Reduction of hexavalent chromium by ascorbic acid in aqueous solutions

Wei

Colloids and Surfaces A: Physicochemical and Engineering Aspect

et al. 2015

h i g h l i g h t s• A simple sensitive colorimetric sensing platform for Cr (III) and Cr (VI) detection.• The strategy relied on Cr (III)-citrate chelation inducing aggregation of Au NPs.• Cr (VI) ion was reduced to Cr (III) by ascorbic acid.• The strategy provided potential for heavy metal speciation analysis. In this work, a simple "red-to-blue" colorimetric method for highly sensitive and selective determination of Cr (III) and Cr (VI) was presented, which was based on the aggregation of Tween 20-stabilized gold nanoparticles (Tween 20-Au NPs). This strategy relied upon the distance-dependent optical properties of gold nanoparticles (Au NPs), strong chelating between Cr (III) and citrate, and the reduction of Cr (VI) to Cr (III) by ascorbic acid (AA). Cr (III) could chelate with citrate to form a stable Cr (III)-citrate complex and thereby induce the aggregation of Tween 20-Au NPs. Thus, the sensing of Cr (III) and Cr (VI) based on aggregation of Au NPs was developed with the color of the Au NPs changing from red to blue, which was readily seen by the naked eye. The color change and surface plasmon resonance (SPR) absorption were used to monitor Cr (III) and Cr (VI) levels. Under the optimal assay conditions, good linear relationship was obtained, and the detection limit of Cr (III) and Cr (VI) were 0.016 M and 0.009 M in standard aqueous solution, respectively. Furthermore, the colorimetric method exhibited a good selectivity over other metal ions and was successfully applied to detect Cr (III) and Cr (VI) in real water samples.

Section: Safety Considerationmentioning

confidence: 97%

Red-to-blue colorimetric detection of chromium via Cr (III)-citrate chelating based on Tween 20-stabilized gold nanoparticles

Wei

Colloids and Surfaces A: Physicochemical and Engineering Aspect

et al. 2015

“…Several synthetic and natural electron-rich compounds are capable of reducing Cr(VI): Fe(II) bearing clay minerals, zero-valent aluminum and Mn(II) have been reported as reducing, and being catalyzing agents in the reduction processes of Cr(VI) [10][11][12]. Natural organic acids including citric, oxalic, ascorbic, tartaric and formic acid have also been examined for the reduction of Cr(VI) from contaminated aqueous and soil matrices [13][14][15][16]. In general, compounds bearing aliphatic or aromatic hydroxyl groups have been found suitable for the reduction of Cr(VI) [15,17].…”

Section: Introductionmentioning

confidence: 99%

“…Many remediation strategies have been advanced to deal with Cr(VI) pollution, including adsorption [6], ion exchange [7], chemical precipitation [8], membrane filtration [9] and reduction [10][11][12][13][14][15][16][17], among others. The reduction of Cr(VI) is among the most widely used strategies in view of the redox activity of chromium.…”

Section: Introductionmentioning

confidence: 99%

Reduction of Hexavalent Chromium Using Sorbaria sorbifolia Aqueous Leaf Extract

Dubey

Varma

2017

Applied Sciences

Aqueous plant leaves extract (PLE) of an abundant shrub, Sorbaria sorbifolia, was explored for the reduction of hexavalent chromium, Cr(VI), to trivalent chromium, Cr(III). The effect of contact time, pH, PLE quantity, ionic strength, hardness, temperature and effective initial Cr(VI) ion concentration were tested; Cr(VI) reduction followed the pseudo-first order rate kinetics and maximum reduction was observed at pH 2. Significantly, Cr(VI) reduction efficacies varied from 97 to 66% over the pH range of 2 to 10, which bodes well for PLE to be used for the reduction of Cr(VI) also at a higher pH. PLE-mediated Cr(VI) reduction displays considerable efficiency at various ionic strengths; however, hardness strongly affects the reduction ability. Higher temperature significantly enhances the Cr(VI) reduction. This study reveals the potential use of PLE as a green reducing agent in aqueous extract for the efficient reduction of Cr(VI) to Cr(III).

“…Studies revealed that chemical reduction of hexavalent chromium, Cr(VI), accompanied by formation of insoluble chromium compounds can be carried out using several different organic and inorganic reductant agents, for instance, sodium ditionate (Na 2 S 2 O 4 ; Su and Ludwig 2005); sodium metabisulphite (NaS 2 O 3 ; Beukes et al 1999Beukes et al , 2000; ferrous sulphate (FeSO 4 ; Seaman et al 1999); calcium polysulphide (CaS 5 ; Jacobs et al 2001); citric and ascorbic acids (Xu et al 2004;Su and Ludwig 2005); zerovalent iron particles (Cao andZhang 2006, Ponder et al 2000;Schrick et al 2004;He et al 2007;Li et al 2006;Xu and Zhao 2007;Franco et al 2009), etc. In light of these considerations, one can argue that chemical reduction is a promising alternative technology for soil remediation where the permanent immobilisation of chromium in soil is considerably desired; the fixation of chromium species in soil matrix avoids the undesirable transport of these metal species across the aquifer zone.…”

mentioning

confidence: 99%

“…Fe(II), sulphites and some type of organic acids (e.g. ascorbic acid)] (Seaman et al 1999;Beukes et al 2000;Xu et al 2004;Su and Ludwig 2005).…”

mentioning

confidence: 99%

Chemical Reduction of Hexavalent Chromium and Its Immobilisation Under Batch Conditions Using a Slurry Reactor

Franco¹,

Silva²,

Jardim³

2009

Water Air Soil Pollut

Chemical reduction of the hexavalent chromium, Cr(VI), present in contaminated soil and groundwater was carried out in a slurry reactor under dynamic conditions (120 rpm and 25°C) using different reductants [ferrous sulphate (Fe(II))], sodium bisulphite, sucrose, ascorbic acid and zerovalent iron (ZVI)] in order to evaluate the influence of the reductant on the redox process. Chemical analysis of the contaminated soil revealed a Cr(VI) concentration of 528±31 mg kg −1 . Batch studies under dynamic conditions (slurry reactor) using different [Cr(VI)]/ [reductant] molar ratios revealed that only Fe(II) and ZVI species can promote both reduction of Cr(VI) and immobilisation of Cr(III) (formation of an insoluble hydroxide compound). It was verified that 1.0 g of ZVI is capable of converting 104±5 mg of Cr (VI) in Cr(III). A kinetic redox study was carried out using ZVI in different conditions. In all cases, it was verified that Cr(VI) reduction follows a pseudo-firstorder kinetic behaviour. The dependence of the pseudo-first-order kinetic rate constant, k obs , on [ZVI] indicates that the redox process taking place in the slurry reactor is rather complex. A phenomenological kinetic equation for the redox process taking place in the slurry reactor was presented in order to describe the behaviour of k obs under nonideal conditions.