Construction of Waste Paper-Chitosan-Based Membranes with pH-Tunable Surface Charge for Efficient Separation of Oil-in-Water Emulsion and Dye

Developing a cost-effective, versatile, biodegradable, and biobased membrane is crucial for the sustainable treatment of complex wastewater. In this work, a multifunctional membrane was fabricated from polydopamine-modified waste paper (WP@PDA) and hydrothermal carbonized chitosan (HTCC), through simple vacuum filtration. This membrane demonstrated high efficiency in separating oil-in-water emulsions and allowed for the in situ dye removal under controllable pH conditions. The results showed that the as-prepared WP@PDA/HTCC membrane exhibited superhydrophilic, oil-resistant, and pH-tunable surface charge features. With the weight ratio of WP@PDA and HTCC of 6:2, it displayed optimal mechanical properties and structural stability in aqueous environments. As expected, the WP@PDA/HTCC membrane achieved outstanding performance in separating different oil-in-water emulsions at 0.05 bar followed by the satisfactory flux of approximately 2400 L m–2 h–1 bar–1 and separation efficiency of around 99.5%. Furthermore, the abundant functional groups on the WP@PDA and HTCC surface also endowed this membrane with a high removal capability for both cationic and anionic dyes. It can efficiently eliminate methyl orange (MO) and methylene blue (MEB) from dye-contaminated wastewater mainly through electrostatic interactions. Even after filtering 1550 L m–2 of MO and 1650 L m–2 of MEB simulated wastewater using WP@PDA/HTCC membrane, its removal efficiencies toward both dyes remained above 90.0%. Interestingly, the WP@PDA/HTCC-1 membrane presented bidirectional controlled dye separation behaviors for the dye mixture under the suitable solution pH due to its pH-tunable surface charge feature. Most importantly, the as-prepared membrane showed excellent reusability and high resistance against harsh chemical corrosions without losing its properties. Therefore, the as-prepared WP@PDA/HTCC-1 membrane could be a promising material for complex wastewater treatment.