Oxygen Adsorption Sites Research Articles

Electrochemical synthesized copper mesh catalysts for catalytic combustion: A comprehensive study of Mn doping and atmospheric conditions during calcination

Metal-based monolithic catalysts offer significant advantages in heterogeneous catalysis attributed to their exceptional thermal conductivity and mechanical strength. However, controlling the loading of active components on metallic substrates remains a major challenge. Here, we synthesized a Mn-doped Cu mesh catalyst using a facile electrochemical method, allowing the active components to grow directly on Cu mesh without extra pretreatments or binding agents. The synthesized catalyst exhibits approximately a 30 % increase in carbon monoxide oxidation activity at 100°C and a 60 % increase in toluene oxidation activity at 240°C compared to the Mn-free Cu mesh catalyst. We found that calcination in inert gases enhances interactions between Cu and Mn species, leading to more oxygen vacancies and adsorption sites for reactants. This investigation paves the way for fabricating multi-metal monolithic catalysts on metallic substrates.

Insights into the in-situ generation of singlet oxygen via molecular oxygen activation over NiO@CuxO NRs/CF nanocomposite catalysts: Mechanisms of singlet oxygen evolution and chloroquine phosphate degradation

Herein, we fabricated a novel NiO@CuxO nanorods (NRs) composite electrode grown in-situ on copper foam (CF), designated as NiO@CuxO NRs/CF. This electrode demonstrates excellent performance in a heterogeneous electro-Fenton-like system. It efficiently activates O2 to generate 1O2 in-situ without the addition of oxidant precursors and effectively degrades chloroquine phosphate (CQ). The combination of NiO and CuxO nanoarrays created multiple synergistic sites for molecular oxygen adsorption and activation. The addition of NiO induced the formation of low-valence Cu species and effectively optimized oxygen reduction reaction (ORR) kinetics. This enhancement led to an increased generation of key intermediates (·O2– and ·OH), which further promoted the efficient production of 1O2 through the chain reaction mediated by ·O2– and ·OH. NiO@CuxO NRs/CF achieved a 3.9-fold increase in 1O2 production compared to the CF electrode. NiO@CuxO NRs/CF electrodes exhibited exceptional performance in degrading CQ across a wide pH range (3-11). Meanwhile, it also displayed remarkable stability and anti-interference capability, highlighting their promising potential for practical applications. The study provides an innovative strategy for the in-situ production of 1O2 through molecular oxygen activation with a bimetallic composite catalyst to efficiently degrade organic pollutants.

Tetraphenylanthraquinone and Dihydroxybenzene-Tethered Conjugated Microporous Polymer for Enhanced CO2 Uptake and Supercapacitive Energy Storage.

Conjugated microporous polymers (CMPs) feature extended excellent porosity properties and fully conjugated electronic systems, making them highly effective for several uses, including photocatalysis, dye adsorption, CO2 capture, supercapacitors, and so on. These polymers are known for their high specific surface area and adjustable porosity. To synthesize DHTP-CMPs (specifically TPE-DHTP CMP and Anthra-DHTP CMP) with abundant nitrogen (N) and oxygen (O) adsorption sites and spherical structures, we employed a straightforward Schiff-base [4 + 2] condensation reaction. This involved using 2,5-dihydroxyterephthalaldehyde (DHTP-2CHO) as the primary building block and phenolic OH group source, along with two distinct structures: 4,4',4″,4"'-(ethene-1,1,2,2-tetrayl)tetraaniline (TPE-4NH2) and 4,4',4″,4"'-(anthracene-9,10-diylidenebis(methanediylylidene))tetraaniline (Anthra-4Ph-4NH2). The synthesized Anthra-DHTP CMP had a remarkable BET surface area (BETSA) of 431 m2 g-1. Additionally, it exhibited outstanding thermal stability, as shown by a T d10 of 505 °C. Furthermore, for practical implementation, the Anthra-DHTP CMP demonstrates a significant capacity for capturing CO2, measuring 1.85 mmol g-1 at a temperature of 273 K and 1 bar. In a three-electrode test, the Anthra-DHTP CMP has a remarkable specific capacitance of 121 F g-1 at 0.5 A g-1. Furthermore, even after undergoing 5000 cycles, it maintains a capacitance retention rate of 79%. Due to their outstanding pore characteristics, abundant N and O, and conjugation properties, this Anthtra-DHTP CMP holds significant potential for CO2 capture and supercapacitor applications. This work will pave the way for the development of materials based on DHTP-CMPs and their postmodification with additional groups, facilitating their use in photocatalysis, photodegradation, lithium battery applications, and so on.

