Abstract
In the current study, tannic acid-functionalized iron oxide nanoparticles have been synthesized using a cost-effective co-precipitation method and subsequently characterized using various instrumentation techniques such as Fourier transform infrared spectroscopy, X-ray diffractometer, field emission scanning electron microscopy, and thermal gravimetric analysis. Further, these surface-modified magnetite nanoparticles have been used for the adsorption of toluidine dye from an aqueous solution. The adsorption process was accompanied using batch procedure, and influences of several factors such as adsorbent dose, contact time, pH, temperature, and initial concentration of adsorbate were inspected concurrently. The maximum adsorption capacity of tannic acid-functionalized magnetite nanoparticles was found to be 50.68 mg/g. The adsorption process was observed to follow the Temkin isotherm model, whereas the kinetic study was well described by pseudo-second order. The thermodynamic study revealed the adsorption process to be endothermic and spontaneous in nature with a high degree of freedom between adsorbent and adsorbate. Therefore, the study indicated that the tannic acid-functionalized magnetite nanoparticles have promising adsorption capability and can be used as an excellent adsorbent for the removal of toluidine blue O dye from the aqueous solution.
HIGHLIGHTS
Tannic acid-tailored magnetite nanoparticles were employed as adsorbents for the removal of coloured pollutants from an aqueous solution.
Batch adsorption techniques were applied to scrutinize the adsorption behaviour of these magnetite nanoparticles.
The adsorption process obeys pseudo-second-order kinetics and the Langmuir model of isotherm.
The desorption study suggested the reusability of adsorbents.
INTRODUCTION
Coloured effluents are major water pollutants produced by various industries including the textile industry in large quantities into nearby water sources that result in adverse effects on aquatic life and the quality of the water and thus can lead to various problems due to water toxicity. These organic substances are mainly responsible for the noxiousness and door of water. Due to their toxic effects, dye effluents are very hazardous to humans because they have both a cancer-causing and venomous perspective and could also have an effect on the direct damage of living aquatic entities (Giridhar 2014; Saura & Galindo 2016). Hence, effluents containing dye residues should be treated before they are discharged into the environment (Lairini et al. 2017). The basic dyes that are also termed cationic dyes including methylene blue and toluidine blue O (TBO) dye are a significant group of organic compounds and possess various scientific as well as industrial applications (Ding et al. 2006; Dow et al. 2009; Ghica & Brett 2009). Toluidine O blue dye is a basic thiazine dye, which belongs to the quinone-imine family and is selectively used in various test reactions as well as in staining acidic tissue components. In terms of wastewater purification, it is very difficult to remove cationic dye from wastewater due to its inefficient adsorption of dye effluents, high rate of redevelopment, and low frequency of flow. This issue has been considered as an attractive opportunity for researchers. In this context, various physical and chemical treatment methodology processes have been used, such as adsorption (Ferrero 2010; Islam et al. 2019; Dai et al. 2021), chemical oxidation (Türgay et al. 2011), electrochemical oxidation (Zhao et al. 2010), membrane separation (Wei et al. 2013), and photocatalytic oxidation (Fernandes et al. 2020). Of these methodologies, adsorption treatment is found to be a more efficient process for dye remediation from aqueous solutions due to its high proficiency, easy usage, and accessibility of several adsorbents. An enormous amount of synthetic as well as natural materials such as activated carbon, synthetic silica, activated aluminum oxide (Mangla et al. 2021), Turkish zeolite (Alpat et al. 2008), magnesium oxide/calcium alginate (Cui et al. 2021), carboxymethyl cellulose-based hydrogel (Ma et al. 2021), and orange peel (Lafi et al. 2015a; Ahmed et al. 2020) have been used commercially. However, such type of adsorbents are very expensive to use and show low efficacy of adsorption, less capability to separate their arduous fabrication involves high consumption of energy. To overcome these demerits, uses of new low-priced, maintainable, and advanced adsorbents are required. So, the adsorbents that possess both properties, i.e. easy separation and good adsorption capacity, are recognized as the most effective and proficient adsorbents. Magnetic separation methodology has exponentially attracted the attention of several researchers as a fast and suitable technology for separating materials. Nowadays, magnetic nanoparticles such as magnetite (Fe3O4) nanoparticles have attracted the eyeballs of scientist considerably due to their special characteristics such as superparamagnetism and large surface area-to-volume ratio. Several researchers have focused on the surface modification of these magnetic nanoparticles with a suitable and appropriate material such as chitosan (Aranaz et al. 2019; Singh et al. 2021), poly-acrylic acid (Liao et al. 2017), aminopropyl triethoxy silane (Rajabi et al. 2015), multiwalled carbon nanotube (Hamidi Malayeri et al. 2012), and gum arabic (Kong et al. 2014). The surface modification helps in enhancing the stability as well as the adsorption capacities of magnetic nanoparticles. Yang et al. have synthesized a nanocomposite of magnetic Fe3O4 for the adsorption of methylene blue from aqueous solution (Yang et al. 2008). Rocher et al. developed alginate beads containing magnetic nanoparticles as well as activated carbon for the removal of organic dyes (Rocher et al. 2008). Adok et al. used surfactant-modified alumina for the removal of crystal violet from aquatic environments (Adak et al. 2005). Amended nanoparticles show better results, and therefore, many organic or inorganic substances have been explored to amend magnetic nanoparticles for the removal of contaminants. Tannic acid (TA) is considered humic-like substance, which can be used for the surface modification of magnetic nanoparticles, which in turn improves the properties and the adsorption capacity for the removal of dye. TA is a natural polyphenolic molecule consisting of sugar esters mainly derived from the breakdown of herbs. It has a lot of phenolic, hydroxyl, and carbonyl groups (Bagtash et al. 2016). Coating of TA on the surface of iron oxide nanoparticles enhances the efficiency of nanoparticles for the remediation of cationic dyes from the aqueous solution.
