Main Intermediates Research Articles

Current insights into the microbial degradation of nicosulfuron: Strains, metabolic pathways, and molecular mechanisms

Nicosulfuron is among the sulfonylurea herbicides that are widely used to control annual and perennial grass weeds in cornfields. However, nicosulfuron residues in the environment are likely to cause long-lasting harmful environmental and biological effects. Nicosulfuron degrades via photo-degradation, chemical hydrolysis, and microbial degradation. The latter is crucial for pesticide degradation and has become an essential strategy to remove nicosulfuron residues from the environment. Most previous studies have focused on the screening, degradation characteristics, and degradation pathways of biodegrader microorganisms. The isolated nicosulfuron-degrading strains include Bacillus, Pseudomonas, Klebsiella, Alcaligenes, Rhodopseudomonas, Ochrobactrum, Micrococcus, Serratia, Penicillium, Aspergillus, among others, all of which have good degradation efficiency. Two main intermediates, 2-amino-4,6-dimethoxypyrimidine (ADMP) and 2-aminosulfonyl-N,N-dimethylnicotinamide (ASDM), are produced during microbial degradation and are derived from the C–N, C–S, and S–N bond breaks on the sulfonylurea bridge, covering almost every bacterial degradation pathway. In addition, enzymes related to the degradation of nicosulfuron have been identified successively, including the manganese ABC transporter (hydrolase), Flavin-containing monooxygenase (oxidase), and E3 (esterase). Further in-depth studies based on molecular biology and genetics are needed to elaborate on their role in the evolution of novel catabolic pathways and the microbial degradation of nicosulfuron. To date, few reviews have focused on the microbial degradation and degradation mechanisms of nicosulfuron. This review summarizes recent advances in nicosulfuron degradation and comprehensively discusses the potential of nicosulfuron-degrading microorganisms for bioremediating contaminated environments, providing a reference for further research development on nicosulfuron biodegradation in the future.

Pyrrole nitrogen coordinated Fe on carbon nitride mediated singlet oxygen formation for efficient degradation of 2-mercaptobenzothiazole

We report a rational and scalable synthetic approach to prepare Fe-decorated carbon nitride materials assisted by carbonized polyamine (C-Fe@PDA-CN). The material exhibited extremely high activity and stability for the degradation of 2-mercaptobenzothiazole (MBT) and other organic pollutants (phenol, BPA, MB, and RhB) under visible light irradiation. Furthermore, escape from CN to C-Fe@PDA provides an electron transfer channel to facilitate carrier separation and accelerate the generation of active species, as confirmed by photoluminescence, photoelectrochemical, and electron paramagnetic resonance (EPR). Fe exists in the material coordinated with the pyrrole nitrogen of polydopamine. This coordination structure is conducive to the generation of singlet oxygen (1O2). It is confirmed by steady-state phosphorescence spectroscopy (PH) that 1O2 originates from electron transfer. Superoxide radicals are generated by electron transfer and then oxidized into 1O2 by holes. The main intermediates of MBT degradation were identified by the LC-MS method, and a possible photocatalytic mechanism based on quenching experiments and EPR tests was proposed.

Indirect photodegradation of ofloxacin in simulated seawater: Important roles of DOM and environmental factors

Dissolved organic matter (DOM) plays a non-negligible role in the indirect photodegradation of organic contaminants. This research investigated the roles of DOM and the environmental factors (salinity, pH, NO3−, and HCO3−) in the indirect photodegradation of ofloxacin (OFX) in simulated seawater. Results showed that DOM can significantly accelerate the indirect photodegradation of OFX, and 1O2 and 3DOM* were the main reactive intermediates (RIs) that could promote the indirect photodegradation of OFX. Fluorescence excitation–emission matrix spectroscopy–parallel factor analysis (EEMs-PARAFAC) was used to divide DOM into four fluorescence components. The indirect photodegradation rate of OFX was affected by DOM structure, and terrigenous DOM usually produced more RIs to promote the indirect photodegradation of OFX. Increased salinity significantly promotes the indirect photodegradation of OFX, while increased NO3− concentration had no effect on the OFX indirect photodegradation. pH affected the formation of RIs and the structure of OFX, thereby affecting the indirect photodegradation of OFX. The indirect photodegradation rate of OFX increased in the HCO3− solution, which is due to the formation of carbonate radical (CO3−). This study is essential in understanding the role of DOM in OFX indirect photodegradation and providing a novel insight into the fate, removal, and transformation of OFX.

