Removal of some organic dyes from aqueous solution by peanut husk

Abo Farha E.S. Adsorption is one of the most promising decolorization techniques in dyeing waste water treatment. Adsorption is a useful and simple technique, which allows kinetic and equilibrium measurements without any highly sophisticated instruments. The main advantage of adsorption recently became the use of low-cost materials, which reduces the procedure cost. Peanut husk (PH) was developed for the removal of acid violet 19 (AV19) and basic red 2 (BR2) in single and binary systems from aqueous solutions. The variation of pH, dose of adsorbent, initial concentration of dyes and temperature were investigated where the removal percent of dyes increase with increasing dose and temperature and decrease with increasing concentration. SEM and IR were used to analyze the morphology and chemical groups of the (PH) and (TPH) before and after dye sorption and also the point of zero charge of adsorbent was investigated. Langmuir and Freundlich isotherm models were used to investigate the adsorption process. It was found that the Langmuir model best described the experimental data. Also the kinetic obtained data were analyzed using pseudo first order, pseudo second order, intraparticle where the experimental results fit well with the pseudosecondorder model. And thermodynamics properties of the process were investigated where adsorption of dyes onto peanut husk (PH) was found to be spontaneous and endothermic in nature.


Abo Farha E.S.
Adsorption is one of the most promising decolorization techniques in dyeing waste water treatment. Adsorption is a useful and simple technique, which allows kinetic and equilibrium measurements without any highly sophisticated instruments. The main advantage of adsorption recently became the use of low-cost materials, which reduces the procedure cost. Peanut husk (PH) was developed for the removal of acid violet 19 (AV19) and basic red 2 (BR2) in single and binary systems from aqueous solutions. The variation of pH, dose of adsorbent, initial concentration of dyes and temperature were investigated where the removal percent of dyes increase with increasing dose and temperature and decrease with increasing concentration. SEM and IR were used to analyze the morphology and chemical groups of the (PH) and (TPH) before and after dye sorption and also the point of zero charge of adsorbent was investigated. Langmuir and Freundlich isotherm models were used to investigate the adsorption process. It was found that the Langmuir model best described the experimental data. Also the kinetic obtained data were analyzed using pseudo first order, pseudo second order, intraparticle where the experimental results fit well with the pseudo-second-order model. And thermodynamics properties of the process were investigated where adsorption of dyes onto peanut husk (PH) was found to be spontaneous and endothermic in nature.

Introduction:-
Water, whether fresh; salted; rain; surface or underground-water may be contaminated with materials that make it harmful. Polluted water is the cause of various diseases that can seriously affect public health. Human are not the only one to suffer the consequences of water pollution, fauna and flora are also victims (Zamouche and Hamdaoui, 2012). Textile industries produce a lot of wastewater, which contains a number of contaminants, including acidic or caustic dissolved solids, toxic compounds, and any different dyes, Many of the organic dyes are hazardous and may affect aquatic life causing various diseases and disorders (Mohammed. 2014). It has been estimated that the total dye consumption in textile industry worldwide is more than 10,000 tonnes per year and about 10-15% of these dyes are released as effluents during the dyeing processes (Sara and Tushar, 2014).
Dyes can have acute and/or chronic effects on exposed organisms depending on the exposure time and dye concentration (Bharathi and Ramesh, 2013). Moreover dye causes eye burns, which may be responsible for permanent injury to the eyes of human and animals. If swallowed, the dye causes irritation to the gastrointestinal tract with symptoms of nausea, vomiting and diarrhea. It may also cause methemoglob inemia, cyanosis, convulsions, tachycardia and dyspnea, if inhaled (Hamdaoui and Chiha, 2007).The main components of dye molecules are: the chromophores, which are responsible for producing the color, and the auxochromes, which can not only supplement the chromophore but also render the molecule soluble in water and give enhanced affinity (to attach) toward the fibers (Gupta and Suhas,2009).Color is a visible pollutant and the presence of even a very minute amount of coloring substance makes it undesirable due to its appearance When the color interferes with penetration of daylight into waters it retards photosynthesis and inhibits the expansion of aquatic aggregation and interferes with gas solubility in water bodies (Zohreh and Anita, 2014).
The removal of color from dye-bearing effluents is a major problem due to the difficulty in treating such waste waters by conventional treatment methods (Pragathiswaran et al ., 2016).Wastewater containing dyes must be appropriately treated before being discharged into the water bodies (Gbekeloluwa et al.,2014).The conventional methods for the treatment of colored wastewater are physical, chemical and biological treatments (Mohammed et al .,2014). However the application of these technologies is sometimes restricted due issues including; incomplete dye removal, requirement of expensive equipment and monitoring systems, high reagent or energy requirements or generation of toxic sludge and other waste products (Gbekeloluwa et al.,2014). Among these physico-chemical methods like adsorption and electrochemical coagulation are the most popular methods in recent days (Arun et al.,  2014). Since adsorption is more effective because adsorption removes the entire dye molecule, leaving no fragments in the effluent (Sara and Tushar 2014).
Dyes can be classified as : anionic (direct, acid and reactive dyes), cationic (basic dyes) and non-ionic (dispersive dyes) (Bharathi and Ramesh, 2013). Acid dyes are belonging to anionic group which there are acid group (sulphonate ,carboxyl) in their molecular structure (Davoud et al.,2016). Acid dyes are used with silk, wool, polyamide, modified acrylic and polypropylene fibers. they have a harmful effect on human beings since they are organic sulphonic acids (Mohamad et al.,2011). While cationic dyes are also called basic dyes due to the presence of positive ions in the molecule's structure. Basic dyes are water soluble and they are highly visible in water even at very low concentration. Basic dyes consist of monoazoic, diazoic and azine compounds. Cationic dyes are used to color wool, silk, nylon, mod-acrylic and polyester materials. Cationic functionality is found in various types of dyes such as cationic azo dyes, methane dyes, anthraquinone, di-and tri-arylcarbenium, phthalocyanine dyes, poly carbocyclic and solvent dyes. Basic dye are toxic and can cause allergic dermatitis, skin irritation, mutations and even cancer. Also, cationic dye scan cause increased in heart rate, shock, vomiting, cyanosis, jaundice, quadriplegia, heinz body formation and tissue necrosis in humans.

