untitled European Journal of Chemistry 3 (4) (2012) 468‐474 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2012 EURJCHEM DOI:10.5155/eurjchem.3.4.468‐474.706 European Journal of Chemistry Journal homepage: www.eurjchem.com The study of kinetics and thermodynamics of selected pharmaceuticals and personal care products on agriculture soil Shehdeh Jodeh Chemistry Department, An‐Najah National University, Nablus, 11347, Palestine *Corresponding author at: Chemistry Department, An‐Najah National University, Nablus, 11347, Palestine. Tel.: +970.59.9590498; Fax: +970.9.2345982. E‐mail address: sjodeh@hotmail.com (S. Jodeh). ARTICLE INFORMATION ABSTRACT Received: 08 November 2012 Received in revised form: 19 November 2012 Accepted: 22 November 2012 Online: 31 December 2012 KEYWORDS Pollution of the aquatic environment by human and veterinary waste pharmaceuticals is an increasing area of concern but little is known about their ecotoxicological effects on wildlife. In this study, three pharmaceuticals were selected (ibuprofen, amoxicillin and caffeine) as examples that are released in the environment. All of them are marketed in the Palestinian market (Pharmacies), private clinics and hospitals. The adsorption of the selected pharmaceuticals was examined by batch sorption experiments onto agriculture soil. Pharmaceuticals adsorption kinetics followed the pseudo‐second‐order adsorption model. Adsorption isotherms were best fitted by the Freundlich isotherm model. The “n” parameters were higher than 1 and the Kf values for all of them were less than 1. High removal rates of amoxicillin and ibuprofen were achieved in acidic media (pH = 1‐4) and reached more than 88% Except for the caffeine increased at higher pH and reached more than 92%. The thermodynamics parameters showed that the adsorption process on soil was spontaneous and exothermic. Soil Slurries Diffusion Isotherm Adsorption Pharmaceuticals 1. Introduction In the recent years, the occurrence and the fate of pharmaceutically active compounds in the aquatic environment has been recognized as one of the emerging environmental issues that have possibly been affecting the ecological system [1,2]. Pharmaceutical compounds may be described as any chemical used for diagnosis, treatment, alteration or prevention of diseases [3]. Taking into account the use of thousands of pharmaceuticals types in human treatment and in agricultural sector (livestock), it’s not limited the size on the negative effects that these compounds will leave on the environment, as well as high cost to eliminate or mitigate these effects. It was discovered; more than 100,000 types of chemicals are used in our everyday life either in households, industries or agriculture [4]. So, pharmaceutical pollution is one of the most modern and chemical contaminants that pose to the environment. The pharmaceutical compounds used mainly by human and livestock are excreted in slightly transformed or even unchanged form, resulting from the body fluids (urine), or from disposing of the expired drugs, causing serious damage to the ecosystem, which is still in the beginning of the study in Palestine, that’s because our conventional wastewater treatment is the primary mechanism by which pharmaceuticals introduced [5,6]. According to recent research, variety of these compounds were detected in various water samples including hospitals wastewater, pharmaceutical industries, waste water treatment plant effluent, surface and ground water, this illustrated by a study entitled, (occurrence of pharmaceuticals and personal care products along the West Prong little Pigeon River in east Tennessee) [7], which pointed out the presence of concent‐ rations of some drugs in ground water and soil. In addition to the quantities of expired medicines which are disposed of in unsafe ways, it’s common to pour them down in the sink, flush them down in the toilet, or throwing them in the trash, without attention to their risks through