Number Of Surface Hydroxyl Groups Research Articles

A novel nanobiosorbent of functionalized graphene quantum dots from rice husk with barium hydroxide for microwave enhanced removal of lead (II) and lanthanum (III)

In this study, rice husk was used as a sustainable source to synthesize graphene quantum dots (GQDOs) with 2D morphology. Chemical modification of GQDOs with Ba(OH)2 was followed to form a novel GQDOs-Ba nanobiosorbent with an increased number of surface hydroxyl groups. The physicochemical properties of GQDOs and GQDOs-Ba were investigated by FT-IR, SEM, TEM, TGA, and XRD. The adsorption parameters of Pb(II) and La(III) onto GQDOs-Ba were optimized using microwave sorption approach. The maximum capacity reached 3400 µmol g−1 (pH 7), and 1500 µmol g−1 (pH 5) at 15 s for Pb(II) and La(III), respectively. The adsorption isotherm models by GQDOs-Ba fitted well with Langmuir. The pseudo-second order was agreed by Pb(II) and La(III) ions. The thermodynamic studies elucidated that Pb(II) and La(III) adsorption onto GQDOs-Ba followed a spontaneous model. The GQDOs-Ba nanobiosorbent accomplished excellent removal percentages from different water samples containing lead (98.5%–99.8%) and lanthanum (94.6%–96.2%).

Effect of preparation method on the catalytic performance of formaldehyde oxidation over octahedral Fe3O4 microcrystals supported Pt catalysts

Several octahedral Fe3O4-supported platinum catalysts were successfully synthesized via impregnation, colloid deposition and co-precipitation methods and characterized using multiple techniques. All Pt/Fe3O4 catalysts demonstrated activity in low-temperature HCHO oxidation, with the catalyst prepared by the co-precipitation method (designated Pt/Fe3O4-CP-80) exhibiting relatively higher catalytic activity. The results of various characterization techniques revealed that the preparation method could influence the strength of metal-support interactions and the number of surface hydroxyl groups of the Pt/Fe3O4 catalysts. It was observed that the metal-support interactions in Pt/Fe3O4 catalysts affected their redox properties. The excellent performance of Pt/Fe3O4-CP-80 catalyst was mainly attributed to the presence of appropriate interaction between Pt and Fe species, which resulted in the formation of more active interface sites (i.e. Pt-O(OH)x-Fe species).

Investigation of the structure and sorption peculiarities of cobalt and uranium ions by nanocomposites based on montmorillonite and tetraethoxysilane

The structure and adsorption characteristics of silica -and montmorillonite-based nanocomposites are investigated. Tetraethoxysilane was used as a source of silica. The porous structure was investigated by the method of low-temperature nitrogen adsorption. According to the research results, it was found that a small amount of silica in nanocomposite samples (14 % SiO 2 ) contributes to the formation of material with a larger specific surface area and greater number of meso- and macropores compared to original montmorillonite. This, in turn, leads to a better diffusion of ions of different nature into the nanocomposite structure. An increase in the silica content (up to 57 % SiO 2 ) allows obtaining microporous samples with a large specific surface area. It was determined that the increase of the montmorillonite content in the investigated samples contributes to the improvement of the adsorption properties of nanocomposites in relation to the removal of cobalt(II) ions from the aqueous medium. At an optimum silica content (3–14 % SiO 2 ), the experimental samples retain high values of maximum cobalt adsorption (14 mg/g), as well as original montmorillonite. It was also found that an increase in the silica concentration in the samples increases the efficiency of removal of uranium(VI) ions from the aqueous medium (from 12 mg/g in original montmorillonite to 25 mg/g for nanocomposites with a silica content of 57 %). This is due to, first, an increase in the specific surface area of the samples, and secondly – an increase in the number of surface hydroxyl groups, which more selectively remove uranium from solutions. Thus, selection of the chemical composition of nanocomposites based on silica gel and montmorillonite allows regulating porous structures and surface chemistry, and thus increasing the sorbent efficiency depending on the task

Enhanced adsorption of arsenate by spinel zinc ferrite nano particles: Effect of zinc content and site occupation

