Visible-Light-Active Photocatalysis E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
A comprehensive and timely overview of this important and hot topic, with special emphasis placed on environmental applications and the potential for solar light harvesting.
Following introductory chapters on environmental photocatalysis, water splitting, and applications in synthetic chemistry, further chapters focus on the synthesis and design of photocatalysts, solar energy conversion, and such environmental aspects as the removal of water pollutants, photocatalytic conversion of CO2. Besides metal oxide-based photocatalysts, the authors cover other relevant material classes including carbon-based nanomaterials and novel hybrid materials. Chapters on mechanistic aspects, computational modeling of photocatalysis and Challenges and perspectives of solar reactor design for industrial applications complete this unique survey of the subject.
With its in-depth discussions ranging from a comprehensive understanding to the engineering of materials and applied devices, this is an invaluable resource for a range of disciplines.
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Veröffentlichungsjahr: 2018
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Table of Contents
Title Page
Copyright
Dedication
Preface
Part I: Visible-Light Active Photocatalysis – Research and Technological Advancements
Chapter 1: Research Frontiers in Solar Light Harvesting
1.1 Introduction
1.2 Visible-Light-Driven Photocatalysis for Environmental Protection
1.3 Photocatalysis for Water Splitting
1.4 Photocatalysis for Organic Transformations
1.5 Mechanistic Studies of Visible-Light-Active Photocatalysis
1.6 Summary
References
Chapter 2: Recent Advances on Photocatalysis for Water Detoxification and CO
2
Reduction
2.1 Introduction
2.2 Photocatalysts for Environmental Remediation and CO
2
Reduction
2.3 Photoreactors for Solar Degradation of Organic Pollutants and CO
2
Reduction
2.4 Conclusion
Acknowledgment
References
Chapter 3: Fundamentals of Photocatalytic Water Splitting (Hydrogen and Oxygen Evolution)
3.1 Introduction
3.2 Strategy for Development of Photocatalyst Systems for Water Splitting
3.3 Electrochemistry of Semiconductors at the Electrolyte Interface
3.4 Effect of Light at the Semiconductor–Electrolyte Interface
3.5 Conversion and Storage of Sunlight
3.6 Electrolysis and Photoelectrolysis
3.7 Development of Photocatalysts for Solar-Driven Water Splitting
3.8 Approaches to Develop Visible-Light-Absorbing Metal Oxides
3.9 Conclusions
References
Chapter 4: Photoredox Catalytic Activation of CarbonHalogen Bonds: CH Functionalization Reactions under Visible Light
4.1 Introduction
4.2 Activation of Alkyl Halides
4.3 Activation of Aryl Halides
4.4 Factors That Determine the Carbon–Halogen Bond Activation of Aryl Halides
4.5 Factors That Determine the Yields of the CH Arylated Products
4.6 Achievements and Challenges Ahead
4.7 Conclusion
References
Part II: Design and Developments of Visible Light Active Photocatalysis
Chapter 5: Black TiO2: The New-Generation Photocatalyst
5.1 Introduction
5.2 Designing Black TiO
2
Nanostructures
5.3 Black TiO
2
as Photocatalyst
5.4 Conclusions
References
Chapter 6: Effect of Modification of TiO2 with Metal Nanoparticles on Its Photocatalytic Properties Studied by Time-Resolved Microwave Conductivity
6.1 Introduction
6.2 Deposition of Metal Nanoparticles by Radiolysis and by Photodeposition Method
6.3 Electronic Properties Studied Time-Resolved Microwave Conductivity
6.4 Modification of TiO
2
with Au Nanoparticles
6.5 Modification of TiO
2
with Bi Clusters
6.6 Surface Modification of TiO
2
with Bimetallic Nanoparticles
6.7 The Effect of Metal Cluster Deposition Route on Structure and Photocatalytic Activity of Mono- and Bimetallic Nanoparticles Supported on TiO
2
6.8 Summary
References
Chapter 7: Glassy Photocatalysts: New Trend in Solar Photocatalysis
7.1 Introduction
7.2 Fundamentals of H
2
S Splitting
7.3 Designing the Assembly for H
2
S Splitting
7.4 Chalcogenide Photocatalysts
7.5 Limitations of Powder Photocatalysts
7.6 Glassy Photocatalyst: Innovative Approach
7.7 General Methods for Glasses Preparation
7.8 Color of the Glass – Bandgap Engineering by Growth of Semiconductors in Glass
7.9 CdS–Glass Nanocomposite
7.10 Bi
2
S
3
–Glass Nanocomposite
7.11 Ag
3
PO
4
–Glass Nanocomposite
7.12 Summary
Acknowledgments
References
Chapter 8: Recent Developments in Heterostructure-Based Catalysts for Water Splitting
8.1 Introduction
8.2 Visible-Light-Responsive Junctions
8.3 Visible-Light-Driven Photocatalyst/OEC Junctions
8.4 Observation of Charge Carrier Kinetics in Heterojunction Structure
8.5 Conclusions
References
Chapter 9: Conducting Polymers Nanostructures for Solar-Light Harvesting
9.1 Introduction
9.2 Conducting Polymers as Organic Semiconductor
9.3 Conducting Polymer-Based Nanostructured Materials
9.4 Synthesis of Conducting Polymer Nanostructures
9.5 Applications of Conducting Polymer
9.6 Conclusion
References
Part III: Visible Light Active Photocatalysis for Solar Energy Conversion and Environmental Protection
Chapter 10: Sensitization of TiO2 by Dyes: A Way to Extend the Range of Photocatalytic Activity of TiO2 to the Visible Region
10.1 Introduction
10.2 Mechanisms Involved in the Use of Dye-Modified TiO
2
Materials for Transformation of Pollutants and Hydrogen Production under Visible Irradiation
10.3 Use of Dye-Modified TiO
2
Materials for Energy Conversion in Dye-Sensitized Solar Cells
10.4 Self-Sensitized Degradation of Dye Pollutants
10.5 Use of Dye-Modified TiO
2
for Visible-Light-Assisted Degradation of Colorless Pollutants
10.6 Water Splitting and Hydrogen Production using Dye-Modified TiO
2
Photocatalysts under Visible Light
10.7 Conclusions
Acknowledgement
References
Chapter 11: Advances in the Development of Novel Photocatalysts for Detoxification
11.1 Introduction
11.2 Theoretical Studies of Photocatalysis
11.3 Metal-Doped Photocatalysts for Detoxification
11.4 Graphene-TiO
2
Composites for Detoxification
11.5 Commercial Applications of Photocatalysis in Environmental Detoxification
11.6 Conclusions
References
Chapter 12: Metal-Free Organic Semiconductors for Visible-Light-Active Photocatalytic Water Splitting
12.1 Introduction
12.2 Organic Semiconductors for Photocatalytic Water Splitting and Emergence of Graphitic Carbon Nitrides
12.3 Graphitic Carbon Nitrides for Photocatalytic Water Splitting
12.4 Novel Materials
12.5 Conclusions and Perspectives
References
Chapter 13: Solar Photochemical Splitting of Water
13.1 Introduction
13.2 Photocatalytic Water Splitting
13.3 Overall Water Splitting
13.4 Oxidation of Water
13.5 Reduction of Water
13.6 Coupled Reactions
13.7 Summary and Outlook
Acknowledgments
References
Chapter 14: Recent Developments on Visible-Light Photoredox Catalysis by Organic Dyes for Organic Synthesis
14.1 Introduction
14.2 General Mechanism
