Sulfur-doped Graphene Research Articles

Magnetic properties of sulfur-doped graphene

While studying magnetism of d- and f-electron systems has been consistently an active research area in physics, chemistry, and biology, there is an increasing interest in the novel magnetism of p-electron systems, especially in graphene and graphene-derived nanostructures. Bulk graphite is diamagnetic in nature, however, graphene is known to exhibit either a paramagnetic response or weak ferromagnetic ordering. Although many groups have attributed this magnetism in graphene to defects or unintentional magnetic impurities, there is a lack of compelling evidence to pinpoint its origin. To resolve this issue, we systematically studied the influence of entropically necessary intrinsic defects (e.g., vacancies, edges) and extrinsic dopants (e.g., S-dopants) on the magnetic properties of graphene. We found that the saturation magnetization of graphene decreased upon sulfur doping suggesting that S-dopants demagnetize vacancies and edges. Our density functional theory calculations provide evidence for: (i) intrinsic defect demagnetization by the formation of covalent bonds between S-dopant and edges/vacancies concurring with the experimental results, and (ii) a net magnetization from only zig-zag edges, suggesting that the possible contradictory results on graphene magnetism in the literature could stem from different defect-types. Interestingly, we observed peculiar local maxima in the temperature dependent magnetizations that suggest the coexistence of different magnetic phases within the same graphene samples.

Sulfur-doped graphene as a catalyst support: Influences of carbon black and ruthenium nanoparticles on the hydrogen evolution reaction performance

We develop an efficient electrocatalyst for hydrogen evolution reaction (HER) based on sulfur doped graphene nanosheets (S-GNs) synthesized with simple, cost effective and scalable method. The structure and morphological characteristics of the fabricated catalysts are investigated by field emission scanning electron microscopy, energy dispersive X-ray diffraction microanalysis, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and electrochemical methods such as voltammetry and impedance spectroscopy (EIS). Electrochemical results show that glassy carbon modified S-GNs heat-treated at 1000°C (GCE-S-GNs-1000) benefit of a good activity toward HER compared to GNs. To improve the characteristics of S-GNs and prevent agglomeration of the layers, the GCE-S-GNs-1000-CB-Ru is fabricated by insertion of carbon black (CB) into S-GNs-1000, and further modification of GCE-S-GNs-1000-CB with ruthenium nanoparticles. The GCE-S-GNs-1000-CB-Ru demonstrated excellent performance for the HER, compared with its ancestors GCE-GNs-1000, GCE-GNs-1000-CB, GCE-S-GNs-1000, GCE-S-GNs-1000-CB as well as with traditional catalysts such as WS2 and MOS2. Analysis of the results obtained by the EIS showed that the increase in the activity of the electrode was partially originated from increase in the double layer capacitance (surface roughness effect) and mostly from increase in the intrinsic activity (synergistic effect).

Sulfur-doped graphene-supported Ag nanoparticles for nonenzymatic hydrogen peroxide detection

Heteroatom doping is an effective way to modulate the physicochemical properties of graphene and its hybrid materials. In this work, sulfur-doped graphene (SG) was used for the first time as a supporting material for loading Ag nanoparticles, and the resulting Ag/SG hybrid with a high S-doping level (2.8 at.%) and a uniform Ag NP decoration was successfully prepared by a microwave-assisted method. Electrochemical measurements revealed that the Ag/SG exhibited a better electrocatalytic activity toward H2O2 reduction than undoped Ag/reduced graphene oxide, which highlighted the important role of S-doping that could not only improve the charge transfer, but also introduce more defects as active sites. The nonenzymatic sensor based on Ag/SG displayed good sensing performances for highly sensitive, selective, and stable detection of H2O2, demonstrating that SG is indeed a promising catalyst-supporting material for electrochemical sensing.

Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction.

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO32− to form graphene, but also sulfur in SO42− from its highest (+6) to lowest valence which was hybridized into the carbon sp2 framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites.

Sulphur-doped graphene as metal-free carbocatalysts for the solventless aerobic oxidation of styrenes

Pyrolysis of λ-carrageenan at 1000°C and subsequent exfoliation lead to a S-doped graphene [(S)G]. Increasing pyrolysis temperature to 1200°C or the use of other carrageenans with lower sulphate content results in the failure of S doping. XPS confirms the presence of S atom (4.5%) with environments alike sulphide and sulphoxide. (S)G promotes the aerobic oxidation of styrenes to their corresponding benzaldehydes accompanied by lesser amounts of styrene oxide. In contrast, under the same experimental conditions reduced graphene oxide exhibits a negligible activity. (S)G was reused with almost coincident catalytic performance.

Electrochemical synthesis of sulfur-doped graphene sheets for highly efficient oxygen reduction

Sulfur (S)-doped graphene sheets were prepared by a facile electrochemical method, which effectively combined exfoliation of graphite and in situ S doping of graphene together. The metal-free S-doped graphene sheets exhibit high electrocatalytic activity, long-term stability, and excellent tolerance to cross-over effects of methanol in alkaline media for the oxygen reduction reaction (ORR), indicating that these S-doped graphene sheets possess great potential for a substitute for Pt-based catalysts in fuel cells.

CuO nanoparticles on sulfur-doped graphene for nonenzymatic glucose sensing

This study reports a novel CuO nanoparticles (NPs) supported on S-doped graphene (CuO/SG) as an electrode material for nonenzymatic glucose detection. The CuO/SG was successfully synthesized by a facile microwave-assisted approach, and CuO/SG composed of ∼13nm of CuO NPs being relatively well-distributed and strongly anchored on SG was obtained. Electrochemical test revealed that the CuO/SG based electrode exhibited a higher electrocatalytic activity toward glucose oxidation than CuO NPs and CuO/reduced graphene oxide (rGO) modified electrodes owing to the synergistic effect between CuO NPs and SG. As a consequence, the CuO/SG based sensor exhibited a rapid response of 2s, a wide linear range of 0.1–10.5mM, a high sensitivity of 1298.6μA·mM−1·cm−2, and a low detection limit of 80nM, along with the excellent selectivity, high stability, and good accuracy in real sample analysis, thus leading to a promising candidate for nonenzymatic glucose detection.

Determination of Dopamine by Dual Doped Graphene-Fe2O3 in Presence of Ascorbic Acid

Both nitrogen and sulfur dual doped graphene supported Fe2O3 (NSG-Fe2O3) have been prepared by hydrothermal methods and subsequently utilized for the electrochemical determination of dopamine (DA) in presence of ascorbic acid (AA). The NSG-Fe2O3 has been characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopic (XPS). The electrochemical detection of DA was measured through the cyclic voltammetry, differential pulse voltammetry, and amperometric techniques in a 0.1 M phosphate buffer solution (PBS) at pH 7.4. Interferences have been investigated in presence of AA, glucose, serotonin, N2H4, and uric acid. The NSG–Fe2O3 has shown good analytical performance for DA with comparatively better sensitivity (29.1 μA mM−1), long linear detection range (0.3–210 μM) and detection limit (0.035 μM) (S/N = 3). The catalytic rate constant for DA detection has been calculated as 9.6 × 104 M−1 s−1 with a good diffusion coefficient of 3.5 × 10−4 cm2 s−1. The electrooxidation of DA may enhances by fast proton acceptance and/or electron donation due to higher electron density for excess loan pair electron that provided from N and S dual-doped graphene sheets.

Sulfur-doped graphene laminates for EMI shielding applications

Herein, for the first time, we demonstrate that a laminated structure of sulfur-doped reduced graphene oxide (SrGO) provides significant potential for electromagnetic interference shielding applications.

Microwave-assisted solvothermal synthesis of sulfur-doped graphene for electrochemical sensing

Heteroatom doping is an effective way to modulate the electronic structure and properties of graphene. Despite a growing interest in sulfur (S)-doped graphene (SG), synthesis of high-quality SG at low cost remains a great challenge. In this study, we developed a rapid, efficient and cost-effective microwave-assisted solvothermal (MAS) method for the preparation of SG. It was found that a short MAS time of 6min could generate few-layer SG (0.5μm in lateral size) having effective oxygen reduction, high level of S-doping, sole thiophene-S bonding configuration, and high electrical conductivity. Furthermore, the resulting SG could serve as an effective electrocatalyst for H2O2 reduction, showing improved electrocatalytic activity over its undoped counterpart and good sensing performances for highly sensitive and selective detection of H2O2, indicating that SG may be a promising candidate for electrochemical sensor applications.

