Advances in Asymmetric Wettable Janus Materials for Oil-Water Separation.

The frequent occurrence of crude oil spills and the indiscriminate discharge of oily wastewater have caused serious environmental pollution. The existing separation methods have some defects and are not suitable for complex oil-water emulsions. Therefore, the efficient separation of complex oil-water emulsions has been of great interest to researchers. Asymmetric wettable Janus materials, which can efficiently separate complex oil-water emulsions, have attracted widespread attention. This comprehensive review systematically summarizes the research progress of asymmetric wettable Janus materials for oil-water separation in the last decade, and introduces, in detail, the preparation methods of them. Specifically, the latest research results of two-dimensional Janus materials, three-dimensional Janus materials, smart responsive Janus materials, and environmentally friendly Janus materials for oil-water separation are elaborated. Finally, ongoing challenges and outlook for the future research of asymmetric wettable Janus materials are presented.

Preparation of Silica Aerogel/Resin Composites and Their Application in Dental Restorative Materials.

As the most advanced aerogel material, silica aerogel has had transformative industrial impacts. However, the use of silica aerogel is currently limited to the field of thermal insulation materials, so it is urgent to expand its application into other fields. In this work, silica aerogel/resin composites were successfully prepared by combining silica aerogel with a resin matrix for dental restoration. The applications of this material in the field of dental restoration, as well as its performance, are discussed in depth. It was demonstrated that, when the ratio of the resin matrix Bis-GMA to TEGDMA was 1:1, and the content of silica aerogel with 50 µm particle size was 12.5%, the composite achieved excellent mechanical properties. The flexural strength of the silica aerogel/resin composite reached 62.9546 MPa, which was more than five times that of the pure resin. Due to the presence of the silica aerogel, the composite also demonstrated outstanding antibacterial capabilities, meeting the demand for antimicrobial properties in dental materials. This work successfully investigated the prospect of using commercially available silica aerogels in dental restorative materials; we provide an easy method for using silica aerogels as dental restorative materials, as well as a reference for their application in the field of biomedical materials.

Green Preparation of Durian Rind-Based Cellulose Nanofiber and Its Application in Aerogel.

In this study, a green, highly efficient and low energy consumption preparation method of cellulose nanofiber (CNF) was developed by using agricultural and forestry waste durian rinds as raw materials. The power of ultrasonic treatment was successfully reduced to only 360 W with low molecular weight liquid DMSO. The obtained durian rind-based CNF had a diameter of 8-20 nm and a length of several micrometers. It had good dispersion and stability in water, and could spontaneously cross-link to form hydrogel at room temperature when the concentration was more than 0.5%. The microscopic morphology and compressive properties of CNF aerogels and composite cellulose aerogels prepared from durian rind-based CNF were evaluated. It was found that CNF could effectively prevent the volume shrinkage of aerogel, and the concentration of CNF had a significant effect on the microstructure and mechanical properties of aerogel. The CNF aerogel with 1% CNF exhibited a sheet structure braced by fibers, which had the strongest compression performance. The porosity of CNF aerogels was high to 99%. The compressive strength of the composite cellulose aerogel with durian rind-based CNF was effectively enhanced.

An eco-friendly versatile superabsorbent hydrogel based on sodium alginate and urea for soil improvement with a synchronous chemical loading strategy.

In this paper, an eco-friendly versatile superabsorbent material was designed for soil improvement, and a synchronous chemical loading strategy was proposed. In this strategy, urea not only acted as fertilizer but also acted as a crosslinker to construct an alginate network. The microstructure, chemical structure, thermal stability and composition of the obtained SA/urea hydrogel were characterized in detail. Adsorption behavior and application performance in agriculture were evaluated. The results demonstrated that urea had two different conformations in the network. The SA/urea hydrogel had abundant pore structures with excellent water absorption performance. It could not only improve the water retention capacity of soil but also release nitrogen, phosphorus and potassium elements with degradation for as long as 9 weeks. Moreover, the hydrogel could promote plant growth, increase the nutritional composition of plants and inhibit the accumulation of harmful nitrate in plants. With advantages, including biodegradability, high water absorption, controllable degradation, excellent water retention, sustained NPK release and improved plant nutrition value, the SA/urea hydrogel has great potential for soil improvement in agriculture as an eco-friendly versatile water retention agent and can be expected to extend to more fields as a novel superabsorbent material.

Construction of strain responsive Ti-containing carboxymethyl cellulose hydrogel with transitional coordination precursor.

