Large Adsorption Capacity for Space Molecular Pollutants Realized by a Metal-Organic Framework.

The rapid development of capable spacecraft coatings for removing volatile organic compounds (VOCs) demands materials with a large adsorption capacity to ensure a long-duration exploration mission in a low Earth orbit (LEO). MIL-53(Al) with abundant sites exhibits resistance to the space environment in the LEO and shows great potential for VOC removal. This study combined an adsorption experiment and first-principles simulations to investigate the adsorption performance of MIL-53(Al). MIL-53(Al) demonstrated an excellent adsorption capacity for various VOCs, reaching 606.04 mg/g for m-xylene and 22.69 cm3/g for methane, which is 6 times higher than traditional adsorption methods. First-principles simulations revealed that the adsorption capacity is significantly influenced by micropores through the pore effect and breath effect, which restrict diffusion and enhance adsorption, respectively. Additionally, we predicted the adsorption properties of VOCs that are difficult to characterize through ground-based simulated experiments, further validating the potential application of MIL-53(Al) for VOC removal in the LEO. This work expands the application range of MIL-53(Al), optimizes VOC removal strategies, and offers a novel approach to protecting spacecraft in the LEO. Our findings contribute to the development of advanced materials for space exploration and provide valuable insights into the design of efficient VOC removal systems for spacecraft in the LEO.

A long-term oxidation barrier for copper nanowires: graphene says yes.

Copper nanowires (Cu NWs) hold great promise for the fabrication of low-cost transparent electrodes. However, the instability of Cu NWs has limited their application into commercial devices. Herein, CVD-grown graphene is transferred onto Cu NW films and the stability of the hybrid films over long time scale under different conditions is investigated systematically. The results reveal that the graphene-Cu NW films can maintain their efficacy (R/R0 < 2) after 180 days of exposure in an ambient atmosphere. Furthermore, a two-step oxidation kinetic mechanism of Cu NWs can be proposed by using Raman and X-Ray photoelectron spectroscopy. The protecting mechanism of graphene on Cu NW films is disclosed to preventing the oxygen species permeation, decelerating the oxidation from Cu to Cu2O and hindering the oxidation of Cu2O to CuO. These results are of referring significance to make metal nanowire based transparent electrodes with both high optical-electrical performance and excellent stability.

A symmetrical bi-electrode electrochemical technique for high-efficiency transfer of CVD-grown graphene.

Graphene transfer is a critical process in the journey from CVD-grown graphene to device application. The current transfer techniques use a chemical-etching method to oxidize the metal catalyst, which is heavily time-consuming and involves a high material cost. In this study, a highly efficient symmetrical bi-electrode technique has been developed to simultaneously delaminate the CVD-grown graphene from the metal catalyst at both the anode and cathode of the electrolytic cell. Raman spectra, UV-visible transmittance, and four-probe measurements confirm that this transfer process is nondestructive and can produce similar electrical properties to those produced by the conventional metal-etching transfer method. This bi-electrode transfer technique possesses the advantages of high efficiency, recyclable use of metal catalyst, and high electrical conductivity, and it can be potentially applied for industrial applications.

A facile method to observe graphene growth on copper foil.

A novel scanning electron microscope (SEM) method is presented for high contrast identification of each layer of pyramidal graphene domains grown on copper. We obtained SEM images by combining the advantages of the high resolution property of the secondary electron signal and the elemental sensitivity of the backscattering electron signal. Through this method, we investigated the difference in the growth mechanisms of mono-layer and few-layer graphene. Due to different lattice mismatches, both the surface adsorption process and the epitaxial growth process existed under the atmospheric growth conditions. Moreover, the copper oxidation process can be easily discovered. It is obvious from the SEM images that the graphene greatly delayed the oxidation process of the copper surface. Finally, the nucleation and growth speed of graphene domains was found to depend on the linear array distribution of surface ledges and terraces of annealed rolled copper foil. This result explains the linear rows of graphene during the growth process and accords with theoretical results.

Synergistic oxygen vacancy-rich CuO/visible light activation of peroxymonosulfate for degradation of rhodamine B: fast catalyst synthesis and degradation mechanism.

