Photocatalytic degradation of insectisides

Introduction: –

The insect powders are widely used for the protection of harvests from harmful insects. However, there is a negative impact for their usage on the environment, beside their effects on human wellness. Insecticides are risky chemical compounds, because they are carcenogenous, and bioaccumulative. Hence, there presence in the food-chain is so a major hazard to human wellness. Many surveies were carried out in seeking to minimise unsafe chemical substances, such as chlorophenols and dyes utilizing accelerators in an aqueous environment. Phenol derived functions are involved in the synthesis of many chemical compounds and are often found as pollutants of natural Waterss. Photochemical transmutation can be utile to extinguish phenolic compounds. The exposure catalytic transmutation of a phenyl-urea weedkiller was investigated utilizing tio2 and zno. Many researches were carried out in seeking to happen ways to photo degrade organic pollutants.

The exposure catalytic debasement of insecticide methomyl in H2O, utilizing TiO2 and ZnO ( Merck ) , under UV ( 366 nanometer ) was studied. The influence of the accelerator concentration and pH was investigated. The optimum concentration of the accelerator was found to be 2.0 g/l. It was found that ZnO is a better accelerator than TiO2 under the same reaction conditions. Besides, the influence of NaCl was studied. The presence of Cl & A ; acirc ; & A ; circ ; ‘ significantly affects the exposure debasement of the pollutant.

Methomyl is a wide spectrum insect powder. It is a really toxic and risky compound and a pollutant of environmental concern because of its high solubility in H2O ( 57,9 g/l at 25 & A ; deg ; C ) . Since the sorption affinity of methomyl to dirty is instead low, it can easy do taint of both land and surface H2O beginnings.

IUPAC name: S-methyl N- ( methylcarbamoyloxy ) thioacetimidate.

Although biological procedures are frequently most economical for a contaminated site killing and an industrial waste intervention, the advanced oxidization procedures ( AOPs ) provide an effectual agencies of quickly treated compounds with the efficient procedure control. Methomyl has besides been photodegradated by utilizing AOP. A different accelerator has been used, largely TiO2 [ 4-8 ] . Photo-Fenton reaction was besides employed.

The purpose of the present work is to analyze the exposure catalytic debasement of insecticide methomyl in H2O utilizing TiO2 and ZnO ( Merck ) under UV visible radiation ( 366 nanometer ) .The influence of the accelerator concentration, pH and NaCl concentration was studied.

Methodology: –

Hydrochloric acid, Na chloride and Na hydrated oxide ( all p.a. ) were obtained commercially.TiO2, Merck Eusolex & A ; reg ; T ( anatase alteration ) , and ZnO ( Merck ) were used as standard. Methomyl was obtained from DuPont ( analytical class, 99.8 % ) . Deionised H2O was obtained from a Milipore Waters Milli Q purification unit. Irradiations under UV visible radiation ( 366 nm ) were performed in an unfastened flask made of a quartz glass ( 20 milliliter volume ) with the UV lamp ( 2×8 W ) placed 5 centimeter from the surface of the reaction mixture.

The exposure debasement of methomyl was studied by fixing a solution incorporating 16.4 mg/l of methomyl and a certain sum of the accelerator. In a typical experiment, 15 milliliter of the solution was used. Then, the lamp was switched on and during the irradiation the agitation was applied, and after an appropriate clip of irradiation the suspension was sampled. The reaction mixtures were kept at 20 & A ; deg ; C. The concentration of methomyl was determined after the centrifugation of a sample by UV-Vis spectrophotometer at & A ; lambda ; max = 234 nanometer, and by HPLC. The features of the HPLC instrument are as follows: HPLC Instrument GBC, a pump LC 1120, a UV-Vis sensor LC 1205, a manual injector RHEODYNE 7725i, a column ZORBAX Eclipse XDB-C8 ( 4.6 & A ; times ; 150 millimeter, 5 & A ; mu ; m ) , a nomadic stage acetonitrile: H2O ( 25:75, flow rate 1.0 cm3 min-1 ) , wavelength 234 nanometer. pH of the samples was adjusted by adding a dilute NaOH and HCl and measured utilizing a pH metre ( PHM93 mention pH metre, Radiometer.

Result and treatment: –

UV-Vis spectra alterations

The alterations in the soaking up spectra of the methomyl solution during the photocatalytic debasement at different irradiation times are presented in Fig 2. The insect powder shows a set with a maximal soaking up at 234 nanometer. The lessening of the soaking up extremum really indicates a rapid debasement of the insect powder.

Fig2. UV-Vis spectra alterations of methomyl ( 16.4 mg/l ) inaqueous TiO2 scattering ( concentration of TiO2: 1 g/l ) irradiated with UV lamp ( 366 nanometer ) .

The consequence of the accelerator concentration

The consequence of the accelerator concentration ( TiO2 ) on the exposure debasement efficiency was shown in Figure3. The exposure debasement efficiency increased with increased concentration of the exposure accelerator, reached

the highest value at 2.0 g/l and than decreased. The possible account for this phenomenon is the fact that when all insect powder molecules are adsorbed on TiO2, the add-on of higher measures of TiO2 would hold no consequence on the exposure debasement efficiency. Negligible debasement consequence was observed if accelerator or irradiation were applied individually.

Figure 3. The consequence of the concentration of TiO2 on the photodegradation

efficiency ( X = ( C0-C ) /C0 ) of methomyl at irradiation

clip of 6.0 H ( concentration of methomyl: 16.4 mg/l ) .

The consequence of pH

It is good known that pH value has an influence on the rate of debasement of some organic compounds in exposure catalytic procedures [ 10,11 ] . The photo debasement of methomyl was studied at three different pH values ( 3.5, 5.6 and 9.0 ) . The pH was adjusted the add-on of HCl ( 3.5 ) or NaOH ( 9.0 ) . The 3rd value is the pH of the pure insecticide solution in deionised H2O. The obtained consequences ( Figure 4 ) imply that the photo debasement rate is highest in the acidic solution and lowest in the alkalic solution.

Figure 4. The consequence of pH on the photodegradation rate of methomyl ( insecticide concentration: 16.4 mg/l ; catalyst concentration: 2.0 g/l of TiO2 ) .

The consequence of NaCl

A common inorganic ion, chloride ion, was employed as Na chloride to analyze the photodegradation rate of methomyl. The influence of different concentrations of Na chloride ( 0-5 % w/v ) on the pho to debasement rate of methomyl is presented in Figure 5. The lessening of the photodegradation of methomyl in the presence of chloride ions is due to the hole scavenging belongingss of chloride ions.

Figure 5. The consequence of NaCl concentration on the photodegradation

rate of methomyl ( insecticide concentration: 16.4 mg/l,

accelerator concentration: 2.0 g/l of TiO2 ) .

The consequence of the accelerator type

ZnO is besides often used in AOP. The biggest advantage of ZnO in comparing to TiO2 is that it absorbs over a larger fraction of UV spectrum. On the other manus, ZnO exhibits a inclination to fade out and photo decompose [ 13 ] . The obtained consequences ( Figure 6 ) showed that the photodegradation was much faster when ZnO was used in comparing to the reaction with TiO2.

Figure 6. The consequence of the accelerator type on the photodegradation rate of methomyl ( insecticide concentration: 16.4 mg/l, accelerator concentration: 2.0 g/l ) .

Decision: –

The obtained consequences of the photodegradation of methomyl by UV visible radiation ( 366 nm ) indicated that the photodegradation was affected by the initial accelerator concentration, pH value and the type of accelerator. The presence of NaCl led to the suppression of the exposure debasement procedure.


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