Holey MoS2 Nanosheets with Photocatalytic Metal Rich Edges by Ambient Electrospray Deposition for Solar Water Disinfection

Interfacial Growth of Large Area Single-Crystalline Silver Sheets Through Ambient Microdroplets

The creation of micrometer-sized sheets of silver at the air-water interface by direct deposition of electrospray-generated silver ions (Ag+) on an aqueous dispersion of reduced graphene oxide (RGO), in ambient conditions, is reported. In the process of electrospray deposition (ESD), an electrohydrodynamic flow is created in the aqueous dispersion, and the graphene sheets assemble, forming a thin film at the air-water interface. The deposited Ag+ coalesce to make single-crystalline Ag sheets on top of this assembled graphene layer. Fast neutralization of Ag+ forming atomic Ag, combined with their enhanced mobility on graphene surfaces, presumably facilitates the growth of larger Ag clusters. Moreover, restrictions imposed by the interface drive the crystal growth in 2D. By controlling the precursor salt concentration, RGO concentration, deposition time, and ion current, the dimensionality of the Ag sheets can be tuned. These Ag sheets are effective substrates for surface-enhanced Raman spectroscopy (SERS), as demonstrated by the successful detection of methylene blue at nanomolar concentrations.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Nanocrystalline BEA-CNT Composites with High Metal Dispersion Obtained via Inter-Zeolite Transformation for Antibacterial Application

The rational design of interface materials containing carbon nanotubes (CNTs) and zeolites (zeolite-CNTs) is a promising perspective in chemical and biochemical communities because they exhibit several outstanding properties such as tunable hydrophobicity-hydrophilicity at interfaces. In this contribution, we report the fabrication of Ag-incorporated nanocrystalline BEA-carbon nanotube (CNT) composites via the one-pot inter-zeolite transformation of the micron-sized FAU-CNT composite in the presence of a Ag precursor. By varying the crystallization time, the inter-zeolite transformation mechanism was explored. Indeed, this process involves an amorphous intermediate of aluminosilicate species with a significant change of the crystal morphology in the presence of CNTs in the synthesis gel. Interestingly, the redispersion of metal particles was observed after the inter-zeolite transformation process, resulting in the high dispersion of metal nanoparticles over BEA nanocrystals. Notably, it was revealed that the Ag sites were also stabilized in the presence of CNT interfaces, leading to the availability of highly active Ag+ ions. To illustrate the beneficial aspect of designer materials, the synthesized Ag-incorporated BEA-CNT composites exhibited high antibacterial activity againstEscherichia coli due to the synergistic effect of the active Ag+ species and appropriate hydrophobic and hydrophilic properties of the hybrid material interfaces. This first example opens up perspectives of the rational design of zeolite-CNT interfaces with high metal dispersion via the inter-zeolite transformation approach for biomedical applications.

Graphene-Based Technologies for Tackling COVID-19 and Future Pandemics

The COVID-19 pandemic highlighted the need for rapid tools and technologies to combat highly infectious viruses. The excellent electrical, mechanical and other functional properties of graphene and graphene-like 2D materials (2DM) can be utilized to develop novel and innovative devices to tackle COVID-19 and future pandemics. Here, the authors outline how graphene and other 2DM-based technologies can be used for the detection, protection, and continuous monitoring of infectious diseases including COVID-19. The authors highlight the potential of 2DM-based biosensors in rapid testing and tracing of viruses to enable isolation of infected patients, and stop the spread of viruses. The possibilities of graphene-based wearable devices are discussed for continuous monitoring of COVID-19 symptoms. The authors also provide an overview of the personal protective equipment, and potential filtration mechanisms to separate, destroy or degrade highly infectious viruses, and the potential of graphene and other 2DM to increase their efficiency, and enhance functional and mechanical properties. Graphene and other 2DM could not only play a vital role for tackling the ongoing COVID-19 pandemic but also provide technology platforms and tools for the protection, detection and monitoring of future viral diseases.

