A mechanistic study of selective propane dehydrogenations on MoS2 supported single Fe atoms

On-purpose propane dehydrogenation (PDH) has emerged as a profitable alternative to the traditional cracking of oil products for propylene production. By means of density functional theory (DFT) calculations, the present work demonstrates that Fe atoms may atomically disperse on MoS₂ (Fe₁/MoS₂) and serve as a promising single-atom catalyst (SAC) for PDH. The catalytic activity of Fe₁/MoS₂ is attributed to the highly exposed d orbitals of single Fe atoms, while the propylene selectivity is originated from the kinetic inhibition of propylene dehydrogenation resulting from fast propenyl hydrogenation. The unique catalytic selectivity of Fe₁/MoS₂ may inspire further investigations of on-purpose dehydrogenations of propane on SACs.     

An in-depth mechanistic insight into the redox reaction and degradation of aqueous Zn-MnO2 batteries

Rechargeable aqueous Zn/MnO₂ batteries raise massive research activities in recent years. However, both the working principle and the degradation mechanism of this battery chemistry are still under debate. Herein, we provide an in-depth electrochemical and structural investigation on this controversial issue based on α-MnO₂ crystalline nanowires. Mechanistic analysis substantiates a two-electron reaction pathway of Mn²⁺/Mn⁴⁺ redox couple from part of MnO₂ accompanying with a reversible precipitation/dissolution of flaky zinc sulfate hydroxide (ZSH) during the discharge/charge processes. The formation of the ZSH layer is double-edged, which passivates the deep dissolution of MnO₂ upon discharging, but promotes the electrochemical deposition kinetics of active MnO₂ upon charging. The cell degradation originates primarily from the corrosion failure of metallic zinc anode and the accumulation of irreversible ZnMn₂O₄ phases on the cathode. The addition of MnSO₄ to the electrolyte could afford supplementary capacity contribution via electro-oxidation of Mn²⁺. However, a high MnSO₄ concentration will expedite the cell failure by corroding the metallic zinc anodes. The present study will shed a fundamental insight on developing new strategies toward practically viable Zn/MnO₂ batteries.     

Z型CdIn2S4/ZnSnO3异质结的构筑及其光催化产氢性能

通过高温煅烧ZnSn(OH)₆前驱体制备了双壳中空立方体结构的ZnSnO₃(ZSO),进而采用水热法将CdIn₂S₄(CIS)纳米晶包裹在ZSO表面,成功制备了CdIn₂S₄/ZnSnO₃(CIS/ZSO)异质催化剂。活性产氢实验结果表明,CIS、ZSO物质的量之比为12%时制备的12% CIS/ZSO具有优异的光催化产氢性能,在3 h内产氢量为1 676.48 μmol·g^-1,分别是ZSO和CIS的12倍和8倍。ZSO光催化析氢反应活性的增强归因于CIS/ZSO异质结构的成功构建,异质界面的形成显著提高了光生电子/空穴对的分离效率,降低了其复合率。通过对电荷转移路径的分析,提出了可能的反应机理。     

Nitrogen-doped mesoporous carbon nanospheres loaded with cobalt nanoparticles for oxygen reduction and Zn–air batteries

Mesoporous carbon supported with transition metals nanoparticles performs desired activities for oxygen reduction reaction (ORR) and clean energy conversion devices such as Zn–air batteries. In this work, we synthesized N-doped mesoporous carbon loaded with cobalt nanoparticles (CoMCN) through self-assembly method. There are sufficient mesopores on the carbon substrate which stem from the pore-forming agent. These mesopores can provide enough accessible active sites and profitable charge/mass transport for ORR. The high content of pyridinic and graphitic N is beneficial for promoting O₂ adsorption and reduction. The smaller value of I_D/I_G indicates the higher degree of graphitization of CoMCN, providing better electronic conductivity. The half-wave potential of CoMCN is 0.865 V in basic solution, which is 24 mV more positive than that of the commercial Pt/C (0.841 V). In addition, CoMCN performs excellent methanol tolerance and stability under both basic and acidic conditions. The Zn–air battery assembled with CoMCN performs the larger power density and open-circuit voltage than the commercial Pt/C-based battery, indicating the potential application in energy conversion systems. This work provides thoughtful ideas for fabricating transition metal nanoparticles based porous carbon for electrocatalysis and metal–air batteries.     

