Optimizing the design and synthesis of supported silver nanoparticles for low cost water disinfection

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Silver Nanowire-Modified Filter with Controllable Silver Ion Release for Point-of-Use Disinfection

Waterborne diseases related to unsafe water are still major threats to public health in some developing countries and rural areas. Providing affordable and safe drinking water globally remains a great challenge in the coming decades. In this study, we develop a high-throughput and conductive silver nanowire (AgNW)-modified composite filter via depositing thin and ultralong AgNWs on a macroporous substrate. An electrochemical filtration cell (EFC) equipped with the composite filter achieves controllable Ag⁺ release at a μg L^-1 level and superior bacterial inactivation performance (>6-log inactivation efficiency) with an operation voltage of only 1 V at a high flux of 100 m³ h^-1 m^-2. Under such operation conditions, each composite filter (effective area: 0.79 cm²) can treat at least 750 mL of the bacterial suspension (∼10⁷ CFU mL^-1 of Escherichia coli) with a low effluent Ag⁺ concentration below 50 μg L^-1 and almost negligible energy consumption of only ∼70 J m^-3.

3,2-Hydroxypyridinone-Grafted Chitosan Oligosaccharide Nanoparticles as Efficient Decorporation Agents for Simultaneous Removal of Uranium and Radiation-Induced Reactive Oxygen Species in Vivo

Most of the key radionuclides in the nuclear fuel cycle, such as actinides, possess a combination of heavy metal chemotoxicity and radiotoxicity and therefore represent a severe threat to the ecological environment and public safety. The radiotoxicity originates from direct radiation-induced organ damage and indirect damage, mostly through radiation-induced reactive oxygen species (ROS). Although effective chelating agents that can accelerate the excretion of actinides, such as uranium, have been developed in the past several decades, very few of them can reduce radiation-induced damage from internal contamination. In fact, the strategy of simultaneous removal of actinides and their induced-ROS in vivo has scarcely been considered. Here, we report a 3,2-hydroxypyridinone-grafted chitosan oligosaccharide nanoparticle (COS-HOPO) as a new type of decorporation agent that is effective for the removal of both uranium and ROS in vivo. The cytotoxicity and decorporation assays indicate that the marriage of chitosan oligosaccharide (COS) and hydroxypyridinone (HOPO) gives rise to a remarkable decrease in toxicity and promotion of the uranium removal capability from both kidneys and femurs. The decorporation efficacy can reach up to 43% in rat proximal tubular epithelial cells (NRK-52E), 44% in kidneys, and 32% in femurs. Moreover, the ROS levels of the cells treated with COS-HOPO are significantly lower than those of the control group, implying a promising radiation protection effect. The detoxification mechanism of COS-HOPO is closely related to both chelating U(VI)- and scavenging U(VI)-induced intracellular ROS.

A novel gravity-driven nanofibrous membrane for point-of-use water disinfection: polydopamine-induced in situ silver incorporation

We report a facile method for preparing silver-loaded membranes for point-of-use disinfection and disaster relief applications. A bio-inspired material, polydopamine, was coated onto a highly porous nanofibrous polyacrylonitrile substrate. We then take advantage of the redox properties of polydopamine to form silver nanoparticles in situ. These nanoparticles were uniformly distributed on the surface of nanofibers with no apparent agglomeration at a silver loading up to 4.36 wt.% (cPAN-Ag1.5). The silver-incorporated membrane cPAN-Ag1.5 achieved a high pure water flux of 130 Lm⁻² h⁻¹ at 10-cm water head, demonstrating the feasibility of energy-efficient gravity-driven filtration and eliminating the need for electrical power. The strong anti-bacterial activity and high physical rejection of the membrane led to an excellent disinfection power, with no viable bacterial cells detected in its permeate water. The membrane exhibited >7 log reduction for E. coli and >6 log reduction for B. subtilis. The strategy reported here provides an efficient and green route to synthesize point-of-use membranes. Combining their excellent permeability and disinfection effectiveness, these membranes offer an ideal solution to water supply in disaster-affected areas.

Uptake and effect of highly fluorescent silver nanoclusters on Scenedesmus obliquus

The release of silver nanoparticles (Ag NPs) in aquatic environment has caused wide public concern about their effects on living organisms (e.g., algae). However, how these small NPs exert cytotoxicity in the living organisms has always been under heated debate. In this study, the uptake and toxicity effects of strongly red-emitting fluorescent silver nanoclusters (r-Ag NCs) exposed to the green algae Scenedesmus obliquus was investigated. Upon exposure to pure r-Ag NCs and r-Ag NCs containing l-cysteine, the algae growth inhibition test showed that Ag(+) ions released from r-Ag NCs played an important role in the toxicity of r-Ag NCs along with the toxicity of intact r-Ag NCs. Furthermore, no signals of intracellular reactive oxygen species (ROS) were observed indicating that r-Ag NCs or released Ag(+) ions - mediated growth inhibition of algae cells was independent of ROS production. Transmission electron microscopy (TEM) and laser scanning confocal microscopy (LSCM) were employed to study cellular uptake and cytotoxicity. Furthermore, analysis of differential expressed gene demonstrated that r-Ag NCs as well as the released Ag(+) ions can simultaneously exist inside the algae cells, and inhibit the transcriptomic process of genes by their "joint-toxicity" mechanism. Taken together, our study provides a new insight into the molecular mechanisms of r-Ag NCs and Ag(+) ions exposure to the aquatic organism and can be applied to early diagnosis of ecologic risk mediated by others metal-based NPs.

Rethinking Stability of Silver Sulfide Nanoparticles (Ag2S-NPs) in the Aquatic Environment: Photoinduced Transformation of Ag2S-NPs in the Presence of Fe(III)

The stability of engineered nanomaterials in a natural aquatic environment has drawn much attention over the past few years. Silver sulfide nanoparticles (Ag2S-NPs) are generally assumed to be stable in a natural environment as a result of their physicochemical property; however, it may vary depending upon environmental conditions. Here, we investigated whether and how the environmentally relevant factors including light irradiation, solution pH, inorganic salts, dissolved organic matter (DOM), and dissolved oxygen (DO) individually and in combination influenced the stability of Ag2S-NPs in an aquatic environment. We presented for the first time that transformation of Ag2S-NPs can indeed occur in the aqueous system with an environmentally relevant concentration of Fe(3+) under simulated solar irradiation and natural sunlight within a short time (96 h), along with significant changes in morphology and dissolution. The photoinduced transformation of Ag2S-NPs in the presence of Fe(3+) can be dramatically influenced by solution pH, Ca(2+)/Na(+), Cl(-)/SO4(2-), DOM, and DO. Moreover, Ag2S-NP dissolution increased within 28 h, followed rapid decline in the next 68 h, which may be a result of the reconstitution of small Ag2S-NPs. Taken together, this work is of importance to comprehensively evaluate the stability of Ag2S-NPs in an aquatic environment, improving our understanding of their potential risks to human and environmental health.