Non-Precious Metal-Doped Carbon Materials Derived From Porphyrin-Based Porous Organic Polymers for Oxygen Reduction Electrocatalysis.

The cathodic oxygen reduction reaction (ORR) is important in the development of renewable energy devices, to produce novel and non-precious metal catalysts with high electrocatalytic activity to reduce the consumption of non-renewable platinum (Pt) catalyst. In this work, we developed N-doped and Fe/N dual-doped porous carbons as catalysts for ORR simply by high-temperature pyrolysis of porphyrin-based conjugated microporous polymers (CMPs). By combination of heteroatom doping, highly porous structure and tubular morphology, the as-prepared carbon samples exhibited high electrocatalytic activity with 4-electron transfer mechanism, nearly close to the commercial Pt/C catalyst. In particular, among these samples, the Fe/N-CMP-1000 displayed a higher onset potential (0.95 eV), positive half-wave potential (0.85 eV) and limiting current density value (5.1 mA cm-2 ) as well as good durability and better methanol tolerance contrasting with Pt/C catalyst, suggesting that the as-prepared metal-free catalysts from porphyrin-based CMPs show great potential for ORR.

Nitrogen-doping hollow carbon nanospheres derived from conjugated microporous polymers toward oxygen reduction reaction.

The exploitation non-precious or metal-free electrocatalysts of oxygen reduction reaction (ORR) is of significance for construction of next-generation fuel cells. In this work, hollow-spherical conjugated microporous polymers (CMPs) comprising porphyrin units were synthesized as precursors to prepare N-doping porous carbon spheres (CMP-NP-x) by a direct pyrolysis method. The as-resulted CMP-NP-x exhibited spherical morphology with hollow structure similar to that of CMPs precursors. The BET surface area of CMP-NP-x can be tailored by the pyrolysis temperature varying from 868 m2 g-1 to 1118 m2 g-1. According to XPS analysis, the pyrrolic N content in the sample decreased but the graphitic N and pyridinic N increased with increasing of the pyrolysis temperature from 800 °C to 1000 °C. Taking advantages of porous structure with large accessible surface areas and N species active sites, the resulting CMP-NP-x showed superior ORR activity and methanol tolerance to commercial Pt/C catalyst. In particular, CMP-NP-900 possesses the highest onset potential (0.930 V), half-wave potential (0.857 V) and limiting current density of 4.45 mA cm-2, compared with Pt/C catalyst and other samples, making it a promising metal-free catalyst superior to commercial Pt/C catalyst in alkalic condition.

Efficient capture of airborne PM by nanotubular conjugated microporous polymers based filters under harsh conditions.

The exploitation of high-performance filters which can capture and remove airborne particulate matter (PM) in harsh conditions is greatly important to limit the serious effect of PM on human health. Herein, we demonstrate a simple approach for the creation of robust and hierarchically porous filters based on conjugated microporous polymers (CMPs) nanotubes for efficient PM capture. Taking advantage of their inherently superhydrophobic wettability, the CMPs-based filters possess high filtration efficiency of higher than 99.4% for PM0.3 and 99.9% for PM2.5 and PM10, respectively, even in high humidity environment (RH ≥ 94%). The CMPs-based filters show highly physicochemical and thermal stability, e.g., by calcination at 500 °C for 2 h, the filtration efficiency of the samples still reaches as great as 99.4% for both PM2.5 and PM10 with a low-pressure drop of only 10 Pa. In addition, these CMPs-based filters can be easily regenerated and their high PM filtration efficiency remains nearly unchanged by a simple methanol washing. More interestingly, the CMPs-based filters also exhibit superior antibacterial performance, which enables them to sterilize or eliminate the bacteria possibly loaded on PM pollutions, thus showing great potential for various applications such as PM removal, air purification and so on.

Analysis of Interface Fusion Effect between Old and New Asphalt under Plant Mixing and Cold Recycling Mode Based on Molecular Dynamics Simulation.

Road construction consumes a lot of resources and produces a lot of waste and other pollutants. With the emergence of a resource and energy crisis, how to make efficient use of rap has become the research focus of scientific researchers. The interface fusion effect of old and new asphalt in plant mixing and cooling recycling mode is analyzed in order to improve the utilization rate of old asphalt in reclaimed asphalt pavement. In this paper, Materials Studio software was used to establish a bitumen model using the method of four components of bitumen, and then the rationality of the model was verified by density, solubility number and atomic radial distribution function, and the diffusion coefficient obtained from the mean square displacement (MSD) was taken as its evaluation index. The results showed that the diffusion model tends to be stable after 20 ps, and the degree of diffusion increases with the increase in temperature. The degree of diffusion of new asphalt to old asphalt and the degree of diffusion of old asphalt to new asphalt are basically very similar; however, there are some differences at different temperatures. Only a small part of the surface contact between old and new asphalt has been fused, which accords with the partial fusion theory. Compared with Panjin 90# asphalt, the diffusion coefficient of Zhonghaiyou asphalt increases faster with the increase in temperature. The diffusion coefficient increases by 64.3% with the increase of the content of rejuvenators after adding different rejuvenators into the new asphalt. Clarifying the interface fusion effect will be helpful to guide the optimization design of cold-mixing recycled asphalt mixture more scientifically and reasonably. Future research should focus on increasing the fusion effect of old and new asphalt, and explore its influence on the conventional road performance of asphalt mixture.

