Sulfate Ions Immobilization of Calcined Layered Double Hydroxides in Hardened Cement Paste and Concrete

The sulfate ions immobilization behavior of calcined layered double hydroxides(CLDHs) in the hardened cement paste was investigated. The experimental results show that the sulfate ions in cement paste are immobilized by CLDHs to reconstruct the layered structure and aggregate around CLDHs. The immobilization amount of sulfate ions by CLDHs reaches 4.74×10^-3 mol/g, while the increasing amount indicates non-linear relation with the addition of CLDHs. The incorporation of CLDHs decreases the amount of ettringite formed to limit the expansion of cement paste, which decays the sulfate reaction to enhance the sulfate resistance of concrete.

Immobilization of Penicillin G Acylase on Calcined Layered Double Hydroxides

A hydrotalcite-like Mg 2+ /Al 3+ layered double hydroxide(LDH) material was prepared by means of a modified coprecipitation method involving a rapid mixing step followed by a separate aging process. LDH calcined at 500 ℃, denoted as CLDH, was characterized by XRD, IR and BET surface area measurements. CLDH has a poor crystalline MgO-like structure with a high surface area and porosity. CLDH was used as a support for the immobilization of penicillin G acylase(PGA). The effect of varying the immobilization conditions, such as pH, contact time and the ratio of enzyme to support, on the activity of the immobilized enzyme in the hydrolysis of penicillin G has been studied. It was found that the activity of the immobilized enzyme decreased slightly with decreasing pH and reached a maximum after a contact time of 24 h. The activity of the immobilized enzyme increased with increasing the ratio of enzyme to support. It was found that the adsorption of PGA inhibited the expected reaction of CLDH with an aqueous medium to regenerate a LDH phase. Its original activity(36%) after 15 cycles of reuse of the immobilized enzyme was retained, but no further loss in the activity was observed.

Studies of the Catalytic Activity and Deactivation of Calcined Layered Double Hydroxides in the Reaction of Ethanol with Propylene Oxide

The reaction of ethanol with propylene oxide over calcined layered double hydroxides(CLDH) was investigated. The results show that CLDH has a good activity and a good selectivity, but the activity and the selectivity of CLDH decrease when CLDH reforms LDH- the so called 'memory effect'. The influence of the 'memory effect' on the CLDH returning to LDH was studied by the hydration reaction. It is shown that the 'memory effect' is not complete, and the decreases of the Mg/Al molar ratio of LDH and the crystallite size due to the increase of the hydration reaction time result in the drop of the activity and the selectivity.

Adsorption of glutamic acid from aqueous solution with calcined layered double Mg-Fe-CO_3 hydroxide

Layered double Mg-Fe-CO3 hydroxide （Mg-Fe-LDH） with a mole ratio of Mg to Fe of 3 was synthesized by coprecipitation method and calcined product Mg-Fe-CLDH was obtained by heating Mg-Fe-LDH at 500 ℃ for 6 h. The as prepared Mg-Fe-LDH and calcined Mg-Fe-CLDH were used for removal of glutamic acid （Glu） from aqueous solution, respectively. Batch studies were carried out to address various experimental parameters such as contact time, pH, initial glutamic acid （Glu） concentration, co-existing anions and temperature. Glu was removed effectively （99.9%） under the optimized experimental conditions with Mg-Fe-CLDH. The adsorption kinetics follows the Ho’s pseudo second-order model. Isotherms for adsorption with Mg-Fe-CLDH at different solution temperatures were well described using the Langmuir model with a good correlation coefficient. The intraparticle diffusion model fitted the data well, which suggests that the intraparticle diffusion is not only the rate-limiting step.

The Adsorbing Effect of Calcined Layered Double Hydroxide for Chloride Ions in Simulated Concrete Pore Solutions

The adsorbing effect of calcined layered double hydroxide （CLDH） for chloride ions in simulated concrete pore （SCP） solutions was investigated with the potentiodynamic polarization method, impedance measurement, ion selective electrode analysis and XRD. CLDH could effectively adsorb Cl^- and increase pH value in SCP solutions containing NaCl. The chloride to hydroxyl ions ratio （[C1^-]/[OH^-]） of the solution greatly decreased by CLDH treatment. In CLDH treated SCP solution with CI-, the pitting potential of carbon steel notably increased, and the surface impedance was much higher, indicating strengthened passivation. The process of CLDH adsorbing chloride ions from SCP solutions was accompanied with the reconstruction of the layered structure.