In this work, zinc ferrite spinel with different zinc contents (ZnxFe3-xO4) was synthesized by a hydrothermal method and used for removing As(V) in aqueous solution. X-ray diffraction (XRD) results indicated that in the crystal structure of ZnxFe3-xO4, the zinc atoms tended to occupy the octahedral sites for x < 0.6 and diffused into the tetrahedral sites gradually with x > 0.6. The size of ZnxFe3-xO4 crystallites increased with the increasing zinc content. Batch adsorption experiments showed that the adsorption isotherms could be well described by the Langmuir model, while the adsorption kinetics followed the pseudo-second-order kinetic model. Zinc ferrite exhibited the highest adsorption capacity towards As(V) when x = 0.6. Study of the mechanism indicated that doping with zinc increased the number of surface hydroxyl groups on ferrite spinel, and thus enhanced the adsorption capacity when x = 0.6. This work revealed the effects of doping site and content of metal atoms on the adsorption ability of ferrite spinel towards As(V).

Facile synthesis of BiFeO3 nanoparticles by modified microwave-assisted hydrothermal method as visible light driven photocatalysts

BiFeO3 nanoparticles (BFO-NPs) have been successfully synthesized through modified microwave-assisted hydrothermal method. The obtained BFO-NP was hexagonal phase with R3c structure and covered with a large number of surface hydroxyl groups. Compared with the bulk BiFeO3 microsphere, BFO-NP has much higher purity and similar band gap energy, about 2.10 eV. The photocatalytic performance of BFO-NP was evaluated by Rhodamine B (RhB) removal without any sacrificial agent under visible-light irradiation. A fivefold increase in the rate of RhB degradation and mineralization was obtained, which should result from effective separation of the electron-hole pairs. Furthermore, the scavenger-experiments reveal that photo-generated holes and hydroxyl radicals were the primary reactive species. This study opens a new pathway to synthesize BiFeO3 nanoparticle by hydrothermal method and provides a referential route for other perovskite photocatalysts.

The effect of Fe-Mn minerals and seawater interface and enrichment mechanism of ore-forming elements of polymetallic crusts and nodules from the South China Sea

Ferromanganese crusts and nodules are important submarine mineral resources that contain various metal elements with significant economic value. In this study, polymetallic crusts and nodules obtained from the South China Sea (SCS) were determined by using X-ray power diffraction (XRD), Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to systematically investigate and analyze the mineralogical and spectral characteristics of the Fe-Mn minerals. XRD measurements revealed that the SCS polymetallic crusts and nodules were composed of vernadite, quartz, and plagioclase. The nodules also contained todorokite. The Fe-phase minerals of the SCS crusts and nodules were composed of amorphous Fe oxide/hydroxide, and the Mn- and Fe-phases minerals exhibited relatively poor degrees of crystallization. FTIR results showed that the Fe-Mn minerals in the crusts and nodules included a large number of surface hydroxyl groups. These surface hydroxyl groups contained protons that could provide reactive sites for complexation of ore-forming elements in seawater. XPS results indicated that the surfaces of the Fe-Mn minerals mainly contained Fe, Mn, and O. Fe was present in the trivalent oxidation state, while Mn, which may contain several bivalent oxidation state, was present in the tetravalent and trivalent oxidation states. The SCS polymetallic crusts and nodules were compared with Pacific seamount crusts, and results showed that the surface hydroxyl (-OH) groups of the SCS crusts and nodules numbered more than the lattice oxygen (O2-). But the lattice oxygen of Pacific seamount crusts numbered more than the surface hydroxyl groups. This characteristic indicated that the degree of crystallization of Fe-Mn minerals from the Pacific Ocean was higher than that of minerals from the South China Sea. Comprehensive studies showed that ore-forming elements in the interface between seawater and the Fe-Mn minerals in the submarine ferromanganese crusts and nodules employed the following enrichment mechanisms: (1) the metal ion complexed with the surface hydroxyl of Fe-Mn minerals to form hydroxyl complexes, which were connected by coordination bonds or stable inner-sphere complexes that exchanged protons on the mineral surfaces; (2) the charged surfaces of the minerals and metal cations formed outer-sphere complexes, which made up the electrostatic double layer, through electrostatic adsorption; and (3) the metal cations isomorphously exchanged the Mn and Fe ions of the mineral lattice structure.

