Electronic Properties of Functionalized Diamanes for Field-Emission Displays

Ultrathin diamond films, or diamanes, are promising quasi-2D materials that are characterized by high stiffness, extreme wear resistance, high thermal conductivity, and chemical stability. Surface functionalization of multilayer graphene with different stackings of layers could be an interesting opportunity to induce proper electronic properties into diamanes. Combination of these electronic properties together with extraordinary mechanical ones will lead to their applications as field-emission displays substituting original devices with light-emitting diodes or organic light-emitting diodes. In the present study, we focus on the electronic properties of fluorinated and hydrogenated diamanes with (111), (110), (0001), (101̅0), and (2̅110) crystallographic orientations of surfaces of various thicknesses by using first-principles calculations and Bader analysis of electron density. We see that fluorine induces an occupied surface electronic state, while hydrogen modifies the occupied bulk state and also induces unoccupied surface states. Furthermore, a lower number of layers is necessary for hydrogenated diamanes to achieve the convergence of the work function in comparison with fluorinated diamanes, with the exception of fluorinated (110) and (2̅110) films that achieve rapid convergence and have the same behavior as other hydrogenated surfaces. This induces a modification of the work function with an increase of the number of layers that makes hydrogenated (2̅110) diamanes the most suitable surface for field-emission displays, better than the fluorinated counterparts. In addition, a quasi-quantitative descriptor of surface dipole moment based on the Tantardini−Oganov electronegativity scale is introduced as the average of bond dipole moments between the surface atoms. This new fundamental descriptor is capable of predicting a priori the bond dipole moment and may be considered as a new useful feature for crystal structure prediction based on artificial intelligence

Current Trends in Nanoporous Anodized Alumina Platforms for Biosensing Applications

Pristine aluminum (Al) has received great deal of attention on fabrication of nanoporous anodized alumina (NAA) with arrays of nanosized uniform pores with controllable pore sizes and lengths by the anodization process. There are many applications of NAA in the field of biosensors due to its numerous key factors such as ease of fabrication, high surface area, chemical stability and detection of biomolecules through bioconjugation of active molecules, its rapidness, and real-time monitoring. Herein, we reviewed the recent trends on the fabrication of NAA for high sensitive biosensor platforms like bare sensors, gold coated sensors, multilayer sensors, and microfluidic device supported sensors for the detection of various biomolecules. In addition, we have discussed the future prospectus about the improvement of NAA based biosensors for the detection of biomolecules

Association between Serum Vitamin B12 Concentration and Obesity Among Adults in The Ksa

Objective: To investigate the relationship between serum vitamin B12 levels and weight among the adult population in KSA. Methods: This research will employ a cross-sectional study design to investigate the association between serum vitamin B12 concentration and obesity among adults in the Kingdom of Saudi Arabia (KSA). Cross-sectional studies are suitable for examining relationships between variables within a specific population at a single point in time. The target population for this study includes all adult residents of the KSA aged 18 years and older. Results: The study included 869 participants. The most frequent weight among them was 51-65 kg (n= 255, 29.3%), followed by 66 -75 kg (n= 214, 24.6%). The most frequent height among study participants was 161-170 cm (n= 324, 37.3%) followed by 151-160 cm (n= 266, 30.6%). The most frequent body mass index (BMI) value among study participants was Normal 18.5-24.9 kg/m2 (n= 344, 39.6%), followed by overweight 25-29.9 kg/m2 (n= 281, 32.3%).  Vitamin B12 varied among study participants, with most of them having a normal range (n= 319, 36.7%) followed by a low range (n= 117, 13.5%) and the least common high range (n= 23, 2.6%). On the other hand, among 410 participants, 47.2% did not know their vitamin B12 value. Wech may indicate a lack of knowledge about the topic. Figure 4 shows the vitamin B12 levels among study participants. Conclusion: Study results showed that most of the study participants do not know their vitamin B12 level and need to increase awareness, followed by those who have a normal vitamin B12 level. The most common BMI was the normal level. There was a relationship between vitamin B12 levels and obesity.

