Control synthesis of high quality large-area graphene on transition metals (TMs) by chemical vapor deposition (CVD) is the most fascinating approach for practical device applications. Interaction of carbon atoms and TMs is quite critical to obtain graphene with precise layer number, crystal size and structure. Here, we reveal a solid phase reaction process to achieve Cu assisted graphene growth in nanoscale by in-situ transmission electron microscope (TEM). Significant structural transformation of amorphous carbon nanofiber (CNF) coated with Cu is observed with an applied potential in a two probe system. The coated Cu particle recrystallize and agglomerate toward the cathode with applied potential due to joule heating and large thermal gradient. Consequently, the amorphous carbon start crystallizing and forming sp(2) hybridized carbon to form graphene sheet from the tip of Cu surface. We observed structural deformation and breaking of the graphene nanoribbon with a higher applied potential, attributing to saturated current flow and induced Joule heating. The observed graphene formation in nanoscale by the in-situ TEM process can be significant to understand carbon atoms and Cu interaction.
Hierarchical Si/ZnO trunk-branch nanostructures (NSs) have been synthesized by hot wire assisted chemical vapor deposition method for trunk Si nanowires (NWs) on indium tin oxide (ITO) substrate and followed by the vapor transport condensation (VTC) method for zinc oxide (ZnO) nanorods (NRs) which was laterally grown from each Si nanowires (NWs). A spin coating method has been used for zinc oxide (ZnO) seeding. This method is better compared with other group where they used sputtering method for the same process. The sputtering method only results in the growth of ZnO NRs on top of the Si trunk. Our method shows improvement by having the growth evenly distributed on the lateral sides and caps of the Si trunks, resulting in pine-leave-like NSs. Field emission scanning electron microscope image shows the hierarchical nanostructures resembling the shape of the leaves of pine trees. Single crystalline structure for the ZnO branch grown laterally from the crystalline Si trunk has been identified by using a lattice-resolved transmission electron microscope. A preliminary photoelectrochemical (PEC) cell testing has been setup to characterize the photocurrent of sole array of ZnO NR growth by both hydrothermal-grown (HTG) method and VTC method on ITO substrates. VTC-grown ZnO NRs showed greater photocurrent effect due to its better structural properties. The measured photocurrent was also compared with the array of hierarchical Si/ZnO trunk-branch NSs. The cell with the array of Si/ZnO trunk-branch NSs revealed four-fold magnitude enhancement in photocurrent density compared with the sole array of ZnO NRs obtain from VTC processes.
Silicon/zinc oxide (Si/ZnO) core-shell nanowires (NWs) were prepared on a p-type Si(111) substrate using a two-step growth process. First, indium seed-coated Si NWs (In/Si NWs) were synthesized using a plasma-assisted hot-wire chemical vapor deposition technique. This was then followed by the growth of a ZnO nanostructure shell layer using a vapor transport and condensation method. By varying the ZnO growth time from 0.5 to 2 h, different morphologies of ZnO nanostructures, such as ZnO nanoparticles, ZnO shell layer, and ZnO nanorods were grown on the In/Si NWs. The In seeds were believed to act as centers to attract the ZnO molecule vapors, further inducing the lateral growth of ZnO nanorods from the Si/ZnO core-shell NWs via a vapor-liquid-solid mechanism. The ZnO nanorods had a tendency to grow in the direction of [0001] as indicated by X-ray diffraction and high resolution transmission electron microscopy analyses. We showed that the Si/ZnO core-shell NWs exhibit a broad visible emission ranging from 400 to 750 nm due to the combination of emissions from oxygen vacancies in ZnO and In2O3 structures and nanocrystallite Si on the Si NWs. The hierarchical growth of straight ZnO nanorods on the core-shell NWs eventually reduced the defect (green) emission and enhanced the near band edge (ultraviolet) emission of the ZnO.
