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

Nano Research - 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...     

Reduced graphene oxide-metal/metal oxide composites: facile synthesis and application in water purification

This paper describes a versatile, and simple synthetic route for the preparation of a range of reduced graphene oxide (RGO)-metal/metal oxide composites and their application in water purification. The inherent reduction ability of RGO has been utilized to produce the composite structure from the respective precursor ions. Various spectroscopic and microscopic techniques were employed to characterize the as-synthesized composites. The data reveal that the RGO-composites are formed through a redox-like reaction between RGO and the metal precursor. RGO is progressively oxidized primarily to graphene oxide (GO) and the formed metal nanoparticles are anchored onto the carbon sheets. Metal ion scavenging applications of RGO-MnO(2) and RGO-Ag were demonstrated by taking Hg(II) as the model pollutant. RGO and the composites give a high distribution coefficient (K(d)), greater than 10 L g(-1) for Hg(II) uptake. The K(d) values for the composites are found to be about an order of magnitude higher compared to parent RGO and GO for this application. A methodology was developed to immobilize RGO-composites on river sand (RS) using chitosan as the binder. The as-supported composites are found to be efficient adsorbent candidates for field application.     

氧化石墨烯负载无纺布复合膜的制备及光热转换性能

氧化石墨烯(GO)是一种性能良好的光热转换材料,广泛用于海水淡化、光电转换和太阳能利用等领域。为了测试GO负载无纺布膜(GO膜)和聚乙烯醇-氧化石墨烯无纺布复合膜(PVA-GO复合膜)的光热水蒸发特性,通过改进Hummers方法制备GO,选取了纤维素和聚酯类型的无纺布,通过浸泡-超声法制得GO膜和PVA-GO复合膜。运用紫外-可见-近红外光谱仪分析了GO膜和PVA-GO复合膜的吸光性能,并通过电子天平测量GO膜和PVA-GO复合膜的蒸发水量。由于PVA具有亲水性,能增大膜的吸水性,因而PVA加入会使蒸发水量增大。通过SEM分析GO膜和PVA-GO复合膜表面特征,发现无添加PVA的GO膜是纤维丝状结构,且纤维清晰可见。加入PVA后,纤维被PVA包裹,说明膜对光的吸收能力增强。当加入6wt% PVA时,无纺布纤维被PVA完全包裹。当用氙灯对两种膜进行水蒸发实验时,GO膜的蒸发速率达到了1.67 kg/(m2·h),PVA-GO复合膜的蒸发速率达到了1.85 kg/(m2·h)。此外,GO膜中出现GO层状结构,在紫外-可见-近红外光谱分析中表现出较好的吸光能力,在光热蒸发实验中表现出较好的光热转换能力。PVA-GO复合膜在PVA质量浓度为4wt%时有较好的光热转换性能和吸光性。      

Nitrogen-doped graphene nanosheets as reactive water purification membranes

Oxidation of organic pollutants by sulfate radicals produced via activation of persulfate has emerged as a promising advanced oxidation technology to address various challenging environmental issues. The development of an effective, environmentally-friendly, metal-free catalyst is the key to this technology. Additionally, a supported catalyst design is more advantageous than conventional suspended powder catalysts from the point of view of mass transfer and practical engineering applications (e.g. post-use separation). In this study, a metal-free N-doped reduced graphene oxide (N-rGO) catalyst was prepared via a facile hydrothermal method. N-rGO filters were then synthesized by facile vacuum filtration, such that water can flow through nanochannels within the filters. Various advanced characterization techniques were employed to obtain structural and compositional information of the as-synthesized N-rGO filters. An optimized phenol oxidative flux of 0.036 ± 0.002 mmol·h^–1 was obtained by metal-free catalytic activation of persulfate at an influent persulfate concentration of 1.0 mmol·L^–1 and filter weight of 15 mg, while a N-free rGO filter demonstrated negligible phenol oxidation capability under similar conditions. Compared to a conventional batch system, the flow-through design demonstrates obviously enhanced oxidation kinetics (0.036 vs. 0.010 mmol·h^–1), mainly due to the liquid flow through the filter leading to convection-enhanced transfer of the target molecule to the filter active sites. Overall, the results exemplified the advantages of organic compound removal by catalytic activation of persulfate using a metal-free catalyst in flowthrough mode, and demonstrated the potential of N-rGO filters for practical environmental applications.

