Quimissorção de cátions divalentes em sílica gel modificada com ácido tioglicólico: a influência do pH e força iônica

A novel type of heavy metal adsorbent was prepared by the covalent grafting of thioglycolic acid molecules on a silica gel surface previsiouly modified with 3-aminopropyltrimethoxysilane. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This material displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting from aqueous solutions cations such as Cu(II), Ni(II), Co(II), influenced by pH and ionic strength. This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. A modified Langmuir equation describes the experimental data.

Utilização e recuperação de sílica gel impregnada com nitrato de prata

Argentation chromatography is used to increase the selectivity of the chromatographic process, chiefly in the resolution of complex mixtures of nonpolar substances. Although efficient, this technique generates residues containing heavy metal which makes its discarding through common procedures impracticable. In the present work a simple method for recycling of silica, and also silver, from argentation chromatography is described. This procedure uses initially a treatment of H2O2/HNO3, with subsequent treatment with H2O2/H2SO4 , allowing an efficient recycling of both components. This methodology is simple, costless, removes impurities efficiently, and does not modify retention parameters nor specific surface in a significant way.

Epoxidação do β-cariofileno com lipases imobilizadas em gel de ágar

The immobilization of enzymes and microorganisms on solid supports has been developed in recent years. These biocatalysts may be used in organic media allowing their storage and reuse, thus reducing costs of the process. Herein, lipases from various sources were immobilized in agar gel and used as catalysts in the chemo-enzymatic epoxidation of β-caryophyllene. Several experimental parameters, such as the use of different organic solvents including ionic liquids, time, temperature, and agitation rate were evaluated. The mono-epoxide was obtained as a single product. The best result was achieved using immobilized F-AP15 lipase, forming the corresponding β-caryophyllene epoxide at a conversion of 96% in an 8h reaction at 35 ºC.