Direct Synthesis of N-formamides by Integrating Reductive Amination of Ketones and Aldehydes with CO2 Fixation in a Metal-Organic Framework.

Formamides are important feedstocks for the manufacture of many fine chemicals. State-of-the-art synthesis of formamides relies on the use of an excess amount of reagents, giving copious waste and thus poor atom-economy. Here, we report the first example of direct synthesis of N-formamides by coupling two challenging reactions, namely reductive amination of carbonyl compounds, particularly biomass-derived aldehydes and ketones, and fixation of CO2 in the presence of H2 over a metal-organic framework supported ruthenium catalyst, Ru/MFM-300(Cr). Highly selective production of N-formamides has been observed for a wide range of carbonyl compounds. Synchrotron X-ray powder diffraction reveals the presence of strong host-guest binding interactions via hydrogen bonding and parallel-displaced π⋅⋅⋅π interactions between the catalyst and adsorbed substrates facilitating the activation of substrates and promoting selectivity to formamides. The use of multifunctional porous catalysts to integrate CO2 utilisation in the synthesis of formamide products will have a significant impact in the sustainable synthesis of feedstock chemicals.

Ultra-fast Proton Conduction and Photocatalytic Water Splitting in a Pillared Metal-Organic Framework.

Proton-exchange membrane fuel cells enable the portable utilization of hydrogen (H2) as an energy resource. Current electrolytic materials have limitation, and there is an urgent need to develop new materials showing especially high proton conductivity. Here, we report the ultra-fast proton conduction in a novel metal-organic framework, MFM-808, which adopts an unprecedented topology and a unique structure consisting of two-dimensional layers of {Zr6}-clusters. By replacing the bridging formate with sulfate ligands within {Zr6}-layers, the modified MFM-808-SO4 exhibits an exceptional proton conductivity of 0.21 S·cm-1 at 85 °C and 99% relative humidity. Modeling by molecular dynamics confirms that proton transfer is promoted by an efficient two-dimensional conducting network assembled by sulfate-{Zr6}-layers. MFM-808-SO4 also possesses excellent photocatalytic activity for water splitting to produce H2, paving a new pathway to achieve a renewable hydrogen-energy cycle.

Insights into the Superior Bioavailability of Biogenic Sulfur from the View of Its Unique Properties: The Key Role of Trace Organic Substances.

Elemental sulfur (S0) is widely utilized in environmental pollution control, while its low bioavailability has become a bottleneck for S0-based biotechnologies. Biogenic sulfur (bio-S0) has been demonstrated to have superior bioavailability, while little is known about its mechanisms thus far. This study investigated the bioavailability and relevant properties of bio-S0 based on the denitrifying activity of Thiobacillus denitrificans with chemical sulfur (chem-S0) as the control. It was found that the conversion rate and removal efficiency of nitrate in the bio-S0 system were 2.23 and 2.04 times those of the chem-S0 system. Bio-S0 was not pure orthorhombic sulfur [S: 96.88 ± 0.25% (w/w)]. Trace organic substances detected on the bio-S0 surface were revealed to contribute to its hydrophilicity, resulting in better dispersibility in the aqueous liquid. In addition, the adhesion force of T. denitrificans on bio-S0 was 1.54 times that of chem-S0, endowing a higher bacterial adhesion efficiency on the sulfur particle. The weaker intermolecular binding force due to the low crystallinity of bio-S0 led to enhanced cellular uptake by attached bacteria. The mechanisms for the superior bioavailability of bio-S0 were further proposed. This study provides a comprehensive view of the superior bioavailability of bio-S0 and is beneficial to developing high-quality sulfur resources.

Highly Efficient Proton Conduction in the Metal-Organic Framework Material MFM-300(Cr)·SO4(H3O)2.

