Riyaz A. Dar

Green synthesis of a silver nanoparticle–graphene oxide composite and its application for As(III) detection

We report a facile and green synthetic approach to synthesize a silver nanoparticle (AgNPs)–graphene oxide (GO) composite using beta cyclodextrin as a stabilizing agent and ascorbic acid as a reducing agent. Further, we demonstrate its application as a highly sensitive and selective electrochemical sensor for selective determination of As(III) in the presence of other elements, such as Cu and some organic and inorganic molecules. The GO sheets provided the surface for the reduction of silver ions. The composite can be easily used for the construction of a disposable electrochemical sensor on a glassy carbon electrode (GCE) using a drop deposition method. The composite was characterized by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray diffraction and electrochemical impedance spectroscopy. Cyclic voltammetry and anodic stripping voltammetry measurements were employed to evaluate the electrochemical properties of beta cyclodextrin stabilized AgNPs–GO/GCE towards arsenic(III) detection. The AgNPs–GO film exhibited distinctly higher activity for the anodic stripping analysis of As(III) compared to the GO film alone with approximately three times enhancement of the peak current. This nanostructured electrode applied for As(III) analysis displayed a wide linear range (13.33–375.19 nM), a high sensitivity (180.5(μA μM−1)) including a 0.24 nM detection limit. We demonstrate the real-life application of the developed sensor by selectively determining the As content in ground and river water samples.

Hierarchically macro/mesostructured porous copper oxide: facile synthesis, characterization, catalytic performance and electrochemical study of mesoporous copper oxide monoliths

Hierarchically macro/meso structured porous copper-oxide monoliths with and without additives (dextran, 1,3,5-trimethylbenzene and silica nanoparticles) were successfully synthesized via a facile sol–gel route and characterized by scanning electron microscopy (SEM/FESEM), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), the Brunauer–Emmet–Teller (BET) adsorption technique and FT-IR study. The results obtained reveal that the effect of additives has enhanced the specific surface area from 0.558 m2 g−1 to 229.5 m2 g−1 and varied the pore size from 8 μm to 39 nm. Furthermore, the hierarchically porous copper-oxide materials have shown excellent catalytic activity towards the wet oxidation of phenol and electrocatalytic performance of mesoporous copper oxide (mpCuO) against p-nitrophenol, demonstrating the significance of the porous nature of copper-oxide monoliths.

Green synthesis of palladium nanoparticles–graphene hybrids as efficient electrode materials for electrochemical double layer capacitors

