Academic literature on the topic 'Sulfur-doped graphene'

In this paper, we present a novel route to prepare sulfur and nitrogen co-doped reduced graphene oxide, in which, two main procedures – the preparation of a sulfur-doped graphite intercalation compound (S-GIC) and the construction of the sulfur and nitrogen co-doped reduced graphene oxide (SN-RGO) are included.

The geometrical and electronic structures of pure graphene and S-doped graphene have been investigated using plane wave pseudopotential method with generalized gradient approximation based on the density functional theory. The local structure change, Mulliken population, density of states, and electron density difference of S-doped graphene have been calculated. It can be observed that the Fermi level shifts towards the conduction band after the doping of sulfur atom. The results also suggest that there are chemical bonds formed between the sulfur and carbon atoms, and the charges transfer from the doped sulfur atom to graphene.

Herein, sulfonated polystyrene thin film was applied as the precursor to synthesize sulfur (S)-doped graphene via thermal annealing process. S atoms were proved to be successfully doped into the lattice of graphene sheets according to the analyses of high resolution transmission microscopy (HRTM) and the corresponding energy dispersive X-Ray spectroscopy (EDX). The high D band detected in the Raman spectrum of S-doped graphene indicates the large amount of defects was introduced into the lattice of graphene, and the in-plane crystallite sizes were calculated to be ca. 21.7 nm. Our method provides an efficient and simple approach for the synthesis of S-doped graphene, which would promote the research for graphene based devices in widespread applications.

SnS nanoparticles are encapsulated into sulfur-doped graphene bubble film presenting a flake-graphite-like structure. The closely packed SnS@G composite shows much lower specific surface area, smaller irreversible Li⁺ consumption.

We calculated the band structures of a variety of N- and S-doped graphenes in order to understand the effects of the N and S dopants on the graphene electronic structure using density functional theory (DFT). Band-structure analysis revealed energy band upshifting above the Fermi level compared to pristine graphene following doping with three nitrogen atoms around a mono-vacancy defect, which corresponds to p-type nature. On the other hand, the energy bands were increasingly shifted downward below the Fermi level with increasing numbers of S atoms in N/S-co-doped graphene, which results in n-type behavior. Hence, modulating the structure of graphene through N- and S-doping schemes results in the switching of “p-type” to “n-type” behavior with increasing S concentration. Mulliken population analysis indicates that the N atom doped near a mono-vacancy is negatively charged due to its higher electronegativity compared to C, whereas the S atom doped near a mono-vacancy is positively charged due to its similar electronegativity to C and its additional valence electrons. As a result, doping with N and S significantly influences the unique electronic properties of graphene. Due to their tunable band-structure properties, the resulting N- and S-doped graphenes can be used in energy and electronic-device applications. In conclusion, we expect that doping with N and S will lead to new pathways for tailoring and enhancing the electronic properties of graphene at the atomic level.

A sulfur–hydrazine hydrate chemistry-based method is reported here to integrate the sulfur and N-doped reduced graphene oxide to obtain S@N-rGO composite with 76% sulfur. The as-obtained S@N-rGO composite displays a good rate capability and excellent stability.

In this paper, gas sensing characteristics of sulfur-doped graphene oxide (S-GO) are firstly presented. The results of the sensing test revealed that, at room temperature (20 °C), S-GO has the optimal sensitivity to NH3. The S-GO gas sensor has a relatively short response and recovery time for the NH3 detection. Further, the sensing limit of ammonia at room temperature is 0.5 ppm. Theoretical models of graphene and S-doped graphene are established, and electrical properties of the graphene and S-doped graphene are calculated. The enhanced sensing performance was ascribed to the electrical properties’ improvement after the graphene was S-doped.

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.

Here we propose, for the first time, a new and green ethanol-thermal reaction method to synthesize highquality and pure thiophene–sulfur doped reduced graphene oxide (rGO), which establishes an excellent platform for studying sulfur (S) doping effects on the physical/chemical properties of this material. We have quantitatively demonstrated that the conductivity enhancement of thiophene–S doped rGO is not only caused by the more effective reduction induced by S doping, but also by the doped S atoms, themselves. Furthermore, we demonstrate that the S doping is more effective in enhancing conductivity of rGO than nitrogen (N) doping due to its stronger electron donor ability. Finally, the dye-sensitized solar cell (DSCC) employing the S-doped rGO/TiO₂ photoanode exhibits much better performance than undoped rGO/TiO₂, N-doped rGO/TiO₂ and TiO₂ photoanodes. It therefore seems promising for thiophene–S doped rGO to be widely used in electronic and optoelectronic devices.

