As newly emerging proton-conducting materials, metal-organic frameworks (MOFs) have been attracting wide attention in the field of proton exchange membrane fuel cells. However, for most of the MOF ...materials, long-term stability is a huge obstacle for practical applications. So, the structural stability of MOFs is the critical prerequisite for the design and development of modified materials with excellent proton conductivity. In this review, stable UiO-66 derivatives were chosen as the research object, and modification methods including post-synthesis modification and hybridization were mainly summarized. Based on the reported typical functionalization strategies, we found that the modified UiO-66 derivatives and their composite membranes demonstrate ultra-high proton conductivity similar to that of commercial Nafion, indicating their great application potential in fuel cells. This Frontier article focuses on the recent development in the modification of UiO-66 type frameworks and their composite membranes and the tuning of proton conductivity with structural factors.
As newly emerging proton-conducting materials, metal-organic frameworks (MOFs) have been attracting wide attention in the field of proton exchange membrane fuel cells.
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•Forest and water were the cooling land cover types in Hangzhou during daytime.•Forest with high aggregation and complex shape behave best in cooling LST.•Complete water bodies had ...better cooling effect than scattered water patches.•The minimum cooling scale of forest and water were 120 m and 150 m.
Rapid urbanization, particularly in developing countries, is widely regarded as one of the most critical global issues in the 21 st century. It is known to exacerbate urban heat island effects, a phenomenon that could affect the livability of cities and the lives and comfort of more than half of the world population who are now living in urban areas. The issue on how to mitigate the impacts of this phenomenon and help urban dwellers adapt to it, has been, and continues to be, an important topic in the context of landscape design and urban planning. This study sought to examine the cooling effects of different land cover types from the perspectives of landscape composition and configuration using Landsat-8 OLI/TIRS data. Various spatial and statistical approaches, including urban-rural gradient, grid-based, landscape metrics, and scatter plot, were employed to analyze the derived land cover and land surface temperature (LST) maps. The results showed that both forest and water had a cooling effect during daytime in Hangzhou. The heat core in Hangzhou was situated close to the central business district and the variance in LST in urban and rural recorded at 3.22 ℃. The correlation of forest density with mean LST could be detected in both large (690 m) and small (210 m) grids, whereas the correlation of water density with mean LST was only observed in small grids. In general, forest with high aggregation and complex shape behave best in cooling LST while huge and complete water bodies had better cooling effect than scattered water patches. Besides, the minimum cooling scale of forest and water were proximately 120 m and 150 m from the cooling resources to the neighboring areas, respectively. The findings were considered valuable for urban planners to spatially and architecturally build and arrange the cooling land cover resources, eventually to fulfill the Chinese government’s new plan of building “livable cities”.
By the formation of a 1:1 cocrystal of caffeine and methyl gallate, we demonstrated that powder compaction properties could be profoundly improved. The selection criterion for cocrystal exhibiting ...superior compaction properties was the presence of slip planes in crystal structure. Bulk cocrystal was prepared by suspending powders of the two pure compounds in ethanol. Fine powders of similar particle size distribution were compressed. Within the whole range of compaction pressure, the tablet tensile strength of methyl gallate was very poor (<0.5 MPa) and severe lamination and sticking occurred in almost all tablets. Tabletability of caffeine was acceptable at <150 MPa. However, at >180 MPa, severe lamination of caffeine tablets suddenly occurred. Tablet tensile strength dropped sharply at >240 MPa. In contrast, the tabletability of the cocrystal was excellent over the entire pressure range. Tablet tensile strength of the cocrystal was ∼2 times that of caffeine at <200 MPa, and the ratio gradually increased with increasing pressure, e.g., ∼8 fold at 350 MPa. Poor tablet tensile strength was always associated with high elastic recovery and low plasticity. The good plasticity and tabletability of the cocrystal validated the selection criterion, i.e., the presence of slip planes in crystal structure.
Effects of particle size, morphology, particle density, and surface silicification, on powder flow properties were investigated using a ring shear tester. Flow properties were quantified by flow ...function (FF), that is, unconfined yield strength, fc, as a function of major principal stress. A total of 11 powders from three series of microcrystalline cellulose (MCC): Avicel (regular MCC, elongated particles), Prosolv (silicified MCC, elongated particles), and Celphere (spherical MCC), were studied. Particle size distribution in each type of MCC was systematically different. Within each series, smaller particles always led to poorer powder flow properties. The slope of FF line was correlated to degree of powder consolidation by external stress. A key mechanism of the detrimental effect of particle size reduction on flow properties was the larger powder specific surface area. Flow properties of Celphere were significantly better than Avicel of comparable particles size, suggesting spherical morphology promoted better powder flow properties. Flow properties of powders different in densities but similar in particle size, shape, and surface properties were similar. When corrected for density effect, higher particle density corresponded to better flow behavior. Surface silicification significantly improved flow properties of finer MCC, but did not improve those of coarser.
Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced ...thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m–1 K–1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m–1 K–1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems.