T paper focusses on the calculation of rate of nucleation and growth of cement systems .The research is focused on the idea of comparing the process of phase change of cement system to nucleation kinetics. Cahn’s and Avrami’s equations are presently popular with the same idea but fail with complex systems and at some temperature and experimental conditions. The main reason for this is that though rate kinetics of cement hydration is similar to the reaction kinetics of nucleation and growth models but the Avrami’s and Cahn’s equations do not model the process. We simulated the cement processes using software, Mic and with the results present formulated tables with different growth rates and initial densities of nucleation. The idea in the new equation proposed to assume the grain boundaries to be spherical in nature (overcoming the limitation of Cahn’s equation pf parallel and perpendicular grain boundaries). On these, spherical boundaries, with a constant initial density of nucleation and fixed rate of growth, the transformed volume at any particular time were calculated. For the same assumptions, the simulated and mathematical results were compared and an empirical equation with a better fit and more accuracy was derived for that particular case. This equation format was generalized which was calibrated for different experimental conditions and results were again observed. The overall efficiency of the results obtained from the empirical equation were about (96-99) %.I recent decades, a class of anionic clays known as Layered Double Hydroxides (LDHs) or hydrotalcite-like compounds has attracted considerable attention from both industries. The general formula for an LDH is [MII(1-x) Mx(OH)2] [An-x/n .mH2O], where MII represents a divalent metal and MIII represents a trivalent metal. An enormous variety of interlayer anions (An-) can be incorporated in LDHs such as CO3 2-, SO4 2-, NO3or Cl-. From a structural viewpoint, the effect of divalent/trivalent cations and interlayer anionic compositions may provide insights regarding the crystal chemistry of different LDHs types, which may ultimately govern their ability to adsorb organic pollutants. In this work, Mg-Al, Ni-Al and Zn-Al layered double hydroxide (LDH) materials with molar ratio (M2+/ Al3+) of 3 were synthesized via a co-precipitation route. The as-synthesized samples were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Simultaneous ThermogravimetricDifferential Thermal Analysis (TGA/DTA). XRD analyses showed that Zn-Al-SO4 had the greatest lattices’ parameters followed by Mg-Al-SO4 and Ni-Al-SO4. FTIR confirmed clearly the presence of sulfate anions in the structure of LDHs in the interlayer. Two major stages of mass loss occurred for all the samples with better thermal stability of Zn-Al-SO4 vs. Ni-Al-SO4 and Mg-Al-SO4. The capability of LDHs for dye removal from aqueous solutions was investigated using methyl orange as a model and an industrial textile effluent. The “batch” method for evaluating the adsorption of methyl orange dye into synthesized LDHs was investigated under various conditions such as solution pH, contact time and initial dye concentration. Experimental results showed that pH is the most affecting factor on the adsorbent effect. The effective pH range for dye removal was between 3.5 and 4.5. The adsorption process can be well described by the pseudo-second-order kinetic model. The equilibrium adsorption data was analyzed using three isotherm models: Langmuir, Freundlich and Dubinin-Radushkevich. The results showed that Langmuir model fit with exceptional maximum adsorption capacities of 2758, 1622 and 800 mg/g, respectively for Zn-Al-SO4, Mg-Al-SO4 and Ni-Al-SO4.G karaya (GK) is a polysaccharide gum from Sterculia urens tree. It is used as an emulsifier and thickening agent in cosmetics and pharmaceuticals. However, it has very strong swelling properties, high viscosity, and low solubility, providing the restricted applications in food industry. The main objective of this study was to investigate the effects of different heat treatment and microwave variables (i.e. time: 8, 10 and 12 min; power: 700 and 1000 W) on the functional properties of gum karaya (GK) in the aqueous system and oil in water (O/W) emulsion. In this regard, the rheological properties, emulsifying activity, average droplet size, and surface morphology of the nativeand microwave-treated gums were analysed and compared. Dynamic oscillatory test indicated that the microwave treated gum karaya had more gel-like behaviour than viscous-like behaviour (G” > G”) at a relatively high concentration (20% or 20 g/100 g). When gum karaya was treated by microwave for 8-12 min, both elastic (G”) and viscous (G”) moduli were declined. The native and microwave treated gum karaya exhibited a shear-thinning (pseudo plastic) behaviour in the aqueous system and O/W emulsion. The results showed that the microwave treated gum karaya had smaller particle than the native gum in the aqueous system. On the other hand, the emulsion containing the microwave treated gum karaya had finer emulsion droplets than the control containing the native gum karaya. This confirmed that the application of microwave treatment led to significantly (p < 0.05) improve the emulsifying activity of gum karaya.Samples from sheets of the polymeric material cellulose triacetate have been exposed to alpha particles in the dose range 20-100 Gy. The modifications induced in its molecular and optical properties due to alpha particles irradiation have been studied through different characterization techniques such as intrinsic viscosity, refractive index and color difference studies. The results indicated that the crosslinking is achieved at the dose range 60-100 Gy. This crosslinking led to an increase in the value of intrinsic viscosity, indicating an increase in the average molecular mass. This was associated with an increase in the refractive index. Additionally, the non irradiated cellulose triacetate samples showed significant color sensitivity towards Alpha particles irradiation. This sensitivity appeared in the change in the blue color component of the non irradiated cellulose triacetate film to yellow after exposure to alpha particles up to 100 Gy. This is accompanied by a net increase in the darkness of the samples.With the current growth of digital media, projected refined silicon supply for the year 2040 cannot satisfy the semiconductor industry needs, and this results in a big shortage of memory materials. Our calculations suggest that worldwide data storage needs will exceed 3×10 24 bits by 2040 (~2 yottabyte or two billiard gigabytes), whereas with the current rate of silicon-based memory growth, only ~2% of that capacity will be achieved. Scaling and energetics of information storage materials are the major