A green extraction process of nanocarbon dots from prawn shells, and its reinforcement in epoxy polymers

Abstract

Exoskeletons of prawn, shrimp, and crab discarded as waste are rich sources of inorganic and organic materials. Currently, these discards are mainly utilized for the extraction of chitin and less attention is paid to the recovery of other organic constituents present in the exoskeletons. The present study aimed to synthesize nano carbon dot (CD) and chitin from prawn shell, and utilization of CD as an additive to epoxy polymers to obtain a corrosion resistant polymer coating. Nano CDs were synthesized through a hydrothermal carbonization process and the characteristics were evaluated using spectrophotometric, fluorescence, and Fourier transform infrared spectroscopy studies. The CD reinforced bisphenol epoxy polymer composite coated over boat building steel exhibited the least defect, which in turn imparted the highest polarization resistance with the lowest capacitance. Chemical and morphological data of epoxy polymer composite highlighted the interaction of NH2 present in CD with polymer matrix. The functional group NH2 from CD synergistically acted along with hardener to form a pore free epoxy coating. Hydrothermal process of prawn shell enabled to extract chitin as evidenced by their spectral signature peaks. This study gave two economically important products through a green synthesis protocol.

Epoxy polymers reinforced with phosphorus‐doped carbon dots for enhanced corrosion protection of carbon steel in marine environments

“…The size of the particle ranges between 6 and 8 nm in diameter. The micrographs were comparable to the TEM image shown for CD derived from prawn shell and fish scale [14,21] F F I G U R E 4 TEM image of phosphorus-doped carbon dot.…”

“…Similar behavior was shown while prawn shell‐derived CD was reinforced in Bisphenol A epoxy polymers. [ 14 ] Multiplets in the 2800–3000 cm −1 region was specifically due to the C–H vibrational stretching under different environments. PCD reinforcement in epoxy 1 exhibited absorption with higher intensities and this was due to the CH 2 /CH 3 groups added to the composite from PCD.…”

“…Epoxy 1 interacted with PCD through conjugated double bonds. [ 14 ] Epoxy 2FTIR spectrum of epoxy 2 and PCD‐epoxy 2 polymeric matrix were shown in Figure 6b. The hydrogen‐bonded OH groups exhibited around 3200–3550 cm −1 with a sharper absorption in the case of PCD‐reinforced epoxy 2 compared to epoxy 2 alone.…”

“…Different concentrations of PCD are added into three different epoxy polymers namely Bisphenol A (epoxy 1), Dobeckot 520 F (hardener 758) (epoxy 2), and Araldite LY556 (epoxy 3). The reinforcement of PCD in the epoxy polymer follows the procedure outlined in Ashraf et al [ 14 ] with additional details provided in Supporting Information: . The resin of the three epoxy polymers is reinforced with moisture‐free nano PCD through sonication and then combined with respective hardeners in a 1:2 ratio.…”

“…PCD reinforcement in epoxy 1 exhibited absorption with higher intensities with PCD through conjugated double bonds. [14] F I G U R E 5 Scanning electron microscope images of (a) (i) epoxy 1 coated steel panel, (ii) phosphorus-doped carbon dot (PCD) reinforced epoxy 1 coated steel panels (b) (i) epoxy 2 coated steel panels (ii) PCD-reinforced epoxy 2 coated steel panels (c) (i) epoxy 3 coated steel panels (ii) PCD-reinforced epoxy 3 coated steel panels.…”