Adsorption mechanism of Cr(VI) onto GO/PAMAMs composites

Abstract

Graphene oxide/polyamidoamine dendrimers (GO/PAMAMs) composites were used to remove Cr(VI) from simulated effluents, the adsorption kinetics and thermodynamics of Cr(VI) onto GO/PAMAMs were systematically investigated. The results showed that the optimum pH value was 2.5, the removal percentage reached 90.7% for 30 mg/L of Cr(VI) within 120 min. The adsorption process was well described by pseudo-second-order kinetic model. The maximum adsorption capacities of Cr(VI) onto GO/PAMAMs were found to be 131.58, 183.82 and 211.42 mg/g at 293.15, 303.15 and 313.15 K, respectively, which were calculated from the Langmuir model equation. The adsorption thermodynamic parameters indicate that the adsorption of Cr(VI) onto GO/PAMAMs is a spontaneous endothermic process. The XPS analysis reveals the adsorption and removal mechanism of Cr(VI) on GO/PAMAMs that first the Cr(VI) binds to the protonated amine of GO/PAMAMs, then Cr(VI) be reduced to Cr(III) with the assistance of π-electrons on the carbocyclic six-membered ring of GO in GO/PAMAMs, and then Cr(III) was released into solution under the electrostatic repulsion between the Cr(III) and the protonated amine groups.

Adsorption of Cr(VI) from aqueous solution on graphene oxide (GO) prepared from graphite: equilibrium, kinetic and thermodynamic studies

“…However, the above results are one cycle regeneration with very short span of time (30 min). Almost similar regeneration status of graphene oxide/polyamidoamine dendrimers by using 0.5 M NaOH was reported by Liu et al (2019) after one cycle. Therefore, it is strongly recommended that for achieving higher level of regeneration both duration and multi-cycling regeneration should be done.…”

“…However, originally graphene has a layer structure. On fictionalization, GO exhibits a three-dimensional network of randomly oriented sheet-like structures with a wrinkled texture and hierarchical pores with a wide size distribution which may be the preferable sites for heavy metal binding (Liu et al 2019). After chromium removal, SEM structure of GO showed a more smooth surface ( Fig.…”

“…Very recently, Samuel et al (2019) reported that hexavalent chromium can be removed at pH 2 by using chitosan-grafted graphene oxide nanocomposite. Cr(VI) ion is mainly available in the form of HCrO 4 − at the pH range from 1 to 4 (Liu et al 2019). However, purely oxoanion, CrO 4 2− will be available in the pH range 4-7 (Yang et al 2014;Dehghani et al 2015).…”

A systematic study of hexavalent chromium adsorption and removal from aqueous environments using chemically functionalized amorphous and mesoporous silica nanoparticles

“…The ΔG° of NH 2 -MSNs was approximately ~1.5 times greater than that of NH 2 -ASNs likely due to the presence of nanopores. The positive value of ΔS° suggests the increased randomness at the liquid-solid interface during Cr(VI) adsorption likely indicates the process is an entropy-driven process rather than enthalpy 97 . Table 4.…”

A theoretical and experimental study of the adsorptive removal of hexavalent chromium ions using graphene oxide as an adsorbent

“…In this case, the adsorption capacity value is q = 240.361 mg/g. A value that is in the same range as the GO/polyamidoamine dendrimer composites for the Cr(VI) adsorption [17].…”