Influence and mechanism of the adsorption and reactions of residual NH3, NO, and O2 on coal ash after the selective noncatalytic reduction process

NH3 as reducing agent in selective noncatalytic reduction (SNCR) is widely used for the deNOx of coal-fired boiler flue gas, where fly ash significantly influences the conversion of residual NH3 that does not participate in deNOx. However, few studies have been conducted on the exact nature of this influence. The adsorption and reaction of NH3, NO, and O2 on the fly ash at 50–850 °C were investigated in this study. At 50–350 °C, NH3, NO, and O2 co-adsorbed on the coal ash surface, and the presence of NO and O2 reduced the physical adsorption of NH3 on the ash and promoted its chemical adsorption on the ash. At 450–850 °C, coal ash catalyzed NO reduction by NH3 and NH3 oxidation by O2. In the presence of O2, the oxidation reaction became dominant and the reduction reaction was inhibited. The mechanism of adsorption and reaction of coal ash showed that NH3 was adsorbed on the Brönsted and Lewis sites on coal ash and NH3 at the Lewis site could be dissociated into *NH2 and *NH. The NO ad-species in coal ash were mainly nitrate and nitrite. *NH2 reacted with NO to form NH2NO, which desorbed as N2 at 450–850 °C. The main oxidation intermediates for NH3 ad-species were monodentate nitrate and bridged nitrate, which desorbed as NO at 450–850 °C. The results provide a theoretical basis for adjusting the migration and conversion of residual NH3 and reducing ammonia slip from power plants.

Degradation of atrazine in river sediment by dielectric barrier discharge plasma (DBDP) combined with a persulfate (PS) oxidation system: response surface methodology, degradation mechanisms, and pathways.

Single degradation systems based on dielectric barrier discharge plasma (DBDP) or persulfate (PS) oxidation cannot achieve the desired goals (high degradation efficiency, high mineralization rate, and low product toxicity) of degrading atrazine (ATZ) in river sediment. In this study, DBDP was combined with a PS oxidation system (DBDP/PS synergistic system) to degrade ATZ in river sediment. A Box-Behnken design (BBD) including five factors (discharge voltage, air flow, initial concentration, oxidizer dose, and activator dose) and three levels (- 1, 0, and 1) was established to test a mathematical model by response surface methodology (RSM). The results confirmed that the degradation efficiency of ATZ in river sediment was 96.5% in the DBDP/PS synergistic system after 10min of degradation. The experimental total organic carbon (TOC) removal efficiency results indicated that 85.3% of ATZ is mineralized into CO2, H2O, and NH4+, which effectively reduces the possible biological toxicity of the intermediate products. Active species (sulfate (SO4•-), hydroxy (•OH), and superoxide (•O2-) radicals) were found to exert positive effects in the DBDP/PS synergistic system and illustrated the degradation mechanism of ATZ. The ATZ degradation pathway, composed of 7 main intermediates, was clarified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). This study indicates that the DBDP/PS synergistic system is a highly efficient, environmentally friendly, novel method for the remediation of river sediment containing ATZ pollution.

Pd nanoparticles decorated BiVO4 pine architectures for photocatalytic degradation of sulfamethoxazole

