Direct conversion of lignin-rich black liquor to activated carbon for supercapacitor electrodes

The escalating industrialization trend underscores the imperative for sustainable waste management practices. The present investigation explores a sustainable methodology for managing the waste generated from the kraft process by directly converting it into activated carbon (BLAC) through a cost-effective hydrothermal-assisted activation method. The research involved a comparative analysis of BLAC with acid-washed black liquor lignin-derived activated carbon (ABLAC) and commercial lignin-derived activated carbon (SALAC). The analysis revealed that BLAC possesses a well-developed micro and mesoporous structure, yielding a significantly higher surface area of 2277.2 m2/g as compared to ABLAC (1260 m2/g) and SALAC (1558.4 m2/g). The presence of inherent alkali in the black liquor is the main factor influencing the surface area of the BLAC. Furthermore, it demonstrated impressive electrochemical performance, showing a specific capacitance value of 871.4 F/g at 1 A/g current density, positioning it as a formidable electrode material for supercapacitor applications. The proposed direct conversion strategy will eliminate the need for high-temperature pre‑carbonization and additional lignin extraction, reducing chemical usage and presenting a greener approach.

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.

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.

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.

Carbon nanotube incorporated eucalyptus derived activated carbon-based novel adsorbent for efficient removal of methylene blue and eosin yellow dyes

Carbon nanotube (CNT) incorporated eucalyptus derived activated carbon-based novel adsorbent is synthesized by a novel route. This adsorbent is investigated for the removal of two different dyes; methylene blue (MB) and eosin yellow (EY) from the waste water. The effect of pH, adsorbent dose, contact time and initial concentration, has been used to measure the dye removal efficiency of the adsorbent. Langmuir isotherm, Freundlich isotherm and D-R isotherm models were used to fit the experimental dye adsorption data, with the D-R model providing the best fit. The maximum adsorption efficiency of adsorbent for MB and EY removal is 49.61 and 49.15 mg/g, respectively. Reaction kinetics studies were also established to further investigate the dye adsorption mechanism. It is observed that pseudo second order model define the reaction kinetics involved in the reaction. This activated carbon adsorbent based on CNTs is shown to be highly promising for water decontamination applications.

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.

Trimetallic composite nanofibers for antibacterial and photocatalytic dye degradation of mixed dye water

Membrane technology is an advanced approach to making a healthier and cleaner environment. Using such catalytic membrane technology to get clean, usable water by removal of dye impurities as well as pathogenic microbes is the main goal behind the research work. Here, we present the synthesis and efficacy study of polymethyl methacrylate (PMMA)-based Ag/ZnO/TiO₂ trimetallic bifunctional nanofibers with antibacterial and photocatalytic activity. The nanofibers have been proven to be effective for the degradation of methylene blue (MB 93.4%), rhodamine B (Rh 34.6%), auramine-O (Au 65.0%) and fuchsin basic (FB 69.8%) dyes individually within 90 min in daylight. The study is further extended in abating a mixture of these dyes from contaminated water using composite nanofibers. Also, in the case of a mixture of these dyes (3 ppm each), nanofibers show dye degradation efficiency (DDE) of 90.9% (MB), 62.4% (Au) and 90.3% (FB and Rh) in 60 min. The role of Ag nanoparticles with a synergic photocatalytic effect on ZnO and TiO₂ is also demonstrated. Also, PMMA/ZnO/TiO₂ composite fiber membrane in synergy with silver particles shows better antibacterial activity against Gram-negative bacteria E. coli, making PMMA/Ag/ZnO/TiO₂ fibers a promising candidate in water purification.

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.

Improved thermomechanical and electrical properties of reduced graphene oxide reinforced polyaniline - dodecylbenzenesulfonic acid/divinylbenzene nanocomposites

HYPOTHESIS

Various efforts are going on to improve the electrical properties of carbon fiber reinforced polymer (CFRP) composites. Conducting polymer is one the promising material to achieve the desired electrical properties of CFRP composites without compromising the mechanical properties as a lighting sticking material.

EXPERIMENTS

In present study, in addition to conducting polymer polyaniline (PANI), another conducting phase reduced graphene oxide (RGO) was incorporated in PANI based system. The RGO was synthesized and incorporated in different weight (0-0.5 wt%) fraction in dodecylbenzenesulfonic acid (DBSA) doped PANI-divinylbenzene (DVB) polymer to get PANI-DBSA/DVB nanocomposite. The mechanical and interfacial interaction was analyzed by universal testing machine (UTM) and transmitted electron microscopy (TEM).

FINDINGS

The addition of optimum 0.3 wt% RGO improved flexural strength and modulus of PANI-DSBA/RGO-DVB composite by 153% and 32% respectively over neat PANI-DBSA/DVB nanocomposite. The maximum electrical conductivity 0.301 S/cm, glass transition temperature (T_g) and thermal stability of nanocomposite realized at 0.3 wt% of RGO. Raman spectroscopy and HRTEM confirmed the improvement of interfacial bonding by H-bonding and π-π interaction. For the 1st time we are reporting RGO utilisation for the improvement of thermomechanical and electrical interfacial properties of PANI-DBSA/DVB nanocomposite for the structural applications.

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.

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.

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.

Novel 3D lightweight carbon foam as an effective adsorbent for arsenic(v) removal from contaminated water

An efficient removal of pentavalent arsenic (As(v)) from water has been developed using novel three-dimensional (3D) light weight carbon foam which exhibit adoption capacity of 38.4 μg g⁻¹.