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Influence of graphene oxide sheets on the pore structure and filtration performance of a novel graphene oxide/silica/polyacrylonitrile mixed matrix membrane

The novel graphene oxide (GO)/silica (SiO₂)/polyacrylonitrile (PAN) mixed matrix membranes (MMMs) with high filtration flux and excellent antifouling performance were designed and fabricated in situ by the method of non-solvent induced phase separation (NIPS) from the precursor of PAN hybridized with GO, tetraethoxysilane and 3-aminopropyltriethoxysilane. The influences of GO sheets on the pore and chemical structure, hydrophilic nature and filtration performance of derived GO/SiO₂/PAN MMMs were investigated by the scanning electron microscopy, field emission scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray, Fourier transform infrared spectrometer, pure water contact angles and filtration performance. Results indicated that in situ incorporation of GO sheets and SiO₂ molecules into PAN matrix via NIPS reconstructs the porous structure of derived GO/SiO₂/PAN MMMs with the upright finger-like holes, porous bottom, thinner top layer and high porosity. The spontaneous surface migration or segregation of hydrophilic GO sheets and SiO₂ molecules as well as their synergistic interaction occurred during NIPS greatly ameliorate the top surface structure and property of derived membranes with smoother surface, uniform pore structure and good hydrophilicity. The derived GO/SiO₂/PAN MMMs exhibit a high water filtration flux of 387 L m^?2 h^?1 with the bull serum albumin rejection rate up to 99% and significant enhancement of antifouling performance.     

A high-flux polydopamine/reduced graphene oxide/MOF-5 composite membrane via a mussel-inspired method for dye wastewater purification

Journal of Materials Science - A novel polydopamine/reduced graphene oxide/MOF-5 (PDA/RGO/MOF-5) composite membrane with high flux, outstanding dye separation performance and anti-fouling ability...     

Pt nanoparticle-reduced graphene oxide nanohybrid for proton exchange membrane fuel cells

A platinum nanoparticle-reduced graphene oxide (Pt-RGO) nanohybrid for proton exchange membrane fuel cell (PEMFC) application was successfully prepared. The Pt nanoparticles (Pt NPs) were deposited onto chemically converted graphene nanosheets via ethylene glycol (EG) reduction. According to the powder X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) analysis, the face-centered cubic Pt NPs (3-5 nm in diameter) were homogeneously dispersed on the RGO nanosheets. The electrochemically active surface area and PEMFC power density of the Pt-RGO nanohybrid were determined to be 33.26 m2/g and 480 mW/cm2 (maximum values), respectively, at 75 degrees C and at a relative humidity (RH) of 100% in a single-cell test experiment.     

Engineered graphite oxide materials for application in water purification

Retaining the inherent hydrophilic character of GO (graphite-oxide) nanosheets, sp(2) domains on GO are covalently modified with thiol groups by diazonium chemistry. The surface modified GO adsorbs 6-fold higher concentration of aqueous mercuric ions than the unmodified GO. "Core-shell" adsorbent granules, readily useable in filtration columns, are synthesized by assembling aqueous GO over sand granules. The nanostructured GO-coated sand retains at least 5-fold higher concentration of heavy metal and organic dye than pure sand. The research results could open avenues for developing low-cost water purification materials for the developing economies.     

Nitrous oxide high purification by membrane gas separation

In this work the scope of nitrous oxide high purification by membrane gas separation was presented. The permeability values of nitrous oxide and its limiting impurities were measured for “Lestosil” membrane at feed pressure in the range from 100 to 400 kPa. The values of ideal selectivity were determined. It was shown that nitrous oxide is more permeable than impurities components. Therefore the process of nitrous oxide high purification was calculated for it carried out in membrane module with a feeding reservoir which is used for purification from low permeable impurities.     

