Chuanjia Jiang

Hierarchical Porous O-Doped g-C3N4 with Enhanced Photocatalytic CO2 Reduction Activity

Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO2 is considered as a potential route for solving ever-increasing energy crisis and greenhouse effect. Herein, hierarchical porous O-doped graphitic carbon nitride (g-C3 N4 ) nanotubes (OCN-Tube) are prepared via successive thermal oxidation exfoliation and curling-condensation of bulk g-C3 N4 . The as-prepared OCN-Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20-30 nm. The hierarchical OCN-Tube shows excellent photocatalytic CO2 reduction performance under visible light, with methanol evolution rate of 0.88 µmol g-1 h-1 , which is five times higher than bulk g-C3 N4 (0.17 µmol g-1 h-1 ). The enhanced photocatalytic activity of OCN-Tube is ascribed to the hierarchical nanotube structure and O-doping effect. The hierarchical nanotube structure endows OCN-Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O-doping optimizes the band structure of g-C3 N4 , resulting in narrower bandgap, greater CO2 affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.

Superb adsorption capacity of hierarchical calcined Ni/Mg/Al layered double hydroxides for Congo red and Cr(VI) ions

The preparation of hierarchical porous materials as catalysts and sorbents has attracted much attention in the field of environmental pollution control. Herein, Ni/Mg/Al layered double hydroxides (NMA-LDHs) hierarchical flower-like hollow microspheres were synthesized by a hydrothermal method. After the NMA-LDHs was calcined at 600°C, NMA-LDHs transformed into Ni/Mg/Al layered double oxides (NMA-LDOs), which maintained the hierarchical flower-like hollow structure. The crystal phase, morphology, and microstructure of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy elemental mapping, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption methods. Both the calcined and non-calcined NMA-LDHs were examined for their performance to remove Congo red (CR) and hexavalent chromium (Cr(VI)) ions in aqueous solution. The maximum monolayer adsorption capacities of CR and Cr(VI) ions over the NMA-LDOs sample were 1250 and 103.4mg/g at 30°C, respectively. Thermodynamic studies indicated that the adsorption process was endothermic in nature. In addition, the addition of coexisting anions negatively influenced the adsorption capacity of Cr(VI) ions, in the following order: CO32->SO42->H2PO4->Cl-. This work will provide new insight into the design and fabrication of advanced adsorption materials for water pollutant removal.

Silver Nanoparticle Behavior, Uptake, and Toxicity in Caenorhabditis elegans: Effects of Natural Organic Matter

Significant progress has been made in understanding the toxicity of silver nanoparticles (Ag NPs) under carefully controlled laboratory conditions. Natural organic matter (NOM) is omnipresent in complex environmental systems, where it may alter the behavior of nanoparticles in these systems. We exposed the nematode Caenorhabditis elegans to Ag NP suspensions with or without one of two kinds of NOM, Suwannee River and Pony Lake fulvic acids (SRFA and PLFA, respectively). PLFA rescued toxicity more effectively than SRFA. Measurement of total tissue silver content indicated that PLFA reduced total organismal (including digestive tract) uptake of ionic silver, but not of citrate-coated Ag NPs (CIT-Ag NPs). The majority of the CIT-Ag NP uptake was in the digestive tract. Limited tissue uptake was detected by hyperspectral microscopy but not by transmission electron microscopy. Co-exposure to PLFA resulted in the formation of NOM-Ag NP composites (both in medium and in nematodes) and rescued AgNO3- and CIT-Ag NP-induced cellular damage, potentially by decreasing intracellular uptake of CIT-Ag NPs.

Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Synthesis of hierarchical porous zinc oxide (ZnO) microspheres with highly efficient adsorption of Congo red

Hierarchical porous zinc oxide (ZnO) was successfully synthesized via a facile hydrothermal method followed by calcination, and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, and Fourier transform infrared spectroscopy analyses. The as-prepared porous ZnO exhibits microsphere morphologies with diameters of 6-8μm, which are assembled from two-dimensional nanosheets. The as-prepared hierarchical porous ZnO microspheres possessed high specific surface areas (57m2/g), and were evaluated for adsorption of Congo red (CR) in aqueous solution. The adsorption kinetics data were described by the pseudo-second-order kinetics and intraparticle diffusion models, while the equilibrium adsorption data were well fitted to the Langmuir model, with a maximum adsorption amount of 334mg/g. The as-prepared hierarchical porous ZnO exhibited higher CR adsorption capacity than commercial ZnO and various other materials, and thus could be an effective adsorbent for removal of anionic organic dyes from wastewater.

