Gold nanoparticles with tailored size through ligand modification for catalytic applications.

The active sites of catalysts can be tuned by using appropriate organic moieties. Here, we describe a facile approach to synthesise gold nanoparticles (AuNPs) using various Au(I) precursors. The core size of these AuNPs can be precisely tailored by varying the steric hindrance imposed by bound ligands. An interesting relationship is deduced that correlates the steric hindrance around the metal to the final size of the nanoparticles. The synthesised AuNPs are immobilised onto TS-1 zeolite (Au/TS-1) with minimal change in the final size of the AuNPs. The catalytic performance of Au/TS-1 catalyst is evaluated for the direct gas phase epoxidation of propylene with hydrogen and oxygen, an environmentally friendly route to produce propylene oxide. The results indicate that smaller AuNPs exhibit enhanced catalytic activity and selectivity. Furthermore, this synthetic approach is beneficial when tailored synthesis of gold nanoparticles of specific sizes is required.

Precisely Engineered Supported Gold Clusters as a Stable Catalyst for Propylene Epoxidation.

Designing a stable and selective catalyst with high H2 utilisation is of pivotal importance for the direct gas-phase epoxidation of propylene. This work describes a facile one-pot methodology to synthesise ligand-stabilised sub-nanometre gold clusters immobilised onto a zeolitic support (TS-1) to engineer a stable Au/TS-1 catalyst. A non-thermal O2 plasma technique is used for the quick removal of ligands with limited increase in particle size. Compared to untreated Au/TS-1 catalysts prepared using the deposition precipitation method, the synthesised catalyst exhibits improved catalytic performance, including 10 times longer lifetime (>20 days), increased PO selectivity and hydrogen efficiency in direct gas phase epoxidation. The structure-stability relationship of the catalyst is illustrated using multiple characterisation techniques, such as XPS, 31 P MAS NMR, DR-UV/VIS, HRTEM and TGA. It is hypothesised that the ligands play a guardian role in stabilising the Au particle size, which is vital in this reaction. This strategy is a promising approach towards designing a more stable heterogeneous catalyst.

Titanium(IV)-induced cristobalite formation in titanosilicates and its potential impact on catalysis.

Cristobalite, a crystalline form of silica, is shown to be formed within an amorphous titanosilicate, at previously unknown conditions. Mesoporous titanosilicate microspheres (MTSM) were synthesized as efficient catalysts for the epoxidation of cyclohexene with tert-butyl hydroperoxide. High-resolution transmission electron microscopy revealed the presence of crystals in this predominantly amorphous material, after calcination at 750 °C. When calcined at 800 °C, the crystals were identified via PXRD as predominantly cristobalite, which possibly marks its first observation in titanosilicates at such a low temperature, without adding any alkali metals during synthesis. Catalytic experiments conducted with MTSM materials calcined at temperatures varying from 650 to 950 °C, reveal that the amount of cristobalite formed increases with temperature, and that it has a significant impact on the pore structure, and, remarkably, correlates with the catalytic activity of titanosilicates.

Exfoliated sheets of MoS2 trigger formation of aqueous gels with acute NIR light responsiveness.

We have developed a unique class of MoS2 entrapped aqueous gels where the exfoliated sheets trigger physical cross-linking of nanofibers of peptide amphiphiles. Strikingly, these aqueous gels show acute responsiveness towards near infra-red light (804 nm), an unprecedented observation for molecular hydrogels.

Efficient MoS2 Exfoliation by Cross-ß-Amyloid Nanotubes for Multistimuli-Responsive and Biodegradable Aqueous Dispersions.

Herein, we report the efficient exfoliation of MoS2 in aqueous medium by short cationic peptide nanotubes featuring the nucleating core (17) LVFFA(21) of ß-amyloid (Aß 1-42), a sequence associated with Alzheimer's disease. The role of morphology, length, and nature of the amyloid surface on exfoliation/dispersions of MoS2 were investigated through specific mutations of the amyloid sequences. Notably, owing to the properties of both the constituents, self-assembled soft nanostructures and MoS2 , the hybrid dispersions responded reversibly to various stimuli, including temperature, pH, and light. Addition of a protease resulted in loss of the dispersions, which are otherwise stable for months at ambient conditions. The design flexibility of the peptide sequences, along with the stimuli-responsiveness and biodegradability, can complement the applications of MoS2 in diverse fields.

Cross-ß Amyloid Nanohybrids Loaded With Cytochrome C Exhibit Superactivity in Organic Solvents.

The present study reports the development of a unique class of Cytochrome C (CytC)-loaded cross-beta amyloid nanohybrids. The peroxidase activity of the bound CytC increased up to two orders of magnitude in organic solvents compared to the activity of unbound CytC in water. The amyloid sequences used in the study feature the nucleating core (17) LVFF(21) of the beta amyloid (Aß), which assembled to form homogenous fibers and nanotubes. The morphology and exposed surface of the amyloid nanohydrids critically modulated the CytC activity. A CytC-Ac-KLVFFAE-NH2 hybrid featuring nanofiber morphology showed 308-fold higher activity than unbound CytC in water, which increased to 450-fold with the nanotube morphology of CytC-Ac-KLVFFAL-NH2 . Notably, activity declined substantially when the exposed surface charge was detuned by replacing lysine with histidine, thus underpinning the importance of surface charge. This enzyme-amyloid nanohybrid system could facilitate the technological application of enzymes.