Concentration Of Surface Hydroxyl Groups Research Articles

Effect of microcrystalline cellulose on the preparation and performance of rigid polyurethane foam

In order to study the effect of microcrystalline cellulose on the reaction kinetics of polyurethane, in this work, the multi-scale microcrystalline cellulose was added to the foaming system of multifunctional polyether and multifunctional MDI polyurethane. While the chemical reaction was carried out, it was found through in situ FTIR combined with in situ rheological analysis that what was different from the usual inorganic fillers, the hydroxyl on the surface of the microcrystalline cellulose could preferentially react with MDI to generate urethane under the action of the catalyst. In the initial 5–6 min of the reaction, the reaction of soft segment chain growth was the main reaction. Then the main reaction quickly converted to the cross-linking reaction, which greatly increased the viscosity of the system. The addition of microcrystalline celluloses accelerated the improvement of the cross-linking degree and viscosity of the system. The higher the surface hydroxyl content of microcrystalline cellulose, the more significant this trend become. In addition, although the amount of microcrystalline cellulose added was different, the ratio of the reaction rate of the isocyanate group with the hydroxyl group and the amine group eventually tended to be constant, which indicated that there was a stable reactivity rate in the gradual addition reaction during the cross-linking reaction. Combined with SEM analysis, it was found that 25–60 μm microcrystalline cellulose with large hydroxyl content could act as a nucleating agent when the addition amount was less than 0.1%, which was beneficial to increase the cell density and reduce the pore size and improved the impact performance of the foam. The microcrystalline cellulose with a length of more than 90 μm continuously penetrated through several cell walls and destroyed integrity of the cell structure, which would consequently reduce the impact strength of the foam. This paper provided theoretical guidance for polyurethane modified by microcrystalline cellulose.

Phenol Removal Performance and Mechanism Using Catalytic Ozonation with the Catalyst of Cobalt-doped α-MnO2

In this paper, Cobalt-doped α-MnO2 (i.e., Co-α-MnO2) were synthesized through hydrothermal method. Phenol was employed as targeted pollutants to investigate the catalytic ozonation performance of Co-α-MnO2. Results showed that Co-α-MnO2 significantly improved the phenol removal increased to 97.47 % after 40 min, which was 16.46 %, 38.92 % higher than that of α-MnO2 catalytic ozonation and single ozonation without catalyst. Additionally, the physicochemical properties of α-MnO2 and Co-α-MnO2 were analyzed using technologies such as XRD, TEM, BET and XPS. Compared to α-MnO2, Co-α-MnO2 has larger specific surface area (79.496 m2/g) and pore volume (0.0396 cm3/g), higher Mn3+ relative content (41.16 %) and adsorbed oxygen content (18.99 %). Also, the oxygen vacancy content, lattice defect content and surface hydroxyl content of Co-α-MnO2 are higher than that of α-MnO2, which could result in higher catalytic oxidation performance of Co-α-MnO2. The influence of masking agent showed that surface hydroxyl group, •OH and •O2- were involved in the catalytic ozonation of phenol. This study could help recognize the role of surface hydroxyl groups and active free radicals and demonstrate the contribution of reactive oxygen species on phenol removal in Co-α-MnO2 systems.

Effect of Surface Hydroxyl Content of Support on the Activity of Cu/ZSM-5 Catalyst for Low-Temperature Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Effect of Surface Hydroxyl Content of Support on the Activity of Cu/ZSM-5 Catalyst for Low-Temperature Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Restructuring Ni/Al2O3 by addition of Ga to shift product selectivity in CO2 hydrogenation: The role of hydroxyl groups

Ni/Al2O3 is an active catalysts for CO2 hydrogenation to both CH4 and CO. By doping with Ga, we succeeded in shifting the selectivity of these catalysts almost completely toward CO. In-situ IR spectroscopy studies showed that the catalyst activity is directly related to the concentration of surface hydroxyl groups that are responsible for the adsorption of CO2 and the formation of intermediate bicarbonates and formates on the catalyst surface. The addition of Ga improved the Ni dispersion which was concomitant with the formation of a Ni-Ga layer on the surface of alumina, thereby reducing the surface hydroxyl concentration. The reduced and weakened interaction between the intermediate products, i.e. bicarbonates and formates, and the catalyst surface, increased the CO selectivity from ∼40 % to 98 %.

