Adsorbed CO Molecules Research Articles

Selenium-modulated Pt/Al2O3 electronic structure induces deactivation during catalytic CO oxidation

Industrial sources, such as steel and power activities continue to emit substantial amounts of CO, but have not received the same level of attention as mobile sources due to a lack of relevant regulations. This work reports that a commercial Pt/Al2O3 catalyst used in vehicle CO catalytic converters may face severe selenium (Se) poisoning deactivation from industrial sources. The turnover frequency (TOF) of the Pt/Al2O3 catalyst (250 °C) decreased from 2.18 s−1 to 0.12 s−1 with only 0.49 wt% (ICP) Se deposition. Se deposition causes the Pt 5d orbital shift to a higher energy state, raising the oxidation state of platinum. As a result, the back-donation from the 5d electrons of Pt to the 2π* antibonding orbital of the adsorbed CO molecule is inhibited, weakening the bonding between Pt/Al2O3 and the CO antibonding orbital, thereby significantly reducing CO activation ability. DRIFTS results, combined with apparent and microscopic kinetics, indicate that the surface of Se deposited Pt/Al2O3 catalyst remains O* available (500 K, θO* = 0.16), and the rate-controlling step changes from O2 + 2* → 2O* to CO + * → CO*. The work suggests that the application of CO catalytic oxidation technology for industrial source should fully consider the toxic effect of Se, but is often neglected.

Adsorption-absorption technique for effective CO2 capture

ABSTRACT This paper presents a study on the removal of CO2 gas from gas mixture (CO2/N2) of 14% CO2 using adsorption onto zeolite 13X in a fluidized bed at 298 K and 1 atm pressure. The effects of static bed height (5–25 cm) and rate of flow of the gas mixture (6–14 L/min) on the breakthrough time were studied. The desorption of CO2 was performed by absorbing the adsorbed CO2 molecules using NaOH solution (0.1 M). The absorption process which was accompanied with chemical reaction achieved two objectives. The first was converting CO2 gas into a valuable substance (Na2CO3) which could be used in many industries. The second was the storage of CO2 gas in what was called a chemical carrier which could emit the gas when it was needed. The effect of static bed height (5–25 cm) on the absorption process in the fluidized bed was also studied. For the adsorption process, the results showed that the breakthrough time increased with decreasing the flow rate but with increasing the static bed height. In the desorption process, the total amount of absorbed CO2 molecules was 396 mg, achieving a recovery of 90.8% at 5 cm static bed height.

Constructing the high-efficiency “celluveyor conveyor” transport systems in membranes by IL@ZIF-8 for efficient CO2/CH4 separation

Inspired by the high-efficiency transport systems combined the “conveyor” transport pathways with the “celluveyor” transport pathways, the ionic liquid imide modified ZIF-8 (IL@ZIF-8) was prepared as a filler and incorporated into the self-polymerization-confined Pebax/polyethylene glycol methyl ether acrylate matrix (SPM) to prepare mixed matrix membranes (MMMs) for efficient CO2/CH4 separation. The incorporated IL@ZIF-8 can construct the high-efficiency “celluveyor conveyor” transport systems that consisted of the “celluveyor” transport pathways and the “conveyor” transport pathways, and it played important roles in MMMs. Therein, the “celluveyor” transport pathways can be constructed with the help of CO2 carriers (Zn2+) in oriented and ordered pore channels of IL@ZIF-8, contributing to promoting rapid CO2 transport in multiple direction. IL was uniformly distributed on ZIF-8, and it acted as “binder” between adjacent ZIF-8 in IL@ZIF-8. IL in IL@ZIF-8 can adsorb CO2 molecules as a consequence of its strong chemical affinity for CO2, and the “conveyor” transport pathways can be constructed with the help of CO2 carriers ([Tf2N]-) in IL for rapid CO2 transport between the adjacent ZIF-8, improving CO2 separation performance of MMMs. Consequently, it was possible to enhance the performance of CO2 separation by constructing the high-efficiency “celluveyor conveyor” transport systems in SPM/IL@ZIF-8 MMMs. Therefore, SPM/IL@ZIF-8 MMMs were endowed with the excellent CO2 separation performance. It showed an enhanced permeability for CO2, which increased by 96.9 %, and a better CO2/CH4 selectivity, which improved by 56.6 %, when compared to the performance of the pure SPM membrane. It implied that the constructed high-efficiency “celluveyor conveyor” transport systems in MMMs were a promising strategy for efficient CO2 separation.