This work outlines the synthesis of copper oxide nanoparticles (CuO-SC) loaded with a number of oxygen vacancies by a fast sodium citrate assisted precipitation method with no need of calcination. X-ray diffraction, scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy, time-resolved fluorescence lifetime and electrochemical impedance spectra were used to characterize the as-synthesized nanocomposites. The results indicated that the CuO-SC nanoparticles had regular fusiform shape with high surface area, wide light harvesting window, fast charge transport and high carrier concentration. As a result, the catalytic activity of the CuO-SC/peroxymonosulfate (PMS)/visible light (Vis) system for the degradation of rhodamine B (RhB) was much higher than that of as-prepared CuO nano powder in the absence of sodium citrate. Almost 98.0% of the initial RhB dyes was decomposed in 20 min with 0.12 g L-1 PMS and 0.3 g L-1 catalyst. Meantime, it exhibited high catalytic stability with little deactivation after four runs and a wide application range of pH. Moreover, RhB can be readily degraded with backgrounds of Cl-, NO3 -, SO4 2-, HCO3 - and low concentration of humic acid in a CuO-SC/PMS/Vis system. Combined with the results of electron spin resonance paramagnetic spectroscopy, X-ray photoelectron spectroscopy and radical quenching experiments, holes, superoxide radicals and a small amount of sulfate radicals, hydroxyl radicals and singlet oxygen were involved in the CuO-SC/PMS/Vis system. Furthermore, a possible degradation mechanism based on the synergistic effect of radical reaction and non-radical reaction was proposed based on the above results.

Fly ash derived calcium silicate hydrate as a highly efficient and fast adsorbent for Cu(ii) ions: role of copolymer functionalization.

The environmental issues caused by heavy metal accumulation from polluted water are becoming serious and threaten human health and the ecosystem. The adsorption technology represented by calcium silicate hydrate has attracted much attention, but suffers from high manufacturing costs and poor stability bottlenecks. Here, we have proposed a "trash-to-treasure" conversion strategy to prepare a thin sheet calcium silicate hydrate material (ACSH) using solid waste fly ash as silicon source and a small amount of Acumer2000 as modifier. The obtained materials showed fast adsorption rates, superior adsorption capacities and remarkable long-term stability for Cu(ii) removal. Under the conditions of 0.5 g L-1 adsorbent concentration and 100 mL Cu(ii) solution with a concentration of 100 mg L-1, ACSH can adsorb 95.6% Cu(ii) within 5 min. The adsorption isotherms conformed to Langmuir models and the maximum adsorption capacity was 532 mg g-1. Using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, specific surface area and pore structure analysis, it was found that the excellent adsorption performance could be attributed to the ultrahigh surface area (356 m2 g-1), abundant pores and multiple active sites induced by Acumer2000 modification. Moreover, the encapsulation effect from carboxylate and long carbon chains in Acumer2000 endowed modified samples with strong corrosion resistance to CO2, which effectively inhibited the formation of by-product CaCO3 and retained the remarkable adsorption performance for more than 100 days. Interestingly enough, the advantages of ACSH in economy and performance could been maintained in ACSH based adsorptive membranes. This work is of great significance for solid waste utilization as well as the preparation of high quality, cost-effective and long-term stability calcium silicate hydrate materials.

Stable Nafion-functionalized graphene dispersions for transparent conducting films.

Nafion was used for the first time to aid in preparing stable graphene dispersions in mixed water/ethanol (1:1) solvents via the reduction of graphite oxide using hydrazine. The dispersion was characterized by ultraviolet-visible (UV-vis) spectra, transmission electron microscopy, zeta potential analysis, etc. It was found that for Nafion-to-graphene ratios higher than 5:1, graphene solutions with concentrations up to 1 mg ml(-1) and stabilities of over three months were obtained. It was proposed that the Nafion adsorbed onto the graphene by the hydrophobic interaction of its fluoro-backbones with the graphene layer and imparted stability by an electrosteric mechanism. Furthermore, transparent and conductive films were prepared using these highly stable Nafion-stabilized graphene dispersions. The prepared Nafion-graphene films possess smooth and homogeneous surfaces and the sheet resistance was as low as 30 kOmega/sq for a transmittance of 80% at 550 nm, which was much lower than for other graphene films obtained by chemical reduction. X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the p-doping of the graphene by Nafion. It was expected that this p-doping effect, as well as the high dispersing ability of Nafion for graphene and the connection of the sp(2) domains by residual Nafion combined to produce good properties of the Nafion-graphene films.

