Adsorption kinetics of simulated mixture wastewaters over porous Bi2MoO6@BiOCl@MOF-199 heterostructure

Abstract

In this work, we mainly investigate the adsorption properties of the simulated single and mixture wastewaters over porous Bi2MoO6@BiOCl@MOF-199 (BMO@BOC@MOF-199), including methylene blue (MB), rhodamine blue (RhB), methyl orange (MO) and chromium (VI). It is found that BMO@BOC@MOF-199 has a high adsorption capacity for MB, but a poor adsorption capacity for MO. Specifically, for single MB solution, 67%, 80% and 96% of MB are adsorbed by BMO@BOC, MOF-199 and BMO@BOC@MOF-199, respectively. The higher adsorption capacity of BMO@BOC@MOF-199 could be due to its higher surface area and larger pore volume. For single MO solution, nevertheless, only 16%, 13% and 7% of MO are adsorbed by BMO@BOC, MOF-199 and BMO@BOC@MOF-199, respectively. The different adsorption efficiency for MB and MO could be relative to their different molecular structures, which have different electrostatic interactions with adsorbent surface. For single RhB and single Cr(VI) solution, BMO@BOC@MOF-199 has adsorbed 30% RhB and 10% Cr(VI). In RhB-MO mixture solution, 32% RhB and 9% MO can be adsorbed by BMO@BOC@MOF-199, while in Cr(VI)–RhB-MO mixture solution, 7% Cr(VI), 3% RhB and 42% MO can be adsorbed by BMO@BOC@MOF-199. It is seen that in RhB-MO mixture solution, the adsorption efficiencies of RhB and MO by BMO@BOC@MOF-199 do not obviously change as compared to single RhB and single MO solution, while in Cr(VI)–RhB-MO mixture solution, the adsorption efficiency of MO has increased by 5 times, compared to single MO solution; but the adsorption efficiency of RhB has decreased by 9.7 times as compared to single RhB solution, and the adsorption efficiency of Cr(VI) has decreased slightly, compared to single Cr(VI) solution. The results are mainly attributed to the competitive adsorption on the adsorbent surface. This work can help us to understand the adsorption process for practical wastewater.