Critical role of zero-valent iron in the efficient activation of H2O2 for 4-CP degradation by bimetallic peroxidase-like.

Peroxidase-like based on double transition metals have higher catalytic activity and are considered to have great potential for application in the field of pollutant degradation. First, in this paper, a novel Fe0-doped three-dimensional porous Fe0@FeMn-NC-like peroxidase was synthesized by a simple one-step thermal reduction method. The doping of manganese was able to reduce part of the iron in Fe-Mn binary oxides to Fe0 at high temperatures. In addition, Fe0@FeMn-NC has excellent peroxidase-like mimetic activity, and thus, it was used for the rapid degradation of p-chlorophenol (4-CP). During the degradation process, Fe0 was able to rapidly replenish the constantly depleted Fe2+ in the reaction system and brought in a large number of additional electrons. The ineffective decomposition of H2O2 due to the use of H2O2 as an electron donor in the reduction reactions from Fe3+ to Fe2+ and from Mn3+ to Mn2+ was avoided. Finally, based on the experimental results of LC-MS and combined with theoretical calculations, the degradation process of 4-CP was rationally analyzed, in which the intermediates were mainly p-chloro-catechol, p-chloro resorcinol, and p-benzoquinone. Fe0@FeMn-NC nano-enzymes have excellent catalytic activity as well as structural stability and perform well in the treatment of simulated wastewater containing a variety of phenolic pollutants as well as real chemical wastewater. It provides some insights and methods for the application of peroxidase-like enzymes in the degradation of organic pollutants.

Efficient Degradation of Sulfamethoxazole by Diatomite-Supported Hydroxyl-Modified UIO-66 Photocatalyst after Calcination.

Sulfamethoxazole (SMX) is a widely used antibiotic to treat bacterial infections prevalent among humans and animals. SMX undergoes several transformation pathways in living organisms and external environments. Therefore, the development of efficient remediation methods for treating SMX and its metabolites is needed. We fabricated a photo-Fenton catalyst using an UIO-66 (Zr) metal-organic framework (MOF) dispersed in diatomite by a single-step solvothermal method for hydroxylation (HO-UIO-66). The HO-UIO-66-0/DE-assisted Fenton-like process degraded SMX with 94.7% efficiency; however, HO-UIO-66 (Zr) is not stable. We improved the stability of the catalyst by introducing a calcination step. The calcination temperature is critical to improving the catalytic efficiency of the composite (for example, designated as HO-UIO-66/DE-300 to denote hydroxylated UIO-66 dispersed in diatomite calcined at 300 °C). The degradation of SMX by HO-UIO-66/DE-300 was 93.8% in 120 min with 4 mmol/L H2O2 at pH 3 under visible light radiation. The O1s XPS signatures signify the stability of the catalyst after repeated use for SMX degradation. The electron spin resonance spectral data suggest the role of h+, •OH, •O2-, and 1O2 in SMX degradation routes. The HO-UIO-66/DE-300-assisted Fenton-like process shows potential in degrading pharmaceutical products present in water and wastewater.

Carbonyl heterocycle modified mesoporous carbon nitride in photocatalytic peroxydisulfate activation for enhanced ciprofloxacin removal: Performance and mechanism.

Polymer carbon nitride is considered to be a promising photocatalyst with broad application prospects in water treatment. However, the defects of pristine polymer carbon nitride (PCN), such as small specific surface area, fast photogenerated electron-hole recombination, and low mass transfer efficiency, limit its photocatalytic activity. In this work, by introducing 2-thiouracil into the precursor, a carbonyl heterocycle-containing mesoporous carbon nitride photocatalyst (TCN) was successfully obtained with significantly enhanced peroxydisulfate (PDS) photocatalytic activity. In this study, the modulation mechanism of carbonyl heterocycle introduction on surface electronic structure and the band structure were fully discussed by means of a combination of experiments and theoretical calculations. The carbonyl and vicinal carbon-modified heterocycles dominated the electrons, while the adjacent heptazine ring dominated the holes. The photogenerated electron-hole pair recombination efficiency and the electron transition energy barrier were greatly reduced. According to the findings of density functional theory (DFT) calculations, the introduction of carbonyl and vicinal C modulated the electronic structure of catalyst, enhanced the adsorption of PDS at the carbonyl ortho N site, which promoted the electronic interaction between TCN and PDS molecules. Experiments showed that the free radical pathway and non-radical pathway coexisted in TCN/PDS/Vis system. The reactive oxygen species were mainly derived from PDS molecules. DFT calculations provided a more comprehensive theoretical basis for the experimental results. This study provided a fresh perspective on the rational design of carbon nitride-based catalysts and the reaction mechanism of persulfate advanced oxidation systems.

