Nitrogen-doped Hydrothermal Carbons

37 downloads 1892 Views 16MB Size Report
1 Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, .... nitrogen-doped HTC materials, it is important to mention that 13C CP MAS ...
Green, Vol. 2 (2012), pp. 25–40

Copyright © 2012 De Gruyter. DOI 10.1515/green-2011-0023

Review

Nitrogen-doped Hydrothermal Carbons Maria-Magdalena Titirici,1; Robin J. White1 and Li Zhao1;2

end applications. Among these, nitrogen-containing carbons have attracted particular interest due to their remarkable performance in industrially and environmentally im1 Department of Colloid Chemistry, Max Planck Institute portant applications such as CO2 sequestration [9], pHof Colloids and Interfaces, MPI Research Campus Golm, responsive adsorbents [10], purification (e.g. contaminant Potsdam, Germany removal from gas and liquid phases) [11], catalysts (or as 2 National Center for Nanoscience and Technology, Beiyi- catalysts supports) [12], or in electrochemistry (e.g. as sutiao, Zhongguancun, Beijing, China percapacitors [8, 13], fuel cells and batteries) [14], where addition of the nitrogen dopant acts to improve the electroAbstract. Nitrogen doped carbon materials are now play- chemical character/capacity parameters of the material [15]. Nitrogen-containing functionalities are of different types ing an important role in cutting edge innovations for energy on carbon materials (Figure 1). They can determine the conversion and storage technologies such as supercapaciacidic or basic character of carbons and thus its surface tors and proton exchange membrane fuel cells as well as chemical reactivity. in catalytic applications, adsorption and CO2 capture. The Traditionally, nitrogen has been introduced into a carbon production of such materials using benign aqueous based material’s structure in two ways [12, 16]: processes, mild temperatures and renewable precursors is of great promise in addressing growing environmental con1. “Post-doping”: Treatment of pre-synthesized carbon cerns for cleaner power sources at a time of increasing materials at high temperatures with nitrogen-containing global demand for energy. In this perspective, we show gases, typically leading to surface modification. that nitrogen doped carbons prepared using sustainable processes such as “Hydrothermal Carbonisation” has advan- 2. “In-situ doping”: Carbonisation of nitrogen containing organic compounds or mixtures of nitrogen-containing tages in many applications over the conventional carbons. precursors with nitrogen-free materials, leading to bulk We also summarize an array of synthetic strategies used to structural doping. create such nitrogen doped carbons, and discuss the application of these novel materials. Treatment of activated carbons with NH3 at high temperatures (e.g. 873–1173 K) is a relatively old but still freKeywords. Hydrothermal carbonization, nitrogen doped quently used method for the synthesis of nitrogen-doped carbon, biomass, energy storage. carbons [17, 18]. The nitrogen content/oxidation state, temperature and pore structure of such doped carbons has been PACS® (2010). 81, 88.

1

Introduction

Carbon materials have found a large number of applications in different domains ranging from environmental science [1, 2], to drug delivery [3, 4], and energy storage [5], according to their structural, morphological and chemical properties [6] Nevertheless, for some specific applications, addition of an appropriate functional surface group/bulk dopant is required [7, 8] In this context, doping of the “carbon” material structure with heteroatoms (e.g. B, N or S) is a popular route to tune both the structural and physico- Figure 1. Types of nitrogen-containing functionalities on chemical properties of such materials for various desired the carbon materials: (A) Pyrrole- like group; (B) Nitrile; (C) Secondary Amine; (D) Nitro Group; (E) Ni* Corresponding author: Maria-Magdalena Titirici, troso Group; (F) Tertiary Amine (G) Primary Amine; (H) E-mail: [email protected]. Pyridine-like Group; (I) Imine; (J) Amide; (K) Lactam; (L) Received: June 13, 2011. Accepted: February 10, 2012. Pyridone; and (M) Quaternary Amine.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

26

M.-M. Titirici, R. J. White and L. Zhao

Figure 3. Biomass-derived nitrogen containing precursors

used in the synthesis of nitrogen-doped carbonaceous materials.

Figure 2. Common “nitrogen” containing organic precur-

sors used in nitrogen doped carbon synthesis. extensively investigated over recent years [10, 19]. Other N-containing gases such as hydrogen cyanide (HCN) [18], or cyanogen (NC-CN) [20] have been similarly applied. As an alternative, N-containing liquid compounds (e.g. ionic liquids) have also been investigated as potential dopant sources in such post-doping approaches [21]. For example, urea has been used as nitrogen source for the production of a series of activated carbon materials [22]. Chemical impregnation of the carbon structure with melamine or other nitrogen-containing solutions followed by heat treatment at temperatures >950 K have also been documented [23]. “In-situ doping” methods offer more scope for significant modification of both structural and (electro)chemical properties of carbon materials, as compared to post-doping approaches. In-situ techniques have commonly been used to obtain nitrogen-doped carbon nanotubes (N-CNT) and nitrogen-doped carbon nanofibers (N-CNF) [24, 25], typically involving a suitable precursor and catalyst, using approaches similar to the methods employed in bulk CNT synthesis, such as high-temperature arc-discharge, laser ablation methods, pyrolysis, chemical vapour deposition (CVD) or solvothermal synthesis. Nitrogen-containing precursors commonly employed in these approaches include poly(acrylonitrile) [26], poly(aniline) [27], phthalocyanines [28], vinylpyridine [29], melamine [30], acetonitrile [31], and N-heterocycles (e.g. pyridine) (Figure 2) [32]. Via such “in-situ” methods, nitrogen can also be incorporated into different types of CNTs; N-doped single-walled carbon nanotubes (SWNTs) [33], double-walled carbon nanotubes (DWNTs) [34], and multi-walled CNx carbon nanotubes/nanofibers (MWNTs/MWNFs) [35]. For many of the applications outlined above, carbon materials with (ordered) nanostructural domains are preferred. In this context research efforts have recently been devoted to the development of template-growth procedures for the preparation of N-CNTs. For example, Xia has synthesized well-ordered porous N-doped carbons via CVD and pyroly-

