Removal of binary dyes mixtures with opposite and similar charges by adsorption, coagulation/flocculation and catalytic oxidation in the presence of CeO2/H2O2 Fenton-like system.

In this study, the removal of binary mixtures of dyes with similar (Orange II/Acid Green 25) or opposite charges (Orange II/Malachite Green) was investigated either by simple adsorption on ceria or by the heterogeneous Fenton reaction in presence of H2O2. First, the CeO2 nanocatalyst with high specific surface area (269 m2/g) and small crystal size (5 nm) was characterized using XRD, Raman spectroscopy and N2 physisorption at 77 K. The adsorption of single dyes was studied either from thermodynamic and kinetic viewpoints. It is shown that the adsorption of dyes on ceria surface is highly pH-dependent and followed a pseudo-second order kinetic model. Adsorption isotherms fit well the Langmuir model with a complete monolayer coverage and higher affinity towards Orange II at pH 3, compared to other dyes. For the (Orange II/Acid Green 25) mixture, both the amounts of dyes adsorbed on ceria surface and discoloration rates measured from Fenton experiments were decreased by comparison with single dyes. This is due to the adsorption competition existing onto the same surface Cex+ sites and the reaction competition with hydroxyl radicals, respectively. The behavior of the (Orange II/Malachite Green) mixture is markedly different. Dyes with opposite charges undergo paired adsorption on ceria as well as homogeneous and heterogeneous coagulation/flocculation processes, but can also be removed by heterogeneous Fenton process.

Capabilities of laser ablation mass spectrometry in the differentiation of natural and artificial opal gemstones.

The potentialities of laser ablation coupled to ion cyclotron resonance Fourier transform mass spectrometry are evaluated to distinguish natural and artificial opals. The detection of specific species in both ion detection modes leads us to obtain relevant criteria of differentiation. In positive ions, species including hafnium and large amounts of zirconium atoms are found to be specific for artificial opal. In contrast, aluminum, titanium, iron, and rubidium are systematically detected in the study of natural opals. Moreover, some ions allow us to distinguish between natural opal from Australia and from Mexico. Australian gemstone includes specifically strontium, cesium, and barium. Moreover, it is also found that the yield of (H2O)0-1(SiO2)nX- (X- = O-, OH-, KO-, NaO-, SiO2-, AlO1-2-, FeO2-, ZrO2-, and ZrO3-) and (Al2O3)(SiO2)nAlO2- ions depends on the composition of the sample when opals are laser ablated. Ions, which include zirconium oxide species, are characteristics of artificial gem. In contrast, natural opals lead us, after laser ablation, to the production of ions including H2O, Al2O3 motifs and AlO-, KO-, NaO-, and FeO2- species.