OPEN ACCESS Asian Journal of Scientific ResearchISSN 1992-1454

DOI: 10.3923/ajsr.2016.45.56

Research ArticlePhysical, Chemical and Adsorptive Characteristics of Local OakSawdust Based Activated Carbons

Atef S. Alzaydien

Department of Chemistry, Mutah University, P.O. Box 7, Jordan

AbstractObjective: The aim of this study was to prepare and characterize activated carbon from local oak sawdust in order to relate thepreparation conditions (carbonization and chemical activation) to the carbon’s essential physical, chemical and adsorptive properties.Methodology: Activated carbons were prepared from raw sawdust carbon (SDC) and by first activation with 3.07 N H3PO4 (PASC).The carbon yield for SDC was 33.8% while, phosphoric acid activated sawdust carbon (PASC) showed 29.4% of carbon yield. The pH valuesfor the SDC and PASC solutions were found to be 7.4 and 6.0, respectively. The electrical conductivities for the SDC and PASC solutionswere found to be 144 and 327 µS cmG1. Moisture contents for SDC and PASC were 5.4 and 4.6% and ash contents for SDC and PASC were6.8 and 6.6% respectively. The surface concentration of the functional groups on SDC titrated by the equilibrium Boehm method is1.508 mmol gG1, of which 1.062 mmol gG1 have acidic and 0.446 mmol gG1 have basic character. While, the surface concentration of thefunctional groups on PASC titrated by the equilibrium Boehm method is 2.615 mmol gG1, of which 2.467 mmol gG1 have acidic and0.148 mmol gG1 have basic character. Results: The values of iodine number obtained for PASC (872.4 mg gG1) is greater thanthe value obtained for SDC (554.6 mg gG1). The methylene blue number obtained for PASC (306.0 mg gG1) is greater than the valueobtained for SDC (180.3 mg gG1). The Langmuir maximum adsorption capacity of phenol on the resultant PASC and SDC was equal99.0 and 72.4 mg gG1 respectively. Conclusion: The results show that agricultural waste oak sawdust can be used as a promising precursormaterial for the production of low cost activated carbon.

Key words: Carbon, SDC, PASC, characterization, phosphoric acid, physical, chemical, adsorptive

Received: January 28, 2016 Accepted: February 16, 2016 Published: March 15, 2016

Citation: Atef S. Alzaydien, 2016. Physical, chemical and adsorptive characteristics of local oak sawdust based activated carbons. Asian J. Sci. Res., 9: 45-56.

Corresponding Author: Atef S. Alzaydien, Department of Chemistry, Mutah University, P.O. Box 7, Jordan Tel: +962-796785513 Fax: +962-32375073

Copyright: © 2016 Atef S. Alzaydien. This is an open access article distributed under the terms of the creative commons attribution License, which permitsunrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

Competing Interest: The authors have declared that no competing interest exists.

Data Availability: All relevant data are within the paper and its supporting information files.

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Asian J. Sci. Res., 9 (2): 45-56, 2016

INTRODUCTION

Activated carbons are produced with a wide range ofproperties and physical forms, which leads to their use innumerous applications. Activated carbon also called asactivated charcoal or activated coal, is a form of carbon thathas been processed to make it extremely porous and thus tohave a very large surface area available for adsorption orchemical reactions. Activated carbons are extremely versatileadsorbents of great industrial significance in the removal ofgas and purification of chemicals1. They are also used ascatalysts and catalyst supports in the catalytic processes2.

Most organic materials rich in carbon that do not fuseupon carbonization can be used as raw material for themanufacture of activated carbon. Raw materials together withthe production method determine the final characteristics ofthe activated carbon product as well as the overall economicviability. Polyacrylonitrile is considered to be best precursor formaking performance carbon fibers. Activated carbons can beprepared from large number of precursor materials with ahigh carbon content and low level ash including coal, woodsand bones2. In addition, some agricultural by-productsresidues from agriculture and agro industries can be also usedas raw materials for preparing activated carbons. Theseincludes olive stones3, almond shells4, apricot and peachstones5, maize cob6, linseed straw7, sawdust8, rice hulls9,cashew nuts10, etc. Besides these other sources are, coconutshells, eucalyptus bark, linseed cake, tamarind seeds and teawaste ash suffocated coal, baggase, ground nut husk,activated bauxite, palm seed coat, de-oiled soya and cementkiln dust.

Activated carbon can be prepared either by physical(or dry) activation or chemical activation. Physical activationinvolves two steps; in first step precursor material willundergo carbonization process (400-900EC) in the absence ofair and second step involves activation/oxidation by gases likecarbon dioxide, oxygen and steam, etc.11-15, whereas, chemicalactivation is one stage process, carbonization and activationof a precursor occur synchronously in the presence ofoxidative chemicals. Chemical activation has more advantagesover physical activation with respect to higher yield, moresurface area and better development of porous structure incarbon. It also helps to develop oxygenated surface complexeson the surface of activated carbon16. The surface oxygenfunctional groups can be easily introduced to the carbon bydifferent activation methods like the reaction between thecarbon surface and solutions of oxidizing agents such asphosphoric acid, nitric acid, hydrogen peroxide, zinc chloride,potassium permanganate, potassium hydroxide, etc. From the

above oxidizing agents, phosphoric acid and zinc chloride areusually used for the activation of lignocellusic materials.However, phosphoric acid activation is widely preferred overzinc chloride because ZnCl2 has had environmental impactand the activated carbon produced when using it can not beused in the food and pharmaceutical industries17.

High surface area activated carbon has alwaysfascinated researchers for its application as adsorbent.Chemical activation using phosphoric acid can easily open uppores and cavity of the prepared activated carbon to enhancetheir adsorption capability. Phosphoric acid activation hasbeen applied to coconut shell, coals, hardwoods, shells of nutslike almond, pecan, black walnut, macadamia nut, cottonstalks and palm date pits18. Mariet19 showed that the reactionof a lignocellulosic precursor with a strong chemical reagent,such as phosphoric acid (H3PO4) at temperatures up to 350ECor above can lead to the formation of a porous carbon.Depending on the reagent, its concentration and the carbonprecursor material, the carbon will possess a highly developedinternal pore structure and be an effective adsorbent formolecules in the gas or liquid phase. Gonzalez-Serrano et al.20,showed that activated carbons with a high BET surface areaand a well-developed porosity have been prepared frompyrolysis of H3PO4 impregnated lignin precipitated from Kraftblack liquors. Impregnation ratios within the range of 1-3 andactivation temperatures of 623-873 K have been used, givingrise to carbons with different porous and surface chemicalstructure. Increasing the activation temperature and theimpregnation ratio leads to a widening of the porousstructure with a higher relative contribution of mesoporosity.Armagan et al.21. In his study, investigated the activationfeatures of phosphoric acid using waste peach stones as theraw material in the production of granular activated carbon.The activated carbon produced was found to be as good asthat of the commercial ones. Physical properties of activatedcarbon, such as ash content and moisture content can affectthe use of a granular AC and render them either suitable orunsuitable for specific applications. While the specific surfacearea of activated carbon and surface chemistry is classified aschemical properties.

In developing countries, the costs associated withmanufacturing or more often importation of water-treatmentchemicals tend to push the costs of processed water tolevels that are not affordable to many people. In a largelyagrarian country such as Jordan, there are so manyagricultural by-products lying waste, littering and pollutingthe environment. The need to research on these wastes toconvert them into agents of environmental control in order toreduce waste and conserve cost is the key to the present

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study. The objective of this study was to prepare andcharacterize activated carbon from local oak sawdust inorder to relate the preparation conditions (carbonization andchemical activation) to the carbon’s essential physical,chemical and adsorptive properties. The chemical speciesused here was phosphoric acid (H3PO4). Surface chemistry wascarried out by FTIR and Boehm titration method.

MATERIALS AND METHODS

Materials: All the chemicals and reagents used were ofanalytical grade and procured from Merck, Fluka andAldrich-Sigma. Following are the chemicals used in this studyare listed in Table 1.

Preparation of activated carbons: Oak sawdust (SD) wascollected from local sawmill. The SD was washed with hotdistilled water to remove dust like impurities. Then it was driedin sunlight until all the moisture evaporated. This SD was usedas a precursor for the preparation of two brands of carbonscarbon. Firstly, 15 g of grounded raw SD was weighed intoclean and weighed crucibles. They were introduce into anelectric furnace at 500EC for 5 min after which they werepoured from the crucible into a bath of ice water. The excesswater was drained off. The carbonized sample was washedsuing 0.1 M HCl to remove surface ash, followed by hot waterwash and further washing with distilled water to removeresidual acid. The resulting sawdust carbon (SDC) was thensun dried and further dried in the oven at 100EC for 1 h. TheSD sample (30 g) was impregnated with 150 g of 3.07 Nphosphoric acid (H3PO4) solution for 140 min under agitationat 160 rpm. The impregnated SD was charred in electricalfurnace (Carbolite Philip Harris limited, UK) at 500EC for35 min to ensure complete charring22. The carbonizationtemperature 500EC was chosen because higher temperatureleads to excess carbonization, excess carbonization leads tothe formation more ash there by produces larger diameterpores by pore widening and pore collapse, this also result in adecrease of surface area. The average weight loss of 37%was obtained during pyrolysis experiment. The charredcarbonaceous material thus prepared is then cooled, washedwith dilute ammonia solution and distilled water successivelyto make it completely acid free. The absence of phosphate ionin solution was also tested by addition of barium nitrate(Ba(NO3)2), the formation of precipitate (Ag3PO4) was notobserved. The resulting phosphoric acid activated sawdustcarbon (PASC) was oven dried at 110EC overnight and nextkept in a tightly closed container for further characterization.

Table 1: Chemicals used in presented studySubstances FormulaPhosphoric acid H3PO4Sulfuric acid H2SO4Hydrochloric acid HClSodium thiosulphate NaS2O3.5H2OPotassium iodate KIO3Iodine I2Potassium iodide KIStarch indicator (1%) (C12H22O11)nSodium hydroxide NaOHSodium carbonate Na2CO3Sodium bicarbonate NaHCO3Methylene blue C16H18ClN3SPhenol C6H6ONicotinic acid C5H4NCOOHPhenolphthalein C20H14O4

Characterization of the activated carbonsPhysical characteristicsCarbon yield: The total yields were determined after sampleprocessing in terms of raw material mass. The dried weight, Woof each pre-treated sample was determined using Metlerbalance and the carbon yield calculated as:

(1)cho

WY = 100W

where, Ych is carbon yield (%), W is dried weight of ACprepared and Wo is pre-treated sample used in thecarbonization and activation processes.

pH and conductivity: The standard test method fordetermination of activated carbon pH ASTMD3838-80 wasused23. The 1.0 g of SDC and PASC was weighed andtransferred into a beaker. One Hundred milliliters of distilledwater was measured and added and stirred for 1 h. Thesamples were allowed to stabilize before the pH wasmeasured. The pH was determined using a pH meter(metrohm 744, USA) and the conductivity was taken usinga conductivity meter (Mettler Toledo, USA) at roomtemperature. Samples were run in duplicates.

Solubility in water and HCI: For water solubility (S), 0.5 g ACsamples were added to 100 mL of distilled water in 250 mLflasks and shaken at 200 rpm in a shaker (Labortechnik mbH,Germany) for 2 h at ambient temperature. The mixtures werefiltered through pre-weighed Whatman No. 1 size 15 filterpapers. The filter papers containing the residual carbons weredried in the oven (Thermo lab industries) for 12 h at 105EC.After cooling to ambient temperature, in a desiccator, thefilter papers together with residual carbons were weighed.

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The percentage solubility in water was calculated as theweight ratio of unrecovered carbon to the original sample.For solubility in HCl, the same method was followed but 0.2 MHCI was used instead of water24:

(2)Loss in weight on dissolutionS (%) = 100

Weight of original carbon

Moisture content: Thermal drying method was used in thedetermination of moisture content of the samples accordingto the method of Rengaraj et al.25. About 1 g of thepowdered air dried activated carbon powder was taken in apreviously weighed crucible. The crucible was placed in anelectric hot air oven maintained at about 110EC. After onehour the crucible is taken out, cooled in a desiccator andweighed again. The loss in weight of the powder reported onpercentage basis gives moisture content in the sample as:

(3)Loss in weight on dryingMoisture (%) = 100

Initial sample weight

Ash content: The ash content of the carbons was determinedusing the standards ASTM procedure26 D2866-94. This methodinvolve heating the sample at 650EC for several hours untilconstant weight has been achieved. The ash is then weighedand the ash content of the AC is calculated as:

(4)D-BTotal ash (%) = 100C-B

where, B is the weight of the crucible (g), C is the weight ofcrucible plus original carbon sample (g) and D is weight ofcrucible plus ash containing sample (g).

Determination of apparent density: An empty drygraduated cylinder was weighed. A samples of dry activatedcarbon SAC and PASC were packed into the cylinder andreweighed27 as:

(5)3Weight of dry activated carbonDensity (g cm¯ ) =

Volume of dry material

Chemical characteristicsAcidic and basic groups: Surface oxygen groups on carbonmaterials are usually determined by titrations in aqueoussolutions. The amount of acidity/basicity of functional groupswas determined by Boehm titration method28. Boehm titrationis an acid-base titration method which is used to determinethe amount of surface oxygen groups (acidic or basic) present

on carbon surfaces (activated carbon, carbon black,graphene, carbon nanotubes, etc). The NaOH solution wasstandardized by standard KHC8H4O4 and the HCl solution wasstandardized by Na2CO3 solution. Both Na2CO3 and NaHCO3were dried in an oven at 110EC for 3 h before thestandardizations were carried out. Similarly, all the producedchars were dried in the oven at 110EC for 3 h before theBoehm titration was carried out. A known amount ofadsorbent was added into 50 mL of the solutions of NaHCO3(0.1 N), Na2CO3 (0.1 N), NaOH (0.1 N) and HCl (0.1 N). Theconical flasks were sealed and shaken at room temperaturefor 44 h. The solutions were then filtered and 10 mL of eachfiltrate was titrated with HCl (0.1 N) and NaOH (0.1 N).The acidic strength was calculated by measuring the volumeof HCl consumed due to the titration with the solutions ofNaOH, Na2CO3 and NaHCO3. Accordingly, the basic strengthwas calculated by measuring the volume of NaOH consumedin order to neutralize HCl. For the titration of HCl and NaOHsolution, phenolphthalein was used as an indicator while forNa2CO3 and NaHCO3, the pH meter was used; the end pointswere 8.3 and 4.5 respectively. The basic group content on thechar was calculated from the amount of HCl that reacted inthe bottle. The acidic groups were calculated using the factsthat:

C NaOH neutralizes carboxylic, phenolic and lactonicgroups

C Na2CO3 neutralizes carboxylic and lactonic groupsC NaHCO3 neutralizes only carboxylic group

Surface functional groups: The IR spectroscopy wasemployed to determine the presence of functional groups inthe adsorbent at room temperature. The IR spectra of SDC andPASC were recorded using a MATTSON 5000 infraredspectrophotometer. A weight of sample (2 mg) was mixedwith 100 mg of IR-grade KBr. The resulting mixture was grindinto powder and pressed into KBr discs. The samples werescanned 20 times at 4 cmG1 resolution in the 4000-500 cmG1

range and then averaged.

Determination of the iodine number: For the iodinenumber test of Gimba and Musa29 was adopted. A stocksolution was prepared containing 2.7 g of iodine crystals and4.1 g of potassium iodide per litre. The prepared stocksolution was standardized using a standard solution of sodiumthiosulphate. Into a 100 cm3 volumetric flask, 0.5 g of theactivated carbon and 10 cm3 of 5% v/v hydrochloric acid wasintroduced. The flask was swirled until the carbon was wetted.Then 100 cm3 of the stock iodine solution was added andagitated at a fast speed using an electric shaker for a period

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of 60 min. The mixtures were filtered through a sinteredglass crucible. An aliquot portion (20 mL) was titrated with0.1 M sodium thiosulphate using starch as indicator. Theconcentration of iodine adsorbed by the activated carbon atroom temperature was calculated as amount of iodineadsorbed in milligrams from the following relationship:

(6)1 s b s2a

M (V V )Amount of I adsorbed (mg g¯ ) =

2M

where, Ms is molarity of thiosulphate solution (mol dmG3),Vs is volume of thiosulphate (cm3) for titration of carbonaliquot, Vb is volume of thiosulphate (cm3) for blank titrationand Ma is mass of carbon sample (g).

Determination of the specific surface areas: The specificsurface areas of SDC and PASC were determined using themethylene blue method described elsewhere30. The 2.0 g ofSDC and PASC powder was dissolved in 200 mL of deionizedwater and 100 mg LG1 methylene blue solution was added tothe adsorbent suspension and agitated in a shaker for 2 h.Thereafter, it was kept for 24 h to reach equilibrium, afterwhich 10 mL aliquot was taken and centrifuged. The aliquotwas then analyzed in a UV/visible spectrophotometer atmaximum wavelength of 660 nm to determine theamount of methylene blue absorbed. Also 200, 300, 400, 600and 700 mg LG1 solutions of methylene blue were then addedsequentially and the previous steps repeated. A graph ofconcentration of MB added versus the absorbed MB was usedto identify the point of complete cation replacement. TheSpecific Surface Area (SSA) was calculated as:

(7)MB V MBs

M A ASSA =

319.98 M

where, MMB is amount of MB absorbed at the point ofcomplete cation replacement, Ms is mass of adsorbent, Av isAvogadro’s number and AMB is the area covered by MBmolecule (assumed to be 130 AE2).

Determination of the phenol number: The 100 cm3 of300 ppm solution of phenol was taken in a 250 cm3 leak proofreaction flask. The pH of the solution was adjusted to neutralby adding 0.1 N NaOH or 0.1 N H2SO4. A known weight of theactivated carbon powder was added to it. The solution wasequilibrated for 48 h at room temperature followed byfiltration and subsequent analysis of the filtrate for phenol

concentration. The residual concentration of phenol wasdetermined by spectrophotometric analysis at a wave lengthof 269 nm31.

Adsorption of nicotinic acid: The study of nicotinic acidadsorption took place in a constant temperature bath (20NC)under continuous shaking. Ultra pure nicotinic acid wasobtained from Merck. A stock nicotinic acid solution wasprepared initially at concentration of 500 mg LG1, usingdistilled and deionised water. Equilibrium experiments werecarried out by the placement of various amounts of activatedcarbons in 250 mL Erlenmeyer flasks and addition of thenicotinic acid solution. The mixtures were then shaken for3 days, this time was considered adequate for nicotinic acidadsorption to reach equilibrium. At the end of the reactiontime, the content of each flask was filtered and the filtratewas analyzed by a UV-spectrophotometer (Spectronic 20D) at 272 nm for the determination of nicotinic acid. The RemovalEfficiency (RE) of nicotinic acid by the activated carbon atspecific time and concentration was calculated according toEq. 1:

(8)Co-CeRE = ×100Co

where, Co and Ce (mg LG1) are the initial and equilibriumconcentrations respectively.

RESULTS AND DISCUSSION

Carbons characterizationPhysical characteristics: Characterization of the carbons isimportant in the formulation of a consistent quality carbonthat can be used in water treatment plants or any otherindustrial applications. The physical characteristics of theprepared carbons are listed in Table 2. The carbon yield forSDC was 33.8% while, PASC showed 29.4% of carbon yield.