(Sara and Tushar,2014)
Research in the past few years was focused on utilizing waste materials from agricultural products because they are inexpensive, ecofriendly, and renewable (Alshabanat et al.,2013).Peanut is an oil plant, which is extensively cultured in China. Thus, peanut husk is an abundant and inexpensive agricultural by-product. The exploitation and utilization of this biomaterial must bring obvious economic and social benefits (Binglu et al.,2014). Peanut husk are the newly thought adsorbents because of their extended surface area, micro porous structure, high adsorption capacity and high degree of reactivity. Peanut husk are totally new adsorbents for waste water treatment. (Mahmudur et al.,2014). Peanut husk or Groundnut shell is easily available at zero prices. Nut shell is carbonaceous, fibrous solid waste, which creates a disposal problem and is generally used for its fuel value.

Materials and Methods:-
All the chemicals used throughout this study were of analytical-grade reagents and the adsorption experiments were carried out at room temperature (25 ± 2 °C)

Adsorbent:-1.Peanut Husk (PH):-
Fresh biomass of peanut husk was collected from its natural habitats in the farmland. The collected biomaterial was extensively washed with tap water to remove soil and dust, and washed with distilled water, next dried in an oven at 80°C for complete dryness. Dry peanut husk was crushed into powder crusher and sieved to different particle sizes 0.335 and 0.850mm and then preserved in the desiccator for use. (Nahal and Azza, 2014 and Taha and El-Maghraby,2016 ) .

Treated peanut husk (TPH):-
A sample of 20 g peanut husk was added to 500 ml of 10% NaOH into three necks round bottom flask and agitated for 1h at room temperature. The half of the solution was removed and immediately 100 ml of distilled water and 160 ml of epoxy chloropropan were added .The mixture was then heated at 65 o C and stirred for 6 h those were carried out in shaking water bath (BS-21) .The solution was removed from heat and 220 ml of 34% tri ethyl amine solution was added .The mixture was heated in 80 o C water bath and agitated for 3 h .The product was washed with ethanol and distilled water. The solution pH was then adjusted around 7 using 0.1M NaOH and 0.1M HCl. Finally, the product was cleaned with distilled water until the pH was around 7. The treated peanut husk (TPH) was dried at 60 o C for 12 h. The dried (TPH) was grounded in a domestic mixer grinder. After grinding, the powder was again washed and dried. Different sized adsorbents 0.335 and 0.850mm were stored in plastic container for further use. (Xiaoyu et al.,2013).

