Rational design of waste anode graphite-derived carbon catalyst to activate peroxymonosulfate for atrazine degradation.

As the rapidly growing number of waste lithium-ion batteries (LIBs), the recycling and reutilization of anode graphite is of increasing interest. Converting waste anode graphite into functional materials may be a sensible option. Herein, a series of carbonaceous catalysts (TG) were successfully prepared using spent anode graphite calcined at various temperatures and applied for activating peroxymonosulfate (PMS) to degrade atrazine (ATZ). The catalyst obtained at 800 °C (TG-800) showed the optimum performance for ATZ removal (99.2% in 6 min). Various experimental conditions were explored to achieve the optimum efficiency of the system. In the TG-800/PMS system, free radicals (e.g., SO4·-, HO·), singlet oxygen (1O2), together with a direct electron transfer pathway all participated in ATZ degradation, and the ketonic (CO) group was proved as the leading catalytic site for PMS activation. The potential degradation routes of ATZ have also been presented. According to the toxicity assessment experiments, the toxicity of the intermediate products decreased. The reusability and universal applicability of the TG-800 were also confirmed. This research not only provides an efficient PMS activator for pollutant degradation, but also offers a meaningful reference for the recovery of waste anode graphite to develop environmentally functional materials.

Intelligent multifunctional ruthenium monoatomic/ZnAl-LDH photocatalysts for simultaneous detection and rapid degradation of antibiotics.

The construction and precise synthesis of materials based on functional and structural orientations have emerged as a pivotal platform in the field of environmental management. In this paper, an efficient and stable catalyst (RuLDH) was constructed to achieve this goal. RuLDH comprises individual Ru atoms that are uniformly dispersed on ZnAl-LDH, achieved by room temperature stirring. Remarkably, RuLDH exhibits exceptional performance under visible light, effectively triggering the photocatalytic degradation of tetracycline hydrochloride (TC) via peroxymonosulfate (PMS) with a remarkable efficiency of 100%, all while avoiding the generation of highly toxic intermediates. In addition, RuLDH0.2 demonstrated its utility in fluorescence detection of TC, showcasing commendable analytical performance characterized by rapid response, low detection limit, and robust resistance to environmental interferences (with a detection limit of 1.0 mg/L). Notably, the RuLDH0.2/PMS/Vis system exhibited remarkable efficacy in treating actual pesticide wastewater, effectively exerting bactericidal and disinfectant effects. This study serves as a source of inspiration for the design of multifunctional single-atom catalysts, thereby pushing the boundaries of "integration of diagnosis and treatment" in environmental management and control.

Activation Model and Origins of Selectivity for Chiral Phosphoric Acid Catalyzed Diradical Reactions.

To develop new radical synthesis strategies, a profound understanding of the electronic transfer mechanism is critical. An activation model called relayed proton-coupled electron transfer (relayed-PCET) was developed and investigated for chiral phosphoric acid-catalyzed diradical reactions by density functional theory (DFT). The driving force of electron transfer from the nucleophile to the electrophile is the proton transfer that occurs via the chiral phosphoric acid (CPA) catalyst to the electrophile. Moreover, the origins of the selectivity can be explained by distortion of the catalyst, favorable hydrogen bonding, and strong interactions of the substrates with substituents of the CPAs.

Insights into the Occurrence, Fate, Impacts, and Control of Food Additives in Food Waste Anaerobic Digestion: A Review.

The recovery of biomass energy from food waste through anaerobic digestion as an alternative to fossil energy is of great significance for the development of environmental sustainability and the circular economy. However, a substantial number of food additives (e.g., salt, allicin, capsaicin, allyl isothiocyanate, monosodium glutamate, and nonnutritive sweeteners) are present in food waste, and their interactions with anaerobic digestion might affect energy recovery, which is typically overlooked. This work describes the current understanding of the occurrence and fate of food additives in anaerobic digestion of food waste. The biotransformation pathways of food additives during anaerobic digestion are well discussed. In addition, important discoveries in the effects and underlying mechanisms of food additives on anaerobic digestion are reviewed. The results showed that most of the food additives had negative effects on anaerobic digestion by deactivating functional enzymes, thus inhibiting methane production. By reviewing the response of microbial communities to food additives, we can further improve our understanding of the impact of food additives on anaerobic digestion. Intriguingly, the possibility that food additives may promote the spread of antibiotic resistance genes, and thus threaten ecology and public health, is highlighted. Furthermore, strategies for mitigating the effects of food additives on anaerobic digestion are outlined in terms of optimal operation conditions, effectiveness, and reaction mechanisms, among which chemical methods have been widely used and are effective in promoting the degradation of food additives and increasing methane production. This review aims to advance our understanding of the fate and impact of food additives in anaerobic digestion and to spark novel research ideas for optimizing anaerobic digestion of organic solid waste.