Table 2: Physical characteristics of SDC and PASCParameters SDC PASCCarbon yield (%) 33.80 29.40pH (1% solution) 7.40 6.00Conductivity (1% solution) (µS cmG1) 144.00 327.00Solubility (%)Water 6.70 8.40HCI 7.80 9.30Apparent density (g cmG3) 0.48 0.59Moisture content (%) 5.40 4.60Ash content (%) 6.80 6.60SDC: Sawdust carbon and PASC: Phosphoric acid activated sawdust carbon

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These values are typical range for most AC prepared fromagro waste. The measured values for the pH, electricalconductivities, solubility in water and HCI, moisture content,ash content and densities of the SAC and PASC are shown inTable 2. The pH values for the SDC and PASC solutions werefound to be 7.4 and 6.0 respectively. The pH Value of activatedcarbon is a measure of whether it is acidic or basic. The pH isdefined as the minus logarithm of the hydrogen ion (H+)concentration. The dissociation constant, kW of water has avalue of 10G14 at 25EC and is equal to [H+][OHG]. The proton ishydrated according to Cπ+2H2O6Cπ·H3O++OHG. Thus, forwater in equilibrium with a carbon, if the water has a pH value

Asian J. Sci. Res., 9 (2): 45-56, 2016

Fig. 1: FTIR spectrum of SDC

Table 3: Results of Boehm titration for SDC and PASCConcentration of surface group (mmol gG1)------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Types of carbon Carboxylic Lactonic Phenolic Total acidic group (mmol gG1) Total basic group (mmol gG1)SDC 0.788 0.175 0.099 1.062 0.446PASC 1.775 0.577 0.115 2.467 0.148SDC: Sawdust carbon and PASC: Phosphoric acid activated sawdust carbon

to be due to the strongest of the organic acids and is assumedto be primarily carboxylic acids, referred to as strong acidfraction. The amount of Na2CO3 neutralized is considered tobe due to the strong organic acid fraction and the moderatestrength organic acids (low pKa phenols) and lactonesfraction. When lactones hydrolyze into carboxylic acids andphenols, the carboxylic acids and some or all of the phenolsare expected to be neutralized37 by the Na2CO3. The results ofthe acid-base neutralization from the respective aqueoussolutions given in Table 3 PASC shows more number of totalacidic groups compared to basic groups which will alsoaccount for efficient uptake of different adsorbates.

FTIR analysis: The infrared spectroscopy that providesinformation on the chemical structure of carbons is shown in

Fig. 1 and 2 and the observed absorption bands in FTIR spectraof SDC and PASC are summarized in Table 4. The activatedcarbons showed a wide band at about 3404-3431 cmG1 thatcan be assigned to the O-H stretching mode of hexagonalgroups and adsorbed water. The band at about2330-2359 cmG1 is assigned for CH3 of alkane while that bandat about 1836 cmG1 is assigned for C=C-H stretching. The FTIR bands can be assigned to the presence of carboxyls, lactonesand phenols groups as reported by the surface chemistryanalysis using Boehm method. The carboxyl groups show twomain absorption features corresponding to a carbonyl (C=O)at 1705 cmG1 stretching vibrations in ketones, aldehydes,lactones and carboxylic groups and C-OH vibrations in therange of 1200-1300 cmG1. Peak appears38 at 1456 cmG1 showsthe C-H bend in CH3. The peaks at 1058, 1217 and 1317 cmG1,

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Fig. 2: FTIR spectrum of PASC

Table 4: FTIR data of SDC and PASCSC PASC--------------------------------------------- -----------------------------------------------Wave No. Assigned Wave No. Assigned(cmG1) functional group (cmG1) functional group3431.58 -OH 3404.58 -OH2361.02 CH3 (alkane group) 3122.95 CH3 (alkane group)2330.16 C=C-H Stretching 2359.09 CH21836.35 Ar-C=O 1919.29 P-O-P asymmetric1705.18 C=C 1618.38 stretching1606.81 CH2 1402.34 C-P stretching1516.15 C-H bend 1188.23 P=O stretching1456.35 C-OH 1070.56 P-P stretching1425.48 Secondary alcohols 962.54 Out-of-plane C-H1317.46 Primary alcohols 636.55 Bending1217.16 C-H 534.321161.221111.071058.99669.34SDC: Sawdust carbon and PASC: Phosphoric acid activated sawdust carbon