Developing next generation secondary batteries has attracted much attention in recent years due to the increasing demand of high energy and high power density energy storage for portable electronics, electric vehicles and renewable sources of energy. This dissertation investigates sulfur based advanced electrode materials in Lithium/Sodium batteries. The electrochemical performances of the electrode materials have been enhanced due to their unique nano structures as well as the formation of novel composites. First, a nitrogen-doped graphene nanosheets/sulfur (NGNSs/S) composite was synthesized via a facile chemical reaction deposition. In this composite, NGNSs were employed as a conductive host to entrap S/polysulfides in the cathode part. The NGNSs/S composite delivered an initial discharge capacity of 856.7 mAh g-1 and a reversible capacity of 319.3 mAh g-1 at 0.1C with good recoverable rate capability. Second, NGNS/S nanocomposites, synthesized using chemical reaction-deposition method and low temperature heat treatment, were further studied as active cathode materials for room temperature Na-S batteries. Both high loading composite with 86% gamma-S8 and low loading composite with 25% gamma-S8 have been electrochemically evaluated and compared with both NGNS and S control electrodes. It was found that low loading NGNS/S composite exhibited better electrochemical performance with specific capacity of 110 and 48 mAh g-1 at 0.1C at the 1st and 300th cycle, respectively. The Coulombic efficiency of 100% was obtained at the 300th cycle. Third, high purity rock-salt (RS), zinc-blende (ZB) and wurtzite (WZ) MnS nanocrystals with different morphologies were successfully synthesized via a facile solvothermal method. RS-, ZB- and WZ-MnS electrodes showed the capacities of 232.5 mAh g-1, 287.9 mAh g-1 and 79.8 mAh g-1 at the 600th cycle, respectively. ZB-MnS displayed the best performance in terms of specific capacity and cyclability. Interestingly, MnS electrodes exhibited an unusual phenomenon of capacity increase upon cycling which was ascribed to the decreased cell resistance and enhanced interfacial charge storage. In summary, this dissertation provides investigation of sulfur based electrode materials with sulfur/N-doped graphene composites and MnS nanocrystals. Their electrochemical performances have been evaluated and discussed. The understanding of their reaction mechanisms and electrochemical enhancement could make progress on development of secondary batteries.

