Chen Wenzhe

An MWCNT-doped SNO2 thin film NO2 gas sensor by RF reactive magnetron sputtering

An MWCNT-doped (multi-walled carbon nanotube) SnO2 thin film NO2 gas sensor, prepared by radio frequency reactive magnetron sputtering, showed a high sensitivity to ultra-low concentrations of NO2 in the parts per billion range. X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy (SEM) characterizations indicated that the MWCNTs were affected by the morphology of the SnO2 thin film and the particle size. The properties of the MWCNT-doped SnO2 sensor, such as sensitivity, selectivity, and response-recovery time, were investigated. Experimental results revealed that the MWCNT-doped SnO2 thin film sensor response to NO2 gas depended on the operating temperature, NO2 gas concentration, thermal treatment conditions, film thickness, and so on. The mechanism of the gas-sensing property of the MWCNT-doped Sn22 thin film sensor was investigated and showed that the improved gas-sensing performance should be attributed to the effects between MWCNTs (p-type) and SnO2 (n-type) semiconductors.

Dimerization of zinc tetrasulfophthalocyanine in sol–gel process

Abstract The issue of dimerization is vital in determining the optical properties of dye-doped sol–gel materials and metallophthalocyanine offers an excellent opportunity to characterize dimmers from monomers because of their identified absorption bands. In this paper, zinc tetrasulfophthalocyanine (ZnTSPc) was encapsulated in silica–xerogel matrix by sol–gel technique. Dimerization of ZnTSPc was studied using UV–Vis optical absorption spectra, correlated with various stages of the sol–gel process. The results show that in the composites ZnTSPc concurrence in forms of monomer and dimmer, and dimerization behaves differently in the sol, gel and xerogel stages. Reasons are given from the change of the microenvironment of the composites in which ZnTSPc existed.

Encapsulation of aromatic oxygen palladium phthalocyanine in silica xerogel and its optical limiting property

Abstract Metallophthalocyanines (MPc) exhibit, among many useful properties, the ability to protect sensors against short, intense pulse deleterious to efficient sensor operation. For the successful application of this optical limiting property, an important issue is the incorporation of MPc molecules in a matrix to fabricate a solid state system. We report here the study of different concentrations of aromatic oxygen palladium phthalocyanine (ArOPdPc) encapsulated in silica xerogel obtained by the sol–gel technique. The resulted composites were transparent and homogeneous with the required optical limiting properties. The trapping effect was confirmed by the characteristic absorption bands of ArOPcPd in the UV–Vis spectra. The optical limiting properties of the composites were measured at 532 nm with 8 ns pulses. The results showed that the composites had obviously optical limiting effect, owing to the existing of large amount of monomers and the introduction of palladium atom in the cavity of phthalocyanine ring.

Dimerization of metallophthalocyanines in inorganic matrix

Abstract Metallophthalocyanine (MPc) and its composites have excellent photo-electricity properties. Here we report the study of MPc doped silica xerogel matrix obtained by sol–gel technique. Because the issue of dimerization is vital in determining the optical properties of dye doped sol–gel materials and MPc offers an excellent opportunity to characterize dimers from monomers because of their identified absorption bands, we studied the dimerization of different kinds of MPc doped silica composites using electronic absorption spectra. Changes in the absorption spectra were correlated with various stages of the sol–gel process. The results show that in the composite MPc molecules concurrence in forms of monomer and dimer, and dimerization is bad during the latter stages of drying because of the rapid decrease of remaining solvent and its ethanol/water ratio. To overcome this problem, a kind of dissociating agent Cremophor EL is added in order to protect the Zinc tetrasulfo-phthalocyanine molecules from dimerization. In the other hand, a newly developed in situ synthesis technique was successfully introduced to synthesize MPc during the sol–gel process. It is found that the in situ synthesized MPc only exist in the form of monomer in the composites.