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Nanocrystals: Synthesis, Characterization and Applications
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... CNCs were investigated as a filling agent for the preparation of the membrane because they have demonstrated significant reinforcing properties in polymer matrices such as water-soluble and water-insoluble polymers to produce reinforced nanocomposites [10][11][12][13][14]. Glycerol is a plasticizing agent commonly used in the preparation of filmforming biopolymers, with the aim to avoid the brittleness of the biopolymeric membrane [15][16][17]. ...
... Cs, GA, Gly and TPP were done with Chemdraw software. CNC formulae was taken from Zhou et al. [13]. ...
This paper presents the development of a support membrane based on chitosan, cellulose nanocrystals and glycerol (m-CCG) for the antibody immobilization by a covalent crosslinking using glutaraldehyde. The chemical characterization of the support by FTIR showed that m-CCG formation process was stabilized by the formation of hydrogen bonding between each component of m-CCG and the reactive amine groups allowing the antibody immobilization on m-CCG via glutaraldehyde. Moreover, this immobilization on m-CCG was optimized by mathematics modeling approaches, and it exhibited robustness and predictable detection in presence of 0.6% of cellulose nanocrystals (CNCs), 0.5 g of CCG solution per well, after 2 h of antibody immobilization. Results also showed that CNCs (0.6% w/v) was the most important factor of the optimization. At this concentration, CNCs improve the resistance of m-CCG during the crosslinking treatment by a modification of the surface topography and the reinforcement of the tensile strength of m-CCG at >30%.
Nanocellulose is increasingly proposed as a sustainable raw material having strong interparticle bonding. However, cellulose alone has limited bending and impact resistance. We newly observe self-assembly between crystalline nanocellulose (CNC) and ultrafine ground chemical-free calcium carbonate nanoparticles (UGCC). The suspension displays an intrinsic gel-like state, and heterogeneous adsorption occurs under the specific conditions where Brownian motion of both species is arrested by application of ultralow shear (0.01 s−1). In contrast, simple static aging of the mixture leads to autoflocculation of each species independently. The heterogeneous adsorption results in compound particle self-assembly leading to multi-level hierarchical structures depending on relative species size and concentration ratio. Fine particles from species 1 adsorb onto the coarser complementary particles of species 2 and vice versa. Depending also on whether CNC or UGCC particles are in excess, the structural assembly occurs primarily through either CNC–CNC hydrogen bonding or CaCO3–CaCO3 autogenous flocculation, respectively. Controlling the hierarchical composite structure bonding in this way, the resulting morphology can express dual or predominantly single either mineralic or cellulosic surface properties. Novel complex hybrid biocomposite materials can therefore be produced having designable compatibility across a broad range of both natural and oil-based polymeric materials. Both CNC and UGCC are exemplified here via commercial products.
The world in the 21st century is confronted with multifaceted challenges against rapid climate change and continuous ecological disturbances caused by revolutionary socio‐economic developments, accelerated expansion of disposable electronic gadgets, and growing dependence on unrecyclable raw materials, among others. The ever‐increasing consumer demand for electronic devices is significantly contributing to the world's fastest‐growing waste stream, known as electronic waste (e‐waste), which is becoming an environmental threat at an alarming rate due to its toxic legacy. The ever‐shortening lifespan of smart technologies has created a “tsunami of e‐waste,” as the United Nations has characterized it, with 50 million tons accumulated each year, of which only 20% undergo formal e‐recycling. Therefore, the challenge of optimizing the current resources management models with an aim of improving the manufacturing processes and lifecycles of electronic devices, as well as building a circular economy, has become significantly prominent. Paper/cellulose, which covers a wide range of essential needs in everyday scenarios (from packaging to writing utilities), constitutes promising candidates for the effective achievement of a circular economy. Particularly, cellulose is revealed as an advantageous material for electronic applications because of its abundant availability, which contributes to its cost‐effectiveness, straightforward fabrication process, and high recyclability and reproducibility. The growing stream of electronic waste or e‐waste, that is created when an electronic product is discarded or expired, is now a big environmental concern. In that context, cellulose or paper can be a promising candidate for Green Technology while promoting zero e‐waste, because of its low‐cost, flexible, abundant, renewable, and eco‐friendly nature.
The study of catalytic water splitting is one of the most active areas of research across many sub-disciplines of chemistry. To understand the mechanistic details and design artificial molecular catalysts for both water reduction (Hydrogen Evolution Reaction, HER) and water oxidation (Oxygen Evolution Reaction, OER) continue to be a challenge for the development of artificial photosynthetic system. This chapter will focus on the summarization of recent development in the rapidly growing field of artificial molecular catalysts with pincer ligand for both HER and OER.
