Hydrogen-bonded organic framework for red light-mediated photocatalysis

The development of heterogeneous molecule-based catalysts for red light-mediated photocatalysis is still challenging due to the improper light absorption for most materials and the photoactivity deactivation for solid assembly.Herein,red light photocatalysis with a hydrogen-bonded organic framework(HOF)is established.This HOF,named HOF-66,is formed from the self-assembly of guanine-decorated naphthalenediimide(NDI)molecule through hydrogen-bonded guanine-quadruplex nodes,showing square grid supramolecular layers confirmed by powder X-ray diffraction analysis.In contrast to unsubstituted NDI HOF,introduction of ethylamino groups to NDI core in HOF-66 tunes strong electronic maximum absorption peak to 619 nm,allowing red light photocatalysis of singlet oxygen evolution proved by 1,3-diphenylisobenzofuran degradation and electron spin resonance determination.Particularly,under the same conditions,the sulfide oxidation rate in the presence of HOF-66 was 28 times higher compared to its unsubstituted analogue.This work integrates the molecular design and aggregation effect towards the application of HOFs,opening a new gate for red light photocatalysts.

Direct observation of epitaxial alignment of Au on M0S2 at atomic resolution

The morphology and structural stability of metal/2D semic on ductor interfaces strongly affect the performa nee of 2D electronic devices and synergistic catalysis. However, the structural evolution at the interfaces has not been well explored particularly at atomic resolution. In this work, we study the structural evoluti on of Au nan oparticles (NPs) on few-layer MoS2 by high resol utio n transmissi on electro n microscopy (HRTEM) an d quan titative high-angle annular dark field seanning TEM. It is found that in the transition of Au from nan oparticles to den drites, a dynamically epitaxial align ment betwee n Au and MoS2 lattices is formed, and Moirc patter ns can be directly observed in HRTEM images due to the mismatch between Au and M0S2 lattices. This epitaxial alignment can occur in ambient conditions, and can also be accelerated by the irradiation of high-energy electron beam. In situ observation clearly reveals the rotation of Au NPs, the atom migration inside Au NPs, and the transfer of Au atoms between neighboring Au NPs, finally leading to the formation of epitaxially aligned Au dendrites on M0S2. The structural evoluti on of metal/2D semico nductor in terfaces at atomic scale can provide valuable information for the design and fabricatio n of the metal/2D semicon ductorn ano-devices with desired physical and chemical performa nces.

Atomic-scaled surface engineering Ni-Pt nanoalloys towards enhanced catalytic efficiency for methanol oxidation reaction

Surface engineering is known as an effective strategy to enhance the catalytic properties of Pt-based nanomaterials.Herein,we report on surface engineering Ni-Pt nanoalloys with a facile method by varying the Ni doping concentration and oleylamine/oleicacid surfactant-mix.The alloy-composition,exposed facet condition,and surface lattice strain are,thereby manipulated to optimize the catalytic efficiency of such nanoalloys for methanol oxidation reaction(MOR).Exemplary nanoalloys including Ni_(0.69)Pt_(0.31)truncated octahedrons,Ni_(0.45)Pt_(0.55)nanomultipods and Ni_(0.20)Pt_(0.80)nanoflowers are thoroughly characterized,with a commercial Pt/C catalyst as a common benchmark.Their variations in MOR catalytic efficiency are significant:2.2 A/mgPt for Ni_(0.20)Pt_(0.80)nanoflowers,1.2 A/mgPt for Ni_(0.45)Pt_(0.55)nanomultipods,0.7 A/mgPt for Ni_(0.69)Pt_(0.31)truncated octahedrons,and 0.6 A/mgPt for the commercial Pt/C catalysts.Assisted by density functional theory calculations,we correlate these observed catalysis-variations particularly to the intriguing presence of surface interplanar-strains,such as{111}facets with an interplanar-tensile-strain of 2.6%and{200}facets with an interplanar-tensile-strain of 3.5%,on the Ni_(0.20)Pt_(0.80)nanoflowers.

Carbon-Involved Near-Surface Evolution of Cobalt Nanocatalysts:An in Situ Study

When carbon-containing species are involved in reactions catalyzed by transition metals at high temperature,the diffusion of carbon on or in catalysts dramatically influences the catalytic performance.Acquiring information on the carbon-diffusioninvolved evolution of catalysts at the atomic level is crucial for understanding the reaction mechanism yet also challenging.For the chemical vapor deposition process of single-walled carbon nanotubes(SWCNTs),we recorded in situ the catalyst state(solid and molten)composition as well as near-surface structural and chemical evolution at the cobalt catalyst-tube interface with carbon permeation using aberration-corrected environmental transmission electron microscopy and synchrotron X-ray absorption spectroscopy.The nucleation of SWCNTs was linked with an alternating dissolving and precipitating cycle of carbon in catalysts close to the nucleation site.Understanding the dynamics of carbon atoms in catalysts brings deeper insight into the growth mechanism of SWCNTs and facilitates inferring mechanisms of other reactions.The methodologies developed here will find broad applications in studying catalytic and other processes.