EFFECT OF OPERATIONAL PARAMETER ON PHOTOCATALYTIC DEGRADATION OF OXAMYL PESTICIDE OF OPERATIONAL PARAMETER ON PHOTOCATALYTIC DEGRADATION OF OXAMYL PESTICIDE.”

: Flower like bismuth oxy chloride (BiOCl) was successfully synthesized by a simple hydrolytic method at room temperature. The precursor and as-prepared samples were characterized by X-ray diffraction (XRD), High Resolution Field Emission Scanning Electron Microscope (HR FESEM). The results indicated that the as-prepared BiOCl sample is self-assembled hierarchically with nano sheets. The photocatalytic activity of BiOCl was tested on the degradation of the Oxamyl (OM) under solar light irradiation. The results showed that pesticide molecules could be efficiently degraded over BiOCl under solar light irradiation. All the experiment were carried out in the following reaction condition, [OM] = 10 -4 mol dm -3 , BiOCl NPs= 40mg/50ml, pH= 6.3. Effect of operational parameter such as concentration of H 2 O 2 , K 2 S 2 O 8 , FeCl 3 , Fenton’s reagent (Fe 3+ /H 2 O 2 ) and N 2 , O 2 purging on the photocatalytic degradation was observed .


Introduction
Oxamyl is a carbamate insecticide/acaricide/nematicide that controls a broad spectrum of insects, mites, ticks, and roundworms. It may work both through systemic distributions in the target pest and on contact. Oxamyl is used on field crops, vegetables, fruits, and ornamental plants and may be applied directly onto plants or the soil surface. Oxamyl is a highly toxic compound in EPA toxicity class I. Oxamyl is extremely toxic to humans whether ingested, inhaled, or contact with the skin [1]. Agricultural wastewater, contaminated with such toxic pesticides, pollutes surface and groundwater through different ways. These types of pollution are very dangerous for eco system. Therefore, removals of such toxic pesticides are very essential to save the ecosystem.
Various methods are available to treat the waste water among this Advance Oxidation Processes (AOPs) are top on the class because it leads complete mineralization of pollutants. The main objective of this research has been the investigation of procedure for the removal of Oxamyl (OM) from polluted waters by using a photocatalysis process involving solar irradiation and

Characterization Methods
X-ray diffraction patterns (XRD) of the prepared samples were recorded on a PANalytical Empyrean PC equipped with Cu Kα radiation (40kV, 20mA). The surface morphology of the samples was observed using High resolution field emission scanning electron microscope (HR FESEM). The HR FESEM is from Zeiss, model name ULTRA Plus.

Measurement of Photocatalytic Activity
Pesticide solution was freshly prepared by dissolving in double distilled/deionized water. Prior to light experiments, dark (adsorption) experiments were carried out to know the extent of adsorption of the pesticide on the catalyst. For solar experiments, pesticide solution of 50 mL was taken in double walled vessel with known amount of the catalyst. The solution was illuminated under bright solar light. At specific time intervals, an aliquot (3 ml) of the mixture was withdrawn and centrifuged for 2 minutes at the rate of 3500 rpm to remove the flower like BiOCl particles. A PC based double beam spectrophotometer 2202 of Systronics has been used for measuring absorbance at different time intervals. The intensity of light was measured by a Lux meter (Lutron LX-101). The pH and conductivity of the solution was constantly been monitored using a pH meter and conductivity meter. pH was adjusted by the addition of either NaOH or H 2 SO 4 . The efficiency of photocatalytic process was calculated as: Where C o is the initial absorbance and C is the absorbance at different time intervals of photocatalytic process.  From the x-ray patterns the broadening of the diffraction peaks of the nanoparticles is obvious which is characteristic of nanosized by applying Debye-scherrer formula.

D =
Where D is the mean particle size, λ is the wavelength of incident X-ray (1.5406 ˚A), θ is the degree of the diffraction peak, and β is the full width at half maximum (FWHM) of the XRD peak appearing at the diffraction angle θ. The broadening of the absorption spectrum could be due to the quantum confinement of the nanoparticles. The mean calculated crystallite size of the BiOCl nanoparticles shows that the synthesized nanoparticle is 45 nm.

