For old ages, personal attention merchandises have made their manner into the environment raising concern about their possible harmful effects on the ecosystem and worlds perchance exposed to these compounds through medium such as H2O ( Daughton and Ternes 1999 ) . Triclosan [ TCS ; 5-chloro-2- ( 2,4-dichlorophenoxy ) phenol ] , a common antimicrobic agent, is a frequent PCP contamination detected in H2O organic structures ( Kolpin et al. 2002 ) and its uninterrupted release into the environment could stand for a menace to H2O systems, including imbibing H2O beginnings and human wellness.
TCS is used in personal attention merchandises such as toothpaste, soaps and detergents, and cosmetics ( European Commission 2009 ) . TCS is extremely hydrophobic, holding a reasonably high log Kow of 4.76, which enables its sorption to particles taking to incomplete remotion during effluent intervention ( Chu and Metcalfe 2007 ; Ying and Kookana 2007 ) . TCS ( pKa = 8.14 ) has been determined in impersonal and anionic signifiers at a 50/50 ratio in effluent intervention installations working at a pH of around 8.0 ( Ngiem and Coleman 2008 ) . Due to its extended usage and uncomplete remotion, TCS can be found in about every aquatic environment, including effluent intervention wastewaters, surface Waterss, lakes, and river deposits ( Wilson et al. 2009 ; Kolpin et Al. 2002 ; Lindstrom et Al. 2002 ; Singer et Al. 2002 ) . Technetium is reported to be highly toxic to a assortment of aquatic beings which includes invertebrates, fish, amphibious vehicles, algae and workss ( Palenske et al. 2010 ; Raut and Angus 2010 ; DeLorenzo and Fleming 2008 ; Dussault et Al. 2008 ; Yang et Al. 2008 ; Coogan et Al. 2007 ; Ishibashi et Al. 2004 ; Orvos et Al. 2002 ) .
*Author to whom all correspondence should be addressed. Electronic mail: felix.roman @ upr.edu
Other surveies reported TCS to organize toxic debasement merchandises ( Aranami and Readman 2007 ) and to develop microbic opposition ( Heath et al. 2000 ; Heath et Al. 1999 ; Heath et Al. 1998 ; Hoang and Schweizer 1999 ; McMurry et Al. 1998a ; McMurry et Al. 1998b ) . In add-on, TCS is reported to respond with free Cl during H2O disinfection organizing by-products that include dioxins, chlorinated phenoxy-phenols, chlorinated phenols, and trihalomethanes ( Buth et al. 2010 ; Buth et Al. 2009 ; Canosa et Al. 2005 ; Rule et Al. 2005 ; Kanetoshi et Al. 1987 ; Onodera et al. 1987 ) .
Assorted attacks have been used to take TCS and other contaminations from aqueous media, peculiarly the usage of membranes for nanofiltration, ultrafiltration and change by reversal osmosis ( Ngiem and Coleman 2008 ; Snyder et Al. 2007 ; Yoon et Al. 2007 ; Yoon et Al. 2006 ) . Other options include the usage of activated Cs ( Behera et al. 2010 ; Fang et Al. 2009 ; Snyder et Al. 2007 ) , chlorination and UV disinfection ( Buth et al. 2011 ) , sonochemical and electro-fenton debasement ( S & A ; aacute ; nchez-Prado et Al. 2008 ; Sir & A ; eacute ; s et Al. 2007 ) and activated sludge ( Bester 2003 ) . Drawbacks originating from these methods are comparatively high cost of operation, C regeneration and disposal related to the usage of membranes and activated Cs, formation of chlorinated debasement merchandises and uncomplete remotion. Therefore, it is imperative to research executable, cost-efficient options for the remotion of TCS and other contaminations from environmental Waterss.
TCR represents a feasible medium for the surface assimilation of contaminations from aqueous solutions. The recycling of this stuff becomes necessary due to the increasing production and accretion of tyres worldwide ( Jang et al. 1998 ) . TCR is composed of of course and man-made gum elastics, largely SBP ( 62.1 % ) , CB ( 10-45.6 % ) , steel, and oxides such as SiO2 and ZnO ( 0.55-2.79 % ) ( ISRI 2007 ; R.M. Association 2006 ; Amari et Al. 1999 ) . CB has been used as adsorbent of chlorophenols, p-nitrophenol, methylbenzene and xylol from aqueous solutions ( Alamo et al. 2011 ; Dom & A ; iacute ; nguez-Vargas et Al. 2009 ; Gonz & A ; aacute ; lez-Mart & A ; iacute ; n et Al. 1994 ) and as molecular screen for trying air contaminations ( Betz and Supina 1999 ) . Therefore, the presence of CB in TCR should lend in the remotion of contaminations through surface assimilation mechanisms ( Alamo et al. 2011 ) . Furthermore, TCR has been used as adsorbent of naphthalene, methylbenzene, xylene, Cd ( II ) , quicksilver ( II ) , lead ( II ) and Cu ( II ) ( Alamo et al. 2011 ; Calisir et Al. 2009 ; Entezari et Al. 2006 ; Gunasekara et Al. 2000 ; Rowley et Al. 1984 ) .
In the present work, the usage of TCR for the remotion of TCS from aqueous solution was studied in batch manner. CB and SBP were besides evaluated individually to compare their sorption capacity with that of TCR, and asses their parts in the overall sorption procedure. Adsorption isotherms were determined and fitted by the Langmuir and Freundlich theoretical accounts. The consequence of solution pH on the surface assimilation procedure was investigated every bit good. Using TCR as adsorptive stuff contributes by spread outing the recyclability options of waste tyre gum elastic, in add-on to its highly low cost ( $ 0.15/lb in Puerto Rico ) , and easiness of managing as a farinaceous sorbent stuff.
MATERIALS AND METHODS
TCR was provided by REMA Inc. , a tyre gum elastic recycling company located in Caguas, Puerto Rico. TCR mesh 30 ( mean diameter 0.67 millimeter ) was washed with deionized H2O for 24 hours and dried at room temperature. CB N330 ( mean atom diameter 46 nanometer ; surface country 80 sq m/g, Othmer 1992 ) was produced by Sid Richardson Carbon Company ( CAS 1333-86-4 ) . SBP was purchased from Sigma Aldrich ( CAS 9003-55-8 ) , and was trimmed to a similar size as TCR ( Alamo et al. 2011 ) .
Triclosan [ TCS ; 5-chloro-2- ( 2,4-dichlorophenoxy ) phenol ] ( ?97 % ) ( CAS # 3380-34-5 ) was purchase from Fisher Scientific, USA. TCS stock solutions were prepared utilizing brownish-yellow volumetric flasks at concentrations of 1000 mg/a„“ in HPLC class methyl alcohol ( Fisher Sci. , USA ) . Solutions were transferred to amber bottles and stored at 4 -C and used within two hebdomads of readying. Methanol was added to the solutions ( 20 % v/v ) as co-solvent to guarantee TCS stableness during sorption trials. Ultra High Quality H2O ( Barnstead, 18.2M?_cm ) were used to fix the aqueous solutions for the surface assimilation trials.
Adsorption experiments were carried out in batch manner utilizing 120 ma„“ gold bottles incorporating 100 ma„“ of 60 mg/a„“ TCS solution. Predetermined concentrations of TCR ( 1 g/a„“ ) , CB ( 3 g/a„“ ) and SBP ( 6 g/a„“ ) were added to the bottles and placed in a thermoregulator controlled shaker ( INFORS AG HT ) at a changeless temperature of 25 -C. Agitation velocity was set at 200 revolutions per minute for 9, 6 and 24 hours for TCR, CB and SBP severally as determined by old kinetic experiments. CB and SBP concentrations were calculated taking into account their concentration in the TCR matrix ( 30 % and 60 % w/w, severally ( Alamo et al. 2011 ) . Samples were analyzed at given clip intervals and experiments were performed in triplicate.
