Role of Activated Carbon Precursor for Mercury Oxidation and Removal: Oxidized Surface and Carbene Site Interaction

Activated carbon (AC) is widely accepted for the removal of inorganic contaminants like mercury; however, the raw material used in the production of activated carbon is not always taken into consideration when evaluating its efficacy. Mercury oxidation and adsorption mechanisms governed by carbene sites are more likely to occur when graphitic-like activated carbons (such as those produced from high-ranking coals) are employed versus lignocellulosic-based ACs; this is likely due to the differences in carbon structures where lignocellulosic materials are less aromatic. In this research, the team studied bituminous coal-based ACs in comparison to coconut shell and wood-based (both less aromatic) ACs for elemental mercury removal. Nitric acid of 0.5 M, 1 M, and 5 M concentrations along with 10 M hydrogen peroxide were used to oxidize the surface of the ACs. Boehm titrations and FTIR analysis were used to quantify the addition of functional groups on the activated carbons. A trend was observed herein, resulting in increasing nitric acid molarity and an increased quantity of oxygen-containing functional groups. Gas-phase mercury removal mechanisms including physisorption, oxygen functional groups, and carbene sites were evaluated. The results showed significantly better elemental mercury removal in the gas phase with a bituminous coal-based AC embodying similar physical and chemical characteristics to that of its coconut shell-based counterpart. The ACs treated with various oxidizing agents to populate oxygen functional groups on the surface showed increased mercury removal. It is hypothesized that nitric acid treatment creates oxygen functional groups and carbene sites, with carbene sites being more responsible for mercury removal. Heat treatments post-oxidation with nitric acid showed remarkable results in mercury removal. This process created free carbene sites on the surface and shows that carbene sites are more reactive to mercury adsorption than oxygen. Overall, physisorption and oxygen functional groups were also dismissed as mercury removal mechanisms, leaving carbene-free sites as the most compelling mechanism.

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Surface Modification and Characterization of Coconut Shell-Based Activated Carbon Subjected to Acidic and Alkaline Treatments

Journal of Applied Science & Process Engineering ◽

10.33736/jaspe.435.2017 ◽

2017 ◽

Vol 4 (2) ◽

pp. 186-194 ◽

Cited By ~ 7

Author(s):

Tan I. A. W. ◽

Abdullah M. O. ◽

Lim L. L. P. ◽

Yeo T. H. C.

Keyword(s):

Activated Carbon ◽

Surface Morphology ◽

Surface Chemistry ◽

Pore Structure ◽

Surface Area ◽

Functional Groups ◽

Activated Carbons ◽

Coconut Shell ◽

Bet Surface Area ◽

Textural Characterization

Activated carbon derived from agricultural biomass has been increasingly recognized as a multifunctional material for various applications according to its physicochemical characteristics. The application of activated carbon in adsorption process mainly depends on the surface chemistry and pore structure which is greatly influenced by the treatment method. This study aims to compare the textural characteristics, surface chemistry and surface morphology of coconut shell-based activated carbon modified using chemical surface treatments with hydrochloric acid (HCl) and sodium hydroxide (NaOH). The untreated and treated activated carbons were characterized for their physical and chemical properties including the Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and textural characterization. The FTIR spectra displayed bands confirming the presence of carboxyl, hydroxyl and carbonyl functional groups. The Brunauer–Emmett–Teller (BET) surface area of the untreated activated carbon was 436 m2/g whereas the surface area of the activated carbon modified using 1M NaOH, 1M HCl and 2M HCl was 346, 525 and 372 m2/g, respectively. SEM micrographs showed that many large pores in a honeycomb shape were clearly found on the surface of 1M HCl sample. The pore structure of the activated carbon treated with 2M HCl and NaOH was partially destroyed or enlarged, which decreased the BET surface area. The modification of the coconut shell-based activated carbon with acidic and alkaline treatments has successfully altered the surface functional groups, surface morphology and textural properties of the activated carbon which could improve its adsorptive selectivity on a certain adsorbate.

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Effect of Ammonia Modification on Activated Carbons for the Removal of Acidic Anthraquinone Dyes

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2018-0216 ◽

2019 ◽

Vol 17 (8) ◽

Author(s):

Hind Yaacoubi ◽

Zuo Songlin

Keyword(s):

Activated Carbon ◽

Adsorption Capacity ◽

Functional Groups ◽

Activated Carbons ◽

Coconut Shell ◽

Diffusion Kinetic ◽

Anthraquinone Dyes ◽

Adsorption Sites ◽

Adsorption Affinity ◽

Adsorption Rates

Abstract The objective of this research is to study the retention of two acidic anthraquinone dyes by Coconut-shell-based activated carbon. Ultimately, this work allows the valorization of this new material as an adsorbent. The effect of ammonia modification on the adsorption capacity of activated carbon towards remazol brilliant blue R19 (RB19) and acid blue 25 (AB25), has been studied. Coconut-shell-based activated carbon material was modified under ammonia flow at 900 and 1000 °C. The adsorption rates and isotherms of RB19 and AB25 on the resultant materials were then tested. The results show that ammonia modification remarkably increases the adsorption capacities of the activated carbons to RB19 and AB25, by a factor of 2–3 after treatment at 1000 °C (From 0.22 mmol g−1 and 1.04 mmol g−1 to 0.76 mmol g−1 and 2.19 mmol g−1 on AC and AC-O-N-1000, respectively). The increased adsorption capacity is attributed to the introduction of basic nitrogen-containing functional groups and enhanced pore development by ammonia modification. The collected experimental kinetic and isotherm data are well compatible with the intraparticle diffusion kinetic model and the Langmuir isotherm model. According to these results, the adsorption affinity is homogeneous in terms of surface functional groups and the surface bears a finite number of identical adsorption sites.

