Effect of an industrial chemical waste on the uptake J. Serb. Chem. Soc. 87 (0) 1–15 (2022) Original scientific paper JSCS–11692 Published 1 August 2022 1 Powdered adsorbent obtained from bathurst burr biomass for methylene blue removal from aqueous solutions GIANNIN MOSOARCA1, COSMIN VANCEA1*, SIMONA POPA1**, MARIA ELENA RADULESCU‑GRAD2 AND SORINA BORAN1 1Politehnica University Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Bd. V. Parvan, No. 6, 300223, Timisoara, Romania and 2”Coriolan Dragulescu” Institute of Chemistry, Romanian Academy, Mihai Viteazu Bd. No. 24, 300223 Timisoara, Romania (Received 16 March, revised 30 April, accepted 4 May 2022) Abstract: Powdered adsorbent obtained from bathurst burr biomass was tested for methylene blue removal from aqueous solutions. SEM and FTIR analyses were used to characterize the adsorbent before and after adsorption. The influ- ence of contact time, adsorbent dose, pH, initial dye concentration, ionic strength and temperature on the process were investigated. Kinetic, equilibrium and thermodynamic studies were conducted to analyse the process. The Tagu- chi method was used to establish the most suitable conditions for the dye ads- orption. The process is spontaneous, favourable, and exothermic and the Freundlich isotherm and pseudo-second order kinetic model best describe it. The Taguchi method indicate that the ionic strength is the factor with the great- est influence on the adsorption process. Keywords: low-cost adsorbent; dye adsorption; kinetic; equilibrium; thermo- dynamic; Taguchi method. INTRODUCTION Methylene blue is a thiazine cationic dye used in various fields and act- ivities. It is widely used in the textile industry for dyeing cotton, wood, and silk due to its ease of application, good material resistance and economic benefits. In medicine it is used to treat methemoglobinemia, cyanide poisoning and urinary tract infections. It is also used as a colouring agent in diagnostic examination and surgery. Even if not strongly hazardous, the methylene blue can have negative effects on humans causing eye irritation, breathing difficulty, nausea, heart-beat increase, vomiting, diarrhea and jaundice. To avoid harmful impacts on aquatic *,** Corresponding authors. E-mail: (*)cosmin.vancea@upt.ro; (**)simona.popa@upt.ro https://doi.org/10.2298/JSC220316039M 2 MOSOARCA et al. life and human health, the dye should be removed from wastewater before their discharging into natural effluents.1–5 Scientific literature mentions many physicochemical and biological methods designed to remove the methylene blue dye from aqueous solutions: adsorption, coagulation, flocculation, ion exchange, precipitation, oxidation, chemical pre- cipitation, electrochemical processes, photocatalytic processes, membrane pro- cesses and biodegradation. Very often, adsorption is the chosen process for dye retention due to its many advantages such as: simplicity, high efficiency, flex- ibility and low costs. An important number of adsorbents are known, among which an important role is played by natural materials that are cheap and avail- able in large quantities.1–10 Bathurst Burr (Xanthium spinosum) is a very invasive plant widespread in Europe, North America, Asia, Australia and partly in Africa. It has a very high resistance to drought, pollution and, in general, to any aggressive environmental conditions. It grows up to one meter tall and has a branched stem full of thorns. It can be found in lowland, hilly and low mountain areas, on pastures, abandoned land and roadsides. Due to its anti-inflammatory, disinfectant, diuretic, antidia- betic and antitumor properties, is used in traditional medicine.11,12 The purpose of this study was to use the bathurst burr powder to remove the methylene blue dye from aqueous solutions by adsorption. The effect of contact time, adsorbent dose, pH, initial dye concentration, ionic strength and tempera- ture on the adsorption process were monitored. Kinetic, equilibrium and thermo- dynamic studies were used to analyse the process. In order to establish the most suitable conditions for the dye adsorption, the process was optimized