Green Photo-active Nanomaterials
Sustainable Energy and Environmental Remediation


RSC Green Chemistry
Editor-in-Chief:
Professor James Clark, Department of Chemistry, University of York, UK

Series Editors:
Professor George A. Kraus, Department of Chemistry, Iowa State University,
Ames, Iowa, USA
Professor Andrzej Stankiewicz, Delft University of Technology, The Netherlands
Professor Peter Siedl, Federal University of Rio de Janeiro, Brazil

Titles in the Series:
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The Future of Glycerol: New Uses of a Versatile Raw Material
Alternative Solvents for Green Chemistry
Eco-Friendly Synthesis of Fine Chemicals
Sustainable Solutions for Modern Economies
Chemical Reactions and Processes under Flow Conditions
Radical Reactions in Aqueous Media

Aqueous Microwave Chemistry
The Future of Glycerol: 2nd Edition
Transportation Biofuels: Novel Pathways for the Production of Ethanol,
Biogas and Biodiesel
10: Alternatives to Conventional Food Processing
11: Green Trends in Insect Control
12: A Handbook of Applied Biopolymer Technology: Synthesis, Degradation
and Applications
13: Challenges in Green Analytical Chemistry
14: Advanced Oil Crop Biorefineries
15: Enantioselective Homogeneous Supported Catalysis
16: Natural Polymers Volume 1: Composites
17: Natural Polymers Volume 2: Nanocomposites
18: Integrated Forest Biorefineries
19: Sustainable Preparation of Metal Nanoparticles: Methods and
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20: Alternative Solvents for Green Chemistry: 2nd Edition
21: Natural Product Extraction: Principles and Applications
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27: Renewable Resources for Biorefineries
28: Transition Metal Catalysis in Aerobic Alcohol Oxidation
29: Green Materials from Plant Oils


30: Polyhydroxyalkanoates (PHAs) Based Blends, Composites and

Nanocomposites
31: Ball Milling Towards Green Synthesis: Applications, Projects, Challenges
32: Porous Carbon Materials from Sustainable Precursors
33: Heterogeneous Catalysis for Today’s Challenges: Synthesis,
Characterization and Applications
34: Chemical Biotechnology and Bioengineering
35: Microwave-Assisted Polymerization
36: Ionic Liquids in the Biorefinery Concept: Challenges and Perspectives
37: Starch-based Blends, Composites and Nanocomposites
38: Sustainable Catalysis: With Non-endangered Metals, Part 1
39: Sustainable Catalysis: With Non-endangered Metals, Part 2
40: Sustainable Catalysis: Without Metals or Other Endangered
Elements, Part 1
41: Sustainable Catalysis: Without Metals or Other Endangered
Elements, Part 2
42: Green Photo-active Nanomaterials: Sustainable Energy and
Environmental Remediation

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Green Photo-active
Nanomaterials
Sustainable Energy and Environmental
Remediation

Edited by

Nurxat Nuraje
Texas Tech University, Lubbock TX, USA
Email:

Ramazan Asmatulu
Wichita State University, Wichita KS, USA
Email:

Guido Mul
University of Twente, Enschede, The Netherlands
Email:


RSC Green Chemistry No. 42
Print ISBN: 978-1-84973-959-7
PDF eISBN: 978-1-78262-264-2
ISSN: 1757-7039
A catalogue record for this book is available from the British Library
r The Royal Society of Chemistry 2016
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Preface
Energy and environmental issues are of great concerns for the public and
will keep increasing in the next few decades. The demand for clean
energy sources in our current society also increases with large-scale economic developments and population growth. It is crucial to build clean
energy systems in order to solve both the environmental issues and the
energy demands. Alternative energy sources to replace fossil and mineralbased fuels have been actively searched for to meet the clean energy
demands. Among the renewable energy sources defined as clean energy from
natural sources, such as solar, rain, tides, wind, waves, biomass, and geothermal heat, solar energy is one of the greatest sources of renewable energy
for meeting the above demands.
Along with developments of related solar technologies, storage of this
energy as chemical energy in the form of hydrogen is a promising method to