Ordering and disordering of in situ grown MgAl-layered double hydroxide and its effect on the structural and corrosion resistance properties

A MgAl-layered double hydroxide(MgAl-LDH)protective film was developed on AA6082 substrates via the in situ hydrothermal growth method to obtain a distinct cauliflower-like LDH structure,and coated substrates were further heat-treated in air at temperatures from 100 to 250℃ to further improve the corrosion resistance of MgAl-LDH by taking advantage of the LDH memory effect;also,the effect of calcination on MgAl-LDH structural stability and the corresponding corrosion resistance properties were investigated.The structural characterization of uncalcined and calcined LDH films were examined using scanning electron microscopy,energy-dispersive spectroscopy,X-ray diffraction,thermogravimetric analysis,differential scanning calorimetry,and Fourier transform infrared spectroscopy.The corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization experiments and by electrochemical impedance spectroscopy.Compared with uncalcined MgAl-LDH,the calcined film showed a relatively lower corrosion current density and a higher impedance value,especially after heat treatment at 250℃.The findings demonstrate that calcination strongly affects the oriented growth of the LDH and causes an increase in the surface area and contraction of the basal spacing,which in turn caused a compact structure that substantially influenced the LDH corrosion resistance properties.

Thermodynamic and Kinetic Studies of Effective Adsorption of 2,4,6-trichlorophenol onto Calcine Mg/Al-CO_3 Layered Double Hydroxide

Adsorption of 2, 4, 6-trichlorophenol（TCP） onto the calcined Mg/Al-CO_3 layered double hydroxide（CLDH） was investigated. The prepared Mg/Al-CO_3 layered double hydroxide（LDH） and CLDH were characterized by powder X-ray diffraction（XRD） and thermo gravimetric analyzer-differential scanning calorimeters（TG-DSC）. Moreover, 2,4,6-trichlorophenol（TCP） was removed effectively（94.7% of removal percentage in 9h） under the optimized experimental conditions. The adsorption kinetics data fitted the pseudosecond-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.

煅烧水滑石对钢筋混凝土的阻锈机理研究

通过线性极化(LPR)、电化学阻抗谱(EIS)、能谱(EDS)、氯离子含量等测试,研究了氯盐-硫酸盐侵蚀下掺入水滑石(LDHs)、煅烧水滑石(CLDHs)对钢筋混凝土的阻锈作用。结果表明:CLDHs、LDHs具有较小的粒径、较大的比表面积,产生的微集料效应可以提高混凝土28 d抗压强度6%左右,并优化了混凝土孔隙结构,提高了混凝土体系氯离子结合率;耦合盐干湿循环侵蚀下,CLDHs和LDHs明显提高了钢筋混凝土内钢筋的极化电阻和容抗弧半径,CLDHs阻锈效率大于LDHs;随着循环次数的增加,阻锈效率下降,但干湿循环90次CLDHs的阻锈效率仍在85%以上,且阻锈机理主要来源于其对自由氯离子的吸附作用,因此,掺入CLDHs能够有效提高钢筋混凝土的抗锈蚀能力。

Salt freezing resistance improvement of cement-based materials incorporated with calcined layered double hydroxide

Salt freezing damage has severe impacts on durability of cement-based materials(CBMs).Calcined layered double hydroxide(CLDH),as an efficient environmental-friendly adsorption material,can impart excellent salt freezing resistance to CBMs.In this work,salt freezing resistance improvement of CBMs incorporated with CLDH was experimentally evaluated by chloride binding capacity,mass loss rate,relative dynamic elastic modulus,setting time,compressive strength,and micro structure tests.Beside these,the salt freezing damage model was established to effectively express the quantitative relationship between influencing factors and evaluation indexes of the salt freezing resistance of CBMs.Results show that CLDH can reconstruct its original layered structure to form reconstructed layered double hydroxide(RLDH).RLDH combines with chloride ions to form RLDH-Cl recrystallization,which can improve chloride binding capacity and pore structures of CBMs to relieve the salt freezing damage.The salt freezing damage model indicates that the suitable CLDH content can evidently alleviate the salt freezing damage,which facilitates the quantitative analysis of the effect of CLDH on the salt freezing resistance of CBMs.

