Surface Oxygen-containing Groups Research Articles

Evaluating the effect of different modified microplastics on the availability of polycyclic aromatic hydrocarbons

Microplastics (MPs) discharged into the natural environment undergo various wearthering pathways, such as mechanical abrasion and ultraviolet (UV) irradiation. However, little is known about the effects of such aged MPs on the bioavailability of hydrophobic organic compounds (HOCs) in aqueous environments. To simulate the natural oxidation and UV-ageing process of MPs, three kinds of modified polyethylene MPs were obtained by plastic etching processes common in industry and UV irradiation, namely, etched MPs (EMPs), UV-aged MPs (UV-MPs), and etched MPs followed by UV ageing (UV-EMPs). The modified MPs showed a higher content of surface oxygen-containing groups than the pristine MPs, and the specific surface area and pore volume increased significantly after etching and ultraviolet ageing, especially for the EMPs (1.67 m2 g−1 and 0.0049 cm³ g−1) and UV-EMPs (2.37 m2 g−1 and 0.0089 cm³ g−1). The effect of modified MPs on the availability of 10 polycyclic aromatic hydrocarbons (PAHs, logKow 4.18–6.20) was evaluated by negligible-depletion solid-phase microextraction (nd-SPME). The free concentrations (Cfree) of most PAHs (except for less hydrophobic PAHs, logKow 4.18 and 4.56) decreased with an increasing concentration of MPs. The logarithms of the sorption coefficients of PAHs with various MPs (logKMPs, logKUV-MPs, logKEMPs and logKUV-EMPs) were linearly correlated with logKow, suggesting that the sorption is hydrophobicity dependent. Compared with the results for pristine MPs (logKMP 3.80–4.95), UV ageing only slightly enhanced the sorption of PAHs by MPs (logKUV-MPs 3.71–4.98), whereas the plastic etching processes significantly enhanced sorption (logKEMPs 3.85–5.18 and logKUV-EMPs 3.90–5.28). The sorption of PAHs to MPs is mainly based on partitioning; however, a mechanism of adsorption also likely takes place in EMPs and UV-EMPs due to hydrogen bonding and π-π interactions. Desorption study indicated that PAH desorption from MPs are dominated by film diffusion. However, intraparticle diffusion also takes great part for the EMPs. These results suggest that modification of MPs in the natural environment will change the availability of HOCs.

Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Spectrometric Evidence for Pt-Catalysed Decarboxylation at Anode-Relevant Potentials.

The carbon oxidation reaction (COR) is a critical issue in proton-exchange membrane fuel cells (PEMFCs), as carbon in various forms is the most used electrocatalyst support material. The COR is thermodynamically possible above the C/CO2 standard potential, but its rate becomes significantly important only at high overpotential (e. g. PEMFC cathode potential). Herein, using on-line differential electrochemical mass spectrometry, we show that oxygen-containing carbon surface groups present on high-surface aera carbon, Vulcan XC72 or reinforced graphite are oxidized at PEMFC anode-relevant potential (E=0.1 V vs. the reversible hydrogen electrode, RHE), but not at E=0.4 V vs. RHE. We rationalized our findings by considering a Pt-catalysed decarboxylation mechanism in which Pt nanoparticles provide adsorbed hydrogen species to the oxygen-containing carbon surface groups, eventually leading to evolution of carbon dioxide and carbon monoxide. These results shed fundamental light on an unexpected degradation mechanism and facilitate the understanding of the long-term stability of PEMFC anode nanocatalysts.

Adsorption performance of activated carbon for methane with low concentration at atmospheric pressure

