Francisco M. Sánchez-Arévalo

Polymeric Carbon Nitride Nanosheets

Polymeric carbon nitride was synthesized by polycondensation in a nitrogen flux using melamine cyanurate as a reagent and sulfuric acid as a catalyst. The product was polymeric-graphitic carbon nitride based on heptazine units. The carbon nitride was composed of nanosheet flakes. This synthesis method seems to be a suitable pathway toward carbon nitride graphene formation.

Synthesis of boron carbon nitride oxide (BCNO) from urea and boric acid

ABSTRACT A solid state synthesis of boron carbon nitride oxide (BCNO) material was carried out starting from urea and boric acid treated at 600°C. The X-ray diffraction pattern corresponded to amorphous BCNO with an interlayer distance of 3.49 Å. The material had a layered structure similar to that of graphite and hexagonal boron nitride (h-BN). Infrared spectroscopy (IR) showed bands which were similar to those typical of BN and carbon nitride. The presence of boron was also confirmed by energy dispersive spectroscopy in an amount compatible with the IR spectrum. The spectra obtained by X-ray photoelectron spectroscopy (XPS) corresponded to those of a BCNO family with a considerable content of oxygen too. The optical band gap was estimated to be 3.22 eV, typical of a wide band-gap semiconductor. The particle size was very dispersed from micro to nanosize. The material dispersed in polar solvents formed stable suspensions due to the presence of hydroxyl groups.

Laser induced deformation in polydimethylsiloxane membranes with embedded carbon nanopowder

We demonstrate optically induced micron-range deformation of polydimethylsiloxane (PDMS) membranes with embedded carbon nanopowder. The mechanical deformation can be controlled by low power laser irradiation of the samples and the resulting surface modifications are analyzed via dynamic speckle measurements. Photothermal effects due to optical absorption by the nanopowder are shown to deform the polymer samples leading to localized mechanical stresses induced via thermal expansion of the PDMS.

Macro- and micromechanical behaviors of poly(lactic acid)–hydroxyapatite electrospun composite scaffolds

It was demonstrated that the macro- and micromechanical behaviors of electrospun composite scaffolds based on PLA and HA can be simultaneously studied using 3D digital image correlation strain measurements coupled with an axial tensile test. It was proven that the addition of a small quantity (2%) of HA particles into PLA electrospun scaffolds decreased their mechanical properties by approximately 40 and 60% at the micro- and macroscales, respectively; nevertheless, when this amount was increased beyond 2% of HA, the composites recovered their stiffness, showing Young’s moduli ranging between 400 and 600 MPa. Hence, the mechanical responses of PLA–4% HA and PLA–6% HA electrospun scaffolds were conveniently enhanced with the addition of hydroxyapatite nanoparticles. The micromechanical measurements were able to capture the microstrain mechanism between electrospun nanofibers and the effect of HA nanoparticles on their mechanical response. This methodology could be a powerful tool for developing scaffolds for specific applications in tissue engineering.

Photothermal Effects and Applications of Polydimethylsiloxane Membranes with Carbon Nanoparticles

The advent of nanotechnology has triggered novel developments and applications for polymer-based membranes with embedded or coated nanoparticles. As an example, interaction of laser radiation with metallic and carbon nanoparticles has shown to provide optically triggered responses in otherwise transparent media. Incorporation of these materials inside polymers has led to generation of plasmonic and photothermal effects through the enhanced optical absorption of these polymer composites. In this work, we focus on the photothermal effects produced in polydimethylsiloxane (PDMS) membranes with embedded carbon nanoparticles via light absorption. Relevant physical parameters of these composites, such as nanoparticle concentration, density, geometry and dimensions, are used to analyze the photothermal features of the membranes. In particular, we analyze the heat generation and conduction in the membranes, showing that different effects can be achieved and controlled depending on the physical and thermal properties of the composite material. Several novel applications of these light responsive membranes are also demonstrated, including low-power laser-assisted micro-patterning and optomechanical deformation. Furthermore, we show that these polymer-nanoparticle composites can also be used as coatings in photonic and microfluidic applications, thereby offering an attractive platform for developing light-activated photonic and optofluidic devices.