Enhanced degradation of sulfamethoxazole by non-radical-dominated peroxymonosulfate activation with Co/Zn co-doped carbonaceous catalyst: Synergy between Co and Zn.

Bimetallic catalysts are often used for peroxymonosulfate (PMS) activation in recent years due to the synergistic effects between two different metal species. However, the synergy between Zn and other transition metal in PMS activation are rarely studied because of the ease of evaporation of Zn species at high temperature. In this work, a Co/Zn co-doped carbonaceous catalyst derived from ZIF-67@ZIF-8 (Z67@8D) was prepared successfully by the core-shell replacement strategy, and used to activate PMS for sulfamethoxazole (SMX) degradation. Due to the co-existence of Co/Zn species (e.g., Co/Zn-N site), Z67@8D showed a much higher catalytic activity than that of Z8D, Z67D, and several commercial oxides. Importantly, the CoZn synergy was deeply revealed by combining experiments and density functional theory (DFT) calculations, in which Zn could adjust the electron distribution of Co, reducing the PMS adsorption energy and thus enhancing PMS decomposition and singlet oxygen (1O2) formation. Moreover, formed ZnO and graphitic structure of Z67@8D could also promote the catalytic activity. In addition, the good stability and reusability, universal applicability, and high environmental robustness of Z67@8D were demonstrated. Our findings may provide a new insight into the Zn-based bimetallic catalysts for PMS activation and pollutant degradation.

Construction of Li/K dopants and cyano defects in graphitic carbon nitride for highly efficient peroxymonosulfate activation towards organic contaminants degradation.

As an emerging peroxymonosulfate (PMS) activation catalyst, graphitic carbon nitride (g-C3N4) is non-toxic and eco-friendly, while its poor catalytic performance hinders the application of pristine g-C3N4. Herein, a simple LiCl/KCl molten salts-assisted thermal polymerization method was adopted to promote the photocatalytic performance of g-C3N4. With the insertion of Li/K dopants and the introduction of surface cyano defects, the modified catalyst exhibited greatly enhanced ability on PMS activation towards acetaminophen removal, observing a 13 times higher rate constant than pristine g-C3N4 (k = 0.0435 min-1 vs. 0.0033 min-1). The main reactive oxygen species for pollutant degradation were identified as sulfate radicals and singlet oxygen. The wavefunction analysis at excited states based on density functional theory suggests that the introduction of cyano defects greatly promotes the separation of photo-generated electron-hole pairs, thereby achieving higher photocatalytic efficiency. In addition, the doping of Li/K significantly enhances the interaction between PMS and the catalyst surface, and orients the electron transfer from PMS to catalyst to generate non-radical species singlet oxygen, which improves the catalyst resistance to anions-containing water matrices.

Roles of alkali metal dopants and surface defects on polymeric carbon nitride in photocatalytic peroxymonosulfate activation towards water decontamination.

Polymeric carbon nitride (PCN) has been extensively employed in peroxymonosulfate (PMS) activation for water decontamination. However, limited photocatalytic efficiency can be achieved by pristine PCN due to its intrinsic deficiencies like high electron-hole recombination rate and resistance to charge transfer. Herein, in a two-stage thermal treatment process, the nontoxic and stable Na and K were successfully anchored among the PCN skeleton with surface defects created, leading to an elevated photocatalytic activity for PMS activation. The SO4·- and 1O2 were identified as the dominant reactive oxygen species, which were generated from electron transfer processes between PMS and catalyst. Experimental and theoretical analyses suggested that the defective structures and metal dopants improved the optical properties of catalyst, endowing it a wider light absorption range and a lower energy barrier for electron transitions. The modified structures were also beneficial to electron transfer processes due to the weaker electron confinement effect, accelerating the production of SO4·- on the defective sites and 1O2 on the metal sites. The synergy of radical and non-radical species weakened the influence of side reactions between radicals from PMS and coexisting inorganic anions in practical water, hence to promote the resistance of modified catalysts in complex water matrices.