ABSTRACT This work reports a novel method of combining both chemical activation and N2 or steam post-treatment at high temperature for producing activated carbon (denoted as AC) used for the selective adsorption and separation of methane from the coal-bed gases. The used AC in the investigation mainly contained three kinds, commercial activated carbon (denoted as GH-8), the prepared activated carbon, denoted as AC-P, and AC-K, which was prepared by chemical activation using phosphoric acid and potassium hydroxide solution, respectively. Textural properties, surface oxygen-containing functional groups and methane adsorption performances of AC-P, AC-K, and GH-8 samples were comparatively investigated. Results demonstrated that both AC-P and AC-K showed higher methane adsorption capacity than the commercial activated carbon sample GH-8. Steaming treatment to AC-P at 800°C significantly enhanced the methane adsorption capacity to 6.5 mg/g, which was approximately two times higher than the commercial sample GH-8 (3.2 mg/g). The pronounced increment of adsorption capacity over AC-PS800 from steam-treatment was attributed to the significant increase of the area of micropores with a pore diameter of 0.45–0.65 nm. The presence of surface oxygen-containing groups on AC was proven to be slightly unfavorable to methane adsorption. CH4 concentration in desorbed gas from AC-PS800 was drastically improved to about 70% in the effluent from about 5% in the feed gas, which demonstrated that the prepared AC-PS800 possessed high selective adsorption capacity for methane. These results would pay the way for concentrating and future utilization of methane in coal-bed gas.

Carbon aerogels with oxygen-containing surface groups for use in supercapacitors

We prepared a series of modified carbon aerogels with oxygen-containing functional groups through a sol–gel process by polycondensation of phloroglucinol, resorcinol and formaldehyde using starch addition. The effect of starch addition on the pore structure and electrochemical performance of the carbon aerogels was investigated. Carbon aerogels were characterized by scanning-electron microscopy, transmission-electron microscopy, surface-area analysis, X-ray diffractometry, Raman spectrometry and X-ray photoelectron spectroscopy. The electrochemical properties were studied by using cyclic voltammetry, galvanostatic charge–discharge measurements and electrochemical impedance spectroscopy. When the starch addition was 25 wt%, the as-prepared sample had a specific surface area of 734 m2 g−1 and an outstanding specific capacitance of 147 F g−1 at 1.0 A g−1. The as-prepared carbon aerogels exhibited a high coulombic efficiency and a stable cycle life at a current density of 1.0 A g−1 over 1000 cycles. This ideal performance was attributed to the addition of starch, which was beneficial for the application of carbon aerogels in supercapacitors.

Sulfur-Doped Reduced Graphene Oxide for Enhanced Sodium Ion Pseudocapacitance.

Sodium-ion capacitors (NICs) are considered an important candidate for large-scale energy storage in virtue of their superior energy–power properties, as well as availability of rich Na+ reserves. To fabricate high-performance NIC electrode material, a hydrothermal method was proposed to synthesize sulfur-doped reduced graphene oxide (SG), which exhibited unique layered structures and showed excellent electrochemical properties with 116 F/g capacitance at 1 A/g as the cathode of NICs from 1.6 V to 4.2 V. At the power–energy density over 5000 W/kg, the SG demonstrated over 100 Wh/kg energy density after 3500 cycles, which indicated its efficient durability and superior power–energy properties. The addition of a sulfur source in the hydrothermal process led to the higher specific surface area and more abundant micropores of SG when compared with those of reduced graphene oxide (rGO), thus SG exhibited much better electrochemical properties than those shown by rGO. Partially substituting surface oxygen-containing groups of rGO with sulfur-containing groups also facilitated the enhanced sodium-ion storage ability of SG by introducing sufficient pseudocapacitance.

Catalytic bromate reduction in water: Influence of carbon support

The classification of bromate as possibly carcinogenic for humans has led to an increasing interest of researchers in the development of effective technologies for its removal from water. Catalytic reduction of bromate into bromide in water under hydrogen flow was studied in detail using Pd and PdCu catalysts supported on multi walled carbon nanotubes with different textural and surface chemical properties. Cu supported catalysts show poor catalytic activity, whereas the coupling of Cu and Pd does not improve the catalytic performance of the Pd supported catalysts, the exception being the bimetallic catalysts supported on CNT-BM-U (sample N-doped using urea as nitrogen precursor). Both the textural and the surface chemical properties of the support play an important role in the catalytic performance. Among the catalysts tested, the N-doped carbon nanotubes sample is the best support for this catalytic process, while the supports with high amounts of oxygen-containing surface groups decrease the catalytic performance of the metal phases.

