Showing papers on "Surface modification published in 2021"

Recent trends in laser cladding and surface alloying

Abstract: Laser cladding and surface alloying are surface modification techniques employed to fabricate thin coating/layer with improved surface properties or to refurbish surface defects by forming highly resistant gradient coatings/layers on the substrate. High energy density and cooling rates make these techniques suitable to process a wide range of materials. In recent years, due to the development of high power lasers, improved controlling and delivery mechanisms have attracted extensive research in laser surface treatment. Researchers have analyzed various process factors to improve process performance. The experimental and theoretical studies show that the performance of laser cladding and surface alloying techniques can be enhanced significantly by the proper selection of input process parameters. This paper summarizes various research works carried out so far in the area of laser cladding and surface alloying of different materials and their applications. It reports the research outcomes of experimental and theoretical studies conducted to improve the process performance. A brief introduction of various laser surface treatment processes is also included. Besides these various problems, their solutions and trend for future works have also been discussed.

The effects of shot peening, laser shock peening and ultrasonic nanocrystal surface modification on the fatigue strength of Inconel 718

Abstract: As most of the failures in engineering components initiate from the surface layer, applying surface treatments can play a crucial role in controlling material performance and lifetime. In this study, different surface severe plastic deformation techniques including severe shot peening, laser shock peening and ultrasonic nanocrystal surface modification have been considered. The effects of process parameters and the kinetic energy of each treatment on the microstructure, mechanical properties and fatigue behavior of nickel-based super-alloy Inconel 718 have been investigated. The results revealed that using the proper parameters to increase the kinetic energy of the applied surface treatments, it is possible to effectively promote surface grain refinement and induce a deep compressive residual stress field in Inconel 718 samples. Among the applied treatments, ultrasonic nanocrystal surface modification was found to be the most efficient one in improving the mechanical properties as it led to the most significant fatigue performance, followed by severe shot peening and laser shock peening.

HCl-Tolerant HxPO4/RuOx–CeO2 Catalysts for Extremely Efficient Catalytic Elimination of Chlorinated VOCs

Abstract: Bulk metal doping and surface phosphate modification were synergically adopted in a rational design to upgrade the CeO2 catalyst, which is highly active but easily deactivated for the catalytic oxidation of chlorinated volatile organic compounds (Cl-VOCs). The metal doping increased the redox ability and defect sites of CeO2, which mostly promoted catalytic activity and inhibited the formation of dechlorinated byproducts but generated polychlorinated byproducts. The subsequent surface modification of the metal-doped CeO2 catalysts with nonmetallic phosphate completely suppressed the formation of polychlorinated byproducts and, more importantly, enhanced the stability of the surface structure by forming a chainmail layer. A highly active, durable, and selective catalyst of phosphate-functionalized RuOx-CeO2 was the most promising among all the metal-doped (Ru, Pd, Pt, Cr, Mn, Fe, Co, and Cu) CeO2 catalysts investigated owing to the prominent chemical stability of RuOx and its superior versatility in the catalytic oxidation of different kinds of Cl-VOCs and other typical pollutants, including dimethyl sulfide, CO, and C3H8. Moreover, the chemical stability of the catalyst, including its bulk and surface structural stability, was investigated by combining intensive treatment with HCl/H2O or HCl with subsequent ex situ ultraviolet-visible light Raman spectroscopy and confirmed the superior resistance to Cl poisoning of the phosphate-functionalized RuOx-CeO2. This work exemplifies a promising strategy for developing ideal catalysts for the removal of Cl-VOCs and provides a catalyst with the superior catalytic performance in Cl-VOC oxidation to date.

Hydroxyapatite Based Materials for Bone Tissue Engineering: A Brief and Comprehensive Introduction

Abstract: Hydroxyapatite (HA) is widely used in bone tissue engineering for its bioactivity and biocompatibility, and a growing number of researchers are exploring ways to improve the physical properties and biological functions of hydroxyapatite. Up to now, HA has been used as inorganic building blocks for tissue engineering or as nanofillers to blend with polymers, furthermore, various methods such as ion doping or surface modification have been also reported to prepare functionalized HA. In this review, we try to give a brief and comprehensive introduction about HA-based materials, including ion-doped HA, HA/polymer composites and surface modified HA and their applications in bone tissue engineering. In addition, the prospective of HA is also discussed. This review may be helpful for researchers to get a general understanding about the development of hydroxyapatite based materials.

Boosting CO 2 Electrochemical Reduction with Atomically Precise Surface Modification on Gold Nanoclusters.

