Synthesis, characterization, and phytotoxicity evaluation of Ce/Zr bimetallic oxides as adsorbents for nitrate decontamination from water

Abstract

The Ce/Zr bimetallic oxides with varying atomic ratios were synthesized by sol-gel combustion technique and used as adsorbents for the nitrate decontamination from water. Thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX) aided FESEM, X-ray diffraction (XRD), and Brunauer-Emmett-Teller surface area analysis (BET) were utilized to characterize the synthesized bimetallic oxides thoroughly. Compared to bimetallic oxides with various Ce/Zr ratios (1:1, 1:2, 1:3, 1:4, and 2:1), bimetallic oxide with an atomic ratio of Ce/Zr (1:3) showed a superior and more efficient performance for capturing nitrate ions. The optimum conditions for maximal nitrate removal were an adsorbent dosage of 0.07 g/L, a solution pH of 7.0, a contact time of 40 min, and a reaction temperature of 40 °C. The models pertinent to the sorption data were those based on the Langmuir adsorption isotherm and pseudo-second-order kinetics. Nitrate adsorption on Ce/Zr (1:3) bimetallic oxide was observed as spontaneous, feasible, and endothermic, according to the thermodynamics investigation. The activation energy value and E parameter of the Dubinin-Radushkevich model demonstrated that the sorption process was governed by a physical phenomenon. The findings from the mass transfer study imply that film diffusion and the particle diffusion mechanism work together in the present sorption process, but the former acts as a rate-limiting phase and controls the overall rate of the nitrate sorption process. The XPS investigation revealed the occurrence of bimetallic oxide-mediated reduction of the adsorbed nitrate into nitric oxide through the formation of nitrite as a transient intermediate. Column adsorption behaviour was also examined by using beads of the bimetallic oxide. The experimental outcome of the column study reveals that the beads possess a high affinity for capturing nitrate ions from an aqueous phase. A phytotoxicity investigation was also conducted to assess any potential adverse environmental effects of the produced bimetallic oxide. The regenerated bimetallic oxide was found to be proficiently recycled up to six successive nitrate removal operations with no substantial loss in the uptake efficacy.