Study of carbon monoxide adsorption on the α- and γ-graphyne nanosheets for the sensor applications

Recently, graphyne-based gas sensors have drawn a lot of interest. One kind of graphene with acetylene bonds connecting its hexagons is graphyne. In this study, the density functional theory (DFT) method was used to investigate the physical parameters of the surface adsorption of carbon monoxide on the [Formula: see text]- and [Formula: see text]-graphyne nanosheet, taking into account van der Waals (vdW) interactions through the use of the SIESTA computational code. CO molecule adsorbed and optimized in two vertical and horizontal states from the side of carbon and oxygen atoms, at different distances and sites relative to the graphyne sheet. After optimization and finding the adsorption energy, the best adsorption sites, equilibrium distance of the molecule from the surface, electronic structure, charge transfer rate, and bandgap changes were calculated. It was observed that the changes in the electronic structure after the adsorption of CO molecule are insignificant and the [Formula: see text]- and [Formula: see text]-graphyne nanosheets remained zero-gap and narrow-gap semiconductors, respectively. The adsorption of CO molecule on the [Formula: see text]- and [Formula: see text]-graphyne nanosheets is physisorption. The results show that the [Formula: see text]-graphyne nanosheet has a good potential for adsorbing and detecting CO molecules and sensor applications.

Synergistic N-heterocyclic carbene and C2N integration for efficient and selective metal-free photocatalytic CO reduction to C2H5OH

In the pursuit of sustainable and highly efficient catalysts for the reduction of CO to valuable multi-carbon fuels, this study presents a novel metal-free catalyst, C/C2N, created by integrating N-heterocyclic carbene (NHC) into a C2N monolayer. Utilizing density functional theory, we demonstrate that this integration effectively addresses the individual limitations of C2N and NHC, neither of which can stably adsorb CO molecules on their own. The synergistic effect of C2N and NHC facilitates distinct CO adsorption energies on the C2N surface (−0.08 eV) and at the NHC site (−0.83 eV), leading to an exceptionally low C–C coupling energy barrier of 0.41 eV, surpassing traditional metal-based catalysts. Computational results reveal that C/C2N exhibits outstanding activity and selectivity in reducing CO to C2H5OH, with a remarkably low free energy barrier of only 0.34 eV, further reducible to 0.20 eV under alkaline conditions. Furthermore, the integration of NHC into the C2N monolayer markedly narrows its band gap, enhancing visible light absorption and optimizing band edge positions, suggesting its potential for visible-light-driven reactions. Our findings establish C/C2N as an effective and selective metal-free photocatalyst with a notably low C–C coupling energy barrier, offering a novel avenue for CO conversion to multi-carbon fuels.

Dry Reforming of Methane to Syngas Mediated by Rhodium-Cobalt Oxide Cluster Anions Rh2CoO.

Dry reforming of methane (DRM) to syngas is an important route to co-convert CH4 and CO2. However, the highly endothermic nature of DRM induces the thermocatalysis to commonly operate at high temperatures that inevitably causes coke deposition through pyrolysis of methane. Herein, benefiting from the mass spectrometric experiments complemented with quantum chemical calculations, we have discovered that the bimetallic oxide cluster Rh2CoO- can mediate the co-conversion of CH4 and CO2 at room temperature giving rise to two free H2 molecules and two adsorbed CO molecules (COads). The only elementary step requiring the input of external energy (e.g., high temperature) is desorption of COads from the reaction intermediate Rh2CoOC2O2-. The doping effect of Co has also been clarified that the Co could tune the charge distribution and orbital energy of the active metal Rh, enabling the enhancement of cluster reactivity toward C-H activation, which is essential to facilitating the DRM to syngas. This work not only underlines the importance of temperature control over elementary steps in practical thermocatalysis but also identifies a promising active species containing the late 3d transition metal to drive DRM to syngas. The findings could provide novel insights into design of bimetallic catalysts for co-conversion of CH4 and CO2 at low temperatures.

Investigating the microscopic enhancement mechanisms of adsorption-based CO2 capture with Cu-loaded γ−Al2O3 using density functional theory

