Surface Chemical Activity Research Articles

Surface chemical states analysis and operational parameters dependent photocatalytic activity of mixed-phase TiO2:Ag photocatalysts

Surface chemical states analysis and operational parameters dependent photocatalytic activity of mixed-phase TiO2:Ag photocatalysts

Reinforcement of polyamide 6 with carbon fiber surface modified by a polar cross-linked network interfacial phase

Carbon fiber-reinforced polyamide 6 (CF/PA6) composite materials have low relative density, high specific strength, and high specific modulus. However, the surface of the CF is smooth and chemically inert, resulting in poor interfacial adhesion in CF/PA6 composites, thereby limiting its application range. Herein, an epoxy resin emulsifier with hydrophilic ends and lipophilic middle was synthesized. After sizing, the surface chemical activity and roughness of the CF were higher. The tensile strength of the prepared CF/PA6 composite material was increased by 38.6%, and the impact strength was increased by 26.4%. By testing the tensile strength and wettability of the CF, as well as the dynamic thermomechanical properties and rheological behavior of the CF/PA6 composites, the influence of the sizing agent on the properties of CF and the interfacial properties of CF/PA6 composites was evaluated, and its mechanism of action is discussed herein.

Synthesis of Hierarchical Layered Quasi-Triangular Ce(OH)CO3 and Its Thermal Conversion to Ceria with High Polishing Performance.

Layered quasi-triangular Ce(OH)CO3 assembled from primary nanoparticles was synthesized via a solvothermal method and converted into CeO2 abrasive particles by calcination at 800-1000 °C. With the increase of calcination temperature, the primary particle size increased and the microstructure, mechanical hardness, and chemical activity of the CeO2 particles changed, thus affecting the polishing performance. The calcined products obtained at 800, 850, and 900 °C maintained the layered edge structure of the Ce(OH)CO3 precursor and had a relatively high specific surface area and surface Ce3+ concentration. The samples calcined at 950 and 1000 °C lost the layered structure due to the large-scale melting of the primary particles, and their surface chemical activity decreased. The polishing experiments on K9 glass showed that, with the calcination temperature rising from 800 to 1000 °C, the material removal rate (MRR) first increased and then decreased sharply. The initial increase of MRR was attributed to the increase of mechanical hardness of the layered quasi-triangular CeO2, and the subsequent decrease of MRR was related to the decrease in surface chemical activity and disappearance of the layered edge structure. The product calcined at 900 °C had the highest MRR and best surface quality after polishing due to the layered edge structure and optimal match of chemical activity and mechanical hardness.

Surface Activation of Wax-Based Additives to Enhance Asphalt Rheological Properties via Rotating Plasma Treatment

Wax-based additives have been widely used in asphalt pavement for their preferable environmental benefits. However, poor compatibility between wax-based warm mix additives and asphalt easily leads to precipitation of wax and cracking of asphalt pavement. Plasma treatment can effectively modify the surface of various materials. This study applies plasma treatment to improve the surface properties of wax-based additives for compatibility improvement in asphalt binder. Compatibility of two different wax-base additives in asphalt binder before and after surface treatment is investigated via cigar tube test and morphology test. In parallel, rheological properties of wax-modified asphalt are characterized from the perspectives of rotational viscosity, rutting resistance, and fatigue performance. Results show the enhanced surface roughness and chemical activity of wax-based additives after plasma treatment. The adhesion between waxes and the asphalt matrix is significantly improved. Waxes within binder are uniformly dispersed after plasma treatment. The incorporation of surface activated wax helps to promote the viscosity reduction of asphalt binder. Furthermore, the high-temperature performance of wax-based asphalt after surface activation treatment of wax is significantly improved, especially for fatty acid amide waxes. As for fatigue performance, plasma treatment improves the fatigue resistance from a compatibility perspective. Therefore, plasma has great promise for facilitating wax-modified asphalt properties from a compatibility perspective.