add to the solar cell technology, due to its sporadic nature. At present, solar
hydrogen production from water has been achieved by the following several
methods:
(1) electrolysis of water using a solar cell
(2) reforming of biomass
(3) photocatalytic or photoelectrochemical water splitting.
Photocatalytic water splitting is an artificial photosynthesis technique and
contributes to a definitive green sustainable chemistry to solve energy and
environmental issues.
This book, entitled Green Photo-active Nanomaterials: Sustainable Energy
and Environmental Remediation, is an advanced book about the fundamentals of solar energy conversion, natural and artificial photosynthetic
systems, nanotechnology and nanoscience, and the application of
RSC Green Chemistry No. 42
Green Photo-active Nanomaterials: Sustainable Energy and Environmental Remediation
Edited by Nurxat Nuraje, Ramazan Asmatulu and Guido Mul
r The Royal Society of Chemistry 2016
Published by the Royal Society of Chemistry, www.rsc.org

vii


viii

Preface

nanoscience and nanotechnology in energy and environmental remediation,
as well as educational and training purposes. Furthermore, nanotechnology
has a great potential to design artificial photosynthesis systems to store solar
energy, produce fuels from biomass, reduce organic contaminants from
the environment, and convert carbon dioxide to useful hydrocarbon fuels

because of the outstanding mechanical, electrical (conductive and semiconductive), optical, magnetic, quantum mechanics, and thermal properties
of nanomaterials. These unique properties of nanoscale materials, such as
nanoparticles, nanotubes, nanowires, nanofibers, nanocomposites, nanopores, and nanofilms, allow them to design the next generation of photosynthetic devices in energy and environmental applications.
Recent publications in green photoactive nanostructured materials for
energy and environment have shown that increased and sophisticated progress has been made using innovatively designed nanostructured materials
in various devices. It is very important for us to provide an advanced book
which can provide the basic science of nanomaterial and solar spectrum
interactions, green synthesis of nanomaterials, and descriptions of natural
photosynthetic systems which will inspire us to design more efficient
photoelectrochemical devices. This book will detail recent developments in
green photo-active nanostructures materials in water splitting, biomass, and
environmental remediation. It also emphasizes the recent development of
nanostructured materials for carbon dioxide conversion, degradation of
pollutants in environment, and green chemistry. The book also discusses the
safety and risk assessments of the nanostructured materials used for various
energy production systems. Therefore, this book will be informative for
researchers in photoactive nanomaterials in energy and environment
application, and also will be an excellent text book for advanced study in the
Universities from fundamental points of views.
Thus, the editors are very pleased to present the recent progress in
photo-active nanomaterials in energy and environment remediation in the
publication of this great book for engineers, scientists and other readers,
policy makers, and scientific communities. We are also thankful for the
authors’ hard work and contributions, and reviewers’ comments and suggestions. During the editing process, we also have received tremendous
support from the editorial team of the RSC, including Dr. Merlin Fox and
Dr. Mina Roussenova. We also specially thank Dr. Sindee Simon (Texas Tech)
for her kind advice and support. We acknowledge all support from Texas
Tech University, MIT, and Wichita State University. Without all the above
support, it would not have been possible for us to publish this book.
Dr Nurxat Nuraje, Texas Tech University, USA

Dr Ramazan Asmatulu, Wichita State University, USA
Dr Guido Mul, University of Twente, The Netherlands


Contents
Chapter 1 Introduction to Green Nanostructured Photocatalysts
R. Asmatulu, N. Nuraje and G. Mul
1.1