by the Taguchi method. EXPERIMENTAL The adsorbent material was obtained from the aerial part of bathurst burr mature plants, which were purchased from StefMar SRL, a local company that process and pack medicinal and aromatic plants. The adsorbent powder obtaining process was described elsewhere.13 The characteristics of adsorbent material, before and after adsorption, were examined by SEM ana- lysis (Quanta FEG 250 scanning electron microscope at 1600× magnitude) and FTIR spectro- scopy (Shimadzu Prestige-21 FTIR spectrophotometer). The point of zero charge (pHPZC) was determined using the solid addition method.3 In the adsorption studies the influence of pH, adsorbent dose, dye concentration, time, temperature, and ionic strength was studied. Three independent replicates were performed for each test. During the experiments a constant mixing intensity was maintained. The pH was adjusted using NaOH and HCl solutions (0.1 M). NaCl as background electrolyte was used to study the effect of ionic strength. The methylene blue concentration was determined using a UV–Vis spectrophotometer at 664 nm wavelength. The equilibrium and kinetics studies were assessed using the nonlinear equations of the Langmuir, Freundlich and Temkin isotherms and also, the nonlinear equations of the pseudo first-order, pseudo second-order and Elovich kinetic models.14-17 Each of these isotherm and kinetic models were evaluated through the statistical parameters determination coefficient BATHURST BURR BIOMASS ADSORBENT 3 (R2), sum of square error (SSE), chi-square (χ2) and average relative error (ARE).17 The higher value for R2 and the lower value for SSE, χ2 and ARE were used as the criterion for deter- mining the most suitable model. The Taguchi method was used to optimize the dye removal experimental conditions. The L27 orthogonal array experimental design was employed to establish the influence of six controllable factors on methylene blue removal. Table I shows these factors and their levels. The Taguchi method evaluates the experimental results by signal-to-noise (S/N) ratio, defining the measurement of the response deviation from the desired value.18-20 “The larger the better” option was used to maximize the S/N ratio and implicitly the highest dye removal efficiency. All calculations were performed with the Minitab 19 Software. TABLE I. Controllable factors and their levels Factor Level 1 Level 2 Level 3 Time, min 1 10 30 Adsorbent dose, mg L-1 0.5 1.5 3.0 pH 2 6 10 Initial dye concentration, mg L-1 50 150 250 Ionic strength, mol L-1 0 0.1 0.2 Temperature, K 284 291 315 RESULTS AND DISCUSSION Adsorbent surface characterization Fig. 1 shows the SEM images of the adsorbent material surface at 3000× magnitude. Before adsorption, the adsorbent surface has a porous aspect, suitable for dye adsorption (Fig. 1A). After adsorption, the surface morphology has changed (Fig. 1B), indicating that pores, voids, or irregularities might be filled with the dye molecules. Fig. 1. SEM images of adsorbent surface: A) before and B) after adsorption. The FTIR spectrum of adsorbent, depicted in Fig. 2, indicates that main components of bathurst burr powder are cellulose, hemicellulose, and lignin. The 4 MOSOARCA et al. identified peaks of the functional groups characteristic of these components are: 3448 cm–1 corresponds to O–H stretching of cellulose, Senthamaraikannan et al.21 found this peak in the spectra of natural cellulosic fibre from bark of Albizia amara; 2340 and 1630 cm–1 indicate O–H bending of adsorbed water, Tsuboi22 identifying both peaks in FTIR spectra of cellulose extracted from natural flax, ramie and cotton fibres and Karimi et al.23 found the second peak in cellulose spectrum isolated from kenaf fibres; 2053 cm–1 – can be assigned to NCO from isocyanate groups, presence of this functional group being reported Salim et al.24 in the lignin spectra extracted from bark of Leucaena leucocephala; 1368 cm–1 corresponds to C–H bending vibration in cellulose and hemicellulose, Labbe et al.25 and Kubovský et al.26 found this peak in spectra of aspen tree bark and oak wood respectively; 1000 cm–1 indicate C–O