PREPARATION OF DESULFURIZING ACTIVATED CARBON FROM CORN STALK AND CHARACTERIZATION OF DESULFURIZING STRUCTURE

This study investigated the optimal conditions for preparing desulfurizing stalk carbon, using corn stalk as a raw material and zinc chloride as an activator. The structure of stalk carbon was characterized using thermogravimetry (TG), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer – Emmelt – Teller (BET). Results found no significant difference in stalk carbon desulfurization properties when using stalk skin, core, or a skin-core mixture as raw material. The desulfurization performance of stalk carbon prepared using a skin-core mixture, was the most effective when the material : liquid ratio was 1:2; activation temperature was 350 °C; and activation time was 70 min. The corresponding H2S adsorption time was 74 min. The large specific surface area of 562.28 m2/g and abundant pore-volume of 0.3851 ml/g was found in the desulfurization stalk carbon prepared using these conditions. The increase in micropores and the abundant oxygen-containing functional surface groups were conducive to H2S adsorption. The desulfurization products were found to be mainly elemental S and sulfite.

Mechanism of Pt interfacial interaction with carbonaceous support under reductive conditions

The interaction of platinum with carbonaceous graphite-like material Sibunit was studied. It was found that carbon covers the platinum particles during the reduction in a hydrogen flow. Chemisorption of CO over such samples has shown that just a small part of Pt surface is opened and accessible for the reagents. The carbon support was additionally pretreated by a high temperature graphitization in nitrogen. The amount of surface oxygen-containing groups was increased by a treatment with nitric acid. An examination of the Pt-loaded samples in hydrogen has revealed that the oxidative treatment does not affect the activity in the carbon hydrogenation process. Both the initial and oxidized Pt-loaded samples facilitate intensive carbon interaction with hydrogen leading to quite similar amounts of methane released. Contrary, the graphitization of the support allows one to minimize the methane formation. Lower specific surface area and absence of amorphous carbon weaken the platinum–carbon interaction and facilitate the formation of larger particles, thus complicating the realization of hydrogenation mechanism.

Advances in the applications of graphene adsorbents: from water treatment to soil remediation

Abstract Graphene, a novel carbon allotrope, is single-layered graphite with honeycomb lattice. Its unique structure endows graphene many outstanding physical/chemical properties and a large surface area, which are beneficial to its applications in many areas. The potential applications of graphene in pollution remediation are adsorption, membrane separation, catalysis, environmental analysis, and so on. The adsorption efficiency of graphene adsorbents largely depends on its surface area, porous structure, oxygen-containing groups and other functional groups, adsorption conditions, and also the properties of adsorbates. With appropriate modifications, graphene materials are mostly efficient adsorbents for organic pollutants (e.g. dyes, pesticides, and oils) and inorganic pollutants (e.g. metal ions, nonmetal ions, and gas). Since our first report of graphene adsorbents in 2010, plenty of studies have been dedicated to developing various graphene adsorbents and to evaluating their performance in treating contaminated water. Recently, there is a growing trend in graphene adsorbents that could be applied in soil remediation, where the situation is much more complicated than in aqueous systems. Herein, we review the design of graphene adsorbents for water treatment and analyze their potential in soil remediation. Several suggestions to accelerate the research on graphene-based soil remediation technology are proposed.

Surface-Group-Oriented, Condensation Cyclization-Driven, Nitrogen-Doping Strategy for the Preparation of a Nitrogen-Species-Tunable, Carbon-Material-Supported Pd Catalyst.

A nitrogen‐carbon framework with the thickness of several molecules was fabricated through a straightforward nitrogen‐doping strategy, in which specially designed surface‐oxygen‐containing groups (SOGs) first introduced onto the porous carbon support were used to guide the generation of a surface‐nitrogen‐containing structure through condensation reactions between SOGs and the amidogen group of organic amines under hydrothermal conditions. The results indicate that different kinds of SOGs generate different types and abundances of N species. The CO‐releasing groups are apt to form a high proportion of amino groups, whereas the CO2‐releasing groups, especially carboxyl and lactones, are mainly transformed into pyrrolic‐type nitrogen. In the framework with dominant pyrrolic‐type nitrogen, an electron‐rich Pd activated site composed of Pd, pyrrolic‐type N and C is built, in which electron transfer occurs from N to C and Pd atoms. This activated site contributes to the formation of electron‐rich activated hydrogen and desorption of p‐chloroaniline, which work together to achieve the superior selectivity about 99.90 % of p‐chloroaniline and the excellent reusable performance. This strategy not only provides low‐cost, nitrogen‐doped carbon materials, but also develops a new method for the fabrication of different kinds of nitrogen species structures.