Sulfamethoxazole (SMX) has been extensively detected in wastewater treatment plant effluents and surface water. Because of its potential risks to ecology and health, treatment for eliminating SMX is urgently required. In this study, we report the application of Pd nanoparticles decorated on BiVO4 pine architecture for the photocatalytic degradation of SMX. The results showed that the barer BiVO4 and Pd–BiVO4 eliminated SMX under visible-light irradiation. After 210 min of irradiation, 98.8% of SMX was substantially eliminated by Pd–BiVO4, whereas bare BiVO4 can degraded approximately 36.3% of SMX. Pd–BiVO4 also exhibited a high mineralization rate (84% of total organic carbon (TOC) removal) compared to bare BiVO4 (51% of TOC removal). Through three-dimensional excitation-emission matrix fluorescence spectra, SMX with high fluorescence intensity can be degraded to non-fluorescence intermediate products, further confirming the high mineralization of SMX over Pd–BiVO4 catalyst. Well-dispersed Pd nanoparticles on the {040} facet of BiVO4 pine architecture can support the recombination of photogenerated charge carriers because of the formation of the Schottky junction at the Pd–BiVO4 interface. Besides, the active species trapping tests indicated that •O2− and h+ radicals dominate SMX photodegradation over Pd–BiVO4. The main degradation intermediates of SMX in the reaction solution was also identified through ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. This investigation can provide insight into designing metallic/semiconductor junctions for antibiotic elimination in water media.

Catalytic ignition of CO over CuCeZr based catalysts: New insights into the support effects and reaction pathways

Self-sustained catalytic combustion is a promising strategy to remove CO from the off-gas produced during steelmaking, where the potential catalysts are bulk copper-cerium-zirconium mixed oxides or those supported on TiO2 or ZSM-5 substrates. In this study, the effects of the catalyst support on the CO catalytic ignition performance and reaction pathways were investigated by FTIR coupled with a novel in-situ cell, together with the state-of-the-art characterization techniques. The Infrared (IR) transmission cell equipped with a magnetically driven system, could effectively prevent overlaps between active intermediate peaks (Cu+-CO and Cu+(CO)2) and gaseous CO peaks. The Cu+ cations located at the phase interface are the main active sites. The Cu and Ce interactions lead to the formation of solid solutions of CuCe0.75Zr0.25Oδ (CuCeZr). The monocarbonyls [Cu+-CO] are the dominant species during CO oxidation, and the vacancies in the solid solutions are occupied by oxygen, accelerating the oxygen cycle. The TiO2 or ZSM-5 supports promote copper dispersion over CuCe0.75Zr0.25Oδ/TiO2 (CuCeZr/T) and CuCe0.75Zr0.25Oδ/ZSM-5 (CuCeZr/Z) catalysts, which can be attributed to their high surface areas (168.2 and 346.3 m2/g, respectively), while the Cu-Ce interactions are less relevant. Hence, CO oxidation mainly occurs at the phase interface between copper oxide and TiO2/ZSM-5. Dicarbonyls [Cu+(CO)2] are the main intermediates for the CuCeZr/T and CuCeZr/Z catalysts, and the Cu2+ species are reduced to form dicarbonyls that also take part in the oxidation process. Although a well copper dispersion enhances the activity of individual copper sites on the CuCeZr/T and CuCeZr/Z catalysts, considering the redshift of the carbonyl bands and the increase in CO adsorption, the close interactions and high contents of Cu and Ce favor the local accumulation of heat and mass transfer over bulk CuCeZr, leading to the ignition of CO at low temperatures.

Efficient removal of petroleum hydrocarbons from soil by percarbonate with catechin-promoted Fe(III)/Fe(II) redox cycling: Activation of ferrous and roles of ·OH and ·CO3-

Advanced oxidation processes are widely used to remove petroleum hydrocarbons from soil, but usually consume large quantities of ferrous and acidify the soil. This study tested an advanced oxidation approach based on percarbonate in laboratory experiments. It removed 88% petroleum hydrocarbons in soil with a pH increase from 8.2 to 10.2. ·OH and ·CO3- were the main reactive species, and degraded 41% and 37% PHCs from soil respectively. The o-dihydroxybenzene structure in catechin was found to reduce ferric to ferrous, and prolong the generation of ·OH from 120 s to over 1800 s. The petroleum hydrocarbons were degraded to intermediates including alkanes and olefins through hydrogen-abstraction by ·OH and ·CO3-, and by dimerization and β-scission of alkyl radicals. These intermediates were then oxidized to CO2 and H2O by ·OH and ·CO3-. The main residual intermediates in the soil were low-molecular-weight n-alkanes and branched alkanes, and they were found to inhibit the growth of oats (Avena sativa L.) much less than the original petroleum hydrocarbons. These findings provide a fundamental basis for designing effective technologies which use percarbonate to remove organic pollutants.