sis at >800ı C by using mesoporous silica (e.g. SBA-15) as template [36]. Other templates, such as zeolite Y [37], and anodic aluminium oxide (AAO) [38], etc. have also found use as sacrificial structure directing media for the synthesis of N-CNTs. The synthesis of this kind of carbon usually involves preparation of the initial sacrificial template, replication of the typically inorganic phase, then subsequent carbonisation and finally template removal process. Although these nitrogen-doped carbons have attracted particular attention, the production methods rely on chemically harsh and multistep processes, typically involving high temperature treatment and often leading to the generation of significant quantities of waste, whilst in some cases the overall carbon yield of the process is rather limited. Furthermore, conventional nitrogen-containing precursors (e.g. poly(aniline)) are not necessarily sustainable and relatively expensive as compared to, for example, abundant biomassderived precursors such as the carbohydrates (Figure 3). In this context, biomass is a qualified carbon raw material for the synthesis of valuable carbon materials as it is available in high volume either as pure carbohydrates or biomass, and can be described as an environmental friendly renewable resource. In this regard the conversion of biomass into highly functional (porous) carbonaceous materials has received increasingly detailed attention in the literature in recent years. Two complimentary processes, namely the hydrothermal carbonisation (HTC) [39] and Starbon® [40] approaches, both attempt to fill the gap in materials technology between more classical (hydrophobic, inert) activated carbons and highly functional (but chemically unstable) inorganic (e.g. siliceous) materials. Both approaches generate valuable carbons via relatively inexpensive and simple routes, making the materials extremely attractive for a variety of (energy-related) applications, but importantly being derived from abundant sustainable biomass sources (e.g. glucose or polysaccharides) [41]. In this review, we will focus on the synthesis and applications of nitrogen-doped carbon materials derived primarily from the HTC approach, but concurrently look at the opportunities offered to the “green” materials chemist by the Starbon® approach, as such nitrogendoped materials are a relatively new addition to the area.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

27

Nitrogen-doped Hydrothermal Carbons

Figure 4. Scanning (a)–(c) and transmission (d)–(f) electron micrographs of the nitrogen-doped carbons obtained upon

hydrothermal carbonisation of (a) and (d) chitosan (HC-CH); (b) and (e) glucosamine (HC-GA) (c) and (f) glucose (HC-G). (Reproduced with permission from ref. [47]). 2 2.1

N-doped HTC from Amino-containing Carbohydrates One-step Approach

The HTC of monosaccharides such as the hexose glucose and related carbohydrates have been previously described [42], demonstrating the efficacy of this process for the preparation of carbonaceous materials [43]. Materials prepared via this approach have since found applications in the fields of heterogeneous catalysis [44], electrochemistry [45] and adsorption [46]. Recently, this approach has been extended to the production of nitrogendoped carbon materials using nitrogen-containing model monosaccharides or more complex polysaccharides (e.g. glucosamine hydrochloride or chitosan) as sustainable precursors [47]. The simple hydrothermal treatment of these precursors at mild temperature (e.g. 180–200ı C; >16 h) yields carbonaceous materials with high nitrogen contents. For chitosan-derived material (denoted as HC-CH) a carbon content of 59 wt% was found, whilst glucosamine and pure glucose-derived carbons (denoted as HC-GA and HCG) possessed ca. 65 wt% C. Nitrogen contents as high as 9.0 wt% were found in HC-CH and 6.8 wt% in HCGA respectively. The effect of the HTC process is to increase the material carbon content, due to a loss of oxygen and hydrogen in the dehydration process of the saccharide. Contrastingly, material nitrogen content was maintained from the precursor into the carbonaceous product in

both cases, demonstrating that no specific mechanism leading to nitrogen elimination occurs at such low processing temperatures, implying that the incorporation of nitrogen into the hydrothermal carbon structure is essentially stored in comparatively stable nitrogen bonding motifs (e.g. pyrrole). Morphologically, these nitrogen-doped HTC materials presented very different particle texture as compared to a reference sample prepared from pure glucose under the same conditions, where hard spherical particles of ca. D  500 nm without inner texture were obtained (Figure 4). In the case of HC-CH and HC-GA respectively, non-spherical particles were obtained, but rather a continuous network of agglomerated primary particles was found, displaying a continuous interconnected structure with interstitial macroporosity. The porosity of these primary particles determined via N2 sorption, demonstrated a lack of any developed porosity accessible to the probe molecule, with SBET 300 m2 g1 / composed of large continuous mesopores, combined with an excellent meso- and macroporous transport architecture; structuring not easily accessible by other synthetic approaches. They are also particularly suitable as potential hosts for the immobilization of biomolecules for biosensors, where a large interconnected pore system with diameters of > 10 nm is needed. We have also demonstrated that is possible to look into naturally occurring bio-nanocomposites for the production of porous nitrogen-doped carbons [69]. In this regard, nanometre scaled materials are familiar to biological systems. The development of novel materials based on these systems can be described as dominant theme in nanomaterials chemistry [40]. This interest is generated from the desire to produce materials that demonstrate the same efficiency, activity, and selectivity as those provided by Nature (e.g. plant photosynthetic systems). The development of said materials utilising natural preorganised systems, particularly those from inexpensive, abundant, and sustainable biomass (e.g. starch granules [70,71]) could go in some way to achieve such a goal and represent a holistic sustainable approach to the production of useful porous media, applicable in the development of tomorrow’s high technology [21].

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

30

M.-M. Titirici, R. J. White and L. Zhao

Figure 6. HR-TEM ((A) and (B)) and SEM images (C) of nitrogen-doped carbonaceous aerogels, “Carbogels” produced

via HTC based on the monosaccharide, Glucose and the nitrogen-containing protein, Ovalbumin, as precursors. (Reproduced with permission from [56].

inorganic (e.g. CaCO3 //organic (e.g. polysaccharide) composites) into porous carbonaceous scaffolds [72, 73]. The self-assembly of polysaccharides into organised structures with a cooperative inorganic component is especially well documented for the exoskeletons of crustaceans [74], where the polysaccharide content is sufficiently high to enable a follow-up conversion chemistry (Figure 8). It was our hope that such crustacean exoskeleton biocomposites could act as useful precursor biomass for the preparation of porous (nitrogen-doped) carbons, whereby the organic component (i.e. chitin (poly-ˇ(1!4)-N -acetylD-glucosamine); the carbon and nitrogen source) can be initially carbonised in the presence of the (structure donating) inorganic component (i.e. CaCO3 ), which finally can Figure 7. Effect of post-synthesis thermal treatment tembe removed via weak Brønsted acid (i.e. Acetic Acid) washperature (Tp ) on the surface nitrogen state in nitrogening. The use of such an acid is not trivial from a process doped HTC “Carbogels” (Reproduced with permission point of view and is to be compared with more aggresfrom [56]). sive reagents usually employed in inorganic template removal in conventional mesoporous carbon synthesis, (e.g. In this context, the wide variety of naturally occurring HF/NH4 F (aq) or caustic NaOH conditions) [49,75]. In our preorganised sugar-based nanostructures generated the in- first attempt we successfully synthesised prawn (shrimp) spiration for the transformation of biominerals (i.e. natural cask-derived carbon scaffolds presenting high surface area

