Charged Alumina Surface Research Articles

Alumina Graphene Catalytic Condenser for Programmable Solid Acids

Precise control of electron density at catalyst active sites enables regulation of surface chemistry for the optimal rate and selectivity to products. Here, an ultrathin catalytic film of amorphous alumina (4 nm) was integrated into a catalytic condenser device that enabled tunable electron depletion from the alumina active layer and correspondingly stronger Lewis acidity. The catalytic condenser had the following structure: amorphous alumina/graphene/HfO2 dielectric (70 nm)/p-type Si. Application of positive voltages up to +3 V between graphene and the p-type Si resulted in electrons flowing out of the alumina; positive charge accumulated in the catalyst. Temperature-programmed surface reaction of thermocatalytic isopropanol (IPA) dehydration to propene on the charged alumina surface revealed a shift in the propene formation peak temperature of up to ΔT peak∼50 °C relative to the uncharged film, consistent with a 16 kJ mol-1 (0.17 eV) reduction in the apparent activation energy. Electrical characterization of the thin amorphous alumina film by ultraviolet photoelectron spectroscopy and scanning tunneling microscopy indicates that the film is a defective semiconductor with an appreciable density of in-gap electronic states. Density functional theory calculations of IPA binding on the pentacoordinate aluminum active sites indicate significant binding energy changes (ΔBE) up to 60 kJ mol-1 (0.62 eV) for 0.125 e- depletion per active site, supporting the experimental findings. Overall, the results indicate that continuous and fast electronic control of thermocatalysis can be achieved with the catalytic condenser device.

Towards enhanced oil recovery: Effects of ionic valency and pH on the adsorption of hydrolyzed polyacrylamide at model surfaces using QCM-D

Adding polymers to the injection water in water-flooding oil recovery increases the viscosity and thereby enhances recovery factor. However, the beneficial effects are often counteracted by adsorption of polymer to the ambient mineral surface. In here, we used Quartz Crystal Microbalance with Dissipation (QCM-D) measurements to study the adsorption of the frequently used hydrolyzed polyacrylamide (HPAM), a weak polyelectrolyte, to silica and alumina model surfaces representing sandstone reservoirs. At pH 6 and 8 and concentrations from 1 mM to 100 mM of NaCl and CaCl2, we find that negatively charged HPAM molecules generally adsorb more strongly to positively charged alumina surfaces. For silica surfaces, the presence of Ca2+ ions, which form strong complexes with the carboxyl groups on the polymer, as evidenced by titration measurements, strongly enhances HPAM adsorption. This effect is attributed to the formation of Ca2+-mediated ion bridges with the substrate. Kinetic measurements suggest a two-step adsorption process consisting of a primary polymer adsorption onto the surface followed – in most cases – by a slower secondary process, which involves rearrangements of previously adsorbed polymer molecules, including polymer-on-polymer adsorption.

Adsorption Behavior of Polyelectrolyte onto Alumina and Application in Ciprofloxacin Removal.

This study aims to investigate the adsorption behavior of a strong polyelectrolyte poly(styrenesulfonate) (PSS) onto alumina particles. Adsorption of PSS onto positively charged alumina surface increased with increasing ionic strength, indicating that non-electrostatic and electrostatic interaction controlled the adsorption. The removal of an emerging antibiotic ciprofloxacin (CFX) from water environment using PSS-modified alumina (PMA) was also studied. The removal of CFX using PMA was much higher than that using alumina particles without PSS modification in all pH ranges of 2–11. The removal of CFX reached 98% under the optimum conditions of pH 6, contact time of 120 min, adsorbent dosage of five milligrams per milliliter and ionic strength 104-M NaCl. The adsorption isotherms of CFX at different salt concentrations fit well with a two-step adsorption model, while the adsorption kinetic fit well with a pseudo-second-order model with a good correlation coefficient (R2 > 0.9969). The CFX-removal from a hospital wastewater using PMA was more than 75%. Our study demonstrates that adsorption of PSS onto alumina to modify the particle surface is important to form a novel adsorbent PMA for CFX-removal from water environments.

The influence of Y3+ and Mg2+ dopants on the transparency behavior of alumina ceramics

The effect of salt solution of magnesium and yttrium addition on the transparent alumina polycrystalline was investigated in the present study. This solution is ionized in the slurry. The ions were adsorbed onto the charged alumina surface by the electrostatic mechanism. Due to the addition of salts solution at the casting stage, the distribution of dopant was uniform. Therefore no secondary phase has been formed in the sample after sintering. The added salts eliminated the intragranular porosity and prevented the growth of the grains. After optimizing the amount of the dispersant (1.3 wt%) and preparing the slurry by using a 3D-mixer, the samples were sintered at a temperature of 1250 °C and at the rate of 20 °C/min by the SPS method, the transparency was increased from 18 to 33% by adding salt solution of the Mg2+ and Y3+ as dopant. Also, the grain size was decreased from 27.37 to 4.29 μm in the sample with dopant, therefore the hardness was increased from 1814 to 2279 HV10.

Effect of salinity on adsorption and interaction forces of hydrophobically modified polyacrylamide on silica and alumina surfaces

In this work, the adsorption behaviors and interaction forces of different polymers on silica and alumina surfaces have been investigated under the effect of KCl concentration using quartz crystal micro-balance with dissipation (QCM-D) monitoring technique, viscosity measurement and atomic force microscopy (AFM) colloidal probe technique. Polyacrylamide (PAM) and hydrophobically modified polyacrylamide (HMPAM) with hydrophobic monomer (i.e., hexadecyl dimethyl allyl ammonium chloride (C16DMAAC)) have been investigated as model polymers. It is found that the adsorption amounts of HMPAM and PAM polymers on negatively charged silica and positively charged alumina surfaces increase with increasing solution salinity (1–100 mM KCl). HMPAM displays higher adsorption capacity than PAM on both silica and alumina surfaces, which is attributed to the hydrophobic interaction originated from the long hydrocarbon chains of HMPAM. Furthermore, the measured adhesion between the polymers and the substrate surfaces is found to decrease for the alumina cases and increase for the silica cases with increasing the salinity, which is due to the weakened electrostatic interactions between the polymers and substrate surfaces under high salinity (i.e., 100 mM KCl). The viscosities of PAM and HMPAM solutions are found to decrease with increasing solution salinity, which could be caused by the much more coiled conformation of PAM and HMPAM chains at higher salinity. Both the interactions between the polymer and substrate surface and the polymer conformational changes play important roles in the polymer adsorption behaviors on silica and alumina surfaces.

Effect of Halide Anions on the Structure and Dynamics of Water Next to an Alumina (0001) Surface

While ions are known to perturb hydrogen bonding networks in bulk water, our understanding of such effects is less developed for interfaces. Alumina/water interfaces are highly ordered due to strong hydrogen bonding interactions between interfacial water molecules and adjacent aluminol groups. However, how ions alter this interaction is not yet known. Herein, to address the effect of sodium halide salts on the hydrogen bonding environment of interfacial water, we investigated charged alumina (0001) surfaces using steady-state and time-resolved vibrational sum frequency generation (vSFG) spectroscopy. Our results indicate that the effect of halide anions on the attenuation of the vSFG signal next to positively and negatively charged alumina surfaces followed the sequence F– ≫ Br– > Cl– > I– (slightly varied direct Hofmeister series) and Br– > I– ≈ Cl– > F– (slightly varied indirect Hofmeister series), respectively. Additionally, time-resolved vSFG reveals that only F– perturbs the vibrational lifetime of w...

Ion effects in the adsorption of carboxylate on oxide surfaces, studied with quartz crystal microbalance

We chose water-soluble sodium hexanoate as a model organic molecule to study the role of salt ions (Ca2+, Na+, Cl−) in the adsorption of carboxylates to mineral surfaces (silica, alumina, gibbsite) of variable surface charge and chemistry. Quartz crystal microbalance (QCM-D) measurements reveal a qualitatively different dependence of the adsorption behavior on the electrolyte composition for the different surfaces at near neutral pH. Overall, hexanoate adsorption is more pronounced on the positively charged alumina surfaces than on negatively charged silica surfaces. On silica, however, Ca2+ ions strongly enhance the adsorption of hexanoate, suggesting that the divalent cations act as bridges between carboxylate and deprotonated silanol surface groups. On alumina, hexanoate adsorption is found to depend only weakly on the salt composition, suggesting a direct interaction of the carboxylate group with the surface, consistent with a ligand-exchange mechanism. The adsorption behavior on partially gibbsite-covered silica surfaces is particularly rich and displays a strong non-monotonic dependence on the CaCl2 concentration. Comparison to earlier work and control experiments suggest an important role of Cl− anions, which compete with the carboxylate group for adsorption sites.

Influence of phenylalanine dispersant on colloidal processing of alumina particles

This paper reports the adsorption behavior of phenylalanine (PHA) onto alumina surfaces in a wide pH range of 3.6–9.5, rheology and packing densities of concentrated alumina suspensions with PHA, and mechanical properties of consolidated alumina compacts with and without PHA. A small amount of PHA was adsorbed on both the positively and negatively charged alumina surfaces and enhanced zeta potential of alumina particles in acidic and basic suspensions. However, the adsorbed and free PHA provided little influence on the dispersibility of primary particles. In the neutral and basic suspensions, the apparent viscosity decreased with addition of PHA because of the formation of weakly coagulated particle clusters, leading to the increase in the packing density for neutral alumina suspensions. During drying of wet alumina compacts, PHA remaining in the alumina compacts relaxed the applied compressive stress. However, added PHA provided no influence on Young׳s moduli and compressive strengths of alumina compacts after calcination.

Interaction of the Physiological Tripeptide Glutathione with Colloidal Alumina Particles

Understanding of the molecular interactions of alumina particles with biomolecules is fundamental for a variety of biotechnological processes. To study the interactions of polypeptides with alumina particles, we have investigated the adsorption and desorption behavior of the physiologically relevant tripeptide glutathione (GSH, γ-glutamylcysteinylglycine) onto colloidal α-alumina particles (CPs). The adsorption of GSH to positively charged alumina particles was rapid, increased proportionally to the concentration of CPs, and shifted the isoelectric point of the CP to a less alcaline pH. Desorption of particle-bound GSH was achieved by increasing the ionic strength after adding salt to the suspension, suggesting that adsorption of GSH to alumina is governed by electrostatic interactions. The presence of negatively charged and GSH-structurally related molecules such as glutamate, γ-glutamylcysteine, γ-glutamylglutamate, or methyl-S-GSH prevented the binding of GSH to the positively charged alumina surface i...

Ethoxy Carboxylate Extended Surfactant: Surface Charge of Surfactant‐Modified Alumina, Adsolubilization and Solubilization of Phenylethanol and Styrene

AbstractAdsolubilization of contaminants by surfactant‐modified material is an important phenomenon for surfactant‐based environmental technologies. Recently, extended surfactants have been shown to enhance the adsolubilization capacity of organic solutes. In this study, two extended surfactants (ethoxy propoxylated carboxylate extended surfactant—C16PO4EO5C and propoxylate extended sulfate surfactant—C16PO4S) were selected for modifying positively charged alumina surfaces with the aim of enhancing adsolubilization of organic solutes with varying degrees of polarity (phenanthrene, styrene, and phenylethanol). The nature of the charged surface as a function of extended surfactant adsorption was evaluated through the zeta potential measurements. The results showed that at maximum bilayer coverage, the zeta potential of the alumina surface remained constant and was oppositely charged (negative) to the unmodified alumina (positive). Zeta potential measurements showed that the adsorbed bilayer of carboxylate‐based extended surfactant produced more negatively charged surface. Surfactant desorption results showed that the surfactant‐modified surface retained their negatively charge, albeit reduced, indicating that partial desorption occurred but not to the point that the positively charged alumina surface was realized. The adsolubilization results suggest a benefit of the ethoxy groups in adsolubilizing the polar phenylethanol in the palisade layer.

Effect of varied powder processing routes on the stabilizing performance and coordination type of polyacrylate in alumina suspensions

Abstract The influence of initial pH and energy input during suspension homogenization on the stabilizing performance and coordination type of commercial available polyacrylate dispersant were studied. Additionally to widely used rheology and electroacoustic measurement techniques the alumina suspensions were analysed with centrifugal separation and in situ ATR-FTIR to study the impact of varied powder processing in detail. In contrast to zeta potential analysis and viscosity measurements only the determination of sedimentation properties by centrifugal separation shows the effect of macroscopic changes in powder processing. A combination of positively charged alumina surface and a high shear homogenization leads to the most stable suspension. Accordingly ATR-FTIR results show a correlation between improved suspension stability and inner-sphere coordination of polyacrylate. Moreover it was possible to determine an optimal pH range for inner-sphere adsorption. It can be shown that macroscopic changes in powder processing influence the coordination of dispersant and thus the suspension stability.

Role of Oxide Surface Chemistry and Phospholipid Phase on Adsorption and Self-Assembly: Isotherms and Atomic Force Microscopy

We have examined the effects of metal oxide surface chemistry and lipid phase on phospholipid adsorption affinity and self-assembly. Adsorption isotherms of ditridecanoylphosphocholine (DTPC) at 40 °C and pH 7.2 on quartz (α-SiO2), rutile (α-TiO2), and corundum (α-Al2O3) particle suspensions indicated oxide-dependent adsorption affinity that decreased as rutile > corundum ≅ quartz at low concentrations and corundum > rutile ≅ quartz at higher concentrations. Significantly, atomic force microscopy of DTPC and dipalmitoylphosphocholine (DPPC) at high concentration on planar oxide surfaces at 25 °C in liquid-crystal and gel phases, respectively, also showed oxide-specific adsorption. Multiple bilayers formed on corundum (100), indicating greater coverage compared to single bilayers, bilayer patches, or supported vesicle layers on the negatively charged surfaces of mica (001), rutile (100), and amorphous silica glass (fused quartz plate). Thus, the amount and self-assembly of adsorbed phospholipid was found to be oxide-dependent regardless of the lipid phase. Significantly, both experimental methods show multiple bilayer formation as a unique feature of the positively charged alumina surface. The observed oxide affinity sequences are interpreted as controlled by van der Waals and electrostatic forces between the oxide surface and the negatively charged (−R(PO4−)R′−) portion of the phosphocholine headgroup. Our results have implications for the interactions of amphiphilic molecules with mineral surfaces in diverse biogeochemical, biomedical, and industrial processes, including membrane-bound biomineralization, cell membrane stability during early evolution of life, organic matter burial in ocean sediments, the design of supported lipid bilayers and biomimetic cell membranes for medical implant devices, enhanced oil recovery, and ore extraction by froth flotation.

The influence of impregnating pH on the postnatal and steam reforming characteristics of a Co-Ni/Al 2O 3 catalyst

Bimetallic alumina supported Co-Ni catalysts were prepared by impregnation under low (2) and high (8) pH values. Support dissolution due to acid attack appeared to be responsible for the low BET surface area for catalyst obtained at pH 2. However, this low-pH catalyst possesses higher dispersion and superior metal surface area. This is ascribed to the charged-induced migration of metal cations towards the grain centre where adsorption sites are located as a result of the formation of positively charged alumina surface at low pH. Ammonia NH 3-TPD analysis showed that the surface of both catalysts was populated with weak Lewis acid sites though a higher site concentration was found on the high-pH catalyst. TEM images further revealed an eggyolk profile for the catalyst impregnated at pH 2 with metal species located in the particle interior; while in the catalyst synthesised at pH 8, the impregnant metal is concentrated around the external surface of the particle. XRD analysis of the catalysts before and after reduction indicates that the basic catalyst was more difficult to reduce probably because of higher metal aluminate content. This was further confirmed by the lower degree of reduction shown for this catalyst during the thermogravimetric TPR–TPO runs. Solid-state kinetic data of the catalyst calcination, reduction and oxidation conformed with the Avrami–Erofeev model. In particular, the ratios of the associated kinetic rate constants for calcination and oxidation parallel those obtained for the deactivation and steam reforming constants, respectively, in both catalysts. Thus, it may be possible to have an a priori knowledge of the comparative reaction and deactivation behaviour of different catalysts from the temperature-programmed kinetics of their nascent solid states.

Enrichment of Traces of Copper From Water Containing Humic Substances by Sorption on Admicelle Particles

The effect of humic and fulvic acids on the enrichment of copper was studied because humic substances are generally present in natural water samples. By mixing an alumina suspension and sodium dodecyl sulfate at pH 2, the anionic surfactant was strongly sorbed on the positively charged alumina surface to form admicelles. When the surfactant was added together with a small amount of dithizone, admicelles incorporating dithizone were obtained These two types of admicelles, in spite of the aggregates of anionic surfactant, completely sorbed negatively charged humic substances and copper-humic complexes. The copper was quantitatively desorbed with 4 mol dm-3 nitric acid for the determination by graphite furnace atomic absorption spectrometry. The proposed method was successfully applied to the analysis of certified reference water samples.

Investigation of alumina/(+)-catechin system properties. Part II: ζ-potential and surface free energy changes of alumina

The effects of (+)-catechin adsorption to the alumina surface were studied by ζ-potential and surface free energy determination. The presence of catechin causes essential changes in the alumina ζ-potential, which at the concentration slightly higher than 10 −5 M reverses from the positive into negative one. At constant concentration of catechin (10 −3 M), the effect on ζ-potential of alumina as a function of pH appears in a drastic shift of the isoelectric point, from pH 8.4 to 4.6, and the equilibrium is established practically within 2 h. This is probably due to relatively low p K a=4.6 for catechin 3′-OH group deprotonation. At high alkaline environment (pH≥10), even in the presence of catechin in the solution, the hydroxyl OH − ions play principal role in the surface charge formation for the alumina. At such pH catechin molecule is double negatively charged and hence its adsorption on highly negatively charged alumina surface is rather restricted. Nevertheless, various dimeric forms of catechin, which are formed at the alkaline pH, probably adsorb on the alumina surface. This appears in small increase in apolar surface free energy component at natural and alkaline pH. On the other hand, at acidic pH 3 small increase of the electron acceptor interaction is observed. This may result from increased number of hydroxyl groups on the alumina surface originating from the adsorbed molecules of catechin, which are mostly undissociated at this pH. The interactions of catechin with alumina surface seems to be also of some specific nature, because neither changes in the ultraviolet–visible (UV–vis) absorbance (Part I) nor in the ζ-potentials had occurred in the silica suspensions in which also catechin was present.

Catechol derivatives and anion adsorption onto alumina surfaces in aqueous media: influence on the electrokinetic properties

Abstract A high state of dispersion of alumina particles can be achieved by using molecules derived from Catechol 1,2(OH)2C6H4, such as Tiron (OH)2C6H2(SO3Na)2 which allows to obtain stable alumina suspensions. In the field of understanding the dispersion mechanism of Tiron and the contribution of each functional group grafted onto the benzene ring of the Tiron molecule, adsorption experiments and surface charge measurements were conducted by using several compounds, containing a benzene ring, and by varying the nature and the number of substituents. The influence of the size and of the charge of the counter ion, electrostatically attracted by a positive charged alumina surface, onto the suspension stability was also studied. Electrokinetic properties of the suspensions versus pH appear to be very useful to characterize the ion adsorption sequence for an oxide surface. With a high immersion heat, an alumina surface better adsorbs ions with a high structuring power for water molecules. This influences the charge developed onto the oxide surface.

Enrichment of Metal-APDC Complexes on Admicelle-Coated Alumina for Water Analysis

Aggregates of sodium dodecyl sulfate (SDS) formed on alumina particles were employed as enrichment vehicles of hydrophobic metal-chelates from water samples. To a 50 cm3 suspension of 1.5 g of purified alumina was added 100 mg of SDS; the mixture was then acidified to pH 2, where the anionic surfactant was strongly adsorbed on positively charged alumina surfaces to form admicelles. Nanogram quantities of heavy metals (Co, Ni, Cu, Cd and Pb) in water were com-plexed with APDC at pH 2 - 6 and quantitatively incorporated in the admicelles. A nearly complete desorption was achieved for those metals (except for Co) in 4 mol dm-3 nitric acid with the aid of ultrasonic irradiation. A multielement determination was performed by ICP-MS. The reliability of the proposed method was evaluated by analyzing a certified reference seawater sample.

Application of NMR to Interfacial Coordination Chemistry: A 195Pt NMR Study of the Interaction of Hexachloroplatinic Acid Aqueous Solutions with Alumina

To understand the mechanism of Pt deposition during the synthesis of supported catalysts, liquid-phase 195Pt NMR spectroscopy was applied first to study the speciation of platinum complexes in aqueous solutions of H2PtCl6 as a function of pH and time of hydrolysis and second to follow the adsorption of platinum complexes on γ-alumina from these solutions. Five of the six Pt complexes that can exist in hydrolyzed H2PtCl6 solutions are identified by their 195Pt chemical shift (δPt): [PtCl6]2-, [PtCl5(H2O)]-, [PtCl5(OH)]2-, [PtCl4(H2O)2], and [PtCl4(OH)2]2-. For [PtCl4(OH)(H2O)]-, which cannot be directly detected in NMR spectra due to fast proton exchange, δPt is calculated from the best fit of the δPt = f(pH) dependence to the experimental data. The acid dissociation constants (pKa) for aquaplatinates are also determined and discussed in comparison to literature data. For H2PtCl6 solution−Al2O3 mixtures, NMR signals of [PtCl6]2- and [PtCl5(OH)]2- at the interface were observed for the first time. The [PtCl6]2- signal has a small negative δPt relative to that in H2PtCl6 solutions, which indicates a slight perturbation of the Pt atom coordination sphere by the alumina surface. It is suggested that adsorbed [PtCl5(OH)]2- results from fast deprotonation of the water molecule ligand in [PtCl5(H2O)]- by alumina basic hydroxyls. Most likely, the platinum anions are held on the positively charged alumina surface by electrostatic interaction. The fraction of adsorbed [PtCl5(OH)]2- rises with increasing initial pH of H2PtCl6 solutions and becomes dominant at higher pH. The [PtCl6]2- and [PtCl5(OH)]2- signals disappear after removal of physisorbed water from alumina powder at room temperature and reappear almost unchanged upon subsequent rewetting of the solid. In contrast, after drying at 90 °C for 1.5 h, no NMR signal can be detected for the dried samples, and much weaker signals than those in the original solid are observed for the rewetted sample. The disappearance of the NMR signals is supposed to be due to formation of lower symmetry grafted Pt complexes with a higher chemical shift anisotropy. The likely mechanisms of platinum deposition from acidic H2PtCl6 solutions on positively charged alumina surface are discussed.

Collection of Trace Heavy Metals on Dithizone-Impregnated Admicelles for Water Analysis

Admicelles formed on alumina were studied from the viewpoint of separation vehicles in trace analysis. Gamma-alumina (1.5 g) was suspended in 40 cm3 of water and mixed with 10 cm3 of ammoniacal solution containing 1.5 mg of dithizone and 100 mg of sodium dodecyl sulfate. The mixture was acidified to pH 2, where the anionic surfactant was strongly adsorbed on the positively charged alumina surface to form dithizone-impregnated admicelles. Metal contaminants in the admicelles were thoroughly removed by washing with 4 mol dm-3 nitric acid. The quantitative adsorption from water was performed at pH 2 - 9 for Cu, pH 3 - 9 for Pb and pH 4 - 9 for Co, Ni and Cd. For seawater, simultaneous collection required adjusting the pH to ca. 8. Humic and fulvic acids did not interfere with the separation. The admicelle column was substantially stable during adsorption and desorption, which allowed the same column to be used at least three times. The proposed method was combined with inductively coupled plasma-mass spectrometry for the analysis of seawater.

Stabilization of aqueous α‐Al2O3 suspensions with block copolymers

AbstractWater‐soluble diblock copolymers (DBCPs) with a polyelectrolyte block are accessible by sequential anionic polymerization of tert‐butylmethacrylate (TBMA) and ethylene oxide (EO), followed by polymer analogous conversion of the PTBMA into poly(methyacrylic acid) (PMAA) blocks. These materials are highly efficient dispersants for oxide ceramic powders in aqueous media. A series of block copolymer samples with Mn ranging from 1300 to 38 900, and (EO:MAA) block length ratios from 0.5 to 11.7 were prepared with polydispersities close to 1.2. The influence of overall molecular weight and block length ratio, pH and ionic strength on the stability of aqueous α‐Al2O3 suspensions was investigated by sedimentation and adsorption experiments, surface plasmon resonance (SPR) and electrokinetic measurements. The copolymers are capable of stabilizing alumina suspensions by a combination of specific adsorption of one block on the particle surface and a shielding effect provided by the nonadsorbing block. In addition, the adsorption of the negatively charged PMAA block on the oppositely charged alumina surface reverses the electrophoretic potential of the oxide particles, a process which is strongly pH dependent. With respect to the powder dispersing efficiency, an optimum was found when the DBCP consisted of a short PMAA anchoring and an approximately tenfold longer PEO stabilizer block with an overall molecular weight of about 5000. Alumina suspensions with the DBCP added were highly dispersed and rather stable against salt addition in a much wider pH window than block‐copolymer‐free suspensions.