Three-dimensional attapulgite with sandwich-like architecture used for multifunctional water remediation

Construction of attapulgite decorated cetylpyridinium bromide/cellulose acetate composite beads for removal of Cr (VI) ions with emphasis on mechanistic insights

Eco-friendly and renewable composite beads were constructed for efficient adsorptive removal of Cr (VI) ions. Attapulgite (ATP) clay decorated with cetylpyridinium bromide (CPBr) was impregnated into cellulose acetate (CA) beads, which were formulated through a simple and cost-effective solvent-exchange approach. FTIR, XRD, SEM, Zeta potential, and XPS characterization tools verified the successful formation of ATP-CPBr@CA beads. The composite beads displayed a spherical and porous shape with a positively charged surface (26.6 mV) at pH 2. In addition, higher adsorption performance was accomplished by ATP-CPBr@CA composite beads with ease of separation compared to their components. Meanwhile, equilibrium isotherms pointed out that the Langmuir model was optimal for describing the adsorption process of Cr (VI) with a maximal adsorption capacity of 302 mg/g. Moreover, the D-R isotherm model verified the physical adsorption process, while adsorption data obeyed the pseudo-second-order kinetic model. Further, XPS results hypothesized that the removal mechanism involves adsorption via electrostatic interactions, redox reaction, and co-precipitation. Interestingly, the ATP-CPBr@CA composite beads reserved tolerable adsorption characteristics with a maximum removal present exceeding 70% after reuse for seven successive cycles, proposing its feasible applicability as a reusable and easy-separable candidate for removing heavy metals from aquatic bodies.

Recent developments in synthesis of attapulgite composite materials for refractory organic wastewater treatment: a review

Attapulgite clay, due to its unique crystalline hydrated magnesium-aluminium silicate composition and layer-chain structure, possesses exceptional adsorption and catalytic properties, which enable it or its composites to be utilized as adsorbents and catalysts for wastewater treatment. But the drawbacks of attapulgite are also very obvious, such as relatively low specific surface area (compared to traditional adsorbents such as activated carbon and activated alumina), easy aggregation, and difficulty in dispersion. In order to fully utilize and improve the performance of attapulgite, researchers have conducted extensive research on its modification, but few specialized works have comprehensively evaluated the synthesis, applications and challenges for attapulgite-based composite materials in refractory organic wastewater treatments. This paper provides a comprehensive review of controllable preparation strategies, characterization methods and mechanisms of attapulgite-based composite materials, as well as the research progress of these materials in refractory organic wastewater treatment. Based on this review, constructive recommendations, such as deep mechanism analysis from molecular level multi-functional attapulgite-based material developments, and using biodegradable materials in attapulgite-based composites, were proposed.

Spherical Attapulgite/Silica Aerogels Fabricated via Different Drying Methods with Excellent Adsorption Performance

Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO₂) gels were initially prepared by easily scalable sol-gel dripping methods and then dried to aerogels with three drying techniques, namely, supercritical CO₂ drying (SCD), freeze-drying (FD), and ambient pressure drying (APD). The effect of the drying techniques and heat-treated temperature on the physical characteristic, morphological properties, microstructure, and chemical structure of the spherical ATP/SiO₂ aerogels were investigated. The macroscopic morphology of the spherical ATP/SiO₂ aerogels was homogeneous and integrated without local cracking. The average pore diameter and specific surface area of the spherical ATP/SiO₂ aerogels prepared by the three drying techniques were in the range of 6.8-8.6 nm and 218.5-267.4 m²/g, respectively. The heat treatment temperature had a significant effect on the pore structure and the wetting properties of the aerogels. The 600 °C heat-treated aerogels were subjected to adsorption tests in methylene blue (MB) solution (60 mg/g, 100 mL), which exhibited a great adsorption capacity of 102.50 mg/g. Therefore, the resulting spherical ATP/SiO₂ aerogels possessed multipath preparation and exhibited an efficient adsorption performance, with the potential to be applied as an adsorbent for dye wastewater.

