Carbon nanotube reinforced nanohybrid urea-hydroxyapatite fertilizer for an improved nutrients utilization efficiency and reducing environmental pollution

Abstract

An upgraded technology is needed in the agricultural sector in order to adopt sustainable practice to maintain high yield as well as reducing environmental pollution due to ammonia emissions attributed to mineral nitrogen fertilization. This study reports a modified urea-hydroxyapatite nanohybrids fertilizers incorporated with carbon nanotube for more efficient sustainable nutrients utilization and reduction of ammonia emissions from fertilizers application. The urea-hydroxyapatite fertilizer was mixed with carbon nanotube at varying ratio by mass percentage (Sample A = 1:0.5. B = 1:1, C = 1:2, and D = 1:3) using simple liquid immersion method. The assessment of all the samples and the control specimen (sample E) was conducted by subjecting them to the analysis of thermogravimetric at intervals of 20 min to 200 min, to determine their nitrogen release behaviour activities. The morphological properties of urea-hydroxyapatite fertilizer with and without carbon nanotubes were compared using spectroscopic analysis (SEM, FTIR and XRD). The mechanical tests were conducted to examine the tensile and compressive strengths of the urea-hydroxyapatite fertilizer with carbon nanotubes using diametral tensile strength technique. The data obtained reveals that the control sample (urea-hydroxyapatite fertilizer) released 70 to 80 % urea within first 50minutes while the samples with carbon nanotubes retained urea for longer and 76 to 90 % amount of nitrogen release was recorded in the first 150minutes. It is revealed that the sample C with mixing ratio 1:2 exhibited best slow-release nitrogen properties. The sample C displayed a moderately large amount of nitrogen in form of urea in the initial phase and followed by slow-release even until the last minutes (200minutes). In the contrary, urea-hydroxyapatite fertilizer (control sample) which released heavily in the initial phase followed by the release of low and non-uniform quantities until its last drop towards 150minutes. SEM result demonstrated that chemical reaction occurred between urea-hydroxyapatites particles and carbon nanotubes. XRD patterns of urea-hydroxyapatites nanohybrid structures with carbon nanotubes demonstrate that the samples show the hydroxyapatite properties with monocrystalline structure. It is confirmed from the FTIR spectra that chemical functionalization cropped up between urea-hydroxyapatites nanohybrid and carbon nanotubes particles. A remarkable increase in the mechanical strength (150 % for the tensile strength and 100 % for the compressive strength) of the sample C structures confirms that introduction of carbon nanotubes improved its strength properties for the purpose of prolong stability while discharging its role as a nutrients slow-release fertilizer. Thus, the designed nano-fertilizer formulation of sample C mixing ratio can therefore be used as alternative way of improving the nutrients usage efficiency for the plants growth as well as to reduce the ammonia emission to the environment as pollutant.