landfills leachates that may eventually reach to ground water. Despite of the need for the drugs used for treatment of many diseases, it was found that they leave an adverse effect on non‐target site, such as water, soil, air, health and others. Therefore, they should be used and dealt in a scientific way to reduce as much as possible of their negative effects, by preventing drugs using randomly from general public, reducing distribution of physician free samples, separation of domestic waste, sewage recycling, improvement sewage infrastructure, public awareness, nutrition and health maintenance, drugs alternatives and research development. Locally amoxicillin, ibuprofen, and caffeine are used in pharmaceutical manufacturing products for human and veterinary sector, whether used through physician prescription or by the person himself, this is clear from my reviews of many pharmacies and Palestinian ministry of health. This research aims to study the kinetics and thermodynamics adsorption of the target pharmaceuticals (amoxicillin, ibuprofen and caffeine) using agricultural soil. From the study of adsorption, this will lead to available information about the possibility of those pharmaceuticals to groundwater 2. Experimental 2.1. Chemicals and reagents Amoxicillin, ibuprofen and caffeine of pure substances were obtained from Alfamox (Teofarman, Italy). Acetonitrile and methanol were purchased from Merck (Darmstadt, Germany). Water was p purification sy acetic acid of Aldrich, USA. Borate buf solution of b adjusting to hydroxide. Acc at the conce transferring 0 a 1.0 mL vo acetonitrile. The HPLC fluorescent d model 515 iso and Milleniu Chromatograp RP‐C18 (125 Merck at 25 oC A mixture (67:1:32, v:v:v elution with a then increased were made u wavelength of UV detection f 2.2. Preparati Standard w mobile phase in a 1.0 L volu were combin solution conce flask, 0.1 mL o stand for 30 HPLC analysi standard wo decomposition areas during a days at +4 oC. 2.3. Soil analy The soil s those mention depth of 20 c dried at 105 Several tests w Table 1. Table 1. Soil sp pollution. Soil properties Specific Gravity pH value Clay (%) Silt (%) Moisture content Organic Carbon ( Organic Matter (% 2.4. Kinetics a 2.4.1. Surface Soils are m of a soil deter particle packi aqueous envir It is well factors influe mineralogy, c purified and d ystem. Boric ac f analytical rea ffer was prepar oric acid with pH = 7 with cQ‐Fluoro reag entration of 0 .05 mL of AccQ lumetric flask C system (Wat detector, a 24 ocratic pump, a um software phic analysis p mm x 4 mm, C. e of acetonitrile v) was applied flow program, d to 3 mL/min using fluoresc f 245 nm and at for control at 24 ion of calibrati working solutio for of 1000 mg umetric flask. Al ed and diluted entration of 5, of AccQ‐Fluor r min. The resu s. Studies on rking solution n products in t analytical proc ysis ample was col ned companies m. The sample oC, before any were conducte pecific gravity, pH t (%) (%) %) and thermodyn e area measure made of mineral rmines the gov ing. Clay mine ronments. known that s ncing the beh ation exchange Jodeh / E deionized by cid, sodium hy agent grade w red by mixing 1 h 100 mL of d 0.05 mol/L s gent (purchased 0.25 mmol/L Q‐Fluro reagent and diluting ter USA) equi 489 spectropho Rheodyne valv for collecting performed on a 5 µm particle e, acetic acid a d as mobile ph from 1.0 mL/m n from 4 to 8 cence detection t an emission o 45 nm. ion curves ons were prep g/L of each of t liquots from ea d with mobile 10, 20, 30 and reagent was ad ulting solutions the stability n showed tha the chromatogr edure, even aft lected from a s from an area e was sieved in y treatment wit ed on the soil s H, texture, and m namics study ement l grains. The gr verning particl erals results fr urface phenom havior of fine‐ e capacity, sur European Journa a SolPure‐7 w ydroxide and g were obtained 100 mL of 0.1 m distilled water solution of so d from Waters, was prepared kit (5 mmol/L) to