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• Richard's equation can be extended to Bingham fluids using the concept of effective viscosity combined with the bundle-of-tube model. • Yield stress has a retarding effect on imbibition, but it can extend the quasi-steady regime on the test line for fan-shaped configuration. • The limiting value for stain growth of sessile droplets of blood in filter papers can be partly attributed to the blood's yield stress and partly to its viscoelasticity. The classic Richards equation is a good model for predicting imbibition of viscous fluids in porous materials such as dry soils or filter papers. It cannot, in principle, be used for physiological fluids such as blood simply because such fluids often exhibit a variety of non-Newtonian behavior such as a yield stress. In the present work, we have theoretically extended the classic Richards equation to viscoplastic fluids obeying the Bingham model using the concept of the effective viscosity together with the bundle-of-tube model. The new imbibition model could partly resolve the discrepancy reported in the literature between the predictions of the classic Richards equation for the stain growth of sessile blood droplets in a typical filter paper. A better fit, however, requires considering other non-Newtonian effects of the blood such as its viscoelasticity. Using the Bingham-modified Richards equation, it is demonstrated that yield stress in a test fluid has a retarding effect on the imbibition phenomenon, so that such fluids may not necessarily reach the test line of a paper-based diagnostic kit. But yield stress is predicted to extend the duration of the quasi-steady regime on the test line of diagnostic kits, which is a desirable effect. The results suggest that inducing (or elevating) the level of yield stress in a test liquid such as blood can be used as a passive means to control imbibition characteristics in paper-based systems. [ABSTRACT FROM AUTHOR]

In the decarbonized society based on the renewable sources, the carbon fiber papers (CFPs) are regarded as key porous materials for the electrochemical energy conversion and storage devices. Searching the optimum microstructure of assembled carbon fiber paper under compression is one of the central challenges in this uprising technology. Herein, we present a tomography-based analytical approach to correlate CFP microstructures and transport parameters under the compressed state. For the sake of artificial intelligence, the prediction accuracy on the pore and solid structures is dramatically improved up to 98 % consistency when compared with the analytical solution, by identifying the true shape of cylindrical carbon fibers. The three-dimensional U-net algorithm was incorporated into the conventional X-ray computed tomography, to gain a complete separation of carbon fiber and binder. Subsequently, the origin of two different microstructures in the through-plane direction, i.e. transitional surface region and core region, are investigated as a function of compression ratio (CR). Finally, the structure-property relationship of CFP is thoroughly evaluated over a wide range of the paper thicknesses, PTFE contents and CRs. We demonstrate that the microstructural three-dimensionality, which is one decisive factor determining the transport and electrochemical properties in energy devices, can be further analysed by exploring the formation factors of solid and pore structures with increasing CRs. The insights gained from this work not only enhance the fundamental understanding of CFP microstructures but also pave the way for optimizing the design and operation of next-generation energy devices, promising a more efficient and sustainable energy landscape. [Display omitted] • AI-based tomographic method is introduced for porous energy materials such as CFP. • Digital twins of compacted CFP distinguishing pore and solid structures is realized. • Origin of core/transition region is verified by varying thickness and PTFE contents. • Binder orientation affects in-plane gas permeability in CFPs under compression. • Formation factors converged to ε2–2.5 and ε3–4 under in-plane and through-plane directions. [ABSTRACT FROM AUTHOR]

[Display omitted] The design and synthesis of advanced electrodes with high conductivity and flexibility are the key to the development of wearable energy storage devices. Herein, a strategy for preparing conductive carbon paper electrode for flexible supercapacitors is reported by vacuum filtration of a mixture of biomass hierarchical porous carbon materials (HPC), cellulose nanofibers (CNFs) from polysaccharide cellulose of plant origin and silver nanowire (AgNWs), in which CNFs serve as substrates for dispersion and crosslinking of HPC. The prepared self-supporting electrode showed multi-scale pore structure and excellent conductivity (14.1 S cm−1). The electrode exhibited the highest specific capacitance of 383 F g−1 at 0.5 A g−1. Even after 10,000 charge and discharge cycles, 95 % of the original capacitance was remained, which means excellent cyclic stability. High strength and flexibility of the as-assembled flexible supercapacitor make the electrochemical performance of this device remain unchanged when bent at any angle. The present research delineates a simple and convenient method to prepare green, efficient and low-cost flexible supercapacitor. [ABSTRACT FROM AUTHOR]

Paper used in the printing industry generally contains a relatively thin porous coating covering a thicker fibrous base layer. The three-dimensional pore structure of coatings has a major effect on fluid flow patterns inside the paper medium. Understanding and quantifying the flow properties of thin coating layers is hence crucial. Pore spaces within the coating have an average size of about 180 nm. We used scanning electron microscopy combined with focused ion beam (FIB-SEM) to visualize the nano-scale pore structure of the paper coating layer. Post-processing of the FIB-SEM images allowed us to reconstruct the three-dimensional pore space of the coating. The 3D FIB-SEM images were analyzed in detail to obtain pore size distribution and porosity value. The permeability was estimated using the GeoDict software, based on solutions of the Stokes equation. By determining the porosity and permeability of increasingly larger domain sizes, we estimated the size of a representative elementary volume (REV) for the coating layer to be 60 µm 3 , which is well within the volume analyzed using FIB-SEM. The estimated porosity and permeability of the REV domain were 0.34 and 0.09 mDarcy, respectively. Using the pore morphology method, capillary pressure-saturation ( P c - S ) and relative permeability curves of the REV domain could be constructed next. The P c -S curves showed that the coating had a high air entry suction, which is very favorable for printing in that ink will invade the coating as soon as it is applied to the coating. Our results are essential for macroscale modelling of ink penetration into a coating layer during inkjet printing. Macroscopic models can be valuable tools for optimization of the penetration depth and the spreading of ink on and within paper substrates. [ABSTRACT FROM AUTHOR]

The transport properties of gas diffusion layer (GDL) in proton exchange membrane fuel cell are important parameters in fuel cell modelling, and one method to measure them is to simulate the transport of each species at spatial resolutions of a few microns in a microstructure of the GDL. One issue in this method is the size of the microstructure as using an unnecessarily big sample could substantially increase the computational cost. Both carbon-paper and carbon-cloth GDLs are investigated and their microstructures are obtained using numerical generation and X-ray micro-tomography respectively at a resolution of 1.733 µm. For each reconstructed GDL, we use the orthorhombic lattice Boltzmann model to simulate fluid flow through some subsamples taken from it in both the in-plane and the through-plane directions; the results show that the permeability of all subsamples is anisotropic in that their permeability in the in-plane direction is higher than in the through-plane direction. For each GDL, we compare its permeability calculated using samples of different sizes and find its representative elementary volume (REV) – a volume above which the calculated permeability represents the average ability of the GDL to conduct fluids. [ABSTRACT FROM AUTHOR]

