Experimental data on adsorption of Cr(VI) from aqueous solution using nanosized cellulose fibers obtained from rice husk

The aim of this study was to evaluate the efficiency of nano-sized cellulose obtained from rice husk for Cr(VI) adsorption. The effect of operational parameters including initial pH (3–10), contact time (0–120 min), adsorbent dosage (0.2–1.5 g/L), and initial Cr(VI) concentration (5–50 mg/L) were investigated according to one factor at time method. The results showed, in pH=6, contact time=100 min, adsorbent dose=1.5 g/L and 30 mg/L initial chromium concentration, the adsorption efficiency reached to 92.99%. Also Langmuir isotherm with (R2=0.998 at 303 °K) and pseudo-first-order kinetic model (R2=0.993) were the best models for describing the Cr(VI) adsorption reactions. The negative values of ΔG∘ and positive value of ΔH∘ showed that, the Cr(VI) adsorption on NCFs was endothermic and spontaneously process. Therefore, it can be concluded that the application this method is recommended for removing Cr(VI) from aqueous solutions.


Subject area
Water pollution More specific subject area

Water and wastewater treatment
Type of data Table and Figure  How data was acquired Experiments were performed according to a designed procedure and output of analytical test were processes in order to perform an analysis of adsorption process.

Data format
Processed Experimental factors Studied variables included pH, contact time, adsorbent dosage, and Cr(VI) concentration which were investigated for Cr(VI) adsorption Experimental features Adsorption of Cr(VI) in a synthetic sample was studied using synthetized nanocellulose Data source location Ahvaz city, Khuzestan province, Iran Data accessibility Data are available in article Value of the data Data are benefit for determination of the isotherm, kinetic, and thermodynamic data and also for predicting and modeling the adsorption capacity and mechanism of chromium (VI) removal by the adsorbent will applicated.
A simple method used for preparation of nano-cellulose fibers from rice husk. The dataset will be useful for Cr(VI) ion removal from water and wastewater.

Data
This data set contains 7 Tables and 7 Figure. Figs. 1-5 shows the effect of different parameters on the removal of chromium with nano-cellulose fibers. Also, Tables 1 and 2 shows isotherm and kinetic equations and the coefficient of correlation this equations is presented in Table 3 and 4. Figs. 6 and 7 shows adsorption isotherm and kinetic curve and regressions of vant Hoff plot for thermodynamic parameters.      Table 1 Characteristics of the isotherms.

Type of isotherm Equation Linear form
Freundlich Langmuir Temkin

Table 2
Kinetic equations and linear forms used in this study.

Kinetics of equation linear form
Pseudo-first-order

Table 3
The results of calculations of the adsorption isotherm.

Materials
Rice husk used in this study was prepared from Northern of Iran. Sodium chlorite (NaClO 2 ), acetic acid glacial (CH 3 COOH), potassium hydroxide (KOH), sulfuric acid (H 2 SO 4 ) and the other chemicals used in this study were prepared from Merck Germany and used without additional treatment.

Experimental procedure
The adsorption experiments were carried out in laboratory scale on synthetic wastewater, inside Erlenmeyer flasks with volume of 200 mL. Besides, HCl and NaOH 1 N were used in order to adjust the pH level at the beginning of each experiment. Mixing was performed using a shaker incubator with 150 rpm at the temperature range of (283-303°K). Effect of operational parameters including as pH (3)(4)(5)(6)(7)(8)(9)(10), reaction time (0-120 min), initial Cr(VI) concentration (5-50 mg/L) and adsorbent dosage (0.2-1 g/L) were assessed. To determine the residual concentration of Cr(VI), samples were centrifuged at 3000 rpm for 10 min. Thereafter the supernatant was used for analysis residual Cr(VI) concentration by flame atomic absorption spectroscopy (FAAS) (Model AAS vario6 Jena, Germany). The Cr(VI) concentration was determined according to standard methods for examination of water and wastewater [1].
In addition, the adsorption capacity (mg/g) and adsorption efficiency (%) were obtained using Eqs. (1) and (2) [2]: Where q e , is the amount of Cr(VI) adsorbed (mg/g), C 0 and C t are initial and final Cr(VI) concentrations, V is the volume (L), and M, is the adsorbent dosage (g).

Preparation of nano-sized cellulose fibers (NCFs)
NCFs were prepared according to the technique given by Lu et al. [3], with some modifications. Briefly, at the first, to remove dirt and soluble substances, rice husk were washed with distilled water four times, and dried overnight in oven at temperature of 313°K. Then rice husk crushed to smaller pieces of (5-10 mm) through a grinder and passed of 60-mesh screen. Afterwards, 30 g of product was soaked in proportion 2:1(v/v) toluene/ethanol (450 mL) mixture for 20 h to remove impurities such as oil and wax, then dried in at 328°K for 24 h. the dewaxed fibers were immersed in sodium chlorite solution (pH ¼ 4) for 1 h at 323°K to remove lignin and then washed with distilled water. Hemicellulose and pectin were treated with 600 mL solution of 5% KOH for 24 h and dried at temperature 363°K for 2 h and then washed with distilled water. Cellulose isolated was hydrolyzed using acid hydrolyzed (40 ml DI water þ 20 ml HCl 12.1 N and 40 ml H 2 SO 4 36 N) for 3 h at 343°K for to obtain soft wood pulp and then washed with distilled water. Finally these fibers were sonicated (Hielsccher: UP 400S, Germany), operating at a fixed frequency of 50 KHZ at 353°K for 3 h, dried and subjected for microscopic analysis (Tables 5-7).

Desorption study
In order to predict reusability of NCFs, four adsorption-desorption cycles were considered. The adsorption was performed using an initial Cr(VI) concentration of 30 mg/L. At the first, metal loaded NCFs obtained from experimental was poured into the Laboratory jar that was contain 50 ml of HNO 3  Table 7 Notation used in the kinetic models and the adsorption isotherms.
Nomenclature K L Langmuir isotherm constants (L/mg) K f Freundlich isotherm constants (L/g) n Adsorption intensity q t Adsorbed metal concentration at time t (mg/g) C e Equilibrium concentration in solution (mg/L) q e Equilibrium adsorbent concentration on adsorbent (mg/g) q e cal Calculated values of q e (mg/g) Q m Maximum monolayer capacity (mg/g) R 2 Correlation coefficients K 1 Pseudo first-order rate constant (1/min) K 2 Pseudo second-order rate constant (g/mg min) K dif Intraparticle diffusion rate constant (mg/g min 0.5 ) β Activity coefficient constant(mol 2 /j 2 ) Ɛ Polanyi potential 0.5 M and rocked for 20-100 min. Then, the sample was centrifuged and using Whatman 42 filter paper to remove any excess of Cr(VI) in the surface of the NCFs was filtered , and regenerated adsorbent for removal Cr(VI) was used [4]. Desorption ratio (DR %) was calculated through Eq. (3), [5].
where: C des (mg/L) is the amount of desorbed metal ion, and C ad is amount of adsorbed metal ion in solution.

Adsorption isotherms
In the current study, the experimental data of adsorption equilibrium were investigated using Langmuir, Ferundlich, Temkin and Dubinin-Radushkevich (D-R) isotherm models. The study of isotherm models were carried out in pH of 6, adsorbent dosage 1 g/L, agitation speed 150 rpm and contact time of 100 min. Equations as well as the linear forms these isotherms are shown in Table 1 [6][7][8].

Adsorption kinetics
In the current study pseudo-first-order and pseudo-second-order kinetic models to determine the adsorption mechanism were investigated. The equations of these Kinetics are shown in Table 2 [9-12].