Controlling graphene conductivity is crucial for its potential applications. With this focus, this paper shows the effect of the non-covalent bonding of a pyrimidine derivative (HIS) on the ...electronic properties of graphene (G). Several G-HIS hybrids are prepared through mild treatments keeping unaltered the structures of both G and HIS. The attachment of HIS to G occurs by π–π stacking of the HIS-aromatic residue with the G surface. This partially blocks the p z electrons of G, giving rise to the splitting of both the valence and conduction bands. Moreover, the width of the splitting is directly related to the HIS content. This fact allows the fine-tuning of the band gap of G-HIS hybrids. Furthermore, HIS keeps its metal-complexing ability in the G-HIS hybrids. Taking advantage of this, a G-HIS–Cu(0) composite was prepared by H2 plasma reduction of a precursor of the G-HIS–Cu(II) type. G-HIS−Cu(0) contains Cu(0) clusters stabilized on the G surface due to interactions with the COO– functions of HIS. In an analogous hybrid, G-HIS–Au(0), the Au(0) NPs are also stabilized by COO– functions. This material, consisting of the coupling of Au(0) NPs and G-HIS, photocatalyzed water reduction under visible light radiation producing 12.5 μmol·g–1·h–1of hydrogen.
DNA molecules containing a 1D silver array may be applied for nanotechnology applications, but first their conducting and photoluminescence behavior must be enhanced. Here we have synthesized and ...characterized three new helical compounds based on stacked silver-mediated cytosine base pairs Ag(mC)
X (mC = N1-methylcytosine; X = NO
(
), BF
(
) and ClO
(
)), that contain uninterrupted polymeric Ag
chains that run through the center of the helixes, comparable to related silver-DNA structures. The exposure of nanostructures of Ag(mC)
BF
(
) to cold hydrogen plasma stimulates the reduction of the prearranged Ag
polymeric chains to metallic silver along the material. This solvent-free reduction strategy leads to the compound Ag
(mC)
X@Ag
(
) that contains uniformly well-distributed silver metallic nanostructures that are responsible for the new conducting and photoluminescence properties of the material. The presence of silver nanostructures alongside compound
has been evaluated by means of X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and X-ray powder diffraction (XRPD). The conducting and photoactive properties of
were studied by electrostatic force microscopy (EFM) and conducting-AFM (c-AFM), and photoluminescence microscopy (PL), respectively. The results demonstrate that the presence of well-organized metallic silver nanoentities on the material is responsible for the novel conductivity and photoactive properties of the material. This methodology can be employed for the generation of multifunctional silver-DNA related materials with tailored properties.
This paper reports a new method to obtain ultra-small Pd and Pt nanoparticles (0.5-1 nm) supported on multi-walled carbon nanotubes (MWCNTs). Even at high loadings of both metals (22.3 and 31.5% ...(wt/wt) of Pd
2+
and Pt
2+
, respectively), very narrow and unimodal particle size distributions are achieved. The complexing capabilities of polyethyleneimine covalently attached to the surface of the tubes are optimal for the retention of Pd
2+
and Pt
2+
from solution. We have addressed the reduction of the retained ions by two approaches: a classical treatment with NaBH
4
in aqueous solution, and a novel method using hydrogen cold plasma to preserve the structural features of the material. Cold plasma produced degrees of reduction similar or even larger than NaBH
4
, supporting the advantage of hydrogen cold plasma as reducing agent as it is a simple, clean and fast (15 minutes) procedure. XPS analysis of the reduced materials show an increase in the electron density near the Fermi level. Pt/MWCNT materials have been tested as anode for methanol electrooxidation, showing a catalytic profile typical of that observed for platinum nanoparticles. The stability after 1000 cycles of the plasma-reduced materials is much larger than these reported for Pt/carbon materials, indicating the stability of the ultra-small nanoparticles.
This paper reports a new method to obtain ultra-small Pd and Pt nanoparticles (0.5-1 nm) supported on multi-walled carbon nanotubes (MWCNTs).
