Acidic Suspension Research Articles

Anodic Electrophoretic Deposition of Graphene Oxide on 316L Stainless Steel with pH-Dependent Microstructures

This paper describes anodic electrophoretic deposition of graphene oxide (GO) on 316L SS with pH-dependent microstructures. GO flakes were synthesized by modified Hummers’ method. Detailed studies on structural characteristics, thermal stability, and elemental composition of the GO flakes were carried out using advanced characterization techniques. Results showed successful oxidation and exfoliation forming GO flakes that are hydrophilic in nature. Acidic (pH 3.4) and basic (pH 11) aqueous GO suspensions were prepared, and the zeta potential as well as the average particle size distribution of the suspensions was ascertained. The GO suspensions were exhibiting zeta potential values of −32.9 and −36.8 mV and average particle size of 1–2 µm and 800–900 nm at acidic pH of 3.4 and alkaline pH of 11, respectively. Using anodic electrophoretic deposition (EPD) methods, GO was coated on 316L SS substrate from acidic and alkaline suspension and coatings were characterized. The increased value of ID/IG by Raman spectra analysis, partial restoration of C = C skeleton in the de-convoluted C 1s XPS spectra analysis, and the presence of C–C and C–H stretching bands in ATR-FTIR spectra were correlated with partial reduction of GO during the deposition on 316L SS surface. Though there was no difference in the chemical composition of the coatings formed from the acidic and alkaline pH suspension, atomic force microscopy and field emission scanning electron microscopy characterization showed difference in topography and morphology of the coatings. 316L SS substrates coated with GO in acidic pH showed higher RMS and average roughness and dense agglomerated wrinkled microstructure compared to substrates coated with alkaline pH suspension. Again GO coating from acidic pH suspension showed hydrophobicity. The present study showed that the microstructures of the GO coatings on 316L SS can be tuned by varying the pH of the GO suspension during EPD process.

Novel pathway to produce high molecular weight kraft lignin-acrylic acid polymers in acidic suspension systems.

Kraft lignin (KL) produced in kraft pulping process has a low molecular weight and solubility, which limits its application in industry. For the first time, KL was polymerized with acrylic acid (AA) in an acidic aqueous suspension system to produce a water soluble lignin–AA polymer with a high molecular weight in this work. The polymerization reaction was carried out using K2S2O8 as an initiator, and the influence of reaction conditions on the carboxylate group content and molecular weight of resultant lignin polymers was systematically investigated. The mechanism of polymerization of KL and AA was discussed fundamentally. The resulting lignin–AA polymer was characterized by Fourier Transform Infrared spectrophotometry (FTIR), proton nuclear magnetic resonance (1H-NMR) and elemental analyses. The results showed that the phenolic hydroxyl group (Ph-OH) content of KL promoted the polymerization under an acidic environment. Under the conditions of 1.5 wt% of initiator, 3.5 of pH, 10.0 of AA/lignin molar ratio, 0.15 mol L−1 of lignin concentration, 3 h and 80 °C, the carboxylate group content and the molecular weight of the polymer were 7.37 mmol g−1 and 7.4 × 105 g mol−1, respectively. The lignin–AA polymer was water soluble at a 10 g L−1 concentration and a pH higher than 4.5. Furthermore, the flocculation performance of lignin–AA polymer in an aluminium oxide suspension was evaluated. Compared with polyAA, the lignin–AA polymer was a more efficient flocculant for aluminium oxide suspension, which shows its potential to be used as a green flocculant in industry.

Comparative performance of flame retardancy, physiological comfort, and durability of cotton textiles treated with alkaline and acidic casein suspension

The objective of the present study was to investigate the effect of coating of different concentrations and pH of aqueous casein suspension on thermo-oxidative properties, flame retardant behavior as well as physiological comfort of cotton fabrics. The flame retardant behavior was found to increase with increase in concentration of casein suspension in both alkaline and acidic pH conditions. The burning rate of 2.1 mm/s and 2.4 mm/s was measured for the samples of 150 g/L casein suspensions in acidic and alkaline pH, respectively. Moreover, better thermo-oxidative properties were obtained for the samples of casein suspension prepared in acidic pH than alkaline pH. The 150 g/L casein produced 19% and 28% residue, respectively for alkaline and acidic suspensions at 600℃. Furthermore, the phenomenon of intumescence was largely observed in case of samples coated with acidic casein suspension due to easier release of ammonia from protonated casein. These samples further exhibited relatively better durability against water washing and UV ageing as compared to those treated with alkaline casein suspension, however delivered poor physiological comfort properties due to blockage of fabric porosity by higher viscosity of casein in acidic pH.

A new alternative self-assembled-monolayer activation process for electroless deposition of copper interconnects without a conventional barrier

Amino-terminated, self-assembled monolayers (NH2-SAMs) are widely used for seeding in electroless metallization, and activation is typically performed in an acidic aqueous suspension of colloidal Pd or Au, generating noble-metal catalytic particles of sizes generally exceeding 10 nm. In this study, we develop a new activation process by which aliphatic NH2-SAMs immobilize Ni particles on low-k (SiOCH) dielectric layers, and which involves a cost-effective basic aqueous solution simply containing Ni2+ ions. Rutherford backscattering spectroscopy suggests that the activated SAMs work effectively as diffusion barriers, enabling integration of Cu with SiOCH without interposing a conventional barrier layer. Moreover, as revealed by transmission electron microscopy, the sizes of the Ni particles adsorbed are extremely small (2–3nm), leading to fast nucleation and the formation of void/seam-free Cu interconnects in 60-nm trenches. Based on the results of X-ray photoelectron spectroscopy, a new model of changes in the surface structure (and the phase transitions of the seeds) leading to effective seeding is proposed.

Induced Mesocrystal-Formation, Hydrothermal Growth and Magnetic Properties of α-Fe2O3 Nanoparticles in Salt-Rich Aqueous Solutions

Iron oxide nanoparticles are widely prevalent in our aqueous environment (e.g., streams, seawater, hydrothermal vents). Their aggregation and crystal growth depend on their chemical surroundings, for instance just a change in pH or salt concentration can greatly affect this. In turn this influences their properties, mobility, fate, and environmental impact. We studied the growth of α-Fe2O3 (hematite), starting from 8 nm hematite particles in weakly acidic (HNO3) aqueous suspension with different states of particle aggregation, using salt (NaCl and NaH2PO4) to control their initial aggregation state. The samples were then subject to hydrothermal treatment at 100–140 °C. We followed the development in aggregation state and particle size by dynamic light scattering, X-ray diffraction, small angle neutron scattering and transmission electron microscopy, and the magnetic properties by Mössbauer spectroscopy. The addition of NaCl and NaH2PO4 both led to aggregation, but NaCl led to linear chains of hematite nanoparticles (oriented parallel to their hexagonal c-axis), such that the crystalline lattice planes of neighboring hematite particles were aligned. However, despite this oriented alignment, the particles did not merge and coalesce. Rather they remained stable as mesocrystals until heat-treated. In turn, the addition of NaCl significantly increases the rate of growth during hydrothermal treatment, probably because the nanoparticles, due to the chain formation, are already aligned and in close proximity. With hydrothermal treatment, the magnetic properties of the particles transform from those characteristic of small (aggregated) hematite nanoparticles to those of particles with more bulk-like properties such as Morin transition and suppression of superparamagnetic relaxation, in correspondence with the growth of particle size.

Adsorption of Antimonate by Kaolinite

Core Ideas Sb(V) adsorption by kaolinite is pH and ionic strength dependent, with adsorption decreasing with increasing pH and ionic strength. Sb(V) adsorption is hysteretic in acidic systems, but reversible in alkaline. Adsorbed Sb(V) generates a downward shift in the isoelectric point and an upward shift in the point of zero net proton charge. Phosphate decreases Sb(V) adsorption, but the influence of sulfate is minimal. The macroscopic findings indicate that Sb(V) is retained by innersphere in acidic and outersphere in neutral to alkaline systems. The environmental fate and behavior of antimony (Sb) is controlled by adsorption processes at the solid–solution interface of surface‐reactive solids. One such solid is kaolinite, which bears the aluminol (≡AlOH) surface functional group. The objectives of this study are to characterize antimonate [Sb(V) in the Sb(OH)6– species] adsorption by kaolinite as a function of pH, ionic environment, and competing ligands (PO4 and SO4); to describe the reversibility of the adsorption and the influence of adsorbed Sb(V) on the surficial properties of kaolinite; and to develop predictive surface complexation models. The results of this study show adsorbed Sb(V) is at a maximum in strongly acidic suspensions, and retention decreases with increasing pH and ionic strength. Adsorption is hysteretic in pH < 5 suspensions, becoming reversible with increasing pH. The point of zero net proton charge (PZNPC) increases from 4.5 in KNO3 to 5.6 in KSb(OH)6. Correspondingly, the isoelectric point decreases from 4.5 in KNO3 to <3 in KSb(OH)6. The macroscopic findings indicate that Sb(V) is retained by a combination of inner and outersphere mechanisms, with the former dominating in acidic suspensions. The inclusion of SO4 had little impact on the retention of Sb(V); however, PO4 reduced Sb(V) retention. The inclusion of both inner‐ and outersphere complexes in the triple layer surface complexation model (TLM) provided an adequate description of the Sb(V) adsorption envelopes. Further, the TLM successfully predicted ligand retention in competitive systems without re‐optimization.

Suspension stability and mobility of Trap-Ox Fe-zeolites for in-situ nanoremediation

With Trap-Ox Fe-zeolites we intend to develop a novel nanoremediation concept, which is based on in situ trapping of organic contaminants by adsorption and catalytic oxidation in combination with oxidants such as hydrogen peroxide. Within this study, colloidal properties including surface charge and suspension stability as well as mobility in porous media were studied under various conditions for two Trap-Ox Fe-zeolite representatives: Fe-BEA35 and Fe-MFI120. These Fe-zeolites can act as adsorbent for contaminants and as micro-reactors for their catalytic Fenton-like oxidation. Both Fe-zeolites under investigation show remarkable suspension stability in slightly alkaline suspension (pH 8–8.5) without any additional stabilizers, but not in acidic suspensions (pH 5.5). Mobility investigations in columns with clean sand and natural sand suggest high mobility at slightly alkaline conditions. Particle breakthrough through 20cm sand columns was >75% for the two zeolites when injected as 10g/L suspensions with a flow velocity of 10m/d. However, under acidic conditions in natural sediment, a long period of near-total deposition of particles is observed before high breakthrough occurs. The pH dependency is believed to be caused by charge inhomogeneity due to Fe-oxide clusters on the zeolites as well as on the sediment grains.

Determination of acoustic fields in acidic suspensions of peanut shell during pretreatment with high-intensity ultrasound

Abstract The benefits of high-intensity ultrasound in diverse processes have stimulated many studies based on biomass pretreatment. In order to improve processes involving ultrasound, a calorimetric method has been widely used to measure the real power absorbed by the material as well as the cavitation effects. Peanut shells, a byproduct of peanut processing, were immersed in acidified aqueous solutions and submitted to an ultrasonic field. Acoustic power absorbed, acoustic intensity and power yield were obtained through specific heat determination and experimental data were modeled in different conditions. Specific heat values ranged from 3537.0 to 4190.6 J·kg-1·K-1, with lower values encountered for more concentrated biomass suspensions. The acoustic power transmitted and acoustic intensity varied linearly with the applied power and quadratically with solids concentration, reaching maximum values at higher applied nominal power and for less concentrated suspensions. A power yield of 82.7% was reached for dilute suspensions at 320 W, while 6.4% efficiency was observed for a concentrated suspension at low input energy (80 W).

Initial biochar properties related to the removal of As, Se, Pb, Cd, Cu, Ni, and Zn from an acidic suspension

This study tests the influence of a diverse set of biochar properties on As(V), Se(IV), Cd(II), Cu(II), Ni(II), Pb(II), or Zn(II) removal from solution at pH 4.5. Six commercial biochars produced using different feedstock and pyrolysis conditions were extensively characterized using physical, chemical, and spectroscopic techniques, and their properties were correlated to anion and cation removal using multiple linear regression. H/total organic C (TOC) ratio and volatile matter were positively correlated to cation removal from solution, which indicate interactions between metals and non-aromatic C. Defining the correlation of ion removal with specific OC functional groups was hindered by the inherent limitations of the spectroscopic techniques, which was exacerbated by the heterogeneity of the biochars. Ash was negatively correlated to Se(IV) and positively correlated to Cd(II), Cu(II), and Ni(II) removal from solution. Interference from soluble P in biochars may partly explain the low Se(IV) removal from solution; and Ca-, P-, and Fe- containing compounds likely sorbed or precipitated Pb(II), Cd(II), Cu(II), Ni(II) and Zn(II). Furthermore, Ca-oxalate identified using X-ray diffraction in willow, may be responsible for willow's increased ability to remove Cd(II), Ni(II), and Zn(II) compared to the other 5 biochars. It was clear that both OC and inorganic biochar components influenced metal(loid) and Se(IV) removal from solution. The non-aromatic and volatile OC correlated to removal from solution may be readily available for microbial degradation, while Mg, N, P, and S are required for biological growth. Biological metabolism and uptake of these compounds may inhibit or destabilize their interaction with contaminants.

Pathways of the photocatalytic reaction of acetate in H2O and D2O: A combined EPR and ATR-FTIR study

The adsorption and photocatalytic degradation of acetate on TiO2 surfaces were investigated in H2O and D2O by ATR-FTIR and EPR Spectroscopy respectively. These studies were carried out in the dark and under UV(A) illumination to gain additional insights into the adsorption behaviour with the identification of paramagnetic species formed during the oxidation of acetate. Isotopic exchange during the adsorption of D2O on the TiO2 surface led to different interactions between the adsorbate and OD groups. At different pH levels, several surface complexes of acetate can be formed such as monodentates or bidentates. Under UV(A) irradiation of TiO2 aqueous suspensions, the formation of hydroxyl and methoxy radicals evidenced as the corresponding spin-adducts, was found to dominate in alkaline and acidic suspensions respectively. Two possible pathways for the oxidation of acetate have been suggested at different pH levels in solution in terms of the source of the spin adduct formed. These proposed pathways were found to be in good agreement with ATR-FTIR and EPR results.

The Effect of Ca2+ and Mg2+ on the Dispersion and Flocculation Behaviors of Muscovite Particles

The dispersion and flocculation behavior of muscovite suspensions in the presence of Ca2+ and Mg2+ are relevant for industrial processing of pre-concentrated muscovite from stone coal, a primary source of vanadium. In this study, the dispersion and flocculation behavior were investigated by means of sedimentation, zeta potential, and ion absorption experiments, as well as the force between particles and ion speciation calculations. The results indicated that the dispersion and flocculation behavior of muscovite particles without excess ions were in qualitative agreement with the classical DLVO theory. The muscovite particles aggregated mainly due to basal surface-edge interactions in acidic suspensions but were dispersed in alkaline suspension by electrostatic repulsion of the total particle surface. In acidic suspensions, the ability of muscovite to form dispersions of muscovite was increased with the decrease in the electrostatic attraction between the basal surface and the edge caused by the compression of the electric double layers withCa2+ and Mg2+. In alkaline suspension, the main adsorption form of Ca2+ and Mg2+ on muscovite surface was the ion-hydroxy complexes. The flocculation behavior of muscovite was affected by the static bridge effect of the ion-hydroxy complexes.

The ability of electrochemical oxidation with a BDD anode to inactivate Gram-negative and Gram-positive bacteria in low conductivity sulfate medium

The disinfection of 100 mL of synthetic water containing 7 mM Na2SO4 with 106 CFU mL−1 of either Gram-negative or Gram-positive bacteria has been studied by electrochemical oxidation. The electrolytic cell was a stirred tank reactor equipped with a boron-doped diamond (BDD) anode and a stainless steel cathode and the trials were performed at acidic and neutral pH, at 33.3 mA cm−2 and 25 °C. Reactive oxygen species, pre-eminently hydroxyl radicals, were efficiently produced in both media from water oxidation at the BDD anode and the bacteria concentration was reduced by ≥ 5 log units after 60 min of electrolysis, thus constituting a good chlorine-free disinfection treatment. All the inactivation kinetics were described by a logistic model, with no significant statistical differences between acidic and neutral suspensions. The electrochemical disinfection with BDD was very effective for Gram-negative bacilli like Escherichia coli and Pseudomonas aeruginosa and Gram-positive ones like Bacillus atrophaeus, whereas the Gram-positive cocci Staphylococcus aureus and Enterococcus hirae were more resistant. Thus, the latter organisms are a better choice than E. coli as process indicators. Scanning electron microscopy highlighted a transition from initial cells with standard morphology supported on clean filters to inactivated cells with a highly altered morphology lying on dirty filters with plenty of cellular debris. Larger damage was observed for Gram-negative cells compared to Gram-positive ones. The inactivation effect could then be related to the chemical composition of the outer layers of the cell structure along with the modification of the transmembrane potentials upon current passage.

Quick cold preparation of TiO2 nanolayers on gold from P25 suspensions – film structure, voltammetric behavior and photocatalytic performance for the oxidation of EDTA under UVA-LED irradiation

Time consuming thermal treatments are a common place in the preparation of photocatalysts and their immobilization on substrates. In this work nanolayers of TiO2 were applied at room temperature on gold surfaces by simply exposing the metal during a minute to an acidic aqueous suspension of P25 TiO2 (10gL−1 in 0.1molL−1 HCl). Repulverization of the commercial semiconductor by dry grinding in a mortar increased the stability of the suspension and more than doubled the photoelectrocatalytic activity of the TiO2 nanolayer. While the average TiO2 particle size in the suspension was of 103±3nm (obtained by DLS), the less than 100nm thick TiO2 nanolayer on the gold surface was dominated by particles with diameters ranging from 20nm (anatase) to 30nm (rutile) (observed by SEM, TEM and EDS). Photooxidation experiments with EDTA −an emerging organic pollutant– revealed a linear relationship between the photocurrent and the potential applied to the TiO2 modified electrode until the saturation photocurrent was attained. For a 1.0mmolL−1 EDTA solution the integrated saturation photocurrent resulted in a net charge, repeatable from one electrode modification to another, of 38±3CLmol−1cm−2 (conditions: 100s irradiation with an UV-LED at 365nm, 91mWcm−2; 0.5V vs. Ag/AgCl applied potential). A micrometric TiO2 layer applied on gold by drop casting enhances this net charge by just 50%. Cyclic voltammograms of the ferrocyanide/ferricyanide redox probe on gold remained undisturbed (in the dark) after the application of the TiO2 nanolayer, but they became distorted with the drop-cast micrometric layer. The photoactivity of the TiO2 nanolayer lasts with little decay for many days of photoelectrocatalytic treatment of EDTA. The simple and quick modification process at room temperature can be easily scaled-up to large areas.

Preparation of nano-structured cryptomelane materials for catalytic oxidation reactions

Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) were prepared via reflux method by synproportionation of KMnO4 and Mn2+ in acidic aqueous suspension. For this method, different manganese anions (sulphate, chloride and acetate) were used, which exert a strong influence on the prepared materials. Several techniques such as X-ray diffraction, Fourier transformer infrared, Raman spectroscopy, transmission electron microscopy, differential and gravimetric thermal analysis and H2-temperature programmed reduction were used to characterize the prepared samples. The results revealed that the prepared samples were mainly pure mono-phase cryptomelane materials. The obtained K-OMS-2 material on using the sulphate anion has more available lattice oxygen as compared to that prepared by the other anions. The catalytic activity of the prepared samples was tested towards the oxidative dehydrogenation of cyclohexane. Over the K-OMS-2RS sample, cyclohexane conversion was significantly higher than the other prepared samples.

Perovskite Solar Cells with Two Dimensional Materials As Hole Extraction Layer

Organometallic halide perovskites have attracted much attention as a promising material for high-efficiency absorber in photovoltaic devices. It is based on organic-inorganic light absorbing semiconducting material with a perovskite polycrystalline structure, CH3NH3PbX3, where X is halogenatoms (Cl, Br, I, or combination of some of them). The poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was usually used as a hole extraction layer in planar type perovskite photovoltaic cells. However, PEDOT:PSS showed several disadvantages such as hygroscopic properties and a highly acidic suspension, which result in poor stability in air. In this respect, we have investigated the possibility of two-dimensional materials including MoS2, WS2, and graphene oxide (GO) as a hole extraction layer in perovskite photovoltaic cells. MoS2 and WS2 layers with a polycrystalline structure were synthesized by a chemical deposition method using uniformly spin-coated (NH4)MoS4 and (NH4)WS4 precursor solutions. GO was made by following Hummer’s method. Raman spectra, transmission electron microscope image, and x-ray diffraction data confirmed the well-synthesis of two-dimensional materials. The device structure is indium tin oxide/PEDOT:PSS or MoS2 or WS2 or GO/CH3NH3PbIxCl3-x/bathocurione/LiF:Al. The PCE values of PEDOT:PSS, GO, MoS2 and WS2-based one are measured to be 9.93, 9.62, 9.53 and 8.02 %, respectively. These result indicated that two-dimensional materials could replace the PEDOT:PSS layer for the improvement of device stability.

Ce-promoted Ni/SBA-15 catalysts for anisole hydrotreating under mild conditions

Ce-containing SBA-15 materials with Ce/Si molar ratio ranging from 0 to 0.08 were prepared by mixing an acidic suspension of colloidal CeO2 particles along with the surfactant during the synthesis of mesostructured silica. The obtained solids were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms, TEM, UV–vis, and Raman spectroscopy. Structural analyses confirmed that all the samples present a well-ordered hexagonal mesoporous structure, with larger pore diameter and volume than unmodified SBA-15 due to the incorporation of the lanthanide promoter. According to the characterization results different cerium species, namely dispersed Ce species and CeO2 crystallites, are formed depending on the Ce/Si ratio of the Ce-SBA-15 materials. On the other hand, Ni/Ce-SBA-15 catalysts were prepared by wet impregnation of the mesoporous supports and the comparison of the different samples showed that the incorporation of Ce progressively enhances Ni dispersion. These catalysts were assayed for hydrotreating of anisole at temperatures in the 270–290°C range and moderate hydrogen pressure (7bar). Such process is relevant for the upgrading of bio-oils derived from the pyrolysis of lignocellulosic biomass. Catalytic activity tests reveal that conversion of anisole progressively improves with increasing Ce/Si ratio and exceeds 30% at 290°C for the catalyst with Ce/Si=0.08. In these conditions the main product is methoxycyclohexane in all cases. However, almost a two-fold increment of benzene yields can be obtained with Ce-promoted catalysts when compared to Ni/SBA-15. This enhancement of the selectivity towards aromatic is very promising for the development of a green route for the production of those chemicals.

Separation of Sulphuric Acid from an Acid Suspension of Cellulose Nanocrystals by Manual Shaking

In this paper, the separation of sulphuric acid from a suspension of cellulose nanocrystal by manual shaking is described. Cellulose nanocrystals are prepared from acid hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 °C for 45 minutes. After the hydrolysis was complete, water was added to dilute the mixture to a resulting concentration of 30 wt% of the acid. This mixture was shaken rigorously in a closed container and after 48 hours, separation occurs such that cellulose nanocrystals float, with the bubbles introduced by the shaking, to give clear acid solution at the bottom. This shaking-floating process is repeatable for several cycles after the acid was removed from the bottom and more water was added. Using this simple process, the total acid recovery of > 90% has been achieved, and the concentration of all the acid recovered combined was 17.5 wt%. This work demonstrates a method that allows energy efficient and up-scalable separation of cellulose nanocrystals from the acidic suspension from which it was extracted.

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.

Different orientation patterns of cellulose nanocrystal films prepared from aqueous suspensions by shearing under evaporation

Oriented films were prepared from aqueous suspensions of cellulose nanocrystal (CNC; microfibril fragment of sulfuric acid-hydrolyzed cotton) by a shearing method. Rotating glass vials each containing a 3–4 wt% CNC/water suspension under evaporation resulted in formation of translucent films of CNC per se. Structural characterization of the dry films was carried out by use of X-ray diffractometry and optical and scanning electron microscopy. The orientation pattern of CNCs in the films was much affected by pH condition of the starting suspensions; that is, the longitudinal axes of CNCs aligned preferentially perpendicular to the shear direction (SD) in the acidic condition of pH = 2.0, while an ordinary orientation of CNCs aligning parallel to SD was observed in the neutral condition of pH = 6.7 (adjusted with NaOH addition to the acidic suspension, however). To interpret the two distinct orientation patterns, first, it was inspected whether a mesomorphic ordered phase arrived or not in the two sheared and dried suspensions, different from each other in the counterions of surface-sulfated CNCs. As to the orientation development from the suspension of pH = 2, it was particularly assumed that the arising nematic planar domains would have been rolled up into a transversely extended body with the director perpendicular to SD. For the two film preparations, the orientation parameter of the longitudinal axis of CNC was quantified by WAXD intensity measurements, and the data were compared with those for other CNC-oriented materials such as CNC/polymer composites synthesized by immobilizing CNC suspensions via magnetic field application.

Toward the control of thickness and uniformity in the coating of TiO2-P25 on glass

ABSTRACTThe deposition of TiO2-P25 on Pyrex glass is studied in order to propose a procedure for obtaining uniform and adherent thin films with a controlled thickness in the range between fractions of micrometer to a few tens of micrometers. Different deposition methods such as spray-coating, dip-coating, and drop-coating of liquid suspensions of TiO2-P25 powder are considered. The effects of pretreatment of the glass support, as well as postdeposition steps such as drying condition and thermal treatment, are also reported. A basic glass pretreatment and an acidic TiO2 suspension are chosen for an optimized adherence of the film. Drop-coating, associated with a slow drying under 55% relative humidity and a high-temperature thermal treatment is the method of choice to prepare coated glass slides in a large range of film thicknesses.