Recent processes for the production of alumina nano-particles

Journal Pre-proofs Recent processes for the production of alumina nano-particles S. Said, S. Mikhail, M. Riad PII: DOI: Reference:

S2589-2991(20)30005-7 https://doi.org/10.1016/j.mset.2020.02.001 MSET 146

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Materials Science for Energy Technologies

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11 September 2019 1 February 2020 1 February 2020

Please cite this article as: S. Said, S. Mikhail, M. Riad, Recent processes for the production of alumina nanoparticles, Materials Science for Energy Technologies (2020), doi: https://doi.org/10.1016/j.mset.2020.02.001

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Article Review

Recent Processes for the Production of Alumina nano-particles By S. Said, S. Mikhail, M. Riad Egyptian Petroleum Research Institute [email protected] Abstract Alumina nano-particles have wide usage in the adsorption and catalysis fields, because of its acid–base properties, high specific area, mechanical and thermal stability. The first part of the review interested on the various processes for the production of nano-particles alumina. The second part outlines the functionalization of nano-particles alumina with different function groups. Finally, the wide applications of nano-particles alumina in different fields are reported. Utilization of nano-particles alumina described in various industrial processes are evaluated from the standpoint of the importance of these reactions for technological applications, as reported in the literature

1. Introduction Nano structural alumina with high surface area, thermal stability, conductivity, mechanical strength, stiffness, inertness to most acids and alkalis, adsorption capacity, wear resistance, oxidation, electrical insulation, and non-toxic; have potential applications in industrial fields [1–4]. Different authors reported the relation between mechanical properties (stiffness and hardness) of alumina nano-particles and their morphological structure. Hossein-Zadeh et al., [5] established the fine flattened nano-structure of alumina particles via scanning electron microscopy (SEM). The addition of nano- particles alumina to molten aluminum modifies the microstructure and mechanical properties of Al–Al2 O3 composite. In addition, Toroghinejad et al., [6] correlate the mechanical properties of alumina nano-particles (tensile and micro-hardness tests) and the microstructural observations with the SEM that confirmed the uniformity of particles distribution that improved the alumina matrix.

Zhao and Li [7] incorporated spherical alumina nano-particles into diglycidyl ether of bisphenol- epoxy resin and study the mechanical properties of the Al2O3/epoxy nanocomposites. The results from tensile tests indicated that the incorporation of the alumina nano-particles into the epoxy can improve the stiffness of the matrix. In general, alumina nano-particles is an amphoteric oxide and occurs in nature as a mineral corundum (Al2O3); diaspore (Al2O3·H2O); gibbsite (Al2O3·3H2O); and most commonly as bauxite, which is an impure form of hexagonal gibbsite [8-13]. The known group of alumina (Fig. 1) is low-temperature alumina Al2O3. n H2O (0-n6). This group obtained via dehydration of boehmite and bayerite at ~ 600oC, (as η, χ, ρ, and γ-Al2O3). Meanwhile, high-temperature alumina (anhydrous Al2O3, as θ, δ, κ, and α-Al2O3) obtained at temperature ranged from ~ 900- 1000oC [14-19] The structure of γ-Al2O3 regarded as a defect spinel with a deficit of cations, and characterized by cubic close-packed oxygen lattices. The aluminum ions in the octa – and tetrahedral interstices form particles with a small and narrow size distribution and possessed a high surface area: ~300 m2/g. Upon the thermal treatment of γ-Al2O3, it transforms to other crystal structures (like α-Al2O3) and both of porosity and surface area diminished; while the pore size is increased. α-Al2O3 (Fig. 2) characterized by hexagonal close-packed lattices contains a closed packed array of oxygen atoms with aluminum ions distributed symmetrically among the octahedral interstices, and possessed a low surface area: ~7 m2/g [20-24]. As well known α – alumina characterized by low surface area, different population of surface active sites and large particle size, which leads to a lower catalytic activity as compared with γ- alumina. The high surface area and open porosity of γ- alumina enable it to be used as catalysts and adsorbents [25, 26]. As known, the industrial catalytic reaction like Fischer -Tropch required medium pore system to enhance higher production of C5+, as compared with the narrow pore. The selectivity for the production of C5+ is increased from γ- to α –alumina by going from the narrow to the medium pore size (Fig. 3). The calcination temperatures are the judgment for this result. The narrow pore samples are heat treated at high temperature to obtain medium pore size ones. The thermal treatment of γ- to δ- alumina cause a natural collapse of finer pores, while new smaller pores are created from δ- to θalumina. The thermal treatment causes a rearrangement of the oxygen lattice that creates tension and crystal breakage. For Co/ α -alumina catalyst larger pores enhance

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chain growth, the cobalt crystallites are rather large, and the polymerization reaction occurs to produce C5+ [27, 28]. The acidity and basicity are also the factors formative the catalytic properties of alumina. Aluminum ions considered as Lewis acid or Bronsted basic sites (an acceptor of electron pair), while Lewis base “Bronsted acid sites” is the donor hydroxyl ions. However, the dehydration of two neighboring hydroxyl ions from the surface of alumina causes the formation of strained oxygen bridge, active Lewis acid sites [29], (Fig. 4). This work highlights the methods for the production and functionalization of alumina nano-particles, with a wide range of potential applications in various industries.