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

31

Nitrogen-doped Hydrothermal Carbons

Figure 8. Major structural features of crustacean (here American Lobster) cuticle at the micrometer level. a) Optical mi-

crograph of cuticle cross section depicting epicuticle and the lamellar structure of the exocuticle and the endocuticle. b) Sketch showing the in-plane chitin-protein fibers forming a rotated plywood structure within the cuticle plane with interpenetrating out-of-plane fibers associated with calcite. c) SEM image of the chitin–protein planes within one inplane layer, showing pore canal tubes which belong to the ion transport system. d) SEM image of cross fractured cuticle from the carapace of the lobster showing the plywood structure formed by the rotating in-plane chitin protein fibers (thin arrows) and the out-of-plane chitin protein fibers (thick arrows) arranged along the cavities of the pore canals (pc) (Reproduced with permission from [73]). (SBET > 300 m2 g1 /, well-developed mesoporosity and high nitrogen content (7.0 wt%), via this truly sustainable approach. Unusual and interesting nanoscale carbon morphology was observed from TEM imaging, demonstrating promising linear, layered, nitrogen-doped material structuring (Figure 9) The textural properties of these exoskeletonderived porous carbons combined large (meso)pore volume in the relevant 2–10 nm mesopore range and good accessibility, with good mechanical stability and linear electronic conduction pathways [69]. This approach has since been extended to use more complex crustacean exoskeletons such as those from lobster [101]. The resulting carbons are arguably far more interesting from a materials science perspective and presumably reflect the increased biomaterial complexity in the lobster exoskeleton as compared to the prawn case. Lobster derived materials possess a very interesting hierarchical textural layering, with weave-like mesh structures at >1 µm level, with well-ordered macroporous structuring (Figure 10). This is complemented with decidedly interconnected slit pore morphology as the mesoscale, with a carbonisation temperature dependent micropore capacity.

Again in both exoskeleton-derived carbon examples, material chemistry can be directed by using post-synthesis carbonisation at elevated temperatures as a control vector. Application of these materials as electrodes for batteries, fuel cells, and supercapacitors are currently under investigation. Such complexity of the resulting carbon materials produced from this approach is presumably a reflection of the highly complex biomineral structures that essentially only nature is able to fabricate at this stage. Therefore this approach represents a somewhat elegant “biomimicry” for the synthesis of promising nitrogen-doped carbon materials, importantly synthesis from waste biomass and via a sustainable, simple, technology platform. The Starbon® Approach

Polysaccharides are renewable resources, readily available, inexpensive and functionally rich (e.g. –OH, -C(O)OH, -NH2 ). Polysaccharides are known to self-associate or order into particular structures, physical forms or shapes upon inducement of an aqueous gel state. Native polysaccharides present negligible surface and pore structure, and there-

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

32

M.-M. Titirici, R. J. White and L. Zhao

Figure 9. TEM images of prawn shell-derived carbon materials: (A) and (B) P1 – 750ı C (before); and (C) to (F) P2 –

750ı C (after acid processing) (taken with permission from [69]). fore in applications where diffusion and surface interactions (i.e. chromatography) are critical to function, polysaccharide use is therefore limited. In the late 1990’s Glenn et al. and Te Wierik et al. independently demonstrated that the low surface area of native starch could be expanded to generate xerogel materials with surface areas (SBET / between 25–145 m2 g1 , depending on preparative route [76–78]. Glenn et al. demonstrated that a highly expanded starch material can be obtained from retrograded starch gels by successively exchanging water for a series of lower surface tension solvents, consequently followed by drying via supercritical carbon dioxide (ScCO2 ) to yield a low density aerogel product. More recently research by the Clark group (Green Chemistry Centre, University of York) has demonstrated the potential of corn starch (73 % amylopectin) in the production of low density, high surface area starch xerogels (SBET  120 m2 g1 / for applications in normal phase chromatography separations [79, 80], and more promisingly microwave-assisted preparation of high amylose starch gels have afforded the preparation of tuneable high surface area highly mesoporous starch derived materials (SBET > 180 m2 g1 ; Vmeso > 0:6 cm3 g1 I > 95 % mesoporosity) [71]. This research demonstrated that the key to the formation of the porous polysaccharide form

in starch was the induction of metastable polysaccharide gel states. Further investigation demonstrated the key to highly mesoporous materials was the content of the linear ˛.1 ! 4/ poly(glucopyranose), amylose, as opposed to the other branched starch polysaccharide, amylopectin [72]. The essence of this approach relies on the inherent ability of polysaccharides to form an aqueous porous gel state, which upon extraction of gel bound water via a solvent exchange process (normally for a lower surface tension alcohol (e.g. ethanol)) produces a low density porous polysaccharide xerogel. The use of ScCO2 for the extraction of alcohol from saturated gel produces the corresponding aerogel gel materials with significantly enhanced porous properties [81]. These original approaches based on the starches, have recently been extended to the use of non-neutral (e.g. acidic) polysaccharides [82]. More recently the production of basic chitosan (poly-ˇ.1 ! 4/ D-glucosamine) based aerogels have been reported, exemplified by the seminal work of the Quignard group [83]. Whilst these polysaccharide aerogel-like materials are very interesting porous media in themselves (e.g. for chromatography, catalyst supports etc.), they are inherently metastable in nature, in the sense that over time the highly energetic porous state will eventually relax, resulting essen-

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

33

Nitrogen-doped Hydrothermal Carbons

Figure 10. Characterisation of Lobster exoskeleton-derived nitrogen-doped carbon (A) N2 sorption isotherm;

(B) (QS)DFT pore size distribution; (C) SEM and (D) TEM images (Taken with permission from 101-not yet accepted).

