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This study optimizes a novel surfactant-assisted green liquor dregs (GLD) pretreatment of paper mill sludge (PMS), both of which are wastes from the kraft pulping industry, using a combined Response Surface Methodology (RSM) design. Optimized conditions give a maximal reducing sugar release of 16.38 g/L. A substantial reduction in heavy metals aluminum, chromium, cobalt, arsenic, lead, and copper after pretreatment illustrates the enhancement of substrate digestibility by reducing toxic elements. Separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) for hydrogen production are assessed. SSF produced a hydrogen yield of 3.72 mL/g, displaying a 36.26% increase from pretreated PMS compared to SHF. These findings provide insights into possible methods of reducing process duration, energy input, and costs incurred with waste disposal within the paper industry. Furthermore, improved hydrogen yield using an SSF process demonstrates the potential beneficiation of pulp and paper GLD and PMS wastes.

In this elucidation, we synthesized novel molecularly imprinted polymers (MIPOH1-4) that were used as organic fillers on bagasse pulp to form cellulosic paper sheets, the formation of MIPOH1-4 from the reaction of enaminone 3 with methyl methacrylate monomer in the presence of ethylene glycol dimethyl acrylate and 2,2’-azobisisobutyronitrile. The obtained MIPOH1-4 was confirmed via FT-IR and SEM with different pore sizes. And we noticed that the increase of template 3 increases the hydrogen bond between monomer and template and gave sponge surface of MIPOH4. Furthermore, the computational energies of the template with different monomers utilize DFT/B3LYP/6-31G (d) level to know the stability of polymers and hydrogen bonding between them. So that we applied that in paper manufacture through the adsorption of MIPOH4 as an organic filler on bagasse pulp to form novel cellulosic paper sheets with different concentrations and these sheets which characteristic through FT-IR, SEM, sizing test, tensile strength, and elucidation their antimicrobial activity with theoretical and docking studies. The MIPOH4 and cellulosic paper sheets showed the thermal stability and high tendency of sizability of these paper sheets and concluded the interaction between cellulose fibers of pulp with MIPOH polymer with physical hydrogen bonding.

Paper and pulp mills generate substantial quantities of cellulose-rich sludge materials that are disposed in landfills at a large scale. For sustainability purposes, sludge materials can be bioprocessed to produce renewable fuels and useful chemicals. The enzymatic hydrolysis of cellulose is the process bottleneck that affects the conversion economics directly by using zero-cost raw materials. In order to study and optimize the process, the characteristics of the sludge raw materials should be first evaluated. In this work, sludge samples were obtained from paper mills located at different locations in Wisconsin and Minnesota. Part of the sludge samples was washed (de-ashed) with hydrochloric acid while the other part remained unwashed. The samples were subjected to multiple spectroscopic analyses techniques to evaluate the morphological properties of cellulose fibers and to estimate the total structural carbohydrate content. The results showed that the de-ashing process changed some fiber characteristics and cellulose crystallinity structure in all sludge samples. Sludge sample A (obtained from Kraft pulp and recycled paper mill region) showed a high percentage of fiber, with crystalline cellulose, compared to the other two sludge samples suggesting that sludge A is a valuable source to make value-added products. Aspen Plus mass and energy calculations performed in view of the ‘zero’ cost and the reliable supply of sludge raw materials producing 2 mol H2/mol glucose. Moreover, the results showed that extracting crystalline cellulose from these sludge samples is more profitable than crystalline cellulose made from the other lignocellulosic feedstocks. The results reported here showed that the utilization of these sludge materials would be an economically attractive and promising alternative for the production of hydrogen.

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

A paper-based membrane coated by graphitic carbon nitride (g-C3N4) is prepared via a dip-coating method and used as a separator for sodium metal batteries with merits of low cost and environment-friendliness. Introduction of g-C3N4 effectively improves the ionic conductivity and the structural stability of the separator. Compared with traditional polyethylene separators and Al2O3-coated separators, the g-C3N4-coated separators show better electrolyte wettability, thermal stability, and electrochemical stability. Therefore, Na||Na3V2(PO4)3 battery using the g-C3N4-coated separator exhibits better cycling stability and higher rate capability. These results prove that the g-C3N4-coated paper-based separator is expected to become the next generation of low-cost and high-safety separator in sodium metal batteries.

