A superhydrophobic, superoleophilic and eco-friendly polycaprolactone composite (PCL_C) membrane with a hierarchical microsphere structure was developed by alternated electrospinning/electrospraying technology. The PCL_C membrane was subtly designed with two parts to imitate the lotus leaf structure: low surface energy SiO₂ nanoparticles on the surface of PCL smooth microspheres (PCL_M) imitate the hydrophobic bio-wax of the lotus leaf surface, and PCL porous microspheres (PCL_M-porous) imitate the surface nano-protrusions of the lotus leaf. The average size of the potholes on the PCL_M-porous surface was only about 300 nm. The combination of small potholes and the hierarchical structure of the PCL_C and SiO₂ nanoparticles contributed to the superhydrophobicity and superoleophilicity of the PCL_C membrane. The water contact angle (WCA) of PCL_C could reach 162.0 ± 1.5°. Compared with membranes based on PCL_M-porous (WCA = 148.9 ± 1.2°) and 4% SiO₂ nanoparticles on PCL_M (WCA = 158.6 ± 2.3°), the PCL_C membrane not only showed higher superhydrophobicity but also ultra-high oil–water separation efficiency, oil flux and stability. Most importantly, the PCL_C membrane exhibited excellent oil adsorption performance for four different oils with different densities, and the separation efficiency remained ultrahigh (>99.93%) even after 10 cycles. This innovative work may provide an effective strategy for the design of biomimetic biopolymers with promising applications in the field of eco-friendly separators.

Chitosan/cellulose acetate (CS/CA) used as a biopolymer systema, with the addition of TiO₂ as photocatalyst (C-T/CA) were fabricated by alternating electrospinning/electrospraying technology. The uniform dispersion of TiO₂ and its recovery after the removal of methyl orange (MO) was achieved by incorporating TiO₂ in CS electrosprayed hemispheres. The effects of pH values, contact time, and the amount of TiO₂ on adsorption and photocatalytic degradation for MO of the C-T/CA were investigated in detail. When TiO₂ content was 3 wt %, the highest MO removal amount for fiber membranes (C-T-3/CA) reached 98% at pH value 4 and MO concentration of 40 mg/L. According to the data analysis, the pseudo-second-order kinetic and Freundlich isotherm model were well fitted to kinetic and equilibrium data of MO removal. Especially for C-T-3/CA, the fiber membrane exhibited multiple layers of adsorption. All these results indicated that adsorption caused by electrostatic interaction and photocatalytic degradation were involved in the MO removal process. This work provides a potential method for developing a novel photocatalyst with excellent catalytic activity, adsorbing capability and recycling use.

Chitosan (CS) stacking mats with excellent performance for adsorption of copper ions (Cu(II)) in wastewater were fabricated by alternating electrospinning/electrospraying. The hierarchical structure of the stacking membranes was designed by CS micro-hemispheres sandwiched between CS fibers. The CS stack membranes prepared by the electrospinning technology could effectively increase the specific surface area, and thus, facilitate the adsorption of copper ions. CS stacking membranes with three layers reached adsorption equilibrium within 60 min, and had a maximum absorbance of 276.2 mg/g. The absorbance performance was superior to most of the reported CS adsorbents. Compared with CS fiber mats which were dominated by CS chemical structure during adsorption, the stacking structure of CS membranes contributed to the high efficient capability, and exhibited the multilayer adsorption behavior. This study may develop a promising method for the design of environmentally-friendly natural polymer adsorbents to remove Cu(II) in wastewater.