Self-powered, wide spectral UV response out-of-plane photodetector based on ZnO/porous silicon heterostructure.

The photoresponse of the ZnO/porous silicon (p-Si) heterojunction is studied in an out-of-plane contact configuration. p-Si substrate is fabricated by anodic etching followed by the electrochemical deposition of ZnO NR film, forming ZnO/p-Si heterojunction. XRD study is done to understand the effect of the substrate on ZnO film growth in terms of strain and crystal size. UV-vis absorbance spectrum shows a broad absorption for wavelengths from 230 to 380 nm. The PL emission shows two narrow and prominent electron transition peaks at 263 and 383 nm and a peak of ∼550 nm corresponding to defects. The 263 nm wavelength responsivity of the photodetector from UV-vis and PL data suggests the presence of a defective SiOxas an intermediate layer between ZnO and p-Si. The photodetector is measured for its spectral selectivity and responsivity for both 266 and 370 nm. Under self-powered conditions, the device shows a low dark current of a few nA and enhancement of ∼100 nA and ∼1.37µA for both wavelengths. A responsivity of 527 mA W-1and 10.5µA W-1and detectivity of 2.5 × 1010and 2.9 × 107Jones at 1 V bias under 266 and 370 nm UV illumination are observed. The fast rise/decay time of 67/65 ms and 29/18 ms is observed for the self-powered condition of the device under both wavelengths respectively. The photoresponse of the modified ZnO/SiOx/p-Si heterojunction for both wavelengths is analyzed for the electron transfer mechanism using the heterojunction band bending model. The short circuit current and open circuit voltage of the photodetector is estimated to be 293 nA, 56.33 mV, and 13.63µA, 124.8 mV for 266 and 370 nm, respectively. It is concluded that the 266 nm responsivity comes from the defects in SiOxintermediate layer, and the photocurrent generated in the device is due to tunneling across the junction.

Highly Luminescent Dual Mode Polymeric Nanofiber-Based Flexible Mat for White Security Paper and Encrypted Nanotaggant Applications.

Increasing counterfeiting of important data, currency, stamp papers, branded products etc., has become a major security threat which could lead to serious damage to the global economy. Consequences of such damage are compelling for researchers to develop new high-end security features to address full-proof solutions. Herein, we report a dual mode flexible highly luminescent white security paper and nanotaggants composed of nanophosphors incorporated in polymer matrix to form a nanofiber-based mat for anti-counterfeiting applications. The dual mode nanofibers are fabricated by electrospinning technique by admixing the composite of NaYF4 :Eu3+ @NaYF4 :Yb3+ , Er3+ nanophosphors in the polyvinyl alcohol solution. This flexible polymer mat derived from nanofibers appears white in daylight, while emitting strong red (NaYF4 :Eu3+ ) and green (NaYF4 :Yb3+ , Er3+ ) colors at excitation wavelengths of 254 nm and 980 nm, respectively. These luminescent nanofibers can also be encrypted as a new class of nanotaggants to protect confidential documents. These obtained results suggest that highly luminescent dual mode polymeric nanofiber-based flexible white security paper and nanotaggants could offer next-generation high-end unique security features against counterfeiting.

Role of limited hydrogen and flow interval on the growth of single crystal to continuous graphene by low-pressure chemical vapor deposition.

A method for defect-free large crystallite graphene growth remains unknown despite much research effort. In this work, we discuss the role of flow duration of H2 gas for the production of graphene as per requirement and production at a minimum flow rate considering the safety issue of hydrogen utilization. The copper substrate used for growth was treated for different time intervals (0 to 35 min) in H2 flow prior to growth. Structural and chemical changes occurring in the copper substrate surface were probed by grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. The results were correlated with the Raman spectroscopy data, which can quantify the quality of graphene. With increasing H2 flow interval, secondary nucleation sites were observed and growth favored few-layer graphene structures. The surface-adsorbed oxygen molecules and its conversion to an OH terminated surface with increasing hydrogen flow interval was found to be a key factor in enhancing nucleation density. The Stranski-Krastanov type of nucleation was observed for samples grown with different time intervals of H2 treatment, except 5 min of H2 flow prior to growth for which the Volmer-Weber type of growth favored monolayer graphene crystallite growth.

Control of layer stacking in CVD graphene under quasi-static condition.

