Removal of chromium(VI) from wastewater is essential as it is toxic. Thus, removal of chromium(VI) was performed using coffee polyphenol-formaldehyde/acetaldehyde resins as adsorbents. Adsorbent resins were prepared by condensation of decaffeinated coffee powder with formaldehyde/acetaldehyde and used for the removal of Cr(VI) ions from aqueous solutions. A simple and sensitive solid phase extraction procedure was applied for the determination of chromium at trace levels by spectroscopic method using 1,5-diphenylcarbazide reagent. The adsorption of Cr(VI) on the coffee polyphenol-formaldehyde/acetaldehyde resins was monitored by FTIR and EDX analysis. The metal adsorption parameters such as contact time, pH, Cr(VI) ion concentration, and adsorbent dose were investigated. For Cr(VI), the maximum adsorption capacity of coffee polyphenol-formaldehyde resins was 98% at pH 2. The experimental results showed that Cr(VI) bound strongly with coffee polyphenol-formaldehyde/acetaldehyde resins and utilization of resins could be improved greatly by reuse.
Metal ions such as Cd, Cr, Co, Cu, Zn, Pd, Hg, Ni, Ag, and Sr and metalloids such as Se, As, and Sb are toxic beyond trace levels. Most of these trace elements are transition metals with variable oxidation states and coordination numbers. Strong exposure to Cr(VI) causes cancer in the digestive tract and lungs. It may also cause gastric pain, nausea, vomiting, severe diarrhea, and hemorrhage [
Treatment of wastewater generated by industrial processes today is of prime concern. Various technologies have been developed over recent years and are available for the removal of toxic metal such as chromium from wastewater [
The two common oxidation states of chromium observed in natural water are Cr(III) and Cr(VI). Cr(III) is not a significant groundwater contaminant, whereas Cr(VI) is approximately 100 times more toxic than Cr(III) [
Conventional methods used for removing Cr(VI) ions from industrial wastewater include reduction followed by chemical precipitation, adsorption on activated carbon, solvent extraction, freeze separation, reverse osmosis, ion exchange, and electrolytic methods. These methods have found limited applications because they often involve high capital and operational costs. Adsorption is an effective and versatile method for removing chromium which solves the problem of sludge disposal and renders the system more economically viable, especially if low-cost adsorbents are used [
A wide range of commercial sorbents including chelating reagents and activated carbon are available for adsorption, but they are relatively expensive. In recent years, low-cost natural materials have been proposed as potential biosorbents. These include moss peat, algae, leaf mould, sea weeds, coconut husk, sago waste, peanut hull, hazelnut, bagasse, rice hull, sugar beet pulp, plant biomass, bituminous coal, and coffee powder [
High proportions of aromatic compounds present in coffee beans are phenolics, presumably derived from chlorogenic acid and melanoidins [
In the present study, adsorbent resins were prepared from condensation of coffee polyphenol and formaldehyde/acetaldehyde for Cr(VI) removal. The effect of various parameters on adsorption of Cr(VI) such as pH, contact time, Cr(VI) concentration, adsorbent dose, and desorption were investigated.
Roasted coffee beans were procured from a local source, crushed in a grinder, and sieved through 355
The composition of reactants is illustrated in Table
Composition of coffee polyphenol-formaldehyde (CFA) resins.
Resin code |
Coffee powder (g) | Formaldehyde (mL) | Ammonia (mL) |
---|---|---|---|
CFA 01 | 4 | 5 | 10 |
CFA 02 | 4 | 10 | 10 |
CFA 03 | 4 | 15 | 10 |
CFA 04 | 4 | 20 | 10 |
CFA 05 | 4 | 25 | 10 |
The composition of reactants is presented in Table
Composition of coffee polyphenol-acetaldehyde (CAA) resins.
Resin code |
Coffee powder (g) | Acetaldehyde (mL) | Ammonia (mL) |
---|---|---|---|
CAA 01 | 4 | 5 | 10 |
CAA 02 | 4 | 10 | 10 |
CAA 03 | 4 | 15 | 10 |
CAA 04 | 4 | 20 | 10 |
CAA 05 | 4 | 25 | 10 |
IR spectra of resins were recorded on FTIR (PerkinElmer) spectrophotometer. The samples were prepared after drying the resins at 80°C for 4 h. Potassium bromide (spectrometry grade) was dried at 150°C for 4 h and pellets were prepared by mixing 1 mg of sample with 100 mg of potassium bromide. IR spectra were recorded from 4000 to 450 cm−1 (8 scans) on potassium bromide pellets. Scanning electron microscope (SEM) and EDX measurements were conducted using BRUKER AXS, X-flash detector 5010 at an acceleration voltage of 0–20 keV. Particle size distribution was determined using Accusizer 780 Optical Particle Sizer (PSS-Nicomp, Particle Sizing System, Santa Barbara, CA, USA).