14.3 Recent Application of Organic Dyes as Visible-Light Photoredox Catalysts
14.4 Conclusion
Abbreviations
References
Chapter 15: Visible-Light Heterogeneous Catalysts for Photocatalytic CO2 Reduction
15.1 Introduction
15.2 Basic Principles of Photocatalytic CO
2
Reduction
15.3 Inorganic Semiconductors
15.4 Organic Semiconductors
15.5 Semiconductor Heterojunctions
15.6 Conclusion and Perspectives
References
Part IV: Mechanistic Studies of Visible Light Active Photocatalysis
Chapter 16: Band-gap Engineering of Photocatalysts: Surface Modification versus Doping
16.1 Introduction
16.2 Doping
16.3 Surface Modification
16.4 Heterojunctions
16.5 Z-Scheme
16.6 Hybrid Nanostructures
16.7 Summary
References
Chapter 17: Roles of the Active Species Generated during Photocatalysis
17.1 Introduction
17.2 Mechanism of Photocatalysis in TiO
2
/Water Systems
17.3 Active Species Generated at the Catalyst/Water Interface
17.4 Oxidative Degradation of Solutes Present in the Aqueous Phase
17.5 Impact of H
2
O
2
on Oxidative Degradation of Solutes Present in the Aqueous Phase
17.6 The Role of Common Anions Present in the Aqueous Phase
17.7 Summary of Active Species Present in Heterogeneous Photocatalysis in Water
References
Chapter 18: Visible-Light-Active Photocatalysis: Nanostructured Catalyst Design, Mechanisms, and Applications
18.1 Introduction
18.2 Historical Background
18.3 Basic Concepts
18.4 Structure of TiO
2
18.5 Photocatalytic Reactions
18.6 Physical Architectures of TiO
2
18.7 Visible-Light Photocatalysis
18.8 Ion Doping and Ion Implantation
18.9 Dye Sensitization
18.10 Noble Metal Loading
18.11 Coupled Semiconductors
18.12 Carbon–TiO
2
Composites
18.13 Alternatives to TiO
2
18.14 Conclusions
References
Part V: Challenges and Perspectives of Visible Light Active Photocatalysis for Large Scale Applications
Chapter 19: Quantum Dynamics Effects in Photocatalysis
19.1 Introduction
19.2 Computational Approaches to Model Adiabatic Processes in Photocatalysis
19.3 Computational Approaches to Model Nonadiabatic Effects in Photocatalysis
19.4 Quantum Tunneling in Adiabatic and Nonadiabatic Dynamics
19.5 The Mechanisms of Organic Reactions Catalyzed by Semiconductor Photocatalysts
19.6 Conclusions and Outlook
References
Chapter 20: An Overview of Solar Photocatalytic Reactor Designs and Their Broader Impact on the Environment
20.1 Introduction
20.2 Materials
20.3 Slurry-Style Photocatalysis
20.4 Deposited Photocatalysts
20.5 Applications
20.6 Conclusion
References
Chapter 21: Conclusions and Future Work
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Part I: Visible-Light Active Photocatalysis – Research and Technological Advancements
List of Illustrations
Chapter 2: Recent Advances on Photocatalysis for Water Detoxification and CO
2
Reduction
Figure 2.1 Photocatalytic generation of ROS.
Figure 2.2 Photoexcitation of a semiconductor photocatalyst and electron transfer processes involved in the reduction of CO
2
. Redox potentials (
E
°) of half cell reactions (4)–(9) are expressed versus NHE and calculated at neutral pH.
Figure 2.3 Transfer of a photogenerated electron from the CB of a semiconductor to the Fermi level of the metal cocatalyst.
Figure 2.4 Band levels and wavelength thresholds of simple semiconductors photocatalysts.
Figure 2.5 Growth diagram of ZnO micro-/nanospheres employed for the mineralization of different endocrine-disrupting chemicals.
Figure 2.6 (a) Tentative process of the degradation of methylene blue by P25 dispersed on the graphene support (P25-GR). (b) TEM image of P25-GR.
Figure 2.7 Schematic structure of cubic perovskite ABO
3
(dark gray, BO
6
units; light gray, A atoms).
Figure 2.8 Reduction of CO
2
to formic acid by perovskite oxynitride CaTaO
2
N coupled to a binuclear Ru(II) complex.
Figure 2.9 (a) TEM image of Rh/Cr
2
O
3
core/shell decorated GaN nanowire (b) Scheme of the photoreduction processes of CO
2
on Rh/Cr
2
O
3
GaN nanowires.
Figure 2.10 (a) Hybrid powder photocatalyst of the Ru(II) binuclear complex adsorbed on Ag-modified TaON. (b) Time courses of HCOOH and H
2
formation by visible-light (
λ
> 400 nm) irradiation of the photocatalyst in EDTA·2Na aqueous solution (4 ml) in the presence of Na
2
CO
3
(0.1 M) under a CO
2
atmosphere.
Figure 2.11 Continuous flow (a) and batch reactor design (b).
Figure 2.12 NCC photoreactor.
Figure 2.13 (a, b) PTC photoreactor and PROPHIS loop.
Figure 2.14 (a, b) Schematic of CPC photoreactor and CPC used for solar photocatalytic water detoxification.
Figure 2.15 CPC photoreactor for photolysis of propranolol.
Figure 2.16 (a, b) Schematic of parabolic dish and parabolic dish reactor.
Chapter 3: Fundamentals of Photocatalytic Water Splitting (Hydrogen and Oxygen Evolution)
Figure 3.1 Band positioning for photoelectrochemical water splitting.
Figure 3.2 Energy levels of different materials: conductor, semiconductor, and insulator.
Figure 3.3 Schematic diagram of the energy levels of (a) an intrinsic, (b) an n-type semiconductor, and (c) a p-type semiconductor.
E
C
is the energy level of the conduction band (CB);
E
V
is the energy level of the VB;
E
F
is the Fermi level energy;
E
A
and
E
D
are the acceptor and donor level energy of the semiconductors, respectively.
Figure 3.4 Effect of varying the applied potential (
E
) on the band edges in the interior of an n-type semiconductor.
Figure 3.5 Effect of varying the applied potential (
E
) on the band edges in the interior of a p-type semiconductor.
Figure 3.6 Band positions of different semiconductors with respect to the thermodynamic potentials of water splitting.
Figure 3.7 Classification of the solar energy conversion processes using directly the solar radiations.
Figure 3.8 Water splitting: (a) electrolysis and (b) photo-assisted electrolysis.
Figure 3.9 PEC water splitting in the presence of sacrificial reagents.
Figure 3.10 Schematic diagram of a prototype photoelectrochemical cell for water splitting.
Chapter 4: Photoredox Catalytic Activation of CarbonHalogen Bonds: CH Functionalization Reactions under Visible Light
Scheme 4.1 Chemical structures of the photocatalysts that are typically used for the activation of alkyl or aryl halides under visible light. The respective reduction potentials are also depicted.
Scheme 4.2 Schematic representation of the generation of alkyl and aryl radicals from their respective halides upon single electron transfer.
Scheme 4.3 Photoredox catalytic reductive dehalogenation of phenacyl bromide.
Scheme 4.4 General mechanism of the reductive halogenation of activated alkyl halide substrates using Ru(bpy)
3
Cl
2
as a photocatalyst and visible light as the energy source. Note that
N,N
-diisopropylethylamine (
i
Pr
2
NEt or DIPEA) is a typical sacrificial electron donor in most photoredox catalytic reductive transformations.
Scheme 4.5 Selected examples of asymmetric alkylation of aldehydes.
Scheme 4.6 Proposed mechanism of the dual catalytic cycle.
