Appearance Of Characteristic Peak Research Articles

Synthesis, characterization, and application of novel reusable clay-based magnetic nanocomposite for the removal of organic dyes from water

In this study, a new synthesized magnetic nanocomposite was used as an adsorbent for the removal of toxic cationic dye methylene blue (MB). The adsorbent incorporated three components to produce a nanocomposite named Fe3O4/GO/natural clay. The characterization techniques were used to study the physical and chemical properties of nanocomposite and approve the successful synthesis. XRD of the Fe3O4/GO/natural clay nanocomposite indicated the crystalline structure with the appearance of characteristic peaks of each component. Also, the FT-IR of Fe3O4/GO/clay nanocomposite showed a significant change in the peak intensity of natural clay after the addition of GO and magnetic NPs which attributed to the successful interaction between GO and magnetic NPs with the functional groups on the surface of clay. The TEM and SEM images of the nanocomposite showed that the magnetic NPs, clay, and GO excellently interacted in one appropriate structure with the deposition of clay and magnetic NPs on the GO surface which serves as a matrix holding them. The MB adsorption system was optimized by varying several parameters, including pH, adsorbent dosage, contact time, starting concentration, ionic strength, and competing ions. Furthermore, the adsorption isotherm showed that the highest adsorption capacities of 999.34 and 1108.54 mg/g for the Fe3O4/GO/natural clay and Fe3O4/natural clay nanocomposites, respectively, followed the Langmuir isotherm. Additionally, the kinetic analysis showed that a pseudo-second-order model better explained the adsorption on both nanocomposites. The nanocomposite can be reused for multiple cycles with a little drop in its initial performance, according to reusability research conducted up to six times using ethyl alcohol as the eluent. As a result, this reasonably priced adsorbent might be employed as a beneficial and effective dye adsorbent for the removal of MB from water while maintaining the safety of the water quality.

Metabolomic profiling and its association with the bio-efficacy of Aspergillus niger strain against Fusarium wilt of guava.

Bio-control agents are the best alternative to chemicals for the successful management of plant diseases. The fungus Aspergillus niger is known to produce diverse metabolites with antifungal activity, attracting researchers to exploit it as a bio-control agent for plant disease control. In the present study, 11 A. niger strains were isolated and screened for their antagonism against the guava wilt pathogen under in vitro and in planta conditions. Strains were identified morphologically and molecularly by sequencing the internal transcribed spacer (ITS), β-tubulin, and calmodulin genes. The strains were evaluated through dual culture, volatile, and non-volatile methods under an in vitro study. AN-11, AN-6, and AN-2 inhibited the test pathogen Fusarium oxysporum f. sp. psidii (FOP) at 67.16%, 64.01%, and 60.48%, respectively. An in planta study was conducted under greenhouse conditions with 6 months old air-layered guava plants (var. Allahabad Safeda) by pre- and post-inoculation of FOP. The AN-11 strain was found to be effective under both pre- and post-inoculation trials. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis was carried out to characterize the volatile compounds of the most potential strain, A. niger. The hexane soluble fraction showed the appearance of characteristic peaks of hexadecenoic acid methyl ester (4.41%), 10-octadecanoic acid methyl ester (3.79%), dodecane (3.21%), undecane (3.19%), gibepyrone A (0.15%), 3-methylundecane (0.36%), and citroflex A (0.38%). The ethyl acetate fraction of the bio-control fungi revealed the occurrence of major antifungal compounds, such as acetic acid ethyl ester (17.32%), benzopyron-4-ol (12.17%), 1,2,6-hexanetriol (7.16%), 2-propenoic acid ethanediyl ester (2.95%), 1-(3-ethyloxiranyl)-ethenone (0.98%), 6-acetyl-8-methoxy dimethyl chromene (0.96%), 4-hexyl-2,5-dihydro dioxo furan acetic acid (0.19%), and octadecanoic acid (1.11%). Furthermore, bio-control abilities could be due to hyper-parasitism, the production of secondary metabolites, and competition for sites and nutrients. Indeed, the results will enrich the existing knowledge of metabolomic information and support perspectives on the bio-control mechanism of A. niger.