Natural cellulose paper is flame retarded using ammonium polyphosphate/montmorillonite (APP/MMT) nanocompound through coating method. Their morphologies are assessed by scanning electron microscopy, chemical components by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, chemical structure by Fourier transform infrared, thermal stability by thermo-gravimetric analysis and fire retardancy by 45° horizontal burning test. The results show that the thermal stability and flame retardancy of coated paper samples are enhanced obviously, and all samples are self-extinguishing during the tests due to the char formation reaction between APP/MMT and cellulose. Then the treated paper, AM-18.3, as surface flame retardant treatment for low specific surface area (SSA) polypropylene (PP) specimens (PP@AM-18.3) also is investigated using cone calorimeter. Compared with two controlled samples, PP@AM-18.3 shows significantly increased time to ignition, the lowest fire growth index and highest fire performance index. This may give a new flame retarded approach for low SSA polymer materials with little amount flame retardants.

Neotame is an artificial sweetener with increasing consumption in recent years, excessive intake of it may bring potential health risk. In this work, a rapid method was developed to detect neotame in instant grain beverages, which was based on surface-enhanced Raman scattering (SERS) technique and filter paper-based silver nanoparticles (AgNPs@FP) substrates. The designed substrate exhibits good SERS activity with an enhancement factor of 105 because of the synergistic effect of the concentrated silver nanoparticles and filter paper. Meanwhile, the stability and repeatability of this fabricated substrate have been investigated with the relative standard deviation of 6.1%. In addition, it shows an excellent linear relationship (R 2 = 0.997) between the SERS signal and the logarithm concentration of neotame with a wide concentration range (0.05–5 g/kg) in the quantitative analysis. The limit of detection of neotame can be as low as 0.01 g/kg in instant grain beverages, which is below the maximum allowable addition level for neotame in instant grain beverages set in China (GB2760-2014, 0.16 g/kg). The proposed method has great potential for the identification and quantification of neotame in food safety applications with high sensitivity.

Flexible thin-film solar cells with high weight-specific power density are highly desired in the emerging portable/wearable electronic devices, solar-powered vehicles, etc. The conventional flexible metallic or plastic substrates are encountered either overweight or thermal and mechanical mismatch with deposited films. In this work, we proposed a novel substrate for flexible solar cells based on graphene paper, which possesses the advantages of being lightweight and having a high-temperature tolerance and high mechanical flexibility. Thin-film amorphous silicon (a-Si:H) solar cells were constructed on such graphene paper, whose power density is 4.5 times higher than that on plastic polyimide substrates. In addition, the a-Si:H solar cells present notable flexibility whose power conversion efficiencies show little degradation when the solar cells are bent to a radius as small as 14 mm for more than 100 times. The application of this unique flexible substrate can be extended to CuInGaSe and CdTe solar cells and other thin-film devices requiring high-temperature processing.

The sensitive quantitative analysis of trace heavy metallic elements (Cd, Mn, Cr, and Cu) in aqueous solutions was achieved successfully through the combination of filter paper enrichment with laser-induced breakdown spectroscopy. Filter paper was enriched with 0.4 mL aqueous solutions to form a homogeneous sample layer on the surface of the metallic target. Considering the limits of detection, the values deduced with calibration curves already exhibited the high performance of the proposed method at several hundred or 10 μg/L (Cd 0.165, Mn 0.035, Cr 0.012, and Cu 0.078 mg/L), lower than or comparable to those using other similar methods. The LIBS results agreed reasonably well with those from ICP-MS for real samples. All results showed that our method was suitable and accurate for rapid on-site detection of trace metals in aqueous solutions. This indicates that filter paper enrichment combined with laser-induced breakdown spectroscopy is a feasible approach to wastewater quality monitoring.

The aim of this work was the wettability improvement of clay-coated paper by ambient air plasma exposure. Industrial corona with a volume dielectric barrier discharge in cylindrical configuration was used as a plasma source; the exposure times varied from 0.25 up to 5 s. Water contact angle (WCA) measurement and surface free energy (SFE) evaluation were carried out for the estimation of wettability changes. Plasma treatment in the duration of 0.25 s was sufficient to decrease the WCA almost to the half of the original value, which was 76 degrees. SFE of paper has increased by 40%-50% after plasma treatment. Long-term ageing effect study of treated samples was carried out up to 3 months after the treatment. WCA did not reach the original value even after 3 months, and it was still 20%-30% lower. O/C ratio increased from 0.7 to 1.8 in case of 5-s plasma treatment, and the new chemical bonds (C=O, O-C=O) were created on the surface.

