Poly(methacrylate)‐derived diblock dispersant for TiO2 in aqueous suspensions

In this paper, we propose a newly designed dispersant, ammonium poly(methacrylate)‐block‐poly(2‐phenoxyethyl acrylate) (PMA‐b‐PBEA), and our rheological and zeta potential test results verify its superior dispersion efficiency for aqueous suspensions in comparison to the commercial dispersant ammonium polyacrylate (PAA‐NH₄). The extremely high dispersion efficiency of PMA‐b‐PBEA correlates closely to its diblock structure, which simultaneously exhibits a less polar anchoring head group and a water‐dissociable stabilizing moiety. The unique structure of PMA‐b‐PBEA accounts for its high powder adsorption effectiveness, which is demonstrated in its adsorption capability being double that of PAA‐NH₄.     

Interactions between Polymeric Dispersants and Calcium Silicate Hydrates

To better understand the mechanism of interaction between hydrating silicate-based cements and polymeric dispersants of the type used as superplasticizers in modern construction concretes, two different types of polymeric dispersant were added (at concentrations of 1 and 10 g/L) during the synthesis of calcium silicate hydrate (C-S-H) via the pozzolanic reaction in dilute slurries of lime and reactive silica, at Ca/Si ratios in the range of 0.66–1.50. Although both polymers gave degrees of adsorption of >79% in all cases studied, no significant structural modifications of the resulting C-S-H products were observed via X-ray diffraction or ²⁹Si magic angle spinning–nuclear magnetic resonance. These results differ from recent work in which it was shown that similar types of polymer could intercalate into the interlayers of C-S-H that was made using an alternative process. It is suggested that the process by which the C-S-H is formed may have a strong influence on whether C-S-H can intercalate polymers. This observation is relevant to understanding the fate of such polymers in concrete.     

Cardanol: A New Dispersant for Alumina in Toluene

Cardanol, which is a naturally occurring C₁₅ unsaturated aliphatic chain-substituted phenol derived from cashew nut shell liquid, was used as a dispersant for alumina in toluene. Adsorption data, along with the results of sedimentation studies, green density, and slurry viscosity (as a function of dispersant concentration), suggest that cardanol adsorption initially proceeded through surface coverage by a phenolic group that lies flat on the surface and that the best powder dispersion occurred at surface saturation by more closely packed end-on adsorbed cardanol molecules. The alkyl-chain unsaturation significantly contributed to dispersion, such that the saturation by hydrogenation led to an increase in the slurry viscosity by a factor of ∼2.5. Concentrated slurries generally showed shear-thinning flow behavior, and the measured viscosity of a highly concentrated (53 vol%) slurry was <1 Pa·s at a shear rate of 93 s⁻¹.     

Dispersing Behavior of Hydroxyapatite Powders Produced by Wet-Chemical Synthesis

Three hydroxyapatite powders with different surface properties were produced by wet-chemical synthesis and characterized. The electrokinetic properties of powders dispersed in water were investigated by electroacoustic spectroscopy measurements. The different surface reactivity (pH_iep and ζ potential versus pH curves) was related to the interplay of dissolution and adsorption of Ca²⁺ ions. With a view toward the preparation of porous bodies by sponge impregnation, the behavior of powder suspensions was studied. Four deflocculants were tested, and the optimum dispersing conditions for each powder were found. Anionic polyelectrolytes resulted in the best effective dispersing agent, with different optimum amounts added to the suspensions.     

Influence of pH and Ionic Impurities on the Adsorption of Poly(acrylic) Dispersant onto a Zinc Oxide Surface

We have studied the properties of aqueous suspensions of ZnO powders with different purities. Our results suggest that powder purity determines the amount of dispersant necessary to form a stable aqueous suspension as well as the maximum adsorption capacity of the dispersant: the higher the positive surface charge of the as-received ZnO powders, the higher the amount of dispersant adsorbed onto the metal oxide surface. The surface charge of the ZnO particles in suspension is affected by the concentration of zinc as well as sulfate ions, which are the major impurities in the supernatant. The pH of the aqueous ZnO suspensions increases with increasing concentration of poly(acrylic) dispersant until the maximum adsorption capacity is attained. Further additions of dispersant do not increase the pH because of a buffer formation with impurity ions.     

Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

A novel dispersant—O-(2-aminopropyl)-O'-(2-methoxyethyl)-polypropylene glycol (AMPG)—was developed to disperse submicrometer-sized Si₃N₄ powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si₃N₄ suspensions can be realized using AMPG.     

Effect of Polyelectrolyte Dispersants on the Preparation of Silica-Coated Zinc Oxide Particles in Aqueous Media

Sodium silicate was utilized to obtain a SiO₂ coating on ZnO particles to prevent a photocatalytic reaction between ZnO and phenol. During the coating process, pH control is important to avoid dissolution of the ZnO as well as to obtain a good dispersion. Two kinds of polyelectrolyte dispersants were used to control the surface charge of the ZnO particles in aqueous media. As a result, poly(ethylenimine) (PEI) shifted the isoelectric point of ZnO from pH 9 to pH 10, whereas poly(ammonium acrylate) (PAA) made the surface charge of ZnO negative between pH 6 and pH 11. The change in the ZnO surface charge produced by adding polyelectrolyte dispersants makes it possible to obtain uniform silica–coated ZnO particle in aqueous media. UV–irradiation experiments showed that PEI, which can make the surface charge opposite to that of SiO₂, is more effective in obtaining a thick silica coating on ZnO.     

二氧化钛悬浮液分散性研究

应用粒度仪和电子显微镜研究了二氧化钛的分散性、浆料的稳定性及二氧化钛在聚酯切片中的形状。结果表明：二氧化钛的分散性与分散介质及电解质有关;聚酯切片中的凝结粒子通常是由二氧化钛粒子无规则的团聚而成。     

Ag/TiO2纳米催化剂的制备及性能

采用溶胶-凝胶法制备了Ag/TiO₂光催化剂。通过X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、N₂吸附-脱附(BET)、透射电子显微镜(TEM)对产物进行了表征。以亚甲基蓝(MB)为降解物,考察了不同Ag含量和不同煅烧温度对样品的光催化性能影响。结果表明,掺杂Ag后,增大了样品的比表面积,800℃时,Ag的引入抑制了TiO₂锐钛矿向金红石相的转变,掺杂后TiO₂的光催化活性大大提高,在500℃煅烧温度下,当Ag的摩尔分数为1%时,在紫外光照射下,经过180min光催化实验,对MB的降解率达到90%.     

Intriguing role of TiO2 in glass‐ceramics: Bioactive and magneto‐structural properties

We report on the structural, magnetic, and bioactive properties of TiO₂‐modified silicate glasses. Addition of TiO₂ and heat treatment, shows remarkable and distinguishable effect on the properties of the glasses. Growth of titania‐modified magnetic nanocrystals played effective role in the evolution of magnetic properties of the glass‐ceramics. Some of the samples exhibit superparamagnetic nature, while others are found to be antiferromagnetic. Interestingly, after heat treatment the magnetization trend of the samples reversed. The in vitro bioactivity of these glass‐ceramics was accessed by the formation of bone‐ like apatite structures on their surfaces after immersion in simulated body fluid. The magnetic properties along with the bioactivity of present glass‐ceramics indicate their usefulness in the magnetically induced hyperthermia treatment of cancer.     

Silicon Nitride Colloidal Probe Measurements: Interparticle Forces and the Role of Surface-Segment Interactions in Poly(acrylic acid) Adsorption from Aqueous Solution

Direct measurements of forces between silicon nitride surfaces in the presence of poly(acrylic acid) (PAA) are presented. The force-distance curves were obtained at pH > pH_iep with an atomic force microscopy (AFM) colloidal-probe technique using a novel spherical silicon nitride probe attached to the AFM cantilever. We found that PAA adsorbs onto the negatively charged silicon nitride surface, which results in an increased repulsive surface potential. The steric contribution to the interparticle repulsion is small and the layer conformation remains flat even at high surface potentials or high ionic strength. The general features of the stabilization of ceramic powders with PAA are discussed; we suggest that PAA adsorbs onto silicon nitride by sequential adsorption of neighboring segments ("zipping"), which results in a flat conformation. In contrast, the long-range steric force found in the ZrO₂/PAA system at pH > pH_iep arises because the stretched equilibrium bulk conformation of the highly charged polymer is preserved via the formation of strong, irreversible surface-segment bonds on adsorption.     

Effect of Magnesium Ions on the Adsorption of Poly(acrylic acid) onto Alumina

The adsorption isotherms of poly(acrylic acid) (PAA) onto alumina powder have been determined as a function of pH, ionic strength, and magnesium-ion concentration. The adsorption of PAA is strongly enhanced by magnesium ions in alkaline media but less affected under acidic conditions. The adsorption isotherms display a maximum when PAA is fully complexed with magnesium ions in the solution, corresponding to a ratio of 0.25 ± 0.05 [Mg²⁺]/[acrylic acid monomer]. The decrease in adsorbed amount with an increase in PAA concentration at constant magnesium-ion concentration is related to a decrease in the complexation ratio.     

Photocatalytic Activity of Monodispersed Spherical TiO2 Particles with Different Crystallization Routes

Monodispersed spherical TiO₂ particles were prepared by hydrothermal crystallization and/or calcination of spherical amorphous particles, synthesized by thermal hydrolysis of TiCl₄. The crystallized spherical particles were secondary agglomerates of primary nanocrystallites. Different crystallization routes and conditions provided the spherical TiO₂ particles with wide particle characteristics, such as the fraction of crystallization, the size and shape of the primary nanocrystallites, and the specific surface area. The photocatalytic activity showed complex dependence on the crystallization routes and conditions. The complex dependence behavior could be explained by combining the effects of the fraction of crystallization, the specific surface area, and the adsorption ability for hydroxyl ions. Especially, in the present study, the hydrothermally crystallized TiO₂ particles with large primary nanocrystallites showed the highest photocatalytic activity. The high photocatalytic activity mainly resulted from the high surface adsorption ability for hydroxyl ions, which was closely related to the well-developed (flat and faceted) morphology of primary nanocrystallite.     

Electrical conductivity and defect disorder of tantalum‐doped TiO2

The present work reports the electrical properties of polycrystalline Ta‐doped TiO₂ (0.39 at.% Ta) determined in situ at elevated temperatures (1173‐1323 K) in the gas phase of controlled oxygen activity (10^?12 Pa to 10⁵ Pa). The effect of oxygen activity on the electrical conductivity and thermoelectric power of TiO₂ is discussed in terms of defect disorder, including (1) the intrinsic electronic disorder that is governed by electronic compensation in the strongly reducing regime, (2) the extrinsic electronic disorder that is governed by electronic charge compensation in the reducing regime, and (3) the extrinsic ionic disorder that is governed by ionic compensation in the oxidizing regime. It is shown that tantalum ions are incorporated into the titanium sublattice of TiO₂ leading to the formation of donor‐type energy levels. The Arrhenius‐type plot of the electrical conductivity data leads to the determination of the formation enthalpy terms. The obtained results are considered in terms of the effect of tantalum and oxygen activity on the defect disorder and the associated key performance‐related properties in the light‐induced partial water oxidation.     

TiO2、ZnO和TiO2/ZnO三种氧化物粉体材料的抗菌性能对比

氧化物具有化学性质稳定、原材料丰富易得的优点,其作为抗菌材料日益受到关注。对氧化物的抗菌性能及影响因素开展深入研究,能够为新型抗菌材料的开发提供科学依据。通过溶胶-凝胶法制备出了TiO₂/ZnO复合粉体,并将其与TiO₂、ZnO进行对比,分别对它们的晶相结构、微观形貌和粒径进行了表征。利用大肠杆菌ATCC25922作为受试菌株,通过抑菌环试验和菌液接触试验对3种氧化物粉体材料的抗菌性能进行测试。考察了钛锌比、光照等条件对抗菌效果的影响。结果表明,所使用的TiO₂主要由锐钛矿相和金红石相组成,ZnO主要为六方纤锌矿相,制备出的TiO₂/ZnO则主要是锐钛矿型TiO₂在六方纤锌矿型ZnO的孔隙间沉积而成,这3种粉体材料的粒径由大到小分别为TiO₂/ZnO、TiO₂和ZnO。从抑菌环和菌液接触试验的结果可以看出,ZnO粉体材料的抗菌效果明显优于TiO₂粉体材料,ZnO和TiO₂/ZnO在黑暗条件下仍有良好的抗菌性能,但在可见光照射条件下抗菌效果更佳。ZnO含量是TiO₂/ZnO复合材料抗菌性能的关键因素。制备TiO₂/ZnO粉体材料时的煅烧温度对其抗菌性能没有明显影响。     

Intensification of photocatalytic pollutant abatement in microchannel reactor using TiO2 and TiO2‐graphene

A microfluidic device was applied to the photocatalytic degradation of methylene blue as a model pollutant. Titanium dioxide nanoparticles (TiO₂–P25) and a synthesized composite TiO₂‐graphene catalyst were immobilized on the inner walls of a borosilicate glass microfluidic chip. The deposition evolution of the nanoparticles was evaluated by monitoring the optical profile of the system. It was found that a higher initial reaction rate was obtained in the microreactor containing composite catalyst (TiO₂‐GR) on the inner walls, but both systems (TiO₂ and TiO₂‐GR) achieved similar reaction rates when the steady‐state was reached. Decolorization rate of methylene blue in our microfluidic chips was found to be approximately one order of magnitude higher than equivalent macroscopic systems reported in the literature at similar experimental conditions. Additionally, computational simulations were performed to investigate the physics involved in these processes. The model was experimentally validated for further scale‐out studies. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2794–2802, 2016     

Characteristics of photocatalytic oxidation of gaseous 2‐propanol using thin‐film TiO2 photocatalyst

This work presents a photocatalysis‐based method to treat and purify air because of its broad applicability to common, oxidizable, air contaminants. The effect of oxygen content, temperature, water vapor, and 2‐propanol concentration on the TiO₂ surface was investigated. The rate of 2‐propanol decomposition increased with increasing the oxygen content, but was reduced at temperatures higher than 100°C. When water vapor concentration was in the range of 10–355 mmol m^?3, the rate of 2‐propanol decomposition was proportional to the water content. However, an opposite result was observed at a higher concentration of water vapor. 2‐Propanol was photooxidized to acetone, and eventually to carbon dioxide and water. The kinetic model of 2‐propanol photooxidation was successfully developed by the competitive Langmuir–Hinshelwood rate form, incorporating the inhibition effect coming from the formation of acetone. Copyright © 2004 Society of Chemical Industry     

TiO2/Al氮化合成复相TiN-Al2O3

从热力学角度讨论了Al作为还原剂还原氮化TiO2制备复相TiN-Al2O3的可行性.利用综合热分析、X射线衍射仪、扫描电镜及能谱仪分析研究了在1 100～1 500℃TiO2和金属Al粉还原氮化过程中样品的质量变化、相组成和显微结构.结果表明:在1 100℃合成产物中已有少量的AlN和TiN,说明A1的氮化反应以及TiO2和Al的还原氮化反应都已开始.在1200～1 300℃,TiN含量明显增加,AIN含量逐渐减少.在1 350℃,合成产物中只有TiN和Al2O3,说明还原氮化反应完成.继续提高温度,在1400～1 500℃,TiN和刚玉的晶粒长大.     

Counterion‐Switched Reversibly Hydrophilic and Hydrophobic TiO2‐Incorporated Layer‐By‐Layer Self‐Assembled Membrane for Nanofiltration

The manipulation of surface wettability has been regarded as an efficient strategy to improve the membrane performances. Herein, the counterion‐switched reversibly hydrophilic and hydrophobic surface of TiO₂‐loaded polyelectrolyte membrane are prepared by layer‐by‐layer assembly of poly(sodium 4‐styrene sulfonate) (PSS) and poly(diallydimethyl‐ammoniumchloride (PDDA) containing TiO₂@PDDA nanoparticles (NPs) on the hydrolyzed polyacrylonitrile (PAN) substrate membrane. The obtained polyelectrolyte multilayer (PEM) membranes [PEM‐TiO₂]_4.5⁺X^? (X^? = Cl^?, PFO^? [perfluorooctanoate] etc.) show different hydrophilicity and hydrophobicity with various counterions. The integration of TiO₂ NPs obviously improves the wettability and nanofiltration (NF) performance of PEM membrane for (non)aqueous system of dyes (crystal violet, eriochrome black T) with a high recyclability. The highly hydrophilic [PEM‐TiO₂]_4.5⁺Cl^? (water contact angle [WCA]: 13.2 ± 1.8°) and hydrophobic [PEM‐TiO₂]_4.5⁺PFO^? (WCA: 115.4 ± 2.3°) can be reversibly switched via counterion exchange between Cl^? and PFO^?, verifying the surface with a reversible hydrophilic–hydrophobic transformation. For such membranes, the morphology, wettability, and NF performance rely on the loading of TiO₂@PDDA NPs and surface counterion. Meanwhile, the motion and interaction of water or ethanol in the hydrophilic or hydrophobic membrane are revealed by low‐field nuclear magnetic resonance. This work provides a facile and rapid approach to fabricate smart and tunable wetting surface for potential utilization in (non)aqueous NF separation.     

吸附相反应技术制备纳米TiO2的反应过程

通过不同水量实验并结合同样条件下的浸渍法实验,研究了吸附相反应技术吸附层中钛酸丁酯的反应过程.用分光光度法测定乙醇体相中Ti含量随反应时间的变化,发现有外加水的条件下,Ti含量曲线都呈现先快后慢的变化趋势,且水量在1.0～1.1 mL时Ti含量曲线出现突变.Ti含量的突变区域通过电子色散能谱仪对载体SiO2表面Ti含量的测定得到了进一步地确定,但浸渍法得到样品的Ti含量变化非常缓慢.透射电子显微镜(TEM)和X射线衍射(XRD)分析结果表明,吸附法得到的TiO2粒子粒径远远小于浸渍法得到的TiO2,而且在Ti含量较高时也能保持非常高的分散性.实验结果发现,由于纳米级吸附层作为反应器的独特性,钛酸丁酯在吸附层中发生的反应有着不同于宏观反应的特点.