Solvothermal synthesis and adsorption performance of layered boehmite using aluminum chloride and high-alumina fly ash

High alumina fly ash(FAHAl)is a kind of bulk solid waste unique to China,whose availability of high-value aluminum and the threat to the environment makes its high-value utilization urgent.In this work,the alumina containing leaching solution obtained from Na_(2)CO_(3) roasting and HCl leaching of FAHAl was used as the mother liquor to prepare layered boehmite in situ.The preparation process with AlCl_(3) as the raw material was also compared.The formation process and mechanism of boehmite,the choice of solvent,along with the adsorption capability of Congo red were analyzed by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,Brunauer-Emmett-Teller method and adsorption experiments.Results showed that during the preparation of layered boehmite,the precursor Al(OH)_(3) from the reaction of Al^(3+) and OH-is transformed into boehmiteγ-AlOOH.The existence of ethanol is beneficial to regulate and promote the growth of boehmite crystal effectively.When water and ethanol are mixed with a volume ratio of 2:1 and used as the solvent,the maximum specific surface area of the boehmite is obtained at 135.7 m^(2)·g^(-1),and 99.16%of Congo red can be absorbed after 10 min when AlCl3 is used as a raw material.As purified leaching solution is used as the mother liquid,the crystallinity of boehmite decreases slightly when the pH value decreases from 12.5 to 11.When pH is 11,the removal efficiency of Congo red reaches a maximum of 72.25%.This process not only achieves the extraction of aluminum and high-value utilization of FAHAl but also provides a thought to prepare layered boehmite with adsorption properties.

Precipitation of spherical boehmite from concentrated sodium aluminate solution by adding gibbsite as seed

The precipitation of spherical boehmite was studied by surface energy calculations, measurements of precipitation ratios, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The surface energy calculation results show that the(001) and(112) planes of gibbsite surfaces are remarkably stable because of their low surface energies. In addition, the(010) plane of boehmite grows preferentially during precipitation because of its low surface energy. Thus, we propose a method to precipitate spherical boehmite from a supersaturated sodium aluminate solution by adding gibbsite as seed in a heterogeneous system. In this method, gibbsite acts as the preliminary seed and saturation modifier. The results show that the fine boehmite first nucleates on the(001) and(112) planes of gibbsite and then grows vertically on the(001) and(112) basal planes of gibbsite via self-assembly, thereby forming spherical boehmite. Simultaneously, gibbsite is dissolved into the aluminate solution to maintain the saturation for the precipitation of boehmite. The precipitation ratio fluctuates(forming an M-shaped curve) because of gibbsite dissolution and boehmite precipitation. The mechanism of boehmite precipitation was further discussed on the basis of the differences in surface energy and solubility between gibbsite and boehmite. This study provides an environmentally friendly and economical method to prepare specific boehmite in a heterogeneous system.

Influence of hydrothermal temperature on structure and microstructure of boehmite

Boehmites(Al2O3·xH2O)were hydrothermally prepared from aluminum alkoxide.The effect of temperature on preparation was studied in the range of 100-180℃.The XRD analysis shows that with temperature increasing,the transformation of pseudo-boehmite into well-crystallized boehmite takes place.The micro-morphologies change also from irregular clew to thin cubic platelets.From the mass loss of the samples prepared at different temperatures,the value of x is estimated to vary between 1.06 and 1.67.γ-Al2O3 obtained by subsequent calcination of boehmite at 600℃is also characterized by XRD and its morphology remains unchanged.

Amine-functionalized boehmite nanoparticle-supported molybdenum and vanadium complexes:Efficient catalysts for epoxidation of alkenes

Boehmite nanoparticles with a high surface area and a high degree of surface hydroxyl groups were covalently functionalized by 3‐（trimethoxysilyl）‐propylamine to support vanadium‐oxo‐sulfate and molybdenum hexacarbonyl complexes. These supported catalysts were then characterized by Fou‐rier‐transform infrared spectroscopy, powder X‐ray diffraction, thermogravimetry and differential thermal analysis, X‐ray‐photoelectron spectroscopy, elemental analysis, inductively coupled plasma, and transmission electron microscopy techniques. The catalysts were subsequently used for the epoxidation of cis‐cyclooctene, and the experimental procedures were optimized. The progress of the reactions was investigated by gas‐liquid chromatography. Recycling experiments revealed that these nanocatalysts could be repeatedly used several times for a nearly complete epoxidation of cis‐cyclooctene. The optimized experimental conditions were also used successfully for the epoxida‐tion of some other substituted alkenes.