Reflective liquid crystal displays are attracting attention as portable information systems because of zero- or extremely low power consumption. In this study, we deal with an electrode-free reflec...

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 novel, simple and low-cost method for fabricating paper-based microfluidic device was presented. A soldering wire was used for making a template with specific pattern, and transfer printing to a ...

International audience; Ultrasonic welding is a serious candidate in the development of methods to assemble papers and paperboards without using additional substances. However, the ultrasonic welding of papers remains a technological challenge considering the low weldability of lignocellulosic materials. This study aims to investigate on the ultrasonic welding process applied to papers in order to identify the processing conditions which favor the formation of strong welded joints. To reach such purpose, an experimental strategy was developed by combining the characterization of welded materials and the monitoring of process parameters. Experimentations were performed using a reference paper displaying a good weldability to specifically highlight the contribution of process parameters. Results indicate that the process is highly sensitive to vibration amplitude, power supplied by the high frequency generator, and sample thickness. Power seems to be a reliable indicator of the severity of the process. A strong decrease in the strength of the welded joints is observed when working with low thicknesses. It seems that the layers coated on top of papers are the main part of the material contributing in the development of adhesion at the welding joint. Overall, instrumenting the device has led to a better understanding of the ultrasonic welding of papers.

Inorganic salt modified paper substrates were developed and utilized in microfluidic paper based sampling coupled with potentiometric ion sensors for the determination of heavy metals, such as Cd2+ and Pb2+. The application of paper based sampling without any paper substrate pre-treatment were characterized with super Nernstian response, while the paper substrates with inorganic salt pre-treatment were characterized with standard Nernstian response. The application of inorganic salt modified paper substrates was found advantageous when the cation of the salt in the conditioning solution was the same as the primary cations of the ion-selective electrodes (ISEs). A relatively high concentration of inorganic salts during pre-treatment of the paper substrates, namely Cd(NO3)2 or Pb(NO3)2 with subsequent measurement of cadmium(II) and lead(II), by Cd2+- and Pb2+-ISEs, respectively was needed to sustain Nernstian response of sensors. It was also found that paper substrates facilitate sorption of metal ions onto the paper substrates, with stronger binding strength given to Pb2+ over Cd2+. Moreover, the metal-paper interactions suggest concentration dependent sorption-desorption of metal ion, which can have direct limitations of the use of paper based analytics for the determination of low analyte concentration of heavy metals. Nanyang Technological University The authors would like to thank NTU-India Connect Research Internship Program for financial support of Ms Tharini Saravana Sundaram from Coimbatore Institute of Technology, India.

In this article, we report the development and optimization of a cost-effective, biodegradable, disposable, and lightweight conductive polymer deposited on exfoliated graphite paper battery. The anode is made of aluminum foil and the cathode using electrochemically deposited anthraquinone conductive polymers on exfoliated graphite paper. Concentrated sodium chloride salt is used as the electrolyte. The battery shows a maximum capacity of 235 mA h g−1 and a superior cyclability of up to 500 cycles at 50.0 mA cm−2 current density.

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.

Paper-based devices have a wide range of applications in point-of-care diagnostics, environmental analysis, and food monitoring. Paper-based devices can be deployed to resource-limited countries and remote settings in developed countries. Paper-based point-of-care devices can provide access to diagnostic assays without significant user training to perform the tests accurately and timely. The market penetration of paper-based assays requires decreased device fabrication costs, including larger packing density of assays (i.e., closely packed features) and minimization of assay reagents. In this review, we discuss fabrication methods that allow for increasing packing density and generating closely packed features in paper-based devices. To ensure that the paper-based device is low-cost, advanced fabrication methods have been developed for the mass production of closely packed assays. These emerging methods will enable minimizing the volume of required samples (e.g., liquid biopsies) and reagents in paper-based microfluidic devices.

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.