concerns of semiconductor industry. Therefore finding alternative sources for information storage is critical. DNA molecules are known to carry information of life by encoding/decoding the life pathways. Nucleic acids are plentiful, recyclable, dense, and their operation energy is very low and thus the DNA memory is a cost effective emerging technology. According to our calculations only 1 kilogram of DNA satisfies the storage needs of year 2040. If stored in silicon based memory, such amount of information should be stored in about 5 billion kilograms of silicon. One other advantage of DNA memory is the long retention time of information comparing to current memory materials. Current digital information storage media have short information retention time of less than a century. DNA is a material that encodes information with a quaternary code of A,T,C,G. According to our calculations DNA Memory has volumetric density of 10 3 times greater and energy of operation 10 7 times less than flash memory that is the industry standard. Reading and writing of arbitrary digital formats is being enabled by the rapid progress in DNA synthesis and sequencing.[1, 2] This study is in pursuit of non-biological and nonvolatile DNA memory applications.A new semiorganic nonlinear optical bis-thiourea nickel barium chloride was synthesized and crystals were grown by slow aqueous solvent evaporation technique. The transparent and colorless crystals having maximum dimensions of 13 mmx8 mmx2.2 mm were obtained. The powder XRD analysis suggested orthorhombic crystal structure with unit cell parameters as: a=9.70 A, b=10.68 A and c=17.95 A. The FTIR spectroscopy study confirmed the presence of various functional groups. The optical parameters were studied by UV-Vis spectroscopy. The dielectric study was carried out in the frequency range of applied field from 500 Hz to 1 MHz. The variations of dielectric constant, dielectric loss were studied with frequency. It was found that the dielectric constant and the dielectric loss decreased as the frequency of applied field increased. The results are discussed.T aim of the present work was to obtain and characterize new compounds which exhibit antimicrobial properties and are efficient in treatment of multidrug resistant infections. The first stage of the synthesis of the compounds N-(p-clorofenil)-N’(2-tenoil)-tiourea (1), N-(p-iodofenil)-N’-(2-tenoil)-tiourea (2), N-(p-bromofenil)-N’-(2-tenoil)-tiourea (3), N-(p-metoxifenil)-N’(2-tenoil)-tiourea (4), N-(p-metilfenil)-N’-(2-tienil)-tiourea (5), N-(p-metilfenil)-N’-(2-tenoil)-tiourea (6), N-(p-metilfenil)-N’-(3tenoil)-tiourea (7) takes place in anhydrous medium for the prevention of acids chloride decomposition in the presence of water trace. In the second stage, the samples were treated with ammonium thiocyanate which was priory dried at 100oC. The inclusion compounds between 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and some new 2-thiophene carboxylic acid thioureides were also obtained. HP-β-CD is designed to have a high solubility and ability to complex a wide range of molecules with different degree of hydrophobicity. Complexation in organic solvent method was used to obtain the solid complexes with 1:1 stoichiometry. The solid powders of pure thioureides, HP-β-CD and complexes HP-β-CD/thioureide were analyzed by thermal methods (TG/DSC), UV-Vis spectrophotometry and Fourier transform-infrared spectroscopy (FT-IR). The fusion enthalpies of the all pure compounds are: 26.0 kJ/mol (1), 27.6 kJ/mol (2), 22.6 kJ/mol (3), 29.5 kJ/mol (4), 27.3 kJ/mol (5), 22.1 kJ/mol (6), 27.4 kJ/mol (7). Pharmacologically, the analgesic effect by chemical stimulus test and the anti inflammatory effect after intra-plantar administration of dextran and caolin have been performed. Sample (3) has a slightly less analgesic effect compared to acetylsalicylic acid and the sample (4) shows the most intense anti inflammatory action, probably through a cyclooxygenase inhibition mechanism.M validation for the identification, isolation, separation and purification of one typical class of biologically active purine based alkaloid viz. Caffeine was carried out using reverse phase High Performance Liquid Chromatography technique (HPLC) in the isocratic mode. Conventional solvent extraction technique involving differential and incremental solvation procedure by binary solvent mixtures was adopted to extract the total alkaloids present in the samples. Non polar protic constitutive solvent (ethylene glycol), Polar aprotic dissociative solvent (1, 4-dioxane) in aqueous medium at a composition of 20%+70% was used for extraction of purine alkaloids from the samples. UV-visible spectrophotometry was used to ascertain the presence of the alkaloid in the samples. The operational parameters (Caffeine); C-18 column, CH3CN + MeOH+H2O at pH =8.8 (phosphate buffer), u =1ml/min, Pinlet= 130-140 bar,λ = 273 nm (VWD), T = ambient at 27oC,η= 10-3 N sec m-2, D = 10-9 m2 sec-1, Φ= 1000, h = 3 and dP = 5 mm was found to be the optimal parametric combination for the effective analysis of this purine based alkaloid by HPLC. Recovery rate of caffeine from samples are estimated to be: 100%, 97%, 98.5%, 98%, 96% & 98.8% for Lamolate®, Coffee beans, Tea Leaves, soft drink -1 (Pepsi), soft drink -2 (Coke) & soft drink -3 (Thums up) respectively.O of the major concerns of scientific community with electrospun nanofibrous scaffolds is the densely packed fibers in 2-D array which impedes their applicability in tissue regeneration. To overcome these problems, a three-dimensional nanofibrous scaffold was fabricated using a noble gas foaming technique and studied for biomedical applications. In this novel approach, Polycaprolactone (PCL) nonwoven membrane was fabricated by electrospinning process and treated with Sodium Borohydride (SB) solution (0.1 M solution prepared in methanol) to modify into 3-D scaffold. We have purposed the mechanism for the fabrication of 3-D scaffold. As the PCL mat was put into the SB solution interconnected pores of a mat are filled with that solution driven by capillary forces where it undergoes hydrolysis to produce hydrogen gas. The in situ generated gas molecules form clusters to minimize the free energy resulting in pore nucleation that reorganizes the nanofibers to form a low density, macroporous, spongy and multi-layered 3-D scaffold. The scaffolds were characterized in terms of porosity, density and biocompatibility. Large pore size and multilayered structure of as fabricated scaffold improved the cell infiltration and growth compared to 2-D electrospun mat. This simple and facile process will reveal a new approach for the fabrication of a three-dimensional, low-density, nanofibrous materials for biomedical and industrial applications using a wide variety of polymers.