Effective diesel removal by a novel electrospun composite nanofibrous membrane with immobilized Bacillus cereus LY-1

Nanofiber membranes have recently been considered as promising supports for the immobilization of microorganisms due to the simplicity and cost-effectiveness of electrostatic spinning technology and the ability to control fiber morphology, such as obtaining higher surface area and porosity. In this study, electrospun polyvinyl alcohol/sodium alginate/attapulgite (PVA/SA/ATP) nanofiber membrane was prepared as support for immobilized Bacillus cereus LY-1 for diesel degradation in an aqueous medium and a significant improvement in diesel removal efficiency was realized. The effect of modified ATP concentration on diesel removal was investigated. The results showed that the nanofiber membranes complexed with cetyl trimethyl ammonium bromide (CTAB) and 1% ATP (w/w) had the best capacity for diesel removing. When the initial diesel concentration was 2 g L^-1, about 87.8% of diesel was removed by the immobilized LY-1 cells after 72 h. Immobilization of bacteria improves the ability of bacteria to survive in adverse environments. Immobilized LY-1 cells maintain the nature to remove diesel at high salinity or pH range of 6-9. Furthermore, the reusability of the LY-1 cells-immobilized PVA/SA/CTAB-ATP nanofiber membrane was tested. A diesel removal rate of 64.9% could be achieved after 4 times of use. PVA/SA/CTAB-ATP nanofibrous membranes with immobilized LY-1 cells are feasible, economical and environmentally friendly for remediation of diesel contamination in the aqueous medium, and have potential applications in the future.

Using PVA and Attapulgite for the Stabilization of Clayey Soil

Considering that, in the context of the ecological restoration of a large number of exposed rock slopes, it is difficult for existing artificial soil to meet the requirements of mechanical properties and ecological construction at the same time, this paper investigates the stabilization benefits of polyvinyl acetate and attapulgite-treated clayey soil through a series of laboratory experiments. To study the effectiveness of polyvinyl acetate (PVA) and attapulgite as soil stabilizer, a triaxial strength test, an evaporation test and a vegetation growth test were carried out on improved soil with different amounts of PVA content (0, 1%, 2%, 3%, and 4%) and attapulgite replacement (0, 2%, 4%, 6%, and 8%). The results show that the single and composite materials of polyvinyl acetate and attapulgite can increase the peak deviator stress of the sample. The addition of polyvinyl acetate can improve the soil strength by increasing the cohesion of the sample; the addition of attapulgite improves the soil strength mainly by increasing the internal friction angle of the sample. The strength of the composite is greatly improved by increasing the cohesion and internal friction angle of the sample at the same time. The effect of adding materials increased significantly with increasing curing age. Moreover, polyvinyl acetate and attapulgite improve the soil water retention of the soil by improving the water-holding capacity, so that the soil can still ensure the good growth of vegetation under long-term drought conditions. The scanning electron microscopy (SEM) images indicated that the PVA and attapulgite of soil affect the strength characteristics of soil specimens by the reaction of PVA and water, which changes the structure of the soil and, by the interweaving of attapulgite soil particles, acts as the skeleton of the aggregate. Overall, PVA and attapulgite can effectively increase clayey soil stability by improving the cohesive force and internal friction angle of clayey soil.

Adsorption Properties and Mechanism of Attapulgite to Graphene Oxide in Aqueous Solution

In order to remove toxic graphene oxide (GO) from aqueous solution, attapulgite (ATP) was used as adsorbent to recycle it by adsorption. In this paper, the effects of different pH, adsorbent mass, GO concentration, time and temperature on the adsorption of GO by attapulgite were studied, and the adsorption performance and mechanism were further explored by XRD, AFM, XPS, FTIR, TEM and SEM tests. The results show that when T = 303 K, pH = 3, and the GO concentration is 100 mg/L in 50 mL of aqueous solution, the removal rate of GO by 40 mg of attapulgite reaches 92.83%, and the partition coefficient K_d reaches 16.31. The adsorption kinetics results showed that the adsorption equilibrium was reached at 2160 min, and the adsorption process could be described by the pseudo-second-order adsorption equation, indicating that the adsorption process was accompanied by chemical adsorption and physical adsorption. The isotherm and thermodynamic parameters show that the adsorption of GO by attapulgite is more consistent with the Langmuir isotherm model, and the reaction is a spontaneous endothermic process. The analysis shows that attapulgite is a good material for removing GO, which can provide a reference for the removal of GO in an aqueous environment.

