The wastage of the cotton stalks (Gossypium hirsutum L.) as low-cost adsorbent for removal of the Basic Green 5 dye from aqueous solutions
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Cotton stalks (Gossypium hirsutum L.) waste was investigated as a low-cost and effective adsorbent for the adsorption of Basic Green 5 dye from aqueous solution. The effects of pH solution, initial dye concentration, contact time, sorbent dosage and temperature on the adsorption parameters were investigated. The Langmuir, Freundlich and Dubinin–Radushkevich adsorption models were evaluated using the experimental data. The maximum adsorption capacity was found to be 42.37 mg g−1 from the Langmuir isotherm model at 20 °C. The dimensionless separation factor (RL) values lie between 0.129 and 0.423, indicated favorable adsorption. The adsorption rate data were analyzed according to the Lagergren pseudo-first- and pseudo-second-order kinetic models. It was found that kinetic followed a pseudo-second-order model. The negative values of the ΔG° at 293–323 K and the positive value of the ΔH° (13.585 kJ mol−1) indicate that the sorption process is spontaneous and endothermic in nature. The positive value of ΔS° (0.0467 kJ mol−1 K−1) shows the increasing randomness during adsorption process. The mean adsorption energy from Dubinin–Radushkevich equation was found to be 11.63 kC mol−1, indicating that the adsorption of the Basic Green 5 by cotton stalks occurred through chemical interaction mechanism. The offered mechanism of adsorptive process of the Basic Green 5 dye on a surface of the sorbent, obtained on the basis of cotton stalks, considers forming a complex between dye and sorbent.
KeywordsBasic Green 5 dye Cotton stalks Adsorption Isotherms Sorption mechanism
Wastewater containing dyes is very difficult to be treated, since the dyes are recalcitrant organic molecules, resistant to aerobic degradation, and stable to light, heat and oxidizing agents (Kyzas et al. 2012). A considerable amount of dyes is released into the aquatic ecosystems through the wastewater streams of industries such as textile, carpet, leather, paper, printing, food, cosmetics, paint, pigments, petroleum, solvent, rubber, plastic and pesticide. (Chowdhury and Saha 2012). Several treatment methods have been developed for dye removal including coagulation, chemical oxidation, membrane separation, electrochemical process and adsorption technique (Gupta 2009; Mohammed et al. 2014; Oladipo et al. 2013). Among these processes, adsorption is an effective method for color removal. Agrowaste materials are available in large quantities and may have potential as a sorbent due to their physicochemical properties and low cost. They contain various organic compounds such as lignin, cellulose and hemicellulose with polyphenolic groups that might be useful for binding dyes through different mechanisms. A number of agricultural waste materials are being studied for the removal of different dyes from aqueous solutions at different operating conditions. The adsorption of methylene blue on teak tree bark powder was carried out as a function of process of parameters including initial methylene blue concentration, dose of adsorbent, pH, agitation time, agitation speed, temperature and particle size (Patil et al. 2011). Freundlich, Langmuir and Temkin isotherm models were used to test the equilibrium data. The best-fitting isotherm models were found to be Langmuir and Freundlich. The monolayer (maximum) adsorption capacity was found to be 333.333 mg g−1. Lagergren pseudo-second-order model best fits the kinetics of adsorption. Thermodynamic analysis showed negative values of ΔG indicating adsorption was favorable and spontaneous, positive values of ΔH° indicating endothermic physical adsorption and positive values of ΔS° indicating increased disorder and randomness at the solid-solution interface of methylene blue with the adsorbent. Adsorption of Direct Red 81 dye was investigated using bamboo sawdust (BSD) and treated with citric acid bamboo sawdust (TBSD) in a batch system with respect to initial dye concentration, adsorbent dose, pH, temperature and contact time (Tabrez et al. 2012). Maximum adsorption capacity obtained from the Langmuir isotherm plots was 6.43 mg g−1 (89%) (BSD) and 13.83 mg g−1 (92%) (TBSD) at 303 K. The adsorption dynamics conformed well to pseudo-second-order kinetic equation. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) suggested the adsorption process to be spontaneous, endothermic with increase in randomness at solid-solution interface. Modified Sugar cane bagasse, an agricultural by-product, acts as an effective sorbent for the removal of both basic and reactive dyes from aqueous solution (Wong et al. 2009). Batch adsorption studies were investigated for the removal of Basic Blue 3 and Reactive Orange 16. The adsorption isotherms fitted well into both the Langmuir and Freundlich equations. Results indicated that according to the Langmuir isotherm, the maximum sorption capacities are 37.59 and 34.48 mg g−1 for Basic Blue 3 and Reactive Orange, respectively. The kinetics of dye sorption processes fit a pseudo-second-order kinetic model. Coffee waste collected from coffee shops has been examined for the removal of two basic dyes, toluidine blue and crystal violet, from aqueous solutions (Lafi et al. 2014). Batch adsorption experiments were conducted under different conditions including contact time, the initial concentration of dye, pH, sorbent dosage and temperature. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms were tested to examine the adsorption behavior. The equilibrium data were well fitted by Langmuir isotherm model. The kinetic study indicates that adsorption follows the pseudo-second-order model. The maximum adsorption capacity was found to be as high as 142.5 mg g−1 for toluidine blue and 125 mg g−1 for crystal violet. In literature, there are few works on the research of adsorption of Basic Green 5 dye from aqueous solutions. In these works, modified natural and synthetic adsorbents were used for removal of Basic Green 5 from aqueous solutions. Spherical biochar derived from saccharides (glucose, sucrose and xylose) was used for removal of Basic Green 5 from water solutions (Tran et al. 2017a). Approximately 54–81% of the total concentration of dye in the solutions were removed within 1–4 min. The glucose biochar sample exhibited the highest adsorption toward Basic Green 5, and the maximum Langmuir adsorption capacity has been 144.7 mg g−1 at 30 °C. Thermodynamic calculations demonstrated that the adsorption process of Basic Green 5 onto glucose biochar occurred spontaneously (− ΔG°) was endothermic nature (ΔH° = + 80.34 kJ mol−1) and resulted in increased system randomness (ΔS° = + 0.386 kJ mol−1). Obtained from Eucalyptus lenceolata wood, activated carbon was used for adsorption of Basic Green 5 from water solution (Alam et al. 2017). Batch studies were performed to address various experimental parameters like, contact time, temperature and adsorbent dosage for the removal of dye. Elovich and Bhangam models were used for adsorption kinetics studies. From adsorption kinetic data, thermodynamic parameters like ΔH, ΔS and ΔG were determined. The results show that the adsorption process is spontaneous and endothermic nature. The negative entropy shows that acid molecules on the surface of adsorbent take an oriented position.