The type of layer stacking in bilayer graphene has a significant influence on its electronic properties because of the contrast nature of layer coupling. Herein, different geometries of the reaction site for the growth of bilayer graphene by the chemical vapor deposition (CVD) technique and their effects on the nature of layer stacking are investigated. Micro-Raman mapping and curve fitting analysis confirmed the type of layer stacking for the CVD grown bilayer graphene. The samples grown with sandwiched structure such as quartz/Cu foil/quartz along with a spacer, between the two quartz plates to create a sealed space, resulted in Bernal or AB stacked bilayer graphene while the sample sandwiched without a spacer produced the twisted bilayer graphene. The contrast difference in the layer stacking is a consequence of the difference in the growth mechanism associated with different geometries of the reaction site. The diffusion dominated process under quasi-static control is responsible for the growth of twisted bilayer graphene in sandwiched geometry while surface controlled growth with ample and continual supply of carbon in sandwiched geometry along with a spacer, leads to AB stacked bilayer graphene. Through this new approach, an efficient technique is presented to control the nature of layer stacking.

Covalent immobilization of xylanase produced from Bacillus pumilus SV-85S on electrospun polymethyl methacrylate nanofiber membrane.

Polymethyl methacrylate (PMMA) nanofiber membrane (NFM) was synthesized by an electrospinning technique. These membranes were utilized as a support for immobilization of xylanase enzyme to study its pH stability, thermal stability, and reusability. The morphology of aligned NFM was studied by optical microscopy and scanning electron microscopy. The PMMA NFM was functionalized with phenylenediamine and activated with glutaraldehyde to yield an aldehyde group on its surface for covalent immobilization of xylanase. The Fourier transform infrared analysis of the covalently immobilized xylanase confirmed that the enzyme was immobilized on PMMA NFM via amide linkages. The immobilization efficiency of covalently bound xylanase was found experimentally to be 90%. A forward shift in pH optima from 6.0-7.0 (soluble enzyme) to 7.0-9.0 (immobilized enzyme) was observed after xylanase immobilization. The pH and temperature stability of xylanase were enhanced upon its covalent immobilization. The immobilized enzyme was active on repeated use and retained ∼80% of its initial activity after 11 reaction cycles. The improved thermal and operational stability of the covalently immobilized enzyme on PMMA NFM might be advantageous for industrial applications.

3D Printed Lattice Template by Material Extrusion Technique for Fabrication of Pixelated Photodetector.

Rigid and flexible, pixelated ultraviolet photodetectors (PD) based on ZnO have been fabricated by material extrusion 3D printing technique. The photoresponse is studied in an out-of-plane configuration. An open lattice structure is printed using PLA over ITO/Glass substrate for rigid, and TPU over ITO/PET substrate for flexible PDs. ZnO slurry is filled selectively into the columnar matrix by the microdispensing technique. The optical detector printed on ITO/Glass substrate shows a sensitivity of 25 and responsivity of 1.55 nA/mW with a rise and decay time of 1.6 and 0.6 s, respectively. Similarly, the flexible PD printed using TPU lattice shows a sensitivity of 9.5 and responsivity of 0.38 nA/mW with a rise and decay time of 1.8 and 0.6 s, respectively. The charge transport mechanism is studied using band diagram analysis. 3D printed open lattice structure is found to be a potential template for sensor fabrication. This work demonstrates the capability of material extrusion 3D printing with an open lattice structure for the fabrication of high-resolution pixelated PDs.

Elucidation of Mg²âº binding activity of adenylate kinase from Mycobacterium tuberculosis H37Rv using fluorescence studies.

Adenylate kinase (AK) is a small ubiquitous enzyme that catalyzes the reversible transfer of the terminal phosphate group from adenine triphosphate (ATP): magnesium ion (Mg²âº) to adenine monophosphate (AMP) to form two molecules of adenine diphosphate (ADP). AK thus maintains the homeostasis of adenine nucleotides in eukaryotes and prokaryotes. Because the [ATP]/[ADP] ratio is an important parameter in energy regulation in cells, Mg²âº-activated AK has an important biological role, particularly in the case of bacteria, as imbalance in the ratio of [ATP]/[ADP] has been associated with alteration in its DNA supercoiling state. In the present study, magnesium-binding assays were carried out by systematically varying the concentrations of Mg²âº, protein, AMP, ATP, and indicator in kinetic experiments. We report evidence that during magnesium-binding assay, the fluorescence level of the indicator "Mag-Indo-1" changes with protein concentration, suggesting that magnesium ions are binding to AK. The dual activity of AK both as nucleoside monophosphate and diphosphate kinases suggests that this enzyme may have a role in RNA and DNA biosynthesis in addition to its role in intracellular nucleotide metabolism. According to the proposed model, the magnesium-activated AK exhibits an increase in its forward reaction rate compared with the inactivated form. These findings imply that Mg²âº could be an important regulator in the energy signaling network in cells.

Development of transmucosal patch using nanofibers.

In the present work we have attempted to develop a novel transmucosal patch of diclofenac sodium using electrospun polycaprolactone (PCL) nanofibers. PCL nanofibers were prepared by electrospinning techniques using different polymer concentrations. Nanofibers formulations were characterized by SEM, FTIR, drug loading, and in-vitro release study using Franz diffusion cell. Studies revealed the nanofibers fabricated from 13% PCL were fracture-free, non-beaded, and ultrafine with 120 nm diameter. Release studies demonstrated the sustained release behavior of PCL nanofibers. Nanofibers can be exploited for transmucosal drug delivery of NSAID with improved therapeutic efficacy.

Palladium encapsulated nanofibres for scavenging ethylene from sapota fruits.

Scavenging ethylene is a useful intervention during the transportation and storage of tropical climacteric fruits like sapota. Sapota (Manilkara achras Mill.) is a delicious tropical fruit with a very high respiration rate and poor shelf life. To prolong its post-harvest shelf life, the use of palladium chloride in electrospun nanomats was evaluated at a concentration varying from 1 to 4% levels. Encapsulation of 1-2% PdCl2 in nanomats increased the ethylene scavenging capacity (ESC) by 47-68%. Although, upon encapsulation, both PdCl2 and potassium permanganate showed significantly the same ethylene scavenging activity, the efficacy of PdCl2 was found better in presence of sapota fruits. The PdCl2 nanomats were brighter (L* > 73) in colour compared to the potassium permanganate mat. The placement of nanomats (2 cm2 × 9 cm2) in corrugated fibre board boxes in which the sapota was packed showed higher quality indices (firmness, TSS, ascorbic acid, and phenolics) along with lower PLW and respiration rate during the 8 days of storage period. Compared to control (8.35%), physiological loss in weight of 4.47% was recorded in fruits stored with ethylene scavenging nanomats. PdCl2 encapsulated PVA nanomats can emerge as a promising option for the retention of quality in fruits during storage and transit.

Recent trends in gas sensing via carbon nanomaterials: outlook and challenges.

The presence of harmful and poisonous gases in the environment can have dangerous effects on human health, and therefore portable, flexible, and highly sensitive gas sensors are in high demand for environmental monitoring, pollution control, and medical diagnosis. Currently, the commercialized sensors are based on metal oxides, which generally operate at high temperatures. Additionally, the desorption of chemisorbed gas molecules is also challenging. Hence, due to the large surface area, high flexibility, and good electrical properties of carbon nanomaterials (CNMs) such as carbon nanotubes, graphene and their derivatives (graphene oxide, reduced graphene oxide, and graphene quantum dots), they are considered to be the most promising chemiresistive sensing materials, where their electrical resistance is affected by their interaction with the analyte. Further, to increase their selectivity, nanocomposites of CNMs with metal oxides, metallic nanoparticles, chalcogenides, and polymers have been studied, which exhibit better sensing capabilities even at room temperature. This review summarizes the state-of-the-art progress in research related to CNMs-based sensors. Moreover, to better understand the analyte adsorption on the surface of CNMs, various sensing mechanisms and dependent sensing parameters are discussed. Further, several existing challenges related to CNMs-based gas sensors are elucidated herein, which can pave the way for future research in this area.

The removal of pentavalent arsenic by graphite intercalation compound functionalized carbon foam from contaminated water.

In the present investigation, Graphite intercalation compound (GIC) functionalized phenolic resin based carbon foam for removal of arsenic (As(V)) from contaminated water is developed by sacrificial template technique followed by carbonization at 1000 °C in N2. The GICCF adsorbent is characterised by scanning electron microscope (SEM) for morphological study, X-ray diffraction (XRD) patterns explains the phase information and interlayer spacing of the adsorbent, whereas Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) gives the information about surface functionality and mechanism of adsorption of As(V) over the surface of adsorbent. The time data is fitted well in pseudo second order kinetics and follows multilinear nature of intra-particle diffusion model. The adsorption nature of adsorbent and adsorbate is explained by Langmuir isotherm better than Freundlich isotherm, Temkin isotherm, and D-R isotherm. The adsorption capacity of adsorbent is 62.5 µgg-1, which is calculated by Langmuir isotherm. Arsenic removal by GICCF is taken place within two hrs up to acceptable limit. The proposed GICCF can be regenerated after treating with 0.1 M HNO3 and 0.1 M HCl solution and it can be used for multiple times.

Synthesis and characterization of multiwalled CNT-PAN based composite carbon nanofibers via electrospinning.

Electrospun fibrous membranes find place in diverse applications like sensors, filters, fuel cell membranes, scaffolds for tissue engineering, organic electronics etc. The objectives of present work are to electrospun polyacrylonitrile (PAN) nanofibers and PAN-CNT nanocomposite nanofibers and convert into carbon nanofiber and carbon-CNT composite nanofiber. The work was divided into two parts, development of nanofibers and composite nanofiber. The PAN nanofibers were produced from 9 wt% PAN solution by electrospinning technique. In another case PAN-CNT composite nanofibers were developed from different concentrations of MWCNTs (1-3 wt%) in 9 wt% PAN solution by electrospinning. Both types of nanofibers were undergone through oxidation, stabilization, carbonization and graphitization. At each stage of processing of carbon and carbon-CNT composite nanofibers were characterized by SEM, AFM, TGA and XRD. It was observed that diameter of nanofiber varies with processing parameters such as applied voltage tip to collector distance, flow rate of solution and polymer concentrations etc. while in case of PAN-CNT composite nanofiber diameter decreases with increasing concentration of CNT in PAN solution. Also with stabilization, carbonization and graphitization diameter of nanofiber decreases. SEM images shows that the minimum fiber diameter in case of 3 wt% of CNT solution because as viscosity increases it reduces the phase separation of PAN and solvent and as a consequence increases in the fiber diameter. AFM images shows that surface of film is irregular which give idea about mat type orientation of fibers. XRD results show that degree of graphitization increases on increasing CNT concentration because of additional stresses exerting on the nanofiber surface in the immediate vicinity of CNTs. TGA results shows wt loss decreases as CNT concentration increases in fibers.

Evaluation of physicochemical and biological properties of chitosan/poly (vinyl alcohol) polymer blend membranes and their correlation for Vero cell growth.

The blend membranes with varying weight ratios of chitosan/poly (vinyl alcohol) (CS/PVA) (1:0, 1:1, 1:2.5, 1.5:1, 1.5: 2.5) were prepared using solvent casting method and were evaluated for their potential application in single-use membrane bioreactors (MBRs). The physicochemical properties of the prepared membranes were investigated for chemical interactions (FTIR), surface morphology (SEM), water uptake, protein sorption (qe), ammonia sorption and growth kinetics of Vero cells. CS/PVA blend membrane having weight ratio of 1.5:1 had shown enhanced membrane flexibility, reduced water uptake, less protein sorption and no ammonium sorption compared to CS membrane. This blend membrane also showed comparatively enhanced higher specific growth rate (0.82/day) of Vero cells. Improved physicochemical properties and growth kinetics obtrude CS/PVA (1.5:1) as a potential surface for adhesion and proliferation with possible application in single use membrane bioreactors. Additionally, new insight explaining correlation between water holding (%) of CS/PVA (1.5:1) blend membrane and doubling time (td) of Vero cells is proposed.

Lightweight and Easily Foldable MCMB-MWCNTs Composite Paper with Exceptional Electromagnetic Interference Shielding.

Lightweight and easily foldable with high conductivity, multiwalled carbon nanotube (MWCNT)-based mesocarbon microbead (MCMB) composite paper is prepared using a simple, efficient, and cost-effective strategy. The developed lightweight and conductive composite paper have been reported for the first time as an efficient electromagnetic interference (EMI) shielding material in X-band frequency region having a low density of 0.26 g/cm(3). The investigation revealed that composite paper shows an excellent absorption dominated EMI shielding effectiveness (SE) of -31 to -56 dB at 0.15-0.6 mm thickness, respectively. Specific EMI-SE of as high as -215 dB cm(3)/g exceeds the best values of metal and other low-density carbon-based composites. Additionally, lightweight and easily foldable ability of this composite paper will help in providing stable EMI shielding values even after constant bending. Such intriguing performances open the framework to designing a lightweight and easily foldable composite paper as promising EMI shielding material, especially in next-generation devices and for defense industries.

