Preparation of New Cementitious System using Fly Ash and Dehydrated Autoclaved Aerated Concrete

We experimentally studied the interaction between pozzolanic material（fly ash） and dehydrated autoclaved aerated concrete（DAAC）. The DAAC powder was obtained by grinding aerated concrete waste to particles fi ner than 75μm and was then heated to temperatures up to 900 ℃. New cementitious material was prepared by proportioning fly ash and DAAC, named as AF. X-ray diffraction（XRD） was employed to identify the crystalline phases of DAAC before and after rehydration. The hydration process of AF was analyzed by the heat of hydration and non-evaporable water content（Wn）. The experimental results show that the highest reactivity of DAAC can be obtained by calcining the powder at 700 ℃ and the dehydrated products are mainly β-C2 S and CaO. The cumulative heat of hydration and Wn was found to be strongly dependent on the replacement level of fl y ash, increasing the replacement level of fl y ash lowered them in AF. The strength contribution rates on pozzolanic effect of fl y ash in AF are always negative, showing a contrary tendency of that of cement-fl y ash system.

FexC enhancing the catalytic activity of FeNx in oxidative dehydration of N-heterocycles

To enhance the catalytic activity by designing metal particles combined with atomically dispersed non-noble metal catalyst is a huge challenge,which yet has not been studied widely in organic reactions.Herein,we describe a simple and efficient method to synthesize FexC combined with Fe single atoms anchored on the Ndoped porous carbon by regulating pyrolysis temperature.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)and extended X-ray absorption fine structure(EXAFS)spectroscopy corroborate the existence of atomically dispersed Fe and the coordination number between Fe and N atoms.The Fe-N-C-800 catalyst exhibits the highest catalytic activity giving the 97%yield of quinoline in dehydration of 1,2,3,4-tetrahydroquinoline(THQ)reaction at a mild condition(60C,O_(2)balloon),and it shows good stability with 80%isolated yield after five consecutive dehydration reactions.Moreover,density functional theory(DFT)calculations reveal that coexistence of Fe_(x)C and FeN_(x)structure exhibits high activity owing to the lowest adsorption energy of co-adsorbed O_(2)and THQ and the longest N-H bond length of THQ,that is because the existence of FexC induces the charges transfer.Our work may open a new route to design metal particles combined with atomically dispersed non-noble metal catalysts with high activity in organic synthesis.

Mechanistic Investigations into the Catalytic Mode of a Dehydratase Complex Involved in the Biosynthesis of Lantibiotic Cacaoidin

Dehydration of serine/threonine residues necessitates the activity of a dehydratase enzyme(domain)during the biosynthesis of RiPP.Recently,it was reported that dehydration in the thioviridamide pathway relies on a distinct dehydratase complex that showcases the activities of a phosphotransferase TvaC for serine/threonine phosphorylation and a lyase TvaD for subsequent phosphate elimination.Herein,we report that dehydration reactions in the pathway of lantibiotic cacaoidin involves a similar dehydratase complex,CaoK/CaoY.Remarkably,this dehydratase complex exhibits flexible enzymatic activity and tolerates significant variations in its substrate peptide sequence.By binding with the leader peptide(LP)sequence of precursor peptide CaoA,the dehydration reactions proceed in a directional manner from the C-terminus of the core peptide(CP)to the N-terminus,and C-terminally truncated variants of CP are acceptable.We show that fusing CaoK to CaoY in a 1:1 molar ratio enables the resulting enzyme CaoYK to exert enhanced dehydration activity.CaoK binds with the LP to improve its own solubility and to ensure the phosphate transfer activity,while CaoY functions in a manner independently of LP.This work advances our understanding of the dehydration process during cacaoidin formation,and provides useful enzymes and methods for the studies of the rapidly emerging RiPPs.

Dehydrated layered double hydroxides： Alcohothermal synthesis and oxygen evolution activity

Layered double hydroxides （LDHs） are a materials with extensive applications and class of two-dimensional （2D） layered well-developed synthesizing methods in aqueous media. In this work, we introduce an alcohothermal synthesis method for fabricating NiFe-LDHs with dehydrated galleries. The proposed process involves incomplete hydrolysis of urea for the simultaneous precipitation of metal ions, with the resulting water-deficient ethanol environment leading to the formation of a dehydrated structure. The formation of a gallery-dehydrated layer structure was confirmed by X-ray diffraction （XRD）, as well as by a subsequent rehydration process. The methodology introduced here is also applicable for fabricating Fe-based LDHs （NiFe-LDH and NiCoFe-LDH） nanoarrays, which cannot be produced under the same conditions in aqueous media because of the different precipitation processes involved. The LDH nanoarrays exhibit excellent electrocatalytic performance in the oxygen evolution reaction, as a result of their high intrinsic activity and unique structural features. In summary, this study not only introduces a new method for synthesizing LDH materials, but also provides a new route towards highly active and robust electrodes for electrocatalvsis.