Mechanistic views and computational studies on transition-metal-catalyzed reductive coupling reactions.

Transition-metal-catalyzed reductive coupling reactions have been considered as a powerful tool to convert two electrophiles into value-added products. Numerous related reports have shown the fascinating potential. Mechanistic studies, especially theoretical studies, can provide important implications for the design of novel reductive coupling reactions. In this review, we summarize the representative advancements in theoretical studies on transition-metal-catalyzed reductive coupling reactions and systematically elaborate the mechanisms for the key steps of reductive coupling reactions. The activation modes of electrophiles and the deep insights of selectivity generation are mechanistically discussed. In addition, the mechanism of the reduction of high-oxidation-state catalysts and further construction of new chemical bonds are also described in detail.

Catalyst-Free Photochemical Activation of Peroxymonosulfate in Xanthene-Rich Systems for Fenton-Like Synergistic Decontamination: Efficacy of Proton Transfer Process.

Catalyst-free visible light assisted Fenton-like catalysis offers opportunities to achieve the sustainable water decontamination, but the synergistic decontamination mechanisms are still unclear, especially the effect of proton transfer process (PTP). The conversion of peroxymonosulfate (PMS) in photosensitive dye-enriched system was detailed. The photo-electron transfer between excited dye and PMS triggered the efficient activation of PMS and enhanced the production of reactive species. Photochemistry behavior analysis and DFT calculations revealed that PTP was the crucial factor to determine the decontamination performance, leading to the transformation of dye molecules. The excitation process inducing activation of whole system was composed of low energy excitations, and the electrons and holes were almost contributed by LUMO and HOMO. This work provided new ideas for the design of catalyst-free sustainable system for efficient decontamination.

Mechanism and Origin of Stereoselectivity of Ni-Catalyzed Cyclization/Carboxylation of Bromoalkynes with CO2.

Bromoalkynes play important roles in coupling reactions because they can show obvious stereoselectivity to form E- and Z-isomers when substituents are different. However, the origin of the stereoselectivity in the bromoalkynes reaction is still unclear. Density functional theory (DFT) calculations were performed to provide an in-depth study of the reaction mechanism, clarifying the mechanistic details of the main reaction and the origin of the stereoselectivity. By comparing the syn-insertion mechanism of alkynes and the radical pathway, it is indicated that the electrostatic effect caused by the different charge distributions of the reactants is the main reason that Ni(I) species are more prone to syn-insertion of alkynes than Ni(II) species. In addition, the lower reaction energy barrier in the radical pathway suggests that it is more advantageous in terms of kinetics. The bond between Ni(I) species and alkenylation products has two directions to generate products of different configurations, which are the direct stereoselectivity-determining stages. The distortion/interaction analysis shows that the distortion energy mainly affects the product configuration, and the steric hindrance is the main factor controlling the stereoselectivity.

Evaluating the effect of diclofenac on hydrogen production by anaerobic fermentation of waste activated sludge.

Hydrogen production from waste-activated sludge (WAS) anaerobic fermentation is considered to be an effective method of resource recovery. However, the presence of a large number of complex organic compounds in sludge will affect the biological hydrogen production process. As an extensively applied prevalent anti-inflammatory drug, diclofenac (DCF) is inevitably released into the environment. However, the effect of diclofenac on hydrogen production from WAS anaerobic fermentation has not been fully investigated. This work therefore aims to comprehensively investigate the removal efficiency of DCF in mesophilic anaerobic fermentation of WAS and its effect on hydrogen yield. Experiment results showed that 32.5%-38.3% of DCF was degraded in the fermentation process when DCF concentration was ranged from 6 to 100 mg/kg TSS (total suspended solids). DCF at environmental level inhibited hydrogen production, the maximal hydrogen yield decreased from 24.2 to 15.3 mL/g VSS (volatile suspended solids) with an increase of DCF addition from 6 to 100 mg/kg TSS. This is because the presence of DCF caused inhibitions to acetogenesis and acidogenesis, the processes responsible for hydrogen production, probably due to that the polar groups of DCF (i.e., carboxyl group) could readily bind to active sites of [FeFe]- Hydrogenase. Besides, the microbial analysis revealed that DCF increased the microbial diversity but had few influences on the microbial structure.

