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Developing efficient and stable non-noble metal oxygen evolution reaction (OER) electrocatalysts for sustainable overall water-splitting is extremely desirable but still a great challenge. Herein, we developed a facile strategy to fabricate Co3O4–CoOOH heterostructure nanosheet arrays with oxygen vacancies grown on carbon paper (Co3O4–CoOOH/CP). Benefiting from the unique 3D architecture, large surface area, synergistic effects between Co3O4, CoOOH and oxygen vacancies, the obtained self-supporting Co3O4–CoOOH/CP presents excellent electrocatalytic OER activity (low overpotentials of 245 and 390 mV at 10 and 100 mA cm−2) and robust long-term stability in alkaline condition. The present strategy provides the opportunities for the future rational design and discovery of high-performance non-noble metal based electrocatalysts for advanced water oxidation and beyond.

By continuously varying the structure of graphene oxide paper (PRGP) using Joule heating annealing, we are able to tune its electrical conductivity (σ) and thermal diffusivity (α) in a very wide range: more than three orders of magnitude for σ (186–503009 S/m) and 10-fold for α (8.31 × 10−7 m2/s to 9.31 × 10−6 m2/s). Excellent coherency-linear relationship between σ and α is discovered although they are sustained by different carriers: electrons and phonons. Such coherency exists over two sections: σ > 2 × 104 S/m, and 103

Paper-based devices are always more gaining a relevant position in the field of sensors. The continuous demand for affordable, simple, sustainable, and portable devices, is making paper as the ideal basis towards the realization of analytical tools for the easy self-testing. In this work, we demonstrate, for the first time, the development of a disposable paper-based printed electroanalytical strip for reliable, rapid, and high-throughput detection of glutathione in blood. The detection is based on the thiol-disulfide exchange reaction, which produces a detectable compound easily oxidizable at a Prussian Blue/carbon black nanocomposite involving a favorable low-interference overpotential. This nanocomposite is mixed within a carbon-based conductive ink and successively screen-printed onto a wax-patterned filter paper. The employment of paper provides a reagent-free device, as a consequence of the reagents pre-loading within the testing area. After the experimental conditions have been optimized, glutathione has been detected up to 10 mM, with a detection limit of 60 μM, and a sensitivity of (0.102 ± 0.005) μA/mM. This sensor showed satisfactory repeatability (relative standard deviation equal to 10%, for detection of glutathione 1 mM), especially by considering the hand-made manufacturing process. The “real-world” applicability of this strip has been evaluated by quantifying blood glutathione at physiological levels and by recovery studies achieving satisfactory values.

A facile and feasible method for decoration of iron oxide (Fe3O4) submicron-sized particles on carbon paper at room temperature in a short time of 10 min is demonstrated in this work. The Fe3O4-particles decorated carbon papers were used as the negative electrode for an Fe-air rechargeable battery in both an alkaline aqueous solution system and an all-solid-state system. As for the all-solid-state Fe-air rechargeable battery, KOH-ZrO2 electrolyte powder developed by our group was used in the battery fabrication. In the alkaline aqueous solution based Fe-air rechargeable battery, a high initial discharge capacity of 460 mAh g−1(Fe) was achieved. Meanwhile, in the novel all-solid-state Fe-air rechargeable battery system, an initial discharge capacity of 70 mAh g−1(Fe) was obtained demonstrating the feasibility of this system that could be further developed towards a practical Fe-air rechargeable battery for portable and lightweight device application.

We introduce a facile and low-cost method for fabricating gold nanostructures on cellulose filter paper (CFP) to prepare a paper-based surface-enhanced Raman scattering (SERS) sensor for label-free molecular detection. Polymerized dopamine (PD) was used as an adhesive layer on the CFP and simultaneously functioned as a reducing agent for gold nanoparticle (AuNP) nucleation. The size of the AuNPs was dependent on the pH of the gold precursor solution, and nanoparticles with an average size of 102 nm were formed on the PD-coated CFP at a pH 3, exhibiting high SERS activity. Finite-difference time-domain (FDTD) simulations of the electromagnetic field enhancement of AuNPs with different sizes and interparticle distances were performed to identify the origin of the SERS effect. The developed paper-based SERS substrate showed uniform and excellent molecular sensitivity with a limit of detection (LOD) of 10−7 M for methylene blue, as measured by a portable Raman spectrometer. Furthermore, as a field application test, surfaces of apples were pretreated with diquat (DQ) and paraquat (PQ) pesticides, which were then detected down to a concentration of 1 ppm after simple attachment of the sensor on the apple peels and performing a SERS measurement. The developed paper-based SERS sensor is expected to be applicable as a label-free sensor for a variety of chemical and biological molecules.

Nano-dielectrics, which were discovered more than 20 years ago, were once considered as promising insulators. Adding or hybridizing inorganic oxides into polymer matrices inevitably results in poor compatibility between multiphase materials and thus results in limited breakdown strength improvement (generally lower than 20%). Therefore, we bypassed the traditional nano-doping method and proposed the direct construction of matrix materials on nanostructures, that is, a ceramic fiber-porous silica composite insulating paper. The breakdown strength of prepared dielectric was remarkably improved by 120.5%. To the best of our knowledge, such a high improvement in electrical performance has not been reported in previous studies.

A simple process of commercial paper functionalisation via in situ polymerisation of conductive polymers onto cellulose fibres was investigated and applied as electrodes in paper-based batteries. The functionalisation involved polypyrrole (PPy) and Poly (3,4-ethylenedioxythiophene) (PEDOT) as conductive polymers with the process of functionalisation optimised for each polymer individually with respect to oxidant-to-monomer ratios and polymerisation times and temperature. Paper with conductivity values of 44 mS/cm was obtained by exposing the samples to pyrrole vapour for a period of 30 min at room temperature; however, polymerisation at temperatures of 40 °C lead to higher conductivity values to up 141 mS/cm. Consequently, functionalised PPy and PEDOT papers were applied as cathodes in batteries with Al foil anodes and commercial paper soaked in an electrolyte solution of NaCl.

