Green synthesis and characterization of iron nano carbon dot fertilizer and its incubation study in a calcareous soil

The most obvious problem of calcareous soils is lack of plant available iron. Nano fertilizers are a suitable option to meet the needs of the plant with the high efficiency. The aim of this study was the green synthesis of nanocarbon dot iron fertilizers in two forms, uncoated and coated with polylactic acid polymer, and the incubation study of these fertilizers in a period of one month in a calcareous soil.

The green synthesis of iron nano carbon dot sample was done using lemon juice (as the carbon base of fertilizer) and Ferrous sulfate heptahydrate by hydrothermal method and the iron nano carbon dot sample was synthesized by polylactic acid polymer coating and test samples after synthesis to confirm the loading of iron on the carbon dot sample and also to confirm the successful coating of the synthesized iron nano carbon dot fertilizer by means of UV, XRD, Fluorescent Spectrophotometric, TEM, FESEM, EDAX, FTIR, DLS and Zeta Potential were characterized. In order to investigate the effect of synthesized iron nanocarbon dot on the availability of iron in a calcareous soil, an incubation experiment was conducted in a completely random design in 3 replications. The treatments include control (without nano carbon dot application), iron sulfate, sequestrin (commercial) and synthesized iron nano carbon dot loaded with iron (as two separate treatments without coating and coated with polylactic acid polymer) at levels 5, 10 and 20 mg Fe kg-1 soil (total of 9 treatments with 3 replications). At the end of the incubation period (720 hours), the extractable iron content of the soil was determined with DTPA. Also, in order to investigate the changes in the extractable iron of soil with DTPA with time, the amount of iron extracted in soil with DTPA in three times of 3, 360 and 720 hours in control treatments without fertilizer, treatment of 5 mg kg-1 soil iron soil from different sources of iron were compared with each other.

The successful loading of iron on the surface of nano-carbon iron dots without coating and coated with polylactic acid polymer was confirmed by XRD, UV-VIS, FTIR and scanning and transmission electron microscopes. The amount of total iron in the uncoated sample was equal to 4.98% and in the sample coated with polylactic acid it was equal to 1%. The results of the incubation showed that extractable iron in the soil with DTPA increased significantly.The highest concentration of iron in the soil at the end of 720 hours is related to the sample coated with iron nano carbon dot with polylactic acid polymer with an iron concentration of 20 mg kg-1 equal to 9.58 mg kg-1. Also, by examining the changes in iron release in treatments with a concentration of 5 mg kg-1 in three time periods of 3, 360 and 720 hours, it was observed that the coated treatment caused a significant increase in iron compared to the iron sequestrin treatment. Iron sequestrin treatment after 720 hours compared to the first 3 hours increased by about 60% (from 5.19 to 8.28 mg kg-1), while the amount of iron extracted with DTPA in the nano carbon dot iron coated treatment In this period of time, it increased by about 400% (from 1.36 to 6.63 mg kg-1).

According to the results of the research, it can be said that among the experimental treatments regarding the slow release of iron, the sample coated with natural and biodegradable polylactic polymer with an iron concentration of 20 mg kg-1has the highest iron release compared to had other treatments,