Multiscale interfacial enhancement of surface grown carbon nanotubes carbon fiber composites

AbstractThe interface properties between surface grown carbon nanotubes carbon fiber (CNTs‐CF) and epoxy resin were investigated by different modification methods. The X‐ray photoelectron spectrometer probations show that the pristine CNTs‐CF has very low contents of both oxygen element and active carbon element. Taking the naked carbon fiber (CF) without CNTs grown as a reference, the interfacial shear strength (IFSS) of CNTs‐CF/epoxy is only 5.6% higher. After heat treatment, chemical modification and sizing treatments, the surface chemical activity of CNTs‐CF is improved considerably. In contrast with the IFSS of standard CF/epoxy, the interfacial strength of chemical‐treated CNTs‐CF‐E1/epoxy is increased to 122.8 MPa by 29.7%. The increasing content of the epoxy active groups at the modified CNTs‐CF‐E1 surface is conducive to forming covalent bonds between the epoxy resin and the CNTs‐CF‐E1 surface particularly the activated nanotube surface. The enhancement of CNT/epoxy interface is beneficial to the over whole interface property of the composites. Hence, the compressive and torsion strength of sizing CNTs‐CF‐E1 bundle combined with epoxy resin are increased by 32.4% and 14.1%, respectively. The SEM images show the failure morphologies of different modification methods, and the enhancement mechanism of multiscale interface is further clarified. Compared with chemical treatment, heat treatment can remove the inert amorphous carbon on the CNTs‐CF fiber surface and improve the interface adhesion of CNT/epoxy and CF/epoxy, and surface sizing treatment improves the CF/epoxy interface. The enhancement mechanisms of these modified CNTs‐CFs/epoxy should be ascribed to the competition and synergetic effects of the multiscale interfaces, including CNT/CF, CNT/epoxy, and CF/epoxy.

Improving the interlaminar bonding and thermal conductivity of polymer composites by using split-radial mesophase pitch-based carbon fiber as reinforcement

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) have excellent properties such as high thermal conductivity and high modulus, but the significant anisotropy and surface inertness of MPCF result in the poor interlaminar thermal conductivity and interface bonding of MPCFRP, which greatly limits its application. To address this issue, MPCF-A with split-radial structure was prepared through fiber structure modulation. Compared with the conventional skin-core fiber (MPCF-B), the higher surface roughness and chemical activity of MPCF-A contribute to stronger mechanical locking and chemical bonding between fibers and resin, meanwhile open wedge crack and better graphite microcrystalline structure of MPCF-A play a positive role in increasing the contact points and reducing the phonon scattering in the heat transfer. Therefore, the interlaminar shear strength (40.7 MPa) and interlaminar thermal conductivity (2.09 W/(m·K)) of MPCFRP-A are 9.12% and 27.4% higher than those of MPCFRP-B, respectively, on the basis of the excellent in-plane thermal conductivity (322.8 W/(m·K)). This study provides a reliable guide to improve the interlayer performance of MPCFRP by tailoring the fiber microstructure.

Conductometric nitrogen dioxide gas sensor based on gallium nitride quantum dots film

Gallium nitride (GaN) has some challenges for gas sensing, such as high detection lower limit (LOD) or complicated epitaxy of nanostructures. To address these issues, we exclusively designed a GaN quantum dots (QDs) film to enhance the gas interaction capability which fabricated by metal-organic chemical vapor deposition (MOCVD). The GaN QDs film gas sensor exhibits a low LOD (5 ppb) to nitrogen dioxide (NO2) at room temperature (RT), which has superior gas performance than other GaN-based sensors. The results of morphology and structure characterization manifest that many ultra-small QDs around 2 nm in diameter were stacked to form QDs of larger size, and confirm the existence of vacancies for the GaN QDs film. And the GaN QDs film sensor displays a ultra-high electron mobility of 1237.37 cm2 V−1s−1 at RT, which is greatly beneficial for gas sensing. The sensing mechanisms were analyzed based on its abundant active sites, ultrahigh carrier mobility, high surface energy and chemical activity, grain boundary barrier and good electrical conductivity. Moreover, the sensor processes high selectivity, repeatability, stability and reusability based on MOCVD technology which can realize precise control of structure and morphology, thus this sensor is expected to achieve rapid industrialization.