Sonocatalytic degradation of various organic dyes (Congo Red, Reactive Blue 4, Methyl Orange, Rhodamine B and Methylene Blue) catalyzed by powder and nanotubes TiO(2) was studied. Both catalysts were characterized using transmission electron microscope (TEM), surface analyzer, Raman spectroscope and thermal gravimetric analyzer (TGA). Sonocatalytic activity of powder and nanotubes TiO(2) was elucidated based on the degradation of various organic dyes. The former catalyst was favorable for treatment of anionic dyes, while the latter was more beneficial for cationic dyes. Sonocatalytic activity of TiO(2) nanotubes could be up to four times as compared to TiO(2) powder under an ultrasonic power of 100 W and a frequency of 42 kHz. This was associated with the higher surface area and the electrostatic attraction between dye molecules and TiO(2) nanotubes. Fourier transform-infrared spectrometer (FT-IR) was used to identify changes that occurred on the functional group in Rhodamine B molecules and TiO(2) nanotubes after the reaction. Sonocatalytic degradation of Rhodamine B by TiO(2) nanotubes apparently followed the Langmuir-Hinshelwood adsorption kinetic model with surface reaction rate of 1.75 mg/L min. TiO(2) nanotubes were proven for their high potential to be applied in sonocatalytic degradation of organic dyes.
The chemical production of methyl oleate using chemically synthesized fatty acid alcohols and other toxic chemicals may lead to significant environmental hazards to mankind. Being a highly valuable fatty acid replacement raw material in oleochemical industry, the mass production of methyl oleate via environmentally favorable processes is of concern. In this context, an alternative technique utilizing Candida rugosa lipase (CRL) physically adsorbed on multi-walled carbon nanotubes (MWCNTs) has been suggested. In this study, the acid-functionalized MWCNTs prepared using a mixture of HNO3 and H2SO4 (1:3 v/v) was used as support for immobilizing CRL onto MWCNTs (CRL-MWCNTs) as biocatalysts. Enzymatic esterification was performed and the efficiency of CRL-MWCNTs was evaluated against the free CRL under varying conditions, viz. temperature, molar ratio of acid/alcohol, solvent log P, and enzyme loading. The CRL-MWCNTs resulted in 30-110 % improvement in the production of methyl oleate over the free CRL. The CRL-MWCNTs attained its highest yield (84.17 %) at 50 °C, molar ratio of acid/alcohol of 1:3, 3 mg/mL of enzyme loading, and iso-octane (log P 4.5) as solvent. Consequently, physical adsorption of CRL onto acid-functionalized MWCNTs has improved the activity and stability of CRL and hence provides an environmentally friendly means for the production of methyl oleate.
Ethanol is a highly combustible chemical universally designed for biomedical applications. In this paper, optical sensing performance of tapered multimode fiber tip coated with carbon nanotube (CNT) thin film towards aqueous ethanol with different concentrations is investigated. The tapered optical multimode fiber tip is coated with CNT using drop-casting technique and is annealed at 70 °C to enhance the binding of the nanomaterial to the silica fiber tip. The optical fiber tip and the CNT sensing layer are micro-characterized using FESEM and Raman spectroscopy techniques. When the developed sensor was exposed to different concentrations of ethanol (5% to 80%), the sensor reflectance reduced proportionally. The developed sensors showed high sensitivity, repeatability and fast responses (<55 s) towards ethanol.
