Fully Inkjet-Printed, 2D Materials-Based Field-Effect Transistor for Water Sensing

Despite significant progress in solution-processing of 2D materials, it remains challenging to reliably print high-performance semiconducting channels that can be efficiently modulated in a field-effect transistor (FET). Herein, electrochemically exfoliated MoS2 nanosheets are inkjet-printed into ultrathin semiconducting channels, resulting in high on/off current ratios up to 103. The reported printing strategy is reliable and general for thin film channel fabrication even in the presence of the ubiquitous coffee-ring effect. Statistical modeling analysis on the printed pattern profiles suggests that a spaced parallel printing approach can overcome the coffee-ring effect during inkjet printing, resulting in uniform 2D flake percolation networks. The uniformity of the printed features allows the MoS2 channel to be hundreds of micrometers long, which easily accommodates the typical inkjet printing resolution of tens of micrometers, thereby enabling fully printed FETs. As a proof of concept, FET water sensors are demonstrated using printed MoS2 as the FET channel, and printed graphene as the electrodes and the sensing area. After functionalization of the sensing area, the printed water sensor shows a selective response to Pb2+ in water down to 2 ppb. This work paves the way for additive nanomanufacturing of FET-based sensors and related devices using 2D nanomaterials

Developing a generic approach to durability

Cementitious Materials become more diverse. In particular, to reduce the CO2 emissions associate with production, it is necessary to increase the levels of replacement of clinker by other materials. A critical consideration is to know how durable different materials will be. Most forms of degradation involve the ingress of different species into the cement paste. The rate of ingress will be controlled by the concrete microstructure. Therefore, in order to predict the durability of new materials we need to understand how the microstructure controls durability: to develop a generic approach. This presentation summarizes a large research programme ongoing at EPFL to identify the features of the microstructure which determine durability. A wide range of materials with different SCMs and at different w/c ratios are investigated. Both the solid phases and porosity are characterized using a combination of analytical methods (XRD, SEM, 1H NMR, MIP). Various experimental techniques are used to investigate transport properties (resistivity, diffusion cells, electrochemically induced migration, etc). Modelling approaches are also used. The initial focus is on ingress of chloride ions. The work, so far, indicates that a least 3 factors affect the rate of ingress of chloride ions:(1) Solid phases (binding), (2) Pore structure and (3) Pore solution composition. The interaction of these 3 factors means that materials with very similar pore structure may show dramatically different resistance to the ingress of chloride ions. This work has very important implications for the choice of materials in aggressive environments and for modelling durabilit

Chloride binding assessment in C3S systems with calcined clay

Chloride binding is an important factor for chloride transport in cementitious materials, which can fix the chloride on the solid phase and decrease the free chloride content. As an alumina-rich supplementary cementitious material, calcined clay can be applied to improve the binding capacity of the system. While the contribution of calcined clay to chemical binding (through the formation of Friedel’s salt) is clear, its influence on physical binding (adsorption on hydration products) is still under debate. In this study, pure C3S instead of cement was used to assess the binding capacity on the presence of calcined clay. In addition, extra limestone was added to investigate the synergetic effect between calcined clay and limestone on binding capacity. Binding capacity was evaluated by an equilibrium method between free chloride in the solution and bound chloride in the solid phase. The evolution of the phase assemblage was analyzed using XRD-Rietveld, the pore structure, and the specific surface area were measured with the nitrogen adsorption method. It was observed that the systems with calcined clay present higher binding capacity than the reference. In addition, the binary system demonstrates similar bound chloride content compared to the ternary system. Characterization results were used to correlate the microstructural properties of cementitious materials to chloride binding capacity. Results showed that the calcined clay contributes to the chemical binding and, that there is no clear relation between specific surface area and physical binding in cementitious materials

The influence of silica-coated nanoscale titanium dioxide on the microstructure, mechanical properties, and carbonation resistance of cementitious materials