stretching, Liang and Marches- sault27 identifying this peak in in FTIR spectra of native cellulose; 542 cm–1 can be attributed to C–H bend, Salim et al.24 found this band in the spectra of lignin extracted from native Leucaena leucocephala bark. After absorption, the FTIR spectrum does not show significant differences compared to the one recorded before adsorption, which indicates that physical interactions are implied in the adsorption process.8,13 Fig. 2. FTIR spectra of adsorbent before and after dye adsorption. The point of zero charge provides information on how an adsorbate will be adsorbed by an adsorbent material depending on the surface electrical charge. If the solution pH is higher than pHPZC, the adsorbent surface is negatively charged while a solution pH lower than pHPZC leads to a positively charged ads- BATHURST BURR BIOMASS ADSORBENT 5 orbent surface. Therefore, the adsorption of methylene blue will be favoured when the pH of the solution is higher than pHPZC. The value of this parameter, determined using solid addition method, was 6.64 (Fig. 3). Fig. 3. Determination of point of zero charge (pHPZC) based on the solid addition method. The influence of contact time on adsorption process In the first few minutes, the adsorption process is fast (Fig. 4) because many active adsorption sites are available on the surface of the material.6,7,10 As time goes on, these sites gradually take over and the adsorption capacity increases more slowly. After 30 min the equilibrium is reached, indicating that all the sur- face of the adsorbent is covered by dye molecules.6,7 Fig. 4. Influence of contact time on ads- orption capacity. The equilibrium times obtained for similar adsorbents used for methylene blue removal from water were: 30 min for Arthrospira platensis biomass,28 50 min for Haloxylon recurvum stem biomass,29 60 min for Euchema Spinosum alga bio- mass30 and 90 min for Phragmites australis biomass.31 6 MOSOARCA et al. The influence of adsorbent dose on adsorption process The adsorbent dose influence upon the adsorption capacity together with the methylene blue removal efficiency are presented in Fig. 5. The two parameters behave differently as the adsorbent dose increases: the adsorption capacity decre- ases while the dye removal efficiency increases. At high adsorbent amounts the aggregation of particles can occur, and a large part of the active sites remains unsaturated. These two phenomena lead to a decrease of the adsorption capa- city.7,9,10 The positive effect of a larger adsorbent quantity upon the removal efficiency is based on an increase of the surface area and thus of the number of sites available for adsorption.3,7,9 Similar observations have been reported in other studies on the methylene blue adsorption on other low-cost plant materials. When Salix babylonica leaves were used as adsorbent, an increase in adsorbent material dose from 0.2 to 15 g L–1 led to an increase in dye removal efficiency of 36.88 % and a decrease in adsorption capacity of 98 %.7 In the case of citrus limetta peel use, it was observed that for an increase of the adsorbent dose from 0.4 to 2.0 g L–1, removal efficiency increased rapidly by about 3 % while the adsorption capacity decreased by 91 %.10 Fig. 5. Influence of adsorbent dose on adsorption capacity and removal efficiency. The influence of pH on adsorption process The effect of solution pH on adsorption capacity is depicted in Fig. 6. Incre- asing the value of this parameter has a positive effect on the adsorption capacity. The best results were obtained at a pH higher than 8. At these pH values, higher than the pH corresponding to the point of zero charge (pHPZC 6.64), the adsorbent material surface is negatively charged, favouring the electrostatic attraction with the dye cations.3,10,32 Similar results were reported in other previous articles publish in scientific literature. At pH > 8, increased adsorption capacities were recorded for adsorbent materials such as: Salix babylonica leaves,7 citrus limetta peel,10 Phragmites australis biomass31 and phoenix tree’s leaves.33 BATHURST BURR BIOMASS ADSORBENT 7 The relatively constant value