SYNTHESIS, CHARACTERIZATION OF ZnO NANO PHOTOCATALYSTS AND THEIR APPLICATION IN PHOTOREMEDIATION OF WASTE WATER

Abstract

Water scarcity and its contamination with toxic metal ions and organic dyes represent a serious worldwide problem in the 21stcentury. Today’s world faces alarming challenges in the rising demand for drinking water and conditions are particularly bad in developing countries with the rapid escalation of industrialization towards a developed society. The waste products generated from the textiles, chemicals, mining and metallurgical industries are mainly responsible for contaminating the water. This contaminated water contains non-biodegradable effluents such as heavy metal ions (Copper, Nickel, Cadmium, Arsenic etc.) and organic materials such as dyes that are carcinogenic to human beings and harmful to the environment because of their bioaccumulation, non-biodegradable property and toxicity even at low concentrations. In an effort to reduce the environmental effects of heavy metals and dyes, various techniques have been employed. However, these techniques are expensive and ineffective resulting in an intensively coloured discharge and high concentration of heavy metals from the treatment facilities. Nanotechnology is a promising field in waste water treatment. This study aimed at assessing the efficiency of synthesized ZnO nanoparticles in photodegradation of synthetic dyes and adsorption of heavy metal ions from waste water. The objectives of this study were to synthesizeZnO nanoparticles, characterize and apply it in adsorption of heavy metals and photodegradation of methyl orange dye. Methyl orange was used as a model dye and the heavy metal determined wereNi2+, Cd2+ and Cu2+. Precipitation technique was used to synthesize ZnO nanoparticles. Two samples L1 and L2 were synthesized. They were characterized using PXRD (Power X-ray Diffraction), FTIR (Fourier Transform Infra-Red), SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray Spectroscopy), methods of analysis. Photodegradation studies were carried out using solar and fluorescent light energy. The EDX results showed elemental composition of ZnO nanoparticles which showed 54.00% Zn, 44.07% O and 1.93% Mn impurities for L1and 55.34% Zn, 42.3% O and 2.37%Mn impurities for L2. The PXRD results showed diffraction peaks which were indexed to ZnO reference as per JCPDS file 80-0075. The average size of ZnO nanoparticles was found to be 26 nm. FTIR spectra showed a broad band at around 430 cm-1 with shoulder shape, characteristics of Zn-O bond. The images obtained by SEM showed rod shaped clusters of nanoparticles. They were distributed well within a range of 100 nm which is a favorable property to exhibit better photo catalytic activity. The results of heavy metal ions adsorption showed an increase in percentage removal with increase in adsorbent dose and contact time. There was a decrease with increase in heavy metal concentration (ppm). For photodegradation, the results indicated an increase in colour removal with increase in photocatalyst dose and contact time and a decrease with increase in concentration of methyl orange. In conclusion, ZnO nanoparticles used as an adsorbent and a photocatalyst is efficient and a promising technique for treatment of waste water from textile, paper and dyeing industry and metallurgical industries. It can act as an adsorbent for heavy metal ions and aphotocatalyst for degradation of synthetic dyes. Future studies could focus on possibilities of improving and commercializing this material through designing a treatment facility that incorporates it, with the aim of being used on large scale waste water treatment.