Mechanism of ethanol/water reverse separation through a functional graphene membrane:a molecular simulation investigation

Reverse-selective membranes have attracted considerable interest for bioethanol production.However,to date,the reverse-separation performance of ethanol/water is poor and the separation mechanism is unclear.Graphene-based membranes with tunable apertures and functional groups have shown substantial potential for use in molecular separation.Using molecular dynamics simulations,for the first time,we reveal twoway selectivity in ethanol/water separation through functional graphene membranes.Pristine graphene(PG)exhibits reverse-selective behavior with higher ethanol fluxes than water,resulting from the preferential adsorption for ethanol.Color flow mappings show that this ethanol-permselective process is initiated by the presence of ethanol-enriched and water-barren pores;this has not been reported in previous studies.In contrast,water molecules are preferred for hydroxylated graphene membranes because of the synergistic effects of molecular sieving and functional-group attraction.A simulation of the operando condition shows that the PG membrane with an aperture size of 3.8Åachieves good separation performance,with an ethanol/water separation factor of 34 and a flux value of 69.3 kg∙m‒2∙h‒1∙bar‒1.This study provides new insights into the reverse-selective mechanism of porous graphene membranes and a new avenue for efficient biofuel production.

Facilely prepared layer-by-layer graphene membrane-based pressure sensor with high sensitivity and stability for smart wearable devices

With the prosperous development of artificial intelligence,medical diagnosis and electronic skins,wearable electronic devices have drawn much attention in our daily life.Flexible pressure sensors based on carbon materials with ultrahigh sensitivity,especially in a large pressure range regime are highly required in wearable applications.In this work,graphene membrane with a layer-by-layer structure has been successfully fabricated via a facile self-assembly and air-drying(SAAD)method.In the SAAD process,air-drying the self-assembled graphene hydrogels contributes to the uniform and compact layer structure in the obtained membranes.Owing to the excellent mechanical and electrical properties of graphene,the pressure sensor constructed by several layers of membranes exhibits high sensitivity(52.36 kPa……-1)and repeatability(short response and recovery time)in the loading pressure range of 0–50 kPa.Compared with most reported graphene-related pressure sensors,our device shows better sensitivity and wider applied pressure range.What’s more,we demonstrate it shows desired results in wearable applications for pulse monitoring,breathing detection as well as different intense motion recording such as walk,run and squat.It’s hoped that the facilely prepared layer-by-layer graphene membrane-based pressure sensors will have more potential to be used for smart wearable devices in the future.

Ion separation and water purification by applying external electric field on porous graphene membrane

Using molecular dynamics （MD） simulations, a porous graphene membrane was exposed to external electric fields to separate positive and negative ions from salt-water and to produce fresh water. It was observed that, by increasing the strength of the applied electric field, ion separation improved noticeably. In addition, to obtain fresh water, the designed system included two graphene membranes, which are exposed to two external electric fields in opposite directions. Ion rejection was found to be greater than 93% for the electric field of 10 mV/A and higher. This atomic-level simulation increases the understanding of electric field effects on desalination using multilayer graphene membranes and can be helpful in designing more efficient membranes.

Pd micro-nanoparticles electrodeposited on graphene/polyimide membrane for electrocatalytic oxidation of formic acid

A novel Pd electrocatalyst with flowerlike micro-nanostructures was synthesized by electrochemical deposition on a flexible graphene/polyimide（Gr/PI） composite membrane and characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）.The Pd micro-nanoparticles were prepared on a COOH-CNTs/PI membrane as a comparative sample.The XRD and SEM investigations for Pd electrodeposition demonstrate that the particle size of Gr/PI composite membrane is smaller than that of COOH-CNTs/PI membrane,while the uniform and dense distribution of Pd micro-nanoparticles on the Gr/PI composite membrane is greater than that on the COOH-CNTs/PI membrane.The electrocatalytic properties of Pd/Gr/PI and Pd/COOH-CNTs/PI catalysts for the oxidation of formic acid were investigated by cyclic voltammetry（CV） and chronoamperometry（CA）.It is found that the electrocatalytic activity and stability of Pd/Gr/PI are superior to those of Pd/COOH-CNTs/PI catalyst.This is because smaller metal particles and higher dense distribution desirably provide abundant catalytic sites and mean higher catalytic activity.Therefore,the Pd/Gr/PI catalyst has better catalytic performance for formic acid oxidation than the Pd/COOH-CNTs/PI catalyst.

