Crystalline Graphite Research Articles

Electron Cloud Densitometry of Inner and Valence Electrons in Carbon Allotropes

Electron cloud densitometry of carbon allotropes is presented in this study. Carbon consists of two inner and four valence electrons. The valence electrons in carbon are hybridized or active. Each active valence electron builds a negatively charged shape due to their delocalization. It is proved that the active valence electron creates the van der Waals force, which bonds layers of crystalline graphite together. An easy quantum mechanical explanation of the electron cloud densitometry is given in this study. In accordance with this effect, an atom begins to illuminate, depicting its shape. Electron cloud densitometry images show the inner and valence electrons in the applied functional materials, such as activated coke, graphite, graphene, and diamond.

A modified spin-casting approach for scalable preparation of ultra-thick reduced graphene oxide films with high thermal conductivity

With the fast development of high-power electronic devices in recent years, the demand for high-performance thermal dissipation films with high thermal conductivity and large thickness has dramatically increased. Graphene has shown great potential in thermal management due to its extremely high thermal conductivity. However, it remains a significant challenge to achieve high thermal conductivity in thick graphene films (≥100 μm). Herein, a scalable strategy combining a modified layer-by-layer ‘spin-casting’ solution deposition method and multi-step annealing post treatment was adopted for preparing ultra-thick, highly thermal conductive graphene films. The properties of the graphene films were characterized by SEM, XRD, Raman, and XPS, exhibiting excellent graphitic crystallinity, well aligned and dense packing assembly structure. These nearly ideal structural features endow the graphene films with high in-plane thermal conductivity of 1265 ± 46 W m−1 K−1 at a large thickness of 100 μm. The ultra-thick graphene films show superior thermal dissipation performance as compared with traditional Cu/Al foil, demonstrating their great potential in the field of highly-efficient heat spreader films for the next generation of high-power devices.

Tribological Characterization of TiAlC Nanostructured Coatings Deposited by DC Pulse Magnetron Sputtering

Abstract To reveal the effect of carbon content on tribological performance of coatings, TiAlC films having four different amounts of carbon content were synthesized using DC pulse magnetron sputtering. The amount of carbon was varied by using different graphite target powers of 400, 450, 500, and 550 W while keeping the TiAl target power fixed at 80 W. Sliding friction and wear behavior of TiAlC nanostructured coatings deposited on Si (100) substrates by (DC) pulse magnetron sputtering was examined against steel ball using a ball on disk configuration’ at a load of 1 N and sliding speed of 7 mm/s. The coating deposited at 500 W graphite target power attained a hardness of 20.24 GPa and elastic modulus of 246 GPa. Tribological test results indicate that the coating deposited at (500 W, 25 at% C) has the lowest coefficient of friction (COF) of 0.29 as well as the wear-rate of 6.52 × 10−13 (mm3/Nm). The observed behavior has been attributed to the increase in crystalline nano graphite phase, increase in compactness of coating, and the formation of compact oxide layer. The nano indentation statistics showed that resistance to plastic deformation (H3/E*2) and elastic strain to failure (H/E*) increased with the increasing target power and reached the highest value at (500 W, 25 at%C) in TiAlC films.

