Number Of Surface Hydroxyl Groups Research Articles

Photogenerated carriers transfer in Pd/TiO2-AgO heterojunction and its photocatalytic behaviors on oxidative dehydrogenation of ethane to ethylene

Photocatalytic oxidative dehydrogenation of ethane to ethylene with a high selectivity is an attractive reaction. In this study, different types of heterojunctions between Pd/TiO2 and a second metal oxide semiconductor were designed and synthesized to realize high activity conversion of C2H6 to C2H4. Pd/TiO2-AgO heterojunction was proved with best reaction performance. The addition of AgO facilitated the activation of reactant molecules. It enhanced directional transfer of electron-hole pairs and separation efficiency of photogenerated carriers. Pd/TiO2-5 % AgO heterojunction was proved with the best separation ability of photogenerated carriers and the largest number of surface hydroxyl groups. Detailed charge transfer path and reaction mechanism were proposed and discussed.

Effect of Surface Treatment of Nanocrystalline CeO2 on Its Dephosphorylation Activity and Adsorption of Inorganic Phosphates.

The surface of nanocrystalline cerium oxide (CeO2) was treated with various chemical agents by a simple postmodification method at 25 °C and atmospheric pressure. Hydrogen peroxide, ammonium persulfate, deionized water, ascorbic acid, and ortho-phosphoric acid were used in order to study and evaluate their effect on surface materials, such as surface area, crystallite size, number of surface hydroxyl groups, particle morphology, and Ce3+/Ce4+ ratio. Paraoxon-methyl (PO) decomposition and inorganic phosphate adsorption were used to evaluate the effect of surface treatment on catalytic and adsorption properties. CeO2 surface was studied by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and acid-base titration. While the treatment procedure affected the number of surface hydroxyl groups and the amount of bulk surface oxygen vacancies, only negligible changes were observed in the Ce3+/Ce4+ ratio. Interestingly, surface treatment affected the ability to decompose PO, but only a small effect on inorganic phosphate adsorption was observed, indicating the robustness of CeO2 for the latter. A mechanism for possible interaction of the used chemicals with the CeO2 surface was proposed.

Self-healing perovskite solar cells based on copolymer-templated TiO2 electron transport layer

Inorganic hole-transport materials (HTMs) such as copper indium disulfide (CIS) have been applied in perovskite solar cells (PSCs) to improve the poor stability of the conventional Spiro-based PSCs. However, CIS-PSCs' main drawback is their lower efficiency than Spiro-PSCs. In this work, copolymer-templated TiO2 (CT-TiO2) structures have been used as an electron transfer layer (ETL) to improve the photocurrent density and efficiency of CIS-PSCs. Compared to the conventional random porous TiO2 ETLs, copolymer-templated TiO2 ETLs with a lower refractive index improve the transmittance of input light into the cell and therefore enhance the photovoltaic performance. Interestingly, a large number of surface hydroxyl groups on the CT-TiO2 induce a self-healing effect in perovskite. Thus, they provide superior stability in CIS-PSC. The fabricated CIS-PSC presents a conversion efficiency of 11.08% (Jsc = 23.35 mA/cm2, Voc = 0.995, and FF = 0.477) with a device area of 0.09 cm2 under 100 mW/cm2. Moreover, these unsealed CIS-PSCs retained 100% of their performance after aging tests for 90 days under ambient conditions and even increased from 11.08 to 11.27 over time due to self-healing properties.

Influence of surface chemical properties of nanocrystalline CeO2 on phosphate adsorption and methyl-paraoxon decomposition

Nanocrystalline cerium oxide (CeO2) was used as an effective catalytic and adsorption material for the safe removal of selected phosphorus compounds. Several CeO2 samples were prepared by a simple coprecipitation method with subsequent annealing at temperatures between 400–600 °C, and their sorption ability for inorganic phosphates was studied together with their ability to decompose the organophosphorus compound - paraoxon methyl (PO) - with the goal to find the relations between the sorption and catalytic activity of the prepared materials. It was found that a complex set of physical and chemical characteristics (surface area, crystallite size, pore volume/size, the number of surface hydroxyl groups) plays a crucial role in the governing of adsorption ability and catalytic activity. From the dependence of some characteristics (i.e., the number of surface hydroxyl groups, BET surface area, crystallite size) on the annealing temperature and their mutual correlations, the model describing the degradation of organophosphate compounds on the surface of cerium oxide was deduced.