Probiotic Lactobacillus paragasseri K7 Nanofiber Encapsulation Using Nozzle-Free Electrospinning.

Probiotics are live microorganisms that can have beneficial effects on humans. Encapsulation offers them a better chance of survival. Therefore, nozzle-free electrospinning was introduced for their embedding in nanofibrous material. Probiotic Lactobacillus paragasseri K7 in lyophilized and fresh form, with and without inulin as prebiotic, was added to a polymer solution of sodium alginate (NaAlg) and polyethylene oxide (PEO). Conductivity, viscosity, pH, and surface tension were determined to define the optimal concentration and volume ratio for smooth electrospinning. The success of the formed nanoscale materials was examined by scanning electron microscope (SEM), while the entrapment of probiotics in the nanofibrous mats was detected by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Spontaneous diffusion of bacteria from electrospun samples in PBS buffer pH 7.4 was studied by plate counting on MRS agar. By exposing polymer solutions containing L. paragasseri K7 and inulin to a high electric field, the nanofilm was formed on a polypropylene substrate, used as collecting material. When polymer solutions without inulin were used, the bead-like nanofibers may have become visible. The SEM results suggest that inulin, in addition to K7 strain, additionally lowers the conductivity of spinning macromolecular solution and hinders the nanofiber formation. The results of ATR-FTIR confirmed the presence of L. paragasseri K7 embedded in nanocomposites by the appearance of characteristic peaks. The samples containing the probiotic regardless of its form with inulin had similar surface composition, except that the sodium content was higher in the samples with fresh probiotic, probably due to greater and thus less easy embedding of the bacteria in NaAlg. Within 2 h, the largest amount of probiotic strain K7 was spontaneously released from the electrospun sample containing the inulin and probiotic in freeze-dried form (44%), while the amount released from the nanofibrous sample, which also contained the inulin and probiotic in fresh form, was significantly lower (21%). These preliminary results demonstrate the potential of nozzle-free electrospinning technology for the development of probiotic delivery systems for short-term use, such as feminine hygiene materials (tampons, pads, napkins).

Enhanced ammonium removal from aquatic systems by a novel copolymer

Abstract A novel copolymer was used as an adsorbent for enhanced ammonium removal in an aqueous system; different ratios of styrene–acrylic acid copolymers were synthesized by random free radical polymerization and followed by a sulfonation of styrene (acrylic acid 25%–sulfonated styrene 75%) copolymer [P(AA25/SS75)] attained the highest ammonium adsorption capacity (55.8 mg/g) due to the electrostatic attraction between positively charged NH4+ and negatively charged –COO− and –SO3- groups. FTIR spectra for sulfonated polymers illustrated the appearance of characteristic peaks at 100–1200 cm−1 indicating that the copolymers were successfully sulfonated. The influence of different experimental factors (i.e., contact time, pH, NH4+ concentration, adsorbent dose) on ammonium ion adsorption was investigated; three adsorption isotherm models including Langmuir, Freundlich, and Temkin were used to study the adsorption mechanism. The results indicated that the equilibrium of adsorption can be reached within 30 min; the highest adsorption capacity can be achieved around pH 7. Furthermore, Freundlich isotherm was the most suitable for fitting the experimental data which might expose the heterogeneity of the adsorbent surface. The regeneration and reusability studies were also implemented, and results showed that P(AA25/PSS75) was stable and regenerable using (1 M) sulfuric acid as a desorbing agent over five cycles.