Novel preparation of attapulgite-reduced graphene oxide hydrogel composite and its application in flexible solid-state supercapacitors

After graphite oxide assisted the liquid phase shear exfoliation of attapulgite, the good dissociation and dispersion of attapulgite rod crystals are realized. Due to the spatial hindrance effect of attapulgite, which prevents the stacking of RGO sheets, the attapulgite-reduced graphene oxide three-dimensional porous hydrogel with abundant pore structure enables rapid transfer of electrolyte ions and exhibits good electrochemical performance and rate performance. The assembled flexible solid-state supercapacitor has a high operating voltage window and good flexibility and cycle stability. At a current density of 0.1 mA cm^-2, it has an area specific capacitance of 127.33 mF cm^-2. A series of solid-state supercapacitors can be used as the power supply for LED lights.

Converting Complex Sewage Containing Oil, Silt, and Bacteria into Clean Water by a 3D Printed Multiscale and Multifunctional Filter

The exacerbating water pollution and water resource shortage pose a great danger to human health and make it imperative to recycle and treat the sewage. In this study, a direct-writing three-dimensional (3D) printing technology was adopted to prepare a 3D sodium alginate (SA)/graphene oxide (GO)/Ag nanoparticle (AgNP) aerogel (SGA), aiming to turn the complex sewage containing oil, silt, and bacteria into clean water depending only on gravity separation. The physicochemical properties and surface structure of the synthesized SGA were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The swelling rate, mechanical properties, antibacterial properties, oil and water separation effect, and durable stability of the filter membrane were also investigated to verify the versatility of the SGA filter. The results showed that GO helped improve the mechanical properties of the printed filter to withstand water impact during the filtration process. The printed filter had a well-designed and multiscale gradient pore structure, which can effectively intercept particles with different sizes to separate the silt from water, and the turbidity of the filtered water can be reduced from 60 to 1 nephelometric turbidity unit (NTU). The presence of SA endowed the printed filter with hydrophilic and oleophobic behaviors, which can effectively separate various kinds of oils from water. The uniform distribution of AgNPs in the filter produced via a facile and green reduction of SA facilitated the efficient bactericidal ability of the printed filter during the filtration process; meanwhile, the lower release concentration of Ag ions ensured drinking safety. What is more, the filter can be easily produced on a large scale and used for different sewage treatment situations with a durable stability of over 30 days. Taken together, the printed SGA filter has a broad application prospect in complex sewage treatment, providing a special solution for sewage treatment in poverty areas.

Easily Fabricated Low-Energy Consumption Joule-Heated Superhydrophobic Foam for Fast Cleanup of Viscous Crude Oil Spills

Effective cleanup of viscous crude oil spills remains a persistent and crippling challenge. Herein, this work presents a Joule-heated superhydrophobic flower-like Cu₈(PO₃OH)₂(PO₄)₄·7H₂O-coated copper foam (SHB-CF@CP) for rapid cleanup of viscous crude oil spills via a facile strategy. The SHB-CF@CP shows outstanding water repellency and excellent stability of hydrophobicity in harsh environments. Due to the high electrical conductivity and thermal conductivity, it requires lower power energy consumption (less than 1 V of voltage input) to raise the temperature significantly, which dramatically reduces the viscosity of crude oil (from ∼2 × 10⁵ to ∼60 mPa s) and then increases the oil absorption rate, effectively avoiding the poor mobility and ineffective absorption of viscous crude oil. Notably, the SHB-CF@CP can achieve continuous and quick cleanup of crude oil under in situ pumping force. The high-performance Joule-heated SHB-CF@CP sorbent with a strong porous skeleton, corrosion resistance, and low predicted operational costs holds a promise of promoting its practical applications in the cleanup of intractable and large-area viscous oil spills.