Evaluation of the stability of shortcut nitrification-denitrification process based on online specific oxygen uptake rate monitoring

Shortcut nitrification-denitrification (SCND) is widely concerned because of its low energy consumption and high nitrogen removal efficiency. However, the current difficulty lies in the stable maintenance of SCND performance, which leads to the challenge of large-scale application of this new denitrification technology. In this study, the nitrogen removal pathway from complete nitrification-denitrification (CND) to SCND was rapidly realized under high free ammonia (FA), high pH and low dissolved oxygen (DO) conditions. The variations of specific oxygen uptake rate (SOUR) of activated sludge in both processes were investigated by an online SOUR monitoring device. Different curves of SOUR from CND to SCND process were observed, and the ammonia peak obtained based on SOUR monitoring could be used to control aeration time accurately in SCND process. Accordingly, the SOUR ratio of ammonia oxidizing bacteria (AOB) to nitrite oxidizing bacteria (NOB) (SOUR_AOB/SOUR_NOB) was increased from 1.40 to 2.93. 16S rRNA Miseq high throughput sequencing revealed the dynamics of AOB and NOB, and the ratio of relative abundance (AOB/NOB) was increased from 1.03 to 3.12. Besides, SOUR_AOB/SOUR_NOB displayed significant correlations to ammonia removal rate (P<0.05), ammonia oxidation rate / nitrite oxidation rate (P < 0.05), nitrite accumulation rate (P < 0.05) and the relative abundance of AOB/NOB (P < 0.05). Thus, a strategy for evaluation the SCND process stability based on online SOUR monitoring is proposed, which provides a theoretical basis for optimizing the SCND performance.     

Pan-cancer analysis of DNA epigenetic modifications by hydrophilic interaction liquid chromatography-tandem mass spectrometry

Accumulating evidence in recent years indicates that DNA methylation (5-methyl-2′-deoxycytidine, 5-mdC) and hydroxymethylation (5-hydroxymethyl-2′-deoxycytidine, 5-hmdC) have been implicated in various biological processes, and the aberrations of these DNA cytosine modifications is tightly associated with cancer. N⁶-methyl-2′-deoxyadenosine (m⁶dA), as a newly discovered epigenetic modification in genome of mammals, has been demonstrated to play vital regulatory roles in tumorigenesis. However, the content information of m⁶dA in human tumor tissues is still limited and pan-cancer analysis of these DNA epigenetic modifications is lacked. Herein, we developed a sensitive and robust stable isotope-diluted hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) method for accurate quantification of m⁶dA, 5-mdC and 5-hmdC in genomic DNA from 82 pairs of human tumor tissues and matched tumor-adjacent normal tissues. The types of tumors included esophagus cancer, lung cancer, breast cancer, liver cancer, pancreatic cancer, gastric cancer, stromal tumor and colorectal cancer. Compared to the normal tissues, we revealed the level of m⁶dA was increased in tumor tissues of esophagus cancer, lung cancer and liver cancer, whereas the level of m⁶dA was diminished in tumor tissues of pancreatic cancer and gastric cancer; while the contents of 5-mdC and 5-hmdC exhibited significant decrease in tumor tissues of most types of cancer. It is worth noting that we revealed, for the first time, the content of genomic m⁶dA in pancreatic cancer, stromal tumor and colorectal cancer. The significant changes of these DNA epigenetic modifications indicate they may serve as indicators of cancers. In addition, this study will benefit for better understanding of the regulatory roles of these DNA epigenetic modifications in cancers.     

Polymeric aluminum porphyrin: Controllable synthesis of ultra-low molecular weight CO2-based polyols