Due to marvelous sensitivity and flexibility, conductive hydrogels are popularly used as strain sensors in intelligent skin and wearable electronic devices fields. However, hydrogel tends to be destroyed after long-term use or in accident, leading to performance degradation. Herein, we developed an environmental-friendly Ti-containing conductive hydrogel. The hydrogel network was constructed via a simple two-step method with coordination reaction and amidation reaction based on a metal ion precursor from transitional coordination. The synergies of reversible metal coordination bonds and dynamic hydrogen bonds endowed the hydrogel with excellent self-healing properties (3 h, 93.66 %), tensile properties (136.46 kPa), compression properties (1.122 MPa), and anti-fatigue performance. At the same time, the hydrogel showed excellent self-adhesion, even underwater. Due to Ti4+, electrical conductivity of the hydrogel was visibly enhanced (σ = 25.64 mS·cm-1), which resulted in fast response (TS [time sensitivity] = 24.78 s-1) and short recovery time (153 ms). As a flexible strain sensor, the hydrogel with stable conductivity and high sensitivity could precisely detect and distinguish a series of human motions, even different letter pronunciations. These remarkable features make it a promising application in the fields of intelligent skin and wearable electronic devices.

A 'top modification' strategy for enhancing the ability of a chitosan aerogel to efficiently capture heavy metal ions.

Chitosan is a promising substitute for heavy metal ion adsorbents. However, traditional pure chitosan adsorbents have certain disadvantages that limit their application. In this paper, a 'top modification' strategy was used to enhance the capturing ability of chitosan adsorbents. A chitosan aerogel was prepared via physical crosslinking and then enhanced by immersion in ethylenediamine tetraacetic anhydride solution. Finally, an enhanced chitosan aerogel was obtained, and analyses were used to describe its structure, adsorption properties and mechanism. Results showed that both the porous structure and the combined complexations dramatically improved the capturing ability of the chitosan aerogel for heavy metal ions. The theoretical adsorption capacities of the enhanced aerogel for Cu2+, Pb2+ and Cd2+ reached 108.14, 143.73 and 84.62 mg/g, respectively. Due to their environmental friendliness, good adsorption performance, easy separation and reusability, enhanced aerogels have become viable solutions to removing heavy metal pollutants from aquatic systems.

Study on swelling and drug releasing behaviors of ibuprofen-loaded bimetallic alginate aerogel beads with pH-responsive performance.

Bimetallic alginate aerogel beads were prepared by ionotropic gelation method with Ca2+-Ba2+ bimetallic solution and ibuprofen was loaded as a model drug. The swelling and drug releasing behaviors of the beads, especially the influence of barium, were investigated in artificial gastric and intestinal fluids. The results showed that these beads presented higher encapsulation efficiency due to the special structure of aerogel, and barium was beneficial for the more stable structure and drug releasing behavior. The lower swelling capacity of bimetallic beads was observed than monometallic beads. A rapid high-level releasing of ibuprofen was achieved in artificial intestinal fluid, which was up to 96.9% within 1 h, while ibuprofen releasing was avoided in artificial gastric fluid effectively. The drug releasing mechanism of these beads was explored in detail. In the bimetallic crosslinking system, Ba2+ presented a special effect on alginate beads with more sensitive pH response performance. Thus, these beads had more widely potential as a site-specific delivery system, especially for intestinal therapy.

A facile slow-gel method for bulk Al-doped carboxymethyl cellulose aerogels with excellent flame retardancy.

Bulk Al-doped carboxymethyl cellulose aerogels were obtained via a facile slow-gel method and freeze-drying technology. In this method, the cross-linker Al3+ was released slowly and completely with enough d-(+)-gluconic acid δ-lactone as a sustained-release agent. Depended on controlled releasing of Al3+, the reaction speed between Al3+ and carboxyl groups was controlled and Al3+ was well-distributed in the aerogels. The coordination type between Al3+ and carboxymethyl cellulose was the bidentate bridging coordination. By adjusting the amount of Al3+ and the degree of substitution of carboxymethyl cellulose, interconnected network and closely packed sheet-like structure presented, respectively. According to the nitrogen adsorption-desorption isotherms, the aerogels were a kind of mesoporous material with pore blocking or cavitation. In addition, the aerogels exhibited outstanding weight-bearing capacity and excellent flame retardancy. This work provided a valuable reference for doping metal ions into polysaccharide aerogels and expanding the application fields of aerogels.

Converting untreated waste office paper and chitosan into aerogel adsorbent for the removal of heavy metal ions.

The utilization of waste paper, an obsolete recyclable resource, helps to save resources and protect environment. In this paper, an aerogel was prepared to convert the waste paper into a useful material, which was used to adsorb heavy metal ions and handle water pollution. Combining waste office paper and chitosan, the aerogel obtained the enhanced mechanical strength, acid resistance and high adsorption capacity (up to 156.3 mg/g for Cu2+). This adsorption process obeyed the pseudo-second order model and the Langmuir model. The research showed that a coordination compound was formed between amino group and Cu2+ during the adsorption process. The adsorbent could be regenerated well in 0.1 M H2SO4 with up to 98.3% desorption efficiency. The low cost, environmental friendliness, excellent adsorption capacity and regeneration ability made this novel aerogel a promising adsorbent for heavy metal ions. And this conversion is an effective reuse way of waste paper too.

Dual responsive aerogel made from thermo/pH sensitive graft copolymer alginate-g-P(NIPAM-co-NHMAM) for drug controlled release.