Scheme 4.7 Selected examples of asymmetric alkylation of aldehydes using organic dyes (in this case, Eosin Y) or semiconductors as photocatalysts.
Scheme 4.8 Photoredox catalytic reductive radical cyclization of malonate bromides.
Scheme 4.9 Mechanism for CH substitution in reductive radical cyclization of malonate bromides.
Scheme 4.10 Intermolecular photoredox catalytic CH functionalizations with malonates.
Scheme 4.11 Synthesis of substituted tetrahydrofurans.
Scheme 4.12 Other α-activated substrates used in CC bond formations.
Scheme 4.13 Synthesis of substituted phenanthridines by a net isocyanide insertion.
Scheme 4.14 Enantioselective perfluoroalkylation of aldehydes by merging photoredox catalysis with organocatalysis.
Scheme 4.15 Trifluoromethylation of aromatic heterocycles.
Scheme 4.16 Visible-light-induced arylthiofluoroalkylations of heteroaromatics and alkenes.
Scheme 4.17 Fluoromethylating reagents typically being used in visible-light photoredox catalysis.
Scheme 4.18 Selected examples of tri- and difluoromethylation of alkenes.
Scheme 4.19 Coupling of bromopyrroloindoline with indoles to access both C
2
′- and C
3
′-substitutions.
Scheme 4.20 Total synthesis of Gliocladin C.
Scheme 4.21 Selective examples of enantioselective α-benzylation of aldehydes.
Scheme 4.22 Proposed catalytic cycle for aldehyde R-benzylation.
Scheme 4.23 Photoinduced enantioselective alkylation of acyl imidazoles with acceptor substituted benzyl bromides and phenacyl bromides.
Scheme 4.24 Proposed mechanism for the enantioselective alkylation of acyl imidazoles.
Scheme 4.25 Reductive cyclizations of alkyl iodides using
fac
-Ir(ppy)
3
and visible light.
Scheme 4.26 Synthesis of hexahydropyridoindoles.
Scheme 4.27 Schematic representation of the proposed conPET catalytic cycle using PDI.
Scheme 4.28 PDI catalyzed photoreduction and CH arylation yields using aryl halides and visible light.
Scheme 4.29 Rhodamine 6G catalyzed chromoselective activations of chemical bonds.
Scheme 4.30 Rhodamine 6G catalyzed CH arylation yields using aryl halide and visible light.
Scheme 4.31 Rhodamine 6G catalyzed CH (hetero)arylation yields using (hetero)aryl bromides and visible light.
Scheme 4.32 CH arylation reactions of uracil using rhodamine 6G as the conPET catalyst and visible light. Yields of the hydrolysis step are also depicted.
Scheme 4.33 Synthesis of pyrrolo[1,2-
a
]quinoline and ullazines using rhodamine 6G as the conPET catalyst and visible light.
Scheme 4.34 Yields of the photo-Arbuzov reaction using rhodamine 6G (Rh-6G) as the conPET catalyst and visible light.
Scheme 4.35 Photoreduction of aryl or alkyl halides using PTH and visible light.
Scheme 4.36 Photoredox catalytic azolylation of arenes and heteroarenes using
fac
-Ir(ppy)
3
as the photoredox catalyst and visible light.
Scheme 4.37 Perfluoroarylation of arenes and heteroarenes using Eosin Y and visible light.
Scheme 4.38 Perfluoroarylation of arenes and heteroarenes via CF bond activation using
fac
-Ir(ppy)
3
and visible light.
Scheme 4.39 Hydrogen atom abstraction of aryl radical from the radical cation of DIPEA.
Chapter 5: Black TiO2: The New-Generation Photocatalyst
Scheme 5.1 Various synthesis routes to black TiO2 nanomaterials.
Chapter 6: Effect of Modification of TiO2 with Metal Nanoparticles on Its Photocatalytic Properties Studied by Time-Resolved Microwave Conductivity
Figure 6.1 Degradation of phenol (2 × 10
−4
M phenol initial concentration) with pure or modified titania (1 g l
−1
photocatalyst) synthesized by sol–gel method (surface modified and nonmodified with Pt salt (II), PtCl
4
2−
; Pt salt (IV), PtCl
6
2−
; Pt cluster, Pt
3
(CO)
6
]
6
2−
): (a) Under UV/vis light; (b) under visible light (>450 nm).
Figure 6.2 TRMC signals after excitation at 355 nm of pure or modified titania with Pt salt (II), PtCl
4
2−
; Pt salt (IV), PtCl
6
2−
; Pt cluster, [Pt
3−
(CO)
6
]
6
2−
: (a) P25; (b) TiO
2
synthesized by sol-gel technique.
Figure 6.3 Diffuse reflectance spectra of pure and modified TiO
2
: (a) P25 and (b) ST-01 with different silver loading (0.5–2% in mass) and recorded, respectively, using BaSO
4
as reference.
Figure 6.4 TEM image showing Ag clusters induced by radiolysis on P25 and TRMC signals of bare and modified with Ag clusters P25 obtained with excitation at 355 nm. Inset: a scheme showing electron scavenging by Ag clusters decreasing the charge-carrier recombination.
Figure 6.5 TEM images of (a) Au
0.5%
/P25; (b) Au
1%
/P25, with the corresponding histogram of the size distribution of Au-NPs. (c) Diffuse reflectance spectroscopy (DRS) spectra of Au/P25 samples, where the LSPR of Au-NPs is observed between marked lines.
Figure 6.6 TRMC signals of pristine and modified TiO
2
-P25 at different excitation wavelengths: (a) 365 and 400 nm UV irradiation, (b) 450 and 470 nm visible irradiation, and (c) 500 and 560 nm (Plasmon excitation).
Figure 6.7 (a) Comparison between DRS spectra and the action spectra of TiO
2
-P25 and modified TiO
2
-P25 with Au 0.5 wt%, (b) superposition of action spectrum (in blue) and absorption spectrum (in red) in the Au plasmon range.
Figure 6.8 Production of H
2
under visible light at: (a)
λ
= 400 nm and (b)
λ
= 470 nm for pure TiO
2
-P25 and TiO
2
-P25 modified with Au-NPs at different loadings. The relative uncertainties at 400 and 470 nm are 5% and 7%, respectively.
Figure 6.9 Mechanism purposed for modified TiO
2
-P25 modified by Au-NPs (a) UV and (b) visible irradiation by electron, and (c) energy transfer.
Figure 6.10 TRMC signal of bare and Bi-modified samples obtained by irradiation at 355 nm (a) and 450 nm (b). Inset: A scheme showing electron injection from Bi nanoclusters in the conduction band of TiO
2
under visible-light excitation.
Figure 6.11 (a) Energy-dispersive X-ray spectroscopy line scans across a nanoparticle of Au–Cu1 : 1/P25 (the profile was taken along the green line, the blue line corresponds to Cu–K, and the red one to the Au–L signal) and corresponding STEM images for the samples. (b) Mapping EDS analysis performed on a nanoparticle of Au–Cu1:1/P25 (left).
Figure 6.12 Rate constants of the first-order kinetics of phenol photodegradation by pure and modified TiO
2
photocatalysts under UV–visible illumination.
Figure 6.13 Time-resolved microwave conductivity signals of modified P25 photocatalysts prepared by the chemical method with THPC. Inset: scheme depicting the electron scavenging and transfer on the Au–Cu-modified TiO
2
surface after the absorption of UV photons.
Figure 6.14 (a) Representative aberration corrected STEM-HAADF image for Ag@CuO1:1/P25 sample, and (b) A schematic morphology of the modified TiO
2
–P25 with Ag–CuO nanoparticles.
