Synthesis Of Macroalgae-based Porous Graphene And Their Application In C0₂ Capture

Porous graphene is a new type of carbon material,for the high specific surface area,good thermal conductivity and chemical stability,are considered to be one of the most promising CO₂ adsorbents.At present,the shortage of graphite,the high requirement of reaction condition,the high cost,the environmental issue and the large-scale industrial production issue in the preparation process are prompting researchers to find a low-cost,environmentally friendly method for preparing porous graphene.In this paper,macroalgae?S.Horneri?exhibited several significant advantages including abundant resources,cost effective and renewability,and was considered as one of the most promising raw material for the production of graphene.Based on chemical compositions,porous graphene was prepared by KOH chemical activation and iron salt catalytic,respectively.The effects of conditions?alkali carbon ratio,metal impregnation ratio,activation temperature?on the formation of graphene,pore structure and surface chemistry.Moreover,the CO₂ adsorption properties of porous graphene were tested.The main results are as follow:?1?Compared to terrestrial plants,S.Horneri had higher ash content and lower fixed carbon content,while the higher nitrogen content and richer metal ions of S.Horneri promoted the formation of porous graphene in the activation process;compared to macroalgae,S.Horneri had lower ash content and higher fixed carbon content,showing potential as an ideal precursor for the preparation of carbon materials.?2?The optimum process condition for the preparation of porous graphene by KOH activation was the carbonization temperature of 400°C,the alkali carbon ratio of 4:1 and the activation temperature of 850°C.The porous graphene displayed high specific surface area?¹411 m²/g?,pore volume?¹.16 cm³/g?,and abundant microporous and mesoporous structures.And the as-prepared porous graphene exhibited CO₂ uptake of 2.78 mmol/g at 30?and 1 bar.?3?Nitrogen-doped porous graphene produced from S.Horneri was prepared by combining the iron salt catalysis?Fe?NO₃?₃·9H₂O?and subsequent KOH activation.During the preparation of nitrogen-doped porous graphene,the S.Horneri could be as a carbon source and nitrogen source,and exhibited strong adsorption of metal ions.The optimum process condition was the carbonization temperature of 400°C,the metal impregnation amount of 10 wt%and the activation temperature of 750°C.The as-prepared graphene consisted of 3-7 multilayers,and displayed utrahigh specific surface area?²311 m²/g?and abundant nitrogen content?1.58 wt%?.And the CO₂uptake capacity reached 4.35 mmol/g at 1 bar and 30?by the as-prepared nitrogen-doped porous graphene.?4?The CO₂ adsorption rate equations of the above two porous graphene materials were consistent with the intraparticle diffusion model,indicating that the CO₂ adsorption was mainly controlled by the intraparticle diffusion resistance.After three adsorption/desorption cycles,the CO₂ adsorption capacity was still 2.09 and 3.26mmol/g,respectively.?5?KOH activation required a large amount of KOH?KOH/C=4:1?,and the prepared porous graphene had low specific surface area and CO₂ adsorption capacity.Due to the catalyzed graphitization of iron salt,the amount of KOH?KOH/C=2:1?reduced siginificantly by the iron salt catalysis,and the specific surface area and CO₂adsorption capacity of porous graphene increased to 2311 m²/g and 4.35 mmol/g,respectively.In addition,S.Horneri played a role as a template,the iron salt and KOH contributed to the catalyze graphitization of S.Horneri and strip graphite to form graphene in the formation of graphene.This work has great significance for the large-scale preparation of graphene and its application in CO₂ adsorption.It also plays an important role in improving the high value-added utilization of macroalgae,which promotes the development of ecological restoration industry of macroalgae.