Carboxyl Methyl Cellulose@Guar Gum@ CuO Nanoparticle as Effective Adsorbent for the Removal of Dye From Aqueous Solution

In the present study, the study and fabrication of inorganic organic nanocomposites with Guar gam and Carboxy methyl cellulose biopolymer substrates. The synthesis nanocomposite of CMC/GG/CuO-3 is biodegradable and biocompatible, and also has a significant efficiency in removing malachite green (MG) dye from aqueous solution. Properties were evaluated by XRD, FTIR, SEM, EDX and BET analysis. Important and influential parameters on the adsorption process such as adsorbent amount, initial dye concentration, pH and contact time on the removal efficiency of contaminants from aqueous solutions were investigated. Maximum removal efficiency and adsorption capacity were 92.4% and 18.6 mg/g, respectively. In order to analyze the mechanism of experimental data, two First-order and Second-order kinetic models were used, which followed the second-order kinetics with R 2 =1. Also, the study of Freundlich and Langmuir isotherms showed that the isotherm model of Freundlich follows the R 2 =0.94, which indicates the non-uniformity of adsorption on the adsorbent surface.


Introduction
In recent years, the industrialization and population growth of the world, due to the limited resources of fresh water, drinking water, as well as climate change due to global warming, has doubled the pressure on existing resources [1]. Many organic pollutants in water sources existing a wide range of compounds, including dyes, insecticides, petroleum products, paper, leather, plastics and rubber, detergents, oils, pharmaceutical and personal care products compounds [2].
Dyes have been widely considered and used in today's advanced industries and technologies.
Colored wastewater produced in many processes in the textile industry generally contains organic compounds due to the formation of strong, toxic, carcinogenic, mutagenic and biodegradable complexes that often cause many environmental problems [3,4]. Organic dyes are chemically stable and can appear as anionic, cationic or non-ionic due to their complex aromatic structures [5]. Malachite green (MG) is a cationic dye in the form of a green crystalline powder with a metallic luster that is widely used in the textile and dyeing industries including leather, silk, cotton, wool, hair dye and paper. Disposal of organic dyes in aquatic ecosystems has adversely affected aquatic species and has become a significant source of pollution [6,7]. The presence of organic dyes in water sources due to the presence of functional groups and aromatic compounds, reduces the penetration of sunlight and affects the photosynthetic activities of aquatic animals [8]. Therefore, an effective, efficient and economical way to reduce the concentration of organic pollutants before release into the aquatic environment is needed [9,10]. Therefore, separation and removal of dyes from industrial effluents has become a very important issue [11]. For this purpose, conventional physical and physicochemical methods including adsorption, biological oxidation, ultrafiltration, membrane, photocatalyst, ion exchange and chemical coagulation have been used to separate and remove colored effluents [12][13][14]. Among the mentioned methods, the absorption process is one of the most common methods due to its high efficiency, economy and simplicity of work [15]. Many researchers today seek to use adsorbents based on metal nanoparticles with biodegradable polymer compounds with high adsorption capacity and low cost, including chitin, alginate, guar gum, carboxy methyl cellulose and copper oxide and graphene oxide pointed [16][17][18][19].
Cellulose is a linear polymer with high molecular weight, natural, renewable and biodegradable with high crystallinity and strong intramolecular hydrogen bonding that is not soluble in most organic solvents [20,21]. The conversion of cellulose to its derivatives such as carboxy methyl cellulose (CMC) based on the Williamson ether reaction is a way to increase the efficiency of cellulose [22,23]. CMC was first produced from linear polysaccharide biopolymers in 1918 and is significant due to its long chain, anionic and water-soluble properties [24,25]. CMC has been considered as an alternative to synthetic polymers due to its cheapness, non-toxicity, production of transparent films, high viscosity, biodegradable and biocompatible. CMC has a variety of applications in various fields including textiles, paper industries, food, detergents, cosmetics and pharmaceuticals. CMC is synthesized from plant biomass, which in the dry state contains 40-forming, viscous and concentration-enhancing agent, cloding and adhesive agent, gelling and even wound healing agent. GG is also used in various applications including food, textile, paint and coating, agriculture, pharmaceutical and personal care products and biological treatment [31,32]. Metal oxides are used to improve or develop the functional properties of polymers.
Copper oxide (CuO) nanoparticles have significant antimicrobial performance and semiconductor properties due to their specific and unique crystal structure. CuO nanoparticles are widely used for various applications in fields such as magnetic storage devices, catalysts, ceramics, thermal sensors and superconducting materials. Table 1 illustrating the removal efficiency of dyes with different adsorbents.
The present study investigated and fabricated an inorganic organic nanocomposite with a biopolymer substrate. In general, cellulose sources can be used as organic matter and metal particles as minerals can be used in this nanocomposite. The nanocomposite is biodegradable, biodegradable and biocompatible, and has also shown significant efficacy in removing malachite green dye. In fact, it can be said to be effective in reducing environmental pollution. Experiments were synthesized at room temperature and used as a biopolymer adsorbent to remove green malachite dye from aqueous solutions. Important and influential parameters on the adsorption process such as adsorbent amount, initial dye concentration, pH and contact time on the removal efficiency of contaminants from aqueous solutions were investigated. In order to analyze the mechanism of experimental data, two pseudo-first-order and pseudo-second-order kinetic models as well as Freundlich and Langmuir isotherms were used.
The chemical structure of Malachite green is illustrating in Fig.1. Dilute HCl and NaOH were used to adjust the pH of the pollutants solution.

