Adsorption of Methylene Blue from Aqueous Solution Using Gelatin-Based Carboxylic Acid-Functionalized Carbon Nanotubes@Metal–Organic Framework Composite Beads

HIGHLIGHTS: A new gelatin composite was used to remove methylene blue. The adsorbent was composed of carbon nanotubes, a metal–organic framework and gelatin. The adsorbent had a simple preparation process and was friendly to the environment. The fixation of carbon nanomaterials with gelatin as the substrate avoided secondary pollution. Using carbon nanotubes as the intermediate improved the adsorption capacity. ABSTRACT: A novel gelatin-based functionalized carbon nanotubes@metal–organic framework (F-CNTs@MOF@Gel) adsorbent was prepared by the green and simple method for the adsorption of methylene blue (MB). Cu-BTC (also known as HKUST-1) was selected as the MOF type. F-CNTs@Cu-BTC particles were fixed by gelatin, thus avoiding the secondary pollution of carbon nanomaterial particles to the environment. CNTs were used as the connecting skeleton to make more effective adsorption sites exposed on the surface of the internal pore structure of the adsorbent. In this paper, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), thermogravimetry (TGA) and BET analysis methods were used to characterize the new adsorbent. The effects of time, temperature, pH, dosage and initial concentration on the adsorption process were investigated by batch adsorption experiments. The adsorption mechanism was further analyzed by several commonly used kinetic and isotherm models, and the reliability of several fitting models was evaluated by the Akaike information criterion (AIC), Bayesian information criterion (BIC) and Hannan information criterion (HIC). After five regeneration experiments, the adsorbent still had 61.23% adsorption capacity. In general, the new adsorbent studied in this paper has an optimistic application prospect.