Adsorption of gas molecules and the induced magnetic properties of metal-decorated graphene

Based on the first-principles of density-functional theory (DFT), the effects of gas adsorption on the change in adsorptive configurations, electronic structures and magnetic properties of graphene with magnetic metal atoms (MMA = Fe, Co, Ni and Mo) systems were investigated. Four metal atoms are strongly trapped at single vacancy graphene (MMA/SV-graphene) and can effectively regulate the adsorption of CO and O₂ molecules. It is found that the positive charged of MMA are more prone to adsorb the O₂ than that of CO molecule, and these gas molecules on MMA/SV-graphene induce a different type of magnetic properties of systems. Hence, the differences in electronic and magnetic properties of MMA/SV-graphene with the gas molecules are expected to design graphene-based gas sensors and spintronic device.     

Study on Graphene Oxide-Modified Polyacrylonitrile Hollow Fiber Membrane

Abstract

In this paper, a multilayer diazo resin-graphene oxide/polyacrylonitrile composite membrane was prepared by layer-by-layer self-assembly and UV-induced modification of commercial polyacrylonitrile (PAN) hollow fiber membranes grafted with diazo resin (DR) and graphene oxide (GO). Scanning electron microscopy (SEM), infrared spectroscopy, contact angle, thermogravimetric analysis (TG), water flux and adsorption properties of heavy metals were studied. The results showed that diazo resin (DR) and graphene oxide (GO) were successfully grafted onto PAN membranes by layer-by-layer self-assembly. Carbonyl and carboxyl groups appeared on the surface of the modified PAN membranes; layer-by-layer self-assembly modification did not destroy the original morphology of PAN membranes, resulting in smaller pore size and higher surface roughness; hydrophilicity of the modified PAN-(DR-GO)₃ membranes. The contact angle of pure water decreases from 87.8 degrees to 55.5 degrees, and the water flux increases from 733.30?g.m^?1.h^?1 to 1250.48?g.m^?1.h^?1. The thermo gravimetric curves of PAN films before and after modification did not change significantly, and the PAN films before and after modification had good thermal stability. The modified PAN membrane can achieve adsorption equilibrium in a relatively short time, and has good adsorption performance for heavy copper ions, with the adsorption rate as high as 92%.     

Dielectric properties and schottky barriers in silver tantalate-niobate thin film capacitors

Abstract

Submicron thick ferroelectric Ag(Ta,Nb)O₃ films have been pulsed laser deposited on the bulk Pt₈₀lr₂₀ polycrystalline substrates. They are ferroelectric at temperatures below 125 K with the remnant polarization of 0.4 μC/cm² @ 77K and paraelectric at higher temperatures with tanδ@ 100 kHz as low as 0.015. Extensive I-V characterization has been performed in a wide temperature range 77 K to 350 K for vertical Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitive cells, where the metals Me = Pd, Au, Cr, and Al have been used as a top electrode. The electronic transport in thin Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitors follows the Schottky emission mechanism with the barrier height for the Pd, Au, Cr, and Al of 0.85, 0.8, 0.74, and 0.69 eV, respectively.     

羧基修饰石墨烯吸附SF6分解组分的DFT计算

为研制高灵敏度SF6气体分解组分检测传感器,利用基于第一性原理的密度泛函理论(DFT)方法,采用分子模拟软件对SF6主要放电分解组分(SO2,SOF2,SO2F2,CF4)在羧基修饰石墨烯表面的吸附特性进行了模拟计算,从微观角度研究了羧基修饰石墨烯检测SF6气体放电分解组分的气敏机理。理论计算了单分子吸附过程中表征吸附性能特征参量的吸附能、吸附距离、净电荷转移量、分子前线轨道以及态密度。结果表明:羧基的修饰能够有效提高石墨烯的吸附性能,且羧基石墨烯效果更好,对4种分子吸附效果强弱依次为SO2>SOF2>SO2F2>CF4,其中SO2在羧基石墨表面发生较为强烈的化学吸附效应。     