Accelerated transformation of plastic furniture into microplastics and nanoplastics by fire

Numerous plastic items are known to gradually degrade and release microplastics and nanoplastics under certain conditions, which can be significantly accelerated by fire combustion. Unfortunately there is a limited knowledge about this burning process because the characterisation on microplastics and nanoplastics is still a challenge. In this study, an outdoor plastic chair is subjected to a combustion process, the change in the surface functional groups (due to different degree of burning) and the release of microplastics and nanoplastics are investigated. During the combustion process, the plastic is molten, burned and deposited on solid surfaces including concrete, stone and glass. Scanning electron microscopy (SEM) results show that the peeling off the deposited plastic generates a large number of fragments. Through Raman imaging, these fragments are characterised as polypropylene (PP) microplastics and nanoplastics due to appearance of characteristic peaks. To further increase the sensitivity, several algorithms are tested and optimised, including logic-based, non-supervised principal component analysis (PCA)-based, algebra-based and their hybrids (to intentionally correct the non-supervised PCA) to enable the effective extraction of the key information towards plastics characterisation, particularly by distinguishing the signal from the background noise towards the visualisation of the different degrees of burning. Based on the findings from Raman imaging and SEM, it is estimated that tens of microplastics and nanoplastics are created per μm2. Overall Raman imaging can be a suitable approach to characterise the microplastics and nanoplastics in a complex background, such as the fire-burned plastic items.

Development of high‐performance biopolymer nanocomposites derived from carboxymethyl chitosan/boehmite via green synthesis

AbstractIn this work, biopolymer nanocomposites derived from carboxymethyl chitosan (CMCS) and boehmite were prepared via an environmentally friendly technique and their structural, morphological, thermal, electrical, dielectric, and mechanical properties were investigated. The successful fabrication of carboxymethyl chitosan/boehmite nanocomposites was evident from the appearance of characteristic peaks of boehmite in FTIR and alteration in the morphology as revealed by optical and SEM micrographs. The glass transition temperature (Tg) and melting temperature (Tm) were increased as the filler content increased. The enhanced thermal stability of nanocomposites was clear from thermogravimetric results. The incorporation of boehmite nanoparticles into CMCS improved the conductivity to a semiconducting range. The dielectric constant of CMCS/boehmite nanocomposites was significantly higher compared to pure CMCS. The influence of temperature on AC conductivity, activation energy, dielectric constant and loss tangent were analyzed. Complex impedance analysis carried out by Nyquist plots and the bulk resistance showed a decreasing trend with temperature, which indicated enhanced conductivity with temperature. Tensile strength and hardness were observed to be increased with boehmite inclusion, whereas elongation at break is reduced. As a result, eco‐friendly CMCS/boehmite biopolymer nanocomposites with good thermal, mechanical, electric, and dielectric properties may be a potential green alternative for flexible electronic, charge storage, and other electrochemical devices.

Microstructure and Antibacterial Properties of Chitosan-Fe3O4-AgNP Nanocomposite.

The goal of this research is to synthesize and characterize Fe3O4@Chitosan-AgNP nanocomposites in order to determine their antibacterial activity. The research methods include the synthesis of Fe3O4@Chitosan-AgNP nanocomposites, as well as the characterization of nanoparticles using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) analysis, and subsequent antibacterial activity tests. The study’s findings demonstrated the successful synthesis of Fe3O4@Chitosan-AgNP nanocomposites, followed by nanoparticle characterization using SEM, TEM, XRD, and FTIR. Based on the XRD results, the conjugation of Fe3O4@Chitosan-AgNP nanocomposites has been successfully formed, as evidenced by the appearance of characteristic peaks of Fe3O4, chitosan, and AgNPs. According to the FTIR results, the interaction between chitosan-AgNPs and conjugated Fe3O4 occurred via the N atom in the NH2 group and the O atom in the OH group, and C=O. The SEM and TEM images also show that the Fe3O4@Chitosan-AgNP conjugation is a nanoparticle-based composite material. The combination of nanocomposites Fe3O4@Chitosan-AgNPs has antibacterial activity, inhibiting the growth of bacteria such as Bacillus cereus and Escherichia coli.

