Efficient adsorptive removal of hazardous congo red dye using Ce-BTC@microcrystalline cellulose composite

Abstract

In this research, we developed a novel composite material, Ce-BTC@MCC, by combining a metal-organic framework (Ce-BTC) with microcrystalline cellulose (MCC), a recyclable natural product. The surface features of the novel Ce-BTC@MCC composite were carefully investigated through infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and N₂-adsorption/desorption. The ratio of Ce-BTC to MCC in the composite was systematically optimized based on adsorption performance experiments. The developed Ce-BTC@MCC composite significantly outperformed its individual components (Ce-BTC and MCC) in removing Congo Red (CR) dye from water. This enhanced performance is due to the synergistic effect between Ce-BTC and MCC, which enhances the adsorption capacity of the designed composite. A comprehensive investigation was conducted to assess the impact of various parameters, including contact time, pH, temperature, and initial concentration, on the adsorption process. The experimental adsorption data for CR were well-described by the Langmuir isotherm model. The optimized Ce-BTC@MCC composite (20 wt% Ce-BTC content) demonstrated a remarkable maximum adsorption capacity of 926.3 mg/g for CR. The adsorption kinetics followed a pseudo-second-order model (R² = 0.988), and both intraparticle and boundary layer diffusion influenced the rate-limiting step of the adsorption process. A plausible mechanism for the adsorption of CR onto the Ce-BTC@MCC surface was proposed. The results highlight the effectiveness, selectivity, and reusability of the eco-friendly Ce-BTC@MCC adsorbent for removing CR from different real water samples.

Keywords: Adsorptive removal; Aqueous environment; Ce-BTC@MCC composite; Congo red; Metal-organic framework (MOF).

Scheme 1

The formation mechanism of the Ce-BTC@MCC composite.

Fig. 1

PXRD patterns of [a] Ce-BTC, [b] MCC, and [c] Ce-BTC@MCC composite.

Fig. 2

FTIR spectra of [a] Ce-BTC, [b] MCC, and [c] the Ce-BTC@MCC composite.

Fig. 3

SEM images of [a] Ce-BTC, [b] MCC, and [c] Ce-BTC@MCC, and EDX images of [d] Ce-BTC, [e] MCC, and [f] Ce-BTC@MCC.

Fig. 4

N₂ adsorption/desorption isotherms with pore size distributions (PSDs; inset) for: [a] MCC, [b] Ce-BTC, and [c] the 20 wt% Ce-BTC@MCC composite.

Fig. 5

(a) Absorption spectra of CR dye in the presence of different adsorbent species and (b) the adsorption efficiency of the adsorbent species (experimental conditions: pH = 5.0, contact time = 30 min, temperature = 298 K, concentration of CR = 100 mg/L, and adsorbent dose = 0.4 g/L).

Fig. 6

(a) Effect of the solution pH (contact time = 30 min, temperature = 298 K, and concentration of CR = 100 mg/L). (b) Effect of contact time (pH = 5.0, temperature = 298 K, concentration of CR = 100 mg/L). (c) Effect of initial concentration (pH = 5.0, contact time = 30 min, temperature = 298 K). (d) Effect of temperature (pH = 5.0, contact time = 30 min, concentration of CR = 100 mg/L) on the adsorption of CR dye onto the Ce-BTC@MCC composite (adsorbent dose = 0.4 g/L).

Fig. 7

(a) Nonlinear fitting plots of the Langmuir, Freundlich, Temkin, Redlich-Peterson, and Hill adsorption isotherm models of CR on Ce-BTC@MCC. (b) Nonlinear fitting plots of pseudo-first-order, pseudo-second order, and Elovich kinetic models for the adsorption of CR on Ce-BTC@MCC. (c) Intraparticle diffusion for the adsorption of CR dye on the Ce-BTC@MCC composite. (d) The thermodynamic parameters were calculated by plotting lnKe versus 1/T. The experimental conditions are similar to those in Fig. 6.

Scheme 2

Adsorption mechanism of CR onto the Ce-BTC@MCC composite.

Fig. 8

FTIR spectra of [a] Ce-BTC@MCC, [b] CR dye, and [c] CR adsorbed at Ce-BTC@MCC.

Fig. 9

(a) Impact of interfering species on the adsorption of CR dye onto the Ce-BTC@MCC composite, (b) the efficiency of CR removal by Ce-BTC@MCC from various real water samples, and (c) the recyclability of Ce-BTC@MCC operated on CR dye (experimental conditions: pH = 5.0, contact time = 30 min, temperature = 298 K, concentration of CR = 100 mg/L, and adsorbent dose = 0.4 g/L).