Semiconductor-based photocatalysis plays a vital role in counteracting worldwide environmental pollution and energy shortage. How to design a visible-light-active photocatalyst is critical for ...efficient solar energy utilization. Many oxides including TiO2 are only photoactive in ultraviolet light and doping is an important strategy to extend the photoactive zone. Anion doping is superior to cation doping, which generates more harmful electron-hole recombination centers. Nitrogen doping is more effective than carbon/sulfur doping to achieve high visible-light response. Since 2001, nitrogen-doped TiO2 photocatalysts have attracted increasing attention due to their strong oxidizing power and considerable visible light response. Considering the fixed atomic environment in simple oxides, complex oxides are more attractive as photocatalysts because of their more flexible physical and chemical properties. To date, no review focuses on the designation strategies for nitrogen-doped simple/complex oxides with high visible-light photoactivity. In this review, the recent progress involving nitrogen-doped simple/complex oxides for photocatalysis is comprehensively summarized. Emphasis is placed on the factors that determine photocatalytic activity and related strategies for the design of active nitrogen-doped oxides. The future challenges are also discussed. This review aims to provide a summary of recent progress in nitrogen-doped oxides for photocatalysis and some useful guidelines for the future development.
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The increasing concerns on toxicity of sulfonamide antibiotics in water require a prompt action to establish efficient wastewater treatment processes for their removal. In this study, ...adsorptive removal of a model sulfonamide antibiotic, sulfachloropyridazine (SCP), from wastewater is presented for the first time using a metal organic framework (MOF). A high surface area and thermally stable MOF, HKUST-1, was synthesized by a facile method. Batch adsorption studies were systematically carried out using HKUST-1. The high surface area and unsaturated metal sites resulted in a significant adsorption capacity with faster kinetics. Most of the SCP was removed in 15min and the kinetic data were best fitted with the pseudo second order model. Moreover, isothermal data were best fitted with the Langmuir model. The thermodynamic results showed that the adsorption is a spontaneous and endothermic process. The adsorption capacity of HKUST-1 is 384mg/g at 298K which is the highest compared to most of the materials for the antibiotics. The high adsorption capacity is attributed mainly to π-π stacking, hydrogen bonding and electrostatic interactions.
The gradual depletion of oil resources and the necessity to reduce greenhouse gas emissions portray a concerning image of our contemporary security of liquid transportation fuels in the event of a ...global crisis. Despite a vast amount of natural gas resources that we have and the huge economic incentive, the conversion of gas to liquid fuels or chemicals is still very limited because of the high technological complexity and capital cost for facilities. However, with the anticipated depletion of liquid petroleum and the soaring price of crude oil, the conversion of natural gas to liquid feedstock or fuels will become more and more important. Higher alcohols are important feedstocks for the chemical and pharmaceutical industries and have wide applications as potential fuel additives or hydrogen carriers for fuel cells for clean energy delivery. There is a long-standing interest in the synthesis of higher alcohols from syngas, an important Fischer–Tropsch technology for natural gas conversion. The purpose of this review is to provide readers with an extensive account of catalytic synthesis of higher alcohols from syngas using various catalysts reviewed from a unique perspective: clarification of the active centers and reaction pathways. In light of the different sources providing the active centers, three major classes of catalysts in terms of monometallic, bimetallic, and trimetallic/multimetallic catalysts are systematically reviewed, and their respective performances are carefully compared. Finally, future works proposed to improve the catalyst design are described.
Cross-linked, N-doped, pillared-layered porous carbons (NCs) were prepared via a one-pot, template-free pyrolysis process at 600 (NC600), 700 (NC700) and 800 °C (NC800), which have bifunctional ...applications in supercapacitors and environmental remediation. NC700 displays a high surface area (2118 m2 g−1) and a specific capacitance of 305 F g−1 at 0.2 A g−1 in a two-electrode setup. The maximum energy density of NC700 was 20.4 W h/kg at a power density of 139 W kg−1 and 89.1% capacitance was retained after 10000 cycles of charge-discharge at 5 A g−1. For water remediation, NC800 displayed high adsorption capacities towards flame retardant tetrabromobisphenol A (TBBPA, 372 mg g−1) and antibiotic sulfachloropyridazine (SCP, 288 mg g−1) solutions, while NC700 showed the most efficient SCP oxidation removal. These results suggest low-cost and green carbon materials as electrodes in flexible energy storage devices, metal-free adsorbents as well as catalysts for high efficient removal of emerging contaminants in aqueous solution.
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We discovered that chemically reduced graphene oxide, with an I D/I G >1.4 (defective to graphite) can effectively activate peroxymonosulfate (PMS) to produce active sulfate radicals. The produced ...sulfate radicals (SO4 •) are powerful oxidizing species with a high oxidative potential (2.5–3.1 vs 2.7 V of hydroxyl radicals), and can effectively decompose various aqueous contaminants. Graphene demonstrated a higher activity than several carbon allotropes, such as activated carbon (AC), graphite powder (GP), graphene oxide (GO), and multiwall carbon nanotube (MWCNT). Kinetic study of graphene catalyzed activation of PMS was carried out. It was shown that graphene catalysis is superior to that on transition metal oxide (Co3O4) in degradation of phenol, 2,4-dichlorophenol (DCP) and a dye (methylene blue, MB) in water, therefore providing a novel strategy for environmental remediation.