Multi-walled carbon nanotube-graphene-polyaniline multiphase nanocomposite with superior electromagnetic shielding effectiveness.

The multiphase approach was adapted to enhance the electromagnetic interference (EMI) shielding effectiveness (SE) of polyaniline (PANI) based nanocomposites. The natural graphite flakes (NGF) incorporated modified PANI was used for the development of multi-walled carbon nanotubes (MWCNTs) based nanocomposites. In PANINGF-MWCNTs composites, multilayer graphene was synthesized in situ by ball milling. The resultant PANINGF-MWCNTs nanocomposites were characterized by different techniques. It was revealed from the transmission electron microscope (TEM) observation that in situ derived multilayer graphene acts as a bridge between PANI and MWCNTs, and plays a significant role for improving the properties of multiphase nanocomposites. It was observed that EMI-SE increases with increasing the MWCNTs content from 1 to 10 wt% in the multiphase nanocomposites. The maximum value of total EMI-SE was -98 dB of nanocomposite with 10 wt% of MWCNTs content. The high value of EMI-SE is dominated by the absorption phenomenon which is due to the collective effect of increase in space charge polarization and decrease in carrier mobility. The decrease in carrier mobility has a positive effect on the shore hardness value due to the strong interaction between the reinforcing constituent in multiphase nanocomposites. As a consequence, shore hardness increases from 56 to 91 at 10 wt% of MWCNTs.

Electrospun polyacrylonitrile nanofibrous membranes for chitosanase immobilization and its application in selective production of chitooligosaccharides.

Polyacrylonitrile nanofibrous membranes (PANNFM) were prepared by electrospinning from 10 wt.% of PAN solution and its surface was modified by amidination reaction. A new chitosan degrading enzyme from Aspergillus sp. was covalently immobilized on PANNFM. Immobilization efficiency of 80% was achieved by activating PANNFM surface for 30 min followed by 2 h treatment with enzyme solution. The optimum temperature and pH for immobilized enzyme were 50°C and 5.8, respectively. The immobilized chitosanase retained >70% activity after ten repeated batch reaction and could be stored up to 60 days at 4°C with minor loss in activity. Chitosan hydrolysis using different substrates were studied using immobilized chitosanase in batch conditions. Continuous selective production of chitooligosaccharides (dimer to hexamer) by changing the temperature was achieved by PANNFM-chitosanase.

Toxicity of graphene in normal human lung cells (BEAS-2B).

Graphite nanomaterials such as thermally exfoliated graphite oxide (GO) are versatile in many applications. However, little is known about its effects on biological systems. In this study we characrerized the GO using dynamic light scattering (DLS) along with the toxicological aspects related to cytotoxicity and apoptosis in normal human lung cells (BEAS-2B). A significant concentration and time dependent decrease in cell viability was observed at different concentrations (10-100 microg/ml) by the MTT assay after 24 and 48 h of exposure and significant increase of early and late apoptotic cells was observed as compared to control cells. Our study demonstrates that GO induces cytotoxicity and apoptosis in human lung cells.

Chitosan-SiO2-multiwall carbon nanotubes nanocomposite: a novel matrix for the immobilization of creatine amidinohydrolase.

A matrix made up of chitosan-SiO(2)-multiwall carbon nanotubes (CHIT-SiO(2)-MWCNTs) nanocomposite was fabricated to investigate the immobilization of creatine amidinohydrolase (CAH). CAH enzyme was covalently immobilized with the CHIT-SiO(2)-MWCNTs matrix using glutaraldehyde as a linker. The resulting CAH/CHIT-SiO(2)-MWCNTs biomatrix was characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and cyclic voltammetry (CV) taking CHIT-SiO(2)-MWNTs as a reference. The influence of various parameters on CAH enzyme activity within the matrix was investigated including pH, temperature, and time. The Michaelis-Menten constant and apparent activities for the CAH enzyme were calculated to be 0.58 mM and 83.16 mg/cm(2), respectively; indicating CHIT-SiO(2)-MWCNTs nanocomposite matrix has a high affinity to immobilize CAH enzyme.