Effects of Oxidation State on Charge Carrier Lifetimes in B,N Codoped Graphene Oxide Quantum Dots

Graphene oxide is an outstanding photocatalyst used in water splitting reaction. However, the oxidation–reduction state causes unstable photocatalytic efficiencies. Electronic structure calculations combined with nonadiabatic molecular dynamics (NAMD) are considered as an effective tool to decipher the catalytic nature in such materials, especially regarding their intrinsic electronic properties. In this work, we performed ab initio NAMD to investigate the phonon-mediated charge relaxation and recombination dynamics in oxidized, partially oxidized, and reduced graphene oxide quantum dots (GOQDs). The relaxation dynamics, such as symmetry and relaxation time, depend on the excitation levels and oxidation states. The partially oxidized and reduced GOQDs exhibit asymmetric relaxations at higher excitation levels, in which the partially oxidized GOQDs exhibit a faster electron decay, whereas the reduced GOQDs exhibit a faster hole decay. At lower excitation levels, the electron decay is faster in oxidized and reduced GOQDs, whereas the hole decay is faster in partially oxidized GOQDs. Oxidation and partial oxidation bring the occupied and unoccupied localized states into the band gaps of GOQDs. In particular, oxidation leads to faster hole trapping, whereas partial oxidation leads to faster electron trapping

Edge-oxidation induced non-radiative recombination dynamics in graphene quantum dots: a theoretical insight from Fermi’s golden rule

The photoluminescence quantum yield of graphene quantum dots (GQDs) can be tuned by chemical functionalization. A rational design of fluorescent probes based on GQDs requires an understanding of the relationship between the chemical structure and the non-radiative recombination decay of GQDs. The oxygen-containing groups modify the edge states and alter the non-radiative decay of GQDs. In this work, we perform density functional theory (DFT) calculations to investigate the non-radiative decay dynamics of GQDs functionalised with different oxygen-containing groups, e.g. carbonyl, hydroxyl, and carboxyl, based on the principle of Fermi's golden rule. The carbonyl group oxidises the GQD edges, reducing the bandgap and red-shifting the absorption spectra. The carboxyl group increases the strength of electron-vibrational coupling of the high-frequency modes, resulting in faster non-radiative decay. The hydroxyl group, on the other hand, reduces the strength of electron-vibrational coupling in the high-frequency modes, thereby reducing non-radiative decay. Overall, this research extends our current knowledge of the role of individual oxygen-containing groups in the non-radiative decay of GQDs.</p

Degradation of Low Concentration Methyl Orange in Aqueous Solution through Sonophotocatalysis with Simultaneous Recovery of Photocatalyst by Ceramic Membrane Microfiltration

Photocatalysis is a promising technology for wastewater treatment, particularly for mineralization of nonbiodegradable and toxic components in wastewater. TiO2 is usually utilized as photocatalyst in slurry reactors in order to overcome mass transfer limitations. The difficulty in recovering TiO2 photocatalyst from treated water hindered its wide application. In this work, a novel process efficiently integrating sonophotocatalysis for methyl orange degradation and ultrasonic-enhanced ceramic membrane microfiltration for TiO2 separation was proposed and demonstrated. The results indicated that ultrasonic introduction could enhance photocatalysis reaction rate through cavitation effect, a synergetic effect between sonolysis and photocatalysis was found, and that is closely related with working conditions. Ceramic membrane microfiltration could efficiently recover TiO2 photocatalyst with a mean granular size of 0.33 μm from slurry reactor, achieving 99.9% recovery rate. Ultrasonic introduction into microfiltration process efficiently increased transmembrane permeation flux, suppressing membrane fouling under optimal working conditions. However, due to the problems associated with conversion efficiency of ultrasonic energy and the uncertain synergistic effect of sonolysis and photocatalysis, there is still much work before application of this process for wastewater treatment

Table_1_Ruthenium Inlaying Porous Aromatic Framework for Hydrogen Generation From Ammonia Borane.DOCX

Porous organic frameworks (POFs) are a new family of porous materials, which are characterized by high chemical and thermal stabilities, structural design-abilities, chemical functionalities, high porosities, etc. Designable skeletons of POFs lead to different applications in many fields. Herein, we report a porous aromatic framework PAF-72 synthesized via ionothermal reaction. The inherently nitrogen contained skeleton of PAF-72 is beneficial for introducing catalytic active center Ruthenium, which is verified by ICP, TGA, and TEM element mapping. Besides, Ru/PAF-72 shows excellent activity in hydrogen generation from hydrolysis of ammonia borane and good cyclic performance.</p