Nanomaterials possess great application prospects in improving the performance of cementitious materials. However, their high agglomeration hinders their efficient utilization in cementitious matrices. Consequently, surface modification has recently attracted attention as a method to enhance dispersibility. In this study, silica was employed to modify the surface of nanoscale titanium dioxide (NT), resulting in the synthesis of silica-coated nanoscale titanium dioxide (SCNT) composite material. In particular, the dispersibility of SCNT was investigated, and its influence on the compressive strength development of modified cement paste was analyzed. Additionally, the mechanisms affecting cement hydration behavior and microstructure evolution were comprehensively analyzed. Lastly, the impact of SCNT on the carbonation resistance of cementitious materials was further explored. Interestingly, the research results indicate that the surface SiO2 coating treatment improves the dispersibility of NT. More precisely, compared to 3 % NT, the addition of 3 % SCNT can increase the compressive strength of cement paste by 20.52 % at 3 days and 16.52 % at 28 days. Specifically, the incorporation of SCNT promotes cement hydration, refines the crystal size of Ca(OH)2, reduces the crystal orientation growth index of Ca(OH)2, and enhances the polymerization degree of calcium silicate hydrate (C-S-H), optimizing the pore structure. Furthermore, the 28-day permeability coefficient of 3 % SCNT mortar is reduced by 99.98 % compared to the blank group, effectively enhancing the carbonation resistance of cementitious materials. Overall, the findings of this study will contribute to the development of high-performance and multifunctional nanocomposite cementitious materials

The performance and functionalization of modified cementitious materials via nano titanium-dioxide: A review

The unique physical and chemical characteristics of titanium dioxide nanoparticles, such as the small size effect and photocatalytic activity, make them popular materials for science and engineering. Numerous studies showed that both the properties and the functionality of cementitious materials can be enhanced by adding titanium dioxide nanoparticles, which makes this topic a popular field of study. This paper reviews the influence of nano-titanium dioxide on both the hydration process of cementitious materials as well as the hydration products. It also covers the mechanisms that govern the microstructural changes following the addition of nano-titanium dioxide. Moreover, an overview of the effect of nano-titanium dioxide on the mechanical properties, durability, and functional properties of cementitious materials is given. Finally, the remaining challenges and anticipated future developments are summarized for nano-titanium dioxide used in cementitious materials in general. This compact review aims to serve as a practical summary/guide for researchers and engineers working with cementitious materials

Improving the chloride binding capacity of cement paste by adding nano-Al2O3: The cases of blended cement pastes

Chloride ingress is one of the main causes for the degradation of reinforced concrete structures. Increasing the chloride binding capacity of concrete is generally thought as a feasible way to restrain the chloride ingress. In our previous study, the γ-phase nano-Al2O3 (NA) was found to be beneficial for improving the chloride binding of plain Portland cement paste as a result of the formation of additional Friedel\u27s salt. Herewith, the cases of blended cement pastes were further investigated, into which supplementary cementitious materials (SCMs) were incorporated, including fly ash (FA), blast furnace slag (SL) and silica fume (SF). NA with a dosage of 1% and 2% was introduced to blended cement paste, and the chloride binding capacity of which were determined with the conventional equilibrium method. The results showed that the use of NA was even viable to improve the chloride binding capacity of blended cement pastes. X-ray diffraction (XRD)/Rietveld refinement method and thermogravimetric analysis (TGA) were performed to unravel the phase assemblages change upon exposure. It was revealed that besides the formation of more Friedel\u27s salt, the addition of NA could allow the enhanced physical binding of chloride as a result of the formation of C-A-S-H, i.e., the substitution of Si by Al in C-S-H gel

Investigation on the sulfate attack of metakaolin blended recycled concrete based on percolation theory

Recycled aggregate concrete (RAC) is one of the most important ways to achieve sustainable development for concrete industry. However, the research on durability, especially on sulfate transport and erosion mechanism, of RAC needs deep investigation. Pore structure evolution is a vital parameter for sulfate transport, which is difficult to be traced. To investigate the dynamic changes of pore structure in metakaolin blended RAC under sulfate erosion, percolation theory is addressed in this study. Firstly, dry and wet cycle was applied to accelerate the sulfate transport in metakaolin (MK) blended RAC systems. Then the compressive strength of the samples after sulfate attack was measured to evaluate the sulfate erosion degree. Furthermore, backscattered electron imaging (BSE) was used to acquire the percolation parameters, such as wet site ratio, percolation probability and so forth. Finally, sulfate content and compressive strength of the sample were related to the percolation probability. Results present that MK exhibits excellent resistance to sulfate erosion and can be used to enhance the performance of RAC. There is a certain correlation between the degree of sulfate erosion, compressive strength, and percolation parameters. The influence of the number of dry–wet cycles and MK content on sulfate ion transport can be demonstrated using percolation theory, which can be employed for predicting sulfate transport and revealing erosion mechanisms. This enables a clear understanding of the ion transport mechanisms within concrete and holds significant importance on the investigation of durability issues of RAC