Preparation of a rice straw-based green separation layer for efficient and persistent oil-in-water emulsion separation

Inefficiency, high cost, and complex operation have emerged as shackles for large-scale separate oil-in-water emulsion. Herein, a low-cost and eco-friendly separation layer with a rough structure and rich anionic groups was fabricated from rice straw (RS) via a simple acid-base treatment and slight squeeze process. The separation layer's morphology, composition, and wettability were investigated. It was then employed to separate oil-in-water emulsion. The RS after acid and alkali treatment (A₁A₂-RS) exhibited a clear fiber structure and abundant humps, which made the separation layer superwettable and highly electronegative (-26.55 mV). The overlapped and intertwined A₁A₂-RS layer structure owned a superior performance for hexadecyl-trimethyl-ammonium-bromide (CTAB) adsorption and tiny oil interception. As a result, the separation layer had stable fluxes (>500 LMH) for multiple CTAB-stabilized emulsions and the obtained filtrates performed low total organic carbon (TOC) contents (<30 mg/L). In addition, the A₁A₂-RS layer had excellent renewability (10 cycles/ 200 mL) and the flux could be substantially recovered merely by aqueous wash. Moreover, filtrate analysis showed that the A₁A₂-RS layer had a good effect on actual emulsion treatment with a TOC removal rate of 89.56%.

Toward Efficient Oil Energy Recovery: Eco-Friendly Fabrication of a Biomimetic Durable Metal Mesh with a Moss-Like Silver Nanocluster Structure

With the purpose of oil energy recovery as well as achieving efficiency of oil/water separation, hydrophobic mesh materials have attracted extensive attention. However, fabrication of the current methods is not environmentally friendly, has high energy consumption, and creates serious pollution. Inspired by lotus leaves and rose petals, a biomimetic superhydrophobic surface was fabricated prepared on a stainless steel mesh by an in situ chemical reduction method with simple operation and mild conditions. The results of SEM, XRD, and XPS demonstrated that the mesh shows a stable and uniform moss-like rough structured surface. The SSM/Ag/ODA mesh, which was modified by moss-like Ag nanoclusters and low surface energy agents, has excellent superhydrophobicity with an excellent oil/water separation efficiency that reached up to 99.8%. The silver mirror phenomenon formed by the Ag nanoclusters further confirmed that silver ions were reduced and attached to the surface of the mesh. Moreover, the mesh can maintain superhydrophobicity under harsh conditions, such as a high concentration of a salty solution, organic solvents, alkaline, acidic solution, and even long-time UV irradiation, etc. More importantly, the modified mesh has excellent physical stability, in which the water contact angle on the mesh can be maintained above 150° after harsh mechanical wear. The hydrophobic mesh showed great potential to be applied for highly efficient oil/water separation and oil energy recovery even under complex and harsh conditions.

Superhydrophobic Waste Cardboard Aerogels as Effective and Reusable Oil Absorbents

As the main component of the municipal waste, waste cardboard has caused a host of environmental problems. Therefore, the reasonable disposal of waste cardboard is of great significance to global sustainable development and green economics. Herein, using waste cardboard as the raw material, a superhydrophobic aerogel has been developed with a unique three-dimensional porous network structure, which exhibits excellent selective oil absorption capacities. The aerogel was made by combining Ca2+ cross-links and postmodification with stearic acid. Superhydrophobic aerogels can absorb various organic solutions and its maximum absorption capacity can reach 47 times its own weight. Meanwhile, the size of aerogels has been further expanded, with a diameter of 21.2 cm and a height of 3.2 cm, which can absorb 34 times its own weight of kerosene. More importantly, the aerogel can also absorb oil droplets in oil/water emulsions with an adsorption efficiency of over 98.5%. Moreover, the aerogel can be employed multiple times without significantly reducing the adsorption capacity via distillation or squeezing, depending upon the type of pollutions. Consequently, we believe that these facile and inexpensive superhydrophobic aerogels can effectively adsorb oily wastewater, which matches well with the requirement for environmentally friendliness from the perspective of practical application.