Introduction
1.1.1 General Background
1.1.2 Nanotechnology in Energy Systems
1.1.3 Environmental Considerations
1.2 Photo-active Nanomaterials
1.3 Microorganisms in Energy Mitigations
1.4 Environmental Health and Safety
1.5 Contents of This Book
1.6 Conclusions
Acknowledgements
References
Chapter 2 Fundamentals of Sunlight–Materials Interactions
Yunhui Zhu and Hang Yu
2.1
2.2

Introduction
Solar Energy and the Solar Spectrum
2.2.1 The Sun as the Ultimate Energy Source
2.2.2 The Spectrum of Sunlight
2.2.3 Interaction of Sunlight with the Atmosphere

on Earth
2.2.4 The Geographic Intensity Distribution of
Sunlight

RSC Green Chemistry No. 42
Green Photo-active Nanomaterials: Sustainable Energy and Environmental Remediation
Edited by Nurxat Nuraje, Ramazan Asmatulu and Guido Mul
r The Royal Society of Chemistry 2016
Published by the Royal Society of Chemistry, www.rsc.org

ix

1

1
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3
4
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Contents

2.3

Interactions of Light and Photo-active Materials
2.3.1 Reflection
2.3.2 Scattering
2.3.3 Absorption
2.3.4 Luminescence
2.3.5 Nonlinear Effects
2.3.6 Transmission
2.4 Quantum Yield in Solar Energy Conversion
2.4.1 Definition of Quantum Yield
2.4.2 Quantum Yield in Light–Materials
Interactions
2.4.3 Beyond Quantum Yield: Eco and
Environmental Sustainability
References
Chapter 3 Green Nanomaterials Preparation: Sustainable Methods
and Approaches
Xiaoyang Xu, Qian Lyu, Joshua Bader and Meagan Accordino
3.1
3.2


Introduction
Titanium Dioxide
3.2.1 Microwave-assisted Hydrothermal Method
3.2.2 Polymer-gel Method
3.3 Cadmium Sulfide
3.3.1 Chemical Precipitation Method
3.3.2 Solvothermal Method
3.4 Zinc Oxide
3.4.1 Microwave-assisted Hydrothermal
Technique
3.4.2 Ultrasound Sonication
3.5 Hybrid Nanomaterial
3.5.1 ZnO/TiO2 Composite
3.5.2 CdS/TiO2 Nanocomposite
3.5.3 Graphene/TiO2 and Graphene/TNT
Nanocomposite
3.6 Conclusion
References
Chapter 4 Natural Photosynthesis System
David S. Gray and Nulazhi Yeerxiati
4.1
4.2

The Wonder and Impact of Photosynthesis
The Method and Products of Photosynthesis

20
20
21

21
23
24
25
25
25
26
31
32

34

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Contents

xi

4.3
4.4
4.5
4.6
4.7
4.8

Harvesting Light Energy
Water Splitting for Supply of Protons and Electrons
Fixation of Carbon from Carbon Dioxide
The Electron Transport Chain (ETC)
Chloroplasts: Containers for Photosynthesis
The Photosynthetic Machinery
4.8.1 PSII
4.8.2 Plastoquinol
4.8.3 Cytochrome b6f Complex
4.8.4 Plastocyanin
4.8.5 PSI
4.8.6 Comparison and Contrast of PSII and PSI
4.8.7 F-ATPase
4.9 Cyclic and Non-cyclic Electron Flow
4.9.1 Light-independent Reactions

4.9.2 Photorespiration (C2 Cycle)
4.9.3 Two Additional Methods of Carbon Fixation
4.10 Actual Efficiency of Photosynthesis
4.11 Recovering from Damage from Light
4.12 Biomass
4.13 Biomimicry
4.14 Evolution
4.15 Conclusion
References
Chapter 5 Bioinspired Photocatalytic Nanomaterials
Md Nasim Hyder and Zakia Sultana
5.1
5.2

