Study on the Hydration and Physical Properties of Cement by M18 Polycarboxylate Superplasticizer Modified Graphene Oxide

Graphene oxide(GO)as a new nano-enhancer in cement-based materials has gained wide attention.However,GO is easy to aggregate in alkaline cement mortar with poor dispersibility.This hinders its application in practical infrastructure construction.In this work,GO-M18 polycarboxylate compound superplasticizer(GM)were obtained by compounding the M18 polycarboxylate superplasticizer with GO solution at different mass ratios.The dispersion of GM in alkaline solution was systematically studied.The phases and functional groups of GM were characterized by XRD and FTIR.The effects of GM on the cement mortar hydration and the formation of microstructure were investigated by measuring the heat of hydration,MIP,TG/DSC,and SEM.The results show that the long-chain structure of the M18 polycarboxylate superplasticizer can increase the interlayer spacing of GO and weaken the force between GO sheets.The modified GO can be uniformly dispersed in the cement slurry.GM can accelerate the early hydration process of cement,which can increase the content of Ca(OH)2 and decrease the grain size.It can optimize the pore size distribution of cement-based materials,increase the density of harmless and less harmful pores,thereby improving mechanical properties.Such methods can transform traditional cement-based materials into stronger,more durable composites,which prolong the life of cement-based materials and reduce the amount of cement used for later maintenance.This provides an idea for achieving sustainability goals in civil engineering.

Highly dispersed Pd nanoparticles on chemically modified graphene with aminophenyl groups for formic acid oxidation

A novel electrode material based on chemically modified graphene （CMG） with aminophenyl groups is covalently functionalized by a nucleophilic ring-opening reaction between the epoxy groups of graphene oxide and the aminophenyl groups of p-phenylenediamine. Palladium nanoparticles with an average diameter of 4.2 nm are deposited on the CMG by a liquid-phase borohydride reduction. The electrocatalytic activity and stability of the Pd/CMG composite towards formic acid oxidation are found to be higher than those of reduced graphene oxide and commercial carbon materials such as Vulcan XC-72 supported Pd electrocatalysts.

Controllable Nucleation of Nanobubbles at a Modified Graphene Surface

The properties of nanoscale gas bubbles at the solid/water interface have been investigated for more than 20 years. However, the stability of nanobubbles remains far from being understood. How to control the formation of nanobubbles is the key issue for understanding their long lifetime. In this work, using molecular dynamics simulations we modify the substrate （graphene） with charge dipoles in which the local properties of the surface could be changed. Nanobubbles could be stabilized on the local hydrophobic area and modified area with the hydrophilic boundary where gas nuclei are deposited beforehand. Those results provide two methods to control the nucleation of gas nanobubbles and fix them on a target area.

Molecular insights on Ca^(2+)/Na+separation via graphene-based nanopores:The role of electrostatic interactions to ionic dehydration

Ca^(2+)/Na+separation is a common problem in industrial applications,biological and medical fields.However,Ca^(2+)and Na+have similar ionic radii and hydration radii,thus Ca^(2+)/Na+separation is challenging.Inspired by biological channels,group modification is one of the effective methods to improve the separation performance.In this work,molecular dynamics simulations were performed to investigate the effects of different functional groups(COO,NH3+)on the separation performance of Ca^(2+)and Na+through graphene nanopores under an electric field.The pristine graphene nanopore was used for comparison.Results showed that three types of nanopores preferred Ca^(2+)to Na+,and Ca^(2+)/Na+selectivity followed the order of GE-COO(4.06)>GE(1.85)>GE-NH3+(1.63).Detailed analysis of ionic hydration microstructure shows that different nanopores result in different hydration factors for the second hydration layer of Ca^(2+)and the first layer of Na+.Such different hydration factors corresponding to the dehydration ability can effectively evaluate the separation performance.In addition,the breaking of hydrogen bonds between water molecules due to electrostatic effects can directly affect the dehydration ability.Therefore,the electrostatic effect generated by group modification will affect the ionic hydration microstructure,thus reflecting the differences in dehydration ability.This in turn affects the permeable and separation performance of cations.The results of this work provide perceptive guidelines for the application of graphene-based membranes in ion separation.

Modified graphene as novel lubricating additive with high dispersion stability in oil

Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a kind of effective dispersant has been successfully developed to achieve the remarkable dispersion stability of graphene in base oil.The stable dispersion time of modified graphene(0.5 wt%)with dispersant(1 wt%)in PAO-6 could be up to about 120 days,which was the longest time reported so far.At the same time,the lubricant exhibits a significant improvement of tribological performance for a steel ball to plate tribo-system with a normal load of 2 N.The coefficient of friction between sliding surfaces was~0.10 and the depth of wear track on plate was~21 nm,which decreased by about 44%and 90%when compared to pure PAO-6,respectively.Furthermore,the analysis of the lubricating mechanisms in regard to the sliding-induced formation of nanostructured tribo-film has been contacted by using Raman spectra and TEM.