We report the application of cyclic voltammetry and absorption spectroscopy to the characterization and study of
the stability of silver colloids in water. The samples are prepared via chemical reduction and the reactions are catalyzed by irradiation with white light. The electrochemical response is related to the characteristic sample
surface-plasmon-resonance (SPR) in the UV-vis absorption spectra. Cyclic voltammetry shows a characteristic reduction peak whose position is specific to each analyzed sample. Optical analysis of a colloid-precursor during a
12 h time span, under low-power white-light irradiation, shows that nanoparticles undergo change in size and surface-state (absorption bands splitting and inversion) to attaining the “stable” colloidal form. While the
absorption-spectrum bands of the precursor return almost periodically to similar positions, the cyclic voltammogram characteristic-reduction-peak is displaced as a function of time. Finally, we follow the SPR changes
of one “stable” colloid being subjected to electrolysis, heating and sunlight irradiation, for environmental remediation purposes. Sunlight exposure produces the most significant SPR intensity drop, but the electrochemical
technique shows itself promising as well.
: The nanomaterial-integrated chitinous polymers have promoted the technological advancements in personal health care apparatus, particularly for enzyme-based devices like the glucometer. Chitin and chitosan, being natural biopolymers, have attracted great attention in the field of biocatalysts engineering. Their remarkable tunable properties have been explored for enhancing enzyme performance and biosensor advancements. Currently, incorporation of nanomaterials in chitin and chitosan-based biosensors are also widely exploited for enzyme stability and interference-free detection. Therefore, in this review, we focus on various innovative multi-faceted strategies used for the fabrication of biological assemblies using chitinous biomaterial interface. We aim to summarize the current development on chitin/chitosan and their nano-architecture scaffolds for interdisciplinary biosensor research, especially for analytes like glucose. This review article will be useful for understanding the overall multifunctional aspects and progress of chitin and chitosan-based polysaccharides in the food, biomedical, pharmaceutical, environmental, and other diverse applications.
Understanding interface processes has been gaining crucial importance in many applications of biology, chemistry, and physics. The boundaries of those disciplines had been quickly vanishing in the last decade, as metrologies and the knowledge gained based on their use improved and increased rapidly. Optical techniques such as microscopy, waveguide sensing, or ellipsometry are significant and widely used means of studying solid‐liquid interfaces because the applicability of ions, electrons, or X‐ray radiation is strongly limited for this purpose due to the high absorption in aqueous ambient. Light does not only provide access to the interface making the measurement possible, but utilizing the phase information and the large amount of spectroscopic data, the ellipsometric characterization is also highly sensitive and robust. This article focuses on ellipsometry of biomaterials in the visible wavelength range. The authors discuss the main challenges of measuring thickness and optical properties of ultra‐thin films such as biomolecules. The authors give an overview on different kinds of flow cells from conventional through internal reflection to combined methods. They emphasize that surface nanostructures and evaluation strategies are also crucial parts of in situ bioellipsometry and summarize some of the recent trends showing examples mainly from their research.
We report on the thorough investigation of light emitting diodes (LEDs) made of core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) in the outer shell, which are grown on patterned substrates by metal-organic vapor phase epitaxy. The multi-bands emission of the LEDs covers nearly the whole visible region, including UV, blue, green, and orange ranges. The intensity of each emission is strongly dependent on the current density, however the LEDs demonstrate a rather low color saturation. Based on transmission electron microscopy data and comparing them with electroluminescence and photoluminescence spectra measured at different excitation powers and temperatures, we could identify the spatial origination of each of the emission bands. We show that their wavelengths and intensities are governed by different thicknesses of the QWs grown on different crystal facets of the NRs as well as corresponding polarization-induced electric fields. Also the InGaN incorporation strongly varies along the NRs, increasing at their tips and corners, which provides the red shift of emission. With increasing the current, the different QW regions are activated successively from the NR tips to the side-walls, resulting in different LED colors. Our findings can be used as a guideline to design effectively emitting multi-color NR-LEDs.