During the last few years, several research methods attracted the eye ball of scientists for the development of novel as well as cost-effective adsorbents. Therefore, the current study emphasizes the cheaper and easier synthesis of magnetic nanoadsorbent, i.e. TA-modified magnetite nanoparticles (TA@Fe3O4), for the removal of TBO dye from the aqueous solution. The physical and chemical characterizations of the synthesized TA@Fe3O4 nanoparticles were accompanied by analytical methods.
MATERIALS AND METHODS
Materials
All chemicals were of analytical reagent grade and were used without any further purification. Ferrous sulphate heptahydrate (FeSO4.7H2O), ferric chloride hexahydrate (FeCl3.6H2O), TA, and 25% ammonium hydroxide solution were purchased from SRL (India). TBO dye was used as an adsorbate throughout the experiments. Distilled water was used for the preparation of solutions.
Methods
Techniques used
A digital mechanical stirrer was used for the preparation of unmodified and TA-modified magnetite nanoparticles (TA@Fe3O4) at 2,000 rpm. The Fourier infrared spectrum of unmodified and TA-modified magnetite nanoparticles was recorded using an MB-3000 ABB FTIR spectrophotometer. Thermograms of synthesized unmodified and modified magnetic nanoparticles were obtained using a thermogravimetric (TG) analyzer, Perkin Elmer STA-6000 TG analyzer under specific conditions (5–80 °C/min heating rate and 20–1,000 °C temperature range). The point of zero charge was determined by Zeta-sizer Nano 90plus (Brookhaven Instruments Corporation). The adsorption of initial and final concentrations of dye solutions was measured by a T90 PG Instrument Limited UV-Visible spectrophotometer in the range of 190–900 nm. The size and morphology of both unmodified and TA-modified magnetic nanoparticles were investigated by Hitachi SU-8000 field emission scanning electron microscope. The X-ray diffraction patterns for synthesized magnetic nanoparticles were obtained by a diffractometer working with Cu Kα radiations of 1.540 Å wavelength over a 2θ range of 20–80°.
Method of preparation
The co-precipitation method was adopted as the easiest and most appropriate route way for the preparation of both unmodified and modified magnetic nanoparticles. The ferric and ferrous salts in a molar ratio of 2:1 were dissolved in 100 mL of distilled water. The aforementioned solution was stirred and heated up to 90 °C. After 10–20 min, 10 mL of ammonium hydroxide solution was added to the aforementioned solution rapidly, and the mixture was stirred for another 30 min at 90 °C. A black-coloured solution was obtained (Jangra et al. 2021). The solution was decanted off using a magnet, and black-coloured precipitates of unmodified magnetite nanoparticles (Fe3O4) were collected. To modify the surface of these synthesized magnetic nanoparticles, the solution of TA, coating material (0.5 g/20 mL), was added to the dispersed solution of unmodified magnetic nanoparticles (1.05 g Fe3O4 in 40 mL, sonicated for about 15 min) and stirred continuously at about 1,800–2,000 rpm for approximately 2 h (Atacan et al. 2016). The solution was cooled, and the black precipitates of TA@Fe3O4 nanoparticles were washed several times with water and separated using an external magnetic field.
Preparation of TBO adsorbate solution
TBO dye solution was used to prepare the stock solution (50 mg/L) by dissolving precisely amount (50 mg) of dye in deionized (1 L) and was consequently diluted to the desired concentrations. Therefore, a graph between various concentrations of TBO dye and their absorbance was plotted to obtain the calibration curve at maximum wavelength.
