Mechano-chemical synthesis of Cu-doped BiVO4 monoclinic nanopowders and investigation of structural, optical and electronic properties.

No abstract

A green method for an efficient synthesis of water-soluble carbon nanoparticles (CNPs), graphitic shell encapsulated carbon nanocubes (CNCs), Carbon dots (CDs) using Camphor (Cinnamomum camphora) is demonstrated. Here, we describe a competent molecular fusion and fission route for step-wise synthesis of CDs. Camphor on acidification and carbonization forms CNPs, which on alkaline hydrolysis form CNCs that are encapsulated by thick graphitic layers and on further reduction by sodium borohydride yielded CDs. Though excitation wavelength dependent photoluminescence is observed in all the three carbon nanostructures, CDs possess enhanced photoluminescent properties due to more defective carbonaceous structures. The surface hydroxyl and carboxyl functional groups make them water soluble in nature. They possess excellent photostability, higher quantum yield, increased absorption, decreased cytotoxicity and hence can be utilized as a proficient bio imaging agent.The remarkable features of photoluminescent nanocarbon family are attributed to their water solubility, good quantum yield, low photobleaching, high biocompatibility and efficient biolabelling agent 1 . They are far more superior to other conventional fluorescent organic dyes and luminescent inorganic cadmium based-quantum dots in terms of photostability and toxicity. Carbon dots (CDs) are one of carbon based nanoallotrope, which has now received major attention since it possesses unique optical, optoelectronic properties exhibiting size and excitation wavelength dependent photoluminescence 1 . These properties are purely due to the most well-known fact that they exhibit quantum confinement effect, emissive traps and edge effects which exists on their surface.

Nanostructured composites based on plasmonic Ag metal nanoclusters with monoclinc‐BiVO4 nanoparticles were prepared by high energy ball milling technique. The agglomerated morphology with a spherical shape of 50–100 nm sized BiVO4 particles associated with homogeneous distribution of 5–10 nm Ag clusters significantly enhanced the photocatalytic activity for the degradation of acid blue dyes. The Ag doping concentration with BiVO4 was optimized at 3 at. % leading to almost 10 folds faster photocatalytic degradation rate as compared to pristine form. Thus, Ag doped BiVO4 nanocomposites show efficient visible light driven photocatalytic activity due to charge distribution at the semiconducting‐metal interfaces from band bending and the involvement of a radiation field enhanced by plasmon resonance effects at the surfaces of Ag‐clusters.

The flexoelectric effect is simply defined as the coupling between the strain gradient and polarization in solid dielectrics. It may be seen as an alternative transduction mechanism to the piezoelectric effect to directly sense the curvature of bent flexible thin structures. In the case of large curvatures, flexible and compliant sensors are required and soft polar elastomers may be suitable for curvature sensing. In this study, we report the flexoelectric characterization of soft semi-crystalline polyurethane (PU) films with thicknesses ranging from 1.7 μm to 350 μm. Dynamic bending experiments have been performed on PU films deposited onto rigid steel substrates in the vicinity of the mechanical resonance frequency of the cantilever beams. Quasi-static flexoelectric coefficients of PU films could be obtained by using a classical oscillating model. A global large increase of μ12′ with the decreasing film thickness was found, especially for thicknesses lower than 25 μm. The variation of μ12′ is explained by the presence of a Young's Modulus gradient through the thickness of PU films. Besides, a concomitant uncommon dramatic decrease in the dielectric constant is observed. The combination of these two effects contributes to enhancing the flexocoupling “F” constant with the decreasing thickness. At last, the potential use of a 6.6 μm-thick soft PU film as a large curvature sensor has been experimentally demonstrated by subjecting a flexible Aluminum foil/Polyethylene terephthalate bilayered cantilever to large deflections. A curvature of about 80 m−1 (radius of curvature of ∼1.2 cm) could be sensed under low frequency (3 Hz) bending motion. These results may pave the way for the development of low cost and easy to implement soft flexoelectric elastomer-based large curvature sensors on highly flexible metallic structures.

Mesoporous thin films of bismuth vanadate were synthesized by sol-gel method with defined deposition parameters and annealing treatments leading to nano-textured surfaces. The stabilization of monoclinic BiVO 4 structure was demonstrated by structural investigations and nano-islands morphology of the films illustrated by Atomic Force Microscopy (AFM) studies. Indoline dyes (D149) were used to sensitize the film surfaces able to show photoinduced charge transfer on the hybrid surfaces using Kelvin force microscopy (KFM). The distributions of the surface electrical potentials were compared as function of the surface texture and the sensitization by dyes. A model of the band alignment in hybrid systems was proposed to account for the observed charge transfer. The photocatalytic activity of the hybrid films was also investigated and discussed.

Among the transduction mechanisms of interest for sensing and/or actuation applications at nano/micro scale, the piezoelectric effect has been widely exploited owing to the solid state nature of piezoelectrics, the large ability of specific classes of materials for the mechanical-to-electrical energy conversion and easy integration. However, every piezoelectric (also generally ferroelectric) presents well-known intrinsic drawbacks such as required poling step and related aging. In contrast, uniquely flexoelectric materials do not suffer from these disadvantages because flexoelectricity, a universal effect in all dielectric solids defined as the electrical polarization induced by a strain gradient, does not imply preliminary electric field-induced macroscopic polarization. Besides, strain gradient may be easily obtained by bending plate or cantilever-shaped structure and in this case it is nothing but the local curvature of the flexible system. Thus, as strain gradient (curvature) inversely scales with both elastic stiffness and thickness, this study will focus on the evaluation of the potentialities of flexoelectric effect in soft polymer films for electromechanical applications, with an emphasis on the thickness influence. In this way, analytical results combined to experimentally obtained effective flexoelectric coefficients for some typical polymer classes may provide guidelines for the development of soft and low frequency flexoelectric mechanical transducers.

No abstract