Chemical functionalization of graphene oxide for improving mechanical and thermal properties of polyurethane composites

Graphene oxide (GO) was chemically functionalized to prepare polyurethane (PU) composites with improved mechanical and thermal properties. In order to achieve a well exfoliated and stable GO suspension in an organic solvent (dimethylformamide, DMF), 4, 4′-methylenebis(phenyl isocyanate) and polycaprolactone diol, which were the two monomers for synthesizing PU, were selectively used to functionalize GO. The obtained functionalized GO (FGO) could form homogeneous dispersions in DMF solvent and the PU matrix, as well as provide a good compatibility with the PU matrix. The most efficient improvement of mechanical properties was achieved when 0.4 wt.% FGO was added into the PU matrix, showing increases in the tensile stress, elongation at break and toughness by 34.2%, 27.6%, and 64.5%, respectively, compared with those of PU. Regarding the thermal stability, PU filled with 1 wt.% FGO showed the largest extent of improvement with T_2% and T_50% (the temperatures at which 2% and 50% weight-loss happened) 16 °C and 21 °C higher than those of PU, respectively. The significant improvement in both mechanical properties and thermal stability of FGO/PU composites should be attributed to the homogeneous dispersion of FGO in the PU matrix and strong interfacial interaction between them.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

Mixed-valence manganese oxide/reduced graphene oxide composites with enhanced pseudocapacitive performance

Journal of Materials Science - As typical pseudocapacitive materials, manganese oxides have attracted great interest due to their high theoretical specific capacitance, abundant oxidation states...     

氧化石墨烯/丁腈橡胶-聚氯乙烯复合材料的隔声性能

为了制备一种轻质隔声复合材料,以氧化石墨烯(GO)为隔声填料,通过熔融共混法制备了GO/丁腈橡胶-聚氯乙烯(GO/NBR-PVC)复合材料。采用SEM、XRD、DMA和万能材料试验机等对GO/NBR-PVC的结构形态、弹性模量和力学性能等进行测试;利用四通道阻抗管系统对隔声性能进行测试。结果表明,GO在NBRPVC基体中分散均匀;GO/NBR-PVC的拉伸强度、弹性模量和阻尼性能明显增大。隔声测试结果表明:GO的添加可以提高GO/NBR-PVC的隔声性能,尤其在低频段。当GO的质量分数分别为0.1%、0.2%、0.3%、0.4%时,复合材料面密度几乎不变,隔声指数分别提高了0.8dB、1.1dB、1.5dB、1.2dB;而添加质量分数为30%的重质金属(HM)时,HM/NBR-PVC面密度明显提高,而隔声指数只提高了0.6dB。     

氧化石墨烯/海藻酸钙水凝胶复合膜对水中Cd(II)的吸附

将氧化石墨烯(GO)、致孔剂与海藻酸钠共混后与CaCl₂交联制备的GO/海藻酸钙（CA）水凝胶复合膜作为含重金属废水的吸附材料。采用SEM和TEM表征了复合膜的表面形貌及透射性能,且分析了GO的加入对复合膜的力学性能、平均孔径、水通量及表面官能团的影响。为探究GO/CA水凝胶复合膜的吸附性能,考察了其吸附Cd(II)的影响因素:pH（6~7）值、初始离子浓度、接触时间、温度（三者均正相关）。用FTIR、XPS在吸附前后对复合膜进行了表征;引入了吸附动力学和等温线模型分析其吸附机制。探究结果表明GO的加入提高了复合膜的力学性能、平均孔径及水通量;吸附过程遵循Langmuir等温线,属于单层吸附,拟合得到的最大吸附量为173.61 mg/g;伪一级和伪二级吸附动力学分别在低浓度和高浓度时能较好地描述吸附过程的动力学行为;吸附机制主要为物理作用力吸附和离子交换。经过5个连续的吸附-解吸循环证明了GO/CA水凝胶复合膜的可重复利用性。      

Enhanced supercapacitive performance of cost-effectively synthesized ZnO-reduced graphene oxide composite

Commercially accessible and long-lasting resources of energy are among the foremost areas of current research. Supercapacitors have taken the position of very thoughtful candidates in the energy-storing field to meet the modern necessities. Several graphene-based materials have been employed for supercapacitor electrodes. Here, we demonstrated an economical and advanced hydrothermal technique using combination of two reducing materials (urea and starch) for the fabrication of reduced graphene oxide/zinc oxide (RGO/ZnO) composite. The X-ray diffraction and scanning electron microscopy analysis were carried out to study the structure and of RGO/ZnO composite. The supercapacitive behaviour of RGO/ZnO composite was studied via cyclic voltammetry and galvanostatic charge/discharge experiments. The results showed enhanced specific capacitance (313.14?F?g^?1) with good cyclic stability (1000 cycles).