Introduction
Mechanism of Photoelectrochemical Water
Splitting
5.3 Materials Design and Synthesis
5.4 Photoelectrochemical Cell Design
5.4.1 Design of Photocatalytic Electrodes
5.4.2 Membrane Separator
5.5 Summary
References
Chapter 6 Hybrid Molecular–Nanomaterial Assemblies for Water
Splitting Catalysis
Nan Jiang, Meili Sheng and Yujie Sun
6.1

Introduction


66
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68
68
71
71
74
78
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Contents

6.2

Hydrogen Evolution Reaction
6.2.1 Hybrid Assemblies Containing Iron Catalysts
6.2.2 Hybrid Assemblies Containing Cobalt
Catalysts
6.2.3 Hybrid Assemblies Containing Nickel
Catalysts
6.3 Oxygen Evolution Reaction
6.3.1 Hybrid Assemblies Containing Ruthenium
Catalysts
6.3.2 Hybrid Assemblies Containing Iridium
Catalysts
6.3.3 Hybrid Assemblies Containing Manganese
Catalysts
6.3.4 Hybrid Assemblies Containing Iron

Catalysts
6.4 Conclusion
References

Chapter 7 Hierarchical Nanoheterostructures for Water Splitting
Md Moniruddin, Sarkyt Kudaibergenov and
Nurxat Nuraje
7.1
7.2

Introduction
Water Splitting by Photocatalysts
7.2.1 Thermodynamic and Kinetic
Considerations
7.2.2 The Mechanism of Photocatalytic Water
Splitting
7.2.3 Standard of Measurement
7.3 Heterostructure Photocatalysts for Water
Splitting
7.3.1 UV Active Photocatalysts
7.3.2 Visible-light-sensitive Photocatalysts
7.3.3 Photocatalysts for the Z-scheme Reaction
7.4 Photoelectrochemical Cells for Water Splitting
7.4.1 Principle of Photoelectrochemical Cells
7.4.2 Fabrication Methods for a Photoelectrode
7.4.3 Metal Oxide-based Photoelectrochemical
Cells
7.4.4 Dye-assisted Photoelectrochemical Cells
7.5 Summary
References


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110
116
121
124
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150
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Contents

xiii

Chapter 8 Nanophotocatalysis in Selective Transformations of
Lignocellulose-derived Molecules: A Green Approach for
the Synthesis of Fuels, Fine Chemicals, and
Pharmaceuticals
Juan Carlos Colmenares
8.1
8.2

Introduction
Basic Principles of Heterogeneous Oxidative
Photocatalysis
8.2.1 Reactive Oxygen Species (ROS) in
Photocatalysis
8.3 Lignocellulose as a Feedstock for Chemicals
8.4 Application of Nanostructured Photocatalysts in
Lignocellulose Valorization
8.4.1 Photocatalytic Production of Hydrogen
8.4.2 Photocatalytic Upgrading of
Lignocellulose-based Molecules: Production
of High-value Chemicals
8.5 Outlook and Future Challenges
Acknowledgements
References


Chapter 9 Photocatalytic CO2 Conversion to Fuels by Novel Green
Photocatalytic Materials
W. A. Maza, Amanda J. Morris and Guido Mul
9.1
9.2

9.3

9.4

Introduction and some Simple Back of the Envelope
Calculations
TiO2 and Metal-doped TiO2 Composites
9.2.1 Background on TiO2-based CO2
Reduction
9.2.2 Earth-abundant Transition Metal/Metal
Oxide–TiO2 Composites
Supported Silica Framework Catalysts
9.3.1 Introduction
9.3.2 Synthesis of Mesoporous Materials
9.3.3 Mechanism of CO2 over Isolated Ti Sites
9.3.4 Metal to Metal Charge Transfer Complexes
9.3.5 Water Oxidation Functionality
9.3.6 Adsorption of CO2 and (Prevention of) Back
Reactions
Graphene/Graphene Oxide–TiO2 Composites