Smart fluid manipulation with automatically controlled paper valves will enable automated and multi-step immunoassays on paper-based microfluidic devices. In this work, we present an integrated paper-based microfluidic platform with shape-memory polymer (SMP)-actuated fluid valves capable of automated colorimetric enzyme-linked immunosorbent assays (ELISAs). A single-layer microfluidic paper-based analytical device (μPAD) was designed to store all the reagents on the chip, and sequentially transfer reagents to a paper test zone following a specific ELISA protocol through automatic fluidic flow control by the multiple SMP-actuated valves. The actuation of a paper valve was based on the thermally responsive, duel-state shape transformation of a SMP sheet attached to the root of a paper cantilever beam for driving a hydrophilic paper bridge to connect and disconnect two paper channels. A portable colorimetric reader was developed to control the on-chip valve operations, quantify the colorimetric signal output, display the assay result, and wirelessly transmit the data to a smart phone for the application of telemedicine. Reliable operations of the paper valve and the entire μPAD were demonstrated with success rates of 97% and 93%, respectively. A detection mechanism for valve malfunction was designed and confirmed effective to identify any mal-operation of individual valves, thus rendering our platform reliable in real assays. For device calibration, we conducted direct ELISAs of rabbit IgG in phosphate-buffered saline (PBS), and achieved a low limit of detection (LOD) of 27 pM (comparable to that of standard and paper-based ELISAs). In order to demonstrate the clinical application of our multi-step immunoassay platform, we also conducted sandwich ELISAs to quantify the protein level of an inflammatory cytokine, namely tumor necrosis factor (TNF)-α, in surgically injured laryngeal tissues of rats. The protein levels of TNF-α were shown similar between the conventional and μPAD ELISAs., Microfluidics: Paper valves open doors to new designs Researchers in Canada have improved the design of paper-based analytical devices by developing paper valves which make it possible to carry out fully-automated multi-step analyses. Previous efforts to incorporate valves have been based on electromagnets or compressed sponges, making them too cumbersome or complicated for reliable use in paper-based analytical devices. To overcome this, a team led by Xinyu Liu of the University of Toronto turned to polymers that reversibly change shape in response to temperature. They combined these with a heating element to produce thermally-activated paper valves. Test devices designed to carry out a multi-step ELISA analysis produced results comparable to a standard commercial ELISA kit. The valve design can be used to create devices for other multi-step diagnostic assays which can be used in contexts where lab equipment and skilled personnel are unavailable.

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.

Selective detection of different explosive materials is essential to the current world scenario from the perspective of health, safety, and environment. Here, we have developed and characterized a couple of bio-based conjugated systems, viz. cholesterol-tryptophan and cholesterol-cysteine for the detection of nitroaromatic explosive chemicals. The presence of tryptophan moiety introduces fluorescence property to the non-fluorescence cholesterol backbone, and hence it was used as a tag molecule to prepare photoluminescent filter papers which serve as indicators for picric acid and dinitrosalicylic acid. These paper strips undergo instant quenching in the presence of the experimental analytes under the UV irradiation, which could be visualized through the naked eye. The amount of quenching is found to be proportional to the concentration of the analytes. The limit of detection for picric acid and dinitrosalicylic acid was estimated to be about 33 nM and 48.7 nM respectively, and the mechanism of this quenching is mainly due to fluorescence resonance energy transfer between the fluorophore and the quencher. Also, the vapor of picric acid completely diminishes the photoluminescence of the filter papers. Such an easy, selective and instant detection of nitroaromatic chemicals is in high demand due to increasing health and security concern worldwide.

One of the most important problems in dark fermentative hydrogen production is the need for the regulation of the ambient pH due to the formation of volatile fatty acids. For this purpose, alkaline chemicals are usually used; however, alkaline addition to the media increases salt formation, which negatively affects microbial activity. In this study, pH adjustment was performed by providing direct current as an alternative to alkali addition. Experiments were carried out batchwise and electricity was only applied to neutralize the acidic pH value. The waste paper hydrolysate was used as a substrate and the effects of applied voltage (0.25-3 V), substrate concentration (4.8-41.2 g/L at 1 V) and electrode distance (0.3-1.3 cm at 1 V) on hydrogen production performance was investigated. Voltages less than 1 V required too much time to keep the pH convenient and voltages more than 1.5 V adversely affected hydrogen production performance. Providing direct current to the fermentation media significantly reduced the adaptation phase. Conditions for optimal pH adjustment and hydrogen production were obtained at 1 V, 20 g glucose/L and 0.5 cm electrode distance. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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.