Hybrid carbon@TiO2 hollow spheres with enhanced photocatalytic CO2 reduction activity

Photocatalytic conversion of carbon dioxide (CO2) into solar fuels is an attractive strategy for solving the increasing energy crisis and greenhouse effect. This work reports the synthesis of hybrid carbon@TiO2 hollow spheres by a facile and green method using a carbon nanosphere template. The carbon content of the carbon@TiO2 composites was adjusted by changing the duration of the final calcination step, and was shown to significantly affect the physicochemical properties and photocatalytic activity of the composites. The optimized carbon@TiO2 composites exhibited enhanced photocatalytic activity for CO2 reduction compared with commercial TiO2 (P25): the photocatalytic CH4 production rate (4.2 μmol g−1 h−1) was twice that of TiO2; moreover, a large amount of CH3OH was produced (at a rate of 9.1 μmol g−1 h−1). The significantly improved photocatalytic activity was not only due to the increased specific surface area (110 m2 g−1) and CO2 uptake (0.64 mmol g−1), but also due to a local photothermal effect around the photocatalyst caused by the carbon. More importantly, UV-vis diffuse reflectance spectra (DRS) showed a remarkable enhancement of light absorption owing to the incorporation of the visible-light-active carbon core with the UV light-responsive TiO2 shell for increased solar energy utilization. Furthermore, electrochemical impedance spectra (EIS) revealed that the carbon content can influence the charge transfer efficiency of the carbon@TiO2 composites. This study can bring new insights into designing carbon@semiconductor nanostructures for applications such as solar energy conversion and storage.

Effects of Natural Organic Matter Properties on the Dissolution Kinetics of Zinc Oxide Nanoparticles

The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L(-1)) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

The effects of Mn loading on the structure and ozone decomposition activity of MnOx supported on activated carbon

Abstract Manganese oxide catalysts supported on activated carbon (AC, MnOx/AC) for ozone decomposition were prepared by in situ reduction of the permanganate. The morphology, oxidation state, and crystal phase of the supported manganese oxide were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, electron spin resonance, Raman spectroscopy, and temperature-programmed reduction. The supported MnOx layer was distributed on the surface of AC with a morphology that changed from a porous lichen-like structure to stacked nanospheres, and the thickness of the MnOx layer increased from 180 nm to 710 nm when the Mn loading was increased from 0.44% to 11%. The crystal phase changed from poorly crystalline β-MnOOH to δ-MnO2 with the oxidation state of Mn increasing from +2.9–+3.1 to +3.7–+3.8. The activity for the decomposition of low concentration ozone at room temperature was related to the morphology and loading of the supported MnOx. The 1.1%MnOx/AC showed the best performance, which was due to its porous lichen-like structure and relatively high Mn loading, while 11%MnOx/AC with the thickest MnOx layer had the lowest activity owning to its compact morphology.

Hierarchical flower-like nickel(II) oxide microspheres with high adsorption capacity of Congo red in water

Monodispersed hierarchical flower-like nickel(II) oxide (NiO) microspheres were fabricated by a facile solvothermal reaction with the assistance of ethanolamine and a subsequent calcination process. The as-synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, zeta potential measurement and Fourier transform infrared spectroscopy. Flower-like nickel(II) hydroxide microspheres with uniform diameters of approximate 6.3μm were obtained after the solvothermal reaction. After heat treatment at 350°C, the crystal phase transformed to NiO, but the hierarchical porous structure was maintained. The as-prepared microspheres exhibited outstanding performance for the adsorption of Congo red (CR), an anionic organic dye, from aqueous solution at circumneutral pH. The pseudo-second-order model can make a good description of the adsorption kinetics, while Langmuir model could well express the adsorption isotherms, with calculated maximum CR adsorption capacity of 534.8 and 384.6mgg-1, respectively, for NiO and Ni(OH)2. The adsorption mechanism of CR onto the as-synthesized samples can be mainly attributed to electrostatic interaction between the positively charged sample surface and the anionic CR molecules. The as-prepared NiO microspheres are a promising adsorbent for CR removal in water treatment.

Hierarchical porous C/MnO2 composite hollow microspheres with enhanced supercapacitor performance

The successful application of supercapacitors in energy conversion and storage hinges on the development of highly efficient and stable electrode materials. Herein, a composite of manganese oxide (MnO2) and N-doped hollow carbon spheres (NHCSs) was fabricated by a facile two-step process for supercapacitor electrodes. The MnO2–NHCS composite had a NHCS core and a shell composed of hierarchical birnessite-type MnO2 nanoflakes. The NHCSs in the composite serve not only as the template for the growth of MnO2 nanoflakes, but also as the electrically conductive channel for electrochemical performance enhancement. The physicochemical and electrochemical properties of the MnO2–NHCS composite were significantly enhanced as compared with those of MnO2 hollow spheres (MnO2 HSs). The asymmetric supercapacitors (ASCs) assembled with MnO2–NHCS anodes and NHCS cathodes exhibited a high energy density of 26.8 W h kg−1 at a power density of 233 W kg−1, which is superior to those of the ASCs assembled with MnO2 HS anodes and NHCS cathodes (13.5 W h kg−1 at 229 W kg−1). The MnO2–NHCS ASCs also show superior cycling stability for 4000 cycles. The enhanced electrochemical performance of the MnO2–NHCSs makes them a promising electrode material for application in supercapacitors and potentially other energy storage devices.