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Activated Carbon Modifications to Enhance Its Water Treatment Applications. an Overview

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Activated Carbon Modifications to Enhance Its Water Treatment Applications. an Overview
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   Journal of Hazardous Materials 187 (2011) 1–23 Contents lists available at ScienceDirect  JournalofHazardousMaterials  journal homepage: www.elsevier.com/locate/jhazmat Review Activated carbon modifications to enhance its water treatmentapplications. An overview  J. Rivera-Utrilla a , ∗ , M. Sánchez-Polo a , V. Gómez-Serrano b ,P.M. Álvarez c , M.C.M. Alvim-Ferraz d , J.M. Dias d a Departamento de Química Inorgánica, F. Ciencias, Universidad de Granada, 18071 Granada, Spain b Dpto. de Química Orgánica e Inorgánica, Universidad de Extremadura, Badajoz 06071, Spain c Dpto. de Ingeniería Química y Química Física, Universidad de Extremadura, Badajoz 06071, Spain d LEPÆ, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal a r t i c l e i n f o  Article history: Received 11 November 2010Received in revised form 4 January 2011Accepted 6 January 2011 Available online 15 January 2011 Keywords: ReviewActivated carbonSurface treatmentsWater treatment a b s t r a c t The main objective of this study was to list and compare the advantages and disadvantages of differentmethodologies to modify the surface of activated carbons (ACs) for their application as adsorbents toremove organic and inorganic pollutants from aqueous phase. These methodologies have been catego-rized into four broad groups: oxidation, sulfuration, ammonification, and coordinated ligand anchorage.Numerousinvestigationsintotheremovalofmetalsfromwaterhavemodifiedcarbonsurfacestoincreasetheir content of acidic surface functional groups by using H 2 O 2 , O 3  and HNO 3 . Because these treatmentscanreducetheACsurfacearea,researchersareseekingalternativemethodstomodifyand/orcreatesur-face functional groups without the undesirable effect of pore blockage. The nitrogenation or sulfurationoftheACsurfacecanincreaseitsbasicityfavoringtheadsorptionoforganiccompounds.Theintroductionof nitrogen or sulfur complexes on the carbon surface increases the surface polarity and, therefore, thespecific interaction with polar pollutants. Different coordinated ligands have also been used to modifyACs, showing that coordinated ligand anchorage on the AC surface modifies its textural and chemicalproperties, but research to date has largely focused on the use of these modified materials to removeheavy metals from water by complexes formation. © 2011 Elsevier B.V. All rights reserved. Contents 1. Introduction.......................................................................................................................................... 2 2. Activated carbon treatments......................................................................................................................... 6 2.1. Oxidation treatments......................................................................................................................... 6 2.1.1. Hydrogen peroxide and nitric acid treatments .................................................................................... 6 2.1.2. Ozone treatment.................................................................................................................... 13 2.2. Sulfuration treatments ....................................................................................................................... 17 2.3. Nitrogenation treatments .................................................................................................................... 19 2.4. Coordinated ligand functionalization treatments ........................................................................................... 19 3. Applications of modified activated carbons in water treatments. Adsorption of pollutants........................................................ 20 3.1. Oxidated activated carbon ................................................................................................................... 