An overview on the synthesis and applications of telechelic perfluoropolyalkylethers (PFPAEs) is presented. First, a non-exhaustive summary on the synthesis and properties of commercially available PFPAEs is supplied, followed by conventional strategies for the preparation of telechelic PFPAEs ranging from direct fluorination, anionic ring-opening polymerization of oxetane and hexafluoropropylene oxide, to photochemical radical polymerization of tetrafluoroethylene, hexafluoropropene, or perfluoromethyl vinyl ether in the presence of oxygen. Properties (chemical, physical, and thermal) and characterizations (NMR, MALDI, rheology, lubricity, and toxicity) of these PFPAEs will also be presented. Telechelic PFPFA bis(acylfluorides) are interesting precursors for a wide range of molecules and copolymers such as: polycondensates (polyesters, polyurethanes, polycarbonates, polyethers), macromonomers that can further be cross-linked, triblock copolymers, and (semi) interpenetrated polymer networks. Furthermore, important applications of these modified PFPAEs will be exhibited. These applications range from self-assembly materials (e.g. amphiphilic and anti-bacterial derivatives, and hydrogels), aerospace materials, microfluidic devices, protective coatings (e.g. low surface tension, anti-fouling, and de-icing), optically transparent films, self-healing materials, thermoplastic elastomers, materials for energy (e.g. zinc-air and lithium ion batteries, polymeric electrolyte membranes for fuel cells), resistant photoresists for lithographic materials, to theranostics (e.g. intracellular pH measurements and in vivo cell tracking technologies using Magnetic Resonance Imaging). This overview summarizes these emerging fields, emphasizing structural variety, end group functionalities, post-polymerization modifications, and applications previously unobtainable without accessible to these new materials.
Cellulose nanocrystals appeared as important bio-based products and the collected information in term of production, characterization and application suggest that this nanomaterial could be easily extrapolated to bioethanol production. This review describes recent published syntheses using chemical and enzymatic hydrolyses and different preparations such as high pressure homogenization. Their industrial and medical applications, such as controled of delivery carriers, suggest a large projection of this nanomaterial. The most important aspect in this collected data is the potential to decrease significantly the final cost of the enzymes or the hydrolysis pre-treatment of lignocellulosic materials of all bioethanol processes in such a way that it could be economically feasible from materials such as bagasse, straw or wood resources.
We report measurements of photoluminescence (PL) from self-assembled
InSb quantum dots (QD's) grown by metal-organic vapor-phase epitaxy in a
matrix of GaSb as a function of excitation power, temperature, and
magnetic field. PL is observed in the region 1.7-1.8 μm from InSb
quantum dots. For low excitation power the PL is dominated by the lowest
quantum dot transition energy. When the excitation power is increased
the quantum dot transition increases in energy by ~11 meV, and further
transitions are observed from the wetting layer, bulk acceptor, and free
excitons. Magneto-PL is used to calculate the in-plane dot confinement
energies by fitting the data to the ground state of a Fock-Darwin set of
energy levels. The in-plane confinement energy deduced increases from ~6
to ~18 meV as the excitation power is increased. This is similar to the
increase in the quantum dot transition energy, and suggests that this is
due to a progressive population of a distribution of strongly
communicating dots with decreasing lateral sizes. Further support for
this picture comes from the temperature dependence of the quantum dot
transition energy, which is also found to increase by a relatively
similar amount as the temperature is raised from 11 to 50 K, following a
correction for the temperature dependence of the bulk energy band gaps.
Diluted magnetic semiconductor nanocrystals, Pb1-xMnxS (x = 0.003, 0.005, and 0.010), of approximately 6 nm were successfully grown in a glass matrix by a combination of fusion and thermal annealing. X-ray diffraction measurements reveal that the as-produced nanocrystals (NC), of group IV–VI, are single-phase, nanosized and crystallized in the rock salt structure with replacement of Pb2+-ions by Mn2+-ions. Magnetic force microscopy images also confirmed the high quality of the Pb1-xMnxS NC samples, showing a uniform distribution of total magnetic moments in the nanocrystals. The observation of characteristic hyperfine structures from electron paramagnetic resonance measurements provided evidence for Mn2+ incorporation within the PbS dot structure. Moreover, low temperature magnetization and susceptibility data showed that most of the magnetic ions hosted by the nanocomposite samples are in a paramagnetic state.
Superabsorbent hydrogels, based on poly(acrylamide-co-acrylate) filled with cellulose nanowhiskers (CNWs), were synthesized by free-radical aqueous copolymerization, using N,N-methylenebisacrylamide (MBAAm), as crosslinker, and potassium persulfate (K2S2O8), as initiator. A series of hydrogels was synthesized varying the percentage of CNWs (1, 2, 5, 10, and 20 wt.%) and the amount of crosslinking agent (0.05, 0.10, 0.15, and 0.20 mol.%). The hydrogels were characterized by FTIR and XRD techniques and their morphologies were investigated by SEM images. Superabsorbent hydrogel with Weq > 1195 gH2OgH2O/ggel was obtained with percentage of 10 wt.% of CNWs and 0.05 mol.% of crosslinking agent. The hydrogel showed to be responsive to the pH-variation (2–12) and also to the presence of salts (NaCl, KCl, MgCl2, and CaCl2). The hydrogel exhibited a pH-responsiveness and cation-sensitivity character so that a swelling–deswelling pulsatile behavior was recorded at pH 2–8 as well as cycles of hydrogel immersion in sodium and calcium salts solutions.