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.

In the last years, the imprinting technology has raised attention and different polymers with artificial recognition sites towards a target molecule have been developed. In this article, a polymerization-free method ―which only requires the dissolution of nylon-6 polymer and its subsequent incubation with the template molecule― has been employed for the preparation of a molecularly imprinted polymer directly immobilized on filter paper, thus increasing the versatility and manageability of the new material. The molecularly imprinted paper-based analytical device (MIP PAD) has been coupled to a fluorimeter via a custom-built platform, which enables direct measurement of the fluorescence at the surface of the MIP PAD. Extraction efficiency of the MIP PAD was evaluated using quinine as model analyte, measuring the fluorescence directly at the MIP PAD surface after incubation on aqueous standards of quinine and soda drink, showing that the performance of the imprinted material was superior to that of the non-imprinted polymer. In addition, the selectivity of the MIP PAD versus analogous organic fluorescent molecules has been further evaluated using norfloxacin, observing that the molecular imprinting results in selective extraction of quinine. The performance of the method has been evaluated for quantitative analysis, achieving limits of detection (LOD) and quantification (LOQ) for aqueous standards of 0.37 and 1.24 mg L−1, respectively, while in the case of spiked soda drink the LOD and LOQ were 0.63 and 2.11 mg L−1, respectively. The reproducibility of the measurements was also evaluated, observing values within range 2.30 and 9.07% measured as relative standard deviation.

The present work focused in assessing the hydrogen production from pretreated wastes of the paper industry (PIW) by simultaneous saccharification and fermentation (SSF) using anaerobic biofilms developed in natural fibers (ixtle) at different conditions. Anaerobic sludge from brewery wastewater treatment was used for biofilms and they were developed in plastic spheres covered with fiber cord from ixtle. The solid wastes of paper industry were previously pretreated with H2SO4 at 2.5% (v/v) at 120 °C by 30 min. The solids pretreated were hydrolyzed and fermented in batch reactors. All reactors were kept at an initial pH of 5.0 and three levels of enzyme loadings (10, 40 and 70 FPU/mL) and temperatures (35, 45, 55 °C) were assessed. The maximum hydrogen obtained (60.75 mmol/h*g volatile solids) was at 45 °C and 70 FPU/mL, moreover, no methane was detected in all cases.

Due to the combined advantages of cellulose and nanoscale (diameter 20–60 nm), bacterial cellulose possesses a series of attractive features including its natural origin, moderate biosynthesis process, good biocompatibility, and cost-effectiveness. Moreover, bacterial cellulose nanofibers can be conveniently processed into three-dimensional (3D) intertwined structures and form stable paper devices after simple drying. These advantages make it suitable as the material for construction of organ-on-a-chip devices using matrix-assisted sacrificial 3D printing. We successfully fabricated various microchannel structures embedded in the bulk bacterial cellulose hydrogels and retained their integrity after the drying process. Interestingly, these paper-based devices containing hollow microchannels could be rehydrated and populated with relevant cells to form vascularized tissue models. As a proof-of-concept demonstration, we seeded human umbilical vein endothelial cells (HUVECs) into the microchannels to obtain the vasculature and inoculated the MCF-7 cells onto the surrounding matrix of the paper device to build a 3D paper-based vascularized breast tumor model. The results showed that the microchannels were perfusable, and both HUVECs and MCF-7 cells exhibited favorable proliferation behaviors. This study may provide a new strategy for constructing simple and low-cost in vitro tissue models, which may find potential applications in drug screening and personalized medicine.