In this study, fabrication of microfluidic paper based analytical devices (μPADs) by microembossing was proposed. Different from the embossing methods described in the literature, the filter paper was embossed such that a protruded structure was formed, which subsequently became the channel after heating the wax at the backside of the filter paper. It was found that, when using the Whatman No. 3 filter paper, the embossing pressure needed to be larger than 50 kg/cm2 in conjunction with using a minimal 2-mm wide channel, and the wax heating time ranged from 15 to 45 s in order to obtain a reliable μPAD with repetitive and consistent results. In addition, there was no need of a hydrophobic material as the backside support. The glucose detection was demonstrated using the μPADs as fabricated and a linear relationship was obtained between 5 and 50 mM glucose concentrations. With the proposed method, the processing time of fabricating μPADs can be reduced within approximately 1 min.

Disposable ion-selective electrodes of high reproducibility of recorded potentials between different sensors have been prepared using carbon-nanotubes modified paper as the transducer and electrical lead, and a poly(vinyl chloride) ion-selective membrane. The conducting paper was obtained using carboxymethylcellulose stabilized carbon nanotubes suspension – combination found to result in high stability of conventional sensors. It was shown for the first time that change of the amount of conducting material used to prepare sensor, from conventional (where it is used as transducer) to disposable sensors (where it is used as transducer and electrical lead), requiring application of much higher amount of carbon nanotubes significantly affects performance of the sensors. Presence of ions in the suspension used results in occurrence of super-Nernstian range on the potentiometric calibration curve of potassium-selective sensor, below 10−5 M KCl. Highly reproducible potential values, between sensors as well as between different calibrations, were achieved introducing mixture of cobalt(II) porphyrin/cobalt(III) corrole to the carbon nanotubes layer, at the back side of the membrane. Presence of porphyrinoids not only stabilizes potential values obtained for the sensors but also tailors ion transport through the membrane, resulting in stable potential of the sensors, although a super-Nernstian region is present on the calibration line.

A recent commentary by Santhosh and Ravindran on our paper (Int. J. Hydrogen Energy 2014, 39:10606) demonstrated that the interaction between H2 and MXene (Sc2C and Ti2C) phases are not Kubas-type and should be of weak physisorption, and thus made a conclusion that 2D Sc2C and Ti2C are not suitable for practical hydrogen storage applications. In this responses, we recalculated hydrogen adsorption on 2D Sc2C and Ti2C by using different exchange-correlation functionals. And based on the calculated results, bare MXenes (especially the Ti2C) are suitable as hydrogen storage materials at temperatures of several tens degrees lower than room temperature. And the hydrogen adsorptions on the MXenes terminated with oxygen group were also investigated. Among the Ti2C, Sc2C and their oxygen-functional counterparts, the binding energy of H2 on Sc2CO2 surface is the closest to the ideal range of 0.16–0.42 eV/H2 at ambient conditions, and thus the Sc2C with oxygen group is expected to be more suitable as hydrogen storage materials.

A paper-based pressure sensor constructed by sandwiching a piezoresistive film between two pieces of paper substrates with silver electrodes is reported in this work. The resulting devices exhibited rapid response and recovery speed, and the response and recovery times were 0.6 s and 0.2 s, respectively, under a pressure of approximately 1.5 kPa. In addition, the device can be especially sensitive to pressures less than 3 kPa. Finally, the devices were used to monitor physiological signals, including the motions of fingers, vocal cord vibration and wrist pulse. The advantages of paper-based devices, such as low cost, portability and flexibility, will have great potential for expanding the application of resultant sensors in wearable medical devices.

There is a high interest in nanomaterials that effectively deactivate different types of bacteria and provide alternatives to chemical substances and antibiotics. This research is reporting the antibacterial performance in contaminated water of flexible structures consisting of thin metallic films deposited on water filter paper. Coatings were performed at low temperatures using high vacuum direct current (DC) magnetron sputtering deposition. The effectiveness of different metallic nanoparticles in functionalizing the fibrous surfaces and deactivating bacteria from water was tested during the experiment. The surface morphology of coated filter paper was characterized using digital optical microscopy and scanning electron microscopy (SEM). The fibrous substrates provided large area of exposure for metals to bacteria. X-ray diffraction and Energy Dispersive X-ray Spectrometer (EDS) were used to identify the chemical composition of the structures. The antibacterial performance was evaluated against Escherichia coli (E-coli) and total coliforms using the standardized membrane filtering technique for water and wastewater examination. Silver and copper effectively deactivate coliforms from water with copper providing higher performance. The antibacterial effect of copper and silver coatings with different thicknesses as well as the nanolayered combination of the two metals was also investigated. It was observed that coatings remained adherent to substrates and the antibacterial performance was maintained over consecutive exposures.

Free-standing hierarchical polyaniline/graphene/MnO2 (PANI/G/MnO2) paper is well constructed using low-cost printing paper by a simple layer-by-layer in situ growth and vacuum filtration method. The PANI nanofiber was polymerized on cellulose fibers, and then the pristine graphene sheet was introduced to generate the polyaniline/graphene paper, whose surface was subsequently scattered with the formed MnO2 nanoflowers through oxidation of the cellulose fiber and graphene. The PANI/G/MnO2 paper possessing a mass loading of 11.75 mg cm−2 is of high flexibility and could serve as a working electrode without using any binder and conductive additives. The electrode shows a sizeable areal capacitance of 3.5 F cm-2 at 5 mA cm−2 and excellent cycling stability of 90% after 1000 bending cycles. All-solid-state supercapacitor assembled with the PANI/G/MnO2 paper exhibits a high energy density of 5.2 mW h cm-3 at 8.4 mW cm-3. Eight supercapacitors connected in series can light a green light-emitting diode of 3 V.

