Recently, market demand for polyglycolic acid (PGA) in the application field of packaging is increasing due to the excellent degradation performance with the promotion of the plastic bag ban. Present investigation was aimed at exploring the pyrolysis kinetics, product distribution, and mechanisms of PGA via experiments and reactive force field molecular dynamic (ReaxFF-MD) simulations to establish a foundation for the recycling of raw materials in the future. Experiment results based on TG analysis showed that the apparent activation energy for PGA pyrolysis ranged from 138.1 to 141.7 kJ/mol by iso-conversional models, and the kinetic reaction was identified to be the contracting cylinder model. The gaseous product was determined to contain carbon dioxide, carbon monoxide, and formaldehyde through TG-IR and TG-MS, and Py-GC/MS results showed that the yield of glycolide reached maximum at 450 °C. Additionally, the microscopic pyrolysis pathway was revealed by ReaxFF-MD simulations, which were consisted with the actual experiments. The results showed that the initial pyrolysis pathway for PGA was the cleavage of alkoxy bond, followed by C-C bond and acyloxy bond with the generation of carbon dioxide, carbon monoxide, formaldehyde, and ethenone. This study would provide comprehensive experiment data and meaningful guidance for recycling PGA to achieve a closed-loop economy.
Electroreduction of CO2 is a promising approach toward artificial carbon recycling. The rate and product selectivity of this reaction are highly sensitive to the surface structures of electrocatalysts. We report here 4H Au nanostructures as advanced electrocatalysts for highly active and selective reduction of CO2 to CO. Au nanoribbons in the pure 4H phase, Au nanorods in the hybrid 4H/fcc phase, and those in the fcc phase are comparatively studied for the electroreduction of CO2. Both the activity and selectivity for CO production were found to exhibit the trend 4H-nanoribbons > 4H/fcc-nanorods > fcc-nanorods, with the 4H-nanoribbons achieving >90% Faradaic efficiency toward CO. Electrochemical probing and cluster expansion simulations are combined to elucidate the surface structures of these nanocrystals. The combination of crystal phase and shape control gives rise to the preferential exposure of undercoordinated sites. Further density functional theory calculations confirm the high reactivity of such undercoordinated sites.
The Morpho butterfly wing with tree-shaped alternating multilayer is an effective chemical biosensor to distinguish between ambient medium, and its detection sensitivity is inextricably linked to the measurement configuration including incident angle, azimuthal angle, and so on. In order to reveal the effects and the selection of measurement configuration. In this work, the model of the Morpho butterfly wing is built using the rigorous coupled-wave analysis method by considering its profile is a rectangular-groove grating. On basis of the above model, the reflectivity of different diffraction orders at a different incident angle and azimuthal angle is calculated, and the influence of incident angle and azimuthal angle on performance of Morpho butterfly scales-based biosensor is analyzed. The optimal incident angle at each azimuthal angle is given according to the proposed choice rule, then the azimuthal angle and the corresponding incident angle can be selected further.
Selective CO2 capture and electrochemical conversion is an important tool in the fight against climate change. Industrially, CO2 is captured using a variety of aprotic solvents due to their high CO2 solubility. However, most research efforts on electrochemical CO2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER; making it important to develop strategies that enable integrated CO2 capture and conversion in an aprotic solvent. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO2 reduction is unclear. In this work, we show that bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst-electrolyte interface. We study different TBA (tetrabutylammonium) salts in two electrolyte systems with glyme-ethers (e.g., 1,2 dimethoxyethane or DME) and dimethylsulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that form within the electrolyte and show how ion-pair formation is prevalent in DME electrolytes and is dependent on anion type. More importantly, we show as ion-pair formation decreases within the electrolyte, CO2 current densities increases, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where ion-pair fraction does not change with anion type (such as in DMSO), a smaller influence of solvation was observed on CO2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte design for efficient and selective CO2 conversion to desired fuels and chemicals
Electroreduction of carbon monoxide (CO) possesses great potential for achieving the renewable synthesis of hydrocarbon chemicals from CO2. We report here selective reduction of CO to acetate using Cu–Pd bimetallic electrocatalysts. High activity and selectivity are demonstrated for CO-to-acetate conversion with >200 mA/cm2 in geometric current density and >65% in Faradaic efficiency (FE). An asymmetrical C–C coupling mechanism is proposed to explain the composition-dependent catalytic performance and high selectivity toward acetate. This mechanism is supported by the computationally predicted shift of the *CO adsorption from the top-site configuration on Cu (or Cu-rich) surfaces to the bridge sites of Cu–Pd bimetallic surfaces, which is also associated with the reduction of the CO hydrogenation barrier. Further kinetic analysis of the reaction order with respect to CO and Tafel slope supports a reaction pathway with *CO–*CHO recombination following a CO hydrogenation step, which could account for the electroreduction of CO to acetate on the Cu–Pd bimetallic catalysts. Our work highlights how heteroatomic alloy surfaces can be tailored to enable distinct reaction pathways and achieve advanced catalytic performance beyond monometallic catalysts.
As a two-dimensional nanomaterial, graphene oxide has attracted much attention for its use in reinforcing cementitious materials. However, the dispersion of graphene oxide in cementitious materials has been found unsatisfactory due to crosslinking of divalent calcium ions. In this study, we propose a modified mixing procedure to improve graphene oxide dispersion in cement mortar by utilizing silica sand to mechanically separate graphene oxide nanosheets. Apart from the improved graphene oxide dispersion, adhesion between sand and cement matrix is also believed to be enhanced due to the improved roughness of the sand surface. According to our mechanical properties study, with the introduction of 0.02% by weight graphene oxide in cement mortar, compressive strength was significantly improved by more than 25% and tensile splitting and flexural strength were improved by around 15%. In a microstructural investigation, the interfacial transition zone in cement mortar was found to be denser due to the addition of graphene oxide. Moreover, graphene oxide incorporated cement mortar also showed pore structure refinement and porosity reduction. Therefore, improvement in mechanical properties may result from an improved interfacial transition zone and a more refined pore structure with the introduction of a small quantity of well-dispersed graphene oxide nanosheets.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(144 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(216 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(288 450 300)'/%3e%3c/svg%3e)