Comparison between discarded facemask and common plastic waste on microbial colonization and physiochemical properties during aging in seawater.

Facemasks are indispensable for preventing the spread of COVID-19. However, improper disposal of discarded facemasks has led to their contamination in the marine environment. To understand the environmental risk of this emerging plastic pollution, it's important to clarify the features that distinguish discarded facemasks from common plastic waste during aging. This study compared the microbial colonization, degradation-related enzymes, and physicochemical properties among surgical masks, polystyrene cups, polycarbonate bottles, and polyethylene terephthalate bottles in their aging processes in natural seawater. Compared to the other plastic wastes, surgical masks were colonized by the most diverse microorganisms, reaching 1521 unique prokaryotic OTUs after 21-day exposure in seawater. Moreover, the activity of eukaryotic enzymes associated with plastic degradation was 80-fold higher than that in seawater, indicating that the colonized eukaryotes would be the major microorganisms degrading the surgical masks. Meanwhile, the nano-sized defects (depth between 8 and 61 nm) would evolve into cracks of bigger sizes and result in the breakage of the microfibers and releasing microplastics into the ocean. Overall, our study demonstrated a distinctive plastisphere occurred in surgical masks from both microbial and physiochemical aspects. This work provides new insights for assessing the potential risk of plastic pollution caused by the COVID-19 pandemic.

Silicon Limitation Impairs the Tolerance of Marine Diatoms to Pristine Microplastics.

Marine diatoms are currently facing increasing threats from microplastic (MP) pollution that is intertwined with the disturbed nutrient stoichiometry in seawater. The effects of nutrient imbalances such as silicon (Si) limitation on the interactions between diatoms and MPs remain poorly understood. In contrast to previous studies which mainly focused on MP toxicity, this study emphasizes how Si availability affects nano-scale interactions between pristine polystyrene MPs and diatom surfaces. Results showed that Si-starved cells were less tolerant to MP toxicity than the Si-enriched counterparts. Si limitation significantly changed the configuration and chemical composition of the perforated frustules, forming less negatively charged, more adhesive, and mechanically weaker cells. All of these changes facilitated the adsorption and hetero-aggregation between the diatom cells and MPs and compromised the diatoms' resistance to MP attack. Our study provides novel insights into the effects of pristine MPs in the marine environment under the context of dynamic nutrient conditions.

Design, optimization and application of a highly sensitive microbial electrolytic cell-based BOD biosensor.

Biochemical oxygen demand (BOD) is an important biochemical indicator for determining the degree of water pollution and guiding the design of wastewater treatment processes. BOD sensors based on microbial electrochemical technology can conduct real-time online monitoring of organic matter and have attracted extensive attention. However, research on microbial electrolytic cell (MEC)-type BOD sensors is at the stage of theoretical exploration. Here, we designed and optimized a highly sensitive MEC-type BOD sensor by screening inoculants, comparing electrode materials, and optimizing the reactor configuration. The results showed that effective means to optimize a BOD sensor for fast activation and sensitive testing included the inoculation of the MEC reactor effluent with large amounts of biomass and highly active bacteria, selection of carbon felt electrodes with excellent adsorption and permeability, miniaturization of the reactor, regulation of suitable electrode spacing, and design of the penetrating fluid structure. Then, the optimized sensing system was applied to determine the BOD concentration in model solutions of sodium acetate in a laboratory environment, where it accurately measured BOD concentrations in the range of 10-500 mg/L and maintained good parallelism during long-term operation. Next, the MEC-type BOD sensors were put into practice in the field as an alarm for accidents at an actual sewage plant. The whole BOD sensing system was quickly assembled on site and started up, and it gave an early warning shortly after the concentration of organic matter in the water suddenly increased, thus showing a high potential for engineering applications. This study broadened the domains of application of MEC-type BOD sensors in environmental monitoring, and promoted the development of technological innovation in water ecology and environmental monitoring.

Near infrared optically responsive Ag-Cu bimetallic 2D nanocrystals with controllable spatial structures.

The optical properties of cost-effective Ag-Cu bimetallic nanocrystals, with synergistically enhanced catalytic and biological activities, are limited within ultraviolet-visible region due to lack of morphology control. In order to overcome this constraint, two-dimensional (2D) Ag-Cu bimetallic heterostructures were designed and synthesized by a seed-mediated colloidal growth method. The conformal Cu domain was epitaxially deposited on Ag nanoplates with different spatial configuration under retention of their 2D shape. Both of the 2D Ag-Cu core@shell and Janus structures display tunable localized surface plasmon resonance from visible to near infrared regions. The results of catalytic reduction of 4-nitrophenol show that the 2D Ag-Cu core@shell structure has better synergistic catalytic performance than Janus structure and Ag plates. In addition to surface-related synergistically enhanced bactericidal performance, their antibacterial effect can also be significantly enhanced by near infrared light irradiation. These results indicate that 2D Ag-Cu heterostructures can benefit from both synergistically improved surface activity and great optical responsive characteristics.

Single-parameter-tuned synthesis for shape-controlled gold nanocrystals stimulated by iron carbonyl.

Shape-controlled synthesis is essential for functional nanomaterials, allowing deeper insights intothe relationship between the structures and the catalytic properties. Synthesis of nanocrystals with particular morphologies are usually studied independently among various synthetic methods, those underline that different surface capping ligands or shape-directing agents bring about disparate shapes. However, a single quantitative parameter method is still lacking to realize precise control of well-defined morphology nanocrystals, especially anisotropic structures, which is essential to understanding the growth process of nanocrystals. Herein, we proposed a single-parameter-tuned synthesis strategy for preparation of shape-controlled gold nanocrystals by regulating the amount of iron carbonyl, by which we produced highly monodisperse Au nanocrystals with various shapes in organic phase including nanoplates (diameter of 16.02 ± 1.13 nm and thickness of 5.35 ± 0.58 nm), nanorods (length of 37.53 ± 3.73 nm and width of 5.26 ± 0.37 nm) and nanospheres (diameter of 8.26 ± 0.38 nm). The single-parameter-tuned method reveals the dual roles of iron carbonyl for controlling the shapes of gold nanocrystals including reductant and oxidative etchant and empowers versatility in synthetic methodology for other noble metals. Moreover, catalytic activity shifting in shapes of nanocrystals was revealed based on the reduction of 4-nitrophenol, showing that the as-synthesized Au nanoplates displayed the enhanced catalytic performance with the lowest activation energy. Our work provides a brand-new pathway for shape-controlled synthesis of noble-metal nanocrystals and has a strong practical value in application fields.