In recent years considerable attention has been attracted to magnesium because of its light weight, high specific strength, and ease of recycling. Because of the growing demand for lightweight materials in aerospace, medical and automotive industries, magnesium-based metal matrix nanocomposites (MMNCs) reinforced with ceramic nanometer-sized particles, graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) were developed. CNTs have excellent material characteristics like low density, high tensile strength, high ratio of surface-to-volume, and high thermal conductivity that makes them attractive to use as reinforcements to fabricate high-performance, and high-strength metal-matrix composites (MMCs). Reinforcing magnesium (Mg) using small amounts of CNTs can improve the mechanical and physical properties in the fabricated lightweight and high-performance nanocomposite. Nevertheless, the incorporation of CNTs into a Mg-based matrix faces some challenges, and a uniform distribution is dependent on the parameters of the fabricating process. The characteristics of a CNTs reinforced composite are related to the uniform distribution, weight percent, and length of the CNTs, as well as the interfacial bonding and alignment between CNTs reinforcement and the Mg-based matrix. In this review article, the recent findings in the fabricating methods, characterization of the composite's properties, and application of Mg-based composites reinforced with CNTs are studied. These include the strategies of fabricating CNT-reinforced Mg-based composites, mechanical responses, and corrosion behaviors. The present review aims to investigate and conclude the most relevant studies conducted in the field of Mg/CNTs composites. Strategies to conquer complicated challenges are suggested and potential fields of Mg/CNTs composites as upcoming structural material regarding functional requirements in aerospace, medical and automotive industries are particularly presented.
For the first time, the fabrication of novel nanorods by the addition of polyaniline (PANI) to polyethylene oxide (PEO) and polyvinyl alcohol (PVA) polymers through electrospinning method is investigated. Field emission scanning electron microscopy observations reveal the formation of nanofibers and nanorods having diameters in the range of 26.87-139.90 nm and 64.11-122.40 nm, respectively, and lengths in the range of 542.10 nm to 1.32 μm. Photoluminescence (PL) analysis shows the presence of peaks which are characteristic of isotactic polymers (363-412, 529-691 nm), 412-529 nm for PVA/PEO and 363-691 nm for PVA/PEO/PANI. PL spectra also show peak bonding at a wavelength of 552 nm. Manufacture of nanorods by electrospinning method gives better options for controlling the diameter and length of nanorods.
A thermoplastic elastomer (TPE) based nanocomposite with the same weight ratio of hybrid nanofillers composed of carbon nanotubes (CNTs) and montmorillonite nanoclay (DK4) was prepared using a melt blending technique with an internal mixer. The TPE composite was blended from polylactic acid (PLA), liquid natural rubber (LNR) as a compatibilizer and natural rubber (NR) in a volume ratio of 70:10:20, respectively. The weight ratio of CNTs and DK4 was 2.5 wt%. The prepared samples were exposed to gamma radiation at range of 0-250 kGy. After exposure to gamma radiation, the mechanical, thermo-mechanical, thermal and electrical conductivity properties of the composites were significantly higher than unirradiated TPE composites as the irradiation doses increased up to 150 kGy. Transmission electron microscopy (TEM) micrographs revealed the good distribution and interaction between the nano-fillers and the matrix in the prepared TPE hybrid nanocomposites. In summary, the findings from this work definite that gamma irradiation might be a viable treatment to improve the properties of TPE nanocomposite for electronic packaging applications.
The enhancement of microwave absorbing properties in nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) via multiwall carbon nanotubes (MWCNT) growth is studied in this research work. Ni0.5Zn0.5Fe2O4 was initially synthesized by mechanical alloying followed by sintering at 1200 °C and the microstructural, electromagnetic and microwave characteristics have been scrutinized thoroughly. The sintered powder was then used as a catalyst to grow MWCNT derived from chemical vapor deposition (CVD) method. The sample was mixed with epoxy resin and a hardener for preparation of composites. The composite of multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 shown a maximum reflection loss (RL) of -19.34 dB at the frequency and bandwidth of 8.46 GHz and 1.24 GHz for an absorber thickness of 3 mm for losses less than -10 dB. This acquired result indicates that multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 could be used as a microwave absorber application in X-band.
Composite materials have increasingly become crucial in manufacturing engineering products and producing commodity
materials in the major industries including; automotive, aerospace, marine, construction, agriculture and health science.
However, several improvements regarding the strength, dimensional stability and the cost of production are required.