Investigation on chloride migration behavior of metakaolin-quartz-limestone blended cementitious materials with electrochemical impedance spectroscopy method

Calcined clay and limestone powder composites offer a viable solution for reducing carbon emissions in building materials by allowing significant cement replacement. However, there is a need for further investigation into their impact on durability, especially for low-grade clays. In this study, different ratios of metakaolin and quartz powder are utilized to simulate various grades of calcined clay, while limestone powder is incorporated as a partial cement substitute. Initially, the influence of metakaolin content on rapid chloride migration was analyzed. Subsequently, various analytical techniques such as free water content, Mercury Intrusion Porosimetry (MIP), X-ray diffraction (XRD)/Rietveld method, and electrochemical impedance spectroscopy (EIS) test were employed to investigate the effects of metakaolin contents on the pore structure, phase assemblage, and electrochemical parameters of the blended cementitious system. The relationship between chloride migration coefficient and free water content, critical pore size, and impedance parameters was established to determine the key indicators for chloride migration. The study revealed that systems with partial metakaolin content demonstrate improved chloride resistance in the blended system, which could be predicted using Rct1 from the EIS test. Furthermore, the inclusion of metakaolin and limestone powder facilitated the formation of Monocarboaluminate (Mc) and Hemicarboaluminate (Hc), leading to the refinement of the pore structure and inhibition of chloride transport within the blended material. This study indicates the potential of low-grade calcined clay to enhance the overall durability of the blended cementitious system while contributing to carbon emissions reduction

Effect of citric-acid-modified chitosan (CAMC) on hydration kinetics of tricalcium silicate (C3S)

Studying the mechanism by which organic admixtures affect the hydration and dissolution of tricalcium silicate (C3S) reveals the effect of organic admixtures on ordinary Portland cement and enables target regulation of cement-based materials. In this study, the effects of citric-acid-modified chitosan (CAMC) on the hydration exotherm, hydration products, and microscopic morphology of C3S were investigated. The interface structures, ion adsorptions, and dissolution properties of CAMC and C3S were analyzed using a molecular dynamics simulation method. The results showed the presence of an attraction between the C3S surface and CAMC due to the existence of Op-Hw, Op-Cas, and Hp-Ow ion pairs. CAMC adsorbed most of the Ca ions released upon dissolution of C3S in the aqueous solution and the resulting pairs exhibited low solubilities. The Ca ions were located on the surfaces of C3S particles, preventing the dissolution of the particles and proving the interference effect of additives on the hydration of the cement silicate phase

Sodium Fluoride under Dose Range of 2.4-24 μm, a Promising Osteoimmunomodulatory Agent for Vascularized Bone Formation

Fluoride has essential effects on bone physiological activity and is widely used in bone biomaterials modification. However, this beneficial effect is highly related to the dose range and improper dosing can lead to pathological conditions such as fluorosis of bone. Therefore, this study first investigated the dose dependent effect of fluoride on bone regeneration. In the range of 0.24–240 μM, in vivo vascularized bone formation can be achieved via fine-tuning the fluoride concentration, and the peak osteogenic effect was found at 2.4–24 μM. The underlying mechanism is related to the modulation of the osteoimmune environment. Fluoride elicited significant osteoimmunomodulatory effect in modulation of the inflammatory cytokines and expression of osteogenic factors (BMP2, OSM, spermine/spermidine) and angiogenic factor (VEGF, IGF-1) during the early response. Fluorine with the doses of 2.4 and 24 μM could increase polyamines and IGF-1 production in macrophages, thus promoting osteogenesis of BMSCs and angiogenesis of HUVECs. These doses could also inhibit the inflammatory response of macrophages. In vitro osteogenesis and angiogenesis were both improved by the fluorine (2.4 and 24 μM)/macrophage conditioned medium, which is consistent with the in vivo results. These results collectively imply that fluoride is an effective osteoimmunomodulatory agent that can regulate both osteogenesis and angiogenesis. “Osteoimmune-smart” bone biomaterials can be developed via incorporating fluorine, and the release concentration should be controlled within the range of 2.4–24 μM for improved bone formation