Ruiyang Zhang

Graphene–carbon nanotube aerogel as an ultra-light, compressible and recyclable highly efficient absorbent for oil and dyes

Carbon nanotubes (CNTs) have good toughness and hydrophobicity. The embedding of CNTs into a graphene aerogel (GA) network could modify various properties of the GA. In this work, we report a facile and green approach to synthesize graphene–CNT aerogels (GCAs) by a one-step hydrothermal redox reaction. The prepared aerogels possess ultra-light densities ranging from 6.2–12.8 mg cm−3. The incorporation of CNTs into the GA could not only improve the morphologies, specific surface areas and hydrophobic properties but also enhance the adsorption capacity and mechanical properties of the GA. Under optimized GO/CNT mass ratio (7 : 1 and 3 : 1) conditions, adsorption capacities 100–270 times of their own weight could be achieved depending on the density of the adsorbed organics. The same trend also appeared in the adsorption of dyes including methylene blue (MB) and methyl orange (MO). Especially, the obtained GCAs exhibited excellent reusability and mechanical strength on the basis of absorption–combustion and adsorption–squeezing experiments. Even after 10 cycles, the macroscopic shape of the aerogels is well kept and almost no decrease in adsorption capacity was observed. Based on the facile preparation process, high adsorption capacity and stable cyclic performance, the GCAs could have promising widespread applications in practical water purification and oil remediation.

Three-dimensional MoS 2 /reduced graphene oxide aerogel as a macroscopic visible-light photocatalyst

Abstract Photocatalysis is regarded as an ideal technology for solving the urgent environmental and energy issues that we face today. Among the reported photocatalysts, molybdenum disulfide (MoS 2 ) is very promising for applications in hydrogen production and pollutant photodegradation. However, its lack of active sites and the difficulty of recovering catalysts in powder form have hindered its wide application. Here, we report the successful preparation of a macroscopic visible-light responsive MoS 2 /reduced graphene oxide (MoS 2 /RGO) aerogel. The obtained MoS 2 /RGO aerogel exhibits enhanced photocatalytic activity towards hydrogen production and photoreduction of Cr(VI) in comparison with the MoS 2 powder. In addition, the low density (56.1 mg/cm 3 ) of the MoS 2 /RGO aerogel enables it to be used as an efficient adsorption material for organic pollutants. Our results demonstrate that this very promising multifunctional aerogel has potential applications in environmental remediation and clean energy production.

Hydrothermal formation of graphene aerogel for oil sorption: the role of reducing agent, reaction time and temperature

Graphene aerogels (GAs) are widely studied in the oil contamination field in recent years. Among the preparation approaches, hydrothermal treatment employing a certain reducing agent has attracted much attention owing to the environmentally friendly and facile synthesis process. In this work, we systematically investigate the effects of various reducing agents including ammonia, ethanediamine (EDA) and vitamin C (VC) at different hydrothermal temperatures (80, 100, 120, 140, 160 and 180 °C) and reaction times (4, 8, 12, 16, 20 and 24 h) on the density, specific surface area (SSA), strength, morphology and adsorption performance of GAs. The results reveal that GAs reduced by VC possess the most outstanding performance for mechanical strength and re-utilization but have poor adsorption capacity (Qwt), whereas the sample obtained with ammonia exhibits the highest Qwt for both lube (160 g g−1) and n-hexane (105 g g−1). However, this sample not only reveals the worst mechanical strength which leads to a sharp decrease of the Qwt during the adsorption–squeezing experiments, but GA reduced by ammonia is also very sensitive to the reaction time and temperature. Therefore, EDA is a very promising reducing agent for the hydrothermal process as the resulting GA can maintain a high Qwt and reveals a wide hydrothermal preparation window.