tially in the collapse of the porosity. This fact is exacerbated by the hygroscopic nature of these hydroxyl rich phases. Therefore, research has recently focused on the transformation of such nanoporous polysaccharide forms into more stable porous carbonaceous forms for high value applications, opening routes to the production of various differently structured porous materials and present a green alternative to traditional materials based on templating methods. The technology involves:

ble in the temperature preparation range from 150 to 1000ı C. At temperature above 700ı C the carbonisation process leads to the synthesis of robust mesoporous carbons with a wide range of technologically important applications. The distinctive feature of this Starbon®technology is the ability (alike to the aforementioned HTC derived materials) to tune the chemical properties of the material between that similar in nature to the original precursor polysaccharides (e.g. starch; high oxygen surface con1. Native polymer expansion via polysaccharide aqueous tent) to an increasingly more classical carbon surface (e.g. graphite-like), combining in a very simple manner the surgel preparation. face accessibility of mesoporous carbons with the com2. Production of solid mesoporous polysaccharide, via sol- plex chemistry of charcoals. In this regard the use of vent exchange/drying. nitrogen-containing precursors for the synthesis of such Starbons® would add a very interesting additive dimension 3. Thermal carbonisation/dehydration. The first generation starch-, pectin- and alginic acid- to material synthesis and allow the preparation of multiderived Starbons®are highly porous and mechanically sta- functional heteroatom-doped carbonaceous materials, ex-

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

34

M.-M. Titirici, R. J. White and L. Zhao

Figure 11. SEM (A & B) and TEM (C & D) images of (A) chitosan-derived aerogel (CA); (B) CA-derived nitrogen-

doped carbon prepared at 450ı C; (C) at 750ı C; and (D) 900ı C (non published results).

tending the application remit of the materials still further. We have recently reported the synthesis of highly porous (SBET > 140 m2 g1 ; Vpore > 1:0 cm3 g1 /, fibrous, chitosan aerogels using a method adapted from the earlier work of Quignard et al. [83] followed by the subsequent thermal (decomposition/dehydration) conversion of this nitrogencontaining porous biomass precursor into nitrogen-doped carbonaceous equivalents. The direct thermal conversion of the polysaccharide aerogel at low carbonisation temperatures (i.e. Tp < 650ı C), yield carbonaceous materials possessing high nitrogen contents (i.e. 7.0–11.0 wt%), whilst retaining in part the advantageous porous properties of the polysaccharide precursor. The carbon nanostructure of said materials was also particularly attractive, retaining the fibrous nature of the parent precursor, at both the macro and nanometre scale. Thermal treatment at temperatures at 750 and 900ı C, however resulted in a partial collapse of the (meso)porous structure and reduction in the promising textural properties presented by lower temperature materials. Characterisation by a combined XPS, TG-IR and electron microscopy, revealed that these textural changes occurred concurrently with a transformation in the surface nitrogen state(s) (i.e. pyrrole to pyridinic transition), a corresponding reduction in surface nitrogen content and a folding/twisting up/densification of the nitrogen doped carbonaceous fibres, with SEM and TEM demonstrating particu-

larly elegantly this morphological transition (Figure 11). The resulting structures in themselves represent surfaces of high curvature nitrogen-doped carbon, which are proving to be useful heterogeneous base catalysts (results not yet published). Since the classical production of nitrogen doped mesoporous carbons usually implies energetically intensive, chemically harsh and multi-step methodologies, the aforementioned HTC and Starbon®-based processes have clear advantages, being green, economical, mild and comparatively fast.

2.3 2.3.1

Applications Heterogeneous Catalysis

The development of greener and more sustainable heterogeneous catalysts and synthetic routes for the synthesis of fine chemicals and pharmaceuticals is evident and paramount in today’s society; carbon materials in this context have found a great number of different applications either as catalysts in their own right [84], as catalyst supports and as purification/separation media [85]. This application and interest of carbon based materials in said areas, derives in part from the mechanical, chemical and thermal stability offered by such media, making carbons excellent candidate materials for the preparation of new heterogeneous catalysts [16]. Recently, nitrogen-containing carbon nanotubes have been

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

35

Nitrogen-doped Hydrothermal Carbons

Figure 12. (A) Achieved turnover numbers in the first run with comparable amounts of Pt species (NDC description: pre-

cursor (NCA/ExLOB) – thermal treatment temperature (750ı C=900ı C); and Recycling tests for Pt@NDC (three runs each or five runs for Pt@ExLOB-900, respectively); (B) Pt content of catalysts prior to reaction; and (C) achieved catalytic activity expressed as turnover number (TON). (Reproduced with permission from [101] (not yet accepted)).

used as heterogeneous catalysts whereby the nitrogen edge groups (e.g. pyridinic) act as basic sites in the classical Knoevenagel condensation of benzaldehyde and ethylcyanoacetate to form ethyl-a-cyanocinnamate [86, 87]. However, the methods for the production of such nitrogen-containing carbon nanotubes rely on rather harsh and multistep processes, involving high temperatures as well as toxic catalysts (e.g. Co) and precursors (e.g. pyridine, acrylonitrile). There is also the associated potential difficulty with product contamination and catalyst recovery. With regard to fuels and platform chemicals, the direct utilization of natural gas (i.e. methane) via C-H activation is hindered by the high binding energy of the methane C-H bond (i.e. 435 kJ mol1 ) [88–93]. The currently most active homogenous catalytic system is that reported by Periana et al. [94–97], based on a dichlorobipyrimidyl platinum (II) complex (i.e. Pt(bpym)Cl2 ). The reaction, performed in fuming or concentrated sulfuric acid, gives methanol selectivities  90 %, via the intermediate methylbisulfate, which is then hydrolyzed to methanol in high overall yields. In this process the solvent is used, simultaneously, as both protecting and oxidizing agent [96, 98]. Recently, solid polymeric

catalysts, mimicking the molecular Periana system by coordinatively binding a Pt2C species to a nitrogen-rich Covalent Triazine Framework (CTF), has been shown to be highly active and recyclable with comparable turnover numbers (TON) to the Periana system [99, 100]. The hydrothermal treatment of inexpensive nitrogen containing biomass-derived precursors and subsequent direction of material chemistry (i.e. by thermal carbonisation), that is the N-doped Carbogel and lobster-shell derived carbons previously mentioned, similarly allowed the coordination of Pt2C species, giving access to novel highly active solid catalysts presenting excellent catalytic activity for direct methane oxidation [101]. The achieved catalytic activity were significantly superior to previously reported solid catalysts and in comparison to the molecular benchmark (i.e. Pt(bpym)Cl2 ) more turnovers were realized, while initial reaction rates are in the same range (Figure 12). The remarkable catalytic performance together with further targeted material development will facilitate new strategies in process development to design viable methane utilization, whilst the combination of excellent catalytic, particularly for the Pt@ExLOB-