The fate of diclofenac in anaerobic fermentation of waste activated sludge.

Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is one of the most commonly detected pharmaceuticals in wastewater treatment plants. However, the fate of DCF in waste activated sludge (WAS) anaerobic fermentation has not been well-understood so far. This work therefore aims to comprehensively reveal whether and how DCF is transformed in WAS mesophilic anaerobic fermentation through both experimental investigation and density functional theory (DFT) calculation. Experimental results showed that ∼28.8% and 45.8% of DCF were respectively degraded during the batch and long-term fermentation processes. Based on the detected intermediates and DFT-predicted active sites, three metabolic pathways, i.e., chlorination, hydroxylation, and dichlorination, responsible for DCF transformation were proposed. DFT calculation also showed that the Gibbs free energy (ΔG) of the three transformation pathways was respectively 19.0, -4.3, and -19.3 kcal/mol, suggesting that the latter two reactions (i.e., hydroxylation and dichlorination) were thermodynamically favorable. Illumina MiSeq sequencing analyses revealed that DCF improved the populations of complex organic degradation microbes such as Proteiniclasticum and Tissierellales, which was in accord with the chemical analyses above. This work updates the fundamental understanding of the degradation of DCF in WAS anaerobic fermentation process and enlightens engineers to apply theoretical calculation to the field of sludge treatment or other complex microbial ecosystems.

How Does Chitosan Affect Methane Production in Anaerobic Digestion?

The expanding use of chitosan in sewage and sludge treatment processes raises concerns about its potential environmental impacts. However, investigations of the impacts of chitosan on sewage sludge anaerobic digestion where chitosan is present at substantial levels are sparse. This study therefore aims to fill this knowledge gap through both long-term and batch tests. The results showed that 4 g/kg total suspended solid (TSS) chitosan had no acute effects on methane production, but chitosan at 8-32 g/kg TSS inhibited methane production by 7.2-30.3%. Mass balance and metabolism of organic analyses indicated that chitosan restrained the transfer of organic substrates from solid phase to liquid phase, macromolecules to micromolecules, and finally to methane. Further exploration revealed that chitosan suppressed the secretion of extracellular polymeric substances of anaerobes by occupying the connection sites of indigenous carbohydrates and increased the mass transfer resistance between anaerobes and substrates, which thereby lowered the metabolic activities of anaerobes. Although chitosan could be partly degraded by anaerobes, it is much more persistent to be degraded compared with indigenous organics in sludge. Microbial community and key enzyme encoding gene analyses further revealed that the inhibition of chitosan to CO2-dependent methanogenesis was much severer than that to acetate-dependent methanogenesis.

Formation of a Supramolecular Polymeric Adhesive via Water-Participant Hydrogen Bond Formation.

A supramolecular polymeric adhesive was prepared from non-viscous, non-polymeric materials by water-participant hydrogen bonds. Pt-pyridine coordination and water-crown ether hydrogen bonding combine to effect the supramolecular polymerization. The supramolecular polymeric adhesive displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolecular materials.

Influence of surfactants on anaerobic digestion of waste activated sludge: acid and methane production and pollution removal.

The objective of this study is to summarize the effects of surfactants on anaerobic digestion (AD) of waste activated sludge (WAS). The increasing amount of WAS has caused serious environmental problems. Anaerobic digestion, as the main treatment for WAS containing three stages (i.e. hydrolysis, acidogenesis, and methanogenesis), has been widely investigated. Surfactant addition has been demonstrated to improve the efficiency of AD. Surfactant, as an amphipathic substance, can enhance the efficiency of hydrolysis by separating large sludge and releasing the encapsulated hydrolase, providing more substance for subsequent acidogenesis. Afterwards, the short chain fatty acids (SCFAs), as the major product, have been produced. Previous investigations revealed that surfactant could affect the transformation of SCFA. They changed the types of acidification products by promoting changes in microbial activity and in the ratio of carbon to nitrogen (C/N), especially the ratio of acetic and propionic acid, which were applied for either the removal of nutrient or the production of polyhydroxyalkanoate (PHA). In addition, the activity of microorganisms can be affected by surfactant, which mainly leads to the activity changes of methanogens. Besides, the solubilization of surfactant will promote the solubility of contaminants in sludge, such as organic contaminants and heavy metals, by increasing the bioavailability or desorbing of the sludge.