Impact of NiCo2O4 Composition on Methylene Blue Photodegradation by Fe3O4/NiCo2O4 Nanocomposites

Fe3O4/NiCo2O4 nanocomposites were successfully fabricated using the coprecipitation method. The fabrication of Fe3O4/NiCo2O4 nanocomposites were carried out by varying the mass percentage of NiCo2O4 with a composition of 0%, 15%, 30%, 45%, and 100% of the mass of Fe3O4. The characterization of the functional groups of Fe3O4/NiCo2O4 nanocomposites was carried out using the FTIR instrument which showed the functional group bonds of the sample corresponding to the constituent atoms. The characterization of the crystal structure of Fe3O4/NiCo2O4 nanocomposites was carried out using an XRD instrument which showed the appearance of characteristic peaks of the Fe3O4 and the NiCo2O4 phases in the X-ray diffraction patterns. The surface morphology of the Fe3O4/NiCo2O4 nanocomposites was characterized using the SEM instrument which produces an image of the surface morphology of the sample. Potential applications of Fe3O4/NiCo2O4 as photodegradation material for methylene blue (MB) were characterized using a UV-Vis instrument and showed that the Fe3O4/NiCo2O4 nanocomposites can be used for water purification with a degradation percentage of 11.99%. The highest absorbance values of the Fe3O4/NiCo2O4 nanocomposites with UV irradiation for interval of 60, 120, and 180 minutes located at wavelength of 613 and 663 nm.

A green chemical approach for synthesis of sponge-like mesoporous gamma alumina and evaluation of three parameters OH/Al, salt concentration and ageing time on BET and BJH properties

Synthetic strategies to control the properties of gamma-alumina mesoporous have been discussed. In this study, the emphasis is placed upon the effect of three parameters pH of the reaction, salt precursor concentration and ageing time on the pore structure of nanoparticles synthesized by precipitation method. The gamma alumina as the only phase was recognized due to the appearance of characteristic peaks based on standard data JCPDS 29-0063 card in XRD pattern. The samples were analyzed by BET and BJH analysis in terms of specific surface area and pore structure (size distribution, morphology, and total pore volume). The results showed that all the synthesized samples are mesoporous. The sample synthesized at a precursor concentration of 0.1 M and pH 8 and the ageing time of 48 h obtained the highest specific surface area (217.02 m2 g−1) among all samples, while the sample prepared at the precursor concentration 0.2 M and pH 8 showed the highest pore volume with a value of 0.31 cm3 g−1. Among the parameters, only pH altered the pore morphologies from spherical to cylindrical while the ageing time and salt concentration did not change the pore morphology of mesoporous alumina samples. The TEM image reveals the sponge-like morphology which implies the appearance of a highly inter-connected pore system.

Plastic driven pollution in Pakistan: the first evidence of environmental exposure to microplastic in sediments and water of Rawal Lake

Microplastic pollution is as an emerging environmental threat. Focus of most of the current researches has been on microplastics in the marine environment. However, there is limited information for microplastic availability in the fresh water, especially in Pakistan. The current study was conducted with the objective of investigating the microplastic presence and concentration in the surface water and sediments of the Rawal Lake, in the capital city of Pakistan. The average microplastic abundance for water and sediments was 0.142 items/0.1L and 1.04 items/0.01kg, respectively. Results indicated that the fibers and fragments were the most dominant types of microplastics. The dominant colors were blue, red, black, and transparent. FTIR analysis of visible microplastic particles displayed a greater similarity with polyethylene, polypropylene, polyesters, polyethylene terephthalate, and polyvinyl chloride because of the appearance of characteristic peaks of these polymers. The study also revealed greater concentration of microplastics in the sediments as compared with water of the Rawal Lake. High population density surrounding lake, improper waste disposal, tourism, and recreational activities may be the major reasons for the microplastic contamination of the lake.