Re-Os systematics and chronology of graphite

Natural graphite forms in a range of metamorphic and hydrothermal environments across timelines spanning from the birth of the solar system, to the evolution of early Precambrian life, and the development of contemporary geotectonic cycles. A precise timeline of these and other graphite-forming events, however, has hitherto been obscured by a lack of radiometric ages and as such, chronologies are inferred from host-rock or hydrothermal mineral ages. Herein we examine the Re-Os systematics and chronology of graphite formed in a suite of terrestrial and extraterrestrial environments (n = 17) with the principal aim of establishing the viability of Re-Os geochronology of natural graphite.Graphite Re and Os contents and isotopic ratios exhibit a wide range of values that extend up to 1520 ppb Re, 19,577 ppt Os, and 4101 and 42.18 for 187Re/188Os and 187Os/188Os ratios, respectively. These values are broadly comparable to those reported for crustal sulfides, organic-rich sedimentary rocks, and hydrocarbons. X-ray diffraction crystallinity data reveals that graphite Re abundances show a broadly inverse correlation with graphite formation temperature and crystallinity (d002 and Lc(002)) with interplanar spacing (d002) having the strongest anti-correlation with graphite Re contents.Graphite Re-Os geochronology is demonstrated with two independent case studies (Wollaston-Mudjatik Transition shear zones, Saskatchewan, Canada and Merelani Hills, Tanzania) yielding precise (<1%) Re-Os isochron dates of 1731.52 ± 7.43 Ma (2σ; MSWD = 1.3) and 586.89 ± 2.39 Ma (2σ; MSWD = 1.2) that are consistent, within uncertainty, to their mineralization ages constrained by other radiometric methods. These data confirm that graphite mineralization was synchronous with Trans-Hudsonian exhumation and tsavorite-tanzanite gemstone mineralization, respectively. Method accuracy, however, appears contingent on the analytical protocols used to isolate graphite, e.g. handpicking vs. heavy liquids (SPT) and water, with the latter perturbing graphite Re-Os systematics by as much as 20%. We, therefore, recommend handpicking paired with magnetic separation and grain mount examination.Our Re-Os age results are then coupled with new SIMS carbon isotope data (Wollaston-Mudjatik Transition graphite: δ13C = −21.64 to −15.28‰; Merelani Hills graphite: δ13C = −25.90 to −24.36‰) and 187Os/188Osi isotope data (Wollaston-Mudjatik Transition graphite = 0.3119 ± 0.0037; Merelani Hills graphite = 1.680 ± 0.038) to constrain graphitic carbon to sedimentary carbonate/organic (Wollaston-Mudjatik Transition graphite) and organic (Merelani Hills graphite) carbon sources. This unique pairing of isotope systems in graphite provides the first detailed chronology of localized carbon mobility in the Earth’s crust.Re-Os graphite geochronology likely has wide applications in ore-deposit and metamorphic geology with the potential to reshape our understanding of carbon cycling in the crust-mantle system, and for graphite exploration initiatives that are critical for a global transition to a green economy.

A process for developing spherical graphite from coal tar as high performing carbon anode for Li-ion batteries

A new cost-effective method is developed to synthesize crystalline spherical graphite known as mesocarbon microbeads (MCMB) by the heat treatment of coal tar without the need of catalysts or additives and tested for its performance as anode material in Lithium-ion batteries (LIB). Two types of MCMB samples with varying morphological properties were prepared by the heat treatment of coal tar. The resulting MCMB samples were graphitized at 2350οC and were tested for their electrochemical performance as an anode for LIBs. Both MCMB electrodes show high specific capacity and good cycling stability for over 60 cycles and high-rate capability. The porous nature of MCMB with spherical morphology provides large surface area and electrolyte percolation while the high conductivity originating from highly graphitized structure could facilitate good electron transport throughout the MCMB surface. Therefore, MCMB synthesized by this additive free synthesis approach can be used for the cost-effective development of high-performing MCMB based electrode for LIBs.

Differences in the structure and functionalities of graphene oxide and reduced graphene oxide obtained from graphite with various degrees of graphitization

Reduced graphene oxide (rGrO) is a promising graphene derivative that attracts attention due to its unique properties. The well-established route to obtain rGrO is a reduction of graphene oxide (GrO) produced by graphite oxidation. In this paper, we demonstrate the correlation between the structure of pristine graphite and the structural and catalytic properties of synthesized GrO and rGrO. We use TEM, SEM, DLS, XRD, FTIR, Raman, XPS, and nitrogen adsorption-desorption to characterize various pristine graphites and synthesized GrOs and rGrOs. These studies show that the formation of different nitrogen-containing groups in rGrO is associated with the treatment of GrO with hydrazine. Catalytic properties of pristine graphites and rGrOs were determined in the hydrogenation of the p-nitrotoluene by molecular hydrogen. Results of this work can provide a new idea that the crystallinity of graphite, quantified by a degree of graphitization, serves as the clue parameter influencing the structure, surface functionality, and catalytic properties of rGrO. We hope that this article will contribute a new insight for the synthesis of rGrO with pronounced properties not only for catalytic applications but also for energy storage due to the possibility of governing rGrO properties by a selection of more suitable pristine graphite.