Abstract: The carbon paper is synthesized by the simple, cheap and large-scale pyrolysis of filter paper and is used as an interlayer for Li–S battery. The as-prepared carbon paper is composed of carbon fiber with porous structure. The specific surface area is 534m2 g−1, and the average pore size is 4.1nm. The porosity of the as-prepared carbon paper lies in favor of the electrolyte permeating through the layer, which allows electrochemical reactions to occur. The prepared carbon paper is used as an interlayer between the cathode and the separator in Li–S battery and can significantly improve the electrochemical performance of the cell with reversible capacity, cycling ability, and rate capability. [Copyright &y& Elsevier]

Abstract: A commercially available GDL based on carbon paper or carbon cloth as a macroporous substrate was characterized by various physical and electrochemical measurements: mercury porosimetry, surface morphology analysis, contact angle measurement, water permeation measurement, polarization techniques, and ac-impedance spectroscopy. SGL 10BB based on carbon paper demonstrated dual pore size distribution and high water flow resistance owing to less permeable macroporous substrate, and more hydrophobic and compact microporous layer, as compared to ELAT-LT-1400W based on carbon cloth. The membrane-electrode-assembly fabricated using SGL 10BB showed an improved fuel cell performance when air was used as an oxidant. The ac-impedance response indicated that a microporous layer which has high volume of micropores and more hydrophobic property allows oxygen to readily diffuse towards the catalyst layer due to effective water removal from the catalyst layer to the gas flow channel. [ABSTRACT FROM AUTHOR]

Porous 3-D current collectors have been shown to be the primary choice in replacing classical 2D aluminum foil in applicable developments, especially those using carbon-based current collectors. In this study, we investigated the impact of using a non-woven carbon (NWC) based current collector for sulfur electrodes, in terms of performance and practical use in a commercial battery, keeping in mind the simplicity of electrode preparation method. The benefits of using NWC as a 3D current collector include high sulfur utilization for even highly loaded electrodes, lower polarization, and the provision of an efficient electrolyte reservoir. High discharge capacities up to ∼1200 mAh g −1 can be obtained at moderate C-rates, with relatively good capacity retention (<1% loss per cycle) and practical loadings as high as 8 mAh cm −2 . [ABSTRACT FROM AUTHOR]

The direct use of environmental paper waste (PW) to create spongy aerogel intended for oil absorption is an interesting green chemistry technique. The oil sorption response, on the other hand, is constrained by a poor oil sorption capacity and lack of stability. To address these concerns for the time being, silica aerogel is being used. Our goal is to use PW aerogel to replace silica aerogels. We made an environmental PW-based aerogel by dispersing PW, polyvinyl alcohol (PVA), and glutaraldehyde (GA). In terms of oil sorption the hybrid PW aerogel performs wonderfully. Notably, it displayed a significant absorption capacity towards various oils of approximately 49–110 times its own mass, dependent on the thickness and density of the oil and solvents within 15–35 s, 25 °C, and 2 × 2 cm dimensions. Additionally, owing to the high sponginess (99.95%), and less density (0.0114 g/cm3), tight bonding between PW and PVA occurs. As a results, the spongy aerogel has an oleophilic nature, superior mechanical power, and high thermal strength. The consistent fibrillar pore linkage gives a high surface to volume ratio, low surface energy, as well as high surface roughness, the aerogel undergoes minimal structural change after numerous recycles. All of these elements have a role in excessive oil absorption. [Display omitted] • A hybrid paper waste (PW) aerogel was created and used for oil absorption. • The homogeneous MTMS surface coating on aerogel has a 147.20o water contact angle. • Aerogel is a porous material (99.95%) with a network of connected fibrillar pores. • The absorption capability of 49–110 times its own mass towards various oils. • Aerogel has a remarkable stability up to 15 recycling reactions. [ABSTRACT FROM AUTHOR]

Abstract Paper cup composed of crude cellulose is a common waste in daily life. In this paper, hierarchical porous carbons have been successfully prepared by an initial hydrothermal treatment and subsequent activation route from abandoned paper cup, and then paper cup derived carbons are used as scaffolds to fabricate serial carbon/Se composites. The optimal composite presents unique 3D porous structure, with amorphous selenium uniformly confined into the micropores of carbon. As the cathode materials of Li-Se battery, this composite reveals an initial reversible discharge capacity of 517.2 mAh g−1 at 0.2C, and a capacity value of 431.9 mAh g−1 can be retained after 60 cycles. Even at a high rate of 4C, a capacity value of 295.8 mAh g−1 can be obtained. By comparison, the improved electrochemical performance of the optimal composite should be attributed to reasonable porous structure and effective encapsulation of amorphous selenium. Graphical abstract Image 1 Highlights • Synthesis of porous carbon/Se composite from abandoned paper cup. • Porous carbon/Se composite delivers a stable discharge capacity of 295.8 mAh/g at 4C. • The structure-function of different carbon/Se composites is studied. [ABSTRACT FROM AUTHOR]

Point-of-care testing (POCT) biosensors are rapidly developing in recent years because of the urgent needs for rapid test and home test. Among various types of POCT biosensors, paper-based biosensors have occupied large market share owing to the advantages of cost-effectiveness, portability and simplicity. To further meet the increasing requirement of POCT in various application scenes, the functionalization of paper is highly demanded. Metal-organic framework (MOF), a multifunctional porous material, is introduced in the design of paper-based biosensors, significantly improving the sensing property and application potential. This review provides a summary of the recent advances and emerging trends of MOF-functionalized paper-based biosensors (MOF@paper), including different types of substrates, fabrication methods, detection mechanisms and applications. On account of the multifunctionality and superior performance of MOF@paper biosensors, this field should possess promising prospect in scientific researches, translational medicine and clinical applications. • Multifunctional MOF endows paper-based biosensors with diverse detection properties. • The substrates and fabrication methods for MOF@paper biosensors are reviewed. • Various detection mechanisms are summarized and discussed. • MOF@paper biosensors are promising in diagnosis, food, environment and other related applications. [ABSTRACT FROM AUTHOR]

