INTRODUCTION:

The survival of humans on earth depends on air, water and food. More than 70% of earth’s surface is covered with water. Most of the water is not suitable for human consumption due large number of contaminants. An increase in population, urbanization, growth of industries, use of chemical fertilizers and lack of environmental awareness has led to an increase in water pollution. The industrial wastewaters are characterized by non-biodegradable organic and inorganic materials including metals, dyes, aerosols, phenols, surfactants, phosphates, high BOD and COD concentrations. The dyes mainly consist of heterocyclic and aromatic compounds with color imparting polar groups. Due to complicated structures, the dyes are difficult to degrade¹.

The source of color in dyes:

Dyes are the organic compounds that impart color to substances such as plastic, leather, plastic, hair, food, hair, paper, textile and wax². Dyes are characterized by two types of groups, the chromophores and auxochromes. The color of the dye is due to the presence of chromophore groups. The most important chromophores are –N=N–, >C=O, –C=C–,–NO₂, --CN, –NO groups. Auxochromes are the electron donating groups that can intensify the color of chromophore and increase the solubility and adherence of the dye with the fibre. Some important auxochromes are –NH₂, –NHR, –NR₂, –COOH, –OH, –SO₃H and –OCH₃ groups³. The dye molecule as a whole is described as chromogen (55). The conventional bio-treatments are not efficient enough to treat the dyed effluents. Adsorption of dyes by activated carbon is one of the most promising treatment techniques for removing the dyes from dyed effluents.

MATERIALS AND METHODS:

Activated carbon was prepared from the leaves of worthless plant Azadirachta indica (Neem). The leaves were thoroughly washed, dried and finally cut into pieces of 2-3 cm size. The carbonized material was then sieved into 300-850 μm particles. The precursor material was then impregnated with boiling solution of 10 % H₃PO₄ for nearly 2 hrs and then kept undisturbed for 24 hrs. At the end, the excess liquid was removed by decantation. The remaining material was dried and carbonized at 400^oC for half an hour in muffle furnace. The carbon obtained was powdered and activated in muffle furnace at 800^oC. The activated carbon prepared was finally washed with excess of water to remove any residual acid present and then dried⁴. The carbon thus obtained from Neem leaves by H₃PO₄ impregnation method is designated as NAC₂.

ADSORPTION STUDIES OF AV49 BY NAC_2:

The respective dye acid violet 49 (AV49) was dissolved in 1000 ml of distilled water to prepare a stock solution of 1000 mg/L of adsorbate. Appropriate concentrations of the stock solution were obtained by diluting it with distilled. The molecular formula and λ_max (nm) of the dye selected for adsorption studies are shown in and some of their properties are given in the table below:

Dye used for adsorption studies	Molecular formula	Molecular weight (g/mol)	λ_max (nm)
Acid Violet 49	C₃₉H₄₀N₃NaO₆S₂	733.87	548

Batch Adsorption Studies:

The batch mode adsorption experiments were carried out by varying the initial dye concentrations, initial pH and temperature. The adsorption studies were carried out in 250 mL tight lid reagent bottles by agitating 100 mg of adsorbent with 200 mL of aqueous dye solution. The agitation was carried out by placing the contents of flask in a temperature controlled orbital shaker (Universal Make). The mixture was withdrawn at specified time intervals and then centrifuged using electrical centrifuge at 5000 rpm for 10 minutes. The un-adsorbed supernatant was analyzed for the residual dye concentration using Bio UV-visible spectrometer (Elico make: BL-198) by fixing λ_max at 548 nm as the absorption wavelength.

Batch Desorption Studies:

At the end of adsorption experiments, the carbon loaded with dye was washed carefully with double distilled water to remove the un-adsorbed dye from it 500 mg of dye loaded carbon was centrifuged with 50 mL of double distilled water at 300 rpm and the supernatant liquid was removed at various values of pH. The desorbed dye solution separated by centrifugation was estimated by the adsorption studies.

RESULTS AND DISCUSSIONS:

Bach Mode Adsorption Studies:

Effect of agitation time and initial dye concentration on adsorption of Acid Violet 49:

The data for the adsorption of AV49 on NAC₂ with respect to the contact time is given in Tables 1 to 5. For evaluating the maximum adsorption capacity of NAC₂, it is important to generate the equilibrium adsorption data at various initial dye concentrations. The plots shown in figures 1 and 2 represent the variation of percentage and amount of dye adsorbed respectively with respect to contact time by NAC₂ at various initial dye concentrations. From fig 1, it is evident that the percentage of dye adsorbed decreased with an increase in the initial dye concentration. However, the amount of dye adsorbed (q_t) per unit mass of adsorbent increased from 47.92 to 171.64 mg/g with an increase in the initial dye concentration from 25 to 100 mg/L. Thus adsorption is highly dependent on the initial dye concentration⁵. The initial dye concentration also provides the necessary driving force for overcoming the resistance due to the mass transfer between solid and aqueous phase⁶. An increase in dye concentration increases the contact between dyes and adsorbent and thus decreases the resistance.