of adsorption capacity at high pH indicates that in addition to the electrostatic attraction, other mechanisms are also involved in the adsorption process.32 Fig. 6. Influence of pH on adsorption cap- acity. The influence of initial dye concentration on adsorption process The adsorption capacity and the dye removal efficiency values at different initial dye concentrations are shown in Fig. 7. The adsorption capacity increases while the dye removal efficiency decreases as the initial dye concentration inc- reases. The first parameter behaviour is caused by the increase of the driving force resulting from the concentration gradient.32,33 The values of the second parameter decrease due to the accumulation of methylene blue molecules on the surface of the adsorbent which leads to saturation of the adsorption sites.6,28 Similar behaviours have been mentioned previously in other adsorption studies. Our study shows that an increase of the initial dye concentration from 50 to 200 mg L–1 leads to an increase of the adsorption capacity from 21.7 to 83.5 mg g–1 and a decrease of dye removal efficiency from 87.18 to 83.19 % respectively. For the same initial dye concentration variation range, other researchers reported an Fig. 7. Influence of dye initial concentration on adsorption capacity and removal efficiency. 8 MOSOARCA et al. increase in adsorption capacity from about 24 to 80 mg g–1 and a decrease dye removal efficiency from 96 to 92 % when using weeping willow leaves7 as an adsorbent. Another study using A. platensis biomass28 as adsorbent, an increase of the initial dye concentration from 6.25 to 100 mg L–1 generates an increase of the adsorption capacity from 8 to 90 mg g–1 and a dye removal efficiency dec- rease from 60 to about 45 %. The influence of ionic strength on adsorption process Increasing the solution ionic strength generates a decrease of the adsorption capacity, illustrated in Fig. 8, due to competition between methylene blue cations and sodium ions to occupy the available adsorption sites on the surface of the adsorbent.32,33 The unfavourable effect of ionic strength on methylene blue ads- orption process was also mentioned in other studies. Thus, for A. platensis bio- mass,28 lotus leaves32 and phoenix tree leaves33 adsorbents an increase in ionic strength from 0 to 0.2 mol L–1 leads to an adsorption capacity decrease of 72, 22 and 7 %, respectively. Fig. 8. Influence of ionic strength on ads- orption capacity. The influence of temperature on adsorption process According to Fig. 9 the adsorption capacity decreases with increasing the temperature indicating that the process is exothermic in nature. The binding forces between the adsorbent surface and the adsorbate molecules become weaker with increasing temperature.34,35 Similar observations have been rep- orted by others previous articles. When Salix babylonica leaves,7 Haloxylon rec- urvum plant stems29 and Natural Muscovite Clay34 were used as adsorbent mat- erials to remove methylene blue from aqueous solutions, a negative effect of tem- perature rise on the adsorption capacity was observed. Equilibrium isotherms In order to study the interactions between the dye molecules and the ads- orbent surface three isotherms were tested: Langmuir, Freundlich and Temkin. BATHURST BURR BIOMASS ADSORBENT 9 Fig. 10 shows the plots of the tested adsorption isotherms (non-linear forms). The values of adsorption isotherms constants and also, of the corresponding error functions (R2, SSE, χ2, ARE) are summarized in Table II. Fig. 10. The tested adsorption isotherms (non-linear forms) for the methylene blue adsorption. Both the Langmuir isotherm and the Freundlich isotherm characterize very well the adsorption process (Fig. 10). Considering the higher value for deter- mination coefficient (R2) and the lower values of SSE, χ2 and ARE it can be con- cluded that Freundlich isotherm best describes the process. The obtained results agree with those mentioned by other researchers in methylene blue adsorption studies, this isotherm characterizing the dye retention processes on adsorbent materials obtained from Elaeis guineensis leaves,4 Haloxylon recurvum stems29 and Euchema Spinosum alga.30 Table III shows a comparison between the maximum adsorption capacities values for methylene blue adsorption using similar low-cost adsorbents. Adsorption kinetics The kinetics of the methylene blue adsorption process on the studied ads- orbent was investigated by means of kinetic models (non-linear forms): pseudo- Fig. 9. Influence of temperature on adsorpt- ion capacity. 