Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Manganese oxides of various structures (α-, β-, and δ-MnO2 and amorphous) were synthesized by facile methods. The electrocatalytic properties of these materials were systematically investigated for catalyzing both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline media. Extensive characterization was correlated with the activity study by investigating the crystal structures (XRD, HRTEM), morphologies (SEM), porosities (BET), surfaces (XPS, O2-TPD/MS), and electrochemical properties (Tafel analysis, Koutechy-Levich plots, and constant-current electrolysis). These combined results show that the electrocatalytic activities are strongly dependent on the crystallographic structures, and follow an order of α-MnO2 > AMO > β-MnO2 > δ-MnO2. Both OER studies and ORR studies reveal similar structure-determined activity trends in alkaline media. In the OER studies, α-MnO2 displays an overpotential of 490 mV compared to 380 mV shown by an Ir/C catalyst in reaching 10 mA cm(-2). Meanwhile, α-MnO2 also exhibits stability for 3 h when supplying a constant current density of 5 mA cm(-2). This was further improved by adding Ni(2+) dopants (ca. 8 h). The superior OER activity was attributed to several factors, including abundant di-μ-oxo bridges existing in α-MnO2 as the protonation sites, analogous to the OEC in PS-II of the natural water oxidation system; the mixed valencies (AOS = 3.7); and the lowest charge transfer resistances (91.8 Ω, η = 430 mV) as revealed from in situ electrochemical impedance spectroscopy (EIS). In the ORR studies, when reaching 3 mA cm(-2), α-MnO2 shows 760 mV close to 860 mV for the best ORR catalyst (20% Pt/C). The outstanding ORR activity was due to the strongest O2 adsorption capability of α-MnO2 suggested by temperature-programmed desorption. As a result, this discovery of the structure-related electrocatalytic activities could provide guidance in the further development of easily prepared, scalable, and low-cost catalysts based on metal oxides and their derivatives.

Structure–Property Relationship of Bifunctional MnO2 Nanostructures: Highly Efficient, Ultra-Stable Electrochemical Water Oxidation and Oxygen Reduction Reaction Catalysts Identified in Alkaline Media

Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals

Recently, various lightweight materials with diverse nanomorphologies that contain heteroatoms such as nitrogen, boron, or fluorine have been actively pursued because of their unusual properties, such as in catalytic applications or as semiconductors. For example, ordered and disordered modifications of carbon nitride (C3N4) extend the property profile of carbon nanostructures and have numerous potential areas of applications ranging from semiconductors to fuel cells. A large number of reports deals with the synthesis of different modifications of bulk CxNy materials. [2] The synthesis of these nitrogen-rich species generally includes thermal condensation of nitrogen-rich precursors, often from molecules containing or generating triazine rings. For example, through a solid-state reaction of 2,4,6-triamino-1,3,5-triazine with 2,4,6-trichloro-1,3,5-triazine at high pressure and high temperature, Wolf and co-workers obtained a well-characterized and highly crystalline graphitic carbon nitride derivative. However, it was shown that the more ideal bulk carbon nitride solids perform rather weakly in some catalytic processes, while more disordered, polymeric versions showed nice activity, as structural defects or surface terminations seemed to play a key role for the catalytic activation. To enhance the performance of carbon nitride both as a support and as a catalyst, the specific surface had to be enhanced, and nanocasting with hard templates using porous silicas has been explored recently for the replication of porous carbon nitride materials with controlled mesopore structures. This nanocasting method is good for the proof of principle, but it is hardly transferable to a practical process, as the templates have to be removed in an extra step involving aqueous ammonium bifluoride (NH4HF2) or hydrogen fluoride (HF), which are hazardous and not environmentally friendly and also prohibit further functionalization. A general and robust method for the synthesis of porous polymeric carbon nitrides without the extra step of removing hard templating silica structures has yet to be developed. Ionic liquids are an especially promising choice to achieve this aim. Ionic liquids are generally defined as organic salts with a low melting point, usually below 100 8C. They inherit many features of inorganic molten salts, such as excellent chemical and thermal stability (in some cases in excess of 400 8C) and negligibly small vapor pressure, with the convenience of being liquid under ambient conditions. They have found application in numerous fields, for example as solvents or catalysts in organic synthesis, as electrolytes, or in chemical separations. Recently, the advantages of ionic liquids in inorganic synthesis have been gradually realized and have received more and more attention. For instance, they turned out to be interesting solvents in the synthesis of nanoparticles owing to their special solvent structure that derives from the ion–ion interaction and extended hydrogen-bonding motifs. From the many different available ionic liquids, we chose a class with BF4 counterions, as the anion might enter the C N condensation scheme, while boron and fluorine doping could improve the catalytic activity of the discussed systems and contribute to the performance of such materials. Herein we demonstrate that the simple, commercially available room-temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) is a unique soft template for the easy synthesis of boronand fluorineenriched mesoporous polymeric carbon nitride, in which an organic precursor, for example dicyandiamide (DCDA), selfcondensed into carbon nitride solids in the presence of BmimBF4. We show that the resulting materials possess high nitrogen, boron, and fluorine contents, high surface area, local graphitic order, and an excellent photoconductivity under visible light. We also demonstrate the catalytic properties of these CNBF materials in the heterogeneous, metal-free oxidation of cyclohexane. The CNBF materials show nice performance in the oxidation of cyclohexane with good conversion and excellent cyclohexanone selectivity. The structures of these hybrid materials were investigated by powder X-ray diffraction (XRD), nitrogen gas adsorption, and transmission electron microscopy (TEM) measurements. The XRD pattern, for example of CNBF-0.3 (r = 0.3, r denotes the mass ratio of BmimBF4 to DCDA), is dominated by the (002) interlayer-stacking peak of carbon nitrides, [*] Dr. Y. Wang, Prof. Dr. X. Wang, Prof. Dr. M. Antonietti Department of Colloid Chemistry Max-Planck Institute of Colloids and Interfaces Research Campus Golm, 14424 Potsdam (Germany) Fax: (+ 49)331-567-9502 E-mail: yong.wang@mpikg.mpg.de

