Adsorption of Phenol Using 8-Hydroxyquinoline Treated and Untreated Tea Waste

Water is an essential resource for the existence of all life forms. Freshwater is important for human and aquatic organisms and for all activities of all living beings; but they are limited due to the increasing population, urbanization and climate changes. This scarcity was due to water pollution that caused by the discharge of untreated or partially treated industrial effluents into the natural ecosystem, posing serious problems. Thus, these industrial effluents, containing several organic and inorganic chemicals as -phenols, formaldehyde, dyes, and heavy metals are the major water pollutants [1].


Introduction
Water is an essential resource for the existence of all life forms. Freshwater is important for human and aquatic organisms and for all activities of all living beings; but they are limited due to the increasing population, urbanization and climate changes. This scarcity was due to water pollution that caused by the discharge of untreated or partially treated industrial effluents into the natural ecosystem, posing serious problems. Thus, these industrial effluents, containing several organic and inorganic chemicals as -phenols, formaldehyde, dyes, and heavy metals are the major water pollutants [1].
Aromatic hydrocarbons are one of the common contaminants of groundwater originating from coal gasification, oil refining process, wood treatment process, fires of forests automobile exhausts and disposal of oils and fuels. Many of these compounds are reported, to be toxic, carcinogenic and tend to accumulate in the aquatic organisms even present in low concentrations. The presence of heteroatom in them makes them more soluble than their homocyclic analogs [2][3][4][5]. One of the aromatic organic compounds is phenol (C 6 H 5 O) white crystalline solid that is volatile. It consists of phenyl (C 6 H 5 -)(-OH) groups which was first extracted from coal tar. It is an important industrial commodity as a precursor to many materials and useful compounds. Their major use involves its conversion to plastic or relates materials [6,7].
Beside their usage phenol and its chemical derivative has a toxic effect on the aquatic organisms and humans. Since phenol and its derivatives are harmful to living even at low concentrations, they known as dubious pollutants. Phenols and its deriv atives removal study have been reported by various researchers [8][9][10].
Several methods for organic pollutants removal from wastewaters, such as precipitation, solvent extraction, and adsorption are usually applied. Adsorption is one of the respective methods for wastewater treatment due to its several advantages such as high efficiency, low cost, simple application and easy recovery of adsorbent [11]. Recently, researchers reported the potential use of tea waste generated from the cafeteria as an adsorbent for removal of heavy metal from aqueous solution [9,[12][13][14].
In this work tea waste collected from the local cafeteria used as an adsorbent for the removal of phenol from aqueous solution. Collected tea wastes were used as an untreated and 8-Hydroxyquinoline treated powder for the potential removal process.

International Journal of Environmental Sciences & Natural Resources
Southwestern, for the removal of phenol from aqueous solution. The collected tea waste washed with tap water followed by drying under sunlight. Then the dried tea waste was powdered to mesh size 150μm and washed with distilled water until neutral pH was observed then kept for drying in an oven at 110 o C. The dried tea waste was now separated into two halves, then one half was treated with an 8-HQ solution; while other part left untreated. Both parts of tea waste were kept in the sample bottle separately for the further experiment.

Preparation of stock solution:
A saturated solution of 8-HQ was prepared by adding an appropriate quantity in 1000ml of distilled water, sonicating for 2hr and then stirred with a magnetic stirrer for another 2hr. The solution was then filtered to remove the undissolved 8-HQ. Four standard solutions (10ppm, 15ppm, 20ppm, and 25ppm) were prepared by adding 0.01gm, 0.015gm, 0.02gm and 0.025gm of phenol to 1L of distilled water respectively.
Preparation of treated tea waste adsorbent: 10gm of dried tea waste powdered was taken into round bottom flask and treated with 8-HQ solution then kept into water bath shaker for 24hrs, after that the solution was taken out from the shaker. The solution was then filtered with filter paper and the filtrate washed until excess 8-HQ was removed.
Calibration of phenol: 1gm of powdered tea waste was weighted and added into four shaking bottles; followed by addition of 100ml of (0.01M, 0.015M, 0.02M, and 0.025M) in each shaking bottle. The sample was shaken for 65min before filtration. The filtered sample was calibrated by UV-Vis spectrophotometer. Maximum absorption was obtained at 285nm.

Adsorption isotherm
In a solid-liquid system, adsorption results in the removal of solutes from solution by accumulating at a solid surface. The solute remaining in the solution reaches a dynamic equilibrium with that adsorbed on the solid phase. The amount of adsorbate that can be taken up by an adsorbent as a function of both temperature and concentration of adsorbate, and the process, at a constant temperature, can be described by an adsorption isotherm according to the general Eq. (1): In this study, the extent of phenol adsorption capacity at equilibrium, q e (mg/g), was calculated The percentage of phenol removal was calculated using, Eq. (3): C 0 corresponds to the initial concentration of C 6 H 5 OH, and C e (mg/g) corresponds to the concentration of phenol at equilibrium. V (L) is the volume of the solution, and W (g) is the mass of the dry adsorbent.

