Fluorine-free Method Research Articles

Enhanced electrochemical performance of molten salt synthesized V2CTx MXene@VOx composite in Zn ion aqueous electrolytes

The development of MXenes using Lewis acidic salts for etching (MS-MXenes) in molten salts presents a novel, fluorine-free method attracting considerable interest. However, the behavior of various MS-MXenes and their derivatives in aqueous environments remains largely unexplored. Particularly, vanadium-based MXenes demonstrate intriguing properties in Zn ion aqueous electrolytes. Herein, a fluorine-free V2CTx MXene@VOx is synthesized by molten salt etching under an argon atmosphere. The electrochemical properties of V2CTx@VOx are tested in various aqueous electrolytes, including Zn(TFSI)2, ZnSO4, ZnBr2, ZnAc2, and ZnCl2 solutions. The V2CTx@VOx shows high redox capacities in all these Zn ion electrolytes, with the peak performance observed in 1 M ZnBr2, achieving a maximum capacity of 172 mAh g−1 at 1 mV s−1. This performance rivals that of V2CTx MXene prepared through wet-chemical methods. These results underscore the potential of MS-MXenes materials in aqueous energy storage applications.

Photothermal superhydrophobic surface with good corrosion resistance, anti-/de-icing property and mechanical robustness fabricated via multiple-pulse laser ablation

Corrosion and ice accumulation occurring on carbon steel bring about huge economy lost, resource waste, and even hazard event. Fabricating black superhydrophobic surfaces is an effective method for improving the anti-corrosion and anti-/de-icing properties of metallic materials. However, it is still a challengeable task to fabricate a robust black superhydrophobic surface on carbon steel through an eco-friendly method. Herein, a black superhydrophobic surface was obtained on 45 steel substrate via a simple and fluorine-free method, i.e., multiple-pulse laser ablation followed by chemical modification with hexadecyltrimethoxysilane (HDTMS). The obtained surface exhibits a water contact angle of 156° and possesses a low reflectance (<9%) in the wavelength range of 400 ∼ 2500 nm. The surface displays an excellent photothermal property with a temperature rise of 52 °C under 1 sun of illumination within 8 min. Electrochemistry data reveals that the surface has good corrosion resistance with 64.78-times lower corrosion current density and 73.81-times higher charge transfer resistance than the steel substrate. Anti-icing test shows that the surface possesses 2547 s longer freezing delay time and at least ∼ 3 times lower de-icing force than the steel substrate, and photothermal de-icing test demonstrates that the ice on the surfaces starts thawing within 60 s under 0.5 sun of illumination, indicating that the surface has excellent anti-/de-icing property. Moreover, after impacting by 2000 g of sands or 400 times of tape peeling tests, the surface still maintains superhydrophobicity, indicating the good mechanical robustness of the surface.

Fluorine-free prepared two-dimensional molybdenum boride (MBene) as a promising anode for lithium-ion batteries with superior electrochemical performance

MBene, an emerging two-dimensional material generated from bulk ternary metallic boride (MAB phase), has gradually attracted increasing research attention. However, the fabrication of MBene is still a great challenge, resulting in no literature reported about the application of MBene in energy storage fields (e.g. lithium-ion batteries). It is not advisable to adopt the same HF etching strategy which is generally used for the fabrication of MXene owing to the severely corrosive and toxic properties of the HF acid. Here, a fluorine-free hydrothermal-assisted alkane solution etching method is used to prepare the two-dimensional (2D) MoB MBene from MoAlB. The 2D MoB MBene as an anode material in LIBs exhibits a high electrochemical performance, the results exhibit a reversible specific capacity of 144.2 mAh g−1 after 1000 cycles at the current density of 2 A g−1, which is higher than many reported MXene anodes. This fluorine-free method provides a promising green strategy for exploring series of MBene materials for a wealth of application fields.

Fluorine-free synthesis of Ti3C2 MQDs for smartphone-based fluorescent and colorimetric determination of acetylcholinesterase and organophosphorus pesticides.

Ti3C2 MQDs were synthesized using an effective fluorine-free method with excitation/emission maxima at 390/490nm and a fluorescence quantum yield of 11.78%. In contrast to the traditional, hazardous, and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. Acetylcholinesterase (AChE) could catalyze the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine which was further reacted with Ehrman's reagent and decomposed to form a yellow product 2-nitro-5-thiobenate anion (TNB). Due to the obvious overlap between the excitation spectrum of Ti3C2 MQDs and the absorption spectrum of TNB, AChE catalyzed the hydrolysis of substrate DTNB/ATCh to form TNB, which can effectively quench the fluorescence of Ti3C2 MQDs through the inner filter effect (IFE). However, the presence of organophosphorus (OPs) inhibited the activity of AChE, leading to a less expressed IFE and increasing recovery of fluorescence. This was used for the quantification of OPs witha detection limit of 0.20μg·L-1. Moreover, with the constant increase of AChE activity, the color of the reaction system changed visibly from colorless to yellow, and then from yellow to colorless with further continuous addition of OPs. A colorimetric detection with a paper-based sensor of AChE activity and OP concentration was also fabricated by analyzing changes in RGB value using a smartphoneAPP. In this work, we proposed an effective fluorescence/colorimetric two-mode detection method, which opened a new horizon to detect other targets.

