Gamma irradiation-induced degradation and mineralization of methocarbamol in aqueous solution.

Gamma irradiation degradation of the extensively used muscle relaxant in the world methocarbamol (MET) was studied. MET aqueous solutions were irradiated by gamma rays emitted by a Cobalt 60 source at doses of 1-4 kGy. Our findings demonstrated that gamma irradiation degraded more than 98.5% of MET. Absorption spectra analysis revealed that when increased irradiation dose, the absorption bands declined with complete disappearance at 4 kGy dose. Additionally, the most radiolytic degradation rate was recorded at neutral pH, marked by Total Organic Carbon (TOC) removal rate of 98% reflecting the total mineralization of MET at 4 kGy. In-depth spectrophotometric analyses advocated a pseudo-first-order type of MET degradation kinetics. The obtained apparent rate constant value was kapp, MET = (0.02167 ± 0.0006) min-1. Gas chromatography-mass spectrometry (GC-MS) allowed the detection of 3-(o-methoxyphenoxy)-1,2 propanediol,2-methoxyphenol, 1,2,3 propanetriol, 1,2-dihydroxybenzene and 1,2,4 benzentriol identified as by-products generated during radiolytic degradation. Finally, an outline of the degradation mechanism was suggested according to the obtained by-products.

On the Mechanism of the Ionizing Radiation-Induced Degradation and Recycling of Cellulose.

The use of ionizing radiation offers a boundless range of applications for polymer scientists, from inducing crosslinking and/or degradation to grafting a wide variety of monomers onto polymeric chains. This review in particular aims to introduce the field of ionizing radiation as it relates to the degradation and recycling of cellulose and its derivatives. The review discusses the main mechanisms of the radiolytic sessions of the cellulose molecules in the presence and absence of water. During the radiolysis of cellulose, in the absence of water, the primary and secondary electrons from the electron beam, and the photoelectric, Compton effect electrons from gamma radiolysis attack the glycosidic bonds (C-O-C) on the backbone of the cellulose chains. This radiation-induced session results in the formation of alkoxyl radicals and C-centered radicals. In the presence of water, the radiolytically produced hydroxyl radicals (●OH) will abstract hydrogen atoms, leading to the formation of C-centered radicals, which undergo various reactions leading to the backbone session of the cellulose. Based on the structures of the radiolytically produced free radicals in presence and absence of water, covalent grafting of vinyl monomers on the cellulose backbone is inconceivable.

Kinetic and mechanism investigation on the gamma irradiation induced degradation of quizalofop-p-ethyl.

An efficient gamma radiolytic decomposition of one of the extensively used herbicides in the world quizalofo-p-ethyl (QPE) was explored under different experimental conditions. Aqueous solutions of QPE were irradiated by gamma rays emitted by a Cobalt 60 source. QPE aqueous solutions were irradiated at doses of 0.5-3 kGy with 26.31 Gy min-1 dose rate. Obtained results indicated that removal efficiency of 98.5% and 73% of QPE were obtained, respectively, in absence and in presence of dissolved oxygen. Change of absorption spectra, pH effect and Total Organic Carbon (TOC) were carried out and studied. It was found that all absorption bands decreased with increasing irradiation dose and disappear totally after 3 kGy applied dose. Three pH conditions (pH = 10, pH = 6.2 and pH = 3) were applied in radiolytic degradation of QPE showing that the best removal efficiency has been found for neutral pH. Interestingly, the % TOC removal reaches 98% at 3 kGy indicated practically total mineralization. Furthermore, spectrophotometric analyses argued in favour of a pseudo-first-order kinetic of QPE degradation. The resulting apparent rate constant value is approximately kapp = (0.012 ± 0.001) min-1. Finally, several by-products such as 6-chloroquinoxalin -2-ol, 2-(4-hydroxy-phenyoxy) propionate, 1,4-hydroquinone, quinone, 4-chlorobenzene-1,2diol and 1,2,4-benzenetriol were identified by gas chromatography-mass spectrometry (GC/MS) evidencing that radiation process starting with the fragmentation of the molecule involving the hydroxyl radical, which is generated by the radiolysis of water. Based on the identification intermediates, a degradation mechanistic schema of QPE has been proposed.

Gamma radiation induced degradation of the phenoxy acid herbicide diclofop-methyl in aqueous solutions.

Gamma radiation of diclofop methyl (DM) an herbicide deriving from aryloxy-propionic acid was investigated. DM aqueous solutions was irradiated at different doses from 1 kGy to 8 kGy. The effects of radiation doses on UV-visible spectroscopy, pH, total inorganic carbon (TOC) and kinetic study have been studied. It was found that absorption bands decrease with increasing radiation dose. The TOC removal efficiency was 97% at 8 kGy. Several degradation by-products such as 4-(2,4-dichlorophenoxy) phenol, 2-hydroxy-propanoic acid methyl ester, 2,4-dichlorophenol, 1,4-hydroquinone, quinone, 2-chloro-1,4-hydroquinone and 1,2,4-benzenetriol were identified by gas chromatography-mass spectrometry (GC/MS) evidencing that radiation process starting with the fragmentation of the molecule involving the hydroxyl radical, which is generated by the radiolysis of water. Based on the identification intermediates, a plausible DM mineralization pathway has been proposed. Finally, a kinetic study was effected and showed that the DM degradation process is a pseudo-first order.