Effects of Different Surface Treatments of Woven Glass Fibers on Mechanical Properties of an Acrylic Denture Base Material

Silanized glass fibers are popular reinforcements of acrylic denture base materials. To increase the number of surface hydroxyl groups and to improve interfacial adhesion between the matrix and reinforcements, acid or base treatments of glass fibers are commonly performed before the silanization. However, limited data are available on the effect of these treatments on the mechanical properties of acrylic matrix composite materials used for denture base applications. In this work, before the silanization of a woven glass fiber fabric (GF) with 3-(trimethoxysilyl) propyl methacrylate, activation pretreatments using HCl and NH4OH aqueous solutions have been performed. To characterize the glass surface, FTIR spectroscopy was used. Specimens of cured acrylic denture base resin and composites were divided into five groups: (1) cured acrylic denture base resin-control group; (2) composite with non-silanized GF; (3) composite with silanized GF; (4) composite with NH4OH activated and silanized GF; (5) composite with HCl activated and silanized GF. The flexural and impact properties of specimens were evaluated by means of three-point-bending tests and Charpy impact testing, respectively. The residual reactivity of the samples was analyzed using differential scanning calorimetry. The results of mechanical testing showed that acid and base pretreatments of the glass fabric had a positive effect on the flexural modulus of prepared composites but a negative effect on their impact strength. Possible interfacial adhesion mechanisms and the diffusion control of isothermal cure reactions due to vitrification have been discussed.

Catalysts for gaseous organic sulfur removal.

Organic sulfur gases (COS, CS2 and CH3SH) are widely present in reducing industrial off-gases, and these substances pose difficulties for the recovery of carbon monoxide and other gases. The reaction pathways and reaction mechanisms of organic sulfur on different catalyst surfaces have yet to be fully summarized. The literature shows that many factors, such as catalyst synthesis method, loaded metal composition, number of surface hydroxyl groups, number of acid-base sites and methods of surface modification, have important effects on the catalytic performance of metal catalysts. Therefore, this paper presents a comprehensive review of the research on the application of catalysts such as zeolites, metal oxides, carbon-based materials, and hydrotalcite-like derivatives in the field of organic sulfur removal. Future research prospects are summarized, more in situ characterization experiments and theoretical calculations are needed for the catalytic decomposition of methanethiol to analyze the coke generation pathways at the microscopic level, while the simultaneous removal of multiple organic sulfur gases needs to be focused on. Based on previous catalyst research, we propose possible innovations in catalyst design, desulfurization technology and organic sulfur resource utilization technology.

Structural diversity in transition metal-doped titanium oxo-alkoxy complexes: Potential sol-gel intermediates for doped titania nanoparticles and complex titanates

Since the discovery of its photocatalytic properties, titanium dioxide has remained one of the most popular and widely used metal oxide photocatalysts. Its major drawback, however, lies in the narrow region (UV) of sunlight necessary to produce reactive oxygen species. This have been countered by sensitizing with organic dyes to red-shift the absorption spectrum but also with doping of other metals and non-metals. Volume doping or surface modification have demonstrated improved photocatalytic efficiency, mainly via red-shifted absorption by introduction of intermediate energy states between the valence band (VB) and conduction band (CB) and increased number of surface hydroxyl groups (which can form reactive hydroxyl radicals) from charge compensation, and in some cases by improved surface-adsorption of organic molecules. Doped titania and complex titanates have traditionally been produced via, for instance, co-precipitation of mixed metal salts or via solid-state synthesis. While these methods usually are simple, they offer limited control over size, shape, and phase composition. An alternative is the use of single-source precursors (SSPs), i.e., molecules already containing the desired metal ratio in a homogenous distribution. The last one or two decades have seen an increased number of reported transition metal-doped titanium oxo-alkoxides (TOA), particularly for the first-row transition metals as potential single-source precursors (SSP) for doped titania and complex titanates. This review aims at providing an overview of TM-doped TOAs, focusing on first and second row TM elements, with special emphasis on their synthesis, photochemical properties, and their applications as SSPs.Graphical abstract

Photoinduced Superhydrophilicity of Gd-Doped TiO2 Ellipsoidal Nanoparticles Boosts T1 Contrast Enhancement for Magnetic Resonance Imaging.