Electrochemical Study and Application on Shikonin at Poly（diallyldimethylammonium chloride） Functionalized Graphene Sheets Modified Glass Carbon Electrode

The electrochemical behaviors of shikonin at a poly（diallyldimethylammonium chloride） functionalized graphene sheets modified glass carbon electrode（PDDA-GS/GCE） have been investigated. Shikonin could exhibit a pair of well-defined redox peaks at the PDDA-GS/GCE located at 0.681 V（Epa） and 0.662 V（Epc）[vs. saturated calo- mel electrode（SCE）] in 0.1 mol/L phosphate buffer solution（pH=2.0） with a peak-to-peak separation of about 20 mV, revealing a fast electron-transfer process. Moreover, the current response was remarkably increased at PDDA- GS/GCE compared with that at the bare GCE. The electrochemical behaviors of shikonin at the modified electrode were investigated. And the results indicate that the reaction involves the transfer of two electrons, accompanied by two protons and the electrochemical process is a diffusional-controlled electrode process. The electrochemical para- meters of shikonin at the modified electrode, the electron-transfer coefficient（a）, the electron-transfer number（n） and the electrode reaction rate constant（ks） were calculated to be as 0.53, 2.18 and 3.6 s^-1, respectively. Under the optimal conditions, the peak current of differential pulse voltammetry（DPV） increased linearly with the shikonin concentra- tion in a range from 9A72×10^-8 mol/L to 3,789×10^-6 mol/L with a detection limit of 3,157× 10^-8 mol/L. The linear regression equation was Ip=O.7366c＋0.7855（R=0.9978; lp： 10-7 A, c： 10-8 mol/L）. In addition, the modified glass carbon electrode also exhibited good stability, selectivity and acceptable reproducibility that could be used for the sensitive, simple and rapid determination of shikonin in real samples. Therefore, the present work offers a new way to broaden the analytical application of graphene in pharmaceutical analysis.

A novel 2D graphene oxide modified α-AgVO_(3) nanorods: Design, fabrication, and enhanced visible-light photocatalytic performance

Silver vanadates are promising visible-light-responded photocatalysts with suitable bandgap for solar absorption.However,the easy recombination of photogenerated carriers limits their performance.To overcome this obstacle,a novel 2D graphene oxide(GO)modifiedα-AgVO_(3) nanorods(GO/α-AgVO_(3) )photocatalyst was designed herein to improve the separation of photocarriers.The GO/α-AgVO_(3) was fabricated through a facile in-situ coprecipitation method at room temperature.It was found that the as-prepared 0.5 wt%GO/α-AgVO_(3) exhibited the most excellent performance for rhodamine B(RhB)decomposition,with an apparent reaction rate constant 18 times higher than that of pureα-AgVO_(3) under visible-light irradiation.In light of the first-principles calculations and the hetero junction analysis,the mechanism underpinned the enhanced photocatalytic performance was proposed.The enhanced photocatalytic performance was ascribed to the appropriate bandgap ofα-AgVO_(3) nanorods for visible-light response and efficient separation of photocarriers through GO nanosheets.This work demonstrates the feasibility of overcoming the easy recombination of photogenerated carriers and provides a valuable GO/α-AgVO_(3) photocatalyst for pollutant degradation.

Detection of dopamine at graphene-ZIF-8 nanocomposite modified electrode

A hybrid graphene-ZIF-8（G-ZIF-8） nanocomposite modified electrode was prepared in our work. SEM characterization shows that nanocrystals of zeolitic imidazolate frameworks（ZIF-8） were homogeneously well-intergrown on the surface of graphene and thus the graphene sheets were refrained from restacking, which implies the high accessible surface area. The BET results further testifies that G-ZIF-8composites had a larger surface area than 3D graphene. G-ZIF-8 modified electrode exhibited excellent electroanalytical performance for dopamine. The linear concentration range was from 3.0 mmol/L to1.0 mmol/L with the detection sensitivity of 0.34 m A/mmol/L and the detection limit of 1.0 mmol/L was obtained. The interference study, electrode stability and reproducibility were carried out. In addition, the prepared sensor was applied to the detection of DA in serum sample with recoveries from 96.8% to100.7%. It is believable that the structure characteristic of G-ZIF-8 nanocomposite is favorable for using MOFs to fabricate highly sensitive electrochemical sensor

A nanosilica/exfoliated graphene composite film-modified electrode for sensitive detection of methyl parathion

