Foration Of 3-D Nanoporous Structures Templating From Coscinodiscus Sp. Frustules

A diversity of structures of diatom frustules from the micro- to nano- scale provides a new interdisciplinary area of materials for its potential applications in nanotechnology. Herein, we demonstrate a multi-equilibrium involving complex ions and slightly soluble ionic compounds to fabricate 3-D zinc oxide and silver porous photoluminescence structures from nano- to micro-scale by templating Coscinodiscus sp. frustules for the first time. Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM) in combination with EDS, FI-IR spectra analysis have been used to detect structures and elements, compared with cleaned Coscinodiscus sp. frustules. Possible reaction mechanism has been advanced. At the same time, Photoluminescence properties of the silica-based ZnO replica by Coscinodiscus sp. frustules have been discussed compared with ZnO particles in the same approach without frustules.Main research results are as follows:(1) Coscinodiscus sp. frustules structures were characterized and the active groups on the surface were figured out. The results of biomicroscope, Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) indicate that Coscinodiscus sp. frustules possess multi-scale porous nanocomb 3-D structures, with the average diameter of epitheca and hypotheca 80 ~ 100μm. The average diameters of Areola, Cribrum and Cribellum are 1.2μm, 100 ~ 200 nm, 70 ~ 80 nm respectively. The average thickness of girdle band is 1μm, with the average diameter of pores is 150 nm. The results of Energy-Dispersive Spectrophotometer (EDS) and Fourier-transform infrared (FT-IR) spectroscope suggest that the percentage of the atom absorbance for Si and O is near, and Si-O-Si and Si-OH groups are the main groups on the surface of frustules. (2) A multi-equilibrium involving complex ions and slightly soluble ionic compounds was set up and used to synthesize uniform, ordered zinc oxide nanoporous structures and silver nanoporous structures by Coscinodiscus sp. frustules for the first time. Under a mild condition, the precursor on the surface of the frustule was synthesized slowly and uniformly through the appearance of the precipitation with coordination actions and shifts of multi-equilibrium. SEM and TEM images show ZnO replica is a uniform one, with 200 nm average length of needle-like ZnO nanoclusters on the surface of the frustule and 5 nm average diameter of ZnO nanoparitcles around the pores. TEM-EDS analysis shows ZnO replica by templating the frustule consists of oxygen, silicon and zinc, and atomic abundance proves that nSi / nZn is about 2.23 / 1. FT-IR spectra shows ZnO chemically reacts with Si-OH groups and Si-O-Si groups on the surface of frustules, and Si-OH groups are the main active groups. Possible reaction mechanism have been advanced as a result of negative polarity of oxygen atom and coordination effect of tetraammine zinc (Ⅱ) ion. Silver nanoporous structures by Coscinodiscus sp. frustules with a high activity in the air were fabricated in a similar way. TEM images show 2 ~ 3 nm average diameter of Ag nanoparitcles around the pores of Coscinodiscus sp. frustules. The white color of the Ag replica has been a result of a quantum size effect. FT-IR spectra shows Ag chemically reacts with Si-OH groups and Si-O-Si groups on the surface of frustules, and Si-OH groups are the main active groups. Possible reaction mechanism have been advanced as a result of negative polarity of oxygen atom and coordination effect of tetraammine silver (I) ion.(3) The property of photoluminescence of zinc oxide nanoporous structures by Coscinodiscus sp. frustules was studied and two possible reasons of the strength of photoluminescence signals were present. Photoluminescence spectra demonstrate that ZnO nanostructures by templating diatom frustules preserve better photonic property compared with ZnO particles in the same approach without frustules. ZnO photoluminescence signals have been improved 14.55% after templating diatom frustules. A quantum size effect and the diatom biosilica possessing a visual photoluminescence effect itself have been regarded as two reasons to intense the energetic positions of the maxima of the emission band.