In this study, composite of Kenaf, multi-wall carbon nanotube (MWCNT) and polypropylene (PP) with maleic anhydridegrafted
polypropylene (MAPP) are examined. The results highlight that increasing MAPP loading, in turn, increases the
value of the mechanical properties. The composites are produced by blending kenaf/MWCNT/PP using a Sigma blade
mixer and injection moulding. Injection moulding is a significant operation used to produce plastic products. In the
study, Kenaf core fibre was mixed with MWCNT and polypropylene, in addition to MAPP. The MAPP is added by applying
different percentage (1, 2, 3 and 4 wt. %) during the blending process. The main objective of the study was to analyse the
effects of MAPP concentrations on the mechanical properties of the Kenaf/MWCNT/PP composite. The results of the study
established that MAPP 3 wt. % concentration with MWCNT 3 wt. % loading and Kenaf 30 wt. % filler provide optimum
results for the composites. There was approximately, a 21% enhance in tensile strength of Kenaf 30 wt. %/MWCNT, 3 wt.
%/MAPP, 3 wt. %/PP observed compared to the (without) MAPP composite. The composites with coupling agent stimulate
better filler dispersion between Kenaf, MWCNT and PP observed using a scanning electron microscope (SEM) and fieldemission
scanning electron microscope (FESEM).
Electrochemical biosensors have shown great potential in the medical diagnosis field. The performance of electrochemical biosensors depends on the sensing materials used. ZnO nanostructures play important roles as the active sites where biological events occur, subsequently defining the sensitivity and stability of the device. ZnO nanostructures have been synthesized into four different dimensional formations, which are zero dimensional (nanoparticles and quantum dots), one dimensional (nanorods, nanotubes, nanofibers, and nanowires), two dimensional (nanosheets, nanoflakes, nanodiscs, and nanowalls) and three dimensional (hollow spheres and nanoflowers). The zero-dimensional nanostructures could be utilized for creating more active sites with a larger surface area. Meanwhile, one-dimensional nanostructures provide a direct and stable pathway for rapid electron transport. Two-dimensional nanostructures possess a unique polar surface for enhancing the immobilization process. Finally, three-dimensional nanostructures create extra surface area because of their geometric volume. The sensing performance of each of these morphologies toward the bio-analyte level makes ZnO nanostructures a suitable candidate to be applied as active sites in electrochemical biosensors for medical diagnostic purposes. This review highlights recent advances in various dimensions of ZnO nanostructures towards electrochemical biosensor applications.
Ultraviolet (UV) photodetectors (PDs) based on high-quality well-aligned ZnO nanorods (NRs) were fabricated using both modified and conventional chemical bath deposition (CBD) methods. The modified chemical bath deposition (M-CBD) method was made by adding air bubbles to the growth solution during the CBD process. The viability and effectiveness of M-CBD were examined by developing UV PDs based on ZnO NRs. The ZnO nano-seed layer was coated on a glass substrate utilizing radiofrequency (RF) sputtering. The impact of the different growth-times on morphology, growth rate, crystal structure, and optical and chemical properties were investigated systematically using different characterization techniques, such as field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) analysis, UV-VIS double beam spectrometer, and energy dispersive X-ray analysis (EDX), respectively. The Al/ZnO UV PDs based on ZnO nanorods were fabricated with optimum growth conditions through the two methods of preparation. This study showed that the synthesized ZnO NRs using the M-CBD method for different growth times possess better properties than the conventional method under similar deposition conditions. Despite having the highest aspect ratio and growth rate of ZnO NRs, which were found at 4 h growth duration for both methods, the aspect ratio of ZnO NRs using the M-CBD technique was comparatively higher than the conventional CBD method. Besides, the UV PDs fabricated by the M-CBD method at 5 V bias voltage showed high sensitivity, short response time, quick recovery time, high gain, low dark current, and high photocurrent compared with the UV PD device fabricated by the conventional CBD method.
