Efficient and Fast Adsorption-Reduction of Cr(VI) with Portable Pd/C-Modified Cellulose Filter Paper

Efficient reduction of Cr^(VI) to Cr^(III) was performed over the modified cellulose filter paper via a simple filtration set-up. A plain cellulose filter paper was covalently functionalized by silane groups followed by Pd/C NPs. The adsorption-reduction took place completely for 30 min under neutral pH, at 25 °C, for 500 mg/L of Cr^(VI) in the presence of formic acid. The best conditions for the reduction were achieved by an experimental design on Design-Expert 13.0.5.0 × 64 software. According to the kinetics studies, the reduction follows a pseudo-second-order kinetics. The positive value of ΔH indicates that the adsorption process of Cr^(VI) by the adsorbent was endothermic. Also, negative ΔG indicates that the reaction is spontaneous. The obtained positive ΔS value also indicates an increase in disorder in the reduction and an increase in adsorption in the expected phase of solid and liquid during the adsorption process. Also, a deep study was conducted over the mechanism of the reduction, wherein a consecutive adsorption-reduction was suggested and the Pd sites and formic acid play a crucial role in the electron transfer and reduction of Cr^(VI) to Cr^(III) ions. The recyclability studies revealed that the filter paper could be reactivated and recycled several times without loss of catalytic activity, as well as physical quality of the filter paper in terms of swellability and shrinkage. Applicability of the filter was also studied on a real industrial wastewater, wherein Cr(VI) reduction/adsorption was carried out without the interference of other anions and cations. The results suggest that the catalytic filter paper can be effectively used in purification systems to reliably remove Cr^(VI).

A new approach has been developed for the efficient reduction of Cr(VI) based on an adsorption-reduction on a modified cellulose filter paper via fast filtration