168


168
169
171
172
173
173

185
196
197
197

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xiv


Contents
IV

9.5 Ti -based Metal Organic Framework Catalysts
9.6 Conclusions and Outlook
References

231
232
234

Chapter 10 Hybrid Inorganic and Organic Assembly System for
Photocatalytic Conversion of Carbon Dioxide
Xin Zhang, Yu Lei and Nurxat Nuraje

240

10.1

Introduction to the Conversion of Carbon Dioxide
and Industrial Applications
10.2 Theories of Carbon Dioxide Conversion
10.2.1 Electrochemistry, Kinetics, and
Thermodynamics of Photoreduction
Reactions
10.2.2 Measuring Criteria for Semiconducting
Particles System under UV and Visible
Spectrum
10.2.3 Measuring Criteria for Molecular
Photocatalyst System under UV and

Visible Spectrum
10.3 Inorganic Semiconducting Materials for
Photocatalytic Reduction of Carbon Dioxide
10.4 General Research Guidance for Molecular
Catalysts of Photocatalytic Reduction of
Carbon Dioxide
10.5 Research Cases
10.5.1 Example 1: Reduction of CO2 to CO
10.5.2 Example 2
10.6 Conclusions
Acknowledgements
References
Chapter 11 Biological Systems for Carbon Dioxide Reductions and
Biofuel Production
E. Asmatulu
11.1

11.2

Introduction
11.1.1 General Background
11.1.2 Microorganisms and Growth Conditions
Algae Processing
11.2.1 Algae Farming Locations and Bioreactors
11.2.2 Algae Fuels

240
243

243


248

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269
271
271

274

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278
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Contents

xv

11.3


Parameters Affecting Algae Growth
11.3.1 Effects of Bubble Size and Mixing
11.3.2 Impacts of Nanomaterials and Processes
on Lipid Accumulations
11.3.3 Nanotechnology and Illumination for
Bioreactor Design
11.4 Nanocatalysts for Algal Fuel Productions
11.4.1 Nanocatalysts in Algae Growth, Lipid
Accumulation, and Extraction
11.4.2 Other Process Parameters Affecting Lipid
Extractions
11.5 Conclusions
References

Chapter 12 Organic Reactions using Green Photo-active
Nanomaterials
Hanying Bai
12.1
12.2

12.3

12.4
12.5

12.6

Introduction
TiO2 Nanostructured and Hybrid
Materials

12.2.1 Photocatalytic Degradation of Organic
Pollutants
12.2.2 Sensors
12.2.3 Antimicrobiological Ability
12.2.4 Other Uses
ZnO Nanostructured and Hybrid Materials
12.3.1 Photocatalytic Degradation of Organic
Pollutants
12.3.2 Sensors
12.3.3 Antibacterial Ability
In2O3 Nanomaterials
Carbon Nanotube (CNT) and Hybridized
Nanocomposites
12.5.1 Photocatalytic Degradation of Organic
Pollutants
12.5.2 Antibacterial Ability
Fullerene (C60) and Hybridized
Nanocomposites
12.6.1 Photocatalytic Degradation of Organic
Pollutants
12.6.2 Antimicrobiological Ability

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xvi

Contents

12.7 Conclusions
References
Chapter 13 Hierarchical Nanoheterostructures: Layered Double

Hydroxide-based Photocatalysts
Luhong Zhang, Zhigang Xiong and George Zhao
13.1
13.2
13.3

Introduction
Structure of LDH
Synthetic Methods for LDH Materials
13.3.1 Co-precipitation Method
13.3.2 Other Methods
13.4 Modification of LDH
13.4.1 Modification of LDH Structures
13.4.2 Coupling with Other Materials
13.4.3 LDH Derivatives
13.5 Photocatalytic Applications of LDH
13.5.1 LDH’s Application in Photocatalytic
Degradation of Organic
Pollutants
13.5.2 LDH’s Application in Photocatalytic
Reduction of Carbon Dioxide
13.5.3 LDH’s Application in Photocatalytic Water
Splitting
13.5.4 Other Applications
13.6 Summary and Future Perspectives
References
Chapter 14 Health and Environmental Aspects of Green Photo-active
Nanomaterials
H. Haynes and R. Asmatulu
14.1

