A Comparative Study of the Interaction of Different Polycyclic Aromatic Hydrocarbons on Different Types of Single Walled Carbon Nanotubes

A comparative study of the solubilising effect of polycyclic aromatic hydrocarbon (PAHs) on single walled carbon nanotubes (SWCNTs) produced by high pressure decomposition of carbon monoxide (HiPco) and the arc discharge (AD) method has been carried out with the aid of fluorescence and Raman spectroscopy. For this study, polyphenyl and polyacene PAHs of different lengths are used. From the study it has been found that the binding energy of PAHs with AD SWCNTs is the same as that with HiPco SWCNTs. Shorter PAHs molecules better solubilise SWCNTs and in general smaller diameter SWCNTs. Thus, given their smaller diameter profile, significantly larger amounts of HiPco SWCNTs are solubilised than AD SWCNTs

Ultrasound-Assisted SWNTs Dispersion: Effects of Sonication Parameters and Solvent Properties

Ultrasonication is widely used for preparing Single-Walled Carbon Nanotube (SWNT) dispersions in different solvent media and it has been shown to play a critical role in dispersing and debundling SWNTs. The strong shear force that can exfoliate the SWNT bundles during sonication comes from cavitation, which entails a process of bubble formation, growth, and collapse. The efficiency of the cavitation process is closely correlated to many solvent parameters, including vapor pressure, viscosity, and surface tension, as well as the sonication frequency, intensity, and time. In this study, SWNTs were dispersed in a range of organic solvents assisted by tip sonication. The effects of sonication intensity and time were investigated in o-dichlorobenzene (o-DCB) and dimethylformamide (DMF). The aggregation fraction below the dispersion limit of SWNTs in the range of organic solvents was found to be influenced by the solvent parameters, particularly solvent vapor pressure and viscosity. It is demonstrated that the parameters associated with the sonication process rather than solvent solubility parameters govern the dispersion process. It is further confirmed that significant degradation of the SWNTs is affected during the dispersion process

Identifying individual nutrient deficiencies of grapevine leaves using hyperspectral imaging

The efficiency of a vineyard management system is directly related to the effective management of nutritional disorders, which significantly downgrades vine growth, crop yield and wine quality. To detect nutritional disorders, we successfully extracted a wide range of features using hyperspectral (HS) images to identify healthy and individual nutrient deficiencies of grapevine leaves. Features such as mean reflectance, mean first derivative reflectance, variation index, mean spectral ratio, normalised difference vegetation index (NDVI) and standard deviation (SD) were employed at various stages in the ultraviolet (UV), visible (VIS) and near-infrared (N.I.R.) regions for our experiment. Leaves were examined visually in the laboratory and grouped as either healthy (i.e. control) or unhealthy. Then, the features of the leaves were extracted from these two groups. In a second experiment, features of individual nutrient-deficient leaves (e.g., N, K and Mg) were also analysed and compared with those of control leaves. Furthermore, a customised support vector machine (SVM) was used to demonstrate that these features can be utilised with a high degree of effectiveness to identify unhealthy samples and not only to distinguish from control and nutrient deficient but also to identify individual nutrient defects. Therefore, the proposed work corroborated that HS imaging has excellent potential to analyse features based on healthiness and individual nutrient deficiencies of grapevine leaves

Applications of LiDAR in Agriculture and Future Research Directions

Light detection and ranging (LiDAR) sensors have accrued an ever-increasing presence in the agricultural sector due to their non-destructive mode of capturing data. LiDAR sensors emit pulsed light waves that return to the sensor upon bouncing off surrounding objects. The distances that the pulses travel are calculated by measuring the time for all pulses to return to the source. There are many reported applications of the data obtained from LiDAR in agricultural sectors. LiDAR sensors are widely used to measure agricultural landscaping and topography and the structural characteristics of trees such as leaf area index and canopy volume; they are also used for crop biomass estimation, phenotype characterisation, crop growth, etc. A LiDAR-based system and LiDAR data can also be used to measure spray drift and detect soil properties. It has also been proposed in the literature that crop damage detection and yield prediction can also be obtained with LiDAR data. This review focuses on different LiDAR-based system applications and data obtained from LiDAR in agricultural sectors. Comparisons of aspects of LiDAR data in different agricultural applications are also provided. Furthermore, future research directions based on this emerging technology are also presented in this review

Selective Solubilisation of Single Walled Carbon Nanotubes Using Polycyclic Aromatic Hydrocarbons

