In-depth understanding of transport behavior of sulfided nano zerovalent iron/reduced graphene oxide@guar gum slurry: Stability and mobility.

Nanoscale zero-valent iron (NZVI), which has the advantages of small particle size, large specific surface area, and high reactivity, is often injected into contaminated aquifers in the form of slurry. However, the prone to passivation and agglomeration as well as poor stability and mobility of NZVI limit the further application of this technology in fields. Therefore, sulfided NZVI loaded on reduced graphene oxide (S-NZVI/rGO) and guar gum (GG) with shear-thinning properties as stabilizers were used to synthesize S-NZVI/rGO@GG slurries. SEM, TEM, and FT-IR confirmed that the dispersion and anti-passivation of NZVI were optimized in the coupled system. The stability and mobility of the slurry were improved by increasing the GG concentration, enhancing the pH, and decreasing the ionic strength and the presence of Ca2+ ions, respectively. A modified advection-dispersion equation (ADE) was used to simulate the transport experiments considering the strain and physicochemical deposition/release. Meanwhile, colloidal filtration theory (CFT) demonstrated that Brownian motion plays a dominant role in the migration of S-NZVI/rGO@GG slurry, and the maximum migration distance can be increased by appropriately increasing the injection rate. Extended-Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the excellent stability and migration of S-NZVI/rGO@GG slurry mainly came from the GG spatial forces. This study has important implications for the field injection of S-NZVI/rGO@GG slurry. According to the injection parameters, the injection range of S-NZVI/rGO@GG slurry is effectively controlled, which lays the foundation for the promotion of application in actual fields.

Response surface design for removal of Cr(VI) by hydrogel-supported sulfidated nano zero-valent iron (S-nZVI@H).

In this study, a new sulfidated nanoscale zero-valent iron (S-nZVI) supported on hydrogel (S-nZVI@H) was successfully synthesized for the removal of chromium (Cr) (VI) from groundwater. The surface morphology, dispersion phenomenon and functional groups of novel S-nZVI@H were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Box-Behnken design (BBD) optimization technology based on response surface methodology (RSM) is applied to demonstrate the influence of the interaction of S-nZVI@H dose, initial Cr(VI) concentration, contact time, and initial pH with the Cr(VI) removal efficiency. The analysis of variance results (F = 118.73, P < 0.0001, R2 = 0.9916) show that the quadratic polynomial model is significant enough to reflect the close relationship between the experimental and predicted values. The predicted optimum removal conditions are: S-nZVI@H dose 9.46 g/L, initial Cr(VI) concentration 30 mg/L, contact time 40.7 min, and initial pH 5.27, and the S-nZVI@H dose is the key factor affecting the removal of Cr(VI). The predicted value (99.76%) of Cr (VI) removal efficiency is in good agreement with the experimental value (97.75%), which verifies the validity of the quadratic polynomial model. This demonstrates that RSM with appropriate BBD can be utilized to optimize the design of experiments for removal of Cr(VI).

Specialized cockroach pollination in the rare and endangered plant Vincetoxicum hainanense in China.

PREMISE: Species of Apocynaceae are pollinated by a diverse assemblage of animals. Here we report the first record of specialized cockroach pollination in the family, involving an endangered climbing vine species, Vincetoxicum hainanense in China. Experiments were designed to provide direct proof of cockroach pollination and compare the effectiveness of other flower visitors. METHODS: We investigated the reproductive biology, pollination ecology, pollinaria removal, pollinia insertion, and fruit set following single visits by the most common insects. In addition, we reviewed reports of cockroaches as pollinators of other plants and analyzed the known pollination systems in Vincetoxicum in a phylogenetic context. RESULTS: The small, pale green flowers of V. hainanense opened during the night. The flowers were not autogamous, but were self-compatible. Flower visitors included beetles, flies, ants and bush crickets, but the most effective pollinator was the cockroach Blattella bisignata, the only visitor that carried pollen between plants. Less frequent and effective pollinators are ants and Carabidae. Plants in this genus are predominantly pollinated by flies, moths and wasps. CONCLUSIONS: Globally, only 11 plant species are known to be cockroach-pollinated. Because their range of floral features encompass similarities and differences, defining a "cockroach pollination syndrome" is difficult. One commonality is that flowers are often visited by insects other than cockroaches, such as beetles, that vary in their significance as pollinators. Cockroach pollination is undoubtedly more widespread than previously thought and requires further attention.