Comparative studies of transformation behaviors and mechanisms of halophenols in multiple chemical oxidative systems

Due to wide applications, halophenols (HPs), especially bromophenols, chlorophenols, and fluorophenols, are commonly detected but resistant to biological removal in wastewater treatment plants (WWTPs). This study investigated the overall transformation behaviors of three representative HPs (2,4-dichlorophenol: 24-DCP, 2,4-dibromophenol: 24-DBP, 2,4-difluorophenol: 24-DFP) in six chemical oxidative systems (KMnO4, K2FeO4, NaClO, O3, UV, and persulfate (PS)). The results revealed fast removal of selected HPs by O3, PS and K2FeO4, while a large discrepancy in their removal efficiencies occurred under UV irradiation, KMnO4 oxidation and particularly chlorination. Based on the analysis of the identified intermediates and products, coupling among the five routes was the general route, and dimers were the main intermediates for HP oxidation. The effect of the halogen atom on the transformation pathways of HPs was highly reaction type dependent. Among the six chemical treatments, PS could induce HPs to yield relatively low-molecular-weight polymers and obtain the highest coupling degree. Transition state (TS) calculations showed that the H atom linked to the phenoxy group of HPs was the most easily abstracted by hydroxyl radicals to form the coupling precursor, i.e., phenoxy radicals. This high coupling behavior further resulted in the increased toxicity to green algae. Characterization revealed that HP reaction solutions treated with PS had a severely negative effect on algae growth, photosynthetic pigment synthesis, and the antioxidant enzyme system. These findings can shed light on the reaction mechanisms of advanced oxidation technologies and some risk management and control of PS technique may be considered when treating phenolic pollutants.

Enhanced catalytic degradation of antibiotics by peanut shell-derived biochar-Co3O4 activated peroxymonosulfate: An experimental and mechanistic study

A peanut shell-derived biochar-Co3O4 (Bio-Co3O4) catalyst prepared by chemical bath deposition (CBD) method exhibited excellent ofloxacin (OFL) degradation ability through a broad pH range for peroxymonosulfate (PMS) activation. The excellent properties and behavior of catalyst were studied by characterization and degradation experiments. Benefiting from the synergy of adsorption and degradation, Bio-Co3O4 composite showed much higher removal efficiency (97.3%) and larger reaction rate constant (k = 0.1411 min−1) than that of biochar or Co3O4 in presence of PMS. Mechanisms exploration suggested that dual active pathways, including singlet oxygen-dominated non-radical pathway and sulfate radical-dominated radical pathway were involved in the reaction mechanism. The graphitized structure, stable redox cycle of Co2+/Co3+ and CO groups in catalyst were mainly responsible for the generation of reactive species. Furthermore, a total of ten main intermediates were detected and OFL degradation pathways as well as catalytic mechanisms were identified and proposed in detail. Overall, our study provides a potential way to activate PMS for the effective removal of abusive antibiotics from aqueous environments.

Biodegradation of diethyl phthalate and phthalic acid by a new indigenous Pseudomonas putida.

Diethyl phthalate (DEP) is one of the extensively used plasticizers which has been considered a priority hazardous pollutant due to its carcinogenic, endocrine disrupter, and multi-toxic effects on humans. The identification of DEP in different parts of the ecosphere has increased the global community's attention to the elimination of this pollutant in a bio-eco-friendly way. In this research, a novel aerobic bacterial strain nominates as ShA (GenBank accession number: MN298858) capable of consuming DEP as carbon and energy sources, was isolated from the upper phase (0-10 cm) of Anzali international wetland sediments by enrichment culture method. Morphological characteristics and 16S rRNA gene sequence analysis demonstrated that strain ShA belonged to Pseudomonas putida. The substrate utilization test demonstrated that strain ShA was able to grow in mineral salt medium containing dimethyl phthalate (DMP) and phthalic acid (PA) isomers including terephthalic and isophthalic acid. Degradation assay showed strain ShA completely degraded 200 mg/L DEP within 22 h (pH 7.0, 30 °C). Surprisingly, PA as the main intermediate of DEP biodegradation was identified by GC-FID. Moreover, the rapid degradation of 2000 mg/L PA to CO2 and H2O was viewed in 22 h by strain ShA. The possible route of DEP degradation was DEP directly to PA and then PA consumption for growth. This study obtained results that provide a great contribution to applying strain ShA in the biodegradation of low molecular weight of PAEs and PA isomers in natural ecosystems. This is the first report of a P. putida strain able to degrade DEP and PA.

