Drum Stick Seed Powder as Smart Material for Water Purification: Role of Moringa oleifera Coagulant Protein-Coated Copper Phosphate Nanoflowers for the Removal of Heavy Toxic Metal Ions and Oxidative Degradation of Dyes from Water

摘要

Seed powder of vegetable drum stick (Moringa oleifera) is a household known material for the coagulation of impurities from water. We find from our lab experiments that this material indeed removes toxic inorganic heavy metal ions and organic dyes; however, the latter can be degraded in the presence of H2O, under Cu2+ as catalyst. To understand the details of the treatment of water that is taking place by this seed powder, a simple inorganic protein nanoflower system was developed using copper phosphate (CuP), and a low molecular weight, cationic, and coagulant protein of Moringa oleifera (MOCP), to result in the nanoflowers (NFs), CuPNF_MOCP. The CuPNE_MOCPs were synthesized at different ratios of inorganic versus protein components and characterized by spectroscopy and microscopy techniques. Both the time- and the protein concentration-dependent flower growth showed complete flower morphology within 24 h with tightly packed petals having smooth surface upon increasing the protein concentration as noticed from SEM. The anionic dyes were adsorbed more preferentially over the cationic ones by these NFs, due to the cationic charge present on MOCP, as understood by studying six different dyes of which three are anionic and three are cationic in nature. The dyes are oxidatively degraded by a Fenton-type mechanism that takes place between Cu2+ present in the NFs and added H2O2 with the generation of (OH)-O-center dot radicals. These NFs also adsorb heavy metal ions, such as Pb2+, Cd2+, and He+, with high selectivity of >99% for Pb2+. Upon adsorption of Pb2+, the surface of the NFs revealed needle-shaped structures at petal edges in their micrographs, where the needles were confirmed by elemental mapping, powder XRD, and energy dispersive X-ray spectroscopy. Thus, the water purification routinely carried out by the households using the drum stick seed powder is essentially due to the coagulant protein present in it. This has been demonstrated in the form of CuPNF_MOCP for scavenging toxic heavy metal ions and organic dyes from water sources. Hence, this study provides a lead for the purification of water in a sustainable manner.