14.2

Introduction
Model Making: Mass, Energy, Risk and Research in
Manufacturing
14.3 Health Impacts of Exposure
14.4 Environmental Release and Impacts
14.5 Biomagnification
14.6 Further Study
14.7 Conclusions
Acknowledgements
References

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303

309

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315
315
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326

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333

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Contents

xvii

Chapter 15 Risk Assessments of Green Photo-active Nanomaterials
Farhana Abedin, Md. Rajib Anwar and Ramazan Asmatulu

364

15.1


Introduction
15.1.1 General Background
15.1.2 Toxicity and Environmental Impacts
15.2 Photosensitive Nanomaterials
15.2.1 Quantum Dots
15.2.2 Metal Oxide Nanomaterials
15.2.3 Metallic Nanomaterials
15.3 Factors Affecting Risk Assessment of
Nanomaterials
15.4 Conclusions
Acknowledgements
References

Chapter 16 Energy Harvesting from Solar Energy Using Nanoscale
Pyroelectric Effects
Armanj Hasanyan, Ramazan Asmatulu and
Davresh J. Hasanyan
16.1
16.2
16.3
16.4

Introduction
Model and Constitutive Equations
Tangential Force and Bending Moment
Equations of Motion of Bilayer
Thermo-electro-elastic Composites
16.5 Problem Formulation for Beam with Arbitrary
Support Locations
16.6 Discussions and Numerical Results

16.7 Conclusions
16.8 Appendix A
16.9 Appendix B
References

Subject Index

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364
365
367
367
369
375
377
379
380
380

385

385
387
390
392
392
397
400
404
405

406
408



CHAPTER 1

Introduction to Green
Nanostructured Photocatalysts
R. ASMATULU,*a N. NURAJE*b AND G. MUL*c
a

Department of Mechanical Engineering, Wichita State University,
1845 Fairmount, Wichita, KS 67260, USA; b Department of Chemical
Engineering, Texas Tech University, P.O. Box 43121, Lubbock, TX 79409,
USA; c Faculty of Science & Technology, University of Twente,
PO Box 217, Meander 225, 7500 AE, Enschede, The Netherlands
*Email: ; ;


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.1 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.1–3 These new sources of
RSC Green Chemistry No. 42
Green Photo-active Nanomaterials: Sustainable Energy and Environmental Remediation
Edited by Nurxat Nuraje, Ramazan Asmatulu and Guido Mul
r The Royal Society of Chemistry 2016
Published by the Royal Society of Chemistry, www.rsc.org

1


2

Chapter 1

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.2 The current energy consumption 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 conversion systems can easily pass the 10% energy conversion levels.2–4
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.4–8 Nanotechnology 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.9 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.10
Nanomaterials are the major building blocks of solar energy conversion
devices and have been applied in the following three ways:2
(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.2–4



Introduction to Green Nanostructured Photocatalysts

3

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.11
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.12–14


4

Chapter 1

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.2
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.2–4
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.3
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 Na2CO3.2
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



Introduction to Green Nanostructured Photocatalysts

5

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 (Zn21, In31, Ga31, Ge41,
Sn41, and Sb51) are effective photochemical water-splitting catalysts under
UV irradiation.3
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 NiOloaded 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.2–4 The
enhanced photocatalytic activity of SrTiO3 was also reported using a new
modified preparation method or suitable metal cation doping (e.g., La31,
Ga31, and Na1).
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 H1-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.2
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 (Zr41)
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


