Ultrasound assisted reductive degradation of toxic textile dye effluents using Sn nanoparticles

In this paper, we report the structural, chemical, and reductive degradation properties of Sn nanoparticles for degradation of Ramazol brilliant blue (RBB) dye effluents. The ultrasound assisted degradation is achieved without use of any harsh reducing agent in dark ambience. Sn nanoparticles with size similar to 15 nm were synthesized by chemical reduction method using NaBH4 (0.6 M) as reducing agent. The synthesized particles had tetragonal structure with orientation along (200), (101), (220), (211), (301), (112), (400), and (321) planes and do not have any additional impurity phases as determined using energy dispersive X-Ray spectroscopy, X-Ray diffraction technique and transmission electron microscopy. XPS analysis confirmed that majority of synthesized particles were in Sn2+ state with spin-orbit splitting at 8.3 eV with corresponding binding energy peaks at 485.8 eV (3d(5/2)) and 494.1 eV (3d(3/2)). A few particles were in Sn4+ state with spin orbit splitting at 8.5 eV and binding energy peaks at 487.1 eV (3d(5/2)) and 495.6 eV (3d(3/2)). The ultrasound assisted dye degradation efficiency of Sn nanoparticles reaches 85% within the initial 10 min of the water treatment process. The fast dye reduction is attributed to the rapid sono-chemical production of hydroxyl radicals and fast interaction between surface electrons of Sn and dye molecules. The Sn2+ ions lose two electrons during the reaction and switch to Sn4+ state leading to generation of hydroxyl radicals which is responsible for the decomposition of the dye molecules. The ultrasound assisted method follows the second order pseudo kinetics and degrades RBB dyes with an efficiency of 99% while the mechanical stirring method which obeys the first-order pseudo kinetics degrades the dye with an efficiency of 90%. The appropriate rate constant was 0.1414 min(-1) for ultrasound assisted method and 0.0512 min(-1) for mechanical stirring method. One of the advantages of the present technique is that it does not require any additional reducing agent to stimulate the reaction. The degradation efficiency (similar to 99%) is the highest for dye solution with neutral pH. The Sn nanoparticles were stable for four cycles and subsequently the efficiency reduces to 71% due to oxidation of the Sn nanoparticles. The XRD pattern of Sn particles after 4 cycles had peaks corresponding to (101), (211), and (112) planes of SnO2 and XPS spectrum show enhanced peaks for Sn4+ for recycled samples indicates the possibility of oxidation of Sn when repeated over 4th cycle.