Transition-metal-loaded γ−alumina (Al2O3) is considered to be an effective adsorbent for CO2 capture, but its microscopic process and mechanisms of CO2 adsorption are not fully understood. To investigate the microscopic enhancement role of Cu atoms in CO2 adsorption, this work compares various adsorption configurations and parameters of CO2 on γ−Al2O3 (110) facets with or without Cu atoms and small Cu cluster loading (Cun (n=1,2,3)/γ−Al2O3) using the first-principles approach. According to the adsorption energy, charge transfer, difference charge density, and other parameters of different configurations, the γ−Al2O3 (110) slab loaded with the Cu atom is found to exhibit enhanced adsorption of CO2 molecules compared to that without Cu loading. Moreover, the surface stability increases with the number of loaded Cu atoms. However, the hydroxyl groups in the active sites partially undermine the adsorption effect during the CO2 adsorption process. The density of states indicates that the doping of Cu atoms in the system creates an orbital peak closer to the Fermi energy level. This facilitates the transfer of charge within the slab, making the activation of CO2 easier and promoting stable adsorption. Finally, the amount of crystal orbital overlap population and crystal orbital Hamilton population shows that the stability of adsorption is due to the formation of C-Cu and C-Al bonds. It is demonstrated that the Cun-loaded γ−Al2O3 (110) slab improves the adsorption performance and contributes to a better understanding of the effect of transition-state metal loaded γ−Al2O3 on CO2 adsorption.

Photocatalytic CO2 Reduction by Near‐Infrared‐Light (1200 nm) Irradiation and a Ruthenium‐Intercalated NiAl‐Layered Double Hydroxide

AbstractNear‐infrared light‐driven photocatalytic CO2 reduction (NIR‐CO2PR) holds tremendous promise for the production of valuable commodity chemicals and fuels. However, designing photocatalysts capable of reducing CO2 with low energy NIR photons remains challenging. Herein, a novel NIR‐driven photocatalyst comprising an anionic Ru complex intercalated between NiAl‐layered double hydroxide nanosheets (NiAl‐Ru‐LDH) is shown to deliver efficient CO2 photoreduction (0.887 μmol h−1) with CO selectivity of 84.81 % under 1200 nm illumination and excellent stability over 50 testing cycles. This remarkable performance results from the intercalated Ru complex lowering the LDH band gap (0.98 eV) via a compression‐related charge redistribution phenomenon. Furthermore, transient absorption spectroscopy data verified light‐induced electron transfer from the Ru complex towards the LDH sheets, increasing the availability of electrons to drive CO2PR. The presence of hydroxyl defects in the LDH sheets promotes the adsorption of CO2 molecules and lowers the energy barriers for NIR‐CO2PR to CO. To our knowledge, this is one of the first reports of NIR‐CO2PR at wavelengths up to 1200 nm in LDH‐based photocatalyst systems.

Photocatalytic CO2 Reduction by Near-Infrared-Light (1200 nm) Irradiation and a Ruthenium-Intercalated NiAl-Layered Double Hydroxide.

Near-infrared light-driven photocatalytic CO2 reduction (NIR-CO2PR) holds tremendous promise for the production of valuable commodity chemicals and fuels. However, designing photocatalysts capable of reducing CO2 with low energy NIR photons remains challenging. Herein, a novel NIR-driven photocatalyst comprising an anionic Ru complex intercalated between NiAl-layered double hydroxide nanosheets (NiAl-Ru-LDH) is shown to deliver efficient CO2 photoreduction (0.887 μmol h-1) with CO selectivity of 84.81 % under 1200 nm illumination and excellent stability over 50 testing cycles. This remarkable performance results from the intercalated Ru complex lowering the LDH band gap (0.98 eV) via a compression-related charge redistribution phenomenon. Furthermore, transient absorption spectroscopy data verified light-induced electron transfer from the Ru complex towards the LDH sheets, increasing the availability of electrons to drive CO2PR. The presence of hydroxyl defects in the LDH sheets promotes the adsorption of CO2 molecules and lowers the energy barriers for NIR-CO2PR to CO. To our knowledge, this is one of the first reports of NIR-CO2PR at wavelengths up to 1200 nm in LDH-based photocatalyst systems.

Tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient CO2 photoreduction

Two-dimension nanosheets are ideal photocatalysts for CO2 reduction due to their high exposure of active sites and short charge transfer pathway. However, 2D photocatalysts have a tendency to agglomeration, thus compromising the performance of photocatalytic CO2 reduction. Trees, one of the most important plants for photosynthesis, have a unique “leaf-on-branch” structure. This unique two-dimension/one-dimension (2D/1D) configuration maximizes the adsorption of CO2 molecules and light harvesting. Herein, a tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient photocatalytic CO2 reduction is reported. The cobalt silicate (CoSi) nanosheets (∼0.68 nm) are in situ grown on the surfaces of hydroxyapatite (HAP) nanowires, creating a well-defined 2D/1D hierarchical structure. The vertical alignment of ultrathin CoSi nanosheets on the HAP nanowires effectively suppresses their agglomeration, leading to a large BET surface area (106.45 m2/g) and excellent CO2 adsorption (8.00 cm3 g−1). The results of photoelectrochemical characterization demonstrate that the 2D/1D hierarchical structure is powerful to expedite charge transfer. As a result, the gas generation rate of CO is as high as 28780 μmol g−1 h−1 over the CoSi-on-HAP 2D/1D heterostructure. In addition, the electron transfer mechanism and reaction pathways of CO2 reduction are revealed by in situ irradiated XPS and in situ DRIFT spectra.