Removal of chlorophenols in the aquatic environment by activation of peroxymonosulfate with nMnOx@Biochar hybrid composites: Performance and mechanism.

Functional nMnOx@RBC composites were synthesized via a simple co-precipitation method. The nanomaterials have efficient activity in activating peroxymonosulfate (PMS) for removal of chlorophenols (CPs). Rice husk biochar (RBC) could support nMnOx, and acted as an electron shuttle to mediate electron transfer reaction. nMnOx@RBC had superior catalytic and adsorption properties and exhibited remarkable synergistic effects. This led to complete degradation of 4-chloro-3-methyl phenol (CMP) in 60 min at the natural pH (7.0). Reactive oxygen species (ROS) were also identified via the corresponding scavengers. The results indicated that singlet oxygen (1O2) played a dominant role in the degradation of CMP within nMnOx@RBC system. Moreover, the mechanism of CMP decomposition was rationally proposed, and possible intermediate products were deduced. The high degradation performances of diverse CPs were also observed in nMnOx@RBC/PMS system. This research aims to offer novel insights into carbon-metal nanomaterials for the elimination of emerging pollutants.

Insights into the photocatalytic peroxymonosulfate activation over defective boron-doped carbon nitride for efficient pollutants degradation.

The metal-free graphitic carbon nitride is a promising photocatalyst for peroxymonosulfate (PMS) activation towards water decontamination, but bearing low efficiency due to its electronic structure and surface chemistry. Herein, the non-metallic element boron was adopted for catalyst development. The boron dopants and defects were simultaneously introduced by potassium borohydride, resulting in an excellent activity towards PMS activation. The dominant reactive oxygen species was singlet oxygen, which was determined to originate from PMS activation over photo-induced holes initiated by an electron transfer process. Calculations based on density functional theory revealed that at excited states, due to the dopants and defects, the electron-hole distribution was altered from an even population to a significant separation, which was beneficial for photocatalytic performance. Besides, the engineered electronic structure weakened the catalyst resistance to charge transfer, enabling easier electron transfer between the catalyst and the PMS. Moreover, the strengthened and enlarged positive electrostatic potential areas on heptazine rings oriented the electron transfer process from the negatively charged PMS to the catalyst, facilitating the generation of singlet oxygen. These findings provide underlying mechanism insights into the contribution of dopants and defects to catalytic performance on persulfate-based photocatalytic water treatment.

Manganese peroxidase mediated oxidation of sulfamethoxazole: Integrating the computational analysis to reveal the reaction kinetics, mechanistic insights, and oxidation pathway.

In this study, manganese peroxidase (MnP) was applied to induce the in vitro oxidation of sulfamethoxazole (SMX). The results indicated that 87.04% of the SMX was transformed and followed first-order kinetics (kobs=0.438 h-1) within 6 h when 40 U L-1 of MnP was added. The reaction kinetics were investigated under different conditions, including pH, MnP activity, and H2O2 concentration. The active species Mn3+ was responsible for the oxidation of SMX, and the Mn3+ production rate was monitored to reveal the interaction among MnP, Mn3+, and SMX. By integrating the characterizations analysis of the MnP/H2O2 system with the density functional theory (DFT) calculations, the proton-coupled electron transfer (PCET) process dominated the catalytic circle of MnP and the transformation of Mn3+. Additionally, possible oxidation pathways of SMX were proposed based on single-electron transfer mechanism, which primarily included the S-N bond cleavage, the C-S bond cleavage, and one electron loss without bond breakage. It was then transformed to hydrolysis, N-H oxidation, self-coupling, and carboxylic acid coupling products. This study provides insights into the atomic-level mechanism of MnP and the transformation pathways of sulfamethoxazole, which lays a significant foundation for the potential of MnP in wastewater treatment applications.

Monocyclic aromatic hydrocarbons production from catalytic cracking of pine wood-derived pyrolytic vapors over Ce-Mo2N/HZSM-5 catalyst.