Zinc oxide (ZnO) nanoparticles (NPs) has become as promising candidate for antibacterial agents against Escherichia coli (E.coli), commensal hospital- acquired infections (HAIs). This study investigates the antibacterial action of ZnO NPs in three difference shapes; nanorod, nanoflakes and nanospheres against E.coli ATCC 25922. The antibacterial activity of ZnO NPs was determine through two standard protocols known as Clinical Laboratory Standards Institute (CLSI) MO2-A11 under light conditions of 5.70 w/m2 and American standard test method (ASTM) E-2149. Preliminary screening shows ZnO NPs did not inhibit the growth of E.coli. Further analysis using ASTM E-2149 in dynamic conditions revealed antibacterial activity after 3 hours with 100% reduction for ZnO NPs nanoflakes and 6 hours with 94.63% reduction for ZnO nanospheres, respectively. It demonstrated the ZnO NPs in nanoflakes and nanospheres exerted higher antibacterial activity possibly through release of ios, free radicals, ROS generation and electrostatic collision which contribute to bacterial death. Further analysis is needed to investigate biocompatibility of these samples for future biomedical applications.
Halloysite nanotubes (HNTs)-polyester nanocomposites with four different concentrations were produced using solution casting technique and the biodegradation effect of short-term seawater exposure (120 h) was studied. Monolithic polyester was observed to have the highest seawater absorption with 1.37%. At 0.3 wt % HNTs reinforcement, the seawater absorption dropped significantly to the lowest value of 0.77% due to increase of liquid diffusion path. For samples tested in dry conditions, the Tg, storage modulus, tensile properties and flexural properties were improved. The highest improvement of Tg was from 79.3 to 82.4 °C (increase 3.1 °C) in the case of 0.3 wt % HNTs. This can be associated with the exfoliated HNTs particles, which restrict the mobility of polymer chains and thus raised the Tg. After seawater exposure, the Tg, storage modulus, tensile properties and flexural properties of polyester and its nanocomposites were decreased. The Young's modulus of 0.3 wt % HNTs-polyester dropped 20% while monolithic polyester dropped up to 24% compared to their values in dry condition. Apart from that, 29% flexural modulus reduction was observed, which was 18% higher than monolithic polyester. In contrast, fracture toughness and surface roughness increased due to plasticization effect. The presence of various microbial communities caused gradual biodegradation on the microstructure of the polyester matrix as also evidently shown by SEM images.
Arrays of TiO2 nanotubes (TiO2 NTs) with grassy surfaces were observed on titanium foil anodised at 60 V in fluorinated ethylene glycol (EG) with added hydrogen peroxide (H2O2). The grassy surface was generated by the chemical etching and dissolution of the surface of the TiO2 NTs walls, which was accelerated by the temperature increase on the addition of H2O2 . Upon annealing at 600 °C, the grassy part of the TiO2 NTs was found to consist of mostly anatase TiO2 whereas the bottom part of the anodic oxide comprised a mixture of anatase and rutile TiO2. The TiO2 NTs were then used to reduce hexavalent chromium (Cr(VI)) under ultraviolet radiation. They exhibited a rather efficient photocatalytic effect, with 100% removal of Cr(VI) after 30 min of irradiation. The fast removal of Cr(VI) was due to the anatase dominance at the grassy part of the TiO2 NTs as well as the higher surface area the structure may have. This work provides a novel insight into the photocatalytic reduction of Cr(VI) on grassy anatase TiO2 NTs.
Skin diseases are the fourth leading non-fatal skin conditions that act as a burden and affect the world economy globally. This condition affects the quality of a patient's life and has a pronounced impact on both their physical and mental state. Treatment of these skin conditions with conventional approaches shows a lack of efficacy, long treatment duration, recurrence of conditions, systemic side effects, etc., due to improper drug delivery. However, these pitfalls can be overcome with the applications of nanomedicine-based approaches that provide efficient site-specific drug delivery at the target site. These nanomedicine-based strategies are evolved as potential treatment opportunities in the form of nanocarriers such as polymeric and lipidic nanocarriers, nanoemulsions along with emerging others viz. carbon nanotubes for dermatological treatment. The current review focuses on challenges faced by the existing conventional treatments along with the topical therapeutic perspective of nanocarriers in treating various skin diseases. A total of 213 articles have been reviewed and the application of different nanocarriers in treating various skin diseases has been explained in detail through case studies of previously published research works. The toxicity related aspects of nanocarriers are also discussed.
