Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Delamination of LDHs is an interesting route for producing positively charged thin platelets with a thickness of a few atomic layers, which can be used as nanocomposites for polymers or as building units for making new designed organic-inorganic or inorganic-inorganic nanomaterials. The synthesis of nanosized LDH platelets can be generally classified into two approaches, bottom-up and top-down. It requires modification of the LDH interlamellar environment and then selection of an appropriate solvent system. In DDS intercalated LDHs, the aliphatic tails of the DDS- anions exhibit a high degree of interdigitation in order to maximize guest-guest dispersive interactions. Bellezza reported that the LDH colloids can also been obtained by employing a reverse microemulsion approach.

Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets.

Recent Advances in Polyoxometalate-Catalyzed Reactions

This review surveys recent advances in the applications of layered double hydroxides (LDHs) in heterogeneous catalysis. By virtue of the flexible tunability and uniform distribution of metal cations in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment and/or reduction-have found many applications as stable and recyclable heterogeneous catalysts or catalyst supports for a variety of reactions with high industrial and academic importance. A major challenge in this rapidly growing field is to simultaneously improve the activity, selectivity and stability of these LDH-based materials by developing ways of tailoring the electronic structure of the catalysts and supports. Therefore, this Review article is mainly focused on the most recent developments in smart design strategies for LDH materials and the potential catalytic applications of the resulting materials.

Catalytic applications of layered double hydroxides: recent advances and perspectives

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

Reducing carbon dioxide to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single atoms of palladium and platinum supported on graphitic carbon nitride (g-C3N4), i.e., Pd/g-C3N4 and Pt/g-C3N4, respectively, acting as photocatalysts for CO2 reduction were investigated by density functional theory calculations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from the hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, deposition of atom catalysts on g-C3N4 significantly enhances the visible-light absorption, rendering them ideal for visible-light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply.

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Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide.

Co 3 O 4 nanoparticles modified g‐C 3 N 4 composites (Co 3 O 4 -g-C 3 N 4 ) were prepared and used as a visible light responsive photocatalyst for the removal of diclofenac sodium (DCF). The Co 3 O 4 -g-C 3 N 4 with 0.20% Co 3 O 4 loading exhibited the highest photocatalytic activity towards DCF degradation among the various Co 3 O 4 loading. In the presence of peroxymonosulfate (PMS), the removal efficiency of DCF with an initial concentration of 10 mg/L was greatly increased from 20% to 100% within 30 min and the first order-kinetic constant was increased from 0.00469 to 0.08403 min −1 . Influencing factors including DCF concentrations, PMS concentrations, and initial pH values were investigated in details. Low pH value was favorable to DCF degradation. Reactive oxygen species generated in the photocatalytic process were identified by radical quenching tests and electron spin response. It was proposed that both sulfate and hydroxyl radicals contributed to the degradation of DCF. PMS could be activated by photogenerated electrons from the Co 3 O 4 -g‐C 3 N 4 hybrids under visible light, as well as the Co 3 O 4 itself to generate sulfate radicals jointly. Hydroxyl radicals were generated from the reaction between sulfate radicals and H 2 O/OH − . As a result, DCF was efficiently degraded.

Synergetic activation of peroxymonosulfate by Co3O4 modified g-C3N4 for enhanced degradation of diclofenac sodium under visible light irradiation

The high-efficiency catalyst is the key factor of volatile organic compounds (VOCs) catalytic combustion. Herein, hierarchical core–shell Al2O3@Pd-CoAlO (Pd-CoAlO-Al) microspheres have been successfully prepared and used for toluene combustion. The experimental results reveal that the core–shell Pd-CoAlO-Al exhibits outstanding catalytic efficiency due to the homogeneous distribution of Pd-CoAlO nanosheets on Al2O3 supports and the strong interaction between the catalytically active Pd-CoAlO nanosheets and the Al2O3 supports. In particular, the catalytically active PdO contributes to the excellent catalytic efficiency. In addition, the in situ DRIFTS results indicate that the benzoate species are the main intermediate species in toluene combustion.

Hierarchical Core–Shell Al2O3@Pd-CoAlO Microspheres for Low-Temperature Toluene Combustion

MOx/ABO3 is a promising catalyst for the high-efficiency removal of volatile organic compounds. However, this catalyst is limited on practical applications due to its complex synthesis procedure and high cost. In this work, the MnO2/LaMnO3 catalyst was prepared in situ using a facile one-step method for the first time, in which partial La cations were selectively removed from three dimensionally chain-like ordered macroporous (3DOM) LaMnO3 material. After selective removal, the obtained MnO2/LaMnO3 sample expressed an excellent catalytic performance on toluene oxidation. Toluene could be completely oxidized into CO2 and H2O at 290 °C over the MnO2/LaMnO3 catalyst with a toluene/oxygen molar ratio of 1/100 and a space velocity of 120 000 mL/(g h). In addition, the apparent activation energy value of MnO2/LaMnO3 was 57 kJ/mol, which was lower than those of other metal oxides catalysts. According to O2-TPD and XPS results, it is concluded that the high catalytic performance of MnO2/LaMnO3 was mainly associat...

A Facile Method for in Situ Preparation of the MnO2/LaMnO3 Catalyst for the Removal of Toluene

Noble metal nanoparticles (noble metal NPs, noble metal = Ag, Pt and Pd) have been successfully immobilized on CoAl-layered double hydroxide (CoAl-LDHs) layers using a simple and facile self-redox process to afford noble metal NPs immobilized on CoAl-LDHs (N–CoAl-LDHs, N = Ag, Pt and Pd). In addition, the CoAl-LDHs and N-CoAl-LDHs were calcined in air at 600 °C to afford the CoAlO and N-CoAlO catalysts for toluene combustion. The catalytic and characterization results indicated that the Pd–CoAlO catalyst exhibited the highest catalytic activity because it possessed the highest low-temperature reducibility and the most abundant surface Co 3+ and surface adsorbed oxygen species. In addition, the noble metal NP sizes of the N–CoAlO catalysts affected the catalytic activity for toluene combustion, and the existence of catalytically active PdO contributes to the excellent catalytic activity of the Pd–CoAlO catalyst for toluene combustion. The comparison experiments reveal that the PdO phase and CoAlO support play significant role in the toluene combustion and they participate cooperatively in the reaction process. In addition, the in situ DRIFTS results indicated that the benzoate species are the main intermediate species in toluene combustion, which should be further oxidized by O 2 to the final products ( i.e ., CO 2 and H 2 O).

Shen Zhao

Papers

Synergetic activation of peroxymonosulfate by Co3O4 modified g-C3N4 for enhanced degradation of diclofenac sodium under visible light irradiation

Hierarchical Core–Shell Al2O3@Pd-CoAlO Microspheres for Low-Temperature Toluene Combustion

A Facile Method for in Situ Preparation of the MnO2/LaMnO3 Catalyst for the Removal of Toluene

Pd–Co based spinel oxides derived from pd nanoparticles immobilized on layered double hydroxides for toluene combustion

Covalent combination of polyoxometalate and graphitic carbon nitride for light-driven hydrogen peroxide production