Experimental study on the influence of surfactants in compound solution on the wetting-agglomeration properties of bituminous coal dust

To investigate the effect of surfactants in compound solution on the wetting-agglomeration properties of the bituminous coal dust, this paper selected anionic surfactants SDS, SDBS and non-ionic surfactants APG0810 and PPG400 for compounding with agglomerated solutions 0.05 wt% XTG (xanthan gum). The sink test, surface tension test, viscosity test, fourier transform infrared spectroscopy(FTIR) and scanning electron microscope(SEM) were used to investigate the wettability and agglomeration of the four compound solutions and analyze the agglomeration wetting mechanism. The results show that SDBS has the most obvious improvement in the wettability of compound solution. The surface tension of SDBS + 0.05 wt% XTG is 28.98 mN/m after CMC value and sinking rate will reach 14.29 mg/s with 0.6 wt% SDBS in compound solution; Furthermore, FTIR results showed that surface hydroxyl content of bituminous coal dust treated by 0.2 wt% SDBS + 0.05 wt% XTG solutions has increased 26.3% than that treated by 0.05 wt% XTG, which promoted the adsorption of xanthan gum molecules on the coal surface. The presence of surfactants decreases the viscosity and surface tension of compound solution, and xanthan gum–surfactants interaction will promote bituminous coal dust agglomeration effect. This agglomeration mechanism is mainly reflected in the distribution mechanism and bituminous coal dust can form to large agglomerates under this action.

Preparation of FeOOH nanoparticles using an impinging stream-rotating packed bed and their catalytic activity for ozonation of nitrobenzene

BackgroundFeOOH has the advantages of low price, high stability and high surface hydroxyl content that make it an excellent catalyst for wastewater treatment. However, it also has the problems of wide particle size distribution, non-uniform dispersion and long preparation time in traditional reactors. MethodsFeOOH nanoparticles were prepared from FeSO4 and NaOH in an impinging stream-rotating packed bed (IS-RPB-FeOOH), and their properties and catalytic activities were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Significant findingsThe prepared FeOOH nanoparticles are shown to be α-FeOOH with a specific surface area of 246.717 m2/g, a surface hydroxyl density of 8.166 mmol/g, a length of 30 nm, and a narrow particle size distribution. Compared with the stirred tank reactor, the reaction time is reduced from 30 min to 4 min and the specific surface area is increased by 2.1 times in IS-RPB. The removal rate of nitrobenzene by IS-RPB-FeOOH can reach 94.3% after 40 min, which is 8.8% and 19.5% higher than that of FeOOH nanoparticles prepared using a stirred tank reactor (STR-FeOOH) and ozonation alone, respectively.

Morphology and surface hydroxyl engineering of H4Nb6O17 nanotubes for enhanced ethyl mercaptan removal

Ethyl mercaptan is usually present in natural gas and biogas, and must be removed due to its toxic, malodorous and corrosive properties. The characteristics content of surface functional groups plays a vital role for the adsorption performance of the adsorbent. In present study, a facile method was proposed to adjust the morphology and structure, as well as the amount of the surface hydroxyl groups of H4Nb6O17 nanotubes. The synthesis of H4Nb6O17 nanotubes with different morphology and structure can adjust the content of surface hydroxyl groups by controlling the flocculation process of [Nb6O17]4- nanosheet sol. By reducing the flocculation rate, more nanosheets are curled to form regular nanotubes, thereby increasing the surface hydroxyl groups of the nanotubes and improving the adsorption capacity of ethyl mercaptan. The dynamic adsorption experiments show that the obtained H4Nb6O17 nanotubes present high ethyl mercaptan adsorption capacity and great cyclic regeneration performance. The high sulfur capacity of H4Nb6O17 nanotubes can be well explained by the abundant surface hydroxyl groups, large specific surface area and hierarchical pore structure. This work provided new insights into design and preparation of high-efficiency adsorbents by morphology and structure engineering.

Comparative study on properties of Pd-Ce-Zr catalysts synthesized by flame spray pyrolysis and solution combustion: Application for methane catalytic oxidation in electric field

A kind of Pd0.01Ce0.75Zr0.25O2 hollow nanospheres surrounded by small nanoparticles prepared by flame spray pyrolysis (FSP) method (Pd0.01Ce0.75Zr0.25O2-F) were used for methane oxidation in electric field. Compared with the samples synthesized by solution combustion method, more Pd active sites is exposed to Pd0.01Ce0.75Zr0.25O2-F catalyst surface and it shows higher redox performance. The methane conversion over Pd0.01Ce0.75Zr0.25O2-F is higher (T50 = 320 °C in 5 mA electric field, GHSV = 50,000 ml·g−1·h−1), and the turnover frequency (TOF) is significantly increased (ΔTOF = 4.33 × 10-4 × s−1) under the effect of electric field. There is a strong interaction between electric field and Ce-Zr metastable structure, which is due to the higher content of surface hydroxyl groups on Pd0.01Ce0.75Zr0.25O2-F surface.