The development of materials showing rapid proton conduction with a low activation energy and stable performance over a wide temperature range is an important and challenging line of research. Here, we report confinement of sulfuric acid within porous MFM-300(Cr) to give MFM-300(Cr)·SO4(H3O)2, which exhibits a record-low activation energy of 0.04 eV, resulting in stable proton conductivity between 25 and 80 °C of >10-2 S cm-1. In situ synchrotron X-ray powder diffraction (SXPD), neutron powder diffraction (NPD), quasielastic neutron scattering (QENS), and molecular dynamics (MD) simulation reveal the pathways of proton transport and the molecular mechanism of proton diffusion within the pores. Confined sulfuric acid species together with adsorbed water molecules play a critical role in promoting the proton transfer through this robust network to afford a material in which proton conductivity is almost temperature-independent.

Selective Utilization of the Methoxy Group in Lignin to Produce Acetic Acid.

Selective transformation of lignin into a valuable chemical is of great importance and challenge owing to its complex structure. Herein, we propose a strategy for the transformation of methoxy group (-OCH3 ) which is abundant in lignin into pure highly valuable chemicals. As an example to apply this strategy, a route to produce acetic acid with high selectivity by conversion of methoxy group of lignin was developed. It was demonstrated that the methoxy group in lignin could react with CO and water to generate acetic acid over RhCl3 in the presence of a promoter. The conversions of methoxy group in the kraft lignin and organosolv lignin reached 87.5 % and 80.4 %, respectively, and no by-product was generated. This work opens the way to produce pure chemicals using lignin as the feedstock.

The molecular clusters in a supercritical fluid-solid system should be considered as a phase-thermodynamic principle and evidence.

In this work we propose a new thermodynamic principle in which a supercritical fluid (SCF)-solid system is divided into a solid phase, a cluster phase, and a bulk fluid phase, i.e., the molecular clusters in the system are considered as an individual phase. The phase equilibria of various SCF-solid systems are calculated using this principle in combination with Monte Carlo simulation and the Peng-Robinson equation of state (PR-EOS). It is shown that in the critical region of the supercritical (SC) solvents where the clustering is significant, the results calculated using this thermodynamic principle are much more consistent with the experimental data than those calculated using the conventional thermodynamic principle, confirming the validity of the principle proposed in this work.

Reducing nitrogen loss during kitchen waste composting using a bioaugmented mechanical process with low pH and enhanced ammonia assimilation.

Exploring the regulation of nitrogen transformation in bioaugmented mechanical composting (BMC) process for rural kitchen waste (KW) is essential to avoid the "not-in-my-backyard" phenomenon caused by nitrogen loss. Herein, nitrogen transformation and loss in BMC versus conventional pile composting (CPC) of KW were compared. The results showed that the total nitrogen loss in the BMC was 6.87-39.32 % lower than that in the CPC. The main pathways to prevent nitrogen loss in the BMC were reducing NH3 by avoiding a sharp increase in pH followed by transforming the preserved NH4+-N into recalcitrant nitrogen reservoir via enhanced ammonia assimilation. The enriched thermophilic bacteria with mineralization capacities (e.g., Bacillus and Corynebacterium) during rapid dehydration and heating in the BMC accumulated organic acids and easy-to-use carbon sources, which could lead to lower pH and ammonia assimilation enhancement, respectively. This study provides new ideas for formulating low-cost nitrogen conservation strategies in decentralized KW composting.

Crystal-phase engineering of PdCu nanoalloys facilitates selective hydrodeoxygenation at room temperature.

Selective hydrodeoxygenation of biomass-derived aromatic alcohols to value-added chemical or fuel is of great importance for sustainable biomass upgrading, and hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is one of the most attractive reactions. Achieving the conversion of HMF to DMF using H2 at ambient temperature is challenging. In this work, we used PdCu nanoalloys to catalyze the selective hydrodeoxygenation reaction of HMF to DMF using H2 as the reducing agent. The reaction path and the product selectivity are governed by the crystallographic phase of the PdCu nanoalloys. It was discovered that body-centered cubic (BCC) PdCu nanoalloys supported on activated carbon (AC) exhibited outstanding performance with 93.6% yield of DMF at room temperature (PdCu/AC-BCC). A combination of experimental and density functional theory (DFT) studies showed that the tilted adsorption modes of furanic intermediates on PdCu-BCC nanoalloy surfaces accounted for the high selectivity of DMF; however, furan ring was activated on PdCu face-centered cubic (FCC) nanoalloy surfaces. Furthermore, PdCu/AC-BCC could also catalyze the hydrodeoxygenation of other aromatic alcohols at room temperature while maintaining the aromatic structures. This work opens the way for selective hydrodeoxygenation of the aromatic alcohols at room temperature with the aromatic ring intact.

