José Aguado

Aqueous heavy metals removal by adsorption on amine-functionalized mesoporous silica

Amino functional mesoporous silica SBA-15 materials have been prepared to develop efficient adsorbents of heavy metals in wastewater. Functionalization with amino groups has been carried out by using two independent methods, grafting and co-condensation. Three organic moieties have been selected to incorporate the active amino sites: aminopropyl (H(2)N-(CH(2))(3)-), [2-aminoethylamino]-propyl (H(2)N-(CH(2))(2)-NH-(CH(2))(3)-) and [(2-aminoethylamino)-ethylamino]-propyl (H(2)N-(CH(2))(2)-NH-(CH(2))(2)-NH-(CH(2))(3)-). Materials have been characterized by XRD, nitrogen sorption measurements and chemical analysis. We have found that all materials preserve the mesoscopic order and exhibit suitable textural properties and nitrogen contents to act as potential adsorbents. Metal removal from aqueous solution has been examined for Cu(II), Ni(II), Pb(II), Cd(II), and Zn(II); adsorption performances of materials prepared by the two functionalization methods have been compared. In addition, copper adsorption process has been thoroughly studied from both kinetic and equilibrium points of view for some selected materials. Aqueous Cu(II) adsorption rates show that the overall process is fast and the time evolution can be successfully reproduced with a pseudo-second-order kinetic model. Whole copper adsorption isotherms have been obtained at 25 degrees C. Significant maximum adsorption capacities have been found with excellent behavior at low concentration.

Removal of cyanides in wastewater by supported TiO2-based photocatalysts

Abstract Titania supported samples on different types of silica have been prepared through a sol–gel method followed by hydrothermal processing. The photocatalytic activity of the samples was tested for free cyanides photo-oxidation. As compared to commercial TiO2 all the synthesised materials showed not only similar photocatalytic efficiencies but improved recovery properties. The degradation of iron(III) cyanocomplexes was also studied in the absence or presence of titania catalyst. In all cases, a photoinduced CN− released from the complex takes place through a homogeneous process. The further oxidation of those cyanides ions to cyanate species is significantly enhanced in the presence of the catalyst in which mesostructured SBA-15 silica is used as support.

Thermal and catalytic cracking of polyethylene under mild conditions

Abstract Thermal and catalytic cracking of both high and low-density polyethylene (HDPE and LDPE, respectively) under mild conditions have been investigated in order to study the properties of the solid waxy product so obtained. The catalysts employed were n-HZSM-5 and HY zeolites, amorphous silica–alumina, activated carbon, Pd charcoal powder and mesoporous aluminosilicate materials (MCM-41), with and without impregnated Pd. The best results achieved in the LDPE degradation with regard to stability and homogeneity of the waxy product were obtained using MCM-41 as catalyst. The high BET surface area, uniform mesoporosity and medium acid strength of this catalyst promotes the polymer cracking according to a random scission mechanism, as well as, the development of hydrogen transfer reactions which reduce the olefinic character of the solid product. On the other hand, the product obtained from HDPE has a higher homogeneity than that coming from LDPE, leading to a waxy product with better quality for potential applications.

Nanocrystalline ZSM-5: a highly active catalyst for polyolefin feedstock recycling

Nanocrystalline HZSM-5 (crystal size around 25–60 nm) shows remarkable activity in the catalytic cracking of LDPE, HDPE and PP despite the low temperatures (340–380 °C) and catalyst loadings used (plastic/catalyst mass ratio=100). Gaseous hydrocarbons are the main products with a maximum centered at C 4 , which are formed through a carbocationic end-chain cracking mechanism. The selectivity towards C 3 −C 5 hydrocarbons is enhanced on decreasing the cracking temperature, reaching a 95–100 % at 340 °C. PIONA analyses of the liquid hydrocarbons obtained at higher temperatures (380 °C) indicate that the highest amount of olefins (47%) is obtained in the cracking of the linear HDPE. In contrast, the branched PP leads mainly towards aromatic compounds (38%).