Adsorption behaviour study
The TA@Fe3O4 nanoparticles were used as adsorbents, and TBO dye was used as adsorbate. For this, the stock solution of TBO dye (50 mg/L concentration) was prepared and used for further process. The effect of several experimental parameters such as pH (2.0–8.0), temperature (298–323 K), adsorbent quantity (05–30 mg), and time (0–80 min) was investigated (Eleryan et al. 2023). The amount of known concentration of adsorbate (10 mL) was used, and the preferred pH was maintained with 0.1 M HCl or 0.1 NaOH for further studies. The values of absorbance of dye solutions before and after the treatment were measured by using a UV-visible spectrophotometer at a maximum wavelength of 630 nm using a calibration curve. To investigate the rate mechanism and nature of the adsorption process, many kinetics and isotherm models such as pseudo-first order (Langergren & Svenska 1898), pseudo-second order (Ho & McKay 1999), Langmuir (1918), Freundlich (Freundlich 1907), and Temkin (Temkin & Pyzhev 1940) were examined accordingly.
Desorption study
After desorption, the coated nanoparticles were recollected and dried. In addition, the adsorption capacity of recycled nanoparticles was investigated again to examine the reusability.
RESULTS AND DISCUSSION
Characterization studies
Fourier transform infrared spectral studies
X-ray diffraction studies
Field emission electron microscopy study
TG studies
Zeta potential
Adsorption analysis
Many adsorption experiments were performed to analyse the effects of variable experimental factors including pH, temperature, adsorbent amount (TA@Fe3O4), adsorption time, as well as initial concentration of adsorbate on the loading capacity and removal efficiency of adsorbent, TA@Fe3O4.
Effects of solution of pH
Effect of time
Effect of temperature
Effect of adsorbent (TA@Fe3O4) amount and initial concentration of adsorbate on percentage removal efficiency
Kinetic study
Adsorption isotherm analysis
Isotherm models . | |||||||||
---|---|---|---|---|---|---|---|---|---|
Langmuir . | Freundlich . | Temkin . | |||||||
R2 . | qm (mg/g) . | KL (L/g) . | RL . | R2 . | n . | KF (mg/g L/mg) . | R2 . | A (L/g) . | B (J/mol) . |
0.913 | 50.68 | 0.14 | 0.59 | 0.889 | 2.32 | 2.7 | 0.996 | 0.314 | 11.03 |
Isotherm models . | |||||||||
---|---|---|---|---|---|---|---|---|---|
Langmuir . | Freundlich . | Temkin . | |||||||
R2 . | qm (mg/g) . | KL (L/g) . | RL . | R2 . | n . | KF (mg/g L/mg) . | R2 . | A (L/g) . | B (J/mol) . |
0.913 | 50.68 | 0.14 | 0.59 | 0.889 | 2.32 | 2.7 | 0.996 | 0.314 | 11.03 |
Note: qm is maximum adsorption capacity, KL is Langmuir isotherm constant, RL is equilibrium parameter, KF and n are Freundlich isotherm constants, while A and B are Temkin constants.
Adsorption thermodynamic analysis
Temperature (K) . | lnKc . | ΔG (kJ/mol) . | ΔH (kJ/mol K) . | ΔS (J/mol K) . |
---|---|---|---|---|
298 | 2.047 | −5.072 | 16.45 | 72.36 |
303 | 2.152 | −5.421 | ||
313 | 2.467 | −6.420 | ||
323 | 2.528 | −6.791 |
Temperature (K) . | lnKc . | ΔG (kJ/mol) . | ΔH (kJ/mol K) . | ΔS (J/mol K) . |
---|---|---|---|---|
298 | 2.047 | −5.072 | 16.45 | 72.36 |
303 | 2.152 | −5.421 | ||
313 | 2.467 | −6.420 | ||
323 | 2.528 | −6.791 |
Note: ΔG is change in Gibbs free energy, ΔH is enthalpy changes, ΔS is entropy changes, and KC is distribution coefficient.
DESORPTION RESULTS
A desorption study was executed to inspect the adsorbent regeneration and recovery. The regeneration capacity of a biosorbent validates its applicability. The reuse of the adsorbent for TBO occurred in two cycles, using ethanol as a desorption solvent. Eighty-seven percent of desorption efficiency was obtained for the adsorbent. In addition, no significant change was observed in the adsorption capacity of recollected TA@Fe3O4 nanoparticles, which revealed that these modified magnetite nanoparticles can be reused for the exclusion of TBO dye from the aqueous solution.
COMPARISON OF PERCENTAGE REMOVAL AND MAXIMUM ADSORPTION CAPACITY OF TBO BY TA@Fe3O4 NANOPARTICLES WITH OTHER REPORTED ADSORBENTS
The percentage removal and maximum adsorption capacity of TBO by TA-functionalized magnetite nanoparticles were compared with already reported adsorbents (Table 3). The comparative study revealed that TA-functionalized magnetite nanoparticles are the most potential candidates among them for the removal of TBO from the aqueous solution.