The figures 1 and 2 also indicate that the maximum amount of dye is adsorbed in initial 40 minutes of contact time, followed by decrease in the rate till equilibrium is attained after 100 minutes of time. The curves obtained in figures 1 and 2 are smooth, single and continuous, leading to saturation, which in turn suggests the possibility of monolayer coverage of dye on the activated carbon surface Similar results were reported previously for the removal of Acidic dyes on Aloe barbadensis mill activated carbon Brilliant Blue FCF on de-oiled soya and Bottom ash⁷ Acid Red 151 and Acid Blue 25 on waste wood pallets activated carbon removal⁸ of Acid Violet 17, Acid Blue 15, Acid Violet 49, Acid Red 119 and Acid Violet 54 by different adsorbents^{9, 10}

Effect of temperature on the adsorption of AV49:

Figures 3 represents the uptake of AV49 on NAC₂ at different temperatures of 30, 40 and 50°C by keeping the initial dye concentration fixed at 50 mg/L. The equilibrium adsorption capacity of AV49 on NAC₂ increased from 93.88 to 95.92 mg/g with an increase in temperature from 30 to 50°C. This increase in uptake of AV49 on NAC₂ with an increase in temperature indicates that the adsorption of AV49 by NAC₂ is endothermic in nature. The increase in adsorption with temperature is due to decrease in thickness of the boundary layer surrounding the adsorbent, which allows the mass transfer resistance of adsorbate. This may have resulted due to increase in the mobility of the dye with the raise of temperature^{11, 12}. Similar results have been reported for the adsorption of Acid Blue MTR by orange peels¹³ and removal of Acid Blue and Acid Red dyes from aqueous solutions by Ashoka leaf powder¹⁴.

Table1: Effect of agitation time and initial dye cone on the absorption of AV49 by

Time (min)	Final Concentration, C_t (mg/L)	Dye adsorbed (%)	Amount of dye adsorbed q_t, mg/g
0	25.0	0.00	0.0
5	19.63	21.48	10.74
10	15.12	39.52	19.76
15	11.03	55.88	27.94
20	7.21	71.16	35.58
30	5.13	79.48	39.74
40	3.32	86.72	43.36
50	2.14	91.44	45.72
60	2.01	91.96	45.98
70	1.55	93.8	46.90
80	1.034	95.864	47.93
90	1.03	95.88	47.94
100	1.03	95.88	49.94
110	1.03	95.88	49.94

Initial dye concentration =25mg/L

pH = 6.25, Temp. =30⁰C

Table 2: Effect of agitation time and initial dye cone on the absorption of AVA9

Time (min)	Final Concentration, C_t (mg/L)	Dye adsorbed (%)	Amount of dye adsorbed q_t, mg/g
0	50.0	0.0	0.0
5	40.25	19.50	19.50
10	33.42	33.16	33.16
15	26.35	47.30	47.30
20	23.51	52.98	52.98
30	17.23	65.54	65.54
40	12.14	75.72	75.72
50	11.26	77.48	77.48
60	8.43	83.14	83.14
70	4.71	90.58	90.58
80	4.25	91.50	91.50
90	3.76	92.48	92.48
100	3.76	92.48	92.48
110	3.76	92.48	92.48

Initial dye cone= 50mg/L pH=6.25 Temp=30°C

Table 3: Effect of agitation time and initial dye conc. on the adsorption of AVA9

Time (min)	Final Concentration, C_t, (mg/L)	Dye adsorbed (%)	Amount of dye adsorbed q_t, mg/g
0	75.0	0.0	0.00
5	64.17	14.44	21.66
10	54.52	27.30	40.96
15	46.91	37.45	56.18
20	39.62	47.17	70.76
30	34.52	53.97	80.96
40	29.04	61.28	91.92
50	25.21	66.38	99.58
60	19.32	74.24	111.36
70	16.11	78.52	117.78
80	14.52	80.64	120.96
90	10.27	86.30	129.46
100	6.92	90.77	136.16
110	6.92	90.77	136.16

Initial dye conc. = 75mg/L pH=6.25 Temp=30⁰C

Table 4: Effect of agitation time and the initial dye conc. on the adsorption of AVA9

Time (min)	Final Concentration, C_t (mg/L)	Dye adsorbed (%)	Amount of dye adsorbed q_t, mg/g
0	100	0.0	0.00
5	86.14	13.86	27.72
10	73.52	26.48	52.96
15	64.03	35.97	71.94
20	55.25	44.75	90.21
30	47.29	52.71	105.42
40	40.10	59.9	119.8
50	36.25	63.75	127.5
60	33.72	66.28	132.56
70	26.22	73.78	147.56
80	22.61	77.39	154.78
90	17.05	82.95	165.90
100	15.13	84.87	169.74
110	15.13	84.87	169.74

