PHOTOCATALYTIC DEGRADATION AND REMOVAL OF HEAVY METALS IN PHARMACEUTICAL WASTE BY SELENIUM DOPED ZNO by Journal 4 Research

Journal for Research | Volume 02 | Issue 05 | July 2016 ISSN: 2395-7549

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor L Shruthi Research Scholar DOS in Environmental Science University of Mysore

Shyni Student DOS in Environmental Science University of Mysore

K Jagadish Research Scholar Centre for Materials Science and Technology University of Mysore

Dr.S.Srikantaswamy Associate Professor DOS in Environmental Science University of Mysore

M.R Abhilash Research Scholar DOS in Environmental Science University of Mysore

Abstract In recent years pharmaceutical wastes (PW) deposal of has become a major difficulty for the environment. Therefore, pharmaceutical waste removal is very necessary before its discharge from the pharma industry. The separation of drugs containing organic compounds in wastewater streams is failed by convectional and biological treatments. Thus, the reduction of harmful effects of pharmaceutical compounds is possible by heterogeneous photocatalysis process. Herein we reported the degradation of pharmaceutical concentration in pharmaceutical waste by heterogeneous photocatalyst ZnO doped with Selenium prepared by cost effective hydrothermal method. In addition the heavy metals in pharmaceutical waste were also removed by ZnO/Se nanocomposite. The average band gap of nanocomposite (~2.5 eV) increase the photocatalytic activity and degrade the organic compounds in pharmaceutical waste. The heavy metals get adsorbed on the high surface area of nanocomposite and removed completely by filtration method. The Selenium doped ZnO photocatalyst semiconductor was characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDAX) and also the characteristic crystalline forms of ZnO/Se nanocomposite was confirmed by XRD. The functional groups and particle size distribution of ZnO/Se nanocomposite was characterized by FTIR and DLS respectively. The reduction of organic compounds in the pharmaceutical waste was confirmed by COD analysis and removal of heavy metals was performed by AAS analysis. Keywords: Sol-gel, Hydrothermal, Nanocomposite, Pharmaceutical, Water Purification _______________________________________________________________________________________________________ I.

INTRODUCTION

The investigation of visible-light active semiconductor photocatalysts has gained huge applications in environmental nanotechnology. The degradation of organic compounds in pharmaceutical wastewater using ZnO and its composites is becoming the most extensive photocatalyst. The primary step in photocatalysis is the creation of pairs of Electron - hole further increasing excitation of band-gap ZnO. Oxidizing species will yield by migration of these pairs interface. Among various semiconductor photocatalysts (Fe2O3, ZnO, WO3, ZnS, CdS and SrTiO3) used, ZnO has emerged to be more efficient catalyst because it’s higher rate mineralization and efficient generation of more number of H 2O2 [1]. ZnO nanoparticle has more number of active sites with high surface activity. Among the various semiconducting materials, the investigation of TiO2 is widely employed, however for the degradation of organic compounds in aquatic systems ZnO exhibits better efficiency than TiO2 [2]. ZnO Doped with metal ions can influence the performance and affects the interfacial charge transfer of the photocatalysts. The largest enhancement of photoactivity through doping can be found in nanosized particles. However, ZnO has a wide band-gap (~3.37 eV) [3] and is excited by sun-light irradiation. Charge separation distances within the ZnO semiconductor particle, recombination speed of e─/h+ is too fast and resulting very less quantum yield [4]. A good photocatalyst ZnO nanocomposite has efficiency of e─/h+ pair separation and many research developed with focusing on increasing the photocatalytic efficiency in visible region. The modification of ZnO with metal, non-metal ion, rare earth metals and surface modificatio [5-16]. Transition metal ions like Fe3+, Cr3+, Co2+ and Mo2+ are usually employed to lower the band-gap and enhance the photocatalytic activity of