Theoretical Study of Diastereoselective NHC-Catalyzed Cross-Benzoin Reactions between Furfural and N-Boc-Protected α-Amino Aldehydes.

The mechanism and origins of syn and anti selectivity of cross-benzoin reactions between furfural and α-amino aldehydes, catalyzed by a triazolium-based NHC, were investigated using density functional theory calculations. N-Boc-α-amino aldehydes were found to react with anti selectivity, while N-Bn-N-Boc-α-amino aldehydes react with syn selectivity. We find that the anti product is more thermodynamically favored than the syn product for reactions with N-Boc-α-amino aldehydes, and that the formation of the syn product for reactions involving N-Bn-N-Boc-α-amino aldehydes is kinetically favored. The switch in selectivity is a result of an intramolecular hydrogen bond in the N-Boc-α-amino aldehyde, whereas switching to N-Bn-N-Boc-α-amine removes the hydrogen bond. The steric and electronic interactions in the transition state are rationalized by a Felkin-Anh model.

Diazo Esters as Dienophiles in Intramolecular (4 + 2) Cycloadditions: Computational Explorations of Mechanism.

The first experimental examples of Diels-Alder (DA) reactions of diazo compounds as heterodienophiles with dienes have been studied with density functional theory (DFT) using the M06-2X functional. For comparison, the reactivities of diazo esters as dienophiles or 1,3-dipoles with 1,3-dienes in intermolecular model systems have been analyzed by the distortion/interaction model. The 1,3-dipolar cycloaddition is strongly favored for the intermolecular system. The intramolecular example is unique because the tether strongly favors the (4 + 2) cycloaddition.

Enzyme-Catalyzed Intramolecular Enantioselective Hydroalkoxylation.

Hydroalkoxylation is a powerful and efficient method of forming C-O bonds and cyclic ethers in synthetic chemistry. In studying the biosynthesis of the fungal natural product herqueinone, we identified an enzyme that can perform an intramolecular enantioselective hydroalkoxylation reaction. PhnH catalyzes the addition of a phenol to the terminal olefin of a reverse prenyl group to give a dihydrobenzofuran product. The enzyme accelerates the reaction by 3 × 105-fold compared to the uncatalyzed reaction. PhnH belongs to a superfamily of proteins with a domain of unknown function (DUF3237), of which no member has a previously verified function. The discovery of PhnH demonstrates that enzymes can be used to promote the enantioselective hydroalkoxylation reaction and form cyclic ethers.

Phenalenone Polyketide Cyclization Catalyzed by Fungal Polyketide Synthase and Flavin-Dependent Monooxygenase.

Phenalenones are polyketide natural products that display diverse structures and biological activities. The core of phenalenones is a peri-fused tricyclic ring system cyclized from a linear polyketide precursor via an unresolved mechanism. Toward understanding the unusual cyclization steps, the phn biosynthetic gene cluster responsible for herqueinone biosynthesis was identified from the genome of Penicillium herquei. A nonreducing polyketide synthase (NR-PKS) PhnA was shown to synthesize the heptaketide backbone and cyclize it into the angular, hemiketal-containing naphtho-γ-pyrone prephenalenone. The product template (PT) domain of PhnA catalyzes only the C4-C9 aldol condensation, which is unprecedented among known PT domains. The transformation of prephenalenone to phenalenone requires an FAD-dependent monooxygenase (FMO) PhnB, which catalyzes the C2 aromatic hydroxylation of prephenalenone and ring opening of the γ-pyrone ring simultaneously. Density functional theory calculations provide insights into why the hydroxylated intermediate undergoes an aldol-like phenoxide-ketone cyclization to yield the phenalenone core. This study therefore unveiled new routes and biocatalysts for polyketide cyclization.

Kinetics and mechanism analysis of advanced oxidation degradation of PFOA/PFOS by UV/Fe3+ and persulfate: A DFT study.

