Density Of Hydroxyl Groups Research Articles

Effects of surface oxidation on the pH-dependent surface charge of oxidized aluminum gallium nitride

Hypothesis: The properties of the oxidized surface for common materials, such as silicon and titanium, are known to be markedly different from the reduced surface. We hypothesize that surface-oxidized aluminum gallium nitride ((oxidized-AlGaN)/GaN) surface charge behavior is different to unoxidized AlGaN (with ultrathin native oxide only), which can be validated via surfactant adsorption. Understanding these differences will explain why (oxidized-AlGaN)/GaN-based sensors are better performing than AlGaN ones, which has been previously demonstrated but not understood.Experiments: The surface of an AlGaN/GaN structure was oxidized with hot piranha solution and oxygen plasma. AFM force measurements and imaging were performed to probe the charge properties of the surface in aqueous solutions of varying pH containing only an acid or base, or with an added ionic surfactant: cationic cetyltrimethylammonium bromide (CTAB) or anionic sodium dodecylsulfate (SDS).Findings: The (oxidized-AlGaN)/GaN surface is positively charged at pH 4 and pH 5.5, although pH 5.5 should be close to the isoelectric point of the surface. The surface is negatively charged at pH 10 and pH 12, and sufficiently charged to attract cooperative adsorption of CTAB aggregates at pH 12. At pH 2, the evidence is inconclusive, but the surface is most likely positively charged. Compared to unoxidized AlGaN, the (oxidized-AlGaN)/GaN surface shows a wider range of surface charge magnitude over pH values between 2 and 12. This suggests that the (oxidized-AlGaN)/GaN surface has a higher surface hydroxyl group density than unoxidized AlGaN, which explains the higher sensitivity for pH sensors based on (oxidized-AlGaN)/GaN structures.

Efficient Activation of Coal Fly Ash for Silica and Alumina Leaches and the Dependence of Pb(II) Removal Capacity on the Crystallization Conditions of Al-MCM-41.

In this study, four different coal fly ashes (CFAs) were used as raw materials of silica and alumina for the preparation of the alumina-containing Mobil Composition of Matter No. 41 (Al-MCM-41) and the exploration of an activation strategy that is efficient and universal for various CFAs. Alkaline hydrothermal and alkaline fusion activations proceeded at different temperatures to determine the best treatment parameters. We controlled the pore structure and surface hydroxyl density of the CFA-derived Al-MCM-41 by changing the crystallization temperature and aging time. The products were characterized by small-angle X-ray diffraction, nitrogen isotherms, Fourier-transform infrared spectroscopy, 29Si silica magic-angle spinning nuclear magnetic resonance, and transmission electron microscopy, and they were then grafted with thiol groups to remove Pb(II) from aqueous solutions. This paper innovatively evaluates the CFA activation strategies using energy consumption analysis and determines the optimal activation methodology and parameters. This paper also unveils the effect of the crystallization condition of Al-MCM-41 on its subsequent Pb(II) removal capacity. The results show that the appropriate selection of crystallization parameters can considerably increase the removal capacity over Pb(II), providing a new path to tackle the ever-increasing concern of aquic heavy-metal pollution.

Super Stretchable and Compressible Hydrogels Inspired by Hook-and-Loop Fasteners.

Inspired by hook-and-loop fasteners, we designed a hydrogel network containing α-zirconium phosphate (ZrP) two-dimensional nanosheets with a high density of surface hydroxyl groups serving as nanopatches with numerous "hooks," while polymer chains with plentiful amine functional groups serve as "loops." Our multiscale molecular simulations confirm that both the high density of hydroxyl groups on nanosheets and the large number of amine functional groups on polymer chains are essential to achieve reversible interactions at the molecular scale, functioning as nano hook-and-loop fasteners to dissipate energy. As a result, the synthesized hydrogel possesses superior stretchability (>2100% strain), resilience to compression (>90% strain), and durability. Remarkably, the hydrogel can sustain >5000 cycles of compression with torsion in a solution mimicking synovial fluid, thus promising for potential biomedical applications such as artificial articular cartilage. This hook-and-loop model can be adopted and generalized to design a wide range of multifunctional materials with exceptional mechanical properties.

