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• NaOH-modified activated carbon fiber removes to heavy metals, cost-effectively. • The NaOH modification induced abundant oxygen functional groups in micropore. • Heavy metals adsorbed by a polar oxygen functional groups and pore filling mechanism. This manuscript describes an efficient and cost-effective method to remove heavy metals of Hg and Cd in aqueous solutions via adsorption on activated carbon fibers after modification with NaOH solution (NaACF). The Hg and Cd metals in the aqueous solution exist as Hg(OH) 2 and Cd2+ in the experimental condition of pH 6–8. Surface characterization of the NaACF reveals uniform and narrower micropores with an increase in oxygen functional groups of phenol and lactone compared with the original ACF (pACF). The NaACF demonstrates a superior adsorption rate to both aqueous samples of heavy metal compounds. The granular activated carbon (GAC) with diverse pore structures consisting of micropores, mesopores, and macropores adsorbed the heavy metals at a relatively slow rate. The adsorption mechanisms of the heavy metals into NaACF pores are proposed as pore-filling with non-ionic Hg(OH) 2 and electron sharing of oxygens in phenolic, lactone, and carboxylic acid groups with ionic Cd2+. The results from continuous feeding are also reported for the sample blend of 10 wt% NaACF and 90 wt% GAC in increasing the cost performance ratio. [ABSTRACT FROM AUTHOR]

• Boron-doped activated carbon fiber effectively sensed to NO 2 gas, repetitively. • Boron doping induced high selectivity toward NO 2 via the strong binding energy. • The shallow, narrow and uniform pores on the surface worked as trap sites for NO 2. In the current work, a high performance NO 2 gas sensors has been fabricated from activated carbon fibers containing enriched boron moieties. The porous carbon fibers decorated with boron moieties exhibited rapid, repetitive and selective NO 2 sensing performance at room temperature. The shallow, narrow and uniform micropores on the surface of the carbon fiber allowed target gases to be adsorbed and desorbed very easily whereas boron moieties induced high selectivity toward NO 2 over NH 3 via the strong binding energy. The excellent NO 2 gas sensing performance of boron doped porous carbon fibers is attributed to synergetic effect of intrinsic pore structure of the carbon fibers and the boron moieties decorated on their surface. [ABSTRACT FROM AUTHOR]