Early and precise diagnosis of cancer is critical for a better prognosis. Here, we describe a simple and cost-effective plasmonic paper as a surface enhanced Raman scattering (SERS) substrate in combination with magnetic separation for cancer screening. The plasmonic paper was fabricated by immersing plain filter paper into gold nanorod solution and the SERS property of the paper was evaluated using 4-mercaptobenzoic acid (4-MBA) and rhodamine 6 G (R6 G), which showed an enhancement factor (EF) in the range of 106–108. HT-29, a colorectal cancer cell line that highly expresses epithelial cell adhesion molecule (EpCAM), served as the target cells; non-EpCAM-expressing cells, namely fibroblasts and red blood cells (RBCs), were used as negative controls. Intrinsic SERS spectra of the target and control cells showed distinctive patterns on the plasmonic paper due to differences in their structure and components. A combination of principal component analysis (PCA) and k-nearest-neighbor algorithm (k-NN) was employed to analyze and distinguish the acquired HT-29 and fibroblast SERS spectra, demonstrating a diagnostic sensitivity and specificity of 84.8% and 82.6%, respectively, whereas the differentiation between HT-29 and RBCs SERS spectra showed a sensitivity and specificity of 96.4% and 100%, respectively. The magnetic separation was applied to capture the target cells from cell mixtures followed by PCA and k-NN analysis. The identification of the captured cells as cancerous cells from the HT-29 and fibroblast mixture indicated an accuracy of 83.7%, while that from a mixture of HT-29 and RBCs was 98.2%. Thus, the simple paper-based SERS substrate with the assistance of magnetic enrichment and multivariate analysis offers a potent new platform for cancer cell detection and screening.

In this communication, a novel surface modification method of the paper surface using 3-aminopropyltriethoxysilane (APTES) and gold nanoparticles is reported. This functionalized paper (flower-shaped paper-based microfluidic devices (F-PMD) for simultaneous assay of multiple analytes) is used for determination of total lipid profiling (TLP) in a single device. Here, we have determined total cholesterol along with low-density lipoprotein (LDL), high-density lipoprotein (HDL) and triglycerides (TGL). The LDL and HDL were estimated by erasing the non-HDL and non-LDL components with a help of precipitating reagents. Standard graphs prepared by the present paper-based method nicely correlates with the conventional method (calculated by Roche- COBAS C111 autoanalyzer) with Pearson Correlation Coefficient (R) of 0.903, 0.9727, 0.9939 and 0.9866 respectively for total cholesterol, LDL, HDL and triglycerides. The present assay device is intended to assist in the screening of individual’s lipid level for diagnosis of disorders involving high cholesterol level in the blood or for metabolic disorders associated with lipid and lipoprotein. As this is affordable, miniaturized, easily portable, self-testing and rapid, the present assay device can be used easily by pre-clinical, non-professionals, children in schools, labs, etc as a point-of-care diagnostics.

In this study, we designed a rapid colorimetric sensing system using competitive ELISA test on a microfluidic paper-based analytical device for the detection of ketamine, a frequently abused drug. Oral fluid was selected for the test to facilitate the collection of samples based on its advantages of low infection risk, noninvasiveness of sample collection, and decreased chance of sample adulteration. After optimization of the operation parameters, including reaction temperature, vibration washing time, reaction time, and antibody concentration, the resulting assay can be completed in as little as 6 min with a detection limit of 0.03 ng/mL. Moreover, we developed an Android smartphone app to analyze and measure the results of the test, further enhancing the test’s portability, and image recording and data transmission capabilities. In order to test the feasibility and performance of the optimized colorimetric assay, 90 oral fluid samples from drug abuse patients were tested. The paper-based platform features 90% sensitivity (confidence interval (CI): 76.34–97.21%) and 92% specificity (CI: 80.77–97.78%) for ketamine analysis. This competitive paper-based ELISA sensing system provides a rapid, convenient, sensitive, and high-throughput approach for drug monitoring.

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.

The interest in and use of microfluidic paper-based analytical devices (μPADs) has grown exponentially over the last decade. Cellulose, and modified cellulose, has been used for centuries for making chemical measurements but devices made with this material traditionally suffered from either poor detection limits and/or limited ability to provide quantitative measurements. μPADs address these problems by patterning paper to create microfluidic channel networks that can direct flow to different regions of the device without the need for external pumps used in most traditional microfluidic devices. Furthermore, because the devices are made from cellulose or modified cellulose using inexpensive manufacturing methods, the devices can be inexpensive and disposable. The ability to carry out multiplexed analysis without external pumps using inexpensive, disposable devices makes μPADs ideal for point-of-care (POC) analysis. The interest in μPADs has led to a number of excellent comprehensive reviews in the field; in this review, we do not attempt to reference the entire field but instead seek to highlight major developments as well as areas that will be important for future development of this field.