Effect of H 2 O 2
Hydroxyl radicals play an important role in the photocatlytic degradation of pesticides. Studies showed that H 2 O 2 could enhance the formation of hydroxyl radicals as well as inhibit the electron/hole (e -/h + ) pair recombination. Therefore the photocatalytic degradation of oxamyl pesticide has been conducted at different concentration of H 2 O 2 as shown in Fig. 3. The results indicated that the rate of degradation of OM increased with increasing concentration up to 4.0 × 10 -6 mol dm -3 of H 2 O 2 above this concentration, degradation efficiency was found to be decreased. This is because hydrogen peroxide could have inhibited the electron-hole recombination by accepting photogenerated electron from the conduction band of semiconductor and promoted charge separation and also form HO• radicals [4] according to Eqs. (1), (2).

Effect of K 2 S 2 O 8
Amount of sulphate ion (SO 4 −• ) is one of the main parameters to influence photocatalytic processes. In this study, to obtain the optimal initial sulphate ion (SO 4 −• ) concentration, the investigation was carried out in the range of 2 x 10 -6 to 1 x 10 -5 mol dm -3 . The results are shown in Fig. 4. It can be seen that degradation rate of Oxamyl distinctly increased with the increasing amount of sulphate ion (SO 4 −• ).
The decreased in rate of photodegradation above optimal concentration 2.0 × 10 -6 mol dm -3 is due to the adsorption of sulphate ions formed during the reaction on surface of BiOCl deactivating a section of photo-catalyst [5].

Effect of FeCl 3
The effect of FeCl 3 on the degradation efficiency has been studied by varying the concentration from 2 x 10 -6 to 10 -5 mol dm -3 . The rate constant values increased 3.22 x 10 -4 s -1 with the increase in concentration of FeCl 3 2.0 × 10 -6 mol dm-3. Thereafter, rate constant values decreased to 1.41 x 10 -4 s -1 on further increase in concentration of FeCl 3 up to 10 × 10 -6 mol dm -3 . The results have been reported in Fig. 5. Ferric ion (Fe 3+ ) are known to behave as an electron scavenger (Eq. (11)) thus preventing the recombination of electron hole pairs. Under the experimental conditions the following reactions become significant [6].

Effect of Fenton's Reagent (Fe 3+ :H 2 O 2 )
Homogenous catalysis by Fenton's reagent has been one of the most applied AOPs for its ability to degrade high loadsof organic compounds even in highly saline conditions. In Fenton's process Fe 3+ If catalyst used with Fenton's process the process become more effective H 2 O 2 might be generated via the BiOCl photocatalysis also participate in the reaction. Many researchers have

Effect of Bubbling of N 2 And O 2
In this parameter the N 2 and O 2 gas purged in the photocatalysis system to know the effect of these gases in photocatalytic degradation of OM under chosen reaction conditions. Two different experiments have been carried out in first experiment N 2 gas purged and in second experiment O 2 gas purged taking same reaction condition. We have observed that dissolved N 2 and O 2 gases play significant role in the degradation of dissolved organic pollutants. The experimental results indicated that the degradation of OM was much higher in the presence of molecular oxygen. [8].
The mechanism can be explained as follows:

Effect of Other Catalyst
The effects of various photocatalysts such as flowerlike nano BiOCl, nano BiOCl, bulk BiOCl, bulk ZnO, nano ZnO on degradation have been investigated at same condition. The results are shown in Fig. 7  and degradation of Oxamyl. The highest photocatalytic activity was observed in the presence of flower like BiOCl. The results showed that flower like nano BiOCl was most efficient than other catalyst. The order of activities of the photocatalysts flowerlike nano BiOCl > nano BiOCl > nano ZnO > bulk BiOCl > bulk ZnO. Hierarchical structures could enhance solar light utilization significantly because of the multiple reflections of ultraviolet and visible light within the interior structure of the flower like BiOCl. Such enhancements could generate more of •OH radiclas, electrons and holes and thus that can promote photocatalytic activity in the flower like nano BiOCl sample [9].

Conclusions and Recommendations
Flower like nano BiOCl synthesized by hydrolysed method. BiOCl shows promising catalytic activity in solar for oxamyl pesticide degradation. Various operational parameters such as H 2 O 2 , K 2 S 2 O 8 , FeCl 3 , Fenton's reagent (Fe 3+ /H 2 O 2 ) and N 2 , O 2 purging etc. affects the photoctalysis poetesses. Addition of oxidants and electron scavenger enhance the photocatalysis process. Homogenous photocatalysis and combination of heterogeneous and homogenous process also a very good technique to treat the waste water. This research opens new possibilities to provide some insight into nano sized and hierarchical structure semiconductors photocatalysts for degrading organic pollutants and other applications.