A novel visual and fluorometric-sensor paper is prepared for the monitoring of atmospheric humidity and ethanol. The paper contains a combination of copper nanoclusters (CuNCs) and carbon dots (CDs), immobilized on a filter paper. This makes it a dual-emission system. The visual sensor shows bright fluorescence and has a diameter of ∼8 cm with uniform and homogeneous surface. The detection mechanism of the sensing paper is based on the fluorescence intensity variation of CuNCs in different environments. Desirable linear relationship is observed between fluorescence intensity ratio (red/blue) and humidity. Visible color transformation of this sensor paper is observed in the humidity range ∼40-80%, implying utility for easy and facile atmospheric humidity determination. Furthermore, due to the water and ethanol have different impacts on the spectrum, this paper-based fluorescent probe shows excellent response to ethanol. Therefore dual-emitting sensing paper, when suitably calibrated, shows promise for visual and fluorometric sensing platforms aimed at humidity or ethanol detection.

L -dopa is a chiral drug that has been extensively used for the treatment of Parkinson’s disease. The concentration of L -dopa plays a vital role in the treatment, and this work emphasizes on designing a versatile platform for the quantitative and selective detection of L -dopa using reduced graphene quantum dot (rGQD). The platform is efficient in three different sensing methods, viz. fluorescence turn-on, filter paper-based sensing, and electronic measurements. The rGQD undergoes a dramatic fluorescence turn-on in the presence of L -dopa in aqueous media and artificial urine with a detection limit as low as 1.307 µM and 1.217 µM respectively. Experimental evidence revealed that the fluorescence enhancement is attributed to aggregation-induced emission mechanism. The system is also applicable for visual detection of L -dopa using filter paper strips treated with rGQD and develops bright fluorescence under ultra-violet irradiation. Apart from this, electrical sensors for L -dopa were also developed by preparing rGQD treated poly-vinyl alcohol films, and the increase in the current conduction with varying concentrations of L -dopa was observed. The films produce 2.5 order higher current conduction at 300 μM of L -dopa with a detection limit of about 13.136 µM. At the final stage, we have designed flexible electronic devices using these materials that develop 1.3 order higher current for L -dopa. The devices exhibit excellent air stability under varied relative humidity conditions as well as high bending stability for potential practical applications.

Microfluidic paper based microbial fuel cells (μP-MFCs) have gained considerable popularity due to their compact, quick and low-cost fluid manipulation paradigm. Compared to conventional technologies, paper as a substrate with advanced nanomaterial electrode material has many distinct advantages from point-of-care monitoring to energy harvesting. As a result, these have been used and are more popular in a variety of fields, such as health diagnostics, environmental and food quality management. By this encouragement, herein a portable microbial fuel cell as an origami array has been demonstrated using custom carbon electrodes with a modified the transition metal oxide MnO2 nanomaterial. This customized electrode design was first printed using a tabletop PCB inkjet printer where the anode was further modified with synthesized MnO2 nanoparticles. The entire cell was formed by folding the paper along predefined edges where the fuel, Shewanella putrefaciens, was streamed continuously via inherent capillary cation. Various studies, such as morphological, surface catalyst coating, amount loading and volumetric culture optimization experiments, have also been accomplished to find the most appropriate optimum parameter to enhance power conversion efficiency. The developed origami arrayed microbial fuel generated an open-circuit potential (OCP) for two parallel connected MFCs of 0.534 V and a maximum power density of 15.9 μW/cm2 with a maximum current density of 130 μA/cm2. In the end, the harvested power was used by powering the digital watch circuit through the ultra-low DC-DC booster board. Such an MFC origami array, with simple electrode manufacturing and modification process, has a great potential and bright future in Internet of Things (IoT) applications by making multiple stacks where the data can be monitored.

Zn/Ce redox flow battery (ZRFB) is emerging as a promising technology to store large amount of energy economically and efficiently, wherein a highly efficient positive electrode with a continuous and fast electronic and ionic transportation path is urgently desired. The unique nanostructure of reduced graphene oxide (RGO) paper electrode is prepared by a simply chemical reduction method, which facilitates transference of the electron and Ce3+/Ce4+ at the electrolyte/electrode interface. Thus ZRFB exhibits superior extent of charge (81.0%) and energy efficiency (71.3%). The results show RGO paper is a good candidate for positive electrode of ZRFB.

Paper-based friction materials contain a variety of inorganic and organic materials, and organosilicon can be well linked with organic and inorganic compounds due to its inorganic and organic functional groups. Therefore, in this work, paper-based friction materials with different organosilicon contents were obtained by the pre-dipping the preform. The results displayed that adding a small amount of organosilicon to the paper-based friction materials could increase the coefficient of static friction, but also reduced the coefficient of dynamic friction and wear rate of the paper-based friction materials. When the content of organosilicon in the materials was more than 5 wt%, the wear rate of the materials tended to be stable. And the paper-based friction materials with 7.5 wt% organosilicon content had the highest coefficient of static friction. By testing the variation of the coefficient of friction, it was found that the materials with 7.5 wt% organosilicon content had the best stability.

Since hydrophobicity can improve the usability and functionality of materials in humid condition, enhancing the hydrophobic behavior of starch films or papers is of importance. In this work, ZnO nanoparticles (NPs) were introduced into the starch solution under ultrasonic and magnetic-stirring, followed by cast filming and paper coating. The contact angles of resulting film and coated paper containing 2% (wt) NPs were increased from 85.73° to 121.45°, 64.47° to 103.94°, respectively. The results from comprehensive characterizations confirmed the hierarchical structure created by ZnO nanoparticles on the surface of starch film as well as the formation of intact layers on coated paper. The excellent miscibility between starch and ZnO NPs was also achieved. The approach developed is promising and facilitates the hydrophobic modification of green-based materials.

Signal amplification in colorimetric biosensors usually requires labile reagents and/or additional steps, which are not ideal for in-field measurements. Here we show that the limit of detection of a gold nanoparticle-labeled colorimetric immunosensor can be decreased 10-fold by performing the assay on a folded piece of paper. In this approach, the intrinsic porosity of the substrate enables generating multiple signals with a single drop of reagent. This yields combined signals with higher optical density thanks to the semitransparent nature of the wet material. It will be shown that this method can decrease the limit of detection 10 times in a model immunosensor for the detection of immunoglobulins. The procedure is so straightforward that it could be easily implemented to decrease the limit of detection of microfluidic paper-based analytical devices with colorimetric readouts.

