Muhammad Irfan Maulana Kusdhany

Engineering the pore structure of biomass‐derived activated carbons is critical for optimizing their performance in adsorption‐based applications. This study demonstrates for the first time that washing hydrochars in solvents of different polarity before activation is a simple yet powerful strategy to tailor pore size distribution. Hydrochar is produced from spent coffee grounds via hydrothermal carbonization, followed by washing in various solvents and activation in KOH. This results in carbons with a very large surface area (∼2700 m ² /g), and washing is demonstrated to significantly increase product yield. Furthermore, washing in non‐polar or mixed‐polarity solvents removes long‐chain carboxylic acids and esters from the hydrochar, promoting the development of narrow micropores while suppressing mesopore formation. To illustrate the impact of this structural control of porous carbons, post‐combustion CO ₂ capture is investigated as a case study. Narrower pore size distribution enhances CO ₂ uptake, significantly improving capacity from 2.8 mmol/g for unwashed samples to 3.8 mmol/g for acetone‐washed samples. Interestingly, moderate pore size (9–12 Å) is shown to be optimal for CO ₂ :N ₂ selectivity, while smaller pores result in lower selectivity due to stronger interactions between N ₂ and the pore walls. These findings highlight the potential role of solvent washing in directing pore architecture of hydrochars for adsorption‐based carbon capture technologies and beyond.

The effect of defects, nitrogen doping, and hydrogen saturation on the work function of graphene is investigated via first principle calculations. Whilst Stone–Wales defects have little effect, single and double vacancy defects increase the work function by decreasing charge density in the π-electron system. Substitutional nitrogen doping in defect-free graphene significantly decreases the work function, because the nitrogen atoms donate electrons to the π-electron system. In the presence of defects, these competing effects mean that higher nitrogen content is required to achieve similar reduction in work function as for crystalline graphene. Doping with pyridinic nitrogen atoms at vacancies slightly increases the work function, since pyridinic nitrogen does not contribute electrons to the π-electron system. Meanwhile, hydrogen saturation of the pyridinic nitrogen atoms significantly reduces the work function, due to a shift from pyridinic to graphitic-type behavior. These findings clearly explain some of the experimental work functions obtained for carbon and nitrogen-doped carbon materials in the literature, and has implications in applications such as photocatalysis, photovoltaics, electrochemistry, and electron field emission.