The unsatisfactory performance of current gadolinium chelate based T1 contrast agents (CAs) for magnetic resonance imaging (MRI) stimulates the search for better alternatives. Herein, we report a new strategy to substantially improve the capacity of nanoparticle-based T1 CAs by exploiting the photoinduced superhydrophilic assistance (PISA) effect. As a proof of concept, we synthesized citrate-coated Gd-doped TiO2 ellipsoidal nanoparticles (GdTi-SC NPs), whose r1 increases significantly upon UV irradiation. The reduced water contact angle and the increased number of surface hydroxyl groups substantiate the existence of the PISA effect, which considerably promotes the efficiency of paramagnetic relaxation enhancement (PRE) and thus the imaging performance of GdTi-SC NPs. In vivo MRI of SD rats with GdTi-SC NPs further demonstrates that GdTi-SC NPs could serve as a high-performance CA for sensitive imaging of blood vessels and accurate diagnosis of vascular lesions, indicating the success of our strategy.

Synthesis of Ce-doped magnetic NaY zeolite for effective Sb removal: Study of its performance and mechanism

A Ce-doped magnetic NaY zeolite adsorbent (NaY@Ce−Fe) was synthesized by co-precipitation method for efficient Sb removal. NaY@Ce−Fe exhibited considerable maximum adsorption capacities of Sb (11.56 ± 0.58 mg/g for Sb(III) and 5.36 ± 0.43 mg/g for Sb(V)) and reusability property and excellent saturated magnetization of 71.1 emu/g. The adsorption data of Sb(III) and Sb(V) were well fitted with the Langmuir isotherm model and Freundlich isotherm model, respectively. Kinetic studies showed that the adsorption processes of Sb(III) and Sb(V) followed the pseudo-second-order kinetic model. The excellent adsorption performance of NaY@Ce−Fe maintained over a wide pH range of 4–9 without the release of Ce and Fe, or in the presence of coexisting anions of Cl−, SO42− and NO3−. The combined results of scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), X-ray Powder Diffraction (XRD), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) further confirmed the successful doping of Ce and Fe3O4 on NaY. Based on the results of batch experiments and physiochemical analyses, the mechanisms controlling Sb adsorption on NaY@Ce−Fe involved the electrostatic attraction, hydrogen bonding, ligand exchange and surface complexation. The abundant number of surface hydroxyl groups promoted the formation of the Ce−O−Sb inner-sphere surface complexes, which was the major contribution to the adsorption of Sb. All the results suggested that NaY@Ce−Fe could be applied as a promising adsorbent for Sb pollution reduction.

Nanocrystalline cerium oxide for catalytic degradation of paraoxon methyl: Influence of CeO2 surface properties

Cerium oxide (CeO2) prepared by annealing of carbonate precursor was tested for degradation of paraoxon methyl (PO) and the relationships between its properties (specific surface area, crystallite size, number of hydroxyl groups) and the catalytic activity were investigated. Lewis and Brönsted acidity surface sites were identified by adsorption of specific probe molecules (pyridine, acetonitrile, and acetone) using Fourier-transform infrared spectroscopy (FTIR). The abundance of Lewis type sites was recognized while Brönsted type sites were present to a lesser extent. The highest catalytic activity had the sample annealed at 500 °C that was highly crystalline, but the sample retained high surface area and a suitable number of surface hydroxyl groups established to be in the range 0.165–0.190 mmol g−1. Furthermore, the annealing has a negligible effect on the point of zero charge (PZC) but significantly affected the Brunauer-Emmett-Teller surface area (BET), crystallite size and number of surface hydroxyl groups that significantly affected also the degradation efficiency. Nevertheless, it was found that the amount of residual carbonate species on the CeO2 surface may also have a crucial influence on its catalytic activity.

Tuning the Interfacial Properties of Spinels to Improve the Antimony Adsorption Ability.