Solvent Effect on the Solvothermal Synthesis of Mesoporous NiO Catalysts for Activation of Peroxymonosulfate to Degrade Organic Dyes.

In this work, we successfully prepared three different mesoporous NiO nanostructures with preferential (111) planes using three different solvents-water, a water-ethanol mixture, and a water-ethylene glycol mixture. The NiO nanosheets prepared from the water-ethylene glycol mixture and denoted as NiO-EG showed a nanosheet morphology thinner than 10 nm, whereas the water-ethanol and water samples were 30-40 nm and above 100 nm thick, respectively. The NiO-EG catalyst was found to exhibit a high catalyzing ability to activate peroxymonosulfate (PMS) for decoloring dyes, by which 94.4% of acid orange 7 (AO7) was degraded under the following reaction conditions: AO7 = 50 mg/L, catalyst = 0.2 g/L, PMS = 0.8 g/L, pH = 7, and 30 min reaction time. The dye degradation rate was investigated as a function of the catalyst dosage, pH, and dye concentration. According to quenching experiments, it was found that SO4 •-, HO•, and O2 •- were the dominant radicals for AO7 degradation, and oxygen vacancies played a significant role in the generation of radicals. High surface area, thin flaky structure, rich oxygen vacancies, fast charge transport, and low diffusion impedance all enhanced the catalytic activity of NiO-EG, which exhibited the highest degradation ability due to its abundant accessible active sites for both adsorption and catalysis.

Synthesis of AuPd nanoparticle-decorated graphene-coated ZnO nanorod arrays with enhanced photoelectrochemical performance and stability.

AuPd nanoparticle-decorated graphene-coated ZnO nanorod (ZNR) array electrodes (ZNR@Gr/AuPd) were synthesized via electrostatic self-assembly followed by solution reduction methods. The morphologies of ZNR@Gr/AuPd were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), which indicated that ZNR was well-coated by graphene with 3-5 layers and uniformly decorated with AuPd nanoparticles (about 5 nm). UV-Vis diffuse reflectance and photoluminescence spectra were obtained to analyze the optical properties. The photoelectrochemical (PEC) properties were also evaluated; the results indicated that the photocurrent density was 2.27 mA cm-2 at 0.8 V versus Ag/AgCl, which was 7.1 times that of bare ZNR. The sample also displayed enhanced PEC stability (91.3%), which prevented photocorrosion. Finally, a proposed PEC mechanism of ZNR@Gr/AuPd was illustrated to explain the charge transfer and the role of graphene and AuPd nanoparticles in the improvement of PEC performance and stability. The ZNR@Gr/AuPd electrode shows excellent PEC performance and stability, exhibiting promising potential in the generation of H2.

Influence of the coexisting contaminants on bisphenol A sorption and desorption in soil.

The effects of different heavy metals (Cd, Pb), surfactants (cetyltrimethylammonium bromide (CTAB), cetylpyridine chloride (CPC)) and the ionic strength (Ca2+, NH4+) on breakthrough curves (BTCs) for sorption and desorption of bisphenol A (BPA) were studied using soil column experiment. Results showed that the presence of heavy metals and cationic surfactants caused a significant increase on the BPA sorption. In addition, the volume required when effluent concentration reached half of the influent concentration (VC1/2) increased due to the introduction of heavy metals and surfactants. It was also found that the larger amount of BPA was absorbed with higher ionic strength. The cationic surfactants enhanced the desorption ability of BPA from the soil. The results provided a better understanding of BPA behavior in environment and facilitated more accurate assessment of its ecological risk and identification of appropriate management strategies.

Influence of the presence of heavy metals and surface-active compounds on the sorption of bisphenol A to sediment.