10 MOSOARCA et al. -first order, pseudo-second order and Elovich. The plots of these kinetic models and the value of their specific constants are illustrated in Fig. 11 and Table IV, respectively. The values of the coefficients of determination (R2) for all models are above 0.96, the highest recorded value was for the pseudo-second order model while the lowest value corresponds to the Elovich model. The calculated values of the error functions (χ2, SSE and ARE) are the lowest for the pseudo- second order model. TABLE II. Adsorption isotherms models constants and the corresponding error functions Isotherm model Parameter Value Langmuir non-linear KL / L mg -1 0.006±0.001 qmax / mg g -1 485.1±9.23 R2 0.9978 χ2 0.78 SSE 17.37 ARE / % 5.08 Freundlich non-linear Kf / mg g -1 4.07±0.74 1/n 0.85±0.07 R2 0.9985 χ2 0.32 SSE 10.90 ARE / % 3.39 Temkin non-linear KT / L mg -1 0.220±0.043 B / kJ g-1 58.77±6.94 R2 0.9584 χ2 7.81 SSE 307.29 ARE / % 18.81 TABLE III. The maximum adsorption capacities (mg g-1) for methylene blue on different low- cost adsorbents Adsorbent Value Citrullus colocynthis seeds6 18.8 Phragmites australis biomass31 22.7 Haloxylon recurvum stems29 22.9 Salix babylonica leaves7 60.9 Daucus carota leaves3 66.5 Phoenix tree leaves33 80.9 Elaeis guineensis leaves4 103.0 Dry bean pods husks8 121.1 Fava bean peel1 140.0 lotus leaf32 221.7 Citrus limetta peel10 227.3 Arthrospira platensis biomass28 312.5 Bathurst burr biomass (this study) 485.1 Euchema Spinosum algae30 833.3 BATHURST BURR BIOMASS ADSORBENT 11 Fig. 11. The tested kinetic models (non- -linear forms) for the methylene blue ads- orption. TABLE IV. Kinetic models constants and the corresponding error functions Kinetic model Parameter Value Pseudo-first order non-linear k1 / min -1 0.648±0.051 qe,calc / mg g -1 40.63±0.4 R2 0.9899 χ2 0.61 SSE 16.37 ARE / % 13.48 Pseudo-second order non-linear k2 / min -1 0.025±0.004 qe,calc / g mg -1 min-1 42.86±0.38 R2 0.9962 χ2 0.17 SSE 5.84 ARE / % 11.59 Elovich non-linear a / g mg-1 0.218±0.048 b / mg g-1 min-1 1434±124 R2 0.9635 χ2 1.95 SSE 57.41 ARE / % 15.84 These results indicate that the adsorption process is best described by this kinetic model. The conclusion is also supported by the calculated value of equi- librium adsorption capacity 42.86 mg g–1 which is very close to experimental value 42.05 mg g–1. The pseudo-second order kinetic model also characterized other similar methylene blue adsorption processes on other adsorbents based on Salix babylonica leaves,7 corn cobs,9 Euchema Spinosum macro-alga,30 Phrag- mites australis biomass31 and lotus leaves.32 Thermodynamic parameters The thermodynamic parameters of dye adsorption process, calculated bases on experimental results obtained at 284, 291, 307 and 315 K, are presented in https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phragmites-australis https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phragmites-australis 12 MOSOARCA et al. Table V. The negative values of standard Gibbs energy change (ΔG0) and stan- dard enthalpy change (ΔH0) indicate a spontaneous, favourable and exothermic process. The positive value of standard entropy change (ΔS0) shows an increase randomness at solid–liquid interface. The value of ΔG0 is in the range –20 to 0 kJ mol–1 and the ΔH0 value is lower than 40 kJ mol–1, therefore the main mechanism involved in absorption is physisorption.7,29,31,34,35 TABLE V. Thermodynamic parameters for the methylene blue adsorption onto bathurst burr powder ΔG0 / kJ mol-1 ΔH0 / kJ mol-1 ΔS0 / J mol-1 K-1 284 K 291 K 307 K 315 K –19.04 –19.18 –19.78 –19.91 –1.26 3.60 Optimization adsorption parameters by Taguchi method The L27 orthogonal array and the obtained results after each