Green Nanotechnology: Paving the Way for Environmental Sustainability

1. Introduction

In the era of rising global population and environmental apprehension, the critical necessity is to bring sustainable solutions through innovations in modern science [1]. In 2017, the United Nations urged all countries, through its Sustainable Development Goals (SDGs), to recognize the interconnectedness in alleviating poverty, health improvement, environmental protection, and economic development in efforts to reduce inequality across multiple sectors [2]. Nanotechnology plays a crucial role in advancing environmental sustainability by providing inventive solutions to compelling environmental challenges and promoting a more efficient and resilient approach to resource management and conservation. In November 2020, representatives from leading nanotechnology research institutes gathered for an international workshop on “Nanotechnology for a Sustainable Future”. This workshop sought to investigate the potential of nanotechnology and its applications in advancing the SDGs, highlighting the imperative of forming an International Network for Sustainable Nanotechnology (N4SNano) to facilitate collaboration between scientists, technologists, governments, and policymakers worldwide. This collaboration aimed to ensure the swift adoption of nanotechnology-based solutions to address pressing global challenges (https://network4sustainablenano.org (accessed on 15 June 2024)). While nanotechnology offers significant promise for tackling sustainability issues, it is crucial not to disregard the harmful effects that nanomaterials can have on both the environment and human health. The integration of the principles of environmental sustainability into nanotechnological methodologies can make them greener, cleaner, and more environmentally friendly [3]. Green nanotechnology has emerged as a widely recognized and promising field of science for environmental sustainability through various applications in renewable energy, environmental remediation, (nano)material synthesis, and biomedicine. It emphasizes the use of eco-friendly methodologies using environmentally sustainable materials to bring a balance between economic, social, and environmental factors to maintain the health and integrity of various ecosystems [2]. The global green nanotechnology market for sustainable environmental applications is significantly increasing and will reach a pinnacle of ~417.35 billion in 2030 (https://www.precedenceresearch.com/press-release/green-technology-and-sustainability-market). In this Special Issue, we aimed to publish articles that address the current problems and present green nanotechnology solutions in various areas, including tapping renewable energy, synthesizing (nano)materials, assessing the impact of various phyto-synthesized metal/metal oxide nanoparticles on food crops, remediating microplastics from different ecosystems, and integrating circular economy using plastic waste.

2. Introduction to the Papers Published in This Special Issue

This Special Issue comprises nine published articles. The article by Adun et al. [4] discusses the effect of nanoparticle size on the thermal efficiency of solar flat plate collectors, which has applications in hot water production, drying, and many more. Three articles addressed the green and agro(industrial) waste-mediated synthesis and characterization of metal and metal oxide nanoparticles and their biological evaluation for biomedical applications [5,6,7]. One article by Wahab and colleagues discusses the recent research progress and future prospects of phyto-synthesized nanoparticles and their interactions with food crops under drought-induced stress [8]. Two articles comprehensively discussed the emerging threat of microplastics to the environment and human health, as well as the remediation of microplastics from aquatic and food ecosystems and the possible economic gains from plastic waste [9,10]. Finally, the research article by Narayanan and coworkers [11] reports on the sustainable production of tissue scaffolds using decellularized cellulose-based and chitin/glucan-based plant materials for their skin tissue engineering applications. These research results are from the Republic of Korea, Cyprus, and Saudi Arabia, and the comprehensive review articles are from India.

Over several years, fossil fuels have been the predominant global energy source to fulfill our energy needs. However, this absolute reliance has shown severe detrimental environmental ramifications, causing the escalation of average global temperatures (global warming). To address this issue, the development of solar energy technologies, renowned for their inexhaustible and renewable energy, is imperative. Solar collector systems, a prevalent type of heat exchanger, typically employ flat-plate collectors (FPCs) to harness sunlight and convert it into thermal energy for various applications. The thermophysical characteristics of nanofluids within FPCs are intricately influenced by nanoparticle composition, dimensions, and morphology. Larger nanoparticles have been reported to cause microchannel clogging within the heat exchanger, resulting in a high-pressure drop in the system and impeding effective flow in the channel. Additionally, they have been associated with increased pipe erosion. Despite the critical role of nanoparticle properties in nanofluids within solar collector systems, there exists a dearth of research in this field. In a study by Adun et al. [4], the impact of silver nanoparticle (AgNP) size within nanofluids on the thermal efficacy of solar plate collectors was evaluated. These nanodimensioned AgNPs (Ag-100) notably influenced the mean fluid temperature, resulting in a peak temperature of 45.8 °C. Furthermore, AgNPs with a size of 100 nm demonstrated the most substantial reduction in collector dimension (18.3%) relative to that of water.