Graphene nanosheets （GS） were easily prepared through liquid-phase exfoliation of graphite powder in N,N-dimethylformamide （DMF） with the assistance of sodium citrate. Then, GS was coated onto a glassy carbon electrode （GCE） surface by drop to fabricate a GS]GCE nanointerface. Subsequently, by using tetraethylorthosilicate sol as precursor, nanosilica was electrochemically deposited onto the GS]GCE surface to produce a nanocomposite film electrode （nanosilicaJGSJGCE）. Electrochemical behaviors of methyl parathion （MP） on the nanosilica/GS/GCE surface were investigated thoroughly. It was found that the nanosilicaJGS nanocomposites can improve the redox peak currents of MP significantly due to the synergetic effect. The oxidation peak current was linearly related to MP concentration in the range from 0.0005 μmol/L to 5.6 μmol/L. The detection limit was calculated to be 0.07 nmol/L （SJN = 3）. The developed method was used to determine MP in real samples. The recoveries were in the range from 95.4% to 104.2%, demonstrating satisfactory results.

Tribological behavior of nanocarbon materials with different dimensions in aqueous systems

Due to the widespread use of nanocarbon materials(NCMs),more researchers are studying their tribological performances.In this work,the tribological behaviors of the following five types of NCMs with different geometric shapes were evaluated in a novel oil‐in‐water system:spherical fullerenes(C60,0D),tubular multi‐walled carbon nanotubes(MWCNT,1D),sheet graphene oxide(GO,2D),sheet graphene oxide derivative(Oct‐O‐GO,2D),and lamellar graphite(G,3D).Among these,GO with two types of oxidation degrees,i.e.,GO(1),GO(2),and Oct‐O‐GO(1)were synthesized and characterized using Fourier‐transform infrared spectroscopy,Raman spectroscopy,x‐ray diffraction,thermogravimetric analysis,scanning electron microscopy,and contact angle measurements.The load‐carrying capacity of the NCM emulsions were evaluated using a four‐ball test machine,and the lubrication performances were investigated using a high‐frequency reciprocating friction and wear tester with a sliding distance of 1,800 mm under different loads(50 N and 100 N)at 0.5 Hz.The results revealed that the Oct‐O‐GO(1)emulsion exhibited the best load‐carrying capacity,and the best friction‐reducing and anti‐wear properties compared to other emulsions.Moreover,the anti‐wear advantage was more prominent under high load conditions,whereas the other emulsions exhibited a certain degree of abrasive or adhesive wear.The lubrication mechanism was determined through the analysis of worn surfaces using scanning electron microscopy/energy‐dispersive x‐ray spectroscopy,micro‐Raman spectroscopy,and x‐ray photoelectron spectroscopy.The results revealed that during frictional sliding,the ingredients in the emulsion can absorb and react with the freshly exposed metal surface to form surface‐active films to protect the surfaces from abrasion.Moreover,it was found that the higher the amount of ingredients that contain alkyl and O‐H/C=O,the better was the lubrication performance in addition to an increase in the carbon residue in the tribofilm generated on the meal surface.

Enhancing Dehydration Performance of Isopropanol by Introducing Intermediate Layer into Sodium Alginate Nanofibrous Composite Pervaporation Membrane

A novel three-tier composite membrane based on highly porous nanofibrous substrate was demonstrated for efficient iso-propanol dehydration by pervaporation.Here,polyethyleneimine(PEI)modified graphene oxide(GO)sheets were vacuum-assistant assembled onto porous electrospun polyacrylonitrile(PAN)nanofibrous substrate to achieve a smooth,hydrophilic and compact PEI-GO intermediate layer.The introduction of PEI chains endowed GO interlayer with sufficient interaction for bonding adjacent GO nanosheets to enhance stability in water/isopropanol mixture and also with the ascended inter-lamellar space to improve the water-sorption ability due to the abundant active amino groups.Benefiting from PEI-GO layer,a defect-free sodium alginate(SA)skin layer could be facilely manufactured with elaborately controlled thickness as thin as possible in order to reduce mass transfer resistant and enhance permeability maximally.Meanwhile,the interlayer would also contribute to enhance interfacial adhesion to promote the structure integrity of three-tier thin-film nanofibrous composite(TFNC)membrane in pervaporation dehydration process.After fine-tuning of membrane preparation process,the SA/PEI(75)-GO-60/PAN TFNC membrane exhibited competitive pervaporation performance with the permeate flux of 2009 g/m2 h and the separation factor of 1276 operated at 70°C for dehydration of 90 wt%isopropanol solution.The unique three-tier composite membrane structure suggested an effective and facile approach to design novel membrane structure for further improvement of pervaporation performance.