Influence of the electrochemical treatment level of carbon fibers on the compression after impact property of carbon fiber/epoxy composites

AbstractIn this paper, carbon fibers (CF) with different electrochemical treatment levels were obtained by changing the parameters of electrochemical treatment, and the effect of electrochemical treatment levels on the surface properties of CF was studied by scanning electron microscope, atomic force microscopy and X‐ray photoelectron spectroscopy. The interfacial shear strength (IFSS) of CF with different electrochemical treatment levels were characterized by single fiber‐composite fragmentation. The effects of electrochemical treatment on the mechanical properties of CF were investigated by monofilament tensile test and composite laminate 0° tensile test. Finally, the carbon fibers were compounded with epoxy resin to prepare composite laminates, whose effect on the macroscopic mechanical properties of the composite, such as short beam shear strength (SBSS) and compression after impact (CAI) strength, was studied. As a result, with the increase of the level of electrochemical treatment, the surface roughness and chemical activity of CF increased first and then decreased, while the surface energy shows a gradually increasing trend. The IFSS of CF‐BX shows a gradually increasing trend, while that of the CF‐SX shows a trend of increasing first and then remaining basically unchanged, while SBSS shows the same trend. The monofilament tensile test and composite laminate 0° tensile test showed that the electrochemical treatment did not have a significant effect on the mechanical properties of CF. The compression after impact test showed that with the enhancement of the electrochemical treatment, the CAI of the composite laminates increased first and then remained roughly unchanged.

Effects of the hardness and roughness on the plastic deformation properties of electroplated gold bumps during thermocompression bonding

Within the scope of this work, an optimization approach of existing investigations on electroplated hard gold contacts is to be developed, which have an initial Vickers hardness of 103 HV. These investigations envisage the height-controlled bonding of structures in the multichip integration of optical components. The investigations relate to the influence of material hardness and roughness on the plastic deformation behaviour during bond formation by thermocompression bonding (TCB). Furthermore, pre-treatments such as mechanical surface planarization and chemical surface activation using atmospheric pressure plasma are employed prior to the bonding process to enable the reduction of the bonding parameters pressure and temperature and consequently contribute to control the plastic deformation during thermocompression and reduce the typical plastic deformation range of 30 % to a deformation range below 5 %. The previous investigations were performed on gold contacts, which have been thermally annealed prior to the bonding process and resulted in a plastic deformation range up to 30 %. With the new approach, i.e. throughout the material hardening and altering the surface condition, a plastic deformation range below 3 % was successfully obtained. The attainable bonding temperatures and bonding pressures were between 190 °C–250 °C and 145 MPa–230 MPa, respectively. The bonding time varied between 30 s and 60 s.

Interaction mechanism between cadmium species and Fe/Mn-doped carbon materials in municipal solid waste incineration flue gas: A density functional theory study

The interaction mechanism between cadmium (Cd) species and Fe/Mn-modified carbon materials is unveiled by density functional theory (DFT) to inspire the clean and efficient disposal of Cd pollutants in municipal solid waste (MSW) flue gas. The interaction of Cd pollutants over the surface mainly includes adsorption and catalysis. Regarding adsorption, the Fe/Mn-doped carbon martial can effectively improve the surface chemical activity and immobilization ability for Cd species, following the order of CdO > CdCl2 > Cd0. As for catalysis, the Fe/Mn doping promotes the accumulation of easy-to-trap CdO by elevating the CdO generation and suppressing the CdO conversion, and the conversion of difficult-to-trap Cd0 to the relatively easy-to-trap CdCl2 is also promoted. Herein, Mn doping exhibits better performance in both adsorption and catalysis than that of Fe. Consequently, the doping of Mn effectively synergizes the adsorption and catalysis on the surface, significantly improving the removal efficiency of Cd contaminants.

Effect of silane coating surface treatment on friction and wear properties of carbon fiber/PI composites

Abstract PAN-based carbon fiber was surface-modified with silane coating, and a composite material was prepared using a PI resin as a matrix. The structure and surface properties of carbon fibers were studied by means of X-ray photoelectron spectroscopy (XPS) and SEM. The tensile strength of the composite was measured by a tensile tester, and the friction properties of the composite were measured by a micro-nano mechanics comprehensive test system. The results show that treatment with silane coating can improve the surface roughness and chemical activity of carbon fiber, improve the interface between carbon fiber and PI resin matrix, and improve the tensile strength and wear rate of the composite.

