Synthesis and characterization of gadolinium doped cobalt ferrite nanoparticles with enhanced adsorption capability for Congo Red

• CoFe2−xGdxO4 nanoparticles are synthesized by an improved hydrothermal method.
• Gd3+ doping enhances the adsorption capacity of Co ferrite nanoparticles for CR.
• The Langmuir maximum adsorption capacity of CoFe1.93Ga0.07O4 for CR is higher.
• The initial adsorption rate is sensitive to the BET surface area of nanoparticles.
• Gd3+ doping decreases Ms and Hc of Co ferrite nanoparticles.

Nanoparticles of CoFe2−xGdxO4 (x = 0, 0.03, 0.05, 0.07, 0.1) are synthesized by an improved hydrothermal method. Here, the doping of Gd3+ ions leads to an obvious enhancement of absorption capability for Congo Red (CR) from aqueous solution onto CoFe2−xGdxO4 nanoparticles. The morphology and structure of the samples have been characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that the obtained samples are pure cubic spinel phase with uniform morphological structure. With increasing the doping amount of Gd3+ ions, the average particle size gradually reduces from 13 to 8 nm. The hysteresis loops are investigated using a vibrating sample magnetometer (VSM), where the saturation magnetization and coercivity decrease with the Gd3+ ions doping, further, a remarkable superparamagnetic behavior gradually exhibits. UV–vis spectrophotometer records the adsorption properties of as-synthesized nanoparticles for CR. Due to the substitution of Gd3+ ions, compared with undoped ferrite, the removal ability for CR increased from 131.1 to 161.1 mg g−1. The absorption kinetics is described well by the pseudo-second-order model. Calculated from Langmuir isotherm model, the maximum adsorption capability of CR dye onto CoFe2−xGdxO4 is up to 263.2 mg g−1, here, x = 0.07. This study demonstrates that the addition of rare earth (RE) ions can further enhance the adsorption capability of ferrite nanoparticles for dyes.