Advanced Materials for Sustainable Energy and a Greener Environment

Authors

  • Prof. Bao-Lian Su ,

    Corresponding author
    1. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology, 122 Loushi Road, 430070 Wuhan, Hubei (PR China), Fax: (+86) 27 87879468;
    2. Laboratory of Inorganic Materials Chemistry (CMI), University of Namur (FUNDP), 61 rue de Bruxelles, 5000 Namur (Belgium)
    • State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology, 122 Loushi Road, 430070 Wuhan, Hubei (PR China), Fax: (+86) 27 87879468;
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  • Prof. Qingjie Zhang,

    Corresponding author
    1. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology, 122 Loushi Road, 430070 Wuhan, Hubei (PR China), Fax: (+86) 27 87879468;
    • State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology, 122 Loushi Road, 430070 Wuhan, Hubei (PR China), Fax: (+86) 27 87879468;
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  • Prof. Davide Bonifazi,

    Corresponding author
    1. Department of Chemistry, University of Namur (FUNDP), 61 rue de Bruxelles, 5000 Namur (Belgium)
    • Department of Chemistry, University of Namur (FUNDP), 61 rue de Bruxelles, 5000 Namur (Belgium)
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  • Prof. Jinlin Li

    Corresponding author
    1. Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and the Ministry of Education, South-Central University for Nationalities, 708, Minyuan Road, 430074 Wuhan (PR China)
    • Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and the Ministry of Education, South-Central University for Nationalities, 708, Minyuan Road, 430074 Wuhan (PR China)
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Abstract

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Materials for sustainability: The consumption rate of fossil fuels compared to the available resources and the calamity of global warming are two problems currently facing humanity. This issue describes research to address these problems, focusing on the use of natural systems to design functional materials, solar energy for environmental remediation, electricity production, and as energy source, and new materials for energy storage and conversion.

The world today is very different from how it once was. The consumption rate of fossil fuels compared to the available resources and the calamity of global warming, due at least in part to the increased emissions of CO2, are two problems currently facing humanity. The entire planet is at risk, but these are our crises. Mankind is the cause and so mankind should find the solution.

Hence, solving the two problems mentioned above has become a top priority. The effects of global warming and the energy crisis have spurred many research projects focused on reducing CO2 emissions and on finding and producing clean energy. The two issues are intimately linked because CO2, a major greenhouse gas, is evolved during the combustion of fossil fuels found buried below the surface, which in turn stem from nature’s assimilation of CO2 several million years ago.

Unfortunately, solutions to the energy crisis often come at the expense of the environment. Any solution that addresses just one aspect will fail. Various alternative forms of energy production using natural resources, taking the environment into consideration, have emerged. The first that should be mentioned is wind turbine technology (WTT). As an alternative to fossil fuels, it is considered plentiful, renewable, widely distributed, clean, and it emits no greenhouse gases during operation. However the cost of electricity produced is high. This technology is also not CO2-neutral, and in the overall wind energy process the reduction of CO2 emissions creates additional costs. The second technology is that of solar cells (SCs), and comprises one of the foremost applications of solar energy. Solar cells are considered a low-maintenance, continuous, and reliable energy conversion technology. The price of solar cells has fallen steadily over the past 40 years owing to progress made in materials science, enabling their worldwide application. Crystalline silicon solar devices are now approaching the theoretical efficiency limit of 29%. Nevertheless, the production of crystalline silicon for solar cells severely pollutes the environment and thus its continuous global use is problematic. The precursor for crystalline silicon production is often SiCl4. The pollution generated by chlorine emitted remains in the country where the SCs are produced while end-users benefit from the zero emissions during use.

Is it really possible to solve the energy crisis and reduce CO2 emissions at the same time? The solution may lie with advanced materials. These could also mitigate the drawbacks that exist in current wind turbine and solar cell technologies, and could improve the performances of these technologies. The ongoing development of our society depends on new advanced materials with multiple functionalities. Materials have changed our society. As materials science evolves, so does our lifestyle as it embraces the new technologies based on such materials. We are convinced that there can be no progress without novel materials.