2. Processes for the production of alumina nano-particles 2.1. Preparation of alumina nano-particles Alumina nano- particles are prepared by different methods such as arc plasma, hydrothermal, sol–gel, and precipitation. Saravanakumar et al., [30] treat aluminum dross (waste generated from aluminum melting process, contains aluminum metal, aluminum oxide, and aluminum oxynitride) using plasma arc melting process. The aluminum dross melted and evaporated by the plasma arc established between a crucible anode and a rod type hollow cathode made of graphite. High temperature and air entrainment into the plasma inside the crucible converted the dross into fine alumina particles with plasma power: 5 - 10 kW. The results informed that arc plasma technology is applied to convert aluminum dross into fine alumina particles. Madhu Kumar et al., [31] prepared alumina nano- particles in a d.c. arc plasma reactor under isochronal oxygen flow conditions. Transmission electron microscopy (TEM) informed the formation of spherical particles (50 nm) and confirmed the existence of the nano-phase structure. The Infrared and the absorption spectrum realized the collisionally quenched structure resulting in very fine particulates condensing from the plasma. Kumar et al., [32] prepared also alumina nano-crystalline particles by the d.c. arc plasma method at atmospheric conditions using aluminum electrodes. TEM established the formation of ultra-fine nature of the particles.

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Fu et al., [33] prepared nano-structured alumina particles by combustion of aluminum powder in microwave oxygen plasma. The results informed the main phase formed is γ-Al2O3, with a small amount of δ-Al2 O3. TEM observed that the particles are truncated octahedral in shape, with mean particle sizes of 21–24 nm. Balasubramanian et al., [34] studied the nucleation of alumina nanocrystalline particles and aluminum oxy-nitride phases by spray drying, and then subjected to plasma melting and quenching. The results revealed that the formed material comprised of nano-crystalline particles of alumina aluminum oxy-nitride. Tesar et al., [35] investigated the hybrid suspension plasma spraying of dry coarse aluminum oxide powder with chromium oxide suspension using hybrid water/argonstabilized (WSP-H 500) plasma torch, which was utilized for the deposition of coatings with very high α-alumina content reaching up to 90%. Stanislaus et al., [36] prepared alumina nano-particles via hydrothermal method and investigate the pore widening of alumina phase during the process in the presence and absence of additives such as P, F, phenol and acetic acid. The results reveal that the pores could be widened selectively with greater than 70% of the total pore volume in the desired pore size range by low temperature hydrothermal treatment. Noguchi et al., [37] prepared alumina nano-crystalline particles via hydrothermal method in supercritical water in a continuous flow reaction system under supercritical conditions of water, temperature range: 400 to 500 ◦C, pressures range: 25 - 35MPa, and the reaction time was 63 ms to 3 s. The results revealed that alumina nanoparticles obtained at 410 ◦C through the dehydroxylation reaction in supercritical water. Qu et al., [38] investigated the preparation of alumina nanotubes by the anionic surfactant and sodium dodecyl sulfonate (SDS) as templates via a hydrothermal method. The results indicated that the prepared alumina nano-particles have outer diameters: 6 - 8 nm with length > 200 nm. However, the common methods to prepare alumina nano-particles with different morphology and sizes are sol-gel and co-precipitation. Hexagonal and spherical alumina particles prepared by the co-precipitation method while spherical alumina particles formed by the sol-gel method [39, 40]. As known, the sol-gel precursors for the preparation of alumina are metal alkoxide. Recently, the alkoxo groups are substituted by chelating ligands such as oximes, schiff’s base, and glycols. So on, the modification of electronic states of the precursor, 4

affects the hydrolysis and condensation reactions, resulted in the alteration of the morphology of the alumina sample. Mirjalili et al., [41] have been prepared alumina nano- particles via sol–gel method using aqueous solutions of aluminum isopropoxide and 0.5 M aluminum nitrate. The stabilizing agents used were disoulfonic acid disodium salt (SDBS) and sodium bis-2ethylhexyl sulfosuccinate (Na (AOT)). The results indicated that the SDBS produced finer particles and spherical shape nanoparticles, compared to Na (AOT). Sainia et al., [42] informed that δ-alumina obtained on using 8-hydroxyquinoline modified Al (III) alkoxide while on using salicylaldehyde, α-alumina obtained as a final product (Fig. 5). The authors investigated the reactions of Al (III) iso-propoxide with acetoxime in benzene to yield complexes of the type [Al (OiPr)3-n{ONC (CH3)2}n] (Fig. 6-a), where n = 1, 2 or 3. TEM results (Fig. 6-b) reveal the formation of cubic phase (γ-alumina) with average crystallites size of 7–30 nm. Optically transparent crack free alumina film was deposited on glass substrate using alumina sol prepared by complex [Al (OiPr){ONC(CH3)2}], through dip coating method (Fig. 6c). The alumina film is found to be 95% optically transparent in the visible region. Esmaeilirad et al., [43] prepared γ-alumina sample by the sol-gel and the coprecipitation methods, as verified via X-ray diffraction analysis (Fig. 7-a). Scanning electron microscopy (SEM) results (Fig. 7-b) established the formation of small crystallite nano-particles, which prepared by sol gel as compared with the coprecipitation methods. The γ -alumina sample prepared by the sol-gel method using ethanol as a solvent (AlSE) was the best support for lanthanum catalyst and its performance for total oxidation of toluene in air is reached to ~90%. Belekar et al., [44] prepared highly porous alumina granules by modified sol–gel method. Activated alumina granules were obtained through hydrolysis of Al (NO3)3 and the reaction was controlled via aqueous ammonia in an ammonia–paraffin oil bath. The results established that the prepared granules are porous amorphous γ alumina nano-particles with an average grain size of 30 nm and a large BET surface area 447m2/g, as compared with commercial alumina. It also shows better fluoride removal from aqueous solution with regeneration and reusability after ten cycles of usage. Xu et al., [45] studied the preparation of transparent nano-composite hydrogels (AD gels) by photo-initiated free radical copolymerization of acrylic acid and N, Ndimethylacrylamide in the colloidal solutions of alumina nano-particles, (Fig. 8-a). 5