Surface charge and hydrophilicity improvement of graphene membranes via modification of pore surface oxygen-containing groups to enhance permeability and selectivity

Graphene is a promising material in membrane separation. However, high water permeability as well as high rejection against contaminants is still demanded yet challenging for graphene-based membranes fabrication. In this work, we synthesized an oxygen-containing group-modified reduced graphene oxide membrane (O-rGOM), which was designed by substituting the surface layers of rGO membranes with GO flakes. The number of oxygen-containing groups on membrane surface was modulated by the [GO]/[rGO] ratio during the construction of O-rGOM. Results demonstrated that a [GO]/[rGO] ratio of 1:4 was optimal, with oxygen-containing groups modifying the pore surface of rGO laminates effectively. Furthermore, the O-rGOM showed improved hydrophilicity and water permeability. In addition, modification of the oxygen-containing groups promoted the zeta potential around the membrane pore, resulting in enhanced electrostatic interaction between the membrane and charged contaminants. The O-rGOM structure exhibited 18.2% and 5.2% improvement in acid orange 7 and methylene blue rejection, respectively, as well as ∼2.6 times enhancement in water permeability compared with the rGOM. This work provides a feasible approach for the design of graphene-based membranes to improve filtration performance with enhanced water permeability.

Oxygen-containing-defect-induced synergistic nonlinear optical enhancement of graphene/CdS nanohybrids under single pulse laser irradiation

Oxygen-containing defects are very important for altering the nonlinear optical (NLO) properties of graphene. To investigate the correlation between oxygen-containing defects and the synergistic NLO response in graphene-based nanocomposites, we attached CdS nanocrystals on the surface of graphene (G) and prepared G/CdS nanohybrids (NHs) consisting of various oxygen-containing functional groups via a chemical method. The NLO absorption and refraction of G/CdS NHs under single pulse laser irradiation are enhanced by 10.8 times with the concentration decrease of surface oxygen-containing groups, which might be attributed to the local field effects and synergetic effects stemming from charge transfer between the two components. However, the optical nonlinearity is decreased with further concentration decrease, which might arise from sp2 fragment interconnection and surface defects in the NHs. The NLO absorption transformation from two-photon absorption to saturable absorption with oxygen decrease is observed, and intensity-related NLO absorption and refraction in NHs are also discussed. Meanwhile, the G/CdS NHs exhibit superior NLO properties, implying potential applications of NH material in NLO devices.

Catalytic approach to the estimation of the influence of carbon nanomaterial structures on surface functional groups

A simple catalytic method is proposed for characterizing oxygen-containing surface groups formed upon post-synthetic treatment, control and regulation of their composition under oxidation. Using a pulsed microcatalytic method, we found that the carbon matrix structure plays a key role in the formation of the functional surface composition of carbon nanomaterials.

Kinetic analysis of nanodiamonds oxidation

This study examines the oxidation kinetics of nanodiamonds (NDs) and carbon black (CB), taken for comparison, in air oxygen . The oxidation rate constants and parameters of the Arrhenius equation were determined under isothermal conditions within a temperature range from 430 to 560 °C. Thermal behavior of both carbon nanomaterials was investigated using non-isothermal thermogravimetric analysis (TGA) experiments in air and argon. Powders of NDs and CB were characterized by nitrogen adsorption, scanning electron microscopy and energy dispersion X-ray microanalysis, ATR Infrared spectroscopy, and the total titration. The effect of various parameters of the carbon nanomaterials on the oxidation rate, such as oxygen content, surface area, ash and admixture contents, and functional groups coverage, was investigated. Overall, this study confirms that the oxygen-containing surface groups generating active sites upon thermal decomposition have a major impact on the oxidation ability of NDs and CB.

