Green Processes for Nanotechnology

In this chapter, selected low (T < 200 °C)-temperature wet-chemistry routes for the synthesis of crystalline inorganic compounds are described and reviewed, outlining their main features and application fields. In particular, the chosen approaches are hydro/solvothermal synthesis, template-assisted approaches, nucleation and growth in solution/suspension, microemulsion and miniemulsion. The described synthetic strategies have been selected since all of them, once optimized the experimental set-up and conditions, comply with the paradigms of green chemistry, being based on low (or even room) temperature of processing, on low chemical consumption (they are all bottom-up approach), in many cases having water as solvent or dispersing medium. In this regard, environmentally friendly methodologies for the controlled synthesis of inorganic nanostructures represent a stimulating research playground, since the use of environmentally friendly, green, cost-effective and technically sound approaches to inorganic crystalline nanostructures does not necessarily imply to sacrifice the sample crystallinity, purity, and monodispersity.

From a clinic or medical viewpoint, it is important that the surgical implant retains a combination of high strength (including surface wear resistance), good biocompatibility, and chemical stability. To enable safe interactions between the surgical implants and tissues, surface modification and functionalization are commonly employed.

Biological coatings such as TiN and titanium oxides are widely adopted and functionalized with various biological properties such as corrosion resistance, bioactivity, cytocompatibility, and bioconductivity. However, failure of the biological coatings due to the long term corrosion and wear or fretting is the main problem and debris from the materials is the main cause of joint replacement failure. Since the surgical implants are implanted into the human body for a long time, cyclic motions between the surgical implants and human tissues may disrupt the protective biological coatings accelerating corrosion and increasing the risks of immunological response by the leached metallic ions.

Therefore, improved metallic biomaterials and the relevant manufacturing techniques are being introduced to meet this demand. Apart from the biocompatibility requirement, metallic biomedical materials also have to meet high standards regarding its performance (functionality, reliability) and selection criteria (cost, manufacturing ability). Up to now, the most often used metallic biomedical materials include stainless steel, cobalt-based alloys, and commercially pure titanium or titanium-based alloys. However, the implant metallic biomaterials, like all mechanical components, are subjected to degradation and have limited lifetime. Damaged implant requires successive operation to replace worn components and so intensive efforts are made to increase durability of implants metallic biomaterials.

For enhancing the mechanical retention, engineered nanostructures on the surface are normally taken to increase effective surface area on implant surfaces (such as both dental and orthopedic applications) to exhibit biological, mechanical, and morphological compatibilities to receiving vital hard/soft tissue, resulting in promoting osseointegration.

The surface engineered nanostructures play a crucial role in biomedical metallic materials because (1) the surface of a biomaterials is the only part contacting with the bioenvironment, (2) the surface region of a biomaterial is almost always different in morphology and composition from the bulk, (3) for biomaterials that do not release or leak biologically active or toxic substance, the characteristics of the surface governs the biological response (foreign material vs. host tissue), and (4) surface properties such as topography affect the mechanical stability of the implant-tissue interface.

Therefore, aim to provide vital information about the growing field of engineered nanostructures on the surface of metallic biomedical materials, the relevant green technologies such as equal channel angular extrusion (ECAE), high pressure torsion (HPT), cold rolling, heat rolling, high energy ball milling, sandblasting, and shot peening are reviewed.

At the same time, implant industry is experiencing rapid growth mainly due to age-related degenerative diseases. with the increase of the need to diagnose diseases at an early stage in accordance with the saying: prevention is better than cure, the future prospects related to the significantly feasible surface nanostructured technology for the foreseeable future are also pointed out. It indicates that new surface bioengineering technologies should be explored to help the scientists and clinicians in the initiation of targeted treatments and in the follow-up of treatment responses.