Aging microplastics in wastewater pipeline networks and treatment processes: Physicochemical characteristics and Cd adsorption.

Despite a wealth of information on removal of the microplastics (MPs) in wastewater treatment plants (WWTPs), little attention has been paid to how wastewater treatment process affect the MP physicochemical and adsorption characteristics. In this study, changes in physicochemical property of three MPs, i.e. polyamide (PA), polyethylene (PE) and polystyrene (PS) through the wastewater pipeline, grit and biological aeration tanks were investigated. The results show that compared with virgin MPs, the treated MPs have higher specific surface area and O content, and lower C and H contents, and glass transition temperature, implying that the three treatments cause the chain scission and oxidation of the MPs. Cd adsorption capacities of the MPs are higher than the corresponding virgin MPs after sulfidation in the pipeline (SWPN) and biological treatment in aeration tank (BTAT). Pearson correlation analysis shows that the increase is mainly resulted from the enhancement of the O-containing groups on the MPs. However, Cd adsorption capacities of the MPs decrease after mechanical abrasion in grit tank (MAGT), corresponding to the decrease in carbonyl index. Two dimensional FTIR correlation spectroscopy demonstrates that the NH bond in the PA plays a more important role than CH bond in the adsorption of Cd, but only change of the CH bond is found in the PE and PS. The findings provide new insights into the effect of WWTPs on the MP aging and physicochemical characteristics.

Selective utilization of methoxy groups in lignin for N-methylation reaction of anilines.

The utilization of lignin as a feedstock to produce valuable chemicals is of great importance. However, it is a great challenge to produce pure chemicals because of the complex structure of lignin. The selective utilization of specific groups on lignin molecules offers the possibility of preparing chemicals with high selectivity, but this strategy has not attracted attention. In this work, we propose a protocol to produce methyl-substituted amines by the selective reaction of the methoxy groups of lignin and aniline compounds. It was found that LiI in the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate could catalyze the reaction efficiently and the selectivity to the N-methylation product could be as high as 98%. Moreover, the lignin was not depolymerized in the reaction. As it was rich in hydroxyl groups, the residual material left over after the reaction was used as an efficient co-catalyst for the cycloaddition of epoxy propane with CO2, using KI as the catalyst.

Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process.

Microplastics (MPs) as new pollutants of environmental concern have been widely detected in sewage sludge, and may act as significant vectors for metal pollutants due to their adsorption property. Our findings show that Cd, Pb, and Co, but not Ni, contents in sewage sludge are lower than that of corresponding metal irons adsorbed on sludge-based MPs, indicating that the MPs accumulate such metal pollutants as Cd in the sludge samples. In contrast to virgin MPs, sludge-based MPs are one order of magnitude higher adsorption capacity for Cd, which reaches up to 2.523 mg g-1, implying that there is a considerable enhancement in adsorption potential of the MPs for metals after the wastewater treatment process. SEM analysis shows that sludge-based MPs have rougher and more porous surface than virgin MPs, and FTIR spectra reveal that functional groups such as CO and OH are found on sludge-based MPs. Further, two-dimensional FTIR correlation spectroscopy indicates that CO and NH functional groups play a vital role in the process that sludge-based MPs adsorb Cd, which are not found in virgin MPs. The results imply that increased adsorption potentials of the sludge-based MPs to Cd are attributed to changes in the MP physicochemical properties during wastewater treatment process. In addition, such factors as pH value, and sludge inorganic and organic components also have an effect on the MP adsorption to Cd. Principal component analysis shows that the MPs could be divided into three categories, i.e. polyamide, rubbery MPs (polyethylene and polypropylene) and glassy MPs (polyvinyl chloride and polystyrene). Their adsorption potentials to Cd follow the decreasing order: polyamide > rubbery MPs > glassy MPs. In summary, these findings indicate that MPs may exert an important influence on fate and transport of metal pollutants during sewage sludge treatment process, which deserves to be further concerned.