Comparative effectiveness of membrane technologies and disinfection methods for virus elimination in water: A review

The pandemic of the 2019 novel coronavirus disease (COVID-19) has brought viruses into the public horizon. Since viruses can pose a threat to human health in a low concentration range, seeking efficient virus removal methods has been the research hotspots in the past few years. Herein, a total of 1060 research papers were collected from the Web of Science database to identify technological trends as well as the research status. Based on the analysis results, this review elaborates on the state-of-the-art of membrane filtration and disinfection technologies for the treatment of virus-containing wastewater and drinking water. The results evince that membrane and disinfection methods achieve a broad range of virus removal efficiency (0.5-7 log reduction values (LRVs) and 0.09-8 LRVs, respectively) that is attributable to the various interactions between membranes or disinfectants and viruses having different susceptibility in viral capsid protein and nucleic acid. Moreover, this review discusses the related challenges and potential of membrane and disinfection technologies for customized virus removal in order to prevent the dissemination of the waterborne diseases.

Protective Face Masks: Current Status and Future Trends

Management of the COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has relied in part on the use of personal protective equipment (PPE). Face masks, as a representative example of PPE, have made a particularly significant contribution. However, most commonly used face masks are made of materials lacking inactivation properties against either SARS-CoV-2 or multidrug-resistant bacteria. Therefore, symptomatic and asymptomatic individuals wearing masks can still infect others due to viable microbial loads escaping from the masks. Moreover, microbial contact transmission can occur by touching the mask, and the discarded masks are an increasing source of contaminated biological waste and a serious environmental threat. For this reason, during the current pandemic, many researchers have worked to develop face masks made of advanced materials with intrinsic antimicrobial, self-cleaning, reusable, and/or biodegradable properties, thereby providing extra protection against pathogens in a sustainable manner. To overview this segment of the remarkable efforts against COVID-19, this review describes the different types of commercialized face masks, their main fabrication methods and treatments, and the progress achieved in face mask development.

Ambient microdroplet annealing of nanoparticles

Conversion of polydisperse nanoparticles to their monodisperse analogues and formation of organized superstructures using them involve post synthetic modifications, and the process is generally slow. We show that ambient electrospray of preformed polydisperse nanoparticles makes them monodisperse and the product nanoparticles self-assemble spontaneously to form organized films, all within seconds. This phenomenon has been demonstrated with thiol-protected polydisperse silver nanoparticles of 15 ± 10 nm diameter. Uniform silver nanoparticles of 4.0 ± 0.5 nm diameter were formed after microdroplet spray, and this occurred without added chemicals, templates, and temperature, and within the time needed for electrospray, which was of the order of seconds. Well organized nanoparticle assemblies were obtained from such uniform particles. A home-made and simple nanoelectrospray set-up produced charged microdroplets for the generation of such nanostructures, forming cm² areas of uniform nanoparticles. A free-standing thin film of monodisperse silver nanoparticles was also made on a liquid surface by controlling the electrospray conditions. This unique method may be extended for the creation of advanced materials of many kinds.

Polydisperse silver nanoparticles were converted to a highly ordered assembly of nanoparticles by microdroplet-induced chemistry, under ambient conditions, within seconds.

Reusable MoS2-Modified Antibacterial Fabrics with Photothermal Disinfection Properties for Repurposing of Personal Protective Masks

The current pandemic caused by SARS-CoV-2 has seen a widespread use of personal protective equipment, especially face masks. This has created the need to develop better and reusable protective masks with built-in antimicrobial, self-cleaning, and aerosol filtration properties to prevent the transmission of air-borne pathogens such as the coronaviruses. Herein, molybdenum disulfide (MoS₂) nanosheets are used to prepare modified polycotton fabrics having excellent antibacterial activity and photothermal properties. Upon sunlight irradiation, the nanosheet-modified fabrics rapidly increased the surface temperature to ∼77 °C, making them ideal for sunlight-mediated self-disinfection. Complete self-disinfection of the nanosheet-modified fabric was achieved within 3 min of irradiation, making the fabrics favorably reusable upon self-disinfection. The nanosheet-modified fabrics maintained the antibacterial efficiency even after 60 washing cycles. Furthermore, the particle filtration efficiency of three-layered surgical masks was found to be significantly improved through incorporation of the MoS₂-modified fabric as an additional layer of protective clothing, without compromising the breathability of the masks. The repurposed surgical masks could filter out around 97% of 200 nm particles and 96% of 100 nm particles, thus making them potentially useful for preventing the spread of coronaviruses (120 nm) by trapping them along with antibacterial protection against other airborne pathogens.