博士
國立交通大學
環境工程系所
107
Nanoscale materials have attracted potentials to impact the broad fields of heavy metal and biological sensing. In addition, the incorporation of nanomaterials and nanostructures into sensors leads to improve performance of detection capability. Fluorescent graphene quantum dots (GQDs) and metal nanoparticles are one of member nanomaterials have evoked significant attention in sensor. Many efforts have been made during recent years to develop portable sensors for environmental monitoring heavy metals. GQDs along doping with hetero structure specially sulfur (S) promise the advantageous physical and chemical properties of GQDs. The unique architecture of sulfur doped graphene quantum dots (S-GQDs) and the outstanding sensing performance provide a powerful impetus to use S-GQDs as a promising material for sensing. Keeping all this in view, this thesis focused on developing novel S-GQDs via bottom up with their characterizations can offer further performance not only sensing but also as reducing agent. Current research includes: First of all, S-GQDs was fabricated using different doping agent as mercaptopropionic acid (MPA), mercaptosuccinic acid (MSA) and thiourea. Then, the optical methods were used to detect pollutant in environment as 4-nitrophenol (4NP) and mercury ion (Hg2+). The S-GQDs show the strong emission band at 450 nm under the irradiation of 330-nm UV light. 4-NP can serve as the fluoresce quencher by the  –  interaction with S-GQD, resulting in the linear decrease in fluorescence intensity after adding various concentrations of 4-NP in the range from 10 nM to 200 µM. As expected, The S-GQDs as the exhibitor shows the high analytical performance on 4-NP detection with limit of detection value of 0.7 nM in deionized water and 3.5 nM in lake water is obtained. Furthermore, S-GQDs based paper strip can rapidly screen 4-NP in wastewater within 1 min. We also investigate the reducing potential of S-GQDs for the fabrication gold nanocomposite. The results obtained in this thesis clearly demonstrate that S-GQDs can reduce Au ions to gold nanocomposite. The particle size of Au@S-GQD is tunable by simply adjusting the Au precursor concentration and the mean diameter increases from 5 to 17 nm when the Au precursor concentration increases from 50 to 150 µM HAuCl4. The Au@S-GQD exhibits good UV-visible absorption property, which is used for the sensitive detection of nanomolar level of 4-nitrophenol. A wide dynamic range of 4 orders of magnitude with the limit of detection (LOD) of 3.5 nM in deionized water is achieved. The UV-visible response of Au@S-GQD also shows good selectivity toward 4-nitrophenol detection over other aromatic and nitroarene compounds. In addition, the Au@S-GQD sensing platform is successfully applied to the detection of 0.05 – 50 µM 4-nitrophenol in highly contaminated food wastewater with LOD of 8.4 nM. Moreover, the N, S-codoped graphene quantum dots (N, S-GQDs) with high quantum yield were also fabricated by one-pot hydrothermal methods for highly sensitive and selective detection of nanomolar level of mercury ions (Hg2+) in water and wastewater. The as-prepared N, S-GQDs are uniform in size with mean particle size of 3.5  0.5 nm. The doping of nitrogen atom increases the quantum yield to 41.9%, while the introduction of S atoms enhances the selectivity of Hg2+ via strong coordination interaction. The fluorescence intensity of N, S-GQDs is quenched proportionally after adding Hg2+ concentrations and a dynamic range of 4 orders of magnitude with limit of detection of 0.14 nM is obtained in deionized water. The N, S-GQDs nanosensing probes can be successfully applied to the sewage and dye wastewater samples and a linear range of 0.1 – 15 µM with recovery of 96 – 116% is obtained. In addition, the coating of N, S-GQDs onto paper strip provides an excellently rapid screening and highly selective technique for Hg2+ detection in real wastewater. Interestingly, the S-GQDs using mercaptosuccinic acid as sulfur source shows better as reduction agent comparing with N,S-GQDs. To the best our knowledge, there are the first time to use S-GQDs without adding any reduction agent and ambient temperature can synthesize gold nanocomposite via one simple step of mixing. In turn, the icosahedron shaped Au@S-GQDs were fabricated using S-GQDs as the linker and reductant. Electrochemical technique was used for sensing analysis 3-nitro L-tyrosine in human serum. There are no researches to fabricate different S-GQDs by using bottom up method for sensing analysis. Particularly, our research opens new strategy of S-GQDs as reducing agent to synthesize gold nanocomposite at room temperature in short time. To the best our knowledge, our work is the first work have successfully fabricated different S-GQDs based on different sulphur sources via bottom up method. We have experimentally demonstrated S-GQDs by using pyrolysis and hydrothermal methods can fabricate different S-GQDs. Sulphur containing in graphene network shows not only good optical properties but also as reducing and capping agent to synthesize different size and shape of gold nanocomposites. On the other hand, our works also indicate that fabricated S-GQDs from different sources may have different applications. In particular, S-GQDs by using pyrolysis show excellent properties to control size and shape of gold nanocomposite. We propose the reason may come from the crystallization and surface-functionalized of GQDs. Our works demonstrate the reductant property of S-GQDs to synthesize gold nanocomposite via one simple mixing step at room temperature without adding any reductant. Our research results suggest a simple route to control different size and shape of gold nanocomposites. These results can be useful for synthesis gold nanocomposites or other metal nanocomposites and different applications.

碩士
國立高雄大學
應用化學系碩士班
106
Lithium-sulfur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. But their practical use is still hindered by several issues including dissolution of lithium polysulfides(LiPSS) in the electrolyte, large volume change between the sulfur (S) and lithiated phase(Li2S), low electronic conductivity of sulfur. In this work, three-dimensional nitrogen-doped graphene by hydrothermal synthesis, as a chemical immobilizer, was designed to bind LiPSS and stabilize sulfur in the cathode for high performance Li-S batteries. The incorporated ni-trogen dopants in the graphene network were found to have a strong binding effect on the LiPSs to improve electrochemical stability and promote fast electrochemical reaction kinetics. Here we report the three-dimensional N-doped graphene as cathode for lithium-sulfur batteries, and the initial discharge capacity is 1253 mAh/g, after 50 cycles, the capacity retention is 80.1%