Alginate was grafted with NIPAM and NHMAM successfully, and a new responsive copolymer, alginate-g-P(NIPAM-co-NHMAM), was obtained. A novel dual responsive polysaccharide-based aerogel with thermo/pH sensitive properties was designed from the copolymer as drug controlled release system. The chemical structure of the copolymer was characterized by FT-IR and 1H NMR. Lower critical solution temperature (LCST) of the copolymer covered a wide temperature range from 27.6 °C to 42.2 °C, which could be adjusted with changing the ratio between NIPAM and NHMAM. The dual responsive aerogel had a three-dimensional network structure. As a drug controlled release system, the aerogel was high responsive to both temperature and pH with drug loading efficiency up to 13.24%. Above LCST, the aerogel had a faster drug release, and drug was completely released in neutral environment, while the drug release was obstructed in acid environment. Furthermore, the drug release mechanism of the aerogel was illuminated. These results indicated that the dual responsive aerogel was a promising candidate for drug carriers.

Excellent reusable chitosan/cellulose aerogel as an oil and organic solvent absorbent.

Absorption is one of the most important methods for oil spill cleanup. An ideal absorbent is expected to possess advantages of low cost, green, high absorption capacity and excellent reusability. In this paper, a new kind of cellulose aerogel was successfully fabricated via cellulose oxidation, crosslinking, freeze drying and cold plasma modification. The obtained aerogel (water contact angle up to 152.8°) exhibited outstanding oil/water selectivity and high absorption capacity (13.77-28.20 g/g) for various oils and organic solvents. What's more, this kind of aerogel could be reused by simple compression. The absorption-desorption process could be repeated for at least 50 cycles. Through the kinetic analysis, it was found that the pseudo-second order model was more appropriate for the aerogel's oil absorption process. Owing to its low cost, hydrophobicity, high absorption capacity and excellent reusability, this kind of aerogel is expected to be used in oils and organic solvents spill cleanup and oil/water separation field.

An environment-friendly and multi-functional absorbent from chitosan for organic pollutants and heavy metal ion.

Developing environment-friendly green absorbents for disposal of wastewater remains to be studied. In this paper, the cross-linked chitosan aerogel (CsA) as an environment-friendly absorbent was obtained by a simple method involving cross-linked process and freeze drying technique. Compared with conventional absorbents, the porous chitosan aerogel was provided with unique properties such as low density (0.0283g/cm(3)), high porosity (97.98%) and outstanding adsorption performance. The chitosan aerogel also displayed good reusability and excellent elasticity with a maximal thickness recovery up to 96.8% of the original thickness. The as-prepared absorbent exhibited preferable adsorption capacities for crude oil, diesel and copper ion (41.07g/g, 31.07g/g and 21.38mg/g, respectively). The aerogel can collect a wide range of organic solvents and oils with absorption capacities up to 40 times their own weight, depending on the density and viscosity of the liquids. The adsorption capacity for heavy metal ion was also considerable and the maximum adsorption capacity (qm) of the aerogel for copper ion was 35.08mg/g according to Langmuir isotherm model. Consequently, the chitosan aerogel with versatile adsorption properties has a good potential for wastewater treatment in environmental application.

Preparation of bulk sodium carboxymethyl cellulose aerogels with tunable morphology.

Homogeneous and bulk carboxymethyl cellulose hydrogel and aerogel were prepared by a novel process, using Fe(3+) and d-(+)-gluconic acid-lactone as cross-linker and releasing agent, respectively. The results showed that the mass fraction of Fe(3+) has a great effect on CMC aerogels' structure, crystallization and morphology. By adjusting the mass fraction of Fe(3+), granular, three-dimensional network and rod-like morphology were obtained, responding to varying density and porosity. The aerogel had low density (low to 0.0568 g/cm(3)) and high porosity (up to 90.45%). Meantime. Combination patterns between carboxylate ion and iron ion were checked by FTIR. Furthermore, with the addition of Fe(3+), lattice mismatch of CMC emerged and led to decreasing crystalline degree and thermal stability. This work would play an important role in the handy and extensive application of CMC aerogels.

Heat insulation performance, mechanics and hydrophobic modification of cellulose-SiO2 composite aerogels.

Cellulose-SiO2 composite hydrogel was prepared by combining the NaOH/thiourea/H2O solvent system and the immersion method with controlling the hydrolysis-fasculation rate of tetraethyl orthosilicate (TEOS). The hydrophobic composite aerogels were obtained through the freeze-drying technology and the cold plasma modification technology. Composite SiO2 could obviously reduce the thermal conductivity of cellulose aerogel. The thermal conductivity could be as low as 0.026 W/(mK). The thermal insulation mechanism of the aerogel material was discussed. Composite SiO2 reduced hydrophilicity of cellulose aerogel, but environmental humidity had a significant influence on heat insulation performance. After hydrophobic modification using CCl4 as plasma was conducted, the surface of composite aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as 132°. The modified composite aerogel still kept good heat insulation performance. This work provided a foundation for the possibility of applying cellulose-SiO2 composite aerogel in the insulating material field.