Structure and interfacial properties are important factors that affect a spinel's adsorption performance. In this article, by changing the water content in a precursor during synthesis, the interfacial properties of normal and inverse spinels were tuned to improve Sb adsorption. The results showed that changing the water content did not alter the crystal structure of synthesized zinc ferrite (ZnFe2O4) and cobalt ferrite (CoFe2O4), but it had a significant effect on the crystallite size and the number of surface hydroxyl groups. For normal spinel ZnFe2O4 and inverse spinel CoFe2O4, the crystallite size decreased while the surface hydroxyl groups increased when the water content gradually increased from 1 to 8 mL. Spinels with smaller crystallite size and more surface hydroxyl groups enhanced Sb adsorption. The adsorption capacity of ZnFe2O4 and CoFe2O4 for low concentrations of Sb(V) increased from 8.45 and 10.64 mg/g to 15.05 and 17.00 mg/g, respectively. This work has greatly improved the adsorption capacity of spinel materials through a simple tunable method and is expected to provide new ideas for the interfacial tuning of spinel materials, which shows great potential applications for wastewater treatment.

Efficient One-Pot Synthesis of 1,4-Dihydropyridine and Polyhydroquinoline Derivatives Using Sulfanilic Acid-Functionalized Boehmite Nano-Particles as an Organic-Inorganic Hybrid Catalyst

Boehmite nanoparticles (BNPs) with a wide surface area and a large number of surface hydroxyl groups were covalently functionalized by 3-chloropropyl trimethoxysilane to support sulfanilic acid. This is a hybrid catalyst was then characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), thermal gravimetric analysis, X-ray diffraction and energy-dispersive X-ray spectroscopy. Accordingly BNPs@Si(CH2)3@NHSO3H was used as an effective catalyst for the one-pot three-component Hantzsch condensation reaction of aryl aldehydes, ammonium acetate and ethylacetoacetate for synthesize polyhydroquinolines and 1,4-dihydropyridine derivatives. These reactions were carried out in ethanol solvent under reflux conditions. This way offered here is operationally easy, environmentally benign, straightforward work-up, short reaction time and has high yield. Further, the heterogeneous catalyst be recycle simply and reused.

Design and One-Pot Synthesis of Capsid-like Gold Colloids with Tunable Surface Roughness and Their Enhanced Sensing and Catalytic Performances.

Viral capsid-like particles tiled with mosaic patches have attracted great attention as they imitate nature's design to achieve advanced material properties and functions. Here, we develop a facile one-pot soft-template method to synthesize biomimetic gold capsid-like colloids with tunable particle size and surface roughness. Uniform submicron-to-micron-sized hollow gold colloidal particles are successfully achieved by using tannic acids as soft templates and reducing agents, which first self-assemble into spherical complex templates before the reduction of Au3+ ions via their surface hydroxyl groups. The surface roughness, the size, and the total number of the patches of the prepared gold particles are further tuned, utilizing a mechanism that offers morphology control by varying the number of surface hydroxyl groups participating in the reduction reactions. Among different capsid-like gold colloids, those possessing a rough surface display superior catalytic properties and show promising results as surface-enhanced Raman spectroscopy (SERS) solid substrates for detecting small organic molecules and biomimetic enzymes in a liquid phase for sensing biomolecules in real samples. These capsid-like gold colloids are also expected to find practical applications in delivery systems, electronics, and optics. We believe that our strategy of imitating nature's design of capsid-like structures should also be used in the design and fabrication of other functional colloidal particles.

Rapid proton exchange between surface bridging hydroxyls and adsorbed molecules on TiO2

Understanding the interactions of adsorbed molecules with TiO2 surfaces is important for diverse applications, such as photocatalysis and self-cleaning surfaces. Herein, we investigated the interactions of adsorbed molecules with surface sites on TiO2. The 1H NMR spectra showed that surface healing led to an interesting upfield shift in the chemical shifts of hydroxyls of adsorbed molecules, which is caused by rapid proton exchange between the defect-involved bridging hydroxyls and adsorbed molecules. Infrared spectroscopy confirmed that surface healing decreases the number of surface hydroxyl groups and enhances the number of non-defective surface Ti sites required for methanol adsorption. Therefore, we proposed that undissociative adsorption of methanol is the preferential interaction mode with the non-defective sites of the TiO2 surface but dynamic equilibrium between dissociative and undissociative adsorption exists around surface defect sites. The increase in non-defective surface sites enhanced the surface ζ potential and hindered interfacial electron transfer activity.