In this chapter we concentrate our attention on the green processes of metal nanoparticles and utilization for catalytic hydrogenation of biomass-derived levulinic acid, from the pioneering studies to the present state of the art. An overview of the different methods and recent advances for the fabrication of metal nanoparticles, especially for the green methods, are commented and compared. Challenges and areas that need improvement are also highlighted in the corresponding area. The resulting catalysts are commented for the catalytic upgrading of levulinic acid which is a chemical building block from lignocellulosic biomass for the production of transportation fuels, as well as useful chemicals. Specific examples are reviewed with emphasis on different synthetic methods, comparing the behavior of different metal catalysts.

In recent years, the development of metallic and metal oxide nanoparticles in an eco-friendly manner using plant materials has attracted considerable attention. The biogenic reduction of metal ions to the base metal is quite rapid, can be conducted readily at room temperature under sunlight conditions, can be scaled up easily, and the method is eco-friendly. The reducing agents involved include various water-soluble metabolites (e.g., alkaloids, terpenoids, polyphenolic compounds) and coenzymes. Noble metals (silver and gold) have been the main focus of plant-based synthesis. These green synthesized nanoparticles have a range of shapes and sizes compared to those produced by other organisms. The advantages of using plant-derived materials for nanoparticle synthesis have attracted the interest of researchers to investigate the mechanisms of metal ions uptake and bio-reduction by plants. These biosynthesized metallic and metal oxide nanoparticles have a wide range of biological applications. This chapter, however, discusses only the antibacterial activities.

Development of green processes for nanotechnology is of great importance for broadening and improving the industrial applications of nanomaterials and nanocomposites. This chapter focuses on the recent developments in green synthesis, its properties, and its potential applications in nanomaterials and biomass nanocomposites. Among the various green processes for nanotechnology, we pay more attention to the microwave-assisted method, which has been accepted as a promising green methodology in the synthesis of nanomaterials and nanocomposites. Undoubtedly, the microwave-assisted method conforms to the principles of green chemistry such as “minimize the use of solvents and other auxiliary substances” and “minimize energy use” due to its characteristics of reduced energy consumption, reduced pollution, shorter reaction time, and higher product yield.

In recent years, rapid progress has been made in the preparation of nanomaterials and nanocomposites by a microwave-assisted method. In this chapter, the green microwave-assisted synthesis of various nanomaterials including metal nanomaterials, metal oxides nanomaterials, metal chalcogenides nanomaterials, bio-nanomaterials, nanocomposites, and biomass nanocomposites is reviewed. Some typical examples by our research group and by other groups are introduced, which would favor the understanding of the green microwave processes for nanotechnology. Finally, we propose the future perspectives of this green methodology for the fabrication of nanomaterials and nanocomposites.

Meeting the growing needs for more ecologically friendly, “green” processes for the functionalization of carbon nanomaterials (CNMs), a variety of chemical reactions proceeding under solvent-free conditions were proposed. Significant advances were achieved in the solvent-free covalent functionalization of carbon nanotubes (CNTs): a number of reactions were proposed to introduce organic moieties into the nanotube ends and sidewalls, which can be initiated by temperature, plasma, or mechanochemical treatment. In a number of instances, however, the concept “solvent-free” is applied to the reaction conditions only, whereas the entire synthetic protocol still requires auxiliary purification steps, which consume organic solvents along with an additional time, labor, and equipment. Our group systematically worked on the development of totally solvent-free functionalization techniques, with an emphasis on the covalent modification of CNTs, and attempting to further apply the same solvent-free protocols to other CNMs, nanodiamond in particular. The functionalization protocols designed by us are based on thermally activated reactions of amidation and nucleophilic addition with chemical compounds (mainly amines and thiols), which are stable and volatile at 150–200 °C under reduced pressure. Among main advantages of this approach is that not only the reactions per se take place at a high rate but also excess reagents are spontaneously removed from the functionalized material, thus making its additional purification unnecessary. As regards other CNMs, while the research effort undertaken for the chemical modification of ND, graphene, and graphene oxide as a whole is significant, the possibility of using solvent-free techniques for this purpose remains strongly underexplored.