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

36

M.-M. Titirici, R. J. White and L. Zhao

Figure 13. Electrochemical performance of different carbons using a three-electrode cell in 1 mol L1 H2 SO4 : a) Cyclic

voltammograms at a scan rate of 1 mVs1 , b) Galvanostatic charge/discharge curves at a current density of 0.2 A g1 , c) Relationship of the specific capacitance with respect to the charge/discharge specific currents, and d) Ragone plots (Taken with permission from [45]).

900 system, and the inexpensive and re-useable nature of Compared with other activated carbon precursors, the catalytic system makes the presented approach suitable biomassderived carbohydrates can be considered as a facile for commercial exploitation. “green”, scalable and inexpensive alternative to more traditional nitrogen-doped materials used in such energy applications. Using glucosamine derived HTC carbons (HCGA) as the base material, a series of nitrogen-containing 2.3.2 Supercapacitors activated carbons (denoted as CA-HC-GA) was syntheSupercapacitors are possible auxiliary energy storage de- sized via chemical activation (with increasing KOH convices to be used in unison with rechargeable batteries. tent) at 600ı C. Characterisation of the capacitive propHigh surface area activated carbons are the most com- erties of these materials by cyclic voltammetry and galmonly used materials in supercapacitors, with the large sur- vanostatic charge/discharge curves, indicated that although face area enhancing capacity for charge accumulation at these carbons presented lower surface areas (from 100 the electrode/electrolyte interface [102, 103]. As a general to 598 m2 g1 / as compared to the state of the art acrule for activated carbons with a specific surface area of tivated carbon systems, these biomass-derived HTC car1000 m2 g1 , the specific capacitance is 150 Fg1 [103]. bons exhibited a surprisingly high capacitive performance, Recently, an increasing number of papers have focused ni- as high as 300 Fg1 , as compared to previously reported trogen doping of activated carbons with the aim of improv- systems with similar surface areas (i.e. specific area < ing electronic conductivity or capacitance behaviour [21,26, 500 m2 g1 , the specific capacitance is assumed to be less 104]. It has to be mentioned that the carbon electrodes for than 100 Fg1 / [105]. The supercapacitive performances supercapacitors are at a relevant cost level, thus the devel- in acidic electrolyte were found to be better than in basic opment of lower-cost carbons with high surface area and electrolyte, believed to be related to the resident surface specific energy is one of the keys for the widespread appli- nitrogen functionalities of those HTC carbons (Figures 13 and 14). cation of supercapacitors.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

37

Nitrogen-doped Hydrothermal Carbons

Figure 14. Electrochemical performance of different carbons using a three-electrode cell in 6 mol L1 KOH: (a) Cyclic

voltammograms at a scan rate of 1 mVs1 , (b) Galvanostatic charge/discharge curves at a current density of 0.2 Ag1 , (c) Relationship of the specific capacitance with respect to the charge/discharge specific currents, and (d) Ragone plots (Taken with permission from ref. [45]).

Briefly, CA-HC-GA materials with high surface area and high nitrogen surface content/functionalities gave the highest supercapacitance, with CA-HC-GA-2 (“2” relates to the weight ratio of activating agent (KOH) to the HC-GA base material) presenting the best performance in both acid and base electrolytes as a result of the combination of high surface area (571 m2 g1 ) and high N content (4.4 wt%). For CA-GA-2, the specific capacitance was found to be 300 Fg1 in 1 mol L1 H2 SO4 and 220 Fg1 in 6 mol L1 KOH at a current density of 0.1 Ag1 , making such materials comparable to previously reported traditional activated carbons (Figures 13 and 14). However these previous systems utilised materials with surface areas in excess of 3000 m2 g1 [105], and a higher nitrogen-content carbon derived from poly(acrylonitrile), giving a specific capacitance of 160 Fg1 [106]. It is also important to note that even after 2000 cycles, a loss of only 5 % and 7 % in capacitance was observed in basic and acidic media respectively (as compared with starting values). Therefore considering the inexpensive nature of the material synthesis and the precursors used, coupled with the high capacities and scope for further property refining, these materials are considered to be promising candidate media for supercapacitor applications

3

Conclusions and Outlook

The conversion of nitrogen-containing inexpensive biomass to useful and applicable nitrogen-doped carbonaceous materials, particularly in high end topical energy related applications (e.g. supercapacitors) represents a useful and holistic approach to challenging today’s and the future energy demands in a green and sustainable manner. The advantage of using hydrothermal carbonisation for the production of heteroatom doped carbons is mainly the fact that it initially allows a chemical reaction to occur between the decomposition products of carbohydrates (HMF) and the nitrogen precursor via Maillard type chemistry. Therefore, the nitrogen is covalently bound to the final carbon structure allowing the possibility of large amounts of dopants to be introduced. This is a significant advantage compare with the classical pyrolytic processes of nitrogen containing precursors where most of the nitrogen is lost as volatile species. The final chemical structure of the resulting carbons can be tuned depending on the desired application. If this is adsorption or catalysis, then a post carbonisation step is not necessary and high nitrogen functionality is desired. If the materials are to be used for electrochemical applications, a post calcination step is necessary. However,

