Alexandre G.S. Prado

Photocatalytic decouloration of malachite green dye by application of TiO2 nanotubes.

The nanotubes of titania were synthesized in a hydrothermal system and characterized by scanning electronic microscopy (SEM), FT-IR, FT-Raman, and surface charge density by surface area analyzer. These nanomaterials were applied to photocatalyse malachite green dye degradation. Photodegradation capacity of TiO(2) nanotubes was compared to TiO(2) anatase photoactivity. Malachite dye was completely degraded in 75 and 105 min of reaction photocatalysed by TiO(2) nanotubes and TiO(2) anatase, respectively. Catalysts displayed high photodegradation activity at pH 4. TiO(2) nanotubes were easily recycled whereas the reuse of TiO(2) anatase was not effective. Nanotubes maintained 80% of their activity after 10 catalytic cycles and TiO(2) anatase presented only 8% of its activity after 10 cycles.

The incorporation of propane-1,3-diamine into silylant epoxide group through homogeneous and heterogeneous routes

The polar organic molecule propane-1,3-diamine reacted: (i) with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous route to yield the product SiHT or (ii) with the same agent before immobilizing it on the support, in a homogeneous method, to produce a SiHM surface. The epoxy group was opened yielding chelating pendant groups bonded to the inorganic surface. Both products were characterized through elemental analysis, infrared spectroscopy, surface area and thermogravimetry. The ligand concentrations were 0.80 (SiHT) and 1.53 mmol (SiHM), per gram of silica. The heterogeneous route is an easier procedure to produce immobilization. However the homogeneous route provided conditions to obtain a higher density of pendant groups on the surface, which are potentially useful for extracting cations from solutions in an effective way.

Different neutral surfactant template extraction routes for synthetic hexagonal mesoporous silicas

The co-condensation of a tetraethoxysilane molecule on a neutral n-octylamine surfactant template is a convenient synthetic methodology for mesostructured material preparations. Distinct routes of template removal were investigated. The neutral surfactant was removed by calcination, hot solvent extraction, heating at 150 °C, in vacuo at room temperature and at 100 °C, and air drying, with the products assigned as HMM, HMS, HME, HMV1, HMV2 and HM, respectively. 29Si NMR, infrared, surface area, pore diameters and pore volume determinations were employed to characterize each sample. Elemental analysis detected the presence of amine residues of 1.8, 1.2, 0.2, 1.6 and 0.30 mmol g−1 for HMA, HME, HMS, HMV1 and HMV2, respectively. The HMM, HMS and HMV2 samples presented a low amount of amine residues, and HMS and HMV2 have the great advantage of permitting template removal without calcination.

Adsorption and separation of cations on silica gel chemically modified by homogeneous and heterogeneous routes with the ethylenimine anchored on thiol modified silica gel

Ethyleneimine (etn) has been covalently bonded onto silica gel via homogeneous (SiSN1) and heterogeneous (SiSN2) routes. Both synthesised silica gel surfaces have been applied to adsorb divalent cations from aqueous solution at room temperature. The series of isotherms of adsorption were adjusted to a modified Langmuir equation, after collecting the data from the solid/MCl2 solution (M = Co, Ni, Cu, Pb and Hg) interfaces. The maximum adsorption were 1.08, 1.20, 1.70, 1.34 and 4.02 mmol g−1 for SiSN1 and 0.72, 1.74, 1.91, 2.19 and 2.89 mmol g−1 for SiSN2, for a the sequence of divalent cations: Co, Ni, Cu, Pb and Hg, respectively. Columns loaded with immobilised silica show resolutions (R) for separating metal ion couples: RCo–Ni = 0.22, RCo–Pb = 0.76, RCo–Cu = 1.12, : RCo–Hg = 2.06, RNi–Pb = 0.50, RNi–Cu = 1.17, RNi–Hg = 2.38, RPb–Cu = 0.33, RPb–Hg = 1.83 and RCu–Hg = 1.60 for the SiSN1 surface. The sequence: RCo–Ni = 1.10, RCo–Pb = 1.44, RCo–Cu = 1.63, : RCo–Hg = 2.26, RNi–Pb = 0.08, RNi–Cu = 0.33, RNi–Hg = 1.40, RPb–Cu = 0.38, RPb–Hg = 1.82 and RCu–Hg = 1.55 was determined for SiSN2.