The Rutile Phase of TiO2/Graphene Films: Sol–Gel Method,Phase Transition,Photocatalytic Properties

Abstract

TiO₂ materials are of great interest in different applications because of the controllable preparation of different structures. In this paper, the TiO₂ and TiO₂/graphene films with different phase structure and inserted graphene layer between Cu substrate and TiO₂ film were prepared by sol–gel method at different annealing temperatures, and then used as catalysts for photo-degradation of methylene blue (MB) dye solution under ultraviolet irradiation using 15?W of ultraviolet lamp. The effects of annealing temperature and graphene layer on the phase structure, morphology, chemical composition, binding energy level, and photocatalytic performance of TiO₂ films were studied in details. XRD results reveal that the anatase phase of TiO₂ films transfers to rutile phase with the increase in annealing temperature, and the introducing of graphene film layer can accelerate the phase transformation of anatase to rutile and improve the crystallization quality of TiO₂ films. It is found that the MB degradation efficiency of TiO₂ and TiO₂/graphene films is enhanced with the increasing annealed temperature, which shows that the existence of rutile phase, well crystalline quality and the better dispersion of the TiO₂ particles are helpful in photocatalytic behavior. In addition, compared to the rutile phase TiO₂ film, the rutile phase TiO₂/graphene films at annealed temperatures of 900?°C exhibit much higher photocatalytic activity due to the introduction of graphene films.     

Water molecule adsorption properties on surfaces of MVO4 (M = In, Y, Bi) photo-catalysts

Water molecule adsorption properties at the surface of InVO₄, YVO₄, and BiVO₄, which have indicated promising photocatalytic properties, have been investigated using an ab initio molecular dynamics approach. It was found that the water molecules were adsorbed dissociatively to the three-fold oxygen coordinated V (3c-V) sites on the (001) surface and 4c-In sites on the (100) surface of InVO₄, however, in a non-dissociated molecular form on the 5c-Bi site on the (100) surface of BiVO₄ and the 7c-Y site on the (010) surface of YVO₄. The adsorption energies of water molecule and geometries of the systems with adsorbed water molecules are reported in detail.     

Computational study of transport properties of graphene upon adsorption of an amino acid: importance of including –$$\hbox {NH}_{2}$$ and –COOH groups

The effects of histidine and its imidazole ring adsorption on the electronic transport properties of graphene were investigated by first-principles calculations within a combination of density functional theory and non-equilibrium Greens functions. Firstly, we report adsorption energies, adsorption distances, and equilibrium geometrical configurations with no bias voltage applied. Secondly, we model a device for the transport properties study: a central scattering region consisting of a finite graphene sheet with the adsorbed molecule sandwiched between semi-infinite source (left) and drain (right) graphene electrode regions. The electronic density, electrical current, and electronic transmission were calculated as a function of an applied bias voltage. Studying the adsorption of the two systems, i.e., the histidine and its imidazole ring, allowed us to evaluate the importance of including the carboxyl (–COOH) and amine (–\(\hbox {NH}_{2}\)) groups. We found that the histidine and the imidazole ring affects differently the electronic transport through the graphene sheet, posing the possibility of graphene-based sensors with an interesting sensibility and specificity.     

Effects of water on the properties of Fe3O4@C superparamagnetic nanospheres

ABSTRACT

Fe₃O₄@C nanospheres have potential applications in the field of magnetic separation, magnetic hyperthermia, magnetic targeting and magnetic resonance imaging (MRI). The carbon layers formed around Fe₃O₄ nanopaticles determined the adsorption properties of this material. In this study, Fe₃O₄@C was prepared by a simple one-pot solvothermal method, in which different amount of water was added to investigate the influences of water on the properties of Fe₃O₄@C nanospheres. The resulted samples were characterized by techniques of TEM, FT-IR, UV–Vis and BET, and found that the thickness of carbon layer, the intensity of surface carboxyl group and the adsorption characters were significantly changed by introducing additional water in autoclave.     