Rational design and electrical study of conducting bionanocomposites hydrogel based on chitosan and silver nanoparticles

The chitosan/polyacrylic acid/polypyrrole/loaded with silver nanoparticles (CS/PAA/PPy/Ag-NPs) bionanocomposite as conductive, biodegradable, and biocompatible hydrogels were prepared by the casting method. Silver nanoparticles (Ag-NPs) were incorporated into the prepared bionanocomposite hydrogels to reinforce the electrical conductivity as well as the antimicrobial properties of the prepared hydrogels. The scanning electron microscopy revealed the compatibility of chitosan, polyacrylic acid, and polypyrrole, as well as Ag-NPs, were inserted in the polymer matrix and dispersed well on the superficies of the prepared bionanocomposites. X-ray diffraction displayed the presence of Ag-NPs into the polymer matrix. Also, the appearance of characteristic peaks in the Fourier transform infrared confirmed the compatibility of three polymers. Additionally, the swelling properties, antimicrobial activity as well as the electrical and dielectric characteristics of the fabricated bionanocomposites hydrogels were investigated. Moreover, the DC-conductivity was studied and our data designated that the DC-conductivity of the prepared bio-nanocomposites was improved by the existence of PPy more precisely than that of Ag-NPs. However, both were of high conductivity compared to that of the CS/PAA and found to follow the BNN universal relation. Also, The activation energy of about 55 kJ/mol of CS:2PAA hydrogel and reduce to about 15 kJ/mol in all the considered bionanocomposites after addition of Ag-NPs. Furthermore, the antibacterial activities of the knowledgeable microbes were improved as a result of the presence of Ag-NPs in bionanocomposites hydrogels.

Synthesis and characterisation of core-shell structure PLA/CS/NIF nanoparticles

To decrease the dissolution of chitosan (CS) in acidic environment, in this paper, poly(lactic acid) (PLA) and CS have been selected to prepare the PLA/CS core-shell structure nanoparticles loading the nifedipine drug (NIF), in which, CS containing NIF is core and PLA is shell. Coating PLA outside the CS carrying drug nanoparticles can help to protect the CS/drug particles in acidic environment of stomach so that the drug is not released or released slowly there. Then, the CS/drug nanoparticles is transported to the small intestine where is frequently perfused by blood, resulting in the most effective absorption of drug in the body. The properties of CS/NIF nanoparticles coated by PLA have been evaluated by Fourier transform infrared spectroscopy (FT-IR), laser scattering, dynamic light scattering (DLS) and differential scanning calorimetry (DSC) methods. The appearance of characteristic peaks for PLA, CS, and NIF in the FTIR spectra of nanoparticles shows that the CS/NIF nanoparticles are covered by PLA. The DLS diagrams indicate that the CS/NIF nanoparticles coated by PLA with a thickness of PLA film about 70-140 nm. The DSC diagrams of CS/NIF nanoparticles coated by PLA film show their melting temperature less than that of the CS/NIF nanoparticles. From the above results, it can be seen that the core-shell structure PLA/CS/NIF nanoparticles is prepared successfully. In addition, NIF release from the CS/NIF nanoparticles and core-shell structure PLA/CS/NIF nanoparticles are investigated and presented. The NIF release from the nanoparticles is a function of pH of immersed solution, immersed time and NIF content. The PLA coating helps to control the NIF release from the core-shell structure PLA/CS/NIF nanoparticles in acidic solution better than that from the CS/NIF nanoparticles at the same testing condition. The different kinetic models of drug release are also calculated and reported in order to perform the type of NIF release mechanism.

Polymeric prodrugs containing neridronate and ferrocene: Synthesis, characterization, and antimalarial activity

ABSTRACTPolyamidoamine prodrugs containing ferrocene derivatives and neridronate were successfully synthesized and characterized by NMR, FTIR, SEM, and EDX analyses. Appearance of characteristic peaks in 1H and 31P NMR or EDX spectra were used to confirm the presence of neridronate or ferrocene in the conjugates and co-conjugates. In vitro evaluation of the new materials revealed improved antimalarial activity, especially for conjugate 5 and corresponding co-conjugate 8, when compared with chloroquine and quinine. Hemolysis studies revealed that synthesized prodrugs had no effect on the integrity of the host red blood cell membrane; a direct effect on the intra-erythrocytic parasite was, however, noted.