Engineered two-dimensional nanomaterials: an emerging paradigm for water purification and monitoring

Water scarcity has become an increasingly complex challenge with the growth of the global population, economic expansion, and climate change, highlighting the demand for advanced water treatment technologies that can provide clean water in a scalable, reliable, affordable, and sustainable manner. Recent advancements on 2D nanomaterials (2DM) open a new pathway for addressing the grand challenge of water treatment owing to their unique structures and superior properties. Emerging 2D nanostructures such as graphene, MoS₂, MXene, h-BN, g-C₃N₄, and black phosphorus have demonstrated an unprecedented surface-to-volume ratio, which promises ultralow material use, ultrafast processing time, and ultrahigh treatment efficiency for water cleaning/monitoring. In this review, we provide a state-of-the-art account on engineered 2D nanomaterials and their applications in emerging water technologies, involving separation, adsorption, photocatalysis, and pollutant detection. The fundamental design strategies of 2DM are discussed with emphasis on their physicochemical properties, underlying mechanism and targeted applications in different scenarios. This review concludes with a perspective on the pressing challenges and emerging opportunities in 2DM-enabled wastewater treatment and water-quality monitoring. This review can help to elaborate the structure-processing-property relationship of 2DM, and aims to guide the design of next-generation 2DM systems for the development of selective, multifunctional, programmable, and even intelligent water technologies. The global significance of clean water for future generations sheds new light and much inspiration in this rising field to enhance the efficiency and affordability of water treatment and secure a global water supply in a growing portion of the world.

The improved photocatalytic activity of highly expanded MoS2 under visible light emitting diodes

Photocatalytic degradation is a promising method to remove organic pollutants from water. Photocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS₂ nanomaterials have gained tremendous popularity. This is due to their narrow band gap and high visible light absorption. Herein, a MoS₂ photocatalyst with highly expanded interlayer spaces of 1.51 nm was synthesized in the presence of Pluronic F-127 as a template by a facile one-pot hydrothermal method. This expanded MoS₂ (MF-1) managed to photodegrade 98% (2.62 × 10^-2 min^-1) of methylene blue (MB) dye under irradiation of 1 W visible light-emitting diode (LED) white light. The dominant performance of MF-1 is attributed to the highly expanded interlayer spacing, which exposed more active edge sites. Moreover, the formation of surface defects such as surface cracks and sulfur vacancies (Sv) facilitates the adsorption capacity and in situ generation of reactive oxygen species (ROS). The dominant ROS responsible for the photodegradation of MB is superoxide radical (˙O₂ ^-). The photocatalyst shows good recyclability without deterioration even after five consecutive cycles.

Structured micro/nano materials synthesized via electrospray: a review

The development of synthetic methods for micro/nano materials with precisely controlled structures, morphologies, and local compositions is of great importance for the advancement of modern nanotechnology. The electrospray method is a "platform" approach for the preparation of a broad range of micro-/nanostructures; electrospray is simple and scalable. This review summarizes recent research on the micro-/nanostructures prepared via the electrospray route. These include spherical structures (e.g. simple, porous, Janus, and core-shell particles), non-spherical structures (e.g. red blood cell-like and spindle-like particles, multi-compartment microrods, 2D holey nanosheets, and nanopyramids), and assembled structures. The experimental details, underlying physical/chemical principles, and key benefits of these structures are comprehensively discussed. The effects and importance of nozzle design, properties of feeding solutions (e.g. concentration of solute, polymer additives, solvent/nonsolvent combinations), working environment (e.g. temperature and humidity), and types of collection media are highlighted.

Clean Water through Nanotechnology: Needs, Gaps, and Fulfillment

Sustainable nanotechnology has made substantial contributions in providing contaminant-free water to humanity. In this Review, we present the compelling need for providing access to clean water through nanotechnology-enabled solutions and the large disparities in ensuring their implementation. We also discuss the current nanotechnology frontiers in diverse areas of the clean water space with an emphasis on applications in the field and provide suggestions for future research. Extending the vision of sustainable and affordable clean water to environment in general, we note that cities can live and breathe well by adopting such technologies. By understanding the global environmental challenges and exploring remedies from emerging nanotechnologies, sustainability in clean water can be realized. We suggest specific pointers and quantify the impact of such technologies.