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1 International Journal of Latest Research in Science and Technology Volume 5, Issue2: Page No47-51, March-April ISSN (Online): ROLE OF METAL ION WITH SAME CONCENTRATION ON PHOTOASSISTED BLEACHING OF MALACHITE GREEN BY Nb 2 O 5 1 Lokesh Gurjar, 2 Prakash C Choudhary, 3 B.K.Sharma 1 PhD Scholar, 2 Assitant professor, 3 Professor 1 Department of Chemistry, Mewar University, Chittorgarh (Raj.) 2 Department of Chemistry, Mewar University, Chittorgarh (Raj.) 3 Department of Chemistry, S.G.G.Government Collage, Banswara (Raj.) 1 District-chittorgarh, State-Rajasthan, Country-India 23jan1983.lg@gmail.com, prakash.ch81@gmail.com,bhoopendrasharma@gmail.com Abstract- Textiles industries are identified by the uses of dyes and Dyes are pollutant materials that are difficult to decompose by microbiological treatment. An alternative way to prevent contamination of the environment by dyes is the oxidation of these materials through photo catalysis, a process by which illumination of an oxide semiconductor produces photo excited electrons and cations that migrate over the surface of the oxide, effectively participating in the chemical reaction Photo catalytic degradation of Malachite Green has been investigated in the presence of Nb 2 O 5 and the progress of reaction was observed spectrophotometrically. Discoloration tests were carried out in a photocatalytic reaction in the presence of light and different operational parameters like concentration of the dye, amount of photo catalyst, ph and nature of photo catalyst.it was also study that what s effect of addition of common cation and anion such as Na +, K +, Ca +2, Ba +, Cl -, SO 4-2 and CO 3-2 It has been found that limited quantity of all metal ions increases the reaction rate to some extent. A tentative reaction and mechanism has been proposed. Key words: Dye, photo degradation, Nb 2 O 5, metal ions, Malachite Green. I. INTRODUCTION Industrial activity causes numerous environmental problems; water contamination by organic molecules is a good example. The growing development of the textile industry is a great contributor, because a large part of these pollutants is dye generated by this type of industry. Due to their own nature, the dyes are easily detected by the naked eye, being visible in some cases at concentrations as low as 1 mg L -1. That behavior presents advantages and disadvantages, because a small amount thrown in aquatic effluents can cause an accentuated change of coloration in the rivers, but can also be easily detected by environmental control authorities.(1) As a result, much effort has been made to degrade and even remove these dyes which constitute an environmental problem and a serious problem faced by modern society.(2) Catalytic processes have been applied to the solution of several environmental problems, because it provides faster, low cost reactions, with higher selectivity. The interest in materials containing niobium oxides (Nb 2 O 5 ) has been increasing in recent years due to the fact that this material can be applied in diverse fields of study,(3)being used as a catalyst and as a catalytic support. The use of niobium oxide in Brazil becomes appealing due to its natural abundance in the country. (4, 5) In the search for new materials with catalytic properties, the interest in the study of the effects of oxide supported metals has been increasing. The metal-oxide interaction induces important modifications in the adsorption and catalysis properties of the metal in different reactions.(6) Furthermore, its use is justified by its having a larger area of contact between the metal and the organic molecule, which is not, observed using the metal alone. The introduction of transition metals, such as tin, on the surface of different supports results in high activity and selectivity for catalysis.(7) The presence of metal dispersed on the surface acts as centers that present Lewis acid characteristics, which are desired as a reinforce of the catalytic activity. In the investigation of surface catalytic properties, the acidity/basicity stands out, because it promotes alterations in the adsorption capacity, related to the properties of the exposed sites. (8) The aim of this work is asses the photocatalytic treatment of Malachite green (MF: C 23 H 25 N 2, MW: ).This dye is selected due to its toxicity, carcinogenic in nature as well as its presence in wastewater of several industries such as textile dying, printing, tannery etc. On irradiation, electron migrates on metal where it becomes trapped and electron hole recombination is suppressed. The hole is then free to diffuse on the semiconductor surface where oxidation of organic species can occur. C N(CH 3 ) 2 N(CH 3 ) 2 Cl ISSN:

