Tuning the thiophilicity of Pr6O11 (PrO1.833) through Pb-substitution to append efficient adsorption characteristics

Abstract

With the intent of enhancing the thiophilic character of Pr6O11 (PrO1.833), pure and Pb-substituted samples were synthesized by combustion synthesis and characterized extensively. We could introduce up to 30 mol % of Pb in PrO1.833, retaining fluorite structure as revealed by powder X-ray diffraction and Raman spectroscopy measurements. The non-linear variation of the cubic lattice parameter of Pb-substituted samples suggested mixed oxidation states of cations, further established with XPS analysis. Pr0.70Pb0.30O2-δ showed porous flaky morphology and had a surface area of 344.4 m2/g. Charge transfer bands dominated in the UV–visible spectra of these samples. The Pb-substituted samples were examined as adsorbents for the harmful dye molecules (Congo red and Xylenol orange) having SO3 groups in their structural skeleton. The Langmuir model described the adsorption process well. Pr0.70Pb0.30O2-δ showed a maximum adsorbent capacity of 909 (CR) and 500 (XO) mg/g, attaining equilibrium rapidly (4 min). The thermodynamics and kinetics of the adsorption process have been examined, and a suitable adsorption mechanism is proposed. After the adsorption experiments, sulfur and PrS1.7 formation on the surface of Pr0.70Pb0.30O2-δ illustrated the exciting red-ox chemistry at the interface.