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

38

M.-M. Titirici, R. J. White and L. Zhao

since the nitrogen is chemically bond to the HTC structure, large amounts of heteroatoms can be maintained even after high temperature treatments. Furthermore, porosity can be introduced into such materials via several template free procedures. The incorporation of inorganic species (e.g. Pt) to the quaternary amino sites in the nitrogen doped carbons represents another interesting possibility to apply such materials in important catalytic reactions such as conversion of methane to methanol or even Oxygen Reduction Reactions (ORR) in Proton Exchange Membrane Fuel Cells (PEMFC). However, here the Pt scarcity and cost will lead to the development of alternative catalyst materials in the future for such applications. In the field of ORR non-noble metal or bio-inspired catalysts including nitrogen doped carbons alone showed almost comparable activities [107]. This is where the nitrogen doped hydrothermal carbons will have a lot of potential to replace the noble metal based composites and preliminary results are very promising. The nitrogen doped carbon materials are interesting since they can be here produced using biomass or biorelated precursors. More and more publications appear each day on this topic and very rarely good correlations between their properties/functions and chemical structures are provided. In this filed, the authors want to underline the importance of a fundamental understanding of each type of nitrogen functionality and final chemical constitution of the materials. Thus studies such as solid-state NMR, XPS and HRTEM mapping are here of a crucial importance since it represents the way to build strong relationship between the materials and their properties. We believe that this field of nitrogen doped carbons is at its very beginning and many other synthetic methods and applications are to be discovered. Particularly important in this respect would be the use of real waste biomass products rich in nitrogen as direct precursors in hydrothermal carbonisation. Algae biomass with their high content of lipids and proteins as well as carbohydrates might represent interesting precursors in this respect.

References [1] M. S. Mauter and M. Elimelech, Environmental Science & Technology 42 2008, 5843. [2] C. P. Huang and M. H. Wu, Water Research 11 1977, 673. [3] D. Pantarotto, J. P. Briand, M. Prato and A. Bianco, Chemical Communications 2004, 16. [4] A. Yan, B. W. Lau, B. S. Weissman, I. Külaots, N. Y. C. Yang, A. B. Kane and R. H. Hurt, Advanced Materials 18 2006, 2373. [5] A. C. Dillon, K. M. Jones, T. A. Bekkedahl, C. H. Kiang, D. S. Bethune and M. J. Heben, Nature 386 1997, 377. [6] A. A. Zakhidov, R. H. Baughman, Z. Iqbal, C. Cui, I. Khayrullin, S. O. Dantas, J. Marti and V. G. Ralchenko, Science 282 1998, 897. [7] C. T. Hsieh and H. Teng, Carbon 40 2002, 667.

[8] D. Hulicova, M. Kodama and H. Hatori, Chemistry of Materials 18 2006, 2318. [9] L. Zhao, Z. Bacsik, N. Hedin, W. Wei, Y. H. Sun, M. Antonietti and M. M. Titirici, Chemsuschem, 3, 840. [10] Y. F. Jia, B. Xiao and K. M. Thomas, Langmuir 18 2002, 470. [11] G. G. Stavropoulos, P. Samaras and G. P. Sakellaropoulos, Journal of Hazardous Materials 151 2008, 414. [12] Y. Shao, J. Sui, G. Yin and Y. Gao, Applied Catalysis B: Environmental 79 2008, 89. [13] M. Kawaguchi, A. Itoh, S. Yagi and H. Oda, Journal of Power Sources 172 2007, 481. [14] W. J. Weydanz, B. M. Way, T. Vanbuuren and J. R. Dahn, Journal of the Electrochemical Society 141 1994, 900. [15] L. Zhao, Y.-S. Hu, H. Li, Z. Wang and L. Chen, Advanced Materials 23, 1385. [16] in Carbon Materials for Catalysis (Eds.: P. Serp and J. L. Figueiredo), John Wiley & Sons, Inc., 2008. [17] J. Mrha, Collection of Czechoslovak Chemical Communications 31 1966, 715. [18] H. P. Boehm, A. R. Derincon, T. Stohr, B. Tereczki and A. Vass, Journal De Chimie Physique Et De PhysicoChimie Biologique 84 1987, 1449. [19] C. L. Mangun, K. R. Benak, J. Economy and K. L. Foster, Carbon 39 2001, 1809. [20] B. Stöhr, H. P. Boehm and R. Schlögl, Carbon 29 1991, 707. [21] J. P. Paraknowitsch, J. Zhang, D. Su, A. Thomas and M. Antonietti, Advanced Materials 22 2009, 87. [22] F. Adib, A. Bagreev and T. J. Bandosz, Langmuir 16 1999, 1980. [23] R. A. Hayden, 5, U.S. patent 1996, pp. 504. [24] C. P. Ewels and M. Glerup, Journal of Nanoscience and Nanotechnology 5 2005, 1345. [25] E. G. Wang, Journal of Materials Research 21 2006, 2767. [26] G. Lota, B. Grzyb, H. Machnikowska, J. Machnikowski and E. Frackowiak, Chemical Physics Letters 404 2005, 53. [27] H. Zengin, W. Zhou, J. Jin, R. Czerw, J. D. W. Smith, L. Echegoyen, D. L. Carroll, S. H. Foulger and J. Ballato, Advanced Materials 14 2002, 1480. [28] L. Zhi, T. Gorelik, R. Friedlein, J. Wu, U. Kolb, W. R. Salaneck and K. Müllen, Small 1 2005, 798. [29] J. Lahaye, G. Nanse, A. Bagreev and V. Strelko, Carbon 37 1999, 585. [30] D. Hulicova, J. Yamashita, Y. Soneda, H. Hatori and M. Kodama, Chemistry of Materials 17 2005, 1241. [31] M. Glerup, M. Castignolles, M. Holzinger, G. Hug, A. Loiseau and P. Bernier, Chemical Communications 2003, 2542. [32] R. Sen, B. C. Satishkumar, S. Govindaraj, K. R. Harikumar, M. K. Renganathan and C. N. R. Rao, Journal of Materials Chemistry 7 1997, 2335. [33] M. Glerup, J. Steinmetz, D. Samaille, O. Stéphan, S. Enouz, A. Loiseau, S. Roth and P. Bernier, Chemical Physics Letters 387 2004, 193. [34] S. Y. Kim, J. Lee, C. W. Na, J. Park, K. Seo and B. Kim, Chemical Physics Letters 413 2005, 300. [35] R. Czerw, M. Terrones, J. C. Charlier, X. Blase, B. Foley, R. Kamalakaran, N. Grobert, H. Terrones, D. Tekleab, P. M. Ajayan, W. Blau, M. Ruhle and D. L. Carroll, Nano Letters 1 2001, 457. [36] Y. Xia and R. Mokaya, Advanced Materials 16 2004, 1553.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