The separation of oil and water mixtures is an important issue in acidic and alkaline conditions. In this paper, the chitosan (CS)-coated filter paper was successfully fabricated for application in the field of oil/water separation by crosslinking filter paper with hydrophilic chitosan through a simple Schiff’s base reaction. The surface of the prepared CS-coated filter paper maintains superhydrophilic and low adhesive ability to oil in water. Besides, this filter paper can resist highly acidic erosion even concentrated sulfuric acid. Surprisingly, CS-coated filter paper can be efficiently applied on the separation of different types of oil/water mixtures in wide pH range conditions and exhibits excellent recyclability and antibacterial property. The antibacterial rate of CS fiber pure textile can reach 99%. The antibacterial rate of blended fabric is about 75%. This separation process has high potential for industrial oilfield wastewater treatment and separation in extreme environments.

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.

Pressure sensor, as one of the most common components in the sensing systems, has attracted plenty of attention in recent years with urgent needs. Herein, a highly sensitive flexible pressure sensor based on conducting polymer (CP)-coated paper is developed via an ultra-simple approach of synthesis and fabrication. This paper-based sensor displays an ultra-low detection limit as low as 0.3 Pa level, and outstanding sensitivity (∼2 kPa−1, P ≤ 75 Pa), which can rank the top among that of the reported pressure sensors. The advantages based on paper framework such as low cost, portability, and easy disposability further enhance its feasibility. Meanwhile, combining its rapid and precise response at room temperature and the recognized stability of PPy in the ambient environment, the sensor would ensure direct and continuous environment monitoring with low energy consumption.

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.

Graphical abstract, Highlights • Detection of cytokine storm biomarkers with mobile biosensors. • Immunosensors are made solely of cellulose modified with antibody-decorated nanoparticles. • Turnaround time under 10 min. • Detection of biomarkers in respiratory samples allows monitoring local inflammation. • Compatible with decentralized health care schemes., Decentralizing COVID-19 care reduces contagions and affords a better use of hospital resources. We introduce biosensors aimed at detecting severe cases of COVID-19 in decentralized healthcare settings. They consist of a paper immunosensor interfaced with a smartphone. The immunosensors have been designed to generate intense colorimetric signals when the sample contains ultralow concentrations of IL-6, which has been proposed as a prognosis biomarker of COVID-19. This is achieved by combining a paper-based signal amplification mechanism with polymer-filled reservoirs for dispensing antibody-decorated nanoparticles and a bespoken app for color quantification. With this design we achieved a low limit of detection (LOD) of 10−3 pg mL-1 and semi-quantitative measurements in a wide dynamic range between 10−3 and 102 pg mL-1 in PBS. The assay time is under 10 min. The low LOD allowed us to dilute blood samples and detect IL-6 with an LOD of 1.3 pg mL-1 and a dynamic range up to 102 pg mL-1. Following this protocol, we were able to stratify COVID-19 patients according to different blood levels of IL-6. We also report on the detection of IL-6 in respiratory samples (bronchial aspirate, BAS) from COVID-19 patients. The test could be easily adapted to detect other cytokines such as TNF-α and IL-8 by changing the antibodies decorating the nanoparticles accordingly. The ability of detecting cytokines in blood and respiratory samples paves the way for monitoring local inflammation in the lungs as well as systemic inflammation levels in the body.

Paper has the potential to dramatically reduce the cost of electronic components. In fact, paper is 10 000 times cheaper than crystalline silicon, motivating the research to integrate electronic materials on paper substrates. Among the different electronic materials, van der Waals materials are attracting the interest of the scientific community working on paper-based electronics because of the combination of high electrical performance and mechanical flexibility. Up to now, different methods have been developed to pattern conducting, semiconducting and insulating van der Waals materials on paper but the integration of superconductors remains elusive. Here, the deposition of NbSe2, an illustrative van der Waals superconductor, on standard copy paper is demonstrated. The deposited NbSe2 films on paper display superconducting properties (e.g. observation of Meissner effect and resistance drop to zero-resistance state when cooled down below its critical temperature) similar to those of bulk NbSe2., Paper has the potential to dramatically reduce the cost of electronic components but the integration of electronic materials is challenging. Here the integration of NbSe2, a van der Waals superconductor, on paper is demonstrated.