Improved high temperature stability of anatase TiO2 photocatalysts by N, F, P co-doping

Among the three commonly occurring phases (anatase, rutile, and brookite) of TiO2, the anatase form is reported to be the best photocatalyst due to the improved charge-carrier mobility and the greater number of surface hydroxyl groups. The anatase to rutile transition in titania photocatalysts usually occurs at a temperature between 500°C to 700°C. Development of a high temperature stable (above 1000°C) anatase phase is important for various environmental applications (e.g. self-cleaning ceramic tiles, anti-microbial sanitary wares, etc.). In this study, the use of ammonium hexafluorophosphate as a single source dopant (method A) and urea, trifluoroacetic acid and phosphoric acid as multiple sources (method B) was undertaken to improving its high temperature stability. Method A was seen to produce a more stable anatase phase, with 68% anatase present at 1100°C, compared to method B which showed 100% rutile at 900°C. Kinetic analysis shows a marked increase in the photocatalytic degradation of a model dye using materials calcined at 1100°C for method A (0.042min−1) compared to that for method B (0.005min−1) and the commercial photocatalyst Evonik-Degussa AEROXIDE® (0.031min−1) at 1100°C. XPS results showed that, the only dopant detected at high temperatures is phosphorus in its P5+ form. The incorporation of phosphorus has proved to be an effective method in stabilising the anatase phase at high temperature. The current investigation also showed that a single source precursor is more favourable to obtain high temperature stable anatase phase photocatalysts.

A comparative study of a series of ferrite nanoparticles as heterogeneous catalysts for phenol removal at neutral pH

This study aimed at understanding and assessing the effect of structural specifications on catalytic properties of several ferrite nanoparticles as the heterogeneous Fenton-like catalysts. Thus, a number of synthetic M-ferrite (where M = Zn, Mn, Fe and Cu) catalysts were compared for efficiency against phenol removal in the presence of hydrogen peroxide. It was found that the copper ferrite is more active than the other studied ferrites for phenol elimination at neutral pH. The effect of pH was studied in pH values of 3, 6, and 10, while the highest phenol removal rate over the Cu-ferrite catalyst was observed at pH 6. Studying the effect of different parameters and catalyst properties on the reaction rate suggested that the hydroxyl radical generation is not the only factor to control the reaction rate, but the roles of surface adsorption of the pollutants and the catalyst specifications are also significant. Besides, in agreement with the previous reports, it was concluded that the number of surface active sites is related to the number of surface hydroxyl groups, which results in the higher surface adsorption and hydrogen peroxide activation.

Role of Fe/pumice composition and structure in promoting ozonation reactions

The catalytic effectiveness and mechanism of Fe/pumice in heterogeneous catalytic ozonation of p-chloronitrobenzene (p-CNB) is investigated in batch mode. The results indicate that Fe/pumice significantly increased the removal efficiency of p-CNB, the utilization efficiency of ozone, and the production of hydroxyl radical (OH) relative to pumice during catalytic ozonation. The mesopority of the Fe/pumice surface is a key factor due to its ozone adsorption ability. The surface hydroxyl groups on Fe/pumice metal oxides are ozone decomposition sites. The dominant oxide species in the ozonation reaction process is OH. The zero-charged surfaces of the Fe/pumice was favorable for catalytic ozonation. The results of the investigation of the enhancement mechanism confirm that Fe-modified pumice increases the number of surface hydroxyl groups and the degree of ozone adsorption on the catalyst surface, resulting in enhanced collision probability between surface hydroxyl groups on Fe/pumice metal oxides and ozone molecules to accelerate OH from ozone decomposition and to promote p-CNB removal from aqueous solution.

Competing surface reactions limiting the performance of ion-sensitive field-effect transistors

Ion-sensitive field-effect transistors based on silicon nanowires are promising candidates for the detection of chemical and biochemical species. These devices have been established as pH sensors thanks to the large number of surface hydroxyl groups at the gate dielectrics which makes them intrinsically sensitive to protons. To specifically detect species other than protons, the sensor surface needs to be modified. However, the remaining hydroxyl groups after functionalization may still limit the sensor response to the targeted species. Here, we describe the influence of competing reactions on the measured response using a general site-binding model. We investigate the key features of the model with a real sensing example based on gold-coated nanoribbons functionalized with a self-assembled monolayer of calcium-sensitive molecules. We identify the residual pH response as the key parameter limiting the sensor response. The competing effect of pH or any other relevant reaction at the sensor surface has therefore to be included to quantitatively understand the sensor response and prevent misleading interpretations.

Surface hydroxyl groups direct cellular response on amorphous and anatase TiO2 nanodots

In this study, we investigated the differences between amorphous and anatase TiO2 at the biomolecular level which could explain differences in the osteoblast response on these surfaces. The number of surface hydroxyl groups in the TiOHT form on amorphous and anatase TiO2 was found to be the most important factor, resulting in adsorption of bovine serum albumin as a monolayer on amorphous TiO2 nanodots but as a multilayer on anatase TiO2 nanodots. The reason for this is that the presence of more TiOHT groups on amorphous TiO2 nanodots attracts more –NH3+ groups on BSA molecules, causing the conformation of surface-bound BSA molecules to differ from those adsorbed on anatase TiO2 nanodots. Fibronectin which is subsequently adsorbed on anatase TiO2 nanodots then retains a more active conformation for osteoblast adhesion and mineralization.

Enhanced adsorption of hydrogen sulfide on mixed zinc/cobalt hydroxides: Effect of morphology and an increased number of surface hydroxyl groups

Mixed zinc and cobalt hydroxides were synthesized using a precipitation method and tested as adsorbents of hydrogen sulfide from either dry or moist air. The adsorption capacity increased with an increase in the content of cobalt in the structure of mixed hydroxides. The synergistic effect was demonstrated by a fourfold increase in the amount of hydrogen sulfide adsorbed on the surface of the best performing mixed hydroxide in comparison with the hypothetical mixture of the two hydroxides. The initial and exhausted materials were characterized by FTIR, thermal analysis, potentiometric titration, X-ray diffraction, SEM/EDX, and adsorption of nitrogen. The results obtained suggest that an increase in the content of cobalt results in an increase in amorphicity level and in an increase in the number of hydroxyl groups. These groups, besides providing higher basicity thereby increasing the extent of H2S dissociation in the presence of water, are the main active centers reacting with hydrogen sulfide. Defects in the structure and oxygen vacancies result in the oxidation of some H2S to sulfites and sulfates.

Influence of the preparation method on the activity of ceria zirconia mixed oxides for naphthalene total oxidation

Cerium/zirconium mixed oxides, with different Ce/Zr ratios, have been synthesised by a co-precipitation method using two different precipitating agents (sodium carbonate and urea) and tested for the total oxidation of naphthalene. Catalysts were characterised by N2 adsorption, XRD, Raman, TPR, XPS and DRIFTS. Ceria prepared by carbonate precipitation had low activity and this is likely to be related to the high concentration of residual surface carbonate that covers catalytic sites and inhibits reaction. For carbonate precipitation, increasing the Zr content to 1% resulted in a significant increase of activity, which is related to the decrease of surface carbonate. Increasing the Zr content up to 50% resulted in catalysts more active than ceria, but activity decreased as Zr content increased. This was in spite of increasing the number of oxygen vacancies, and this effect has been related to the decrease in the number of surface hydroxyl groups, which favours naphthalene adsorption. Ceria prepared by urea precipitation was markedly more active than that produced by carbonate precipitation. The urea-derived catalyst with 1% Zr is marginally more active than pure ceria, whilst for higher Zr contents activity was marginally lower. Two factors can account for these observations; they are the increase of oxygen vacancies contributing positively to activity and the opposing negative effect of decreasing the number of surface hydroxyl groups when the zirconium content increases.

