Synthesis Of Functionalized Layered Double Hydroxides For Pollutant Removal

Pollutants enter the human body through the food chain,posing a serious threat to human health.Therefore,the management of environmental pollutants has always been an important research issue for environmental scientists.This paper applied the methods of different surface functionalization to prepare uncalcined glycerol-modified nanocrystallined Mg/Al layered double hydroxides(named as G-LDH)and calcined G-LDH(named as G-LDO),nanobelt-like Ca/Al layered double hydroxides(CA-LDH),layered double oxides(denoted as LDO)and layered double oxides/carbon dots nanocomposites(denoted as LDO-C),which were Detailed characterization analysis and used as adsorbents to remove pollutants Specific research contents were as follows:1)The uncalcined glycerol-modified nanocrystallined Mg/Al layered double hydroxides(named as G-LDH)and calcined G-LDH(named as G-LDO)with Mg/Al molar ratio of 3:1 were successfully synthesized by an easy and green hydrothermal method,and were characterized by scanning electron microscopy,transmission electron microscopy,N2brunauer-emmett-teller surface area measurement,Fourier transformed infrared spectroscopy(FT-IR)and X-ray diffraction(XRD).The as-synthesized G-LDH and G-LDO were applied as adsorbents to remove methyl orange(MO)from aqueous solutions at different experimental conditions,and the results showed that the interaction of MO with G-LDH and G-LDO were strongly dependent on pH and independent of ionic strength.Kinetic study indicated the MO adsorption on G-LDH and G-LDO were well simulated by both pseudo-first-order and pseudo-second-order models.The MO adsorption on G-LDH and G-LDO were well simulated by Langmuir model,and the maximum adsorption capacity of G-LDO(qmax=1062.3mg/g)was much higher than that of G-LDH(qma= 443.5 mg/g)at pH=4.5.The thermodynamic parameters calculated from temperature-dependent isotherms indicated that the adsorption was spontaneous and exothermal process.The FT-IR and XRD analysis further evidenced that the interaction of MO with G-LDH was mainly dominated by electrostatic interaction,ion exchange,hydrogen bonding and surface complexation,whereas the the uptake of MO to G-LDO was mainly attributed to electrostatic interaction and surface complexation.2)A novel nanobelt-like Ca/Al layered double hydroxides(CA-LDH)was synthesized and applied as efficient coagulant for the removal of GO from aqueous solutions.The results indicated that neutral pH,co-existing cations and higher temperature were beneficial to the coagulation of GO.The sequence of cation effect for promoting of GO coagulation was Ca2+>Mg2+>K+>Na+,whereas the effect of anions on GO coagulation was PO43->CO32->SO42->Cl".Comparing with anions,the cations showed more dominate effect for GO coagulation than anions.Hydrogen bonds and electrostatic interaction were the main coagulation mechanisms for GO coagulation,which were evidenced by FT-IR and XPS analysis.Specifically,for the first time,the reclaimed product of CA-LDH after GO coagulation(CA-LDH+GO)was applied as adsorbents for the secondary application in the removal of heavy metal ions from aqueous solutions.Interestingly,the CA-LDH+GO still had high adsorption capacities,i.e.,the maximum adsorption capacities(qmax)for Cu(?),Pb(?),and Cr(VI)were 122.7 mg/g,221.2 mg/g and 64.4 mg/g,respectively,higher than other similar materials.3)A practical and simple calcination method was used to synthesize layered double oxides(denoted as LDO)and layered double oxides/carbon dots nanocomposites(denoted as LDO-C)for U(VI)efficient removal.The U(VI)adsorption on LDO and LDO-C were investigated under various experimental conditions,and the results indicated that U(VI)uptake on LDO and LDO-C were consumingly dependent on pH and ionic strength at pH>6,and independent of ionic strength at pH<6,and the interaction was mainly attributed to surface complexation and electrostatic interactions.The maximum adsorption capacity of U(VI)on LDO-C was calculated to be 354.2 mg/g at pH=5.0 and T=298 K,which was significantly higher than that of U(VI)on LDO(237.6 mg/g).Particularly,BET,FT-IR,XPS and EXAFS analysis suggested that the higher adsorption capacity of LDO-C was mainly attributed to higher specific surface area and more abundant surface oxygen-containing functional groups(e.g.C-OH),and the main interaction mechanisms were surface complexation and electrostatic interaction.