Taking on board these two existential problems and searching for the new and sustainable solutions, this thematic issue of ChemSusChem is devoted to providing a current perspective on materials for sustainable energy and a greener environment. It contains 15 contributions, with 6 Reviews and Minireviews, 2 Communications, and 7 Full Papers. Most of the papers feature content presented during the “International Materials Forum: Materials for Sustainable Energy and Greener Environment” held at Wuhan University of Technology, Hubei, PR China on October 14, 2010. Other contributions are invited papers by authors with great expertise in their fields.

This special issue can be classified into three categories (see front cover image): (1) the use of natural systems to design functional materials for sustainable energy and greener environment; (2) the use of solar energy for environmental remediation, electricity production, and as energy source for chemical transformation; and (3) new materials for energy storage and conversion and for more efficient chemical processes, in view of energy and raw materials economy.

Natural systems

Nature is efficient: it uses compounds found in the environment and the needed quantity of energy for production and reproduction, adapts forms to follow function, and recycles everything under normal conditions. It teaches us how to live and how to survive. The growth mechanisms of natural materials have been found to use only weak interactions and ambient conditions, and thus are a source of inspiration for a rapidly growing community of materials scientists.1 Biomimicking and bioinspiration are two widespread strategies used to fabricate new advanced materials with desired functionalities. However, both can have a negative impact on the environment, as manmade materials often require high-temperature fabrication processes, resulting in higher energy demands than in nature.2

More recent studies have shown the possibility of directly using biological systems for green energy production, CO2 mitigation, and environmental remediation.3 Two excellent Reviews in this issue, by Fan et al. and Xu et al., address recent developments in the direct use of biological systems for sustainable energy production and a greener environment. The strategies used by these two groups are rather different. Fan et al. use biological systems as templates to fabricate advanced materials, keeping the fine structures and functionalities of the biological precursors, while Xu et al. directly use the biological organisms for environmental applications. These two approaches are complementary and in line with recent progress in the design of living hybrid materials for green energy production, environmental remediation, and smart cell therapy for health care developed by Su et al.

Fan and co-workers have reviewed the synthesis and application of biotemplated materials in key areas related to energy and environmental technologies, namely: photocatalytic hydrogen production, photocatalytic degradation, and gas/vapor sensing. They highlighted the role of four typical structures, derived from biological systems, which are exploited to optimize properties: hierarchical (porous) structures, periodic (porous) structures, hollow structures, and nanostructures. An accent has been made on the utilization of photosynthetic organisms, either as templates or as active systems to elaborate artificial leaves4 or leaf-like materials3 for the photocatalytic splitting of water for bio-H2 production and for biofuel production from CO2 and water by photosynthesis. Finally, they discuss the challenges of achieving the desired performance for large-scale applications and provide some useful prototypes from nature to design new materials or systems by biotemplating. This is a very comprehensive Review with a detailed analysis of the field. Xu and co-workers describe the idea of using the functionality of living cells, and finding appropriate methods to conserve these functionalities to serve in environmental remediation technologies. They developed a very elegant method to protect and extend the lifetime of living cells.5 Their work holds much potential for the design of biosensors, bioreactors and self-powered devices.6

The success of these strategies that directly use biological systems either as templates or as functional materials can generate an ideal scenario that could solve our two main problems simultaneously. A lesson can be drawn that in future mankind should do as nature, work as nature, produce as nature, and even exploit nature to ensure the continuing development of the humanity.

Solar energy

Every hour, the sun provides the Earth with more energy than our civilization uses in a whole year. If scientists could enable to convert even a fraction of that energy into a directly utilizable form, our addiction to using fossil fuels in everyday life, and the problems that these fuels cause, can end. A technology that would allow chemicals, or other forms of energy, to be made directly from sunlight in an efficient and costless way with minimal unrecyclable waste would be a game-changer. Tremendous efforts have been devoted to the development of materials and devices for the conversion of sunlight into useful chemicals by photosynthesis and photocatalysis and into electricity by SCs. A third of the papers in this thematic issue deal with this pressing problem.

In a Full Paper contributed by Aprile et al., highly efficient, stable, and reusable photocatalysts for the photocatalytic degradation of phenol in aqueous medium and acetaldehyde in air have been prepared by a non-aqueous synthesis under supercritical CO2 condition.

A high sunlight utilization rate is essential for a good turnover of photocatalytic reactions and an increased efficiency of solar cells. Doping materials is one solution to improve photon absorption efficiency as it can shift the absorption window from UV to visible light and thus increase the photon capture rate. Tremendous effort has been devoted to this aspect. In a Full Paper, Wu et al. propose to use a new concept to improve photocatalytic reaction efficiency: the slow photon. They demonstrated an example of a slow-photon-amplified photochemical reaction using three dimensional macroporous inverse TiO2 opaline structures (3DOM), where the reduction in the group velocity of light near the photonic band edge increased the absorption of photons within TiO2 to yield a great enhancement in the material’s efficiency in the photodegradation of Rhodamine B dye molecules. It is well-known that photonic crystals have a periodic dielectric contrast and possess a photonic band gap. Light with certain energies is forbidden to propagate because of Bragg diffraction. This leads to a stop-band reflection. At the frequency edges of stop bands, photons propagate with substantially reduced group velocity leading to the appearance of slow photons.610 The effect of the pore size of an inverse TiO2 opal in relation to photocatalytic activity has been studied since the stop band position depends on the macroporous size.

Instead of degrading organics, a Minireview contributed by Palmisano’s group proposed a new strategy to use photocatalytic reactions for organic synthesis by selective oxidation, for example, the hydroxylation of benzene to form various aldehydes. This is a new and sustainable solution to use organic pollutants as valuable chemical feedstocks. Cheng et al. have developed mesoporous TiO2 beads with various diameters which were used as working electrodes for dye-sensitized solar cells. Larger beads achieved the highest light conversion efficiency due to the highest electron diffusion co-efficient. Wu et al. prepared a TiO2/FTO (FTO: fluorine-doped tin oxide) electrode which showed very low splitting voltage during the production of hydrogen from formic acid. The use of sunlight as energy source or the conversion of sunlight energy into usable forms will attract growing attention in the coming years, making it a fundamental research field.

Energy storage and efficiency

A fuel cell (FC) is an electrochemical cell that converts chemical energy from a fuel into electrical energy via a constant-temperature process. Electricity is generated by a reaction between a fuel supply and an oxidizing agent. The reactants flow into the cell and the products flow out, while the electrolyte remains within. Two leading FC technologies under development today are PEMFCs (proton exchange membrane fuel cells) and SOFCs (solid oxide fuel cells).11 In a Full Paper. Lobato et al. describe a promising TiOSO4 composite polymer-based membrane for high-temperature PEMFCs. The current density produced and the stability of FCs are still two challenges that researchers need to take into account.

Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. Energy storage methods can be chemical, (e.g., H2 and hydrocarbons), biological (e.g., glycogen starch), electrochemical (e.g., batteries). electrical (e.g., capacitors, supercapacitors), mechanical (e.g., compressed air energy storage), thermal (e.g., ice storage and stem accumulator), and so on. Nevertheless, some disadvantages arise, related to low energy and power densities, large volume changes on reaction, safety, and costs. In a very comprehensive Review, Schwenzer et al. comment on recent membrane developments for vanadium redox flow batteries (VRFBs), aimed at improving the efficiency of VRFBs and making the technology cost-competitive. Finally they provided promising research strategies, materials, and suggestions on how various issues could be overcome. To complete the energy storage topic, Liu et al. present work on lead-free ceramics for energy storage device design.

Current chemical processes usually feature sequential and independent operations, generally including pretreatment of the starting materials, the chemical conversion of these materials into valuable products, and the purification of the resulting product mixtures in down-stream processes. As industry strives for sustainable process development, much effort has been devoted to the reduction of the number of reaction and separation steps. Recently, a comprehensive and precise concept was proposed: “hierarchical catalysis”.12 Hierarchical catalysis aims to integrate multistep processes in one single reactor, on the basis of a single hierarchical nanocatalyst. This would minimize the number of reaction steps involved in chemical conversions and, thus, reduce energy consumption and the amount of waste products, enhance performance, and increase operational safety. Su et al. and Siffert et al. discussed how to design hierarchically structured porous materials for hierarchical catalysis and their use in the total oxidation of volatile organic compounds. In a Minireview, Yuan and co-workers describe the synthesis of mesoporous non-silica-based organic–inorganic hybrid materials that can be used as efficient adsorbents for heavy metal ions, CO2, and aldehydes, as well as in the separation of polycyclic aromatic hydrocarbons. These materials have also been used as photocatalysts for dye molecule photodegradation.

