Nisar Ali

Papain/Zn3(PO4)2 hybrid nanoflower: preparation, characterization and its enhanced catalytic activity as an immobilized enzyme

Flower-like papain/Zn3(PO4)2 hybrid materials are synthesized via a facile, rapid and low-cost method in this study. The growth process of the nanoflowers has been studied in detail and a four-step formation mechanism, including coordination, precipitation, self-assembly and size growth, has been clarified. The concentration of papain mainly affects the morphology of the products by regulating the assembly and crystal growth. The enzyme activity of papain/Zn3(PO4)2 hybrid nanoflowers, a novel immobilized enzyme, was calculated by monitoring the hydrolysis reaction of casein. The results show that the catalytic properties of papain immobilized on hybrid nanoflowers are enhanced compared with that of free papain. The as-prepared hybrid nanoflowers exhibited excellent reusability, high thermo stability and long storage life. The results indicate that the well-designed materials have great potential in industrial applications.

Fabrication of a Fe3O4@SiO2@mSiO2-HPG-COOH-Pd(0) supported catalyst and its performance in catalyzing the Suzuki cross-coupling reaction

In this paper, magnetic Fe3O4@SiO2@mSiO2 microspheres with core–shell structure were chosen as a catalyst support, then hyperbranched polyglycerol (HPG) was successfully grafted onto the exterior surface and mesopore wall of this material under the catalysis of isopropanol aluminum. Subsequently, the terminal hydroxyl groups of HPG were successfully transformed into carboxyl groups after modification with succinic anhydride. Ultimately, palladium nanoparticles (Pd NPs) were successfully anchored onto the surface of the aforementioned magnetic Fe3O4@SiO2@mSiO2 microspheres with high density carboxylic HPG, nanocrystallization by the complexation between Pd2+ ions and carboxyl groups and the subsequent reduction, a novel Fe3O4@SiO2@mSiO2-HPG-COOH-Pd(0) supported catalyst was successfully obtained. This novel supported Pd NP catalyst is very conducive to the transference and exchange of each component in the reaction system for the orderly mesoporous opening structure. Furthermore, the introduction of a magnetism nucleus can provide convenient magnetic separation. More importantly, the numerous terminal carboxyl groups on the surface of the magnetic Fe3O4@SiO2@mSiO2 microspheres can provide plenty of sufficient binding sites for Pd NPs, and the unique hyperbranched structure is very conducive to capture uniformly dispersed nanosized palladium and can effectively enhance the catalytic activity and stability. Research indicates that this novel supported Pd NP catalyst not only possesses extremely high Pd NPs loading capacity but also shows remarkable catalytic activity to the Suzuki cross-coupling reaction between aryl halides and phenylboronic acid. Simultaneously, the catalytic activity of this supported catalyst did not show evident loss after being used at least eight times.

Polymer melt flow through nanochannels: from theory and fabrication to application

Polymer nanotubes/nanorods have recently received much more interest and have become an important topic in the interdisciplinary field of nanoscience and nanotechnology. Generally, they can be easily fabricated by template wetting of polymer melts. This short review presents effective ways to enhance polymer melt flow in nanochannels, typically focused on influencing wetting parameters including time, temperature, size of nanochannels and surface properties of the inner wall of nanochannels. Then, the investigation progress on polymer nanotubes/nanorods nanofabrication by nanoporous alumina template wetting is discussed. Many applications of polymer nanotubes/nanorods fabricated by template wetting from photonics to sensors and medical devices are summarized in the last section of this review.

Laser irradiation effects on the surface, structural and mechanical properties of Al–Cu alloy 2024

Laser irradiation effects on surface, structural and mechanical properties of Al–Cu–Mg alloy (Al–Cu alloy 2024) have been investigated. The specimens were irradiated for various fluences ranging from 3.8 to 5.5 J/cm2 using an Excimer (KrF) laser (248 nm, 18 ns, 30 Hz) under vacuum environment. The surface and structural modifications of the irradiated targets have been investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. SEM analysis reveals the formation of micro-sized craters along the growth of periodic surface structures (ripples) at their peripheries. The size of the craters initially increases and then decreases by increasing the laser fluence. XRD analysis shows an anomalous trend in the peak intensity and crystallite size of the specimen irradiated for various fluences. A universal tensile testing machine and Vickers microhardness tester were employed in order to investigate the mechanical properties of the irradiated targets. The changes in yield strength, ultimate tensile strength and microhardness were found to be anomalous with increasing laser fluences. The changes in the surface and structural properties of Al–Cu alloy 2024 after laser irradiation have been associated with the changes in mechanical properties.

Synthesis of fibrous and non-fibrous mesoporous silica magnetic yolk–shell microspheres as recyclable supports for immobilization of Candida rugosa lipase

The mesoporous yolk-shell nanoparticles (MYSNs), with a movable Fe3O4 core inside the hollow capsules, with two different morphologies (1) Fe3O4@SiO2@hollow@fibrous SiO2 (Yolk Shell-1) (2) Fe3O4@SiO2@hollow@mesoporousSiO2 (Yolk Shell-2) were fabricated as carriers for Candida rugosa lipase (CRL) immobilization, through a template-assistant selectively etching method. Firstly the hydrophilic Fe3O4 nanoparticles were synthesized according to the solvothermal method. Then, SiO2 shell was coated on the Fe3O4 nanoparticle surface by a sol-gel reaction. Subsequently, the resorcinol farmaldehyde (RF) shell was covered on the surface of as-prepared Fe3O4@SiO2 composites and sandwiched Fe3O4@SiO2@RF composites were formed, which were finally provided with mesoporous fibrous (KCC) in the Yolk Shell-1 and mesoporous Silica in the Yolk Shell-2(Non fibrous). After selectively etching CTAB and the middle RF layer, the two kinds of yolk/shells composites were obtained. By utilization of their large and open mesopores (20-50nm) with good surface area (457.78-625.54m2/g,) CRL was immobilized after amino functionalization using glutaraldehyde as a linker. The ICRL on Y.S-1, Y.S-2 showed good loading (797-501mg/g) and enzyme activity of (1503-837U/g) respectively. Thermal stability, resistance to pH, recycling and storage capacity were improved as compare to free lipase.