39

Nitrogen-doped Hydrothermal Carbons

[37] P.-X. Hou, H. Orikasa, T. Yamazaki, K. Matsuoka, A. Tomita, N. Setoyama, Y. Fukushima and T. Kyotani, Chemistry of Materials 17 2005, 5187. [38] S. Kubo, I. Tan, R. J. White, M. Antonietti and M. M. Titirici, Chemistry of Materials 22 2010, 6590. [39] M. M. Titirici and M. Antonietti, Chemical Society Reviews 39 2010, 103. [40] R. J. White, R. Luque, V. L. Budarin, J. H. Clark and D. J. Macquarrie, Chemical Society Reviews 38 2009, 481. [41] B. Hu, K. Wang, L. H. Wu, S. H. Yu, M. Antonietti and M. M. Titirici, Advanced Materials 22 2010, 813. [42] M. M. Titirici, M. Antonietti and N. Baccile, Green Chemistry 10 2008, 1204. [43] M. M. Titirici, A. Thomas, S. H. Yu, J. O. Muller and M. Antonietti, Chemistry of Materials 19 2007, 4205. [44] P. Makowski, R. D. Cakan, M. Antonietti, F. Goettmann and M. M. Titirici, Chemical Communications 2008, 999. [45] L. Zhao, L. Z. Fan, M. Q. Zhou, H. Guan, S. Y. Qiao, M. Antonietti and M. M. Titirici, Advanced Materials 22 2010, 5202. [46] R. Demir-Cakan, N. Baccile, M. Antonietti and M. M. Titirici, Chemistry of Materials 21 2009, 484. [47] L. Zhao, N. Baccile, S. Gross, Y. J. Zhang, W. Wei, Y. H. Sun, M. Antonietti and M. M. Titirici, Carbon 48 2010, 3778. [48] N. Baccile, G. Laurent, C. Coelho, F. Babonneau, L. Zhao and M. M. Titirici, Journal of Physical Chemistry C 115 2011, 8976. [49] C. Liang, Z. Li and S. Dai, Angewandte Chemie International Edition 47 2008, 3696. [50] C. O. Ania, V. Khomenko, E. Raymundo-Pinero, J. B. Parra and F. Beguin, Advanced Functional Materials 17 2007, 1828. [51] M. Rzepka, P. Lamp and M. A. de la Casa-Lillo, Journal of Physical Chemistry B 102 1998, 10894. [52] A. Linares-Solano, D. Lozano-Castello, M. A. LilloRodenas and D. Cazorla-Amoros, Chemistry and Physics of Carbon 30 2008, 1. [53] K. Jurewicz, K. Babel, A. Ziolkowski and H. Wachowska, Journal of Physics and Chemistry of Solids 65 2004, 269. [54] F. Beguin, K. Szostak, G. Lota and E. Frackowiak, Advanced Materials 17 2005, 2380. [55] E. Frackowiak and F. Beguin, Carbon 39 2001, 937. [56] R. J. White, N. Yoshizawa, M. Antonietti and M. M. Titirici, Green Chemistry 13 2011, 2428. [57] K. Nakanishi and N. Soga, Journal of the American Ceramic Society 74 1991, 2518. [58] O. Nunez, K. Nakanishi and N. Tanaka, Journal of Chromatography A 1191 2008, 231. [59] K. Nakanishi and N. Tanaka, Accounts of Chemical Research 40 2007, 863. [60] M. Terrones, P. M. Ajayan, F. Banhart, X. Blase, D. L. Carroll, J. C. Charlier, R. Czerw, B. Foley, N. Grobert, R. Kamalakaran, P. Kohler-Redlich, M. Ruhle, T. Seeger and H. Terrones, Applied Physics a-Materials Science & Processing 74 2002, 355. [61] Y. Xu, A. Tomita and T. Kyotani, Journal of the American Chemical Society 127 2005, 8956. [62] H. J. Burch, J. A. Davies, E. Brown, L. Hao, S. A. Contera, N. Grobert and J. F. Ryan, Applied Physics Letters 89 2006. [63] D. Mang, H. P. Boehm, K. Stanczyk and H. Marsh, Carbon 30 1992, 391.

[64] M. H. Nguyen and L. H. Dao, Journal of Non-Crystalline Solids 225 1998, 51. [65] S. C. Roy, A. W. Harding, A. E. Russell and K. M. Thomas, Journal of the Electrochemical Society 144 1997, 2323. [66] R. A. Sidik, A. B. Anderson, N. P. Subramanian, S. P. Kumaraguru and B. N. Popov, Journal of Physical Chemistry B 110 2006, 1787. [67] L. Jiang and L. Gao, Carbon 41 2003, 2923. [68] G. Reichenauer, A. Emmerling, J. Fricke and R. W. Pekala, Journal of Non-Crystalline Solids 225 1998, 210. [69] R. J. White, M. Antonietti and M. M. Titirici, Journal of Materials Chemistry 19 2009, 8645. [70] V. L. Budarin, J. H. Clark, R. Luque, D. J. Macquarrie and R. J. White, Green Chemistry 10 2008, 382. [71] R. J. White, V. L. Budarin and J. H. Clark, Chemsuschem 1 2008, 408. [72] L. Addadi and S. Weiner, Angewandte ChemieInternational Edition in English 31 1992, 153. [73] A. Al-Sawalmih, C. H. Li, S. Siegel, H. Fabritius, S. B. Yi, D. Raabe, P. Fratzl and O. Paris, Advanced Functional Materials 18 2008, 3307. [74] A. Sugawara, T. Nishimura, Y. Yamamoto, H. Inoue, H. Nagasawa and T. Kato, Angewandte Chemie-International Edition 45 2006, 2876. [75] R. Ryoo, S. H. Joo and S. Jun, Journal of Physical Chemistry B 103 1999, 7743. [76] G. M. Glenn and D. J. Stern, United States Patent 1999, 5958589. [77] G. M. Glenn and D. W. Irving, Cereal Chemistry 72 1995, 155. [78] G. H. P. T. Wierik, J. Bergsma, A. W. ArendsScholte, T. Boersma, A. C. Eissens and C. F. Lerk, International Journal of Pharmaceutics 134 1996, 27. [79] V. Budarin, J. H. Clark, F. E. I. Deswarte, J. J. E. Hardy, A. J. Hunt and F. M. Kerton, Chemical Communications 2005, 2903. [80] F. E. I. Deswarte, Fractionation of Wheat Straw Waxes, PhD Thesis, University of York, UK 2006. [81] F. Cansell, C. Aymonier and A. Loppinet-Serani, Current Opinion in Solid State & Materials Science 7 2003, 331. [82] R. Gavillon and T. Budtova, Biomacromolecules 9 2008, 269. [83] R. Valentin, K. Molvinger, F. Quignard and D. Brunel, New Journal of Chemistry 27 2003, 1690. [84] P. Serp, M. Corrias and P. Kalck, Applied Catalysis aGeneral 253 2003, 337. [85] R. A. Sheldon, Green Chemistry 10 2008, 359. [86] S. van Dommele, K. P. de Jong and J. H. Bitter, Chemical Communications 2006, 4859. [87] S. van Dommele, K. P. de Jong and J. H. Bitter, Topics in Catalysis 52 2009, 1575. [88] H. Arakawa, M. Aresta, J. N. Armor, M. A. Barteau, E. J. Beckman, A. T. Bell, J. E. Bercaw, C. Creutz, E. Dinjus, D. A. Dixon, K. Domen, D. L. DuBois, J. Eckert, E. Fujita, D. H. Gibson, W. A. Goddard, D. W. Goodman, J. Keller, G. J. Kubas, H. H. Kung, J. E. Lyons, L. E. Manzer, T. J. Marks, K. Morokuma, K. M. Nicholas, R. Periana, L. Que, J. Rostrup-Nielson, W. M. H. Sachtler, L. D. Schmidt, A. Sen, G. A. Somorjai, P. C. Stair, B. R. Stults and W. Tumas, Chemical Reviews 101 2001, 953. [89] R. H. Crabtree, Dalton Transactions 2001, 2437. [90] J. H. Lunsford, Catalysis Today 63 2000, 165.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26