Initial dye concentration = 100mg/L pH=6.25

Temp=30⁰C

Table 5: Effect of agitation time and temperature on the absorption of AV49

Time (min)	Final Con-centration, C_t, (mg/L)	(%) Dye adsorbed, 30 ⁰C	(%) Dye adsorbed, 40 ⁰C	(%) Dye adsorbed, 50 ⁰C
0	50.0	0.0	0.00	0.00
5	36.73	19.50	26.54	37.22
10	29.24	33.16	41.52	48.20
15	25.35	47.30	49.30	58.48
20	21.62	52.98	56.76	66.72
30	16.27	65.54	67.46	78.94
40	13.62	75.72	72.70	82.42
50	11.45	77.48	77.10	87.36
60	9.89	83.14	80.22	88.06
70	7.62	90.58	84.70	88.78
80	5.55	91.50	88.90	90.82
90	4.92	92.48	90.16	91.96
100	3.53	92.48	92.94	93.80
110	3.53	92.48	92.94	93.80

Initial dye concentration = 100mg/L pH = 6.25

Fig. 1

Fig. 2

Fig 1 and 2: Effect of agitation time and initial dye concentration on the adsorption of AV49 dye by NAC₂.

Fig 3: Effect of agitation time and temperature on the adsorption of AV49 dye.

Desorption studies of Activated Carbon:

Desorption studies are carried to recycle the spent adsorbent. The desorption of AV49 was carried out by using dil. NaOH with a pH range of 2 to 12. It was found that desorption of AV49 from the surface of activated carbon (NAC₂) increased with an increase in pH from 2 to 12. The percent of desorption observed at pH 12 was 48.65 %. Greater the percentage of desorption, more easily an adsorbent can be recycled.

CONCLUSION:

The batch mode adsorption studies of activated carbon (NAC₂) prepared by H₃PO₄ on acid violet 49 indicates that NAC₂ could be effectively and conveniently used as a low cost adsorbent. The activated carbon prepared from Neem precursor could also serve as better alternative to the commercial activated carbon. The treatment process may be effectively used for treating the dyed industrial effluents of textile and paper industries for addressing the pollution problem arising due to color. Further, this treatment method makes it possible to recycle the maximum possible amount of spent adsorbent for further use.

REFERENCES:

1. Chipasa K. Limits of physicochemical treatment of wastewater in the vegetable oil refining industry. Polish Journal of Enviro Studies. 2001; 10:141-147.

2. Saunamaki R. Activated sludge plants in Finland. Water Sci Technol. 1997; 35:235- 243.

3. Lawrence K. Wang, Yung-Tse Hung, Howard H. Lo, Constantine Yapijakis. Handbook of industrial and hazardous wastes treatment (2nd ed.). CRC Press; 2004. ISBN:0-8247-4114-5.

4. APHA.; Standard methods for the examination of water and wastewater, 1998; 20th edn. DC, New York.

5. Arivoli, S., Sundaravadivelu, M. and Elango, K.P. “Removal of Basic and Acidic dyes from aqueous solution by adsorption on a low cost activated carbon: Kinetic and thermodynamic study”, Indian J. Chem. Tech., 2008; 15, 130

6. Monika, Drivjot and Amita “Adsorption of dyes from Aqueous solution using Ornagel Peels: Kinetics and Equilibrium Studies”, J. Adv. Lab. Res. Bio., 2012; 3, 1-10.

7. Gupta, V.K. and Suhas. “Application of low-cost adsorbents for dye removal –A review”, J. Environ. Manage., 2009; 90, 2313-2342.

8. Tsai, W.T., Chang, C.Y., Ing, C.H. and Chang, C.F. “Adsorption of acid dyes from aqueous solution on activated bleaching earth”, J. Colloid. Interf. Sci., 2004; 275, 72-78.

9. Sumanjit, T.P.S., Walia, S. and Kaur, R. “Removal of health hazards causing acidic dyes from aqueous solutions by the process of adsorption”, Ojhas, 2007;. 6, 1-10.

10. Sumanjit T. P., Singh W. and Ishu K. “Removal of Rhodamine-B by adsorption on Walnut shell charcoal”, J. Surface Sci. Technol., 2008; 24, 179-193.

11. Aksu, Z., Tatli, A.I. and Tunc, O. “A comparative adsorption/biosorption study of Acid Blue 161: Effect of temperature on equilibrium and kinetics parameters”, Chem. Eng. J., 2008; 142, 23-39, 2008.

12. Aksu, Z. and Kabaskal, E. “Batch adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution by granular activated carbon”, Separ.Purif. Technol., 2004; 35, 223-240, 2004.

13. Monika, Drivjot and Amita “Adsorption of dyes from Aqueous solution using Ornagel Peels: Kinetics and Equilibrium Studies”, J. Adv. Lab. Res. Bio., 2012; 3, 1-10.

14. Shelke, R.S., Bharada, J.V., Madjea, B.R and Ubalea, M.B. “Studies on the removal of acid dyes from aqueous solutions by Ashoka leaf powder”, Der. Chemica. Sinica., 2011; 2, 6-11.

Received on 10.05.2017 Modified on 18.05.2017

Asian J. Research Chem. 2017; 10(3):345-348.

DOI: 10.5958/0974-4150.2017.00058.X