Synthesis of paramagnetic dendritic silica nanomaterials with fibrous pore structure (Fe3O4@KCC-1) and their application in immobilization of lipase from Candida rugosa with enhanced catalytic activity and stability

Paramagnetic mesoporous fibrous silica (Fe3O4@KCC-1) was prepared and its surface was functionalized with 3-aminopropyltriethoxysilane (APTES) to obtain amino functionalized magnetic nanoparticles. Lipase from Candida rugosa was immobilized on functionalized magnetite Fe3O4@KCC-1-NH2 using glutaraldehyde (GLU) as the linker. The nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and Fourier transformed infrared spectroscopy (FTIR). The characterization results revealed successful immobilization of lipase on functionalized magnetite with a saturation magnetization of 62.73 and 42.65 emu g−1 for magnetic nanoparticles and carbonyl functionalized carriers, respectively. The applied approach for support preparation, activation, and optimization of immobilization conditions, with a good lipase loading of 283 mg g−1 of carrier, provided better resistance to temperature and pH inactivation than free lipase and hence expanded the reaction pH and temperature regions, with an optimum pH of 6 and temperature of 35 °C. Immobilized Lipase Candida rugosa (ICRL) showed enzyme activity of 630 U g−1, maintained above 560.7 U g−1 (89%) of the initial activity after 28 days and 434.7 U g−1 (69%) after 10 cycles. Thus, ICRL showed improved storage stability and reusability.

Effect of excimer laser fluence on the surface structuring of Ti under vacuum condition

The effect of variation of excimer laser fluences on the surface structuring of titanium (Ti) targets has been investigated. The KrF excimer laser (λ = 248 nm, t = 20 ns, repetition rate 20 Hz) has been employed for this purpose. The targets were irradiated for various laser fluences ranging from 0.86 J cm−2 to 1.27 J cm−2 under vacuum condition. Various diagnostic techniques like scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) have been utilized to investigate the surface topography and structural changes of laser ablated targets. SEM analysis reveals the formation of laser-induced periodic surface structures (LIPSS) at the central ablated region. The periodicity of LIPSS increases from 5 μm to 88 μm with the increase of fluence from 0.86 J cm−2 to 1.27 J cm−2. The formation of grains is observed at the peripheral ablated region for all laser fluences. Reduction in grain size from 7.7 μm to 3.8 μm is observed with increasing fluence from minimum to maximum v...

First principles study of the adsorption and dissociation mechanisms of H2S on a TiO2 anatase (001) surface

The adsorption and dissociation mechanisms of H2S on a TiO2 (001) surface were elucidated using first principles calculation based on the density functional theory. The interaction of the intermediates involving S, HS and OH species has been discussed in detail. For these species, the most favorable adsorption sites were determined and led to further computations involving dissociation of H2S into HS and H and bonding of H-atom with the OH to form water on the surface. The creation of vacancies along with the presence of S on the surface enhanced the H2S adsorption energy slightly. However, addition of OH in the system caused H2S to bind on the surface sufficiently strongly. Additionally, H2S decomposition was found to be a spontaneous process in the presence of OH radicals.

PREPARATION OF FLOWER-LIKE Co3O4/Fe3O4 MAGNETIC MICROSPHERES FOR PHOTODEGRADATION OF RhB UNDER UV LIGHT

Flower-like Co3O4/Fe3O4 magnetic microspheres were prepared by coprecipitation of Fe2+ and Fe3+ in presence of flower-like Co3O4 microspheres as template. The preparation process included three steps: preparation of flower-like Co3O4 microspheres by hydrothermal method; immersion of Fe2+ and Fe3+ ions; coprecipitation in the presence of OH-. Rhodamine B (RhB) was chosen as model pollutants to investigate the photodegradation capacities of Co3O4/Fe3O4 magnetic microspheres. The results showed that the microspheres exhibited excellent degradation property and can be recycled to use again. After four times use the degradation efficiency was still above 90%.

Synthesis, preparation of micro/nanofibers by electrospinning and surface morphology of PS

This study focuses on well known successful preparation of linear polystyrene by Reversible addition-fragmentation transfer (RAFT) polymerization that is coupled with CTA, fabricated via electro spinning technique to form ultrafine fibers. At polymer parameter such as polystyrene (PS) molecular weight, solution parameter such as concentration, concludes the change of polystyrene in micro/nanofibers, beads and fibers while keeping other parameters constant such as viscosity, surface tension, conductivity and parameters of instruments. Finally interesting phenomenon is observed in the form of small particles, beads, ribbon like fibers, and uniform fibers having size 800 nm to 900 nm. As molecular weight increases from 6000g/mole to 10,000g/mole to 100,000g/mole, we achieved smooth or uniform nanofibers. Similarly concentration also affects to tend beads into fibers. Beads free fibers are obtained at higher concentration having average size 400nm.