Sr. No. . | Adsorbent used . | pH . | Isotherm . | Kinetic order . | % Removal of TBO . | Adsorption capacity qm (mg/g) . | Ref . |
---|---|---|---|---|---|---|---|
1. | Magnesium oxide | 8 | – | Pseudo-first order | ∼90 | – | Mohammad Salim & Mohammad Salih (2015) |
2. | Turkish zeolite | 11 | Langmuir and Freundlich | Pseudo-first order | – | 33.03 | Alpat et al. (2008) |
3. | Fly ash | – | Freundlich | Pseudo-second order | – | 6 | Talman & Atun (2006) |
4. | Starch sulphate | 5 | Toth | Pseudo-first order | – | 47.13 | Guo et al. (2011) |
5. | Gypsum | 6.5 | Langmuir | Pseudo-second order | – | 28 | Rauf et al. (2009) |
6. | Multiwalled carbon nanotubes @NiFe2O4 | – | Langmuir | Pseudo-first order | 65.8 | 25 | Bahgat et al. (2014) |
7. | Pulp fibre | 6.5 | Langmuir | Pseudo-second order | – | 25 | van de Ven et al. (2007) |
8. | Orange peel | 6 | Langmuir | Pseudo-second order | 72.9 | – | Lafi et al. (2015b) |
9. | TA@Fe3O4 nanoparticles | 8 | Temkin | Pseudo-second order | 97.23 | 40.28 | The present study |
Sr. No. . | Adsorbent used . | pH . | Isotherm . | Kinetic order . | % Removal of TBO . | Adsorption capacity qm (mg/g) . | Ref . |
---|---|---|---|---|---|---|---|
1. | Magnesium oxide | 8 | – | Pseudo-first order | ∼90 | – | Mohammad Salim & Mohammad Salih (2015) |
2. | Turkish zeolite | 11 | Langmuir and Freundlich | Pseudo-first order | – | 33.03 | Alpat et al. (2008) |
3. | Fly ash | – | Freundlich | Pseudo-second order | – | 6 | Talman & Atun (2006) |
4. | Starch sulphate | 5 | Toth | Pseudo-first order | – | 47.13 | Guo et al. (2011) |
5. | Gypsum | 6.5 | Langmuir | Pseudo-second order | – | 28 | Rauf et al. (2009) |
6. | Multiwalled carbon nanotubes @NiFe2O4 | – | Langmuir | Pseudo-first order | 65.8 | 25 | Bahgat et al. (2014) |
7. | Pulp fibre | 6.5 | Langmuir | Pseudo-second order | – | 25 | van de Ven et al. (2007) |
8. | Orange peel | 6 | Langmuir | Pseudo-second order | 72.9 | – | Lafi et al. (2015b) |
9. | TA@Fe3O4 nanoparticles | 8 | Temkin | Pseudo-second order | 97.23 | 40.28 | The present study |
PROPOSED ADSORPTION MECHANISM OF ADSORPTION OF TBO DYE ON THE SURFACE OF TA@Fe3O4 NANOPARTICLES
The adsorption of TBO dye from an aqueous solution by TA-modified magnetite nanoparticles may be explained well on the basis of different functional groups present on the surface of these nanoadsorbents. TBO may be adsorbed onto the surface of TA-modified magnetite nanoparticles via different kinds of interactions like H-bonding, π-π interactions, and electrostatic interactions (Keshvardoostchokami et al. 2018). The adsorption of imidacloprid on the surface of TA-modified magnetite nanoparticles was found maximum at pH 8.0 as at this pH, hydrogen bonding and electrostatic attraction between them is maximum. From the isotherm studies, it was found that the adsorption of the adsorbate over the surface of the adsorbent was homogenous and multilayer adsorption.
CONCLUSION
The present study illustrated the synthesis and characterization of unmodified and TA-modified magnetite nanoparticles using several techniques such as Fourier transform infrared (FTIR) spectral study, X-ray diffraction analysis, field emission scanning electron microscopy, and TG study. In addition, numerous experiments were performed to evaluate the adsorption capacity of these nanoparticles for the degradation of TBO dye. Characterization studies suggested the successful coating of TA onto the surface of bare Fe3O4 nanoparticles, and FESEM images confirmed the size, 11 and 35 nm of synthesized bare Fe3O4 and TA@Fe3O4 nanoparticles, respectively. The isotherm and kinetic study depicted that the adsorption process followed the Temkin model of isotherm and pseudo-second-order kinetic with good correlation coefficients, respectively. The thermodynamic study suggested the endothermic and spontaneous nature of the adsorption process. The TA@Fe3O4 nanoparticles show better adsorption properties for the elimination of TBO dye. Thus, the overall study revealed that the TA@Fe3O4 nanoparticles can be employed as an efficient as well as eco-friendly adsorbent for the adsorption of dyes.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.