Boron- and Fluorine-Containing Mesoporous Carbon Nitride Polymers: Metal-Free Catalysts for Cyclohexane Oxidation†

https://escholarship.org/content/qt50r1b9sg/qt50r1b9sg.pdf?t=ok16ag

Engineered nanomaterials for water treatment and remediation: Costs, benefits, and applicability

Cryptomelane-type K-OMS-2 nanomaterials with high surface area (156 m2/g) have been synthesized via a low-temperature solvent-free method in a very short time (1 h). Field emission scanning electron microscopy and high-resolution transmission electron microscopy images reveal that these materials have nanorod morphologies with average diameters of about 10 nm and lengths of about 50 nm. These are different from the long fiberous morphologies of OMS-2 materials made by conventional reflux or hydrothermal methods. X-ray diffraction and Brunauer−Emmett−Teller studies indicate that these materials have small crystallite sizes (∼9.8 nm) and that they are mesoporous with a uniform pore size distribution centered at 12 nm. These K-OMS-2 materials show improved catalytic activity for the oxidation of alcohols compared with the conventional K-OMS-2 materials, which may be due to their higher surface areas and novel surface properties. This fast, inexpensive, and environmentally friendly solvent-free method has the...

Synthesis and Catalytic Activity of Cryptomelane-Type Manganese Dioxide Nanomaterials Produced by a Novel Solvent-Free Method

Cyclohexane oxidation catalyzed by manganese oxide octahedral molecular sieves—Effect of acidity of the catalyst

Tandem catalysis: Direct catalytic synthesis of imines from alcohols using manganese octahedral molecular sieves

Territorial boundaries between conspecific social insect colonies are maintained through a highly developed nestmate recognition system modulated by heritable and, in some instances, nonheritable cues. Argentine ants, Linepithema humile, use both genetic and environmentally derived cues to discriminate nestmates from nonnestmates. We explored the possibility that intraspecific aggression in the Argentine ant might diminish when colonies shared a common diet. After segregating recently field-collected colony pairs into high or moderate aggression categories, we examined the effect of one of three diets: two hydrocarbon-rich insect prey, Blattella germanica and Supella longipalpa, and an artificial (insect-free) diet, on the magnitude of aggression loss. Aggression diminished between colony pairs that were initially moderately aggressive. However, initially highly aggressive colony pairs maintained high levels of injurious aggression throughout the study, independent of diet type. Each diet altered the cuticular hydrocarbon profile by contributing unique, diet-specific cues. We suggest that acquisition of common exogenous nestmate recognition cues from shared food sources may diminish aggression and promote fusion in neighboring colonies of the Argentine ant.

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Diet-related modification of cuticular hydrocarbon profiles of the Argentine ant, Linepithema humile, diminishes intercolony aggression.

Here, we describe an ammonia gas sensor comprising of thin film of octahedral molecular sieves of OMS-2 nanofibers deposited on insulation substrate having gold-coated copper electrodes. We demonstrate that the OMS-2 nanofibers can exhibit reversible changes in its electrical resistance due to the adsorption and desorption of ammonia on its acidic sites. OMS-2 exhibits high sensitivity for the ammonia gas in air.

Ranjit Kumar

Papers

Synthesis and Catalytic Activity of Cryptomelane-Type Manganese Dioxide Nanomaterials Produced by a Novel Solvent-Free Method

Cyclohexane oxidation catalyzed by manganese oxide octahedral molecular sieves—Effect of acidity of the catalyst

Tandem catalysis: Direct catalytic synthesis of imines from alcohols using manganese octahedral molecular sieves

Diet-related modification of cuticular hydrocarbon profiles of the Argentine ant, Linepithema humile, diminishes intercolony aggression.

Ammonia Gas Sensing Using Thin Film of MnO 2 Nanofibers