The effect of tensile strain in Pd-Ni core-shell nanocubes with tuneable shell thickness on urea electrolysis selectivity.

Expanding our understanding of the structure-performance relationship in nanoscale electrocatalysts for urea electrolysis is crucial for efficient urea waste treatment and concomitant cathodic hydrogen production or CO2 reduction. Here, we elucidate the effect of the lattice strain in Pd-Ni core-shell nanocubes on the dominance of urea overoxidation pathway.

Synergistic Effect of MIL-101/Reduced Graphene Oxide Nanocomposites on High-Pressure Ammonia Uptake.

Ammonia has emerged as a potential working fluid in adsorption heat pumps (AHPs) for clean energy conversion. It would be necessary to develop an efficient adsorbent with high-density ammonia uptake under high gas pressures in the low-temperature range for waste heat. Herein, a porous nanocomposite with MIL-101(Cr)-NH2 (MIL-A) and reduced graphene oxide (rGO) was developed to enhance the ammonia adsorption capacity over high ammonia pressures (3-5 bar) and low working temperatures (20-40 °C). A one-pot hydrothermal reaction could form a two-dimensional sheet-like nanocomposite where MIL-A nanoparticles were well deposited on the surface of rGO. The MIL-A nanoparticles were shown to grow on the rGO surface through chemical bonding between chromium metal centers in MIL-A and oxygen species in rGO. We demonstrated that the nanocomposite with 2% GO showed higher ammonia uptake capacity at 5 bar compared with pure MIL-A and rGO. Our strategy to incorporate rGO with MIL-A nanoparticles would further be generalizable to other metal-organic frameworks for improving the ammonia adsorption capacity in AHPs.

Silver-Nanoparticle-Assisted Modulation of NH3 Desorption on MIL-101.

Ammonia has recently emerged as a promising hydrogen carrier for renewable energy conversion. Establishing a better understanding and control of ammonia adsorption and desorption is necessary to improve future energy generation. Metal-organic frameworks (MOFs) have shown improved ammonia capacity and stability over conventional adsorbents such as silica and zeolite. However, ammonia desorption requires high temperature over 150 °C, which is not desirable for energy-efficient ammonia reuse and recycling. Here, we loaded silver nanoparticles from 6.6 to 51.4 wt% in MIL-101 (Ag@MIL-101) using an impregnation method to develop an efficient MOF-based hybrid adsorbent for ammonia uptake. The incorporation of metal nanoparticles into MIL-101 has not been widely explored for ammonia uptake, even though such hybrid nanostructures have significantly enhanced catalytic activities and gas sensing capacities. Structural features of Ag@MIL-101 with different Ag wt% were examined using transmission electron microscopy, X-ray powder diffraction, and infrared spectroscopy, demonstrating successful formation of silver nanoparticles in MIL-101. Ag@MIL-101 (6.6 wt%) showed hysteresis in the N2 isotherm and an increase in the fraction of larger pores, indicating that mesopores were generated during the impregnation. Temperature-programmed desorption with ammonia was performed to understand the binding affinity of ammonia molecules on Ag@MIL-101. The binding affinity was the lowest with Ag@MIL-101 (6.6 wt%), including the largest relative fraction in the amount of desorbed ammonia molecules. It was presumed that cooperative interaction between the silver nanoparticle and the MIL-101 framework for ammonia molecules could allow such a decrease in the desorption temperature. Our design strategy with metal nanoparticles incorporated into MOFs would contribute to develop hybrid MOFs that reduce energy consumption when reusing ammonia from storage.

Nanoscopic morphological effect on the optical properties of polymer-grafted gold polyhedra.

Plasmonic nanoparticles show highly sensitive optical properties upon local dielectric environment changes. Hybridisation of plasmonic nanoparticles with active polymeric materials can allow stimuli-responsive and multiplex sensing over conventional monotonic sensing capacity. Such heterogeneous adlayers around the plasmonic core component, however, are likely to perturb the local refractive index in the nanometre regime and lead to uncertainty in its intrinsic sensitivity. Herein we prepare a series of polystyrene-grafted polyhedral gold nanoparticles, cubic and concave cubic cores, with different edge lengths and polymer thicknesses with precise synthesis control. Their localised surface plasmon resonance (LSPR) spectral changes are monitored to understand the effect of core morphological details in the interplay of nanoscale polymeric shells. Quantitative image analysis of changes in the core and shell shape contours and finite-difference time-domain simulations of the corresponding LSPR spectra and electric field distributions reveal that the magnitude of the LSPR spectral shift is closely dependent on the core morphology, polymer shell thickness and electric field intensity. We also demonstrate that the polystyrene-grafted gold concave cube displays higher sensitivity for nanoscale refractive index change in the polymer shell than the polystyrene-grafted gold cube at different temperatures. Our systematic investigation will help design polymer-composited plasmonic nanosensors for desirable applications.

Controllable coating and reshaping of gold nanorods with tetracyanoquinodimethane.

Various nanoparticle surface layers allow unique functionalities. We developed a coating method with tetracyanoquinodimethane that forms solid layers through π stacking on gold nanorod surfaces. Its reaction mechanism was investigated with reaction time, aging time and surfactant concentration. Our method could be generalizable to different nanoparticle shapes and crystal facets.