Thiophene-Based Covalent Organic Frameworks: Synthesis, Photophysics and Light-Driven Applications

Porous crystalline materials, such as covalent organic frameworks (COFs), have emerged as some of the most important materials over the last two decades due to their excellent physicochemical properties such as their large surface area and permanent, accessible porosity. On the other hand, thiophene derivatives are common versatile scaffolds in organic chemistry. Their outstanding electrical properties have boosted their use in different light-driven applications (photocatalysis, organic thin film transistors, photoelectrodes, organic photovoltaics, etc.), attracting much attention in the research community. Despite the great potential of both systems, porous COF materials based on thiophene monomers are scarce due to the inappropriate angle provided by the latter, which hinders its use as the building block of the former. To circumvent this drawback, researchers have engineered a number of thiophene derivatives that can form part of the COFs structure, while keeping their intrinsic properties. Hence, in the present minireview, we will disclose some of the most relevant thiophene-based COFs, highlighting their basic components (building units), spectroscopic properties and potential light-driven applications.

Accessibility of Pores to Methane in New Albany Shale Samples of Varying Maturity Determined Using SANS and USANS

The accessibility of pores to methane has been investigated in Devonian New Albany Shale Formation early-mature (Ro = 0.50%) to post-mature (Ro = 1.40%) samples. A Marcellus Shale Formation sample was included to expand the maturation range to Ro 2.50%. These are organic matter-rich rocks with total organic carbon (TOC) values of 3.4 to 14.4% and porosity values of 2.19 to 6.88%. Contrast matching small-angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) techniques were used to generate porosity-related data before and after pressure cycling under hydrostatic (in a vacuum and at 500 bar of deuterated methane) and uniaxial stress (0 to ca. 350 bar) conditions. Our results showed that the accessible porosity was small for the samples studied, ranging from zero to 2.9%. No correlation between the accessible porosity and TOC or mineralogical composition was revealed, and the most likely explanation for porosity variation was related to the thermal transformation of organic matter and hydrocarbon generation. Pressure caused improvements in accessible porosity for most samples, except the oil window sample (Ro = 0.84%). Our data show that densification of methane occurs in nanopores, generally starting at diameters smaller than 20 nm, and that the distribution of methane density is affected by pressure cycling.

Influence of NaOH treatment of rubber aggregates on the durability properties of rubberized mortars

The work presented in this paper aims to study the durability of mortars, in which part of the sand has been replaced with rubber aggregates from used tires and have undergone a surface treatment with a sodium hydroxide solution (NaOH). The substitution rates studied are 10%, 17.5%, and 25%. The results are compared with ordinary mortar and mortars with untreated rubber aggregates while samples with the same substitution rates were used. To do this, the following properties have been studied: compressive strength, flexural tensile strength, water absorption by capillarity, water absorption by total immersion, water-accessible porosity, water permeability, and resistance to the chemical degradation by sulfuric acid H2SO4. The results obtained show that the treatment of rubber aggregates by the solution method (NaOH) presented a considerable improvement in mechanical performance (increase in compressive strength and flexural tensile strength) and better durability compared to reference mortar and mortar with untreated rubber granulate.

A Statistical Evaluation to Compare and Analyze Estimations of the Diffusion Coefficient of Pertechnetate (99TcO4−) in Compacted Bentonite

Various numerical methods have been being extensively used to estimate the diffusion parameters of pertechnetate (99TcO4−) in compacted MX80 bentonite clay using through-diffusion (TD) techniques. In this study, an improved TD column test was applied, and the diffusion fluxes of tritium (HTO) as a non-reactive radionuclide, and 99TcO4− with various dry densities, were compared under the same experimental conditions. Similar results were obtained for the apparent diffusion coefficients of HTO and 99TcO4− using three estimation methods: a graphical method applying the asymptote calculation, an analytical solution using Lsqcurvefit installed in MATLAB, and the Marquardt–Levenberg optimization algorithm in the HYDRUS-1D inverse method. The statistical analysis showed that the densities using a one-way analysis of variance (ANOVA) for the three estimation methods ranged from 1200 to 2000 kg/m3, which indicated that there were no obvious differences between HTO and 99TcO4−. In general, the diffusion parameters of 99TcO4− were lower than those for HTO due to anion exclusion effects and lower accessible porosity.

