Pathways to Green Nanomaterials: Plants as Raw Materials, Reducing Agents and Hosts

Nanoparticles (NPs) have become a hot research material in many fields, such as catalysis, sensing, clinical diagnosis, medical treatment, antimicrobial agents, and environmental remediation, due to their small size, high surface area, high reactivity, and unique optical, electrical, and thermodynamic properties. The type, morphology, size, and surface function modification of NPs determine their performance and application scope. The development of green, simple, and controllable NP synthesis methods is an important research direction at present. The biosynthesis of NPs is a kind of green synthesis method that uses organisms or biomolecules to reduce NP precursors. The reaction conditions are mild, the energy consumption is low, and there is no need for expensive equipment or harmful chemicals. It has been developed into an important branch of nanobiotic technology. This chapter summarizes the latest progress in the synthesis of NPs from different plant tissue extracts. It also summarizes the biosynthesis mechanism and application of NPs, analyzes the main problems faced by the biosynthesis method, and prospects its future research direction.

Plants contain the most abundant natural polymer cellulose in nature. Plants have a multilayered structure, made up of cells at the microscopic level. The main material of cells exists in the cell wall, mainly in the form of cellulose nanofilament-matrix composite structure, which plays a crucial role in the performance and function of plants. Nanocellulose, as a kind of environmentally friendly renewable polymer material, has great application potential and ecological benefits. In this chapter, the structural properties and preparation methods of nanocellulose are introduced, and the characterization methods and modification methods of nanocellulose are summarized. Finally, the design and construction of new nanocellulose materials in the future are prospected.

Plant-derived biochar is derived from biomass as a carbon source. It has a large specific surface area, high pore capacity, adjustable surface functional groups, and good environmental compatibility. Its raw material, plant-derived biomass, is widely available and renewable. It is a cheap and efficient adsorbent. Most biochar contains more than 70 percent carbon. Biochar can adsorb heavy metal ions, hormones, and organic pollutants. It can also be used for soil improvement, carbon sequestration, and the development of new materials with BC as the main component. In this chapter, biochar preparation and plants’ selection are introduced. How to characterize biochar is also discussed. In addition, biochar adsorption applications in different fields are also introduced.

Plant extracellular vesicles (EVs) are membranous vesicles secreted by plant cells, with a lipid bilayer as the basic skeleton, which encapsulates various active substances such as proteins and nucleic acids. Plant exosomes are nanoscale vesicles secreted by plant cells, containing DNA, small RNA, sRNA, microRNA, miRNA and proteins, which mediate cell-to-cell communication. Plant exosomes play anti-inflammatory, antiviral, anti-fibrosis, anti-tumor and other roles through the substances contained in them, and participate in the defense response to pathogen invasion. Plant exosome nanoparticles are mostly edible and can be used as delivery vehicles for specific drugs without toxicity or side effects. In this chapter, the recent literature reports on plant exosomes are reviewed, and the sources and functions of plant exosomes are summarized and analyzed.

The precursors of nanomaterials can be transformed into nanomaterials in plants. This chapter introduces plants as hosts for nanomaterial synthesis. Although the synthesis of nanomaterials by this method cannot be obtained in large quantities, the existence of nanomaterials in plants will have a certain impact on the growth of plants. This technique may not be useful in the synthesis of nanomaterials, but it has potential applications in agriculture. 

Plant polyphenols are important secondary metabolites in plants. They have strong antioxidant activity, which has a certain effect on the prevention of cardiovascular diseases and other chronic diseases, and can be widely used as antioxidants in food, drugs, and many other fields. The use of nanotechnology to make polyphenolic compounds into nanoparticles can effectively protect polyphenols from destruction, and improve the antioxidant and stability of polyphenols. In this chapter, the preparation technology and functional characteristics of polyphenol nanoparticles are discussed in detail, and the preparation and application of polyphenol nanoparticles are provided with references. 

The increasingly wide application of artificial nanomaterials is bound to lead to a large number of nanomaterials in the ecological environment, so the possible environmental pollution and ecological effects of nanomaterials have also attracted great attention. Plants are an important part of the ecosystem. On the one hand, nanomaterials may affect the development and growth of plants. On the other hand, the metabolic activities of plants can affect the migration and transformation behavior of nanomaterials in the environment and their transmission in the food web. This chapter reviews recent studies on the interaction between nanomaterials and plants, and discusses the toxic effects of different nanomaterials on plants from the plant to the plant cell level, as well as the process of plant uptake and transport of nanomaterials.

In order to ensure the needs of survival and reproduction, plants have formed various, diverse, multi-dimensional, and multi-scale fine and subtle configurations for millions of years, which provides rich inspiration for scientific research in many fields today. Research on morphology genetic material converts natural biological components into target materials by directly using biological structures as templates and selecting appropriate physicochemical methods while maintaining the fine-graded structure of the template. It can be used to prepare new functional materials with a biological finely-graded structure. This section describes methods for preparing functional materials with biological structures using morphology genetic material research ideas. In this chapter, we briefly introduce the structure of residual materials prepared by using several typical plant structures as templates, and discuss the related functional performance of materials with different structural characteristics. 

Plant virions, as nano-sized particles, have the advantages of high accumulation levels in plant cells, low regeneration cost, simple purification process and safety for the human body. They are ideal natural nanomaterials. With the development of bio-nanotechnology, plant virus nanoparticles show more and more applicable potential in the field of medicine. This chapter reviews the research progress and application of plant virus nanoparticles in the field of medicine, focusing on targeted drug delivery, molecular imaging and vaccine preparation.