Use of Spent Tea Wastes-Chitosan Capsules for the Removal of Divalent Copper Ions
Yewoon Choi, Paul Isaac, Saidakbar Irkakhujaev, Md. Emran Masud, Abel E. Navarro1*
1Science Department, Borough of Manhattan Community College, City University of New York, NY, USA
The growth of metallurgy and metal-mechanic industries demands an intense extraction of metals. This causes the discharge of
metal-containing solution to lakes, rivers and oceans. This study proposes the use of hydrogel beads of chitosan and spent tea waste from peppermint teabags in a hybrid composite for the elimination of copper ions from solutions. Chitosan and its hybrid were also cross-linked with glutaraldehyde to improve the chemical and mechanical resistance. Batch experiments are room temperature were carried out to determine the optimum conditions to maximize the removal of copper. Results indicate that native chitosan-encapsulated peppermint tea waste show a higher adsorption when compared to the native chitosan and to the cross-linked samples. Experimental data indicates that maximum adsorption is achieved at pH 6, using a mass of 150mg of dry adsorbent, in the absent of surfactants. Salinity had a positive effect on the adsorption, mostly due to osmosis changes. Finally,adsorption was studied by EDAX analyses that confirmed the presence of copper on the adsorbent’s surface; and SEM demonstrated that these materials have a very homogeneous surface with small valleys, indicating their high porosity. These proposed adsorbents open up new alternatives for the elimination of heavy metals, using low-cost and biodegradable materials.
Keywords: spent tea waste; chitosan; adsorption; copper (II) ions; cross-linkage; glutaraldehyde
As industrialization is taking root in third world countries, heavy metal contamination is affecting more and more people every day. Levels of heavy metals in the water run-offs from the factories are increasing [1,2]. Because contaminated water affects so many people in a devastating way, it is crucial to find effective solutions to remove harmful pollutants from water. Research shows that heavy metals have detrimental effects such as kidney damage and increased risk of certain cancers including skin cancer . Some research even found ties between heavy metal consumption and Parkinson’s disease . One heavy metal that is frequently found in wastewaters is copper. Copper is crucial for the function of the human body as it plays a role in the formation of hemoglobin, absorption of iron in digestion, and other processes. However, pollution with copper causes Wilson disease, an illness that affects the liver and the brain, causing organ damage and cell death .
Many organizations dedicate resources to developing various ways to improve water quality, such as installing wells in developing countries. However, in many rural areas, these developments are luxuries because of the financial and practical challenges. In addition, disadvantages to such approach hinder their effectiveness. For example, although wells supply clean water, the well water itself can be contaminated by improper waste disposal.
Recent research has shown biosorption as a “green alternative” for the decontamination of organic and metal pollutants. Biosorption is defined as the adsorption of pollutants onto non-living biomasses through physico-chemical interactions using the chemical groups that are present on their surfaces. Chemical groups such as carboxyl, amine, and hydroxyl groups have proven to be crucial in the adsorption of pollutants. The elimination of lead, cadmium and other heavy metals from water has been done in the past with algae [5,6], fungus [7,8], and other adsorbents.
Because of its adsorbing properties, chitosan (CH), a derivative of chitin and a polymer found in seashells, was used as the main adsorbent in this experiment . The seafood industry generates large amount of seashells that end up in the garbage. he
management of this waste becomes a municipal concern and an extra expense for their industries. Chemically speaking, chitosan is a polymer of glucosamine (Figure 1), with many amine groups attached to glucose units that act as adsorption sites. Amines are well-known nucleophiles in organic reactions and one of the most powerful Lewis bases that are able to attract positively charge species and electron-deficient groups .
Figure 1. Chemical structure of chitosan, showing the amino groups.
Although chitosan has the potential of adsorbing different types of pollutants, it is highly soluble in acidic conditions. Most industrial runoffs are acidic and may dissolve chitosan. This property renders an adsorbent much less valuable, because adsorbents should be thermally, chemically and mechanically resistant. This limitation can be overcome by a simple chemical modification called cross-linking. In this reaction, imine bonds are formed using the amino groups of chitosan and glutaraldehyde (cross-linker). Previous studies showed that this modification of the chitosan greatly increases the resistance to acidic conditions [11,12]. The reaction scheme is displayed in Figure 2, where glutaraldehyde undergoes a condensation reaction with amines (i.e. from chitosan) to produce Shift bases .