To generate nanoparticles with particular shapes and dimensions, various techniques including physicochemical and biological routes have been developed. The physical and chemical processes are typically expensive and require hazardous chemicals. In this chapter, we introduce current advancements in the green synthesis of nanoparticles as eco-friendly, cost-effective, and simple approaches. The microbial synthesis of nanoparticles using bacteria, fungi, and viruses; phototrophic eukaryotes including plants, diatoms, and algae; heterotrophic human cell lines and some other biological agents is especially emphasized in this review. It also declares the applications of these nanomaterials in a broad range of potential areas, such as medical biology, labeling, sensors, drug delivery, dentistry, and environmental cleanup.

Biological synthesis of nanoparticles has been present in living organisms over the course of evolution to serve a variety of purposes. In this chapter, we discuss the latest trends and application for nanoparticle synthesis via plants, algae, yeast, bacteria, fungi, etc. There exists several review articles among others documenting studies about various biogenic sources and associated nanoparticle synthesis; we have rather emphasized on recent research works which probed into novel applications of these bio-nanoparticles along with some important historical findings. Also, we have discussed the challenges faced by biogenic methods along with possible areas to tweak in order to standardize this synthesis technique. Biogenic synthesis of nanoparticles has the potential to provide cost-effective, eco-friendly alternative to work as “biological nanofactories”/functionalization method once the attention has been shifted to understand the underlying mechanism, its in vitro replication and obtaining shape/size control over the nanoparticles being synthesized.

Metal nanoparticles (MNPs) have been widely used in a range of recent scientific and technological applications. They can be produced by conventional chemical synthesis or green synthesis methods. Green synthesis consists of a myriad of promising approaches for the production of MNPs with desired properties. Plants represent the most explored group of living organisms for the green synthesis of MNPs, and to date, hundreds of species have been used. However, several factors that should be taken into account when performing green synthesis of MNPs remain underestimated or unexplored. This chapter does not focus on any specific plant species or experimental conditions leading to the synthesis of MNPs since there are numerous recent publications reviewing the literature in this outstanding field. The present chapter instead focuses on the trends and challenges in MNPs synthesis using plants which include reproducibility, scale-up, predictability, and development of strategies for effective management of governance, regulatory, and compliance risks. Finally, the major aim of this chapter is to provide an overview of relevant concerns raised or neglected by the available scientific literature regarding the green synthesis of MNPs using plants.

Nanostructured soft materials combine structure and function to produce effects inspired by natural systems. Recent innovations in polymer science and supramolecular chemistry have led to the development of materials that can respond to and control their microenvironment, allowing them to increase the efficiency of chemical processes while decreasing their ecological impact. Size effects are profound at the nanoscale, allowing for a broad range of applications. This chapter features synthetic biomimetic nanosystems at different size regimes and match them with biological counterparts from tissues through cell walls to vesicles and proteins. The application of soft, bioinspired nanomaterials in fields ranging from medicine to sustainable energy represents a fundamental advancement in science and technology.

Thin film depositions by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique have been intensively used in order to obtain nanoarchitectonics with different biomedical applications, like drug delivery systems, tissue engineering, implants with improved biocompatibility, improved adherent surfaces, antibacterial surfaces, etc. This chapter presents a description of the latest research regarding magnetite-based thin films and hybrid organic–inorganic thin films obtained by MAPLE. The most encountered preparation methods for magnetite-based thin films and several hybrid organic–inorganic systems are presented. Regarding the biomedical applications, our attention is directed to the antibacterial properties of differently modified surfaces for implants and medical devices.