Unveiling the hydroxyl-dependent viscosity of water in graphene oxide nanochannels via molecular dynamics simulations

We present a molecular dynamics study on the viscosity of water confined in graphene oxide (GO) nanochannels, with a major consideration of its dependence on the density of hydroxyl groups on GO sheets. The results show that the anisotropic water viscosity exhibits a nonmonotonic variation with the density of hydroxyl groups, owing to the coupling interactions between water molecules and GO sheets and their relating momentum dissipation among water molecules within water layers, viscous friction among water layers. The calculated viscosity is consistent with the experimentally and numerically reported water viscosity in literature and the Eyring’s absolute action theory.

Increased Hydrophilicity of Silicon Surface through Plasma Treatment with Hydrogen Peroxide Gas

Increased Hydrophilicity of Silicon Surface through Plasma Treatment with Hydrogen Peroxide GasSpiegelman, D. Alvarez, C. Ramos (RASIRC), K. Andachi, G. Tsuchibuchi, and K. Suzuki (Taiyo Nippon Sanso Corporation)Wafer bonding is a critical step in the development of advanced semiconductor and MEMS devices.1 Wafer bonding enables the bonding of dissimilar materials as well as the union of separate manufacturing pathways where the pathway steps are dissimilar and frequently incompatible to a single wafer process. Oxide wafer bonding is a common bonding method that requires the wafer surface to have a uniformly flat surface with sufficiently dense hydroxyl (-OH) groups. The hydroxyl groups provide a pathway for chemical covalent bonding between two wafer surfaces (EG Si-O-Si). Ultimately, the wafer bonding strength is a function of the density of the hydroxyl groups populated on the wafer surface before bonding.Several challenges are associated with functionalizing wafer surfaces. Wet Thermal oxidation is a common method for incorporating surface hydroxyl groups on silicon, however this process typically takes place at very high temperatures (>600C °) where surface hydroxyl groups may reversibly desorb, thus limiting surface functionalization. Surface oxidation by Oxygen plasma is another common method for the creation of hydrophilic surfaces,2 however, this property may be attributed to bridging oxides on the surface, where hydroxyl groups may not be present. In the latter case, residual charge or surface radical species may lead to the observed improvement in wafer bonding properties. Plasma oxidation allows for lower temperature activation.2 Oxygen or clean dry air are frequently used in the plasma process with argon.Our investigation involves the use of hydrogen peroxide gas. In recent years this material has become available in the gas phase where:Gas-phase H2O2/H2O mixture is delivered from an ampoule-based formulation. (RASIRC® BRUTE® Peroxide)High concentration H2O2/H2O is vaporized by in situ concentration methods and use of a membrane vaporizer as a gas generator. (RASIRC Peroxidizer®)Early studies by Kummel3 demonstrated that Hydrogen peroxide gas provides a denser hydroxyl surface on SiGe and Ge vs water. Here, all thermal methods were utilized at reduced temperatures.Before our current work, the creation and use of gas-phase hydrogen peroxide plasma has not been addressed. The objective of this work is to demonstrate the generation of hydrogen peroxide plasma and compare its surface functionalization characteristics to those of water and oxygen plasma methods.A constant gas stream of H2O2/H2O mixture in a carrier gas was introduced to a remote plasma source (MKS). (Figure 1). The use of an argon carrier gas led to stable ignition of the plasma mixture. The subsequent addition of oxygen gas gives rise to plasma instability.In the comparative study, the H2O2 gas stream was mixed with water vapor, molecular oxygen, and argon in different ratios, subjected to a remoted plasma. Functionalization was then carried out on a Si-H terminated surface (HF last silicon wafer surface). Thermal effects without plasma were also compared. Surface hydrophilicity (relative Hydroxyl density) was determined by contact angle measurements with the use of a goniometer.The initial wafer surface after HF clean had a water contact angle of 84.9 °. The smallest wetting angle was found for H2O2/H2O/Ar plasma at 4 °. Water alone led to a wetting angle that was 62.5% larger than the hydrogen peroxide mixture. The angle increased with increasing oxygen concentration in the H2O2 gas stream. The wetting angle with dry oxygen at 200C ° was 27.3°. Thermal only H2O2 gas at 150C° was 47.3 ° and further reduced to 11.4 ° when the temperature was increased to 300C °. (Figure 2). These results along with mechanism and ramifications for wafer bonding will be discussed.