The obtained hydrogels displayed well-defined porous structures (SEM, Fig. 8 – b) and outstanding mechanical properties with tensile and compressive strength up to 1.88 MPa and 28 MPa, respectively. The FT-IR spectra (Fig. 8–c) indicated the presence of strong chelation reactions between alumina and polymer matrix, which are responsible for the formation of AD gels and their excellent mechanical performance. Feng et al., [46] prepared dispersed alumina powders via non-aqueous precipitation process using aluminum powders as aluminum source, and acetic acid as precipitant. The mechanism of preparation of ultra-fine alumina powders via oxygen donor and assisted by alcohol as solvent such as methanol, ethanol, isopropanol, is observed as follow:

Lisitsyn et al., [47] prepared pure alumina nano-particles via thermal treatment of boehmite in vacuum furnace. The aluminum powder is fully oxidized in few seconds in presence of water steam at temperature ~300oC. The product of this oxidation is single crystal boehmite, with size ranged from 10 to 200 nm, and the primary crystals are agglomerated into the particles with the size of ~10 nm. After that, the boehmite is thermally treated at first in muffle furnace at 600oC to remove crystallized water and then in vacuum furnace at ~ 1600 oC to produce α-Al2O3.

2.2. Extraction of alumina a. from clay The increase demand of alumina directed the attention to develop technologies to produce alumina from low-grade ores, such as extraction of alumina from clays (kaolin).

Kaoline

is

abundant

mineral

consists

mainly

from

kaolinite

Al2O3.2SiO2.2H2O (high alumina content ~ 25-40 %). Kaolin characterized by its

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unique physical and chemical properties because it is chemically inert at a wide pH range [48]. The processes used for extracting alumina from clays are; an acid process that uses sulfuric acid, hydrochloric, or nitric acid to dissolve the alumina selectively, usually after the clay has been roasted. Acid leaching is used to extract heavy metal ores contained in the clay using any suitable acid leachant. The basic reaction for the process is given by: Al2O3H2O + 3H2SO4

Al2 (SO4)3 + 4H2O

Yadav and Bhattachary [49] prepared α - and γ - alumina beads via the acid leachate of kaolinite by an oil-drop method. In this process, alumina sol is converted to a semigel form for the fabrication of beads (Fig. 9). The results indicated that γ -alumina beads were found to have a higher surface area and porosity than α- alumina beads. The uni-modal distribution of pores in the meso-porous region of γ- alumina beads suggests the possible application of these beads in the adsorption process. El Deeb et al., [50] study the extraction of alumina from the kaolin by the leaching process, using an aqueous solution of sodium carbonate as a leaching agent. The kaolin is firstly sintered before the leaching process, to achieve the dehydroxylation of the kaolinite, which is the main mineralogical phase in the kaolin. After that, the kaolinite is heat treated to transform to meta-kaolin. Meta-kaolin is an amorphous alumino-silicate structure, from which alumina could be easily leached. About 87% of the alumina in the kaolin was extracted at 1360 °C and briquetting pressure of 5 MPa.

b. from Coal fly ash Coal fly ash is rich with alumina (nearly 50%) and is equivalent to mid-grade bauxite. The processes for the extraction of alumina from coal fly ash included; sintering, hydro-chemical, and acid processes (Fig. 10, 11). The sintering process usually coupled a reaction of coal ash with sintering agent powder to form soluble alumina compounds under high temperature [51]. The soluble alumina is treated with sodium carbonate to extract the alumina particles. The hydro-chemical process included the extraction of alumina in a wet alkaline process [52].

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The acid process included the reaction of hydrochloric (or sulfuric acid) to produce aluminum chloride (or aluminum sulfate) [53], which crystallized from the acid medium and are subsequently decomposed to separate aluminum. Sun et al., [54] applied a new process of alumina extraction from coal fly ash by using ammonium sulfate in high temperature fluidized bed to form NH4 Al(SO4)2 in solid state. High purity alum is precipitated by the reaction of NH4 Al(SO4)2, dissolved in water and then followed by crystallization. Coal ash and ammonium sulfate mixed, and granulated in the presence of binder material (Fig.12). The high temperature fluidized bed reactor is used for the first time to recover the alumina (90%) in solid state. The circulating fluidized bed boilers with lower combustion temperature can produce higher quality coal ash. The thermal treatment of high-alumina coal ash converts the content γ –Al2O3 into θ- Al2O3 that converted into α- Al2O3 at ~1000 °C [55]. Yao et al., [56] studied the recovery of alumina from coal fly ash based on the autodisintegration of sinter containing calcium aluminates and di-calcium silicate. Shi et al., [57] used a clean and efficient two-membrane and three-chamber electrolysis approach to extract alumina from coal fly ash (Fig.13). The process involves the mixing of coal fly ash with H2SO4 to obtain sulfuric acid leachate then extract Al (OH)3 from leachate as followed:

It is clear that, sulfuric acid and oxygen are produced in the anodic chamber, whereas Al (OH)3 and H2 are produced in the cathodic chamber. The formed aluminum hydroxide is considered as an alumina resource, while hydrogen is a source of clean fuel. Li et al., [58] study the extraction of alumina from coal fly ash using a mixed alkali consisted from sodium and calcium hydroxide via the hydrothermal method. The results indicate that the extraction of alumina increased with the increase in the reaction temperature, the alumina extraction ratio could reach 91.3%.

