Arsenic removal from water/wastewater using adsorbents—A critical review

Some aspects of the surface chemistry of carbon blacks and other carbons

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is pro- posed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver im- mediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (<10-20% after 5-10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350-500 ◦ C common for pyrolysis). Existing slash-and- burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr −1 . Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5-9.5 Pg C yr −1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr −1 ). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.

/pdf/bio-char-sequestration-in-terrestrial-ecosystems-a-review-11nd7n5wu0.pdf

Bio-char sequestration in terrestrial ecosystems - a review

Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.

Carbon Materials for Chemical Capacitive Energy Storage

2010 WILEY-VCH Verlag Gm Graphene-based materials are promising building blocks for future nanodevices owing to their superior electronic, thermal, and mechanical properties as well as their chemical stability. However, currently available graphene-based materials produced by typical physical and chemical routes, including micromechanical cleavage, reduction of exfoliated graphene oxide (GO), and solvothermal synthesis, are generally micrometer-sized graphene sheets (GSs), which limits their direct application in nanodevices. In this context, it has become urgent to develop effective routes for cutting large GSs into nanometer-sized pieces with a well-confined shape, such as graphene nanoribbons (GNRs) and graphene quantum dots (GQDs). Theoretical and experimental studies have shown that narrow GNRs (width less than ca. 10 nm) exhibit substantial quantum confinement and edge effects that render GNRs semiconducting. By comparison, GQDs possess strong quantum confinement and edge effects when their sizes are down to 100 nm. If their sizes are reduced to ca. 10 nm, comparable with the widths of semiconducting GNRs, the two effects will become more pronounced and, hence, induce new physical properties. Up to now, nearly all experimental work on GNRs and GQDs has focused on their electron transportation properties. Little work has been done on the optical properties that are directly associated with the quantum confinement and/or edge effects. Most GNRand GQD-based electronic devices have been fabricated by lithography techniques, which can realize widths and diameters down to ca. 20 nm. This physical approach, however, is limited by the need for expensive equipment and especially by difficulties in obtaining smooth edges. Alternative chemical routes can overcome these drawbacks. Moreover, surface functionalization can be realized easily. Li et al. first reported a chemical route to functionalized and ultrasmooth GNRs with widths ranging from 50 nm to sub-10 nm. Very recently, Kosynkin et al. reported a simple solution-based oxidative process for producing GNRs by lengthwise cutting and unraveling of multiwalled carbon nanotube (CNT) side walls. Yet, no chemical routes have been reported so far for preparing functionalized GQDs with sub-10 nm sizes. Here, we report on a novel and simple hydrothermal approach for the cutting of GSs into surface-functionalized GQDs (ca. 9.6-nm average diameter). The functionalized GQDs were found to exhibit bright blue photoluminescence (PL), which has never been observed in GSs and GNRs owing to their large lateral sizes. The blue luminescence and new UV–vis absorption bands are directly induced by the large edge effect shown in the ultrafine GQDs. The starting material was micrometer-sized rippled GSs obtained by thermal reduction of GO sheets. Figure 1a shows a typical transmission electron microscopy (TEM) image of the pristine GSs. Their (002) interlayer spacing is 3.64 A (Fig. 1c), larger than that of bulk graphite (3.34 A). Before the hydrothermal treatment, the GSs were oxidized in concentrated H2SO4 and HNO3. After the oxidization treatment the GSs became slightly smaller (50 nm–2mm) and the (002) spacing slightly increased to 3.85 A (Fig. 1c). During the oxidation, oxygen-containing functional groups, including C1⁄4O/COOH, OH, and C O C, were introduced at the edge and on the basal plane, as shown in the Fourier transform infrared (FTIR) spectrum (Fig. 1d). The presence of these groups makes the GSs soluble in water. A series of more marked changes took place after the hydrothermal treatment of the oxidized GSs at 200 8C. First, the (002) spacing was reduced to 3.43 A (Fig. 1c), very close to that of bulk graphite, indicating that deoxidization occurs during the hydrothermal process. The deoxidization is further confirmed by the changes in the FTIR and C 1s X-ray photoelectron spectroscopy (XPS) spectra. After the hydrothermal treatment, the strongest vibrational absorption band of C1⁄4O/COOH at 1720 cm 1 became very weak and the vibration band of epoxy groups at 1052 cm 1 disappeared (Fig. 1d). In the XPS C 1s spectra of the oxidized and hydrothermally reduced GSs (Fig. 2a), the signal at 289 eV assigned to carboxyl groups became weak after the hydrothermal treatment, whereas the sp carbon peak at 284.4 eV was almost unchanged. Figure 2b shows the Raman spectrum of the reduced GSs. A G band at 1590 cm 1 and a D band at 1325 cm 1 were observed with a large intensity ratio ID/IG of 1.26. Second, the size of the GSs decreased dramatically and ultrafine GQDswere isolated by a dialysis process. Figure 3 shows typical TEM and atomic force microscopy (AFM) images of the GQDs. Their diameters are mainly distributed in the range of 5–13 nm (9.6 nm average diameter). Their topographic heights are mostly between 1 and 2 nm, similar to those observed in functionalized GNRs with 1–3 layers. More than 85% of the GQDs consist of 1–3 layers.

Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots

Heretofore disconnected experimental observations are combined with a theoretical study to develop a model of the chemical composition of the edges of graphene sheets in both flat and curved sp2-hybridized carbon materials. It is proposed that under ambient conditions a significant fraction of the oxygen-free edge sites are neither H-terminated nor unadulterated σ free radicals, as universally assumed. The zigzag sites are carbene-like, with the triplet ground state being most common. The armchair sites are carbyne-like, with the singlet ground state being most common. This proposal is not only consistent with the key electronic properties and surface (re)activity behavior of carbons, but it can also explain the recently documented and heretofore puzzling ferromagnetic properties of some impurity-free carbon materials.

On the chemical nature of graphene edges: origin of stability and potential for magnetism in carbon materials.

Evidence for the protonation of basal plane sites on carbon

Carbon materials as adsorbents in aqueous solutions

Importance of carbon active sites in the gasification of coal chars

An experimental and theoretical study of the adsorption of aromatics possessing electron-withdrawing and electron-donating functional groups by chemically modified activated carbons

Ljubisa R. Radovic

Papers

On the chemical nature of graphene edges: origin of stability and potential for magnetism in carbon materials.

Evidence for the protonation of basal plane sites on carbon

Carbon materials as adsorbents in aqueous solutions

Importance of carbon active sites in the gasification of coal chars

An experimental and theoretical study of the adsorption of aromatics possessing electron-withdrawing and electron-donating functional groups by chemically modified activated carbons