Simultaneous removal of dye and heavy metal by banana peels derived hierarchically porous carbons

Abstract The dye and heavy metal are two principal concomitant pollutants in industrial wastewaters, posing a serious threat to public health and the environment. Herein, we developed a novel strategy to convert banana peels into hierarchically porous carbon (BPCA) and porous carbon oxide (BPCAO) for the simultaneous removal of methylene blue (MB) and Co(II). The as-prepared carbons were systematically characterized by SEM, TEM, BET, FT-IR and XPS. Compared to BPCA, BPCAO showed a better adsorption performance due to its abundant surface oxygen-containing groups. In the mono-component systems, both MB and Co(II) adsorption onto BPCAO were well described by the pseudo-second-order and Langmuir models. The maximum adsorption capacities of MB and Co(II) were calculated to be 1303.54 and 122.39 mg/g at 298 K, respectively. In the binary system, the interaction between MB and Co(II) was determined and it depended on the initial concentration of Co(II). The adsorption mechanism of MB involved electrostatic interaction, π-π stacking and hydrogen-bonding while that of Co(II) was mainly ruled by the complexation and/or ion-exchange. This study indicated BPCAO could be a favorable biomass-derived adsorbent for the simultaneous removal of the dye and heavy metal.

The Effect of Phosphoric Acid Functionalization of Para-aramid Fiber on the Mechanical Property of Para-aramid Sheet

The mechanical properties of para-aramid sheet (PAS) are mainly dependent on the interfacial property between para-aramid chopped fibers and fibrids. However, the chemical inertness and smooth surface of para-aramid chopped fiber lead to the poor interfacial adhesion between para-aramid chopped fibers and fibrids. In this study, para-aramid chopped fiber was treated by phosphoric acid (PA) solution with different concentration in order to prepare PAS with high mechanical strength. It was shown that PA -treatment can increase the surface roughness and improve the surface oxygen-containing active groups of para-aramid chopped fibers. In addition, there is a critical value of PA-concentration (20%). Proper PA-treatment gives rise to an increased tensile strength of PAS from 2.41 to 3.41 kN/m by an increment of 41.49%. However, excessive PA -treatment results in a dramatic reduction of tensile strength for para-aramid fibers and also for PAS possibly due to the structure destruction of para-aramid fiber. This work shows a simple but highly-efficient approach for improving the mechanical property of PAS via PA-treatment of para-aramid chopped fibers, and simultaneously elaborating the reinforcing effects for high-performance PAS especially through optimizing the interfacial property between para-aramid chopped fibers and fibrids.

Tribocharging of macerals with various materials: Role of surface oxygen-containing groups and potential difference of macerals

Triboelectrostatic separation of vitrinite and inertinite depends on their differences in tribocharging behavior. In the present study, charge-to-mass ratios of two macerals with six tribocharging materials, i.e., aluminum, stainless steel, copper, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamide (PA) were conducted for the first time under various environmental factors. PA was found to be the preferred material for tribocharging because vitrinite and inertinite displayed opposite charge polarity with it. Characterization of surface oxygen-containing groups on macerals and their quantitative estimation were conducted by X-ray photoelectron spectroscopy (XPS) technique. Polar groups such as OH and COOH were detected to be the major proportion in inertinite whereas vitrinite exhibited mainly nonpolar groups of O, which indicate tendency of their surface charge. For the first time, atomic force microscopy (AFM) was utilized to investigate the surface topography and potential difference of macerals. Inertinite showed 0.42 V higher surface potential than vitrinite, which well fits with their charge polarity and movement during triboelectrostatic separation. However, the instability of surface potential difference on inertinite may leads to disorder in its charge polarity, which makes Cu as an alternative material because both macerals have great charge gap with Cu and they also have same charge polarity.

