Quantitative determination of hexavalent chromium in aqueous solutions by UV-Vis spectrophotometer

Abstract

In the last decade, different methods have been developed for the determination of chromium(VI) concentration in water. These methods use high cost equipment or they require a long preparation time. Because of their drawbacks, this paper describes an on-line, rapid and sensitive procedure for the determination of Cr(VI) concentrations in aqueous solutions via pH and absorption measurements. Only four Cr(VI) species are considered. The effects of pH and of total amount of chromium on the Cr(VI) speciation are investigated. The molar absorptivities of four chromium species at 371 nm are determined by minimising an objective function. The knowledge of these molar absorptivities and the measurements of pH and absorption at 371 nm lead to a rapid determination of total Cr(VI) concentration. The reliability and applicability of the method were confirmed using synthetic water samples.

Visible light photocatalysis by metal-to-metal charge transfer for degradation of methyl orange

“…As shown above, XPS of this material shows chromium present as both chromium (III) and chromium (VI) ( Figure 1b); solutions of chromium (VI) compounds have a characteristic spectrum, with absorbance in the UV region centred around 275 nm (4.5 eV) and 375 nm (3.3 eV). 22 The diffuse reflectance of 3%CrOx-Nb2O5 shows a hump and shoulder between 2.1 eV and 3.5 eV. This feature, which is absent pre-calcination, concurs with the XPS data by indicating chromium (III), chromium (VI) transitions.…”

“…The spectrum, (Figure 1c) with significant peaks centered at 256 nm and 350 nm, is characteristic of chromium (VI) as Cr2O7 2-, indicating that chromium (VI) is leaching out of the composite. 22 If this process is repeated, essentially washing the material, a significant decrease in intensity of the chromium (VI) peak can be observed in the washings, indicating chromium (VI) is being removed from the 3%CrOx-Nb2O5. By repeating this cycle an additional three times, the amount of chromate leaching out of the catalyst into the deionized water becomes undetectable by UV/Vis This journal is © The Royal Society of Chemistry 20xx…”

Removal of Cr(VI) Species from Aqueous Solution by Different Nanoporous Materials

“…In more specific terms [33][34][35], only chromate ion exists at basic medium, the predominant species at neutral conditions are the presented in the spectra shown in Figure 1, the Cr(VI) solutions showed two peaks at ~260 and ~360 nm, which on the basis of the above discussion and the experimental conditions are assigned to CrO 4 2− and HCrO 4 − , respectively. As such, the total concentration of Cr in the solution is the sum of those of bichromate and chromate ions.…”

Specification of the Operational Parameters Contribution in the Efficiency of TiO2-P25 Nanoparticles in the Photocatalytic Removal of Cr(VI) by Taguchi Method

“…The Taguchi's experimental design methodology shows that among the effective parameters on Cr(VI) photocatalytic removal efficiency, the greater effect is related to pH. The results revealed that the optimal conditions for the photocatalytic removal of Cr(VI) are initial concentration of Cr(VI) at level 1 (20 mg L and solution pH at level 1 (2). This indicates that Taguchi's experimental design is a fast, reliable and efficient way of determining the optimum conditions of the process.…”

“…Therefore, in this method, with 3 repetitions of the 8 experiments, we will have a total of 24 experiments that will help us understand the extent of the effect of the mentioned parameters. By considering the five factors in 2 levels of change ), the time of light irradiation is level 2 (30 min), the intensity of UV irradiation is level 2 (33.26 W m -2 ) and the solution pH is level 1 (2). Because, in this study, the performance statistics of ''the bigger -the better'' was used to define the optimum conditions.…”