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

In this work, we mainly investigate the adsorption properties of the simulated single and mixture wastewaters over porous Bi2MoO6@[email protected] ([email protected]@MOF-199), including methylene blue (MB), rhodamine blue (RhB), methyl orange (MO) and chromium (VI). It is found that [email protected]@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 [email protected], MOF-199 and [email protected]@MOF-199, respectively. The higher adsorption capacity of [email protected]@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 [email protected], MOF-199 and [email protected]@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, [email protected]@MOF-199 has adsorbed 30% RhB and 10% Cr(VI). In RhB-MO mixture solution, 32% RhB and 9% MO can be adsorbed by [email protected]@MOF-199, while in Cr(VI)–RhB-MO mixture solution, 7% Cr(VI), 3% RhB and 42% MO can be adsorbed by [email protected]@MOF-199. It is seen that in RhB-MO mixture solution, the adsorption efficiencies of RhB and MO by [email protected]@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.