On the Harmonic Index of Triangle-Free Graphs

The harmonic index of a graph?G? is defined as where d(u) denotes the degree of a vertex u in G . In this work, we give another expression for the Harmonic index. Using this expression, we give the minimum value of the harmonic index for any triangle-free graphs with order n and minimum degree δ ≥ k for k≤ n/2? and show the corresponding extremal graph is the complete graph.

On Harmonic Index and Diameter of Graphs

The harmonic index of a graph G is defined as , where d(u) denotes the degree of a vertex u in G. It has been found that the harmonic index correlates well with the Randi c' index and with the π-electronic energy of benzenoid hydrocarbons. In this work, we give several relations between the harmonic index and diameter of graphs.

Metal–organic framework wafer enabled fast response radiation detection with ultra-low dark current

Semiconductive metal–organic frameworks(MOFs)have attracted great interest for the electronic applications.However,dark currents of present hybrid organic–inorganic materials are 1000–10,000 times higher than those of commercial inorganic detectors,leading to poor charge transportation.Here,we demonstrate a ZIF-8(Zn(mim)_(2),mim=2-methylimidazolate)wafer with ultra-low dark current of 1.27 pA·mm^(-2) under high electric fields of 322 V·mm^(-1).The isostatic pressing preparation process provides ZIF-8 wafers with good transmittance.Besides,the presence of redox-active metals and small spatial separation between components promotes the charge hopping.The ZIF-8-based semiconductor detector shows promising X-ray detection sensitivity of 70.82μC·Gy^(-1)·cm^(-2) with low doses exposures,contributing to superior X-ray imaging capability with a relatively high spatial resolution of 1.2 lp·mm^(-1).Simultaneously,good peak discrimination with the energy resolution of~43.78%is disclosed when the detector is illuminated by uncollimated 241Am@5.48 MeVα-particles.These results provide a broad prospect of MOFs for future radiation detection applications.

Plasma-etching on monolithic MOFs-based MIM filter boosted chemical sensing

Metal-insulator-metal(MIM)cavity as a lithography-free structure to control light transmission and reflection has great potential in the field of optical sensing.However,the dense top metal layer of the MIM prohibits any external medium from entering the dielectric insulation layer,which limits the application of the cavity in the sensing field.Herein,we demonstrate a series of monolithic metal-organic frameworks(MOFs)based MIM cavities,which are treated by plasma etching to provide channels for chemical diffusion and to advance sensing.We modulate the bandwidth of the MIM filters by controlling the MOF thickness as insulator layers.Oxygen plasma-etching is applied to build channels on the top metal layer without altering their saturation and brightness for chemical sensing performance.The etching time regulates the number and size of channels on the top metal layer.Sensing behavior is demonstrated on the plasma-etched MOFs-based MIM cavity when external chemicals diffuse in the cavity.In addition,we generate patterned structure of the MOFs-based MIM cavity via plasma-mask method,which can transfer to different substrates and produce a controllable structure color change for chemical sensing.Our MIM cavity may promote the advancement and applications of structural color in security imaging,color display,information anticounterfeiting,and color printing.

Efficient water disinfection with ball milled Mg-biochar: The key role of trace Cu

In this study, magnesium and coconut shell carbon (CSC) were prepared by a ball milled process and used for water disinfection with adsorbing tiny amounts of copper(II). Dissolved oxygen (DO) was reduced to hydrogen peroxide (H_(2)O_(2)) via a two-electron pathway by Mg corrosion. Cu(II) in the wastewater will be enriched on the CSC surface and efficiently catalyzes H2O2 for inactivating E. coli. The results show that E. coli with an initial concentration of approximately 106 CFU/mL was under the detection limit (<4 CFU/mL) within 15 min. All of the Cu(II) could be adsorbed by the composite and catalyzed H2O2 to different active species. The quenching experiments, electron spin resonance (ESR) capture measurements and the UV-vis spectroscopy detection confirmed the present of the hydroxyl radicals (·OH), superoxide radicals (·O_(2)^(-)) and Cu(III). Different with tradition Fenton like process, Cu(III), rather than radicals, played the major role during the Mg-CSC/Cu(II) process. In addition to the cellular membrane damage, most of the bacterial genomic DNA was also be degraded and the bacterial reactivation was avoided. The Mg-CSC/Cu(II) process also showed a satisfied disinfection performance in real wastewater treatment. Overall, this study provides a new strategy for water disinfection.