Chemical Orderings in CuCo Nanoparticles: Topological Modeling Using DFT Calculations.

The orderings of atoms in bimetallic 1.6-2.1 nm-large CuCo nanoparticles, important as catalytic and magnetic materials, were studied using a combination of DFT calculations with a topological approach. The structure and magnetism of Cu50Co151, Cu101Co100, Cu151Co50, and Cu303Co102 nanoparticles; their resistance to disintegrating into separate Cu and Co species; as well as the exposed surface sites, were quantified and analyzed, showing a clear preference for Cu atoms to occupy surface positions while the Co atoms tended to form a compact cluster in the interior of the nanoparticles. The surface segregation of Co atoms that are encapsulated by less-active Cu atoms, induced by the adsorption of CO molecules, was already enabled at a low coverage of adsorbed CO, providing the energy required to displace the entire compact Co species inside the Cu matrices due to a notable adsorption preference of CO for the Co sites over the Cu ones. The calculated adsorption energies and vibrational frequencies of adsorbed CO should be helpful indicators for experimentally monitoring the nature of the surface sites of CuCo nanoparticles, especially in the case of active Co surface sites emerging in the presence of CO.

Healable multilayered photocatalysts promote durability and productivity of solar-driven CO2 conversion

Numerous studies have focused on efficient CO2 photoreduction on short notice. However, more hours of efficient and selective CO2 and pure water photoconversion without precious metals or sacrificing reagents should be emphasized. Herein, a multilayer (SrTiO3/Ce:CaF2/CuNi/Ce:CaF2/TiN) is utilized with a high selectivity of 87 % for healable photocatalytic CO2 and pure water conversion without sacrificial reagents and the longest service life for the Cu nanolayers, to the best of our knowledge. Meanwhile, the photocatalytic activity, optical absorption, and charge separation ability of SrTiO3/Ce:CaF2/CuNi/Ce:CaF2/TiN can be recovered after regeneration. The deactivation and healable mechanism are illuminated that the adsorption of CO2 molecules at the photocatalyst surface is changed from M-CO2 to MO-CO2, due to the oxidation of active sites, resulting in the deactivation of CO2 reduction. The Ce:CaF2 nanolayers can accommodate oxygen atoms effectively to heal the photocatalyst. The article proposes a feasible way for commercial CO2 and pure water photoconversion.

Copper/Polyaniline Interfaces Confined CO2 Electroreduction for Selective Hydrocarbon Production.

Polyaniline (PANI) provides an attractive organic platform for CO2 electrochemical reduction due to the ability to adsorb CO2 molecules and in providing means to interact with metal nanostructures. In this work, a novel PANI supported copper catalyst has been developed by coupling the interfacial polymerization of PANI and Cu. The hybrid catalyst demonstrates excellent activity towards production of hydrocarbon products including CH4 and C2H4, compared with the use of bare Cu. A Faradaic efficiency of 71.8 % and a current density of 16.9 mA/cm2 were achieved at -0.86 V vs. RHE, in contrast to only 22.2 % and 1.0 mA/cm2 from the counterpart Cu catalysts. The remarkably enhanced catalytic performance of the hybrid PANI/Cu catalyst can be attributed to the synergistic interaction between the PANI underlayer and copper. The PANI favours the adsorption and binding of CO2 molecules via its nitrogen sites to form *CO intermediates, while the Cu/PANI interfaces confine the diffusion or desorption of the *CO intermediates favouring their further hydrogenation or carbon-carbon coupling to form hydrocarbon products. This work provides insights into the formation of hydrocarbon products on PANI-modified Cu catalysts, which may guide the development of conducting polymer-metal catalysts for CO2 electroreduction.

