| Arsenic has become one of the current challenges in water environmental governance due to its high toxicity and high mobility.Research and development of arsenic removal adsorbents with excellent performance is the key to controlling arsenic pollution in the water environment.This paper uses functionalized MOF graphene and two water-stable iron-based MOFs and zinc-based MOFs to synthesize MIL100（Fe）/rGO/δ-Mn O2 and Zn-MOF-74/rGO/PAM nanocomposites.The mechanism of eliminating trivalent arsenic（As（III））and pentavalent arsenic（As（V））in aqueous solutions was discussed and applied to the adsorption and removal of arsenic in water.In this study,a Fe-based metal-organic framework（MOF）（Institut Lavoisier materials:MIL-100（Fe））was functionalized with reduced graphene oxide（rGO）using a simple hydrothermal method and coated with birnessite type manganese oxide（δ-Mn O2）using a one-pot reaction process（MIL-100（Fe）/rGO/δ-Mn O2 nanocomposites）.To fully evaluate the adsorption of As（III）and As（V）on the MIL100（Fe）/rGO/δ-Mn O2nanocomposite,several control studies were carried out.The effect of controlling factors such as effect of p H,contact time,adsorbent dosage,temperature,initial concentration,and interferin g ions on As（III）and As（V）absorption was investigated.The adsorbent material has an As（III）adsorption capacity of 192.67 mg/g at p H 2 and an As（V）adsorption capacity of 162.07 mg/g.The composite material demonstrated efficient adsorption in a p H 2–9 solution due to the reduced graphene oxide flakes.The adsorption mechanism is confirmed by the pseudo-second-order kinetic model and the Langmuir isotherm model,verifying chemical adsorption and monolayer adsorption.The major processes that promote As ion adsorption are electrostatic interaction,oxidation,and complexation on the inner surface of the adsorbents.The graphene-enhanced MOF composite materials were developed by combining zinc-based metal organic framework particles with polyacrylamide polymer（PAM）and incorporating them with reduced graphene oxide flakes.A Zn-MOF-74/rGO/PAM adsorbent is used to effectively remove As（III）from water.More than 99.8%of As（III）can be removed in a 0.2 mg/L solution in 15 minutes to reach a drinkable level.The experimental kinetic data fits well with the pseudo-second-order kinetic model.According to the Langmuir model,the adsorption capacity of(qmax)is 282.4 mg/g at a p H of 10 and 25°C.The interaction of As ions with a large number of functional groups on the adsorbent’s surface is responsible for the efficient adsorption.Because the amino groups are linked to the metal clusters and the hydroxyl groups are widely distributed on the reduced graphene oxide flakes,As ions are more easily absorbed.The FTIR and XPS results indicate that As（III）is adsorbed on the composite material via chelation and ion exchange.According to thermodynamic data,the reaction is endothermic and spontaneous.The composite material has excellent p H stability,selectivity,and reusability.According to the aforementioned experimental results and conclusions,the adsorption capacity of MOF-based graphene nanocomposites for arsenic is substantially greater than that of conventional adsorbents.Furthermore,both adsorbents possess excellent adsorption capacity,selectivity,and regeneration capacity.The characteristics listed above are essential factors that should be considered throughout the process.At the same time,we summarize some strategies for addressing the new MOFs/rGO hybrid adsorbents include;（1）enhancing the durability of MOFs through the addition of functional groups;（2）modify the system structure of ultra-high porosity MOFs with many adsorption sites in the morphology to better optimize dispersion on the surface;（3）developing MOF-based graphene nanocomposites to improve recyclability and reusability;（4）more active adsorption sites might be obtained by controlling shape and structure. |
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