Catalytic Reduction of Hexavalent Chromium in Aqueous Systems

Hexavalent chromium (Cr(VI)) is a widespread environmental contaminant, typically arising from electroplating, leather tanning, textile processing and chromate production. Its high solubility and carcinogenicity pose serious threats to human health and aquatic ecosystems. Catalytic reduction transforms Cr(VI) into the far less toxic trivalent form (Cr(III)), enabling subsequent precipitation or adsorption for removal. Recent advances have centred on nanostructured catalysts—including zero‐valent metals, bimetallic systems and supported noble metals—to achieve rapid kinetics, high selectivity and ease of catalyst recovery. Photocatalytic processes using semiconductors can drive redox reactions under illumination, while chemical reductants such as formic acid or hydrogen supply electrons in heterogeneous systems. Biogenic and green synthesis routes for nanoparticles offer eco‐friendly preparation methods, often yielding finely dispersed catalysts with enhanced surface activity. Key challenges remain in preventing catalyst fouling by Cr(III) deposition, maintaining activity across a range of pH values, scaling up for industrial waste streams and integrating continuous‐flow reactor designs. The global significance of these technologies is underscored by regulatory limits on Cr(VI) in drinking water, prompting multidisciplinary efforts spanning materials science, environmental engineering and surface chemistry to develop robust, cost‐effective remediation strategies.

Research from Nature Portfolio

One study reported the synthesis of highly recyclable biogenic palladium nanoparticles (PdNPs) with a narrow size distribution (3–25 nm), which achieved complete conversion of high‐concentration Cr(VI) to Cr(III) without pH adjustment. These PdNPs sustained over 90 % activity over multiple cycles without requiring additional reductant, demonstrating significant improvements in catalyst stability and operational simplicity.

A comparative analysis of biologically versus chemically synthesised PdNPs revealed that biologically derived catalysts exhibit smaller particle size and higher dispersion, resulting in faster reduction kinetics and lower product inhibition by Cr(III). Kinetic modelling using the Langmuir–Hinshelwood mechanism confirmed superior adsorption and turnover frequencies for bio‐PdNPs compared with their chemical counterparts.

Another investigation introduced a polymer‐coated Macadamia nutshell biomass support bearing PdNPs (Pd@Polym‐MNS) immobilised in a basket reactor. This design facilitated easy catalyst recovery, minimised nanoparticle aggregation and maintained consistent pseudo‐first‐order rate constants across successive batches. Thermodynamic analysis highlighted the exothermic yet non-spontaneous nature of the redox reaction, offering insights into electron‐donor interactions and catalyst reuse.

Catalytic Reduction of Hexavalent Chromium in Aqueous Systems publication trend

The graph below shows the total number of articles in catalytic reduction of hexavalent chromium in aqueous systems across all publications each year (not limited to Nature Index journals).

Technical terms

Hexavalent chromium (Cr(VI)): The +6 oxidation state of chromium, notable for its high solubility and toxicity in water.

Zero-valent nanoparticles: Metallic particles in the 0 oxidation state that act as strong electron donors in reduction reactions.

Photocatalysis: A process in which light energy generates electron–hole pairs within a semiconductor to drive redox reactions.

Langmuir–Hinshelwood mechanism: A surface reaction model in which both reactants adsorb onto a catalyst surface before reacting.

Adsorption isotherm: A mathematical relationship describing the equilibrium uptake of a solute by an adsorbent at constant temperature.

References

1. Green synthesis of sulfur nanoparticles and evaluation of their catalytic detoxification of hexavalent chromium in water. RSC Advances (2018).
2. Reclamation of hexavalent chromium using catalytic activity of highly recyclable biogenic Pd(0) nanoparticles. Scientific Reports (2020).
3. Comparative analysis of biological versus chemical synthesis of palladium nanoparticles for catalysis of chromium (VI) reduction. Scientific Reports (2021).
4. Application of polymer-coated Macadamiaintegrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation. Scientific Reports (2021).
5. Efficient Reduction of Cr (VI) to Cr (III) over a TiO2-Supported Palladium Catalyst Using Formic Acid as a Reductant. Catalysts (2022).
6. Critical Parameters and Mechanisms of Chromium Removal from Water by Copper-Based Nanoparticles. Water, Air, & Soil Pollution (2022).