Dehai Wu

Carbon Nanotube Sponges

[*] Prof.D.Wu,X.Gui,Prof. J.Wei.Prof. K.Wang, Prof.H.Zhu, Y. Jia,Q.Shu Key Laboratory for Advanced Materials Processing Technology, Ministry of Education Department of Mechanical Engineering, Tsinghua University Beijing 100084 (P. R. China) E-mail: wdh-dme@tsinghua.edu.cn Prof. A. Cao Department of Advanced Materials and Nanotechnology College of Engineering, Peking University Beijing 100871 (P. R. China) E-mail: anyuan@pku.edu.cn

Graphene-On-Silicon Schottky Junction Solar Cells

www.MaterialsViews.com C O M Graphene-On-Silicon Schottky Junction Solar Cells M U N I By Xinming Li , Hongwei Zhu , * Kunlin Wang , * Anyuan Cao , Jinquan Wei , Chunyan Li , Yi Jia , Zhen Li , Xiao Li , and Dehai Wu C A IO N Graphene, a single atomic layer of carbon hexagons, has stimulated a lot of research interest owing to its unique structure and fascinating properties. [ 1 ] Graphene has been produced in the form of ultrathin sheets consisting of one or a few atomic layers by chemical vapor deposition (CVD) [ 2–4 ] or solution processing [ 5 , 6 ] and can be transferred to various substrates. The two-dimensionality and structural fl atness make graphene sheets ideal candidates for thin-fi lm devices and combination with other semiconductor materials such as silicon. These fi lms typically show sheet resistances on the order of several hundred ohm per square at about 80% optical transparency. [ 7 ] With modifi cation on the electronic properties and improvement of processing techniques, graphene fi lms show potential for use in conductive, fl exible electrodes, as an alternative for indium tin oxide (ITO). Graphene applications are just starting, and current investigations are on a number of areas such as fi llers for composites, nanoelectronics, and transparent electrodes. [ 8 ] For applications related to solar cells, graphene microsheets were dispersed into conjugated polymers to improve exciton dissociation and charge transport. [ 9–11 ] Also, solution-processed thin fi lms were used as conductive and transparent electrodes for organic [ 12 ] and dyesensitized [ 13 ] solar cells, although the cell effi ciency is still lower than those with ITO and fl uorine tin oxide (FTO) electrodes. Compared with carbon nanotube fi lms that have been extensively studied, graphene fi lms may have several advantages. A continuous single-layer graphene fi lm could retain high conductivity at very low (atomic) thickness, and avoid contact resistance that occurs in a carbon nanotube fi lm between interconnected nanotube bundles. In addition, graphene fi lms have minimum porosity and, in small areas, can provide an extremely fl at surface for molecule assembly and device integration. There are many opportunities in utilizing distinct properties of graphene and exploring novel applications. Bulk heterojunction structures based on carbon materials have attracted a great deal of interest for both scientifi c fundamentals and potential applications in various new optoelectronic devices,

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H2O2, KMnO4, and HNO3. Their physicochemical properties were investigated by BET N-2 adsorption, laser particle examination, Boehms titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g(-1), while it reaches 2.6, 5.1 and 11.0 mg g(-1) for the H2O2, HNO3 and KMnO4 oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg 1(-1). Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO3 and KMnO4 oxidized CNTs is more obvious than that of the as-grown and H2O2 oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO4 oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H2O2 and HNO3 oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO4 oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent

COMPETITIVE ADSORPTION OF PB2+, CU2+ AND CD2+ IONS FROM AQUEOUS SOLUTIONS BY MULTIWALLED CARBON NANOTUBES

Abstract The individual and competitive adsorption capacities of Pb 2+ , Cu 2+ and Cd 2+ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb 2+ , 24.49 mg/g for Cu 2+ and 10.86 mg/g for Cd 2+ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb 2+ >Cu 2+ >Cd 2+ . The Langmuir adsorption model can represent experimental data of Pb 2+ and Cu 2+ well, but does not provide a good fit for Cd 2+ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb 2+ , Cu 2+ and Cd 2+ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.