Figure 6.15 Degradation curves of phenol under (a) UV and (b) visible light (
λ
> 450 nm) of pure system TiO
2
-P25 and modified systems with, Ag, Ag@CuO1:1and CuO.
Figure 6.16 SEM images of pure TiO
2
nanotubes (a–c) and AgCu-NT III sample (d); STEM image of AgCu-NT III sample (e).
Figure 6.17 Proposed mechanism of phenol decomposition in the presence of TiO
2
nanotubes decorated with metal nanoparticles under UV–vis irradiation.
Figure 6.18 Absorption spectra (photon absorption), TRMC spectra (charge-carrier creation), and action spectra (apparent quantum efficiency) of modified samples, metal loading of 0.5 at %.
Figure 6.19 A proposed mechanism for H
2
production on NiAu/TiO
2
samples.
Figure 6.20 Light absorption, charge-carrier separation and H
2
evolution of (a) bare TiO
2
(b) 0.5-Ni
10
Pd
1
/TiO
2
and (c) 1-Ni
1
Pd
10
/TiO
2
measured by DRS, TRMC and action spectra respectively.
Figure 6.21 Schematic representation of (a) H
2
evolution using metal NPs/TiO
2
as photocatalysts where the proton reduction occurs on the surface of TiO
2
while the molecular H
2
is generated on the surface of metal NPs, (b) H
2
evolution using metal Ni
10
Pd
1
/TiO
2
as photocatalysts, and (c) H
2
evolution using metal Ni
1
Pd
10
/TiO
2
as photocatalysts.
Chapter 7: Glassy Photocatalysts: New Trend in Solar Photocatalysis
Figure 7.1 Schematic diagram showing (a) the industrial Claus process and (b) photocatalytic solar H
2
production from H
2
S decomposition.
E
°, standard-state energy of the reaction;
G
°, standard-state Gibbs energy; F, Faraday constant.
Figure 7.2 Band edge position of several semiconductors using the normal hydrogen electrode (NHE) as a reference.
Figure 7.3 Schematic representation of the light absorption by a semiconductor.
Figure 7.4 Schematic of H
2
S splitting. (a) H
2
S gas generator, (b) empty trap for H
2
S storage, (c) calibrated water bubbler to know the rate of H
2
S gas, (d) CaCl
2
trap, (e) photo-reactor with water jacket, (f) lamp to expose reactor contents, (g) two NaOH traps, (h) H
2
gas collection cylinder, (i) water bath, and (j) H
2
measuring cylinder.
Figure 7.5 Various steps involved in formation of glass by melt-quench technique.
Figure 7.6 (A) XRD of different % of SiO
2
and CdS in glass, (B) UV–vis spectra of 60% SiO
2
0.75% CdS glass is heat treated at various temperatures, (C) photograph of host and heat-treated glasses.
Figure 7.7 TEM images of CdS QDs in CdS–glass nanocomposites (a) without heat treatment and annealed at (b) 575 °C, (c) 600 °C, (d) 625 °C, and (e) SEAD pattern.
Figure 7.8 AP glasses of unstriked and heat-treated glasses at different temperatures (A) photograph, (B) UV–vis spectra, (C) photoluminescence spectra; APD glasses of unstriked and heat-treated glasses at different temperatures, (D) photograph, (E) UV–vis spectra, (F) photoluminescence spectra.
Figure 7.9 HRTEM images of (a,b) APD510, (c,d) APD520, (e,f) APD530, and (g,h) APD540 samples. Insets show the SAED patterns of respective samples.
Figure 7.10 Photographs of separated photocatalysts after H
2
S splitting (a) pure Ag
3
PO
4
and (b) Ag
3
PO
4
–glass nanocomposite.
Chapter 8: Recent Developments in Heterostructure-Based Catalysts for Water Splitting
Figure 8.1 Mechanism of solar-driven water splitting on nanocrystalline TiO
2
.
Figure 8.2 Band alignment in type I, II, and III heterojunctions.
Figure 8.3 Band bending and alignment in (a) S–S, and (b) S–M (S–C) junctions. In both cases photogenerated charges are driven in opposite directions due to favorable differences in band energies and the formation of an electric field.
Figure 8.4 (a) Design strategy of a CoPi/BiVO
4
/ZnO heterojunction by Moniz
et al
. [50] involving (i) increased light absorption and charge generation in both BiVO
4
and ZnO in conjunction with light-trapping effect of the nanorods, (ii) electron injection into ZnO nanorods followed by prompt electron transport along ZnO nanorods, and (iii) simultaneous hole transfer to CoPi for efficient water oxidation; (b) charge transfer mechanism proposed by Fu
et al
. [59] involving spatial transfer of visible-light-excited high-energy electrons from BiVO
4
to ZnO.
Figure 8.5 (a) Schematic illustration of the TiSi
2
/α-Fe
2
O
3
nanonet photoanode. Efficient charge collection is achieved when the hematite thickness is smaller than the charge-diffusion distance. (b) TEM image of the TiSi
2
core/hematite shell nature. (c) High-resolution (HR) TEM images of the junction.
Figure 8.6 (a) UV–vis absorption spectra of C
3
N
4
(black curve) and CDots-C
3
N
4
(red curve) catalysts; (b) Band structure diagram for CDots-C
3
N
4
; (c) H
2
and O
2
production from water under visible-light irradiation (
λ
> 420 nm) catalyzed by CDots-C
3
N
4
; (d) Wavelength-dependent quantum yield (red dots) of water splitting by CDots-C
3
N
4
.
Figure 8.7 Band alignment in a Cu
2
O photocathode using TiO
2
and Al-doped ZnO protection layers.
Figure 8.8 Band energy positions for the Cu
2
O/AZO/TiO
2
/MoS
2+
x
photocathode biased at 0 V versus RHE in the dark, assuming pinning of the band edges of the semiconductor at the interfaces.
Figure 8.9 (a) Cross-section of the α-Fe
2
O
3
/IrO
2
photoanode; (b) Performance of the unmodified α-Fe
2
O
3
photoanode (solid black trace), and the same anode that was functionalized with IrO
2
nanoparticles (solid grey trace). The dashed trace is the photocurrent for the former state-of-the-art hematite photoanode.
Figure 8.10 TAS spectra of CoPi/Fe
2
O
3
, indicating a long-lived hole (580 nm) population. (a) α-Fe
2
O
3
. (b) α-Fe
2
O
3
/CoPi
Figure 8.11 (a) Phenomenological kinetic scheme for PEIS analysis; (b) typical Nyquist plot showing the origin of
Z
1
and
Z
2
.
Figure 8.12 Nyquist plot and fitted equivalent circuit model of the CdS-based heterojunctions proposed by Zhong
et al
. for improved PEC water splitting.
Figure 8.13 Schematic diagrams of the surface photovoltage effect. In panel (a), we observe upward band bending in a typical n-type semiconductor surface; in panel (b), the absorbed photons produce free charge carriers resulting in a partial band flattening; and in panel (c) the largest SPV saturation occurs to completely flatten bands.
Figure 8.14 SPV spectra of 0.5 mg Rh(3 mol%):SrTiO
3
on 1 cm
2
gold-coated glass in the presence of redox reagents with schematic mechanism (inset).
Chapter 9: Conducting Polymers Nanostructures for Solar-Light Harvesting
Figure 9.1 Molecular structure of some representative conducting polymers.
Figure 9.2 Photocatalytic degradation of (a, b) phenol and (c, d) methyl orange (MO) in the presence of commercial P25 TiO
2
and Ag-TiO
2
, PDPB nanofibers and the synthesized PEDOT vesicles and PEDOT nanospindles under UV (a, c) and visible-light (>450 nm) (b, d) irradiation.