Developing high-performance electrode is crucial to energy storage performance of vanadium redox battery. Herein, TiO 2 decorated carbon paper was developed by hydrothermal route with various treatment time, and employed as negative electrode for vanadium redox battery. TiO 2 can be in situ covered on carbon paper by hydrothermal route. Wetting performance of carbon paper is markedly enhanced by introduction of TiO 2 . Compared with raw carbon paper, TiO 2 decorated carbon paper demonstrates excellent electrochemical performance towards V 3+ /V 2+ couple. The sample treated for 6 h (CP-H06) exhibits the best electrochemical properties. The enhanced performance comes from the accelerated transfer of vanadium ions and electrons. The single cell testing indicates that the cell performances are improved significantly by using CP-H06 as negative electrode in terms of increased discharge capacity and energy efficiency. Discharge capacity and energy efficiency increase by 17.8% and 6.4% by using CP-H06 at 100 mA cm −2 , respectively. Our study reveals that TiO 2 decorated carbon paper with outstanding electrochemical performance exhibits a promising prospect in the energy storage system of vanadium redox battery.

We proposed a new type of freestanding Catalase (EC 1.11.1.6) (Cat) modified paper electrode based on Fe3O4 crystals decorated freestanding reduced graphene oxide (rGO) paper (Cat-Fe3O4/rGO) using a facile electrodeposition method. This enzyme modified paper electrode was used for the specific determination of hydrogen peroxide (H2O2). Structural, chemical, and morphological characterization of the Fe3O4 crystals formed on rGO paper was investigated by (i) using scanning electron microscopy (SEM), (ii) energy-dispersive X-ray spectroscopy (EDS), (iii) X-ray photoelectron spectroscopy (XPS), (iv) X-ray diffraction spectroscopy (XRD), (v) Raman spectroscopy, (vi) electrochemical impedance spectroscopy (EIS) and (vii) cyclic voltammetry (CV) techniques. The Cat enzyme was successfully adsorbed on the Fe3O4 nanocrystals surface which was demonstrated by fluorescence microscopy. The Cat-Fe3O4/rGO paper electrode showed excellent electrocatalytic activity toward H2O2. It is found that Cat-Fe3O4/rGO paper electrode shows a wide linear range, high sensitivity, and a low detection limit for H2O2 detection.

In this study, a facile method was applied to modify the hydrophobicity of filter paper, and the application of the filter paper in water-oil separation was investigated. The modification was accomplished by immersing the filter paper into the modifier solution containing poly(methylhydrosiloxane) (PMHS) for only 2 min at room temperature. PMHS was found to be covalently grafted onto the surface of filter paper. After PMHS modification, the hydrophobicity of filter paper was significantly improved, as indicated by the increase of the water contact angle from 19.0° to 131.8°. Because PMHS has very low surface energy, after modification, the wettability of filter paper was transformed from hydrophilic to very hydrophobic and subsequently to oleophilic; therefore, the modified filter paper presented excellent performance in water-oil separation. The separation efficiency of diesel and n-hexane from water was more than 94.3% and 80.0%, respectively. This method is simple and based on commercially available materials; moreover, it can be applied to the hydrophobic modification of not only filter paper but also any materials containing hydroxyl groups.

Control over the mechanical properties of cellulose-based artifacts (e.g. paper) is highly important in cultural heritage science. Especially, a non-aqueous method that does not cause swelling but can be applied to either single paper sheets or bound cellulose items (e.g., books) without any preselection is currently needed. Herein, we present a new multilayer deposition method that can simultaneously deposit alkaline reserve and improve the mechanical properties of historic wood pulp (HWP) paper, which often suffers from high fragility and brittleness. Alkaline nanoparticles (magnesium hydroxide Mg(OH) 2 NPs) stabilized by hydrophobic cellulose derivative i.e., trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane (HMDSO) are prepared and deposited in the form of multiple layers on HWP paper by a technically effortless dip coating procedure. An enhanced and irreversible deposition of Mg(OH)2 NPs–TMSC and an alkaline reserve (AR) up to 4% (139 meq[OH − ]/100g) are achieved as revealed by infrared spectroscopy and back-titration measurement. The tensile strength of uncoated HWP paper (1.6 MPa) is increased to 5.5 MPa after coating with Mg(OH) 2 NPs/TMSC (before aging) and then to ca 9 MP (after accelerated aging). In the latter case, the TMSC is transformed to cellulose by cleaving of O–Si bonds. The surfaces are evenly covered with thin and transparent coatings of hydrophobized nanoparticles as demonstrated by electron scanning microscopy and contact angle measurements.

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.

The oil pollution is an increasing threat to nature and human health. Therefore, effective separation of oil from the oily wastewater is a challenging task. Through the nonsolvent vapor method, a superhydrophobic paper can be self-assembled by dropping the conjugated poly-p-phenylenes solution on the commercial filter paper in a nonsolvent vapor atmosphere. The numerous nano-mircostructral particles composed of polymer nanowires covered on the filter paper, just like the morphology of lotus leaves, lead to the excellent superhydrophobic effect. Moreover, the polymer-coated filter paper not only exhibits good mechanical stability, long-term durability, self-cleaning, but also has superhydrophobicity and superoleophilicity. The as-prepared paper possess remarkable oil/water separation ability for a variety of oil/water mixtures, including bromoethane, hexane, cyclohexane, petroleum ether, gasoline, dodecane, and the mixed oil of gasoline and diesel, demonstrating that it can be a good candidate for the treatment of industrial oil-polluted water.