Effect of boron content on the microstructure and electromagnetic properties of SiBCN ceramics

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was −35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached −29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.

Exploring the Limits of the Rapid-Charging Performance of Graphite as the Anode in Lithium-Ion Batteries

Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ∼2 C (∼740 mA g−1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4–20 C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8 C, even with a standard electrolyte and NMC811 cathode and in cells with 1.0 mAh cm−2 loadings. As a rule, capacity and specific energy are inversely proportional to crystallite size at high rates; performance can likely be improved by electrolyte/cathode tuning.

Activated carbon from almond shells using an eco-compatible method: screening, optimization, characterization, and adsorption performance testing.

Activated carbon as a low-cost adsorbent prepared from almond shells using H3PO4 as a chemical activator and room vacuum pyrolysis as a physical activator, which is considered to be an eco-compatible preparation process. Experimental design methodology was used to study and optimize the effects of eight preparation parameters on I2 adsorption expressed by the iodine index (mg g-1). It was found that optimum activated carbon was obtained by chemical activation with H3PO4 at first, followed by physical treatment at 420 °C under a vacuum pressure of -0.8 bar. The obtained activated carbon was characterized by a thermogravimetric analyzer, scanning electron microscopy coupled to EDX, X-ray diffraction, and Fourier transform infrared absorption spectroscopy. The zero-charge pH and the characteristics of surface chemistry by Boehm titration were determined to predict the acid-base properties of the prepared material. An adsorption efficiency study of crystal violet dye on the optimally produced activated carbon was carried out. The obtained results of physicochemical characterization showed interesting properties of our activated carbon in comparison with those produced by other methods. Among these properties, an important porous surface, high thermal stability, and a disorganized graphitic crystalline structure were revealed. In addition to the carbon and oxygen elements, EDX analysis revealed the presence of phosphorus element, and the FTIR analysis indicated the existence of phosphonate groups and an acidic character, which resulted from chemical activation by H3PO4. An iodine index of 824.85 mg g-1 was achieved for optimal preparation. Crystal violet adsorption studies show a pseudo-first-order kinetic process and fit well with the Freundlich isotherm model, and thus, the predicted adsorption capacity was 364.27 mg g-1.

Metamorphic evolution of graphite in the Paleoproterozoic Savo Schist Belt (SSB), Central Finland: Constraints from geothermetric modeling

Flake graphite deposits of the Savo Schist Belt (SSB), Central Finland are mainly hosted by quartz-mica schist, hornblende biotite gneiss, and to a minor extent in amphibolite. These rocks represent high-grade metamorphic conditions of the SSB. Raman spectroscopy measurements on graphite flakes provide quantitative information on the degree of graphitization, which can be correlated to the grade of metamorphism. The metamorphic conditions of the graphite-bearing metapelites have been determined by P-T pseudosection modelling and three types of geothermometers: garnet-biotite (GB), Ti-in biotite and Raman spectroscopy of carbonaceous material (RSCM) geothermometry. The calculated P-T pseudosections indicate peak P-T conditions of ca. 5–6 kbar and 650 °C for two garnet-bearing hornblende biotite gneiss samples, and slightly higher conditions of ca. 5–6 kbar and 700 °C for a quartz mica schist sample. The GB thermobarometer yielded a temperature and pressure range of 600–725 °C and 5.2–8.0 kbar. The Ti-in-biotite applied to the same samples produced temperature ranging between 570 and 735 °C, and the Raman (RSCM) geothermometers indicated temperatures between 550 and 670 °C. For the garnet-bearing hornblende biotite gneiss samples there is no significant (<10–50 °C) difference between temperatures determined using the P-T pseudosections and mean temperatures calculated using RSCM, GB and Ti-in-biotite methods. Although the peak temperature in some highly crystalline graphite flakes of studied samples calculated by (RSCM) geothermometer yield temperatures of 641 °C with the Beyssac et al. 2002 method and 737 °C with the Rahl et al. (2005) method, which are the highest temperature for this calibration. Raman spectroscopy is now part of a wide selection of tools that can be used to identify the ordering of the graphite crystallinity, which is including the number of layers, quality of layers, doping level and confinement in graphene structures. The results of this work show that Raman spectroscopy is a simple and fast way to determine the peak metamorphic temperature of carbonaceous material CM in amphibolite facies metasedimentary rocks.

