Review pubs.acs.org/CR Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications † ‡ § † § ∥ † ⊥ # Hongli Zhu,*, , , Wei Luo, , Peter N. Ciesielski, Zhiqiang Fang, J. Y. Zhu, Gunnar Henriksson, ∥ † Michael E. Himmel, and Liangbing Hu*, † Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States ‡ Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, United States ∥ Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States ⊥ Forest Products Laboratory, USDA Forest Service, Madison, Wisconsin 53726, United States # Division of Wood Chemistry and Pulp Technology, Department of Fiber and Polymer Technology, Royal Institute of Technology, KTH, Stockholm, Sweden ABSTRACT: With the arising of global climate change and resource shortage, in recent years, increased attention has been paid to environmentally friendly materials. Trees are sustainable and renewable materials, which give us shelter and oxygen and remove carbon dioxide from the atmosphere. Trees are a primary resource that human society depends upon every day, for example, homes, heating, furniture, and aircraft. Wood from trees gives us paper, cardboard, and medical supplies, thus impacting our homes, school, work, and play. All of the above-mentioned applications have been well developed over the past thousands of years. However, trees and wood have much more to offer us as advanced materials, impacting emerging high-tech fields, such as bioengineering, flexible electronics, and clean energy. Wood naturally has a hierarchical structure, composed of well-oriented microfibers and tracheids for water, ion, and oxygen transportation during metabolism. At higher magnification, the walls of fiber cells have an interesting morphologya distinctly mesoporous structure. Moreover, the walls of fiber cells are composed of thousands of fibers (or macrofibrils) oriented in a similar angle. Nanofibrils and nanocrystals can be further liberated from macrofibrils by mechanical, chemical, and enzymatic methods. The obtained nanocellulose has unique optical, mechanical, and barrier properties and is an excellent candidate for chemical modification and reconfiguration. Wood is naturally a composite material, comprised of cellulose, hemicellulose, and lignin. Wood is sustainable, earth abundant, strong, biodegradable, biocompatible, and chemically accessible for modification; more importantly, multiscale natural fibers from wood have unique optical properties applicable to different kinds of optoelectronics and photonic devices. Today, the materials derived from wood are ready to be explored for applications in new technology areas, such as electronics, biomedical devices, and energy. The goal of this study is to review the fundamental structures and chemistries of wood and wood-derived materials, which are essential for a wide range of existing and new enabling technologies. The scope of the review covers multiscale materials and assemblies of cellulose, hemicellulose, and lignin as well as other biomaterials derived from wood, in regard to their major emerging applications. Structure−properties− application relationships will be investigated in detail. Understanding the fundamental properties of these structures is crucial for designing and manufacturing products for emerging applications. Today, a more holistic understanding of the interplay between the structure, chemistry, and performance of wood and wood-derived materials is advancing historical applications of these materials. This new level of understanding also enables a myriad of new and exciting applications, which motivate this review. There are excellent reviews already on the classical topic of woody materials, and some recent reviews also cover new understanding of these materials as well as potential applications. This review will focus on the uniqueness of woody materials for three critical applications: green electronics, biological devices, and energy storage and bioenergy. CONTENTS 2.2.3. Lignin 9318 2.3. Biopolymer Extraction 9321 1. Introduction 9306 3. One-, Two-, and Three-Dimensional Nanostruc- 2. Wood Structure and Chemistry 9306 tures from Wood Biomaterials: Synthesis and 2.1. Multiscale Structure and Morphology of Characterization 9323 Wood and Wood-Derived Materials 9306 3.1. Multifunctional Fibers 9323 2.2. Wood Chemistry: Molecular and Macro- molecular Structure of Cell Wall Biopolymers 9308 2.2.1. Cellulose and Nanocellulose 9308 Received: April 19, 2016 2.2.2. Hemiscellulose 9316 Published: July 26, 2016 © 2016 American Chemical Society 9305 DOI: 10.1021/acs.chemrev.6b00225 Chem. Rev. 2016, 116, 9305−9374 Chemical Reviews Review 3.1.1. Mechanically Strong Fibers 9323 1. INTRODUCTION 3.1.2. Electrically