the mark pped with a otometric dete ve with a 20 µL g data was a Lichrosphere size) column nd deionized w hase at an isoc min initially to 4 min. Measurem n at an excit of 368 nm and u ared individua the pharmaceu ch working solu e phase to yie d 40 mg/L. To dded and allow were subjecte of the analyte at there were ram or differen fter storage for field far away a of 1000 m2 a n 2.0 mm sieve th pharmaceut sample as show moisture for soil b Result 2.34 7.14 41 71 29 7.34 10.36 ain size distrib e level forces, rom weatherin mena are impo ‐grained soils. rface area, and al of Chemistry 3 water lacial from mol/L r and dium USA) d by ) into with 2475 ector, L loop used. e 100 from water cratic 4 min, ments tation using lly in ticals ution eld a each ed to ed to es in e no nce in r four from and a e, and ticals. wn in before ution inter ng in ortant Clay d clay fract sign of fi refer m2/g adso temp adso was the s Figu 2.4.2 A thre dilut stud stud effec thre Erle conc sorb shak TEC 25±1 were aque NaO were influ were solu by resp T 1. eq whe drug of th The eval 2.4.3 T impo capa 2.4.4 I adso (4) (2012) 468‐4 tion are all im ificant influenc ine‐grained soi rs to the area/u g. The measu orption of sim peratures, wi orption isotherm applied. The s shape of grain s ure 1. SEM for the 2. Adsorption e As mentioned e pharmaceuti ted to the des dies. Batch ads dy the effect of ct and both ki e drugs. The nmeyer flasks centration of 5 bent. The soil king using a th H, Korea) and e 1 oC to determi e then centrifug eous phase. Th H in the rang e set between uence on adso e the initial s tion volume to varying them pectively. The adsorption   0 - / c mg g  ere C0 and Ce (m gs initially and he solution (L) a data were fitte uate the adsorp 3. Adsorption i The equilibrium ortant factor ability. 4. Langmuir eq It assumes a orbent surface 474 mportant factors ce on many phy ils. The term " unit mass of so rement of ext mple molecules th surface a m data and the surface area wa size is shown in shape of particle g experiments above a stock icals were pre sired concentra sorption exper contact time, p inetics and the batch experim included 50 mL 50 mg/L for ea suspension w hermo stated sh equilibrated for ine equilibrium ge at 6708 g for e pH values we e between 1 t 15 to 45 oC to orption process sorbent and a find out their m between 10 n capacity of th - eC v m mg/L) are the li at equilibrium, and m is the m ed to Langmuir ption paramete isotherm m distribution to determine quation mono layer with energeti s. Surface area ysical and chem "Specific Surfac oil and is usuall ternal surface s, such as nit areas being application of B as found to be n Figure 1. grains for the soil u solution of 50 pared in distil ations for the riments were pH, dosage effec ermodynamics ments were don L of drugs solu ach one and 1 was continuou haker bath (BS r 24 h at room t m concentration r 15 min to sep ere adjusted by to 12. Solution understand th s. Other studie adsorbent conc effects on adso 0‐50 mg/L an he drugs is show iquid‐phase con , respectively. v ass of dry adso r and Freundlic rs. n of drugs in t the maximum adsorption on cally identical 469 a can exhibit a mical properties ce Area" (SSA) ly expressed as areas by the trogen at low derived from BET theory [8], 340 m2/g and used as a sorbent. 00 mg/L of the lled water and whole desired carried out to ct, temperature study for the ne in 100 mL tion with same 1.0 g of soil as usly mixed by S. II digital, JEI. temperature of s. The contents parate solid and y 0.1 N HCl and n temperatures he temperature ed parameters centration and orption process nd 0.5‐2.5 g, wn in Equation (1) ncentrations of v is the volume orbent used (g). ch isotherms to the solution is m of sorption nto a uniform sorption sites a s ) s e w m , d e d d o e e L e s y . f s d d s e s d s , n f e . o s n m s 470 Jodeh / European Journal of Chemistry 3 (4) (2012) 468‐474 [9]. The linear form of Langmuir isotherm equation is given by Equation 2. 