Electron beam evaporated carbon nanotube dispersed SnO2 thin film gas sensor

Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO₂powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO₂thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO₂layer. Experimental results indicate that the sensitivity to ethanol of SnO₂thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250–300^∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced by CNT protrusion.     

Stability of perovskite-type clusters in melts for relaxor ferroelectric crystal growth

Relaxor ferroelectric single crystals with perovskite structure were novel materials which might revolutionize some applications in medical ultrasonic imaging, telecommunication and ultrasonic devices. But during crystal growth and melt solidification, pyrochlore-type phase presented now and then, which reduced the integrality and properties of ferroelectric single crystals. This work dealt with the stability of perovskite-type clusters in melts for relaxor ferroelectric crystal growth by quenching and slow cooling. Differential thermal analysis (DTA) and X-ray diffraction (XRD) were employed to ascertain the transformation temperature between perovskite-type and pyrochlore-type clusters. Investigated results indicated that clusters in Pb(Mg_1/3Nb_2/3)O₃–32PbTiO₃ (PMN–32PT) melt which was under suitable temperature and prepared by proper pre-synthetic method were all and singular of perovskite-type structure, which established the fundament of PMN–32PT relaxor ferroelectric crystal growth from melts by Bridgman method. Whereas, clusters in Pb(Zn_1/3Nb_2/3)O₃–9PbTiO₃ (PZN–9PT) melt were of perovskite-type structure, pyrochlore-type structure, homologous PbO structure or homologous ZnO structure. During crystal growth from melts by Bridgman method, the pyrochlore phase always appeared.     

Synthesis of monodispersed pH-sensitive Ni0.5Zn0.5Fe2O4 magnetic nanoparticles and the potential medical application of adsorption for bovine serum album

We synthesized Ni_0.5Zn_0.5Fe₂O₄ magnetic nanoparticles (MNPs) by co-precipitation method and performed its adsorption of bovine serum albumin V(BSA (V)). The Ni_0.5Zn_0.5Fe₂O₄ MNPs in nitrogen atmosphere annealed at 400, 500, 600, 700 and 800°C, respectively. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer(VSM) were used to characterize the resulting powders of the structure and properties. XRD results show that the Ni_0.5Zn_0.5Fe₂O₄ powder is a typical single-phase cubic spinel structure, and has no impurity phases. TEM results show that the Ni_0.5Zn_0.5Fe₂O₄ crystalline size is approximately 30–50 nm, which is similar with the XRD estimate results. The magnetic measurements show that Ni_0.5Zn_0.5Fe₂O₄ samples, super paramagnetic material, have high saturation magnetization and small coercivity properties. Moreover, We adopted ultraviolet spectrophotometer to analysis adsorption of BSA(V) on the Ni_0.5Zn_0.5Fe₂O₄ MNPs at room temperature, which show that annealed temperatures, pH, and stirring time can affect BSA(V) adsorption on the Ni_0.5Zn_0.5Fe₂O₄ MNPs. Most importantly, when ultrasonic stirring 2 hours in the liquor BSA(V) at pH = 7.0, the Ni_0.5Zn_0.5Fe₂O₄ samples annealed at 600°C has a highest value of 39.81mgg^?1. From above these results, Ni_0.5Zn_0.5Fe₂O₄ MNPs reveals a great adsorbing ability for BSA(V) that probable are a potential BSA-carrier candidate.     

Multiscale modeling of screening effects on conductivity of graphene in weakly bonded graphene-dielectric heterostructures

Graphene is often surrounded by different dielectric materials when integrated into realistic devices. The absence of dangling bonds allows graphene to bond weakly via the van der Waals interaction with the adjacent material surfaces and to retain its peculiar linear band structure. In such weakly bonded systems, however, the electronic properties of graphene are affected by the dielectric screening due to the long-range Coulomb interaction with the surrounding materials. Including the surrounding materials in the first principles density functional theory (DFT) calculations is computationally very demanding due to the large supercell size required to model heterogeneous interfaces. Here, we employ a multiscale approach combining DFT and the classical image-potential model to investigate the effects of screening from the surrounding materials (hBN, SiC, SiO₂, Al₂O₃, and HfO₂) on the dielectric function and charged impurity scattering limited conductivity of graphene. In this approach, the graphene layer is modeled using DFT and the screening from the surrounding materials is incorporated by introducing an effective dielectric function. The dielectric function and conductivity of graphene calculated using the simplified two-band Dirac model are compared with DFT calculations. The two-band Dirac model is found to significantly overestimate the dielectric screening and charged impurity scattering limited conductivity of graphene. The multiscale approach presented here can also be used to study screening effects in weakly bonded heterostructures of other emerging two-dimensional materials such as metal dichalcogenides.     

