Search

Ultrathin two-dimensional (2D) nanosheets with efficient light-driven proton reduction activity were obtained through the exfoliation of novel metal-organic frameworks (MOF), which were synthesized by using a bis(4'-carboxy-2,2':6',2″-terpyridine) ruthenium complex as a linker and 3d transition-metal (Mn, Co, Ni, and Zn) anions as nodes. The nanosheet of the Ni2+ node exhibits a photocatalytic hydrogen evolution rate of 923 ± 40 μmol g-1 h-1 at pH = 4.0, without the presence of any cocatalyst or cosensitizer. A combined experimental and theoretical study suggests a reductive quenched pathway for the photocatalytic hydrogen evolution by the nanosheet. The transition-metal nodes at the edge of the nanosheets are proposed as the active sites. Density functional theory (DFT) calculations attributed the different catalytic activities of the nanosheets to the discrepancy of H adsorption free energy at various transition-metal nodes.

In this study, we successfully synthesized a thin-slice layer of graphitic carbon nitride (g-C3N4) with abundant irregular holes by a facile two-step method using Pluronic P123 as a template (CN-P1...

Using nanomaterials to achieve functional enzyme mimics (nanozymes) is attractive for both applied and fundamental research. Laccases are multicopper oxidases highly important for biotechnology and environmental remediation. In this work, we report an exceptionally simple yet functional laccase mimic based on guanosine monophosphate (GMP) coordinated copper. It forms an amorphous metal–organic framework (MOF) material. The ratio of copper and GMP is 3:4 as determined by isothermal titration calorimetry. It has excellent laccase-like activity and converts a diverse range of phenol containing substrates such as hydroquinone, naphthol, catechol and epinephrine. Comparative work shows that the activity is originated from guanosine coordination instead of phosphate binding in GMP. Cu2+ is required and cannot be substituted by other metal ions. At the same mass concentration, the Cu/GMP nanozyme has a higher Vmax and similar Km compared to the protein laccase. To achieve the same catalytic efficiency, the cost ...

In this second paper of a series dealing with the film-forming behavior of latex systems, we show the relationship between the kinetics of film formation and rheological properties. The kinetics of...

We discuss mechanisms that have been proposed for film formation from latex systems and point out that major problems exist, in that the relative role played by the water/air, the polymer/air, and the polymer/water interfacial tensions in promoting film formation has not been established. Even the relative role played by plasticization of latex polymers by water has remained as an unanswered question. In order to clarify this problem, we have investigated the rate of film formation of wet and dry latex systems by atomic force microscopy. The role of the water surface tension (in creating a capillary pressure) was clearly revealed by forming a wet latex system through condensation of water into the interstitial space of initially dry latex particles. Poly(iso-butyl methacrylate) (PiBMA) was used as the model latex because of its appropriate glass transition temperature, T g ∼ 65 °C, and its hydrophobic character. The rate of film formation (at 70°C) was found to be approximately 10-times faster under wet conditions than when dry. Separate experiments showed that T g of PiBMA was unaffected by water, and hence plasticization was not a factor in the enhanced rate. These results clearly show in this system that the dominant factor in promoting film formation was the water surface tension and resulting negative capillary pressure. Furthermore, it is shown that the capillary pressure in wet systems can be of sufficient magnitude to explain the observed deformation of the latex particles at 50 °C, i.e., 15 °C below T g . Capillary pressures and forces increase with decreasing amounts of water in the interstitial regions of spherical particles, and capillary pressures can reach very high values with seemingly insignificant amounts of water. The equilibrium between the amount of interstitial water and the relative humidity of the atmospheric water is shown, and it indicates that even with low relative humidities the capillary pressures can still be quite large. We maintain that capillary pressure typically is the dominant driving force for film formation. These results are in contrast to the conclusions of others.