Predictive models for the transport of volatile organic compounds in paper need to consider the complex interplay of diffusion, adsorption, desorption, or chemical reactions. The relative importance of each of these processes is determined by the polarity of the volatile. Hence, it is challenging to pick a valid theoretical model that correctly predicts transport regardless of the polarity. Here, physics-informed neural networks (PINNs) assess which of five different models correctly describe transport of DMSO as polar and n-tetradecane as apolar model compound: (i) a pseudo first-order adsorption model for an irreversible sorption process, (ii) a first-order kinetics model allowing reversible sorption, (iii) a second-order model with a reversible process, and an effective diffusion model accounting for a constant (iv) and for a variable effective diffusivity (v). Each tested model is given as set of partial differential equations (PDE). Considering the model under testing and experimentally obtained spatially and temporally resolved concentration profiles through stacks of paper sheets, PINNs predict concentration of the volatiles and associated material constants such as sorption constants and effective diffusion coefficients by solving the inverse problem. Our PINNs revealed two models, pseudo first-order sorption and second-order reversible sorption, that correctly predict concentration profiles and polarity-driven differences in sorption times. While a PINN-based picking of valid transport models has important implications for the development of effective methods for controlling emission of volatiles from paper materials, PINNs represent a versatile mathematical tool to validate or refute the capability of PDE-based theoretical models to describe experimental data. • PINNs evaluate sorption kinetics in porous materials. • Focus: Transport of organic volatiles in cellulose. • Pseudo first-order model suits organic volatiles. • Predicting transport of volatiles through paper. [ABSTRACT FROM AUTHOR]

Abstract: Production of porous and light-weight bricks with reduced thermal conductivity and acceptable compressive strength is accomplished. Paper processing residues were used as an additive to an earthenware brick to produce the pores. SEM-EDS, XRD, XRF and TG-DTA analysis of the paper waste and brick raw material were performed. Mixtures containing brick raw materials and the paper waste were prepared at different proportions (up to 30wt%). The granulated powder mixtures were compressed in a hydraulic press, and the green bodies were dried before firing at 1100°C. Dilatometric behaviours, drying and firing shrinkages were investigated as well as the loss on ignition, bulk density, apparent porosity, water absorption and thermal conductivity values of the fired samples. Their mechanical and microstructural properties were also investigated. The results obtained showed that the use of paper processing residues decreased the fired density of the bricks down to 1.28g/cm3. Compressive strengths of the brick samples produced in this study were higher than that required by the standards. Thermal conductivity of the porous brick produced in this study (<0.4W/mK) showed more than 50% reduction compared to local brick of the same composition (0.8W/mK). Conversion of this product to a perforated brick may reduce its thermal conductivity to very low values. Successful preliminary tests were conducted on an industrial scale. [Copyright &y& Elsevier]

Abstract: In this paper, the disciplines of experimental research and computational science are conjoined with an objective geared towards an improved understanding of permeability in porous coatings. Three packing structures were considered, each one comprising a distribution with particles of similar shape. Models were built to mimic the experimental structures and then used for computational fluid dynamics (CFD) simulations as well as statistical analyses. Calculations of permeability are reported to within one order of magnitude of the experimental equivalents. A correlation is found to exist between statistical pore space disorder and the variation of permeability within the same packing microstructure. [Copyright &y& Elsevier]

Modeling morphological and hydraulic properties of thin porous media, such as filter layers and papers is highly relevant to various industries. In our previous studies, the X-ray tomography and FIB-SEM methods were applied to capture micro- and nano-scale pores in uncoated paper and coated layer, respectively. Here, the reconstructed pore structures were used to investigate two-phase water imbibition in these porous media. The obtained pore size distributions showed a log-normal probability density function. Such a distribution, together with concepts from critical path analysis and percolation theory, was applied to calculate relative permeability over a wide range of water saturations. Comparison with pore-scale numerical simulations showed the capability of this method to estimate water relative permeability for coated and uncoated papers. [ABSTRACT FROM AUTHOR]

Abstract: TiO2/carbon paper composite materials with a hierarchically porous structure were synthesized by employing a filter paper as the support material and carbon source. The resorcinol–formaldehyde–block copolymer nanocomposite formed by the self-assembly of phenolic resin and F127 under acidic condition was selected as modifier of the microstructure of carbon paper. Results show that the as-adjusted carbon paper preserved the nanostructure of a pure carbonized filter paper. An ordered mesostructure was also formed. This micromorphology resulted in the increased specific surface area, as well as micropore and mesopore volumes, compared with the pure carbonized filter paper. When mesoporous TiO2 was deposited on the carbon paper with ordered mesopore by the evaporation-induced self-assembly route, the TiO2/carbon paper composite materials displayed excellent adsorption property and enhanced photocatalytic activity of methylene blue. [Copyright &y& Elsevier]

Abstract: The effect of the microporous layer (MPL) and wet proofing on the MacMullin number has been evaluated for a custom series of Toray TGP-H-060 carbon paper gas diffusion layer (GDL). Complementary characterizations for these GDLs were performed by using scanning electron microscopy (SEM) images, pore size distribution (PSD) and fuel cell performance. The GDLs were customized by the addition of a microporous layer (MPL) and the treatment of, either or both, the substrate and MPL with 10% and 40% hydrophobic agent. SEM images correlated very well with the data shown for PSD. Distinction between the substrate layer and the MPL were clearly shown as two different slopes in the integral distribution and two different peaks in the differential distribution. The MacMullin number increased with increase in wet proofing but decreased with the addition of the MPL. The MacMullin number is a key parameter that contains the missing information for the path length in GDLs, which is generally approximated with the Bruggeman expression. The results provided an overview for the interpretation of the combined effect of the substrate and MPL properties as well as the cell operating conditions. [Copyright &y& Elsevier]

Abstract: In this paper, we present an experimental study on measurement of the thermal conductivity and heat pipe effect in both hydrophilic and hydrophobic (Toray TGP-H60) carbon papers (around 200μm thickness) with/out liquid water. An experimental setup is developed for measuring thermal conductance at different liquid water contents and temperatures without dissembling the testing device for water addition. Theoretical analysis is also performed to evaluate the apparent conductance of heat pipe effect. We found that liquid water presence inside these materials increases the overall thermal conductivity. At high temperature around 80°C, the heat pipe effect is evident for the hydrophilic paper; while for the hydrophobic one, the heat pipe effect is found to be smaller. The distinction is likely due to the different patterns of the capillary liquid flow in the two media. For the hydrophobic paper, liquid water flows back to the evaporation side when the breakthrough pressure is reached and flow is through preferred routes of small flow resistance. As a result, heat pipe effect is active only in part of the medium, therefore smaller than that in the hydrophilic one. The results are important for understanding the heat transfer phenomena occurring in porous media and effects of material surface property. [Copyright &y& Elsevier]

