Just as graphene triggered a new gold rush, three-dimensional graphene-based macrostructures (3D GBM) have been recognized as one of the most promising strategies for bottom-up nanotechnology and become one of the most active research fields during the last four years. In general, the basic structural features of 3D GBM, including its large surface area, which enhances the opportunity to contact pollutants, and its well-defined porous structure, which facilitates the diffusion of pollutant molecules into the 3D structure, enable 3D GBM to be an ideal material for pollutant management due to its excellent capabilities and easy recyclability. This review aims to describe the environmental applications and mechanisms of 3D GBM and provide perspective. Thus, the excellent performance of 3D GBM in environmental pollutant adsorption, transformation and detection are reviewed. Based on the structures and properties of 3D GBM, the removal mechanisms for dyes, oils, organic solvents, heavy metals, and gas pollutants are highlighted. We attempt to establish "structure-property-application" relationships for environmental pollution management using 3D GBM. Approaches involving tunable synthesis and decoration to regulate the micro-, meso-, and macro-structure and the active sites are also reviewed. The high selectivity, fast rate, convenient management, device applications and recycling utilization of 3D GBM are also emphasized.

The pH-dependent adsorption of perchlorate (ClO4(-)) by wood-derived biochars produced at 200-700 °C (referred as FB200-FB700) was investigated to probe the anion retention mechanisms of biochars and to identify the interactions of water and biochar. ClO4(-) adsorption was controlled by the surface polarities and structural compositions of the organic components of biochars, rather than their inorganic mineral components. FB500-FB700 biochars with low polarity and high aromaticity displayed a superior ClO4(-) adsorption capacity, but which was affected by solution pH. Besides electrostatic interaction, hydrogen bonding to oxygen-containing groups on biochars was proposed the dominant force for perchlorate adsorption, which led to the maximum adsorption occurring near pHIEP, where surface charge equals zero. The dissociation of these surface oxygen-containing groups was monitored by zeta potential curves, which indicated that the H-bonds donors on biochar surface for ClO4(-) binding were changed from -COOH (ClO4(-)···HOOC-) and -OH (ClO4(-)···HO-) to -OH alone with an increase in pH. The H-bond force was strengthened by the condensed aromatic surfaces, since high temperature biochars provided a hydrophobic microenvironment to accommodate weakly hydrated perchlorate and facilitated the H-bonds for ClO4(-) binding to functional groups by the large π subunit of their aromatic substrate. Lastly, the batch and column tests of ClO4(-) adsorption showed that biochars like FB700 are effective adsorbents for anion pollutant removal via H-bonding interaction.

No abstract

Solar steam generation is considered to be a promising strategy for sustainable clean water supply. An easily made and robust solar still can practically meet any contingency in wilderness survival, compared to high-cost and delicate solar thermal materials, for example, plasmonic metals, carbon nanotubes, or graphene-based materials. Inspired by rice plants with high transpiration, we develop a universal solar steam-generation device from wasted rice straw for robust clean water production. The upper leaves of rice straw are carbonized and composited with bacterial cellulose to function as a superior light absorber and the lower culms are designed as excellent water pumps. The unique capillary structures and multilevel geometrical structures of the rice culms contribute to their outstanding water pumping capacity for surface evaporation, resulting in an evaporation rate of 1.2 kg m–2 h–1 with 75.8% conversion efficiency. The rice straw-derived solar still has a daily clean water yield of 6.4–7.9 kg m–2 on sunny days and 4.6–5.6 kg m–2 on cloudy days over 14 days of operation. More attention-grabbing aspect is that this evaporation device is applicable to various water-bearing media, for example, sand, soil, and seawater, to collect clean water with a stable evaporation performance, and the unique multilevel structures of the culms make great contribution to the unimpeded water channels. By turning “waste” to “wealth,” this project shines significant light on a facilely fabricated, robust, and efficient solar still, especially designed for urgent priority in wilderness survival.