run, for dye removal efficiency and the S/N ratios, are summarized in Table VI. The order of the controllable factors’ significance (Table VII) was established using the rank of S/N ratio and delta values (difference between the highest and lowest average response values for each factor).18 TABLE VI. Experimental layout of L27 orthogonal array  / min Adsorbent dose, mg L-1 pH Initial dye concen- tration, mg L-1 Ionic strength mol L-1 T / K Removal efficiency, % S/N 1 0.5 2 50 0.0 284 18.73 25.45 1 0.5 2 50 0.1 291 10.97 20.80 1 0.5 2 50 0.2 315 7.74 17.78 1 1.5 6 250 0.1 284 40.27 32.09 1 1.5 6 250 0.2 291 23.59 27.45 1 1.5 6 250 0.0 315 16.64 24.42 1 3.0 10 150 0.2 284 44.93 33.05 1 3.0 10 150 0.0 291 26.32 28.40 1 3.0 10 150 0.1 315 18.57 25.37 10 0.5 10 250 0.2 284 27.61 28.82 10 0.5 10 250 0.0 291 19.52 25.81 10 0.5 10 250 0.1 315 40.25 32.09 10 1.5 2 150 0.0 284 56.74 35.07 10 1.5 2 150 0.1 291 40.12 32.06 10 1.5 2 150 0.2 315 82.71 38.35 10 3.0 6 50 0.1 284 42.06 32.47 10 3.0 6 50 0.2 291 29.74 29.46 10 3.0 6 50 0.0 315 61.31 35.75 30 0.5 6 150 0.1 284 23.53 27.43 30 0.5 6 150 0.2 291 48.60 33.73 30 0.5 6 150 0.0 315 28.42 29.07 30 1.5 10 50 0.2 284 30.66 29.73 BATHURST BURR BIOMASS ADSORBENT 13 TABLE VI. Continued  / min Adsorbent dose, mg L-1 pH Initial dye concen- tration, mg L-1 Ionic strength mol L-1 T / K Removal efficiency, % S/N 30 1.5 10 50 0.0 291 63.32 36.03 30 1.5 10 50 0.1 315 37.02 31.37 30 3.0 2 250 0.0 284 42.43 32.55 30 3.0 2 250 0.1 291 87.64 38.85 30 3.0 2 250 0.2 315 51.25 34.19 TABLE VII. Response table for signal-to-noise ratios Level Time Adsorbent dose pH Initial dye concentration Ionic strength Temperature 1 26.78 28.76 26.10 30.57 33.94 30.74 2 31.85 30.70 32.21 30.21 29.74 30.29 3 32.24 31.40 32.55 30.08 27.18 29.83 Delta 5.46 2.63 6.46 0.49 6.75 0.92 Rank 3 4 2 6 1 5 The factor having the highest influence on the adsorption process was the ionic strength while the factor with the least influence was initial dye concen- tration. Correlating the data from Table I and Table VI, the optimum adsorption conditions were: time 30 min, adsorbent dose 3 mg L–1, pH 10, initial dye con- centration 50 mg L–1, no ions and temperature 284 K. CONCLUSION Powdered material obtained from bathurst burr biomass is an efficient low- cost and easily available adsorbent for methylene blue removal from aqueous solutions. The adsorption is influenced by contact time, adsorbent dose, pH, ini- tial dye concentration, ionic strength and temperature and is best described by Freundlich isotherm and pseudo-second order kinetic model. The process is spontaneous, favourable and exothermic and the main mechanism involved is physisorption. The ionic strength is the factor with the highest influence on the process and initial dye concentration least influences the adsorption. И З В О Д АДСОРБЕНТ У ПРАХУ ДОБИЈЕН ИЗ БИОМАСЕ Xanthium spinosum ЗА УКЛАЊАЊЕ МЕТИЛЕНСКОГ ПЛАВОГ ИЗ ВОДЕНИХ РАСТВОРА GIANNIN MOSOARCA1, COSMIN VANCEA1, SIMONA POPA1, MARIA ELENA RADULESCU‑GRAD2 и SORINA BORAN1 1Politehnica University Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Bd. V. Parvan, No. 6, 300223, Timisoara, Romania и 2”Coriolan Dragulescu” Institute of Chemistry, Romanian Academy, Mihai Viteazu Bd. No. 24, 300223 Timisoara, Romania Адсорбент у праху добијен из Xanthium spinosum биомасе је испитиван за уклањање метиленског плавог из водених раствора. SEM и FTIR анализе су коришћене за каракте- ризацију адсорбента пре и након адсорпције. Испитан је утицај времена контакта, дозе 14 MOSOARCA et al. адсорбента, pH, почетне концентрације боје, јонске јачине и температуре на процес адсорпције. Кинетичка, равнотежна и термодинамичка испитивања су вршена ради ана- лизе процеса адсорпције. Тагучи метод је коришћен да би се одредили најбољи услови за адсорпцију боје. Процес је спонтан, фаворизован, егзотерман, описује га Фројндлихова изотерма и кинетички модел псеудо-другог реда. Тагучи метод указује да је јонска јачи- на фактор који има највећи утицај на процес адсорпције. (Примљено 16. марта, ревидирано 30. априла, прихваћено 4. маја 2022) REFERENCES 1. O. S. 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