Influence of structure and composition of diamond-like nanocomposite coatings on cell viability

This paper investigates the influence of the structure and properties of diamondlike nanocomposite (DLN or a-C:H:SiOx) coatings synthesized by plasma-assisted chemical vapor deposition on cell viability and coating biocompatibility. The structure and properties of the DLN coatings are changed by the negative pulse amplitude of the bipolar bias voltage of the substrate. The structure of the obtained DLN coatings is studied by Fourier-transform infrared spectroscopy and Raman spectroscopy. Atomic force microscopy provides angstrom-level surface-profiling information. The microhardness testing of the DLN coatings is performed on a nanohardness indenter of a three-sided Berkovich pyramid. It is shown that the higher roughness of the substrate surface, the growth in the crystalline graphite content in the coating, and Si—C bonds improve the DLN coating biocompatibility deposited at a −500 V bias voltage and the cell viability (&amp;gt;98% of HeLa cells), resulting in a lower cell death (1–2%). It is demonstrated that DLN coatings can be applied in biomedicine.

2D material has record-breaking thermal properties

A material made by stacking 2D sheets of molybdenum disulfide is a strong thermal conductor in two dimensions but blocks heat transfer from layer to layer. The material conducts heat 900 times as well in-plane as it does perpendicularly ( Nature 2021, DOI: 10.1038/s41586-021-03867-8 ). This is threefold higher than the previous record holder, single crystalline graphite. Materials engineered to carefully control the flow of heat could prevent computer chips from overheating and keep electronic devices cool to the touch. But when using conventional materials, making heat move only in a particular direction is challenging, says Jiwoong Park , a materials chemist at the University of Chicago. Park and his collaborators, David Cahill at the University of Illinois and Paul Erhart of the Chalmers University of Technology, were curious about how well sheets of randomly stacked, atomically thin crystals would do. Other researchers have tried to create such directional insulation

Hyphenated SEM-Raman Characterization for Matrix Graphite of HTGR Spherical Fuels

Matrix graphite (MG) is an important material for the spherical fuel elements of high temperature gas-cooled reactors (HTGR). After carbonization, the matrix material is composed of three isomers of natural graphite, artificial graphite, and carbon derived from phenolic resin (resin carbon) with the same element but different structure. According to previous study, the three components have different effect on the fission products diffusion and adhesion in the irradiated fuel. However, the characterizing methods to discriminate natural graphite, artificial graphite and resin carbon are rare. In this study, Raman Imaging and Scanning Electron (RISE) microscopy was used to study the structure and distribution of natural graphite, artificial graphite, resin carbon and graphite oxides produced from electrochemical deconsolidation of MG in post-irradiation examination (PIE). Natural graphite and artificial graphite have only a couple of Raman-active bands visible in the spectra between 1100-2400 cm-1, including the strong G band at ~1580 cm-1 and the weak D band at ~1350 cm-1. The D band is activated once the defects are introduced into sp2 hybridized carbon networks, and the intensity of D band is proportional to the defect concentration. Resin carbon has a strong D band, which can be easily distinguished from natural graphite and artificial graphite. The results show that the resin carbon is evenly coated on the surface of the natural and artificial graphite particles, and the network frame is formed during the pressing process to fix the graphite particles. This work also revealed that the changes of surface morphologies of MG after electrochemical deconsolidation by In-situ SEM analysis, of which a lot of cracks and holes on the surface of MG. Meanwhile, Raman spectra suggest that crystalline graphite and resin carbon have different oxidation behaviors. This work will provide a new method for MG components discriminating.