00 1 q C bqq C e e e  (2) where Ce is the equilibrium concentration of the adsorbate (mg/L), qe is the amount of adsorbate per unit mass of adsorbent (mg/g), q0 and b are Langmuir constants related to adsorption capacity and rate of adsorption, respectively. 2.4.5. Freundlich equation It describes equilibrium on heterogeneous surfaces and hence does not assume mono layer capacity [9]. The well‐ known logarithmic form of the Freundlich isotherm is given by Equation 3. efe C n Kq log 1 loglog       (3) where Ce is the equilibrium concentration of the adsorbate (mg/L), qe is the amount of adsorbate per unit mass of adsorbent (mg/g), Kf and n are Freundlich constants with n giving an indication of how favorable the adsorption process is. Kf ((mg/g) (L/mg) 1/n) is related with adsorption capacity of the adsorbent. The slope (1/n) ranging between 0 and 1 is a measure of surface heterogeneity, becoming more hetero‐ geneous as its value gets closer to zero [10]. A value for (n) below one indicates a normal Langmuir isotherm, while (n) above one is indicative of efficient adsorption [11]. 2.4.6. Kinetics experiments Removal process can be explained by using several kinetics models. In this study both the order of the rate and the rate constants can be determined from those models. Those constants are significant for designing an effective process. In this study we used the first and pseudo second order models [12]. 2.4.7. First order kinetics model The simple form of first order model by applying the boundary conditions, qt = 0 at t = 0 and qt = qt at t = t, is shown in Equation 4. tkqqq ete 1ln)ln(  (4) where k1 is the rate constant, qe is the drug equilibrium concentration (mg/g); qt (mg/g) is the amount of adsorbed drugs at any time t (min). 2.4.8. Pseudo second order model The general form of the model is given as Equation 5. 2 2 )( te qqk dt dq  (5) by integration and linearization of Equation 5 gives t qqkq t eet 11 2 2  (6) in which, k2 is the equilibrium rate constant (g/mg.min) of pseudo‐second‐order chemical sorptin; qe is the amount of adsorption sorbed at equilibrium (mg/g); qt is the amount of adsorbate sorbed at t (min). The straight line plots of (t/qt) vs t have been tested to obtain rate parameters [12]. Adsorption kinetics is usually controlled by different mechanisms of which the most general are the diffusion mechanisms which can be explained by intraparticle diffusion model proposed by Weber and Morris. Intra‐particle diffusion model can be expressed as [13], qt = kit0.5 + A (7) where ki is the intraparticle diffusion constant and the intercept A reflects the boundary layer effects. The value of ki will be calculated from the slope of plotting qt vs t0.5. 3. Results and discussions 3.1. Soil tests Samples of red soil were analyzed in order to evaluate the soil texture, moisture, pH value, and specific gravity. Table 1 shows the results obtained from these tests. From the table above it was noticed that the clay percentage is larger than the slit, and both organic carbon and organic matter are high which increase the adsorption capacity of drugs. 3.2. Effect of contact time Experiments were conducted for various time intervals to determine duration required to reach adsorption equilibrium (Figure 2). Adsorption increased with increasing contact time for all pharmaceutical solutions, due to a large number of vacant surface sites are available for adsorption during initial stage, after a while remaining vacant surface sites are very difficult to be occupied because of the repulsive forces between solute molecules in solid and bulk phases [14]. Removal of amoxicillin, ibuprofen and caffeine were 88, 82 and 72%, respectively. Adsorption appeared to be governed by two transport processes. During first stage, during first stage, the drugs were rapidly adsorbed for the first two hours. In the second stage, slower migration of the drugs to less accessible sites. Slow uptake of adsorbates and establishment