The stability and spatial separation of nanoparticles (NP's) is essential for employing their advantageous nanoscale properties. This work demonstrates the entrapment of gold NP's embedded in a porous inorganic matrix. Initially, gold NP's are decorated on fibrous nylon-6, which is used as an inexpensive sacrificial template. This is followed by inorganic modification using a novel single exposure cycle vapor phase technique resulting in distributed NP's embedded within a hybrid organic-inorganic matrix. The processing is extended to the synthesis of porous nanoflakes after calcination of the modified nylon-6 yielding a porous metal oxide framework surrounding the disconnected NP's with a surface area of 250 m(2)/g. A unique feature of this work is the use of a transmission electron microscope (TEM) equipped with an in situ annealing sample holder. The apparatus affords the opportunity to explore the underlying nanoscopic stability of NP's embedded in these frameworks in a single step. TEM analysis indicates thermal stability up to 670 °C and agglomeration characteristics thereafter. The vapor phase processes developed in this work will facilitate new complex NP/oxide materials useful for catalytic platforms.
A facile ultraviolet assisted metalized laser printing technique is demonstrated through the ability to control selective photodeposition of silver on flexible substrates after atomic layer deposition pretreatment with zinc oxide and titania. The photodeposition of noble metals such as silver onto high surface area, polymer supported semiconductor metal oxides exhibits a new route for nanoparticle surface modification of photoactive enhanced substrates. Photodeposited silver is subsequently characterized using low voltage secondary electron microscopy, x-ray diffraction, and time of flight secondary ion mass spectroscopy. At the nanoscale, the formation of specific morphologies, flake and particle, is highlighted after silver is photodeposited on zinc oxide and titania coated substrates, respectively. The results indicate that the morphology and composition of the silver after photodeposition has a strong dependency on the morphology, crystallinity, and impurity content of the underlying semiconductor oxide. At the macroscale, this work demonstrates how the nanoscale features rapidly coalesce into a printed pattern through the use of masks or an X-Y gantry stage with virtually unlimited design control.
This work explores the photoremediation of hexavalent chromium from aqueous solutions on to nonwoven polyethylene terephthalate substrates modified by nanoscale atomic layer deposition coatings of ZnO. Removal of Cr6+ is observed to increase with ZnO thin film thickness up to 500 atomic layer deposition cycles (∼90 nm) with a maximum Cr6+ removal of 67% after an exposure of 540 J/cm2. Instead of reducing Cr6+ to Cr3+, this work shows that the mechanism for removal of the Cr ion from solution is by sorption and photoreduction of the metal onto the ZnO surface. Additionally, mixed solutions with Cr6+ and As3+ ions were tested for simultaneous photoreduction and photooxidation, showing that mixed ion solutions may better utilize photogenerated electrons and holes, simultaneously. The reported demonstration and analysis represents a facile route for reclamation of toxic components in an aqueous media.
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