博士
國立交通大學
分子醫學與生物工程研究所
106
Nowadays our electricity production is mostly based on a non-renewable energy resources, mainly fossil fuels which are projected to deplete in near future. Renewable energy resources available today are still not efficient enough to satisfy our constantly growing energy demand. One of the proposed scenarios is to produce hydrogen from water by solar light, and use it as the energy carrier in a hydrogen fuel cells, producing only water without any pollutants. Hence, searching for novel photocatalysts based on nonprecious metals or metal-free, especially carbon materials, which are abundant and environmentally friendly, has attracted considerable attention from both industrial and academic researchers. Graphene quantum dots (GQDs), small graphene fragments of size ranging from 2 to 20 nm, have received considerable attention due to its interesting phenomena different from those in quantum dots of any other semiconductors. In recent years, GQDs receives increasing attention owing to their properties like chemical inertness, low cytotoxicity, excellent dispersibility in water and relatively stable photoluminescence. Further researches showed that GQDs doped with heteroatoms can effectively modulate their band gap and electronic density leading to enhanced chemical activity, new optical properties, and selectivity. In this work we focus on the photocatalytic hydrogen production activity in aqueous media by using sulfur-doped graphene oxide quantum dots (S-GOQDs). S-GOQDs have been synthesized by hydrothermal method with “bottom-up” approach. As investigated by atomic force microscopy (AFM), the synthesized S-GOQDs possessed bi- and tri-layer graphene thickness. As illustrated by transmission electron microscopy (TEM), the synthesized S-GOQDs exhibited high crystallinity and size ranging from 3-10nm. Successful doping of S atoms in graphene quantum dot lattices was proven by X-ray photoelectron spectroscopy (XPS) and electron dispersive spectroscopy (EDS) characterization. The UV‒vis, FT‒IR, and photoluminescent spectra of the synthesized S-GOQDs exhibited three absorption bands at 333, 395, and 524 nm, characteristic of C=S and C-S stretching vibration signals at 1075 cm-1 and 690 cm-1, and two excitation wavelength independent emission signals with maxima centered at 451 and 520 nm, respectively, confirming the successful doping of S atom into the GOQDs. Electronic structural analysis suggested that the S-GOQDs exhibited conduction band minimum (CBM) and valence band maximum (VBM) levels suitable for water splitting. Under a 500 W Xe-lamp irradiation, the S-GOQDs exhibited a high hydrogen generation efficiency of 351 μmol∙h-1∙g-1 in pure water, which is enhanced 4.2-fold to 1471 μmol∙h-1∙g-1 when the use of 80% ethanol as an electron donor. Under direct sunlight irradiation, an initial rate of 18,166 μmol∙h-1∙g-1 in pure water and 30,519 μmol∙h-1∙g-1 in 80% EtOH aqueous solution were obtained. Therefore, metal-free and inexpensive S-GOQDs hold great potential in the development of sustainable and environmental-friendly photocatalysts for efficient hydrogen generation from water-splitting.