One step synthesis of Fe3O4/GO nanocomposites at 100°C and its magnetic properties

ABSTRACT

In the research work, we had planned a one-step procedure to prepare magnetite/graphene oxide (Fe₃O₄/GO) nanocomposites by using chemical co-precepitation method. The polycrystalline phase formation of the magnetite nanoparticles was confirmed by using X-ray diffraction setup. Structural and surface morphology properties of Fe₃O₄/GO nanocomposites are analysed by scanning electron microscopy and transmission electron microscopy. The Raman spectrum of Fe₃O₄/GO nanocomposites shows the enhancement of D and G band, which are associated with GO sheets due to the presence of Fe₃O₄ nanoparticles. Magnetic property measurement was carried out by physical property measurement system (PPMS), which shows its superparamagnetic behaviour.     

Comparative Characteristics of Na0.5K0.5NbO3 Films on Pt by Pulsed Laser Deposition and Magnetron Sputtering

Ferroelectric Na_0.5K_0.5NbO₃ (NKN) thin films were grown on the Pt₈₀Ir₂₀ polycrystalline substrates by pulsed laser deposition (PLD) and radio frequency-magnetron sputtering (RF) technique using the same stoichiometric Na_0.5K_0.5NbO₃ ceramic target. X-ray diffraction proved both PLD- and RF-made Na_0.5K_0.5NbO₃/Pt₈₀Ir₂₀ films are single phase and have preferential c-axis orientation. Temperature dependence of dielectric permittivity reveals the presence of two phase transitions around 210 and 410°C. Capacitance vs. applied voltage C-V @ 100 kHz, I-V, and P-E hysteresis characteristics recorded for the vertical capacitive structures yielded loss tanδ = 0.026 and 0.016, tunability about 44.5 and 30% @ 100 kV/cm, Ohmic resistivity 6.7 × 10¹² Ω·cm and 0.2 × 10¹² Ω·cm, remnant polarization 11.7 and 9.7 μC/cm², coercive field 28.0 and 94.6 kV/cm for PLD- and RF-films, respectively. Piezoelectric test carried out in hydrostatic conditions showed piezoelectric coefficient d _H = 21 for PLD-NKN and 15 pC/N for RF-NKN film.     

Effect of alloying platinum bottom electrode with silver: In relation to CSD processing of PZT thin films

Abstract

A quantity of silver was evaporated onto platinised-silicon (Pt/Ti/SiO₂/Si) and then annealed in air to form a silver-platinum alloy. The lattice spacing of the alloy matched that of the composition of lead zirconate titanate (PZT) used. The surface of the silver-platinum alloy was covered in hillocks. It was found that after PZT was deposited by chemical solution deposition (CSD) these hillocks had disappeared. The presence of mobile Pb and the formation of a transient intermetallic phase (Pt₃Pb) was taken as the cause for this planarisation. Nucleation of perovskite PZT occurred earlier on silver-platinum compared to a film deposited onto platinised-silicon. The degree of preferred orientation developed for the film on the alloyed electrode was not as good as that found on platinised-silicon.     

