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Combining functional response materials into colloidal photonic crystals is an accepted encryption strategy for information security. Here, bilayer inverse heterostructure photonic crystals that enable instantaneously transparentizing of the top layer and simultaneously releasing the reflected light of the bottom layer when exposed to ethanol are reported. The transition can quickly return to its original state after the evaporation of ethanol. In addition, the bilayer film is responsive to water, which shows redshift of the bandgap position. The mechanism of the design involves optical scattering and diffraction in the fabricated periodic nanostructures and uses the infiltration and capillary evaporation of fluids with low surface tension to realize the spectral diversity of reflectance. The effects of scattering and color superposition of the upper layer can be obliterated and re-established for the fact of the infiltration and capillary evaporation of fluids with low surface tension; meanwhile, it provisionally displays the pattern of the bottom layer. Multiple reversible ways to hide and display information could be easily realized by these characteristics. Reconfigurable bilayer inverse heterostructure photonic crystals simultaneously provide a simple and sensitive optical technique for investigating the intriguing encryption effects at the nanoscale.

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Combining responsive colloidal photonic crystals into invisible wettability patterns is important in steganography and watermarking for information encoding and decoding. Using a bilayer photonic crystal as a regionally functionalized porous carrier, a dual‐responsive surface with tunable wettability, reversible switching between wetting and no wetting, and responsivity to pressure and solvents are reported. The mechanism of the design involves reversible switching of micropore shapes and optical diffraction in the fabricated periodic nanostructures, and uses the infiltration and capillary evaporation of fluids to realize the spectral diversity of reflectance. It generates different invisible wettability patterns that are regulated by induced pressure and the Donnan equilibrium osmotic pressure. Immersion of the sample in water induces the varying degrees of infiltration and immediately displays multiple colors. It enables instantaneously transparentizing the full infiltration parts of the top layer and simultaneously releasing the reflected light of the corresponding bottom layer. Moreover, those invisible patterns can be reset by wiping with ethanol. Multiple ways to encode and reveal invisible complex information can easily be realized due to these characteristics. This work opens a new avenue for encoding complex information in a single material platform and extends the design approach of invisible patterns for information coding.

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a b s t r a c tHigh sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3e6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01 mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.