In analytical science, it is always of great scientific and practical significances to explore convenient, rapid, and reliable methods/devices to trace the H2O2 level in various matrices. Herein, we fabricated a ready-to-use paper-based chemosensor by using mesoporous carbon-dispersed Pd nanoparticles (Pd NPs/meso-C) as a promising peroxidase mimic for the visual determination of H2O2. Thanks to the large exposed surface of the meso-C support and the highly dispersed active Pd NPs, the synthesized Pd NPs/meso-C exhibited favorable catalytic performance to trigger the chromogenic reaction of colorless TMB to blue TMBox mediated by H2O2, providing a Kcat of 326.67 s−1 for H2O2 and 0.55 s−1 for TMB, larger than the bare Pd NPs and even comparable to the activity of natural horse radish peroxidase. As demonstrated, this principle could be employed to colorimetrically detect H2O2 in the linear scope of 5–300 μM. By simply immobilizing the Pd NPs/meso-C mimic and the TMB substrate onto a common filter paper, ready-to-use paper-based sensors were further prepared. By combining these test strips with a smartphone and an easy-to-access color-scanning APP together, the integrated platform could be used for the quantitative analysis of H2O2 with advantages of simple operation, fast response, low cost, and good selectivity and repeatability. Furthermore, reliable sensing of the target in milk matrices suggested great promise of the integrated platform in practical applications.

Cost-effective, simple and flexible hydrogen gas sensors operating at room temperature were demonstrated based on DC magnetron sputtered palladium thin films. The main idea is to use commercial microfiber filtration paper as a cheap, fibrous and flexible substrate for palladium. With this objective, Pd thin films with 21, 38 and 54 nm thicknesses were deposited and characterized by grazing incident X-ray diffraction (GIXRD) and scanning electron microscope (SEM). The gas sensing behavior was tested by hydrogen gas in the concentration rang of 0.5–10%. GIXRD showed a PdX/Pd phase and SEM revealed existing of many structural nanocracks. An activation process was needed where sensors were heated up to 110 °C in the presence of 10% H2. Then a desirable hydrogen sensitivity with good stability based on hydrogen induced lattice expansion (HILE) effect in which conductance increases was observed. However, for low Pd thicknesses (21 and 38 nm) and at below 4% H2, an inverse effect was observed in which the conductance decreased instead of increasing. For all samples the response time is incremental in the range of 0.5–4% and declining for 4–10%. Moreover, the deposited Pd sensors operate well when they are bent inward or outward. The governed physical mechanism was expressed and discussed.

Here we report the construction of CoFe2O4 coating on carbon fiber and the coated paper was used as the interlayer between the separator and cathode of Li-S batteries. The amorphous CoFe2O4 coating was deposited by the industry-oriented spray pyrolysis technique and carbon fiber was completely enwrapped by the coating. Compared to the non-coated carbon fiber, the coated carbon fiber as the interlayer exhibits a superior reversible capacity of 1086 mA h g−1 at moderate current of 0.1C and a low decay rate in the capacity of 0.043% per cycle after 1000 cycles at 1C. Excellent long-term cycling life and rate capacity were also achieved through the coated interlayer. The specially designed interlayer showed remarkable capability to trap effectively the intermediate LPS (lithium polysulfide). The significantly inhibited “shuttle effect” of LPS would give insight into designing and making the interlayer by using new coating materials for enhanced performances of the Li-S batteries.

A simple, low cost, and lightweight three-dimensional (3D) primary alkaline Zn/Fe3O4 origami-battery fabricated from Whatman 1 paper was developed. The battery was created using printed wax to define the hydrophobic and hydrophilic barriers and active electrocatalytic materials for fabricating the electrodes. The boat-shaped 3D-battery consisted of two screen-printed Zn/Fe3O4 batteries connected in series that were activated with a small volume of aqueous KOH solution. The metallic electrodes were first characterized outside the folded battery using electrochemical techniques. Subsequently, the electrodes and separator were assembled together in a triangle-shaped battery resembling the main structure of the boat-shaped 3D-device and this triangle-shaped battery was further optimized. The addition of water triggered the activation of the 3D battery delivering a maximum current and power of 7 mA and 3 mW, respectively. The 3D-Zn/Fe3O4-battery displayed an OCP of 2.2 V and a maximum current and power of 22 mA and 7.5 mW, respectively, in the presence of 6 M KOH electrolyte. These results demonstrate the potential of 3D origami-based structures and Zn/Fe3O4 batteries as an alternative low cost energy source to power portable devices.

Filter paper (FP) with superhydrophobicity and high water adhesion was prepared by adsorption and simple immersion process. The surface morphologies displayed the micro-nano structure of FP. The surfaces composition was investigated by Fourier transform IR, X-ray photoelectron spectrum and X-ray diffractometer. The superhydrophobic surfaces with a water contact angle of 153° benefited from the Fe(OH)3 nanostructure formed on FP and subsequent stearic acid (STA) modification. The as-prepared superhydrophobic surfaces could firmly pin the water droplet even when the surfaces turned upside down. The wettability properties of the FP surfaces could be repaired by immersing the damaged samples into the solution again.

Sandwich-type hybrid structure consisting of etched nitrogen-doped graphene paper (ENGP) and flower-like MnO2 are fabricated through a three-step method. The ENGP were synthesized by vacuum assisted flow-filtration of the dicyandiamide (DCD) and graphene oxide (GO) aqueous solution through filter membrane, followed by a carbonization process, and then by an electrochemical etching method to improve the surface active-sites and wettability. The MnO2 nanoflowers consisting of multiple thin MnO2 nanosheets were anchored on both side of ENGP by electrodeposition techniques. The optimized hybrid electrodes exhibited a high specific capacitance of 368.3 F/g at 0.2 A/g, and excellent cycling performance of 98.4% capacitance retention over 3000 cycles.