In the past decade, rechargeable batteries attracted the attention from the researchers in search for renewable and sustainable energy sources. Up to date, lithium-ion battery is the most commercialized and has been supplying power to electronic devices and hybrid and electric vehicles. Lithium-ion battery, however, does not satisfy the expectations of ever-increasing energy and power density, which of their limits owes to its intercalation chemistry and the safety.1-2 Therefore, metal-air battery drew much attention as an alternative for its high energy density and a simple cell configuration.1 There are several different types of metal-air batteries that convey different viable reaction mechanisms depending on the anode metals; such as Li, Al, Ca, Cd, and Zn. Redox reactions take place in a metal-air cell regardless of the anode metal; oxidation reaction at the anode and reduction reaction at the air electrode. Between the two reaction, the oxygen reduction reaction (ORR) at the air electrode is the relatively the limiting factor within the overall cell reactions. The sluggish ORR kinetics greatly affects the performance of the battery system in terms of power output, efficiency, and durability. Therefore, researchers have put tremendous efforts in developing highly efficient metal air batteries and fuel cells, especially for high capacity applications such as electric vehicles. Currently, the catalyst with platinum nanoparticles supported on carbon material (Pt-C) is considered to exhibit the best ORR activities. Despite of the admirable electrocatalytic performance, Pt-C suffers from its lack of practicality in commercialization due to their prohibitively high cost and scarcity as of being a precious metal. Thus, there is increasing demand for replacing Pt with more abundant metals due economic feasibility and sustainability of this noble metal.3-5 Two different attitudes are taken for solution. The first approach is by optimizing the platinum loading in the formulation, or the alternatively the platinum can be replaced with non-precious materials. The purpose of this work is to discover and synthesize alternative catalysts for metal-air battery applications through optimized method without addition of precious metals. Different non-precious metals are investigated as the replacement of the precious metal including transition metal alloys, transition metal or mixed metal oxides, and chalcogenides. These types of metals, alone, still exhibits unsatisfying, yet worse, kinetics in comparison to the precious metals. Nitrogen-doped carbon material is a recently well studied carbon based material that exhibits great potential towards the cathodic reaction.6 Nitrogen-doped carbon materials are found to exhibit higher catalytic activity compared to the mentioned types of metals for its improved conductivity. Benefits of the carbon based materials are in its abundance and minimal environmental footprints. However, the degradation of these materials has demonstrated loss of catalytic activity through destruction of active sites containing the transition metal centre, ultimately causing infeasible stability. To compensate for these drawbacks and other limits of the nitrogen-doped carbon based catalysts, nitrogen-doped carbon nanotubes (NCNT) are also investigated in the series of study. The first investigation focuses on a development of a simple method to thermally synthesize a non-precious metal based nitrogen-doped graphene (NG) electrocatalyst using exfoliated graphene (Ex-G) and urea with varying amounts of iron (Fe) precursor. The morphology and structural features of the synthesized electrocatalyst (Fe-NG) were characterized by SEM and TEM, revealing the existence of graphitic nanoshells that potentially contribute to the ORR activity by providing a higher degree of edge plane exposure. The surface elemental composition of the catalyst was analyzed through XPS, which showed high content of a total N species (~8 at.%) indicative of the effective N-doping, present mostly in the form of pyridinic nitrogen groups. The oxygen reduction reaction (ORR) performance of the catalyst was evaluated by rotating disk electrode voltammetry in alkaline electrolyte and in a zinc-air battery cell. Fe-NG demonstrated high onset and half-wave potentials of -0.023 V (vs. SCE) and -0.110 V (vs. SCE), respectively. This excellent ORR activity is translated into practical zinc-air battery performance capabilities approaching that of commercial platinum based catalyst. Another approach was made in the carbon materials to further improve the cost of the electrode. Popular carbon allotropes, CNT and graphene, are combined as a composite (GC) and heteroatoms, nitrogen and sulfur, are introduced in order to improve the charge distribution of the graphitic network. Dopants were doped through two step processes; nitrogen dopant was introduced into the graphitic framework followed by the sulfur dopant. The coexistence of the two heteroatoms as dopants demonstrated outstanding ORR performance to those of reported as metal free catalysts. Furthermore, effects of temperature were investigated through comparing ORR performances of the catalysts synthesized in two different temperatures (500 ??? and 900 ???) during the N-doping process (consistent temperature was used for S-doping). Through XPS analysis of the surface chemistry of catalysts produced with high temperature during the N-doping step showed absence of N-species after the subsequent S-doping process (GC-NHS). Thus, the synergetic effects of the two heteroatoms were not revealed during the half-cell testing. Meanwhile, the two heteroatoms were verified in the catalyst synthesized though using low temperature during the N-doping process followed by the S-doping step (GC-NLS). Consequently, ORR activity of the resulting material demonstrated promising onset and half-wave potentials of -0.117 V (vs. SCE) and -0.193 V (vs. SCE). In combination of these investigations, this document introduces thorough study of novel materials and their performance in its application as ORR catalyst in metal air batteries. Moreover, this report provides detailed fundamental insights of carbon allotropes, and their properties as potential elecrocatalysts and essential concepts in electrochemistry that lies behind zinc-air batteries. The outstanding performances of carbon based electrocatalyst are reviewed and used as the guides for further direction in the development of metal-air batteries as a promising sustainable energy resource in the future.

Yes
We deposited Os atoms on S- and Se-doped boronic graphenic surfaces by electron bombardment of micelles containing 16e complexes [Os(p-cymene)(1,2-dicarba-closo-dodecarborane-1,2-diselenate/dithiolate)] encapsulated in a triblock copolymer. The surfaces were characterized by energy-dispersive X-ray (EDX) analysis and electron energy loss spectroscopy of energy filtered TEM (EFTEM). Os atoms moved ca. 26× faster on the B/Se surface compared to the B/S surface (233 ± 34 pm·s–1 versus 8.9 ± 1.9 pm·s–1). Os atoms formed dimers with an average Os–Os distance of 0.284 ± 0.077 nm on the B/Se surface and 0.243 ± 0.059 nm on B/S, close to that in metallic Os. The Os2 molecules moved 0.83× and 0.65× more slowly than single Os atoms on B/S and B/Se surfaces, respectively, and again markedly faster (ca. 20×) on the B/Se surface (151 ± 45 pm·s–1 versus 7.4 ± 2.8 pm·s–1). Os atom motion did not follow Brownian motion and appears to involve anchoring sites, probably S and Se atoms. The ability to control the atomic motion of metal atoms and molecules on surfaces has potential for exploitation in nanodevices of the future.
We thank the Leverhulme Trust (Early Career Fellowship No. ECF-2013 414 to NPEB), the University of Warwick (Grant No. RDF 2013-14 to NPEB), the EPSRC (EP/G004897/1 to RKOR), and ERC (Grant No. 247450 to PJS) for support.