Selective catalytic transformation of lignin with guaiacol as the only liquid product.

Guaiacol is an important feedstock for producing various high-value chemicals. However, the current production route of guaiacol relies heavily on fossil resources. Using lignin as a cheap and renewable feedstock to selectively produce guaiacol has great potential, but it is a challenge because of its heterogeneity and inert reactivity. Herein, we discovered that La(OTf)3 could catalyze the transformation of lignin with guaiacol as the only liquid product. In the reaction, La(OTf)3 catalyzed the hydrolysis of lignin ether linkages to form alkyl-syringol and alkyl-guaiacol, which further underwent decarbonization and demethoxylation to produce guaiacol with a yield of up to 25.5 wt%, and the remaining residue was solid. In the scale-up experiment, the isolated yield of guaiacol reached up to 21.2 wt%. To our knowledge, this is the first work to produce pure guaiacol selectively from lignin. The bio-guaiacol may be considered as a platform to promote lignin utilization.

A new route to synthesize aryl acetates from carbonylation of aryl methyl ethers.

Ether bond activation is very interesting because the synthesis of many valuable compounds involves conversion of ethers. Moreover, C-O bond cleavage is also very important for the transformation of biomass, especially lignin, which abundantly contains ether bonds. Developing efficient methods to activate aromatic ether bonds has attracted much attention. However, this is a challenge because of the inertness of aryl ether bonds. We proposed a new route to activate aryl methyl ether bonds and synthesize aryl acetates by carbonylation of aryl methyl ethers. The reaction could proceed over RhCl3 in the presence of LiI and LiBF4, and moderate to high yields of aryl acetates could be obtained from transformation of various aryl methyl ethers with different substituents. It was found that LiBF4 could assist LiI to cleave aryl methyl ether bonds effectively. The reaction mechanism was proposed by a combination of experimental and theoretical studies.

Transformation of alcohols to esters promoted by hydrogen bonds using oxygen as the oxidant under metal-free conditions.

One-pot oxidative transformation of alcohols into esters is very attractive, but metal-based catalysts are used in the reported routes. We discovered that the basic ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM] OAc) could effectively catalyze this kind of reaction using O2 as an oxidant without any other catalysts or additives. The oxidative self-esterification of benzylic alcohols or aliphatic alcohols and cross-esterification between benzyl alcohols and aliphatic alcohols could all be achieved with high yields. Detailed study revealed that the cation with acidic proton and basic acetate anion could simultaneously form multiple hydrogen bonds with the hydroxyl groups of the alcohols, which catalyzed the reaction very effectively. As far as we know, this is the first work to carry out this kind of reaction under metal-free conditions.

Microplastics in sewage sludge from the wastewater treatment plants in China.

Sludge disposal such as land application is suspected as a significant source of microplastic (MP) pollution in the environment. To examine such a hypothesis, the present study was conducted to investigate the occurrence of MPs in sludge by analyzing 79 sewage sludge samples collected from 28 wastewater treatment plants (WWTPs) in 11 Chinese provinces. MP concentrations in the sludge samples ranged from 1.60-56.4 × 103 particles per kilogram of dry sludge, with an average of 22.7 ±â€¯12.1 × 103 particles per kilogram of dry sludge. Thereinto, the sludge-based MP contents were greater in eastern China than in western China and varied during different months. Their colors and types were mainly white (59.6%) and fibers (63%), respectively. Microscope Fourier Transform infrared spectroscopy revealed that most of MPs belonged to polyolefin, acrylic fibers, polyethylene and polyamide. Some WWTP parameters, such as servicing area, proportion of industrial wastewater, secondary treatment and sludge dewatering may have affected MP concentrations in sludge. Based on the total sludge production in China, the average amount of sludge-based MPs entering into natural environmental was estimated to be 1.56 × 1014 particles per year. The findings confirmed that sewage sludge discharge is an important source of MP pollution in the environment. Further evaluation of the associated environmental hazards with MPs is deemed necessary.

