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1853DEVELOPMENT OF LOW COST METHOD FOR REMOVAL OF FLUORIDE
FROM GROUND WATER USING TITANIUM OXIDE NANOPARTICLES
Chandra Prakash Lora
Department of Chemistry, Vivekananda Global University, Jaipur, India-303012
Email: [email protected] , [email protected]
ABSTRACT
Ground water is the most common and safest source of drinking water over the years. Flouride contamination is ground water leading to endemic fluorosis is a major health care issue in state having scarcity of drinking water like Rajasthan, India. Titanium oxide has developed as important compound for treatment of water due to its non-toxic nature, good chemical stability, high adsorption efficiency and low-cost. In the present research paper an improved method for removal of fluoride from water with the help of titanium oxide nanaoparticles is being reported. Method development for treatment include photocatalytic remediation with optimization of treatment conditions which include the effect of doze, contact time, initial fluoride concentration, pH and temperature. The developed method was successfully applied for removing fluoride from underground water without any hazardous effects.
Keywords: deflourination, photocatalytic technique, titanium oxide
I. INTRODUCTION:
Ground water is the most common and safest source of drinking water over the years. Ground water gets polluted due to organic and inorganic agents and the most serious threat is fluoride ion contamination [7,8]. Sources of fluoride contamination are natural, like rocks and minerals as well as industrial products like glass and ceramic industries, semiconductor manufacturing, coal-fired power stations, brick and iron works, fertilizers production, aluminum smelters etc. [1,16]. Looking at the severity of health problems related to high fluoride contamination the permissible limit of fluoride in drinking water as per WHO is 1.5 mg/l and 1.2 mg/l.
Fluorine is responsible for causing diseases like osteoporosis, arthritis, neurological damage, Alzheimer’s Syndrome, thyroid disorder, infertility and cancer, dental and skeletal fluorosis [5]. Researchers have reported many methods of removing fluoride which include precipitation and flocculation [15], membrane separation [14], electrodialysis [12], and adsorption [3]. The reported methods have their own drawbacks as, in precipitation and flocculation process the generated secondary waste as insoluble precipitate of fluoride has its own solubility due to which the fluoride concentration remains about 8.0 mg/L even after treatment [18,17]. Membrane separation process using reverse osmosis and nanofiltration involve high energy consumption and membrane fouling [6]. In electro-dialysis process is not at all economical and get easily influenced by presence of coexisting ions.[11,10]. Compared to other reported methods adsorption is more applicable due to its easy operation and low energy consumption[9]. But it suffers from generation of huge amount of secondary waste whose disposal is a major problem. There is an urgent need to find a deflorination technique which is economical, easily to apply as well as has zero waste generation[19][20][21]. The developed method include photocatalytic remediation using nanostructured titanium oxide particles which is simple, versatile, economical and most important with zero waste generation.
II. MATERIALS:
2.1 Fluoride solution:
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1854 water. The stock solution was diluted with double distilled water to get other subsequent concentrations as when required. For plotting the calibration curve 10ml of stock solution was diluted to 100ml using distilled water (10 ppm solution).2.2 Reagents for titanium oxide nanoparticle synthesis:
Synthesis of titanium oxide nanaoparticles was carried out using sol gel method. The chemicals required include titanium (IV) isopropoxide (TTIP) and isopropyl alcohol which were procured from Sigma–Aldrich. These chemicals were used without further purification. All the aqueous solutions were prepared using double distilled water.
2.3 Reagents fluoride determination:
Determination of fluoride in aqueous solution was carried out using SPADNS colorimetric method. The chemicals required include SPADNS solution; zirconyl chloride octahydrate and concentrated hydrochloric acid were procured from Sigma–Aldrich and were used without further purification
III. CHARACTERIZATION:
3.1 X-Ray powder diffraction (XRD) -
X-ray diffraction (XRD) patterns of the samples for structural characterization have been recorded on PANalytical make X’Pert PRO MPD diffractometer (model 3040) at University of Rajasthan, Jaipur.
3.2 pH meter
A pH meter (make : century Instruments (p) Ltd, Chandigarh, India ) was used to determine the pH of the solution. Each time the electrode was thoroughly washed with de-ionized water before and after the dipping inside the buffer solutions.
