Post-KOH activation of nitrogen-containing porous carbon with ordering mesostructure synthesized through a self-assembly

N-doped and activated porous biochar derived from cocoa shell for removing norfloxacin from aqueous solution: Performance assessment and mechanism insight

Environmental pollution has worsened as a result of antibiotic overuse. Nitrogen doping of biochar increases its ability to adsorb antibiotics and has been widely applied as an adsorbent. In this study, we synthesized nitrogen-doped biochar (N-A) from cocoa shell wastes calcined with urea and sodium bicarbonate (NaHCO₃) as nitrogen sources and green activators, respectively. An analysis of the biochar morphology, structure, specific surface area, and functional groups provided an understanding of its properties. As indicated by increased surface area, micropores, and surface functional groups, biochar was enhanced in its performance for norfloxacin adsorption when activated using NaHCO₃ and nitrogen doped. Adsorption experiments revealed that N-A biochar at 700 and 400 °C had a high adsorption capacity for NOR of 134 mg/g (N-A-CSB700) and 112.31 mg/g (N-A-CSB400) when compared to pristine biochar at 59.27 mg/g (CSB700) and 56.34 mg/g (CSB400), indicating that N-A doped modification on biochar greatly improved adsorption capacity. The Langmuir model demonstrated better NOR adsorption isotherms. The pseudo-second order and Elovich models closely followed the adsorption kinetics. Further investigations were conducted to determine how environmental factors influence biochar interaction with NOR. The results indicated a stable NOR removal efficiency was kept at a wide pH range, whereas the ionic strength inhibited the NOR adsorption process. The investigation into the sorption mechanism revealed that pore filling, H-bonding, π-π EDA interactions, ion exchange, and electrostatic attraction may all be implicated in the NOR adsorption process. Specifically, pore filling played the dominant role for N-A-CSB700, while N-A-CSB400 sorption occurred mainly via H-bonding. Since N-A-CSB700 doped biochar combines high adsorption capacity with a low inhibition effect of environmental factors (Na⁺/Ca²⁺), it has a high potential for future practical applications as an environmentally sustainable alternative. It uses low-cost solid waste to produce an adsorbent to cope with emerging contaminants such as antibiotics.

Synthesis of N-doped hierarchical porous carbon with excellent toluene adsorption properties and its activation mechanism

Typical organic pollutants from coal-combustion flue gas such as volatile organic compounds (VOCs) need to be effectively controlled. This work synthesized a series of nitrogen-doped hierarchical porous carbons (NHPCs) by one-step activation with various proportions of cellulose, (NH₄)₂C₂O₄ and KHCO₃/NaHCO₃. The NHPCs have a high specific surface area and pore volume up to 2816 m²/g and 1.413 cm³/g as well as a hierarchical porous structure with micro-meso-macropores distribution. The dynamic adsorption tests of toluene at 600 ppm showed that NHPCs have a high adsorption capacity up to 585 mg/g (NHPC(K)131), this was about 3 times more than that of AC (208 mg/g), and is a better absorbent compared to many other carbon adsorbents. The porous characteristics and toluene adsorption properties of NHPCs improved along with the fluctuation of the proportions of raw materials and active agents. The micropore size of the material is the main factor that affecting the toluene adsorption capacity. The analysis of toluene dynamic adsorption breakthrough curves revealed that NHPCs had great toluene adsorption kinetics with high adsorption rate constants and short mass transfer zone. The excellent toluene adsorption kinetics of NHPCs can be attributed to the hierarchical porous structure. The abundant 2-10 nm mesopores and macropores of NHPCs act as mass transfer channels for toluene molecules. The XPS analysis showed that the NHPCs have nitrogen doping up to 6.71% (NHPC(Na)161) and they effectively promote toluene adsorption. The nitrogen doping mechanism can be attributed to the reactions between cellulose pyrolysis substances and NH₃ which decomposed from (NH₄)₂C₂O₄. Moreover, the pore forming reactivity of KHCO₃ is better than that of NaHCO₃ in the NHPCs activation process.

Rapid removal of nitrate from liquid dairy manure by cationic poly (vinyl alcohol-co-ethylene) nanofiber membrane

Elevated levels of nitrate in surface water is a leading concern, which impacts human and animal health, and controlling it requires improved and sustainable methods capable of removing nitrate anions from source waste water to reduce nitrate anions transport to environment. In liquid dairy manure, nitrogen content can vary from 200 to 600 ppm and the transport of manure nitrogen into ambient water through hydrologic processes has a potential to exceed the maximum contaminant level limit (10 ppm) of nitrate nitrogen for regulated public water systems. Dairy manure is considered as a reservoir of nitrate. This research investigates on the determination of optimal designing of nanofiber membrane to remove nitrate anions from liquid dairy manure. A cationic poly (vinyl alcohol-co-ethylene) nanofiber membrane (EVOH) NFM was grafted via UV with 2-(methacryloyloxy) ethyl trimethylammonium chloride (DMAC) monomers. The adsorption efficiency of nitrate by the membrane was determined on liquid manure of dairy lagoons located in Central Valley of California. Initial nitrate concentrations in dairy manure varied from 75 to 100 ppm. Results showed that nitrate in dairy water was removed by 70% in 40 min. Tortuous structure and chemical stability of membrane resulted in nitrate dynamic binding capacity of 40 mg g^-1. Furthermore, it exhibits efficient reusability without significant changes in its performance using 0.5 M sodium hydroxide solution for nitrate desorption. Results showed that change in pH, and multi-anion conditions had limited effects on nitrate removal efficiency, and EVOH NFM can be a viable option to remove nitrate of liquid manure. This could be used for mitigating transport of excess nitrate from manure to environment. Overall, the results suggest that EVOH-g-DMAC NFM is efficient, low-cost (13 USD/m³) and recyclable material for sustainable removal of nitrate from dairy manure wastewater without requiring any ionic strength or pH adjustment.