Enhanced room temperature NO2 sensing performance based on N-doped carbon nanosheets@ZnO nanoplates by morphology transition and white light illumination

Highly-sensitive gas sensors operating at room temperature (RT) have been pursued by researchers due to their high security, energy saving and long-term stability. Herein, N-doped carbon nanosheets-incorporated zinc oxide (NCZ) was synthesized via solution calcination combined with hydrothermal method and utilized for ppb level detection of NO2 at RT. Intriguingly, the construction of N-doped carbon nanosheets was accompanied by generation of ZnO nanoparticles, and then be transferred into mesoporous nanoplates. The as-synthesized NCZ(120)-300 nanocomposites demonstrated high sensitivity to 3 ppm NO2 (|Rg-R0|/R0=∼28.2), along with fast response/recovery (60 s/129 s) speed, excellent selectivity and cyclic stability. In particular, the morphology transition of ZnO greatly enhanced the RT NO2 sensing performance of the as-prepared sensor. Meanwhile, the white light illumination further ameliorated the sensor’s properties involving ∼ 2.1 times enhancement of sensitivity and shorter recovery process (accelerated from 563 s to 129 s). These enhancements are ascribed to the heterostructure between ZnO nanoplates and N-doped carbon nanosheets, and the modulation of electron structure by photo-generated electron-hole pairs. In addition, the 2D N-doped carbon nanosheets and mesoporous ZnO nanoplates offer numerous active adsorption-sites, which improved the surface chemical activity of NCZ(120)-300.

Significantly improved interfacial properties and wave-transparent performance of PBO fibers/cyanate esters laminated composites via introducing a polydopamine/ZIF-8 hybrid membrane

Polydopamine hybrid zeolitic imidazolate framework-8 (PDA*ZIF-8) membrane, synthesized by zinc nitrate hexahydrate (ZnNO3•6H2O), 2-methylimidazole (2-MI), and dopamine (DA), uniformly grows on the surface of poly(p-phenylene-2, 6-benzobisoxazole) (PBO) fibers by heterogeneous nucleation method to obtain PBO@PDA*ZIF-8 fibers. PBO@PDA*ZIF-8 fibers are then applied as the reinforcement, bisphenol A dicyanate ester (BADCy) as the matrix, and PBO@PDA*ZIF-8 fibers/BADCy wave-transparent laminated composites are prepared by high-temperature molding. Results indicate that PDA*ZIF-8 membrane increases the surface roughness and chemical activity of PBO fibers. The interlaminar shear strength (ILSS) and flexural strength of PBO@PDA*ZIF-8 fibers/BADCy laminated composites are 45.3 and 656.3 MPa, respectively, which are increased by 23.4% and 11.7% compared with those of PBO fibers/BADCy composites (587.4 and 36.7 MPa). The dielectric constant and dielectric loss values at 1 MHz are 2.76 and 0.0046, respectively, lower than PBO fibers/BADCy (3.06 and 0.006). At 0.3–40 GHz, PBO@PDA*ZIF-8 fibers/BADCy laminated composites have excellent wave-transparent performance (The simulated wave-transparent rate is greater than 87%, d = 1.5–3.5 mm). Meanwhile, the corresponding volume resistivity and breakdown strength are 3.7 × 1015 Ω•cm and 23.61 kV/mm, higher than PBO fibers/BADCy composites (2.2 × 1015 Ω•cm and 17.69 kV/mm), respectively.

