Inorganic nanoparticles for reduction of hexavalent chromium: Physicochemical aspects

Abstract

Hexavalent Chromium [Cr(VI)] is a highly carcinogenic and toxic material. It is one of the major environmental contaminants in aquatic system. Its removal from aqueous medium is a subject of current research. Various technologies like adsorption, membrane filtration, solvent extraction, coagulation, biological treatment, ion exchange and chemical reduction for removal of Cr(VI) from waste water have been developed. But chemical reduction of Cr(VI) to Cr(III) has attracted a lot of interest in the past few years because, the reduction product [Cr(III)] is one of the essential nutrients for organisms. Various nanoparticles based systems have been designed for conversion of Cr(VI) into Cr(III) which have not been critically reviewed in literature. This review present recent research progress of classification, designing and characterization of various inorganic nanoparticles reported as catalysts/reductants for rapid conversion of Cr(VI) into Cr(III) in aqueous medium. Kinetics and mechanism of nanoparticles enhanced/catalyzed reduction of Cr(VI) and factors affecting the reduction process have been discussed critically. Personal future insights have been also predicted for further development in this area.

Keywords: Chemical reduction; Hexavalent chromium; Metal nanoparticles; Nanocatalysis; Water pollution.

Graphical abstract

Fig. 1

Pt nanoparticles decorated on the surface of polystyrene-b-poly(4-vinylpyridine) nanospheres (Pt@PS-b-PVP) (A) adopted with permission from reference Zhang et al. (2018) (Copyright Springer 2018), Core-shell morphology of trimetallic nanoparticles with Au-Pd core and Pd shell (B) adopted with permission from reference (Shao et al., 2017) (Copyright Elsevier 2017), Nickel nanoparticles embedded carbon based yolk-shell system derived from Ni-MOF (C) adopted with permission from reference Lv et al. (2020) (Copyright Elsevier 2020) for Cr(VI) reduction to Cr(III).

Fig. 2

Immobilization of palladium nanoparticles in electrospun polyethyleneimine and polyvinyl alcohol (PEI/PVA) nanofibers crosslinked by glutaraldehyde using in-situ reduction of K₂PdCl₄ with NaBH₄ in aqueous medium. Reproduced with permission from reference Huang et al. (2012). Copyright American Chemical Society 2012.

Fig. 3

Synthesis of platinum nanoparticles by in-situ reduction of [PtCl₆]²⁻ with NaBH₄ in bi-functional Fe₃O₄/mesoporous silica core/shell nanoparticles (FMSNs) modified by thiol groups (-SH) on their outer surfaces and amine groups in their inner surfaces. Reproduced with permission from reference Mai et al. (2017). Copyright Elsevier 2017.

Fig. 4

Synthesis of silver nanoparticles decorated magnetic carbonized spheres obtained from self-polymerization of dopamine in the presence of iron salt. Reproduced with permission from reference Chen et al. (2018a). Copyright Elsevier 2018.

Fig. 5

Synthesis of nickel nanoparticles (Ni NPs) embedded in reduced graphene oxide (RGO) by hydrothermal method. Reproduced with permission from reference Bhowmik et al. (2014). Copyright American Chemical Society 2014.

Fig. 6

Schematic illustration of two possible mechanisms of catalytic Cr(VI) reduction to Cr(III).

Fig. 7

Schematic illustration of mechanism of catalytic Cr(VI) reduction to Cr(III) with formic acid (HCOOH) using supported Pt nanoparticles. Reproduced with permission from reference Mai et al. (2017). Copyright Elsevier 2017.

Fig. 8

Mechanism of catalytic Cr(VI) reduction to Cr(III) with formic acid (HCOOH) using silver nanoparticles as catalyst.

Fig. 9

Process of reductive removal of Cr(VI) from Soil using FeS nanoparticles as reductant. Reproduced with permission from reference Wang et al. (2019). Copyright Elsevier 2019.

Fig. 10

Use of magnetic core-shell nanoparticles with zerovalent iron core and iron sulfide shell for Cr(VI) reductive removal from ground water. Reproduced with permission from reference Gong et al. (2017). Copyright Elsevier 2017.

Scheme 1

Mechanism of Cr(VI) reduction to Cr(III) by zerovalent iron nanoparticles in aqueous medium.

Fig. 11

Reduction of Cr(VI) to Cr(III) with zerovalent iron nanoparticles promoted by copper coated on Fe(0) nanoparticles in aqueous medium. Reproduced with permission from reference Hu et al. (2010). Copyright Elsevier 2010.

Fig. 12

Time dependent UV–vis spectra of reduction of Cr(VI) by formic acid (HCOOH) in the presence of biomass derived carbon stabilized palladium nanoparticles at different catalyst contents [(a) 0.50, (b) 1.00 and (c) 2.00 mg]. Insets of (a), (b) and (c) are plot of ln(A/A_o) vs time plots for determination of apparent rate constant at different catalyst loadings. Vials given in (d) represent sample before and after Cr(VI) reduction along with confirmation of Cr(III) by addition of sodium hydroxide. Reproduced with permission from reference Veerakumar et al. (2017). Copyright American Chemical Society 2017.

Fig. 13

UV Visible spectra of reaction mixture after one minute (a), plot of ln (C/C_o) versus time (b), Arrhenius plot (c) and Eyring plot (d) for catalytic Cr(VI) reduction to Cr(III) by mixture of formic acid and sodium format in the presence of Pd nanoparticles supported on amine functionalized silica at five different values of temperature in aqueous medium. Reproduced with permission from reference Celebi et al. (2016). Copyright Elsevier 2016.

Fig. 14

Recycling of Pd nanoparticles supported on lignin based phenolic spheres in case of reduction of Cr(VI) (a), TEM images of recycled catalyst (b-c) and before their use as catalyst (d-e). Adopted with permission from reference Chen et al. (2020). Copyright Elsevier 2020.