Photonic crystals constructed by isostructural metal-organic framework films

Metal-organic framework(MOF)-on-MOF structure allows stacking various types of MOFs with different lattice constants for molecule sieving or filtering.However,the multilayered MOFs-based optical devices have incoherent interference due to the lattice-mismatch at the interface and refractive index(RI)indifference.This paper reports isostructural MOFs-based photonic crystals(PCs)designed by stacking Bragg bilayers of lattice-matched MOFs thin films through a layer-by-layer assembly method.Colloidal nanoparticles(NPs)were homogenously encapsulated in some layers of the MOFs(HKUST-1@NPs)to tune their intrinsic RI during the spraying coating process.The isostructural MOFs-based PCs were constructed on a large scale by sequentially spraying coating the low RI layer of HKUST-1 and high RI layer of HKUST-1@NPs to form the desired number of Bragg bilayers.X-ray photoelectron spectroscopy(XPS)depth profiling proved the Bragg bilayers and the homogenous encapsulation of nanomaterials in certain layers of MOFs.Bandwidth of the PCs was tailored by the thickness and RI of the Bragg bilayers,which had a great consistent with finite difference time domain(FDTD)simulation.Importantly,reflectivity of the isostructural MOFs-based PCs was up to 96%.We demonstrated high detection sensitivity for chemical sensing on the PCs,which could be advanced by encapsulating different types of nanomaterials and designing wide-band isostructural MOFs-based PCs.

Fluorinated graphene quantum dots with long-term lubrication for visual drug loading and joint inflammation therapy

Osteoarthritis(OA)treatment mainly relies on developing new drugs or nanocarriers,while little attention is paid to building novel remedial mode and improving drug loading efficiency.This work reports an integrated nanosystem that not only realizes visual drug loading and release,but also achieves enhanced lubrication and effective joint inflammation therapy based on fluorinated graphene quantum dots(FGQDs).Oxygen introduction promotes FGQDs outstanding water-stability for months,and layered nano-sized structure further guarantees excellent lubricating properties in biomimetic synovial fluid.The special design of chemistry and structure endows FGQDs robust fluorescence in a wide range of pH conditions.Also,the excitation spectrum of FGQDs well overlaps the absorption spectrum of drugs,which further constructs a new concept of internal filtering system to visually monitor drug loading by naked eyes.More importantly,extraordinary long-term lubrication performance is reported,which is the first experimental demonstration of concentration-dependent mutations of coefficient of friction(COF).Cell incubation experiments indicate that drug-loaded FGQDs have good biocompatibility,tracking property of cellular uptake and drug release,which show efficient anti-inflammation potential for H2O2-induced chondrocyte degradation by up-regulated cartilage anabolic genes.This study establishes a promising OA treatment strategy that enables to monitor drug loading and release,to enhance long-time lubricating property,and to show effective anti-inflammatory potential for cartilage protection.

Nanotribology of SiP nanosheets: Effect of thickness and sliding velocity

Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups.As a typical 2D group IV–V material,SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility,appropriate bandgap,high thermal stability,and low interlayer cleavage energy.However,its adhesion and friction properties have not been extensively grasped.Here,large-size and high-quality SiP crystals were obtained by using the flux method.SiP nanosheets were prepared by using mechanical exfoliation.The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated.The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers.The coefficient of friction of multilayer SiP is 0.018.The mean friction force,frictional vibrations,and the friction strengthening effect can be affected by sliding velocity.Specially,the mean friction force increases with the logarithm of sliding velocity at nm/s scale,which is dominated by atomic stick-slip.The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality.The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets.These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems.