In this study, sulfidized nanoscale zerovalent iron (S-nZVI) supported by oyster shell (OS) powder (S-nZVI@OS) was synthesized by controlling the initial S/Fe ratios (0.1–0.5) to explore the potential synergistic effects during the adsorption and reduction of Cr (VI). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses showed that Fe (0) and FeS were well dispersed on the OS surface. Furthermore, the stability of S-nZVI@OS composite was higher than that of nZVI, which was proved by the material ageing experiment. The effects of different S/Fe molar ratios, time, temperature, the initial concentration of Cr (VI), and initial pH on the removal efficiency were also studied. The results indicated that with the increase of the S/Fe molar ratio, the removal capacity of Cr (VI) first increased rapidly and then decreased slowly. Batch experiments showed that an optimal S/Fe molar ratio of 0.2 offered a Cr (VI) removal capacity of about 164.7 mg/g at pH 3.5. The introduction of S can not only promote Cr (VI) reduction but also combine with Cr (III) by forming precipitate on S-nZVI@OS mainly as CrxFe(1−x) OOH and Cr2S3. The adsorption thermodynamics and kinetics demonstrated that the Langmuir model and pseudo-second-order kinetics model can describe the adsorption isotherms and kinetics. These results suggest that S-nZVI@OS is an effective and safe material for removing Cr (VI) from aqueous solutions.
The present study investigated the removal of As(III) from low-arsenic water through adsorption on amorphous mesoporous TiO 2 . The mesoporous TiO 2 adsorbent size was 3.92 nm as calculated by adsorption average pore width. The Brunauer-Emmett-Teller surface area was 205 m 2 /g. A 0.2 g adsorbent treatment during five hours resulted in less than 4 lg/L remaining As(III) in the water, and nearly 84% of As(III) in the solution were removed in only 20 min. The As(III) adsorption kinetics data were well described by the pseudo-second-order model. The maximum adsorption pH value of 9.3 coincided with the first pK 1 dissociation constant of H 3 AsO 3 of 9.22. The Dubinin-Radushkevich and Langmuir isotherms provided maximum adsorption capacity of 4.57 and 4.79 mg/g, respectively, under low equilibrium concentration. These values possibly indicate the excellent capacity of amorphous mesoporous TiO 2 on As(III) removal from low-arsenic water. Given by the b-value of Langmuir isotherm under different pH, the average standard Gibbs free energy changes (ΔG o ) was -11.6 kJ mol À1 , which indicated spontaneous adsorption.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.