**Preface**

Sustainably providing a safe and secure food supply will be a significant challenge in the coming years, and the field of nanotechnology is well positioned to have a tremendous positive impact on these efforts. The potential benefits are numerous, including the enhancement of food quality and safety, the reduction of environmental waste and agricultural inputs, and the absorption of nanoscale nutrients from soil. Nanotechnology could also better enable plants to respond to a changing environment. It can also play an important role in crop productivity through controlling nutrient availability and utilization, as well as through mediating nutritional status in the presence of biotic and abiotic stress. Nanoscale platforms can also be used to monitor water quality parameters, including pesticide residue presence, in efforts to promote the sustainable development of agriculture. Nanomaterials have tremendously diverse functionality, making it difficult to perform a general assessment of crop health and environmental risks. For example, although dose is clearly one of the most important factors differentiating benefit from toxicity, factors such as environmental conditions and species sensitivity can dramatically shift that dividing line. In addition, the properties (other than size) of nanoparticles that influence toxicity include chemical composition, shape, surface structure, surface charge, and the extent of particle aggregation (clumping) or disaggregation. For this reason, even nanomaterials of the same chemical composition with different sizes or shapes can exhibit different toxicities or benefits.

There is also a general lack of understanding of how transformation processes in biotic and abiotic media influence overall nanomaterial activity. Regardless, nanotechnology applications in the agricultural sector have been a topic of intense interest, and many argue that it is a key factor for sustainable development. To explore this important topic, we have assembled a Special Issue in *Coatings* to encourage researchers and to provide them with a platform to publish their novel studies on the subject of "Functional Nanoparticles for Environmental Contaminants Removal and Agricultural Application".

> **Yu Shen** *Editor*

**Ran Tao 1,2, Mengmeng Kong <sup>3</sup> , Yinlong Zhang <sup>1</sup> and Yu Shen 1,2,\***


Currently, increasing demands are being placed on agricultural production, presented with the challenge of finding sustainable ways to meet the needs of the world's growing population [1]. Global warming and climate change have become a "wifi" contributing to agricultural and environmental issues, with rising global temperatures and extreme weather events leading to crop failures and impacting food security [2]. Furthermore, intensive agricultural practices and unsustainable land use are causing soil erosion, a loss of fertility, and reduced productivity [3]. Limited access to water, over-extraction, and pollution pose major challenges to agriculture, particularly in arid and semi-arid regions [4]. Additionally, the spread of pests and diseases has become increasingly challenging to control due to factors such as global trade and climate change [5].

Nanotechnology, and particularly the field of nanomaterials, holds the potential to revolutionize agriculture and the environment [6]. It can be utilized to enhance crop production efficiency [7], reduce the use of pesticides and fertilizers [8], and improve food quality [9]. Nanotechnology can also contribute to the development of novel materials that enhance irrigation efficiency, crop storage, and various other aspects of farming [10]. Moreover, nanotechnology has the potential to create sensors capable of detecting changes in soil quality, enabling farmers to make more informed decisions about land management [11]. Encouragingly, significant progress has been made in the field of nano-agriculture and environmental applications, as highlighted in our Special Issue "Functional Nanoparticles for Environmental Contaminants Removal and Agricultural Application" in *Coatings*.

Nanotechnology has played a positive role in agriculture. Guo et al. (2022) observed that silver nanoparticles outperformed other nanoparticles in terms of final crop seed germination percentages, and zinc nanoparticles were found to be the most effective in promoting root length growth during seed germination in a meta-analysis conducted between 1950 and 2021 [12]. Hexaconazole is a widely used, broad-spectrum, and highly efficient triazole fungicide, but its extensive use can lead to environmental disasters [13]. In response, Pan et al. (2021) applied azobenzene-modified bimodal mesoporous silica nanoparticles (BMMs-Azo) in conjunction with β-cyclodextrin to control the release of hexaconazole, reducing its environmental impact [14]. Biochar is known for its numerous surface functional groups and porous structure, which can reduce nutrient loss and enhance nutrient uptake by plants [15]. Combining Methylotrophic bacillus, colloidal biochar (containing dissolved nanoparticles), and organic fertilizer significantly increased the contents of lycopene, vitamin C, total sugar, and soluble sugar in tomato fruits by 58.40%, 46.53%, 29.45%, and 26.65%, respectively [16]. Additionally, Yang et al. (2022) demonstrated that biochar nanoparticles, acting as nanocarriers, substantially increased the fertilizer utilization of Chinese cabbage and promoted plant growth by over 50% [17]. Copper

**Citation:** Tao, R.; Kong, M.; Zhang, Y.; Shen, Y. Special Issue: Functional Nanoparticles for Environmental Contaminants Removal and Agricultural Application. *Coatings* **2023**, *13*, 1633. https://doi.org/ 10.3390/coatings13091633