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Guo et al., [59] studied the extraction of alumina from coal fly ash by predesilicating—Na2CO3 activation—acid leaching process (Fig. 14). This process aimed to decrease and to adjust the Al/Si molar ratio in coal fly ash. The results showed that the dissolution of SiO2 reached 37.3% at 1 mL/g of liquid to solid ratio, 100 °C and 2.0 h, then the Al/Si molar ratio in coal fly ash could be raised to 1.21. The mixing of desilicated and the as-received coal fly ash causes an increase in the dissolution of Al2O3 reached to ~87%. The consumption of sodium carbonate upon the predesilication process is shown to be a low value as compared with that in the direct activation process. Guo et al., [60] were also studied the alumina extraction from co-treated coal fly ash (CFA) and red mud (RM) -Na2 CO3 system (Fig. 15). Results showed that the complete dissolution of alumina in CFA and RM reached 90.4%. The consumption of sodium carbonate reduced about 80% for CFA-RM-Na2CO3 system, as compared to that for CFA-Na2CO3 system. Tripathy et al., [61] studied the extraction of alumina from coal fly ash and alkali treated fly ash residue (to remove silica) via leaching in sulfuric acid medium. Solubilisation of alumina in the acidic medium is shown to be more efficient process for the alkali treated fly ash residue as compared to the fly ash. Besides, the leaching recovery for alumina is improved upon the addition of NaF in the acidic leaching medium. Xue et al., [62] investigated the extraction of alumina and production of ferrosilicon alloy from coal fly ash by a vacuum technology. The process included, vacuum thermal reduction, sieving and magnetic separation. The results indicated a vacuum environment could promote the decomposing of mullite at a lower temperature with the formation of ferrosilicon alloys. Sieving and magnetic separation processes extract both of the ferrosilicon alloys and the alumina. The recovery rate of alumina is 82.61%, and the content of alumina in the non-magnetic portion was 87.02%.

3. Functionalization of alumina nano-particles Alumina nano-particles have some disadvantages as: their surfaces are hydrophilic and so have high chemical activity, besides their high surface area and surface energies, allow it to aggregate to minimize the surface energies. In order to avoid these disadvantages, the functionalization of alumina surface is applied. Surfactant

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comprised of polar and non -polar functional groups, the polar groups can decrease the surface force of the hydroxyl groups. As a result, the organic chains adsorbed or bonded on the particles surface, prevented the formation of oxygen bridge bonds and agglomeration between alumina nano-particles [63, 64].

3.1. Chemical surface functionalization Chemical functionalization depends on the covalent linkage of functional groups (silane, cyano, carboxylic acid, and epoxy groups) on the surface of nano-particles alumina [65, 66]. Konx et al., [67] and Pesek et al., [68] were among the first to use silane groups for functionalization of alumina. Figure (16) shows that the hydroxyl groups on the surface of alumina can react with the silane alkoxy groups to form AlO-Si bonds. The function groups of silane presented reactive groups on the surface, which creates sites to anchor the immobilization linkers. The steric hindrance and electrostatic repulsion between the particles arising from the silane groups could prevent further aggregation of the alumina nano-particles, as confirmed from TEM results (Fig. 17).

3.2. Functionalization of the alumina nano-particles by grafting This method increases the functionality, creates a new surface electron distribution, and enhances the particles dispersion via repulsion force of alumina nano-particles [69, 70]. The method depends on the propagating of the grafted polymers from the surface of metal oxide, which can involve radical, anionic, or cationic polymerization processes [71]. The grafting process is classified into two types; the first described the reaction of reactive end groups of pre-fabricated polymers with the functional groups on the surface of nano-particles, which called (grafting to) [72]. The second is (grafting from), in which the surface immobilized initiators are utilized to grow polymers in situ to generate a polymer brush, the polymer grafting of alumina nano-particles is observed in Fig. (18, 19), as discussed by He et al., [73]. While, Cheikh et al., [74] studied the grafting using acrylic co-polymer molecules containing both carboxylic and hydroxyl-vinyl groups on the alumina surface. The carboxylic groups in the acrylic copolymers interact with hydroxyl groups on the alumina surface, and hydroxyl vinyl groups are expected to act as a binder. Kima et al, [75] prepared polystyrene-grafted alumina nano-particles via silane coupling method between dimethyl-chloro-silane - polystyrene (PS) and γ-alumina

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nanoparticles (Fig. 19-a). This material has an efficient power to act as a surface passivity film on the oxide layers. SEM images (Fig. 20 -b, c) of the alumina nanoparticles before and after the grafting process, reveal the formation of spherical nanoparticles with a diameter of ∼50 nm and the average diameter was estimated to be 51.8 nm. Carreño et al., [76] prepared super hydrophobic surfaces with silica and alumina nano-particles on a polyurethane-based paint. The preparation method depends on spraying functionalized nano-particles on the partially cured polymer matrix. Liu et al., [77] studied a green method for the modification of alumina surface using fatty acids (oleic acid) and only water as a dispersing medium. The alumina nanoparticles were separated from water, while water will recycle. Finally, alumina keeps its crystalline structure with a higher dispersion in organic medium than the raw ones. Kamboj et al., [78] prepared functionalized alumina via a wet combustion technique using iron oxide as oxidant nano-particles, in presence of urea and glycine (as fuel). The product obtained on using glycine is FeAl2O4 with crystallite size of 12 nm (Fig. 21). While, AlFeO3 is formed with crystallite size of 21 nm when urea is used as a fuel (Fig. 22). The agglomerates of spherical nano-particles of γ-Fe2O3 (crystallite size <15 nm) were homogenously distributed over the alumina framework structure.

4. Applications of alumina nano-particles 4.1. Alumina nano-particles as additive Alumina nano-particles are used as fuel additives due to its positive influence on liquid fuels’ combustion and emission performance [79]. Kannaiyan and Sader [80] used dispersed alumina nano-particles as additive to improve the spray characteristics of liquid fuel as the density, viscosity, and surface tension that are relevant to the atomization process. The nano-particles dispersed in liquid fuel tend to slightly alter the transient nature of the spray formation, enhance the liquid sheet instability, reduce the breakup length, and decrease the mean droplet sizes when compared to those of the pure liquid fuel. Hosseini et al., [81] used also alumina nano-particles additives to improve the thermophysical properties of the diesel fuels as; thermal conductivity, mass diffusivity, flash point, fire point, and kinematics viscosity. Ben Romdhane et al., [82] reported also the use of alumina particles as additive (have size of few micrometers) can enhance the combustion quality of fuels.

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Khalilpourazary and Salehi [83] discussed the role of alumina nano-particles on improving the surface characteristics (surface roughness/microhardness, and hardness) of alloys. Lonia et al., [84] investigated a solar-driven organic rankine cycle with alumina/oil based solar dish concentrator. The results reveal that, the thermal performance of this cell and the electricity production are improved by increasing the alumina nanoparticles concentration. Ilyas et al., [85] prepared functionalized oleic acid coated alumina and dispersed it in thermal oil to enhance its thermo-physical properties for advanced cooling systems (Fig. 23). Arani et al., [86] informed that the hydrophilic nature of alumina nanoparticles enabled it to act as a nano-filler in the polymer processing to form nanocomposites.

4.2. Alumina as a ceramic material Ceramic membrane filtration has attracted great attention due to the potential for the improvement in energy saving, operation costs, and environmental impact [87]. Alumina was used as a ceramic membrane filtration and stationary phase in chromatography for separation of various materials. The pre-coat filtration method is operated to decrease the fine undesirable particles in the treated feed. Pre-coat filter is prepared via the precipitation of the diatomaceous earth (DE) or twinned alumina nano-sheets (TAN) particles on a substrate [88]. The TAN particles (Fig. 24) were prepared by the hydrolysis of metal salt. The results show that the TAN pre-coat has superior flow properties and can decrease the turbidity of the filtrate faster than the DE pre-coats. The better efficiency of the TAN pre-coat related to: - the resistance of the TAN pre-coat to the compaction during filtration, because the unique twinning of the alumina nano-sheets forming the TAN particles, - the isotropic permeability of the TAN aggregates. Alumina is a typical engineering ceramic and can used in aerospace, biomedical, and ballistic applications. The ceramic membrane support layers was prepared using pyrophyllite and alumina treated at 1350 °C, and subsequently coated with alumina powder suspension to form a narrow pore size material [89]. The performance of the membrane is tested in water resource recovery facility, to improve nitrogen removal and produce high quality effluent.

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Porous alumina ceramics were prepared from rice husk and sugarcane bagasse through the powder metallurgy technique (Fig. 25). The results showed that, the porosity (44–67%) and the pore size (70– 178 μm) of porous alumina samples maintained a linear relationship with the potential agricultural wastes as pore-forming agents loading. The prepared alumina showed tensile and compressive strengths of 20.4 MPa and 179.5 MPa, respectively [90]. Shahzada et al., [91] prepared an alumina-carbon nano-tube composite membrane through a powder metallurgical method (Fig. 26). The membrane was fabricated via uni-axial pressing of the composite powder mixture. The gum arabic and sodium dodecyl sulfate were used as dispersants to offer dispersion of the carbon nano-tubes within the alumina matrix. Upon increasing the compaction load and sintering temperature from 50 to 200 kN and 1200 to 1500 °C, the porosity of the membrane reduced from 65% to 31% and its strength raised from 0.76 to 15.64 MPa, respectively. The prepared membrane used as adsorbent for the adsorption of the cadmium. The membrane showed 93% removal of the Cd ions from a water solution containing 1 ppm Cd at pH 6. The membranes were also prepared via a carbon transmittance method, which considered as a continuous growth method for carbon nanotubes (CNTs). In this method, a catalyst-embedded membrane separates one chamber containing carbon source gas and another chamber filled with an inert gas for CNT growth. The membranes were fabricated by filling the nano-pores of a self-supporting anodic alumina membrane with chemical-vapor-deposited Fe using Fe(CO)5 as a precursor (Fig. 27). Nano-carbon was grown by a catalytic chemical vapor deposition (CCVD) method, which is a standard technique for CNT growth, at 700 °C using C 2H2 as a carbon source. The embedded Fe was oxidized during the temperature rise proceeding to C2H2 addition. When the pores of the anodic alumina membrane were loaded with Fe oxide, the loaded Fe oxide functioned as a good catalyst [92]. Mg-MOF-74 is a metal organic framework with the highest CO 2 adsorption efficiency. Thicker films (up to 14 μm) were prepared via raising the fraction of ethanol and water in reaction solution, to control the thickness of Mg-MOF-74 membranes. Films were produced on porous tubular alumina supports, CO 2 flow of 7.4 x10-7 mol m-2 s-1 Pa-1 and an ideal CO2/CH4 selectivity of 0.5 were resulted [93]. Deposition of γ-alumina film by spraying alumina granules in a vacuum at room temperature was operated using an aerosol deposition method, which had a 13