Sonochemical synthesis of S-scheme CuO/CeO2 heterojunction for enhanced photocatalytic degradation of rhodamine B dye under solar radiations

CeO2 is renowned photocatalyst with 2.8 eV band gap energy and exceptional optical features. However, the slow charge transportation and the fast recombination of the electron-hole pair hindered the photocatalytic efficiency. In this pioneering research, S-scheme CuO/CeO2 heterojunctions were engineered sonochemically with rational compositions of CeO2 and CuO nanoparticles for enhanced the photocatalytic efficiency of CeO2 in destructing rhodamine B dye under full solar radiations. Diffuse reflectance spectrum [DRS], photoluminescence [PL], high resolution transmission electron microscope [HRTEM], selected area electron diffraction [SAED], N2-adsorption-desorption isotherm, X-ray photoelectron spectroscopy [XPS] and X-ray diffraction [XRD] investigated the physicochemical properties of CuO/CeO2 heterojunction. Monoclinic CuO nanoparticles of 8 nm size are facilely incorporated in cubic CeO2 crystallites of 27.3 nm through substitution of Ce4+ by Cu2+ ions which ascribed to smaller ionic radii of Cu2+ compared with Ce4+ and Ce3+ ions. Homogeneous distribution of CuO nanoparticles on CeO2 surface was further investigated by SEM and TEM analysis. HRTEM, XRD, SAED and XPS analysis recorded the co-existence of crystalline peaks of CeO2 and CuO implying the successful construction of CuO/CeO2 heterojunction. The depression in the surface area of CeO2 from 91.4 to 83.6 m2/g with incorporating 5 wt % of CuO revealed the deposition of CuO on CeO2 surface. XPS analysis implied the existence of Ce3+ and oxygen vacancies that provide more adsorption sites for oxygen, which are beneficial for enhancing the catalytic performance of catalysts. CuO nanoparticles with 1.3 eV band energy enhanced the visible light absorbability of the heterojunctions in deep visible region for broading the photocatalytic response. Significant reduction in photoluminescence signals intensity by 60 % with incorporation 5 wt % of CuO revealed the favorable reduction in the rate of electron-hole recombination. In particular, CeCu5 containing 5 wt % CuO expelled 96 % of RhB dye within 6-h under solar simulator compared with 13 % removal on pristine CeO2 and CuO surface. Hot radicals and positive holes degraded RhB dye molecules on the heterojunction surface as elucidated from scavenger experiments and PL analysis of terephthalic acid. The exceptional removal of RhB dye under solar radiation was ascribed to the alignment in the band structure of CeO2 and CuO nanoparticles and the successful production of an efficient S-scheme heterojunction with strong redox potential and better electron transportation and separation.

Monolithic polar conjugated microporous polymers: Optimisation of adsorption capacity and permeability trade-off based on process simulation of flue gas separation

The challenge in developing porous materials that significantly reduce energy consumption in industrial gas separation lies in striking a balance between adsorption capacity and permeability. Herein, the precise anchoring of polar oxygen adsorption sites in a robust porous conjugated backbone is achieved through the directed self-assembly of building blocks, resulting in the formation of oxygen-enriched conjugated microporous polymers (O-CMPs). O-CMPs serve as attractive porous hosts for the synergistic separation of CO2 and PM in exhaust gases emitted from point sources. As analyzed by surface electrostatic potential, the introduction of oxygen-doped π-conjugated systems induced surface charge redistribution, enhancing the CO2 quadrupole-dipole effect within a widely distributed microporous network. The O-CMPs exhibited a high CO2 adsorption capacity of 125.84 mg/g at 273 K and 1.0 bar. The monolithic O-CMPs incorporate permanently integrated hierarchical pores with a high micropore ratio. This transport channel can enhance the transfer rate of gas flow while selectively intercepting CO2 and PM. The rigid conjugated molecular chains and hollow nanotube microstructure effectively prevent material densification, yielding a minimal gas permeation resistance of only 5 Pa. Additionally, O-CMPs also demonstrate outstanding stability and PM separation performance under humid and acid/alkaline condition. The visual process simulations serve to further validate that aforementioned design strategy can optimize the trade-off between adsorption capacity and permeability.