Sulfur-doped graphene derived from cycled lithium-sulfur batteries as a metal-free electrocatalyst for the oxygen reduction reaction.

Heteroatom-doped carbon materials have been extensively investigated as metal-free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li-air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene-based sulfur composites have been recently developed to prolong the cycling life of Li-S batteries, one of the most attractive energy-storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li-S batteries. Herein, we report a green and cost-effective method to prepare sulfur-doped graphene, achieved by the continuous charge/discharge cycling of graphene-sulfur composites in Li-S batteries. This material was used as a metal-free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.

Multigrain platinum nanowires consisting of oriented nanoparticles anchored on sulfur-doped graphene as a highly active and durable oxygen reduction electrocatalyst.

Direct growth of multigrain platinum nanowires on sulfur-doped graphene (PtNW/SG) is reported. The growth mechanism, including Pt nanoparticle nucleation on SG, followed by nanoparticle attachment with orientation along the <111> direction is highlighted. PtNW/SG demonstrates improved Pt mass and specific activity compared with commercial catalysts toward oxygen reduction, in addition to dramatically improved stability through accelerated durability testing.

Synthesis of sulfur-doped p-type graphene by annealing with hydrogen sulfide

Doping is an important method to modulate the electronic properties of graphene. Among various types of doped graphene, sulfur-doped graphene is expected to have a wider band gap due to the electron-withdrawing character of sulfur. However, it is difficult to dope graphene with S because S atom is much larger than C atom. In this paper, S-doped graphene is synthesized by a simple method with hydrogen sulfide annealing. It is confirmed by high-resolution transmission electron microscopy diffraction and Raman spectra that S-doping in graphene is surface adsorption doping forming carbon–sulfur compound crystal domains. We are also noted that the doping intensity is affected by annealing time indicating the doping process is controllable. Electrical measurements show that sulfur plays an acceptor role in S-doped graphene leading to a p-type behavior, and after sulfur-doping, graphene exhibits higher resistance and larger on/off ratio.

New approach of nitrogen and sulfur-doped graphene synthesis using dipyrrolemethane and their electrocatalytic activity for oxygen reduction in alkaline media

We have been prepared a series of heteroatoms (N and/or S) doped graphene in different ratios from various doping precursors (pyridine, thiophene and bithiophene combined separately with dipyrrolemethane and used as single N and/or S precursor) by thermal reaction. The as synthesized heteroatoms-doped graphene materials have also been characterized via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The XPS and Raman investigations suggest a better dual-doping with higher conversion rate of graphitic-N and thermal reduction of oxygen into the graphene sheets. The electrochemical investigation reveals that the both N and S-doped graphene (S1N2-GN800 and S2N2-GN800) have better catalytic activity on oxygen reduction reaction (ORR) than only N-doped graphene (N3-GN800) with the assistance of synergistic effect of dual-doping. Particularly, the high thermal treated final product, N and S dual-doped graphene (S2N2-GN1000) shows remarkable electrocatalytic activity towards the ORR which not only establishes a pathway of four-electron transfer reaction but also exhibits a better fuel selectivity and stability than that of commercially available 20wt% Pt/C electrode.

Sulfur-doped graphene quantum dots as a novel fluorescent probe for highly selective and sensitive detection of Fe(3+).

Sulfur-doped graphene quantum dots (S-GQDs) with stable blue-green fluorescence were synthesized by one-step electrolysis of graphite in sodium p-toluenesulfonate aqueous solution. Compared with GQDs, the S-GQDs drastically improved the electronic properties and surface chemical reactivities, which exhibited a sensitive response to Fe(3+). Therefore, the S-GQDs were used as an efficient fluorescent probe for highly selective detection of Fe(3+). Upon increasing of Fe(3+) concentration ranging from 0.01 to 0.70 μM, the fluorescence intensity of S-GQDs gradually decreased and reached a plateau at 0.90 μM. The difference in the fluorescence intensity of S-GQDs before and after adding Fe(3+) was proportional to the concentration of Fe(3+), and the calibration curve displayed linear regions over the range of 0-0.70 μM. The detection limit was 4.2 nM. Finally, this novel fluorescent probe was successfully applied to the direct analysis of Fe(3+) in human serum, which presents potential applications in clinical diagnosis and may open a new way to the design of effective fluorescence probes for other biologically related targets.