of equilibrium over a long period indicates strong chemical binding of adsorbates with adsorbent [15,16]. The study showed that the concentrations of ibuprofen, amoxicillin in the supernatant are decreased with increasing in their adsorption on soil for the first hour, then started to decrease in their adsorption due to its starting degradation, for this reason it’s written on the medicine must be kept cool place [17]. Figure 2. Effect of contact time on the removal of pharmaceuticals by soil at (initial conc. = 50 mg/L, initial pH = 4, temperature = 25 oC and solid/liquid ratio = 1.0 g/50 mL). Jodeh / European Journal of Chemistry 3 (4) (2012) 468‐474 471 3.3. Effect of adsorbent dosage An increase in adsorbent dosage increased percentage removal of pharmaceuticals. In this study various weights of 0.5, 0.7, 0.9, 1.2, 1.5, 2.0 and 2.5 g of soil were used in the presence of 50 mg/L of each drug. The increase of removal of drugs from solution with increasing dosage can be attributed to the increase number of available sites in the soil [18]. From Figure 3 it looks like all drugs showed the same behavior of removal with the order of Amoxicillin> Ibuprofen> Caffeine with percentage exceeding 90% in case of amoxicillin at 2.5 mg/L dosage. Figure 3. Effect of adsorbent dosage on pharmaceuticals removal soil at (initial conc. = 50 mg/L, initial pH = 4, temperature = 25 oC and contact time = 120 min). 3.4. Effect of pH At a pH value between pKa values of compounds, the drugs exist predominantly as neutral species. Nature of solid surface, like hydrophobic or hydrophilic, and electrical interaction, play an important role in adsorption kinetics of contaminants at solid liquid interface. In this study, a range of pH varies from 1.5 to 12 were taken and the results are shown in Figure 4. Figure 4. Effect of pH on to the removal of pharmaceuticals by soil at (initial conc. = 50 mg/L, temperature = 25 oC, contact time = 120 min and solid/liquid ratio = 1.0 g/50 mL). The adsorption and hydrolysis of the selected pharmaceuticals was influenced by pH and time, as clearly seen in Figure 4. The effect of pH on amoxicillin hydrolysis and soil adsorption was the highest amoxicillin adsorption at pH acidic and alkaline conditions with more stable over the pH range 4.0‐ 7.0. This may be due to two facts, the first is the presence of large quantities of OH− ions on the catalysis surface as well as in the reaction medium favors the formation of OH• radical. Second is the hydrolysis of these antibiotics since instability of β‐lactam ring at high pH [13], but its hydrolysis didn’t affected at neutral pH. The study showed that the soil adsorption efficiency of ibuprofen was more efficient under acidic at pH (1.5 and 4.0) and neutral condition than that in alkaline media as shown in Figure 3. This due to that it consists of hydrophilic and hydrophobic feature, and has dipolar nature of its functional group, with pKa value of 4.91, so the carboxyl group of ibuprofen should be at least partly protonated leading to a sorption onto soil particles. While the maximum hydrolysis of ibuprofen was observed in the pH range of 7‐12, due to the presence carboxylic group in its structure, this has been demonstrated in several studies [16‐19]. The results also, showed that the lowest of caffeine soil adsorption concentration was at acidic conditions of pH = 1.5, 4.0, and increased at alkaline pH = 12, and this is due to caffeine is an acidic compound and dissolves in acidic media [20], and tend to more binding with carboxylic group at alkaline condition. 