Anchored Graphene Oxide Nanocomposite And Application In The Removal Of Fluoride From Water Synthesis Of Iron (Oxy)Hydroxide

Excessive fluoride in drinking water has become a serious environmental problem effecting millions of people in various regions. The most crucial part of study is to develop a technology which should be efficient, low-cost and environmental-friendly.Goethite anchoring regenerated Graphene Oxide (α-FeOOH@rGO) nanocom-posite was synthesized via one-step facile hydrolysis pathway with ferrous sulfate as starting material. Akaganeite anchoring Graphene Oxide (β-FeOOH@GO) nanocomposite was synthesized via one-step facile hydrolysis pathway with ferric chloride as starting material. The two new nanocomposites are applied as adsorbents for the removal of fluoride from drinking water in this paper. And research of their application in the removal of fluoride from water. Including the effect of solution pH, initial fluoride concentration, contact time, temperature, common ions(SO42-, Cl-, NO3-, HCO3-, SiO32-,PO43-, HA) and cycles of regeneration.The results of adsorption kinetics study show that the pseudo pseudo-second-order kinetic model is more suitable to describe the adsorption of fluoride. The main adsorption process is chemical adsorption. They remove fluoride quickly. The results of the thermodynamics isotherm indicated that Freundlich isotherm model is better than Langmuir isotherm model in describing the fluoride adsorption characteristic. Two adsorbents show the characteristics of chemical adsorption in adsorption process, they have a high affinity for fluoride. The fluoride adsorption capacity of α-FeOOH@rGO and β-FeOOH@GO is 24.67 mg/g and 17.67 mg/g, respectively. In the study of Gibbs free energy, enthalpy and entropy, the results show that the fluorine ion is adsorbed to the surface of the adsorbent. The adsorption is spontaneous, endothermic, not entropy driven by α-FeOOH@rGO. And the adsorption is spontaneous, exothermic, entropy driven by β-FeOOH@GO.The results of pH effect experiment indicated that the removal rate of fluoride was almost constant at pH<12.13 and slightly decreased at pH>12.13 by α-FeOOH@rGO. The removal rate of fluoride was almost constant at acidic and neutral solution but decreased at pH>9.94 by β-FeOOH@GO. The result show that the surface with a positive charge is formed in neutral and acidic solution, the electrostatic attraction is suitable for fluoride adsorption. When the pH increases to very alkaline, negatively charged surface is formed.The results of common ions effect on fluoride removal show that two adsorbents are anti-interference. Common ions have no effect on fluoride removal from two adsorbents, only high concentrations of HCO3- and HA will caused lightly decreased of the removal rate. The results of experiments on six consecutive adsorption-desorption cycles are indicated that a lot of the surface adsorption sites were occupied by the fluoride after first adsorption. With the adsorption continuing, available sites on the goethite surface subsequently decreased, so the adsorption capacity of adsorbents would be decreased accordingly. The effect of acid elution is better than alkali elution.XRD analysis results show that the characteristic peaks are observed, which indicated that two nanocomposites are well crystal form and high purity. They are almost identical to the characteristic peaks of α-FeOOH and β-FeOOH. SEM and TEM showed that they are well dispersed on the surface of rGO and GO sheet. The FTIR and XPS results proved that the remove fluoride by α-FeOOH@rGO by an ion-exchange mechanism with α-FeOOH crystal structure containing sulfate accompanying. Similarly, β-FeOOH@GO is by an ion-exchange mechanism with β-FeOOH crystal structure containing chloride accompanying.