Terminal Hydroxyl Groups on Al2O3 Supports Influence the Valence State and Dispersity of Ag Nanoparticles: Implications for Ozone Decomposition.

Ozone is a poisonous gas, so it is necessary to remove excessive ozone in the environment. Catalytic decomposition is an effective way to remove ozone at room temperature. In this work, 10%Ag/nano-Al2O3 and 10%Ag/AlOOH-900 catalysts were synthesized by the impregnation method. The 10%Ag/nano-Al2O3 catalyst showed 89% ozone conversion for 40 ppm O3 for 6 h under a space velocity of 840 000 h–1 and a relative humidity of 65%, which is superior to 10%Ag/AlOOH-900 (45% conversion). The characterization results showed Ag nanoparticles to be the active sites for ozone decomposition, which were more highly dispersed on nano-Al2O3 as a result of the greater density of terminal hydroxyl groups. The understanding of the dispersion and valence of silver species gained in this study will be beneficial to the design of more efficient supported silver catalysts for ozone decomposition in the future.

Cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM.

Atomic layer deposition (ALD) provides uniform and conformal thin films that are of interest for a range of applications. To better understand the properties of amorphous ALD films, we need an improved understanding of their local atomic structure. Previous work demonstrated measurement of how the local atomic structure of ALD-grown aluminum oxide (AlOx) evolves in operando during growth by employing synchrotron high-energy X-ray diffraction (HE-XRD). In this work, we report on efforts to employ electron diffraction pair distribution function (ePDF) measurements using more broadly available transmission electron microscope (TEM) instrumentation to study the atomic structure of amorphous ALD-AlOx. We observe electron beam damage in the ALD-coated samples during ePDF at ambient temperature and successfully mitigate this beam damage using ePDF at cryogenic temperatures (cryo-ePDF). We employ cryo-ePDF and reverse Monte Carlo (RMC) modeling to obtain structural models of ALD-AlOx coatings formed at a range of deposition temperatures from 150 to 332 °C. From these model structures, we derive structural metrics including stoichiometry, pair distances, and coordination environments in the ALD-AlOx films as a function of deposition temperature. The structural variations we observe with growth temperature are consistent with temperature-dependent changes in the surface hydroxyl density on the growth surface. The sample preparation and cryo-ePDF procedures we report here can be used for the routine measurement of ALD-grown amorphous thin films to improve our understanding of the atomic structure of these materials, establish structure–property relationships, and help accelerate the timescale for the application of ALD to address technological needs.

Thermally Stimulated Wettability Transformations on One-Cycle Atomic Layer Deposition-Coated Cellulosic Paper: Applications for Droplet Manipulation and Heat Patterned Paper Fluidics.