The sum of TCS adsorbed was calculated from the difference between the initial TCS concentration and the one staying in solution after equilibrium was reach by utilizing the undermentioned equation:
( 1 )
where qe is the concentration of TCS adsorbed ( mg/g ) , C0 and Ce are the initial and equilibrium liquid-phase concentrations of TCS in the solution ( mg/a„“ ) , severally, V is the volume of the solution ( a„“ ) and W is the sum of adsorbent used ( g ) .
Determination of the pH of the point of zero charge ( pHpzc ) .
The pHpzc of TCR, CB and SBP was determined utilizing the batch equilibrium technique ( Far & A ; iacute ; a et Al. 2004 ) . 50 milliliter of 0.01M NaCl solutions were placed in closed gold bottles. The pH was adjusted to a value between 2 and 12 by adding HCl or NaOH 0.1M solutions. Then, 0.15 g of TCR, CB and SBP were added and the concluding pH measured after 48 hours of uninterrupted agitation at room temperature. The difference between the initial and concluding pH value was plotted against the initial pH value. Therefore, the pHpzc is the point where the curve intersects the abscissa ( Rao et al. 2011 ) . Figure 1 show the pHpzc determined for TCR ( 7.01 ) , CB ( 8.03 ) and SBP ( 4.99 ) .
All analyses were performed with an Agilent 1200 Series HPLC system ( Agilent Technologies, USA ) equipped with a Zorbax Eclipse XDB C-8 column ( 4.6 mm-150 millimeter, 5µm ) , a binary pump ( model G1312A ) and a diode array sensor ( model G1315D ) at a sensing wavelength of 280 nanometers. The nomadic stage used was 70 % acetonitrile and 30 % deionized H2O, flow was set at 1 ma„“/min, sample injection volume was 20 µa„“ and column temperature was maintained at 25 -C throughout the analyses.
RESULTS AND DISCUSSION
3.1. Consequence of solution pH on TCS remotion
The consequence of solution pH on triclosan surface assimilation utilizing TCR, CB and SBP was evaluated in batch experiments in a pH scope of 3 to 9. TCS solutions of 10 mg/a„“ were placed in contact with 0.1, 0.3 and 0.6 g of TCR, CB and SBP severally at 25 -C. Solutions pH was adjusted utilizing 0.1M HCl or NaOH solutions. As shown in figure 2, TCS remotion utilizing TCR and CB decreased as pH increased. These consequences are consistent with those reported in the literature utilizing activated C and clays ( Behera et al. 2010 ) . As solution pH exceeds TCS dissociation invariable ( pH & A ; gt ; pKa ) , the anionic signifier of TCS is expected to be at a higher ratio than the impersonal signifier in solution ( Ngiem and Coleman 2008 ) .
Solution pH besides affects the surface chemical science of the stuffs. When the solution pH & A ; gt ; pHpzc ( 7.01 and 8.03 for TCR and CB severally ) , the net surface charge of TCR and CB surfaces are negative. Therefore, at pH 9, TCS sorption on TCR and CB is cut down due to electrostatic repulsive forces between the anionic TCS signifier and the negatively charge TCR and CB surfaces. TCS remotion with TCR and CB decreased from ~ 89 and 95 % in pH 3 to ~69 and 83 % in pH 9 severally ( Table 1 ) . Sing SBP ( phpzc = 4.99 ) , no important consequence was observed on TCS remotion with alterations in pH ( ~93 % remotion in all pH evaluated ) ( Table 1 ) , which suggest a strong soaking up mechanism lending along with the surface assimilation based one ( Alamo et al. 2011 ) . TCS molecules could be preponderantly absorbed inside the SBP polymeric ironss, whereas electrostatic repulsive forces are minimized, non been the instance with TCR and CB where surface assimilation onto surface is the dominant mechanism.
3.2. Adsorption isotherms
In order to understand the surface assimilation mechanisms of TCS onto TCR, CB and SBP, two good known surface assimilation isotherm theoretical accounts, Langmuir and Freundlich were used to suit the surface assimilation experimental consequences. The Langmuir theoretical account assumes that surface assimilation takes topographic point at specific homogenous sites within the adsorbent. A additive signifier of the Langmuir equation may be written as:
( 2 )
where qe is the sum of TCS adsorbed at equilibrium ( mg/g ) , Ce is the TCS equilibrium concentration ( mg/a„“ ) , b is a coefficient related to the affinity between the adsorbent and TCS ( a„“/mg ) and qm is the maximal surface assimilation capacity ( mg/g ) . If TCS sorption onto TCR, CB and SBP are fitted by the Langmuir equation, qm and B can be evaluated from the incline and the intercept of the secret plan 1/qe versus 1/Ce.
In order to measure the favorability of the surface assimilation procedure, the separation factor ( RL ) , a dimensionless invariable based on the Langmuir equation was calculated:
( 3 )
where B is the Langmuir invariable and C0 is the initial TCS concentration in solution. It is stated that the RL values are declarative of the type of isotherms to be irreversible ( RL = 0 ) , favourable ( 0 & A ; lt ; RL & A ; lt ; 1 ) , additive ( RL =1 ) or unfavourable ( RL & A ; gt ; 1 ) . RL values calculated for TCS surface assimilation onto TCR, CB and SBP at assorted pH values and concentrations were less than 1 and greater than zero bespeaking favourable surface assimilation ( Table 2 ) .
Similarly, the Freundlich theoretical account is normally used to depict sorption onto heterogenous surface. A additive signifier of the Freundlich equation may be written as:
( 4 )
where KF represents the comparative surface assimilation capacity of the adsorbent [ ( mg/g ) ( a„“/mg ) 1/n ] and N is a changeless declarative mood of the strength of the surface assimilation procedure. If sorption of TCS onto TCR, CB and SBP are fitted by the Freundlich equation, KF and Ns can be obtained from the secret plan of log qe versus log Ce.
The uptake dependence ( qe ) of TCS on the equilibrium liquid-phase concentration ( Ce ) , every bit good as the Langmuir and Freundlich isotherm secret plans of TCS sorption onto TCR, CB and SBP at 25 -C and pH 3 are shown in Figures 3-5 severally. The Langmuir invariables B and qm and the Freundlich invariables KF and n every bit good as their correlativity coefficients ( R2 ) obtained from the secret plans of 1/qe versus 1/Ce ( Langmuir theoretical account ) and log qe versus log Ce ( Freundlich theoretical account ) for the surface assimilation of TCS onto TCR, CB and SBP at assorted pH values are listed in Tables 3-5 severally.
In general, the arrested development coefficient ( R2 ) determined from additive arrested development analyses is the most widely used standards in measuring how good the selected theoretical account tantrum to the experimental information. Still, the average comparative per centum divergence modulus ( P ) is widely employed because it gives a clear thought of the average divergency of the predicted information from the experimental information, and therefore supplying more precise information about the tantrum of experimental informations to the evaluated isotherm theoretical accounts, peculiarly when there are no appreciable difference between the arrested development coefficients obtained for different isotherm theoretical accounts ( Ayar et al. 2008 ) . The P value can be calculated by utilizing the undermentioned equation:
( 5 )
where qe ( exp ) is the experimental value, qe ( pred ) is the predicted value and N is the figure of observations. In general, it is stated that a P value smaller than 5 indicates an highly good tantrum ; a P value between 5 and 10 represents a reasonably good tantrum ; and a P value greater than 10 shows a hapless tantrum. Calculated P values used to measure which isotherm theoretical account best explain the sorption of TCS onto TCR, CB and SBP are listed in tabular arraies 2-4.