Synthesis of Carbon Nanotube (CNT) Composite Membranes

Carbon nanotubes are attractive approach for designing of new membranes for advanced molecular separation because of their unique transport properties and ability to mimic biological protein channels. In this work the synthetic approach for fabrication of carbon nanotubes (CNTs) composite membranes is presented. The method is based on growth of multi walled carbon nanotubes (MWCNT) using chemical vapour deposition (CVD) on the template of nanoporous alumina (PA) membranes. The influence of experimental conditions including carbon precursor, temperature, deposition time, and PA template on CNT growth process and quality of fabricated membranes was investigated. The synthesis of CNT/PA composites with controllable nanotube dimensions such as diameters (30–150 nm), and thickness (5–100 µm), was demonstrated. The chemical composition and morphological characteristics of fabricated CNT/PA composite membranes were investigated by various characterisation techniques including scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDXS), high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD). Transport properties of prepared membranes were explored by diffusion of dye (Rose Bengal) used as model of hydrophilic transport molecule

Carbon nanotube composites: advanced properties for emerging applications

Carbon nanotubes (CNTs) have been considered as an outstanding nanomaterial, envisaged for developing a new generation of membranes for advanced molecular separation as a result of their unique transport properties and ability to mimic biological protein channels. Nevertheless, the excellent physical and chemical properties of CNTs make this material attractive for other potential applications. For example, free-standing or liberated CNTs are nanostructures with excellent properties to develop smart nanocarriers for targeted and localized drug delivery. Before these applications become feasible, however, the fabrication process of CNTs must be entirely understood in order to produce nanostructures with totally controlled dimensions and properties. So far, some approaches have been used to synthesise CNTs, the most representative of which are arc discharge, laser ablation and catalytic chemical vapor deposition (C-CVD). However, these fabrication methods present many fundamental disadvantages (e.g. expensive equipment, high temperature of synthesis, use of toxic and hazardous materials, impurities/contaminations, etc.). Therefore, the physical and chemical properties of the resulting CNTs rely both on fabrication method and manufacturer, thus preventing the production of standardized CNTs. In this scenario, this thesis puts forward a catalyst-free CVD approach for fabricating CNTs with totally controlled properties (e.g. geometry, shape, chemical composition, surface chemistry, etc.) by using nanoporous templates with well-defined chemistry and geometry. As a result of its simplicity, versatility, scalability and cost-competitive fabrication process, this approach is envisaged for producing CNTs featuring standardized properties, which are required for a broad range of applications (e.g. separations, drug delivery, etc.). To develop this CVD approach, the optimal conditions for the fabrication of catalyst-free CNTs were determined by varying such parameters as temperature, reaction path length, absence or presence of catalyst, type of nanoporous template (i.e. nanoporous anodic alumina (NAA) or titania nanotubes (TNTs)) and type of carbon source. The most relevant aspects of this study were: 1 – Carbon Source: Two unconventional carbon sources were explored: namely, a mixed solution of toluene and ethanol and non-degradable grocery plastic bags. 2 – Nanoporous Template: To understand the mechanism of this catalyst-free CVD approach using nanoporous templates, a set of experiments comparing the growth of CNTs inside NAA and TNTs were performed. This made it possible to understand the role of the nanoporous template in the growth of CNTs as well as to establish of the mechanism of growth of CNTs inside these nanoporous templates. 3 – Geometry and Shape: CNTs with different geometries and shapes (e.g. periodically modulated diameters) were fabricated by using NAA templates featuring different geometries and shapes. This confirmed the capability of the proposed CVD approach to synthesise CNTs with desired shapes and geometries, offering new opportunities to develop innovative nanostructures for emerging applications. 4 – Chemical Composition: The presence of heteroatoms has a direct impact over the synthesis of CNTs. To throw light on this question, the effect of such heteroatoms as nitrogen (N), sulfur (S), phosphorus (P) and co-doped sulfur/phosphorus (S/P) on the quality of the resulting CNTs was investigated. 5 – Surface Chemistry Functionalization: Chemical modification of the inner surface of CNTs was achieved through gas-phase and solvent-free functionalization with different functional compounds (i.e. 1-octadecylamine (ODA), 1,8-diaminooctane (DO) and polyethyleneimine (PEI)). 6 – Applications: Finally, CNT membranes and free-standing CNTs obtained by the above-mentioned CVD approach were used in two significant applications: ◆ Sophisticated separation nanodevices (separation): To demonstrate the capability of these membranes to selectively tune molecular transport as a function of the interaction between molecules and inner surface of CNTs, the transport performance of these membranes was analyzed when transporting several dye molecules with positive, negative and neutral charge. ◆ Smart nano-carriers for delivering chemotherapeutic drugs (drug delivery): Free standing CNTs with hydrophilic core were used as nanocontainers for delivering anti-cancer drug. These CNTs were loaded with doxorubicin (Dox) and its external surface was chemically functionalized with a biodegradable polymer (chitosan) by anchoring its polymeric chains to functional groups on the external surface of CNTs. The presented results are expected to be the starting point of the development of new nanodevices based on innovative CNTs featuring totally controlled properties (i.e. standardized product), which could be used in a broad range of research fields and commercial applications.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2014

