Controlling Nanorod Oligomer Aggregation in Solutions

Controlling the size of ordered nanorod aggregates in colloidal dispersions is a challenge. Here, we employ Brownian dynamics to explore the dependence of the nanorod aggregate size and structure on the molecular weight of a polyelectrolyte attached to one end of the nanorod and on the nature of the solvent. Upon increasing the polyelectrolyte molecular weight (the length of the polyelectrolyte), the size of the aggregates decreases because of increasing electrostatic repulsion. The critical van der Waals interaction strength for transition from individual nanorods to nanorod dimers/trimers+ (trimers and larger aggregates) increases with increasing polyelectrolyte molecular weight. In a medium with a dielectric constant of 1.0, upon increasing the van der Waals interaction between nanorods, the individual nanorods aggregate as dimers and trimers+, with approximately 50% of individual nanorods forming dimers. In a solvent with a sufficiently large dielectric constant (e.g., ≥10.0), upon increasing the van der Waals interaction between nanorods, most nanorods aggregate into trimers or larger aggregates; few dimers are generated. A lower solvent dielectric constant and a higher polyelectrolyte molecular weight favor formation of more uniform aggregates. As the charge of the segments of the polyelectrolyte increases, the fraction of nanorod dimers increases and the fraction of nanorod trimers+ decreases. In media with the dielectric constant of water, aggregation was insensitive to the temperature. In low dielectric constant media, aggregate formation was sensitive to the temperature for high molecular weight polyelectrolytes, but insensitive to the temperature for low molecular weight polyelectrolytes

Micellar Structures in Nanoparticle-Multiblock Copolymer Complexes

Brownian dynamics simulation is employed to examine the structure changes of complexes composed of a hydrophobic nanoparticle and a multiblock copolymer molecule (MCP). The dependence of the structure transitions on the radius of the nanoparticle, on the interactions between the hydrophobic segments of the MCP, and on the interactions between the hydrophobic segments and hydrophobic nanoparticle is examined. It is shown that the multiblock copolymer adsorbed on a nanoparticle can acquire the structure of a micelle.To better characterize the micelle generated and the structure changes in the nanoparticle–MCP complex, the mass dipole moment of the complex [the distance between the center of mass of MCP and the center of the nanoparticle minus the radius of the nanoparticle (DCC)], the density profiles of MCP segments around its center of mass and around the nanoparticle, the radius of gyration of the MCP, and the thickness of the micelle around the nanoparticle are determined. It was found that, when structural transition of the complex occurs, the above quantities change dramatically. The present simulation may provide new insights regarding the drug-loaded micelle interacting with a virus represented by a nanoparticle

Tunable Primary and Secondary Encapsulation of a Charged Nonspherical Nanoparticle: Insights from Brownian Dynamics Simulations

Surface properties of encapsulated nanoparticles play a central role in colloidal stability and in diverse applications of colloidal nanomaterials. In this paper, by employing Brownian dynamics simulations, we simulate the environment-dependent primary encapsulation of a charged nonspherical nanoparticle (NSNP) by Janus particles (JPs). We propose and determine, for the first time, the secondary encapsulation (i.e., reconfiguration of encapsulants on the surface of the NSNP), which also depends on the environment. The adsorption phase behavior and configuration transformation are strongly correlated with temperature and Bjerrum length. Bjerrum-length-induced order–order structural transitions and temperature-induced disorder–order/order–order structural transitions are found. Interestingly, electric double layers on the surfaces of the NSNP can form upon changing the environment. Our detailed results of primary encapsulation and secondary reconfiguration of encapsulants on the surface of the NSNP indicate that the surface properties of the charged NSNP are tunable and reversible. Such transformations should be readily detected experimentally by techniques such as zeta potential measurement. We also find that the primary encapsulation occurred via sequential adsorption and assembly of JPs, whereas the secondary encapsulation process involved adsorption/desorption of JPs and rotation of their configurations as well as their reassembly. These new insights may provide useful information in design and modulation of nanomaterials with surface properties that respond to their environment, for applications such as drug or gene delivery

Highly Selective Ethylene Production from Solar-Driven CO₂ Reduction on the Bi₂S₃@In₂S₃ Catalyst with In–S_V–Bi Active Sites

Photothermal catalysis that utilizes solar energy to not only generate charge carriers but also supply heat input represents a potentially sustainable strategy for the efficient conversion of CO2 to valuable chemicals. It is highly desirable to develop photothermal catalysts with broadband light absorption across the whole solar spectrum, efficient photothermal conversion, and appropriate active sites. In this work, the Bi2S3@In2S3 heterostructure catalyst is fabricated via one-step solvothermal synthesis, where Bi2S3 serves as a photothermal material and synchronously affords photoexcited charge carriers. Experimental results indicate that the photoinduced charge carriers trigger H2O-assisted CO2 reduction and the elevated temperature kinetically accelerates the reaction. Furthermore, the tightly bonded heterointerfaces provide unique In–SV–Bi active centers consisting of adjacent Bi and In atoms coupled with sulfur vacancies, which reduces the energy barriers of CO2 activation and C–C coupling, facilitating the generation and dimerization of CO intermediates for highly selective C2H4 production. The integration of In–SV–Bi active sites and the photothermal effect into the Bi2S3@In2S3 catalyst induces a high rate of 11.81 μmol gcat–1 h–1 and near 90% selectivity for CO2 conversion to C2H4 under simulated sunlight without extra heat input. The catalytic mechanism is expounded by in situ characterizations and theoretical calculations. This work would provide some enlightening guidance to construct efficient photothermal catalysts for the direct transformation of CO2 to multicarbon (C2+) products with solar energy

Capture of pure toxic gases through porous materials from molecular simulations

<p>In the last three decades, the air pollution is the main problem to affect human health and the environment in China and its contaminants include SO_2, NH_3, H₂S, NO₂, NO and CO. In this work, we employed grand canonical Monte Carlo simulations to investigate the adsorption capability of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for these toxic gases. Eighty-nine MOFs and COFs were studied, and top-10 adsorption materials were screened for each toxic gas at room temperature. Dependence of the adsorption performance on the geometry and constructed element of MOFs/COFs was determined and the adsorption conditions were optimised. The open metal sites have mainly influenced the adsorption of NH₃, H₂S, NO₂ and NO. Especially, the X-DOBDC and XMOF-74 (X = Mg, Co, Ni, Zn) series of materials containing open metal sites are all best performance for adsorption of NH₃ to illustrate the importance of electrostatic interaction. Our simulation results also showed that ZnBDC and IRMOF-13 are good candidates to capture the toxic gases NH_3, H₂S, NO₂, NO and CO. This work provides important insights in screening MOF and COF materials with satisfactory performance for toxic gas removal.</p