Figure 9.3 Rate of photocatalytic hydrogen production can be correlated with the optical gap in the polymers. Data shown for networks CPCMP1−15 (black squares) and analogous linear polymers (discussed below), P16−18 (open squares); all measurements relate to 100 mg catalyst in water containing 20 vol% diethylamine as an electron donor under filtered, visible irradiation (
λ
> 420 nm,
E
< 2.95 eV).
Figure 9.4 (a) Structures of comonomers (M0−M11) used for the preparation of PCP photocatalysts PCP0−PCP11, where the number refers to the number in comonomer used by Suzuki Coupling. (b) Photocatalytic hydrogen production rates of PCP0−11 under full-arc irradiation for 2 h. (c) Wavelength-dependent apparent quantum yields (AQY) for PCP10 with and without loading 2 wt% Pt cocatalyst.
Figure 9.5 (a) Chemical structures of PBDT-bpy and PPDI-bpy conjugated polymers used for hydrogen generation. (b) Time course of H
2
production from water for polymer PBDT-bpy with [CoCl
2
]/[bpy] = 0.1. (c) [CoCl
2
]/[bpy] dependence of the rate of photocatalytic hydrogen production from water. (d) Wavelength-dependent AQYs of water splitting for polymers PBDT-bpy and PPDI-bpy.
Figure 9.6 Transmission electron microscopic images of (a) PDPB nanofibers and (b) PDPB-ZnO light-harvesting nanoheterojunction (LHNH).
Scheme 9.1 Schematic representation of the formation of different types of charge carriers in conducting polymers upon doping.
Scheme 9.2 Schematic representation of the modifications in the band structure of conducting polymers after the creation of the localized defects upon doping.
Scheme 9.3 Difference between band structure of conventional polymer, undoped, and doped conducting polymer.
Scheme 9.4 Methods of synthesis of conducting polymer nanostructures.
Scheme 9.5 Schematic representation of polymerization of diphenylbutadiyne (DPB) by UV irradiation.
Scheme 9.6 Schematic representation of chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) using FeCl
3
as chemical oxidant.
Scheme 9.7 Schematic presentation of (a) the cosensitization of different PDPB oligomers to ZnO NPs and molecular structure of PDPB polymer (b) the interfacial carrier dynamics at the heterojunction showing the photocatalytic degradation of MO in aqueous solution.
Chapter 10: Sensitization of TiO2 by Dyes: A Way to Extend the Range of Photocatalytic Activity of TiO2 to the Visible Region
Figure 10.1 Comparison of the photocatalytic mechanisms with TiO
2
particles under (a) UV irradiation and (b) by the self-photosensitized pathway under visible light irradiation.
Figure 10.2 Electron injection from the excited state of a dye (dye*) into the CB of the SC.
Figure 10.3 Electron transfer mechanism in TiO
2
nanoparticles modified with dyes and noble-metal nanoparticles under visible-light irradiation.
Chapter 11: Advances in the Development of Novel Photocatalysts for Detoxification
Figure 11.1 The mechanism of photocatalysis.
Figure 11.2 Examples of results on formation of new electronic states in metal- and nonmetal-doped TiO
2
from DFT simulations. (a) Formation of in-gap electronic states in Fe- and N-doped TiO
2
.
Figure 11.3 Examples of results on TiO
2
with a high degree of hydrogen incorporation. (a) Schematic of the effect of hydrogenation on the optical and EPR characteristics of TiO
2
.
Figure 11.4 (a) Schematic of different cation, anion codoping scenarios in bulk anatase TiO
2
.
Figure 11.5 (a) Schematic of alignment of TiO
2
energy levels with water oxidation and reduction potentials.
Figure 11.6 (a) Computed spin density and electronic density of states for (top panel) excess electron (middle panel) excess hole and (bottom panel) electron–hole pair in anatase (101); the yellow isosurfaces show the location of the spins.
Figure 11.7 Representation of narrowing the bandgap of anatase TiO
2
by doping of metal ions.
Figure 11.8 (a) Proposed diagram of the photocatalytic mechanism for graphene- wrapped TiO
2
nanoflowers. The main photodegradation pathways include (1) the reduction and oxidation of adsorbed water species by a photogenerated electron–hole pair and (2) oxidation of MB by donating an electron to graphene (or the photocatalyst); (b) SEM images of the as-prepared TiO
2
nanoflowers; and (c) G–TiO
2
composite (TiO
2
is highlighted in red, and graphene is highlighted in blue).
Figure 11.9 (a) Photodegradation of MB with time under visible-light irradiation, (b) lnC/Co versus time plot for determination of rate of constant. (c) Schematic representation of the possible mechanism of photocatalytic activity for degradation of MB under visible light.
Figure 11.10 (A) Schematic diagram illustrating the adsorption behaviors of cationic and anionic dyes on TiO
2
surface with controllable microstructures. (B) Schematic diagram illustrating the controllable preparation of various photocatalysts and (C) their corresponding XPS N 1s spectra: (a) TiO
2
, (b) PhNH
2
/TiO
2
, (c) rGO-TiO
2
, and (d) PhNH
2
/rGO-TiO
2
.
Figure 11.11 (a) Schematic representation of a liquid drop on a hydrophilic and a hydrophobic surface.
Figure 11.12 Schematic representation of the working principle of self-cleaning glasses showing (from the left to right) the accumulation of dust/pollutants on glass, activation of the photocatalytic material by sunlight, photocatalytic decomposition of the pollutants, and finally cleaning of the degraded materials by rain water.
Figure 11.13 Self-cleaning cement coated on (a) Roof of Dubai Sports City's Cricket Stadium.
Figure 11.14 Schematic diagram showing the mechanism of antibacterial action of TiO
2
nanotubes.
Figure 11.15 Schematic representation of a parabolic trough collector.
Figure 11.16 Schematic representations of (a) SOLARIS reactor and (b) PROPHIS reactor.
Figure 11.17 Schematic representation of a compound parabolic concentrator.
Chapter 12: Metal-Free Organic Semiconductors for Visible-Light-Active Photocatalytic Water Splitting
Figure 12.1 Polymerization and pathways (a and b) for graphitic carbon nitride synthesis.
Figure 12.2 (a) Chemical structure of graphitic carbon nitride sheets, and (b) bandgap structure (pH = 7) comparison of g-CN with titanium dioxide (TiO
2
), a reference photocatalyst.
Figure 12.3 (a) XRD pattern of g-CN sample and XPS spectra of the g-CN prepared by pyrolysis of urea at 550 °C (b) C1s spectra. (c) N1s spectra.
Figure 12.4 The sol–gel route to obtain porous carbon nitride and silica by hard template approach.
Figure 12.5 AAO templating approaches toward g-CN rods using cyanamide as precursor and SEM images of g-CN rods.
Figure 12.6 (a–g) Preparation procedure of monolayer of mesoporous g-CN nanomesh and (h–j) solvothermal exfoliation from bulk mpg-CN to nanomesh.
Figure 12.7 Photograph and TEM images of pure g-CN and sulfur-modified g-CN.
Figure 12.8 Schematic diagram of the solid-state Z-scheme photocatalytic mechanism in g-CN/WO
3
composites (SHE = standard hydrogen electrode).
Figure 12.9 (a) UV–vis absorption spectrum and photograph (inset) of polyimide (PI), (b) Mott-Schottky plot of PI, (c) band structure and (d) VB XPS of g-CN and PI.
Figure 12.10 (a) Chemical structure and (b) band position of g-CN and MgPc.
Scheme 12.1 Solar-light-driven water splitting using g-CN.
Chapter 13: Solar Photochemical Splitting of Water
Figure 13.1 Schematic illustration of (a) the processes involved and (b) relative energy levels and mechanism of photocatalytic water splitting. (c) Representation of band positions of semiconductors relative to the redox potentials of water. Dashed lines indicate the water reduction and oxidation potentials.
Figure 13.2 Schematic representation of light-harvesting units in (a) sensitizer-relay (b) sensitizer-semiconductor, and (c) semiconductor photocatalytic systems.
Figure 13.3 Transfer of charge carriers on (a) large and (b) small semiconductor particles in the presence of an electron acceptor (A) and a donor (D).
Figure 13.4 Schematic illustration of mechanism of water splitting in (a) two-step and (b) one-step excitation processes.
Figure 13.5 (a) Comparison of quantum efficiencies of water splitting with the absorption spectrum of ZnO:GaN. (b) Rate of evolution of hydrogen and oxygen with ZnO:GaN.
Figure 13.6 (a) Band positions of CoO nanocrystals (right) and micropowders (left) relative to the water reduction and oxidation potentials. (b) Production of hydrogen and oxygen from CoO nanoparticles as a function of incident laser power (
λ
= 532 nm).
Figure 13.7 Schematic illustration of redox-shuttle meditated two-step (Z-scheme) photoexcitation process.
Figure 13.8 Generation of hydrogen and oxygen as a function of time in (a) the presence of only the H
2
-evolution catalyst (Pt-SrTiO
3
: Cr, Ta) and (b) the presence of both H
2
- and O
2
-evolution ((Pt-SrTiO
3
: Cr, Ta) and Pt-WO
3
) catalysts.
Figure 13.9 (a) Amount of oxygen evolved per mole of Co by Li
x
Co
2
O
4
with different amount of Li. (○) Li
2
Co
2
O
4
and (□) Li
1.1
Co
2
O
4
. (b) Amount of oxygen evolved per mole of transition metal in (i) LaCoO
3
, (ii) Li
2
Co
2
O
4
, (iii) Mn
2
O
3
, and (iv) LaMnO
3
.
Figure 13.10 (a) SEM images of Pt and MnO
x
deposited BiVO
4
. (b) Schematic illustration of mechanism of water splitting on Pt and MnO
x
deposited BiVO
4
. (c) Comparison of photocatalytic activity of Pt and MnO
x
photodeposited BiVO
4
, with the activities of other photocatalysts.
Figure 13.11 (a) Schematic illustration of mechanism of hydrogen generation on CdS-graphene-Pt and (b) comparison of activities of photocatalysts with different amount graphene loading.
Figure 13.12 (a) UV–visible absorption spectrum, (b) electronic structure, and (c) molecular structure of g-C
3
N
4
.
Figure 13.13 (a) The crystal-field-splitting induced electronic configuration of 2H-MoS
2
and 1T-MoS
2
and proposed mechanism for photocatalytic activity of 1T-MoS
2
. (b) Time course of photocatalytic H
2
evolved by freshly prepared 1T-MoS
2
.
Figure 13.14 (a) Schematic illustration of structure and relative energy levels and (b) comparison of photocatalytic activity of different configuration of CdSe/CdS/Pt.
Figure 13.15 (a) Function of water redox potentials, hydroxyl anion and ethanol oxidation potentials with pH. (b) Variation efficiency with the pH.
Figure 13.16 Schematic representation of process of hydrogen generation on ZnO/Pt/CdS heterostructures.
Figure 13.17 (a) Visible light (
λ
> 395 nm) induced H
2
evolution with ZnO/Pt/Cd
0.8
Zn
0.2
S as a function of time and (b) comparison of the AQYs obtained upon irradiation of selected wavelengths of light, with the absorption spectrum of ZnO/Pt/Cd
0.8
Zn
0.2
S.
Figure 13.18 Comparison of photocatalytic activities of ZnO/Pt/CdS and ZnO/Pt/Cd
0.8
Zn
0.2
S obtained with a coupled organic reaction (PhCH
2
OH oxidation) and inorganic sacrificial reactions. (
Chapter 14: Recent Developments on Visible-Light Photoredox Catalysis by Organic Dyes for Organic Synthesis
Scheme 14.1 Common organic dyes for visible-light photoredox catalysis.
Scheme 14.2 Photophysical and electrochemical processes in organic dyes.
Scheme 14.3 Oxidative and reductive quenching cycles of a photoredox catalyst.
Scheme 14.4 Net redox outcomes in photoredox transformations.
Scheme 14.5 The redox potentials of Eosin Y in CH
3
CN–H
2
O (1:1) in ground and corresponding excited states.
Scheme 14.6 Perfluoroarylation of arenes.
Scheme 14.7 Perfluoroarylation of arenes mechanistic proposal.
Scheme 14.8 Synthesis of benzo[
b
]phosphole oxides.
Scheme 14.9 Mechanism for synthesis of benzo[
b
]phosphole oxides.
Scheme 14.10 Direct CH arylation of heteroarenes.
Scheme 14.11 Proposed mechanism for direct CH arylation of heteroarenes.
Scheme 14.12 Synthesis of 1,2-diketones from alkynes.
Scheme 14.13 Plausible mechanism for synthesis of 1,2-diketones from alkynes.
Scheme 14.14 Thiocyanation of imidazoheterocycles.
Scheme 14.15 Suggested mechanism for thiocyanation of imidazoheterocycles.
Scheme 14.16 Generation of excited photosensitizer states and reactive dioxygen species.
Scheme 14.17 Aerobic indole C-3 formylation reaction.
Scheme 14.18 A plausible mechanism for aerobic indole C-3 formylation reaction.
Scheme 14.19 Decarboxylative/decarbonylative C3-acylation of indoles.
Scheme 14.20 Proposed mechanism for decarboxylative/decarbonylative C3-acylation of indoles.
Scheme 14.21 Oxidative annulation of arylamidines.
Scheme 14.22 Mechanistic proposal for oxidative annulation of arylamidines.
Scheme 14.23 Cross-dehydrogenative coupling of tertiary amines with diazo compounds.
Scheme 14.24 Suggested cross-dehydrogenative coupling of tertiary amines with diazo compounds.
Scheme 14.25 α-Functionalization of tertiary amines.
Scheme 14.26 Ugi-multicomponent reaction in flow.
Scheme 14.27 Oxidative cross-coupling of thiols with P(O)H compounds.
Scheme 14.28 Suggested mechanism for oxidative cross-coupling of thiols with P(O)H compounds.
Scheme 14.29 Oxidative hydroxylation of arylboronic acids.
Scheme 14.30 A plausible mechanism for oxidative hydroxylation of arylboronic acids.
Scheme 14.31 Radical trifluoromethylation.
Scheme 14.32 Proposed mechanism for radical trifluoromethylation.
Scheme 14.33 Synthesis of 2-substituted benzimidazole and benzothiazole.
Scheme 14.34 Suggested mechanism for synthesis of 2-substituted benzimidazole and benzothiazole.
Scheme 14.35 Oxidation of alcohols to carbonyl derivatives.
Scheme 14.36 A plausible mechanism oxidation of alcohols to carbonyl derivatives.
Scheme 14.37 Oxidative coupling of primary amines.
Scheme 14.38 Oxidative coupling of primary amines mechanistic proposal.
Chapter 15: Visible-Light Heterogeneous Catalysts for Photocatalytic CO2 Reduction
Figure 15.1 Photoinduced formation of an electron–hole pair in a semiconductor photocatalyst with possible decay paths. A = electron acceptor, D = electron donor.
Figure 15.2 Conduction and valence band potentials and bandgap energies of various semiconductors relative to the redox potentials of compounds involved in CO
2
reduction at pH 7.
Figure 15.3 Bandgap and band-edge potentials of WO
3
with different morphologies.
Figure 15.4 (a) Photographs of TiO
2
with different amount of Co-doping (b) methane and carbon monoxide evolution rates by various catalysts under visible-light irradiation. Co:Ti ratio is 0, 0.002, 0.005, 0.01, 0.025, 0.05, 0.1, 0.15, 0.2 for OMT, Co-OMT-1, Co-OMT-2, Co-OMT-3, Co-OMT-4, Co-OMT-5, Co-OMT-6, Co-OMT-7, Co-OMT-8, respectively.
Figure 15.5 (a) FESEM image of Bi
2
WO
6
nanoplates and (b) CH
4
generation over nanoplates and the SSR sample as a function of visible-light irradiation times (
λ
> 420 nm).
Figure 15.6 Photocatalytic CO
2
reduction activity by MnCo
2
O
4
(a) under visible-light irradiation, (b) under different wavelengths of light irradiation (line spectrum indicate absorption of Ru-dye and inset shows the DR UV–vis spectrum of MnCo
2
O
4
)
Figure 15.7 (a) The band structures of ZGNO-SSR, ZGNO-tube, ZGNO-nanotube and ZGNO-nanorod at pH 7. The time course evolution of methane yields by CO
2
photoreduction under visible-light irradiation over ZGNO-nanotube, ZGNO-SSR, ZGNO-tube, and ZGNO-nanorod (b) a comparison of full-arc and visible-light irradiation over ZGNO-nanotube (c).
Figure 15.8 Schematic diagram of photocatalytic CO
2
reduction of Ru/CN composite under visible-light illumination.
Figure 15.9 Diagrammatic representation of photocatalytic CO
2
reduction over NH2-MIL-101(Fe) under visible-light irradiation.
Figure 15.10 Schematic illustration of CTF film photocatalyst-enzyme coupled system involved in exclusive production of formic acid from CO
2
. Rhox = [Cp*Rh(bipy)H
2
O]
2+
, Rh
red1
= Cp*Rh(bipy), Rh
red2
= [Cp*Rh(bipy)H]
+
; Cp* = pentamethylcyclopentadienyl, bpy = 2,2′-bipyridine.
Figure 15.11 Schematic illustrations of three kinds of charge-transfer mechanisms in composite semiconductors (a) sensitization mechanism, (b) p–n junction mechanism, (c) Z-scheme mechanism.
Chapter 16: Band-gap Engineering of Photocatalysts: Surface Modification versus Doping
Figure 16.1 Three schemes of the band-gap modifications for visible-light sensitization with lower shift of CBM (a), a higher shift of VBM (b), and impurity states (c).
Figure 16.2 Schematic diagram to illustrate the mechanism of (a) photocatalytic degradation of 2,4-dichlorophenolunder visible-light irradiation on V-doped titania
Figure 16.3 (a) Comparison of atomic p levels among anions. The band-gap of TiO
2
is formed between O 2pπ and Ti 3d states
Figure 16.4 Spatial and energetic distribution of electrons and holes in N-doped TiO
2
powder after weak femtosecond laser excitation at (a) 360 nm, and (b) 450 nm. V
O
indicates an oxygen vacancy.
Figure 16.5 Schematic drawings of the band structure of (a) boron and nitrogen-doped red TiO
2
depicting band-gap gradient, and (central and right) N doped
Figure 16.6 Illustration of the energy bands for Ti
3+
self-doped TiO
2−
x
with high oxygen vacancy concentration and the photoinduced charge transfer processes.
Figure 16.7 (a) Titania sensitization by platinum(IV) chloride complexes
Figure 16.8 Electron transfer (a, b) and energy transfer (c, d) mechanisms for plasmonic photocatalysts; (b) oxidative decomposition of organic compounds (OCs) by electron transfer mechanism for titania modified with NPs/NRs of gold with different sizes.
Figure 16.9 Schemes showing core(gold)–shell(Ag) structures covered with titania layer of different thicknesses for which mechanism of electron (a) and energy (b) transfers are proposed under visible-light irradiation.
Figure 16.10 Mechanism of photocatalysis on C-modified NaTaO
3
used for NO oxidation.
Figure 16.11 Schematic diagram of electron transfer processes in DSSCs; forward processes: [P1] photoexcitation of dye (1), [P2] electron injection from dye to titania (2), [P3] redox couple regeneration (3 [left]), [P4] dye regeneration (4 [left]) and 3 [right]); and backward processes: [P5] recombination of CB electrons with the oxidized dye (4 [right]) and [P6] recombination of CB electrons with the oxidized electrolyte (5 [right]).
Figure 16.12 Mechanism of urea-induced titania modification.
Figure 16.13 Schematic diagram of the energy levels of the CFO/WO
3
composites: (a) perfect junction, (b) with defects at interface, (c) ohmic contact junction.
Figure 16.14 Z-scheme photocatalytic systems with (a) and without (b) redox mediator.
Figure 16.15 (a) Schematic diagram for the band structure of titania doped with nitrogen and surface modified with nickel chloride and the photocatalytic mechanism
Chapter 18: Visible-Light-Active Photocatalysis: Nanostructured Catalyst Design, Mechanisms, and Applications
Figure 18.1 The Photocatalytic Mechanism. The photogenerated charge mechanism in TiO
2
consisting of electron and hole separation and recombination and reactions with adsorbed molecules.
Figure 18.2 Water splitting using photocatalysis with oxygen evolution on irradiated TiO
2
and hydrogen evolution on dark Pt [1].
Figure 18.3 Energy-level diagram of (a) conductor (b) insulator, and (c) semiconductor as a function of bandgap width.
Figure 18.4 (a) Band bending upward in a n-type nanosized semiconductor where electrons from close to the CB are transferred to the surface states; (b) band bending downward in a p-type semiconductor since electrons are transferred from surface states to acceptor levels near the valence band [6].
Figure 18.5 Valence and conduction bands for a variety of semiconducting materials on a potential scale (V) versus the normal hydrogen electrode (NHE). Redox potentials for the water-splitting half reactions are indicated by the dotted lines. In order for a semiconductor to be an effective catalyst its conduction band energy should be higher than the H
2
producing reaction potential and its valence band energy should be lower than the O
2
producing reaction potential.
Figure 18.6 Crystal structures of TiO
2
(a) anatase (b) rutile, and (c) brookite.
Figure 18.7 Surface band bending in the (a) anatase and (b) rutile phases of TiO
2
. The
x
-axis simply represents depth within the material with the surface of the material being indicated by the vertical line at the right-hand side of each schematic.
Figure 18.8 Mechanism by which hydroxyl radicals are formed on the surface of anatase and rutile.
Figure 18.9 (a) Photocurrent efficiency as a function of applied potential for nanotube arrays anodized on a planar foil, a half-pipe of 3.75 mm diameter and a full-pipe of 3.75 mm diameter and aspect ratio 1.7. (b) Total reflectance measurements for the three geometries.
Figure 18.10 SEM images of Bi
12
TiO
20
structures (a,b) prepared at 150 °C and (c,d) prepared at 180 °C. (a,c) overall product morphology; (b,d) enlarged image of the flower-like and nanowire structures.
