The synthesis and characterization of a novel nanocomposite is reported that was developed as an efficient adsorbent for the removal of toxic methylene blue (MB) and methyl violet (MV) from aqueous solution. The nanocomposite comprises hydrolyzed polyacrylamide grafted onto xanthan gum as well as incorporated nanosilica. The synthesis exploits the saponification of the grafted polyacrylamide and the in situ formation of nanoscale SiO2 by a sol-gel reaction, in which the biopolymer matrix promotes the silica polymerization and therefore acts as a novel template for nanosilica formation. The detailed investigation of the kinetics and the adsorption isotherms of MB and MV from aqueous solution showed that the dyes adsorb rapidly, in accordance with a pseudo-second-order kinetics and a Langmuir adsorption isotherm. The entropy driven process was furthermore found to strongly depend on the point of zero charge (pzc) of the adsorbent. The remarkably high adsorption capacity of dyes on the nanocomposites (efficiency of MB removal, 99.4%; maximum specific removal Qmax, 497.5 mg g(-1); and efficiency of MV removal, 99.1%; Qmax, 378.8 mg g(-1)) is rationalized on the basis of H-bonding interactions as well as dipole-dipole and electrostatic interactions between anionic adsorbent and cationic dye molecules. Because of the excellent regeneration capacity the nanocomposites are considered interesting materials for the uptake of, for instance, toxic dyes from wastewater.

We report on the rapid production, characterization, and spectral properties of highly uniform, ultra narrow semiconductor (ZnS, ZnSe, CdS, CdSe) nanorods and nanowires by microwave irradiation. Quantum-confinement effects are manifested in the light absorption and the PL of the rods and wires. The uniformity of the rods and of the wires is demonstrated in their spontaneous assembly into highly ordered 2D supercrystals. We also observed the stepwise growth of the rods originating from nearly spherical nuclei.

Zinc selenide is an important wide-bandgap (2.8 eV) material [1] with a broad range of potential applications. It exhibits interesting photophysical phenomena involving green-blue light emission and high transmission in the infrared and the visible electromagnetic spectrum.[2] Nanoparticles of ZnSe, via quantum confinement, shape, size and surface dependent effects, hold promise for tuning the optical properties and for assembling the particles in nanoscale structures. ZnSe has been studied to a lesser extent compared with its 'closest of kin', CdS, CdSe, and ZnS nanoparticles. Spherical ZnSe particles have been produced and studied by several groups. [3][4][5] ZnSe shapes other than spheres have been synthesized and studied to a more limited extent. Several pioneering reports [6][7][8][9][10][11] have described various synthetic routes to produce ZnSe nanowires, and focus on their structural characterization and, occasionally, on their photoluminescence (PL) properties. The nanowires were typically ∼ 10-100 nm wide and several micrometers long. The narrowest reported ZnSe wires were 3-5 nm wide (with an average diameter of 19 nm) [7] and 5-50 nm wide.[8] Except for these narrowest of wires, all the other reported wires are wider than the Bohr diameter of (bulk) ZnSe (9 or 11.4 nm), [12] which limits the expected quantum confinement effects. We have found only one recent allusion to the production of ZnSe nanorods. [13] In a few cases, authors have used the term 'nanorods' for wide ZnSe particles with dimensions of 40-70 nm × 1.5-3 lm, [9] 50-100 nm × 5-15 lm, [10] and 16-20 nm × 120-279 nm, [11] all with relatively large aspect ratios. Here, both of the major dimensions of the particles are larger than the Bohr radius, and quantum confinement effects are expected to be very limited.In this communication, we report the production of uniform wurtzite ZnSe ultranarrow width (1.3 nm), 4.5 nm long nanorods, and 100-200 nm long nanowires with the same width, their characterization and their spectroscopic properties. The development of rods from more spherical nuclei is illustrated. Quantum-confinement effects are manifested in the light absorption and the PL of the particles. The narrow width, ∼ 1 nm, is reflected in the Raman spectrum. The uniformity of the rods and the wires is demonstrated by their spontaneous assembly into highly ordered two-dimensional (2D) supercrystals. This high uniformity and order, together with an intrinsic chemical bipolarity of the rods, is responsible for their one-dimensional growth and for the various unique, essentially one-dimensional processes they undergo, as well as for the polarization properties of their spectra.The synthesis makes use of ligating solvents, i.e., long-chain alkylamines, which enable a low temperature, one step, bench-top reaction of the relatively innocuous zinc acetate and selenourea precursors, to produce wurtzite ZnSe nanorods and nanowires. The nanorods and nanowires are of a uniform width and the nanorods are of a uniform length. The relative amount of r...

No abstract

No abstract

No abstract

No abstract

One-dimensional semiconductor quantum wires are expected to play a key role as functional components and interconnects in future electronic and optical devices. [1][2][3][4] Over the past few years, several research groups have synthesized a variety of nanowires [5][6][7][8][9][10] and managed to assemble them into components for electronic devices. [11][12][13] One of the great challenges in developing nanometer-scale devices is to achieve large areas containing an ultrahigh density of arrays with complex structures built of nanometer-scale elements in a controllable manner. [14][15][16] In addition, feature-size minimization is also a strong motivation due to the limitations of conventional fabrication techniques. The successful alignment and patterning of nanowires would significantly impact many areas in nanometer-scale electronics, optoelectronics, and sensors. The technological advantage of the Langmuir-Blodgett (LB) method has been widely recognized for inducing nanowire alignment on a large scale into two-dimensional (2D) assemblies. [17][18][19][20][21][22] However, all the reported works [17][18][19][20][21][22] required an additional post-deposition secondary treatment for further patterning due to the side-by-side alignment of the nanowires. While previous reports have shown organization of nanowires in nematic or smectic arrangements, [19,23] end-to-end registry, which is very important for unidirectional growth of nanowires and for the fabrication of nanocircuits, has never been demonstrated. However, in the present case, we are able to align the nanowires in areas spanning over two micrometers using the LB technique. Moreover, this process does not require any post-deposition secondary patterning technique for further alignment. The aligned nanowires exhibit remarkable end-to-end registry along with side-by-side registry, practically without any deviation over a two micrometer range while retaining a ∼ 1.3 nm width of the nanowires. The nanowires in the hierarchical array have a very high aspect ratio that exceeds 10 3 with a very tight registry. To the best of our knowledge, this has not previously been reported for any bottomup technique. Moreover, the direct fabrication of complex three-dimensional (3D) patterns is achieved through subsequent layer-by-layer assembly (as shown in Fig. 1