This study fabricated a portable, high-performance, and reagentless electrochemical devices using CO 2 laser-scribing process, which allowed localized carbonization of a non-conductive and low-cost polymer platform, i.e., phenolic-paper. The carbonized material was extensively characterized by Raman spectroscopy, XPS, XRD, SEM, and electrochemical impedance spectroscopy. The carbon-based electrodes were obtained from the photothermal process induced by CO 2 laser radiation and subsequently subjected to electrochemical treatment to fabricate a functional material with excellent conductivity and low charge-transfer resistance. Additionally, the laser-scribed electrodes presented a porous structure with graphene-like domains, thus indicating both potential for on-site electroanalytical applications and better performance than conventional carbon electrodes. Image 1 [ABSTRACT FROM AUTHOR]

Porous piezoelectric ceramics with an interconnecting pore network (3-3 piezoceramic-air-composites) are a compromising material for sensor applications. Using a biomorphous approach with pre-pyrolysed cellulose fiber paper as template for the impregnation process leads to a novel porous piezoelectric ceramic with a fiber microstructure and benefits on easy shaping of complex structures and high porosity (∼90 vol%). The templates were impregnated by a non-aqueous lead zirconate titanate (PZT) slurry (solid fracture of 52.3%). After residual slurry and binder removal and cellulose/carbon burn-out, sintering was carried out at 1150 °C. Microstructure and composition analyses were done by µCT (“Skyscan 1172”, Bruker), SEM (FESEM, Helios NanoLab 600i FIB Workstation, FEI) and X-ray diffraction measurements (Kristalloflex D500, Siemens AG) evaluation. Geometric density decreased by 30% compared to dense PZT (as reference) a porosity increased from 2.4% up to 86%. The piezoelectric properties as d 33 , relative permittivity and d 31 (measured by “Piezo-Meter PM 300″, Piezo Test) decreased up to 99%. [ABSTRACT FROM AUTHOR]

Electrical contact resistance (ECR) at the interface is of significant importance in many fields of science and engineering. Current methods for contact resistance estimation are based on the typical nearly incompressible rough surfaces, which is not suitable for porous material with large deformation in the compression process. The objective of this work is to build an analytical model for ECR between solid material and porous material, for example, which could be used to predict power loss between carbon fiber paper and bipolar plate in the fuel cell. First, mathematical description of solid roughness surface is built by classic Greenwood and Williamson model. Considering the porous structure, carbon fiber paper is modeled by multi-layer construction based on random line network model. Effect of large compression of carbon paper on contact behavior is furtherly given necessary attention in this study. Contact pressure and resistance are calculated based on statistical methods with consideration of multi-deformation states. Then, experiments are carried out to validate the numerical model. The results show good agreements with the numerical model. Finally, influences of carbon paper compression and main parameters are systematically discussed based on the numerical model. The model developed will enhance our understanding regarding the relation between contact pressure and contact resistance at the interface for solid material and fiber-structure material. [ABSTRACT FROM AUTHOR]

The medical field and public health rely on diagnostics carried out by sensors and laboratory testing methods. However, conducting laboratory tests is a demanding task, requiring both substantial equipment and the skilled touch of experienced operators. The microfluidic field has tackled this challenge over recent years. Paper microfluidic devices have become popular recently due to their testing speed, low cost, and accessibility. They are more suitable for field operations and developing regions with limited access to centralized healthcare centers and medical laboratories since they do not require external flow control instruments and are much cheaper to make when compared to conventional microfluidic chips. However, the majority of paper-based analytical devices tend to be qualitative or semi-quantitative; consequently, there is a significant need for paper-based quantitative transduction methods, given their expanding range of applications. Here, we introduce a novel microwave paper-based metamaterial-inspired transduction method that relies on dielectric sensing. Using paper as both the microfluidic channel and the resonator substrate hugely reduces the sensing device's costs, complexity, and environmental impact. We designed the metamaterial-based transducer using computational methods and demonstrated its fabrication and operation experimentally. Dielectric sensing of multiple analytes with different permittivities is demonstrated as a proof of concept. Although the device has a non-linear response curve in a wide range of permittivity change, the response can be assumed linear in the shorter spans. The results for permittivities lower than 30 show a 2.14 MHz/RPU sensitivity. This design is a prototype demonstrating the possibility of integrating a porous media microfluidic channel and paper-based microwave resonators. The linear sensing performance illustrated by the platform indicates its potential applications in the biosensing field. [Display omitted] • A novel paper-based metamaterial-inspired transducer is introduced. • Paper serves as microfluidic channel and substrate, reducing costs and eco impact. • This unique transduction method is a new type of quantitative analysis for μ PADs. • The linear sensing concept is demonstrated using various solutions. • This approach has implications for affordable quantitative μ PADs. [ABSTRACT FROM AUTHOR]

To effectively improve the power density and rate capability of layered double hydroxide (LDH) based supercapacitors, a hybrid supercapacitor (HSC) comprising of hierarchical ultrathin NiAl-LDH nanosheet arrays on carbon nanotube paper (CNP-LDH) is developed with porous graphene nanosheets as the negative electrode for the first time. SEM image shows that hierarchical NiAl LDH nanosheet arrays are assembled by numerous ultrathin nanosheets with thickness of a few to tens of nanometers. Remarkably, with an operating voltage of 1.6 V, the HSC possesses a high energy density of 50.0 Wh kg −1 at an average power density of 467 W kg −1 . Even at a fast discharging time of 3.9 s, a high energy density (23.3 Wh kg −1 ) could also be retained at a power density of 21.5 kW kg −1 . Moreover, the HSC exhibits cycling stability with a retention rate of 78% after 5000-cycle charge-discharge test at 5 A g −1 . The results inspire us to propose our high-performance CNP-LDH as a promising electrode for energy storage applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An ultrasensitive and highly flexible glucose biosensor is constructed. • Porous copper networks are integrated with a laser-scribed carbon paper substrate. • A wide linear glucose determination range from 1.0 μM to 7.96 mM. • An ultrahigh sensitivity, a fast response and ultra-low limit of detection. • Excellent flexibility, good accuracy and satisfactory specificity. Abstract Owing to the high specific surface area and easy accessability to targeting biomolecules, emerging non-noble-metal networks are developed as an ultra-active catalyst for molecular detection. In this work, a facile flexible enzyme-free glucose sensor with superior sensing performance has been successfully constructed by integrating laser-scribed carbon paper (LSCP) with copper network (CN). Remarkably, operation parameters are modeled and optimized by Central Composite Design (CCD) to obtain an optimal conductivity of 4.783 × 107 S·m−1 for CN. Due to the great electronic/ionic pathway between LSCP of ample active sites and CN of excellent conductivity, the disposable biosensor exhibits fast electron transfer kinetics. For glucose detection, LSCP/CN exhibits an excellent sensitivity of 3626.6 μA mM−1 cm−2, a wide linear range from 1 μM to 7.96 mM, an ultra-low detection limit of 30 nM (S/N = 3) as well as favorable reusability. Satisfactory anti-interference capacity to electro-active oxides and selectivity against carbohydrates studied for concentrations up to normal physiologic levels and higher concentrations are systematically investigated. The applications of glucose determination in human serum and perspiration samples are also successful, with recoveries of 100.8% (± 2.28%) and 92.1% (±3.61%), respectively. Experimentally, the current response of the LSCP/CN biosensor is resilient to mechanical deformation with less than 8% decay even after 1000 cycles of 1 mm repeated bending and 180° cyclical folding tests. As such, LSCP/CN can be applicable for flexible, attachable and potentially wearable biosensors to attain real-time physiological monitoring. [ABSTRACT FROM AUTHOR]

