The method of micro bubbles is widely applied in the fields of water and soil treatment. A novel treatment method of NO in flue gas through a gas–liquid two-phase system formed by micro bubbles is proposed in this study. The system depends on the generation of hydroxyl radicals. The NO removal performance of the micro gas–liquid dispersion system induced by catalysts and O 3 was explored and the reaction pathways were elucidated. Micro bubbles, Fe 2+ , and Mn 2+ in solution improved NO removal performance significantly. Salinity and surfactants affected the removal performance of NO by altering micro bubbles. In the presence of Fe 2+ , the NO removal rate reached 65.2% at pH 5, 75.8% under 0.5 g/L NaCl and 82.1% under 6 mg/L sodium dodecyl sulfate. In the presence of Mn 2+ , the NO removal rate reached 69.2% at pH 5, 83.2% under 0.5 g/L NaCl and 92.3% under 6 mg/L sodium dodecyl sulfate. However, in the presence of both Mn 2+ and Fe 2+ , NO conversion rate was 93.2%. The NO removal rate in the presence of O 3 was further improved under the same conditions. The study provides the basis for the application and development of micro bubbles in flue gas treatments for NO removal. The results can help to solve the problems of high operating cost, large oxidant consumption, secondary pollution, and high energy consumption in traditional NO removal methods. Graphic abstract

Nano-scale graphene has been employed to remove dye pollutants in wastewater treatment. However, engineering concerns associated with inconvenient recollection of nano-graphene and bio-toxicity to human cells significantly hampered its application for environmental protection. In this study, monolithic form of graphene was fabricated by urea assisted self-assembly protocols and applied as an adsorbent to remove model organic pollutant, methylene blue dye (MB). The fabricated material was characterized by scanning electron microscopy (SEM), Fourier transmission infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photo electron spectroscopy (XPS), Thermogravimetric analysis (TGA) and nitrogen adsorption-desorption isotherms. Characterization results show that graphene monolith with tailored macroscopic dimension, highly porous network and active binding sites (e.g., functional groups and aromatic domains) could provide facile mass transfer of pollutant and cost-effective recollection. Adsorptive removal of MB best suited to Langmuir isotherm, pseudo-second-order kinetics, and intra particle diffusion kinetics models. Complete removal of MB (>98%) was achieved under optimum conditions (e.g., alkaline pH, 160 mM of salt and 1 g/L adsorbent dose at 25 degrees C). Removal of MB using monolith was favorable, spontaneous and exothermic adsorption process. Electrostatic and pi-pi staking interactions were identified as major interaction process. A monolithic form of graphene demonstrates the advantageous potential for the safe and efficient treatment of environmental pollutants.