Recebido em 12/12/08; aceito em 24/7/09; publicado na web em 8/1/10 Pharmaceutical compounds have been detected in sewage treatment plant (STP) effluents, surface waters and, less frequently, in groundwater and drinking water, all over the world. Different sources are responsible for their appearance in the aquatic environment, however, it is widely accepted that the main sources of this type of pollutant are STP effluents. The adverse effects of pharmaceuticals in the environment include aquatic toxicity, development of resistance in pathogenic bacteria, genotoxicity and endocrine disruption. Thus, the discharge of these compounds to the environment in STP effluents should be minimized.

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The reduction of SO 2 on carbons proceeds through reactive intermediates bound to the carbon matrix, which were postulated to be 1,2-oxathiene 2-oxide (or sultine), and 1,3,2-dioxathiolane that decomposes to produce an episulfide and CO 2 . The reactivity of these intermediates was studied in this work through several reactions, using XPS and NMR spectra to postulate their mechanisms. When modified activated carbon obtained after reaction with SO 2 at 630 °C was heated at 900 °C, it was observed that the changes of the XPS spectrum resulted from the forward reaction of decomposition of the oxidized intermediate with S-transfer to produce the episulfide and CO 2 and the reverse reaction with expulsion of SO 2 . Strong bases hydrolyzed the dioxathiolane intermediate and the episulfide. The thiolysis, aminolysis, and reaction of alkyl halides with modified activated carbon occurred with the insertion of the organic moiety in the carbon matrix. Laser photolysis at 266 nm in t-butanol showed insertion of t-butoxide on the matrix. Consistent mechanisms for these reactions were postulated. These results provide additional evidence on the mechanism of reduction of SO 2 on carbons and the chemical nature of the intermediates, offering a new method to modify the physical and chemical properties of a carbon matrix by functionalization with an organic moiety.

dGraphite particles (0.505 mm) were oxidized to graphite oxide with KClO3 in a H 2 SO 4 /HNO 3 mixture. Graphite and graphite oxide particles were modified by reaction with SO 2 at 630°C. Thiolysis with sodium dodecane-1-thiolate and aminolysis with dodecane-1-amine of these particles occurred with the insertion of the organic moiety in the carbon matrix. Graphite microparticles (6.20 μm) were oxidized by H 2 SO 4 / KMnO 4 / H 2 O 2 mixture and were exfoliated to graphene oxide sheets (MPGO). MPGO was modified by reaction with SO 2 at 630°C. The modified MPGO was refluxed in DMSO with dodecane-1-thiol, dodecane-1-amine, and hexadecane-1-bromide. The reactions occurred with the insertion of the organic moiety in the carbon matrix, according to the X-ray photoelectron and nuclear magnetic resonance spectra. Mechanisms for the reactions were postulated using the atom inventory technique. Despite the structural differences, graphite, graphite oxide, and graphene oxide present the same selectivity for aminolysis and thiolysis reactions, with respect to the oxidized and non-oxidized intermediates of the reduction of SO 2 , as was found for the activated carbon.

X‐ray photoelectron spectroscopy (XPS) allows the analysis of the surface atomic composition of a solid and can be used for mechanistic studies of solid–gas and solid–liquid reactions. The change of atomic composition of a surface after a reaction can be calculated considering hypothetical mechanisms based on the known reactivity of the organic moieties bound to the solid surface. Atom inventory of the elements involved in the reactions was used to quantify the components of the XPS spectrum after the reaction and consequently the change of concentration in at%. The method was used to study the basic hydrolysis and photolysis of the intermediates bound to the carbon matrix after the reduction of SO2 on activated carbon. Consistent mechanisms were postulated for these reactions. Basic hydrolysis hydrolyzed the sultine intermediate, and the attack of hydroxide ion on the episulfide formed a sulfide anion, eliminating S2− in a consecutive step. Laser photolysis of modified activated carbon in t‐butanol showed the insertion of the organic moiety in the carbon matrix with expulsion of an SO2 radical anion that oxidized to ${\rm SO}_4^{2 - } $. Copyright © 2008 John Wiley & Sons, Ltd.

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Graphite microparticles (d50 6.20 μm) were oxidized by strong acids, and the resultant graphite oxide was thermally exfoliated to graphene oxide sheets (MPGO, C/O 1.53). Graphene oxide was treated with nonthermal plasma under a SO2 atmosphere at room temperature. The XPS spectrum showed that SO2 was inserted only as the oxidized intermediate at 168.7 eV in the S 2p region. Short thermal shocks at 600 and 400 °C, under an Ar atmosphere, produced reduced sulfur and carbon dioxide as shown by the XPS spectrum and TGA analysis coupled to FTIR. MPGO was also submitted to thermal reaction with SO2 at 630 °C, and the XPS spectrum in the S 2p region at 164.0 eV showed that this time only the nonoxidized episulfide intermediate was inserted. Plasma and thermal treatment produced a partial reduction of MPGO. The sequence of thermal reaction followed by plasma treatment inserted both sulfur intermediates. Because oxidized and nonoxidized intermediates have different reactivities, this selective insertion would allow the addition of selective types of organic fragments to the surface of graphene oxide.

Surface‐science studies of some reactions have allowed postulating the mechanisms using a variety of techniques. The surface chemistry of Group IV elements has been particularly studied recently because Si, Ge, and C are semiconductors, and the surface organic chemistry to functionalize these elements has seen immense progress in recent years. In this review article we describe the methodology used to study the mechanism of a solid–gas reaction, the reduction of SO2 on carbons, and the necessary conditions that allowed the measurement of the solid conversion and product distribution when the kinetics was chemically controlled and the reaction had reached the steady state. The reaction was first‐order with respect to SO2 and with respect to carbon and the stoichiometry was determined from the product distribution. The reaction proceeds through two thermally stable reaction intermediates bound to the surface, a six‐membered ring 1,3,2‐dioxathiolane and a five‐membered ring 1,2‐oxathietene 2‐oxide or γ‐sultine, both species being in equilibrium. The reaction was shown to be reversible. The primary product is an episulfide that, after a series of consecutive reactions of atomic sulfur, is able to free sulfur. The reactivity of the intermediates and the episulfide was studied for several reactions and consistent mechanisms were postulated from the X‐ray photoelectron spectroscopy and solid state nuclear magnetic resonance spectra. Aminolysis and the reaction with alkyl halides resulted on the insertion of the alkyl moiety in the episulfide primary product, while the thiolysis and photolytic alcoholysis resulted in the insertion of the alkyl moiety in the oxidized intermediates. Copyright © 2012 John Wiley & Sons, Ltd.