In this work, fibrous silica-titania (FST) was successfully prepared by the microemulsion method prior to the addition of three types of carbonaceous materials: graphitic-carbon nitride, g-C3N4 (CN), graphene nanoplatelets (GN), and multi-wall carbon nanotubes, MWCNT (CNT), via a solid-state microwave irradiation technique. The catalysts were characterized using XRD, FESEM, TEM, FTIR, UV-Vis DRS, N2 adsorption-desorption, XPS and ESR, while their photoactivity was examined on the degradation of toxic 2-chlorophenol (2-CP). The result demonstrated that the initial reaction rate was in the following order: CNFST (5.1 × 10-3 mM min-1) > GNFST (2.5 × 10-3 mM min-1) > CNTFST (2.3 × 10-3 mM min-1). The best performance was due to the polymeric structure of g-C3N4 with a good dispersion of C and N on the surface FST. This dispersion contributed towards an appropriate quantity of defect sites, as a consequence of the greater interaction between g-C3N4 and the FST support, that led to narrowed of band gap energy (2.98 eV to 2.10 eV). The effect of scavenger and ESR studies confirmed that the photodegradation over CNFST occurred via a Z-scheme mechanism. It is noteworthy that the addition of green carbonaceous materials on the FST markedly enhanced the photodegradation of toxic 2-CP.
This paper addresses the growth of nano-structured MgZnO thin films by sol-gel spin coating method which will be used as a template layer to grow carbon nanotubes. The nano-structured MgZnO films were deposited on platinized (100) silicon substrates. In this work, we focused on the effect of aging and Mg content on the film structure and resistivity. Sols with Mg content of 10, 30 and 50 at.% were subjected to aging times of between 3 to 240 hours. Results from scanning (SEM) and field emission scanning electron (FESEM) microscopes and surface profiler (SP) showed that the sol aging increased the thickness, grain size and surface roughness for aging up to 240 hours. The energy dispersive analysis by X-ray (EDAX) confirmed the element of Mg in the ZnO films. The electrical resistivity also increased with aging time as confirmed by four point probe method. The results suggest that appropriate aging of the sol is important for improving physical quality and electrical performance of MgZnO thin films derived from sol-gel technique.
Magnetic nanoparticles in the hollow region of carbon nanotubes have attraction due to their changing physical electrical and magnetic properties. Nickel zinc ferrite plays an important role in many applications due to its superior magnetic properties. Ni0.8Zn0.2Fe2O4 single crystals were encapsulated in multiwall carbon nanotubes (MWCNTs). The magnetic nano crystals were prepared using a sol-gel self combustion method at the sintering temperature of 750 degrees C and were characterized by XRD, FESEM, TEM and VSM. Initial permeability, Q-factor and relative loss factor were measured by impedance vector network analyzer. XRD patterns were used for the phase identification. FESEM images show morphology and dimensions of the grains of Ni0.8Zn0.2Fe2O4 single crystals and Ni0.8Zn0.2Fe2O4 single crystals in MWCNTs. TEM images were used to investigate single crystal and encapsulation of Ni0.8Zn0.2Fe2O4 single crystals in the MWCNTs. VSM results confirmed super paramagnetic behaviour of encapsulated Ni0.8Zn0.2Fe2O4 single crystals. It was also attributed that encapsulated Ni0.8Zn0.2Fe2O4 single crystals in MWCNTs showed a higher initial permeability (51.608), Q-factor (67.069), and low loss factor (0.0002) as compared to Ni0.8Zn0.2Fe2O4 single crystals. The new encapsulated Ni0.8Zn0.2Fe2O4 single crystals in the MWCNTs may have potential applications in electronic and medical industries.