Determination of the point of zero charge:-
The point zero charge (pHpzc) of adsorbent was determined by the solid addition method. The net charge of surface is zero on the adsorbent surface at pHpzc. Batch equilibrium method was used for the determination of point of zero charge. To each of the flask 1 g of adsorbent was added including 50 ml solution KNO 3

Dye Solutions:-
A stock dyes solution of basic red 2 was prepared by dissolving 1.75g in 500 ml distilled water and acid violet 19 was prepared by dissolving 2.93 g in 500 ml distilled water.

Effect of some parameters on dye adsorption
The effects of various experimental parameters have been investigated using a batch adsorption technique to obtain information on treating effluents from the dye industry.

Effect of pH on dye adsorption by PH
The effect of pH on the removal of AV19 and BR2 was analyzed over the pH range 2.0 -9.0. The pH was adjusted using 0.05 M NaOH or 0.05 M HCl solutions. In this study 150 ml of dyes solutions with fixed initial concentrations 5.85 mg/L and 3.51mg/L, respectively was taken in a conical flask at room temperature (25 o C) and was agitated at 130 rpm with 0.75 g of untreated and treated of PH. The particle size of adsorbent was 0.335 mm.

Effect of initial concentration
The effect of initial concentration on the removal of AV19and BR2 was analyzed at (5.85, 11.71, 17.57, 23.42 and 40.99mg/L) and (3.51, 7.02, 10.52, 14.03 and 24.55 mg/L), respectively. In this study 150 ml of dyes solutions at pH5, pH6for (TPH and PH), respectively were taken in a conical flask at room temperature (25 o C) and were agitated at 130 rpm with 0.75 g of untreated and treated of (PH). The particle size of adsorbent was 0.335 mm.

Effect of dose:-
The effect of untreated and treated of (PH) dose on the amount of AV19 and BR2 adsorbed was obtained by contacting 150 ml of dyes solutions with initial concentration 5.85 mg/L and 3.51 mg/L, respectively with different amount of (TPH) are 0.25g, 0.5g, 0.75g, 1g at pH5 and different amount of (PH) are 0.25g, 0.5g, 0.75g, 1g and 1.5g at pH6, respectively into a number of 250 ml conical flask and at room temperature(25 o C). The flasks were agitated at 130 rpm. The particle size of adsorbent was 0.335 mm.

Effect of temperature:-
The effect of temperature on AV19 and BR2 dyes solutions was obtained by contacting 150 ml of dyes solutions with initial concentration (5.85 and 3.51) mg/L with 0.335 mm of treated and untreated of (PH), 0.75g of PH (treated and untreated) into a number of 250 ml conical flask at pH5 ,pH6 of (TPH and PH), respectively and at different temperature values (30 o C, 50 o C and 70 o C).

Adsorption isotherm:-
The results obtained for adsorption of dye were analyzed by use of well-known models given by the Langmuir and Freundlich isotherms. (Smitha and Santhi,2015).

Langmuir isotherm:
The Langmuir model is based on the assumption that adsorption takes place at specific homogenous sites within the adsorbent .The saturated monolayer curve can be represented by the expression ( q e = q max K L C e / (1 + K L C e ) (II.1) a linear form of this expression is: C e /q e = 1/ q max K L + C e /q max (II.2) Where C e is the concentration of the dye solution (mg L -1 ) at equilibrium, q e the amount of dye adsorbed per unit weight of adsorbent (mg g -1 ) and K L is the constant related to the free energy of adsorption (L mg -1 ). q max is the maximum adsorption capacity (mg g -1 ). dq t / dt = k 1 (q e − q t ) (II. 5) After definite integration by applying the initial conditions t= 0 to t and q t = 0 to q t , equation (II.5) becomes: log (q e −q t )= log q e −k 1 t /2.303 (II.6) where q e and q t is the amount of dye sorbed per unit weight of sorbent (mg/g) at equilibrium and at time t (min) respectively, k 1 is the rate constant of the pseudo-first order sorption (min -1 ). The plot of log (q e −q t ) versus t gives a straight line for the pseudo-first-order adsorption kinetics. The values of k 1 and q e were obtained from the slopes and intercept of the straight lines.

