Synergism of Fe and Al salts for the coagulation of dissolved organic matter: Structural developments of Fe/Al-organic matter associations.

Dissolved organic matter (DOM) is distributed ubiquitously in water bodies. Ferric ions can flocculate DOM to form stable coprecipitates; however, Al(III) may alter the structures and stability of Fe-DOM coprecipitates. This study aimed to examine the coprecipitation of Fe, Al, and DOM as well as structural developments of Fe-DOM coprecipitates in relation to changes in Fe/Al ratios and pHs. The results showed that the derived Fe/Al/DOM-coprecipitates could be classified into three categories: (1) at pH 3.0 and 4.5, the corner-sharing FeO6 octahedra associated with Fe-C bonds with Fe/(Fe + Al) ratios ≥0.5; (2) the Fe-C bonds along with single Fe octahedra having Fe/(Fe + Al) ratios of 0.25; (3) at pH 6.0, the ferrihydrite-like Fe domains associated with Fe-C bonds with Fe/(Fe + Al) ratios ≥0.5. At pH 3.0, the Fe and C stability of the coprecipitates increased with increasing Al proportions; nonetheless, pure Al-DOM coprecipitates were unstable even if they exhibited the maximum ability for DOM removal. The associations of Al-DOM complexes and/or DOM-adsorbed Al domains with external surfaces of Fe domain or Fe-DOM coprecipitates may stabilize DOM, leading to lower C solubilization at pH 4.5. Although the preferential formation of Fe/Al hydroxides decreased Fe/Al solubilization at pH 6.0, adsorption instead of coprecipitation of DOM with Fe/Al hydroxides may decrease C stabilization in the coprecipitates. Aluminum cations inhibit DOM releases from Fe/Al/DOM-coprecipitates, promoting the treatment and reuse efficiencies of wastewater and resolving water shortages. This study demonstrates that Al and solution pH greatly affect the structural changes of Fe-DOM coprecipitates and indirectly control the dynamics of Fe, Al, and C concentrations in water.

Cross-redox and simultaneous removal of Cr(VI) and As(III): Influences of Fe(II), Fe(III), oxalic acid, and dissolved organic carbon.

Hexavalent chromium [Cr(VI)] and arsenite [As(III)] are hazardous to both human and ecosystem. While their cross-redox reaction decreases both their toxicities, the interferences from ubiquitous substances like Fe (Fe(II) and Fe(III)) and organic compounds (oxalic acid and soil-extracted dissolved organic carbon (DOC)) on such interaction are rarely reported; thence, inspires the investigation in this study. Results showed that the cross-redox, in the absence of interfering substances, only occurred at pH≤2.0, with reaction orders of 0.676 and 0.783 in respect to the concentration of Cr(VI) and As(III). The pseudo-reaction constant, k', of such reaction was recorded at 0.087 m1.377/(mmol0.459 min). With the addition of Fe(II), the rate of Cr(VI) reduction is promoted in conjunction with suppressed As(III) oxidation. Upon neutralizing to pH 6.0, such reduced Cr can be entirely removed via Fe(II)-assisted adsorption and/or co-precipitation. Meanwhile, the elimination of aqueous As is relatively inferior (36 %), attributed to the largely preserved As(III), which is less susceptible to adsorptive/co-precipitative removal. Unlike Fe(II), Fe(III) did not alter Cr(VI)-As(III) cross-redox path, but triggered high adsorptive and/or co-precipitative removals of Cr and As (90 %). In contrast, both organically-altered systems exhibits plummeted As(III) oxidation, under distinctive mechanisms: oxalic acid competes with As(III) in the redox interactions while DOC reduces As(V) into As(III). Also, DOC would undergo complexion with metals and/or blocked the adsorption or co-precipitation sites, leading to even lower Cr and As precipitation. This study unravelled the interference from ubiquitous species in the co-removal of Cr(VI) and As(III), which provides insightful remediation for heavy metal contaminations.

Use 3-D tomography to reveal structural modification of bentonite-enriched clay by nonionic surfactants: Application of organo-clay composites to detoxify aflatoxin B1 in chickens.

Although nonionic surfactants are relatively eco-friendly compared with cationic and anionic surfactants, few studies have investigated their application in modified clay. Herein we prepared organo-clay composites (OCCs) by mixing bentonite-enriched clay (BEC) with nonionic surfactants (Brij 30 and Igepal CO-890) and determined if these modifications would enable chickens to detoxify aflatoxin B1 (AFB1). For the first time, in situ three-dimensional (3-D) microstructures of modified BEC was characterized in suspension using transmission X-ray microscopy. Although X-ray diffraction patterns indicated the expansion in the spacing between planes of atoms (basal spacing) of surfactant-modified BEC, 3-D images indicated shrinkage in its microscale porous framework with increasing surfactant additions from 1 to 30 wt%. Such declining trends in porous dimensions caused by the dehydration in interlayer galleries of clays positively correlated with sorption amounts of AFB1 on OCCs. After chickens had consumed amended feeds for 11 weeks, AFB1 concentrations in liver, kidney, and plasma were significantly lower than in the control treatment. Thus, we suggest using BEC with 1 wt% surfactant addition, an amendment to chicken feeds, to detoxify AFB1. Modifying BEC with nonionic surfactants show the promise in mitigating AFB1 accumulation in chickens, which should improve food safety and reduce environmental contamination.

Improving resolution of second harmonic generation microscopy via scanning structured illumination.

Second harmonic generation microscopy (SHGM) is a well-known technique for examining the noncentrosymmetric structures in biomedical research. However, without real-state transitions, fluorescence-based superresolution methods cannot be applied. To improve the resolution, fringe-scanning SHGM (FS-SHGM), which combines SHGM with structured illumination based on point-scanning, is introduced in this paper. The scanning path was modulated to generate illumination patterns. For the coherent parts of SHG signals, a mathematical model of image formation and reconstruction was established. Both simulations and experiments showed a resolution improvement factor of ~1.4 in the lateral and 1.56 in the axial directions for chicken tendons and mouse skin.