Batch method was used to investigate the adsorption study of Cr(VI) onto CFA and CAA resins. To study the effect of pH on Cr(VI) sorption, 100 mg of resin was immersed into 10 mL (17.6 ppm) Cr(VI) stock solution at different pH. The mixture was stirred at room temperature for 24 h. The concentration of Cr(VI) ions in the effluent was determined spectrophotometrically by the development of a pink color with a complexing agent 1,5-diphenyl carbazide in acidic solution. Absorbance of the pink-colored solution was measured at
Aromatic compounds found in coffee beans are mainly phenolic compounds. Robusta coffee has slight higher phenolic content than Arabica [
Chlorogenic acid and its roasted form.
Comparison plot of adsorption of chromium with blank coffee power, coffee-polyphenol-formaldehyde, and coffee-polyphenol-acetaldehyde resins is shown in Figure
Comparison of coffee polyphenol based resins on chromium adsorption. CFA: coffee polyphenol-formaldehyde resins; CAA: coffee polyphenol-acetaldehyde resins; BCP: blank coffee powder.
In this case, formaldehyde acts as a cross-linker and forms coffee polyphenol-formaldehyde/acetaldehyde resins. Coffee contains polyphenols which are linked together by forming –CH2– bridges. The resins prepared by condensation polymerization of coffee polyphenols with formaldehyde/acetaldehyde are thus insoluble in acidic as well as basic media and increasing reusability and simultaneously turn over number.
Mainly two cross-linkers such as formaldehyde and acetaldehyde were studied to see the effect on chromium metal adsorption. It was observed that formaldehyde (pKa, 13.3) showed higher chromium adsorption than acetaldehyde (13.57) due to more acidic nature and steric hindrance.
FTIR spectroscopy was used to identify the functional groups present in roasted coffee bean powder. Roasted coffee bean powder has a variety of functional groups such as hydroxyl, carboxyl, carbonyl, amino and imino, which are important sites for metal sorption. The FTIR spectra of blank decaffeinated coffee powder (A), coffee polyphenol-formaldehyde resins (B), and Cr(VI) adsorbed coffee polyphenol-formaldehyde resins powder (C), respectively, are depicted in Figure
FTIR spectra of decaffeinated coffee powder (A), coffee polyphenol-formaldehyde resins (virgin) (B), and coffee polyphenol-formaldehyde resins with Cr(VI) (C).
The pH of aqueous solution is a significant parameter for the removal of metal ions by adsorption [
Effect of pH on Cr(VI) adsorption by CFA resins.
Effect of pH on Cr(VI) adsorption by CAA resins.
The experimental results reveal that Cr(VI) removal efficiency increases with the decrease in pH and reached up to 99.7% at pH 2. Cr(VI) exists in aqueous phase in different anionic forms such as chromate (
Speciation of Cr(VI).
Time of contact has a significant influence on the adsorption of Cr(VI). The adsorption experiments were carried out with respect to contact time ranging from 10 to 150 min and the results are presented in Figure
Effect of contact time on Cr(VI) adsorption.
The mechanism of solute transfer to the solid includes diffusion through the fluid film around the adsorbent particle and pores to the internal adsorption sites. Initially, the concentration gradient between the film and the solid surface is high, and hence the transfer of solute onto the solid surface is faster. Thus, it takes a smaller amount of time to attain 81% percent removal of Cr(VI). As the contact time increases, intraparticle diffusion becomes predominant. Hence, after 81% adsorption, solute takes more time in the transfer of Cr(VI) from solid surface to internal adsorption sites through the pores. Therefore, the optimum time for adsorption of Cr(VI) on coffee polyphenol-formaldehyde/acetaldehyde resins is 150 min for all batch studies.
The morphological analysis of coffee resins was performed by SEM as shown in Figure
Particle size analysis of coffee resins.
Sr. no. | Resin code | |||||
---|---|---|---|---|---|---|
1 | CFA | 01 | 02 | 03 | 04 | 05 |
Particle size ( |
— | 28.89 | 18.79 | 28.43 | 20.85 | |
| ||||||
2 | CAA | 01 | 02 | 03 | 04 | 05 |
Particle size ( |
16.71 | 26.23 | 20.64 | 22.70 | 20.77 |
SEM photographs of coffee resins.
EDX spectra of coffee resins.
Particle size distribution of coffee resins.
Adsorption of Cr(VI) is significantly influenced by the concentration of Cr(VI) in aqueous solutions. The adsorption of Cr(VI) was examined with respect to the amount of Cr(VI) in solution. The Cr(VI) concentration varied from 5 to 20 ppm. The effect of initial concentration on percentage removal of Cr(VI) is depicted in Figure
Effect of Cr(VI) concentration on adsorption.
