A simple and fast fabrication method to create high-performance pencil-drawn electrochemical sensors is reported for the first time. The sluggish electron transfer observed on bare pencil-drawn surfaces was enhanced using two electrochemical steps: first oxidizing the surface and then reducing it in a subsequent step. The heterogeneous rate constant was found to be 5.1 × 10 cm s, which is the highest value reported so far for pencil-drawn surfaces. We mapped the origin of such performance by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Our results suggest that the oxidation process leads to chemical and structural transformations on the electrode surface. As a proof-of-concept, we modified the pencil-drawn surface with Meldola's blue to electrocatalytically detect nicotinamide adenine dinucleotide (NADH). The electrochemical device exhibited the highest catalytic constant (1.7 × 10 L mol s) and the lowest detection potential for NADH reported so far in paper-based electrodes.

In this work, we demonstrate the first example of fully printed carbon nanomaterials on paper with unique features, aiming the fabrication of functional electronic and electrochemical devices. Bare and modified inks were prepared by combining carbon black and cellulose acetate to achieve high-performance conductive tracks with low sheet resistance. The carbon black tracks withstand extremely high folding cycles (>20 000 cycles), a new record-high with a response loss of less than 10%. The conductive tracks can also be used as 3D paper-based electrochemical cells with high heterogeneous rate constants, a feature that opens a myriad of electrochemical applications. As a relevant demonstrator, the conductive ink modified with Prussian-blue was electrochemically characterized proving to be very promising toward the detection of hydrogen peroxide at very low potentials. Moreover, carbon black circuits can be fully crumpled with negligible change in their electrical response. Fully printed motion and wearable sensors are additional examples where bioinspired microcracks are created on the conductive track. The wearable devices are capable of efficiently monitoring extremely low bending angles including human motions, fingers, and forearm. Here, to the best of our knowledge, the mechanical, electronic, and electrochemical performance of the proposed devices surpasses the most recent advances in paper-based devices.

electronics that withstand mechanical stress. Successful applications of such devices are spread in areas of health, environment, and energy. [1-3] For instance, electronic skin, [4] human-robot interfaces, [5] stretchable electrodes, [6] supercapacitors, [7] transistors, [8] and electrochemical wearable devices [9] have been extensively studied in this direction. In particular, electrochemical devices often permeate into different areas bringing a plethora of high-performance applications. Most of the fabrication methods used to fabricate stretchable electrochemical devices consist of combining elastomers, such as polydimethylsiloxane (PDMS), Ecoflex, Silbione, or polyurethane, with conductive structures. The reported methods are divided into two main routes: i) mixing the elastomer with conductive structures in a single step [6] or ii) preparing the elastomeric substrate in a first step followed by transfer [9-13] or printing [14-17] the conductive materials in a second step. Among the different conductive materials (conductive polymers, Au, and Ag), carbonbased materials are well-known due to their high sensitivity, stability, remarkable electrical properties, and the possibility of functionalization by several routes. [10,11,14-16] Carbon nanotubes and graphene have shown interesting properties for several applications in the field of flexible and stretchable devices. Their high aspect-ratio plays an important role in maintaining their electrochemical performance under mechanical stress (bend, twist, crumple, stretch). [2] However, their high preparation cost, low production yields, and the sophisticated equipment needed for their synthesis, in addition to their environmentally harmful preparation processes, are some drawbacks that need to be circumvented. Therefore, there is an increasing interest in preparing conductive carbon-based materials from low-cost, abundant, and sustainable sources. Due to the environmentally friendly characteristic and large-scale production, raw materials as biopolymers and some synthetic polymers have been used in the process of carbonization, such as natural and synthetic silk, [18-21] sponges, [22] and various types of cellulose-based substrates Pyrolyzed cellulose-based materials are extensively used in many fields for many different applications due to their excellent electrical properties. However, pyrolyzed materials are extremely fragile and prone to crack. To address this issue, a new fabrication method is reported to delay the capillary flow of elastomeric materials into the porous structure of the paper. By changing the surface chemistry and porosity of the material, the capillary flow of the elastomer through the porous structure is delayed. Delayed capillary flow of elastomers (DCFE method) ensures both extremely high mechanical stability and electrochemical performance to the devices. Impressively, the electrochemical devices can be bent, folded, twisted, and stretched at 75% of their original length without hindering their electrochemical response. Moreover, cooper...

Surface-Mounted Metal–Organic Frameworks (SURMOFs) growth orientation in [100] or [111] can be deterministically controlled by the SAM chain length, regardless of the surface nature (metallic or insulating).

Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion-exchange properties of the functionalized porous solid (SBA-15/R(+)Cl(-)) toward AuCl(4)(-) anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (t(Q) = 0.79 mmol g(-1)) indicate that the AuCl(4)(-) species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl(4)(-) ions were submitted to a chemical reduction process with NaBH(4), converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

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The environmental contamination of soils by polymeric and nanomaterials is an increasing global concern. Polymeric composites containing silver nanoparticles (AgNP) are collectively one of the most important products of nanotechnology due to their remarkable antimicrobial activity. Biochars are a promising resource for environmental technologies for remediation of soils considering their high inorganic and organic pollutant adsorption capacity and microbial soil consortium stimulation. In this work we report, for the first time, the use of biochar material as a tool to accelerate the degradation of polyhydroxybutyrate-co-valerate (PHBV) and PHBV composites containing AgNP in a tropical soil system, under laboratory conditions. This positive effect is associated with microbial community improvement, which increased the degradation rate of the polymeric materials, as confirmed by integrated techniques for advanced materials characterization. The addition of 5–10% of sugarcane bagasse biochar into soil has increased the degradation of these polymeric materials 2 to 3 times after 30 days of soil incubation. However, the presence of silver nanoparticles in the PHBV significantly reduced the degradability potential of this nanocomposite by the soil microbial community. These results provide evidence that AgNP or Ag+ ions caused a decline in the total number of bacteria and fungi, which diminished the polymer degradation rate in soil. Finally, this work highlights the great potential of biochar resources for application in soil remediation technologies, such as polymeric (nano)­material biodegradation.

Size-controlled europium(III)-doped SnO 2 nanoparticles dispersed inside of porous Vycor glass (PVG) were synthesized using the impregnation and decomposition cycle (IDC) method. XRD, DRS, and TEM analyses proved that the observed cumulative mass gain after each IDC is associated to a controlled growing of the SnO 2 nanoparticles. Europium(III) emission spectra were acquired for all samples and clear differences on the relative intensity of the 5 D 0 f 7 F 2 / 5 D 0 f 7 F 1 transitions were observed for different SnO 2 nanoparticle sizes. The changes in the europium(III) emission spectra could be correlated with the increase of nanoparticle sizes. The smaller superficial nanoparticle area decreases the amount of europium(III) at the surface, where it can be located in different environments over distorted symmetry sites, compared to the crystal lattice sites, where the ions probably are located, when the particles become bigger with no changes in their crystallinity degree. The linear plot between the asymmetric intensity ratio of the 5 D 0 f 7 F 2 / 5 D 0 f 7 F 1 transitions and the particles area/volume ratio calculated from the XRD Scherrer data and particle size frequency counts (∼1/d) confirmed this behavior.