A Rare Earth Chalcogenide Nonlinear Optical Crystal KLaGeS4: Achieving Good Balance among Band Gap, Second Harmonic Generation Effect, and Birefringence.

Midinfrared nonlinear optical (NLO) rare earth chalcogenides have attracted extensive research interest in recent several decades. Employing charge-transfer engineering strategy in the early stage, rigid tetrahedral [GeS4] was introduced into rare-earth sulfides to synthesize KYGeS4, which had an enlarged band gap while maintaining a strong second harmonic generation (SHG) effect. Based on KYGeS4, La was equivalently substituted to successfully synthesize KLaGeS4 with a stronger SHG effect (dij = 1.2 × AgGaS2) and lower cost. Meanwhile, a larger band gap (Eg = 3.34 eV) was retained and realized phase matching (Δn = 0.098 @ 1064 nm). KLaGeS4 enabled an effective balance among band gap, SHG effect, and birefringence, making it a promising candidate for infrared NLO optical materials among various rare-earth sulfides.

CEA cell adhesion molecule 5 enriches functional human hematopoietic stem cells capable of long-term multi-lineage engraftment.

Hematopoietic stem cell (HSC) surface markers improve the understanding of cell identity and function. Here, we report that human HSCs can be distinguished by their expression of the CEA Cell Adhesion Molecule 5 (CEACAM5, CD66e), which serves as a marker and a regulator of HSC function. CD66e+ cells exhibited a 5.5-fold enrichment for functional long term HSCs compared to CD66e- cells. CD66e+CD34+CD90+CD45RA- cells displayed robust multi-lineage repopulation and serial reconstitution ability in immunodeficient mice compared to CD66e-CD34+CD90+CD45RA-cells. CD66e expression also identified almost all repopulating HSCs within the CD34+CD90+CD45RA- population. Together, these results indicated that CEACAM5 is a marker that enriches functional human hematopoietic stem cells capable of long-term multi-lineage engraftment.

Identification of active sites of B/N co-doped nanocarbons in selective oxidation of benzyl alcohol.

Developing highly active and stable nanocarbon catalysts for selective oxidation reactions has attracted much attention due to their potential as an alternative to traditional metal-based or noble metal catalysts. However, the nature of active sites and the reaction mechanism of nanocarbon catalysts for oxidation reactions still remains largely unknown, which hinders the rational design and development of highly efficient carbon-based catalysts. Here we report a facile strategy for the synthesis of boron and nitrogen co-doped carbon nanosheet material (BNC), which exhibits excellent catalytic activity with 91% conversion and 99% selectivity in selective oxidation of benzyl alcohol into benzaldehyde, superior to those of traditional carbon materials (oxidized carbon nanotubes, graphites and commercial nanocarbons). Structural characterizations and kinetic measurements are studied to clarify the active site, in which phenolic hydroxyl on BNC is responsible for the production of benzaldehyde. Meanwhile, we put forward a possible reaction mechanism and point out the key factors in determining the reactivity for this reaction. Therefore, the present work provides new insight into structure-function relationships, paving the way for the development of highly efficient nanocarbon catalysts.

A facile strategy based on the metal-free design of carbon to deliver an insight into the active sites for liquid phase carbocatalysis.

An effective method to study the active sites for carbocatalysis is proposed based on designing a carbon catalyst in the absence of metal as the growth catalyst. The results suggest that the oxygenated groups on the aromatic carbons are mainly responsible for the catalytic reduction of nitrobenzene and some other reactions.

Nucleobase derived boron and nitrogen co-doped carbon nanosheets as efficient catalysts for selective oxidation and reduction reactions.

The search for active, stable and cost-efficient carbocatalysts for selective oxidation and reduction reactions could make a substantial impact on the catalytic technologies that do not rely on conventional metal based catalysts. Here we report a facile strategy for the synthesis of boron (B) and nitrogen (N) co-doped carbon nanosheets (BNC) by using biomolecule guanine as a carbon (C) and N source and boric acid as the B precursor. The whole synthesis process which leads to the formation of a two dimensional (2D) structure and mesoporosity with high surface areas is simple, metal-free and template-free. The as-synthesized carbon nanosheets possess a series of merits, such as relatively high specific surface area, satisfactory pore structure, enough structural defects, abundant B and N dopants as well as oxygen functional groups. The catalytic assessments demonstrate that the presented carbon catalyst is highly active and selective for the liquid phase oxidation of ethyl lactate to ethyl pyruvate and the reduction of nitrobenzene to aniline and outperforms other equivalent benchmarks. Control experiments confirm the importance of the B and N co-doping as well as the carbon matrix which benefit the electron transfer. The carbonyl group masking test indicates that carbonyl groups play an important role in both the selective oxidation and reductions. Given the diversity in the structure of the nucleobase moiety, they represent ideal building blocks for the catalyst-free and metal-free formation of 2D carbon architectures, only induced by hydrogen bonds. This B and N co-doped synthesis strategy provides guidance for the design of carbon-based catalysts for selective oxidation and reductions.

The durability of carbon nanotubes in the selective reduction of nitrobenzene.