锂离子电池高镍三元正极材料LiNi1-x-yCoxMnyO2的改性研究进展

新能源产业的快速发展对储能材料与器件的综合性能提出了更高的要求。锂离子电池正极材料,尤其是高镍三元材料（LiNi_1-x-yCo_xMn_yO₂）具有高能量密度、高工作电压及优异的化学稳定性等特点,因而被认为是下一代动力电池商业化正极材料的优越选择。系统总结了高镍三元材料LiNi_1-x-yCo_xMn_yO₂的优势并指出了其亟待解决的问题;在此基础上,综述了其各类改性方法,包括各类阴阳离子掺杂、表面包覆、浓度梯度材料设计以及石墨烯复合等方法;最后对其发展方向及商业化应用进行了展望。     

Short-range potential scattering and its effect on graphene mobility

Over the past few years, the amazing properties of graphene have led to predictions for its use in a variety of areas, not the least of which is in semiconductor devices. However, it appears that graphene is dominated by short-range potential scattering which can arise from intrinsic defects which limit the mobility to relatively low values, well below those predicted based upon its intrinsic band structure. Here, we examine the mobility in graphene on BN, SiC, and SiO₂ when it is dominated by these defects.     

Selective adsorption and separation of adenine by molecularly imprinted polymethacrylic acid on surface of silica particles

ABSTRACT

Adenine molecular imprinted polymethacrylic acid (PMAA) was in situ prepared on the surface of silica (SiO₂) microspheres, constituting a thin and rough molecular imprinted polymer (MIP) layer as characterized by SEM, TEM and FT-IR. Dynamic method and competitive adsorption experiments were used to investigate the adsorption kinetics, adsorption isotherms, selective recognition and adsorption reproducibility of MIP-PMAA/SiO₂ particles toward adenine. The results showed that the obtained particles have strong selective affinity, specific recognition and excellent reusability for adenine. MIP-PMAA/SiO₂ particles were further used as stationary phase for high performance liquid chromatography (HPLC) and separation of adenine from other nucleic bases was achieved successfully.     

The effect of double impurity cluster of Ni and Co in TiO<Subscript>2</Subscript> bulk; a DFT study

The geometrical structure, electronic properties and stability energy of different arrangements of double cluster of Ni-Ni, Co-Co and Ni-Co in rutile and anatase bulk were investigated. Our calculated results showed that Co-Co preferred to state in the nearest distance (nn arrangement) in both anatase and rutile unit cells. While, the Ni-Ni and Ni-Co clusters showed the most stability with the nn form in rutile structure, they preferred the n arrangement (next to the nearest neighbor) in anatas one. These results can be explained by the crystalline structure of rutile that provides the stronger metal-metal interaction by lower distance and also the activity of Co rather than Ni. The band structure results showed a high, moderate and slight decline in the band gap of anatase and rutile in the presence of Co-Co, Ni-Co and Ni-Ni clusters, respectively. An interesting result was shown by altering the direct band gap of pure rutile to the indirect band gap in effect of Co-Co cluster that introduces the Co/rutile structure with an obvious photo-activity. Ni-Ni and Ni-Co impurities show an inverse behavior in anatase phase by changing the indirect band gap of pure anatase to the direct band gap. This may be the main reason to explain the lower photo-efficiency of Ni/TiO₂ than pure TiO₂ under UV illumination. In the last section we show that the Co impurity energetically prefer to state in TiO₂ bulk versus the Ni one by energy of 5 eV.     

Novel SnO2@open microcell-liked graphene network as efficient detection for NO2

Abstract

The design of reduced graphene oxide (RGO) with novel porous structure has attracted tremendous attention owing to their larger specific surface area. Herein, three-dimensional open microcells, bowl-shaped RGO were fabricated through spray drying method which employed polystyrene spheres as a sacrificial template. The bowl-shaped, open microcell-liked pores observed in the RGO network had an average diameter of ≈1?μm. Subsequently, the catalytic SnO₂ nanoparticles were loaded on RGO network via a simple solvothermal method (SnO₂@RGO), and their gas sensing properties were investigated at room temperature (RT). In a comparison with pristine RGO network, the SnO₂@RGO composite exhibited almost 4 times higher response to 400?ppm NO₂ at RT and rapid recovery time. The extraordinary sensing performance can be attributed to the novel open microcell-liked porous microstructure with the SnO₂ catalyst nanoparticles.