Comparative evaluation of BiOCl–NPls–AC composite performance for methylene blue dye removal from solution in the presence/absence of UV irradiation: Kinetic and isotherm studies

Abstract

This research is focused on two removal procedures namely adsorption and synergetic adsorption-photodegradation of methylene blue (MB) from aqueous solution by using bismuth oxychloride nanoplates loaded on activated carbon composite (BiOCl–NPls–AC composite) as a novel adsorbent/photocatalyst. In the present work, for the first time, the results of various and well-known kinetic and isotherm models of MB adsorption onto the BiOCl–NPls–AC composite (without UV irradiation) were reported and compared with those obtained from synergetic adsorption–photodegradation MB removal (under UV irradiation). After synthesizing the BiOCl–NPls by using a simple and low-cost method, the newly synthesized BiOCl–NPls and BiOCl–NPls–AC composite were characterized by using different methods (e.g. field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS), Brunauer, Emmett and Teller (BET), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), UV–Vis and raman spectroscopy). The effects of BiOCl–NPls–AC dose, pH, initial MB concentration, and contact time on the removal efficiency of MB were also investigated and optimized values established. The Langmuir model yields, with maximum adsorption capacities of 17.470 and 84.021 mg g−1, could describe the adsorption processes better than other isotherm models for both adsorption and especially synergetic adsorption–photodegradation procedures. Moreover, the adsorption processes were fitted to the pseudo-second-order and Elovich models better than other kinetic models for both adsorption and synergetic adsorption-photodegradation procedures. The results showed that the removal efficiency and adsorption capacity (98.88% and 86.021 mg/g) are higher for synergetic photodegradation and adsorption under UV light irradiation than only adsorption of the MB onto the BiOCl–NPls–AC composite in a dark place (72.50% and 17.470 mg/g). Finally, the stability of the BiOCl–NPls–AC composite regarding Bi leaching was evaluated.