Manipulating the self-assembly behavior of graphene nanosheets via adenine-functionalized biodegradable polymers

Electrically conductive supramolecular polymer composites, based on a combination of natural graphite and the adenine-functionalized biodegradable oligomer 3A-PCL, are able to directly exfoliate crystalline graphite into highly disordered graphene nanosheets with well-tailored structural and physical properties. Herein, we discover 3A-PCL can self-assemble into well-ordered lamellar nanostructures on the surface of graphite due to the strong affinity between 3A-PCL and graphite, and thus lead to direct exfoliation of graphite into well-suspended graphene nanosheets in an organic solvent. Furthermore, after drying, the resulting graphite/3A-PCL composites exhibit stable thermoreversible phase transition behavior between viscous and elastic states, and the number of graphene layers exfoliated can be controlled by tuning the content of 3A-PCL within the composites. Importantly, these newly developed graphene composites possess a low electrical resistivity of 1.5 ± 0.7 mΩ·cm at a graphite loading of 23 wt%, which is more than an order of magnitude lower than that of pristine graphite. Given the simplicity of the production process, well-tailored physical properties and excellent conductive performance, this development offers a highly efficient process for the fabrication of multifunctional supramolecular graphene nanosheets that holds great potential for conductive device applications.

Effect of Crystallinity of Synthetic Graphite on Electrochemical Potassium Intercalation into Graphite

Effect of Crystallinity of Synthetic Graphite on Electrochemical Potassium Intercalation into Graphite

Modulating carbon growth kinetics enables electrosynthesis of graphite derived from CO2 via a liquid–solid–solid process

Highly graphitic carbon materials have gained considerable interests in practical applications, however, an efficient and cost-effective synthesis strategy using low-grade carbonaceous precursors is still in urgent need. In this work, we successfully synthesize well-crystalline graphite derived from CO2 by molten carbonate electrolysis under a mild operating temperature, where the as-formed carbon atoms follow a “dissolution–precipitation” process on a Ni cathode. Attributed to that Ni cathode can in situ act as a solid solvent for periodically accommodating/dissolving the as-formed carbon atoms, deliberately coordinating carbon formation flux with carbon dissolution flux can lead to the consecutive production of highly crystalline graphite, without contamination of transition metal catalyst. It was found that a low carbon deposition current density and a relatively high operating temperature (650–750 °C) both facilitate the growth of graphite structures, because a moderate current density enables a suitable carbon flux originating from the electro-reduction of the captured CO2 (in the form of CO32− in molten salts), which can more accessibly match the carbon dissolution flux in Ni substrate at an elevated temperature. The thickness of graphite can be easily controlled by electrolysis durations. This work provides a simple strategy to convert CO2 into graphitic carbon products with both promising purity and crystallinity.

Features of determination of native carbon in carbon-containing rocks on the analyzer of carbon and water

The largest deposits of graphite in the Russian Federation are located in the Middle and South Urals. However, several manifestations, e.g., «Opytnyi» sector, which have not yet been placed under production, require substantiation of the strategies for their integrated development, which, in turn, requires gaining the reliable data on the content of graphite in carbon-containing rocks. A method for simultaneous determination of organic and native carbon in carbon-containing rocks using an ELTRA CW MULTIPHASE carbon and water analyzer is proposed. The method is based on the combustion of organic carbon (coal, shale) in a stream of oxygen at 550°C and native carbon (graphite) in the temperature range 550 – 1000°C with subsequent IR-spectroscopic determination of the content of gaseous carbon dioxide. The interfering effect of magnesium carbonate and calcium carbonate on the determination of organic and native carbon was taken into account in the calculations. The carbonate content was determined using a separate sample in a nitrogen flow by decomposition of magnesium carbonate at 550°C and calcium carbonate within a temperature range of 550 – 1000°C. The content of chemically bound water in the composition of the minerals of carbon-containing rocks, was determined simultaneously with carbon. The only one type of carbon — graphite — was observed in the studied samples of the carbon-containing rock from «Opytnyi». The different combustion capacity of graphite was revealed: some of the crystals almost completely burn out at a temperature below 800°C and others above 800°C, which suggests the presence of cryptocrystalline and explicit crystalline graphite in the rocks. The developed method is rapid and corresponds in accuracy to the method for native carbon determination ±0.27 C % – 0.01 C % developed and approved by the Research Council for Analytical Methods of Research (NSAM).