Mild hydrogenation of quinoline to decahydroquinoline over rhodium nanoparticles entrapped in aluminum oxy-hydroxide

Abstract An Rh/AlO(OH) catalyst was prepared by a sol–gel method. This catalyst showed an excellent catalytic performance for the complete hydrogenation of quinoline to decahydroquinoline at relatively mild conditions. The growth of Rh-particle size and the decrease in the number of surface hydroxyl groups during heat treatment resulted in a significant decrease in catalytic properties. The excellent catalytic performance of the fresh Rh/AlO(OH) was attributed to the cooperation between the hydroxyl groups on the support and on the active metal centers.

Super-Hydrophilicity of Stainless Steel Surface Induced by Heat Treatment with Gaseous Ozone

The hydrophilic states of stainless steel surface treated by the separate or combined use of gaseous ozone and heat were investigated by measuring the contact angle of a water droplet, the content of the surface carbon contaminants, and the adsorption isotherm of water vapor. Super-hydrophilic states of stainless steel plates were achieved only by the combined gaseous ozone/heat treatment. The contact angle of a water droplet on the plate decreased from 81° to less than 5° after treating at 120 to 180 °C under 2 vol% ambient gaseous ozone. It was found that the super-hydrophilization proceeded according to two different mechanisms. One is the decomposition of surface contaminants. There was a good correlation between the surface carbon content and the water contact angle over the range of 15 to 81°. The other is the once removal of surface hydroxyl groups followed by chemisorption of water on these dehydroxylated sites. As a result of the removal of contaminants and the rehydration, the total number of surface hydroxyl groups on stainless steel became larger than that on the original surface.

Characteristics of Granular Boehmite and Its Ability to Adsorb Phosphate from Aqueous Solution

In this study, we investigated the surface properties of granulated boehmite with vinyl acetate (G-BE20) and measured the amount of phosphate it adsorbed and the effect of contact time and solution pH on the adsorption process. The specific surface area (144.9 m(2)/g) and the number of surface hydroxyl groups (0.88 mmol/g) of G-BE20 were smaller than those of virgin boehmite (BE), which gave a specific surface area and number of surface hydroxyl groups of 297.0 m(2)/g and 1.08 mmol/g, respectively. The amount of phosphate adsorbed increased with the temperature. The isotherm model of Langmuir was used to fit experimental adsorption equilibrium data for phosphate adsorption onto G-BE20. The calculated thermodynamic parameters show the spontaneous and endothermic nature of the adsorption process. The equilibrium adsorption onto G-BE20 was reached within 16 h and the amount of phosphate adsorbed was 8.4 mg/g. The kinetic mechanism of phosphate uptake was evaluated with two different models: the Largergren pseudo first- and pseudo second-order models. The data obtained showed a better fit to the pseudo second-order model (0.991) than to the pseudo first-order model (0.967), as indicated by the r values. The rate constants for the adsorption of phosphate onto G-BE20 were calculated as 0.481 1/h and 0.029 g/mg h. The adsorption of phosphate onto G-BE20 was the maximum in the pH range 3.0-4.0.

High photocatalytic activity of oxychloride CaBiO2Cl under visible light irradiation

Oxychloride CaBiO2Cl was shown as a highly active photocatalyst which can efficiently decompose methylene blue (MB), and yield high photocurrent density under ultraviolet (UV) light or visible-light irradiation. Density functional calculations revealed that the valence band (VB) was not only composed of the O 2p hybridized orbital, but also a little the Cl 3p and Bi 6p orbitals. During the calcination synthesis process, a certain amount of oxygen vacancies existed in the prepared samples, which resulted in the formation of surface hydroxyl groups. The photocatalytic activities for MB degradation were strongly dependent on the surface hydroxyl groups. By evaluation of the infrared transmission spectra (FTIR) of the series of samples, a correlation between the number of surface hydroxyl groups and the photocatalytic activity was revealed. The surface hydroxyl groups were important active sites for producing active hydroxyl radicals and a dominant factor in controlling the performance of the samples.