A comparative study on the synthesis of magnesium ferrite for the adsorption of metal ions: Insights into the essential role of crystallite size and surface hydroxyl groups

Metal ferrites with spinel structure are widely used as magnetic adsorbents and catalysts for solving myriads of environmental problems. This study was focused on the evaluation of factors influencing the adsorption properties of magnesium ferrite towards metal ions. Specifically, the effect of the synthesis method (glycine-nitrate, citrate–nitrate, and co-precipitation, abbreviated as gn, cn, cp) and the calcination temperature (range of 300–800 °C) on the crystal structure, texture, and adsorption characteristics of magnesium ferrite nanoparticles were studied. The adsorption affinity of heavy metal ions onto magnesium ferrites obeyed the following order gn-MgFe2O4 > cn– MgFe2O4 > cp-MgFe2O4. An increase in the calcination temperature of gn-MgFe2O4 and cn-MgFe2O4 from 300 to 800 °C leads to a decrease in the adsorption capacity and this may be attributed to a significant increase in the size of the crystallites, a decrease in the specific surface area and the removal of surface hydroxyl groups. The amorphous cp-MgFe2O4-80 and cp-MgFe2O4-800 samples demonstrated the equal adsorption capacity for metal ions and characterized by specific surface area of 179 and 13 m2/g, respectively. It was shown that the crystallites size and the concentration of surface hydroxyl groups are the main factors determining the adsorption performance of the synthesized novel adsorbents.

Fabrication, characterization and high photocatalytic activity of Ag-ZnO heterojunctions under UV-visible light.

Pure ZnO and Ag–ZnO nanocomposites were fabricated via a sol–gel route, and the obtained photocatalysts were characterized by XRD, SEM, TEM, BET, XPS, PL and DRS. The results showed that Ag0 nanoparticles deposit on the ZnO surface and Ag modification has negligible impact on the crystal structure, surface hydroxyl group content and surface area of ZnO. However, the recombination of photogenerated electrons and holes was suppressed effectively by Ag loading. The photocatalytic activity was investigated by evaluating the degradation of MB under xenon lamp irradiation as the UV-visible light source, and the results show that the photocatalytic activity of ZnO significantly improved after Ag modification. Ag–ZnO photocatalysts exhibit higher photocatalytic activity than commercial photocatalyst P25. The degradation degree of MB for 1%Ag–ZnO was 97.1% after 15 min. ˙O2− radicals are the main active species responsible for the photodegradation process, and Ag–ZnO heterojunctions generate more ˙O2− radicals, which is the primary reason for the improved photocatalytic performance.

The Bonding Mechanism of the Micro-Interface of Polymer Coated Steel.

As food and beverages require more and more green and safe packaging products, the emergence of polymer coated steel (PCS) has been promoted. PCS is a layered composite strip made of metal and polymer. To probe the bonding mechanism of PCS micro-interface, the substrate tin-free steel (TFS) was physically characterized by SEM and XPS, and cladding polyethylene terephthalate (PET) was simulated by first-principles methods of quantum mechanics (QM). We used COMPASS force field for molecular dynamics (MD) simulation. XPS pointed out that the element composition of TFS surface coating is Cr(OH)3, Cr2O3 and CrO3. The calculation results of MD and QM indicate that the chromium oxide and PET molecules compound in the form of acid-base interaction. The binding energies of Cr2O3 (110), (200), and (211) with PET molecules are −13.07 eV, −2.74 eV, and −2.37 eV, respectively. We established a Cr2O3 (200) model with different hydroxyl concentrations. It is proposed that the oxygen atom in C=O in the PET molecule combines with –OH on the surface of TFS to form a hydrogen bond. The binding energy of the PCS interface increases with the increase of the surface hydroxyl concentration of the TFS. It provides theoretical guidance and reference significance for the research on the bonding mechanism of PCS.