Microenvironment tailoring mediated highly dispersed Mn-O-Ce interface for low-temperature NH3-SCR of NOx

In creating Ce-Mn oxide catalysts for low-temperature NH3-SCR reactions, conventional pyrolysis usually leads to agglomeration on the catalyst surface, making it difficult to expose its active components. The realization of microenvironmental modulation to expose more Mn-O-Ce active interfaces remains a formidable task. In this work, we successfully synthesized Ce-Mn oxides with abundant and highly dispersed Mn-O-Ce interfaces via microwave radiation. This microwave-mediated microenvironmental modulation promotes high surface area, surface oxygen adsorption and acidic sites, which exhibit outstanding low-temperature NH3-SCR reaction performance. Meanwhile, this work also provides new ideas for microenvironmental modulation to synthesize high-performance catalysts.

Bi-Doped and Bi Nanoparticles Loaded CeO2 Derived from Ce-MOF for Photocatalytic Degradation of Formaldehyde Gas and Tetracycline Hydrochloride.

Bi/CeO2 (BC-x) photocatalysts are successfully prepared by solvothermal loading Bi nanoparticles and Bi-doped CeO2 derived by Ce-MOF (Ce-BTC). Formaldehyde gas (HCHO) and tetracycline hydrochloride (HTC) are used to evaluate the photocatalytic activity of the synthesized Bi/CeO2. For BC-1000 photocatalyst, the degradation of HTC by 420nm < λ < 780nm light reaches 91.89% for 90min, and HCHO by 350nm < λ < 780nm light reaches 94.66% for 120min. The photocatalytic cycle experiments prove that BC-1000 has good cyclic stability and repeatability. The results of photoluminescence spectra, fluorescence lifetime, photocurrent response, and electrochemical impedance spectroscopy showed that the SPR (Surface Plasmon Resonance) effect of Bi nanoparticles acted as a bridge and promoted electron transfer and enhanced the response-ability of Bi/CeO2 to visible light. Bi-doping produced more oxygen vacancies to provide adsorption sites for adsorbing oxygen and generated more ·O2 - thus promoting photocatalytic reactions. The mechanism of photocatalytic degradation is analyzed in detail utilizing active free radical capture experiments and electron paramagnetic resonance (EPR) characterization. The experimental results indicate that ·O2 - and h+ active free radicals significantly promote the degradation of pollutants.

Ultrahigh-Efficient N,O-Functionalized covalent organic framework towards thorium adsorption from uranium and rare earth elements

The development of novel porous materials as adsorbents for highly effective separation of thorium from ore or nuclear wastewater co-existing with uranium and rare earth elements is one of the most desirable methods but remains challenging. In this work, we prepare a N,O-functionalized two-dimensional covalent organic framework (2D COF), namely TAPT-DHTA, with a permanent porous structure and plenty of nitrogen and oxygen adsorption sites throughout the skeletons, which displays an ultrahigh Th(IV) saturated adsorption capacity of 1394 mg g−1 (at pH = 4.0), higher than all adsorbents reported so far. Moreover, the TAPT-DHTA COF has a large distribution coefficient (Kd) of up to 5.2 × 104 mL g−1, implying its extremely strong affinity for Th(IV) due to the collaborative coordination interactions between N/O atoms and Th(IV) as well as their specific binding mechanism. The distinguished adsorption behavior of the TAPT-DHTA COF affords an important platform for highly selective separation of Th(IV) from uranium and rare earth elements, thereby shedding some light on the design of novel adsorbents for thorium separation in the thorium fuel cycle.