supplemental and carrier gas flow lines. Granule spray in vacuum is a technique for precipitation of dense nano-structured ceramic film at room temperature by spraying granules that are flow able agglomerates of fine ceramic particles [94-96]. Multi walled carbon nano-tubes filled alumina composites with concentrations ranging from 2.5 to 12.5 vol.% are used for machining. Proper machine-ability is observed with concentration of 7.5 vol.% [97]. Alumina borate nano-fibers were prepared via electro-spinning combined with sol-gel technique; Al2O3-B2O3 binary systems are ceramic material has high melting point, low thermal expansion, density, and good chemical inertness [98]. In addition, calcium-magnesium-alumina-silicate material (CMAS) has been used in thermal barrier coatings technique (TBCs). The prepared TBC ceramics, BaLn2Ti3O10 (Ln=La, Nd), have resistance to the diffusion of molten CMAS at 1250 °C. The gathering of Ba in the molten CMAS activated the crystallization of the melt, resulted in the formation of many BaAl2Si2O8 crystals, which could reduce the mobility of the molten CMAS [99]. The mullite (3Al2O3.2SiO2) is a traditional ceramic and has different applications especially in refractory materials [100]. The most frequent methods used to prepare mullite based on the thermal decomposition of clay or kaolin, supplemented with alumina to achieve the desired stoichiometry, or also by mixing silica with alumina at suitable thermal treatment [101].

4.3. Alumina as an industrial material Alumina is used as a support material due to its unique porosity. Cobalt supported on γ-alumina is an efficient catalyst for Fischer–Tropsch reaction; the catalyst has efficiency to maximize the yield of higher hydrocarbons and selectivity to C5+ [102]. Co3O4 spinel active phase dispersed over alumina extradites (9 × 25 mm) was prepared by incipient wetness impregnation using glycerol-assisted the impregnation technique [103]. The prepared catalysts are tested for the de-nitrogenation reaction. The results show that the dispersion of spinel active phase offer high activity when the catalyst is prepared in the presence of the organic components of the precursor (glycerol or urea). Kungurova et al., [104] prepared ruthenium (0.2–1 wt.%) promoted cobalt supported on δ-Al2O3 catalysts and investigated their activity in Fischer-Tropsch reaction. It

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was shown that cobalt in oxide precursors is a component of the spinel-like Со3xAlxO4,

which has superior activity towards higher hydrocarbon production.

The impact of sulfur poisoning during dry reforming of methane on a Rh/ γ-Al2O3 catalyst was investigated by adding up to 30 ppmv of SO2 or H2S to the feed (CH4/CO2/N2= 1/1/2) at 800–900◦C. Alumina support increase the metallic species interaction and retard the catalyst poisoning [105]. The platinum promoted sasol catalyst is prepared using γ –alumina as a support via impregnation with tetra-ethoxy- silane (Puralox SCCa-2/150 or -5/150: pore volume 0.5 mL/g; surface area 150 m2/g) and the catalyst is thermal treated to give a surface concentration of 2.5 Si atoms/nm2 [106]. The catalytic behavior and stability of rhodium supported on La-doped alumina were studied towards the CO oxidation reaction. Alumina doping with La leads to alteration of the alumina donor sites and increase the catalyst efficiency [107]. Chromium oxide/ Zr adapted alumina catalyst is used for stable and selective propane dehydrogenation in fluidized moving bed process and in the absence of oxygen [108]. Alumina is used as a coat for natural clay pyrophyllite material; the resulted material is used as a support for catalytic active metals [109]. New non-fluorinated precursors (Pd (PTQD)2 and Pd (DGM)2) derived from Pd complexes of di- methyl-glioxime and phenanthrene quinine dioxime were used for supercritical carbon dioxide deposition of Pd on γ-alumina support. The prepared nano-particles were used as catalysts for Suzuki- Miyaura reactions of bromobenzene and phenylboronic acid in two different solutions of n-methyl-2-prolydon and dimethyl formamide at 60 °C [110, 111]. Moreover, the addition of alumina confines the grain growth of zirconia, and the segregation of alumina to the grain boundaries gives significant strengthening and toughening effect. Alumina- zirconia ceramic has improved mechanical properties at high temperatures such as good thermal stability, resistance to wear, and low thermal conductivity. In addition, both alumina and yttria (7.5 mol) can stabilize zirconia, to prepare stable non-transformable tetragonal zirconia while decreasing the possibility of reaction of yttria and alumina to form additional phases [112]. Garbarino et al., [113] prepared high-pore-volume alumina and La-doped alumina and tested as catalysts for ethanol conversion to ethylene and diethyl ether and for diethyl ether cracking.