40

M.-M. Titirici, R. J. White and L. Zhao

[91] A. E. Shilov and G. B. Shul’pin, Activation and catalytic reactions of saturated hydrocarbons in the presence of metal complexes Vol. 21, Kluwer, Dordrecht, 2000. [92] J. A. Labinger and J. E. Bercaw, Nature 417 2002, 507. [93] A. E. Shilov and G. B. Shul’pin, Chemical Reviews 97 1997, 2879. [94] R. A. Periana, D. J. Taube, S. Gamble, H. Taube, T. Satoh and H. Fujii, Science 280 1998, 560. [95] D. Wolf, Angewandte Chemie-International Edition 37 1998, 3351. [96] B. L. Conley, W. J. Tenn, K. J. H. Young, S. Ganesh, S. Meier, V. Ziatdinov, O. Mironov, J. Oxgaard, J. Gonzales, W. A. Goddard and R. A. Periana, Methane Functionalization, Wiley-VCH Verlag GmbH & Co. KGaA, 2006. [97] R. A. Periana, G. Bhalla, W. J. Tenn, K. J. H. Young, X. Y. Liu, O. Mironov, C. J. Jones and V. R. Ziatdinov, Journal of Molecular Catalysis A: Chemical 220 2004, 7. [98] I. H. Hristov and T. Ziegler, Organometallics 22 2003, 1668. [99] R. Palkovits, M. Antonietti, P. Kuhn, A. Thomas and F. Schüth, Angewandte Chemie-International Edition 48 2009, 6909. [100] R. Palkovits, C. von Malotki, M. Baumgarten, K. Mullen, C. Baltes, M. Antonietti, P. Kuhn, J. Weber, A. Thomas and F. Schüth, Chemsuschem 3 2010, 277. [101] M. Soorholtz, R. J. White, M. M. Titirici, M. Antonietti, R. Palkovits and F. Schüth, Chem. Commun., 2011, Submitted. [102] R. Kotz and M. Carlen, Electrochimica Acta 45 2000, 2483. [103] C. Vix-Guterl, E. Frackowiak, K. Jurewicz, M. Friebe, J. Parmentier and F. Béguin, Carbon 43 2005, 1293. [104] D. Hulicova-Jurcakova, M. Kodama, S. Shiraishi, H. Hatori, Z. H. Zhu and G. Q. Lu, Advanced Functional Materials 19 2009, 1800. [105] E. Raymundo-Piñero, K. Kierzek, J. Machnikowski and F. Béguin, Carbon 44 2006, 2498. [106] E. Frackowiak, G. Lota, J. Machnikowski, C. Vix-Guterl and F. Béguin, Electrochimica Acta 51 2006, 2209. [107] A. Morozan, B. Jousselme and S. Palacin, Energy & Environmental Science 4 2011 1238.

Robin White obtained his PhD at the Green Chemistry Centre of Excellence (York, UK), under the supervision of Prof. James Clark. He is currently a post-doctoral researcher at the Max Planck Institute of Colloids and Interfaces (Potsdam, Germany), working with Dr. MariaMagdalena Titirici and Prof.  Markus Antonietti. His research Interests focus on the development of novel sugar biomass derived porous carbons including ordered mesoporous materials, aerogels, hollow nanospheres, and naturally inspired systems, for applications as separation media, in electrochemistry and heterogeneous catalysis. Li Zhao obtained her PhD at the University of Potsdam while conducting the research at the Max Planck Institute of Colloids and Interfaces (Potsdam, Germany) under the supervision of Dr. Maria-Magdalena Titirici and Prof. Markus Antonietti. Currently Dr. Li Zhao is an Associate Professor at the National Center for Nanoscience and Technology Beijing China. Her research Interests focus on the development of sustainable materials for applications, in electrochemistry, particularly in the area of supercapacitors.

Magdalena Titirici obtained her PhD at the University of Dortmund, Germany under the supervision of Dr. Börje Sellergreen working in the filed of “Molecularly Imprinted Polymers”. Since 2006 she is leading the group “Sustainable Materials for Energy Storage” at the Max Planck Institute of Colloids and Interfaces, Potsdam, Germany within the “Colloid Chemistry Department” directed by Prof. Markus Antonietti. Her research interests include porous materials, hydrothermal carbonization, innovative utilization of biomass, biofules, thermoresponsive polymers, molecularly imprinted polymers and their applications as separation media, adsorption and gas storage, in electrochemistry (secondary batteries, supercapacitors) and heterogeneous catalysis.

Bereitgestellt von | De Gruyter / TCS (De Gruyter / TCS ) Angemeldet | 172.16.1.226 Heruntergeladen am | 24.04.12 09:26