Carbon dioxide-based polyols with ultra-low molecular weight (ULMW, M_n < 1000 g/mol) are emergent polyurethane precursors with economic and environmental benefits. However, the lack of effective proton-tolerant catalytic systems limits the development of this field. In this work, the polymeric aluminum porphyrin catalyst (PAPC) system was applied to the copolymerization of CO₂ and propylene oxide, where sebacic acid, bisphenol A, poly(ethylene glycol), and water were used as chain transfer agents to achieve the controlled synthesis of CO₂-polyols. The molecular weight of the resulting CO₂-polyols could be facilely regulated in the range of 400–930 g/mol at low catalyst loadings, fully demonstrating its catalytic advantages of high activity, high product selectivity, and excellent proton tolerance of PAPC. Meanwhile, the catalytic efficiency of PAPC could reach up to 2.1–5.2 kg/g under organic CTA conditions, even reaching 1.9 kg/g using water as the CTA. The cPC content could be controlled within 1.0 wt% under the optimized conditions, indicating the excellent controllability of the PAPC system. ULMW CO₂-polyols combines the advantages of low viscosity (∼3000 mPa s at 25 °C), low glass transition temperature (∼−73 °C), and high carbonate unit content (∼40%), which is important for the development of high-performance polyurethanes.     

Degradable nanocatalyst enables antitumor/antibacterial therapy and promotion of wound healing for diabetes via self-enhanced cascading reaction

Diabetic patients often have problems such as residual tumor and wound infection after tumor resection, causing severe clinical problems. It is urgent to develop effective therapies to reach oncotherapy/anti-infection/promotion of wound healing combined treatment. Herein, we propose CS/MnO₂-GOx (CMGOx) nanocatalysts for the specific catalytic generation of ^•OH to inhibit tumors and bacteria in a hyperglycemic environment. The good biocompatible chitosan (CS), as a carrier for the catalyst, exhibits excellent antibacterial effect as well as promotes wound healing. Glucose oxidase (GOx) is loaded on the surface of CS nanoparticles to generate H₂O₂ and gluconic acid by consuming glucose (starvation therapy, ST) and O₂. The MnO₂ depletes glutathione (GSH) to produce Mn²⁺, amplifying oxidative stress and further promoting the activity of Mn²⁺-mediated Fenton-like reaction to produce ^•OH (chemodynamic therapy, CDT) in weak acidic environment. Moreover, the produced gluconic acid lowers the pH of the environment, enhancing chemodynamic therapy (ECDT). The tumor cells and bacteria are efficiently eliminated by the synergistic effect of ST and ECDT. The MnO₂ nanoparticles at neutral environment decomposes H₂O₂ into O₂, which cooperate with CS to promote healing. The self-enhanced cascade reaction of CMGOx in situ exhibits excellent effects of antitumor/antibacterial therapy and promotion of wound healing, offering a promising integrated treatment for diabetic patients after tumor surgical resection.     

TBAI/H2O-cooperative electrocatalytic decarboxylation coupling-annulation of quinoxalin-2(1H)-ones with N-arylglycines

The first example of TBAI/H₂O cooperative electrocatalytic coupling-annulation of quinoxalin-2(1H)-ones with N-arylglycines was developed. A broad range of tetrahydroimidazo[1,5-a]quinoxalin-4(5H)-ones were obtained in good to excellent yields with exclusive chemoselectivities and excellent regioselectivities. The H-hydrogen bond served as a key factor for the electrocatalytic production of aminomethyl radical at lower oxidative potential.     

Ethylene glycol-regulated ammonium vanadate with stable layered structure and favorable interplanar spacing as high-performance cathode for aqueous zinc ion batteries

Ammonium vanadate compounds featuring large capacity, superior rate capability and light weight are regarded as promising cathode materials for aqueous zinc ion batteries (AZIBs). However, the controllable synthesis of desired ammonium vanadates remains a challenge. Herein, various ammonium vanadate compounds were successfully prepared by taking advantage of ethylene glycol (EG) regulated polyol-reduction strategy and solvent effect via hydrothermal reaction. The morphology and crystalline phase of resultant products show an evolution from dendritic (NH₄)₂V₆O₁₆ to rod-like NH₄V₄O₁₀ and finally to lamellar (NH₄)₂V₄O₉ as increasing the amount of EG. Specifically, the NH₄V₄O₁₀ product exhibits a high initial capacity of 427.5 mAh/g at 0.1 A/g and stable cycling with a capacity retention of 90.4% after 5000 cycles at 10 A/g. The relatively excellent electrochemical performances of NH₄V₄O₁₀ can be ascribed to the stable open-framework layered structure, favorable (001) interplanar spacing, and peculiar rod-like morphology, which are beneficial to the highly reversible Zn²⁺ storage behaviors. This work offers a unique way for the rational design of high-performance cathode materials for AZIBs.