Abstract Al 2 O 3 /Cu-O composites were fabricated from the paper-derived alumina matrix infiltrated with a Cu-3.2 wt% O alloy. Paper-derived alumina preforms with an open porosity ranging from ∼ 14 to ∼ 25 vol% were prepared by sintering of alumina-loaded preceramic papers at 1600 °C for 4 h. Pressureless infiltration at 1320 °C for 4 h of the preforms with Cu–O alloy resulted in the nearly dense materials with good mechanical and electrical properties, e.g. fracture toughness up to 6 MPa m0.5, four-point-bending strength up to 342 MPa, Young's modulus up to 281 GPa and electrical conductivity up to 2 MS/m depending on the volume fraction of copper alloy in the composites. The technological capability of this approach was demonstrated using prototypes in various engineering fields fabricated by lamination, corrugating and Laminated Object Manufacturing (LOM) methods. [ABSTRACT FROM AUTHOR]

A paper-based channel is a useful platform for the facile development of analytical devices implementing various chemical or biological reactions. To improve the analytical performance for various applications, it was necessary to analyze the detailed mixing characteristics within a paper-based channel. In this paper, we proposed a mathematical model to predict a concentration field created as a result of the imbibition of multiple fluids within a porous material. Interestingly, we found that the model exhibited a constant interdiffusion width within a paper-based channel even though the flow front velocity decreased over time. We were able to verify that our model accurately predicted the concentration field by comparing the experimental and numerical results for mixing in a 2 inlet-channel. Finally, we designed and fabricated paper-based channels to generate two (linear and non-linear) concentration gradients based on predictions made by the model. Both the experimental and numerical results were in good agreement, demonstrating that our model was accurate and useful for developing a paper-based analytical device utilizing the mixing characteristics of a sample and reagent flow system. [ABSTRACT FROM AUTHOR]

Liquid spreading on solid surfaces and penetration into porous matrices (powders and coated papers) are investigated. The influence of chemical and structural heterogeneity on equilibrium and dynamic surface wetting is evaluated both experimentally and theoretically. Single capillary systems are used to identify the predominating mechanisms for acceleration, momentum, inertial and viscous liquid penetration. Different stages of vertical and horizontal penetration of liquids from non-limited, restricted (sessile drop) and cut-off sources into powders and papers are evaluated with reference to a range of frequently used models. For all types of liquid transport power-law exponents are used to relate all observations. The applicability of models from which the exponents are derived is discussed. Results are compared to theoretical predictions for liquid penetration. Models are of general validity, but the focus is placed on probe liquid spreading on and penetrating into coated and uncoated papers. This sets a particular challenge, since papers are heterogeneous layered composites of powder compacts on fibrous network. For the evaluation of models published results are supported by extended original results. [ABSTRACT FROM AUTHOR]

This paper presents a novel design and operation of microbial fuel cells (ΜFCs), which contain monolayer paper-based substrate/electrodes and microchannels with co-laminar flow. The electrodes with multi-wall carbon nanotubes are fabricated by the screen-printing method and the microchannels are patterned using photo-lithography. A double-inlet and diverging channel design is incorporated in the fuel cell configuration and demonstrated significantly improved performance. The fluid flows of electrolytes through the porous paper media are simulated using steady-state and transient computational fluid dynamics The best performance is achieved under the following conditions: an electroactive microbial (S. oneidensis) concentration of OD 600 1.5, 50 mM electron donor (lactate), and direct immobilized of the inoculum on the anode surface. The developed MFCs achieves a peak power density of 19.4 ± 0.23 μW cm−2 and maximum current density of 190.4 ± 1.39 μA cm−2, surpassing the performance of all previously reported paper-based single MFCs that utilize paper-based electrodes. In addition, hybrid-type MFCs that containing enzymatic air-breathing cathodes are investigated to enhance their performance. The novel paper based self-pumping MFC has the potential to make lab-on-a-chip type portable medical diagnosis devices with integrated power sources practical and feasible. [Display omitted] • A paper-based membraneless co-laminar flow microbial fuel cell was developed. • Microfluidic fuel cell was micromachined as a monolayer structure in paper substrate. • Co-laminar flow of the electrolyte through paper was simulated using CFD analysis. • Inoculation method, anolyte type, and cell configuration were tested and optimized. • A hybrid microbial-enzymatic fuel cell was also examined for performance improvement. [ABSTRACT FROM AUTHOR]

Abstract: Production of porous anorthite ceramics from mixtures of paper processing residues and three different clays are investigated. Suitability of three different clays such as enriched clay, commercial clay and fireclay for manufacturing of anorthite based lightweight refractory bricks was studied. Porous character to the ceramic was provided by addition of paper processing residues (PPR). Samples with 30–40wt% PPR fired at 1200–1400°C contained anorthite (CaO·Al2O3·2SiO2) as major phase and some minor secondary phases such as mullite (3Al2O3·2SiO2) or gehlenite (2CaO·Al2O3·SiO2), depending on the calcite to clay ratio. Anorthite formation for all clay types was quite successful in samples with 30–40wt% of paper residues fired at 1300°C. A higher firing temperature of 1400°C was needed for the fireclay added samples to produce a well sintered product with large pores. Gehlenite phase occurred mostly at lower temperatures and in samples containing higher amount of calcium (50wt% PPR). Compressive strength of compacted and fired pellets consisting of mainly anorthite ranged from 8 to 43MPa. [Copyright &y& Elsevier]

Highly porous cellulose beads of controllable sizes were successfully prepared from regenerated cellulose of printed paper wastes based on a facile dissolution and controlled precipitation approach. Pure and dispersed cellulose fibers were isolated from finely ground paper wastes by undergoing initial pretreatment and maceration processes in sodium hydroxide solution (NaOH, 12 wt%). Dispersed cellulose fibers were subsequently dissolved in an ionic liquid (1-allyl-3-methylimidozoium chloride, AMIMCl) to form a homogenous cellulose solution. Highly porous cellulose beads of controllable sizes within the range of 0.4–2.2 mm in diameter were prepared by precipitation in a coagulation bath of ultrapure water under controlled conditions. Cellulose beads of various mean sizes exhibited substantially different specific surface area which ranged between 107 m 2 /g and 498 m 2 /g. Cellulose beads of biocompatibility, high porosity and specific surface area are therefore potentially useful as drug delivery carriers. [ABSTRACT FROM AUTHOR]