A series of Mo2N/HZSM-5 and transition metal modified Mo2N/HZSM-5 catalysts were prepared for the catalytic upgrading of pine wood-derived pyrolytic vapors for the selective production of monocyclic aromatic hydrocarbons (MAHs), while restraining the formation of polycyclic aromatic hydrocarbons (PAHs). Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed to determine the effects of several factors on selective MAHs production, including Mo2N loading on HZSM-5, transition metal (Fe, Ce, La, Cu, Cr) modification of Mo2N/HZSM-5, pyrolysis temperature, and catalyst-to-biomass ratio. In addition, quantitative experiments were conducted to determine the actual yields of major aromatic hydrocarbons and the source of aromatic hydrocarbons from basic biomass components. Results indicated that among the various catalysts, the Ce-10%Mo2N/HZSM-5 exhibited the best performance on promoting the formation of MAHs and restraining the generation of PAHs. Under the optimal conditions, the actual yields of MAHs and PAHs from Ce-10%Mo2N/HZSM-5 catalytic process were 99.8mg/g and 7.5mg/g, while those from HZSM catalyst were only 77.2mg/g and 23.7mg/g respectively. Furthermore, the possible catalytic mechanism of the Ce-Mo2N/HZSM-5 catalyst was proposed based on the catalyst characterization.

Catalytic Fast Pyrolysis of Biomass Impregnated with Potassium Phosphate in a Hydrogen Atmosphere for the Production of Phenol and Activated Carbon.

A new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K3PO4 in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K3PO4 and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K3PO4 at 550°C in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using CO2 activation method, the specific surface area was as high as 1,605 m2/g.

Selective Conversion of 5-Hydroxymethylfuraldehyde Using Cp*Ir Catalysts in Aqueous Formate Buffer Solution.

The highly selective hydrogenation/hydrolytic ring-opening reaction of 5-hydroxymethylfuraldehyde (5-HMF) was catalyzed by homogeneous Cp*Ir(III) half-sandwich complexes to produce 1-hydroxy-2,5-hexanedione (HHD). Adjustment of pH was found to regulate the distribution of products and reaction selectivity, and full conversion of 5-HMF to HHD with 99 % selectivity was achieved at pH 2.5. A mechanistic study revealed that the hydrolysis/ring-opening reaction of 2,5-bis-(hydroxymethyl)furan is the important intermediate reaction step. In addition, an isolated yield of 85 % for HHD was obtained in a 10 g-scale experiment, and the reaction with fructose as the starting material also led to a 98 % GC yield (71.9 % to fructose) of HHD owing to the excellent tolerance of the catalyst under acidic conditions.

Alkanes from Bioderived Furans by using Metal Triflates and Palladium-Catalyzed Hydrodeoxygenation of Cyclic Ethers.

Using a metal triflate and Pd/C as catalysts, alkanes were prepared from bioderived furans in a one-pot hydrodeoxygenation (HDO) process. During the reaction, the metal triflate plays a crucial role in the ring-opening HDO of furan compounds. The entire reaction process has goes through two major phases: at low temperatures, saturation of the exocyclic double bond and furan ring are catalyzed by Pd/C; at high temperatures, the HDO of saturated furan compounds is catalyzed by the metal triflate. The reaction mechanism was verified by analyzing the changes of the intermediates during the reaction. In addition, different metal triflates, solvents, and catalyst recycling were also investigated.

Aerobic oxidation of hydroxymethylfurfural and furfural by using heterogeneous Cox Oy -N@C catalysts.

2,5-Furandicarboxylic acid (FDCA) is considered to be a promising replacement for terephthalic acid since they share similar structures and properties. In contrast to FDCA, 2,5-furandicarboxylic acid methyl (FDCAM) has properties that allow it to be easily purified. In this work, we reported an oxidative esterification of 5-hydroxymethylfurfural (HMF) and furfural to prepare corresponding esters over Cox Oy -N@C catalysts using O2 as benign oxidant. High yield and selectivity of FDCAM and methyl 2-furoate were obtained under optimized conditions. Factors which influenced the product distribution were examined thoroughly. The Cox Oy -N@C catalysts were recycled five times and no significant loss of activity was detected. Characterization of the catalysts could explain such phenomena. Using XPS and TGA, we made a thorough investigation of the effects of ligand and pyrolysis temperature on catalyst activity.