Figure 2. Chemical cross-linking of chitosan chains with glutaraldehyde. Even though there are various ways to clean water, chitosan is inexpensive, easily accessible, and biodegradable; thus, it is a promising candidate .
On the other hand, spent tea wastes have also been identified as great candidates for the removal of pollutants. These materials are mainly composed of cellulose and lignin  and are byproducts of the preparation of bottled iced tea from industries like Snapple and Arizona. Therefore, it would be beneficial to recycle these wastes and use them in a decontaminating technique. Moreover, in a recent study, Zahir et al.  reported the good adsorption capacity of spent green tea, chamomile and peppermint tealeaf wastes for the removal of hair dyes. For this study, the selection of PM as the encapsulated tealeaf was decided based on a preliminary experiment (data not shown). The best adsorbing tealeaf waste was chosen amongst peppermint, chamomile, and green tea using copper, cobalt and zinc solutions as pollutants. Since PM had the highest adsorption capacity with copper metal, it was used for the preparation of chitosan hybrid capsules.
The motivation of this project was the development of a new material that combines the gel and adsorption properties of native and cross-linked chitosan and the structural rigidity and adsorption properties of spent peppermint tea leaf waste (PM) for their use in the removal of pollutants. All possible adsorbent combinations were explored to lead to higher adsorption of heavy metals [14,16,17]: native chitosan (CH), cross-linked chitosan (CCH), spent peppermint waste in native chitosan bead hybrid (CH-PM) and spent peppermint waste in crosslinked chitosan beads (CCH-PM). The encapsulating properties of chitosan and its adsorptive properties were combined with the low-cost of PM for the decontamination of copper as model heavy metal.
Although extensive research has been done on chitosan and its pollutant adsorbing characteristics, only a few studies exist on the adsorptive effect of hydrogel as encapsulating agents . Thus, this study investigates whether the removal of the copper metal ions can be improved through the collaborative effect of tea leaf wastes and chitosan.
Reagents and Solutions
All solutions of copper metal were made from a stock solution of Cu (II) ions by dissolving CuSO4.5H2O (Sigma Aldrich, USA) in 1 L of deionized water. The stock solution was refrigerated when not in use. The solutions were prepared in desired concentrations ranging from 40 ppm to 250 ppm by dilution with deionized water. The pH levels of the solution were adjusted with a daily calibrated pH meter (Accumet AB15, Fisher Scientific, USA) by adding aliquots of NaOH and HNO3 solutions.
Preparation of the Adsorbents
To study the combined adsorptive properties of chitosan and tea leaves; chitosan was made into beads and, the tea leaf waste were encapsulated. Chitosan powder (reagent grade, Sigma Aldrich) was made into a thick gel using an optimum ratio of water and acetic acid (4% v/v); 24 g of chitosan was mixed with 24 mL of acetic acid and 576 mL of deionized water. This procedure was taken from previous studies (Guibal et al., 1998). The gel was hand-stirred with a glass rod until all the chitosan particles were totally dissolved. Then, the gel was added drop by drop into a 2.5 M solution of NaOH using a peristaltic pump to from CH beads. This process was done in a plastic bucket using magnetic stirring. Later, the beads were extensively rinsed with deionized water. Finally, the beads were stored in glass bottles with deionized water, to avoid dryness, in the refrigerator until use.
For the preparation of CH-PM, peppermint teabags (brand Celestial) were purchased from a local market and boiled in distilled water and deionized water to remove color, taste and smell. Then, the teabags were cut-open and stored in plastic containers. The encapsulation of PM in the chitosan beads was carried out by suspending 8 g of the spent tea wastes in the chitosan solution prior contact with the NaOH. The formation of the CH-PM then followed the same treatment as the one used for the preparation of CH beads.
Some of both the pure chitosan beads were also chemically modified by covalent cross-linking to increase the mechanical strength of the beads. This modification was done by mixing the chitosan gel beads with a 2.5% v/v solution of glutaraldehyde (cross-linker) in a 12.5 cross-linker/bead mass ratio. This mixture was stirred overnight at room temperature. After cross-linkage, the cross-linked beads were also rinsed with deionized water to eliminate any side-products or impurities from the reaction. Characterization of the obtained product was is reported elsewhere .