Highly Efficient Oxidation of Biomass Xylose to Formic Acid with CeOx-Promoted MnOx Catalyst in Water

Formic acid is a versatile chemical, which is industrially produced from fossil resources. In this work, biomass-derived xylose was used as a potential feedstock to synthesize formic acid with Mn–Ce oxides as the catalyst in water. Among the Mn–Ce oxides with different molar ratios, Mn4Ce0.05Ox showed the best catalytic activity, offering a formic acid yield up to 65.1% at 160 °C with 3 MPa of O2, which was much higher than that using pristine MnOx (40.5%) and CeOx (9.9%). In addition, Mn4Ce0.05Ox was shown to be tolerant to a higher xylose concentration. The introduction of CeOx into MnOx increased the total surface area (55.8 vs 33.7 m2 g–1), gave a higher ratio of (Mn2++Mn3+)/Mn4+ (1.94 vs 1.54), and produced more surface adsorbed oxygen (39.0% vs 26.0%). The DFT calculations revealed that the adsorption energy of xylose on the Ce site (−1.231 eV) was much lower than that on the Mn site (−0.884 eV), thus facilitating the binding of xylose on the catalyst. Mechanism studies of xylose–catalyst–water reaction systems indicated that glyceric acid and glycolic acid were the main intermediates, while CO2 was cogenerated with the formic acid.

Heteroepitaxial chemistry of zinc chalcogenides on InP nanocrystals for defect-free interfaces with atomic uniformity

Heteroepitaxy on colloidal semiconductor nanocrystals is an essential strategy for manipulating their optoelectronic functionalities. However, their practical synthesis typically leads to scattered and unexpected outcomes due to the intervention of multiple reaction pathways associated with complicated side products of reactants. Here, the heteroepitaxy mechanism of zinc chalcogenide initiated on indium phosphide (InP) colloidal nanocrystals is elucidated using the precursors, zinc carboxylate and trialkylphosphine selenide. The high magnetic receptivity of 77Se and the characteristic longitudinal optical phonon mode of ZnSe allowed for monitoring the sequence of epilayer formation at the molecular level. The investigation revealed the sterically hindered acyloxytrialkylphosphonium and diacyloxytrialkylphosphorane to be main intermediates in the surface reaction, which retards the metal ion adsorption by a large steric hindrance. The transformation of adsorbates to the crystalline epilayer was disturbed by surface oxides. Raman scattering disclosed the pathway of secondary surface oxidation triggered by carboxylate ligands migrated from zinc carboxylate. The surface-initiated heteroepitaxy protocol is proposed to fabricate core/shell heterostructured nanocrystals with atomic-scale uniformity of epilayers. Despite the large lattice mismatch of ZnS to InP, we realised a uniform and interface defect-free ZnS epilayer (~0.3 nm thickness) on InP nanocrystals, as evidenced by a high photoluminescence quantum yield of 97.3%.