2 EXPERIMENTAL SECTION Stock solutions of Malachite green, 0.01 M (0.33g/100ml) Time(In minutes) Optical density 1+log Optical D. was prepared in purified water and as per desired concentration aqueous solution was ready from stock solution. The desired ph was adjusted by H 2 SO 4 and NaOH solutions Photocatalytic activity test A tungsten lamp (Philips) o f W was used as the visible light source and photo catalytic activity of the Nb 2 O 5 was investigated by the degradation of Malachite green in visible light at lmax = 615 nm.for removal of thermal radiation, cutoff filter was placed outside the beaker (Pyrex). A 50 ml beaker was filled with 40 ml of dye solution containing photo catalyst. The sample of mixture has been taken outside at fixed time interval and optical density measured. The change in the maximum absorption versus irradiation time was obtained. The typical run is presented in Table 1. It is observed that the optical density (O.D.) of Malachite green solution decreases in presence of the semiconductor, metal ions and light. The plot of log OD vs time is found to be linear and hence, this reaction follows pseudo-first order kinetics. The rate constant for this reaction was determined using the expression k = slope. Procedure and Analysis In this experiment, known amount of malachite green solution and semiconductor were taken in beaker and cutoff water filter were placed on beaker to avoid thermal reaction. The solution was irradiating by visible tungsten lamp. Dye sample of about 2-3 ml was taken out at a regular time interval from the solution and optical density (O.D.) was recorded spectrophotometrically (systronics spectrophotometer).light Intensity was measured by suryamapi (CEL Model SM201). Attempts have been made to study the effect of addition of common cations and common anions such as Na +, K +,Ca +2, Ba +, Cl -, SO 4-2 and CO 3-2. RESULTS AND DISCUSSION The plot of 1+log O.D. vs. time was found straight line suggesting that degradation of dye by Nb 2 O 5 follows pseudo first order rate law. Rate constant was calculated by graphs as follows K1 = X slope A typical run is given in Table-1 and Figure.1 Table - 1 A Typical Run [Malachite green] = M, ph = 8.5 Light Intensity = 37.0 mwcm -2, Nb 2 O 5 = 0.10 gm logD Time(min) Figure 1- Photochemical degradation of Malachite green Rate (k) = Slope Variation in ph and its effect The ph of solution has play important role in dye degradation. ph is directly shows the effect on semiconductor surface property. The result of ph on photo catalytic bleaching of Malachite green with Nb 2 O 5 was determine in the range of 5 to 9 ph under visible light source. When increase the ph from 6.5 to 8.5, It was observed that the rate of photo catalytic degradation increases after that increasing in ph reaction rate is going down. Its due to that as ph of reaction mixture increases more OH + ions forms and this ions generate more radical and as per study it s clear that *OH are strong oxidant which can be easily oxidize the chemicals. As the OH - ions increases this will form the negatively charged surface of Nb 2 O 5 and due to this dye molecule not attract towards the semiconductor surface, because of both are having same charges (anionic dye and semiconductor surface) and due to repulsive force decrease in rate of photo catalytic degradation of dyes. ISSN:

3 ph k x 10 5 (sec -1 ) International Journal of Latest Research in Science and Technology Semiconductor (gm) k x 10 5 (sec -1 ) Sec ph Figure.2: Effect of ph variation on malachite dye degradation Variation in amount of catalyst and its effect [Nb 2 O 5 ] At the different amount of Nb 2 O 5, dye degradation rate is investigated and its found that it is varying with the amount of semiconductor. The Nb 2 O 5 amount was varying from.06 to0.20gm. And the result shows that the dye degradation rate is going in higher side as the promoter amount up to 0.10 gm. and away from this, the degradation rate going constant. (Figure.3). The reason of this is due to in starting if quantity of semiconductor increases the active sites on semiconductor surface is increase and more radicals form and this radicals are strong oxidant but after some amount,dye molecule are not available for adsorption. Hence others semiconductor particles not take part in degradation of dyes. Sec semiconductor Figure.3: Effect of amount variation of Nb 2 O 5 on malachite dye degradation, Effect of concentration variation of Dye and its effect [Malachite green] The concentration of dyes varies from M to M. at fixed concentration of Nb 2 O 5 =0.10 gm., ph= 8.5, the maximum effectiveness was observed at 8x10-5 concentration after that if concentration of dye increases adverse effect will be show. (Figure-4). It will be explained like that if irradiation period and semiconductor amount kept constant and dye concentration increase then more dye molecule will be present for absorbance on the semiconductor surface but after a certain amount if more dye was added, it imparts a darker color to the solution and acts as filter to the light reaching the semiconductor surface and degradation rate of Malachite green decreases. ISSN:

