Fabrication of Graphene-Based Nanofiltration Membrane from Fractionated Bamboo Lignin for Dye Removal and Desalination

The growing demand for sustainable and renewable materials has driven extensive research into the use of lignocellulosic biomass as a promising feedstock for the development of advanced biobased membranes. In this present work, we established the viability of producing greener lignin-derived graphene oxide (bGO) and reduced graphene oxide (brGO) membranes from bamboo biomass to fabricate an ordered two-dimensional (2D) laminar channel for nanofiltration. It is imperative to emphasize that our methodology is intricately designed as a sequential strategy for the synthesis of bGO and brGO. This meticulously orchestrated sequence encompasses graphitization followed by consecutive oxidation and reduction processes, all unfolding prior to the subsequent facile layer-by-layer deposition, a pivotal step in membrane fabrication. The as-prepared bGO and brGO membranes showed nanosize pore openings of 1.15 and 0.03 nm and water pathway lengths of 65.15 and 49.09 nm, respectively. Pronounce enhancement by 52- to 60-fold in water permeance was exhibited using the brGO membrane for rejection of organic dyes (methylene blue, MB; direct red 81, DR-81) and salt (sodium sulfate, Na2SO4) solutions compared to lignin-derived graphene oxide (bGO) membrane while the rejections remained comparable at 88, 99, and 57.6% for Na2SO4, MB, and DR-81, respectively. The brGO membrane's remarkable mechanical stability was also proven in an ultrasound test, withstanding up to 2 h without swelling and hence resistant to disintegration under solution immersion conditions. This work provides insight into the fabrication of graphene-based membranes from biomass for highly efficient nanofiltration performance and sheds some light on the transport mechanism within 2D laminar channels.