Identification of the optimal site for oxygen adsorption in chemisorbed and oxidized states on pseudomorphic Fe/Ru(0001) surface: A density functional theory computational investigation

The oxidation state and charge distribution of FexOy binaries, including strained monolayers on transition metal surfaces, is a topic of significant interest. The p(2 × 2) and c(4 × 2) superstructures are two stable surface structures of chemisorbed oxygen on the pseudomorphic Fe/Ru(0001) surface that may coexist at 0.25 ML oxygen coverage. Density functional theory calculations were used to investigate the possibility of these two structures occurring on the surface. The calculations considered the effect of magnetic ordering on the choice of adsorption site for oxygen. Paramagnetic ordering of the Fe monolayer favors oxygen adsorption at the hcp site, while antiferromagnetic ordering favors oxygen adsorption at the fcc site at 0.25 ML oxygen coverage. Interestingly, in the case of antiferromagnetic ordering, although the adsorption of 1 ML coverage of oxygen for the oxidation reaction energetically prefers the hcp site, the chemisorbed structures at 0.25 ML coverage are found to prefer the fcc site on the pseudomorphic Fe/Ru(0001) surface. The DFT calculations suggest that both the p(2 × 2) and c(4 × 2) structures of oxygen are exothermic, indicating the possibility of coexistence on the pseudomorphic Fe/Ru(0001) surface and occurrence at room temperature. However, the use of the Hubbard potential parameter, which is used to correctly describe the electronic band structure of FeO and other Mott insulators, also revealed that the oxidation reaction of the pseudomorphic Fe monolayer is endothermic on the Ru(0001) surface.

Enhanced dual gas sensing performance of MoS2/MoO3 nanostructures for NH3 and NO2 detection

Highly sensitive p-MoS2/n-MoO3 nanocomposite-based chemo-resistive gas sensors are synthesized by varying the reducing agents using hydrothermal synthesis followed by thermal annealing in an Ar environment for NH3 and NO2 detection at 50 °C. Structural characterizations confirmed the existence of MoS2 nanoflakes and MoO3 nanoplatelets and the appearance of abundant oxygen adsorption sites and sulfur vacancies in the nanocomposites. The MoS2:MoO3-based sensor (without any reducing agent) showed preferential detection of NH3 with 52% sensor response for 5 ppm gas concentration having response/recovery times of 28 s/97 s with n-type sensing behavior dominated by MoO3 charge carriers. On the contrary, NO2 gas attracts electrons from the MoS2 surface, exhibiting p-type sensing behavior with a sensor response of 42 % consisting of response/recovery times of 56 s/116 s with 5 ppm concentration at 50 °C. More interestingly, different adsorption sites and conductive channels play a huge role in the MoS2:MoO3 nanocomposite for exhibiting opposite sensing behaviours upon exposure to NH3 and NO2 gases. Enhanced sensitivity is dedicated to synergistic effects appearing due to the construction of p-n heterojunction to strengthen carrier transport by enhancing the sensor response. The present work provides a unique methodology for constructing MoS2:MoO3-based sensors and the effect of reducing agents on various MoS2:MoO3-based sensors. Moreover, our study recommends the plausible use of the MoS2:MoO3 composite-based heterojunctions to provide a constructive strategy for improving the performance of gas sensors.

Bimetallic niobium-iron oxynitride as a highly active catalyst towards the oxygen reduction reaction in acidic media

Developing cost-effective acidic oxygen reduction reaction (ORR) catalysts with high performance is of great significance for proton exchange membrane fuel cells (PEMFCs) but very challenging. Transition-metal oxynitrides have high tolerance to harsh acidic media due to their excellent corrosion resistance, but they suffer from low acidic ORR activity. Here we report the discovery of a carbon-supported bimetallic niobium-iron oxynitride as a highly active and robust ORR catalyst in acidic media. This catalyst shows much higher ORR activity than its monometallic niobium oxynitride counterpart and exhibits a record high ORR activity among transition-metal oxynitrides, with an optimal ORR half-wave potential of 0.75 V vs. RHE, approaching those of atomically dispersed metal-N-C materials. It is revealed that the optimal catalyst has two types of Fe species with low oxidation state and two additional oxygen adsorption sites with high reactivity in comparison to its monometallic niobium oxynitride counterpart, therefore resulting in its remarkable ORR activity. Our work provides a new direction to explore efficient acidic ORR catalysts with low costs.

Palladium functionalized carbon xerogel nanocomposite for oxygen reduction reaction

The design of an electrocatalyst with high efficiency and stability for oxygen reduction reaction is a crucial parameter in the field of fuel cells. Herein, a facile synthesis for palladium/carbon xerogel is reported. The effect of acidic and basic preparation conditions on the surface area, crystallite size, particle size, and morphology of the palladium/carbon composite was studied. Carbon-isolated spheres with lower crystallite size were obtained in case of acidic preparations than in basic preparations. While, upon application as electro-catalysts for the oxygen reduction reaction in an alkaline medium (0.1 M KOH), better activity was achieved for the palladium/carbon xerogel prepared in basic conditions. A promising limiting current density of −9.8 mA cm−2 is achieved at a rotating speed of 2500 rpm at a scan rate of 5 mV s−1. In addition, the lowest onset potential, Vonset of 0.8 V is also delivered by Pd/CB against RHE. Moreover, enhanced stability that reaches 99 % is obtained after 100th repetitive cycles. This higher activity for Pd/CB may be attributed to (i) its large pore width of 4.1 nm, (ii) higher crystallite size of 23.1 nm, (ii) high concentration of Pd nanoparticles over the carbon surface, and (iv) high content of oxygen surface which can act as additional active sites for oxygen adsorption. The acidic preparation method for palladium-doped-carbon can open the door for future research in preparing well-dispersed and low-size palladium nanoparticles inside the support material, hence reducing its leaching into the liquid phase, and improving its stability.

Exploring the factors influencing the low temperature CO gas production characteristics of low-metamorphic coal

CO as an important indicator gas for predicting early spontaneous combustion of coal mainly comes from the oxidation of residual coal in goaf. Low-metamorphic coal has a stronger tendency for spontaneous combustion and is more prone to oxidation to produce CO gas at low temperatures. For example, there are no signs of natural combustion in certain goaf areas of mines, but the CO concentration in the working face continues to exceed the limit, which misleads early natural combustion prediction and warning work. Therefore, taking low metamorphic coal as the main research object, the CO gas production characteristics of different coal samples at low temperatures were determined through temperature-programmed experiments. It was found that the CO gas production rate and concentration of CYM at low temperatures were much higher than those of the other two metamorphic coal samples (approximately 2 times RNM and 3–10 times QM); Determination of content and proportion changes of hydroxyl, aliphatic, Aromatic hydrocarbon and oxygen-containing functional groups in different coal samples before and after heating by Fourier transform infrared spectroscopy. Based on the analysis of CO gas production characteristics of different coal samples, it was found that the intermolecular hydrogen bonds in the hydroxyl groups of CYM and the C-O bonds in the oxygen-containing functional groups decreased significantly. The strongest correlation between intermolecular hydrogen bonds in hydroxyl groups and C-O bonds in oxygen-containing functional groups and the low-temperature CO gas production characteristics of coal is demonstrated; Finally, scanning electron microscopy was used to study the differences in apparent characteristics of different coal samples before and after heating, to determine more complex apparent structures that increase oxygen adsorption sites and promote low-temperature oxidation and CO production of coal during the low-temperature stage. Further guidance will be given to the research on the suppression of intermolecular hydrogen bonds and C-O bonds, as well as the sealing of coal micro pores and crack structures, to improve the targeted application and fire prevention efficiency of fire prevention materials.

Molecular simulation of Cu, Ag, and Au-decorated Molybdenum doped graphene nanoflakes as biosensor for carmustine, an anticancer drug

This study delves into the fascinating realm of molybdenum-doped graphene ([email protected]) complexes, featuring captivating adsorption sites for oxygen (O) and chlorine (Cl), adorned with the mesmerizing presence of silver (Ag), gold (Au), and copper (Cu). These alluring metal-doped compounds have been proposed as potential biosensor materials, with a particular focus on their prowess in the adsorption of carmustine (cmt). Employing the formidable density functional theory (DFT) at the B3LYP-GD3BJ/def2-SVP computational approach. Enveloped by the intrigue of two distinct adsorption sites—O and Cl—we stumbled upon a remarkable revelation. Among the contenders, [email protected][email protected] emerged triumphant with the lowest energy gap at the Cl site of carmustine adsorption, an astonishingly meager value of 0.082 eV. Following closely behind, [email protected][email protected] boasted a respectable energy gap of 0.852 eV. However, [email protected][email protected] and [email protected]@GP took the stage with their grandiose energy gaps, exhibiting values of 1.128 eV and 1.843 eV, respectively. Substantially, the captivating saga unfolds, presenting the distribution of adsorption energies as follows: [email protected]@GP > [email protected]@GP > [email protected][email protected] > [email protected][email protected] > [email protected][email protected] > [email protected][email protected] In a captivating interplay of energies, the system [email protected] unveils its preferences: the O site reigns supreme with an Eads of -0.59 eV, while the Cl site humbly follows with an Eads of -0.03. Meanwhile, within the realm of the [email protected] system, the Chlorine site claims dominance, boasting an Eads of -1.30eV, while the Oxygen site asserts its presence with an Eads of -0.21 eV. As for the [email protected] system, the Chlorine site emerges as the epitome of favorability, commanding an Eads of -0.83 eV, while the Oxygen site modestly exhibits an Eads of -0.29 eV. Through meticulous exploration, the results unequivocally demonstrate the remarkable qualities of the investigated complexes, positioning them as promising nanomaterials for the realm of drug delivery.