Paper microfluidics technology requires effective handling and control of fluids, and this remains as asignificant obstacle for their accessibility by end-users, inhibiting their transition from the laboratory intothe market. Here, the synthesis, characterisation and performance as negative passive pumps of choliniumbased poly(ionic liquid) hydrogels are presented, for the manipulation of fluid flow in microfluidic paper-based analytical devices. The hydrogel was able to direct the fluid flow preferentially, and prevent fluidfrom flowing in other directions, thus opening possibilities for effective fluid flow manipulation in microPADs.Moreover, the hydrogel ‘passive pump’ improves the water retention capacity of the microPAD by a factor ofnine when compared to the bare microPAD. Furthermore, the operational lifetime of this microPAD configuration was greatly increased by the integration of the hydrogel passive pumps. The project was carried out with the support of the Ramón y Cajal programme (Ministerio de Economía y Competitividad). A.T.,L.F., and D.D. are grateful for financial support from the Marie Curie Initial Training Network OrgBIO funded by the European Community’s FP7 People Programme (Marie Curie ITN, GA607896). F.B.L., L.B.D. and D.D. also acknowledge funding from the European Union’s Seventh Framework Programme (FP7) for Research, Tech-nological Development and Demonstration under grant agreement no. 604241 (NAPES) and L.F. and D.D. acknowledge funding fromScience Foundation Ireland (SFI) under the Insight Centre for Data Analytics initiative, Grant Number SFI/12/RC/2289. F.B.L. acknowledges the Gobierno Vasco, Dpto. Industria, Innovación, Comercio yTurismo under ELKARTEKKK-2016/00088 and the funding support from Gobierno de España, Ministerio de Economia y Competitividad, with Grant No. BIO2016-80417-P. FBL and TA personally acknowledge Marian M. de Pancorbo for letting them to use her laboratory facilities at UPV/EHU. Authors also acknowledge Adhesive Research for the donation of the PSA samples.

The exploration of efficient catalysts toward hydrogen evolution reaction (HER) is still an urgent task. In this paper, Ni/Mo/Cu/C and Ni/Mo/C electrode were obtained by conventional pulse voltammetry, which acted as cathode in microbial electrolysis cells (MECs). The prepared samples are analyzed using SEM, XRD, XPS and electrochemical analysis techniques. Results indicated that the Ni/Mo/Cu coating has a rough and globular structure and presents high current density, a lower Tafel slope of 23.9 mV/dec than 30 mV/dec of Pt, which exceeds the electrochemical activity of Pt electrode. Its remarkably enhanced electrocatalytic activity is attributed to the high surface area, high conductivity as well as synergistic interaction among Ni, Mo and Cu.

A paper-based colorimetric sensor was fabricated using polymethylacrylic acid-templated silver nanoclusters (AgNCs) as a sensing probe for the detection of Fe 2+ and employing an ion exchange polymeric membrane as a coating layer. AgNCs were impregnated on a cellulose filter paper. The AgNC-impregnated filter paper was then lacquered with a hydrophobic membrane of polyvinyl chloride plasticized with o -NPOE incorporating a hydrophobic cation exchanger. Due to the ion exchange phenomenon at the membrane surface, Fe 2+ was extracted into the paper layer, and the bound Ag + on the AgNCs was reduced by Fe 2+ . The growth of the cluster could be observed by measuring the increase in the silver nanoparticle (AgNP) plasmon band. The maximum plasmon band on the paper at 447 nm increased as a linear function of the increasing Fe 2+ concentration. The proposed sensor was highly selective to Fe 2+ over Fe 3+ and other cations. The proposed sensor was optimized and could be used to detect Fe 2+ solution concentrations as low as 50 μM, with a wide working linear concentration range of 0.2–1.0 mM. The sensor was applied to determine Fe 2+ in iron supplement tablet samples with satisfactory results.

Patterning of hydrophobic barriers is duly important for designing paper-based analytical devices. Hydrophobic ink composing of solubilized poly(methyl methacrylate) was re-filled into the commercially available correction pen that was used to draw microzones/hydrophobic barriers on filter paper surface. The stability of hydrophobic barriers was strong enough to withstand elevated surrounding temperatures. The hand-drawn optical assay plate (OAP) was subsequently used for rapid and precise determination of Ag+ ions using 6-hydroxy-3-(2-oxoindolin-3-ylideneamino)-2-thioxo-2H-1,3-thiazin-4(3H)-one (HOTT) as a chromogenic reagent. Within the microzones, the developed reddish brown colored Ag-HOTT chelate was easily visualized by naked eyes at trace level (10−1 μM) of Ag+ in water. The assay sensitivity on the proposed platform was 3-orders of magnitude lower to the similar assay executed on pristine filter paper. Quantitative analysis of Ag-HOTT complex by image analysis software showed a linear dynamic range between (101–104 μM) with a regression coefficient (R2) of 0.995. The proposed Ag+ assay offers easy colorimetric read-out and flexibility in point-of-use testing. The versatility of the in-house fabricated OAP can be easily extended towards other analytes as well especially in resource limited areas.

Surface-enhanced Raman scattering (SERS) has been widely used in biomedical sensing with the advantages of high sensitivity and label-free. However, the fabrication of SERS substrates with good Raman activity, reproducibility, and low cost is still under development in practical applications. This paper presents a practicable method for fabricating Au NP/paper strips by using inkjet printing and seed mediated growth. Small gold seed synthesized by borohydride reduction was used as ink and printed on the filter paper. The printed gold seed grew in situ in the growth solution and formed the gold nanoparticle (Au NP)/paper strips. The fabricated paper strip was characterized by diffuse reflectance spectroscopy and scanning electron microscopy (SEM). The diffuse reflectance spectra indicated that the Au NP/paper strips had two local surface plasmon resonance (LSPR) peaks: the short one at around 540 nm and the long one located in the range of 640–840 nm. And the long LSPR peak firstly shifted to red then to blue with the increased concentrations of silver ions in growth solution. From the SEM images, the shape of grown Au NPs was diverse, including sphere, rod, ellipsoid, dimer, trimer, and big aggregates. We thought the short peak came from the LSPR of nanospheres and the transvers LSPR of rod and ellipsoid like particles, while the long peak mainly came from the plasmonic coupling of dimer along the inter-particle axis. The obtained Au NP/paper strip with the long peak located around 650 nm had the highest SERS activity, which could be attributed to the plasmon resonance induced local field enhancement and nanogap effect. Also, the SERS performance results indicated the printed SERS strips exhibited satisfied uniformity and stability, demonstrating the potential of Au NP/paper strip in real-world applications.

