A mesoporous structure for efficient photocatalysts: anatase nanocrystals attached to leached clay layers

Increasing the content of anatase nanocrystals and improving the accessibility of these crystals to reactants (UV photons, organic contaminant molecules and oxygen molecules) will enhance photocatalytic performance. Thus we designed a synthesis approach to achieve such structures. The synthesis involves reaction of clay suspensions with TiOSO4, which leads to formation of anatase nanocrystals attaching to leached clay layers through Ti-O-Si bonds. It is also discovered that the crystal size, the pore size and the specific surface area of the catalysts, can be tailored by manipulating the acidity, the ratio of Ti/clay and the hydrothermal temperature of the synthesis systems. Such a synthesis is different from the conventional approach of pillared intercalated layered clays. The activity of these catalysts for the degradation of phenol was investigated, and we find that the catalytic activity increases with the increasing volume of the pore larger than 3 nm because formation of mesoporous system and anatase nanocrystals leads to improvement in the photocatalytic activity of photocatalysts. This new structure is a more efficient photocatalyst structure for degradating organic pollutant in water, compared to the conventional titania pillared layered clay. The knowledge acquired in this study is useful for designing photocatalysts with high efficiency. (C) 2007 Elsevier Inc. All rights reserved.Increasing the content of anatase nanocrystals and improving the accessibility of these crystals to reactants (UV photons, organic contaminant molecules and oxygen molecules) will enhance photocatalytic performance. Thus we designed a synthesis approach to achieve such structures. The synthesis involves reaction of clay suspensions with TiOSO4, which leads to formation of anatase nanocrystals attaching to leached clay layers through Ti-O-Si bonds. It is also discovered that the crystal size, the pore size and the specific surface area of the catalysts, can be tailored by manipulating the acidity, the ratio of Ti/clay and the hydrothermal temperature of the synthesis systems. Such a synthesis is different from the conventional approach of pillared intercalated layered clays. The activity of these catalysts for the degradation of phenol was investigated, and we find that the catalytic activity increases with the increasing volume of the pore larger than 3 nm because formation of mesoporous system and anatase nanocrystals leads to improvement in the photocatalytic activity of photocatalysts. This new structure is a more efficient photocatalyst structure for degradating organic pollutant in water, compared to the conventional titania pillared layered clay. The knowledge acquired in this study is useful for designing photocatalysts with high efficiency. (C) 2007 Elsevier Inc. All rights reserved

Ferric ions doped 5A molecular sieves for the oxidation of HCHO with low concentration in the air at moderate temperatures

Zeolitc 5 A molecular sieve was doped with iron ions Fe3+ by ion exchange and the catalytic activity of lie obtained solids for the formaldehyde oxidation was investigated. The catalysts are able to oxidize formaldehyde (if a very low concentration at moderate temperatures, The light-off temperatures were about 70-100 C and the temperatures for the complete oxidation were about 100 190 C,The oxidation reaction product contains HCOOH, and its formation is associated with the silanol groups on the catalyst structure, The pH value of the suspension during the ion exchange and the temperatures at which the catalysts were calcined has profound influence on the amount of the silanols. in the catalysts. Ferric species are also active sites on the zeolite, which are more active at higher temperature than silanols and responsible for producing carbon dioxide. (c) 2005 Elsevier B.V. All rights reserved.Zeolitc 5 A molecular sieve was doped with iron ions Fe3+ by ion exchange and the catalytic activity of lie obtained solids for the formaldehyde oxidation was investigated. The catalysts are able to oxidize formaldehyde (if a very low concentration at moderate temperatures, The light-off temperatures were about 70-100 C and the temperatures for the complete oxidation were about 100 190 C,The oxidation reaction product contains HCOOH, and its formation is associated with the silanol groups on the catalyst structure, The pH value of the suspension during the ion exchange and the temperatures at which the catalysts were calcined has profound influence on the amount of the silanols. in the catalysts. Ferric species are also active sites on the zeolite, which are more active at higher temperature than silanols and responsible for producing carbon dioxide. (c) 2005 Elsevier B.V. All rights reserved

Study on the modified montmorillonite for adsorbing formaldehyde

It is very important to develop a cost-effective and environmentally friendly adsorbent for the efficient removal of indoor formaldehyde (HCHO). Herein we present the modified montmorillonite as adsorbents for HCHO. A series of alumina cross-linked montmorillonite with surfactant modification (Al-SCLM) were synthesized in the presence of polyvinyl alcohol (PVA). These adsorbents are safe and cheap, in rich sources, acceptable appearance for daily use. By the characterization such as XRD, FTIR, HCHO adsorption/desorption capacity measurement, it is found that the interlayer environment is a key factor for the superior adsorption capacity of the modified montmorillonite. The introduction of surfactant molecules is very favorable for the improvement of the montmorillonite's adsorption capacity. With optimization, the adsorbing capacity of HCHO over Al-SCLM is obviously superior to conventional inorgano-montmorillonite and organo-montmorillonite, and can be over 80% of that over activated carbon with the same volume. We can conveniently recover the adsorbents by heating them to 353 K. The strategy that improving the adsorbing capacity by increasing the interlayer distance of materials with surfactant modification will be crucial for developing highly effective adsorbents for hazardous wastes, and has a good prospect for getting rid of HCHO in industrialization. (C) 2015 Elsevier B.V. All rights reserved

Gold catalysts supported on the mesoporous nanoparticles composited of zirconia and silicate for oxidation of formaldehyde

Gold was loaded onto porous nanocomposite of ZrO(2) and silicate by deposition-precipitation. The resulting Au/ZrO(2)-nanocomposites are found to be superior catalysts for removal of formaldehyde from indoor air at moderate temperature by oxidation. They have large specific surface areas and allow the gold to be adequately dispersed as small nanoparticles (NPs). According to the analysis of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), in the as-prepared catalyst, gold was well dispersed and in an oxidized state of Au(3+); and it was reduced to metallic crystals (Au(0)) during its use as catalyst. The temperature programmed desorption (TPD) results show that gold species in the two states strongly adsorb HCHO molecules at ambient temperature. The adsorbed HCHO molecules convert rapidly into formate species, as observed by the infrared spectra. The temperature programmed surface reaction (TPSR) study reveals that at temperatures below 450 K, the HCHO oxidation involves reaction between adsorbed formate species and adsorbed oxygen molecules. This explains why the gold species in both states are the active sites for HCHO oxidation, and also indicates that HCHO adsorption on the gold species and oxygen adsorption on the support are crucial steps for the oxidation. (C) 2009 Elsevier B.V. All rights reserved

Oxidation of lean formaldehyde in air over an Au/CeO2 catalyst and its kinetics

The oxidation of low concentration formaldehyde in air over Au/CeO2, prepared by co-precipitation, was investigated. Power-law kinetic models were proposed and the parameters were estimated, which are r = -0.46 x e(-14612/RT) C-HCHO(303 K &lt; T &lt; 363 K) and r = -295.78 x e(-34178/RT) C-HCHO (363 K &lt; T &lt; 413 K). The mechanism of the reaction at low temperatures might be different from that at high temperatures.The oxidation of low concentration formaldehyde in air over Au/CeO2, prepared by co-precipitation, was investigated. Power-law kinetic models were proposed and the parameters were estimated, which are r = -0.46 x e(-14612/RT) C-HCHO(303 K < T < 363 K) and r = -295.78 x e(-34178/RT) C-HCHO (363 K < T < 413 K). The mechanism of the reaction at low temperatures might be different from that at high temperatures