20 3.2. Sulfurized activated carbons ................................................................................................................. 20 3.3. Nitrogenated activated carbons.............................................................................................................. 20 3.4. Activated carbons functionalizated with coordination ligands.............................................................................. 20 4. Conclusions .......................................................................................................................................... 20 Acknowledgements.................................................................................................................................. 21 References ........................................................................................................................................... 21  Abbreviations:  AC,activatedcarbon;HT,heattreatment; S N2 ,surfaceareameasuredbyN 2  adsorptionat77K; S BET ,BETsurfacearea; V  t ,totalporevolume;C-dmea,N,N-dimethylethanolamine; C-dmpa, N,N-dimethyl-1,3-propanedamine; DCM, dicyanodiamine; DCD, N,N-dimethylformamide; MM, melamine; EDA, ethylenediamine; DMF,dimethylformamide. ∗ Corresponding author. Tel.: +34 958248523; fax: +34 958248526. E-mail address:  jrivera@ugr.es (J. Rivera-Utrilla).0304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2011.01.033  2  J. Rivera-Utrilla et al. / Journal of Hazardous Materials 187 (2011) 1–23 1. Introduction Activated carbon (AC) has been proven to be an effective adsor-bentfortheremovalofawidevarietyoforganicandinorganicpol-lutants from aqueous or gaseous media. It is widely used due to itsexceptionally high surface area (ranges from 500 to 1500m 2 g − 1 ),well-developed internal microporosity, and wide spectrum of sur-face functional groups. While the effectiveness of ACs to act asadsorbents for a wide range of contaminants is well documented,researchonACmodificationisgainingprominenceduetotheneedto develop the affinity of AC for certain contaminants to facilitatetheir removal from water. It is essential to understand the factorsthat influence the adsorption of ACs prior to their modificationin order to tailor their specific physical and chemical propertiesand enhance their affinity for metals and inorganic and/or organicspecies present in waters. These properties include their specificsurfacearea,pore-sizedistribution,porevolume,andthepresenceof different types of surface functional groups.The use of oxidizing agents is the most common method-ology to modify AC surface [1–68], however, in general this treatment reduces the AC surface area; therefore, researchersare investigating alternative methods like (i) sulfuration [69–83](ii) ammonification [84–116] and/or (iii) coordinated ligandanchorage to increase activated carbon adsorption capacity[117–125,112,126–129].The main objective of this study was to list and compare theadvantages and disadvantages of existing AC surface modificationtechniques in relation to the application of the resulting AC as anadsorbent to remove organic and inorganic pollutants from aque-ous phase. Based on the extensive literature on this topic, we havecategorized the techniques into four broad groups: oxidation, sul-furation, ammonification, and coordinated ligand anchorage.  Table 1 Hydrogen peroxide oxidation treatments.Raw material Experimental conditions Textural modifications Chemical modifications Observations Reference(Commercial) Activatedcharcoal cloth (FM250) fromCharcoal Cloth Ltd; Activatedgranular charcoal (ACG 80)by Active Carbon Ltd.Preparation of srcinalmaterials. Demineralization:HCl 6N, HF 22N, and HCl 12N;Drying: air oven at 110 ◦ Covernight, nitrogen gas for 5hat the same temperature inhorizontal furnace. Oxidationof srcinal materials. Contactwith 30% H 2 O 2  (1g of AC:10mL solution) for 48h.Washing. Hot double-distilledwater. Drying overnight at110 ◦ C under nitrogen flow.Surface area decreased.Microporositypersisted afteroxidation.Oxygen contentincreased due to theformation of surfaceoxygen complexes.Oxidized samples have almostthe same or slightly higheracidity  versus  srcinalmaterials; Minimum decreasein adsorption capacity(according to N 2  adsorptionisotherms) Adsorption capacityof granular ACs was increasedin comparison to activatedcharcoal cloth.