Zeolite crystallization from organofunctionalized seeds

A novel synthesis method has been applied to different zeolites (ZSM-5, ZSM-11 and Beta), based on the crystallization of silanized seeds, as a way to perturb the subsequent crystal growth step and to modify the zeolite textural properties. The zeolitic materials so obtained exhibit unique properties, such as the presence of ultra-small nanocrystals and supermicropores and enhanced overall and external surface areas. Moreover, these samples possess a high catalytic activity for the conversion of bulky molecules.

Photocatalytic gold recovery from spent cyanide plating bath solutions

A new procedure is presented for the photocatalytic treatment of the highly stable gold-cyanide complexes remaining in spent plating bath solutions. The process allows the recovery of gold by photocatalytic reduction, increasing simultaneously the availability of cyanide for removal treatment. Gold recovery requires a non-oxidant atmosphere and the presence of hydroxyl radical scavengers. The use of mixed TiO2/SiO2 photocatalysts leads to an improvement in the gold recovery rate.

24-P-13-Catalytic properties of micelle templated microporous and mesoporous materials for the conversion of low-density polyethylene

Publisher Summary This chapter presents the catalytic properties of micelle templated microporous and mesoporous materials for the conversion of low-density polyethylene. Both microporous and mesoporous micelle-templated aluminosilicates exhibit high catalytic activity for the low-density polyethylene (LDPE) cracking. Aluminium (Al)-SBA-15 materials are used for the first time as higly effective catalyts for the conversion of polyolefins. The most active catalyts, according to their turnover frequency (TOF) values, are those with the highest silicon (Si)/A1 atomic ratios, which has been assigned mainly to a lower deactivation kinetic. For all the samples investigated, the main products are liquid hydrocarbons within the range C5–C14.

Enantioselective styrene epoxidation using the Jacobsen catalyst immobilized on functionalized SBA-15

The chiral Jacobsen complex has been immobilized by anchoring on organofunctionalized SBA-15 supports. Two types of functionalization agents have been tested: 3-aminopropyltrimethyxysilane and p -aminophenyltrimethoxysilane. The different materials so obtained have been checked as catalysts in the enantioselective styrene epoxidation, several reusing tests being carried out in order to find out the activity and stability of the heterogeneized systems. The best results were obtained with the catalyst prepared by anchoring on a SBA-15 support previously functionalized with aminophenyl groups, since after three reaction tests this system is still active and enantioselective in the epoxidation reaction while it retains 72% of the Mn(salen) complex contained in the raw catalyst. A study of the catalyst stability related with the amount of oxidant and catalyst in the reaction medium is presented. The Jacobsen complex leaching was almost removed by working at both high substrate/oxidant and catalyst/substrate ratios.

Controlling the generation of hierarchical porosity in ZSM-5 by changing the silanization degree of protozeolitic units

ZSM-5 zeolite with hierarchical porosity has been synthesized employing a new method based in the organofunctionalization of protozeolitic units using a silanization agent. The organosilane is grafted onto the external surface of the zeolitic nanounits hindering their further aggregation. The materials obtained exhibit hierarchical porosity and enhanced textural properties. In this work, we report the results obtained when the amount of silanization agent is varied as a means of controlling the contribution of the secondary porosity so generated, showing that the textural properties of the zeolite can be tailored by adjusting the organosilane/silica ratio during the protozeolitic silanization step.

Heavy metals removal from water by adsorption on propylthiol-functionalised mesoporous silica obtained by co-condensation

Propylthiol-functionalised mesoporous silica SBA-15 prepared by co-condensation has been tested for heavy metal removal. Adsorption from aqueous solution was examined for Cu(II), Pb(II), Cd(II), and Hg(II). Adsorption isotherms were determined at 20°C and Langmuir and Freundlich models were fitted to experimental data. The results from adsorption experiments indicate that mercury is efficiently removed from water. Copper, lead and cadmium uptakes from aqueous solution are noticeable but significantly smaller than mercury removal; moreover, lead and cadmium adsorption isotherms exhibit no adsorption maximum within the investigated range of concentration. The influence of solution pH on lead adsorption was also investigated.