Studies of Macromolecule/Molecule Adsorption and Activity at Interfaces

Interfaces are ubiquitous in our daily life. A good understanding of the interfacial properties between different materials, or a single material in different physical states is of critical importance for us to explore the current world and bring benefits to mankind. In this work, interfacial behavior was investigated with the help of surface analysis techniques, such as quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and atomic force microscopy (AFM), in order to gain better understanding on biofuel conversion, gene/drug delivery, and chemical fixation of CO2.

Biomimetic chelator-mediated Fenton (CMF) non-enzymatic degradations on cellulose and chitin thin films was studied by liquid-phase QCM-D and AFM. QCM-D is a powerful tool to monitor the kinetics of hydrolysis of regenerated cellulose and chitin model surfaces. Results from QCM-D and AFM showed that the majority of the biomass of the two model surfaces can be hydrolyzed by the CMF system. The initial degradation rates for both model surfaces by the CMF system are faster than that of the corresponding enzyme systems. The CMF system, which is a good non-enzymatic pretreatment agent for cellulose and chitin, may work on a wide variety of polysaccharide systems.

Adsorption of cationic cellulose derivatives onto self-assembled monolayer (SAM) surfaces was investigated using liquid-phase SPR. Results from SPR showed that depending upon the cellulose derivative structure, irreversible adsorption ranging from a monolayer to ~1.6 layers of cellulose derivative were formed on the SAM-COOH surface based upon a charge neutralization mechanism. At low salt concentrations, the long-range electrostatic attraction between the cationic cellulose derivatives (6-PyrCA and 6-MeIMCA) and the SAM surfaces facilitates the formation of a 2-dimensional monolayer. While, for TMACE, the energy gained through the hydrophobic interaction between adjacent long polyelectrolyte branches may afford the electrostatic repulsion and chain entropy penalties, resulting in the formation of 3-dimensional adsorbed polyelectrolyte layers.

Adsorption of 1,2-epoxybutane gas molecules onto/into VPI-100 metal–organic frameworks (MOFs) was studied by gas-phase QCM-D experiments. Results from QCM-D demonstrated that VPI-100 (Ni) MOFs have higher irreversible adsorption per unit cell (θ) and faster diffusion coefficients (D) than VPI-100 (Cu) MOFs. The presence of bound counter-balancing ions on the metallo-cyclam core was attributed as the cause of the higher θ and faster D through the Ni analogue, which suggests the MOF-epoxide interaction occurs at the metallo-cyclam. This study shed light upon tuning MOF structures for better CO2 sorption and epoxide activation to gain higher catalytic efficiency.

Finally, in operando high energy X-ray diffraction (HEXRD) was used to monitor the phase transition of the NaxNi1/3Co1/3Mn1/3O2 cathode material during the sintering process. The first charge/discharge cycle of the NaxNi1/3Co1/3Mn1/3O2 cathode materials in different phases were also studied by in operando HEXRD. It was found that the intergrowth P2/O1/O3 cathode (NCM-Q cathode) can inhibit the irreversible P2–O2 phase transition and simultaneously improve the structural stability of the O3 and O1 phases during cycling. The NCM-Q cathode with triple-phase integration demonstrates highly reversible phase evolution during high voltage cycling, possibly leading to a highly reversible capacity and good cycle stability.