Monolithic aerogel photocatalysts: a review

Photocatalysis has been considered as one of the most promising technologies for solving environmental pollution and energy crisis. However, photocatalysts in the powder form usually suffer from the strong tendency to agglomerate and intricate operation for recycling, which significantly limit their practical application. In comparison, monolithic aerogel photocatalysts with their highly macroscopic operability and recoverability as well as impressive specific surface area have attracted tremendous attention in recent years. With the development of synthesis technology, the types of aerogel photocatalysts have broadened from traditional oxide and chalcogenide aerogels to the current composite aerogels. Meanwhile, their application has also spread from primary physical adsorption to the present photochemical reactions including environmental remediation and clean energy production. In this review, the different synthesis strategies and photocatalytic applications of aerogel photocatalysts have been discussed. We summarize the currently available synthesis methods and widespread applications of aerogel photocatalysts. In particular, we highlight recent developments for the assembling of aerogel photocatalysts by direct synthesis and grafting photocatalysts to aerogel supports, as well as updated applications on the removal of aqueous pollutants, water splitting and gas phase photocatalysis. Finally, we outline the challenges and potential advances associated with the aerogel photocatalysts for future scientific research and commercial applications.

Controllable and green synthesis of robust graphene aerogels with tunable surface properties for oil and dye adsorption

Recently, graphene aerogels (GAs) with abundant pores, ultra-light density and excellent adsorption capacity have been regarded as promising high efficiency oil/water and dye/water separation materials and attracted much attention for water remediation. However, the green and controllable synthesis of GAs with tunable surface properties and high mechanical strength remains a challenge. In this work, we develop a facile hydrothermal method using vitamin C (VC) as a green reducing agent. It is found that VC ensures high mechanical strength while the surface hydrophobicity can be easily controlled at different pH values. The hydrophobic and robust GA obtained at pH 5 demonstrates outstanding oil–water separation capabilities in both non-turbulent and turbulent oil–water mixtures under continuous adsorption, whereas the hydrophilic GA obtained at pH 11 shows excellent dye–water separation performance. This artificial controllable strategy for the modification of GAs with expected properties paves a promising route to develop GAs for various applications.

Compressible and Recyclable Monolithic g-C3N4/Melamine Sponge: A Facile Ultrasonic-Coating Approach and Enhanced Visible-Light Photocatalytic Activity

Powdery photocatalysts seriously restrict their practical application due to the difficult recycle and low photocatalytic activity. In this work, a monolithic g-C3N4/melamine sponge (g-C3N4/MS) was successfully fabricated by a cost-effective ultrasonic-coating route, which is easy to achieve the uniform dispersion and firm loading of g-C3N4 on MS skeleton. The monolithic g-C3N4/MS entirely inherits the porous structure of MS and results in a larger specific surface area (SSA) than its powdery counterpart. Benefit from this monolithic structure, g-C3N4/MS gains more exposed active sites, enhanced visible-light absorption and separation of photogenerated carriers, thus achieving noticeable photocatalytic activity on nitric oxide (NO) removal and CO2 reduction. Specifically, NO removal ratio is as high as 78.6% which is 4.5 times higher than that of the powdery g-C3N4, and yield rate of CO and CH4 attains 7.48 and 3.93 μmol g−1 h−1. Importantly, the features of low-density, high porosity, good elasticity, and firmness, not only endow g-C3N4/MS with flexibility in various environmental applications, but also make it easy to recycle and stable for long-time application. Our work provides a feasible approach to fabricate novel monolithic photocatalysts with large-scale production and application.

Superhydrophobic, mechanically flexible and recyclable reduced graphene oxide wrapped sponge for highly efficient oil/water separation

Water pollution has become an urgent issue for our modern society, and it is highly desirable to rapidly deal with the water pollution without secondary pollution. In this paper, we have prepared a reduced graphene oxide (RGO) wrapped sponge with superhydrophobicity and mechanically flexibility via a facile low-temperature thermal treatment method under a reducing atmosphere. The skeleton of this sponge is completely covered with RGO layers which are closely linked to the skeleton. This sponge has an abundant pore structure, high selectivity, good recyclability, low cost, and outstanding adsorption capacity for floating oil or heavy oil underwater. In addition, this sponge can maintain excellent adsorption performance for various oils and organic solvents over 50 cycles by squeezing, and exhibits extremely high separation efficiencies, up to 6 × 106 and 3.6 × 106 L·m–3·h–1 in non-turbulent and turbulent water/oil systems, respectively. This superhydrophobic adsorbent with attractive properties may find various applications, especially in large-scale removal of organic contaminants and oil spill cleanup.