Pseudo second-order kinetic model:-
The pseudo-second order rate equation (Ho. 2006  dq t /dt = k 2 (q e2 -q t ) 2 (II.7) Integrating equation (II.11) for the boundary conditions t= 0 to t= t and q t = 0 to q t = q t , gives: 1/( q e2 -q t )= 1/q t + k 2 t (II.8) Where k 2 is the equilibrium rate constant of pseudo-second order sorption (g/mg min). Equation (II.12) can be rearranged to obtain a linear form : t/q t = (1/ k 2 (q e2 ) 2 ) + (1/ q e2 ) t (II.9) The equilibrium adsorption capacity (q e2 ), (mg/g) and the second-order constants k 2 (g/mg min), can be determined experimentally from the slope and the intercept of plot t/q t versus t.

The intraparticle diffusion kinetic model:-
The dyes sorption is usually governed by either the liquid phase mass transport rate or the intraparticle mass transport rate (Han et al.,2008 ; Ho  q t = k i t 1/2 + C (II.10) Where C (mg/g) is constant and k i is the intra particle diffusion rate constant (mg/g min 1/2 ) which determined from the intercepts and slopes.

Thermodynamic parameters:-
The thermodynamic parameters provide in-depth information regarding the inherent energetic associated with adsorption; therefore, they should be properly evaluated. The

Solid state analysis:-
The peanut husk (PH) was analyzed before and after treatment and measured point of zero charge of it. As well as studies of dye sorption are focused on one-component and competition between dyes for sorption sites before and after adsorption. SEM and IR were used to analyze the morphology and chemical groups of the (PH) and (TPH) .

Scanning electron microscopy (SEM):-
The results of SEM of PH are shown in Fig.III.1 (a-e). Fig. III.1 (a) shows (PH) before treatment and after treatment with tri ethyl amine solution Fig.III.1 (b), it was found that TPH surface occupies with amino groups which modified the surface and increases the positivity of the surface.   The SEM micrographs of (PH ) (a) and after treatment (b) and after adsorption of AV19 (c) and BR2 (d) and after adsorption of binary system (AV19 and BR2)on TPH (e).

Fourier transformed infrared spectroscopy studies:-
The FTIR technique was an important tool to identify functional groups, which are capable of adsorbing pollutant dyes. FTIR spectroscopy was therefore, done for preliminary quantitative analysis of major functional groups presented in PH (Nahla and Azza,2014). Some distinct changes are noted in the spectrum between PH and TPH Fig.III.2 (a and b) where the bands at (1738, 1377 and 1039 cm -1 ) were disappeared but two new peak appears at 1420 and1139 cm -1 . Moreover, the peak at 2923 cm -1 shifted to 2937 cm -1 .These peaks indicate that NaOH treatment in the first stage of the synthesis process further removed some soluble lignin in TPH. Epoxy chloropropane introduced new CH 2 groups to the cellulose molecules. There is a new adsorption peak associated with the stretching vibration of C-N band at1420cm -1 ,and abroad band of the skeletal vibration of the quaternary ammonium salt, which was successfully grafted onto the cellulose skeleton (Cao et al .,2011).       adsorption of AV19 (c) and BR2 (d) and binary system (e).

Determination of the point of zero charge of (PH and TPH):-
The point of zero charge (pHpzc) is an important parameter for biosorbent to characterize the sensitivity to the pH and their surface charges, (Sadaf et al .,2013). The activation of acidic or basic functional groups of adsorbents approaches zero at point of zero charge , ( Mohamad et al.,2012 and Noureddine et al.,2016). The point zero charge of (PH and TPH) was determined and the results are shown in Fig.III.3(a and b). The pHpzc was found to be 5, 8 for (PH and TPH), respectively. Values (5 and 8, respectively) represent pHpzc value, when the sorbent surface was neutral. At values of pH < pHpzc, the sorbent surface is positively charged and susceptible to electrostatic interactions with the polar portions of the anionic dye molecules (dissociated sulphonic groups). At pH > pHpzc, the sorbent surface was negatively charged and was available to bind the cationic dye(dissociated amino groups) (Daniela et al., 2010 and Moawed and El-Shahat,2016).