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Removal of Gas-Phase Elemental Mercury by Bromine-Impregnated Activated Carbon

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.356-360.1660 ◽

2011 ◽

Vol 356-360 ◽

pp. 1660-1663 ◽

Cited By ~ 2

Author(s):

Jiang Wu ◽

Jie He Chen ◽

Shuai Bo Zhang ◽

Ping He ◽

Ji Hui Fang ◽

...

Keyword(s):

Activated Carbon ◽

Gas Phase ◽

Removal Efficiency ◽

Activated Carbons ◽

Physical Adsorption ◽

Fixed Bed ◽

Elemental Mercury ◽

Adsorption Ability ◽

Bromine Concentration ◽

Fixed Bed System

Br-impregnated activated carbon for gas-phase elemental mercury adsorption experiments were carried out at a fixed-bed system to get the suitable mass fraction of KBr impregnation solution. Hg removal efficiency of 1% wt KBr-ACs was 69.0%, while that of 10% wt KBr-ACs was 57.9%. Both of them were higher than that of the raw activated carbon, 42.2%. The removal efficiency of Hg0 was not proportional to bromine concentration. Under 80-180°C, Hg removal efficiency of 1% wt KBr-ACs were 68.3%-71.8%, and at 140°C it reached the highest due to the increasing chemical adsorption ability of the functional groups which was on the surfaces of activated carbons by impregnating. At 160°C, Hg removal efficiency was lower than that at 140°C due to desorption making physical adsorption decrease, so that the total adsorption decreased.

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Effects of oxygen functional groups and FeCl3 on the evolution of physico-chemical structure in activated carbon obtained from Jixi bituminous coal

RSC Advances ◽

10.1039/c7ra12928a ◽

2018 ◽

Vol 8 (16) ◽

pp. 8569-8579 ◽

Cited By ~ 4

Author(s):

Dongdong Liu ◽

Boyin Jia ◽

Xiujuan Liu ◽

Bojun Zhao ◽

Jihui Gao ◽

...

Keyword(s):

Activated Carbon ◽

Functional Groups ◽

Chemical Structure ◽

Bituminous Coal ◽

Oxygen Functional Groups ◽

Physico Chemical

Effects of oxygen functional groups and FeCl3 on evolution of physico-chemical structure in activated carbon to increase its value SBET/burn-off.

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Design of sulfur treated activated carbon fibers for gas phase elemental mercury removal

Fuel ◽

10.1016/j.fuel.2013.08.063 ◽

2014 ◽

Vol 116 ◽

pp. 560-565 ◽

Cited By ~ 72

Author(s):

Yaxuan Yao ◽

Vedagiri Velpari ◽

James Economy

Keyword(s):

Activated Carbon ◽

Gas Phase ◽

Carbon Fibers ◽

Elemental Mercury ◽

Mercury Removal ◽

Activated Carbon Fibers

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Increasing oxygen functional groups of activated carbon with non-thermal plasma to enhance mercury removal efficiency for flue gases

Chemical Engineering Journal ◽

10.1016/j.cej.2014.10.090 ◽

2015 ◽

Vol 263 ◽

pp. 1-8 ◽

Cited By ~ 132

Author(s):

Bi Zhang ◽

Ping Xu ◽

Yong Qiu ◽

Qiao Yu ◽

Jingjing Ma ◽

...

Keyword(s):

Activated Carbon ◽

Functional Groups ◽

Removal Efficiency ◽

Thermal Plasma ◽

Flue Gases ◽

Mercury Removal ◽

Oxygen Functional Groups ◽

Non Thermal Plasma

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The Analysis of Pore Development and Formation of Surface Functional Groups in Bamboo-Based Activated Carbon during CO2 Activation

Molecules ◽

10.3390/molecules26185641 ◽

2021 ◽

Vol 26 (18) ◽

pp. 5641

Author(s):

Krittamet Phothong ◽

Chaiyot Tangsathitkulchai ◽

Panuwat Lawtae

Keyword(s):

Activated Carbon ◽

Functional Groups ◽

Active Sites ◽

Activated Carbons ◽

Carbonization Temperature ◽

Activation Process ◽

Activation Time ◽

Oxygen Functional Groups ◽

Porous Properties ◽

Activation Conditions

Pore development and the formation of oxygen functional groups were studied for activated carbon prepared from bamboo (Bambusa bambos) using a two-step activation with CO2, as functions of carbonization temperature and activation conditions (time and temperature). Results show that activated carbon produced from bamboo contains mostly micropores in the pore size range of 0.65 to 1.4 nm. All porous properties of activated carbons increased with the increase in the activation temperature over the range from 850 to 950 °C, but decreased in the temperature range of 950 to 1000 °C, due principally to the merging of neighboring pores. The increase in the activation time also increased the porous properties linearly from 60 to 90 min, which then dropped from 90 to 120 min. It was found that the carbonization temperature played an important role in determining the number and distribution of active sites for CO2 gasification during the activation process. Empirical equations were proposed to conveniently predict all important porous properties of the prepared activated carbons in terms of carbonization temperature and activation conditions. Oxygen functional groups formed during the carbonization and activation steps of activated carbon synthesis and their contents were dependent on the preparation conditions employed. Using Boehm’s titration technique, only phenolic and carboxylic groups were detected for the acid functional groups in both the chars and activated carbons in varying amounts. Empirical correlations were also developed to estimate the total contents of the acid and basic groups in activated carbons in terms of the carbonization temperature, activation time and temperature.

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