Confined nanoreactor for synthesis of MnCe composite oxide nanowires with enhanced catalytic activity towards aromatic VOCs oxidation

A novel Mn–Ce composite oxide nanowires (MnCe-NWs) catalyst with a high specific surface area has been successfully fabricated via restricting the growth of nanocrystal within a confined nanoreactor offered by the Santa Barbara Amorphous-15 (SBA-15) template. The characterizations of X‐ray diffraction (XRD), N 2 adsorption-desorption, and Energy Dispersive X-Ray mapping (EDX-mapping) showed the Mn–Ce oxide nanowires generated in a confined nanoreactor had a homogeneous cubic fluorite structure with good metal distribution and high porosity. The X‐ray photoelectron spectroscopy (XPS), Raman, H 2 temperature-programmed reaction (H 2 -TPR), and O 2 temperature‐programmed desorption (O 2 -TPD) determined that the Mn–Ce oxide nanowire increased the lattice defects, active oxygen species, and reducibility compared to the one (MnCe-DC) generated by direct calcination in open space. Owing to these excellent properties, the Mn–Ce oxide nanowire exhibited much better catalytic performance in both toluene and benzene oxidation. The conversion efficiency of toluene and benzene can reach 90% at 199 °C and 211 °C over MnCe-NWs (100 ppm, space velocity = 60,000 mL g −1 h −1 ) while the corresponding temperature increased by 30 and 52 °C respectively over MnCe-DC. The influence of space velocity and concentration of toluene/benzene on the catalytic oxidation of toluene/benzene has also been investigated. The catalytic oxidation mechanisms of toluene/benzene and main intermediates are deduced based on the meditator of the reactions. Moreover, the durability test and the water effect test demonstrated that it has remarkable stability and high toleration of high moisture.

Antioxidant Activities of Hydroxylated Naphthalenes: The Role of Aryloxyl Radicals.

Herein is delineated a first systematic framework for the definition of structure-antioxidant property relationships in the dihydroxynaphthalene (DHN) series. The results obtained by a combined experimental and theoretical approach revealed that 1,8-DHN is the best performing antioxidant platform, with its unique hydrogen-bonded peri-hydroxylation pattern contributing to a fast H atom transfer process. Moreover, the comparative analysis of the antioxidant properties of DHNs carried out by performing DPPH and FRAP assays and laser flash photolysis experiments, revealed the higher antioxidant power associated with an α-substitution pattern (i. e. in 1,8- and 1,6-DHN) with respect to DHNs exhibiting a β-substitution pattern (i. e. in 2,6- and 2,7-DHN). DFT calculations and isolation and characterization of the main oligomer intermediates formed during the oxidative polymerization of DHNs supported this evidence by providing unprecedented insight into the generation and fate of the intermediate naphthoxyl radicals, which emerged as the main factor governing the antioxidant activity of DHNs.

Reaction Mechanism for the Removal of NOx by Wet Scrubbing Using Urea Solution: Determination of Main and Side Reaction Paths

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H+] and [NO3-] was greater than 0.87~1.22 mol3/L3. The effects of the urea concentration (5-20%) and reaction temperature (30-70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.

Effect of Zinc on the Structure and Activity of the Cobalt Oxide Catalysts for NO Decomposition

Co4−iZniMnAlOx mixed oxides (i = 0, 0.5 and 1) were prepared by coprecipitation, subsequently modified with potassium (2 or 4 wt.% K), and investigated for direct catalytic NO decomposition, one of the most attractive and challenging NOx abatement processes. The catalysts were characterised by atomic absorption spectroscopy, powder X-ray diffraction, Raman and infrared spectroscopy, temperature-programmed reduction by hydrogen, the temperature-programmed desorption of CO2 and NO, X-ray photoelectron spectroscopy, scanning electron microscopy, the work function, and N2 physisorption. The partial substitution of cobalt increased the specific surface area, decreased the pore sizes, influenced the surface composition, and obtained acid-base properties as a result of the higher availability of medium and strong basic sites. No visible changes in the morphology, crystallite size, and work function were observed upon the cobalt substitution. The conversion of NO increased after the Co substitution, however, the increase in the amount of zinc did not affect the catalytic activity, whereas a higher amount of potassium caused a decrease in the NO conversion. The results obtained, which were predominantly the acid-base characteristics of the catalyst, are in direct correlation with the proposed NO decomposition reaction mechanisms with NOx− as the main reaction intermediates.

SnO2 and CuO anchored on zeolite as an efficient heterojunction photocatalyst for sunlight-assisted degradation of cefixime.

