Graphene-based Schottky Device Detecting NH3 at ppm level in Environmental Conditions

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Effect of graphene nano-platelet morphology on the elastic modulus of soft and hard biopolymers

Abstract Free-standing biocomposites were fabricated by solvent casting and hot-pressing employing two bio-polyesters having diverse elastic (Young's) moduli (soft and hard), reinforced with different graphene nanoplatelets (GnPs). Systematic mechanical measurements were conducted to investigate the effect of GnP thickness and lateral size on the elastic moduli. Comparisons were made with other reinforcing nanostructured filers such as organoclay, MoS 2 , Fe 2 O 3 , carbon black and silica nanoparticles. Upon solvent casting, GnPs did not perform better than the other model fillers in increasing the elastic modulus of the soft bio-polyester. Upon hot-pressing however, large (>300 nm) multi-layer GnPs (≥8 layers) more than doubled the elastic modulus of the soft bio-polyester matrix compared to other GnPs and fillers. This effect was attributed to the optimized alignment of the large 2D GnP flakes within the amorphous soft polymer. In contrast, hot-pressing did not yield superior elastic modulus enhancement for the hard bio-polyester when hot-pressed. GnPs only induced 30% enhancement for both processes. Moreover, multi-layer large GnPs were shown to suppress the thermally-induced stiffness reduction of the soft bio-polyester near its melting temperature. A theoretical analysis based on the spring network model is deployed to describe the impact of the GnP alignment on the elastic moduli enhancement

Optimization of multilayer graphene-based gas sensors by ultraviolet photoactivation

Nitrogen dioxide (NO2) is a potential hazard to human health at low concentrations, below one part per million (ppm). NO2 can be monitored using gas sensors based on multi-layered graphene operating at ambient temperature. However, reliable detection of concentrations on the order of parts per million and lower is hindered by partial recovery and lack of reproducibility of the sensors after exposure. We show how to overcome these longstanding problems using ultraviolet (UV) light. When exposed to NO2, the sensor response is enhanced by 290 % − 550 % under a 275 nm wavelength light emitting diode irradiation. Furthermore, the sensor’s initial state is completely restored after exposure to the target gas. UV irradiation at 68 W/m2 reduces the NO2 detection limit to 30 parts per billion (ppb) at room temperature. We investigated sensor performance optimization for UV irradiation with different power densities and target gases, such as carbon oxide and ammonia. Improved sensitivity, recovery, and reproducibility of UV-assisted graphene-based gas sensors make them suitable for widespread environmental applications

From graphene to graphene-based gas sensors operating in environmental conditions

The thesis work is focused on two major items: 1. growth and characterization of graphene films; 2. test of the material sensing properties towards analytes by employing graphene-based chemi-resistors as transducers. The mostly exploited techniques for the graphene production are Liquid Phase Exfoliation (LPE) and Chemical Vapor Deposition. The material characterizations performed through Raman spectroscopy, Atomic Force Microscopy and Transmission Electron Microscopy are presented. The experimental results allow to argue the morphological and structural nature of such prepared materials. The issue regarding the GR defects is also addressed with the purpose to better understand the strong sensitive of material in the sensing field. The sensors, operating at room temperature and pressure as well as in presence of humidity, are tested towards several analytes, such as NO2, H2 and NH3. The sensors are calibrated in the sub-ppm range of NO2 so that the devices result to be particularly appealing as graphene-based sensors for NO2 operating in wet environment

Significant strain and force improvements of single-walled carbon nanotube actuator: A metal chalcogenides approach

Carbon nanotube actuators possess the requirements to be used in soft robotic applications as they are lightweight, simple to assemble and can operate at low voltage. However, there is still a need to further enhance their performances - in particular strain and blocking force - in order to render their implementation in devices more viable. In this study, we report the electrochemical and electromechanical properties of carbon nanotube-polymer actuators containing metal chalcogenides (BN, WS2 and MoS2). We demonstrate that the incorporation of such particles in the carbon-based electrodes results in a remarkable increase of the actuators' performances. Indeed, by tuning the amount of metal chalcogenides, we improve both the strain and blocking force responses of the actuators by 60%

A study on the physicochemical properties of hydroalcoholic solutions to improve the direct exfoliation of natural graphite down to few-layers graphene

Straightforward methods to produce pristine graphene flakes in large quantities are based on the liquid-phase exfoliation processes. These one-step physical transformations of graphite into graphene offer many unique advantages. To date, a large number of liquids have been employed as exfoliation media exploiting their thermodynamic and chemical features as compared to those of graphene. Here, we pursued the goal of realizing water based mixtures to exfoliate graphite and disperse graphene without the aid of surfactants. To this aim, aqueous mixtures with suitable values of surface tension and Hansen solubility parameters (HSPs), were specifically designed and used. The very high water surface tension was decreased by the addition of solvents with lower surface tensions such as alcohols, obtaining, in this way, more favourable HSP distances. The specific role of each of these thermodynamic features was finally investigated. The results showed that the designed hydroalcoholic solutions were effective in both the graphite exfoliation and dispersion without the addition of any surfactants or other stabilizing agents. Stable graphene suspensions were obtained at concentration comparable to those produced with low-boiling solvents and water/surfactants