Improving bond strength and mass transport properties of spacer-concrete interface with textured spacers

Spacers are important devices used in all concrete structures to support reinforcing steel and achieve the required cover. However, spacers induce a weak, porous and microcracked interface that facilitates ingress of aggressive agents. This paper aims to address the problem by developing a method to produce cementitious spacers with a range of small-scale surface textures including grooves, squares, rectangles, hemispheres and pyramids. The textured spacers were cast in Portland cement mortar or concrete, cured up to 28 days, and tested for tensile bond strength, accessible porosity and mass transport properties. The properties were correlated to surface characteristics to establish the effects of texture on spacer-concrete interface. Results show that textured spacers promote mechanical interlocking with concrete, thereby increasing bond strength, resistance against microcracking and pressure-induced flow. The use of certain textures can compensate for the negative effects of spacers, achieving similar bond strength and permeability to monolithic concrete without the interface.

Performance Evaluation of Cementitious Composites Containing Granulated Rubber Wastes, Silica Fume, and Blast Furnace Slag

In this study, rubberized cementitious materials are produced with recycled rubber waste as an alternative to fine aggregate. Mixtures with different additions to rubber wastes (RW), silica fume (SF), and blast furnace slag (BFS) have been designed and characterized. Hardened properties including compressive and bond strength, shrinkage, water-accessible porosity, rapid chloride migration, and microstructure were investigated. The results show that the addition of SF and BFS improves the performances of rubberized mortars and reduces shrinkage. The incorporation of 5% RW with 20% BFS increases compressive strength and reduces water-accessible porosity. Ion chloride resistance was enhanced by a combination of 15% RW, 8% SF, and 20% BFS. The addition of SF and BFS as cement replacement improves the performance of mortars due to their filling effect and a pozzolanic reaction, which has been verified by a microstructural analysis.

Recent advances in mechanochemical synthesis of mesoporous metal oxides

There is a growing interest in mesoporous metal oxides due to their unique properties such as highly accessible porosity, stability, catalytic activity and diversity of nanostructures. Mechanochemical fabrication of mesoporous...

Insight into the secondary imbibition rate of concrete and its relationship with curing time

Long-term capillary imbibition in cementitious materials is relevant to describe their durable behaviour. Many structures are exposed to long-term contact with moisture, such as foundations or wastewater installations. After several weeks, when capillary rise is no longer progressing, a distinguished change in the slope (from the mass gain - fourth root of time relation) is noticed. Primary and secondary imbibition rates (PIR and SIR, respectively) can be obtained from such behaviour. Contrary to the widely investigated PIR, usually defined as the capillary absorption rate, the SIR has been scarcely examined. Data from literature of tests in concrete lasting more than 7 days is very limited. To form a better view of this process, we contrasted values of SIR and porosity (water accessible porosity under vacuum and intrudable porosity by mercury intrusion porosimetry). Moreover, we used statistical inference to evaluate the evolution of the SIR of mixes with different composition and curing age. This paper presents the effect of curing on the SIR and the relation between porosity changes and SIR. Despite the decrease in capillary porosity and intrudable porosity, SIR increases with curing time. This is probably due to a connection between SIR and the increasing C-S-H content with time.

Combined effects of vertical spacers and segregation on mass transport properties of reinforced concrete

All concrete structures contain reinforcement spacers, and deep sections can be affected by bleeding and segregation without displaying visible indications during casting. However, their effects on mass transport and long-term durability are not well studied. In this paper, reinforced concrete columns were prepared with plastic and cementitious spacers to achieve 50 mm cover, and compacted at different vibration frequencies and durations. 28d cured samples were extracted along the height, conditioned to equilibrium (21 °C, 75% RH or 50 °C, 7% RH), and then subjected to water absorption, electrical conduction, epoxy impregnation and fluorescence imaging. Samples from the top of the column consistently gave higher accessible porosity and mass transport compared to samples from the bottom. Presence of spacers caused additional increases in mass transport because of preferential flow through the spacer-concrete interface which is more porous and microcracked compared to bulk concrete farther away. Image analysis on cross-sections showed that the columns experienced some aggregate segregation despite care taken to avoid over-compaction. The resistance of concrete to ingress of aggressive agents decreases with increasing height due to the combined negative effects of reinforcement spacers and segregation.