Effect of chromium dopant on electrospun zinc oxide nanostructure: A room temperature ethanol sensor

Nanomaterials-based gas sensors represent a ground-breaking endeavour that establishes a systematic and methodical approach to the detection of deleterious contaminants on a broad scale, particularly within the environmental and healthcare domains. In this context, we have commenced the synthesis of chromium-doped (0, 0.5, and 1 wt%) zinc oxide nanostructures through the utilization of an electrospinning technique, subsequently followed by a calcination process. The resultant chromium-doped zinc oxide nanostructures have been subjected to rigorous analysis, affirming their polycrystalline nature as well as the discernible impact of chromium dopants, as confirmed by the X-ray diffraction pattern. Interconnected irregularly shaped multi-grain particles with higher oxygen adsorption sites were confirmed by scanning electron microscope and X-ray photoelectron spectrometer. After analyzing the electrical and optical features, the fabricated sensing elements were tested for their sensing behaviour at room temperature and found to have a selective response towards ethanol vapour. Among the samples, 0.5 wt% chromium-doped zinc oxide exhibited a sensing response (S = 9.03 for 100 ppm) towards ethanol at room temperature. Additionally, the lower limit of detection was found to be 1 ppm, and the response and recovery times towards 100 ppm of ethanol are 41 & 81 s. Further, a thorough investigation into the influence of chromium dopants on the ZnO lattice has been conducted, revealing their pivotal role in augmenting the gas-sensing characteristics of the material.

Synergistic effect of nickel and calcium dual-atomic sites to facilitate electrochemical CO2 reduction to methanol: Combining high activity and selectivity

Atomically dispersed transition metal sites embedded into nitrogen-doped graphene provide promising potential for the electrochemical CO2 reduction to CO, but the catalytic efficiency for further hydrogenation to methanol is seriously restricted. Herein, combining the advantage of single transition metal, alkaline-earth metal, and multiple active sites, we designed nickel and calcium dual-atomic site catalysts (Ni-Ca DACs) supported on N-doped graphene to enable CO2 hydrogenation. First-principles calculations reveal that the electron-rich Ni atom serves as the carbon adsorption site, and the adjacent Ca atom with electron-deficient properties acts as the oxygen adsorption site, which largely stabilizes many CHxOy species through the O-Ca bond, especially the *OCHO, thus facilitating CO2 reduction. More importantly, a synergistic adsorption process on Ni-Ca sites promote the formation of *CHO species that is considered as the key intermediate for generation of multi-electron products. Different from the single Ni or Ca catalysts that produce mainly CO or HCOOH, the Ni-Ca DACs can selectively catalyze CO2 reduction to CH3OH, with a low limiting potential of −0.52 V, while suppressing the hydrogen evolution reaction. The outstanding catalytic activity originates from the tuned polarized charge and d-band center of active sites by synergistic interaction of adjacent Ni and Ca atoms.

Self-Assembly and the Properties of Micro-Mesoporous Carbon.

This study introduces a new approach for constructing atomistic models of nanoporous carbon by randomly distributing carbon atoms and pore volumes in a periodic box and then using empirical and ab initio molecular simulation tools to find the suitable energy-minimum structures. The models, consisting of 5000, 8000, 12000, and 64000 atoms, each at mass densities of 0.5, 0.75, and 1 g/cm3, were analyzed to determine their structural characteristics and relaxed pore size distribution. Surface analysis of the pore region revealed that sp atoms exist predominantly on surfaces and act as active sites for oxygen adsorption. We also investigated the electronic and vibrational properties of the models, and localized states near the Fermi level were found to be primarily situated at sp carbon atoms through which electrical conduction may occur. Additionally, the thermal conductivity was calculated using heat flux correlations and the Green-Kubo formula, and its dependence on pore geometry and connectivity was analyzed. The behavior of the mechanical elasticity moduli (Shear, Bulk, and Young's moduli) of nanoporous carbons at the densities of interest was discussed.