Superhydrophobic Poly(l-lactic acid) Membranes with Fish-Scale Hierarchical Microstructures and Their Potential Application in Oil-Water Separation

In this work, superhydrophobic poly(l-lactic acid) (PLLA) hierarchical membranes exhibiting excellent oil-removal performance, which is of great importance in curbing the oil-pollution environment, were fabricated by a simple solvent-evaporation-induced precipitation method. PLLA membranes with hierarchical micro/nanostructures (fish scales, fibrous sheets, and petal-like morphology) can be conveniently prepared by adjusting the preparation parameters including PLLA concentration, precipitation temperature, type of solvent and nonsolvent, and the addition of nano-SiO₂. The results show that the water contact angle of the fish-scale-structured PLLA membrane was 138.6°, revealing that water repellency was significantly improved compared to that of the solvent-casting PLLA membrane (∼72.8°). Moreover, the PLLA/SiO₂ nanocomposite membrane with a dense hierarchical micro/nanostructure had a water contact angle greater than 167.1°, which has great potential in oil-water separation.

Effective multi-functional biosorbent derived from corn stalk pith for dyes and oils removal

In this study, malic acid-modified corn stalk pith (MA-CSP) was prepared as an environmentally friendly multi-functional bio-sorbent for adsorbing of dyes and oils. The sorption capacity of the MA-CSP for single and binary dyes is 328.46 mg/g - 566.27 mg/g. In addition, the MA-CSP also had good sorption for lubricating oil, soybean oil, diesel oil, and isopropyl alcohol, which were 37.2 g/g, 44.1 g/g, 33.8 g/g, and 29.3 g/g, respectively. Physical and statistical models were used to analyze the adsorption behavior of methylene blue (MB) and crystal violet (CV). And its sorption behavior for dyes was also affected by the co-existing salts in water. The sorption mechanism of the dye was mainly electrostatic attraction and hydrogen bonding action. The sorption of oil was primarily via the role of van der Waals force and hydrophobic interaction. The MA-CSP, as an eco-friendly, economical and efficient multi-functional sorbent, holds promise for effective dyes and oil removal from contaminated water, and its application in other fields is also highly anticipated.

Surface Modification of Attapulgite by Grafting Cationic Polymers for Treating Dye Wastewaters

In this study, the cationic polymer poly-epichlorohydrin-dimethylamine was immobilized on natural attapulgite to improve the dye adsorption capacities. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscope (SEM) analysis, zeta potential analysis, and particle size analysis were used to determine the characteristics of modified attapulgite. Results showed that the poly-epichlorohydrin-dimethylamine had been successfully grafted onto the surface of attapulgite without altering its crystal structure. After cationic modification, the specific surface area of attapulgite obviously decreased, and its surface zeta potentials possessed positive values in the pH range from 3 to 11. The cation-modified attapulgite displayed high adsorption capacities for anionic dyes, and its maximum adsorption capacities were 237.4 mg/g for Reactive Black 5 and 228.3 mg/g for Reactive Red 239; this is corroborated by Langmuir’s isotherm studies. It was demonstrated that the two reactive dyes could be 100% removed from effluents when cation-modified attapulgite was used in column operation modes. Its treatment capacities were more than three times larger than that of activated carbon. The regeneration study verified better utilization and stability of the fabricated adsorbent in column operation. This work has conclusively confirmed the potential of the new modified attapulgite for effectively treating dye wastewaters.

Facile preparation of cotton fabric with superhydrophilicity–oleophobicity in air and superoleophobicity under water by using branched polyethyleneimine/perfluorooctanoic acid composites

Preparation of cotton fabric with superhydrophilicity-oleophobicity in the air and superoleophobicity under water by using branched polyethyleneimine/perfluorooctanoic acid composites and its application in gravity-controlled oil-water separation.