4 [Malachite Green] x 10-4 M k x 10 5 (sec -1 ) Figure.5: Variation in light intensity Effect of metal ions (common cation with same concentration) on degradation of malachite green The effect of addition of metal ions (Na +, Cl -, SO 4-2 and CO 3-2 ) on photo degradation efficiency of Nb 2 O 5 has been investigated, and results are reported in fig. (6).The result shows that the trace quantities of all the added metal ions enhance the rate of photocatalytic bleaching of Malachite green to some extent. Figure.4: Varying in dye concentration and its effect Variation in light intensity and its effect Light Intensity variation has been done and observation on degradation of malachite green are mentioned in given table and according to result it s clear that degradation rate is increases as the intensity of light increase, because if intensity amount increases it will increase the number of photons striking per unit time per unit area of the semiconductor. An almost linear behavior (Figure.5) shows between light intensity and rate of reaction. However, higher intensities are avoided due to thermal effects. Light Intensity (mw cm -2 ) k x 10 5 (sec -1 ) Figure. 6: Effect of common cataion on photo catalytic bleaching of Malachite green by Nb 2 O 5, Malachite green = 8x 10-5 M, Nb 2 O 5 = 0.10 g, M n+ = 0.5x10-3 M, ph= 8.5 The increase in the photocatalytic activity may be due to introduction of new trapping sites by incorporation of transition metal ions. On irradiation, electron migrates on metal where it becomes trapped and electron hole recombination i s suppressed. The hole is then free to diffuse to the semiconductor surface where oxidation of organic species can occur. (Scheme 2) As the surface of catalyst particles is negatively charged and hence, it permits more metal ions to get adsorbed on the Nb 2 O 5 particles surface and as consequence, the surface of semiconductor will become positively charged. As methylene blue dye is anionic dye, so it will face more Electrostatic attraction with cations (M n+ ) adsorbed on the semiconductor surface. The electron from Nb 2 O 5 conduction band is transferred to metal ion to convert it into its lower oxidation state, in turn transfer this electron to oxygen molecule. Thus prevent electron-hole recombination. At the same time, the positively charged vacancies(h + ) remaining in the valence band of Nb 2 O 5 can extract electron from hydroxyl ions in the solution to produce the hydroxyl radicals( OH). These hydroxyl radicals oxidize the dye molecule into colorless products. ISSN:

5 H + + H 2 O (ads) OH + H + H + + 2OH - OH + OH - The concentration of metal ions is very small and large concentrations are detrimental. Metal modification 1 Dye + hí 1Dye 1 (singlet excited state) 1 Dye 1 3 Dye 1 (triplet excited state) Nb 2 O 5 M n+ + e - M(n-1)+ + O2 M n+ +O 2 -. Nb 2 O 5 * (h + vb)+oh - Nb 2 O 5 * (h + vb + e - cb) M(n-1)+. Nb 2 O 5 + OH 3 Dye 1 + OH Degradation of the dye Super oxide ions (O 2 ) is reduced by H +, accounting for hydroperoxyl radical (HO 2 ) and hydroxyl radical production. O 2 + H + HO 2 2 O H + 2 OH + O 2 HO 2, OH and O 2 are strong oxidizing species and they react with dye molecules to oxidize them. In the second pathway where a dye absorbs radiation of suitable wavelength and excited to its first singlet state followed by intersystem crossing to triplet state. 1 Dye 0 hí 1 Dye 1 The excited dye may be oxidize to product by highly reactive hydroxyl radical ( OH). (5 (6 1 Dye 1 (singlet excited sta 3 Dye 1 (triplet excited stat 3 Dye 1 + OH / HO 2 /O 2 Products (Degradation) (9) Colorless End Figure 7. Metal-modified semiconductor photo catalyst particle The participation of OH radical as an active oxidizing species was confirmed using its scavenger, i.e. 2-propanol, where the rate of bleaching was drastically reduced. After continuous irradiation the formation of CO 2, sulphate ions and nitrate ions in bleached dye solution show that there is total destruction of organic compounds in this process. The end products are simple molecules and harmless to the environment. The whole process can be summarized as: C 23 H 25 N 2 (Malachite green) REFERENCES OH / HO 2 /O 2 CO 2 + NO SO H + + Na + + H 2 O + Cl - Int Mechanism: Photocatalytic over a semiconductor oxide such as Nb 2 O 5 is initiated by the absorption of photons with energy equal to, or greater than the band gap energy of the semiconductor (3.2 ev for anatase), producing electron hole (e-/h+) pairs. Where cb is conduction band and vb is valence band. The photo produced holes and electrons may migrate to the particle surface, where the holes can React with surface-bound hydroxyl groups (OH - ) and water molecules to form hydroxyl radicals ( OH). h + + OH - OH (2) h + + H 2 O The electrons in conduction band react with the adsorbed oxygen molecules to form super oxide ions (O 2 ). OH + H + (3) e - + O 2 (ads.) O 2 (ads.) (4) 1. Guaratini, C. C. I.; Zanoni, M. V. B.; Quim. Nova 2000, 23, Costa, R. C. C.; Lelis, M. F. F.; Bergo, R.; Fabris, J. D.; Ardisson, J. D; Lago, R. M.; Anais do 13º Congresso de Catálise, Foz do Iguaçu, Brasil, Ziolek, M.; Catal. Today 2003, 78, Oliveira, L. C. A.; Gonçalves, M.; Guerreiro, M. C.; Fabris, J. D.; Nb 2 O 5 + hí Nb 2 O 5 * + h + (vb) + e - (cb) Couceiro, P. R. C.; Sapag, (1) K.; Anais do 13º Congresso Brasileiro de Catálise, Foz do Iguaçu, Brasil, Oliveira, L. C. A; Ramalho, T. C.; Gonçalves, M.; Cereda, F.; Carvalho, K. T.; Nazarro, M. S., Sapag, K.;Chem. Phys. Lett. 2007, 446, Noronha, F. B.; Aranda, D. G. A.; Ordine, A. P.; Schmal, M.; Catal. Today 2000, 57, Nowak, I.; Ziolek, M.; Chem. Rev. 1999, 99, Gervasini, A.; Bennici, S.; Aueoux, A.; Guimon, C.; Appl. Catal. A: Gen. 2007, 331, 129. ISSN: