A Facile Ginger Straw-Based Self-Nitrogen-Doped Biochar Activated by NaHCO3: Fast and Efficient Adsorption Toward Food Dyes of Tartrazine and Carmine

Food industry wastewater containing synthetic dyes threatens ecological safety and human health. Therefore, efficient and environmentally friendly adsorbents that can remove synthetic food dyes from wastewater are urgently needed. In this work, a self-nitrogen-doped biochar (GSNBC), used for adsorption of food dyes including carmine and tartrazine, was facilely prepared by employing ginger straw waste as the carbon precursor and NaHCO3 as a mild and relatively benign pore-forming agent via one-step pyrolysis. The as-prepared GSNBC featured well-developed porous structures, a specific surface area of 1712.52 m2 g−1, and rich oxygen- and nitrogen-containing functional surface groups. Particularly, GSNBC performed ultrafast adsorption, with approximately 90% of the equilibrium capacity within 1 min (600.13 mg g−1 and 580.24 mg g−1 for carmine and tartrazine, respectively), and reached adsorption equilibrium at about 10 min. In addition, it exhibited excellent regenerability. The adsorption kinetics and isotherms fit well with pseudo-second-order and Langmuir models. DFT calculations indicated that π–π stacking and hydrogen bonding were mainly responsible for the adsorption. This study presents not only a promising and efficient adsorbent for the remediation of dye-laden food industry wastewater but also a sustainable route for the resource utilization of ginger straw waste.