STUDY OF STRUCTURAL AND SPECTRAL CHARACTERISTICS OF CRYSTAL Y3Al5O12, Al2O3 AND SrTiO3 DOPED BY 3d- OR 4f- IONS

The subject of our research is a study of the effects of various treatments on the structural and spectral characteristics of oxides (Y3Al5O12, Al2O3 and SrTiO3) belonging to the group of ionic crystals with a wide energy band gap. We have investigated the dielectric and optical characteristics of single laser crystals of Y3Al5O12 (YAG) doped by ions from the group of iron (3d-), Al2O3 single crystal and SrTiO3 crystals doped by 3d and 4f- ions. Dielectric properties of the investigated single crystals were analyzed using dielectric spectroscopy (80 kHz – 15 MHz) in a wide temperature range (50 – 400 K). The comparison of the temperature dependence of the dielectric permittivity (εr) and dielectric loss (tanδ) at different test frequencies for undoped and doped crystals was performed. The optical properties were studied on the basis of the absorption spectra in the UV-Vis region. The experiment results showed that presence of 3d dopants in YAG crystal caused a displacement of the absorption edge and appearance of characteristic peaks. The differences observed in the absorption spectra were probably the result of the 3d ions incorporation on two possible symmetrically different positionings of aluminum ions –tetrahedrical and octahedrical– in the YAG crystal lattice. The dielectric spectroscopy measurements for samples of SrTiO3 doped by 4f ions showed anomalous behaviors of the dielectric permittivity at temperatures around the temperature of the structural phase transition 105 K.

STUDY OF STRUCTURAL AND SPECTRAL CHARACTERISTICS OF CRYSTAL Y3Al5O12, Al2O3 AND SrTiO3 DOPED BY 3d- OR 4f- IONS

The subject of our research is a study of the effects of various treatments on the structural and spectral characteristics of oxides (Y3Al5O12, Al2O3 and SrTiO3) belonging to the group of ionic crystals with a wide energy band gap. We have investigated the dielectric and optical characteristics of single laser crystals of Y3Al5O12 (YAG) doped by ions from the group of iron (3d-), Al2O3 single crystal and SrTiO3 crystals doped by 3d and 4f- ions. Dielectric properties of the investigated single crystals were analyzed using dielectric spectroscopy (80 kHz – 15 MHz) in a wide temperature range (50 – 400 K). The comparison of the temperature dependence of the dielectric permittivity (er) and dielectric loss (tanδ) at different test frequencies for undoped and doped crystals was performed. The optical properties were studied on the basis of the absorption spectra in the UV-Vis region. The experiment results showed that presence of 3d dopants in YAG crystal caused a displacement of the absorption edge and appearance of characteristic peaks. The differences observed in the absorption spectra were probably the result of the 3d ions incorporation on two possible symmetrically different positionings of aluminum ions –tetrahedrical and octahedrical– in the YAG crystal lattice. The dielectric spectroscopy measurements for samples of SrTiO3 doped by 4f ions showed anomalous behaviors of the dielectric permittivity at temperatures around the temperature of the structural phase transition 105 K.

Graphene Device Fabrication and Applications in Communication Systems

High carrier mobility, saturation velocity and thermal conductivity make graphene a promising material for high-frequency, analog and communication applications. The ambipolar properties of graphene provide opportunities for increased functionality in unconventional circuit architectures. In this dissertation, I describe the fabrication process of graphene devices, including the optical and Raman spectroscopic characterization and electron-beam lithography. The different electrical characteristics of the single-layer and bilayer graphene field-effect devices reflect differences in the electron band structures of the two systems. The fabricated graphene transistors have been used to design and experimentally demonstrate electronic circuits with communication functionalities such as phase-shift keying, frequency-shift keying and phase detection. Compared with conventional semiconductor electronic designs based on multiple unipolar transistors, the demonstrated graphene amplifiers and phase detectors have advantage of a simplified structure. An important issue for high-frequency and analog applications is the low-frequency noise, which up-converts and contributes to the phase noise of the systems. It was found that the low-frequency noise in graphene devices is dominated by 1/f noise in the frequency range from 1 Hz to 100 kHz (f is the frequency). The device exposure to different gases results in appearance of characteristic peaks in the noise spectral density. The latter can be utilized for selective gas sensing with graphene. The metal-graphene contact contributions to the 1/f noise can be strongly reduced via the use of the graded thickness graphene channels in the device structure. I have also investigated a possibility of tuning graphene properties via controllable exposure to the low-energy electron-beam irradiation. It was found that the charge neutrality point and resistivity can be tuned over a wide range of values. The obtained results are important for the proposed applications of graphene in analog electronics, communications and sensors.