Dispersion of surface-modified, aggregated, fumed silica in polymer nanocomposites

Surface modification of model silica to enhance compatibility in nanocomposites has been widely studied. In addition to model spherical silica, several authors have investigated the impact of surface conditions on compatibility in commercial aggregated carbon black and silica. In this paper, dispersion is investigated for a series of nanocomposites produced from commercially modified fumed silica mixed with styrene butadiene rubber, polystyrene, and polydimethylsiloxane. Surface modification includes variation in surface hydroxyl content, siloxane, and silane treatment. Qualitatively, hydroxyl groups on the silica surface are considered incompatible with non-polar polymers, while methyl groups are compatible with oleophilic polymers. X-ray scattering was used to analyze the filler aggregate structure before and after dispersion, and the second virial coefficient was used to quantify nanodispersion. The content of surface moieties was determined from Fourier-transform infrared spectroscopy. It is observed that modified silica can display mean field or specific interactions as reflected by the presence of a correlation peak in x-ray scattering. For systems with specific interactions, a critical ordering concentration is observed related to the free energy change for structuring. A van der Waals model was used to model the second virial coefficient as a function of accumulated strain, yielding the excluded volume and an energetic term. The excluded volume could be predicted from the structural information, and the bound polymer layer was directly related to the surface methyl content, whereas the energetic term was found to synergistically depend on both the methyl and hydroxyl surface content.

Towards a comparison between the hybrid ozonation-coagulation (HOC) process using Al- and Fe-based coagulants: Performance and mechanism

In this study, the removal performance of a hybrid ozonation-coagulation (HOC) process using AlCl36H2O (Al–HOC) and FeCl36H2O (Fe–HOC) as coagulants for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP) was investigated. Compared with the conventional coagulation process and pre-ozonation-coagulation process, much better organic matter removal performance can be achieved for both the Al–HOC and Fe–HOC processes. The Fe–HOC process showed an obviously higher dissolved organic carbon (DOC) removal efficiency than that of the Al–HOC process. Surface hydroxyl groups were determined to be the active sites in generating OH in the HOC process, and the hydrolysed Fe species possessed a higher content of surface hydroxyl groups than the hydrolysed Al species according to fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS) analyses. In addition, the hydrolysed Fe species contained a higher portion of tetrahedral sites that were more likely to be stronger Lewis acid sites to react with ozone to generate OH. Furthermore, peroxone reactions in the HOC process were other possible way to enhance the OH generation, and higher H2O2 generation was observed in the Fe–HOC process due to higher O2− generation. Therefore, better removal performance of the Fe–HOC process can be obtained due to the increased OH generation in the Fe–HOC process.

Ionic liquid-assisted hydrothermal preparation of BiOI/BiOCl heterojunctions with enhanced separation efficiency of photo-generated charge pairs and photocatalytic performance

In this contribution, BiOI/BiOCl heterojunctions were successfully synthesized with the assistance of reactable ionic liquid (IL) 1-propyl-3-methylimidazolium iodide ([PrMIm]I) via a hydrothermal method. The crystal structures, morphologies, chemical compositions, optical properties and separation efficiency of photo-generated charge pairs of the as-prepared BiOI/BiOCl heterojunctions were characterized by various analytic methods. Surface photovoltage spectroscopy (SPS) and photoelectrochemical measurements reveal that the BiOI/BiOCl heterojunctions exhibit higher separation efficiency of photo-generated charge pairs than the reference BiOCl and BiOI. XPS results reveal that I element exists in the as-prepared samples with a chemical valence of −1, and when the mass ratio of [PrMIm]I/BiOCl is 8%, the sample holds the highest surface hydroxyl content. Photocatalytic performance of the as-fabricated photocatalysts was evaluated by abatement of rhodamine B (RhB) aqueous solution under simulated sunlight irradiation. BiOI/BiOCl heterojunctions exhibit enhanced photocatalytic performance; the 8% sample displays the highest photocatalytic activity. Trapping experiments certify that the superoxide radicals (O2−) is the predominant active free radicals in the photocatalytic degradation process of RhB over the BiOI/BiOCl heterojunctions. In light of experimental results, a possible Z-scheme photocatalytic degradation mechanism was discussed to elaborate the separation and migration of the photo-induced electron-hole pairs. This study provides a useful reference for ILs assisted fabrication of high efficiency photocatalytic materials.

Effect of NaOH concentration on antibacterial activities of Cu nanoparticles and the antibacterial mechanism.

A series of Cu nanoparticles (NPs) have been prepared by a facile hydrothermal method at 180°C using different concentrations of NaOH solutions and characterized by XRD, SEM, TEM and FT-IR spectra. Their antibacterial activities were assessed by means of Gram-positive S. aureus and Gram-negative E. coli bacteria, where various dosages (3, 5, 7, 10mg) of the antibacterial agents were applied, and compared with that of the commercial CuSO4 salt. The antibacterial mechanism was explored based on series of control experiments. The results show that the NaOH concentration affects the crystallinity, crystal size and surface hydroxyl content of the Cu NPs, which significantly influence the antibacterial activities. Compared to the commercial CuSO4 salt, the four Cu samples prepared using no <4molL-1 of NaOH display excellent antibacterial activities with low concentrations of copper leachates, which is great beneficial to the practical applications. The experimental results support that the highly reactive and soluble copper species in the antibacterial system of the Cu NPs is a Cu (II)-peptide complex, but not free Cu2+ ions.