ELECTROCHEMICAL PROCESSES ON DISPERSE GRAPHITE ELECTRODES IN HNO3 SOLUTIONS

The mechanism and kinetics of anodic processes on a dispersed graphite electrode are investigated by a potentiodynamic method. Variation of the reversal potential in the anode zone on potentiodynamic curves PDC allow to estimate the ratio of the anode and cathode capacities and to determine the coefficient of reversibility of electrochemical reactions. By the degree of reversibility of electrochemical reactions, three potential zones are distinguished: Ist - E ... 1.15 V; II-1,15 ... 1,4V; III -> 1.4B corresponding to the sequential course of the intercalation of graphite with nitrate ions, oxidation of the surface functional groups, the formation of oxide-like graphite compounds. In the zone of potentials I, the maximum reversibility of the anodic process is noted, due to the intercalation-deintercalation process, with the formation of graphite intercalation compounds. Then, a regular decrease in the coefficient of reversibility associated with the occurrence of reactions involving surface oxygen-containing groups and reactions involving oxygen is noticed. This complex of electrochemical processes is accompanied by the formation of graphite intercalation compounds of non-stoichiometric composition and, probably, the oxide of similar structures. The transition to the potential of zone III is characterized by an abrupt decrease in the coefficient of reversibility and the growth of anode currents, which decrease with cycling. Under these conditions, oxidation reactions of the graphite matrix are likely to occur with the formation of CO and CO2. An increase in the rate of irreversible reactions is revealed with a decrease in the concentration of HNO3. In 45% HNO3, the re-oxidation reactions of graphite intercalation compound and the formation of oxide compounds of graphite are significantly accelerated. In 30% HNO3, the highest anode currents of the first cycle from the solutions studied are recorded on a dispersed graphite electrode, and the reversibility of the anode processes is lower than in 60% HNO3. It has been shown that in HNO3 with a concentration of less than 15%, the intercalation of graphite proceeds at a low rate and is accompanied by the surface reactions involving oxygen.For citation:Yakovlev A.V., Yakovleva E.V., Rakhmetulina L.A., Solovyova N.D., Lopukhova M.I. Electrochemical processes on disperse graphite electrodes in HNO3 solutions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 121-128

Significance of surface oxygen-containing groups and heteroatom P species in switching the selectivity of Pt/C catalyst in hydrogenation of 3-nitrostyrene

The selectivity of 3-nitrostyrene (NS) hydrogenation over 0.5 wt-% Pt catalysts supported on carbon materials can be switched simply by changing reduction temperature. When the reduction temperature was 150 °C, 1-ethyl-3-nitrobenzene (ENB) was mainly produced in a selectivity of 93% at a conversion of 95% (at 100 °C). When the reduction was conducted at a higher temperature of 450 °C, in contrast, the main product was switched to 3-aminostyrene (AS) in a selectivity of 96% at a conversion of 91%. That is, the Pt/C catalysts reduced at low and high temperatures could preferentially catalyze the hydrogenation of vinyl and nitro groups of NS, respectively. This switching of the product selectivity may be ascribed to actions of surface oxygen-containing functional groups and surface hetero P species. The quantity and nature of these surface species were examined in detail by a few different methods. For the low-temperature reduced catalyst, surface acidic groups present close to Pt nanoparticles (∼2 nm) would interact with the nitro group of a NS molecule and make its vinyl group more likely to interact with the surface active metal species of Pt nanoparticles; this facilitates the hydrogenation of the latter and produces ENB selectively. For the high-temperature reduced catalyst, however, P species would interact with Pt and form Pt-POx complex, on which a NS molecule is likely to be adsorbed with its nitro group, facilitating the selective production of AS via its hydrogenation. It is demonstrated that surface functional groups and surface hetero atoms (like P), in addition to main active metal species (like Pt), should have direct actions in the catalysis for such a catalyst that exposes a larger quantity of surface functional groups and/or hetero atoms compared to the number of supported metal nanoparticles.

Multi-walled carbon nanotubes photochemistry: A mechanistic view of the effect of impurities and oxygen-containing surface groups

Continuous photolysis experiments and transient absorption spectroscopy were performed in combination with other techniques including HRTEM, XPS, Raman, TGA, and ESR spectroscopy, to investigate the role of residual metals and amorphous carbon on the photochemical process taking place after 350–355 nm light irradiation of as obtained commercial multi-walled carbon nanotubes, denoted as pCNT.The results indicate that 350–355 nm photolysis of pCNT leads to the oxidation of surface oxygen-containing groups and defects which in turn are eliminated leading to more graphitic –like multi-walled carbon nanotubes (MWCNT). Residual metal catalysts and oxygen containing amorphous carbon and oxidized C-functionalities of MWCNT play an important role in the generation of MWCNT photoinduced charge-separated states. The process of 350 nm excitation of pCNT leads to exciton formation followed by hole transfer to metal oxides and further oxidation of C-O functionalities. A plausible mechanism explaining the elimination of oxidized groups attached to pCNT graphene walls and amorphous carbon and leading to more graphite-like CNTs is discussed. The results presented may have implications in the nanoscale semiconductor materials for optoelectronics applications.