Effect of some parameters on dye adsorption:-2.1. Effect of pH on dye adsorption by PH (untreated and treated) in both single and binary dye solutions:-
At low pH solution, the percentage of dye removal will decrease for cationic dye adsorption, while for anionic dyes the percentage of dye removal will increase. In contrast, at a high pH solution the percentage of dye removal will increase for cationic dye adsorption and decrease for anionic dye adsorption (Ihsan. 2016).In single system the adsorption of AV19 dye by (PH) is low at pH 0.2. Since the maximum AV19 dye adsorption by (TPH) is at pH 0.5. While the maximum BR2 dye adsorption by(PH) is at pH6. Since BR2 molecules compete with positively charged surface of (TPH), thus a very lower adsorption results expected. However, the adsorptions of AV19 and BR2 by (TPH) in binary system were less than those for the single systems as shown in Table (III.1) and Fig.(III.4). This result indicated that the dye competed with other dye ions for the same sites on adsorbent. For example the sorption of binary dye molecules by (TPH) is based on the electrostatic attraction as postulated Where SO 3 --AV19-SO 3 represents the structure of AV19 and BR2-N + represents the BR2 dye ion. According to the conversion scheme above, surface group of TPH will bind with each dye. These results reinforce an enhancement of the removal of binary dye molecules by TPH.

Effect of initial dye concentration on adsorption by PH (treated and untreated) in both single and binary dye solutions:-
The percentage of dye removal by PH (treated and untreated) decreased with increasing initial AV19 and BR2 dyes concentration. This may be probably as a result of the fact that for a fixed adsorbent dose, the total available adsorption sites remain invariable for all the concentrations checked. With increasing concentration the available adsorption sites become fewer (Noureddine et al.,2016). From this study concluded that the less initial dyes concentration (5.85 and 3.51 mg/L) for AV19 and BR2, respectively give the high removal percentage of dye as shown in

Effect of adsorbent dosage on adsorption dye by PH (treated and untreated) in both single and binary dye solutions:-
The removal percentage of AV19 and BR2 dyes increase with the increasing dosage of PH (treated and untreated) until reached at certain dosage after this dosage take place decrease in removal percentage as shown in Fig.(III.6).Because of the increase in adsorbent dosage lead to increasing in available sorption sites. These results may be due to the overlapping of adsorption sites as a result of adsorbent particle overcrowding (Garg et al., 2003 and Aseel.2016). This study show the best dose that give high removal percent is 0.75 g for (PH and TPH) in single system while in binary system the best dose is 1g for TPH.

Effect of temperature on dye sorption by PH (treated and untreated) in both single and binary dye solutions
The adsorption of AV19 and BR2 increases with increasing the temperature as shown in

Adsorption isotherm:-3.1. Langmuir adsorption isotherm:-
Assume that the adsorption occurs at specific homogeneous sites within the adsorbent. It also assumes that the adsorption sites on adsorbent have the same affinity for the adsorption of a single molecular layer of dye, with no interaction between the adsorbed molecules of the dye. And from this study the R L values are between 0 and 1 indicate favorable adsorption and r 2 is 0.99 (Amir et al., 2016).

Freundlich adsorption isotherm:-
Freundlich equation fits in nearly all experimental adsorptiondesorption data and is especially useful for data from highly heterogeneous sorbent systems. From the Freundlich isotherm, since the values of 1/n < 1 in all the sorption processes studied indicate the adsorption was favorable. Where r 2 is lower than that result from Langmuir isotherm. So the data follow Langmuir adsorption isotherm (Manimekalai et al., 2015).

Pseudo-second-order model
The pseudo second-order model is based on the assumption that the rate-determining step may be a chemical sorption involving valence forces through sharing of electrons between adsorbent and adsorbate. The correlation coefficients were all extremely high and all greater than 0.97 indicate that pseudo second-order model is the best model for adsorption and the adsorption process is indicative of a chemisorption mechanism.

4.3.The intraparticle diffusion kinetic model
Show two stage the initial stage of the adsorption process within the first minutes indicating also a high affinity between dyes and adsorbent surfaces due to the intraparticle diffusion of dye molecules. Following this phase, the adsorption process slows suggesting a gradual equilibrium, possibly finally, the saturation is reached, and showing the final equilibrium beyond which no adsorption takes place.

Conclusion:-
The present study results showed that the both untreated peanut husk (PH) and treated peanut husk (TPH) have the ability to asorption the dye from the effluent. The pHpzc was found to be 5 for (PH) and 8 for (TPH) .It was found the removal efficiency increased with increase pH until it reached to limited pH then decreased and increase with increase in dose and temperature and decrease with increase in concentration .Where the experimental results fit Langmuir isotherm which indicate to mono layer adsorption and fit also pseudo-second-order which indicate to a chemisorption mechanism and thermodynamic parameters indicated to adsorption process was spontaneous and endothermic in nature. It was also found that the adsorbed species/solute may either block the access to the internal pores or cause particles to aggregate and there by resulting in the availability of active sites for adsorption.