Figure 3. Image of the four adsorbents (from left to right: CCH, CHPPM, CH, CCH-PPM)
Therefore, four different types of beads were prepared for this experiment as shown in Figure 3: native chitosan beads (CH), native chitosan beads with peppermint tealeaves (CH-PM), cross-linked chitosan beads (CCH), and cross-linked chitosan with peppermint tealeaves (CCH-PM).
Adsorption experiments of pH, mass, concentrations, salinity, and crowding agent were performed by duplicates and compared to a control sample that was identical to the adsorption sample, but without adsorbent. Since all of the chitosan beads were stored in water, a calibration curve to determine the wetdry conversion was elaborated. A given number of wet beads were weighed out and then put in an oven for at least 12 h at a temperature not higher than 60°C. In this process, the water evaporated and the new dry masses were recorded. Then, a calibration curve, wet versus dry masses, was plotted to obtain a conversion factor. These conversion factors can be observed on the labels of each adsorbent in Figure 3.
Experiments were carried out in plastic tubes and placed in an incubator under orbital agitation (New Brunswick Scientific model C24) at 200 rpm for at least 24 hours (preliminary results indicated that less than 24 h are needed to achieve total adsorption). Each parameter was studied at the time, and the optimized parameters were always taken to the next experiment to accomplish a progressive optimization of the process. Upon equilibrium, the solution was separated from the beads and the remaining copper concentrations were indirectly measured by a microplate reader (Synergy4, Biotek) and read at a wavelength of 600 nm . This methodology consists of the chemical reaction of trace copper (not colored) with an organic dye, zincon (red wine color) that turns into a blue complex. This method is able to detect copper concentrations as low as 0.5 mg/L .
Characterization of the adsorbents and adsorption mechanism Surface texture and morphological properties of the adsorbents were studied by scanning electron microscopy (SEM) using a Tabletop microscope (TM3000, HITACHI) with low vacuum. No gold coating was needed for any of the samples. The presence of copper on the surface of the adsorbents was confirmed by X-ray energy dispersion analysis (EDAX) that is coupled with the SEM. For EDAX analyses, samples before and after adsorption were studied.
The amount of copper metal ions adsorbed onto the adsorbents was expressed as Adsorption Capacity (q, mg/g) and calculated as shown in equation (1):
where m is the dry mass of the adsorbent in grams, V is the volume of the solution in L, and Ci and Ceq are the average of duplicate samples of the initial and at equilibrium concentrations of copper ions in mg/L. A statistical error of less than 5% was achieved for each of the experiments.
A different way to express the adsorptive properties of a given adsorbent is Adsorption Percentage (%ADS) where the initial and final adsorbent concentrations are compared and expressed as percentage as shown in equation (2). All graphs and statistical analysis were done using the software Origin v8.0.
%ADS= (ci-ceq)*100 (2)
Results and discussion
Effect of Solution Initial pH
The initial pH of the solution is one of the most important features of biosorption because the acidity levels of the solution can alter the chemical groups attached to the surface of the substance. In heavy metal adsorption, not only can the pH affect the ionization of functional groups on the adsorbent itself, but also it can decrease the sorption availability of the heavy metals by the formation of aquo- and hydroxo-complexes [2,20].
Figure 4 depicts the pH effect on the adsorption ability of the new adsorbents in a 100 ppm copper solution. Although the data produced 4 varying curves, the optimum pH level was 6 in all cases. The adsorption capacity for any type of bead did not surpass 50% at pH 3; but at pH 6, the adsorption dramatically increased as shown in the curves of the graphs in Figure 4. In acidic conditions, the excess amount of protons hinders the chitosan’s binding to the copper ions because the amine groups bond with the hydrogen protons instead. However, pH levels beyond 7 were not tested in these experiments because the copper ions began reacting with the hydroxide ions (turning into a solid), skewing the data. Since pH 6 was the optimum pH level for the adsorbents, all adsorption experiments occurred at a pH level of 6.