Theoretical characterization of sulfur and nitrogen dual-doped graphene

We have employed density functional theory to unravel the structural and electronic properties of sulfur and nitrogen dual-doped graphene. In the preferred configuration, the sulfur and nitrogen atoms replace the carbon atoms of a CC bond, but they are not bonded. Thus, the nitrogen atom adopts a pyridinic arrangement and the sulfur atom an edge like bonding pattern, since it is solely bonded to two carbon atoms. The formation energy determined for sulfur and nitrogen dual-doped graphene was 1.36eV smaller than the sum of the formation energies (FE) of sulfur doped graphene and nitrogen doped graphene. There is a synergic effect between sulfur and nitrogen which lowers the FE as compared with separated doping. This particular arrangement of the dopants enhances the reactivity of the sheet. For example, it facilitates the addition of molecular oxygen to sulfur to form SO2 functionalities. In general, the introduction of sulfur and nitrogen opens a band gap as indicated by HSE calculations.

Enhanced electrocatalytic activity due to additional phosphorous doping in nitrogen and sulfur-doped graphene: A comprehensive study

Abstract Effect on oxygen reduction reaction (ORR) of ternary-doped reduced graphene oxide (RGO) as an electrocatalyst is evaluated by employing thiourea as a single source of nitrogen (N) and sulfur (S), and triphenylphosphine for phosphorous (P) as precursors for heteroatom doping. The topographical studies show that by doping the RGO, disruption in surface charge and spin asymmetry is introduced into the carbon matrix due to the difference in the bond length and electronegativity between carbon and heteroatoms, which makes carbon lattice ORR active. Ternary (N, S and P)-doped RGO shows excellent ORR activity, which is ∼2 times better than that of binary (N and S)-doped RGO, and ∼5 times better than that of single (P)-doped RGO. The catalytic activity of the ternary-doped carbon even exceeds the commercial Pt in alkaline medium. Additional P doping causes remarkable synergistic effect on binary N and S-doped RGO by generating active P–N species, improving graphitic order and increasing surface area as well as mesopore volume, which in turn enhances the ORR activity.

Single source precursor-based solvothermal synthesis of heteroatom-doped graphene and its energy storage and conversion applications.

Solvothermal processes are considered efficient approaches for the gram-scale production of graphene. Further modification of graphene by chemical doping is an important approach to tailor its properties. In this work, we successfully synthesized sulfur-doped graphene by using a solvothermal method with dimethyl sulfoxide as a precursor, which is a common laboratory reagent. Nitrogen-doped graphene was produced to demonstrate the generality of this process. These heteroatom-doped graphene materials exhibited high surface areas and high contents of heteroatoms. Furthermore, the lithium-ion storage properties and oxygen reduction reaction catalytic activity of these materials were also investigated. The success of this approach might facilitate the development of other advanced graphene-based materials with relative simplicity, scalability, and cost effectiveness for use in various potential applications.

Catalytic Effects of Heteroatom-doped Graphene Nanosheets on the Performance of Li-O2Batteries

Graphene nanosheets (GNS), nitrogen-doped graphene nanosheets (N-GNS), and sulfur-doped graphene nanosheets (SGNS) were successfully synthesized, and their catalytic effects on the oxygen reduction reaction (ORR) in Li-O2 batteries were compared. The S-GNS electrode exhibited the highest ORR catalytic activity, resulting in enhanced discharge capacity and power capability. We attributed the enhanced ORR catalytic activity to the increased defect sites on graphene.

Catalytic Effects of Heteroatom-doped Graphene Nanosheets on the Performance of Li-O2 Batteries

Graphene nanosheets (GNS), nitrogen-doped graphene nanosheets (N-GNS), and sulfur-doped graphene nanosheets (S-GNS) were successfully synthesized, and their catalytic effects on the oxygen reduction reaction (ORR) in Li-O2 batteries were compared. The S-GNS electrode exhibited the highest ORR catalytic activity, resulting in enhanced discharge capacity and power capability. We attributed the enhanced ORR catalytic activity to the increased defect sites on graphene. Keywords: Li-O2 batteries, graphene, doping, nanosheets, heteroatom