[8](Commercial) GAC from CECA;previously demineralised bytreatment with HF and HClsolutions.Treatment with an H 2 O 2 solution.Surface area increased;Mesopore volumemarkedly increased;Textural parameterswere similar.Surface oxygenchemical groupsincreased in numberafter treatment.Chemical groups wereintroduced on both externaland internal surfaces.[7]Almond shells Raw material preparation.Pyrolysis: at 900 ◦ C in nitrogenflow for 1h; Activation: steamflow at 850 ◦ C for differentperiods of time (final particlesize range between 0.15 and0.25mm).Oxidation. 1g of carbon: 10mL of concentrated H 2 O 2  (9.8M) at25 ◦ C in shaking bath for 48h.Surface area and poretexture were similarafter treatment.Carboxyl, ketone, andether groups andprobablecarboxyl-carbonatestructures weredetected.Oxygen surface complexeswere fixed at the entrance of the micropores in somesamples, causing restricteddiffusion of N 2  at 77K.[93](Commercial) Coconut shell Oxidation. Immersion in H 2 O 2 10–30%, ratio of H 2 O 2  tocarbon of 2.5–10mL/g at roomtemperature. Drying 95 ◦ C for12h.Porous structuralparameters and surfacearea not affected.Oxygen contentincreased afteroxidation; CO 2 evolving groups mightbe largely induced onthe surface withoxidation at <100 ◦ C.H 2 O 2  oxidation is verypractical, since it is performedat <100 ◦ C; Simple drying isrequired as post-treatment; Noharmful gas is evolved duringthe process.[1](Commercial) Norit ROX 0.8;pellets (0.8mm diameter,5mm length), neutral pH,3wt.%. ash contentMixing. 1g: 25cm 3 of H 2 O 2 1M at room temperature untilcomplete degradation of H 2 O 2 .Washing. Distilled water untilneutral pH. Drying at 110 ◦ C for24h.Minimal changes inmicropore volume andmesopore surface area.No significantdifferences comparedto the srcinal sample(according totemperature-programmeddesorption spectra).No major effect on surfacechemistry.[6](Commercial) WaterlinkSutcliffe Carbons; Grade: 207A; Mesh: 12 × 20.Oxidation. 10g of carbon:100mL of H 2 O 2  (15% and 30%,v/v) stirred at roomtemperature for 3h. Washingand Filtration. Drying 110 ◦ Covernight.No marked changes. CO 2 -evolving groupsslightly increased andCO-groups slightlydecreased withincreases in oxidantconcentration.The modified material showedsimilar porosity and surfacechemistry.[5](Commercial) Coal particlescarbonized and steamactivated at 850 ◦ C, BETsurface area 770.4m 2 /g.Heat treatment. 500 ◦ C innitrogen. Oxidation.Concentration of oxidizingagent 3–15%, 100 ◦ C, 1h.Washing Distilled water untilneutral pH.Not evaluated. Carboxylic groups onthe surface decreased.Oxidation with 15% H 2 O 2 introduced a large number of lactone and phenol groups onthe surface.[11]   J. Rivera-Utrilla et al. / Journal of Hazardous Materials 187 (2011) 1–23 3  Table 2 Nitric acid oxidation treatments.Raw material Experimental conditions Textural modifications Chemical modifications Observations Reference(Commercial) Merck Oxidation. 50mL of concentrated nitric acid addedto 5g of AC. Heating 353K untildry.Washing. Distilled water untilno nitrates were present.Drying. 383K in ovenovernight.Meso- and macro-porositydecreased; Poreconstrictions by fixation of oxygen groups at theentrance of the pores.Considerable amounts of oxygen were fixed, largely inthe form of carboxylic acidgroups and nitro and nitratearomatic compounds.Chemical and texturalproperties changed; meso andmacropores partially destroyedby loss of pore walls.[13]Spanish Lignite Preparation of originalmaterials. Demineralizationwith HCl and HF; Pyrolysis: at840 ◦ C in N 2  flow; Elementalanalysis (wt.%, dry basis):C-80.2; H-1.5; N-1.0; S-2.6;O-12.6, ash content-2.1.Activation: in CO 2  flow at800 ◦ C up to 18% burn-off.Oxidation 1g of carbon treatedfor 48h with 10cm 3 of concentrated H 2 O 2  at 25 ◦ C(final analysis, O (wt.