The fabrication of heterojunction nanocomposites has been proven as a highly efficient strategy to achieve promising photocatalysts. In this study, tin oxide (SnO2) and copper oxide (CuO) nanoparticles (NPs) were synthesized in situ using Rosmarinus officinalis and simultaneously anchored on zeolite for the fabrication of zeolite/SnO2/CuO as a novel heterojunction photocatalyst. The performance of zeolite/SnO2/CuO was assessed against photodegradation of cefixime as a model pharmaceutical contaminant. A good catalytic potential and synergistic effect was obtained for zeolite/SnO2/CuO compared to pure SnO2 and CuO NPs. Under optimum conditions, 89.65% of cefixime was degraded after 2.5 h under natural sunlight. Based on radical quenching experiments, the importance of involved oxidizing species in the photodegradation of cefixime using zeolite/SnO2/CuO was in order of h+ > •OH > [Formula: see text]. Among studied anions, the highest inhibitory effect was observed for nitrate ion. Also, the main intermediates of the photodegradation process of cefixime in zeolite/SnO2/CuO system were determined by HPLC-MS and the possible pathways were suggested. More than 83% cefixime was removed after three catalyst reuse cycles, indicating a cost-effectiveness potential in the reusability of zeolite/SnO2/CuO. Also, the toxicity and plant growth tests revealed the feasibility of discharging the treated cefixime solutions to irrigate agricultural crops. Overall, the obtained results provide a promising technique with a synergistic feature for the efficient removal of organic pollutants.

Mechanistic stages of the SCR reaction – Insights into the trade-off between NO reduction and NH3 oxidation over CuSSZ-13 catalysts via isotopic 15NH3 and 18O2 TPSR and steady state studies supported by IR 2D COS and DFT modeling

Isotopic labeling investigations into SCR reaction were performed over CuSSZ-13 zeolites, obtained by one-pot synthesis or impregnation, and characterized by XRD, HR-SEM, TEM/EDX, EPR, and IR techniques. The course of SCR and internal ammonia oxidation (i-AMO) was revealed by isotopic TPSR and steady-state investigations using 15NH3 and 18O2 joined with IR Rapid Scan 2D-COS spectroscopy. The 14N15N and 15N2 profiles allowed for quantification of the relative contributions of the concurrent SCR and i-AMO reactions. Interpretation of the results was ascertained by DFT and first-principles thermodynamic modeling. Three temperature regions of SCR reactions, corresponding to NH3-rich, lean and dry conditions, were distinguished, and the main processes and intermediates involved in each stage were identified. For the conceptualization of SCR, a 2D diagram of the reactants and intermediates stoichiometry, oxidation state, and charge commensurability was constructed, and used for rationalization of the reaction mechanism.

Catalytic performance and mechanism of bismuth molybdate nanosheets decorated with platinum nanoparticles for formaldehyde decomposition at room temperature

Catalytic oxidation at room temperature is considered as a promising strategy for removal of formaldehyde (HCHO), a widely occurring indoor air pollutant. A series of Bi2MoO6 nanosheets were prepared via one-step hydrothermal synthesis in this study, followed by decoration with Pt nanoparticles (NPs). The catalyst with Bi2MoO6 support prepared at 180 °C exhibited high and stable activity in catalytic oxidation of HCHO at room temperature. The excellent catalytic performance was attributed to its large specific area and pore volume, high level of surface active oxygen species, high content of metallic Pt NPs, and abundant oxygen vacancies. The good synergy and interaction between Pt and Bi2MoO6 promoted electron transfer, and facilitated the adsorption and oxidation of HCHO. The electronic interaction between Pt NPs and Bi2MoO6 accelerated the activation of oxygen species due to weakening of the surface BiO or MoO bonds adjacent to Pt NPs. Infrared spectra indicated that dioxymethylene and formate species were the main intermediates of HCHO oxidation. Density functional theory calculations showed that the dehydrogenation of HCO2, with an energy barrier of 282.1 kJ/mol, was the rate-determining step in catalytic oxidation process. This study provides new insights on the construction of high-efficiency catalysts for indoor formaldehyde removal.