Highly ordered CaO from cuttlefish bone calcination for the efficient adsorption of methylene blue from water

Abstract

The aim of this study is to synthesize cheap and highly ordered CaO from cuttlefish bone (CFB) as a green alternative to conventional adsorbents such as activated carbon. This study focuses on the synthesis of highly ordered CaO via calcination of CFB, at two different temperatures (900 and 1000°C) and two holding times (0.5 and 1 h), as a potential green route for water remediation. The as-prepared highly ordered CaO was tested as an adsorbent using methylene blue (MB) as a model compound for dye contaminants in water. Different CaO adsorbent doses (0.05, 0.2, 0.4, and 0.6 g) were used, keeping the MB concentration fixed at 10 mg/L. The morphology and crystalline structure of the CFB before and after calcination was characterized via scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, while the thermal behavior and surface functionalities were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy, respectively. Adsorption experiments using different doses of CaO synthesized at 900°C for 0.5 h showed an MB removal efficiency as high as 98% by weight using 0.4 g (adsorbent)/L(solution). Two different adsorption models, the Langmuir adsorption model and the Freundlich adsorption model, along with pseudo-first-order and pseudo-second-order kinetic models, were studied to correlate the adsorption data. The removal of MB via highly ordered CaO adsorption was better modeled by the Langmuir adsorption isotherm giving (R² =0.93), thus proving a monolayer adsorption mechanism following pseudo-second-order kinetics (R²= 0.98), confirming that chemisorption reaction occurs between the MB dye molecule and CaO.

Keywords: calcination; calcium oxide (CaO); cuttlefish bone; methylene blue (dye); water remediation.

Schematic illustration of the proposed work.

FIGURE 1

CFB used for this study: (A) front side and (B) back side.

FIGURE 2

SEM images of cuttlefish bone: (A) pure washed CFB top dorsal part before calcination, (B) washed CFBP lamellae part before calcination, (C) washed CFBP calcined at 900°C 0.5 h, (D) washed CFBP calcined at 900°C 1 h, (E) washed CFBP calcined at 1000°C for 0.5 h, and (F) washed CFBP calcined at 1000°C 1 h.

FIGURE 3

EDS image of calcined cuttlefish bone.

FIGURE 4

BET adsorption and desorption isotherm for calcined CFB.

FIGURE 5

Pore size distribution of calcined CFBP.

FIGURE 6

Particle size distribution of calcined CFB. (A) CFB calcined at 900°C for 0.5 h, (B) CFB calcined at 900°Cfor 1.0 h, (C) CFB calcined at 1000°C for 0.5 h, and (D) CFB calcined at 1000°C for 1.0 h.

FIGURE 7

RD spectrum of CFB and calcined CFB at 900°C with a holding time of 0.5 h.

FIGURE 8

FTIR spectra of pure CFBP (referred to as CB in the picture) and calcined CFBP.

FIGURE 9

TGA and DTA curves of CFBP raw material.

FIGURE 10

UV-Vis spectrum of MB on different CaO bio sorbent dosage for different contact time, (A) UV-Vis spectra of methylene blue with 0.05 g CaO/20ml MB solution up to 24 Hour time, (B) UV-Vis spectra of methylene blue with 0.2 g CaO/20 ml MB solution up to 24 h, (C) UV-Vis spectra of methylene blue with 0.4 g CaO /20 ml MB solution up to 24 h and (D) UV-Vis spectra of methylene blue with 0.6 g CaO/20 ml MB solution up to 24 h.

FIGURE 11

Change in MB color (A) without addition of CaO and (B) upon addition of 0.05 g CaO after 24 h.

FIGURE 12

Removal % efficiency of 0.05 g, 0.2 g, 0.4 g, and 0.6 g calcined CFBP doses using 10 mg/L MB concentration.

FIGURE 13

UV–Vis spectra of MB solution with different doses of CaO for 24 h in natural light and in dark.

FIGURE 14

Langmuir isotherm studies for 0.05 g CaO adsorbent dose per 20 ml MB (10 mg/L).

FIGURE 15

Freundlich isotherm studies for 0.05 g CaO adsorbent dose per 20 ml MB (10 mg/L).

FIGURE 16

First-order kinetic model plot of 0.05 g/20 ml MB concentrations.

FIGURE 17

Second-order kinetic model plot of 0.05 g/20 ml MB concentrations.