An innovative flake graphite upgrading process based on HPGR, stirred grinding mill, and nanobubble column flotation

Physical upgrading of graphite is typically achieved with many stages of grinding and flotation to produce a concentrate with approximately 95% carbon grade. An innovative grinding and column flotation process has been developed for efficient graphite upgrading to substantially simplify the process flowsheet and reduce operating costs. In this process, a high-pressure grinding roller (HPGR) and a stirred mill were employed as primary comminution techniques and a nanobubble flotation column as a key separation process. The results obtained with a crystalline flake graphite sample with a carbon grade of 11.15% show that the novel process can produce a concentrate with 94.82% carbon grade and 97.89% recovery from an open circuit of one rougher and two cleaner flotation stages. Scanning electron microscope (SEM) microphotographs indicate that HPGR offers the advantage of more effective protection of graphite flakes during crushing. Grinding test results show that stirred mill could not only protect graphite flakes but also promote the efficient liberation of graphite. Compared with the traditional flotation process, nanobubble flotation can effectively recover ultrafine graphite. The new process possesses a number of important advantages over the traditional method, including substantially higher graphite recovery, greatly simplified process flowsheet, better protection of flake size, reduced reagent consumption and process costs, etc.

Demonstration of electronic devices in graphitic carbon nitride crystalline film

Graphitic carbon nitride (g-C3N4) exhibits semiconducting properties and is a promising candidate for use as a metal-free functional material. Electronic transport in g-C3N4 depends on the crystal orientation, resulting in the anisotropic characteristics of low out-of-plane and high in-plane resistivity. We investigated a Schottky barrier diode (SBD) and a heterojunction diode (HJD) with out-of-plane transport properties and a top-gate device with in-plane transport properties. The SBD with a Cr/Au Schottky contact exhibited rectifying behavior with a turn-on voltage of ∼1.0 V and estimated series resistance and barrier height at the interface of 1.63 kΩ and 344 meV, respectively. The HJD comprises a g-C3N4 film and an n-type hexagonal silicon carbide (4H–SiC) substrate, with a turn-on voltage of 4.0 eV. The HJD belonged to a type-II band alignment with a staggered-gap; it had a thin insulator-based van der Waals gap at the interface, thereby inducing tunneling transport. In-plane carrier transport control was carried out by the top-gate device with a Parylene-C film gate dielectric and was achieved only when the negative bias voltage was applied along the out-of-plane direction, indicating the realization of the normally off switch that utilizes the intrinsic transport characteristics and a simple device structure.

Removal of hexavalent chromium from graphene oxide supported on a cellulose acetate and polyacrylic acid membrane

This work focused on the study of the hexavalent chromium removal process from graphene oxide supported on a cross-linked cellulose acetate and polyacrylic acid polymeric membrane. The membranes were synthesized by the phase inversion method and Graphene oxide was added in proportions of 1% by weight to the polymeric material. Graphene oxide was obtained from crystalline graphite (Electron Microscope Science, No. 70230). The graphite was oxidized using the improved method of Hummers. The characterization of polymer and graphene oxide was made by Raman spectroscopy. The surface charge and point of zero charge of the materials were evaluated using a potentiometric titration method proposed by Loskutov and Kuzin. The removal of Cr (VI) was studied as a function of contact time and of initial concentration of Cr (VI). The removal of Cr (VI) (~90%) mainly occurs in a contact time from 32 to 64 h when the initial concentration of Cr (VI) is 1 mg/L.