3.3 Centrifuge-Sample were centrifuged after treatment in order to separate the titanium oxide particles from the
sodium fluoride (NaF) solution. A compact laboratory centrifuge Hitachi High-speed Micro Centrifuge, Model CF15RX was used. Sample were centrifuged at a speed of 14,500 RPM until the solution appeared completely free of titanium oxide particles.
3.4 Conductivity meter-The conductivity of a solution in the EC bath was measured using a digital conductivity
meter (Make: Electronics Pvt Ltd, India Model:VSI) before and after the treatment to match with the recommendation limit of 0.2 mmhos.
3.5 FTIR spectrometer-
Shimadzu make IIRPrestige-21 FTIR spectrometer was used for FTIR characterization at University of Rajasthan, Jaipur
3.6 UV-Visible Spectrometer- Elico SL-159 spectrophotometer (double beam) was used for all UV-Visible
spectrophotometric observations at Vivekanada global University Jaipur, Rajasthan
IV. METHOD
4.1 Preparation of TiO2 nanoparticles
Titanium oxide nanoparticles were prepared via sol-gel method using the titanium isopropoxide, double distilled water and isopropyl alcohol as the starting materials. 100 mL of isopropyl alcohol was added to 15 mL of 1M titanium isopropoxide. The mixture solution is stirred for 15 minute using magnetic stirrer.10 mL of double distilled water was added drop wise to the mixed solution. Then the mixture solution was stirred continuously for 2 hours. A white precipitate was obtained, which was filtered and washed with distilled water. The obtained gel was left for 24 h in dark then dried using muffle furnace. The dried TiO2 is ground to fine po`wder using mortar
and calcined at 350 °C for 30 mins in muffle furnace. During the synthesis of TiO2 nanoparticles, the following
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1855 Ti(𝑂𝐻)3 → 𝑇𝑖𝑂2 + 𝐻2𝑂4.2 Method of determination of fluoride in water sample:
For determination of fluoride in water sample by SPADNS spectrophotometric method equal volumes of SPADNS solution and zirconyl acid reagent were mixed. The combined reagent is stable for at least 2 years. For reference the solution was prepared by adding 10 ml SPADNS solution to 100ml distilled water followed by addition of 7ml of concentrated HCl to it. The resulting solution was used for setting the reference point (zero) and is stable for atleast one year. Standard curve was plotted at 470 nm using following combination of sample solutions which were kept for 1 hour on shaker at 150rpm and 30oC. A set of 7 combination was prepared by mixing solutions in amount mentioned in table 1.
Table 1: Composition of different sets prepared for batch adsorption study
Batch adsorption with above combination of set was carried out by adding different amount of titanium oxide 50 ppm solution acting as adsorbent and then kept on shaker for 1 hour at 150 rpm and 30oC. Initial fluoride concentration was kept as mentioned in the table above. Fluoride concentration after adsorption was determined by spectrophotometric method using SPADNS-zirconium reagent and were plotted on standard calibration curve. Adsorption studies were carried out by varying the parameters like: adsorbent dose, pH, time, Initial fluoride concentration and temperature.
V. RESULT AND DISCUSSION
5.1 .Characterization of adsorbent
The structural analysis of prepared TiO2 nanoparticles was done using the X-ray diffraction (XRD)technique and
XRD patterns were recorded on PANalytical make X’Pert PRO MPD diffractometer (using CuKα radiation of λ = 1.5418Å) within 2θ range of 10° to 70° with a step of 0.1972°. Figure 1 showed the typical X-ray diffraction pattern of the synthesized TiO2 nanoparticles. The XRD pattern exhibits the characteristics peaks at 2θ value of
25.2°, 25.8°, 37.2° and 48° confirms anatase phase structure of TiO2 nanoparticles and are in close agreement
with previously reported the XRD pattern of TiO2 nanoparticles in literature [4,2,13,19]. There is no additional
diffraction peak appeared corresponding any other element which confirms the purity of as synthesized sample. The sharp and intense peaks indicate that prepared nanoparticles are crystalline in nature.
.