Solvothermal synthesis and photocatalytic application of porous Au/TiO2 nanocomposites

Porous titania networks embedded with gold nanoparticles have been synthesized and tested in photocatalytic applications. A solvothermal method was adopted for the in situ reduction of the gold precursor to gold nanoparticles within a preformed TiO2 matrix synthesized by combining a templating technique and sol–gel chemistry. The titania materials were crystalline with anatase crystals of 13 ± 2 nm in diameter; XRD peaks of metallic gold were observed when the gold content was over 1 wt% (gold crystal diameters of 18–25 nm for 1–8 wt% Au). The variation in gold particle size for different gold content was observed by transmission electron microscopy, which also confirmed highly porous structures of the final Au/TiO2 composites. The actual gold content generally increased with the Au content used during synthesis; was enhanced when the pH of the gold precursor solution increased from 2 to 10; and remained relatively constant with changes in the solvothermal temperature (120–180 °C). UV-Visible diffuse reflectance spectra of the Au/TiO2 showed strong absorption at ∼550 nm due to the successful addition of gold nanoparticles to the titania. The number of surface hydroxyl groups was influenced by solvothermal treatment temperature, synthesis pH and gold content. The addition of gold nanoparticles to the TiO2 significantly suppressed recombination of the photon-induced electron–hole pairs. The photocatalytic efficiency of the composites was assessed by monitoring the photocatalytic degradation of methylene blue in aqueous solution; maximum efficiency was more than double that of the pure TiO2 control when using 2.0 to 4.0 wt% gold solutions at pH 7 and optimized solvothermal conditions of 180 °C for 14 h. The photocatalytic efficiency was significantly altered with the addition of gold and was greatly influenced by the anatase crystal size and relative XRD peak intensity, the gold content, and the capability of the material to decrease photon-induced electron–hole recombination.

Surface hydroxyl concentration on Zr(OH) 4 quantified by 1H MAS NMR

Zirconium hydroxide (Zr(OH) 4) is a catalytic support material whose reactivity depends on intrinsic surface hydroxyl groups. Here we present a 1H MAS NMR study where we identify bridging and terminal hydroxyl groups along with their concentrations even in completely dehydrated material. The dehydrated material contains 13 mmol/g bridging hydroxyl groups and 3.9 mmol/g terminal hydroxyl groups, yielding a ratio of 3.4:1, and is verified by XPS. Upon hydration, the number of surface hydroxyl groups remains constant while only bulk water is adsorbed on the surface. Knowing both the types and amounts of surface hydroxyl groups on Zr(OH) 4 helps explain the catalytic activity of Zr(OH) 4 in many applications.

Effect of alkyl functionalization on charging of colloidal silica in apolar media

The present work examines the effect of alkyl-silane treatment on the charging of colloids in apolar solvent using two otherwise identical 250 nm diameter, spherical silica particles, one with untreated surface and the other treated with hexadecyltrimethoxysilane (C16), dispersed in an apolar isoparaffin solvent (Isopar-L) containing one of three oil-soluble surfactants: Aerosol-OT, OLOA 11,000, and zirconyl 2-ethyl hexanoate. The electrophoretic mobility of each dispersion was determined using phase angle light scattering (PALS). It was found that at sufficiently high surfactant concentration, i.e., where micelles begin to form in the bulk, the particle surfaces could be electrically charged. All three surfactants studied imparted a negative surface charge to the untreated silica particles. In all cases, the C16-treated particles were also found to be negatively charged but had a much higher magnitude of mobility than the untreated silica. Although the increase in magnitude of mobility as a result of the alkyl functionalization was surprising, it could be attributed to the increase in the number of surface hydroxyl groups arising from the hydrolysis of unbound methoxy groups of the silane molecules. The added hydroxyl groups provided additional potential acid-base interaction sites, resulting in higher particle mobility. It was also found that further increases in surfactant concentration lowered the particle mobility, attributed to the increasing concentration of electrically charged micelles, which may partially neutralize the surface charge or compress the electrical double layer.