The various doses consisting of the adsorbents (100 mg to 300 mg) were mixed with metal ion solutions and kept at room temperature for 24 h. The adsorption capacities for different doses were determined by keeping all other factors constant, for example, pH and temperature. The effect of adsorbent dose on the adsorption of Cr(VI) is presented in Figure
Effect of adsorbent dose on Cr(VI) adsorption.
Desorption studies help to elucidate the nature of adsorption and recycling of the adsorbent. Adsorption of any solute on adsorbent takes place by physical bonding, ion-exchange, or a combination of both. If the adsorbed Cr(VI) is desorbed by water at neutral pH, then the bonding of Cr(VI) with the adsorbent is physical. If hydrochloric acid or alkaline solution desorbed the Cr(VI), then the adsorption takes place by ion exchange. If organic acids, like acetic acid, desorbed the Cr(VI), then the Cr(VI) is held by chemisorption [
The reusability of the resin is important to reduce the process cost. Desorption was performed by using 1 M hydrochloric acid. The metal desorbed resin was reused for three times and it shows good results. Figure
Adsorption-desorption cycle of CFA 01 resin.
Adsorption isotherms of Cr(VI) were investigated with respect to biomaterials using an electrolyte solution at the optimum pH 2. The adsorption data were fitted by least square method to linearly transformed Freundlich and Langmuir adsorption isotherms.
The Freundlich adsorption isotherm was applied for the adsorption of Cr(VI) onto coffee polyphenol-formaldehyde resins. The linear Freundlich equation is mentioned below:
Freundlich isotherm for adsorption of Cr(VI).
The Langmuir adsorption was applied to the present study to estimate the adsorption capacity of coffee polyphenol-formaldehyde resins. The linear form of the Langmuir adsorption isotherm is presented below:
The results obtained from the adsorption experiments conducted at room temperature are fitted in Langmuir equation; linear plot was obtained for
Langmuir isotherm for adsorption of Cr(VI).
These results indicated that adsorption of Cr(VI) followed both adsorption isotherm models. Freundlich isotherm model is fitted better than Langmuir, because the correlation between calculated and experimental (found) values as well as regression factors is in good agreement with Freundlich isotherm rather than Langmuir.
Langmuir constants were determined and are presented in Table
|
|
|
|
---|---|---|---|
16.551 | 19.342 | 0.1007 | 0.9485 |
Freundlich constants were determined and are depicted in Table
|
|
|
|
---|---|---|---|
0.3517 | 2.727 | 2.0214 | 0.9897 |
To evaluate sorption dynamics, it requires consideration of two important physicochemical parameters such as kinetics and equilibrium of adsorption. Kinetics describe the solute uptake rate which governs the contact time. The study of equilibrium is determining the distribution of solute between solid-liquid phases and determining the feasibility and capacity of the sorbent for adsorption. Several kinetic models, currently in use to explain the mechanism of adsorption progress, are most simple and widely used is pseudo-first order equation of Lagergren [
Pseudo-first order reaction.
On the other hand, equilibrium capacity may be expressed by pseudo-second order equation as follows:
Pseudo-second order reaction.
The adsorption capacity of coffee polyphenol resins compared to other materials is reported in the literature [
Comparison of adsorption of Cr(VI) with naturally occurring adsorbents.
Sr. no. | Biosorbent |
Cr(VI) (mg/g) | Reference no. |
---|---|---|---|
1 | Rice husk carbon | 45.6 | [ |
2 | Iron(III) hydroxide | 0.47 | [ |
3 | Waste tea | 1.63 | [ |
4 | Irish sphagnum moss peat | 119 | [ |
5 | Saw dust | 10.1, 16.05, 4.44 | [ |
6 | Blast furnace slag | 7.5 | [ |
7 | Activated red mud | 1.6 | [ |
8 | Waste tyre | 58.48 | [ |
9 | Olive cake | 33.44 | [ |
10 | Distillery sludge | 5.7 | [ |
11 | Coffee husk | 44.95 | [ |
12 | CFA and CAA resins | 175.44, 143.32 | This study |
Most of the low-cost adsorbents have the limitations such as low adsorption capacity and also generate more solid waste causing disposal problems. Hence, there is a need to explore low-cost adsorbents with high adsorption capacity. In our study, we have prepared particulate systems where average particle size ranges are 20.85 to 28.89
The use of bioadsorbent prepared from coffee powder, capable of adsorption of Cr(VI) from aqueous stream, is cost effective and efficient. The maximum adsorption of Cr(VI) took place at pH 2. The active form of Cr(VI) adsorbed onto coffee polyphenol-formaldehyde/acetaldehyde resins at lower pH is found to be
The authors would like to thank the Department of Science and Technology, New Delhi, India, for their generous support in this research under the Program no. SR/S3/CE/0049/2010.