Coaxial electrospun nanofibrous aerogels for effective removal of oils and separation of water-in-oil emulsions

Superabsorbents, used in the removal ofoilsandorganicsolvents, play a extremely important role in environmental protection. There is an urgent demand for environment-friendly and high-performance absorbent materials with high selectivity for oils and organic solvents, and is also challenging. Herein, a facile and fluorine-free method to fabricate Polyacrylonitrile @ Polydimethylsiloxane (PAN@PDMS) coaxial nanofibrous aerogels (NFAs) was developed. The steps for synthesis included: coaxial electrospinning - freeze drying - in situ polymerization. The obtained PAN@PDMS NFAs displayed excellent absorption capacities for various oils and organic solvents (55.43–127.37 times of its weight), and efficient water-in-oil emulsions separation with high separation flux (1718 ± 45 L·m−2·h−1) and excellent separation efficiency (above 99.47 wt%). Particularly, the NFAs showed outstanding mechanical resilience (above 83% recovery after repeating 200 cycles at 80% strain) and could be reused by simply squeezing the oil/organic solvent out of it. More importantly, the PAN@PDMS NFAs showed good resistanceagainstvarious chemicals such asacids and alkalis. Therefore, this study offers a facile methodology for the fabrication of NFAs that are expected to be promising candidate materials for practical oily wastewater treatment in environmental protection.

Robust superhydrophobic surface fabrication by fluorine-free method on filter paper for oil/water separation

Robust superhydrophobic surface exhibiting anti-fouling and self-cleaning ability were successfully fabricated by nano TiO2 modified by γ-aminopropyltriethoxysilane (KH550) and polydimethylsiloxane (PDMS) via wire rod coating. Due to the lower surface energy of PDMS and the hierarchical structure caused by the different aggregation sizes of TiO2 nanoparticles, the contact angle of the resulting superhydrophobic coating was 154.5° and the rolling angle was 3.5°. And the coated paper still had good non-wettability under water immersion. In addition, the coated paper was tolerant to mechanical damage and various temperature conditions. Even after 40 sandpaper wear cycles, the coating can still maintain good mechanical stability and superhydrophobicity. The superhydrophobic paper was used for oil-water separation, the separation efficiency was about 98% even after used 10 times. Furthermore, the prepared superhydrophobic paper exhibited excellent self-cleaning and anti-fouling properties, as well as demonstrated superb resistance to various water solutions owing to its high hydrophobicity. Moreover, the prepared superhydrophobic paper has application prospects in the industry of special wetting materials.

A mild strategy to construct superhydrophobic cotton with dual self-cleaning and oil–water separation abilities based on TiO2 and POSS via thiol-ene click reaction

In this work, we proposed a mild and fluorine-free strategy for fabricating robust superhydrophobic coatings with TiO2, 3-mercaptopropyltriethoxysilane (MPTS) and polyhedral oligomeric silsesquioxanes using dip-coating and thiol-ene click reaction. The modified cotton exhibited superb superhydrophobicity with a WCA of 157.6°, which showed anti-wetting property in both water and air. Moreover, the durability of the treated cotton against acid and alkaline solutions, different temperatures, abrasion and peeling tests was verified. The highlight is the dual self-cleaning afforded by superhydrophobicity and photocatalytic degradation. The oil red O was adopted as organic pollutant model and could be decomposed completely with the aid of resultant coating after UV irradiation for 3 h. In addition, the modified cotton could be used as filter material and has the potential in the application of oil–water separation. After seven separation cycles, the separation efficiency still maintained 99.0%, while the WCA of cotton kept as high as 154.6°. Therefore, the above-mentioned features demonstrated that this fluorine-free method could reduce the usage of long-chain fluorinated polymers and prepare superhydrophobic cotton which could be applied in self-cleaning as well as oil–water separation fields.