Figure 4. Initial pH effect on adsorption of 100ppm copper solution at room temperature
The results also show that CH-PM beads have a better affinity towards copper. In summary, the adsorption efficiency can be described as: CH-PM>CH>CCH-PM>CCH. Cross-linked adsorbents display a lessened adsorption as a consequence of the chemical modification. The cross-linkage of chitosan is achieved by covalent bonding between chitosan chains and consumes active sites of chitosan that are commonly used for the adsorption of pollutants. Although a more resistant and harder adsorbent is obtained, nevertheless, the adsorption is decreased. These results highlight the way in which physical resistance is gained at the expense of less adsorption. However, considerable adsorption is still observed. Experimental data indicate the applicability of both types of adsorbents; native chitosan (CH and CH-PM) will show high recovery at medium acidic and neutral conditions, whereas cross-linked samples will be more suitable under harsh solution conditions. In both cases, copper is efficiently eliminated.
Another significant result is that CH-PM is a better adsorbent than CH, just as CCH-PM is a batter adsorbent than CCH. In both cases, the presence of PM enhanced the adsorption capacity, suggesting that CH and PM do not compete for copper. In fact, the two different substances could be following different adsorption mechanisms so that both contribute to elimination of copper from the solutions. The relationship between the CH and PM, similar to CCH and PM, is a synergistic adsorption, in which all the participating materials contribute to the overall removal by non-competitive mechanisms.
Figure 5. Mass effect on the adsorption of 100 ppm copper solution at room temperature at pH 6
Effect of Mass of Adsorbent
A mass effect experiment was also performed in order to determine the optimum mass per 50 mL of copper solution. The concentration of the copper solution was 100 ppm and the pH level was 6. A mass of 150 mg was chosen as optimum because after that amount the rate of adsorption is steady as indicated by the curve leveling off (Figure 5).
However, before 150 mg, %ADS is not high enough to call any of them the optimum mass for maximum absorption. This can be explained by the slow saturation of active sites. The number of active sites in a given mass is smaller than the pollutant present and adsorption does not reach its maximum value. The adsorption stabilizes at higher mass, as there are more adsorption sites, available for the copper. Larger masses do not cause substantial changes in the adsorption, since the reverse case occurs; there are more available active sites than pollutants in the solution. Thus, for the rest of the experiment, 150mg of adsorbent were added to every 50mL of copper solution.
Figure 6. Metal concentration effect on copper adsorption with concentrations ranging from 40 to 250 ppm
Effect of Initial Metal Concentration
After the optimal pH and mass of adsorbent were determined, the adsorption capacity of the four beads was studied. The experimental data that was obtained in this experiment were the adsorption capacities of the four different types of beads: chitosan, chitosan with peppermint tealeaf waste, cross-linked chitosan, and cross-linked chitosan with peppermint tea leaf waste.
Figure 6 shows the graph of the adsorption capacity, which is the amount of copper adsorbed per gram of adsorbent, of the four beads. As shown in the graph, the addition of PM improved the adsorbing effect of the chitosan and the cross-linked chitosan beads, confirming that the combination of chitosan and PM had a positive effect.
In addition, there was a big difference in the adsorption capacity of the natural chitosan beads and the cross-linked chitosan beads. Again, this discrepancy can be explained by the loss of active sites due to cross-linkage. However, some adsorption is still observed for CCH and CCH-PM. These results indicate that some adsorptive ability of the chitosan had to be sacrificed in order to increase the physical durability of the beads. A variety of isotherm models have been developed, some of which have a theoretical basis and some of empirical nature [2,20]. The adsorption of copper ions onto the new adsorbents was analyzed by the conventional models of Langmuir and Freundlich. Equilibrium data were fitted to these theories, and important parameters were obtained. Linear regression was used to fit all the data points. Correlation coefficient and p-values were determined as statistical significance testing.
The Langmuir theory assumes uniform adsorption energy on the surface of the adsorbent, where the migration of the pollutant among neighboring active sites is restricted [2,21]. The form of the Langmuir isotherm is calculated with Equation 3:
where qmax (mg/g) and b (L/mg) are the Langmuir constants related to the maximum adsorption capacity and to the adsorption
energy, respectively. The qmax constant represents the total number of available adsorption sites for one adsorbent and is commonly used to compare adsorbents based on their ability to remove pollutants. The b constant is also important because it allows us to compare the adsorption efficiency between two different adsorbents under the same experimental conditions. A higher b constant means a higher adsorbent/pollutant affinity.