attributable to C-O absorption, probably phenol, aromaticether and OH deformation structure. The C-O stretching bandat 1217 cmG1 confirms the lignin structure of the carbons. Thepeaks at 1606 cmG1, the well-known carbonaceous hand

which is variously attributed to aromatic structure and tounconjugated, chelated carbonyl group and the peaks at1618 cmG1 attributable to C-O stretch, probably carbonyl(conjugated C = 0) and/or carboxyl structure. The bandsbetween 1161 and 1111 cmG1 are assigned to C-O stretchingvibration in phenol and alcohol groups. The vibration of band669 cmG1 was attributed to aromatic C-H bending. The bandobserved at 1402 cmG1 is ascribed to C-O-H stretchingvibration in carboxylic group which shows stronger intensitiesat higher temperature. Peaks at 534 and 636 cmG1 areassigned to the out-of-plane C-H bending mode39. Somefundamental IR absorption frequencies of phosphorizedactivated carbon are given in Table 4. The IR spectrum showsabsorption bands due to aliphatic (2359 2361 cmG1) andaromatic structures (2730 cmG1). A strong new band at1618 cmG1 on the phosphoric acid treatment is assigned toC=O stretch in carboxylate, ketones, lactones and aldehydes.The absorption peak at (1170-1188 cmG1) reported theappearance of C-P bonds in carbon obtained from activationby phosphoric acid, this peak was assigned to phosphates.P-OH bending, P-O asymmetric stretching and P=O

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Table 5: Adsorptive characteristics of SDC and PASCParameters SDC PASCIodine number (mg gG1) 554.3 862.1Methylene blue number (mg gG1) 180.3 306.0Specific surface area (m2 gG1) 571.8 970.6Phenol number (mg gG1) 72.4 99.0Nicotinic acid number (mg gG1) 178.5 238.0SDC: Sawdust carbon and PASC: Phosphoric acid activated sawdust carbon

stretching were shown in phosphate-carbon complexes40. Itcan be notified that increasing the intensity of the FT-IRspectra for C=O (carboxylic group), O-H (hydroxyl group) andC-O (phenol group) stretching vibrations indicate thepresence more oxygen functional groups on the phosphorizedactivated carbon40. The processes occurring during thereaction of phosphoric acid at low temperatures are probablyanalogous to acid-catalyzed cracking reactions in coalliquefaction using Lewis acids. Acid catalysts can promoterupture of methylenic, etheric and thioetheric linkagesbetween cyclic structures in carbon by ionic mechanismswhich involve protonation followed by bond scission41.Proton donation from phosphoric acid to aromatic entities,-Ar- can be represented as:

….-Ar-…+H3PO46….-(ArH+)-…+ H2PO4G (9)

Adsorptive characteristicsIodine number: Adsorptive properties are directly linked withthe porosity of activated carbon as the highly porous carboncan adsorb relatively large quantities of adsorbate. Iodinenumber can be correlated with ability to adsorb low molecularweight substances as the iodine molecule is relatively smalland so provides a measure of surface area or capacity availableto small adsorbates. Iodine numbers for commercial

adsorbents range from 300-1200 mg gG1. Iodine number is afundamental parameter used to characterise activated carbonperformance. It is a measure of the micropore content of theactivated carbon and is obtained by the adsorption of iodinefrom solution by the activated carbon sample. The microporesare responsible for the large surface area of activated carbonparticles and are created during the activation process. It is inthe micropores that adsorption largely takes place. Table 5suggested that the values of iodine number obtained for PASC(872.4 mg gG1) is greater than the value obtained for SDC(554.6 mg gG1). The iodine number is used to measure theporosity of the activated carbon by adsorption of iodine fromsolution. Each 1.0 mg of iodine adsorbed is ideally consideredto represent 1.0 m2 of activated carbon internal surface area.Hence, the internal surface areas of SDC and PASC can beestimated to be 554.6 and 872.4 m2 gG1 respectively.