Recently, triboelectric nanogenerator (TENG) has aroused considerable interest due to various advantages. Particularly, one benefit which sand out is that the triboelectric pair of TENG is very tolerant to the material composition. Thus, it is possible and significant to develop cost-effective TENG using commercial and inexpensive material. In this work, we present a paper TENG by repeated folding completely using commercially available commodity materials, such as paper, brush pen, Teflon tape, and conductive ink. Paper is used as functionally triboelectric pair and spring-like supporting structure. The stacked paper TENG is fabricated and large enhancement of output performance is observed. The generated electric outputs have been used to directly light-up commercial LEDs. The proposed TENG has demonstrated simplicity and cost-effective, which is suitable for flexible electronics.

Noncovalent side-wall functionalization of SWCNT with a pyrene bearing calix[4]pyrrole is reported. The modified SWCNT has been characterized by scanning electron microscopy, electron dispersive spectroscopy, and thermogravimetric analysis. This calix[4]pyrrole-decorated SWCNT based sensor was implemented on filter paper. The resistance change of SWCNT network upon VOC exposure was monitored in the chemiresistors approach. The calix[4]pyrrole-decorated SWCNT sensor on filter paper was found to show fast and selective sensing of acetone when compared with pristine SWCNT-on-paper sensor due to the binding of acetone by calix[4]pyrrole molecules. The sensor showed logarithmic response toward acetone in a concentration range between 20–500 ppm.

In this paper, a simple but efficient electrochemical biosensing platform was developed for ATP assay based on the preparation of paper-based working electrodes. In contrast to the electrochemical response of commercial glassy carbon electrode (GCE), improved voltammetric signals were achieved at the paper-based electrode. In particular, the surface contamination arising from oxidation product, a prominent challenge for ATP detection, was effectively eliminated by the paper-based system, endowing reliable analysis with high reproducibility. Moreover, the practical application value of the system was verified by assay of ATP in human serums, cancer cells, and normal cells with satisfactory results. Compared with the detection performances of traditional strategies, the advantages involved in the system were exhibited to be rapid, accurate, convenient, and inexpensive, which confer the proposed sensing platform promising for applications in public health as well as the fundamental research of molecular biology.

Paper-based microfluidic chips have shown great potential for use in rapid clinical diagnostics. In this work, we present a paper-based device that integrates an electromagnetically actuated valve and an adjustable time controller for the simultaneous detection of multiple tumor biomarkers. The time controller consists of a timing channel and two movable conductive iron bands that function as an electric switch. Once the conductive iron bands are connected by the fluid flow, the circuit would be closed to actuate the magnetic valve, initiating chemiluminiscent immunoassay (CLIA) reactions. Using a HRP- O -phenylenediamine-H 2 O 2 detection system, simultaneous detection of different concentrations of carcinoembryonic antigens (CEA) was demonstrated. The resulting CLIA peak intensity exhibited a good linear relationship with the logarithm of the CEA concentration from 0.1–80 ng mL −1 . Further experiments showed that the developed device was capable of detecting multiple tumor biomarkers simultaneously. We can program different incubation times for the detection of different biomarkers by moving the conductive bands on this paper-based device. In this study, only 16 min was required to complete CEA detection. This strategy greatly shortens detection time compared to the conventional chemiluminiscence technique for CEA detection (nearly 2 h). This paper-based device provides a simple and inexpensive platform for immunoassay-based detection of disease-related biomarkers.

Membrane heat exchangers were used for moisture and heat recovery from a hot and humid natural gas stream in indirect contact with an air stream. A plate membrane module with spiral channels on each side was designed to configure gas and air streams in co-current and counter-current flow. Two types of membranes, a commercial kraft paper, and a laboratory-made thin-film composite membrane, were used as the module core. The thermal efficiency and the water recovery from the humid gas were calculated and compared under different operating conditions. At a unit flow ratio of air/gas, the greatest effectiveness was achieved at a methane flow of 100 cm3/min, but water recovery increased at higher gas flows. For the counterflow configuration, an air/methane flow ratio of 2 was sufficient to achieve the highest total effectiveness and water recovery; however, larger air/gas ratios were beneficial to improve heat and moisture transfer for the co-current configuration. The highest water recovery by the kraft paper and composite membrane was achieved (approximately 15 mgH2O/cm2.h) for the input gas with the highest humidity. The dehumidification performance of kraft paper as a porous and hydrophilic membrane was slightly better than that of the composite membrane containing a dense hydrophilic polymer thin film in most cases. A relatively low heat transfer coefficient was found for the module, which was increased by using higher gas flow rates at higher humidity conditions.

As a typical membrane matrix with attractive flexibility, paper has exhibited great feasibility to serve as surface-enhanced Raman scattering (SERS) substrate in the environmental monitoring and surveillance. In this research, we have designed and fabricated a distinctive hydrophilic-hydrophobic SERS substrate utilizing several ordinary papers loaded with Ag nanowires (Ag NWs). Remarkable SERS activities with an enhancement factor (EF) up to 2.63 × 106 was successfully achieved in the assembly Ag NWs with the optimal amount of nanotips and overlaps. The hydrophilic-hydrophobic strategy could contribute to anchoring microdroplets and thus enrich analytes to improve the homogeneity of substrate with a low relative standard deviation of 10.6%. Furthermore, the sophisticated SERS substrate was also applied in the in-situ detection of trace furazolidone on fish under the interference of malachite green and the reliable recovery rates were demonstrated as well.

Low-cost, paper-based platforms are gaining increasing relevance in modern diagnostics and biosensing. Most diagnostic systems using blood samples require blood-plasma separation to reduce complexity and achieve better results. Blood plasma separation is often carried-out by using various membrane based filters. This paper presents a new method for capturing red blood cells on Whatman filter paper with no. 1, 2, 5 and glass fiber discs. All four paper types were subjected to modification with hydrothermally grown zinc oxide nanorods. Growth and morphologies of zinc oxide nanorods were confirmed by SEM, XRD and XPS studies. The blood plasma separation experiments were done by cutting the papers into identical strips with dimension of 5 × 20 mm2. 3 μL of blood was mixed with equal volume of antibody solution and pipetted on each strip. The colored antibody solution was used to track the path of antibody, eventually the separated plasma. The dried strips were scanned and the difference in the distance travelled by colored solution of antibodies was measured. From the results, it is clear that all four paper strips covered with nanorods have shown more distance travelled and better separation than their control samples.

