Smart bifunctional covalent organic frameworks for water treatment: Reversible colorimetric pH detection and photocatalytic removal of pollutants

Covalent Organic Frameworks (COFs) with uniform aperture size, high surface area and tunable structure have been proposed as a potential material in water treatment. In this work, we utilized methoxy based covalent organic frameworks (COF–OMe) at room temperature as a dual-role smart material. For one thing, it can respond to the pH of solutions by visual, colorimetric change. Due to the protonation effect of methoxy groups in its pore skeleton, the fluorescent intensity of COF–OMe went down and the color changed from yellow to black as the pH decreased reversibly. For another, the abundant pores and ordered conjugated structure endowed it with a large surface area and light absorption ability. Therefore, the light-triggered oxidase-mimic porous COF–OMe can be applied in the synergistic removal of organic pollutants with synergistic physical absorption and light degradation. The outstanding and sensitive response to pH, great removal efficiency and dual function made it applied in water treatment with great potential, achieving killing two birds with one stone.