Hydrophilic porous substrates, in particular paper, are now widely used for the fabrication of microfluidic devices. These materials are very attractive because of their low-cost and their ability to generate capillary flow. Such materials avoid the need of external pressure sources or syringe pumps. However, capillary flows wicking a hydrophilic fiber matrix experience non-specific adsorption and depend on environmental conditions such as humidity. In this article a novel fabrication method is proposed to create low-cost embossed-paper microfluidic devices allowing for spontaneous capillary flow. Thus, embossing is used to design hollow microfluidic channels and chambers on a waterproof and hydrophilic paper surface. Because the hollow-channels obtained are fiber-free, the issues of imbibition are avoided. Besides, the paper surface being hydrophilic, the capillary flow in the embossed device is spontaneous. Thus, such microfluidic devices provide an efficient support to perform diagnostics in resource-poor settings. In this work, it is shown that a colorimetric glucose detection can be achieved using embossed-paper channels. The detection is achieved in twelve minutes, either by naked eyes or by analyzing pictures taking with a smartphone camera for quantification. [ABSTRACT FROM AUTHOR]

A method for manufacturing durable superhydrophobic and superoleophilic filter paper for oil-water separation was developed via colloidal deposition. A porous film composed of PTFE nanoparticles was formed on filter paper, which was superhydrophobic with a water contact angle of 155.5° and superoleophilic with an oil contact angle of 0°. The obtained filter paper could separate a series of oil-water mixtures effectively with high separation efficiencies over 99%. Besides, the as-prepared filter paper kept stable superhydrophobicity and high separation efficiency even after 30 cycle times and could also work well under harsh environmental conditions like strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. Compared with other approaches for fabricating oil-water materials, this approach is able to fabricate full-scale durable and practical oil-water materials easily and economically. The as-prepared filter paper is a promising candidate for oil-water separation. [ABSTRACT FROM AUTHOR]

Since 2007, the world of microfluidics saw an emergence of a new era of low cost, simple, quick fabrication, abundantly available, and environmentally friendly microfluidic paper-based analytical devices (μPADs) capable of clinical diagnostics, food quality control as well as environmental monitoring. Although many fabrication techniques have evolved as a result of its broad application spectrum and ease of use, the technology has still barely scratched the surface of its potential in terms of its underlying fundamental principle, i.e., fluid flow analysis. In this study, we report the comparison of flow profile attained by using two of the most promising techniques of photolithography and wax printing from a hydrodynamic point of view. A modified protocol for synthesizing an epoxy based negative photoresist (SU-8) channel and wax-based channel was created by optimizing a few process parameters of our equipment. Water and oil (oleic acid) are selected as the hydrophilic and hydrophobic fluids, respectively, and their flow was analyzed in straight channels using a paper device. A new approach to vary the flow velocity is described in detail involving cylindrical dots as the resistance inside the paper channel. Observing the length-time curve for the two fluids, it becomes evident that both follow the Lucas–Washburn equation if the width of the channel is large enough. Various configurations of dots indicate that different longitudinal flow velocity implying its application in simultaneous addition of chemicals without the need to change the channel width or length. [ABSTRACT FROM AUTHOR]

We propose here a quick and easy procedure for preparing pencil leads doped with Ag and AgCl suitable for the reproducible and easy drawing on paper or other porous supports of carbon based Ag/AgCl conductive lines for the use as reference electrodes. They were prepared by careful electrodeposition of silver and silver chloride on carbon powder (conductive material) which was then mixed with sodium bentonite (binding agent) and sodium silicate (hardening agent). Extrusion at room temperature of these mixtures from a suitable die allowed thin rods to be obtained, which were then inserted in commercial lead holders to facilitate their use for drawing electrodes on paper. Their performance was evaluated by voltammetric measurements conducted by using hexacyanoferrate(II) and 1,2-hydroxybenzene as probe species known to display a reversible electrochemical behaviour. The results found pointed out that the potential exhibited by these drawn reference electrodes was fully reliable only when small but controlled amounts of chloride ions can be added to assayed samples, without interfering investigated processes. Conversely, a poorer reliability characterise these reference electrodes when chlorides cannot be added, in that they display potentials higher of about 100–150 mV than their theoretical value. Their reproducibility (± 0.02 V), controlled on a series of different PEDs wetted with the same sample, was however so narrow for voltammetric investigations as to make their use preferable to usual pseudo-reference electrodes whose potential is remarkably affected by the different components present in assayed samples. [ABSTRACT FROM AUTHOR]

The diverse physicochemical properties of polymers make them perfect candidates for developing biosensor elements when combined with porous substrates. For example, microfluidic channels, valves, reservoirs and biorecognition elements have been proposed that rely on filling the cavities of porous cellulose with different polymers. Yet, highly concentrated polymers are often too viscous to dispense them with precision using conventional printing methods. This increases the manufacturing variability, which degrades the performance of the biosensors. Here this issue is solved with a new method for infusing porous materials (filter paper) with concentrated polymers (PSS) that circumvents the dropwise addition of highly viscous reagents. The resulting films contain homogenously distributed polymers, which reduces the intra- and inter-batch variabilities of biosensors based on dispensing nanoparticles from the reservoirs. The proposed method was utilized to develop immunosensors for detecting the cytokines IL-6 and IL-5 in aerosols, which were trapped by the polypropylene layer of a surgical face mask (limit of detection 10−2 pg·mL−1). Using this approach, we were able to detect elevated levels of airways cytokines when exacerbated COPD patients and eosinophilic asthma patients wore the face mask for 30 min. The results shown here pave the way for upscaling the manufacturing of paper-based nanoparticle biosensors, which is a crucial step towards their future commercialization. [Display omitted] • Nanoparticle reservoirs are fabricated by infusing filter paper with polystyrene sulfonate • The proposed method reduces the intra- and inter-batch fabrication variability • Biosensors against IL-6 and IL-5 in aerosols are developed • Non-invasive detection of airways cytokines in patient samples is demonstrated [ABSTRACT FROM AUTHOR]