Figure 1: The X-ray diffraction patterns of synthesized TiO2 nanoparticles
Flask No( set) 1 2 3 4 5 6 7
NaF solution in ml Blank 0.5 1.0 1.5 2.5 5.0 6.30
Zr-SPADNS mix in ml 10.0 10.0 10.0 10.0 10.0 10.0 10.0
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18565.2 Effect of contact time
For optimization of contact time, 10 drops of 50ppm titanium oxide was added to set 6 prepared as per the combination mentioned in table 1, containing 1.0 ppm fluoride. The flask was then kept on magnetic stirrer at temperature 30°C. Fluoride concentration was then measured at 470 nm spectrophotometrically at different time intervals ranging from 5 min – 24 hours. Graph 1 was then plotted between contact time and percentage of fluoride removed. It was found that at initially adsorption of fluoride occurred fast, followed by slower adsorption till the equilibrium was reached. The equilibrium was achieved in 5 hrs with 84% fluoride removal in initial one hour.
Graph 1 : Effect of contact time plot
5.3 Effect of initial concentration
To study the effects of initial concentration of fluoride solution on adsorption capacity of adsorbent, different flasks with 25 ml of fluoride ion solution in the concentration range 0.1ppm to 5.0ppm is taken and to each flasks 10 drops of 50ppm titanium oxide was added. The flasks were then kept on shaker for contact time of 1 hour maintaining temperature 30°C. After shaking for 1 hour solutions are filtered and fluoride concentration is measured at 470 nm using UV-visible spectrophotometer. Graph 2 was plotted between initial concentration and % removal of fluoride keeping the adsorbent concentration constant. From graph 2, it is visible that adsorption capacity increases with an increase in fluoride concentration attributed to increased diffusivity and then decreases after certain concentration since saturation value is attained.
0 1 2 3 4 5 6 -10 0 10 20 30 40 50 60 70 80 F lo u ri d e% R emo v al Fluoride Concentration in ppm
Graph 2 : Effect initial concentration plot
5.4 Adsorbent dose effect
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1857 were then filtered and fluoride concentration was measured at 470 nm using UV-visible spectrphotemeter. Graph 3 was plotted between doze of titanium oxide added and % of fluoride removed, from the graph it is clearly visible that % removal increases with the increase in adsorbent doze. This happens because as the amount of adsorbent increases the number of active adsorption sites available is capable to accommodate fluoride ions. As seen in graph 3 there is a break at 5 drops, thus 5 drops per 25 ml was fixed as optimum doze for further studies.0 5 10 15 20 25 30 0 20 40 60 80 100 F lu o ri d e % R e mo va l
Number of drops of Titanium dioxide
Graph 3 : Dose effect plot of titanium oxide
5.5 pH effect
The pH of solution is an important factor which affects the adsorption process. Hence, the determination of pH at maximum adsorption condition is must. For the study of pH effect on the adsorption capacity of titanium oxide, 25 ml of 10ppm fluoride ion solution is taken in various flasks and there pH is balanced between 3 to 11. To each flask, optimized doze, i.e 5 drops of 50ppm TiO2 adsorbent was added and kept on shaker at 150 rpm maintaining
temperature 30°C. Solutions are then filtered and fluoride concentration was measured at 470 nm using UV-visible spectrophotometer. Graph 4 was plotted between pH and % removal of fluoride. The results of the graph 4 show that titanium oxide has high adsorption capacity in the pH range 5 to 6. This is because the H+ ions present in the solution reacts with the fluoride ions leading to formation of HF at pH less than 4. Since HF is stable molecule which cannot be ionized easily, at low pH the adsorption of fluoride ion decreases. The removal capacity of fluoride decreases in pH above 8, which is generally due to the adsorbent surface tending to behave is negatively charged one where the concentration of hydroxyl ions increase and they compete with fluoride ions for adsorption.
Graph 4 : pH effect plot
5.6 Temperature effect
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1858 temperature. The continuous increase in percentage removal with temperature indicated that the adsorption process was endothermic in nature.VI. CONCLUSION
In this study, TiO2 nanoparticles were synthesized and used for the removal of fluoride from water sample. TiO2
adsorption capacity increased after its conversion in nanoparticle since surface area was increased greatly. Deflourination capacity was maximum in pH range 5-6 and temperature 50-60 oC The maximum defluorinaion was 78% . The study reveals that use titanium oxide nanoparticle for defluorination is very effective and can be applied for removing fluoride from groundwater samples. .
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