Simple Preparation and Formation Mechanism of Two-Dimensional Nanomaterials at Room Temperature

Two-dimensional (2D) nanomaterials have been and continue to be of great interest to researchers since the experimental discovery of graphene. A reason for their very interesting properties is the large number of surface atoms with unsaturated bonds thus providing special properties to these materials. Rational fabrication of these materials is the first step towards their commercial application. Advance in this area has been promoted by the development of various synthesis strategies, especially wet-chemical synthesis with great potential in large-scale production and wide applicability. However, the existing wet-chemical methods suffer from high cost, tedious operation, low product quality and eco-unfriendly processing, motivating researchers to propose a simple and universal synthesis route. Besides, the performance improvement of 2D materials by tuning the thickness, composition, crystal phase and arrangement of nanosheets, is in the same predicament. This dissertation presents new synthetic methods to solve the above-mentioned problems, making a significant contribution to the fundamental research and practical application of 2D nanomaterials.publishe

Synthesis of ultrathin metal oxide and hydroxide nanosheets using formamide in water at room temperature

The rational preparation of ultrathin two-dimensional metal oxide and hydroxide nanosheets is the first and crucial step towards their utilization in both fundamental research and practical applications. From the perspective of the production cost, the further development of such materials remains a challenging task. Therefore, it is highly desirable to synthesize these materials via a simple and general strategy at room temperature. Besides, less attention has been paid to investigate their growth process, leading to ambiguous formation mechanisms and the lack of guiding principles for designing the targeted ultrathin 2D metal oxides and hydroxides. Here, 6 different ultrathin (2 groups of the formamide molecules. These findings broaden the fundamental understanding of 2D material formation mechanisms and inspire interest in extending this strategy to further systems. Our study opens a new avenue for an easy, general and room temperature synthesis of ultrathin 2D metal oxides and hydroxides.publishe

Synthesis of two-dimensional layered double hydroxides : a systematic overview

Two-dimensional (2D) layered double hydroxides (LDH) are classic materials in fundamental research and practical application. 2D LDH have unique structural features, such as high aspect ratio, high specific surface area, quantum confinement in one direction, layered structure, tunable intercalated anions/interlayer spacing/metal-cation compositions, etc., which endow 2D LDH with excellent chemical and physical properties. Since rational production is the first and crucial step towards their utilization, numerous efforts have been devoted to explore innovative and effective methods for their preparation. This review is a comprehensive overview of synthesis methods and aimed to capture the features of different synthesis methods to enable the selection of a suitable method to achieve the desired LDH characteristics. Therefore, we systematically summarized various preparation methods of 2D LDH, including a top-down approach, bottom-up approach, and decomposition-regrowth strategy. Besides, we listed and compared the important parameters relating to both the synthesis process and the obtained products of various synthesis methods, such as the synthesis temperature/pressure, the used device, the utilized reactants, the presence or absence of pre/post-treatment, the yield, the crystallinity and the lateral size and thickness. Finally, some current challenges and further tasks regarding the synthesis of LDH are presented.publishe

Synthesis of hierarchical transition metal oxyhydroxides in aqueous solution at ambient temperature and their application as OER electrocatalysts

First-row (3d) transition metal oxyhydroxides have attracted increasing attention due to their various advantages. Although investigating the oxidation mechanism and processing such materials into hierarchical architectures are greatly desired for their further development, it remains unclear how the oxidation state change occurs, and efforts to produce hierarchical oxyhydroxides in compliance with high ecological and economic standards have progressed slowly. Here, we describe a facile one-step coprecipitation route for the preparation of hierarchical CoOOH, NiOOH and MnOOH, which involves the diffusion of NH3 originating from ammonium hydroxide solution into an aqueous solution containing metal ion salts and K2S2O8. Comprehensive characterizations by scanning electron microscope, transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy and in situ pH measurement demonstrated that K2S2O8 induces the oxidation state change of metal ion species after the start of hydrolysis. Meanwhile, it was found that, benefiting from the OH– concentration gradient created by the NH3 diffusion method and the suitable growth environment provided by the presence of K2S2O8 (high nucleation rate and secondary nucleation), the formation of hierarchical oxyhydroxide structures can be realized in aqueous solution at ambient temperature without the use of heat energy and additional structure-directing agents. The hierarchical CoOOH structures are performed as the electrocatalysts for the oxygen evolution reaction in alkaline media, which exhibit good activity with an overpotential of 320 mV at 10 mA cm−2 and a low Tafel slope of 59.6 mV dec–1, outperforming many congeneric electrocatalysts. Overall, our study not only provides important insights to understand the formation mechanism of hierarchical oxyhydroxides, but also opens up new opportunities for the preparation of hierarchical oxyhydroxides via a facile, green and low-cost method.publishe

Mesh independent analysis based on mass flow rate and velocity outlet.

Mesh independent analysis based on mass flow rate and velocity outlet.</p

Different surface deposition fractions in the isolation ward under different cases.

Different surface deposition fractions in the isolation ward under different cases.</p

Fig 2 -

Layout of isolated wards based on ventilation strategies: (a)case1; (b)case2; (c)case3; (d)case4; (e)case5.</p

Sizes of the air supply inlets and exhaust air outlets.

Sizes of the air supply inlets and exhaust air outlets.</p

Fig 1 -

Physical model of the negative pressure isolation ward: (a) schematic layout of the ward; (b) with a patient in the supine position; (c) with a patient in the sitting position.</p

Boundary condition.

Due to the serious global harm caused by the outbreak of various viral infectious diseases, how to improve indoor air quality and contain the spread of infectious bioaerosols has become a popular research subject. Negative pressure isolation ward is a key place to prevent the spread of aerosol particles. However, there is still limited knowledge available regarding airflow patterns and bioaerosol diffusion behavior in the ward, which is not conducive to reducing the risk of cross-infection between health care workers (HCWs) and patients. In addition, ventilation layout and patient posture have important effects on aerosol distribution. In this study, the spatial and temporal characteristics as well as dispersion patterns of bioaerosols under different ventilation patterns in the ward were investigated using the computational fluid dynamics (CFD) technique. It is concluded that changes in the location of droplet release source due to different body positions of the patient have a significant effect on the bioaerosol distribution. After optimizing the layout arrangements of exhaust air, the aerosol concentration in the ward with the patient in both supine and sitting positions is significantly reduced with particle removal efficiencies exceeding 95%, that is, the ventilation performance is improved. Meanwhile, the proportion of aerosol deposition on all surfaces of the ward is decreased, especially the deposition on both the patient’s body and the bed is less than 1%, implying that the risk of HCWs being infected through direct contact is reduced.</div