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Cobalt impregnated silica nanoparticles (Co–SiO2) were synthesized via one pot method involving supercritical drying followed by in‐situ reduction. The prepared nanoparticles were characterized by nitrogen‐Brunauer Emmett Teller (N2‐BET) isotherm studies, X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), zeta particle size analyzer and vibrating sample magnetometer (VSM) techniques. The Co–SiO2 nanoparticles were evaluated for adsorptive removal of methylene blue (MB), trinitrotoluene (TNT), and mercury ions [Hg (II)]. The equilibrium adsorption data were analyzed using Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Adsorption of MB and Hg(II) were best fitted by Langmuir isotherm model depicting their homogenous monolayer adsorption with maximum adsorption capacity of 250 and 40.24 mg/g, respectively, while TNT adsorption was best fitted by Freundlich isotherm model indicating a heterogeneous adsorption with 20.49 mg/g adsorption capacity. The mean adsorption energy calculated through D–R model indicated physisorption of all the three contaminants by the adsorbent. Thermodynamic studies showed that the adsorption of these contaminants was spontaneous and endothermic process with increased randomness at the solid/solution interface. The magnetic Co/SiO2 nanoparticles were easily separated after adsorption process with the help of a magnet and showed a reusability upto three cycles without much loss in adsorption efficiency. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S42–S53, 2019 [ABSTRACT FROM AUTHOR]

Cerium oxide (CeO2) nanoparticles of size 3–5 nm and surface area 257 m2 g−1 were synthesized using simple, single‐pot, and surfactant‐free aerogel process. Efforts were made to tune the surface area and porosity of CeO2 nanoparticles by changing the concentration of precursors. CeO2 nanoparticles were characterized by TEM, SEM, XRD, N2‐BET, and FTIR. Prepared CeO2 was used to remove As(III) and As(V) from water at variable contaminant concentrations (25–100 ppm) and pH (3–10). The adsorption process found extremely fast for the first few minutes of exposure. CeO2 nanoparticles indicated adsorption capacities of 71.9 and 36.8 mg g−1 against As(III) and As(V), respectively. The adsorption data best fitted with Redlich–Peterson model, depicting monolayer adsorption. The adsorption followed pseudo‐second‐order kinetics and intraparticle diffusion with three‐step diffusion process. The effect of co‐existing anions (H2 PO 4 −, SO 4 2 −, and HCO 3 −) indicated 80–96% reduction in adsorption capacity. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 221–231, 2018 [ABSTRACT FROM AUTHOR]