Augmenting the adsorption parameters of palladium onto pyromellitic acid-functionalized nanosilicas from aqueous solution

Many industrial wastewaters contain large amounts of palladium and the recovery of palladium from wastewater has great significance. Here, a new adsorbent (PMA-SNP) was synthesized by modifying nano-silica with pyromellitic anhydride to selectively adsorb Pd(II) in wastewater. Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller equation, X-ray photoelectron spectroscopy and transmission electron microscopy were employed to characterize the adsorbent. At 25 °C, the adsorbent has the higher adsorption rate in the pH range of 2 to 5. The adsorption equilibrium is reached in 480 min and the maximum adsorption capacity is 53.61 mg/g. The adsorption kinetics and isotherms accord with pseudo-second-order and Langmuir models, respectively. The results show that the adsorption process is monolayer adsorption and the rate-limiting step is chemical adsorption. After five cycles, the removal rate of Pd(II) by PMA-SNP decreased slightly from 71.18% to 66.11% with good reusability. The thermodynamic data revealed that the adsorption was a spontaneous exothermic process. PMA-SNP can selectively adsorb palladium from wastewater containing various coexisting ions. Adsorption mechanism is based on the electrostatic and chelation interaction between Pd(II) ion and the O and N atoms. It can be concluded that PMA-SNP is an effective and promising adsorbent for the recovery of palladium from wastewater.