Study on Performance Damage and Mechanism Analysis of Asphalt under Action of Chloride Salt Erosion.

This study aims to investigate the performance evolution and mechanism of asphalt under action of chloride salt erosion. Asphalt samples soaked with five different snow melting chloride salt concentrations were taken as the research object. Then, the high-temperature performance, low-temperature performance, temperature sensitivity and asphalt-aggregate adhesion property of asphalt samples were carried out. Additionally, Fourier transform infrared spectroscopy (FTIR) was used to explore the mechanism of chloride salt erosion on asphalt. Test results showed the linear variation relationships of high-temperature performance, low-temperature performance and temperature sensitivity with chloride salt concentrations. The high-temperature performance of asphalt would be improved by chloride snowmelt salt. With the increase in the chloride salt solution concentration, the low-temperature performance of asphalt became worse, and the temperature sensitivity increased. Moreover, after the effect of the chloride salt solution, the asphalt-aggregate adhesion property decreased with the increase in the chloride salt solution concentration. It is necessary to control the amount of chloride snowmelt salt in the actual snow removal projects. Finally, based on Fourier transform infrared spectroscopy, the mechanism of chloride salt erosion on asphalt was preliminarily explored. With the increase in the chloride salt solution concentration, the proportion of light components (saturated fraction, aromatic fraction) in asphalt decreased, and the proportion of heavy components (resin and asphaltene) with good thermal stability increased.

Performance Evaluation of Styrene-Butadiene-Styrene-Modified Stone Mastic Asphalt with Basalt Fiber Using Different Compaction Methods.

Superpave gyratory compaction (SGC) and Marshall compaction methods are essentially designed according to volumetric properties. In spite of the similarity, the optimum asphalt contents (OAC) of the two methods are greatly affected by the laboratory compaction process, which would further influence their performance. This study aims to evaluate the performance of styrene-butadiene-styrene (SBS)-modified stone mastic asphalt (SMA) with basalt fiber by using SGC and Marshall compaction methods. Basalt fiber was proved to improve and strength the basic properties of SBS-asphalt according to test results of asphalt binder. The effects of SGC and Marshall compaction methods on OAC and volumetric properties, i.e., density, air voids (VA), voids in mineral aggregates (VMA), and voids filled with asphalt (VFA), were evaluated in detail. Finally, the pavement performance of asphalt mixture prepared by SGC and Marshall compaction methods were compared in order to analyze the high-temperature creep, low-temperature splitting, and moisture stability performance. Results showed that the OAC of SGC (~5.70%) was slightly lower than that of Marshall method (5.80%). Furthermore, the pavement performance of SGC specimens were improved to a certain extent compared with Marshall specimens, indicating that SGC has a better compaction effect and mechanical performance.

Multi-Objective Optimization Design and Test of Compound Diatomite and Basalt Fiber Asphalt Mixture.

This study focuses on improving the performance of asphalt mixture at low- and high- temperature and analyzing the effect of diatomite and basalt fiber on the performance of the asphalt mixture. Based on the L16(45) orthogonal experimental design (OED), the content of diatomite (D) and basalt fiber (B) and the asphalt-aggregate (A) ratio were selected as contributing factors, and each contributing factor corresponded to four levels. Bulk volume density (γf), volume of air voids (VV), voids filled with asphalt (VFA), Marshall stability (MS) and splitting strength at -10 °C (Sb) were taken as the evaluation indexes. According to the results of the orthogonal experiment, the range analysis and variance analysis were used to study the effect of the diatomite content, basalt fiber content and asphalt-aggregate ratio on the performance of the asphalt mixture, and the grey correlation grade analysis (GCGA) was used to obtain the optimal mixing scheme. Furthermore, the performance tests were conducted to evaluate the performance improvement of asphalt mixtures with diatomite and basalt fibers, and the scanning electron microscopy (SEM) tests were carried out to analyze the mechanism of diatomite and basalt fibers in asphalt mixtures. The results revealed that the addition of diatomite and basalt fiber can significantly increase the VV of asphalt mixture, and reduce γf and VFA; the optimal performance of the asphalt mixture at high- and low-temperature are achieved with 14% diatomite, 0.32% basalt fibers and 5.45% asphalt-aggregate ratio. Moreover, the porous structure of diatomite and the overlapping network of basalt fibers are the main reasons for improving the performance of asphalt mixture.