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In this study, binary metal organic frameworks (MOFs) with HKUST-1 and UiO-66 have been synthesized in a one-pot process. The synthesized MOFs were characterized by Fourier transform ...infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption, and thermogravimetric analysis (TGA). The meso-porosity and thermal stability of the binary MOFs were higher than those of single HKUST-1 or UiO-66. The synthesized MOF hybrids were then tested for adsorptive removal of methylene blue (MB) from wastewater in terms of kinetic and isothermal adsorption as compared to a commercially available activated carbon (AC). All the synthesized MOFs showed significant removal of MB under a wide range of pH. The adsorption capacities of HKUST-1 are higher than UiO-66 and commercial AC while the binary MOFs presented an even higher adsorption capacity than single MOFs. This is the first time that binary HKUST-1 and UiO-66 MOFs have been successfully synthesized and demonstrated enhanced adsorptive removal of contaminants.
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•Mn3O4, Co3O4 and Fe3O4 were synthesized and tested for peroxymonosulfate activation.•Mn3O4 exhibited the highest activity in peroxymonosulfate activation for phenol ...degradation.•Phenol degradation on Mn3O4 followed the first order kinetics with low activation energy.•Nanostructured Mn3O4 presented stable performance excellently.
Spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles were prepared, characterized, and tested in degradation of aqueous phenol in the presence of peroxymonosulfate. It was found that Mn3O4 and Co3O4 nanoparticles are highly effective in heterogeneous activation of peroxymonosulfate to produce sulfate radicals for phenol degradation. The activity shows an order of Mn3O4>Co3O4>Fe3O4. Mn3O4 could fast and completely remove phenol in about 20min, at the conditions of 25ppm phenol, 0.4g/L catalyst, 2g/L oxone®, and 25°C. A pseudo first order model would fit to phenol degradation kinetics and activation energies on Mn3O4 and Co3O4 were obtained as 38.5 and 66.2kJ/mol, respectively. In addition, Mn3O4 exhibited excellent catalytic stability in several runs, demonstrating that Mn3O4 is a promising catalyst alternative to toxic Co3O4 for water treatment.
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Metal-free semiconductors offer a new opportunity for environmental photocatalysis toward a potential breakthrough in high photo efficiency with complete prevention of metal leaching. ...In this study, graphitic carbon nitride (GCN) modified by oxygen functional groups was synthesized by a hydrothermal treatment of pristine GCN at different temperatures with H2O2. Insights into the emerging characteristics of the modified GCN in photocatalysis were obtained by determining the optical properties, band structure, electrochemical activity and pollutant degradation efficiency. It was found that the introduction of GCN with oxygen functional groups can enhance light absorption and accelerate electron transfer so as to improve the photocatalytic reaction efficiency. The photoinduced reactive radicals and the associated photodegradation were investigated by in situ electron paramagnetic resonance (EPR). The reactive radicals, O2− and OH, were responsible for organic degradation.
A green and facile protocol of thermal treatment of graphene oxide (GO) with urea was adopted to synthesize nitrogen-doped graphene (NG-Urea-air) at a low temperature (350 °C) in the static air. The ...resulting sample exhibited outstanding catalytic performance to activate peroxymonosulfate (PMS) toward organic degradation. The NG-Urea-air induced 49.7- and 11.5-fold enhancement over GO and pristine reduced graphene oxide (rGO-air). Moreover, the influences of nitrogen precursors including organic chemicals (urea, cyanamide, and melamine) and inorganic salts (ammonium nitrate and ammonium chloride) were investigated, and urea was demonstrated to be the best precursor for synthesizing N-doped graphene with a relative high doping level (18.7 at.%). The classical radical quenching and advanced in situ electron paramagnetic resonance (EPR) technology revealed that the outstanding oxidative effectiveness of PMS/NG-Urea-air system was originated from the nonradical oxidation pathway, in which PMS was activated by the positively charged carbon domains next to nitrogen atoms and the phenol was oxidized simultaneously on the carbon network via rapid charge transfer. Meanwhile, singlet oxygen and radicals may also partially contribute to the complete phenol degradation. This study facilitates a fundamental investigation of heteroatom doping progress during thermal treatment and sheds light on the insights into carbocatalysis in environmental remediation.
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Heteroatom (nitrogen and sulfur)-codoped porous carbons (N-S-PCs) with high surface areas and hierarchically porous structures were successfully synthesized via direct pyrolysis of a mixture of ...glucose, sodium bicarbonate, and thiourea. The resulting N-S-PCs exhibit excellent adsorption abilities and are highly efficient for potassium persulfate activation when employed as catalysts for the oxidative degradation of sulfachloropyridazine (SCP) solutions. The adsorption capacities of N-S-PC-2 (which contains 4.51 atom % nitrogen and 0.22 atom % sulfur and exhibits S BET of 1608 m2 g–1) are 73, 7, and 3 times higher than those of graphene oxide, reduced graphene oxide, and commercial single-walled carbon nanotube, respectively. For oxidation, the reaction rate constant of N-S-PC-2 is 0.28 min–1. This approach not only contributes to the large-scale production and application of high-quality catalysts in water remediation but also provides an innovative strategy for the production of heteroatom-doped PCs for energy applications.
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