The data were also analyzed by the model of Freundlich that is derived assuming a logarithmic decrease in the enthalpy of adsorption with the increase in the fraction of occupied sites and based on sorption on heterogeneous surfaces [20,-22]. Freundlich’s expression is given by equation 4:
q= k*ceq1\n (4)
where k and n are the Freundlich constant, related to the adsorption capacity and the adsorption intensity, respectively. If n=1, then the partition between the two phases are independent of the concentration. If n>1, a normal adsorption is suggested, whereas n<1 suggests cooperative adsorption [14,18].
Table 1. Langmuir and Freundlich Isotherm Constants for the adsorption of Copper ions by the adsorbents.
Table 1 summarizes the adsorption isotherms for the three adsorbents. According to the results, the maximum adsorption capacities follow the trend: CH>CHPM>CCHPM>CCH. Surprisingly, the modeling indicates that CH is a better adsorbent than CHPM. It is important to highlight that isotherm models consider the adsorption at equilibrium conditions and when the plateau in the concentration curve is achieved. In other words, the observed qmax consider high copper concentrations, at which CH seems to be a better adsorbent. The elimination of heavy metals as trace pollutants in water is actually a concern due to the small amounts in wastewaters and therefore it is more important to evaluate the adsorption capacity at very diluted concentrations. CHPM shows a better adsorption (Figure 6) and this is confirmed by the b Langmuir value for CHPM, which is almost three times the value of CH. Previous studies with other biological adsorbents with copper ions report lower or similar adsorption capacities (qmax). For example, Kaewsarn used pre-treated algae Padina sp., observing an adsorption of 51 mg/g . Khan et al. reported qmax of 31.14 and 14.7 mg/g using saw dust and citrus peels, respectively . Kim et al. obtained a qmax of 16.28 mg/g using chai tea residues . The n Freundlich constant also indicates that the adsorption of copper (II) ions is favorable for CH and CHPM. The other two adsorbents show a borderline kF, supporting the loss of active sites by the cross-linking of chitosan chains with glutaraldehyde [2,20]. Finally, statistical significance indicates that the Langmuir and Freundlich models fit the adsorption of copper (II) ions onto all the studied adsorbents, suggesting a combined adsorption mechanism.
Effect of Salinity
As shown through the pH effect experiment, absorption capacity is heavily influenced by electrostatic interactions. Thus, the salinity effect on the adsorption of copper ions was also studied in this project. The presence of ions can increase or decrease the competition for active sites on the adsorbent. In this project, three different salts were added to the copper solutions in different concentrations. NaCl imitated the conditions of sea water, NaNO¬3 was tested because it is a standard salt for salinity effect in the scientific literature, and Ca(NO3)2 was added to see if the higher charge of the calcium ion affected the adsorption process. As shown below, it was found that the presence of the salts increased the adsorption capacity of all of the four beads.
Figure 7. Effect of NaCl, NaNO3, Ca(NO3)2 salts on adsorption of 180 ppm copper solution at pH 6
Figure 7 shows that all of the adsorption capacities increased for all four beads in the presence of a salt. NaCl enhanced the adsorption capacity the most, with the non-cross linked beads having an adsorption capacity of about 90% and the crosslinked beads having an adsorption capacity of about 60%. Overall, these results suggest that the presence of a salt increases adsorption capacity of the beads, enhancing the function of the beads. This could be explained first, by the no-competition between the Na and Ca cations for the adsorption sites with copper ions. The second and perhaps the most important explanation is osmosis. Chitosan beads are soft and watery adsorbents with pores that allow the transit of species through the bead. Under these conditions, the pore sizes are so large that they allow the entrance and fast evacuation of copper ions. However, due to the presence of the salts, water is taken out from the bead by changes in osmotic pressure, allowing shrinkage, structural reorganization in the beads and reduction in the pore size. Once the pores size are decreased, copper ions have a smaller change to escape from the bead and therefore, increase their removal from the solutions. These results demonstrate that spills in seawater or industrial runoffs with high salt content can be efficiently cleaned up with these new adsorbents. This behavior is somewhat unusual for heavy metals and other pollutants that have reported negative effect on the adsorption with salts [14,15,18,25].
