49Direct exfoliation of lactate-intercalated ]-LDH nanocomposites 50 (LCT-LDH) into single-layer LDH nanosheets in water media, termed LDHNSs, to 51 enlarge the overall surface area and adsorption rate. The LDHNs were then used as 52 adsorbents to remove Cr(VI) from aqueous solution by batch adsorption method. 53 Adsorption experiments considered the effects of various factors such as pH, dosage, 54 contact time, and temperature on Cr(VI) removal efficiency. The morphology, texture, 55 and surface properties of the [MgAl-NO 3 ]-LDH, LCT-LDH, LDHNSs, and 56Cr-LDHNSs were characterized by HRTEM, AFM, XRD, FT-IR, XPS, elemental 57 analyzer and zeta potential analyzer. It was found that the optimum pH for Cr(VI) 58 maximum removal efficiency onto LDHNSs was pH 6.0. Adsorption data were found 59 to be better fitted by the Langmuir isotherm, and the maximum adsorption capacity of 60 LDHNSs for Cr(VI) was 125.97 mg/g at 308K. The adsorption of Cr(VI) onto 61 LDHNSs was rapid, and the contact time required to reach complete adsorption 62 equilibrium within 8 min. Thermodynamic analysis showed that the adsorption 63 process was endothermic, spontaneous, and physical in nature, involving weak 64 interactions such as electrostatic attraction, ion-exchange, and hydrogen bonding 65 between the Cr(VI) species and the binding sites on the LDHNSs. 66 67 Nanosheets 69 70 71 4 1. Introduction 72Heavy metal pollution is mainly caused by the indiscriminate disposal of 73 wastewater from different chemical engineering processes, including alloys and steel 74 manufacturing, electroplating, leather tanning, metal finishing, oxidative dyeing, and 75 pigments synthesis [1,2]. There is increasing demand for rapid and effective methods 76 to remove heavy metal because heavy metal pollution is a hazardous threat to 77 environment and human health. Among various heavy metals, chromium gives rise to 78 harmful effects on ecosystems and human beings because of its highly toxicity, 79 carcinogenicity and mutagenicity, and thus chromium has become an important 80 environment concern[3, 4]. In aqueous systems, chromium (Cr) usually exists in two 81 stable oxidation states: Cr(III) and Cr(VI), which exhibit very different toxicity, 82 solubility and mobility [5, 6]. Cr(III) has less toxicity and is an essential micronutrient 83 for normal glucose metabolism at low concentrations. Cr(VI) is of particular 84 importance due to its great toxicity, which is reported to be five hundred times more 85 toxic than the Cr(III) [5, 6]. Therefore, it is imperative to develop rapid and effective 86 approaches for Cr(VI) removal from wastewater before being discharged into the 87 aquatic environments. 88 Different techniques are available: electrochemical oxidation, bioremediation, 89 chemical coagulation, membrance technologies, ion-exchange, adsorption, etc. The 90 adsorption has been proved to be a most economical and efficiency technology for the 91 removal of Cr(VI) from aqueous solution[6,7]. For this purpose, a number of 92 adsorbents have been ...
