Hui Ou

Facile synthesis of gradient mesoporous carbon monolith based on polymerization-induced phase separation

In this paper, a gradient mesoporous carbon (GMC) monolith derived from the mixtures of phenolic resin (PF) and ethylene glycol (EG) was prepared by a facile route based on polymerization-induced phase separation under temperature gradient (TG). A graded biphasic structure of PF-rich and EG-rich phases was first formed in preform under a TG, and then the preform was pyrolyzed to obtain the GMC monolith. The TG is mainly induced by the thermal resistance of the preferential phase separation layer at high temperature region. The pore structure of the monolith changes gradually along the TG direction. When the TG varies from 58°C to 29°C, the pore size, apparent porosity and specific surface area of the monolith range respectively from 18 nm to 83 nm, from 32% to 39% and from 140.5 m2/g to 515.3 m2/g. The gradient porous structure of the monolith is inherited from that of the preform, which depends on phase separation under TG in the resin mixtures. The pyrolysis mainly brings about the contraction of the pore size and wall thickness as well as the transformation of polymerized PF into glassy carbon.

Enhanced electrochromic properties of TiO2 nanoporous film prepared based on an assistance of polyethylene glycol

Polyethylene glycol (PEG) was employed as pore-forming agent to prepare TiO2 nanoporous film based on spin-coating a TiO2 nanoparticle mixed paste on fluorine doped tin oxide (FTO) glass. The electrochromic and optical properties of the obtained TiO2 film were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and UV–Vis spectrophotometer. The results show that the PEG in the mixed paste endows the TiO2 film with well-developed porous structure and improves the uniformity of the TiO2 film, which are helpful for the rapid intercalation and extraction of lithium ions within the TiO2 film and the strengthening of the diffuse reflection of visible light in the TiO2 film. As a result, the TiO2 film derived from the mixed paste with PEG displays higher electrochemical activity and more excellent electrochromic performances compared with the TiO2 film derived from the mixed paste without PEG. The switching times of coloration/bleaching are respectively 10.16/5.65 and 12.77/6.13 s for the TiO2 films with PEG and without PEG. The maximum value of the optical contrast of the TiO2 film with PEG is 21.2% while that of the optical contrast of the TiO2 film without PEG is 14.9%. Furthermore, the TiO2 film with PEG has better stability of the colored state than the TiO2 film without PEG.

The Influence of NaOH Concentration on the Performance of ZnO by a Hydrothermal Process

Zinc oxide (ZnO) with various morphologies have been successfully prepared by a hydrothermal process from zinc acetate (Zn (CH3COO)2) and sodium hydroxide (NaOH) solution. The influence of NaOH concentration on the morphology of ZnO was investigated. And ZnO with various morphologies were applied in dye-sensitized solar cells (DSCs) as the photoelectrodes. Results show that the c-axis preferred growth of ZnO is becoming increasingly obvious with the increase of NaOH concentration. There are a lof of differences in the photovoltaic performances of DSCs, which are based on ZnO with various morphologies as the photoelectrodes. DSC consisted of ZnO nanoparticles has optimal performances, the corresponding short circuit photocurrent density (Jsc), open circuit voltage (Voc), fill factor (FF) and photoelectric conversion efficiency (η) are 3.97 mA/cm2, 0.653 V,0.59 and 1.52 %, respectively.

A Comparative Investigation of the Electrocatalytic Oxidation of Methanol on Pt Modified TiO2 Nanotube Electrodes with Two Methods

In this work, it was investigated and compared that electro-catalytic oxidation of methanol in acidic medium at TiO2 nanotube (TNT) electrode modified by platinum (Pt) with two methods. Pt modified TNT electrodes were prepared by thermal decomposition (TD) and electrolytic deposition (ED). The so-prepared TD-Pt/TNT and ED-Pt/TNT electrodes were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical investigations indicate that ED-Pt/TNT has higher electro-catalytic activity and better tolerance to poisoning species in methanol oxidation than TD-Pt/TNT, which can be ascribed to the higher dispersion and stability of ED-Pt than TD-Pt on TNT electrode. The present work provides some basis for the design of high performance catalysts for direct methanol fuel cells.

A Novel Approach Based on Polymerization-Induced Phase Separation to Prepare Carbon Monolith with Oriented Flat Porous Structure

A novel approach has been developed to fabricate an oriented flat porous carbon (OFPC) by combining the polymerizationinduced phase separation and pyrolysis (PIPSP) and the directional compressive deformation (DCD). At first, an elastic body in the shape of cylinder is obtained by controlling the polymerization degree of resin, and then the application of symmetrical axial pressures results in the directional deformation of two interconnected phases (of a polymerized resin phase and a poreforming agent phase) in the elastic body. Then the elastic deformed body is transformed to the rigid deformed body by precuring and further to the cured body by curing. At last, the cured body is pyrolyzed to form an OFPC. The pressures are removed after precuring. The pores in the OFPC are survived as the discs in the radial direction. Both flat pores and carbon skeletons in the OFPC are oriented toward a radial direction. The OFPC has comparable pore volume with a normal porous carbon, which is fabricated by the PIPSP with same process except for the application of the DCD.

Investigation on the Structure and Luminescence Performance of Tb-Doped ZnO Nanocrystals Prepared by Direct Precipitation

Terbium-doped zinc oxide (ZnO:Tb) nanocrystals were prepared by a direct reactive precipitation progress. Incorporation of terbium in ZnO nanocrystals had been proved by X-ray diffraction (XRD), transmission electron microscope (TEM) and fluorescence spectrophotometer. XRD investigations confirm that the samples of ZnO:Tb nanocrystals with a hexagonal wurtzite crystalline structure don’t exist the diffraction peaks of the compounds of terbium. The results of TEM analysis show that the as-prepared samples with an average particle size less than 20 nm were obtained. The photoluminescence (PL) spectra suggest that there is no luminescence peaks corresponding to the terbium compounds in ZnO:Tb samples; the green emission intensity gradually decreases with the increase of the Tb-doped concentration in ZnO matrix. A core-shell model of rare earth (RE) passivated ZnO is proposed, which the passivation layer existing on the ZnO surface, can generate a barrier to impede the formation of oxygen vacancy, corresponding to the green emission.