Green Photo-active Nanomaterials: Sustainable Energy and Environmental Remediation
449
Green Photo-active Nanomaterials: Sustainable Energy and Environmental Remediation
449Hardcover
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Overview
Product Details
| ISBN-13: | 9781849739597 |
|---|---|
| Publisher: | RSC |
| Publication date: | 11/12/2015 |
| Series: | Green Chemistry Series , #42 |
| Pages: | 449 |
| Product dimensions: | 6.15(w) x 9.20(h) x (d) |
About the Author
Ramazan Asmatulu is an Associate Professor at Wichita State University. His research activities are focused on novel materials used for solar cells, batteries, nanocomposite fibres for biosensors, and nanocomposite coatings for protection of materials against corrosion and UV degradation.
Guido Mul is a Professor in the MESA+ Institute for Nanotechnology at the University of Twente, heading the photocatalytic synthesis group. His research activities are aimed at developing innovative materials and concepts to run photocatalytic reactions with high efficiency.
Read an Excerpt
Green Photo-active Nanomaterials
Sustainable Energy and Environmental Remediation
By Nurxat Nuraje, Ramazan Asmatulu, Guido Mul
The Royal Society of Chemistry
Copyright © 2016 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-1-84973-959-7
CHAPTER 1
Introduction to Green Nanostructured Photocatalysts
R. ASMATULU, N. NURAJE AND G. MUL
1.1 Introduction
1.1.1 General Background
Fossil fuel-based sources of energy, such as coal, oil, and natural gas, have been used to meet the world's energy demands for centuries; however, overproduction and overconsumption of these fuels have created many known and unknown concerns. Knowledge about the sources of mineral fuel, including nuclear energy, are also inadequate in terms of long-term waste disposal and lack of technology. Fossil fuel-based energy systems have a huge impact on the environment and are considered to be the major cause of global warming as well as air, soil, and water contamination and pollution. Because of dramatic economic development, population growth, environmental and health concerns, and increasing demands on clean energy sources, many countries have been seeking to find alternative energy sources to replace fossil and mineral-based fuels. These new sources of energy should be renewable, minimize/eliminate concerns, and, at the same time, be inexpensive and affordable by many nations of the world.
Renewable energy is usually defined as clean energy, which mainly comes from natural sources such as sunlight, rain, tides, wind, waves, biomass, and geothermal heat, and can be naturally replenished in a shorter period of time without harming the Earth. Solar energy is one of the greatest sources of renewable energy for meeting the world's demand because of its enormous magnitude – approximately 105 terawatts. The current energy con- sumption of the world is about 12 terawatts; this represents only 0.01% of the total amount of the Sun's energy that reaches the Earth's surface. This energy could be generated from an area 105 km2 in size that is installed with solar cells working at 10% efficiency. However, today, many energy con- version systems can easily pass the 10% energy conversion levels.
Even though energy from the Sun is one of the most widely considered renewable energy sources, new studies need to be conducted to address some concerns with solar energy, such as harnessing incident photons, lowering production costs, enhancing efficiency, storing energy, eliminating waste materials, eliminating health and environmental risks, dealing with seasonal changes, addressing the lack of technology, and so on. Nano-technology is an emerging technology that could address these concerns by using innovative strategies.
1.1.2 Nanotechnology in Energy Systems
Nanotechnology is the development of materials, components, devices, and/ or systems at the near-atomic level or nanometer scale. One of the dimensions of nanotechnology is between 1 and 100 nm. This technology mainly involves fabricating, measuring, modeling, imaging, and manipulating matter at the nanoscale. Nanotechnology consists of highly multidisciplinary fields, including chemistry, biology, physics, engineering, and some other disciplines. For more than two decades, significant progress has been made in designing, analyzing, and fabricating nanoscale materials and devices, and this trend will continue for a few more decades in various fundamental studies and in research and development fields.
Nanomaterials are the major building blocks of solar energy conversion devices and have been applied in the following three ways:
(a) the assembly of molecular and clusters of donors–acceptors mimicking photosynthesis
(b) the production of solar fuel using semiconductor-assisted photocatalysis
(c) the use of nanostructured semiconductor materials in solar cells.
Among the nanostructured solar energy conversion systems and devices, binary and ternary metal oxides are the most widely used and have a promising future in this field.
Even though several books have been published on renewable energy, solar cells, solar conversion, and solar fuels, very few books have been published on green photo-active nanomaterials and their major applications. Most books cover a broad spectrum of photocatalysts, including metal oxides and non-metal oxides. However, this book introduces and summarizes the fundamentals of harnessing solar energy using nanomaterials, synthetic approaches to green photo-active nanomaterials and their applications in designing artificial photochemical systems for solar energy conversion, and microorganisms found in solar energy conversion up until the present time. It describes the natural photosynthetic system in plants, the mechanisms involved in photosynthesis, and how components contribute to this sophisticated orchestration. Relevant cell biology as well as variations of the process used by plants in hot and dry environments are also discussed. The potential for biomass to contribute to meeting humanity's growing need for sources of energy is described, and a context is provided to frame efforts in mimicking natural photosynthesis in order to generate energy.