Continuous Movement Mechanism of Oil Droplets Adhered on Surfaces with Different Wettability in the Flow Field

In this aticle, the continuous movement patterns and characteristic parameters of oil droplets on surfaces with different wettability immersed in a laminar flow field were observed, and the change rules of the geometric parameters of oil droplets under different experimental conditions were obtained. Then, the factors influencing the continuous moving behaviors of the oil droplets were analyzed, and the continuous movement velocity of the oil droplets under different experimental conditions was demonstrated. On this basis, the change law of the continuous movement velocity of oil droplets with the flow velocity was discussed. In addition, the coupling effect of the oil drops' height, surface properties, and water flow velocity on the continuous movement of oil droplets was studied, and the critical conditions for the continuous movement were obtained. According to the critical conditions, the mathematical model which described the law of continuous motion of the oil droplets adhered on surfaces with different wettability in the laminar flow field was established. The quantitative relationships among the average continuous moving velocity of oil droplets, physical properties, geometric parameters, water flow velocity, and surface wettability were obtained, which defined the necessary conditions for the uniform and accelerated movement of oil droplets, providing an important basis for choices of suitable surface wettability and flow field conditions in practical engineering applications.

Robust and continuous oil/water separation with superhydrophobic glass microfiber membrane by vertical polymerization under harsh conditions

We report a robust and continuous oil/water separation with nanostructured glass microfiber (GMF) membranes modified by oxygen plasma treatment and self-assembled monolayer coating with vertical polymerization. The modified GMF membrane had a nanostructured surface and showed excellent superhydrophobicity. With an appropriate membrane thickness, a high water intrusion pressure (< 62.7 kPa) was achieved for continuous pressure-driven separation of oil/water mixtures with high flux (< 4418 L h-1 m-2) and high oil purity (> 99%). Under simulated industrial conditions, the modified GMF membrane exhibited robust chemical stability against strong acidic/alkaline solutions and corrosive environments. The proposed superhydrophobic composite coating technique is simple, low cost, environmentally friendly, and suitable for the mass production of scalable three-dimensional surfaces. Moreover, its stability and customizable functionality offers considerable potential for a wide range of novel applications.

Facile Fabrication of Marine Algae-Based Robust Superhydrophobic Sponges for Efficient Oil Removal from Water

Water pollution caused by oil spillages has aroused worldwide attention. Therefore, it is of great significance to develop low-cost, environmentally friendly materials to remove oil contaminants from water. Herein, a "green" superhydrophobic sponge made from marine algae was fabricated by one-step growth of silicone nanofilaments onto a AgNP-decorated alginate sponge via chemical vapor deposition of an azeotrope of (CH₃)₃SiCl and SiCl₄. The reaction of the azeotrope with the alginate sponge was termed "instant", as it took only a few minutes (5 min) at room temperature to achieve superhydrophobicity (152.0°). Such sponges resist high temperatures, UV irradiation, organic solvents, and mechanical abrasion without losing the superhydrophobicity. The sponges absorbed oil droplets within seconds (1.3-7.0 s) with 11.7-17.1 g/g of sorption capacities for oils of different viscous levels (0.56-1775.00 mPa·s). These sponges could retain 90% of the initial oil sorption capacities after 10 consecutive oil sorption/desorption cycles. Benefiting from the superhydrophobicity and superoleophilicity, the sponges also exhibited high efficiency in oil/water mixture separation. Once the oil/water mixture was injected into the sponge, oil drops were retained in inner pores while water was rejected and spouted from the surface. These excellent performances make the resultant sponge a competitive material for oil spill emergency remediation.

Efficient separation of crude oil-in-water emulsion based on a robust underwater superoleophobic titanium dioxide-coated mesh

Robust underwater superoleophobic TiO₂-coated meshes were used for the separation of crude oil-in-water emulsion and photocatalytic degradation.

A facile surface modification of a PVDF membrane via CaCO3 mineralization for efficient oil/water emulsion separation

A facile modification of a PVDF membrane using CaCO₃ inorganic particles via a layer-by-layer self-assembly process for efficient oil/water separation.