Surface oxidized carbon nanotubes (oCNTs) were quite stable for the selective reduction of nitrobenzene, while notable deactivation was observed for the un-oxidized sample (rCNTs). The adsorption of N-containing compounds had a negligible effect, but the formation of a carboxyl group and anhydride was mainly responsible for the deactivation of rCNTs.

Highly Efficient Metal-Free Nitrogen-Doped Nanocarbons with Unexpected Active Sites for Aerobic Catalytic Reactions.

Nitrogen (N)-doped nanocarbons (NDN) as metal-free catalysts have elicited considerable attention toward selective oxidation of alcohols with easily oxidizable groups to aldehydes in the past few years. However, finding a new NDN catalytic material that can meet the requirement of the feasibility on the aerobic catalytics for other complicated alcohols is a big challenge. The real active sites and the corresponding mechanisms on NDN are still unambiguous because of inevitable coexistence of diverse edge sites and N species based on recently reported doping methods. Here, four NDN catalysts with enriched pyridinic N species and without any graphitic N species are simply fabricated via a chemical-vapor-deposition-like method. The results of X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectra suggest that the dominating N species on NDN are pyridinic N. It is demonstrated that NDN catalysts perform impressive reactivity for aerobic oxidation of complicated alcohols at an atmospheric pressure. Eleven kinds of aromatic molecules with single N species and tunable π conjugation systems are used as model catalysts to experimentally identify the actual role of each N species at a real molecular level. It is suggested that pyridinic N species play an unexpected role in catalytic reactions. Neighboring carbon atoms in pyridinic N species are responsible for facilitating the rate-determining step process clarified by kinetic isotope effects, in situ nuclear magnetic resonance, in situ attenuated total reflectance infrared, and theoretical calculation. Moreover, NDN catalysts exhibit a good catalytic feasibility on the synthesis of important natural products (e.g., intermediates of vitamin E and K3) from phenol oxidation.

A comparative study of nitrobenzene reduction using model catalysts.

A zigzag-type quinone performs better than an armchair-type quinone in the reduction of nitrobenzene. When different kinds of functionalities co-exist, the reaction is dominated by the most active sites, but the most negative sites should also be taken into consideration if the acitive sites have zigzag structures.

Insights into the surface chemistry and electronic properties of sp2 and sp3-hybridized nanocarbon materials for catalysis.

Ultra-dispersed nanodiamond and its derivatives (UNDDs), including bucky nanodiamond and onion-like carbon, offer superior catalytic behavior relative to other nanocarbons. However, a systematic study of their unique properties has been rarely achieved. Their surface chemistry and electronic properties are therefore studied to reveal the essential differences of UNDDs compared to other nanocarbons for catalysis.

Carbocatalysis in Liquid-Phase Reactions.

There is broad interest in metal-free catalysis for sustainable chemistry. Carbocatalysis is a "green" option for catalytic transformations in the gas phase as well as in the liquid phase. This is evident by the numerous reports on gas-phase dehydrogenation and selective oxidation where carbon can be used as a successful alternative to metal oxide systems. Carbocatalysis for liquid-phase reactions, especially for organic synthesis, is an emerging research discipline and has undergone rapid development in recent years. This Review provides a critical analysis on the state-of-the-art of carbocatalysts for liquid-phase reactions, with a focus on the underlying mechanisms as well as the advantages and limitations of metal-free carbocatalysts.

Efficient and highly selective boron-doped carbon materials-catalyzed reduction of nitroarenes.

Exploring the potential catalytic applications of boron-doped carbon materials is a fascinating challenge. Here we describe that boron-doped onion-like carbon and carbon nanotubes as metal-free catalysts exhibit excellent catalytic activity and stability in nitroarene reduction under a stoichiometric amount of reductant.

Active sites and mechanisms for direct oxidation of benzene to phenol over carbon catalysts.

The direct oxidation of benzene to phenol with H2 O2 as the oxidizer, which is regarded as an environmentally friendly process, can be efficiently catalyzed by carbon catalysts. However, the detailed roles of carbon catalysts, especially what is the active site, are still a topic of debate controversy. Herein, we present a fundamental consideration of possible mechanisms for this oxidation reaction by using small molecular model catalysts, Raman spectra, static secondary ion mass spectroscopy (SIMS), DFT calculations, quasi in situ ATR-IR and UV spectra. Our study indicates that the defects, being favorable for the formation of active oxygen species, are the active sites for this oxidation reaction. Furthermore, one type of active defect, namely the armchair configuration defect was successfully identified.

Carbon nanotubes oxidized by a green method as efficient metal-free catalysts for nitroarene reduction.

Hydrogen peroxide (H2O2) functionalized carbon nanotubes exhibited better catalytic performance than their nitric acid oxidized counterparts in the reduction of nitrobenzene. One important reason may be attributed to the notably less negative oxygenated groups on the surface of the former one.

Surfactant-free hydrothermal synthesis of sub-10 nm γ-Fe2O3-polymer porous composites with high catalytic activity for reduction of nitroarenes.

Porous γ-Fe2O3-polymer composites were synthesized by a novel one-pot surfactant-free hydrothermal approach. The γ-Fe2O3-polymer composites consisting of 3.5 nm γ-Fe2O3 nanoparticles and porous polymers exhibited high catalytic activity and recycling performance in the reduction of nitroarenes.