Controlling the chemistry on the surface of new carbon materials is a key factor to widen the range of their applicability. In this paper we show a grafting methodology of polyalkylamines to the ...surface of carbon nanomaterials, in particular, carbon nanotubes and a carbon black. The aim of this work is to reach large degrees of covalent functionalization with hyperbranched polyethyleneimines (HBPEIs) and to efficiently preserve the strong chelating properties of the HBPEIs when they are fixed to the surface of these carbon materials. This functionalization opens new possibilities of using these carbon nanotubes-based hybrids. The results show that the HBPEIs are covalently attached to the carbon materials, forming hybrids. These hybrids emerge from the reaction of amine functions of the HBPEIs with carbonyls and carboxylic anhydrides of the carbon surface which become imine and imide bonds. Thus, due to the nature of these bonds, the pre-oxidized samples with relevant number of C=O groups showed an increase in the degree of functionalization with the HBPEIs. Furthermore, both the acid-base properties and the coordination capacity for metal ions of the hybrids are equivalent to that of the free HBPEIs in solution. This means that the chemical characteristics of the HBPEIs have been efficiently transferred to the hybrids. To reach this conclusion we have developed a novel procedure to assess the acid-base and the coordination properties of the hybrids (solids) by means of potentiometric titration. The good agreement of the values obtained for the hybrids and for the free HBPEIs in aqueous solution supports the reliability of the procedure. Moreover, the high capacity of the hybrids to capture Ni
2+
by complexation opens new possibilities of using these hybrids to capture high-value metal ions such as Pd
2+
and Pt
2+
.
Hyperbranched polyethylenimines are covalently fixed to the surface of carbon materials, so the chemical characteristics of the amines are transferred to the hybrid materials.
The selective functionalization of carbon nanotube surfaces is crucial for many potential applications of these materials. For this purpose several oxidants, among other substances, are used. The aim ...is to reach a large degree of functionalization which depends on the oxidant character of the reagent. For this reason the functionalization of multiwall carbon nanotubes (MWCNTs) by treatment with ozone in basic solution is studied. At basic pHs, ozone results into hydroxyl radicals whose reduction potential is very high (E° = 3.06 V). The results have been compared to those obtained by ozone in gas phase and with cold oxygen plasma. The oxidation with ozone in basic solution seems to be kinetically restricted. As a consequence, the degree of oxidation in this medium is smaller than this of ozone gas, in spite of the larger oxidation capacity of the former. The oxygen-containing groups fixed by these two treatments are mainly attached to defects of the nanotubes. Moreover, no modification of the graphene layers and no porosity result from these treatments. The oxygen plasma treatment stands out in the content of oxygen groups fixed to the MWCNTs, as it is by far more effective, although some of these groups have relatively low thermal stability. Nevertheless, this treatment mainly fixes the oxygen groups on the walls of the nanotubes.
The covalent bromination of multi-walled carbon nanotubes by the reaction with a solution of IBr in CCl4 at mild temperatures and by CH3Br cold plasma is reported. The samples have been analyzed by ...X-ray photoelectron spectroscopy, thermal programmed desorption, thermogravimetry, Raman spectroscopy, X-ray diffraction and nitrogen adsorption. Both treatments preserve the structure of the nanotubes. The degree of bromination reached by the simple reaction of the first method rises up to 3.5at.%. An important advantage of this procedure is that the oxygen content of the nanotubes does not increase with respect to the raw material (an unresolved problem of previously reported methods), and that 96% of the bromine is covalently bound. The bromination reached by the second procedure is even larger so that 4.9at.% is achieved in only 10min. Moreover, 99% of this bromine is covalently bound to the nanotubes. It is shown that, without a doubt, the bromine is covalently bound, that it appears in three chemical environments and that the thermal stability of bromine containing groups depends on the treatment. An important consequence of the bromination is that the brominated nanotubes have a valence band distinctive of semiconductors.
The continuous and dramatic increase of global demand for energy resources makes it urgent to develop affordable nanostructured materials to act as efficient electrocatalysts (ECs) in the ...energy-related reactions. Metal–organic framework (MOF) template pyrolysis for the production of nanostructured carbon-based materials is a very promising methodology to produce carbon-based ECs. Herein, we report the preparation, characterization (XPS, CHNS analysis, ICP-OES, XRD, TEM, and SEM/EDS), and application as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) ECs of a plethora of nanostructured carbon materials derived from RT-synthesized (RT, room temperature) MOF-74 with different metal compositions, Co, Ni and Co/Ni, and dopant heteroatoms, N–, S– and N/S-dual-doping. This has allowed the study of the aforementioned parameters’ influence on the OER and ORR electrocatalytic activity in alkaline medium. Highly synergetic effects have been detected in two cases: (1) when N/S-dual-doped carbon is produced from a monometallic Co-MOF-74 template, N,S–Co@C, and (2) when an undoped carbon is derived from bimetallic Co/Ni-MOF-74, Co/Ni@C. These two samples achieve OER performances with η10 = 0.41 and 0.44 V, respectively, along with Tafel slopes of 101 and 93 mV dec–1, being close to the state-of-art OER catalyst performance. In addition, ORR tests showed that the effect of heteroatom doping on ORR activity is always positive, regardless of metal composition.