3.5. The effect of temperature on (amoxicillin, ibuprofen, and caffeine)‐soil adsorption The effect of temperature on the adsorption of pharmaceuticals was studied in the range of 15‐45 oC and shown in Figure 5. As shown from Figure 5, there is a slight increase in adsorption in both amoxicillin and Ibuprofen and a decrease in removal of caffeine. Figure 5. Effect of temperature on pharmaceuticals removal by soil at (initial conc. = 50 mg/L, initial pH = 4, contact time = 120 min and solid/liquid ratio = 1.0 g/50 mL). To clarify the extent of the impact of temperature on the adsorption of drugs on the soil, the degradation of the selected pharmaceuticals was also influenced by microbial activities, oxygen status in the soil, soil type and compound characteristics. While the more decreasing of soil adsorption for caffeine with increasing temperature because it considered as hydrophilic compound and dissolves in water. 3.6. Adsorption isotherms In this study both Langmuir and Freundlich isotherm models were used to describe the relationship between the pharmaceuticals adsorbed and its equilibrium concentration in solution at 25 oC. Adsorption isotherms are shown in Figure 6 and 7. The fittings were investigated by plotting Ce/qe vs Ce for Langmuir and log Ce vs log qe for Fruindlich. Freundlich adsorption equation is perhaps the most widely used mathematical description of adsorption in aqueous systems, while the Langmuir adsorption isotherm is commonly applied to monolayer chemisorption of gases. 472 Jodeh / European Journal of Chemistry 3 (4) (2012) 468‐474 (a) (b) (c) Figure 6. Langmuir plot for pharmaceuticals adsorption onto soil at T = 25 oC, pH = 4 and solid/liquid ratio 1.0 g/50 mL for a) amoxicillin b) ibuprofen c) caffeine. This isotherm is mainly applied when no strong adsorption is expected and when the adsorption surface is uniform. To apply the Freundlich Equation on our work various concentrations of pharmaceuticals ranging between 5‐50 mg/L were adsorbed at constant weights of 1.0 g of soil after 2 hrs of adsorption. The isotherm equilibrium results are shown in Table 2. Table 2. Langmuir and Freundlich isotherm model parameters and correlation coefficient of pharmaceuticals adsorption. Isotherm Langmuir parameters Freundlich parameters Adsorbate q0 (mg/g) B (L/mg) R2 Kf ((mg/g) L/mg)1/n) n R2 Amoxicillin 20.88 0.34 0.972 0.107 1.26 0.997 Ibuprofen 20.44 0.70 0.991 0.080 1.15 0.996 Caffaeine 14.10 0.38 0.977 0.120 4.49 0.963 Both the Freundlich and Langmuir adsorption isotherms showed linear relationship results as shown in Figure 6 and 7. For the Freundlich and Langmuir adsorption isotherms, the R2 for the Freundlich adsorption isotherms is closer to 1 more than that in Langmuir adsorption isotherms. The n values for all the drugs were larger than 1 and this implies stronger interaction between the adsorbate and the adsorbent. The k values for all the drugs were lower than 1 which indicate that the adsorption capacities were low, and it leaves the soil quickly due to the small surface area of soil [18,21,22]. Generally, higher Kf values were associated with soil with higher OM content. Our results of ibuprofen agree with previous studies [21,22]. (a) (b) (c) Figure 7. Freundlich plot for pharmaceuticals adsorption onto soil at T = 25 oC. pH = 4 and solid/liquid ratio 1.0 g/ 50 mL for a) amoxicillin b) Ibuprofen c) caffaeine. 3.7. Kinetics of pharmaceuticals adsorption In order to investigate the mechanism of pharmaceuticals adsorption process on soil, the pseudo‐first‐order kinetic model, the pseudo‐second‐ order kinetic model and the intra‐ particle diffusion model were all used to test the experimental data. The results are shown in Figure 8‐10. The correlation coefficients and other parameters calculated for the pseudo‐ first‐order model, pseudo‐second‐order model and the intra‐ particle‐diffusion kinetics are listed in Table 3 and 4. Jodeh / European Journal of Chemistry 3 (4) (2012) 468‐474 473 Figure 8. Kinetics of pharmaceuticals removal according to the pseudo‐first‐ order model by soil at initial concentration of 50 mg/L, pH = 4, T = 25 oC and solid/liquid ratio = 1.0 g/50 mL. Figure 9. Kinetics of pharmaceuticals removal according to the pseudo‐ second‐order model by soil at initial concentration 50 mg/L, pH = 4, T = 25 oC, and solid/liquid ratio = 1.0 g/50 mL. Figure 10. Kinetics of pharmaceuticals removal according to the intra‐ particle diffusion model by soil at initial concentration 50 mg/L, pH = 4, T = 25 oC and solid/liquid ratio = 1.0 g/50 mL. For the intra‐particle‐diffusion the straight lines did not pass through the origin, this indicates that the rate is limited by mass transfer across the boundary layer and the mechanism of removal of those pharmaceuticals is complex and both the surface adsorption and intra‐particle diffusion may contribute to the rate‐determining step [23]. The results are shown in Figure 10 and Table 4. Table 3. Pseudo‐first order and pseudo‐second order kinetic model parameters for pharmaceuticals adsorption onto soil. Adsorbate Pseudo‐first order parameters Pseudo‐second order parameters K1 (1/min) qe (Calc.) R2 K2 (g/mg.min) qe (Calc.) R2 Amoxicillin 0.0303 19054 0.974 0.0175 1.09 0.976 Ibuprofen 0.0221 141 0.986 0.0128 1.21 0.969 Caffaeine 0.0132 21 0.989 0.0135 1.53 0.953 Table 4. Intra‐particle diffusion kinetic model parameters for pharma‐ ceuticals adsorption onto soil. Adsorbent Kp (mg/g min1/2) A R2 Amoxicillin 0.051 0.027 0.990 Ibuprofen 0.048 ‐0.093 0.976 Caffaeine 0.046 ‐0.134 0.970 3.8. Adsorption thermodynamics The thermodynamic parameters including changes in standard enthalpy (ΔH°), standard entropy (ΔS°) and standard free energy (ΔG°) of adsorption can be calculated by means of Equations 8‐10 [24]. TR H R S kd 1 ln      (8) where R (8.314 J/mol.K) is the universal gas constant, T (K) is the absolute solution temperature and Kd is the distribution coefficient which can be calculated as: Kd = CAe/Ce (9) where CAe (mg/L) is the amount adsorbed on solid at equilibrium and Ce (mg/L) is the equilibrium concentration. ΔG° can be calculated using the relation below: ΔGᴼ = ‐RT ln Kd (10) The values of ΔH° and ΔS° are calculated from the slopes and intercepts of the linear variation of ln Kd with reciprocal temperature (1/T) Figure 11. The obtained thermodynamic values are given in Table 5. Table 5. The values of thermodynamics of adsorption of pharmaceuticals on soil. Pharmaceuticals ΔHᴼ (KJ/mol) ΔSᴼ (J/mol K) ΔGᴼ (KJ/mol) 285 K 294 K 312 K 322 K Amoxicillin ‐ 19.70 ‐0.85 ‐2.85 ‐2.20 ‐1.37 ‐0.53 Ibuprofen ‐ 15.07 ‐0.66 ‐2.08 ‐1.54 ‐0.70 ‐0.40 Caffaeine ‐ 9.97 ‐0.44 ‐1.42 ‐0.86 ‐0.51 ‐0.13 The negative values of ΔG° at various temperatures indicated that the adsorption process on soil is spontaneous and the negative values of ΔH° show that the adsorption is exothermic. Furthermore, the negative value of entropy indicates the affinity of adsorbent material for drugs. Increase in the value of ΔG° with rise in temperature show that the adsorption is more favorable at lower temperature. 4. Conclusion The adsorption characteristics of Pharmaceuticals in soils and ground water are of great importance environmentally, because such process is associated with the ecotoxicity, degradation, transportation, and bioaccumulation of them in 474 Jodeh / European Journal of Chemistry 3 (4) (2012) 468‐474 the soil environment. Adsorption of ibuprofen, amoxicillin, and caffeine was studied and the following results were obtained: Amoxicillin and ibuprofen soil adsorption in this study was increased with increasing temperature versus time due to their high solubility of water. The caffeine showed lower adsorption. The effect of pH showed higher removal of both amoxicillin and ibuprofen in the acidic medium at pH = 1‐4, while caffeine showed higher adsorption in the basic medium. All the studied pharmaceuticals followed the Freundlich isotherm with n > 1 and caffeine showed about 4.5 which means they have very high interaction with soil. For the kinetic studies they followed the pseudo‐second‐order model and the thermodynamics parameters showed that the adsorption process on soil was spontaneous and exothermic. (a) (b) (c) Figure 11. Plot of ln Kd vs 1/T for 50 mg/L concentration of a) amoxicillin b) ibuprofen c) caffeine. 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