Study of the effect of CNTs, and (CNTs-ZnO) on the porous silicon as sensor for acetone gas detection

This work deals with a thin coating of nanoparticles zinc oxide (ZnO) doped with carbon nanotubes (MWCNTs) about (30−70) % respectively, that deposited on porous silicon (PSi) surface. the PS were prepared by photoelectrochemical etching (PECE) at different etching current densities: J= 12, 24, and 30 mA/cm2 for 10 min of etching time and 40% hydrofluoric acid concentration, while the zinc nanoparticles (ZnO) were prepared by the precipitation method. the suspension solution of ZnO-MWCNTs was prepared by mixing 30% of ZnO with 70% of MWCNTs by using a magnetic stirrer for 20 min then in ultrasonic in 30 min for prepare homogeneity solution. the drops-casting method was used for departed 5 drops of,MWCNTs and (30–70) % ZnO-MWCNTs on PS surface. The structural, morphological, and optical properties were conducted for all samples using X-ray diffraction (XRD) analysis, Raman Spectroscopy, Field emission scanning electron microscopy (FSEM), atomic force microscopy(AFM), Transition Electron Microscope (TEM), and photoluminescence (PL) tests. At room temperature, all PS, MWCNTs/PS, and MWCNTs -ZnO/PS samples were used as acetone gas sensors.the best sensitivity was at MWCNT after doping with ZnO on PS samples at etching current density 30 mA/cm2, about (2.940814) at a concentration of 500 ppm. In comparison to MWCNTs/PS around (2.567534) and only PS surface (2.413857) This is due to the fact that after being deposited with ZnONPs, MWCNT nanostructures have a high surface chemical activity and a big specific surface area. This makes MWCNTs act as highly sensitive to many gases such as ethanol, and acetone gases at room temperature (RT).

Simultaneous ambient pressure x-ray photoelectron spectroscopy and grazing incidence x-ray scattering in gas environments

We have developed an experimental system to simultaneously measure surface structure, morphology, composition, chemical state, and chemical activity for samples in gas phase environments. This is accomplished by simultaneously measuring x-ray photoelectron spectroscopy (XPS) and grazing incidence x-ray scattering in gas pressures as high as the multi-Torr regime while also recording mass spectrometry. Scattering patterns reflect near-surface sample structures from the nano-scale to the meso-scale, and the grazing incidence geometry provides tunable depth sensitivity of structural measurements. Scattered x rays are detected across a broad range of angles using a newly designed pivoting-UHV-manipulator for detector positioning. At the same time, XPS and mass spectrometry can be measured, all from the same sample spot and under ambient conditions. To demonstrate the capabilities of this system, we measured the chemical state, composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in O2 atmosphere at various temperatures. These simultaneous structural, chemical, and gas phase product probes enable detailed insights into the interplay between the structure and chemical state for samples in gas phase environments. The compact size of our pivoting-UHV-manipulator makes it possible to retrofit this technique into existing spectroscopic instruments installed at synchrotron beamlines. Because many synchrotron facilities are planning or undergoing upgrades to diffraction limited storage rings with transversely coherent beams, a newly emerging set of coherent x-ray scattering experiments can greatly benefit from the concepts we present here.

Facile synthesis of macroalgae-derived graphene adsorbents for efficient CO2 capture

Graphene, emerging as one of the most promising class of adsorptive separation carbon material for its high specific surface area and strong surface chemical activity. Biomass especially sustainable biomass as graphene sources shows great potential at large scales under energy shortage era. In this paper, a kind of subtropical macroalgae (Sargassum Horneri, S.H.) was selected as the precursor, and a facile synthesis method based on KOH activation was used to prepare graphene. A continuous monitoring on the formation of graphene and a systematic investigation into biomass precursor were performed, paying special attention to parameters including activation temperature, the alkali and carbon ratio, the corresponding pore structure, and surface chemistry variation. Moreover, the CO2 adsorption properties of porous graphene were tested. The results showed that, S.H. is a kind of ideal graphene precursor. The optimum preparation of porous graphene by KOH activation was the carbonization temperature of 400 °C, the alkali carbon ratio of 4:1 and the activation temperature of 850 °C. The porous graphene displayed high specific surface area (∼1411 m2/g), pore volume (∼1.16 cm3/g), and abundant microporous and mesoporous structures. The as-prepared porous graphene exhibited good CO2 uptake capacity as 2.78 mmol/g at 30 °C and 1 bar. The CO2 adsorption rate equations of the graphene were consistent with the intraparticle diffusion model, indicating that the CO2 adsorption was mainly controlled by the pore structure, and additionally influenced by the chemical functional groups especially N on the surface.