Cellulosic materials are widely used in daily life for paper products and clothing as well as for emerging applications in sustainable packaging and inexpensive medical diagnostics. Cellulose has a high density of hydroxyl groups that create strong intra- and interfiber hydrogen bonding. These abundant hydroxyl groups also make cellulose superhydrophilic. Schemes for hydrophobization and spatially selective hydrophobization of cellulosic materials can expand the application space for cellulose. Cellulose is often hydrophobized through wet chemistry surface modification methods. This work reports a new modification method using a combination of atomic layer deposition (ALD) and atmospheric heating to alter the wettability of purely cellulosic chromatography paper. We find that once the cellulosic paper is coated with a single ALD cycle (1cy-ALD) of Al2O3, it can be made sticky superhydrophobic after a 150 °C ambient post-ALD heating step. An X-ray photoelectron spectroscopy investigation reveals that the ALD-modified cellulosic surface becomes more susceptible to adsorption of adventitious carbon upon heating than an untreated cellulosic surface. This conclusion is further supported by the ability to use alternating air plasma and heat treatments to reversibly transition between the hydrophilic and hydrophobic states. We attribute the apparent abruptness of this wetting transition to a Cassie-Wenzel-like phenomenon, which is also consistent with the sticky hydrophobic wetting behavior. Using scanning probe methods, we show that the surfaces have roughness at multiple length scales. Using a Cassie-Wenzel model, we show how a small change in the surface's Young's contact angle-upon adsorption of adventitious carbon-can lead to an abrupt increase in hydrophobicity for surfaces with such roughnesses. Finally, we demonstrate the ability to spatially pattern the wettability on these 1cy-ALD-treated cellulosic papers via selective heating. This ALD-treated hydrophobic paper also shows promise for microliter droplet manipulation and patterned lab-on-paper devices.

Simulations of the IR and Raman spectra of water confined in amorphous silica slit pores.

Water in nano-scale confining environments is a key element in many biological, material, and geological systems. The structure and dynamics of the liquid can be dramatically modified under these conditions. Probing these changes can be challenging, but vibrational spectroscopy has emerged as a powerful tool for investigating their behavior. A critical, evolving component of this approach is a detailed understanding of the connection between spectroscopic features and molecular-level details. In this paper, this issue is addressed by using molecular dynamics simulations to simulate the linear infrared (IR) and Raman spectra for isotopically dilute HOD in D2O confined in hydroxylated amorphous silica slit pores. The effect of slit-pore width and hydroxyl density on the silica surface on the vibrational spectra is also investigated. The primary effect of confinement is a blueshift in the frequency of OH groups donating a hydrogen bond to the silica surface. This appears as a slight shift in the total (measurable) spectra but is clearly seen in the distance-based IR and Raman spectra. Analysis indicates that these changes upon confinement are associated with the weaker hydrogen-bond accepting properties of silica oxygens compared to water molecules.

Ternary catalyst Mn-Fe-Ce/Al2O3 for the ozonation of phenol pollutant: performance and mechanism.

In this study, a novel ternary catalyst Mn-Fe-Ce/Al2O3 was synthesized by co-impregnation method, and was characterized by XRD, SEM, XPS, and FTIR. The catalytic performance of this ternary catalyst was evaluated in the heterogeneous catalytic ozonation of phenol pollutants and it improved the removal rate and mineralization degree of phenol pollutants. The changes of dissolved ozone in water and the TBA experiment proved that the ternary catalyst could accelerate the decomposition of ozone into hydroxyl radicals, thus accelerating the oxidation of phenol. Phosphate experiments and surface hydroxyl density measurements proved that surface hydroxyl was the active site of the catalyst. XPS analysis showed that the ternary catalysts accelerated electron transfer through the redox cycles of Mn2+-Mn3+-Mn4+, Fe2+-Fe3+, and Ce3+-Ce4+, which also contributed to the high catalytic activity. Moreover, the catalyst maintained high catalytic activity after five cycles of use. Therefore, the ternary catalyst was considered an efficient and promising catalyst for catalytic ozonation system.

Silicon redistribution, acid site loss and the formation of a core–shell texture upon steaming SAPO-34 and their impact on catalytic performance in the Methanol-to-Olefins (MTO) reaction

SAPO-34 is a commercially-implemented silicoaluminophosphate catalyst for selective high yield production of ethene and propene from methanol, but high temperature regeneration in the presence of steam leads to its deactivation. A comprehensive investigation of the effect of prolonged hydrothermal treatment on the structure and properties of SAPO-34 explains the changes in its catalytic methanol-to-olefins (MTO) performance. Microcrystalline powdered SAPO-34 (ca. 3 µm crystals, Al17.1P15.6Si3.3O72) and two batches of larger single crystals of SAPO-34 of different Si concentration (20–100 µm; Al17.3P14.7Si4.0O72 and Al17.7P12.3Si5.9O72) were steamed (pH2O = 0.95 atm) at 873–1023 K for up to 240 h. The acidity (NH3-TPD), crystallinity (PXRD), framework cation environment (solid-state 27Al, 29Si and 31P MAS NMR) and porosity were followed for all materials; larger crystals were amenable to single crystal X-ray diffraction, FIB-SEM and synchrotron IR microspectroscopy, including operando study during methanol and dimethyl ether conversions. Some level of steaming improved the lifetime of all SAPO-34 materials in MTO catalysis without affecting their olefin selectivity, although more severe conditions led to the formation of core–shell structures, microporosity loss and eventually at 1023 K, recrystallization to a dense phase. All these irreversible changes occurred faster in crystals with higher Si contents. The initial increase in catalytic lifetime results from an activated reduction in acid site density (Eact = 146(18) kJ mol−1), a result of redistribution of Si within the SAPO framework without porosity loss. Operando IR with online product analysis during methanol conversion suggests similar reaction pathways in calcined and steamed crystals, but with greatly reduced methoxy group densities in the latter. The gradual development of optically dark crystal cores upon progressive steaming was shown by FIB-SEM to be due to the formation of regions with meso- and macropores, and these were shown by IR mapping to possess low hydroxyl densities.

Facet-controlled activation of persulfate by goethite for tetracycline degradation in aqueous solution

Advanced oxidation processes (AOPs) based on the activation of persulfate (PS) by minerals have been widely used in environmental remediation. Herein, two goethite materials with different contents of exposed {021} facet were synthesized and used as the catalysts for PS activation to degrade tetracycline. Results showed that exposed facets significantly affected their catalytic activity. Goethite exposed with more {021} facet exhibited better catalytic performance. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical analysis suggested that the surface Fe(II)/Fe(III) redox cycle, the abundant surface hydroxyl density and the easier generation of active radicals by activating PS were responsible for the excellent catalytic performance of goethite with more {021} facet exposed. Furthermore, the density functional theory (DFT) calculations further confirmed that {021} facet was more favorable for the activation of PS than {110} facet. The electron paramagnetic resonance (EPR) and radical scavenging experiments indicated that both sulfate radicals and hydroxyl radicals participated in the degradation process. This study provides new insights into the PS heterogeneous activation by facet-dependent goethite in environmental catalysis.

Adsorption of double-stranded ribonucleic acids (dsRNA) to iron (oxyhydr-)oxide surfaces: comparative analysis of model dsRNA molecules and deoxyribonucleic acids (DNA).

Double-stranded ribonucleic acid (dsRNA) molecules are novel plant-incorporated protectants expressed in genetically modified RNA interference (RNAi) crops. Ecological risk assessment (ERA) of RNAi crops requires a heretofore-missing detailed understanding of dsRNA adsorption in soils, a key fate process. Herein, we systematically study the adsorption of a model dsRNA molecule and of two double-stranded deoxyribonucleic acid (DNA) molecules of varying lengths to three soil iron (oxyhydr-)oxides - goethite, lepidocrocite, and hematite - over a range of solution pH (4.5-10), ionic strength (I = 10-100 mM NaCl) and composition (0.5, 1, and 3 mM MgCl2) and in the absence and presence of phosphate (0.05-5 mM) as co-adsorbate. We hypothesized comparable adsorption characteristics of dsRNA and DNA based on their structural similarities. Consistently, the three nucleic acids (NAs) showed high adsorption affinities to the iron (oxyhydr-)oxides with decreasing adsorption in the order goethite, lepidocrocite, and hematite, likely reflecting a decrease in the hydroxyl group density and positive charges of the oxide surfaces in the same order. NA adsorption also decreased with increasing solution pH, consistent with weakening of NA electrostatic attraction to and inner-sphere complex formation with the iron (oxyhydr-)oxides surfaces as pH increased. Adsorbed NA concentrations increased with increasing I and in the presence of Mg2+, consistent with adsorbed NA molecules adopting more compact conformations. Strong NA-phosphate adsorption competition demonstrates that co-adsorbates need consideration in assessing dsRNA fate in soils. Comparable adsorption characteristics of dsRNA and DNA molecules to iron (oxyhydr-)oxides imply that information on DNA adsorption to soil particle surfaces can inform dsRNA ERA.

