Enhanced arsenic removal by graphene oxide chitosan composites through FeOx decoration: Influences and mechanism.

Iron decoration has been recognized as one of the most important paths to enhance contaminant adsorption by carbon-based composites. In this study, varying amounts of Fe (II) are used for the modification of graphene oxide chitosan (GOCS) materials to assess the impact of iron oxide (FeOx) morphology on the composites and their efficiency in arsenic (As) removal. Results show that incorporating 0.08 mol Fe(II) into GOCS yields better As removal performance, leading to a remarkable enhancement by 5 times for As(V) and 6 times for As(III). The iron minerals in the material consist of goethite (FeO(OH)) and magnetite (Fe3O4), with FeO(OH) playing a predominant role in As removal through the complexation and electrostatic attraction of -OH and Fe - O groups. The adsorption capacity for As (Qe) decreases with the increasing pH and the mass and volume ratio (m/v) but increases with the increasing initial concentration (C0). Besides, the presence of SO42- and HPO42- can significantly reduce As removal by the FeOx-modified GOCS. Under the conditions of pH = 3, m/v = 1.0 g/L, and C0 = 10 mg/L, a maximum Qe value reaches 61.94 mg/g. The adsorption is well-fitted to a pseudo-second-order kinetic model and is an endothermic, spontaneous, and monolayer adsorption process.

As(III) removal by a recyclable granular adsorbent through dopping Fe-Mn binary oxides into graphene oxide chitosan.

Graphene oxide chitosan composite (GOCS) is recognized as an environmentally friendly composite adsorbent because of its stability and abundant functional groups to adsorb heavy metals, and Fe-Mn binary oxides (FMBO) have attracted increasing interest due to their high removal capacity of As(III). However, GOCS is often inefficient for heavy metal adsorption and FMBO suffers poor regeneration for As(III) removal. In this study, we have proposed a method of dopping FMBO into GOCS to obtain a recyclable granular adsorbent (Fe/MnGOCS) for achieving As(III) removal from aqueous solutions. Characterization of BET, SEM-EDS, XRD, FTIR, and XPS are carried out to confirm the formation of Fe/MnGOCS and As(III) removal mechanism. Batch experiments are conducted to investigate the effects of operational factors (pH, dosage, coexisting ions, etc.), as well as kinetic, isothermal, and thermodynamic processes. Results show that the removal efficiency (Re) of As(III) by Fe/MnGOCS is about 96 %, which is much higher than those of FeGOCS (66 %), MnGOCS (42 %), and GOCS (8 %), and it increases slightly with the increasing molar ratio of Mn and Fe. This is because amorphous Fe (hydro)oxides (mainly in the form of ferrihydrite) complexation with As(III) is the major mechanism to remove As(III) from aqueous solutions, and it is accompanied by As(III) oxidation mediated by Mn oxides and the complexation of As(III) with oxygen-containing functional groups of GOCS. Charge interaction plays a weaker role in As(III) adsorption, therefore Re is persistently high over a wide range of pH values of 3-10. But the coexisting PO43- can greatly decrease Re by 24.11 %. As(III) adsorption on Fe/MnGOCS is endothermic and its kinetic process is controlled by pseudo-second-order with a determination coefficient of 0.95. Fitted by the Langmuir isotherm, the maximum adsorption capacity is 108.89 mg/g at 25 °C. After four times regeneration, there is only a slight decrease of <10 % for the Re value. Column adsorption experiments show that Fe/MnGOCS can effectively reduce As(III) concentration from 10 mg/L to <10 µg/L. This study provides new insights into binary polymer composite modified by binary metal oxides to efficiently remove heavy metals from aquatic environments.