Durable underwater superoleophobic hydrogels for oil- and Cu(II)-containing water purification

Purifying oily and Cu²⁺ ions-containing waste waters is still a challenge over the world. Traditional adsorption materials struggle to efficiently remove both pollutants. In this study, an underwater superoleophobic polyvinyl alcohol (PVA) and tannic acid (TA) based PVA-TA hydrogel was first prepared for the removal of both oils and Cu(II) ions. CaCO₃ was subsequently incorporated to enhance the mechanical properties and Cu²⁺ adsorption capacities through electrostatic attractions. Both PVA-TA and PVA-TA/CaCO₃ hydrogel-intermediated materials exhibited underwater superoleophobic and can be used to purify oily water, achieving separation efficiencies exceeding 99.20 % even after 60 cycles. Furthermore, these materials demonstrated excellent self-cleaning performance against viscous oil. The addition of CaCO₃ can also improve the mechanical durability and chemical resistance of the PVA-TA under robbing, varying pH levels, and saline conditions. Moreover, the maximum Cu(II) adsorption capacity and removal efficiency of the PVA-TA/CaCO₃ are 62.11 mg g⁻¹ and 86.71 %, respectively; surpassing those of the PVA-TA due to increased micro-hole density and electrostatic interactions between CaCO₃ and Cu(II). These porous materials can be further applied to purify real-life wastewater, indicating their potential for efficient practical wastewater treatment. This work not only provides effective porous materials for purifying oily and Cu²⁺-containing waste waters but also improves a simple method for preparing underwater superoleophobic hydrogel-intermediated materials.