Covalent and non-covalent functionalized MWCNTs for improved thermo-mechanical properties of epoxy composites

Two simplified methods for non-covalent and covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with surfactants were developed, the functionalization degree and properties of their epoxy nanocomposites were studied. Physical absorption and covalent attachment of nonionic surfactants was proved by an increase of the mass loss in TGA and the appearance of characteristic peaks in XPS. The DSC analysis of the epoxy nanocomposites proved a low catalytic influence of 1% modified MWCNTs on the epoxy curing process, while DMA showed a higher flexibility compared with the neat epoxy. Dispersion state of modified MWCNTs in epoxy was related to their functionalization degree.

Preparation and characterization of chitosans carrying aldehyde functions generated by nitrogen oxides

Abstract In this work, aldehyde-functionalized chitosan is produced by the reaction of chitosan with nitrogen oxides generated in situ from a HNO 3 /H 3 PO 4 –NaNO 2 mixture. This method is more advantageous than the existing approaches, since the depolymerization is slower and the purification process is straightforward. The appearance of characteristic peaks in the Fourier transform infrared and carbon-13 nuclear magnetic resonance spectra (1733 cm −1 and 183.4 ppm, respectively) of the product confirms the presence of the aldehyde functionality in the modified chitosans. The 1 H NMR spectra also revealed the presence of aldehyde groups. Furthermore, the gradual disappearance of the peaks due to aldehyde protons and a concomitant appearance of a new resonance at ∼8.05 ppm with increasing pH indicate the formation of Schiff's base between the aldehyde and the free amine groups. The aldehyde-functionalized chitosan prepared with 6 h of reaction time (chitosan-6h) forms a gel in situ without any added external crosslinker and it may potentially be useful as a vehicle for drug delivery.

Assembly and Characterization of Polyurethane–Gold Nanoparticle Conjugates

AbstractThe PU/Au‐NPs conjugates based on poly(vinyl alcohol)‐containing polyurethane microparticles coated with Au‐NPs are prepared by a heat‐treated method. The PU/Au‐NPs conjugates are characterized by FT‐IR, SEM, TEM analysis. The appearance of characteristic peaks in the FT‐IR spectra at 1574 and 1624 cm−1, which are attributed to urethane groups, are presented for both PU and PU/Au‐NPs conjugate. The absorption band at 1716–1718 cm−1, attributed to the hydrogen‐bonded urethane carbonyl groups of PU/Au‐NPs(13nm)‐A is higher than that obtained for unmodified PU. The Au‐NPs(13nm) are found to be well dispersed in the PU. The Au‐NPs(3.5nm) tend toward agglomeration when they are entrapped within PU. It is determined, that Au‐NPs present in PU‐Au conjugates quench the luminescence of PU.

Kinetic roughening and mound surface growth in microcrystalline silicon thin films

AbstractThe roughening evolution of the hydrogenated microcrys‐talline silicon (μc‐Si:H) film by plasma enhanced chemical vapor deposition (PECVD) and hot wire chemical vapor deposition (HWCVD) were investigated using atomic force microscopy (AFM). It is found that the kinetic roughening of the μc‐Si:H film surface can not be described by the traditional dynamic scaling approach. The appearance of characteristic peaks in the power spectral density (PSD) curves, calculated from the AFM images, indicates the mounded growth characteristic of μc‐Si:H film. The correlation between the mounded surface growth of μc‐Si:H thin films and the shadowing effect has been studied. It is found that high hydrogen dilution ratio in the early growth stage retards the formation of the mound structure (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)