Zhongmin Liu

Enhanced Cr(VI) removal from aqueous solutions using Ni/Fe bimetallic nanoparticles: characterization, kinetics and mechanism

In this study, Ni/Fe bimetallic nanoparticles were prepared by a liquid-phase chemical reduction method and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) with image mapping, transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The as-prepared Ni/Fe material was applied to remove Cr(VI) via a coupled adsorption/reduction process. It was found that Cr(VI) removal followed pseudo-second-order reaction kinetics. Acidic pH favored the efficient removal of Cr(VI) due to the abundance of reactive H˙ species that were mediated by the Ni catalyst. XPS studies demonstrated that Cr(VI) removal on the surface of the bimetallic nanoparticles was a synergistic adsorption and reduction process. The introduction of nickel to nZVI not only controls iron passivation but also facilitates the efficient flow of electron transfer between iron and Cr(VI), and thus the efficient reduction of Cr(VI) to Cr(III). Hydroxylated Cr(OH)3 and co-precipitation of CrxFe1−x(OH)3 were the final products of Cr(VI) removal by the Ni/Fe material.

Synthesis of magnetic orderly mesoporous α-Fe2O3 nanocluster derived from MIL-100(Fe) for rapid and efficient arsenic(III,V) removal

A calcination time regulation method has been unprecedentedly used to adjust the orderly meso-structure of novel α-Fe2O3 nanoclusters derived from MIL-100(Fe) (MIL: Materials of Institute Lavoisier). The as-synthesized magnetic orderly mesoporous α-Fe2O3 nanoclusters were characterized by XRD, SEM, TEM, TGA, N2 adsorption-desorption isotherms, VSM, Zeta potential, FTIR and XPS. The 6h calcinated α-Fe2O3 nanocluster exhibited the optimal properties, including the high specific surface area and the orderly mesoporous properties, which facilitate the arsenic(III,V) adsorption capacity. The maximum adsorption capacities of As(III) and As(V) were 109.89 and 181.82mgg-1, respectively, and adsorption equilibrium can be reached just within 30min. The kinetics intra-particle diffusion model and adsorption isotherms reveal that the adsorption rate is controlled by pore diffusion and the adsorption process belongs to Langmuir monolayer adsorption. These results indicate that the orderly mesoporous structure of α-Fe2O3 nanoclusters plays a key role in rapid and efficient adsorption for arsenic(III,V). Meanwhile, adsorption mechanism verifies that arsenic can react with active sites (Fe-OH) to form complexes by Fe-O-As bond. Moreover, α-Fe2O3 nanocluster can be separated easily due to its excellent magnetism. Above all, the magnetism orderly mesoporous α-Fe2O3 nanocluster is a promising adsorbent for emergent treatment of arsenic in practice.

Effective elimination of As(III) via simultaneous photocatalytic oxidation and adsorption by a bifunctional cake-like TiO2 derived from MIL-125(Ti)

A bifunctional cake-like TiO2 was successfully synthesized via calcination of MIL-125(Ti) at a suitable temperature by a one-step method and was applied for As(III) removal by simultaneous photocatalytic oxidation and adsorption. The as-synthesized samples were characterized by XRD, TGA/DSC, SEM, TEM, N2 adsorption–desorption isotherms, PL spectra, photocurrent, FTIR and XPS. The effects of calcination temperature on the specific surface areas of the samples, transformation of the TiO2 crystal phase and properties of As(III) removal were investigated. The results showed that higher calcination temperature resulting in a lower specific surface area and more transformations of the TiO2 crystal phase from anatase to rutile. The TiO2 calcined at 380 °C (MIL-125(Ti)-380 °C) exhibited excellent properties for As(III) removal, including photocatalytic oxidation of As(III) and simultaneous adsorption of the generated As(V). In addition, MIL-125(Ti)-380 °C could be reused at least four times without significant reduction in the photocatalytic oxidation and adsorption performances. The excellent photocatalytic oxidation and adsorption abilities of MIL-125(Ti)-380 °C can be attributed to the synergistic effects of strong photogenerated electron–hole separation and high specific surface area. The bifunctional cake-like TiO2 provides a wonderful strategy to remove As(III) completely from contaminated water using a single step.