol(2,4-DP)within 2 min.Electron paramagnetic resonance(EPR)and radical quenching experiments confirmed that the reaction was a nonradical reaction on the catalyst surface.And singlet oxygen and Fe(IV)are the key active species.

Coupling of sulfur and boron in carbonaceous material to strengthen persulfate activation for antibiotic degradation:Active sites,mechanism,and toxicity assessment

Carbon-mediated persulfate advanced oxidation processes(PS-AOPs)are appealing in contaminant remediation.For the first time,S,B-co-doped carbon-based persulfate activators were synthesized through direct carbonization of sodium lignosulfonate and boric acid.By degrading sulfamethoxazole(SMX),CSB-750 obtained 98.7%removal and 81.4%mineralization within 30 min.In comparison with solo S or B doping,S and B co-doped carbon showed the coupling effect for enhanced catalysis.The rate constant(kobs)of 0.1679 min^(-1)was 22.38-and 279.83-fold higher than those of CS-750(0.0075 min^(-1))and CB-750(0.0006 min^(-1)),respectively.The degradation was efficient at strong acidic and weak basic conditions(pH 3-9).Substantial inhibition effect was presented at strong basic condition(pH 10.95)and in presence of CO_(3)^(2-).The CO_(3)^(2-)-caused inhibition was the combined result of the cooperation of pH and quenching O_(2)^(·-).Thiophene sulfur,BC_(3),BC_(2)O,and structural defects were identified as the active sites for PS activation.Radical and nonradical pathways were both involved in the CSB-750/PS/SMX system,where^(1)O_(2)dominated the degradation,SO_(4)^(·-),·OH and direct electron transfer played the subordinate role,and O_(2)^(·-)served as a precursor for the formation of partial^(1)O_(2).The toxicity of degradation system,the effect of real water matrix,and the reusability of carbocatalysts were comprehensively analyzed.Nine possible degradation pathways were proposed.This work focuses on the catalytic performance improvement through the coupling effect of S,B co-doping,and develops an advanced heteroatom doping system to fabricate carbonaceous persulfate activators.

Topological defects strengthened nonradical oxidation performance of biochar catalyzed peroxydisulfate system

Nonradical oxidation based on peroxydisulfate(PDS)activation has attracted increasing attention for selective degradation of organic pollutants.Herein,topological defects were introduced into biochar(BC)via removing N atoms in N-doped BC(NBC)in an attempt to improve the nonradical catalytic performance.Compared to the pristine BC and NBC,the introduction of topological defects could achieve up to 36.6-and 8.7-times catalytic activity enhancement,respectively.More importantly,it was found that the catalytic activity was dominated by topological defects,which was verified by the significant positive correlation between the pseudo-first-order rate constants and the content of topological defects.Theoretical calculations suggested that topological defects enhanced the electrondonating ability of BC by reducing the energy gap,which made the electrons transfer to PDS molecules more easily.As a result,holes were generated after the carbon defects lost electrons,and induced a nonradical oxidation process.Benefiting from the merits of nonradical oxidation,the developed BC/PDS system showed superior performance in removing electron-rich contaminants in the presence of inorganic anions and in the actual environments.This study not only provides a potential avenue for designing efficient biochar-based catalysts,but also advances the mechanism understanding of nonradical oxidation process induced by carbon defects.

Mg-induced g-C_(3)N_(4) synthesis of nitrogen-doped graphitic carbon for effective activation of peroxymonosulfate to degrade organic contaminants

The nitrogen-doped carbon derived from graphitic carbon nitride(g-C_(3)N_(4))has been widely deployed in activating peroxymonosulfate(PMS)to remove organic pollutants.However,the instability of g-C_(3)N_(4)at high temperature brings challenges to the preparation of materials.The nitrogen-doped graphitic carbon nanosheets(N-GC750)were synthesized by magnesium thermal denitrification.Magnesium undergoes the displacement reaction with small molecules produced by the pyrolysis of g-C_(3)N_(4),thereby effectively fixing carbon on the in-situ template of Mg_(3)N_(2)and avoiding direct product volatilization.N-GC750 exhibited excellent performance during the PMS activation process and bisphenol A(BPA,0.2 g/L)could be thoroughly removed in 30 min.A wide range of pH(3–11),temperature(10–40℃)and common anions were employed in studying the impact on system.Additionally,N-GC750 showed satisfactory reusability in cycle tests and promising applicability in real water samples.Quenching experiments and electron paramagnetic resonance(EPR)measurements indicated that singlet oxygen was the main active species coupled with partial electron transfer in N-GC750/PMS system.Furtherly,the oxidation products were identified,and their ecotoxicity was evaluated.This work is expected to provide a reference for the feasibility of preparing g-C_(3)N_(4)derived carbon materials and meaningful for PMS activation.