Microwave assisted synthesis of ZnO-PbS heterojuction for degradation of organic pollutants under visible light

Abstract

PbS heterojunction were prepared by microwave irradiation to improve the organic pollutants degradation under visible light irradiation. Hexagonal (wurtzite) and cubic crystal structure of ZnO and PbS respectively were confirmed by PXRD. Nano-plate, nano-sponge and nano-sponge imprinted over nano-sheet like morphology of ZnO, PbS and ZnO-PbS respectively were revealed through FESEM analysis. HR-TEM analysis provides the formation of heterojunction. XPS analysis shows the presence of the ZnO-PbS heterojunction. UV-Visible spectroscopy confirms the enhanced visible light response of Zno-pbS heterojunction than the bare Zno. the pL and eiS results indicate ZnO-PbS heterojunction exhibited lowest recombination of excitons and electron transfer resistance. Synergistic effect of ZnO-PbS heterojunction leads to efficient degradation against organic pollutants than bare ZnO and PbS. Aniline and formaldehyde were successfully degraded around 95% and 79% respectively, under solar light irradiation. As-prepared photocatalysts obeys pseudo first order reaction kinetics. HPLC analysis also confirms the successful mineralization of organic pollutants into water and co 2 .Lead sulfide (PbS) has broad spectral response form visible to near-IR region due to its narrow direct band gap (0.41 eV). In recent years, PbS sensitized nanomaterial's are increased the visible light response and photo-conversion efficiencies. It has unique photo physical properties such as multi exciton generation (MEG), high absorption coefficients, size dependent optical properties and optoelectronic properties 23,24 .Recently, several methods are adopted for the preparation of ZnO-PbS heterojunction such as chemical bath deposition 25 , ultrasound deposition method 26 , low temperature method 27 , successive Ionic Layer Adsorption and Desorption method 28,29 , Radio Frequency Sputtering 30 and spin coating method 31 . In all the above methods, most of them have some difficulties and limitations to produce ZnO-PbS heterojunction such as long reaction time and cost of the equipment. Therefore, novel techniques required to overcome this problem to prepare the semiconductor coupled ZnO-PbS photocatalyst in large-scale production without any sacrification in efficiency.Microwave irradiation technique is a best alternative heating source for the preparation of nano materials due to its rapid chemical reaction with short span of time when compared to conventional methods. Microwave irradiation involves through dipolar polarization and ionic conduction, which helps for the preparation of nanostructured materials 32 . Microwave method is fast, uniform heat distribution, energy efficient and simple than other conventional methods. The size and morphology of the material can be easily controlled by the microwave parameters such as frequency, time and operating power. Therefore, microwave method is leading technique for homogeneous nucleation and fast crystallization, which leads to the preparation of nano-structured inorganic semiconductor photocatalyst. In recent ...

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