Figure 18.11 Percentage of photodegradation of model pollutant BB (Basic Blue 41) as a function of Cr
3+
concentration. Dark bars: UV–Vis excitation; light bars: visible excitation.
Figure 18.12 Schematic mechanism of bandgap narrowing in anion doped TiO
2
.
Figure 18.13 Schematic representations of B, C, N, and F doping in TiO
2
.
Figure 18.14 Electronic structure of black hydrogenated TiO
2
.
Figure 18.15 Mechanism of dye-sensitized photocatalytic hydrogen production on the surface of a metal-oxide semiconductor (such as TiO
2
) under visible-light irradiation.
Figure 18.16 Electron transfer mechanism in silver-loaded TiO
2
.
Figure 18.17 Mechanism for light absorption of silver supported in TiO
2
.
Figure 18.18 Modification of TiO
2
nanoparticles with silver using silver nitrate and formaldehyde as a metal source and reducing agent, respectively, the resultant color change of the powder after treatment is also shown on the right [12, 30].
Figure 18.19 Diffuse reflectance spectroscopy (DRS) of TiO
2
and Ag–TiO
2
at silver loadings from 1–12 mol% following a 300 °C heat treatment for 30 min.
Figure 18.20 Plasmonic light harvesting using core–shell metal-insulator nanoparticles.
Figure 18.21 Electron transfer mechanism in composite semiconductor.
Figure 18.22 Photocatalytic mechanisms in TiO
2
–CNT composites (a) sensitization by carbon, (b) reduced recombination by a carbon actings as an electron–hole sink, and (c) presence of intraband states by carbon doping.
Chapter 19: Quantum Dynamics Effects in Photocatalysis
Figure 19.1 Schematic representation of (a) adiabatic and (b) nonadiabatic electron dynamics. The PESs that correspond to two different electronic states are shown.
Figure 19.2 Tunneling and superexchange as the consequences of representation choice. and are the eigenstates of the isolated donor (left) and acceptor (right), respectively. These states are non-stationary from the point of view of the adiabatic states of the overall system A–C–B, {|
ψ
i
⟩} (dotted line), but they can be regarded as the diabetic states. The time evolution of the projections describes the kinetics of tunneling.
Figure 19.3 PES for the rearrangement of H
3
CCOH in Ar matrix (11 K). H tunneling leads to the experimentally observed product H
3
CCHO. Δ
H
indicates the relative enthalpy changes (in kilocalories per mole) along the reaction coordinate.
Figure 19.4 Reactions that are dominated by C atom tunneling: (a) the automerization of cyclobutadiene; (b) the Cope rearrangement of semibullvalene; (c,d) the ring opening of cyclopropylcarbenyl radical and tetrahedryl-tetrahedrane; (e–g) the ring expansion of 1-methylcyclobutylfluorocarbene, noradamantylchlorocarbene, and benzazirine; and (h) the decomposition of C(CH
3
)
5
+
.
Figure 19.5 Possible two-photon mechanism for the photoinduced oxidation and CC coupling reactions of CH
3
OH over TiO
2
. (a) thermal or photoinduced CH
3
O generation, (b) oxidation of CH
3
O to CH
2
O, and (c) CC coupling of CH
3
O and CH
2
O producing HCO
2
CH
3
.
List of Tables
Chapter 2: Recent Advances on Photocatalysis for Water Detoxification and CO
2
Reduction
Table 2.1 Main features of NCCs, PTCs, CPCs (see Ref. [93] for further details).
Chapter 7: Glassy Photocatalysts: New Trend in Solar Photocatalysis
Table 7.1 Semiconductor–glass nanocomposites with growth parameters, optical properties, and volume of H
2
evolved
Chapter 8: Recent Developments in Heterostructure-Based Catalysts for Water Splitting
Table 8.1 Summary of recent key advances in BiVO
4
-based heterojunction photoanodes
Chapter 11: Advances in the Development of Novel Photocatalysts for Detoxification
Table 11.1 The different metal-ion-doped TiO
2
as photocatalyst for detoxification of water
Chapter 12: Metal-Free Organic Semiconductors for Visible-Light-Active Photocatalytic Water Splitting
Table 12.1 Surface area and photocatalytic performances of mesoporous g-CN using different templates
Chapter 14: Recent Developments on Visible-Light Photoredox Catalysis by Organic Dyes for Organic Synthesis
Table 14.1 Photophysical properties of rose bengal and methylene blue
Chapter 17: Roles of the Active Species Generated during Photocatalysis
Table 17.1 One-electron reduction potentials of active species commonly present or generated upon heterogeneous photocatalysis in aqueous systems
Chapter 18: Visible-Light-Active Photocatalysis: Nanostructured Catalyst Design, Mechanisms, and Applications
Table 18.1 Standard electrochemical reduction potentials of common oxidants.
Visible-Light-Active Photocatalysis: Nanostructured Catalyst Design, Mechanisms, and Applications
Edited by Srabanti Ghosh
Dr. Srabanti Ghosh
CSIR - Central Glass and Ceramic Research Institute
Fuel Cell & Battery Division
196, Raja S. C. Mullick Road
700 032 Kolkata
India
Cover
Background image Fotolia: Dudarev Mikhail
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I dedicate this book to my HUSBAND and PARENTS.
Preface
In the last decades, photocatalysis has been demonstrated to be one of the most promising approaches to environmental protection, solar energy conversion, as well as in the sustainable production of fuels from water and carbon dioxide. Visible-light-induced photocatalysis is relatively a new area of material science, but the major problem remains as poor solar energy conversion efficiency. The development of novel nanoscale structures as visible-light-responsive photocatalysts causes a dramatic improvement in energy conversion and generation. This book includes the visible-light-active photocatalysis to cover the entire field, focusing on fundamentals, size and shape tunable nanostructures, and the evaluation of their effectiveness as well as perspectives, technologies, applications, and the latest developments, including pollutants degradation by oxidative or reductive processes, organic transformations, CO2 reduction to produce low-carbon fuels, water electrolysis for hydrogen generation, and photoelectrochemistry for water splitting to produce hydrogen and oxygen and put forward future directions in solar light harvesting.
The book begins with a brief introduction of visible-light-induced photocatalysis by various nanomaterials in chapter 1, followed by chapters 2–15 dealing with the organic pollutants degradation, water detoxification, organic transformations, water splitting, and CO2 reduction. There are chapters 2, 5–9, 12 devoted to metal-oxide-based photocatalysts, plasmonic catalysts, heterogeneous inorganic semiconducting materials such as metal oxides, nitrides, sulfides, oxynitrides, etc., heterostructures-based catalysts, conducting polymers nanostructures, organic polymeric semiconductors, and metal–organic complex. Effects of bandgap engineering of photocatalysts, mechanistic studies, particularly, roles of the active species on photocatalysis are covered in a separate chapter 16, 17, 18. Chapter 19 is dedicated to the computational modeling of photocatalysis, with an emphasis on reactive dynamics and quantum effects. This book also promotes the idea about solar photocatalytic reactor designs and their broader impact on the environment for large-scale applications in chapter 20. Finally, the last chapter 21 outlines a brief summary of the work and puts forward future directions in perspective of the solar light harvesting. In order to make each contribution complete in itself, there is some unavoidable overlap among the chapters.
We believe this book endows with essential reads for university students, researchers, and engineers and allows them to find the latest information on visible-light-active photocatalysis, fundamentals, and applications.
Kolkata, 2018
Srabanti Ghosh
Part IVisible-Light Active Photocatalysis – Research and Technological Advancements
Chapter 1Research Frontiers in Solar Light Harvesting
Srabanti Ghosh