Carbon nanotubes (CNTs) have been widely studied in very diverse fields, ranging from electronics, optics, solar cells and catalysis. Prato, Paolucci, Bonchio and co-workers show how covalently and noncovalently functionalized CNTs, bearing positively charged groups, can be used as scaffolds, undergoing self-organization with inorganic catalysts and yielding robust nanomaterials for electrocatalytic water splitting. In another work, Bonifazi and co-workers provide some new perspectives on the first utilization of functionalized CNTs for depolluting waste solvents from metal ions. The authors showed that pyridyl-derived CNTs could reversibly and selectively trap transition-metal ions, featuring a fully sustainable material.

We hope that this very brief introduction to the content of this very exciting thematic issue in a very hot research field stimulates the readers to learn more, and can serve as a guide to further reading. We also sincerely hope that readers find inspiration in this issue, and will take part in finding solutions to two fundamental problems of humanity and in the development of this rapidly evolving field.

Acknowledgements

We thank Dr. Christoph F. Meunier and Dr. Joanna C. Rooke for their assistance. The guest editors are also grateful to the authors for contributung to this thematic issue.

Biographical Information

Prof. Bao-Lian Su joined the faculty of the University of Namur (Belgium) in 1995, and there formed the Laboratory of Inorganic Materials Chemistry. He has received the Invention Award, Sinopec (PR China) in 1992 and the A. Wetrems Prize of the Royal Academy of Belgium in 2007. He is currently a member of the Royal Academy of Belgium (Class of Sciences) and a Full Professor of Chemistry, Director of the Research Centre for Nanomaterials Chemistry. He holds Changjiang Professorship at Wuhan University of Technology and appointed as an ‘‘Expert of the State’’ in the frame of ‘‘Thousands Talents’’ program, PR China. His current research fields include the synthesis, properties, and molecular engineering of organized, hierarchically porous, and bioinspired materials, living materials, and the immobilization of bio-organisms for artificial photosynthesis (leaf-like materials), nanotechnology, biotechnology, information technology, cell therapy and biomedical applications.

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Biographical Information

Prof. Qingjie Zhang is President of Wuhan University of Technology (PR China) and Director of the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Chair Scientist of National Basic Research Project (973 Project) for Thermoelectrical Materials and Devices and Vice-President of Chinese Energy Society. He has published more than 140 scientific papers and holds more than 10 patents, and obtained a series of national awards. His research interests focus on the design and applications of new composite materials (nanocomposite materials, hierarchically composite materials) and new energy materials.

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Biographical Information

Davide Bonifazi joined the group of Prof. François Diederich at the Swiss Federal Institute of Technology (ETH), Zürich (Switzerland) for a PhD degree from 2000–2004. He was awarded the Silver Medallion of the ETH for his doctoral dissertation (2005). After a post-doctoral fellowship with Prof. Maurizio Prato at the University of Trieste (Italy), he joined the Department of Pharmaceutical and Chemical Sciences as research associate. Since September 2006, he is junior professor in the Department of Chemistry at the University of Namur (Belgium). In 2010, he was awarded the “Ciamician Medal” of the Organic Division of the Italian Chemical Society. His research interests focus on the self-assembly/self-organization of optically active molecules, luminescent materials, organic porphyrin and peptide chemistry, BN-doped materials and functionalization of carbon-based nanostructures.

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Biographical Information

Prof. Jinlin Li was born in September 1963. He obtained his PhD from University of the Witwatersrand, Johannesburg (South Africa) in 1998. After a post-doctoral stay at the Center for Applied Energy Research, University of Kentucky (USA) from 1999 to 2002, he became Dean of the College of Chemistry and Materials Science, South-Central University for Nationalities (PR China) in 2003. He is currently Vice-President of South-Central University for Nationalities. He is a member of the Catalysis Society of China. He was awarded the Prize of Science and Technology Progress, Hubei Province (PR China) for his work on Fischer-Tropsch synthesis in 2006. His research includes the synthesis, characterization, and catalytic properties of Fischer-Tropsch catalysts.

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