UV/Fe3+ and persulfate are two promising advanced oxidative degradation systems for in situ remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), yet a lack of comprehensive understanding of the degradation mechanisms. For the first time, we used density functional theory (DFT) to calculate the entire reaction pathways of the degradation of PFOA/PFOS in water by UV/Fe3+ and persulfate. In addition, we have deeply explored the different attack pathways driven by •OH and SO4-•, and found that SO4-• determines PFOA/PFOS to obtain PFOA/PFOS free radicals through single electron transfer to initiate the degradation reaction, while •OH determines the speed of PFOA/PFOS degradation reaction. Both degradation reactions were thermodynamically advantageous and kinetically feasible under calculated conditions. Based on the thermodynamic data, persulfate was found to be more favorable for the advanced oxidative degradation of Perfluorinated compounds (PFCs). Moreover, for SO4-• and •OH co-existing in the persulfate system, pH will affect the presence and concentration of these two types of free radicals, and low pH is not necessary for the degradation of PFOA/PFOS in the persulfate system. These results can considerably advance our understanding of the PFOA/PFOS degradation process in advanced oxidation processes (AOPs), which is driven by •OH and SO4-•. This study provides a DFT calculation process for the mechanism calculation of advanced oxidation degradation of other types of PFCs pollutants, hoping to elucidate the future development of PFCs removal. Further research should focus on determining the advanced oxidation degradation pathways of other types of PFCs, to support the development of computational studies on the advanced oxidation degradation of PFCs.

Enantioselective Synthesis of Axially Chiral Sulfone-Containing Styrenes Based on Ion-Exchange Strategy.

A novel ion exchange strategy has been developed to enable the asymmetric construction of axially chiral sulfone-containing styrenes. This approach provides a practical synthesis pathway for various axially chiral sulfone-containing styrenes with good yields, exceptional enantioselectivities, and nearly complete E/Z selectivities. Additionally, the reaction mechanism is elucidated in detail through density functional theory (DFT) calculations.

Benzethonium chloride affects short chain fatty acids produced from anaerobic fermentation of waste activated sludge: Performance, biodegradation and mechanisms.

Benzethonium chloride (BZC) is viewed as a promising disinfectant and widely applied in daily life. While studies related to its effect on waste activated sludge (WAS) anaerobic fermentation (AF) were seldom mentioned before. To understand how BZC affects AF of WAS, production of short chain fatty acids (SCFAs), characteristics of WAS as well as microbial community were evaluated during AF. Results manifested a dose-specific relationship of dosages between BZC and SCFAs and the optimum yield arrived at 2441.01 mg COD/L with the addition of 0.030 g/g TSS BZC. Spectral results and protein secondary structure variation indicated that BZC denatured proteins in the solid phase into smaller proteins or amino acids with unstable structures. It was also found that BZC could stimulate the extracellular polymeric substances secretion and reduce the surface tension of WAS, leading to the enhancement of solubilization. Beside, BZC promoted the hydrolysis stage (increased by 7.09 % to 0.030 g/g TSS BZC), but inhibited acetogenesis and methanogenesis stages (decreased by 6.85 % and 14.75 % to 0.030 g/g TSS BZC). The microbial community was also regulated by BZC to facilitate the enrichment of hydrolytic and acidizing microorganisms (i.e. Firmicutes). All these variations caused by BZC were conducive to the accumulation of SCFAs. The findings contributed to investigating the effect of BZC on AF of WAS and provided a new idea for the future study of AF mechanism.

Theoretical study on the mechanism of stereoselective synthesis of oxazolidinones.

Oxazolidinones can be synthesized through an organocatalytic cascade reaction of stable sulfur ylides and nitro-olefins. This process, sequentially catalyzed by thiourea and N,N-dimethylaminopyridine (DMAP), is theoretically studied using density functional theory by the continuum solvation model. It is shown that the rate- and stereoselectivity-determining step is the addition reaction of sulfur ylide to the nitro-olefin with two competing reaction channels. One channel is where the nitro-cyclopropane is generated first and then converted into isoxazoline N-oxide through a DMAP-catalyzed rearrangement. The other channel is the direct generation of the isoxazoline N-oxide intermediate. DMAP plays an important role in the reaction as a nucleophilic catalyst. The mechanism for the important rearrangement reaction proposed by Xiao et al. (J. Am. Chem. Soc. 2008, 130, 6946-6948) is not appropriate as the reaction energy barrier is too high; a 10-step mechanism determined by our theoretical calculations is more feasible as the energy barrier is becoming much less than that by Xiao. It is the first time that the Hofmann rearrangement involved in the cascade organocatalysis is confirmed by theoretical calculations. Our result of the stereoselectivity for the synthesis of oxazolidinones is in good agreement with the experiment.