Study on poly(methyl methacrylate)/carbon nanotube composites

Carbon nanotubes (CNTs) can be used to compound poly (methyl methacrylate)/carbon nanotube (PMMA/CNT) composites by an in situ process. The experimental results show that CNTs can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNTs and the PMMA matrix. Through the use of an improved in situ process, the mechanical properties and the heat deflection temperatures of composites rise with the increase of CNTs. The dispersion ratio of CNTs in the PMMA matrix is proportional to the reaction time of polymerizing MMA before CNTs are added into the PMMA mixture.

Lead adsorption on carbon nanotubes

Carbon nanotubes (CTNs) show exceptional adsorption capability and high adsorption efficiency for lead removal from water. The adsorption is significantly influenced by the pH value of the solution and the nanotube surface status, which can be controlled by their treatment processing. The adsorption isotherms are well described by both Langmuir and Freundlich models, Our results suggest that CNTs can be good Pb2+ adsorbers and have great potential applications in environmental protection

Adsorption of fluoride from water by amorphous alumina supported on carbon nanotubes

A new candidate for fluoride adsorption from water, amorphous Al2O3 supported on carbon nanotubes (Al2O3/CNTs), is reported in this Letter. The adsorption isotherms show that the best fluoride adsorption of Al2O3/CNTs occurs at a pH range of 5.0-9.0. The adsorption capacity for Al2O3/CNTs is about 13.5 times higher than that of AC-300 carbon, 4 times higher than that of gamma-Al2O3 at equilibrium fluoride concentration of 12 mg/l. The broad range of the pH values and high adsorption capacity of Al2O3/CNTs make it very suitable for potential applications in fluoride removal from water

Selective Ion Penetration of Graphene Oxide Membranes

The selective ion penetration and water purification properties of freestanding graphene oxide (GO) membranes are demonstrated. Sodium salts permeated through GO membranes quickly, whereas heavy-metal salts infiltrated much more slowly. Interestingly, copper salts were entirely blocked by GO membranes, and organic contaminants also did not infiltrate. The mechanism of the selective ion-penetration properties of the GO membranes is discussed. The nanocapillaries formed within the membranes were responsible for the permeation of metal ions, whereas the coordination between heavy-metal ions with the GO membranes restricted the passage of the ions. Finally, the penetration processes of hybrid aqueous solutions were investigated; the results revealed that sodium salts can be separated effectively from copper salts and organic contaminants. The presented results demonstrate the potential applications of GO in areas such as barrier separation and water purification.

Adsorption of fluoride from water by aligned carbon nanotubes

Aligned carbon nanotubes (ACNTs), a new type of carbon material, were prepared by catalytic decomposition of xylene using ferrocene as catalyst. The kinetics experiment of ACNTs shows that fluoride adsorption rate is fast in the first 60 min and the adsorption capacity reaches 3.0 mg/g rapidly, then it decreases and adsorption achieves equilibrium gradually in about 180 min. The fluoride adsorption of ACNTs depends slightly on the solution pH value. The highest adsorption capacity of ACNTs occurs at pH 7 and reaches 4.5 mg/g at equilibrium fluoride concentration of 15 mg/l. The experimental results indicate that ACNTs are promising candidate materials for fluoride removal

Stretchable and highly sensitive graphene-on-polymer strain sensors

The use of nanomaterials for strain sensors has attracted attention due to their unique electromechanical properties. However, nanomaterials have yet to overcome many technological obstacles and thus are not yet the preferred material for strain sensors. In this work, we investigated graphene woven fabrics (GWFs) for strain sensing. Different than graphene films, GWFs undergo significant changes in their polycrystalline structures along with high-density crack formation and propagation mechanically deformed. The electrical resistance of GWFs increases exponentially with tensile strain with gauge factors of ~103 under 2~6% strains and ~106 under higher strains that are the highest thus far reported, due to its woven mesh configuration and fracture behavior, making it an ideal structure for sensing tensile deformation by changes in strain. The main mechanism is investigated, resulting in a theoretical model that predicts very well the observed behavior.