Enhancement on Synthesis of Boehmite Through a Precarbonizationassisted Hydrogen Peroxide Route in Highly Alkaline Sodium Aluminate Solutions

Hydrogen peroxide(H2O2)precipitation from sodium aluminate(SA)solution at close-ambient temperature is an efficient method to synthesize boehmite and its derived alumina with high surface area,but the precipitation yield of Al2O3 is usually below 50%in highly alkaline SA solutions.Here the synthesis of boehmite is enhanced through a precarbonization-assisted H2O2 route in highly alkaline SA solutions.It is found that the crystal structure of the precipitation product is evidently influenced by the precipitation conditions.As the precipitation temperature increases from 273 to 325 K,a small amount of gibbsite by-product is formed.As the aging temperature increases from 301 to 333 K,the crystallinity of boehmite decreases and part of the boehmite dissolves due to an increase in the pH value.Based on the above results,a precarbonization-assisted H2O2 route is proposed to obtain pure boehmite with more complete recovery of Al2O3 from highly alkaline SA solutions.The route includes a controllable precarbonization step of SA solutions with a molar ratio of Na2O to Al2O3 higher than 2:1,followed by the H2O2-precipitated step with a molar ratio of H2O2 to Al2O3 less than 7:1.Because of its facile operation conditions,no extraneous impurity,time saving and a possible recycle of the filtrate,the route has great potential to be an alternative method for preparation of boehmite and its derived alumina.

Preparation and Properties of Poly(Ethylene Terephthalate)/Boehmite Nanocomposite

Colloidal boehmite particles have been included into a polyethylene terephthalate matrix by in situ polymerization. Boehmite nanoparticles were produced by the controlled hydrolysis of aluminium isopropylate. The nanoparticles were characterized using Transmitted Electronic Microscopy (TEM) and X-ray Diffraction (XRD), which revealed the particles of magnitude about 10 nm. The particles have been used without any surface modification. Characterization of the nanocomposite has been carried out using TEM and differential scanning calorimetry (DSC). TEM images indicate that the particles have been homogeneously dispersed in the polymer. DSC results show that the presence of boehmite affects the process of crystallization of polyethylene terephthalate.

Adjustment on gibbsite and boehmite co-precipitation from supersaturated sodium aluminate solutions

Gibbsite is the usual precipitation product from alumina refineries with either Bayer or sintering process.However,the advantage of boehmite precipitation over gibbsite precipitation is the significant energy saving in the subsequent calcination step.The current investigation takes a pragmatic approach to measure precipitation ratios,determine product phase,morphology and particle size distribution,and assess the impacts and adjustment capability of main parameters such as seed,temperature,ethanol medium,and supersaturation on the precipitation kinetics and alumina hydrate type during co-precipitation process.The results clarify that gibbsite and boehmite both can be precipitated from supersaturated sodium aluminate solutions simultaneously,and the competitive formation between Al(OH)3 and γ-AlOOH determines the main precipitate phases from pregnant liquor.Boehmite seeds,high temperature and ethanol addition can promote the boehmite precipitation and improve the mass fraction of boehmite in products.Co-precipitation changes the multimodal distribution of seeds to a normal and well distribution of products,and the particle size is more than several times that of seeds.

Solvothermal Synthesis of Boehmite and γ-Alumina Nanorods

Boehmite nanorods were synthesized by a solvothermal method using AICl3·6H2O in mixed solvents of water and aniline. The solvothermal time, heating temperature and the concentration of aniline have effects on the morphology of boehmite. γ-alumina nanorods were prepared by a simple thermal transformation of boehmite nanorods. A rational mechanism based on the oriented attachment is proposed for the formation of boehmite nanorods. The products were characterized by X-ray powder diffraction （XRD） and transmission electron microscopy （TEM）. Photoluminescence （PL） spectrum of the boehmite nanorods was also investigated.