Calibration of phenol
Calibration curve was plotted for the solution of phenol at different concentrations shows the maximum peak at 285 nm. At the same wavelength, the different absorbance of the C 6 H 5 OH solution formed due to the concentration difference, as shown in Figure 1  (a & b).   Figure 2 (a & b) depict the SEM micrographs for tea waste untreated powder before and after phenol adsorption it is evident from the figure that the surface is porous for both treated and untreated tea waste powder. However, apparently this porosity was

International Journal of Environmental Sciences & Natural Resources
shown disappeared in Figure 2 (c & d). This may be due, to the fact that diffusion of phenol on to the surface of the adsorbent might have occurred for adsorption [9]. Time is one parameter that has an influence on surface property of an adsorbent. This effect of time was observed at which adsorbent and solution exist together. As the solution stays for a longer time by shaking with an adsorbent, the number of particles of solute adsorbed to the surface increases. More attachment of solute particles to the adsorbent surface increases the percent of adsorption. Also, modification of the surface increases the percent of adsorption by increasing the surface of the adsorbent. Figure 3 below is showing time influence and difference of percent adsorption of treated and untreated tea waste.

Adsorption isotherm study
Adsorption isotherm is a basic requirement for the design of an adsorption system. The adsorption mechanism was investigated using Langmuir and Freundlich models. The two models differ from each other in their assumption concerning of existence of fine adsorption capacity [15]. Langmuir isotherm describes quantitatively for the formation of a monolayer on the outer surface of the adsorbent and after that, no further adsorption takes place, Figure 4a. The Langmuir isotherm is valid for monolayer adsorption onto the surface contain a fine number of the identical site [16][17][18][19][20].
The linear form of Langmuir isotherm is given by the following equation.
Where ' q e' and q max are equilibrium and maximum uptake capacity (mg/g) respectively, b L is related to the free energy of adsorption and represent the Langmuir adsorption constant, C eq is the equilibrium adsorbate concentration in morality. The Langmuir constant that is, related to the maximum capacity (q max ) and energy adsorption (b L ), was calculated from the slope & intercept of linear plot C e /q eq versus C eq . The essential characteristics of the Langmuir equation can be expressed in terms of a dimensionless factor, R L that is given by ( Table 1) Where b L is the Langmuir constant and C 0 is the initial concentration of the adsorbate in solution. The values of R L indicates the type of isotherm to be irreversible (R L =0), favorable (0<R L <1), linear (R L =1), or unfavorable (R L >1). The value of R L is found to be 1.588x10 -4 and 5.026x10 -4 mg/L at 303K for untreated and treated tea waste adsorption experiment respectively. This indicates that adsorption of phenol is favorable on both 8-HQ treated and untreated tea waste adsorbent.
Where q e is the adsorption density (mg/g), C e is the concentration of the adsorbate in solution at equilibrium (mg/L); K F and International Journal of Environmental Sciences & Natural Resources 1/n are the Freundlich constants. The plot of log q e versus log C e yields a straight line indicating to obey a Freundlich adsorption isotherm. This isotherm does not predict any saturation of the sorbent by the sorbate; thus, mathematically infinite surface coverage is predicted, indicating multilayer adsorption on the surface. Freundlich adsorption isotherm gives an expression encompassing the surface heterogeneity and the exponential distribution of active sites and their energies indicate a multilayer sorption of the surface. The binding capacity and affinity between the adsorbent and phenol ions reach the highest value with high KF and 1/n. Favorability of adsorption gives by the magnitude of the exponent n. As can be seen from Table 1 and Figure 4b, treated tea waste is a good adsorbent for phenol adsorption.

Adsorption kinetics
To evaluate the kinetics of the adsorption process, the experimental data were compared to those predicted by two kinetic models, the pseudo-first order and pseudo-second order. The pseudo first order equation can be expressed, as Where q e and q t the amount of adsorbate in mg at equilibrium at any time t, k 1 is the first order rate constant (min -1 ). Rate constant, k 1 and theoretical q e was calculated from the slope and intercept from the plot of log (q e -q t ) versus t, Figure 5a Pseudo-second order equation expressed as follow.   Figure 5b, Table 2 below.
Adsorption of phenol onto tea waste show rapid initial adsorption rate flowed by slower rate. Initially, the adsorption site is abundantly available, and phenol interacts easily, hence the higher rate of adsorption was observed. However, after initial periods lower adsorption may be due to slower diffusion of adsorbate into the interior adsorbent. The two kinetics models mentioned above has been used to understand the adsorption kinematics and correlation coefficient, R 2 . The linearity of these plots indicates the capacity of the two models. The correlation coefficient adsorption kinematics is 0.895 for untreated and 0.922 for treated adsorbents for pseudo first order and 1.00 1.00 for second order respectively. The correlation coefficient shows that the pseudo-second-order models fit better to the experimental data for both treated and untreated tea waste.

Conclusion
Adsorption of phenol from aqueous solution was investigated experimentally using tea waste as an adsorbent. The batch experiment revealed that the equilibrium adsorption attained at 30 and International Journal of Environmental Sciences & Natural Resources 25 minutes. The isothermal data were examined by employing two isotherm models, Langmuir, and Freundlich where the experimental data fitted very well to the Langmuir isotherm model indicating chemisorption of the adsorbate on powdered tea waste surface. Results of kinetics study indicate that the pseudo-second-order kinetics can simulate the adsorption process with a high accuracy for the adsorption of phenol from aqueous solution.