Conductive Carbon Fibers 9324 With the arising of global climate change and resource shortage, 3.1.3. Other Functional Fibers 9324 in recent years, increased attention has been paid to environ- 3.2. Multifunctional Membranes, Films, and Paper 9325 mentally friendly materials. Trees are sustainable and renewable 3.2.1. Optically Transparent Paper and Its fi materials, which give us shelter and oxygen and remove carbon Modi cations 9325 dioxide from the atmosphere. Trees are a primary resource that 3.2.2. Mesoporous Membrane with Tailored human society depends upon every day, for example, homes, Porosity 9327 heating, furniture, and aircraft. Wood from trees gives us paper, 3.2.3. Photonic Film with CNC 9328 cardboard, and medical supplies, thus impacting our homes, 3.2.4. Other Multifunctional Papers 9328 school, work, and play. All of the above-mentioned applications 3.3. Three-Dimensional Aerogels and Hydrogels 9332 have been well developed over the past thousands of years. 3.3.1. Lightweight and Mechanically Robust However, trees and wood have much more to offer us as Aerogel 9332 advanced materials, impacting emerging high-tech fields, such as 3.3.2. Conductive Aerogel 9333 bioengineering, flexible electronics, and clean energy. 3.3.3. Application of Aerogel 9334 Wood naturally has a hierarchical structure, composed of well- 3.3.4. Hydrogel Made from CNF and CNC 9334 oriented microfibers and tracheids for water, ion, and oxygen 4. Wood-Derived Green Electronics 9335 transportation during metabolism. At higher magnification, the 4.1. Unique Properties of Cellulosic Biopolymers 9335 walls of fiber cells have an interesting morphologya distinctly 4.1.1. Optical Properties 9335 mesoporous structure. Moreover, the walls of fiber cells are 4.1.2. Mechanical Properties 9336 composed of thousands of fibers (or macrofibrils) oriented in a 4.1.3. Thermal Properties 9338 similar angle. Nanofibrils and nanocrystals can be further 4.1.4. Refraction Index and Dielectric Constant 9338 liberated from macrofibrils by mechanical, chemical, and 4.1.5. Barrier Properties 9338 enzymatic methods. The obtained nanocellulose has unique 4.2. Cellulosic Biopolymer-Based Green Elec- optical, mechanical, and barrier properties and is an excellent tronics 9339 candidate for chemical modification and reconfiguration. Wood 4.2.1. Overview of Green Electronics Using is naturally a composite material, comprised of cellulose, New Materials 9339 hemicellulose, and lignin. Wood is sustainable, earth-abundant, 4.2.2. Flexible Transistors 9340 strong, biodegradable, biocompatible, and chemically accessible 4.2.3. Organic Light-Emitting Diode (OLED) for for modification; more importantly, multiscale natural fibers Lighting 9341 from wood have unique optical properties applicable to different 4.2.4. Printed Antenna and Radiofrequency fi kinds of optoelectronics and photonic devices. Today, the Identi cation (RFID) Devices 9342 materials derived from wood are ready to be explored for 4.2.5. High-Performance Loudspeaker 9343 applications in new technology areas, such as electronics, 4.2.6. Lightweight Paper Actuators 9344 biomedical devices, and energy. 4.2.7. Touchscreens by Writing 9344 The goal of this study is to review the fundamental structures 5. Wood-Derived Biological Applications 9345 and chemistries of wood and wood-derived materials, which are 5.1. Surface-Enhanced Raman Spectroscopy essential for a wide range of existing and new enabling (SERS) 9345 technologies. As outlined in Figure 1, the scope of the review 5.2. Bioplasmonic Sensor on Paper 9345 fl covers multiscale materials and assemblies of cellulose, hemi- 5.3. Micro uidic Devices for Diagnostics 9346 cellulose, and lignin, as well as other biomaterials derived from 5.4. Biosensor on Paper 9348 wood, in regard to their major emerging applications. Structure− 5.5. Bioactive Paper 9348 properties−application relationships will be investigated in 6. Wood-Derived Sustainable Energy 9350 detail. Understanding the fundamental properties of these 6.1. High-Performance Solar Cells Enabled by structures is crucial for designing and manufacturing products Printing and Advanced Light Management 9350 for emerging applications. Today, a more holistic understanding 6.2. Biofuels from Woody Feedstocks and Other of the interplay between the structure, the chemistry, and the Biomass 9351 performance of wood and wood-derived materials is advancing 6.2.1. Biochemical Conversion Processes 9351 historical applications of these materials. This new level of 6.2.2. Thermochemical Conversion Processes 9355 understanding also enables a myriad of new and exciting 6.3. Batteries and Electrochemical Capacitors 9356 applications,