%)-18.2)Heat treatment. He flow atdifferent temperatures up to1000 ◦ C. After-treatmentprocedure exposure to ambientair for two years.Not evaluated. Basic group regeneration(evolved as CO) less sensitiveto the outgassing temperaturein comparison to acid groups.Ageing for two years inambient air of a previouslyoutgassed oxidized AC restoredthe pre-outgassing surfaceoxygen complexes of thecarbon; The higher theprevious outgassingtemperature, the greater wasthe regeneration. There was amemory effect in addition tooxygen migration to and acrossthe surface during theoutgassing process.[15](Commercial)Merck-9631, 18–35mesh ASTMOxidation. 200cm 3 of concentrated nitric acid heated(25, 60 and 90 ◦ C) and 20g of AC added and mixed for 3h.Washing. Distilled water untilneutral pH. Drying. Left undernitrogen atmosphere at 283Kovernight.Not evaluated. Carbonyl, lactone, ether andhydroxyl groups were formed.The quantity of the evolvedgases increased with highertreatment temperature.[4](Commercial) Coconutshell based carbon(activation in steamat around 900 ◦ C)Extraction. Soxhlet extractionwith water to remove solublematerials. Oxidation. Carbonrefluxed in 7.5M HNO 3 solution for 4 and 48h; soxhletextraction with water untilconstant pH to remove residualHNO 3 ; vacuum-drying at 75 ◦ C.Heat treatment At 10 ◦ C min-1under helium flow to thedesired temperature, holdingfor 1h at the maximumtemperature (300 or 800 ◦ C).Micropore volume (CO 2 )and total pore volume (N 2 )decreased; Pore volumesshowed greater reductionwith longer oxidationtimes; Surface area andboth micropore and totalpore volumes weregradually increased by heattreatment.Oxygen, nitrogen, andhydrogen content increasedand carbon content decreased;Oxygen largely introduced intothe carbon.Increasing oxidation timeincreased oxygen functionalgroups; Small amounts of nitrogen were alsoincorporated into the carbon;The structural changes notcompletely reversed by heattreatment at 800 ◦ C.[16](Commercial)Activated charcoalcloth (FM250) byCharcoal Cloth Ltd;Activated granularcharcoal (ACG 80) byActive Carbon Ltd.Preparation of srcinalmaterials Demineralization:HCl 6N, HF 22N, and HCl 12N;Drying: in air oven at 110 ◦ Covernight; Nitrogen gas for 5hat the same temperature inhorizontal furnace. Oxidationof srcinal materials Boiling in1N HNO 3  (1g of AC:10mL of solution) for 24h with refluxcondenser.Washing. Double distilledwater until free of nitrate ionsthen further reflux withdistilled water for 3–4h.Drying 110 ◦ C overnight undernitrogen flow.Heat treatment. Oxidizedsamples under N 2  for 5h at600 ◦ C in horizontal furnace.Surface area decreased;ACs retained theirpredominantlymicroporous nature.Oxygen content markedlyincreased due to the formationof surface oxygen complexes.Total acidity increasedthree-fold due to the presenceof stronger acidic groups; N 2 adsorption isotherms showedmarked decrease in adsorptioncapacity, which was moremarked for granular ACs thanfor activated charcoal cloth.[8](Commercial) NoritROX; Hydraffin(Degussa).Preparation of the raw materialACs ground and sieved to200–300  m prior to their use.Oxidation HNO 3  5N solution atboiling temperature for 3h.Washing Boiling distilled watertill pH 5.5. Drying. 110 ◦ Covernight.Micropore volumesignificantly decreased;Mesopore surface areaincreased 10%.CO and CO 2  markedlyincreased, releasing groups onboth Hydraffin and Noritsamples; Acidity increased.The decrease in microporevolume was explained by thecollapse of pore walls due tothe attack of highlyconcentrated nitric acid.[17]  4  J. Rivera-Utrilla et al. / Journal of Hazardous Materials 187 (2011) 1–23 Table 2 ( Continued )Raw material Experimental conditions Textural modifications Chemical modifications Observations Reference(Commercial) Q andCV, commonly usedby thepharmaceuticalindustry.Oxidation HNO 3  at differentconcentrations (1, 20 and 60%,v/v); 1g of carbon: 10mL of acidsolution boiled until dryness.Washing. Distilled water untilnitrate elimination.Micro- and mesoporosityincreased at lowconcentrations of theoxidizing agent; Texture of the carbons significantlydestroyed by severeoxidation conditions.Surface oxygen contentincreased, being greater athigher concentrations (20 and60%).Oxidation alters not only thechemical properties but alsothe texture of the surfaces[9]Almond shells. Preparation of the raw materialPyrolysis at 900 ◦ C in nitrogenflow for 1h, activation withsteam flow at 850 ◦ C for differenttimes; final particle size rangebetween 0.15 and 0.25mm.Oxidation. 