Although arrested development coefficients obtained for TCS sorption on TCR, CB and SBP utilizing the Langmuir theoretical account were somewhat higher than those obtained with Freundlich ‘s, ( tables 2-4 ) , calculated P values were lower for the Freundlich theoretical account in all the adsorbents at all pH values evaluated compared to those calculated with Langmuir ‘s. These consequences indicate that sorption of TCS onto TCR, CB and SBP could be best explained by the Freundlich theoretical account. For TCR and CB, the consequence of pH was noticeable on the deliberate Freundlich surface assimilation capacity ( KF ) . As pH increased, KF besides decreased ( table 2-3 severally ) which is in understanding with what was observed in figure 2 ; electrostatic repulsive forces affects TCS sorption on TCR and CB as pH additions. In the other manus, no drastic alterations in KF were obtained for SBP as pH increased ( table 4 ) , which is in understanding with what was antecedently observed in figure 2, connoting a prevailing soaking up procedure. Therefore, TCS sorption behaviour onto SBP could depend on the polymer-water divider coefficient and non on the surface features ( Alamo et al. 2011 ) .
Valuess of Freundlich ‘s n parametric quantity for TCR were over 1 in all instances, proposing that sorption onto surface favours at lower concentrations as evidenced by the higher remotion per centums shown in table 1a. For CB, n values were over 1 in a pH scope of 3-7, but at pH 8 and 9 Ns values were below 1, proposing that sorption onto surface at that peculiar pH values favours at high concentrations ( table 1b ) . CB remotion per centums in the concentration scope of 30-60 mg/a„“ did non demo drastic differences when changing pH values ( table 1b ) ; the same could non be said for the remotion percentages for the 10 and 20 mg/a„“ solutions which removal % decreased with alterations in pH. For SBP, Freundlich ‘s n parametric quantity was similar at all pH values studied ( n ~1.3 ) ( table 1c ) . In add-on, no considerable differences were observed in the remotion percentages at the concentrations and pH values evaluated, which suggest that soaking up is the dominant mechanism in the remotion of TCS with SBP. These observations are in understanding with what was seen in the literature ( Alamo et al. 2011 ) ; sing that TCR is a composite stuff, the ascertained sorption capacity can be explained as the consequence of a combined consequence of surface assimilation by CB nanoparticles and soaking up by the SBP matrix.
3.3. Desorption experiments
Desorption surveies were carried out in batch manner utilizing same conditions as in the surface assimilation experiments. After surface assimilation equilibrium was reached, TCR with the adsorbed TCS was removed from solution and washed with deionized H2O and transferred to clean brownish-yellow bottles incorporating 25 ma„“ methyl alcohol. Methanol was choose as extractant for the desorption of TCS from TCR, CB and SBP because it has been demonstrated to hold no consequence on the physical construction of polymeric stuffs ( Prpich et al. 2008 ) . The bottles were placed in a thermoregulator controlled shaker ( INFORS AG HT ) at a changeless temperature of 25 -C with an agitation velocity set at 200 revolutions per minute. As with the surface assimilation experiments, samples were analyzed at given clip intervals and experiments were performed in triplicate.
Figure 6 shows the desorption behaviour of TCS from TCR utilizing methyl alcohol as the extractant. Previous to the desorption experiments, the concentration of TCS adsorbed onto TCR was calculated ( concentration scope of ~1.1 to 16.5 mg/g ) . Consequences of TCS desorption experiments are listed in table 4. As seen in figure 6, TCS desorption was achieved in 5 hours contact clip with a maximal desorption of ~89 % at the lowest concentration evaluated.
The capacity of TCR to take TCS from aqueous solutions was demonstrated. TCS surface assimilation is pH-dependent with maximal remotion happening at pH 3 ( ~89 % ) . The surface assimilation informations was best fitted by the Freundlich isotherm theoretical account. Desorption of TCS from TCR was achieved ( ~89 % ) , which suggest the viability of this stuff as a low cost, inexpensive alternate adsorbent for the remotion of TCS from aqueous media.
The writers acknowledge the support Rubber Recycling and Manufacturing Company ( REMA ) , the Puerto Rico Water Resources and Environmental Research Institute ( PRWRERI ) , the TOYOTA Foundation, Solid Waste Management Authority of Puerto Rico ( ADS ) and the United States Department of Agriculture- ( 2008-02146 USDA-HSI Program ) .