Molecular characteristics of the refractory organic matter in the anaerobic and aerobic digestates of sewage sludge.

The chemical characteristics of the refractory organic matter in anaerobic and aerobic digestates are hardly known although they are significant for further improving the degradation of organic matter during sludge digestion. Thus, in this study, various techniques are used to analyze the molecular properties of the total organic matter in raw sludge and mesophilic anaerobic and aerobic digestates (AnD and AoD, respectively). The results show that AnD has lower organic matter content, but the maturity and aromatization of its organic matter are lower than those of AoD. The FTIR and XPS spectra show that AoD has higher proportions of protein-like and aromatic groups and lower percentages of polysaccharide-like materials and ammonia nitrogen compared with AnD. The solid-phase fluorescence spectra indicate that AoD has a higher content of fluorescence organic matter, but its biodegradability and chemical accessibility are lower than those of AnD. Pyrolysis GC/MS analysis shows that the digestates are enriched with more lignin-like and aromatic groups and contain lower oxycompounds compared with raw sludge, especially AoD. These findings provide new insights into the molecular characteristics of the refractory organic matter in anaerobic and aerobic digestates and also provide a possible strategy to further enhance the degradation of organic matter in sewage sludge.

Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles promoted by the cooperation of steric and electronic effects.

The selective hydrogenation of α,ß-unsaturated aldehydes to unsaturated alcohols can reach high selectivity and activity at room temperature using Pt nanoparticles immobilized on a non-porous Al2O3 support stabilized by aspartic acid. Aspartic acid molecules had a significant steric effect on C[double bond, length as m-dash]C hydrogenation and could modify the electronic state of metal particles.

Effect of anaerobic digestion on sequential pyrolysis kinetics of organic solid wastes using thermogravimetric analysis and distributed activation energy model.

Thermogravimetric analysis, Gaussian-fit-peak model (GFPM), and distributed activation energy model (DAEM) were firstly used to explore the effect of anaerobic digestion on sequential pyrolysis kinetic of four organic solid wastes (OSW). Results showed that the OSW weight loss mainly occurred in the second pyrolysis stage relating to organic matter decomposition. Compared with raw substrate, the weight loss of corresponding digestate was lower in the range of 180-550°C, but was higher in 550-900°C. GFPM analysis revealed that organic components volatized at peak temperatures of 188-263, 373-401 and 420-462°C had a faster degradation rate than those at 274-327°C during anaerobic digestion. DAEM analysis showed that anaerobic digestion had discrepant effects on activation energy for four OSW pyrolysis, possibly because of their different organic composition. It requires further investigation for the special organic matter, i.e., protein-like and carbohydrate-like groups, to confirm the assumption.

Synthesis of nitrogen and sulfur co-doped hierarchical porous carbons and metal-free oxidative coupling of silanes with alcohols.

Hierarchically porous N and S co-doped carbon was prepared by using 2,5-dihydroxy-1,4-benzoquinone as the carbon source, thiourea as the N and S source, and SiO2 particles as the template. Using the material as the catalyst, oxidative coupling of silanes with alcohols was conducted for the first time under metal-free conditions.

Solvent effects on geometrical structures and electronic properties of metal Au, Ag, and Cu nanoparticles of different sizes.

Study of the geometrical structures and electronic properties of metal nanoparticles is a very interesting topic. In this work we studied the effects of cyclohexane, benzene, ethanol, and water on bond lengths, Mulliken charge distributions, binding energy (BE), energy gap between highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) (Δ(HL)), ionization potential (IP) and electron affinity (EA) of Au20, Ag20, Cu20, Au38, Ag38, and Cu38 nanoparticles by using density functional theory (DFT). The results indicated that the properties of the solvents influence the geometrical structures and electronic properties of the metallic nanoparticles considerably, and the solvent effect depends on the properties of the solvents, the size of the metal particles, and the category of the metals. Generally, the properties of smaller particles are more sensitive to the change of the solvents, and the polar solvents have larger effect on the properties.