A fluorine-free method for fabricating multifunctional durable superhydrophobic fabrics

In this study, fly ash (FA), which is a waste product of common flue gas, was used to effectively fabricate multifunctional superhydrophobic surfaces. FA was first coated with a TiO2 shell layer to form a core (FA)-shell (TiO2) structure via charge adsorption. FA-TiO2 was then grafted with polydimethylsiloxane (PDMS) molecules to form FA-TiO2-PDMS particles, which exhibited superhydrophobicity. The PDMS molecules were grafted firmly on the TiO2 shell through covalent bonds, therefore endowing the particles a series of durable properties. The superhydrophobic FA-TiO2-PDMS particles mixed with PDMS could form homogenous coating solution, which was coated onto fabrics to obtain superhydrophobic surfaces. The resulting superhydrophobic fabric exhibited the “Lotus-effect” and excellent self-cleaning ability. It also showed excellent photocatalysis ability that could repeatedly photodegrade various oils and dyes. Moreover, the coated fabric showed durable and stable superhydrophobicity, which could withstand repeated abrasion treatments, recycled peeled tests using an adhesive tape, long-duration boiling-water immersion, and recycled solvent immersion. In addition, the surface exhibited strong self-healed superhydrophobicity after a simple heat treatment even after being repeatedly treated by plasma or immersed into a strong alkali/acid solution for 8 h. The superhydrophobic fabrics also achieved self-quenched fire-retardance and could efficiently separate various oil-water mixtures.

Fabrication of robust superhydrophobic filter paper for oil/water separation based on the combined octadecanoyl chain bonding and polymer grafting via surface-initiated ATRP

Effective separation of oil and water has always been a long-term challenge. Here we introduce a facile and fluorine-free method to fabricate superhydrophobic and superoleophilic filter paper without the decoration of solid particles for robust oil/water separation. After chemically bonding octadecanoyl and α-bromoisobutyryl groups on the surface of filter paper through simultaneous esterification with stearoyl chloride and α-bromoisobutyryl bromide (BiBB) to obtain C18-FP-g-Br, superhydrophobic poly(styrene-co-acrylonitrile) (SAN) grafted filter paper (C18-FP-g-SAN) was fabricated via surface-initiated atom transfer radical polymerization. The obtained C18-FP-g-SAN showed a water contact angle of 153° and achieved a separation efficiency exceeding 98.5% after ten different typical oil/water separation processes due to the synergistically combined contributions of bonded octadecanoyl chain and grafted SAN. C18-FP-g-SAN remained high separation efficiency after 10 cycles of use and treatment with strong acidic or basic solution. The excellent reusability and chemical stability of C18-FP-g-SAN promise its practical applications of continuous oil/water separation and oil spillage cleanup.

Fluorine-Free Synthesis of High-Purity Ti3 C2 Tx (T=OH, O) via Alkali Treatment.

MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy-related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium-ion battery and supercapacitor performance. Here an alkali-assisted hydrothermal method is used to prepare a MXene Ti3 C2 Tx (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti3 C2 Tx with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti3 C2 Tx film electrode (ca. 52 μm in thickness, ca. 1.63 g cm-3 in density) is 314 F g-1 via gravimetric capacitance at 2 mV s-1 in 1 m H2 SO4 . This surpasses (by ca. 214 %) that of the multilayer Ti3 C2 Tx prepared via HF treatments. This fluorine-free method also provides an alkali-etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.

Fluorine-free preparation of titanium carbide MXene quantum dots with high near-infrared photothermal performances for cancer therapy.

Titanium carbide MXene quantum dots (QDs) were synthesized using an effective fluorine-free method as a biocompatible and highly efficient nanoagent for photothermal therapy (PTT) applications. In contrast to the traditional, hazardous and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. More importantly, abundant Al oxoanions were found to be modified on the MXene QD surface by the fluorine-free method, which endowed the QDs with strong and broad absorption in the NIR region. As a result, the as-prepared MXene QDs exhibited an extinction coefficient as large as 52.8 Lg-1 cm-1 at 808 nm and a photothermal conversion efficiency as high as 52.2%. Both the values are among the best reported so far. The as-prepared MXene QDs achieved simultaneous photoacoustic (PA) imaging and the remarkable PTT effect of tumors. Moreover, MXene QDs showed great biocompatibility without causing noticeable toxicity in vitro and in vivo, indicating their high potential for clinical applications.

Morphology and orientation of curling of kaolinite layer in hydrate

In order to determine if there are curlings along other directions than [100] and [010] in kaolinite (Kaol) layer, 1nm Kaol hydrate with 85% yield was synthesized by the fluorine-free method. Its structure and morphology were investigated by X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM) and selected area electron diffraction (SAED). The results show that: (1) there are not only single curling and two opposite parallel curlings, but also two adjacent curlings with about 120° angle in one single layer; (2) there are four new orientations of curlings [11¯0], [110], [310] and [31¯0] in Kaol hydrate. The reasons that Kaol layers can curl along multiple directions may be that: first, two types of incompatible matchings between tetrahedrons and octahedrons; second, the hexagonal distribution and the zigzag distribution of two types of matchings.