Abstract: Thiolate-protected gold nanoclusters (NCs) are promising catalytic materials for the electrochemical CO2 reduction reaction (CO2 RR). In this work an atomic level modification of a Au23 NC is made by substituting two surface Au atoms with two Cd atoms, and it enhances the CO2 RR selectivity to 90-95 % at the applied potential between -0.5 to -0.9 V, which is doubled compared to that of the undoped Au23 . Additionally, the Cd-doped Au19 Cd2 exhibits the highest CO2 RR activity (2200 mA mg-1 at -1.0 V vs. RHE) among the reported NCs. This synergetic effect between Au and Cd is remarkable. Density-functional theory calculations reveal that the exposure of a sulfur active site upon partial ligand removal provides an energetically feasible CO2 RR pathway. The thermodynamic energy barrier for CO formation is 0.74 eV lower on Au19 Cd2 than on Au23 . These results reveal that Cd doping can boost the CO2 RR performance of Au NCs by modifying the surface geometry and electronic structure, which further changes the intermediate binding energy. This work offers insights into the surface doping mechanism of the CO2 RR and bimetallic synergism.

Surface and Interface Engineering: Molybdenum Carbide–Based Nanomaterials for Electrochemical Energy Conversion

Abstract: Molybdenum carbide (Mox C)-based nanomaterials have shown competitive performances for energy conversion applications based on their unique physicochemical properties. A large surface area and proper surface atomic configuration are essential to explore potentiality of Mox C in electrochemical applications. Although considerable efforts are made on the development of advanced Mox C-based catalysts for energy conversion with high efficiency and stability, some urgent issues, such as low electronic conductivity, low catalytic efficiency, and structural instability, have to be resolved in accordance with their application environments. Surface and interface engineering have shown bright prospects to construct highly efficient Mox C-based electrocatalysts for energy conversion including the hydrogen evolution reaction, oxygen evolution reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction. In this Review, the recent progresses in terms of surface and interface engineering of Mox C-based electrocatalytic materials are summarized, including the increased number of active sites by decreasing the particle size or introducing porous or hierarchical structures and surface modification by introducing heteroatom(s), defects, carbon materials, and others electronic conductive species. Finally, the challenges and prospects for energy conversion on Mox C-based nanomaterials are discussed in terms of key performance parameters for the catalytic performance.

Effect of surface energy and roughness on cell adhesion and growth – facile surface modification for enhanced cell culture

Abstract: In vitro, cellular processing on polymeric surfaces is fundamental to the development of biosensors, scaffolds for tissue engineering and transplantation. However, the effect of surface energy and roughness on the cell–surface interaction remains inconclusive, indicating a lack of complete understanding of the phenomenon. Here, we study the effect of surface energy (Es) and roughness ratio (r) of a polydimethylsiloxane (PDMS) substrate on cell attachment, growth, and proliferation. We considered two different cell lines, HeLa and MDA MB 231, and rough PDMS surfaces of different surface energy in the range Es = 21–100 mJ m−2, corresponding to WCA 161°–1°, and roughness ratio in the range r = 1.05–3, corresponding to roughness 5–150 nm. We find that the cell attachment process proceeds through three different stages marked by an increase in the number of attached cells with time (stage I), flattening of cells (stage II), and elongation of cells (III) on the surface. Our study reveals that moderate surface energy (Es ≈ 70 mJ m−2) and intermediate roughness ratio (r ≈ 2) constitute the most favourable conditions for efficient cell adhesion, growth, and proliferation. A theoretical model based on the minimization of the total free energy of the cell–substrate system is presented and is used to predict the spread length of cells that compares well with the corresponding experimental data within 10%. The performance and reusability of the rough PDMS surface of moderate energy and roughness prepared via facile surface modification are compared with standard T-25 cell culture plates for cell growth and proliferation, which shows that the proposed surface is an attractive choice for efficient cell culture.

Bioinspired dopamine and zwitterionic polymers for non-fouling surface engineering.

Abstract: Biofouling is a serious problem in the medical, marine, and all other industrial fields as it poses significant health risks and financial losses. Therefore, there is a great demand for endowing surfaces with antifouling properties to mitigate biofouling. Zwitterionic polymers (containing an equimolar number of homogeneously distributed anionic and cationic groups on the polymer chains) have been used extensively as one of the best antifouling materials for surface modification. Being a superhydrophilic polymer, zwitterionic polymers need a strong binding agent to continue to remain attached to the surface for long-term applications. The use of a mussel-inspired dopamine adhesive functional layer is one of the most widely exploited approaches for the attachment of a zwitterion layer on the surface via thiol and amine chemistry. Based on recent studies, we have categorized this dopamine and zwitterion conjugation into four different approaches: (1) conjugation of dopamine with zwitterions by direct modification of zwitterions with the dopamine functional moiety; (2) co-deposition of dopamine with zwitterionic polymers; (3) zwitterionic post modification of the polydopamine (PDA) coated surface; and (4) surface-initiated polymerization of zwitterionic polymers using dopamine modified initiators. In this review, we have briefly discussed about all the possible conjugation mechanisms and reactions for this promising dopamine and zwitterion conjugation and how this conjugated system significantly contributes to the development of non-fouling surfaces along with the other applications.

Modulation of the Electronic Properties of MXene (Ti3C2Tx) via Surface-Covalent Functionalization with Diazonium.