Preparation and Phase Transformation Behavior of Boehmite via Heat Treatment in Water Vapor

Boehmite was prepared under heat treatment in water vapour, and the phase transformation of gibbsite heat-treated at various temperatures was investigated. The sample was characterized by scanning electron microscopy(SEM), X-ray diffraction (XRD), thermogravimetry and differential thermalanalysis (TG-DTA), fourier transform infrared (FTIR),and BET surface area.Effect of temperature on preparation was studied in the range of 155°–195°.With the increase in temperature, transformation of gibbsite into crystalline boehmites took place as indicated by the X-ray diffraction (XRD). The shape of the grains in the prepared sample was cube-like morphology.In water vapour gibbsite transform into boehmite by a dissolution - precipitation mechanism.

Submicron γ-LiAlO_2 Powder Synthesized from Boehmite

The present study reports a simple,effective and energy-efficient method to prepare γ-LiAlO2 powder as a matrix in a molten carbonate fuel cell(MCFC).In our experiments,aqueous solution based sol-gel technique was used to synthesize γ-LiAlO2.Highly dispersed AlOOH·nH2O and LiOH·H2O aqueous solutions were mixed to form a colloid mixture,which was calcined to synthesize γ-LiAlO2.Thermogravimetric analysis(TGA),X-ray dif-fraction(XRD),and scanning electron microscopy(SEM) were used to study the composition and morphology of the intermediate and final products.The analysis results showed that an intermediate product Li2Al4CO3(OH)12 was produced after the colloid mixture was dried at 80 ℃,and highly purified γ-LiAlO2 powder with fine particle size was resulted from the subsequent calcinations.A single MCFC was assembled with a matrix of the γ-LiAlO2 pow-der.The testing results showed that the matrix performed well in preventing gas leakage.

Influence of Nanoparticle Shapes of Boehmite Alumina on the Thermal Performance of a Straight Microchannel Printed Circuit Heat Exchanger

The efficiency and irreversibility defined based on the second law of thermodynamics provide a new path for heat exchangers design and make performance analysis more straightforward and elegant.The second law of thermodynamics is applied in a Straight Microchannel Printed Circuit heat exchanger to determine the thermal performance of different shapes of Boehmite Alumina compared to Al2O3 aluminum oxide.The various forms of non-spherical Boehmite Alumina are characterized dynamically and thermodynamically through dynamic viscosity and thermal conductivity,using empirical coefficients.The non-spherical shape includes platelet,cylindrical,blades,and bricks forms.Graphical results are presented for thermal efficiency,thermal irreversibility,heat transfer rate,and nanofluid exit temperature.The non-spherical shapes of Boehmite Alumina show different thermal characteristics concerning the spherical shape when there are variations in fluid flow rates and the nanoparticles fraction.Furthermore,it was theoretically demonstrated that non-spherical particles have higher heat transfer rates than spherical particles,emphasizing platelets and cylindrical shapes for the low volume fraction of nanoparticles and bricks and blades for high volume fraction.

Formation of CoAl layered double hydroxide on the boehmite surface and its role in tungstate sorption

Sorption of tungstate on boehmite（γ-Al OOH）is increased by co-sorption with Co^（2＋）over the near-neutral p H range.Batch uptake experiments show up to a 3-fold increase in tungstate uptake over the range WO4^（2-）=50–1000μmol/L compared to boehmite not treated with Co^（2＋）.Desorption experiments reveal a corresponding decrease in sorption reversibility for tungstate co-sorbed with Co^（2＋）.Reaction of boehmite with Co^（2＋）results in the formation of Co Al layered double hydroxide（LDH）,as confirmed by X-ray diffraction and X-ray absorption spectroscopy.Tungsten L3-edge X-ray absorption near edge structure（XANES）reveals that W（VI）is octahedrally coordinated in all sorption samples,with polymeric tungstate species forming at higher tungstate concentrations.X-ray diffraction and X-ray absorption spectroscopy indicate that the mechanism for enhancement of tungstate uptake is the formation of surface complexes on boehmite at low tungstate concentrations,while exchange into the Co Al LDH becomes important at higher tungstate concentrations.The results provide a basis for developing strategies to enhance tungstate sorption and to limit its environmental mobility at near-neutral pH conditions.