A simple liquid state 1H NMR measurement to directly determine the surface hydroxyl density of porous silica.

Silica is widely used in industrial applications and its performance is partially decided by its surface hydroxyl density αOH. Here we report a quick, simple liquid 1H NMR method to determine αOH using a benchtop 1H NMR spectrometer. The results show excellent agreement with the literature with an αOH range from 4.16 to 6.56 OH per nm2.

UV-activated adsorbents as novel materials for enhanced removal of malodorous gases

The performance of UV-activated Fe2O3-containing ZSM-5 (UFZ5) and silica (UFS) as adsorbents for the removal of low concentration of volatile organic sulfur compounds (VOSCs) was investigated in ambient conditions. A ∼99.9% and ∼89.2% removal of 10 ppm DMDS was observed for UFZ5 and UFS, respectively, due to a higher proportion of iron in UFZ5. The N2 adsorption isotherm confirmed an unpredictable increase in the surface area and pore volume of adsorbents after the fifth adsorption-oxidation cycle, which made adsorbents highly reusable for multiple cycles. The spectroscopic analysis predicted an increase in the hydroxyl density along with the resistance of catalytic sites against sulfur deactivation, which favored the adsorption-oxidation process. The adsorption capacity of UFZ5 remained in the range of 0.12–0.22, 0.26–0.48, 0.40–0.75 mg g−1 for methyl mercaptan (MM), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), respectively which were significantly higher than those calculated for UFS. The analysis confirmed SO2, CO, CH3OH, H2O, and elemental S as by-products. The UFZ5 was found competent and robust for the treatment of VOSCs-contaminated indoor air.

Effects of Annealing Atmosphere on Electrical Performance and Stability of High-Mobility Indium-Gallium-Tin Oxide Thin-Film Transistors

In this study, we examined the effects of the annealing atmosphere on the electrical performance and stability of high-mobility indium-gallium-tin oxide (IGTO) thin-film transistors (TFTs). The annealing process was performed at a temperature of 180 °C under N2, O2, or air atmosphere after the deposition of IGTO thin films by direct current magnetron sputtering. The field-effect mobility (μFE) of the N2- and O2-annealed IGTO TFTs was 26.6 cm2/V·s and 25.0 cm2/V·s, respectively; these values were higher than that of the air-annealed IGTO TFT (μFE = 23.5 cm2/V·s). Furthermore, the stability of the N2- and O2-annealed IGTO TFTs under the application of a positive bias stress (PBS) was greater than that of the air-annealed device. However, the N2-annealed IGTO TFT exhibited a larger threshold voltage shift under negative bias illumination stress (NBIS) compared with the O2- and air-annealed IGTO TFTs. The obtained results indicate that O2 gas is the most suitable environment for the heat treatment of IGTO TFTs to maximize their electrical properties and stability. The low electrical stability of the air-annealed IGTO TFT under PBS and the N2-annealed IGTO TFT under NBIS are primarily attributed to the high density of hydroxyl groups and oxygen vacancies in the channel layers, respectively.

Water adsorption on silica and calcium‐boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

AbstractAdsorption isotherm of water on silica (modeled with fused quartz) and calcium‐boroaluminosilicate (Ca‐BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub‐monolayer regime (<30% RH), differences between the water spectra on fused quartz and Ca‐BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x‐ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca‐BAS surfaces diminishes as the humidity increases. In the multilayer regime (>60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.

The use of biodegradable polymer as an alternative raw material for the production of new ecopolyol

The current development trend in the polyurethane industry is the replacement of petrochemical polyols by polyols derived from renewable sources (biopolyols) or from chemical recycling (ecopolyols). A method of synthesis of a new polyol raw material based on pure polylactide (PLA) derived from corn and diethylene glycol (GDE) was developed as a result of the research. A number of tests were carried out to characterize the obtained product in terms of application for the polyurethane industry. The research carried out determinations of the hydroxyl number, acid value, density, viscosity and water content. Spectroscopy analyses in FT-IR, 1H NMR and 13C NMR were model in order to confirm the assumed chemical structure of the obtained product and the presence of reactive hydroxyl groups. GPC (Gel Permeation Chromatography) analysis was also performed to determine the average weight and average number molecular weight, and dispersion of the obtained ecopolyol. Studies have confirmed that the obtained polyol raw material can be successfully used in the polyurethane industry and can be a green alternative to petrochemical polyols.

Role of solution chemistry in the attachment of graphene oxide nanoparticles onto iron oxide minerals with different characteristics.

Given the ubiquity and abundance of the iron oxide minerals and their important roles in affecting the environmental fate of graphene oxide (GO) nanoparticles, the attachment of GO onto three iron oxide minerals (i.e., hematite, goethite, and ferrihydrite) under different solution chemistry conditions was investigated in this study. The main mechanism of the attachment of GO was electrostatic interaction. Calculations based on the DLVO theory showed that the attachment was a favorable process. Interestingly, the affinity of GO towards three iron oxide minerals was in the order of ferrihydrite > goethite > hematite. This result indicates that different characteristics of various iron oxides (e.g., specific surface area, crystal structure, and surface charge, and surface hydroxyl densities) can influence their attachment capacities for GO. The attachment of GO depended on the solution pH and ionic strength. Electrostatic attraction and hydrogen bonding were the important retention mechanisms for GO attachment when pH < pHPZC (the point of zero charge) and pH > pHPZC, respectively. The attachment capacities of iron oxides decreased with increasing ionic strength at lower pH because of the decrease of the electrostatic attraction. Meanwhile, the presence of divalent cations (i.e., Ca2+ and Cu2+) could significantly promote GO attachment mainly by the surface-bridging mechanism. Meanwhile, the enhancement effect of Cu2+ was greater than Ca2+ due to the greater complexation affinity of Cu2+. Furthermore, attachment isotherms showed that the presence of phosphate could inhibit the attachment of GO onto minerals obviously. Because phosphate could form inner-sphere surface complex on the iron oxide surface, and consequently decreased the electrostatic attraction between nanoparticles and minerals. Our study has important implications for predicting the fate of GO in natural environment where amounts of iron oxide minerals are present.

Surface Modification of 1-Butyl-3-Methylimidazolium Chloride -Treated Lignocellulosic Materials

Lignocellulosic materials are generally considered hydrophilic due to the high density of hydroxyl groups. The use of lignocellulosic materials in hydrophobic systems thus require surface modification. Therefore, in this study, cellulose (MCC) and sawdust (SD) have been pretreated with ionic liquid, 1-butyl-3-methylimidazolium chloride (BMIMCl) prior to surface modification with cationic surfactant, hexadecyl trimethylammonium bromide (CTAB). The effect of BMIMCl pretreatment prior to surface modification has been investigated. Crystallinity, functional group changes, morphology and thermal stability of the sawdust and cellulose upon BMIMCl pretreatment and surface modification have been studied using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric Analysis (TGA). XRD results showed that the structure of lignocellulosic materials became more amorphous upon pretreatment with BMIMCl. FTIR results indicated that the modification of lignocellulosic is more efficient in BMIMCl-pretreated samples. Percentage of decomposition is higher for the BMIMCl-pretreated and CTAB modified samples.