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A novel sol–gel dip‐coating process to fabricate nanocrystalline TiO2 photocatalytic membranes with a robust hierarchical mesoporous multilayer and improved performance has been studied. Various titania sols containing poly(oxyethylenesorbitan monooleate) (Tween 80) surfactant as a pore‐directing agent to tailor‐design the porous structure of TiO2 materials at different molar ratios of Tween 80/isopropyl alcohol/acetic acid/titanium tetraisopropoxide = R:45:6:1 have been synthesized. The sols are dip‐coated on top of a homemade porous alumina substrate to fabricate TiO2/Al2O3 composite membranes, dried, and calcined, and this procedure is repeated with varying sols in succession. The resulting asymmetric mesoporous TiO2 membrane with a thickness of 0.9 μm exhibits a hierarchical change in pore diameter from 2–6, through 3–8, to 5–11 nm from the top to the bottom layer. Moreover, the corresponding porosity is incremented from 46.2, through 56.7, to 69.3 %. Compared to a repeated‐coating process using a single sol, the hierarchical multilayer process improves water permeability significantly without sacrificing the organic retention and photocatalytic activity of the TiO2 membranes. The prepared TiO2 photocatalytic membrane has great potential in developing highly efficient water treatment and reuse systems, for example, decomposition of organic pollutants, inactivation of pathogenic microorganisms, physical separation of contaminants, and self‐antifouling action because of its multifunctional capability.

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The small size and high surface-to-volume ratio makes nanoiron attractive for in situ remediation of groundwater contaminants that are susceptible to reductive transformation, e.g. trichloroethylene (TCE). Nanoiron synthesized from borohydride reduction of dissolved iron is the most widely studied. Its reactivity with chlorinated organics such as trichloroethylene (TCE) is unique compared to other nanoiron and to iron filings that are typically used for in situ groundwater remediation, e.g. (1) higher surface-area normalized TCE dechlorination reaction rate constants, (2) the formation of saturated reaction products, and (3) higher reaction rates in the presence of H2. The objectives of this study were to confirm the ability of monometallic Fe(B) to activate and use H2 for TCE hydrodechlorination and to determine how the nanoiron chemical composition and the degree of crystallinity influence nanoiron reactivity with TCE. Fresh (Fe(B)), partially oxidized (Fe(B)ox), and annealed (Fe(B)cr) nanoiron samples made from borohydride reduction of dissolved Fe(II) in a water/methanol solution were characterized by HRTEM, XRD, XPS, and N2-BET. The TCE dechlorination rate and products and the dissolved iron and boron released during reaction with TCE were measured. Fe(B) and Fe(B)ox were poorly ordered and could activate and use H2 to reduce TCE to ethane. Fe(B)cr was crystalline and could not activate and use H2 and reduced TCE to acetylene. The poorly ordered structure rather than the presence of boron (up to 5 wt %) provided the ability of Fe(B) and Fe(B)ox to activate and use H2 for TCE dechlorination. Fe(B) and Fe(B)ox underwent oxidative dissolution during TCE dechlorination, and the Fe0 in the particles was fully accessible. Particle dissolution suggests that normalizing the observed reaction rate constants with the measured specific surface area for comparison with other types of Fe0 may be inappropriate.