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

ZnO. Metal ion doped ZnO nanoparticle has considerable effects in the photocatalytic activity that photocatalytic degradation increases with metal ions doping. In our previous article the industrial wastewater treatment was carried out by using multiwalled carbon nanotube and polyvinyl alcohol nanocomposite for the degradation of organic compounds and removal of heavy metals [17]. The motivation of this study is in the published paper by Amal et al. [18]. The authors investigated the characteristics of selenium (Se IV) ions in aqueous TiO2 suspensions and they observed that a red-shift in the absorption threshold. In this research work, the attempt was made to dope ZnO with selenium (IV) ions to obtain a visible-light active photocatalyst. Song et al. [19] have synthesized Se (II)-doped In OOH by a mild solvothermal method and concluded that Se (II)-doping narrows the band-gap of the photocatalyst. This paper has the purpose of determining the photocatalytic properties of Se doped nano-ZnO, to elucidate the chemical nature, morphology and the effect of the selenium dopant on the activity of the photocatalyst. In the experimental part of the study, a series of Se doped ZnO nano-photocatalysts were prepared by means of a hydrothermal method and characterized by structural, chemical techniques. The photocatalytic activity of the Se doped ZnO was also determined by investigating the photocatalytic degradation of pharmaceutical and industrial wastewater. II. EXPERIMENTAL METHOD Synthesis of ZnO Nanoparticles by Sol-gel Method ZnO nanoparticles were synthesized by sol gel method using zinc nitrate and KOH as precursors. In this work, the aqueous solution (0.2 M) of zinc nitrate (Zn(NO3)2.6H2O) and the solution (0.4 M) of KOH were prepared with deionized water. The zinc nitrate weighed around 2.9749 g and it is taken in a beaker and exactly 1.22 g of KOH pellets were taken in another beaker. Measure 50 mL of deionised water and pour in to respected beakers. The KOH solution is taken in the beaker and slowly added into zinc nitrate solution which is taken in another beaker and it is kept on magnetic stirrer which helps in the proper mixing of both the solutions at room temperature which resulted in the formation of a white precipitation. The white product was centrifuged at 5000 rpm for 20 min and washed three times with distilled water. Then it is filtered by watsman’s filter paper. This filter paper was removed after filtration and kept for drying in hot air oven at the temperature of 60-80 oC for 3 hours. The calcinations were carried out for the obtained product at 500 °C in the presence of atmosphere air for 3 hr. Reaction between zinc ntrate and potassium hydroxide for the synthesis of Zinc oxide nanoparticle. Zn(NO3)2 + 2 KOH  ZnO + 2K(NO3)2 +H2O Preparation of Zinc Oxide Doped Selenium Nanocomposite The synthesis of ZnO-Se has been carried out using Moray autoclaves provided with the Teflon liners. The condition selected for the synthesis of ZnO-Se particles are T= 150 oC temperature. ZnO nanoparticles prepared by the solgel method were taken and around 0.2 g of this ZnO is weighed and taken in the Teflon liners. Around 0.2 g of selenium is weighed and taken in the same Teflon liners. Then exactly measure 15 ml of ethanol and it is poured in to the same Teflon liners. These contents are mixed thoroughly using glass rod to obtain a homogenous and relatively viscous solution. Stir the content for 10 minutes. Then these Teflon liners are placed in a Moray autoclave. Then the autoclaves were placed in the oven provided with temperature controller. The temperature of the oven was raised upto predetermined temperature for a desired period (5 hours). After 5 hours the autoclave is cooled in room temperature. The contents of the liners are thoroughly washed in ethanol repeatedly and later dried in an oven at 60 oC for 3 hours. These dried ZnO-Se nanoparticles were characterized like XRD, SEM, FTIR and UV and visible spectroscopy. Treatment of Pharmaceutical waste with ZnO-Se Nanocomposite The pharmaceutical waste samples were collected from the Jubilant Jenerics which is situated in Nanjanagud for physiochemical characterizations like AAS, DO, BOD, COD, TDS, pH and alkalinity. 20 mL of pharmaceutical wastewater is taken in conical flasks. Different concentration of ZnO-Se nanoparticles such as blank, 0.1g, 0.25g, 0.5g are added to the three respected conical flasks and kept in the presence of sunlight for around 12 hours and conical flask is kept in a mechanical shaker whole night (~12 hr). Then the above said blank and three treated samples were tested for COD to get the optimum concentration. In addition the different concentrations of composite (ZnO-Se) were analyzed in different pH condition to optimize the photodegradation level. The different pH conditions were 4, 7 and 10. The pH is reduced by adding 0.1M of HCl solution and the pH is increased by adding 0.1M of NaOH. III. RESULTS AND DISCUSSION X-Ray Diffraction (XRD) The crystalline study of obtained ZnO-Se Composite analysis was performed on XRD instrument of type a Rigaku desktop miniflex II X-ray powder diffractometer with Cu Kα radiation, (λ= 1.5406 °A) as the energy source.

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

Fig. 1: XRD spectra of ZnO-Se nanocomposite

An XRD analysis has been carried out to identify the formation of the Se doped ZnO phase. As shown in Fig. 1. The spectra shown different planes such as 100, 002, 101, 102, 110, 103, and 112 which are corresponds to the crystalline phase of ZnO. The different planes such as 100, 110, 102 and 201, are corresponding to the presence of Selenium metal in crystal form. The observed powder data for reveals the formation of Se doped ZnO a single phase wurtzite structure. As seen in the XRD patterns (Fig. 1), the substitution of Se did not cause any marked changes in the structure. Scanning Electron Microscope (SEM) SEM analysis was carried out on a ZEISS SEM microscope, model-evo/IS 15, Tokyo, Japan. Micrographs were taken at 5 kV and composites were coated with graphite before analysis.