The effects of different heavy metals (Cd, Pb), cationic surfactants cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecylbenzenesulfonate (SDBS) and the chemistry of the solution (pH and ionic strength) on the sorption of bisphenol A (BPA) to sediment were studied. Results showed that the presence of Cd and Pb caused a significant increase on the sorption of BPA to sediment and the sorption isotherms were in good agreement with Freundlich equation. The effect of surfactants on the adsorption of BPA onto sediment was found to strongly depend on the type of the surfactants. The presence of CTAB promoted BPA sorption and the amount of BPA adsorbed onto sediment increased linearly with concentration of CTAB. In contrast, the presence of anionic surfactant (SDBS) caused a slight reduction on the sorption of BPA. It was also found that the sorption behavior of BPA was affected by solution pH and ionic strength. The larger amount of BPA was absorbed with higher ionic strength and lower pH. This study may provide important insights into the understanding of the transport and fate of BPA in the environment.

Free-standing and binder-free lithium-ion electrodes based on robust layered assembly of graphene and Co3O4 nanosheets.

Free-standing and binder-free Co3O4/graphene films were fabricated through vacuum filtration and thermal treatment processes, in which sheet-like Co3O4 and graphene were assembled into a robust lamellar hierarchical structure via electrostatic interactions. The morphological compatibility coupled with strong interfacial interactions between Co3O4 and graphene significantly promoted the interfacial electron and lithium ion transport. When used as a binder-less and free-standing electrode for lithium-ion batteries, the hybrid film delivered a high specific capacity (~1400 mA h g(-1) at 100 mA g(-1) based on the total electrode weight), enhanced rate capability and excellent cyclic stability (~1200 mA h g(-1) at 200 mA g(-1) after 100 cycles). This effective strategy will provide new insight into the design and synthesis of many other composite electrodes for high-performance lithium-ion batteries.

Effective post treatment for preparing highly conductive carbon nanotube/reduced graphite oxide hybrid films.

SWCNT-reduced graphite oxide hybrid films were prepared by a filtration method. An efficient post-treatment procedure was designed to reduce GO and remove dispersants simultaneously. The sheet resistance decreased significantly after treatment, by a factor of 4-13 times. Films with excellent performance (95.6%, 655 Ω per square) were obtained and had great potential applications.

Humic Acid fouling mitigation by antiscalant in reverse osmosis system.

The mitigation of humic acid (HA) fouling on reverse osmosis (RO) membrane was investigated by using an environmentally benign antiscalant, polyaspartic acid (PASP). In the presence of PASP, HA fouling decreased with increasing Ca(2+) concentration. This positive effect of Ca(2+) was not due to the electrostatic repulsion as measured by zeta potential, but probably due to the formation of a stable water-soluble complex HA-Ca-PASP through Ca(2+) bridging. Fouling inhibition efficiency phi increased with increasing PASP concentration, but overdosing could lead to an adverse effect. At higher feedwater pH, HA fouling was alleviated and the phi was slightly improved. HA fouling increased when increasing initial permeate flux and decreasing cross-flow velocity, but the fouling behaviors became less susceptible to the two hydrodynamic parameters in the presence of PASP. The phi was hardly affected by the initial permeate flux and the cross-flow velocity. HA fouling decreased with decreasing feed temperature in the presence of PASP, likely owing to the improved stability of HA-Ca-PASP at lower temperature. The implication of this paper is that it presented an attractive and feasible approach for organic fouling control in RO system by dosing antiscalant.

Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM.

The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been studied in two heat transfer systems: recirculating cooling water and pool boiling systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasing fluid velocity for the cooling water system, whereas in the presence of inhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decreases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results show that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FTIR analyses demonstrate that for the CaCO(3) formed in the pool boiling system, the content of vaterite increases with the increase of inhibition effects. The metastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. The step morphology has been observed by atomic force microscopy. It is shown that the step space on the CaCO(3) surface increases in the presence of inhibitors. Moreover, with the increase in inhibition effect, both the step space and the fractal dimension increase. Step bunching is also found and discussed in this paper. Copyright 2001 Academic Press.