Unexpected Selective Absorption of Lithium in Thermally Reduced Graphene Oxide Membranes

Lithium plays an increasingly important role in scientific and industrial processes, and it is extremely important to extract lithium from a high Mg^(2+)/Li^(+) mass ratio brine or to recover lithium from the leachate of spent lithiumion batteries. Conventional wisdom shows that Li^(+) with low valence states has a much weaker adsorption(and absorption energy) with graphene than multivalent ions such as Mg^(2+). Here, we show the selective adsorption of Li^(+) in thermally reduced graphene oxide(rGO) membranes over other metal ions such as Mg^(2+), Co^(2+), Mn^(2+),Ni^(2+), or Fe^(2+). Interestingly, the adsorption strength of Li^(+) reaches up to 5 times the adsorption strength of Mg^(2+),and the mass ratio of a mixed Mg^(2+)/Li^(+) solution at a very high value of 500 : 1 can be effectively reduced to 0.7 : 1 within only six experimental treatment cycles, demonstrating the excellent applicability of the rGO membranes in the Mg^(2+)/Li^(+) separation. A theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cation–π interaction and steric exclusion when hydrated cations enter the confined space of the rGO membranes.

Mechanical responses of the bio-nano interface: A molecular dynamics study of graphene-coated lipid membrane

Bio-nano interfaces between biological materials and functional nanodevices are of vital importance in relevant energy and information exchange processes, which thus demand an in-depth understanding. One of the critical issues from the application viewpoint is the stability of the bio-nano hybrid under mechanical perturbations. In this work we explore mechanical responses of the interface between lipid bilayer and graphene under hydrostatic coating provides remarkable resistance to the pressure or indentation loads, We find that graphene loads, and the intercalated water layer offers additional protection. These findings are discussed based on molecular dynamics simulation results that elucidate the molecular level mechanisms, which provide a basis for the rational design of bionanotechnology- enabled aoolications such as biomedical devices and nanotheraoeutics.

Highly efficient separation of Sc^(3+) and Y^(3+) in acid solution by a graphene oxide membrane with interlayer sieving

Sc and Y are key rare earth elements and are widely used in lamp phosphors,lasers and high-performance alloys.However,highly efficient extraction and separation of Sc^(3+) and Y^(3+) is laborious,harmful,slow,and costly,strongly necessitating more efficient extraction and separation techniques.Here,we produced hydrated Sc^(3+)-and hydrated Y^(3+)-controlled graphene oxide(GO) membranes and find that both hydrated cations were completely self-rejected by the membrane.By combining this selfrejection effect of the larger hydrated Y^(3+)-controlled GO membrane and the rapid passage of the membrane through the smaller hydrated Sc^(3+),we proposed a strategy to separate Sc^(3+) and Y^(3+) by using a hydrated Y^(3+)-controlled GO membrane.The experimental results show that the permeation rate of Sc^(3+) exceeds that of Y^(3+) when the separation factor reaches 4.02,which can be attributed to the interlayer sieving effects of the GO membrane.Our finding illustrates the use of a forward osmosis process with a GO membrane for the efficient separation of Sc^(3+) and Y^(3+) by interlayer sieving,which provides a new effective and eco-friendly method for the separation of rare earth elements.

Constructing 2D ultrathin graphene oxide membranes with supramolecular-assembled nano-adhesives for enhancing water stability

Atomic-thick two-dimensional(2D)graphene oxide(GO)has emerged as an ideal building block in developing ultrathin 2D membranes for separating substances.However,due to the negative charge of GO sheets when hydrated,electrostatic repulsion causes GO membranes to disintegrate easily in water,limiting their wide application in aqueous solutions.Here,we introduce and apply the concept of localized gluing by designing ultra-small supramolecular-assembled nanoparticles as nanoadhesives(NPA)to construct robust GO membranes with a thickness of only 24 nm.The supramolecular-assembled NPA were synthesized by cyclodextrin(CD)and tannic acid(TA)with a uniform size distribution of about 4.5 nm,and exposed surface pyrogallols that could strongly interact with GO sheets.The physical sizing of the NPA confines the interlayer spacing and maintains the nanochannel,while the natural molecular properties of the NPA enhance the connection between adjacent layers and inhibit swelling detachment.The fabricated ultrathin 2D membranes show a remarkable two times enhancement of water permeance over pristine GO membranes and exhibit excellent durability with record-breaking stability for 720 h immersion in water.This strategy provides meaningful insights into the design and fabrication of robust ultrathin membranes for practical application.

The use of graphene oxide membranes for the softening of hard water

Strong chemical interactions between the oxygen-containing functional groups on graphene oxide(GO)sheets and the ions of divalent metals were exploited for the softening of hard water.GO membranes were prepared and evaluated for their ability to absorb Ca2+and Mg2+ions.These GO membranes can effectively absorb Ca2+ions from hard water;a 1 mg GO membrane can remove as much as 0.05 mg Ca2+ions.These GO membranes can be regenerated and used repeatedly.

Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation

Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide （GO） nanosheets and titanium dioxide （TiO2） nanotubes for oil/water separation. GO/TiO2 membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO2 membrane shows greater water permeability with the water flux up to 531 L/ （m^2·h·bar）, which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO2 membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO2 nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO2 membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO2 membrane in oil-water treatment.

Theoretical study on Janus graphene oxide membrane for water transport

Graphene oxide(GO)membranes have received considerable attention owing to their outstanding water-permeation properties;however,the effect of the membrane’s microstructures(such as the distribution of oxidized and pristine regions)on the transport mechanism remains unclear.In this study,we performed molecular simulations to explore the permeation of a water-ethanol mixture using a new type of Janus GO membranes with different orientations of oxidized and pristine surfaces.The results indicate that the oxidized upper surface endows the GO membrane with considerable water-capture capability and the in-built oxidized interlayer promotes the effective vertical diffusion of water molecules.Consequently,using the optimized Janus GO membrane,infinite water selectivity and outstanding water flux(-40.9 kg·m^(-2) h^(-1))were achieved.This study contributes to explaining the role of oxidized regions in water permeation via GO membranes and suggests that Janus GO membranes could be used as potential candidates for water-ethanol separation.

Ion sieving in graphene oxide membranes via cationic control of interlayer spacing

With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Prof.Fang Haiping(方海平)from Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Prof.Wu Minghong(吴明红)from Shanghai Applied Radiation Institute。

Phase-selective graphene oxide membranes for advanced microfluidic flow control

For the first time,we harness the unique phase-selectivity of chip-integrated graphene oxide(GO)membranes to significantly enhance flow control on centrifugal microfluidic platforms.In this paper,we present novel processes for the assembly of these GO membranes into polymeric microfluidic systems and demonstrate that multilayer GO membranes allow the passage of water while blocking pressurized air and organic solutions.

快速微波还原电化学衍生氧化石墨烯制备高结晶石墨烯膜

电化学氧化石墨,可用于大规模合成氧化石墨烯,是一种可持续且直接的方法.然而,关于电化学衍生氧化石墨烯(EGO)进一步还原的研究却很缺少.本文中,我们报道了EGO膜的快速微波还原过程.化学法合成的氧化石墨烯膜需要数分钟微波辐射才能被还原,但是我们制备的EGO膜经3秒微波辐射即可转化为高结晶石墨烯膜(HCGM),并且该过程无需对膜进行预处理或添加微波增敏剂.与以前报道的微波法制备的石墨烯相比,本文制备的HCGM具有大尺寸芳香区(约100 nm)、高碳/氧原子比(约33)和高电导率(约5×10^(4)S m^(−1)).EGO的高微波还原效率可以归因于其独特分子结构,EGO中丰富的芳香区可高效吸收微波,引发EGO膜实现瞬时体相加热.该研究加深了对氧化石墨烯微波还原机理的理解,并为HCGM的生产提供了一条便捷途径.

Ag–AgBr/TiO_2/RGO nanocomposite:Synthesis,characterization,photocatalytic activity and aggregation evaluation

Ag-AgBr/TiO2 supported on reduced graphene oxide （Ag-AgBr/TiO2/RGO） with different mass ratios of grapheme oxide （GO） to TiO2 were synthesized via a facile solvothermal-photo reduction method. Compared to the single-, two- and three-component nanocomposites, the four-component nanocomposite, Ag-AgBr/TiO2/RGO-1 with mass ratio of GO to TiO2 at 1%, exhibited a much higher photocatalytic activity for the degradation of penicillin G （PG） under white light-emitting diode （LED-W） irradiation. The PG degradation efficiency increased with the increase of mass ratio of GO to TiO2 from 0.2% to 1%, then it decreased with the increase of mass ratio of GO to TiO2 from 1% to 5%. The zeta potentials of RGO-nanocornposites became more negative with the presence of humic acid （HA） due to the negatively charged HA adsorption, resulting in the shift of points of zero charge to lower values of pH. The aggregations of nanocomposites were more significant due to the bridging effect of HA. Furthermore, the aggregated particle sizes were larger for ROO-nanocomposites compared to other nanoparticles, due to the bindings of the carboxylic and phenolic functional groups in HA with the oxygen-containing functional groups in the RGO-nanocomposites. The microfiltration （MF） membrane was effective for the nanocomposites separation. In the continuous flow through submerged membrane photoreactor （sMPR） system, backwashing operation could efficiently reduce membrane fouling and recover TiO2, and thus indirectly facilitate the PG removal.