Synergistically enhanced ultraviolet aging resistance and interfacial adhesion of poly (p‐phenylene benzobisoxazole) fiber with soluble naphthalimide sizing

AbstractAmino‐terminated naphthalimide (NDI) with ultraviolet (UV) absorptivity was synthesized to sizing on poly(p‐phenylene benzobisoxazole) (PBO) fiber surface, and UV aging resistance PBO fiber and interfacial adhesion of their composites was investigated. Compared with pristine PBO fiber, the surface chemical activity and roughness of NDI‐PBO fiber were increased. In comparison with pristine PBO fiber, tensile strength, intrinsic viscosity ([η]), and diameter of NDI‐PBO fiber showed a better retention, and the enhanced UV‐aging resistance was verified by hardly visible macroscopic defects on NDI‐PBO fiber. Meanwhile, transverse fiber bundle test strength of NDI‐PBO fiber composites was promoted by stronger mechanical interlocking and chemical interaction. The synergistic improvement in UV aging resistance and interfacial adhesion of PBO fiber was attributed to undamaged crystal and molecular structure from UV protection effects of NDI layer and strong chemical bonding between reactive groups of NDI and epoxy matrix.

Enhanced interfacial properties of carbon fiber/epoxy composites by coating carbon nanotubes onto carbon fiber surface by one-step dipping method

A type of carbon fiber/carbon nanotubes (CF/CNTs) multi-scale reinforcement was prepared by one-step dipping method, in which silane coupling agent (3-glycidyl ether oxy-propyl trimethoxy silane, KH560) was used as the bridge between CF and CNTs. Results showed that CNTs were uniformly coated onto CF surface, and the surface chemical activity, wettability and single fiber tensile strength of modified CFs were all improved significantly. More importantly, the interfacial shear strength (IFSS) of CF/CNTs reinforced epoxy composite, CF/CNTs composite, observed by SEM, showed good interface adhesion. It was also found that the silane coupling agent and CNTs would enhance the interfacial properties synergistically. Besides, the bridging effect of CNTs as the interfacial reinforcing mechanism for CF/CNTs multi-scale reinforcement composite was put forward. This special reinforcing mechanism may be as the guiding principle for CF surface modification and interfacial properties enhancement.

Exfoliation Energy as a Descriptor of MXenes Synthesizability and Surface Chemical Activity.

MXenes are two-dimensional nanomaterials isolated from MAX phases by selective extraction of the A component—a p-block element. The MAX exfoliation energy, Eexf, is considered a chemical descriptor of the MXene synthesizability. Here, we show, by density functional theory (DFT) estimations of Eexf values for 486 different MAX phases, that Eexf decreases (i) when MAX is a nitride, (ii) when going along a metal M component d series, (iii) when going down a p-block A element group, and (iv) when having thicker MXenes. Furthermore, Eexf is found to bias, even to govern, the surface chemical activity, evaluated here on the CO2 adsorption strength, so that more unstable MXenes, displaying larger Eexf values, display a stronger attachment of species upon.

LCA of laser surface activation and traditional pre-treatments for adhesive bonding of engineering polymers

The use of engineering polymers for mechanical applications has seen increasing uptake due to properties such as low density, flexibility, ease of manufacturing and cost effectiveness. Despite these advantages, joining and assembly methods for these types of materials is still an open issue. Traditional assembly processes such as screw fastening and riveting are increasingly being replaced by new processes such as adhesive bonding. Engineering polymers, however, are difficult to bond using adhesives due to their low surface energy and low wettability. For this reason, surface chemical activation techniques with primers are often used. The utilization of various chemicals associated with such pre-treatments has a significant environmental impact. Within this context, the present paper aims to compare the environmental performance of four adhesive bonding pre-treatments: (i) mechanical (i.e., abrasion), (ii) chemical (i.e., primer), (iii) plasma and (iv) laser activation. The work was performed in three phases: (i) setup of the surface activation processes, (ii) mechanical characterization of bonded joints (static tests) and (iii) LCA analysis to evaluate and compare the different pre-treatments. The outcome of this study provides important insight into the development of laser and plasma technologies as sustainable surface activation methods for polymers through the creation of models correlating process parameters to the type of surface and joint strength.