Study On The Adsorption Mechanism Of Pollutants By GS@LDO And Its Engineering Application

Layered double hydroxides（LDHs）,served as excellent adsorbents,have been widely applied for water pollution treatment.However,the solid products after adsorption of pollutants are generally considered as hazardous waste.The current traditional disposal techniques suffer from drawbacks of causing secondary pollution（e.g.,releasing CO₂,SO₂,NO_x）and wasting precious resources.Therefore,developing high-value resource-utilization strategy for spent adsorbent disposal,as well as exploring its engineering application have become an important task for environmental protection and comprehensive utilization of waste resources in China,possessing social significance and economic value.In this work,we employed organic layered double hydroxide loaded with sodium dodecyl sulfate（O-LDH）to prepare sulfur-rich graphene-like carbon/layered double oxides（GS@LDO）via“precursor-calcinaiton”strategy and applied to efficiently remove heavy metals and organics from water.On the basis of the deep exploration of adsorption performance,influencing factors and removal mechanism of contaminants,a sewage removal device was designed to be suitable for the practical application of GS@LDO composite in wastewater treatment.The main mechanism and influencing factors on the mixed adsorption of GS@LDO in the device was also investigated via computer simulation.The results showed that GS@LDO and its device could successfully remove water pollutants in an efficient and rapid manner.Moreover,the materials could be well recycled and reutilized.The detailed results were as follows:（1）In virtue of“precursor-calcinaiton”strategy,GS@LDO was prepared via the calcination of organic layered double hydroxide loaded with sodium dodecyl sulfate（O-LDH,the representative of layered waste）at 700℃under the protection of argon（Ar）gas.The specific surface area of GS@LDO was 30.2 m²/g and the pore volume was 0.18 cm³/g.Besides,GS@LDO exhibited a three-dimensional flower-like structure,with the diameter of 3μm and neutral surface.The main compositions of GS@LDO were LDO and S doped graphitic carbon,wherein the doped sulfur（S）was bonded to the carbon by covalent bonds and incorporated into the carbon lattice（2）The adsorption of heavy metals on GS@LDO showed that:the equilibrium time of Pb（II）、Cd（II）、Co（II）was 60 min.The maximum saturated adsorption capacity of GS@LDO for Pb（II）,Cd（II）and Co（II）was 720.01,473.11 and 170.91 mg/g,respectively,when adsorbent dosage was 1 g/L and the initial metal concentration was 2000 mg/L.Besides,the adsorption of metal ions was scarcely affected by the solution p H,with the removal efficiency more than 95%at the p H=2-6.（3）The removal behavior of GS@LDO for metal ions conformed to the pseudo-second-order model and Langmuir model,indicating that the adsorption of metal ions was monolayer chemical adsorption.Combied with the characterization analysis of solid production and DFT results,the removal pathway of heavy metals on GS@LDO followed:?the OH-released by the hydration reaction of LDOs precipitated with metal ions;?surface complexation of metal ions with functional groups（O-C=O）of GS;?the interaction of S and metal ions to form M-SOx compound（M represented for metal ions）.In addition,the recycling experiments demonstrated that the adsorption efficiency of metal ions could still maintain more than 90%after 5 runs,indicating that GS@LDO possessed excellent regenration properties.（4）The adsorption of methyl orange（MO）and acid orange（AO7）on GS@LDO showed that:the equilibrium time of MO and AO7 was 30 and 60 min,respectivelly,with the removal efficiency of 100%.The maximum adsorption capacity of GS@LDO for MO and AO7 was 1870 and 1852 mg/g,respectively,when adsorbent dosage was 1 g/L and the initial organic concentration was 2000 mg/L.Besides,GS@LDO exhibited a well anti-p H-interference ability owing to the surface rich groups（such as-COOH,-C-S and-OH）of GS@LDO.（5）The removal of MO and AO7 by GS@LDO fitted well with the pseudo-second-order model,indicating that the adsorption of dyes by GS@LDO was controled by chemisorption.The results of XRD,FT-IR and XPS analysis unveiled that?LDOs components contributed to the dyes removal via the reconstruction of LDHs structure wherein the dye molecules as interlayer anions in virtue of"memory effect";?the metal-oxygen bond（e.g.,Mg-O,Al-O）complexed with dye molecules;?the O-C=O and C-S groups on the surface of GS@LDO exhibitedπ-πelectron donor-acceptor（EDA）effect with dyes.In addition,GS@LDO showed excellent regenration properties,with the removal efficiency of 90%after 5 cycles.（6）Flow simulation study of GS@LDO in the design of new sewage treatment device demonstrated that:under the action of spiral arranged blade blades,?the mixed fluid moved around the stirring shaft in annular tangential direction,accompanying by slow axial push flow;?high intensity turbulent diffusion occurs in the whole tank due to the unique dislocation distribution of the agitator;?the stirring speed was 10rpm to achieve uniform suspension and mixing of GS@LDO and contaminated water;?when the stirring speed was 10 rpm,the concentration distribution of solid particles with particle size of 3 and 50μm was uniform,but the size of 50μm was more conducive for the separation and recovery of GS@LDO.The new sewage treatment device could effectively promote the mixing of GS@LDO in sewage,thereby presenting well adsorption performance.In conclusion,the as-prepared GS@LDO and its adsorption device could effectively remove heavy metals and dye pollutants from wastewater,with low environmental requirements,wide applicability and advancement.which provides theoretical basis and technical support for the engineering application of GS@LDO.