Rapid urbanization is one of the most concerning issues in the 21st century because of its significant impacts on various fields, including agriculture, forestry, ecology, and climate. The urban heat ...island (UHI) phenomenon, highly related to the rapid urbanization, has attracted considerable attention from both academic scholars and governmental policymakers because of its direct influence on citizens’ daily life. Land surface temperature (LST) is a widely used indicator to assess the intensity of UHI significantly affected by the local land use/cover (LULC). In this study, we used the Landsat time-series data to derive the LULC composition and LST distribution maps of Nanjing in 2000, 2014, and 2018. A correlation analysis was carried out to check the relationship between LST and the density of each class of LULC. We found out that cropland and forest in Nanjing are helping to cool the city with different degrees of cooling effects depending on the location and LULC composition. Then, a Cellar Automata (CA)-Markov model was applied to predict the LULC conditions of Nanjing in 2030 and 2050. Based on the simulated LULC maps and the relationship between LST and LULC, we delineated high- and moderate-LST related risk areas in the city of Nanjing. Our findings are valuable for the local government to reorganize the future development zones in a way to control the urban climate environment and to keep a healthy social life within the city.
Nanoparticle-based drug delivery system offers a promising platform for combination cancer therapy. However, the inefficient drug release in cells reduces the therapeutic efficacy of cancer ...nanomedicines. Herein, a PEGylated poly(α-lipoic acid) copolymer (mPEG-PαLA) was prepared and used as a reduction/pH dual responsive nanocarrier to simultaneously deliver paclitaxel (PTX) and doxorubicin (DOX) for osteosarcoma therapy. The amphiphilic mPEG-PαLA could efficiently encapsulate both PTX and DOX during its self-assembly into micelles in aqueous solution to generate PTX and DOX co-loaded nanoparticles (NP-PTX-DOX). The as-prepared NP-PTX-DOX showed enhanced PTX and DOX release in response to reductive and acidic stimuli. Moreover, the dual-drug loaded nanoparticles were efficiently internalized by K7 osteosarcoma cells and released drugs intracellularly, as confirmed by flow cytometry analysis and confocal laser scanning microscopy. Consequently, NP-PTX-DOX exhibited synergistic therapeutic effects and induced enhanced cell apoptosis in K7 cells. Furthermore, NP-PTX-DOX presented improved biodistribution and higher tumor growth inhibition efficacy compared to the control groups in a murine osteosarcoma model. Altogether, the results of this work indicate that the proposed strategy is promising for osteosarcoma therapy using mPEG-PαLA copolymer as a dual-responsive nanocarrier to co-deliver anticancer drugs.
Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, ...biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.
With the increasing integration of devices in electronics fabrication, there are growing demands for thermal interface materials (TIMs) with high through-plane thermal conductivity for efficiently ...solving thermal management issues. Graphene-based papers consisting of a layer-by-layer stacked architecture have been commercially used as lateral heat spreaders; however, they lack in-depth studies on their TIM applications due to the low through-plane thermal conductivity (<6 W m–1 K–1). In this study, a graphene hybrid paper (GHP) was fabricated by the intercalation of silicon source and the in situ growth of SiC nanorods between graphene sheets based on the carbothermal reduction reaction. Due to the formation of covalent C–Si bonding at the graphene–SiC interface, the GHP possesses a superior through-plane thermal conductivity of 10.9 W m–1 K–1 and can be up to 17.6 W m–1 K–1 under packaging conditions at 75 psi. Compared with the current graphene-based papers, our GHP has the highest through-plane thermal conductivity value. In the TIM performance test, the cooling efficiency of the GHP achieves significant improvement compared to that of state-of-the-art thermal pads. Our GHP with characteristic structure is of great promise as an inorganic TIM for the highly efficient removal of heat from electronic devices.
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The impact of drug loading on the compaction properties of itraconazole (ITZ)- poly(vinylpyrrolidone-co-vinyl-acetate) (PVPVA) amorphous solid dispersions (ASDs) was studied. Neat ...amorphous ITZ, amorphous PVPVA, and their ASDs from 20% to 80% ITZ loadings were prepared by spray drying. Physical characterization showed that all powders have comparable particle size and morphology. All samples were equilibrated under 33% RH prior to compaction studies using a compaction simulator. Tabletability and compactability profiles of the ASD powders differed significantly, while their compressibility was similar. At compaction pressures from 50 to 150 MPa, tensile strength of ASD compacts increased with the increase of ITZ loading, reaching to the maximum at 40–60% ITZ loadings and then decreased as ITZ loading further increased. However, at the compaction pressure of 200 MPa, a monotonic decrease of tensile strength with the increase of ITZ loading was observed. In addition, except for the ASD with 20% ITZ loading, the detrimental effect of compaction pressure on tensile strength was observed at pressures at or above 150 MPa. Overall, this work highlights the importance of evaluating the compaction properties of ASD intermediates prior to downstream tablet development, especially if a high drug loading ASD is desired.
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