Investigating the Support Effect for Catalytic Elimination of Methyl Mercaptan: Role of Hydroxyl Groups over Cr-based Catalysts

The support effect for HZSM-5 and Al2O3-supported chromium (Cr) catalysts on the catalytic decomposition of methyl mercaptan (CH3SH) is investigated. Characterization results reveal that the distribution, reducibility, oxidation states and coordination environment of chromium species mightily depend on the nature of support. Al2O3 support is covered by surface hydroxyl groups, thus conducing to the formation of monochromatic Cr(VI) species with tetrahedral coordination, which remarkably increases the reducibility and dispersion of chromium species. In contrast, plenty of inactive α-Cr2O3 particles are formed on the surface of Cr/HZSM-5 catalyst due to the lack of adequate hydroxyl sites. Furthermore, a positive correlation is established between the content of active Cr(VI) species and the number of surface hydroxyl groups over Cr/Al2O3 catalysts. Reactivity data suggest that the addition of chromium species can observably enhance the conversion of CH3SH for both two supports. More importantly, 5% Cr/Al2O3 catalyst features the superior catalytic performance at 400 °C (100% conversion). The promoting effect can be attributed to the high-content hydroxyl groups on Al2O3, which are proven to stabilize monochromatic Cr(VI) species. This result also provides evidence for the active sites of CH3SH decomposition reaction.

The Mechanism of Mechanochemical Interaction between Amorphous Silicon Dioxide and Pyrocatechol

The products of solid-phase mechanochemical interaction between pyrocatechol and silicon dioxide yielding a powdered composite were studied using a number of physicochemical methods. This interaction is shown to give rise to surface complexes via the reaction of silanol groups and other active sites on the silicon dioxide surface with the hydroxyl group of pyrocatechol. The interaction efficiency increases with rising number of surface hydroxyl groups. The hypotheses regarding the possible mechanisms for this reaction are put forward. The potential surface complex species (intermediates) that play a decisive role in obtaining of soluble chelate complexes of silicon by adding water to the composites are proposed. Obtaining the composites that contain surface complexes is an efficient method to enhance the silicon dioxide solubility due to complexation.

Surface Functional Group Engineering of CeO2 Particles for Enhanced Phosphate Adsorption.

Surface functional groups play a dominating role in determining the adsorption performance of metal oxide particles. The ability to manipulate the surface functional groups is vital in designing an effective adsorbent for water decontamination. In this study, a facile method is proposed for tuning the amount of the surface hydroxyl groups of CeO2 particles. The volume of water added during the ethylene glycol-mediated solvothermal synthesis of CeO2 particles can be used to adjust the amount of surface hydroxyl groups. By simple reduction in the volume of water, the number of surface hydroxyl groups of CeO2 particles can be increased and the phosphate adsorption capacity can be greatly improved. Our results show that the obtained CeO2 particles have high phosphate adsorption capacity at low phosphate concentrations, fast adsorption kinetics, and the ability to achieve an ultralow phosphate concentration in the real sewage effluent. This study provides an effective strategy for designing highly effective metal oxide adsorbents through surface functional group engineering.

Non-equilibrium organosilane plasma polymerization for modulating the surface of PTFE towards potential blood contact applications.

We report a novel and facile organosilane plasma polymerization method designed to improve the surface characteristics of poly(tetrafluoroethylene) (PTFE). We hypothesized that the polymerized silane coating would provide an adhesive surface for endothelial cell proliferation due to a large number of surface hydroxyl groups, while the large polymer networks on the surface of PTFE would hinder platelet attachment. The plasma polymerized PTFE surfaces were then systematically characterized via different analytical techniques such as FTIR, XPS, XRD, Contact angle, and SEM. The key finding of the characterization is the time-dependent deposition of an organosilane layer on the surface of PTFE. This layer was found to provide favorable surface properties to PTFE such as a very high surface oxygen content, high hydrophilicity and improved surface mechanics. Additionally, in vitro cellular studies were conducted to determine the bio-interface properties of the plasma-treated and untreated PTFE. The important results of these experiments were rapid endothelial cell growth and decreased platelet attachment on the plasma-treated PTFE compared to untreated PTFE. Thus, this new surface modification technique could potentially address the current challenges associated with PTFE for blood contact applications, specifically poor endothelial cell growth and risk of thrombosis.

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).