1g of carbon treatedwith 10mL of concentratedHNO 3  (13.9M) at 80 ◦ C untildryness.Washing. Residue washed withdistilled water until nitrateremoval.Surface area andmicroporosity decreased;Effects increased withstronger degrees of activation.Carboxyl groups and probablecarboxylcarbonate structuresas well as nitro and nitrategroups were detected aftertreatment.Stronger acid groups wereintroduced by treatment with(NH 4 ) 2 S 2 O 8  versus  treatmentwith HNO 3 , in spite of thefixation by HNO 3  of moreCO 2 -evolving oxygen surfacecomplexes.[93](Commercial) Coconutshell.Oxidation. HNO 3  4N at roomtemperature for 10h. Drying70 ◦ C in a rotary evaporator.Heat treatment N 2  flow at 400 ◦ Cfor 1h.Surface area markedlyreduced.Oxygen content markedlyincreased.Temperaturetreatmentneededto eliminate the remainingoxidants on the surface; Theharmful gases involved, such asSO 3 , SO 2 , NO 2  and NO must beeliminated after treated.[1]Corncob. Raw material preparation. Driedand crushed corncobs at 500 ◦ Cwith N 2  flow, activation withsteam/N 2  at 850 ◦ C; Steampyrolysis of the raw precursor at600 and 700 ◦ C; Activation: with50% H 3 PO 4  at 500 ◦ C.Oxidation. HNO 3  (50cm 3 :5g of prepared carbon), at 60 ◦ C withconstant stirring for 1h.Washing. Distilled water. Drying110 ◦ C.Totalsurfaceareamarkedlydecreased (from 13 to25%); Mesopore volumeslightly increased andsome pores were widened.Increased density of acidicoxygen groups at carbonsurface.Large amount of oxygenfunctionalities on the carbonsurface, especially whencarried out under severe acidicconditions; simultaneouspartial destruction ordegradation of the porousstructure.[14]Olive stones. Preparation of the raw material.Washing with sulfuric acid andagain with distilled water up tosulfate ion elimination,carbonization at 1000 ◦ C for 1hunder N 2  flow, activation withstream of carbon dioxide at840 ◦ C for 16h (grains of 1–1.4mm). Oxidation treatment.80cm 3 of concentrated HNO 3 solution (15M): 4g of materialand then left in contact withnitric acid at ambienttemperature for 24h. Washing.Distilled water until neutral pH.Separation Filtration. Drying.Vacuum at 50 ◦ C overnight.Surface area decreased. CO 2 -evolving oxygen groupsstrongly increased.Oxidized samples have smallersurface area; The subsequentpartial outgassing increasedthe surface area but to lowervalues than before oxidation.[2](Commercial)Bituminous-coal BPL and WPL, fromCalgon CarbonCorporation.Pre-treatment De-ionized waterwashing and air-drying.Oxidation 6M HNO 3  solution atroom temperature for 5h.Washing De-ionized water.Drying 110 ◦ C overnight.Surface areas and porevolumes slightlydecreased, possibly as aresult of the destruction of some of the thin pore wallsand blocking of the poreentrances by oxygenfunctional groups.Total oxygen concentrationssignificantly increased; acidicgroup formation.Strong chemical effectproduced by treatment,creating oxygen surfacefunctional groups and resultingin low CO/CO 2  ratio; Highermercury adsorption.[10](Commercial) NoritROX 0.8; pellets(0.8mm diameter,5mm length),neutral pH, ashcontent of 3wt. %.Soxhlet extraction 5M HNO 3 , 9gof AC, 3h reflux.Washing. Distilled water untilneutral pH. Drying. 110 ◦ C for24h.Micropore volumedecrease was more drasticwhen degree of oxidationincreased.Large amount of surfaceoxygen-containing groups.Textural modifications due tothe drastic conditions used,leading to the collapse of somepore walls. Acidic surface wasdue to the acid character of themajority of the surfaceoxygen-containing groups.[6](Commercial)Filtrasorb 200(Calgon Corp.),particles with 20–32mesh size.Oxidation. 1g carbon to 10mL HNO 3  (10, 30, 50% andconcentrated HNO 3 ).Washing. De-ionized water ortreatment with concentratedHCl followed by washing withde-ionized water.Surface area not affected. Surface functional groups suchas carbonyl, carboxyl andnitrate groups were formed.Chemical properties of carbon(pH and total acidity capacity)significantly changed.[12]
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