6

Chapter 1

(including La2TiO5, La2Ti3O9, 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.2
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.11–14
Microorganisms such as bacteria, viruses, algae, molds, and fungi are
living creatures and have survived in extreme environmental conditions for
millions of years. They usually deposit fat, lipids/oil, glucose, starch, and
other hydrocarbons and organic substances in their bodies that can be extracted and converted into useful products.
Bacteria are a single-cell form of life, and each individual cell is unique.
They often grow into different colonies; however, each bacteria cell has its
own independent life. New bacteria are reproduced by a process known as
cell division. It is estimated that more than 3000 species of bacteria are living
in totally different environments and conditions. Nevertheless, some of
them are found only in a very specific environment, thus requiring specialized types of food, temperature, and light.11
A virus is a small infectious organism that can only replicate inside living
cells of other cells and organisms. They can infect all kinds of animals,
bacteria, plants, and so on. Unlike bacteria, viral populations do not grow
through cell division since they are acellular, instead they use the machinery
and metabolism of a host cell to produce multiple copies of themselves and
then assemble inside those cells. To date, approximately 5000 viruses have
been scientifically described in detail. A group of scientists has recently
announced that they can successfully modify a virus to split water molecules,

which can be an efficient and non-energy-intensive method of producing H2.


Introduction to Green Nanostructured Photocatalysts

7

These scientists genetically modified a commonly known, harmless bacterial
virus in order to assemble the components for separating water molecules
into H2 and O2 molecules, in turn yielding a fourfold boost in production
efficiency. This novel process mimics plants that use the power of sunlight to
make chemical fuel for their growth. In this research, the scientists engineered the virus as a kind of biological scaffold to split a water molecule.12
Algae comprise several different species (2800) of relatively simple living
organisms that are found all over the world, capturing light energy through
photosynthesis and converting inorganic/organic substances into simple
sugars and other substances using photon energy. Algae can be considered
the early stage of simple plants, and some are closely related to more
complex plants as well. Some algae also appear to represent different protist
groups (large and diverse groups of eukaryotic microorganisms), alongside
other organisms that are traditionally considered more animal-like (e.g.,
protozoa). Therefore, algae do not represent a single evolutionary direction
but rather a level of organization that may have developed several times in
the early history of microorganism life on the earth’s crust.13
Some microorganisms usually require the following conditions for their
growth:
 pH of 5–9 (lower pH may be seen)
 presence of organic substances (waste water, city waste, leaves)
 temperature between 4 1C and 40 1C; sulfur-, iron-, copper-, zinc-, cobalt-, and manganese-rich conditions;
 the presence of carbon and CO2, nitrogen, phosphoros, oxygen,
hydrogen, and sunlight (more sunlight, less UV rays).

As an example, the growth conditions of microorganisms found in
Yellowstone National Park, which is an extremely hot, and mineral- and ionrich environment, are totally different than the growth conditions of similar
species that live in coastal and lake areas.14
Botryococcus braunii, a green algae with a pyramid-shaped planktonic
structure, is one of the most important algae in biotechnology. These algae
colonies are held together by a lipid biofilm and are usually found in tropical
lakes, rivers, and creeks. They will bloom in the presence of dissolved inorganic phosphorus and other nutrients in a growth condition. B. braunii
has great potential for algae farming because it produces hydrocarbons,
which can be chemically converted into different fuels. It has been estimated
that up to 86% of the dry weight of this alga can be composed of long-chain
hydrocarbons, and some of its useful hydrocarbon oils can be found outside
of the cell. B. braunii can convert 61% of its biomass into oil, which drops to
only 31% under different conditions. It grows best between 22 1C and 25 1C,
and is a great choice for biofuel production.12
Recently, nanotechnology-associated studies have been conducted on
microorganisms to increase the efficiency of their growth and rates of fuel
conversion. Nanotechnology probes tap into algae and bacteria cells to extract
electrical energy. It has been postulated that Chlamydomonas reinhardtii, a