Effect of Binding Geometry on Charge Transfer in CdSe Nanocrystals Functionalized by N719 Dyes to Tune Energy Conversion Efficiency

Semiconductor quantum dots (QDs) functionalized by metal–organic dyes show great promise in photocatalytic and photovoltaic applications. However, the charge transfer direction and rateskey processes governing the efficiency of energy conversionare strongly affected by the QD–dye interactions, insights on which are challenging to obtain experimentally. We use density functional theory (DFT) and constrained DFT calculations to investigate a degree of sensitivity of the electronic level alignment and related QD–dye electronic couplings to binding conformations of N719 dye at the surface of the 1.5 nm CdSe QD. Our calculations reveal a lack of direct correlations between the strength of the QD–dye interaction in terms of their binding conformations and the donor–acceptor electronic couplings. While the QD–dye binding conformations are the most stable when the N719 dye is attached to the QD via two carboxylate groups, the strongest electronic coupling between the QD as an electron donor and the dye as an electron acceptor is observed in structures bonded via the isocyanate ligands. Such strong electronic couplings also are responsible for significant stabilization of the dye’s occupied orbitals deep inside in the valence band of the QD making the hole transfer from the photoexcited QD to the dye thermodynamically unfavorable in structures bound via isocyanates. Our results suggest that the most probable binding conformations are those occurring via two carboxylate linkers, which exhibit very weak electronic couplings contributing to the electron transfer from the photoexcited CdSe QD to the N719 dye but provide the most favorable conditions for the hole transfer. Overall, our computational work provides an insightful view about the surface chemistry of CdSe regarding the donor–acceptor interaction, energy level alignment, and charge transfer between CdSe and dye molecule, which can guide the rational design of QD-based materials for energy conversion applications

Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic Ancillary Ligand

The macrocyclic diamino diamine (1,7-Me₂TACD)­H₂ (1,7-Me₂TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me₂[12]­aneN₄), reacted under propylene elimination with [Ln­(η³-C₃H₅)₃(diox)] (Ln = Y, La) to give the mono­(allyl) complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)]₂ (Ln = Y (<b>1a</b>), La (<b>1b</b>)). A single-crystal X-ray diffraction study shows <b>1b</b> to be a centrosymmetric dimer with lanthanum atoms bridged by one of the two amido nitrogen atoms. Complexes <b>1a</b>,<b>b</b> were treated with 2 equiv of the potassium allyl KC₃H₅ to give the corresponding heterometallic allyl complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)₂K­(THF)]_<i>n</i> (Ln = Y (<b>2a</b>), La (<b>2b</b>)). A single-crystal X-ray diffraction study revealed that <b>2a</b>,<b>b</b> are polymeric in the solid state with allyl ligands bridging the metal centers in addition to the presence of μ₂-amido functions of the 1,7-Me₂TACD ligand. Hydrogenolysis of the yttrium compound <b>2a</b> with 1 bar of H₂ led to the formation of the heterometallic Y₄K₂ hydrido complex [(1,7-Me₂TACD)₂Y₂H₃K­(THF)₂]₂ (<b>3a</b>), which can also be synthesized from a 1:1 mixture of <b>1a</b> and KC₃H₅ with 1 bar of H₂. A single-crystal X-ray diffraction study of <b>3a</b> revealed a dimer of heterotrinuclear Y₂K trihydride aggregate. Treatment of <b>2b</b> with 1 bar of H₂ afforded the heptanuclear La₃K₄ heptahydrido complex [(1,7-Me₂TACD)₃La₃H₇K₄(THF)₇] (<b>3b</b>)

Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic Ancillary Ligand

The macrocyclic diamino diamine (1,7-Me₂TACD)­H₂ (1,7-Me₂TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me₂[12]­aneN₄), reacted under propylene elimination with [Ln­(η³-C₃H₅)₃(diox)] (Ln = Y, La) to give the mono­(allyl) complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)]₂ (Ln = Y (<b>1a</b>), La (<b>1b</b>)). A single-crystal X-ray diffraction study shows <b>1b</b> to be a centrosymmetric dimer with lanthanum atoms bridged by one of the two amido nitrogen atoms. Complexes <b>1a</b>,<b>b</b> were treated with 2 equiv of the potassium allyl KC₃H₅ to give the corresponding heterometallic allyl complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)₂K­(THF)]_<i>n</i> (Ln = Y (<b>2a</b>), La (<b>2b</b>)). A single-crystal X-ray diffraction study revealed that <b>2a</b>,<b>b</b> are polymeric in the solid state with allyl ligands bridging the metal centers in addition to the presence of μ₂-amido functions of the 1,7-Me₂TACD ligand. Hydrogenolysis of the yttrium compound <b>2a</b> with 1 bar of H₂ led to the formation of the heterometallic Y₄K₂ hydrido complex [(1,7-Me₂TACD)₂Y₂H₃K­(THF)₂]₂ (<b>3a</b>), which can also be synthesized from a 1:1 mixture of <b>1a</b> and KC₃H₅ with 1 bar of H₂. A single-crystal X-ray diffraction study of <b>3a</b> revealed a dimer of heterotrinuclear Y₂K trihydride aggregate. Treatment of <b>2b</b> with 1 bar of H₂ afforded the heptanuclear La₃K₄ heptahydrido complex [(1,7-Me₂TACD)₃La₃H₇K₄(THF)₇] (<b>3b</b>)

Versatile Reactivities of <i>ansa</i>-Heteroborabenzene Divalent Ytterbium Amide toward Alkali-Metal Salts and the Generation of Heterometallic Ytterbium−Alkali-Metal Boratabenzene Complexes

Reactions of the ansa-heteroborabenzene divalent ytterbium amide [C5H5BCH2(CH3)2P→BC5H5]YbN(SiMe3)2 (1) with alkali-metal salts (KC5Me5, NaOiPr, NaOAr, LiNHAr, LiN(SiMe3)2, LiNEt2, and KCH2Ar) were studied. The reaction of 1 with KC5Me5 caused a ligand displacement of neutral borabenzene by KC5Me5 at the Yb ion to give a heterometallic Yb−K boratabenzene complex with a polymeric structure, while that with NaOiPr caused a ligand displacement of the anionic amido ligand at the Yb ion by an isopropoxyl ligand to give a heterometallic Yb−Na boratabenzene complex with a polymeric structure. When LiNEt2 or KCH2Ar was employed as the reagent, the [NEt2]− or [CH2Ar]− group underwent nucleophilic attack at the B atom on the neutral borabenzene to cause the disassociation of the P→B coordination bond and the generation of new boratabenzene ligands

Structure and Capacitive Performance of Porous Carbons Derived from Terephthalic Acid–Zinc Complex via a Template Carbonization Process

High-performance porous carbons as supercapacitor electrode materials have been prepared by a simple but efficient template carbonization process, in which commercially available terephthalic acid–zinc complex is used as a carbon source. It reveals that the carbonization temperature plays a crucial role in determining the structure and capacitive performance of carbons. The <b>carbon-1000</b> sample has high surface area of 1138 m² g^–1 and large pore volume of 1.44 cm³ g^–1 as well as rationally hierarchical pore size distribution. In a three-electrode system, the <b>carbon-1000</b> sample possesses high specific capacitances of 266.0 F g^–1 at 0.5 A g^–1 and good cycling stability. In a two-electrode system, the operation temperature (25/50/80 °C) can greatly influence the electrochemical performance of the <b>carbon-1000</b> sample, especially with an extended voltage window (∼ 3 V). The temperature-dependent operation makes it possible for the application of supercapacitors under extreme conditions

Versatile Reactivities of <i>ansa</i>-Heteroborabenzene Divalent Ytterbium Amide toward Alkali-Metal Salts and the Generation of Heterometallic Ytterbium−Alkali-Metal Boratabenzene Complexes

Reactions of the ansa-heteroborabenzene divalent ytterbium amide [C5H5BCH2(CH3)2P→BC5H5]YbN(SiMe3)2 (1) with alkali-metal salts (KC5Me5, NaOiPr, NaOAr, LiNHAr, LiN(SiMe3)2, LiNEt2, and KCH2Ar) were studied. The reaction of 1 with KC5Me5 caused a ligand displacement of neutral borabenzene by KC5Me5 at the Yb ion to give a heterometallic Yb−K boratabenzene complex with a polymeric structure, while that with NaOiPr caused a ligand displacement of the anionic amido ligand at the Yb ion by an isopropoxyl ligand to give a heterometallic Yb−Na boratabenzene complex with a polymeric structure. When LiNEt2 or KCH2Ar was employed as the reagent, the [NEt2]− or [CH2Ar]− group underwent nucleophilic attack at the B atom on the neutral borabenzene to cause the disassociation of the P→B coordination bond and the generation of new boratabenzene ligands