Synthesis of Carbon Nanotubes (CNTs) from Poultry Litter for Treatment of Heavy Metals

Abstract

Poultry litter is one type of agricultural waste being generated in our country as a result of raising more than 146 million commercial and domestic poultry birds. This waste find its final disposal in the field as soil fertilizer or amendment. However, the uncontrolled use of poultry litter for this purpose can result in environmental impacts such as the emission of methane, a greenhouse gas. Various other options like thermochemical conversion of this waste can be a solution to this problem. Poultry litter can be a low-cost carbon sources for synthesis of Carbon Nanotubes (CNTs). In this study efforts have been mad to utilize the cheap and readily available carbon source for synthesis of CNTs in the presence of Ni/Mo/MgO as a catalyst through combustion technique. Molar ratios of Ni, Mo and MgO as catalytic precursors were optimized using response surface methodology (RSM) to obtain the maximum CNTs yield. The optimum mole ratio of catalyst (4:0.2:1) was found to yield more carbon product. Further, process parameters such as combustion temperature, time, and polymer & catalyst weight were also optimized by RSM using Box– Behnken three-level and four-factorial design. The best possible combination of process parameters noted were (combustion time of 12 min, at a temperature of 825oC, and catalyst weight of 100 mg) in order to gain yield of CNTs (44.21%). Structure and morphology was confirmed through X-ray Diffractometer (X-RD) & Scanning Electron Microscopy (SEM). The environmental application of these carbon nanotubes was tested in lab with synthetic chromium solution. Different experimental conditions (pH, dosage of adsorbent and the contact time) that enhances the adsorption of Cr (VI) by carbon nanotubes were studied. UV-Visible spectrophotometer was used to measure the absorbance of Cr (VI) at 540 nm. It was found that 81.83% of Cr (VI) removal is achieved by using 8 mg of CNTs at pH 3 with 400 rpm, and 180 min of contact time. This makes CNTs from poultry waste as potential adsorbent for heavy metals.