This book also focuses on applications of organic and inorganic nanomaterials utilized for fuel production from carbon dioxide and biomass, removal of contamination, water splitting, modeling, and health and environmental aspects of these green photo-active nanomaterials.
1.1.3 Environmental Considerations
Industrialization has significantly increased gas emissions and suspended particulate concentrations, and these concerns will likely continue for the next few decades, in turn further worsening the quality of air, soil, and water in the world and jeopardizing human life over the long term. Methane, carbon dioxide (CO2), and nitrogen oxide (NOx) are the primary greenhouse gas sources involved in global warming and climate change, so reducing these emissions is now a worldwide challenge. Microorganisms (e.g., microalgae, bacteria, viruses, fungi, and molds) can be an effective way of addressing some of these concerns. Nanomaterials can also offer structural features for reducing CO2 and other emissions in an environmentally friendly manner.
Combining microorganisms with nanomaterials can effectively capture greenhouse gasses from the atmosphere and convert them into carbon sources for the production of biomass and biofuels for industrial and household heating, transportation, agriculture practices, and many other uses. Also, plants can naturally absorb CO2 emissions and other contamination for their growth media and reduce toxicity levels. As an outcome of this cycle, concentrations of specific pollutants in the air, soil, and water can be significantly decreased. Carbon dioxide contains an abundant source of carbon, which supports the growth of microbial species and plants in the environment, and can be biochemically transformed into biomass and renewable energy sources to meet the world's demands.
1.2 Photo-active Nanomaterials
Some binary and ternary metal oxides are photoactive and are used for photocatalytic activities in solar cells, water splitting, and other solar-driven reactions. Synthetic methods for binary and ternary metal oxide photocatalysts emphasize green reaction processes. The advent of green, facile, and benign methods of producing these nanomaterials is necessary to comply with modern environmental concerns. An important aspect for such green methods is low temperature, fast reaction rate, and reduced toxic agents. The second chapter of this book highlights new techniques to produce photo-active nanomaterials in order to minimize the use and generation of hazardous substances during the manufacturing process. Such techniques include hydrothermal approaches along with the polymer gel method, chemical precipitation technique, solvothermal method, ultrasound sonication, and hybrid synthesis method. For example, even though several methods are currently available, such as solid state reactions, the polymerizable complex method, and the hydrothermal method, titanium dioxide (TiO2) is usually synthesized via sol–gel methods. Typically, particles synthesized by soft methods, including the polymerizable complex and sol–gel methods, provide higher performance than those synthesized using a solid state reaction because of the small particle size, shape, and good crystallinity.
The band gaps of metal oxides with d0 metal ions are usually formed from O 2p orbitals and nd orbitals from a metal cation, which are more negative than the zero potential of hydrogen ions. The band gaps of metal oxides are usually in the ultraviolet (UV) range. Powdered titania photocatalysts cannot split water without modification, such as a platinum (Pt) cocatalyst. Hydrogen production experiments have been conducted using a TiO2 photocatalyst with a band gap of 3.2 eV under different conditions, including pure water, vapor, and an aqueous solution including an electron donor with the assistance of a cocatalyst. Sodium hydroxide (NaOH) or sodium carbonate (Na2CO3) have been used to split water with a loaded Pt. Under UV irradiation, the efficiency of titania doped with other metal ions is considerably improved.
Zirconium dioxide (ZrO2) with a band gap of 5.0 eV is a photocatalyst that can split water without a cocatalyst under UV irradiation owing to the position of its high conduction band. Photocatalytic activity of ZrO2 decreased when it was loaded with cocatalysts, such as Pt, copper (Cu), gold (Au), and ruthenium oxide (RuO2). It is likely that the height of the electronic barrier of the semiconductor band metal impeded electron transport and stopped further molecular water-splitting reactions. Nevertheless, photocatalytic activity improved with the addition of Na2CO3.
Niobium pentoxide (Nb2O5) with a band gap of 3.4 eV is not active without any modification under UV irradiation. It decomposes water efficiently in a mixture of water and methanol after being loaded with a Pt cocatalyst. Its higher photocatalytic activity under UV irradiation was observed as assembled mesoporous Nb2O5. Tantalum pentoxide (Ta2O5) with a band gap of 4.0 eV is also a well-known photocatalyst. It can produce a small amount of hydrogen and no oxygen without any modification. Ta2O5 loaded with nickel oxide (NiO) and RuO2 shows great photocatalytic activity for generating both hydrogen and oxygen. The addition of Na2CO3 and a mesoporous structure of the catalyst showed enhanced photocatalytic activity. Nanostructured vanadium dioxide (VO2) with a body-centered cubic (BCC) structure and a large optical band gap of 2.7 eV demonstrated excellent photocatalytic activity in hydrogen production from a solution of water and ethanol under UV irradiation. It also exhibited a high quantum efficiency of 38.7%.2 Additionally, all of the metal oxides with d10 metal ions (Zn2+, In3+, Ga3+, Ge4+, Sn4+, and Sb5+) are effective photochemical water-splitting catalysts under UV irradiation.
