We demonstrated high-performance gas sensors based on graphene oxide (GO) sheets partially reduced via low-temperature thermal treatments. Hydrophilic graphene oxide sheets uniformly suspended in water were first dispersed onto gold interdigitated electrodes. The partial reduction of the GO sheets was then achieved through low-temperature, multi-step annealing (100, 200, and 300 degrees C) or one-step heating (200 degrees C) of the device in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally-reduced GO showed p-type semiconducting behavior in ambient conditions and was responsive to low-concentration NO2 and NH3 gases diluted in air at room temperature. The sensitivity can be attributed mainly to the electron transfer between the reduced GO and adsorbed gaseous molecules (NO2/NH3). Additionally, the contact between GO and the Au electrode is likely to contribute to the overall sensing response because of the adsorbates-induced Schottky barrier variation. A simplified model is used to explain the experimental observations.

An alkali-acitvated method was explored to synthesize activated carbon nanotubes (CNTs-A) with a high specific surface area (SSA), and a large number of mesopores. The resulting CNTs-A were used as an adsorbent material for removal of anionic and cationic dyes in aqueous solutions. Experimental results indicated that CNTs-A have excellent adsorption capacity for methyl orange (149 mg/g) and methylene blue (399 mg/g). Alkali-activation treatment of CNTs increased the SSA and pore volume (PV), and introduced oxygen-containing functional groups on the surface of CNTs-A, which would be beneficial to improving the adsorption affinity of CNTs-A for removal of dyes. Kinetic regression results shown that the adsorption kinetic was more accurately represented by a pseudo second-order model. The overall adsorption process was jointly controlled by external mass transfer and intra-particle diffusion, and intra-particle diffusion played a dominant role. Freundlich isotherm model showed a better fit with adsorption data than Langmuir isotherm model. Adsorption interactions of dyes onto CNTs-A from aqueous solutions were investigated using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) method. The remarkable adsorption capacity of dye onto CNTs-A can be attributed to the multiple adsorption interaction mechanisms (hydrogen bonding, π-π electron-donor-acceptor interactions, electrostatic interactions, mesopore filling) on the CNTs-A. Results of this work are of great significance for environmental applications of activated CNTs as a promising adsorbent nanomaterial for organic pollutants from aqueous solutions.

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As a novel material, double network hydrogel has attracted great attention in recent years for its excellent mechanical properties; however, several other characteristics are yet to be improved. Here we report on the synthesis of a novel alginate/reduced graphene oxide (RGO) double-network (GAD) hydrogel through a facile method, and investigate the GAD's mechanical properties, stability, and adsorption capacity compared with alginate/RGO single network hydrogel (GAS). To produce the GAD, the first network of alginate is formed with randomly distributed graphene oxide (GO), resulting in the GAS; then the GAS is treated by a hydrothermal reduction, through which the GO is reduced and selfassembles into a second RGO network interpentrating with the first, alginate network, forming the double network GAD. The mechanism of the GAD formation is investigated and the property differences between GAS and GAD are examined. The resulting GAD exhibits a higher Young's modulus than GAS, and the modulus increases with GO concentrations. The GAD also has a lower swelling ratio than GAS, which leads to improved gel stability in highly concentrated alkali/salt solutions. The GAD beads exhibit an excellent adsorption capacity (Cu 2+ ,169.5 mg/g and Cr2O7 2-,72.5 mg/g) for heavy metal ions, far better than that of GAS. Even after 10 regeneration cycles, both GAS and GAD can still retain their considerable adsorption capacity for metals. Results of this work are of great significance to double network gel research, especially for environmental applications. With good stability, adsorption capacity, and regeneration ability, the double network gel could be a promising adsorbent nanomaterial for pollutant removal from aqueous solutions.We designed and prepared a novel alginate/reduced graphene oxide double-network hydrogel through a facile method, and investigated the mechanical properties, stability and adsorption capacity compared to an alginate/reduced graphene oxide single network.

In this study, a novel mixed Ce-Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method. The CF-CNTs material was characterized by various methods, including BET surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was found that the Ce-Fe oxide was uniformly dispersed on the surface of CNTs with a mean size of 7.0 nm. The obtained CF-CNTs material was used as an adsorbent to remove arsenic from aqueous solutions. The adsorption experimental results showed that this CF-CNTs material had an excellent adsorption performance for As(V) and As(III). The adsorption processes of As(V) and As(III) could be well described by the pseudo-second-order model. The mechanistic study showed that different interactions were involved in As(V) adsorption, including electrostatic attraction and surface complexation. For As(III) adsorption, partial As(III) was oxidized to As(V) followed by the simultaneous adsorption of As(V) and As(III). It was also found that intra-particle diffusion existed in the process of adsorption on CF-CNTs, but that it was not the only rate-limiting step. The resulting CF-CNTs material can be used in a broad pH range, which suggests its great potential for the decontamination of arsenic-polluted water.

We report a one-pot method to synthesize magnetic iron oxide/CNT composites (MI/CNTs) based on as-prepared CNTs (APCNTs) using KOH activation. MI/CNTs have high specific surface area, good dispersion and magnetic properties, making them promising for use as adsorbents for arsenic removal. The results of this work are highly significant for large-scale applications of APCNTs containing Fe catalytic particles without the need for prior purification.

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Recently, metal oxides with novel nanostructured architectures have been prepared by annealing the polyol-based metal alkoxides for water treatment. However, these materials often exhibit relatively low adsorption capacities possibly attributable to the decomposition of surface groups during the calcination process. In this work, we successfully synthesized a novel nanostructured hollow iron-cerium alkoxide (NH-ICA) with a high surface area and abundant surface functional groups through an ethylene glycol mediated solvothermal method. Cerium ion doping significantly influenced the morphologies, microstructures and adsorption performance of NH-ICAs. Interestingly, the synthesized NH-ICAs showed significantly higher affinity to As(III) than the iron alkoxide material without cerium doping. Moreover, a much higher adsorption capacity of the NH-ICAs for As(III) than As(V) was found. When the molar ratio of Fe to Ce was 5:1, the product with uniform nanostructured hollow architectures exhibited the best adsorption capacities for both As(V) and As(III) (206.6 and 266.0 mg g(-1), respectively). The mechanistic study revealed that As(V) adsorption involved ion-exchange between the As(V) species and three types of negatively charged groups, including surface hydroxyl groups, CO3(2-) and unidentate carbonate-like species. For As(III) adsorption, surface complexing was proposed. A broad adaptation pH range for both As(V) and As(III) adsorbed by the resulting product indicates its promising application perspective for decontamination of arsenic-polluted water.