Received: 5 September 2023 Accepted: 13 September 2023 Published: 18 September 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

nanoparticles have widespread applications in various industries, but their effects in agriculture and the environment vary. Yang et al. (2022) observed that 5 ppm copper nanoparticles caused the slight swelling of epithelial cells in the epididymal duct of Chinese soft-shelled turtles, while higher copper ion concentrations severely damaged the epithelial structure of the epididymal tube [18]. Faraz et al. (2022) reported on the foliar application of 2–16 ppm copper oxide nanoparticles (CuO NPs) on Brassica juncea 25 days after sowing, whereby 8 ppm resulted in optimal chlorophyll content, net photosynthetic rate, leaf proline content, and antioxidant enzyme activity [19]. However, the effectiveness of this concentration may vary for other plants. Surface coating is another factor affecting the interaction of CuO NPs with plants. Deng et al. (2022) found that the foliar spraying of 300 ppm bare NPs yielded similar results to 75 ppm citric-acid-coated NPs, with Cu NPs increasing the yield by approximately 170% compared to the control [20]. Interestingly, soil amendment with both bare and coated NPs did not significantly impact the plant mass relative to untreated plants. The use of manufactured nano-objects (MNOs), including carbon nanotubes (CNTs), nanoparticles (NPs), and nanopesticides, raises concerns, as these substances can impact the life cycle and not only accumulate in soils but also in other environmental components, negatively affecting the soil biota and processes. MNOs can interfere with soil physicochemical properties and microbial metabolic activity in rhizospheric soils [21]. Notably, negatively charged CuO NPs were found to significantly reduce disease progression and increase biomass, whereas positively charged NPs and a CuSO4 salt control had little impact on plants [22]. Based on element characteristics, it has been reported that magnesium nanoparticles (Mg-NPs) are more effective in enhancing the development of 'Superior Seedless' berries during various growth stages (flowering, fruit set, version, and harvest) compared to sulfate magnesium (MgSO4·7H2O) and magnesium disodium EDTA (Mg-EDTA) [23]. As we move forward in the realm of coated nanoparticles for environmental remediation and agricultural use, recent studies have shown promise. It has been reported that β-carotene-coated chitosan nanoparticles (CNPs) have the potential to block polycyclic aromatic hydrocarbons (PAHs) and protect crops in PAH-contaminated soil. Under specific conditions of 20 ◦C, pH 6, and 10 mg/mL TPP, spinach biomass significantly increased, and the transfer of PAHs from the soil to the roots was reduced [24]. In agricultural activities, insecticides and pesticides can have unintended effects, and the nanofeature of higher efficiency is utilized to reduce ecotoxicity. Alginate CNPs have been employed in combination with DMT to reduce insecticide toxicity in zebrafish larvae while reducing the required dose [25]. Furthermore, CNPs can serve as a core for novel SnS<sup>2</sup> quantum dots with Azadirachta indica leaf extract, with coated CNPs exhibiting an enhanced removal of crystal violet dye [26]. Overall, our Special Issue reflects the cutting-edge trends in nanotechnology applications in agriculture and the environment.

Environmental catalysis has garnered significant attention for its clean methods of producing useful chemicals and facilitating various chemical processes. This approach can decompose and eliminate organic pollutants from aqueous environments while enabling the production of valuable chemicals [27]. Liu et al. (2023) synthesized novel N-doped biochar nanoparticles through the one-step pyrolysis of algal sludge without external nitrogen sources, yielding a highly active and cost-effective carbon-based catalyst capable of activating new oxidants for contaminant removal [28]. Additionally, Liu et al. (2022) found that Sedum plumbizincicola nanoparticles can effectively remove Bisphenol A (BPA) from complex wastewater, demonstrating stable and efficient reactions [29]. Nanoscale schwertmannite (nano-SWT) was prepared using an indoor temperature synthesis method with the assistance of polyvinylpyrrolidone, and nano-SWT was found to be effective in reducing sulfamethoxazole in the presence of Fenton-like catalysts using hydrogen peroxide (H2O2) [30]. Currently, Fenton catalysts are widely employed in conjunction with nanoparticles for environmental contaminant removal. Manganese tetroxide (Mn3O4) nanoparticles have been reported to simultaneously degrade estriol and 17αethinylestradiol (E3/EE2) with removal efficiencies of 97.5% and 96.4% for E3 and EE2, respectively, using Fenton-like catalysts [31]. Copper–iron peroxide nanoparticles (CFp

NPs) have been designed for tumor-microenvironment-mediated synergistic therapy in a heterogeneous chemodynamic therapy system. CFp NPs generate oxygen during catalysis and exhibit a tumor-microenvironment-responsive T1 magnetic resonance imaging contrast enhancement, aiding in tumor oxygenation and in vivo tumor monitoring [32]. Furthermore, it has been reported that S-doped carbon and Fe7S8 nanoparticles interact effectively for the high-efficiency removal of antibiotics through a Fenton-like degradation process. Within 40 min under neutral pH conditions, amoxicillin, norfloxacin, and tetracycline hydrochloride were removed at rates of 98.9%, 97.8%, and 99.3%, respectively, with the catalyst demonstrating excellent cycle stability [33]. At the same time, with the oxygen atoms in the sulfonic acid group cooperating with Ag+ to form a synergistic complexation, a novel magnetic fluorescent nanoprobe (Fe3O4@ZnS@MPS(MFNPs)) was designed for Ag+ detection in aquatic media [34]. These findings underscore the significant progress made in leveraging nanomaterials and catalytic processes for cleaner and more efficient environmental solutions, offering promise for a sustainable future.

In conclusion, the advancements in nano-agriculture and environmental applications are evident from the research covered in the Special Issue "Functional Nanoparticles for Environmental Contaminants Removal and Agricultural Application" in *Coatings*. Noteworthy examples include the use of silver nanoparticles to enhance crop seed germination and the application of azobenzene-modified bimodal mesoporous silica nanoparticles to control the release of the fungicide hexaconazole, thereby reducing environmental impacts. While nanotechnology presents exciting prospects, it is crucial to consider its potential ecological effects and develop responsible applications. Overall, the progress in nanotechnology applications in agriculture and the environment underscores the field's potential to contribute to a more sustainable future.

**Funding:** This research was funded by the National Science Foundation, grant number 31872415.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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