The development of Fe 2 O 3 with high conductivity and energy density is crucial for practical utilizations of supercapacitors. Here, we demonstrated the preparation of novel Fe 2 O 3 /graphene oxide paper (Fe 2 O 3 /GP) hybrid electrode for high density supercapacitors. Due to the characteristic features of large surface areas and fast electron transportation, the specific areal capacitance of the Fe 2 O 3 /GP was around 3.08 F cm −2 at the charge-discharge current density of 5 mA cm −2 , which is nearly 14 times of the Fe 2 O 3 /carbon paper (Fe 2 O 3 /CP, 0.22 F cm −2 ). More importantly, the Fe 2 O 3 /GP hybrid electrode also retained about 95% of the initial capacitance after long-term cyclic process. These findings would help us to develop high effective and stable materials for energy storage devices.

paper-like films of reduced graphene oxide with controllable shapes and thickness were prepared via funnel filtration and thermal reduction of graphene oxide (GO), which could work as flexible surface-enhanced Raman scattering (SERS) substrates to detect Rhodamine 6G (R6G) molecules. The SERS signal intensity of R6G on annealed films was found to be related with the annealling temperature. The most intense signal was observed for the film obtained at 800 °C. While for the sample annealed at 1000 °C, no SERS signal could be detected. The underlying mechanism for the difference was discussed. The reported preparation process of flexible rGO paper is simple and cost-effective, which shows great potential in rapid biochemical analysis of agricultural products with irregular surfaces.

Nanoparticles are used in several applications due to the unique properties they possess compared to bulk materials. Production techniques have continuously evolved over the years. Recently, there has been emphasis on environmentally friendly manufacturing processes. Substrate properties often limit the possible production techniques and, for example; until recently, it has been difficult to incorporate nanoparticles into paper. Chemical reduction of a precursor in the presence of paper changes the bulk properties of paper, which may limit intended end-use. In this study, we present a novel technique for incorporating silver nanoparticles into paper surface using a flame pyrolysis procedure known as Liquid Flame Spray. Papers precoated with mineral pigments and plastic are used as substrates. Silver nanoparticles were analyzed using SEM and XPS measurements. Results show a homogeneous monolayer of silver nanoparticles on the surface of paper, which demonstrated antibacterial properties against E. coli . Paper precoated with plastic showed more nanoparticles on the surface compared to pigment coated paper samples except for polyethylene-precoated paper. The results demonstrate a dry synthesis approach for depositing silver nanoparticles directly onto paper surface in a process which produces no effluents. The production technique used herein is up scalable for industrial production of antibacterial paper.

This study aimed at the quantification of thermochemical behaviors of textile dye sludge (TDS), paper mill sludge (PMS), and their various blend ratios during (co-)combustion. Changes in mass loss percentage (MLP) and rate (MLR) were estimated as a function of temperature, heating rate, and blend ratio. Our results pointed to a direct influence of blend ratios on mass loss percentage. Stochastic uncertainties and sensitivities associated with best-fit predictions of MLP and MLR responses were detected using all-at-once versus one-at-a-time Monte Carlo simulations. Co-combustion of TDS and PMS provided more flame stability owing to their volatile matter contents than did the combustion of pure TDS or PMS. The high C and H contents of TDS relative to those of PMS led to high lower heating value (higher energy). Effect of increased temperature on the co-combustion manifested itself in the breakdown of (hemi-)cellulose initially and lignin progressively in TDS and PMS. The increasing TDS of the blend ratio increased both MLP and MLR. Stochastic uncertainty analysis of the deterministic empirical models pinpointed overestimation by 15.6% in mean MLP and by 50% in mean MLR. Sensitivity analysis pointed to blend ratio as the most influential predictor on both MLP and MLR.

A dual-readout paper-based sensor with smartphone detection is developed for quantitative determination of penicillinase. The sensor is accomplished with the aid of penicillinase-mediated alginate hydrogelation, which changes both the viscosity and pH of the reaction solution. The solution is dropped on a mixed cellulose ester filter paper for sensing, which is coated with a color indicator, bromothymol blue-cetyltrimethylammonium bromide-alginate complex. Dual signals of the targets are easily achieved from the sensing spot on the paper since the modulations of viscosity and pH of the reaction solution would result in changes of diffusion diameter and color of the spot, respectively. A smartphone-based readout device is developed to record and analyze both the diffusion diameter and color signal for quantitative detection of penicillinase. The wide linear range (8.00 × 10−3 - 2.67 mU/μL for distance-readout and 8.00 × 10-2 to 2.67 mU/μL for color-readout) with low limit-of-detection (2.67 × 10-3 mU/μL for distance-readout and 2.67 × 10-2 mU/μL for color-readout) have been achieved using the dual-readout paper-based sensors. The proposed method is successfully applied for the detection of penicillinase in milk samples with excellent sensitivity and reproducibility, showing its potential value for analysis of complex real samples.

To solve the issues of energy shortage and environmental pollution, it is essential to develop highly effective catalysts for hydrogen evolution reaction (HER) in water electrolysis. Herein, we report a facile and rapid fabrication of a Cu–Co–P catalyst on a carbon paper (CP) substrate using electrodeposition. First, the deposition conditions for Co–P/CP were optimized. The prepared Co–P consisted of numerous spheres and exhibited acceptable catalytic activity towards HER in an alkaline medium with an overpotential of 72 mV at current density of −10 mA/cm2. Further performance enhancement was achieved by the incorporation of Cu to modify the electronic structure of the Co–P catalyst. In a half-cell test, the optimized Cu–Co–P/CP exhibits remarkable performance, achieving −10 mA/cm2 at an overpotential of 59 mV, and the Tafel slope is 38 mV/dec. In a single-cell test, an anion exchange membrane water electrolyzer with a Cu–Co–P/CP cathode and commercial IrO2/CP anode exhibited high current density of 0.70 A/cm2 at 1.9 Vcell.