Synergistic effect on static and dynamic mechanical properties of carbon fiber-multiwalled carbon nanotube hybrid polycarbonate composites

The synergistic effect of reinforced non-functionalized and functionalized MWCNTs accompanied by CF is observed on the mechanical properties in a polycarbonate matrix.

Three-dimensional and highly ordered porous carbon–MnO2 composite foam for excellent electromagnetic interference shielding efficiency

The combination with MnO₂ nanoparticles in carbon matrix, the carbon foam exhibit absorption dominating specific EMI shielding value of −150 dB cm³ g⁻¹ with high strength of 7.8 MPa.

In situ growth of silicon carbide–carbon nanotube composites

SiC-single walled carbon nanotube composites were prepared through the novel route of d.c. arc discharge technique using silicon powder as a filler in a graphite anode and confirmed using X-ray diffraction, Raman spectroscopy and transmission electron microscopy techniques.

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.

Evaluating the potential of chitosan/poly(vinyl alcohol) membranes as alternative carrier material for proliferation of Vero cells

Chitosan/poly(vinyl alcohol) (CS/PVA) blend membranes were prepared using the casting method and their physiochemical properties were analyzed using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). FTIR and XRD demonstrated possible hydrogen bonds between CS and PVA. The addition of PVA to CS resulted in surface roughness as analyzed by SEM. The CS/PVA blend membrane exhibited high tensile properties (81.62%) and reduced water-holding capacity (53.8%) compared to a pure CS membrane (control). Cell viability and proliferation were assessed via an MTT assay with Vero cell culture. Associated with improved physicochemical properties, the CS/PVA blend membrane promotes cell proliferation of Vero cells with high specific growth rate (0.582 day-1). The results demonstrate that the blending of CS and PVA could significantly alter the surface rugosity, water-holding capacity and improve the mechanical and biological properties of the membrane. Interestingly, this concept can be extended for different anchorage-dependent cell lines, as an alternative carrier material.

Mesocarbon microsphere composites with Fe3O4 nanoparticles for outstanding electromagnetic interference shielding effectiveness

In situ, development of mesocarbon microsphere (MCMS) composites with magnetic Fe₃O₄ nanoparticles for outstanding electromagnetic (EMI) shielding effectiveness.

Cerium functionalized PVA–chitosan composite nanofibers for effective remediation of ultra-low concentrations of Hg(ii) in water

Functionalized PVA–chitosan composites nanofibers effective for removal of very low concentration of mercury.

Nanoparticles-decorated coal tar pitch-based carbon foam with enhanced electromagnetic radiation absorption capability

Carbon foam decorated with magnetic and dielectric nanoparticles exhibited significantly improved EM radiation absorption in the X-band frequency region.

Depression in glass transition temperature of multiwalled carbon nanotubes reinforced polycarbonate composites: effect of functionalization

Acid functionalized MWCNTs/PC composites showed significant improvement in storage modulus upto 57% in glassy and 400% in rubbery region over pure polycarbonate.

Superior nano-mechanical properties of reduced graphene oxide reinforced polyurethane composites

RGO reinforced polymer composites with significantly enhanced nanomechanical properties useful for automobile, wind mill blade industries and also in hard and scratch-less coatings on automotive vehicles have been synthesized.

The role of substrate purity and its crystallographic orientation in the defect density of chemical vapor deposition grown monolayer graphene

Here, we are reporting about the role of the copper substrate purity and its crystallographic orientation in the quality of the graphene grown using a low pressure chemical vapor deposition technique.

Polymer nanocomposite foam filled with carbon nanomaterials as an efficient electromagnetic interference shielding material

Among different carbon nanomaterial foam-filled polymer composites, graphene-based foam gives superior specific shielding effectiveness when compared to typical metals.

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 composite nanofiber-based transmucosal patch for anti-diabetic drug delivery

The intention of the present investigation was to develop an oral formulation for an anti-diabetic drug that not only could deliver it in the active form but also provide a sustained and controlled release profile. A biodegradable poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) electrospun composite nanofiber based transmucosal patch was developed and the anti-diabetic drug insulin was loaded in it by active loading. The drug entrapment in the composite nanofibers during the processing was confirmed by scanning electron microscopy, atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The in vivo studies were carried on male Wistar rats by the sublingual route. The mucoadhesive strength results confirmed that the drug loaded PVA-NaAlg nanofiber patch had the highest strength among the PVA, PVA-NaAlg and drug loaded PVA-NaAlg samples, due to its higher water holding capacity. The in vitro activity provided a sustained and controlled release pattern of the drug from the nanofiber patch. In vivo activity validated the fact that insulin was delivered in its active state and showed appreciable results when compared to the commercial formulation. The insulin release follows first order kinetics followed by an initial burst release necessary to produce the desired therapeutic activity. Furthermore an encapsulation efficacy of 99% of the experimental formulation provides sufficient indication that the composite nanofibers serve as an ideal carrier for the delivery of insulin via the sublingual route. Thus the present investigation gives impetus to work in the direction of delivering anti-diabetic drugs (proteins and peptides) via the oral route using electrospun composite nanofiber transmucosal patches.

Elucidation of Mg²⁺ 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 (Mg²⁺) 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, Mg²⁺-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 Mg²⁺, 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 Mg²⁺ could be an important regulator in the energy signaling network in cells.

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.