Solvothermal preparations of α-alumina and boehmite crystallites and investigations on the formation of their morphologies

The solvothermal preparations of α alumina and boehmite crystallites have been investigated, and the effects of solvothermal conditions such as reactive medium and temperature on the phase, crystallization morphology and size of the crystallites have been discussed. The calculation of the stability energies of the growth units of the crystallites has been performed based on the model of anion coordinate polyhedron’s growth unit. The results could explain the formation mechanisms of the crystallites.

Pristine point of zero charge (p.p.z.c.) and zeta potentials of boehmite’s nanolayer and nanofiber surfaces

The pristine point of zero charge(p.p.z.c)and zeta potential as a function of pH of boehmite oxide/hydroxide(α-Al_(2)O_(3)·H_(2)O)have been determined for three filter media.The active component in the first two filter media is boehmite nanofibers,only 2 nm in diameter and about 300 nm long.Boehmite nanofibers create high zeta potential(ζtrue≥46 mV)in aqueous solutions in the pH range of 3–8.The p.p.z.c.values were determined to be 11.60±0.15 for nanofibers grafted onto microglass fibers and 11.40±0.15 for agglomerated nanofibers.In the third filter media,a boehmite nanolayer in the form of monocrystalline oxide/hydroxide with a thickness of approximately 1.2 nm is electroadhesively deposited onto siliceous support material with large surface area of about 50 m^(2)/g,therefore forming a highly electropositive composite of boehmite nanolayer on the second highly electronegative solid.Boehmite’s oxide-hydroxide nanolayer surface creates high zeta potential(ζtrue≥50 mV)in aqueous solutions in the pH range of 3–8.The p.p.z.c.value was determined to be 11.38±0.15.The reported values are within accuracy,but they are much higher than the values reported in the literature.X-ray powder diffraction data were supplemented by microscopy,infrared spectroscopy in order to characterize fully synthetic boehmite surfaces.

Kinetics of AlOOH dissolving in caustic solution studied by high-pressure DSC

Mechanism functions and kinetic parameters of AlOOH（boehmite or diaspore） dissolving in sodium hydroxide solution were researched.The mixture of boehmite or diaspore and caustic solution was scanned by high-pressure differential scanning calorimetry（DSC） instrument with heating rate of 10 ℃/min,and differential equation method was used to analyse the DSC curves,combining with iterative method and linear least square method.The most probable mechanism functions for both boehmite or diaspore and caustic solution reactions were logically selected from 30 types of non-isothermal kinetics differential equations,according to the calculated results obtained by Matlab program.The most probable differential mechanism function of boehmite dissolving in caustic solution is f（α）=1-α,which reveals the first-order reaction with apparent activation energy of 79.178 kJ/mol and the preexponential constant 1.031×108 s-1.The function,f（α）=2（1-α）3/2,can describe the dissolution of diaspore sample in sodium hydroxide solution.The calculated results of kinetic parameters are apparent activation energy of 73.858 kJ/mol,preexponential constant of 5.752×107 s-1 and reaction order of 1.5.

Rotating hydrothermal route to red mud derived uniform hierarchical porous flowerlike boehmite(γ-AlOOH)microspheres:Force analysis on formation mechanism and superior adsorption performances for anionic dyes removal