Fig. 2: Morphology and microstructure analysis of a) ZnO and b) ZnO-Se nanocomposite by SEM

The SEM picture in Fig. 2a shows the typical ZnO nanoparticles have a diameter ranging from ~100 to 200 nm with a typical length up to ~1 micrometer. Fig. 2b shows a SEM image of Se doped ZnO nanoparticles, the nanoparticles will be growing on the sol gel and hydrothermal reaction and the non-uniformity of local precursor concentration and temperature causes the morphology of the products. This explains the near exact similarity in the morphology and dimensions of Se doped ZnO nanoparticles. Energy-Dispersive X-Ray Spectroscopy (EDAX) The energy-dispersive X-ray spectroscopy (EDAX) spectrum sample reveals only ZnO and Se signal peaks (Fig. 3). The approximate atomic ratio of Zn, O and Se is found to be 67.13, 24.96 and 7.92 respectively. This spectrum indicates that the ZnO/Se nanocomposite is in pure phase with showing nearly 10 at % doping of Se in the system. The EDAX spectrum also shows the weight percentage of Zn, O and Se nanocomposite in which the weight such as 44.61, 23.82 and 31.36 respectively.

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

Fig. 3: EDAX spectra of ZnO-Se nanocomposite

Fourier Transform Infra-Red Spectroscopy (FTIR) The Fourier Transform Infrared Spectra (Fig. 4) of the Se doped samples has been recorded in the 4000–400 cm-1 region to confirm the presence of Se doped ZnO material. The FTIR spectra was recorded for the nanocomposite ZnO/Se by KBr palette method and the absorption band in the region of 3550–3250 cm-1 has been assigned to the stretching vibration mode of a hydroxyl group. The first overtone at 1750 cm-1 is a crucial stretching mode of OH molecule in which it designate the presence of bound H2O on the surface of the sample. The band located at 450–510 cm-1 can be attributed to the ZnO stretching mode and O-Se-Se bond in the ZnO/Se nanocomposite.

Fig. 4: FTIR result of ZnO-Se nanocomposite

Dynamic Light Scattering (DLS) DLS is the most useful technique for characterizing nanomaterials in solutions, because of the Brownian motion of particles. The particle sizes of dispersed ZnO-Se were analyzed by using DLS. The as synthesized ZnO-Se nanoparticle were dispersed in a solvent nanopure water for the particle size distribution analysis. The particle size distribution was recorded in the different parameter, in which as synthesized nanomaterial distributed from 80 to 1100 nm with different percentage filling. The average particle size 184 was observed by the DLS (Fig. 5) analysis and also this results correlates the results of SEM analysis corresponds to dispersion.

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

Fig. 5: Particle size distribution of ZnO-Se nanocomposite

UV-Visible Spectra (UV-VIS) UV-Visible spectrum (Fig. 6) of Se-doped ZnO over the range of 200-800 nm showed that the synthesized nanoparticles are photoactive under visible light irradiation. The band gap of Se-doped ZnO was calculated using Tauc plot. For a semiconductor sample, it is, possible to determine the optical absorption near the band edge by the equation h= A(h-Eg)n/2 where , h , , Eg and A are absorption coefficients, plank’s constant, radiation frequency, band gap and a constant respectively. Where the n value is 1 to 4 in which it is the characteristics of the transition in a direct or indirect semiconductor. Construction of (h)1/2 versus h also called Tauc plot is necessary in order to get an accurate value of the band gap of solids. The band gap energy could be thus estimated to be 2.5 eV for Se-doped ZnO nanoparticles.

Fig. 6: UV-Visible spectra Se-doped ZnO nanoparticles

Atomic Absorption Spectroscopy Analysis (AAS) Pharmaceutical waste (PW) was analysed for heavy metals by Atomic absorption spectroscopy (AAS). The analysis shows that the presence of heavy metals copper (Cu), Nickel (Ni), cadmium (Cd), zinc (Zn) chromium (Cr) and lead (Pb) (Table 1). The sample was rich in copper content among all the heavy metals 1.158 mg/kg. Metals such as Chromium 0.415 mg/kg and lead 0.247 mg/kg were found at lower concentrations whereas cadmium, Nickel and zinc concentration was found to be 0.127, 0.145 and 0.131 mg/kg respectively. Table – 1 Heavy metal concentrations for the Pharmaceutical Waste (PW) Before treatment-pH7) Sl. No. Heavy Metal Concentration (mg/kg) 1 Copper 1.158 2 Cadmium 0.127 3 Lead 0.247 4 Chromium 0.415 5 Zinc 0.131 6 Nickel 0.145