15

Mikhail and Riad [114] prepared 20 wt% MoO3 supported on nano-particles alumina, magnesium–aluminum and chromium–aluminum mixed oxide materials via impregnation technique and tested for the dehydrogenation reaction of cyclohexane. The results showed that Mo/magnesium–aluminum oxide and Mo/chromium– aluminum oxide catalysts show high activity (96.0% and 91.0%) and selectivity (96.0% and 95.0%, respectively) toward benzene formation at 400 oC, as compared with Mo/alumina one. Alumina–carbon composite catalysts (Al2O3-S) were prepared by reacting Al (NO3)3. 9H2O and the polyether-based surfactant used for the development of chemicals derived from biomass. Upon the increase in surfactant amount, the resulting Al2O3-S shows an increase in carbon content, surface area, and acidic/basic sites concentration. Transfer hydrogenation of furfural to furfuryl alcohol using the catalyst revealed that Al2O3-S, which had the highest carbon content, had the highest catalytic activity: furfuryl alcohol yield of 95.8% at 130 0C for 6 h. The reuse of the catalyst, leads to the decrease of the activity. The main reason of the deactivation was found to the decrease in aluminum content by leaching during the reaction [115]. Sabaghi et al., [116] prepared aluminum oxynitride powder (AlON which has great resistance against chemical attacks and isotropic optical properties) by carbothermal reduction nitridation method. Al2O3/C core-shell nano-particles were prepared via the pyrolysis of Al2O3/polyacrylonitrile (PAN) nano-composite precursor at 800 °C for 2 h in an argon atmosphere. Alumina/PAN precursor was prepared by ultrasonic method at room temperature. Then, by two-step thermal treatment of Al2O3/C coreshell nano-particles are operated at 1500–1600 °C for 2 h, followed by subsequent heating at 1750 °C for 1 h in N2 flow to obtain AlON (Fig. 28, 29). The zirconia-loaded alumina was self-prepared, and then used as support for Pt-Sn-In catalysts for propane dehydrogenation reaction. The activity and behavior of Pt-Sn-In/ xZr-Al catalysts were compared with those of both Pt-Sn-In/Al and Pt-Sn-In/ Zr, (Fig. 30) [117]. Graphene oxide- alumina matrix composites were prepared via powder metallurgy and consolidated by spark plasma sintering. Results reveal an increase (35%) of the fracture toughness for composites containing 0.5 wt % graphene oxide compared to sintered pure alumina [118]. The activity of ZnCl2/ Al2O3 catalyst was measured towards the conversion of isopropanol and HCl to isopropyl chloride in a continuous reactor. The results 16

indicate that the highest yield of isopropyl chloride was obtained over 5 wt. % ZnCl2 on commercial Al2O3 (95.3 %) [119]. Alumina is used as support for biodiesel production catalysts. Alumina-supported potassium oxides catalysts were prepared via impregnation method for the transesterification reaction of vegetable oils for biodiesel production (Fig. 31). KF/Al2O3 showed higher catalytic activity and a small amount of catalyst requirement in the trans-esterification reaction, indicating that it can be applied as a potential catalyst in the industry [120]. Phenol-formaldehyde resin was prepared, and adapted by alumina nano-particles (ANPs). The resin was used in the manufacture of plywood, the curing time and the bonding strength was considered. The results revealed, the suitable doping amount of ANPs, the curing rate, and the bonding strength were increased considerably [121]. Nano-particles alumina with different acid-base properties have been used for the dehydration of glucose to 5-hydroxymethylfurfural (HMF). The acidic alumina observed the highest total acidity, and the best catalytic activity, but the HMF yield was ~20%. Upon the addition of CaCl2 in the reaction medium the catalytic activity was markedly improved at short time. Thus, the conversion of glucose and HMF yield was enhanced (96%, at 175◦C after 15 min) in presence of 0.65 g calcium chloride and acidic alumina as catalyst [122]. Alumina as also used to support Er3+ catalyst (0.1–0.17 at. %), which observed visible light photoluminescence [123]. Mayordomo et al., [124] studied the adsorption of strontium metal ions using binary mixtures of smectite and γ-alumina nano-particles under various parameters of pH, ionic strength, and adsorbate concentration. In smectite, strontium adsorption occurs via cation exchange, meanwhile the two adsorbents showed surface complexation with a non-electrostatic model. The addition of alumina nano-particles to smectite enhanced the strontium adsorption under alkaline pH and high ionic strength. Under acidic pH and low ionic strength, no adsorption improvement was marked upon adding alumina nano-particles. However, surface interactions between alumina particles and smectite layers may be shielding the charge, hindering contaminant access to exchangeable sites in smectite and lead to this observation. Red mud is a residue obtaine on the alumina production from the Bayer process, comprised mainly of Fe2O3, Al2O3, SiO2 and minor amounts of TiO2, CaO and Na2O. This material is a cost-effective adsorbent for the adsorption of arsenic compounds from water [125]. 17

Nano- perfluorooctyl alumina powders were tested as adsorbents for the adsorption of methyl-tri-butyl-ether from aqueous solutions. On the surface of perfluorinated alumina, the perfluorinated chains set on the surface from one end of the chain and the surface has gained hydrophobic and nonpolar properties. As a result, the organic molecules are quite adsorbed on the surface [126]. A fungus hyphae-supported alumina (FHSA) bio-nano-composite was prepared, and tested for the adsorption of fluoride from water. The results revealed that the FHSA has high activity at adsorption conditions of pH range of 3–10 with high fluoride removal efficiencies (>66.3%). The adsorption capacity was 105.60 mg g_1 for FHSA, much higher than that for the alumina nano-particles (50.55 mg g_1) and pure fungus hyphae (22.47 mg g_1). The adsorption capacity calculated by the pure content of alumina in the FHSA is 340.27 mg g -1 of alumina. The high adsorption power of FHSA for fluoride is related to the surface complexes formation of fluoride with polar surface of alumina (AlOH) and the attraction between protonated ANH2 and fluoride through hydrogen bonding [127, 128].

5. Conclusions Due to the increasing demand of alumina nano-particles, this review provides interesting studies of the different methods of preparation, recovery, functionallization and application of alumina nano-particles. Alumina nanoparticles are prepared via different methods including arc plasma, hydrothermal, sol–gel, and precipitation. Alumina nano-particles are recovered from clay materials and from coal fly ash via acid, alkali besides clean and efficient electrolysis membrane methods. Alumina nano-particles are functionalized via surface modification and/ or grafting using polymer molecules to improve their performance. Accordingly, this new alumina design will guarantee increased overall process efficiency through; lower investment costs. The applications of alumina- nano-particles in different fields such as membrane, catalysts support, and adsorption were reviewed.

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Fig. (1): Crystal phases of alumina starting from two different hydrates [19]

Fig. (2): Structure of α-alumina [ 24]

Fig. (3): Illustration of entanglement of cobalt oxide of CoFT (yellow) within alumina pores (red) and illustration of pore size effect on cobalt crystallite of same size [27]

Fig. (4): Lewis and Bronsted acid sites of alumina [29]

30

. Fig. (5): Preparation of Alumina Nano-particle via Sol-Gel method [42]

(a)

(b)

(c)

Fig. (6): (a) Structure of [Al(OiPr){ONC(CH3)2}], (b) TEM of Alumina nanoparticles (c) Preparation of alumina nano-particles, [42]

Fig. (7): (a)XRD patterns of AlCP and AlSE. (b) SEM images for AlCP and AlSE. [43]

.

31

Fig. 8: (a) Illustration of the preparation of AD gels; (b) Typical SEM image of AD gels; (c) FT-IR spectra of Al2O3 NPs, neat copolymer and AD gels. [45]

Fig. (9): Process flow chart for the fabrication of porous Al2O3 beads [49]

32

Fig. (10): Schematic diagram of: (a) limestone sintering process, (b) combined pre-desilication and lime–soda sintering process. .[53]

Fig. (11): Schematic diagram of the one-step direct hydrochloric acid leach process.[53]

33

Fig. (12): Diagram of the new alumina extraction process [54].

Fig. (13): Process flo diagram of electrolysis of aluminum sulphate aqueous solution [57]

34

Fig. (14): Diagram of “Pre-desilicating—Na2CO3 activation—acid leaching” process [59].

35

Fig. (15): The co-treatment of coal fly ash and red mud for alumina extraction process [60].

Fig. (16): Silian surface coating of alumina nano-particles [67]

36

Fig. (17): TEM images of pure Al2O3 /sPP nanocomposite : (a) intermediate magnification, (b) higher magnification image of aggregated particles and (c) well-dispersed region [68]

Fig. (18): Schematic description of grafting-to and grafting-from approaches for the synthesis of PINCs [72].

Fig. (19): Schematic representation for grafting Al2O3 membranes with POEGMA brushes [72].

37

Fig. (20): (a) Preparation of Al2O3-PS core-shell nanoparticles. (b) SEM of pristine , (c) SEM of Al2O3-PS (inset: particle size distribution) [74].

38

Fig. (21): Functionalization of alumina via iron nitrate- glycine system [78].

Fig. (22): Functionalization of alumina via iron nitrate-urea system [78].

.

Fig. (23): The interaction between the COO- group of Oleic acid and the aluminum atom [85]

.

39

Fig. (24): Stacking of (a) TAN particles settled under gravity or precoat formed order flow, (b) DE particles settled under gravity, (c) pre-coat from DE particles [88]

Fig. (25): Procedure for the fabrication of the agro-waste shaped porous alumina samples [90]

Fig. (26). Flow chart of the alumina/CNT membrane synthesis process.[91]

40

Fig. (27): Membrane fabrication process [92]

Fig. (28): preparation of Al2O3/Polyacrylonitrile nanocomposite [116]

41

Fig. (29): preparation of Al2O3/C core-shell nanoparticle and AlON powder [116].

Fig. (30): The Model for PtSnIn/xZr-Al [117]

+K2O

Alumina

modified alumina

Fig. (31): Modification of alumina with K2O [120]

42

Graphical abstract

Functionalization of alumina nano-particles by iron species

Dear Editor The authors have no any conflict of interest authors

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