Preparation of CMC/GG nanocomposite
The CMC/GG mixture was dissolved in 1 g of dried CMC hydrogel in 100 ml of deionized water at room temperature under intense magnetic stirring at 700 rpm for 1 h. Then 1 g GG was added to CMC hydrogel. The resulting mixture was subjected to intense magnetic stirring for 3 h for complete dissolution and the formation of a clear gel. The prepared CMC/GG hydrogel was dried at room temperature.

Preparation of CMC/GG/CuO nanocomposite
In order to synthesize the biopolymer/nanoparticle nanocomposite, 1 g of dried CMC hydrogel in 100 ml of deionized water was subjected to intense magnetic stirring at 700 rpm for 1 h. Then 1 g of GG was added to CMC hydrogel. Then 1 mg/ml of CuO was gently added to the hydrogel mixture containing CMC/GG. The resulting mixture was continuously stirred vigorously with a high-speed magnetic stirrer (700 rpm) for 3 h for complete and uniform dissolution and the formation of a clear gel. The prepared CMC/GG/CuO hydrogel was dried at room temperature.
In order to optimize the adsorbent, different wt% of CuO were prepared according to the above formulation (1, 3 and 5 wt%).

Apparatus
The Fourier Transform Infrared Spectroscopy (FT-IR) device made by Perkin Elmer Company was used to identify the properties of biopolymer nanocomposite materials synthesized in the range of 450-4000 cm -1 . X-ray diffraction (XRD) to record the structure and crystalline nature of the samples using X-Ray Diffractometer with Cukɑ beam irradiation with a step size of .05 XRD pattern was recorded. The specific area and porosity of the adsorbents were determined using nitrogen gas adsorption method and BET isotherm model (S BET ) at 77 ° K and at atmospheric pressure. From the visible-ultraviolet (UV/Vis) spectrophotometer with Lambda-25 Perkin Elmer model, the light absorption of the sample was examined. In order to study the crystal structure and morphology of the scanning electron microscope (SEM) was used using the instrument model (Zeiss EM900).

