Preparation Of Nitrogen-doped Porous Carbon By Hydrothermal Carbonization And Its Adsorption Properties

Porous carbon derived from biomass has attracted more and more attention in energy storage,gas adsorption and wastewater treatment due to its low cost and green sustainability.In this paper,chitosan and glucose were used as carbon sources to construct several nitrogen doped porous carbon materials by hydrothermal carbonization,and they were used as adsorbents to capture carbon dioxide and remove organic dyes from organic wastewater.Specifically,the research content of this paper includes the following three aspects:First,Hydrothermal pre-treatment of biomass was effective to produce coal-like hydrochar under mild condition while hydrochar usually had low surface areas restricted the direct use for CO₂capture.Herein,chitosan as a biomass derivative was selected as precursor for carbons via hydrothermal pre-treatment,followed by a mild KOH activation.The effects of additive salt in hydrothermal system and activation temperature on porosity of carbons were studied.The higher temperature would largely enhance porosity,while the additive salt seemed to be slightly adverse as activated at600 and 700? probably due to mesopores introduction in hydrochar.Importantly,the carbons had much larger CO₂uptake as compared with the counterparts without salt,i.e.AC-0-700 and AC-5-700 had CO₂uptake of 2.97 and 3.45 mmol/g at 25?,respectively,even if AC-5-700 had slightly smaller surface areas of 1944 m²/g,suggesting the porosity of carbons was not a single factor in determining uptakes,and the additive salt was efficient to reduce N-species loss during activation.The CO₂uptake on AC-5-600obtained from KOH activation at 600? with additive salt in hydrothermal system was even highly up to 4.41 mmol/g at 25?,ascribing to synergistic effects from high microporosity and moderate N-species.This work indicated that the chitosan hydrochar was suitable precursor for high-surface-areas carbons,providing significant guidance for the further search of solid adsorbents for CO₂capture with low cost,environment friendship and high capture capability.Secondly,we use glucose as carbon source and urea as nitrogen source.The hydrothermal method is also used to prepare hydrothermal carbon,but the temperature of oxidation in air is changed.Then a series of different porous carbon materials are prepared under different carbonization activation temperature with KOH.Among the carbon materials,the specific surface area and pore volume can reach 2832 m²/g and1.48 cm³/g respectively.However,the results show that high specific surface area and pore volume ratio may not lead to high CO₂adsorption.However,the existence of layered pores and higher micropore content will have a positive effect on CO₂adsorption.The CO₂adsorption capacity of the prepared glucose based porous carbon was 9.86 mmol/g and 5.55 mmol/g at 0? and 25? 1 bar,respectively.Finally,we still use glucose as carbon source,urea as nitrogen source,through hydrothermal,air oxidation and KOH activation.The pore structure and surface chemical properties of carbon materials can be controlled by adjusting the activation temperature.However,the carbon materials which were not modified by urea showed more mesoporous structure and smaller specific surface area compared with nitrogen.The specific surface area of nitrogen doped porous carbon can reach 3282m²/g,and the adsorption capacity of Rhodamine B can reach 5181 mg/g at room temperature.