Abstract: Porous structure-tuned cellulose nanofiber paper separators (designated as S-CNP separators) are demonstrated as a promising alternative to commercial polyolefin separators for use in lithium-ion batteries. A new architectural strategy based on colloidal silica (SiO2) nanoparticle-assisted structural control is presented to overcome the difficulty in forming controllable porous structure of pure cellulose nanofiber paper separators (designated as CNP separators) from densely-packed cellulose nanofibers (CNFs). The new S-CNP separators proposed herein incorporate SiO2 nanoparticles as a CNF-disassembling agent (i.e., as non-conductive spacer particles). This structural uniqueness allows loose packing of CNFs, thereby facilitating the evolution of more porous structure. The unusual porous structure of S-CNP separators can be fine-tuned by varying SiO2 contents in the CNF suspension. Notably, the S-CNP separator (fabricated with 5 wt.% SiO2 content) exhibits the highest ionic conduction due to the well-balanced combination of nanoporous structure and separator thickness, thus contributing to excellent cell performance. This study underlines that the colloidal SiO2 nanoparticle-directed structural tuning of CNPs offers a promising route for the fabrication of advanced paper separators with optimized attributes and functionality. [Copyright &y& Elsevier]

Herein, porous WP 2 nanosheet arrays integrated on graphite paper (P-WP 2 NSs/GP) as 3D flexible cathode for electrocatalytic hydrogen evolution reaction (HER) are prepared by in situ phosphidation via vacuum encapsulation assisted by pulsed laser deposition technique. Compared to the electrode without pre-deposition process, the enhanced catalytic activities are attributed to the increased effective catalyst loading and the reinforced charge transport kinetics. The results make the present P-WP 2 NSs/GP as a promising cathode for energy conversion and paves a new way for designing and fabricating efficient electrodes toward HER. [ABSTRACT FROM AUTHOR]

Titania-based nanostructures and porous MnO 2 layer are deposited onto carbon fiber paper (CFP) conductive support using hydrothermal method. TiO 2 nanoparticles and leaf-like Na 2 Ti 3 O 7 nanosheets are synthesized through the hydrolysis of TiF 4 and post-treatment in NaOH aqueous solution. Electrochemical tests reveal that CFP@TiO 2 @MnO 2 has a better performance with areal specific capacitance of 744 mF cm −2 at 0.25 mA cm −2 , compared with that (600 mF cm −2 ) of CFP@Na 2 Ti 3 O 7 @MnO 2 . The possible mechanism is that TiO 2 has higher surface area and better electronic conductivity than those of Na 2 Ti 3 O 7 . However, the cycling performance of CFP@TiO 2 @MnO 2 is limited with capacitance retention of 17.7% after 1000 cycles while CFP@Na 2 Ti 3 O 7 @MnO 2 keeps this retention up to 59.9%. [ABSTRACT FROM AUTHOR]

Abstract: This thesis deals with SiC/Si honeycomb ceramics carrier, which was prepared by ordinary papers through series of techniques including sol–gel technology, processes of folding, pasting, bio-mimetic design, low-temperature carbonization, high-temperature reduction carbonization and Si-removing. The phase composition, microstructure and mechanical properties of this carrier were analysed by XRD, SEM, TEM, three-bending tests, and the results showed that after carbonizing the ceramic paper turned into amorphous carbon, and through silicon infiltrating in the vacuum environment, the phase was composed of β-SiC, Si, and C. The bending strength of SiC/Si honeycomb ceramics carrier is 200MPa. The more silicon removing time is, the porosity of porous SiC will be increased, while its strength and toughness will be decreased. [Copyright &y& Elsevier]

Abstract: Heat management is crucial to polymer electrolyte membrane (PEM) fuel cell commercialization. Numerical modeling is often used to simulate heat transfer in the various components of the cell and specifically the gas diffusion layer (GDL). Due to the porous nature of the gas diffusion layer and its complexity of anisotropy, the effect of the structure on the thermal conductivity is usually taken into account by introducing an effective thermal conductivity. In this study, the effective thermal conductivity of carbon paper diffusion media was estimated numerically. Carbon paper is often used as the GDL in PEM fuel cells due to its ability to efficiently transport electrons, heat and gaseous species. Using the GeoDict code, a realistic three-dimensional pore morphology of carbon paper was used as the modeling domain and the governing mathematical equations were solved using the commercial software package Fluent (6.3.26) and the ThermoDict solver. The geometrical effects on the effective thermal conductivity were investigated for different geometries. It was found that the effective thermal conductivity is highly sensitive to the geometry of the porous material under investigation. The effective thermal conductivity is much larger in the in-plane direction when compared with the value in the through-plane direction. Further, the change of the effective thermal conductivity due to porosity and compression was studied. Finally, correlations for the through-plane and in-plane effective thermal conductivity were developed. [Copyright &y& Elsevier]

Abstract: The catalytic activity towards the oxygen reduction reaction (ORR) of a novel material consisting of clusters of Pd nanoparticles directly deposited on porous carbon paper by electroless deposition, has been investigated in sulphuric acid medium. It is shown that this new material exhibits a very high electrocatalytic activity for the ORR, compared to the commercial carbon paper-supported Pt. [Copyright &y& Elsevier]

Regular monitoring of glucose and ketone contents in the body is vital for diabetic patients. Although estimation of the ketone content is necessary for proper healthcare monitoring, the research on the detection of ketone bodies is still nascent. Moreover, inaccurate eye-estimations and reliability are the key limitations of the widely used methodologies for estimating glucose in urine. Hence, simple procedures for fabricating reliable sensors are crucial for on-demand healthcare monitoring. Herein, we posit that a commercially available laser printer, without any added modifications, can be used to make paper-based sensors for colorimetric estimation of glucose and ketone in urine. We conducted a comprehensive experimental investigation to optimize the device designs for rapid estimation of the biomarkers. Also, for the first time, we present a detailed dynamic model of the flow-field in a variable cross-section paper device while considering the species transport and reaction kinetics within the porous media. Finally, we performed experiments with real urine samples to validate that our devices could detect results with zero false negatives. We believe that our present investigation and methodology can enable rapid and reliable fabrication of paper-based sensors for several fundamental studies and applications on affordable and non-invasive healthcare monitoring. [Display omitted] • A simple laser printer was used to make paper-based sensors for reliable estimation of glucose and ketone in urine. • A model was developed considering the variable channel area, the species transport and reaction kinetics in a paper device. • A desktop-based application was also developed for automatic estimation of the biomarkers in urine. • The methodology detected results with zero false negatives for complex real diseased samples. [ABSTRACT FROM AUTHOR]

It is still a challenge to control the structure and functionality of a porous material in a way that its properties can be changed by external triggers. To this end, the combination of porous paper substrates with redox-responsive ferrocene-containing polymer brushes is a promising approach. Here, surface-initiated Atom Transfer Radical Polymerization (SI-ATRP) protocols for a ferrocenyl methacrylate derivative, i.e. (2-(methacryloyloxy)ethyl ferrocenecarboxylate) (FcMA), were applied. The redox-responsiveness of the polymer-modified paper substrate was shown by chemical means and Kelvin probe force microscopy (KPFM), while X-ray photoelectron spectroscopy (XPS) revealed insights into the oxidation states of the ferrocene moieties. The control over the oxidation state enabled the precise control over the material's wettability as shown by contact angle (CA) measurements and capillary rise tests. Thus, these redox-mediated functional papers open a variety of applications for microfluidic devices. [ABSTRACT FROM AUTHOR]