Single-walled carbon nanotubes (SWCNTS) are proposed to be one of the most promising nanomaterials, with unique electronic and mechanical properties which lend themselves to a variety of applications. In all cases the quality of the SWCNT material is important, and for some applications it is paramount. Despite sustained efforts, all currently known SWCNT synthetic techniques generate significant quantities of impurities. They also grow in bundles or ropes and are largely insoluble in common organic solvents. SWCNTS can have a range of structures and their electronic properties (metallic or semiconducting) depend on their structure and as well on their diameters. Currently there is no production process that can produce only one particular type of SWCNTs. For these reasons, carbon nanotubes have been slow to reach maximum potential applications. To speed up the potential applications of SWCNTS it has now become mandatory to purify, increase the solubility, disperse and separate SWCNTs according to their electronic properties in a simplified and economical way. In this project polycyclic aromatic hydrocarbons (PAHs) of two oligomer series, namely the polyacene series and polyphenyl series, of systematically varied length, were used to selectively solubilise, disperse and separate SWCNTs produced by the pressure decomposition of carbon monoxide (HiPco) and arc discharge (AD) methods according to their electronic properties. The interactions and debundling of SWCNTs are investigated through a fluorescence based concentration dependent model. This model defines the concentration range where aggregated and isolated SWCNTs exist. If was found that regardless of the type of SWCNTs (HiPco of AD), the binding energy between SWCNTs and PAHS was the same and it increases as the molecular weight of PAHs increases, thereby establishing a linear relationship between binding energy of SWCNTs with PAHs and molecular weight of the corresponding PAHS, indicating the structure property relationship governing this solubilistion process. Atomic force microscopy was used to visualise the dispersed and isolated SWCNTs. To explore the selective solubilisation of SWCNTS with the aid of PAHS, Raman spectroscopy was used. From the Raman spectrosocopy study it was found that a broad range of HiPco and AD SWCNTs were solubilised with little evidence of true structural selectivity of HiPco SWCNTs. It can be stated that although the longer PAHS have the capacity to solubilise larger diameter SWCNTs due to their increased binding energy, in general a preference for smaller diameter SWCNTs were evident. This preference for smaller diameter nanotubes is reflected in the quantitative comparison of the solubilities of the two different types of SWCNTs, the smaller diameter HiPco SWCNTs being solubilised to a greater extent than the larger AD SWCNTs

A Raman Spectroscopy Study of the Solubilisation of SWCNTS by POlycyclic Aromatic Hydrocarbons

The effectiveness of polycyclic aromatic hydrocarbons (PAHs) for selective solubilisation of single walled carbon nanotubes (SWCNTs) has been studied by Raman spectroscopy. Polyphenyl and polyacene PAHs of different lengths are used. Selective interaction between the PAHs and SWCNT is investigated by analyzing the Raman radial breathing modes the frequency positioning of which yields information concerning the diameter distribution of the SWCNT sample. Samples were dispersed at concentrations below the debundling limit and deposited on quartz substrates. A combination of four laser excitation energies was utilized to establish the distribution of diameters present. The results show that the PAHs interact with a range of SWCNT diameters. In general a preference for smaller diameter SWCNTs is evident, although the longer PAHs have the capacity to solubilise larger diameter SWCNTs, due to their increased binding energy. Although a small degree of structural specificity is evident, all PAHs solubilise both chiral and nonchiral SWCNTs

A Systematic Study of the Dispersion of SWNTs in Organic Solvents

Dispersions of as-produced HiPco single-walled carbon nanotubes (SWNTs) in a series of organic solvents were prepared by dilution with the aid of tip sonication. Mild centrifugation (~ 945 g) was carried out to remove large bundles. Atomic force microscopy (AFM) studies revealed that the bundle size decreased as the dispersion was diluted. By measuring the UV-vis-NIR absorption before and after centrifugation as a function of the concentration, the dispersion limit of SWNTs in each solvent can be determined. Correlations between the dispersion limit and solvent solubility parameters, including the Hildebrand solubility parameter and three dimensional Hansen solubility parameters, are explored, demonstrating that SWNTs are easily dispersed in solvents with Hildebrand solubility parameter range from ~22-24 MPa1/2 and Hansen polarity component (δP) ~12-14 MPa1/2. No clear correlation between dispersion limits and the dispersion force (δD) or hydrogen bonding force (δH) are evident. It is found, however, that the degree of dispersion depends critically on sample preparation conditions and in particular sonication time. Increased sonication times increase the amount of SWCNTs debundled and solubilised but do not appear to affect the dispersion limit. However, increased sonication also induces discernible changes to the SWNTs themselves and in itself influences their solubility, under which conditions no clear solubility parameters can be determined