Towards increasingly severe worldwide pollution of industrial solid waste red mud(RM)released from aluminum industry,constitutional valuable element Al has been successfully separated for a novel mild rotating hydrothermal synthesis(150℃,12 h,5 Hz)of the uniform hierarchical porous flowerlike boehmite(γ-AlOOH)microspheres in the presence of appropriate urea,which exhibit distinctly small average diameter(1.52μm)and narrow particle size distribution(PSD:1.12–1.97μm),as well as high specific surface area(129.37 m2 g^(−1)).On the one hand,the rotating hydrothermal synthesis promotes the mass and heat transfer,enablingγ-AlOOH microspheres at a lower temperature within a shorter time.On the other hand,moderate rotation provides predominant shear force,rendering the uniformγ-AlOOH microspheres with small average diameter and narrow PSD.The optimal AlOOH–U2M-R5Hz microspheres demonstrate satisfactory adsorption performance for Congo Red(CR)and Methyl Blue(MB),with the maximum adsorption capacities of 602.4 and 1208.7 mg g^(−1),respectively.Various isotherm models of Langmuir,Freundlich,Temkin and Dubinin-Radushkevich are utilized,adsorption kinetics are analyzed,adsorption mechanism is uncovered based on hydrogen bonding and electrostatic attraction.The increase in the temperature or the presence of coexisting cations facilitates the adsorption of CR,whereas coexisting anions weaken the adsorption of CR on the AlOOH–U2M-R5Hz microspheres.Furthermore,the excellent recycling performances and especially dynamic adsorption(retainment of removal efficiency of approx.99.0%within 1000 min)as well as authentic water bodies(e.g.tap water and river water)simulated wastewater treatment undoubtedly indicate great practical applications of the AlOOH–U2M-R5Hz microspheres,towards cleaner aluminum production and cost-effective sustainable solution to anionic dye-bearing wastewater.

Synthesization and crystallization mechanism of nano-scale γ-AlOOH with various morphologies

Nano-scale γ-AIOOH with various morphologies, such as whisker, bar, ball, and sheet, was synthesized successfully and control- lably through a facile hydrothermal method just by adjusting the pH value of the solvent. Based on the analysis of the experimental data, the growth mechanism of nano-scale γ-AlOOH in the hydrothermal process was established. It is proposed that the growth unit and the growth direction are determined by the pH value of the solution and the growth unit, respectively. One-dimensional γ-AlOOH, such as whisker and bar, is formed in lower pH ranges, while two-dimensional γ-AlOOH sueli as sheet is formed only in high pH environment following the plane expansion crystallization mechanism.

载体改性及其对负载型Fe催化剂降解苯酚废水性能的影响

采用聚乙二醇(Polyethylene glycol,PEG)改性的Boehmite为载体,利用浸渍法制备了Fe为活性组分的负载型催化剂。考察了催化剂对苯酚废水降解的催化活性,并通过SEM、BET以及XRD等技术手段对改性前后的Boehmite进行了表征。结果表明,改性后的Boehmite比表面积及孔体积都有所增大,孔径分布更加集中。催化剂活性显示:利用改性Boehmite所制得的Fe/PEG-Boehmite催化剂在苯酚废水降解过程中活性优于没有利用PEG改性的催化剂,二者在反应60 min后对苯酚废水化学需氧量(Chemical demand oxygen,COD)去除率分别为93%和67%。因此,对于活性组分含量相同的催化剂而言,PEG对Boehmite载体的改性有助于所制备催化剂对苯酚废水COD去除率的提高。

Rehydration and Phase Transformation of Aluminas

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Impact of nanoparticle shape on thermohydraulic performance of a nanofluid in an enhanced microchannel heat sink for utilization in cooling of electronic components

In this article,the thermal–hydraulic efficacy of a boehmite nanofluid with various particle shapes is evaluated inside a microchannel heat sink.The study is done for particle shapes of platelet,cylinder,blade,brick,and oblate spheroid at Reynolds numbers(Re)of 300,800,1300,and 1800.The particle volume fraction is assumed invariant for all of the nanoparticle shapes.The heat transfer coefficient(h),flow irregularities,pressure loss,and pumping power heighten by the elevation of the Re for all of the nanoparticle shapes.Also,the nanofluid having the platelet-shaped nanoparticles leads to the greatest h,and the nanofluid having the oblate spheroid particles has the lowest h and smallest pressure loss.In contrast,the nanofluid having the platelet-shaped nanoparticles leads to the highest pressure loss.The mean temperature of the bottom surface,thermal resistance,and temperature distribution uniformity decrease by the rise in the Reynolds number for all of the particle shapes.Also,the best distribution of the temperature and the lowest thermal resistance are observed for the suspension containing the platelet particles.Thereby,the thermal resistance of the nanofluid with the platelet particles shows a 9.5%decrement compared to that with the oblate spheroid particles at Re=300.For all the nanoparticle shapes,the figure of merit(FoM)uplifts by elevating the Re,while the nanofluids containing the brickand oblate spheroid-shaped nanoparticles demonstrate the highest FoM values.