In non-aqueous Li–O 2 batteries, relatively large amounts of discharge products are formed on air cathodes. As such, the expansion of air cathodes is a critical issue that remains to be solved. Here, we report the fabrication of highly porous free-standing graphene paper by introducing macropores within the paper using polystyrene colloidal particles as a sacrificial template. The as-prepared macroporous graphene paper (mp-GP) have a large Brunauer–Emmett–Teller (BET) surface area ( ca . 373 m 2 g −1 ), a large pore volume ( ca . 10.9 cm 3 g −1 ), and a high porosity (91.6%). Owing to the high surface area and large pore volume, the mp-GPs exhibit a high specific capacity of ca . 12,200 mAh g −1 at a current density of 200 mA g −1 , as well as good rate capability, when used as an air cathode in a non-aqueous Li–O 2 battery. Moreover, the mp-GP shows good stability up to 100 and 78 cycles at a current density of 500 mA g −1 and 2000 mA g −1 respectively, with a limiting capacity of 1000 mAh g −1 . It is found that formation and decomposition of the discharge product, Li 2 O 2 , occur within the macropores, and thus, the mp-GP maintains its original structure without considerable expansion during cycling. [ABSTRACT FROM AUTHOR]

Laser-induced graphene (LIG) is a foam-like porous material consisting of few-layer graphene obtained by laser irradiation of a wide range of carbon-containing substrates. Among these, the ability to synthesize LIG from paper and other cellulose-related materials is particularly exciting, as it opens the door to a wide assortment of potential applications in the form of low-cost, flexible, and biodegradable devices. Here, the synthesis of this material, dubbed paper-LIG , on different types of filter papers and xylan biopolymer is discussed. In particular, we report the formation of paper-LIG by single-step irradiation, providing an improvement over the conventional multiple lasing approach and giving an explanation of the conditions that allow this simplified synthesis. All the relevant process parameters are covered, assessing their effect on the resulting electrical properties, structure, and morphology. Additionally, we demonstrate the application of LIG obtained from xylan, an abundant and often underutilized biopolymer, for temperature sensing. These results provide a better understanding of the conditions required for the synthesis of highly conductive LIG from paper and related materials, paving the way for its application, with reduced cost and low environmental impact, in fields ranging from biomonitoring to consumer electronics. [Display omitted] • Synthesis of laser-induced graphene from filter paper by a single irradiation step • Synthesis of laser-induced graphene by irradiation of filter paper containing activated charcoal • Laser-induced graphene from a xylan substrate, valorizing this underutilized natural product • Temperature sensor employing laser-induced graphene obtained from modified xylan [ABSTRACT FROM AUTHOR]

Electrostatic spinning (electrospinning) is a useful technique for producing ultrafine fibers with large specific surface areas and porous structures. Polyvinylidene fluoride (PVDF) is a chemically stable material with extraordinary properties. In this research, PVDF fiber membranes were produced directly on paper surfaces by electrospinning to protect brittle paper relics from environmental damage. Tensile strength and elongation tests for paper with and without the deposited PVDF membranes show that the PVDF fiber membranes can effectively protect paper under an externally applied force under both ambient and aging conditions. Water, insects, dust and mould can be isolated by the compact fiber structure while common gases can pass through freely to maintain a favorable environment for the paper relics. [ABSTRACT FROM AUTHOR]

This paper is a reply to the discussion by S.A. Walling and J.L. Provis on our papers “Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements” and “Enhancing the carbonation of MgO cement porous blocks through improved curing conditions”. Walling and Provis discuss the assignment of X-ray diffraction patterns, the use of acid digestion to quantify the degree of carbonation, the interpretation of thermal analysis data, and the stability of hydrated magnesium carbonates. In this reply, we confirm the conclusions made in the two papers based on the combined evidence of microstructural and mechanical performance results. [ABSTRACT FROM AUTHOR]

• A screen-printed sensor for direct measurement on concrete structures by filter paper. • The sensor is able to switch from corrosion probability evaluation to pH measurement. • The portable experimental setup was applied for on-site measurements in a museum. Reinforced concrete has been employed worldwide as a leading building material for public and private structures as well as in modern sculptural art. Although the unrivalled mechanical strength and modelling versatility of this material, several interrelated processes are responsible for its progressive degradation (e.g., carbonation, penetration of aging-promoting agents), decreasing its long-last durability and representing a risk for the public security or the cultural heritage. With the aim to tackle this issue, the present work reports a novel configuration of a screen-printed sensor, obtained by the combination of flexible and robust polyester support and wax-printed filter paper device for the direct application on the concrete surface. Our sensor consists of a polyester-printed three-electrochemical cell that allows dual measurements on reinforced concrete, namely (i) the evaluation of corrosion probability of the metallic reinforcements (which outperforms the half-cell potential standard method) and (ii) the employment of a pH-sensitive iridium oxide film for the measurement of the pH of concrete. The paper was used as a porous material capable of ensuring the electrochemical connection between the Ag/AgCl printed electrode and the concrete solid matrix, acting also as a protective envelope for the electrode. After the laboratory tests, which revealed the noteworthy performances of the sensors in distinguishing among different levels of corrosion as well as measuring the pH of concrete, the developed sensor was applied for on-site measurement at the Giacomo Manzù Museum (Ardea, Italy), demonstrating its suitability for the real application to cultural heritage conservation. Overall, this easy-to-handle and non-invasive diagnostic device provides an innovative analytical approach for the on-site and prompt multiparametric monitoring of the physico-chemical phenomena that endanger the long-lasting preservation of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

The fabrication process of anodic aluminium oxide (AAO) on a paper-based substrate is challenging because the use of a highly economical, conformable and ecological substrate. This process is based on a simple, cost-effective, self-ordering anodization of aluminium, which yields a vertically aligned and a highly ordered nanoporous structure. The manufacturing process on a flexible substrate with the use of phosphoric acid is described, and a capacitive sensor produced on this layer is investigated versus the humidity concentration and the frequency. The AAO morphology and the structure obtained were analysed, and the electrical properties of the sensing layer were investigated, using a 4192A LF network analyser in a climatic chamber. The surface conduction mechanism and the effect of humidity on the dielectric properties of a porous anodic aluminium oxide are discussed. [ABSTRACT FROM AUTHOR]