Several metal/metal oxide NPs exhibit unique physical, chemical, and biological properties compared to their bulk counterparts, and these NPs are chemically and physically synthesized using expensive instrumentations and toxic materials. Therefore, there is a need to synthesize low-cost and eco-friendly metal/metal oxide NPs through sustainable and greener methodologies. In the research article by Hussien and coworkers [7], they successfully synthesized low-cytotoxic zinc oxide (ZnO) NPs against human skin fibroblasts (HSFs) in an eco-friendly and sustainable manner using agro-wastes of banana peel and date seed extracts. Another research article by Hussien [6] demonstrated the antimicrobial potential of green synthesized ZnO NPs using banana peel and date seed extracts against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli and Salmonella enteritidis) bacterial strains. Silver (Ag) and titanium oxide (TiO₂) nanoparticles were also green synthesized by Al Malki et al. [5] using biodegradable wastes of tea and eggshells. They also assessed the cytotoxicity of ZnO NPs and Ag NPs against HSFs, which exhibited non-cytotoxicity and high cytotoxicity (IC50 = 54.99 µg/mL), respectively. Over the past two decades, the greener, eco-friendly, and sustainable syntheses of these metal/metal oxide nanoparticles using phytoextracts or phytochemicals such as alkaloids, terpenoids, polyphenols, and flavonoids as reducing agents have provided a sustainable and greener route of synthesis over conventional methods. The review article by Wahab and colleagues [8] focuses on the greener synthesis and characterization of various phyto-synthesized metal and metal oxide NPs, such as silver, gold, copper, ZnO, TiO₂, and iron oxide, using plant extracts and their bioactive compounds. The nanoparticles’ interaction with plants and their mechanisms for enhancing drought tolerance and mitigating drought stress in plants were also elaborately discussed. These findings demonstrate that phyto-synthesized nanoparticles can improve the germination of seeds and the growth of seedlings, regulate water balance, enhance photosynthesis, increase chlorophyll content, and trigger antioxidant defense mechanisms in plants under drought stress. Furthermore, these nanoparticles regulate plant hormones, providing essential protection against the impacts of drought stress while simultaneously increasing agricultural productivity.

Microplastics are tiny pieces of plastic fragments measuring less than 5 mm in size (<5 mm) derived primarily from larger plastic items such as polyethylene terephthalate (PET) bottles, bags, synthetic paints, tire dust, polyester textiles/fabrics, acrylic, and nylon products. Globally, approximately 9 million tons of plastic waste enter the ocean annually (https://www.theseacleaners.org/plastic-pollution/). It is considered an emerging contaminant in various environments, including the soil, air, freshwater, and marine ecosystems. The review article by Ghosh et al. [10] discusses the impact of microplastics on marine life and other ecosystems, focusing on their ingestion by marine animals and subsequent effects on reproductive systems and mortality rates. Furthermore, it addressed the potential health risks posed by the inhalation, ingestion, and dermal contact of microplastics, including respiratory, digestive, and reproductive issues, autoimmune disorders, neurodegenerative diseases, cancer, and endocrine disorders in humans. Additionally, microplastics may contribute to disruptions in sleep patterns, obesity, and diabetes. This article also discussed a multifaceted approach to mitigating plastic usage, proper disposal and recycling methods, and innovative technologies for detecting and removing microplastics from the environment. Dhiman et al. [9] discussed the remediation of microplastics in aquatic and food ecosystems through nanotechnological methodologies, along with exploring circular economy solutions aimed at transforming plastic waste removed from the aquatic and food-based ecosystems into valuable resources and the various governmental policies of different countries for microplastics management. Several natural and synthetic tissue scaffolds have applications in musculoskeletal, dermatological, and cardiovascular tissue engineering and regenerative medicine. The global tissue scaffolds market is experiencing significant growth driven by the increasing demand for regenerative medicine, and it is projected to grow by 16.29% from 2024 to 2032 (https://www.astuteanalytica.com/request-sample/scaffold-technology-market). The research article by Narayanan et al. [11] demonstrated the formation of three-dimensional decellularized tissue scaffolds using green and low-cost sustainable mushroom and plant-based materials. They also assessed the in vitro cytocompatibility of these scaffolds for skin tissue engineering applications.

3. Conclusions

In conclusion, as the name implies, green nanotechnology has a certain green purpose for the environment and sustainable development. This Special Issue provides methodologies for the green synthesis of various materials and nanomaterials and their role in tackling environmental challenges, biomedicine, and agriculture. Through the principles of green chemistry, green nanotechnology helps us to discern superior sustainable products and procedures without affecting the environment, though there is always plenty of room for improvement. Additionally, government policies should be set in place to guarantee the eco-friendliness and safety of nanomaterials and processes, effectively manage waste disposal, tackle regulatory challenges, and promote public awareness and acceptance of innovative green nanotechnology solutions, which additionally strengthens environmental sustainability within a circular economy framework.