Figure 8. Effect of polyethylene glycol, a crowding agent, on adsorption at pH 6 and room temperature
Effect of Crowding Agent
The effect of a crowding agent was also observed in this study. A crowding agent, Polyethylene glycol (PEG), was added to the copper solution to imitate other substances that are usually found in waste waters that have high concentrations of heavy metals. PEG resembles any covalent compound that might be present in wastewaters such as soluble lipids, proteins, and sugars that do not represent competitors for active sites due to charge similarities, but when present in the solution, delay and even prevent the interaction between copper ions and the adsorbents. A preliminary experiment demonstrated that PEG is not adsorbed on the adsorbents and does not adsorb copper ions from solutions. As observed in Figure 8, the presence of PEG made it difficult for the copper ions to bind to the activities sites of chitosan, decreasing the adsorption capacity of the beads compared to the zero PEG sample.
Figure 9. Scanning electron images of the adsorbents: CH(top left), CCH (top right), CH-PM (bottom), before the adsorption of copper (II) ions.
Adsorbent characterization and elucidation of the adsorption mechanism
Scanning electron micrographs were taken for all adsorbents and are shown in Figure 9. From the images, all the adsorbents display a very smooth surface with small hills and valleys on their surfaces. The high porosity of chitosan hydrogel is well known, but its pore size is too small to be visualized by SEM. However, it is important to notice that there are no surface changes after cross-linking; therefore the changes are at the molecular level. Conversely, CHPM displays a more heterogeneous surface with cracks and pockets. This could be due to the hybridization with PM that interrupts the formation of a perfect bead. However, for the rest of the surface, similar morphologies are observed when compared to CH.
EDAX studies were also carried out for all the adsorbents. Images of CHPM before and after the adsorption of copper ions are shown in Figure 10. The results demonstrate the presence of biological elements such as carbon, nitrogen and oxygen in large amounts and smaller amounts of other microelements including magnesium and silicon. Upon copper adsorption, copper peaks are clearly observed immediately after the oxygen peak and a second peak is observed on the far right of the spectrum. This demonstrates that copper is actually housed on the surface of CHPM and not lost by micro-precipitation, coagulation, or complexation with exo-polysaccharides that could give a false positive adsorption result [2,22].
Figure 10. EDAX studies of CHPM before (left) and after (right) of copper ions showing the presence of the metal on the surface.
This work demonstrates that the encapsulation of spent peppermint tea leaf waste in chitosan hydrogel beads provides potential adsorbents for the removal of heavy metals, specifically copper, from wastewaters. Chemical and mechanical properties can be enhanced by cross-linking of chitosan with glutaraldehyde. This cross-linking reduces the adsorption of copper, but a significant removal is still observed. Four different adsorbents were used in this project: CH, CH-PM, CCH, and CCHPM. Batch experiments were conducted at room temperature to optimize the adsorption of divalent copper from solutions. Data from the pH effect experiment showed that the optimum pH was 6, which falls in the range of acidity of water in nature of 5-7 using adsorbent doses of 150 mg. Salinity had a positive effect, apparently due to changes of osmotic pressure. Conversely, presence of a crowding agent, PEG, slightly decreased the adsorption. This suggests that this method will work in real life conditions (real wastewaters). Experimental results were also fitted according to the adsorption models of Langmuir and Freundlich, indicating a maximum adsorption capacity of 61.84, 45.25, 17.06, and 12.84 for CH, CH-PM, CCHPM and CCH, respectively. In all the cases, the incorporation of spent tea wastes increased the adsorption of the metal ion at low concentrations. These new adsorbents are biodegradable, inexpensive, and easily accessible, making them favorable materials for use in water purification.
The application of this new alternative needs to be optimized after experimental exploration of parameters like acidity, adsorbent mass, initial metal concentrations, and effects of salinity and covalent compounds. The optimization of these parameters will attract the attention o industries and treatment plants, motivating them to compare these techniques with the techniques that are commonly used for the removal of heavy metals.
In sum, although further research is needed, this study suggests that peppermint tealeaf wastes encapsulated by chitosan present a promising method of purifying wastewaters and contaminated freshwaters, creating a safer environment for humans and other organisms all over the world.
The authors are grateful to CSTEP, BMCC Foundation, CRSP and the Science Department at BMCC for their financial support and laboratory facilities for carrying out this work. A.N. is recipient of the BMCC Faculty Development Grant. The Material Characterization Center in Puerto Rico and Dr. Liz Diaz are greatly thanked for the SEM and EDAX facilities.
Cite this article: Navarro A E. Use of Spent Tea Wastes-Chitosan Capsules for the Removal of Divalent Copper Ions. J J Environ Sci. 2015, 1(1): 003.