Dye Adsorption Experiment
The adsorption experiment of green malachite cationic dye in 100 ml of decolorizing glass containing dye was investigated using biopolymer nanocomposite adsorbents. Dye solution with a specific initial concentration (20 mg/l) was prepared from the adsorbent and their pH was adjusted using solutions of hydrochloric acid and sodium hydroxide in the range of 3.5 to 6.5.
Then, by adding 0.1 g of adsorbent to the solution, they were stirred for 90 min at specified intervals by a magnetic stirrer at ambient temperature. After the agitation and centrifugation process, the absorption spectra of each solution were read by a single-beam spectrophotometer at 9 adsorption capacity (mg/g) qt for dyes at time t (min) and the adsorption capacity at equilibrium (mg/g) qe were calculated from the following equations (1), (2):

FTIR
In order to understand the chemical nature and identify the functional groups of the materials used, FTIR analysis was performed. Weak strips of about 707 cm -1 are due to ring tension and ring deformation of the joints.
Similarly, the FTIR spectrum of CMC is shown in Fig.2

SEM
The surface morphology of the samples used was determined using scanning microscope images.
SEM images are shown in Fig.4. As can be seen from Fig.4-a, CuO nanoparticles have a monodisperse morphology with a distinct crystalline structure and are almost uniform in that the diameter of CuO nanoparticles varies from 30 to 50 nm [38,39]. The SEM image of the CMC biopolymer shows an irregular shape and an uneven surface ( Fig.4-b) [40,41]. GG image has cavities, irregular, layered and heterogeneous appearance (Fig.4-c) [42].

EDX
EDX analysis was performed to evaluate the structural analysis and chemical properties of the samples used. Table 2 shows the results obtained. According to Table 3,

BET
BET theory is based on the extended Langmuir theory and is based on the multilayer adsorption of gas molecules on the solid surface due to the non-uniformity of the adsorbent surface and the interaction of gas molecules with each other. The porosity and specific surface area of the samples were measured by nitrogen adsorption and desorption isotherms at 77 ° K. Table 3 lists the specific BET level for all samples. According to Fig.5, the behavior of the samples reversibly shows the isothermal behavior of the III type. The hysteresis ring expresses the structure of the mesopores. According to the results presented in Table 3, CMC/GG/CuO-1 composite has a larger surface area and pore size than other composites. This increase can be attributed to the nonblockage of pores and cavities by CuO functional groups.

Effect Ratio
To optimize the adsorbent, the effect of different ratios of CuO (1, 3, 5 mg/ml) on the biopolymer CMC/GG was loaded at room temperature (Fig.6). According to the results shown in Fig.6, by changing the load of CuO, the amount of adsorption capacity changes significantly. As can be seen, the amount of loading agent 1 mg/ml has a higher adsorption capacity (18.6 mg/g) than the other two values. Increasing the load of CuO causes blockage of pores and pores of biopolymer nanocomposites. Therefore, the optimal dose of CuO on CMC/GG biopolymers was selected to be 1 mg/ml.

Initial concentration pollutant
The effect of initial dye concentration on the removal of MG dye with synthesized adsorbents was studied. The amount of 0.1 g of adsorbent was determined in 100 ml of dye solution at different concentrations (20, 30, 40 and 50 mg/l) and with optimal pH adjustment (6.5).
Approximately 89% dye removal occurs with an initial concentration of 20 mg/L in the first 15 min of the process. According to Fig.7, with increasing the initial concentration of dye solution, the percentage of dye removal decreased [43]. The final amount of removal efficiency 92.4% percentage and the amount of adsorption capacity 18.5 mg/g were obtained. By increasing the concentration of dyes, repulsion is created between the dyes molecules and they are prevented from being absorbed by the adsorbent [42,44].