Composite Fiber Based on Sisal Fiber and Calcium Carbonate

The impregnation of a raw sisal fiber in a saturated solution of calcium hydroxide generated a fiber coated by a remarkable quantity of calcium carbonate and calcium oxide. However, some detachments of the inorganic coating were observed at microscopic level, and interstices in the external walls, filled by the precipitated material, were less visible than in raw fiber. Additionally, some fiber components have been removed by the preliminary sodium silicate washing. The final composite exhibited more amorphous characteristics than the original raw fiber, as well as its mechanical behavior was very similar to an elastomeric material with more homogeneous mechanical properties than the original raw fiber.

Synthesis and characterization of Cu-doped polymeric carbon nitride

ABSTRACT Polymeric carbon nitride doped with copper through a solid-state reaction was characterized by several techniques, among them are UV-visible spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, etc. The material is a semiconductor with a wide band gap of 2.74 eV. Sites of both Cu(I) and Cu(II) were detected, apparently only coordinated by the polymer. The material comprises crumpled nanosheets, and is substantially an amorphous layered material with a prevalent 2D structure with low inter-planar interactions, as shown by X-ray diffractometry and TeraHertz spectroscopy. Photo-oxidation of benzyl alcohol was used to probe the active sites of the material, comparing them with the non-doped material. The higher activity and selectivity toward salicylic alcohol of the non-doped material can be due to both a more localized electron transfer and a longer lifetime of the hole–electron pair. Cu-CN favored the oxidation of hydroxymethyl group. Therefore, the presence of copper can favor different reaction pathways with respect to the non-doped material.

Molecular dynamics simulations of nanosheets of polymeric carbon nitride and comparison with experimental observations

ABSTRACT A computational study of the properties of polymeric carbon nitride using molecular dynamics is presented. The analysis of ideal infinite-extent sheets permits to evaluate the effect of temperature on the network of hydrogen bonds responsible for the linkage of the material. The weakening of this binding mechanism at sufficiently high temperatures, together with the inter-layer interactions characteristic of this type of 2D materials, is shown to determine the conformation properties of polymeric carbon nitride at the nanoscale. The results obtained from the simulation of finite samples in the canonical ensemble at varying temperatures are consistent with those from the characterization of our experimentally synthesized samples. Hydrogen bonding between adjacent polymer ribbons leads this process and is the cause of the typical crumpled structure of this material.

Photocatalytic activity of a new composite material of Fe (III) oxide nanoparticles wrapped by a matrix of polymeric carbon nitride and amorphous carbon

ABSTRACT Polymeric carbon nitride was synthesized from urea and doped with Cu and Fe to act as co-catalysts. The material doped with Fe was a new composite material composed of Fe(III) oxides (acting as a co-catalyst) wrapped by the polymer layers and amorphous carbon. Furthermore, the copper doped material was described in a previous report. The photocatalytic degradation of the azo dye direct blue 1 (DB) was studied using as photocatalysts: pure carbon nitride (CN), carbon nitride doped with Cu (CN-Cu) and carbon nitride doped with Fe (CN-Fe). The catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), by X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller method (BET), etc. The adsorption phenomenon was studied using the Langmuir and Freundlich models. For the kinetic study, a solution of 500 mg L−1 of DB1 was treated with each catalyst, visible light and H2O2. The dye concentration was measured by spectrophotometry at the wavelength of 565 nm, and the removal of the total organic content (TOC) was quantified. BET analysis yielded surface areas of 60.029, 20.116 and 70.662 m2g−1 for CN, CN-Cu and CN-Fe, respectively. The kinetics of degradation were pseudo-first order, whose constants were 0.093, 0.039 and 0.110 min−1 for CN, CN-Cu and CN-Fe, respectively. The total organic carbon (TOC) removal reached the highest value of 14.46% with CN-Fe.

Mechanical assessment of bovine pericardium using Müeller matrix imaging, enhanced backscattering and digital image correlation analysis.

Mechanical characterization of tissue is an important but complex task. We demonstrate the simultaneous use of Mueller matrix imaging (MMI), enhanced backscattering (EBS) and digital image correlation (DIC) in a bovine pericardium (BP) tensile test. The interest in BP relies on its wide use as valve replacement and biological patch. We show that the mean free path (MFP), obtained through EBS measurements, can be used as an indicator of the anisotropy of the fiber ensemble. Our results further show a good correlation between retardance images and displacement vector fields, which are intrinsically related with the fiber interaction within the tissue.