Poly(p-phenylene benzobisoxazole)/multiwalled carbon nanotubes (PBO-MWCNT) composites with different MWCNT compositions were prepared through in situ polymerization of PBO in the presence of carboxylated MWCNTs. The nanocomposite's structure, thermal and photophysical properties were investigated and compared with their blend counterparts (PBO/MWCNT) using Fourier transform infrared spectra, Raman spectra, Wide-angle X-ray diffraction, thermogravimetric analysis, UV-vis absorption, and photoluminescence. The results showed that MWCNTs had a strong interaction with PBO through covalent bonding. The incorporation of MWCNTs increased the distance between two neighboring PBO chains and also improved the thermal resistance of PBO. The investigation of UV-vis absorption and fluorescence emission spectra exhibited that in situ PBO-MWCNT composites had a stronger absorbance and obvious trend of red-shift compared with blend PBO/MWCNT composites for all compositions. This behavior can be attributed to the efficient energy transfer through forming conjugated bonding interactions in the PBO-MWCNT composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 (7) and 319 (10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phases were found to have very similar bulk moduli [208 (28) and 206 (44) GPa].
Measurements of resistivity and impurity concentration in heavily doped silicon are reported. These and previously published data are incorporated in a graph showing the resistivity (at T = 300°K) of n- and p-type silicon as a function of donor or acceptor concentration.
The relationship between surface concentration and average conductivity of diffused layers in silicon has been calculated for Gaussian and complementary error function distributions. The results are shown graphically. Similar calculations for subsurface layers, such as a transistor base region, are also given.
The electronic-structure and magnetic properties of hydrogenated silicon
nanocrystals doped with pairs of manganese atoms are investigated using
spin-density-functional theory. Formation energies and total magnetic
moments sensitively depend on the two sites occupied by manganese.
Usually pairs at interstitial and substitutional sites with small total
moment are energetically favored. Pairs at sites with the same character
tend to ferromagnetic spin arrangements which are, however,
significantly influenced by their noncollinearity. The resulting
magnetic ordering is clearly related to the impurity levels and their
occupation. The magnetic coupling is distance dependent,
antiferromagnetic for small distances, and almost ferromagnetic for
larger Mn-Mn distances. A Rudderman-Kittel-Kasuya-Yoshida-type exchange
mechanism may describe the distance dependence but simultaneously not
its magnitude.
Zn1−xMnxO nanocrystal samples have been successfully synthesized using the chemical precipitation method in aqueous solution. Comparing with pure ZnO NC, the Raman data recorded from the manganese-doped nanocrystals shows an enhancement of the peaks located at 334 and 439 cm−1. Besides, a new feature at 659 cm−1 emerges. X-ray diffraction (XRD) of the as-precipitated nanocrystal samples illustrates that Mn-doping only makes the XRD peaks of the as-precipitated Mn-doped nanocrystals shift towards lower angle values, but the crystal structure of bulk ZnO is still preserved in the Mn-doped samples. Hence, the high quality Zn1−xMnxO (x ⩾ 0) nanocrystals are formed through the replacement of zinc ions by manganese ions.
Alumina is utilized as a catalyst and catalyst support, applications that can benefit from a high surface area and significant mesopore volume. Such characteristics can be achieved through ambient pressure drying (APD) using a methodology similar to that which has proven successful with silica. Alumina gels were synthesized using aluminum tri-sec-butoxide (AltsB) and ethyl acetoacetate (EtAc). Azeotropic distillation with toluene was then used to reduce the surface tension of the solvent and to create `poor wettability' (non-polar solvent, polar oxide network surface) in the gel. The latter factor reduces the capillary stresses that arise at the liquid–vapor interface, which in turn limits shrinkage during APD. The opposite poor wettability condition (non-polar surface in contact with a polar solvent), created by reacting the gel with silylating reagents in the mother liquor (primarily ethanol and water), did not provide significant porosity. Adding more water during sol–gel processing aided the preservation of mesopores during APD.