镁铝水滑石的焙烧筛选及磷吸附机理综合实验设计

针对水体富营养化问题,设计了镁铝水滑石的焙烧筛选、结构表征及磷吸附机理研究的综合实验。该实验考察了不同温度制备的焙烧镁铝水滑石(LDO)的除磷性能,筛选出500℃焙烧制备的镁铝水滑石(LDO-500)作为后续磷吸附研究,并对吸附磷前后的LDO-500进行了FTIR、XRD和SEM结构表征,探索了其吸附机理。不仅能让学生熟悉并掌握多种分析仪器的操作技能,还可提升学生的科研素养,增强其科研思维能力。

镁铝层状双金属氢氧化物及其煅烧产物对水体W(Ⅵ)的吸附特征与机制

采用微波陈化法制备了物质的量比为2:1的硝酸型镁铝层状双金属氢氧化物(LDH),系统地研究了LDH及其煅烧产物(CLDH)对W(Ⅵ)的吸附特征,并通过对吸附W(Ⅵ)前后LDH和CLDH的结构进行表征阐明相关吸附机制.LDH和CLDH对W(Ⅵ)的吸附动力学更符合拟二级动力学模型,表明化学吸附是决定吸附速率的关键.LDH和CLDH对W(Ⅵ)具有较高的亲和性,最大吸附量分别达176.0,124.5mg/g,远高于同类LDH.LDH吸附W(Ⅵ)的最佳pH值范围为4.0~10.0,酸性条件有利于CLDH吸附W(Ⅵ).综合对比,LDH具有更高的吸附容量、更快的吸附速率以及更弱的水质影响(Mg、Al溶出低,pH变化小),更适宜用于W(Ⅵ)吸附.LDH吸附W(Ⅵ)的主要机制包括离子交换、外层络合和内层络合,而CLDH对W(Ⅵ)的吸附机制还包括重构层状结构时仲钨酸盐(W_(7)O_(24)^(6-))的插层作用.以上结果表明,采用微波法合成LDH和CLDH均可高效地吸附污染水体的W(Ⅵ),是一类性能优越的W(Ⅵ)吸附材料.

矿渣-粉煤灰基胶凝材料性能调控及其在铅锌矿尾砂胶结充填中的应用

尾砂胶结充填(Cemented Paste Backfill,CPB)是目前大规模消纳尾矿的主要方式,然而作为CPB中最常用的胶凝材料,普通硅酸盐水泥(Ordinary Portland Cement,OPC)的高成本限制了CPB的大规模推广应用,并且OPC大量使用不利于“双碳”目标的实现,因此需要研发新型的充填胶凝材料。利用煅烧层状双氢氧化物(CLDH)对Na_(2)CO_(3)激发高炉矿渣(Blast Furnace Slag,BFS)-粉煤灰(Fly Ash,FA)基胶凝材料进行改性,使其适用于铅锌矿尾砂胶结充填。一方面CLDH可以消耗反应体系中的CO^(2-)_(3),提高反应体系的pH值,进而促进反应,另一方面CLDH在重新水化过程中生成LDH,有利于对重金属的固化。通过研究胶凝材料的水化热、反应产物以及CPB样品的流动性、抗压强度和重金属固化效果,得出胶凝材料的最优配比。研究结果表明,样品B50FA50-CL5-Ca5具有最佳的综合性能。当胶凝材料和尾砂重量比为1∶6、料浆浓度为70 wt%时,充填体3 d和28 d抗压强度分别为1.21 MPa和2.77 MPa,并且重金属的固化效果符合国家相关标准。

焙烧水滑石吸附脱除水中硫酸根离子的研究

利用焙烧水滑石对水中硫酸根离子进行吸附性能研究,考查了初始pH值、吸附时间、吸附剂用量等条件对吸附的影响。结果表明,焙烧水滑石对水中硫酸根离子具有良好的吸附能力。X射线衍射分析结果表明,水滑石及其焙烧产物对硫酸根的吸附机理不同。pH值对吸附的影响较大,pH值较低时吸附效果较好。吸附平衡符合Langmuir方程,室温下饱和吸附量为32.895 mg/g。

双金属复合氧化物的结构与紫外阻隔性能

The XRD patterns of different calcined layered double hydroxides(CLDH) and their ultraviolet absorbing and screening properties have been investigated. It has been found that a calcined layered double hydroxide(CLDH) containing zinc is very effective in absorbing and screening ultraviolet radiation. The crystal structure of a CLDH containing zinc is similar to that of ZnO and is not related to the crystal structure of Al 2O 3. It is not a simple combination of zinc oxide and aluminium oxide but a calcined layered double hydroxide in which part of the Zn 2+ cations is replaced by Al 3+ cations.