Hexagonal mesoporous silica modified with copper phthalocyanine as a photocatalyst for pesticide 2,4-dichlorophenoxiacetic acid degradation

A new mesoporous catalyst was prepared by the reaction between 3-aminopropyltrimethoxisylane and Cu(II)-hexadecafluorophthalocyanine, followed by co-condensation of tetraethylorthosilicate around a micelle formed by n-dodecylamine. The surfactant was removed from the pores by continuous extraction with ethanol, giving the Si-CuF16Pc catalyst. This catalyst was characterized by SEM, FTIR, TGA, 29Si NMR, N2 adsorption and X-ray diffraction. SEM images confirmed that the catalyst material is formed by nanoaggregates with a diameter of 100 nm. N2 adsorption isotherms showed that Si-CuF16Pc has a surface area of approximately 200 m2 g(-1) and a porous diameter of 7.7 nm, characterizing the mesoporosity of this product. This novel material shows an excellent photocatalytic activity, degrading almost 90% of 2,4-dichlorophenoxyacetic acid (2,4-D) up to 30 min, while only approximately 40% of photodegradation was obtained in its absence.

Estudo da adsorção/dessorção do ácido 2,4 diclorofenoxiacético (2,4d) em solo na ausência e presença de matéria orgânica

The herbicides are being used in huge quantities for various porpouses. Once the herbicide finds its way into the environment, a major part of it comes in contact with soil. Humic substances are major organic constituents of soil. These substances may interact with herbicides in different modes and adsorption is probably the most important one. Adsorption will control the quantity of herbicide in the soil solution, and determines its persistence, leaching, mobility and bioavailability. In this work we studied the interaction between the herbicide 2,4D and soil in the presence and absence of organic matter. The methodology utilized for the determination of 2,4D was gas chromatography with eletron capture detector. The behavior of 2,4D was evaluated through Freundlich isotherms. It was verified that the herbicide 2,4D has a large adsorption in the humic acid .

Immobilization of the pesticide 2,4-dichlorophenoxyacetic acid on a silica gel surface.

A route for the immobilization of 2,4-dichlorophenoxyacetic acid (2,4-D) on silica gel has been developed. In the first step the precursor was prepared by reacting the silylating agent 3-(trimethoxysilyl)propylamine with silica gel. Nitrogen analysis of this anchored compound showed the presence of 1.16 mmol of amine groups per gram of support. The herbicide was covalently bonded to the amine groups previously anchored onto silica gel. Infrared, [ 13 C] and [ 29 Si] NMR spectra supported the reaction between the nitrogen of the amine group of the anchored silica with the carbon on the para-position of the aromatic ring of 2,4-D. The reaction yield, 90.3%, was confirmed through elemental analysis.

Adsorption, separation, and thermochemical data on the herbicide picloram anchored on silica gel and its cation interaction behavior

The herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram), chemically anchored on silica gel surface (SiPi), has been used for divalent cation M(2+) (Cu, Ni, Zn, and Cd) adsorption from aqueous solutions at room temperature. The series of adsorption isotherms were adjusted to a modified Langmuir equation from data obtained by suspending the solid with MCl(2) solutions, which gave the maximum number of moles adsorbed as 9.27, 7.54, 5.12, and 1.54 x 10(-4) molg(-1) for Cu, Ni, Zn, and Cd, respectively. The minimum cation retention capacity from aqueous solution was observed at pH 1, increasing up to pH 4, and was maintained constant at pH 5 for all cations. The maximum retention capacity followed the sequence Cu>Ni>Zn>Cd. SiPi-M (Cu, Ni) interactions presented endothermic enthalpic values, which contrasted with exothermic values for SiPi-M (Zn, Cd) interactions. The anchored herbicide was also used to separate the cations when loaded in a column. Their resolutions were determined as the ability of this surface to separate cations, to give Rs(Cd-Zn)=2.33, Rs(Cd-Ni)=3.16, Rs(Cd-Cu)=7.21, Rs(Zn-Ni)=1.31, Rs(Zn-Cu)=2.55, and Rs(Ni-Cu)=0.72.

Química verde, os desafios da química do novo milênio

The fundamental concepts of the green chemistry are highlighted in order to present the enormous number of challenges to develop a new chemistry in research, industry and education. The practice of an environmental friendly chemistry are presented to improve the economics of chemical manufacturing and to enhance the much-tarnished image of chemistry and to present the opportunities to discover and apply this new chemistry. The challenges and opportunities of green chemistry in the world and Brazil are introduced and discussed in this report.

The toxic effect on soil microbial activity caused by the free or immobilized pesticide diuron

The pesticide diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) was anchored onto silica gel to yield a new surface. Both free and immobilized pesticide were applied on typical Brazilian agricultural soil and the toxic effects on microbial activity of this red Latosol soil was followed by microcalorimetry. The activity of the microorganisms on 1.50 g of soil sample was stimulated by addition of 6.0 mg of glucose plus 6.0 mg of ammonium sulfate under 34.8% controlled humidity at 298.15 ± 0.02 K. The activity was recorded through power–time curves for increasing amounts of the active principle, varying from 0 to 333.33 gg −1 . The increasing amounts of diuron, either free or immobilized, caused a decrease of the original thermal effect. The calorimetric data showed that the anchored pesticide presented a much lower toxic effect than free diuron on microbial activity.