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•H2 plasma removes oxygen groups but not the sulfonyl and sulfonic groups.•Water treatment + H2 plasma treatment removes 60% of oxygen and 100% of sulfur.•This methodology removes as ...much oxygen as NaBH4 but is simpler, faster and cleaner.•The oxygen remaining after H2 plasma reduction forms labile surface groups.•Three GOs were tested rendering similar results.
We report the reduction of GO by hydrogen cold plasma as an effective alternative to the usual chemical (with harsh reducing agents) or physical (through high-temperature treatments) methods. The hydrogen plasma is generated through microwave radiation and the reduction is performed barely above room temperature, avoiding structural degradation of the graphene oxide. Three commercial GOs, with several oxygen and sulfur contents, have been used in this study. As a consequence of the exposure to the hydrogen plasma, the oxygen content is decreased in large extent while sulfur is scarcely removed. Thus a two-stage methodology consisting of a simple water treatment under reflux conditions of GO (to remove sulfur) and further treatment with H2 plasma is proposed. The combination of both steps allows the total elimination of sulfur while achieving very high degrees of reduction, lowering the initial oxygen content by more than 60%. These degrees of reduction are comparable to those obtained when the reduction is carried out by using the standard procedure with NaBH4 on the same materials. The reduction with hydrogen plasma clearly shows advantages over the conventional reduction procedures due to its simplicity: no chemicals or high temperatures are needed, and the procedure is very fast.
This article reports a new way to covalently bond chlorine to multiwalled carbon nanotubes (MWCNTs) by using a carbon tetrachloride cold plasma treatment. Several factors controlling the efficiency ...of the plasma treatment were considered. In particular, the methodology to produce the plasma and the temperature and time of treatment were taken into account. The largest chlorine surface concentration was obtained when the MWCNTs were treated with helium plasma before the CCl4 plasma to activate the surface. Short periods of plasma treatment (5–10 min) were then sufficient to reach high degrees of chlorination (up to 19.2% by weight) much larger than those previously reported. The functionalization takes place mainly in the borders and defects of the tubes, thus preserving the conjugation existing in the graphene layers. Moreover, the treatments show no influence on the textural characteristics of the nanotubes (i.e., porosity and interlayer spacing). Therefore, the method proposed in this work is an excellent approach to introducing surface chlorine atoms, capable of acting as leaving groups, as a first step for further functionalization with more complex molecules, while preserving the morphology and mechanical properties of the nanotubes still intact.
DNA molecules containing a 1D silver array may be applied for nanotechnology applications, but first their conducting and photoluminescence behavior must be enhanced. Here we have synthesized and ...characterized three new helical compounds based on stacked silver–mediated cytosine base pairs Ag(mC)2X (mC = N1-methylcytosine; X = NO3 (1), BF4 (2) and ClO4 (3)), that contain uninterrupted polymeric AgI chains that run through the center of the helixes, comparable to related silver-DNA structures. The exposure of nanostructures of Ag(mC)2BF4 (2) to cold hydrogen plasma stimulates the reduction of the prearranged AgI polymeric chains to metallic silver along the material. This solvent-free reduction strategy leads to the compound AgI(mC)2X@Ag0 (2H) that contains uniformly well-distributed silver metallic nanostructures that are responsible for the new conducting and photoluminescence properties of the material. The presence of silver nanostructures alongside compound 2H has been evaluated by means of X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and X-ray powder diffraction (XRPD). The conducting and photoactive properties of 2H were studied by electrostatic force microscopy (EFM) and conducting-AFM (c-AFM), and photoluminescence microscopy (PL), respectively. The results demonstrate that the presence of well-organized metallic silver nanoentities on the material is responsible for the novel conductivity and photoactive properties of the material. This methodology can be employed for the generation of multifunctional silver-DNA related materials with tailored properties.
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