Abstract: The physical and chemical properties of MXenes are strongly dependent on surface terminations; thus, the tailoring of surface functional groups in two-dimensional transition-metal carbides (MXenes) may extend the applicability of these compelling materials to a wider set of fields. In this work, we demonstrate the chemical modification of Ti3C2Tx MXene via diazonium covalent chemistry and the subsequent effects on the electrical properties of MXene. The 4-nitrophenyl group was grafted onto the surface of MXene through a solid-liquid reaction, which was confirmed by various characterization methods, including X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, electron energy loss spectroscopy, atomic force microscopy, and transmission electron microscopy. The degree of modification of MXene is expediently tunable by adjusting the concentration of the diazonium salt solution. The work function of functionalized MXene is modifiable by regulating the quantity of grafted diazonium surface groups, with an adjustable range of around 0.6 eV. Further, in this study, the electrical properties of modified MXene are investigated through the fabrication of field-effect-transistor devices that utilize modified MXene as a channel material. It was demonstrated that with increasing concentration of 4-nitrophenyl groups grafted onto the surface the on/off current ratio of the modified MXene was improved to as much as 3.56, with a corresponding decrease in conductivity and mobility. The proposed approach of controlled modification of surface groups in Ti3C2Tx may imbue Ti3C2Tx with favorable electronic behaviors and demonstrate prospects for use in electronic field applications.

Recent advances in nanocellulose processing, functionalization and applications: a review

Abstract: In recent years, environmental and ecological concerns have become a major issue owing to the expansion of petroleum-based synthetic materials and products, and therefore the development of novel and effective synthetic materials that have ecofriendly and economical properties is of significant interest. With the improvements in nanotechnology, biopolymer nanocellulose has gained further attention owing to its remarkable properties and easy availability from various plant species and agricultural waste products, such as rice husk, tea leaves, sugarcane bagasse and so forth. Nanocellulosic materials have wider applications, for example they are used in bio-sensing, catalysis, wastewater treatment, drug delivery, tissue engineering, flame retardants and so on, owing to their long-lasting nature, anisotropic shape, splendid biocompatibility, potent surface chemistry, and efficacious mechanical and optical properties. Chemical, mechanical, physicochemical and enzymatic pretreatments can be utilized to synthesize nanocellulose from cellulosic waste. The features of nanocellulosic materials are mainly dependent on the extraction technique, source and efficient subsequent surface functionalization. Surface functionalization of nanocellulosic materials involves various routes of functionalization, for example, to provide ionic charges on the surface of nano-cellulose via phosphorylation, carboxymethylation, oxidation and sulfonation on nanocellulosic surfaces, or to generate a hydrophobic surface on a nanocellulosic material via acetylation, etherification, silylation, urethanization and amidation. Functionalization of nanocellulose through grafting of a polymer onto its backbone is also an interesting route owing to its wider applications in various dimensions. These modifications provide potential nanomaterials which can be utilized as reinforcing agents in various nanocomposites and also promotes specific features for the production of novel cellulosic nanomaterials, with the objective of promoting their applications in the field of functionalized nanomaterials.

Functionalized carbon nanotubes: synthesis, properties and applications in water purification, drug delivery, and material and biomedical sciences

Abstract: Carbon nanotubes (CNTs) are considered as one of the ideal materials due to their high surface area, high aspect ratio, and impressive material properties, such as mechanical strength, and thermal and electrical conductivity, for the manufacture of next generation composite materials. In spite of the mentioned attractive features, they tend to agglomerate due to their inherent chemical structure which limits their application. Surface modification is required to overcome the agglomeration and increase their dispersability leading to enhanced interactions of the functionalized CNTs with matrix materials/polymer matrices. Recent developments concerning reliable methods for the functionalization of carbon nanotubes offer an additional thrust towards extending their application areas. By chemical functionalization, organic functional groups are generated/attached to the surfaces as well as the tip of CNTs which opens up the possibilities for tailoring the properties of nanotubes and extending their application areas. Different research efforts have been devoted towards both covalent and non-covalent functionalization for different applications. Functionalized CNTs have been used successfully for the development of high quality nanocomposites, finding wide application as chemical and biological sensors, in optoelectronics and catalysis. Non covalently functionalized carbon nanotubes have been used as a substrate for the immobilization of a large variety of biomolecules to impart specific recognition properties for the development of miniaturized biosensors as well as designing of novel bioactive nanomaterials. Functionalized CNTs have also been demonstrated as one of the promising nanomaterials for the decontamination of water due to their high adsorption capacity and specificity for various contaminants. Specifically modified CNTs have been utilized for bone tissue engineering and as a novel and versatile drug delivery vehicle. This review article discusses in short the synthesis, properties and applications of CNTs. This includes the need for functionalization of CNTs, methods and types of functionalization, and properties of functionalized CNTs and their applications especially with respect to material and biomedical sciences, water purification, and drug delivery systems.

Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives.

Abstract: Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content ≤20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally cross-linked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content ≥30% allowed both inter- and intraparticle cross-linking at >150 °C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).