Remediation of Heavy Metals

International audienceThe book presents recent remediation techniques for heavy metal contamination in wastewater, with a focus on recently-developed and sustainable materials such as metal oxides and their composites, two-dimensional materials, organic-inorganic ion exchange materials, nanomaterials, bagasse, and olive-oil waste chelating materials. Chapters also describe the analysis of heavy metals, membranes for water treatment, sources and impact of heavy metals and opportunities and challenges in heavy metal remediation

Influence of dimensions, inter-distance and crystallinity of titania nanotubes (TNTs) on their photocatalytic activity

The aim of this study is to explore the influence of structural parameters of titania nanotubes (TNTs) including pore diameters, length, nanotube inter-distance and crystallinity on their photocatalytic properties. TNTs were prepared under various experimental conditions of applied potential, anodization time and the electrolyte water content. The morphology and crystalline structures of the prepared TNTs were characterized using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results showed that the nanotube length, diameters and nanotube inter-distance were significantly affected by different anodization conditions. The photocatalytic activities of the prepared TNTs were evaluated via the degradation of rhodamine B in aqueous solution under mercury–xenon (Hg(Xe)) lamp irradiation monitored by UV–visible spectroscopy. The influence of TNT structural properties including tube length, inter-tube distance and crystallinity on their photocatalytic activity was evaluated. It was found that TNTs with shorter and larger nanotube inter-distances have better degradation rates of rhodamine B than long tubes. Moreover, the TNTs annealed at 650 °C to produce an anatase–rutile mixture (86.5 and 13.5% respectively) exhibited higher photocatalytic activity than other TNTs annealed at 250 °C, 450 °C, and 850 °C.Mohammed Alsawat, Tariq Altalhi, Joe G. Shapter and Dusan Losi

Carbon nanotube-nanoporous anodic alumina composite membranes with controllable inner diameters and surface chemistry: influence on molecular transport and chemical selectivity

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic-hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications

Luminescent porous silicon nanoparticles for continuous wave and time-gated photoluminescence imaging

Luminescent porous silicon nanoparticles (LpSiNPs) display red-orange photoluminescence (PL) that provides large penetration depth for precise deep-tissue imaging and diagnostics. Herein, we describe in detail the fabrication process of porous silicon nanoparticles (pSiNPs), activation of photoluminescence, quantum yield measurement, and PL imaging. LpSiNPs perform as imaging probe for both the continuous wave and time-gated PL imaging

Synthesis of Carbon Nanotube (CNT) Composite Membranes

Carbon nanotubes are attractive approach for designing of new membranes for advanced molecular separation because of their unique transport properties and ability to mimic biological protein channels. In this work the synthetic approach for fabrication of carbon nanotubes (CNTs) composite membranes is presented. The method is based on growth of multi walled carbon nanotubes (MWCNT) using chemical vapour deposition (CVD) on the template of nanoporous alumina (PA) membranes. The influence of experimental conditions including carbon precursor, temperature, deposition time, and PA template on CNT growth process and quality of fabricated membranes was investigated. The synthesis of CNT/PA composites with controllable nanotube dimensions such as diameters (30–150 nm), and thickness (5–100 µm), was demonstrated. The chemical composition and morphological characteristics of fabricated CNT/PA composite membranes were investigated by various characterisation techniques including scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDXS), high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD). Transport properties of prepared membranes were explored by diffusion of dye (Rose Bengal) used as model of hydrophilic transport molecule