Synergistic enhancement of photocatalytic molecular oxygen activation by nitrogen defect and interfacial photoelectron transfer over Z-scheme α-Fe2O3/g-C3N4 heterojunction

Photoinduced molecular oxygen activation offers a promising strategy for oxidative degradation of organic pollutants, but the critical step of oriented electron delivery from the active sites into the stable O2 molecules presents a considerable challenge. Herein, we report the construction of a direct Z-scheme heterojunction with abundant nitrogen defects (α-Fe2O3/g-C3N4) for powering molecular oxygen activation by steering a specific migration route. This specific interfacial photoelectron transfer pathway showcases the establishment of an effective sequential photoelectron transfer channels between α-Fe2O3 and g-C3N4. The nitrogen defects on the g-C3N4 surface can not only serve as the oxygen adsorption sites, but also can act as the terminal electron sink to donate photoexcited high-energy electrons to the adsorbed O2. Therefore, the optimized α-Fe2O3/g-C3N4 exhibits greatly enhanced catalytic performance for molecular oxygen activation, and the degradation rate constant of tetracycline is 4.7 and 12 times higher than g-C3N4 and α-Fe2O3, respectively.

Single-atom Cu anchored on N-doped graphene/carbon nitride heterojunction for enhanced photocatalytic H2O2 production

Photocatalytic production of H2O2 by polymeric carbon nitride has been regarded as a promising approach for the conversion of solar energy into valuable chemicals. However, the efficiency of pristine carbon nitride is limited by the rapid charge recombination and the lack of suitable active sites. Herein, we introduce single-atom Cu anchored on N-doped graphene (Cu-NG) as a cocatalyst coupled with carbon nitride via covalent bonding to enhance photocatalytic H2O2 production. The Cu-NG/carbon nitride could broaden the light absorption from UV to near-infrared region, contributing to the photocatalytic process. Moreover, NG containing electron-rich N atoms could serve as anchoring sites for stabilizing single-atom Cu. Importantly, the single-atom Cu acts not only as an electron sink to steer the interfacial charge separation but also as an active site for molecular oxygen adsorption and activation. With the synergistic effect of the enhanced interfacial charge separation and suitable active sites, Cu-NG/carbon nitride exhibits improved photocatalytic performance with an H2O2 generation rate of 2856 µmol g−1 h−1, which is 2.6 times that of pristine carbon nitride. This work provides a protocol for high-performance photocatalytic H2O2 production using a single-atom cocatalyst.

Valorization of manganese residue to construct amorphous MnO2/α-Fe2O3@geopolymer Z-scheme heterojunction for efficient Cr(VI) reduction and ciprofloxacin degradation

To effectively utilize the hazardous industrial solid waste manganese residue (MR), a MR-derived Fe2O3-baesd photocatalyst with efficient charge transfer, abundant reactive sites and high redox performance was developed for simultaneously removing organic pollutants and heavy metals. Herein, a novel “confined growth” strategy was proposed to fabricate an amorphous MnO2 decorated α-Fe2O3@geopolymer sphere (A-MnO2/Fe2O3@GS) Z-scheme heterojunction by ion exchange method, which was used as a photo-Fenton catalyst for efficiently reducing Cr(VI) and degrading ciprofloxacin (CIP). Characterization results reveal that the 3D hydrangea-like MnO2 with low crystallinity could not only capture and accelerate electron transfer but also act as an electron conduction bridge and a surface oxygen adsorption site, resulting in efficient separation and utilization of charge. More importantly, the photocatalytic reduction capacity was greatly enhanced in Z-scheme heterojunction owing to the lower conduction band potential of MnO2. A-MnO2/Fe2O3@GS showed excellent photocatalytic activity with CIP removal of 99.1% within 40 min and Cr(VI) removal of 97.6% within 50 min, which were 8.13 and 3.47 times higher than those catalyzed by Fe2O3@GS, respectively. This can be ascribed to the formation of intimate interface, internal electrostatic field, and rich structure defects in the Z-scheme heterojunction. This work offers a new idea to construct Z-scheme photocatalysts with high reactivity for environmental modification.