Nanotechnology is one of the exciting, albeit infrequent, technological change that can influence all industries. It holds the potential for pervasive and revolutionary changes. These changes can either follow a path leading to waste, pollution and energy inefficiency or follow a path of green nanotechnology to a more sustainable future. It is our choice while the window of opportunity still remains open. Green nanotechnology offers the opportunity to head off adverse effects before they occur. It can proactively influence the design of nanomaterials or products by eliminating or minimizing pollution from the production of the nanomaterials, taking a life cycle approach to nanoproducts to estimate and mitigate where environmental impact might occur in the product chain, designing toxicity out of nanomaterials and using nanomaterial to remediate existing environmental problem.

Nonequilibrium dynamical processes in nanoscale materials involving electrons, excitons, and vibrations are under active experimental investigation. Corresponding theoretical studies, however, are much scarcer. This chapter starts with the basics of time-dependent density functional theory, recent developments in nonadiabatic molecular dynamics methods, and the fusion of the two techniques. Ab initio simulations of this kind allow us to directly mimic a great variety of time-resolved experiments performed with pump-probe laser spectroscopies. We systematically investigate two important building blocks of modern nanotechnology, namely, quantum dots (QDs) and titanium dioxide (TiO₂). The focus is on the ultrafast photoinduced charge and exciton dynamics at interfaces formed by two complementary materials, including QD-TiO₂ hybrids, organic-QD and organic-TiO₂ interfaces, and all organic systems. These interfaces involve bulk semiconductors, metallic and semiconducting nanoclusters, graphene, carbon nanotubes, fullerenes, polymers, molecules and molecular crystals. The detailed atomistic insights available from time-domain ab initio studies provide a unique description and a comprehensive understanding of the competition between various dynamical processes (e.g., electron transfer, thermal relaxation, energy transfer, and charge recombination). These advances now make it possible to directly guide the development of organic and hybrid solar cells, as well as photocatalytic, electronic, spintronic, and other devices relying on complex interfacial dynamics.

Nanotechnology has wide range of applications. This paper emphasizes the need to conduct “life cycle”-based assessments as early in the new product development process as possible, for a better understanding of the potential environmental and human health consequences of nanomaterials over the entire life cycle of a nano-enabled product. This is further supported through an illustrative case study on automotive exterior body panels, which shows that the perceived environmental benefits of nano-based products in the Use stage may not adequately represent the complete picture, without examining the impacts in the other life cycle stages, particularly Materials Processing and Manufacturing. Nanomanufacturing methods often have associated environmental and human health impacts, which must be kept in perspective when evaluating nanoproducts for their “greenness.” Incorporating life cycle thinking for making informed decisions at the product design stage, combining life cycle and risk analysis, using sustainable manufacturing practices, and employing green chemistry alternatives are seen as possible solutions.

One of the impact promises associated with nanotechnology is that it will facilitate greener and more sustainable economic growth. We explore the extent to which nanotechnology development and commercialization is achieving this goal, drawing on secondary sources and available data. After defining the concepts of nanotechnology and green and sustainable development, we examine six nanotechnology application areas that are pertinent to green growth and sustainability. These application areas are assessed relative to their scale and scope through market forecasts, green benefits and potential issues and limitations. These six application areas are: nano-enabled solar cells, energy storage, nanogenerators, thermal energy, fuel catalysis, and water treatment. Nanotechnology-enabled applications in these areas offer potential benefits, such as reduced costs, less toxicity, greater efficiency, operating frequency, voltage, reduced complexity, and reliability. However, many sales forecasts associated with these applications have been adjusted downwards not only as a result of the economic downturn in the first decade of the 2000s but also due to the limited value offered by these nanotechnology-enabled application compared to what is already on the market (the incumbent technology). We find that while green nanotechnologies have the potential to make contributions both to addressing green challenges and to fostering sustainable economic development, development and diffusion is taking longer than previously anticipated, and in some cases the promised scale of benefits is unlikely to be realized. Additionally, the potential life cycle environmental overheads of some complex engineered nanomaterials must be taken more fully into account in assessing net contributions to green growth.