焙烧层状氢氧化镁铝对溴离子吸附性能研究

研究了500℃下焙烧层状氢氧化镁铝对溴离子吸附性能,考察了吸附时间、吸附剂用量、吸附温度、吸附初始pH值等条件对吸附性能的影响。实验结果表明,焙烧层状氢氧化镁铝对溴离子具有较好的吸附性能,35℃下饱和吸附量为133.33mg/g,其吸附等温线可以用Langmuir等温方程描述。

层状双金属氢氧化物在有机污染物吸附方面的应用

层状双金属氢氧化物(LDHs)因其独特的层状结构、较高的阴离子交换容量等优点,作为吸附剂在水环境污染中的治理日益受到重视,其中有关LDHs对有机污染物吸附的研究已有广泛报道。综述了LDHs及其焙烧产物层状双金属氧化物LDO去除有机物的种类以及影响吸附和离子交换过程的各项因素,包括材料的组成和结构、pH、温度、共存竞争物质等。除此之外,还进行了LDHs去除有机污染物的机理探讨。

镁铝复合氧化物在醇醚合成反应中的催化性能

以镁铝层状双金属氢氧化物(LDH)为前体焙烧得到的镁铝复合氧化物(CLDH)为催化剂,催化乙醇和环氧丙烷反应合成醇醚.系统研究了CLDH的孔结构和化学组成对催化剂活性和产物选择性的影响,并考察了催化剂的寿命.结果表明,随CLDH碱性增强及比表面积增大,催化剂活性提高,且催化剂孔分布对醇醚产物有择形性.

AB24在MgAl-LDO上的吸附性能及机理研究

本文探讨了nMg/nAl=3的水滑石焙烧产物（MgAl-LDO）对染料酸性黑24（AB24）的吸附性能及其机理。考察了不同因素对MgAl-LDO吸附AB24性能的影响，并研究了吸附过程的热力学和动力学机理。实验结果表明：MgAl-LDO对AB24具有优异的吸附性能，在298 K，pH=10条件下，1.0 g·L^-1 MgAl-LDO对1 000 mg·L^-1 AB24溶液的吸附容量和去除率分别达到998.31 mg·g^-1和99.83%。动力学和热力学研究表明：MgAl-LDO对AB24的吸附过程同时符合Langmuir和Freundlich等温吸附方程，并且是个放热、自发的过程。计算所得的吉布斯自由能绝对值在10-15 kJ·mol^-1，这主要是由染料分子与水滑石层板的氢键作用产生，结合Materials Studio 5.5软件模拟AB24染料分子在MgAl-LDHs上的排列分布，推测MgAl-LDO对AB24的吸附机理是表面吸附（占优势）与层间插层的协同作用。同时，该吸附过程符合准二级反应动力学模型。

类水滑石Ti/Li/Al-LDHs的制备及其CO_2吸附性能

采用共沉淀法制备了一系列新型的类水滑石Ti/Li/Al-LDHs材料,通过原子吸收光谱(AAS)、X射线衍射(XRD)、扫描电镜(SEM)、热重分析(TG)和傅里叶变换红外光谱(FT-IR)等技术对其进行了表征,研究了不同金属元素比例和焙烧温度对该Ti/Li/Al-LDHs材料的结构、形貌及其CO_2吸附性能的影响。结果表明,当Ti/Li/Al比为1∶3∶4时,水滑石Ti/Li/AlLDHs的结晶度最好,形貌最规整,而Ti/Li/Al比为1∶3∶2、300℃下焙烧后得到的Ti_1Li_3Al_2-LDHs_(300)的CO_2吸附性能最好。Ti_1Li_3Al_2-LDHs_(300)上CO_2吸附量可达53.5 mg/g,10次循环吸附后,CO_2吸附量仅下降了2.4%。

用焙烧复原法插层组装有机层柱双氢氧化物

Organic acid radical-pillared hydrotalcites of the type of M6Al2（OH）16〔CnH2n+1COO-〕（M=Mg,Zn;n=13,17）have been successfully assembled by calcination of M6Al2（OH）16CO3·mH2O〕（M=Mg,Zn）and rehydration of MgAlO and ZnAlO in tetradecylic acid solvent and stearic acid solvent respectively and characterized by IR and XRD.The experimental results show that the method of calcination-rehydration could be used to prepare the organic acid radical-pillared MAl-LKHs（M=Mg,Zn）which have good crystallinity,regular layered structure and large interlayer distance (d003(M6Al2（OH）16〔CnH2n+1COO-〕)=2.74nm（M=Zn,n=13）,2.90nm（M=Mg,n=13）,3.24nm（M=Zn,n=17）,3.22nm（M=Mg,n=17）.