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

Fig. 7: Graphical representations of Heavy metal concentrations in PW Table â&#x20AC;&#x201C; 2 Heavy metal concentration in different concentration of ZnO/Se composite Heavy metals concentration (mg/kg) ZnO/Se composite (g) Copper Chromium Lead Nickel Zinc Cadmium 0.0 1.158 0.415 0.247 0.145 0.131 0.127 0.1 1.104 0.397 0.216 0.113 0.114 0.121 0.25 0.972 0.351 0.197 0.001 0.105 0.113 0.5 0.421 0.211 0.147 0 0 0.097

Fig. 8: Graphical representation of treatment of pharmaceutical waste with different weight of ZnO/Se composite

The pharmaceutical effluent was treated with 0.0, 0.1, 0.25 and 0.5 g of ZnO-Se nanocomposite semiconductor photocatalyst in the presence of sunlight and the concentration was recorded before and after the treatment for the analysis of heavy metals (Table 2). The pharmaceutical effluent treated with 0.5 g of ZnO/Se nanocomposite is found to be optimum and the reduction of heavy metals concentration observed. The heavy metals such as nickel and zinc have removed completely and the gradual reduction of copper concentration is possible by using ZnO/Se nanocomposite. Here the pharmaceutical effluents were prepared for different pH conditions like 4, 7 and 10 by pH monitoring reagent 0.1 M HCl and 0.1 M NaOH. And these effluents were treated with 0.5 g of ZnO-Se. The Fig.4.11 shows that all the heavy metals degradation in pH 4 and pH 7 and pH 10. This shows that pH condition of the treatment method of the effluent alters the degradation effectively. The degradation was more in pH 4 (acidic condition) when compare to pH 7 and 10 due to surface charge on the nonmaterial, which increases the degradation process.

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

Fig. 9: Graphical representation of Heavy metal concentrations in PW after treatment with 0.5 g ZnO-Se composite at different pH condition

Chemical Oxygen Demand (COD) The analysis of organic content in the pharmaceutical waste was analyzed by using COD technique. The titration value is determined the organic content in mg/L (ppm) which is about presence of oxygen in the organic molecules which is present in the industrial pharmaceutical effluent. Table – 3 COD analysis for the PW in different ZnO-Se composite (pH 7) Sl No. ZnO/Se nanocomposite (g) COD (mg/kg) 1 0.0 1770 2 0.1 1650 3 0.25 960 4 0.5 250

Fig. 10: Graphical representation of COD in for the PW in different ZnO-Se composite (pH 7) Table – 4 COD analysis for the PW in different pH condition at 0.5 ZnO-Se concentrations Sl. No. Different pH condition for the ZnO-Se metal concentration (0.5 g) COD values Mg/L 1 4 120 2 7 250 3 10 255

Chemical Oxygen demand for the untreated and treated PW using ZnO-Se metal nanocomposite was performed and found that the presence of highest organic content in pharmaceutical waste. Furthermore 0.5 g of ZnO-Se metal nanocomposite to the PW at the acidic condition reduces the organic content by degrade the organic molecule in the presence of sunlight. IV. CONCLUSION The above study is very much important considering the effect of removal of heavy metals and degradation of pharmaceutical waste using ZnO/Se nanocomposite. The nanocomposite photocatalysts was prepared by an cost effective hydrothermal method and its having high surface area and surface charge which act as semiconductor materials with effective band gap energy. Characterization techniques showed that the Se is in O–Se–O linkages in the crystal lattice, the spherical images of nanomaterial

Photocatalytic Degradation And Removal of Heavy Metals in Pharmaceutical Waste by Selenium Doped ZnO Nano Composite Semiconductor (J4R/ Volume 02 / Issue 05 / 008)

with high surface area, particle size distribution with average particlae size 184 nm and the band gap energy 2.5 eV with semiconducting properties. The uses of selenium as dopant with ZnO nanoparticle increase the photocatalytic performance of nanocomposite. The heavy metals in pharmaceutical waste such Cu, Pb, Ni, Zn, Cd and Cr were reduced and the Ni and Zn were completely removed by treatment with the 0.5 g of nanocomposite. The COD values of pharmaceutical waste were reduced gradually by treatment with nanocomposite in which the organic compound presents in waste were degraded to purify in the pharmaceutical waste. REFERENCES [1] [2]

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