Enhanced photocatalytic performance of BiOCl benefited from the effective separation of photogenerated carriers and enhanced surface hydroxyl content

Enhanced photocatalytic performance of BiOCl benefited from the effective separation of photogenerated carriers and enhanced surface hydroxyl content

Ionic liquid assisted hydrothermal preparation of TiO2 with largely enhanced photocatalytic performance originated from effective separation of photoinduced carriers

In this paper, TiO2 with enhanced photocatalytic activity was prepared with the aid of ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF6) through a conventional hydrothermal method. The effects of different amounts of [BMIm]PF6 on the preparation and corresponding photocatalytic activity of TiO2 were investigated. Preparation of TiO2 was optimized by controlling the mass ratio of [BMIm]PF6 and TiO2. Photocatalytic property of TiO2 prepared was investigated using RhB as a simulated pollutant. The results show that TiO2 prepared with the aid of [BMIm]PF6 exhibits superior photocatalytic activity to the reference TiO2, when the mass ratio of [BMIm]PF6/TiO2 is 8%, TiO2 prepared has the highest separation rate of photogenerated charge pairs, leading to the highest photocatalytic activity. The enhanced photocatalytic performance of TiO2 prepared with the aid of [BMIm]PF6 is attributable to high surface hydroxyl content and enhanced separation of photoinduced charge pairs.

Effect of Base on the Facile Hydrothermal Preparation of Highly Active IrOx Oxygen Evolution Catalysts

The efficient electrochemical splitting of water is limited by the anodic oxygen evolution reaction (OER). IrO2 is a potential catalyst with sufficient activity and stability in acidic conditions to be applied in water electrolyzers. The redox properties and structural flexibility of amorphous iridium oxo-hydroxide compared to crystalline rutile-IrO2 are associated with higher catalytic activity for the OER. We prepared IrOx OER catalysts by a simple hydrothermal method varying the alkali metal base (Li2CO3, LiOH, Na2CO3, NaOH, K2CO3, KOH) employed during the synthesis. This work reveals that the surface area, particle morphology, and the concentration of surface hydroxyl groups can be controlled by the base used and greatly influence the catalyst activity and stability for OER. It was found that materials prepared with bases containing lithium cations can lead to amorphous IrOx materials with a significantly lower overpotential (100 mV @ 1.5 mA·cm–2) and increased stability compared to materials prepared with other bases and rutile IrO2. This facile method leads to the synthesis of highly active and stable catalysts which can potentially be applied to larger scale catalyst preparations.

P123-assisted preparation of Ag/Ag2O with significantly enhanced photocatalytic performance

Preparation of photocatalysts with excellent performance has drawn considerable attention. Herein, we report a facile and reliable method to promote the photocatalytic performance of Ag/Ag2O with the assistance of surfactant EO20PO70EO20 (P123). The samples prepared (P123–Ag2O) were characterized by some analytic methods. The results reveal that the presence of P123 in the synthetic system largely boosts the separation rate of photoinduced e−/h+ pairs, accelerates the formation of •O2− due to plasmon effect of Ag0 particles and promotes the surface hydroxyl content, proven by the surface photovoltage spectroscopy (SPS), nitrotetrazolium blue chloride (NBT) and X-ray photoelectron spectroscopy (XPS) results. Photocatalytic abilities of the samples toward abatement of methyl orange (MO) were evaluated under simulated sunlight illumination. The results reveal that the photocatalytic activity of P123–Ag2O is five times of that of Ag2O. More importantly, P123–Ag2O possesses excellent stability and has great potential applications in environmental purification.

Photocatalytic activity of TiO2 prepared by different solvents through a solvothermal approach

In this work, TiO2 was prepared by different solvents through a solvothermal approach using tetrabutyl titanate as raw material, afterward the samples were calcined at 723 K. The samples were investigated by Brunauer -Emmett-Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis diffuse reflectance (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS), and surface photovoltage spectroscopy (SPS). The photocatalytic activity of the samples was investigated using rhodamine B (RhB) as a model contaminant. TiO2 prepared using ethanol as solvent has the best photocatalytic performance under irradiation of 500 W Xe lamp. Compared with the samples without calcination, all samples after calcination display significantly improved photocatalytic performance, which can be tightly attributed to the enhanced separation of photoinduced carriers and relative high surface hydroxyl content.