develop next-generation anode materials. [3] Of all possible candidates, lithium metal anode is considered as the ultimate one, owing to its highest theoretical specific capacity (3860 mA h g −1 ), lowest negative electrochemical potential, and light weight. [4] In fact, Li metal anode was commercialized decades ago, but severe safety issue induced by inevitable lithium dendrite growth led to the fading of public concern. Now, current Li-ion batteries are approaching their limitation of energy density based on "rocking-chair" energy storage mechanism. Thus, the research interests in Li metal anodes reemerge in recent years due to the urgent requirement for high energy density Li-ion batteries. [5] For Li metal anodes, repeated charge/ discharge processes induce severe dendrite formation and volume expansion, which impedes the release of its theoretical capacity and causes rapid capacity decay and potential safety hazard. During past decades, three main strategies have been established and employed to solve these problems: (1) developing new electrolytes to form stable solid electrolyte interphase (SEI); [6] (2) manipulating surface roughness of Li foil; [7] (3) SEI stabilization by well-designed nanostructures, such as carbon shell [8] and insulating 3D porous matrix. [9] Although valuable progresses have been achieved, few researches concern about structure design of Li metal itself. In previous researches, nearly all reported Li anodes were based on Li foil with planar morphology, which provided extremely limited reaction sites for Li ions. Consequently, dendrite growth and volume expansion are easily initiated. [10] According to Sand's time model, Chazalviel indicated that concentration of Li ions will go to zero near surface of bulk Li anode at high current densities, [11] leading to initial nucleation of lithium dendrite and formation of dead Li during cycling (Figure 1a-c). In contrast, 3D porous construction of Li metal anode can enormously increase the surface area, which dissipates the high current densities to low local ones. [12] Meanwhile, porous microstructures are beneficial for uniform distribution of Li ions to prolong Sand's time. [13] Moreover, 3D construction provides more nucleation sites which serve as charge centers for creating less local space charge to delay initiation of nucleation. Also, the plating of Li ions taking place on the inner surface of 3D Li anode overwhelms that on the outer surface, which not only alleviates the dimension change but also eliminates the surface dendrite growth of Li metal anodes

No abstract

Self-assembly based on graphene building blocks are an important strategy for three-dimensional (3D)architectures, but their fabrication and application in water purification remain challenging. Here, we report a facile one-step approach to prepare 3D graphene oxide (GO) hydrogels and aerogels containing nanoscaled layered double hydroxides (LDHs). The LDHs acted as cross-linking agent molecules ("buttons") to join GO nanosheets into a 3D network via charge-assisted hydrogen bonds and latticelattice cation-p interactions. The resultant aerogels exhibited high hydrophilicity and excellent structural stability/plasticity in water environments, which guarantee the availability of their effective active sites in aqueous solution and overcome the utilization restrictions of neat GO aerogels due to their fragile morphology. The obtained LDH + GO aerogels showed a high capability for removal of dye (methylene blue) and heavy metal (Cd 2+ ) pollutants from water. The addition of LDH nanoparticles assisted the aerogels in maintaining their 3D monoliths and made it easy for separation and collection after use, and improved the adsorption capacities for environmental pollutants via reducing the stacking of GO sheets and exposing more active adsorption sites. Thus the obtained LDH + GO aerogels have a great potential for water purification as highly efficient and stable adsorbents.

Interfacial solar steam generation is a green and promising technique to capture solar energy for brine water desalination; however, it still faces grand challenges of thermal loss and salt fouling to promote the practical application with high performance and durability. In this study, we report that activated carbon fiber cloth (ACFC) with hierarchical microstructures shows superior light-thermal property for solar steam generation. A well-matching water supply path manipulated by cotton fiber nonwoven fabrics (CFNF) can bring about a high evaporation rate of 1.59 kg m–2 h–1 with optimum conversion efficiency of 93.3% under 1 sun. Rate matching between the water supply and vapor evaporation is revealed to be of great importance to full heat exploitation and efficient solar desalination. Moreover, the extra water supply pathway provided by CFNF completely eliminates the salt fouling phenomenon via timely salt dredging, guaranteeing the durability of the self-cleaning solar steam generation system. Thus, the appropriate ACFC+CFNF configuration shows its great potential application in durable and highly efficient solar desalination.