Methylene blue number and surface area: Methylene bluenumber indicates ability of adsorbing high molecular weightsubstances and colour. The adsorption isotherms ofmethylene blue onto PASC and SDC are shown in Fig. 3. Byusing Langmuir isotherm equation the methylene bluenumber obtained for PASC (306.0 mg gG1) was greater thanthe value obtained for SDC (180.3 mg gG1). Any carbonshowing methylene blue number above 200, indicates thecarbon with good activity for adsorption. So results ofadsorptive properties indicate that sawdust is a very goodsource of raw material for the production of activated carbonof high efficiency. The surface areas calculated frommethylene blue monolayer adsorption for PASC and SDC werefound to be 970.6 and 571.8 m2 gG1 respectively.

The adsorption isotherms of phenol onto PASC and SDCare shown in Fig. 4. The Langmuir maximum adsorptioncapacity of phenol on the resultant PASC and SDC was equal99.0 and 72.4 mg gG1 respectively. The adsorption isothermsof nicotinic acid onto PASC and SDC are shown in Fig. 5.The Langmuir maximum adsorption capacity of nicotinic acidon the resultant PASC and SDC was equal 99.0 mg gG1 and72.4 mg gG1 respectively. The results obtained show that theprepared activated carbons can serve as a good adsorbents.

Cost estimation: The economic viability of the adsorptionprocess depends on the cost effectiveness as well as theavailability of adsorbent. Because of their great capacity toadsorb pollutants ACs are the most effective adsorbents.However, commercial AC is quite expensive and the higher thequality, the greater the cost. The precursor use in the presentstudy, sawdust, was collected free of cost from the nearby

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inic

aci

d (m

g g

)G1

Concentration of nicotinic acid (mg LG1)

Fig. 4: Adsorption isotherms of phenol onto SDC and PASC

Fig. 5: Adsorption isotherms of nicotinic acid onto SDC andPASC

located sawmill. After consideration the expenses for transport($20 tG1), chemicals ($40 tG1), electrical energy ($20 tG1) andman power ($20 tG1), the final developed carbon would costapproximately $100 tG1. The cheapest variety of commercialgrade ACs available in Jordan cost approximately$900-$1100 tG1. This big difference in cost confirms the viableapplication of sawdust AC as a low cost adsorbent.

Results of this study could provide activated carbonconsumers with cost effective and environmentally friendlyalternative sources. The study aims to promote innovative useof local raw materials and relatively low-cost techniques inproduction of activated carbon. In the present studies relatedto the production of powdered activated carbon, by using oaksawdust, as a precursor material and phosphoric acid (H3PO4)

as an activating agent are presented. Phosphoric acidactivation has been applied to coconut shell, coals,hardwoods, shells of nuts like almond, pecan, black walnut,macadamia nut, cotton stalks and palm date pits18. Mariet19

showed that the reaction of a lignocellulosic precursor with astrong chemical reagent, such as phosphoric acid (H3PO4), attemperatures up to 350EC or above can lead to the formationof a porous carbon. The activated carbons thus obtained werecharacterized based on the following parameters viz., pH,conductivity, solubility, moisture content, ash content andapparent density. Chemical characterization of the resultantactivated carbons was studied by Fourier transform infraredspectroscopy and Boehm titration which revealed thepresence of oxygen containing surface functional groupslike carboxylic, lactonic, phenolic in the carbons. Theresults of FTIR (Fourier-transform infrared spectroscopy)strongly support significant chemical and spectral changesoccurring with the activation of the sawdust for phosphoricacid treatment. Phosphoric acid treatment resulted in theintroduction of more acidic groups (carbonylic, phenolic,carboxylic and lactonic). The final developed carbon wouldcost approximately $100 tG1.

CONCLUSION

The results show that agricultural waste oak sawdust canbe used as a promising precursor material for the productionof low cost activated carbon. The result obtained also showsthat these activated carbons can serve as a good adsorbents.

ACKNOWLEDGMENTS

The author acknowledges Mr. Sayel Alnezami forproviding help in carbonization of sawdust samples andUV-VIS measurements, Mr Hmood Alhamaideh for help in FTIRanalysis.

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