The research results on the removal of the Basic Green 5 from water solutions by cotton stalk, which is an agrowaste material, were given in the presented work. The effects of the sorbent dosage, initial dye concentration, contact time and temperature were studied, and equilibrium isotherm data were analyzed by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The sorption properties of the cotton stalks waste toward Basic Green 5 are executed for the first time, and it defines the novelty of this work.
Materials and methods
Preparation of the sorbent
The adsorbent used in the present study is cotton stalks (CS) that were collected from cotton plantations of the central regions of Azerbaijan Republic. CS of 1–2 mm in size were washed thoroughly with heated distilled water to remove dust and other impurities. Then, CS were washed repeatedly with acetone and were grounded in a mixer grinder. After grinding, the powders were again washed with acetone and dried at 40 °C in the vacuum oven.
It has a molecular weight of 364.9 and absorption maximum 660.607 (Conn), 657.618 nm (Aldrich). A stock solution of 250 mg L−1 was prepared in double-distilled water, and the experimental solutions of the desired concentration were obtained by successive dilutions.
Result and discussion
Effect of pH
Effect of sorbent dosage
Dependence of sorption degree from sorbent dosage (C0 = 50 mg L−1, 30 min, 20 °C, pH 6, V = 0.04 L)
Sorbent dosage (g L−1)
Effect of adsorption time
Dependence of sorption degree from contact time (C0 = 50 mg L−1, sorbent dosage 1.25 g L−1, 20 °C, pH 6, V = 0.04 L)
Effect of initial concentration of dye and sorption isotherm of sorbent
Langmuir, Freundlich and Dubinin–Radushkevich isotherms
Parameters of the Langmuir, Freundlich and D–R equations (C0 = 50 mg L−1, V = 0.04 L, sorbent dosage 1.25 g L−1, 30 min, 20 °C)
qmax (mg g−1)
KL (L mg− 1)
BDR (mg g−1)
E (kC mol−1)
Kinetics and thermodynamic
Regression parameters for the kinetic models C0 = 50 mg L−1, V = 0.04 L, sorbent dosage 1.25 g L−1, 20 °C)
qe (mg g−1)
K2 (L mg−1 min−1)
Comparison of the obtained data shows that the sorption process of the BG 5 from aqueous solutions with CS is better described by the pseudo-second kinetic model with determination coefficient 0.9978. Calculated value of sorption capacity from the equation pseudo-second model is equal to be 38.46 mg g−1, which is closer to the value of the experimental sorption capacity, obtained from the adsorption isotherm (33.2 mg g−1).
Comparison of BG 5 dye uptake data with other adsorbents on the basis of an agricultural wastage
qmax (mg g−1)
C0 (mg L−1)
Adsorbent (g L−1)
Tran et al. (2017a)
Golden shower pod
Tran et al. (2017b)
Tran et al. (2017b)
Tran et al. (2017b)
In this study
Deng et al. (2011)
Bulut and Aydin (2006)
Brazil nut shells
Oliveira Brito and Andrade (2010)
Malik et al. (2016)
Sorption thermodynamic parameters
∆G° (kJ mol−1)
∆H° (kJ mol−1)
∆S° (kJ mol−1 K−1)
Mechanism of the adsorption
In this study, the efficiency of cotton stalks, collected from cotton plantations of the central regions of Azerbaijan as sorbent for removal of Basic Green 5 dye from aqueous solutions, was investigated. Batch mode sorption studies indicate that the sorption process was strongly dependent on initial dye concentration, sorbent dose, contact time and temperature. The equilibrium sorption data obtained at different initial concentrations of dye fitted well in the Langmuir and Freundlich isotherms model. The maximum monolayer sorption capacity was found to be 42.37 mg g−1, which is close to value of equilibrium sorption capacity experimentally obtained from sorption isotherm (33.2 mg g−1). Kinetic studies show that the dye removal followed pseudo-second-order rate equation, while thermodynamic studies suggest that the sorption process was spontaneous and endothermic in nature. The positive value of ∆S° shows the increasing randomness during adsorption process. The offered mechanism of adsorptive process of the Basic Green 5 dye on a surface of the sorbent, obtained on the basis of cotton stalks, considers forming a complex between dye and sorbent. Finally, it can be concluded that cotton stalks, common and easily available agrowaste material, can be used as a sorbent for the removal of BG from aqueous solutions.
The authors gratefully acknowledge Dr. Elvin Y. Malikov for the help for editing the English text. This study was funded by the Science Development Foundation under the President of the Republic of Azerbaijan—Grant №. EIF–2012–2(6)– 39/26/4.
Compliance with ethical standard
Conflict of interest
The authors declare that they have no conflict of interest.
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