Even though binary metal oxides with d0, d10, and f0 metal ions show efficient photocatalytic activity, their ternary oxides have been widely studied and proven to have the same photocatalytic effects. For instance, strontium titanate (SrTiO3) with a band gap of 3.2 eV and potassium tantalite (KTaO3) with band gap of 3.6 eV photoelectrodes can be photoactive without an external bias because of their high conduction bands. These materials can be employed as powder photocatalysts for solar cells and water splitting. Domen and co-workers studied the photocatalytic performance of NiO-loaded SrTiO3 powder for water splitting. A reduction in hydrogen gas (H2) is responsible for the activation of the NiO cocatalyst for H2 evolution. Then, subsequent oxygen gas (O2) oxidation to form an NiO/Ni double-layer structure provides a further path for the electron migration from a photocatalyst substrate to a cocatalyst surface. The NiO cocatalyst prevents the back reaction between H2 and O2, which is totally different for Pt. The enhanced photocatalytic activity of SrTiO3 was also reported using a new modified preparation method or suitable metal cation doping (e.g., La3+, Ga3+, and Na+).
Many ternary titanates are efficient photocatalysts for water splitting under UV irradiation. The H2 evolution of photocatalysts of sodium titanate Na2Ti3O7 (layered crystal structure), potassium titanate K2Ti2O5 (layered crystal structure), and potassium titanate K2Ti4O9 (layered crystal structure) from aqueous methanol solutions in the absence of a Pt cocatalyst was reported. The quantum yield of materials studied for H+-exchanged K2Ti2O5 reaches 10%. The method of catalyst preparation also shows a different activity. Barium titanate (BaTiO3) with a band gap energy of 3.22 eV and perovskite crystal structure prepared using a polymerized complex method has high photocatalytic activity in comparison with materials prepared by the traditional method because of the smaller size and larger surface area.
Calcium titanate (CaTiO3) with a band gap energy of 3.5 eV and perovskite crystal structure loaded with Pt showed good photocatalytic activity under UV irradiation. The activity of CaTiO3 doped with a zirconium ion (Zr4+) solid solution was further increased. Quantum yields were reported to be up to 1.91% and 13.3% for H2 evolution from pure water and an aqueous ethanol solution, respectively. A number of lanthanum titanate perovskites (including La2TiO5, La2Ti39, and La2Ti2O7) with layered structures were reported with much higher photocatalytic activities under UV irradiation than bulk LaTiO3. The photoactivities of La2Ti2O7 doped with barium (Ba), strontium (Sr), and (calcium) Ca was improved sufficiently. The lanthanum titanate perovskite La2Ti2O7 (band gap energy of 3.8 eV) prepared using a polymerized approach showed higher photoactivity than when the traditional solid-state method was used.
Biological materials used as templates, such as bacteriophages, offer environmentally friendly synthesis and organization of functional materials at the nanoscale, where there is an efficiency of energy transfer by increasing the probability of the energy transfer groups being precisely positioned. A biological system such as M13 viruses presents a rational design and assembly of nanoscale catalysts based on biological principles (which are required for the water-splitting reaction) for the production of oxygen and hydrogen gas driven by light.
1.3 Microorganisms in Energy Mitigations
Recent studies have indicated that nanotechnology materials and processes could be applied to microorganism growth processes to potentially improve biological biomass production from the atmosphere. This technology can significantly enhance biodiesel production and biomass conversion rates. It can also improve enzyme immobilization, lipid accumulation and extraction, enzyme loading capacity, nanoscale catalysis activity, storage capacity, separation and purification rates of liquid from other liquids and solids, and bioreactor design and applications.
(Continues...)
Excerpted from Green Photo-active Nanomaterials by Nurxat Nuraje, Ramazan Asmatulu, Guido Mul. Copyright © 2016 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Table of Contents
Introduction to Green Nanostructured Photocatalysts;Fundamentals of Sunlight-Materials Interactions;
Green Nanomaterials Preparation: Sustainable Methods and Approaches;
Natural Photosynthesis System;
Bioinspired Photocatalytic Nanomaterials;
Hybrid Molecular-Nanomaterial Assemblies for Water Splitting Catalysis;
Hierarchical Nanoheterostructures for Water Splitting;
Nanophotocatalysis in Selective Transformations of Lignocellulose-derived Molecules: A Green Approach for the Synthesis of Fuels, Fine Chemicals, and Pharmaceuticals;
Photocatalytic Carbon Dioxide Conversion to Fuels by Novel Green Photocatalytic Materials;
Hybrid Inorganic and Organic Assembly System for Photocatalytic Conversion of Carbon Dioxide;
Biological Systems for Carbon Dioxide Reductions and Biofuel Production;
Organic Reactions using Green Photo-active Nanomaterials;
Hierarchical Nanoheterostructures: Layered Double Hydroxide-based Photocatalysts;
Health and Environmental Aspects of Green-photoactive Nanomaterials;
Risk Assessments of Green Photo-active Nanomaterials;
Energy Harvesting from Solar Energy Using Nanoscale Pyroelectric Effects