Effect pH
The pH of the solution is one of the most important factors in the adsorption process that can change the surface charge of the adsorbents as well as the separation of the functional groups present in the adsorbent adsorption active sites. In order to investigate the effect of pH on the adsorption of MG dye with biopolymer adsorbents, a dye solution with an initial concentration of 20 mg/l and an optimal adsorbent dose of 0.1 g was prepared and their pH was diluted with hydrochloric acid and sodium hydroxide in different pH ranges to 3.5 to 6.5 (Fig.8). Since MG dyes change structure at pH above 7, it was not tested above 6.5. The results of this study are shown in Fig.8. The max removal efficiency (92.4%) of MG was observed at pH = 6.5. The MG dye is positively charged when dissolved in water. In other words, by lowering the pH (in an acidic environment), the number of positively charged sites increases and the removal efficiency decreases. As can be seen, when the pH of the solution is increased from 3.5 to 6.5, the adsorbent

Effect Dosage
Adsorption of cationic dyes on CMC/GG and CMC/GG/CuO biopolymer nanocomposite adsorbents by changing the amount of adsorbent from 0.05 g to 0.1 g at constant room temperature, initial concentration 20 mg/l and pH 6.5 were studied. According to the results observed in Fig.10, by increasing the amount of adsorbent from 0.05 to 0.1 g, the amount of adsorption increases significantly, this increases the desired level of adsorbent and the availability of more active adsorption sites for adsorption. Dye molecules are attributed.
However, by changing the amount of adsorbent from 0.05 -0.1 g, the amount of dye removal increases significantly (from 67.6 to 92.4%). Therefore, 0.1 g was selected as the optimal absorbent dose for all experiments [49,50].

Adsorption Isotherms
Isotherm expresses the relationship between the concentration of adsorbent in solution and the amount of adsorbent on the adsorbent surface physically or chemically at a constant temperature.
In this way, the adsorption capacity of the adsorbent in equilibrium is determined with the help of special constants that indicate the surface properties as well as the adsorbent tendency to adsorb the contaminant. In this study, Langmuir and Freundlich isotherms were used. Fig.11 shows the results of the Langmuir and Freundlich isotherm study in the adsorption process with biopolymer adsorbents CMC/GG and CMC/GG/CuO. Table 4 In these relations, C e is the concentration of dye in equilibrium (L/mg) and q e is the amount of adsorbed material per absorbent body in equilibrium (mg/g). The q l and K f constants show the adsorption capacity of the monolayer. Also, the dimensionless constants n and Kf indicate the adsorption capacity and intensity, respectively.

Adsorption kinetic
The adsorption kinetics investigates the relationship between the reaction rate and the interactions between the adsorbent and the adsorbent. Using equilibrium data of adsorption, the kinetics of reaction and its degree of agreement with quasi-first-order quasi-equations were investigated. Fig.13 shows the results of a pseudo-first-order and second-order kinetic study in  the adsorption process of biopolymer adsorbents CMC/GG and CMC/GG/CuO. Table 5 presents the results of data fitting on first-order and second-order kinetic models of the mentioned adsorbents. According to the values of R 2 (correlation coefficient) obtained for both kinetic models, with biopolymer adsorbents CMC/GG and CMC/GG/CuO greater R 2 (R 2 =1) value in the second-order model compared to the first-order model, in the presence of both adsorbents it can be stated that the process under study Follows the second-order model [53,[55][56][57].
Second order kinetics (6): Where k l (min -1 ) and k 2 (g/mg.min) are the first-order and second-order absorption equilibrium constant rates, respectively. Also, qe is the amount of material adsorbed per unit mass in equilibrium and qt (mg/g) is the amount of capacity of the adsorbed material at time (t). Table 5 The kinetics coefficients of MG dye adsorption at different adsorbent doses.

Conclusion
According to the results of the experiments, it can be said that the biopolymer adsorbent based on copper oxide (CMC/GG/CuO) nanoparticles is a good adsorbent for cationic dye bleaching of MG. So that by using the optimal amount of adsorbent 0.1 g with an initial concentration of dye of 20 mg/L at a pH of 6.5 and within 90 min to achieve the removal efficiency 92.4% and adsorption capacity 18.6 mg/g. The adsorption kinetics follow a second order with a correlation coefficient R 2 =1. The isothermal model also follows the Freundlich correlation coefficient R 2 =0.9437, which indicates the non-uniformity of the adsorption position on the adsorbent surface.