Addressing the Activity and Selectivity Challenges for CO2 Reduction via Transition‐Metal‐Free Homo‐ and Hetero‐Biatomic Catalysts Embedded in Two‐Dimensional Networks

AbstractDesigning low‐cost and stable electrocatalysts with enhanced activity and selectivity for CO2 valorization to useful chemicals and fuels faces enormous challenges to address the pressing climate change concerns. Synergistic interactions between the atoms in double atom catalysts has emerged as a promising tool to tune and boost CO2 activation and reduction. In this work, we systematically designed highly stable transition‐metal‐free homo‐ and hetero‐biatomic catalysts based on Al, Be, B and Si supported on TCNQ monolayer for CO2 reduction to C1 products using dispersion corrected periodic density functional theory calculations. Our findings reveal that transition‐metal‐free homo‐and hetero‐biatomic TCNQ catalysts can effectively capture and activate the CO2 molecule with binding energies ranging from 0.09 to 2.35 eV. Extensive free energy calculations to screen the favourable reaction pathways to different C1 products (CO, HCOOH, CH3OH and CH4) demonstrate that Al2‐TCNQ, AlBe‐TCNQ and BeSi‐TCNQ stand out as potential candidates for catalyzing CO2RR to methanol in a selective manner, suppressing the competitive HER simultaneously. Remarkably, BeSi‐TCNQ shows the best catalytic activity towards CO2 reduction to methanol at record low limiting potential of −0.29 V with spontaneous desorption of the final product. From the in‐depth examination of the electronic structure details, integrated projected density of states and crystal orbital Hamilton populations are used to understand and rationalize the binding interactions between the adsorbed CO2 molecule and the homo‐ or hetero‐biatomic TCNQ catalysts. Moreover, the ΔG*COOH‐ΔG*CO2 and ΔG*HCOOH‐ΔG* OCHO/*COOH values are found to provide reasonable guidance to evaluate the overall CO2RR performance of homo‐ and hetero‐biatomic TCNQ catalysts, respectively. Therefore, our findings provide significant insights for designing transition metal‐free homo‐ and hetero‐biatomic catalysts with intriguing properties for improving CO2 utilization and conversion.

Sorption-enhanced intensified CO2 hydrogenation via reverse water–gas shift reaction: Kinetics and modelling

Intensification of CO2 hydrogenation via the reverse water–gas shift (RWGS) reaction for CO production can be achieved through in situ removal of water when hydrophilic adsorbents are incorporated alongside the catalyst in the reaction bed. In this work, seeking to move a step closer to the industrial implementation of this innovative CO2 valorization process, a comprehensive reactor model, validated by experimental data obtained in a fixed-bed reactor, was developed to simulate the behavior of this sorption-enhanced (SE) RWGS process. Simulation and experimental data matched with good accuracy, demonstrating the striking benefits brought by the adsorbent addition, such as an almost doubling of the CO production rate at 300 °C. The kinetics of RWGS reaction over a Cu-based catalyst and H2O adsorption on a 13X zeolite adsorbent were studied both experimentally and theoretically and the kinetic models were integrated into the reactor model to assess the performance of SE-RWGS process. Fitting of the RWGS reaction rates by a Langmuir-Hinschelwood-Hougen-Watson-type heterogeneous kinetic model suggested that the rate-determining step of the reaction is the surface interaction between an adsorbed CO2 molecule and a H* species on catalytic sites of different nature. Meanwhile, the dynamic behavior of water adsorption was effectively simulated by a semi-empirical double-stretched exponential model combined with the Sips isotherm model. The results of this work could be applied to the design and scale-up of the SE-RWGS process, which offers considerable improvements over the thermodynamically constrained conventional process. The intensified approach represents a promising avenue for the effective conversion of carbon dioxide into CO, as well as into other value-added chemicals as part of a multi-stage CO2 reduction process.

Regulating the d-band center of Cu nanoparticles for efficient photo-driven catalytic CO2 reduction

The conversion of CO2 into solar fuels via photo-driven catalytic reduction presents a promising avenue toward achieving carbon neutrality. Herein, copper-based catalysts are prepared and explored for photo-driven photothermal CO2 reduction reaction. The optimized catalyst exhibits a consistent CO production rate of 165.9 mmol g−1 h−1 and 100% CO selectivity at ambient pressure. We unveil the intricate adsorption dynamics at play: H2 molecules predominantly interact with and activate at Cu sites, while CO2 molecules preferentially adsorb and activate at interfacial sites within the composites. Furthermore, we elucidate how the positive shift of the d-band center (εd) for Cu 3d orbitals significantly enhances H2 adsorption and activation. Crucially, the subsequent dissociation of H2 molecules at Cu sites drives the efficient conversion of adsorbed CO2 molecules at interfacial sites into CO. Overall, our findings not only advance the theoretical understanding but also offer practical insights for realizing photothermal catalytic CO2 reduction reactions.

Unlocking the Potential of Cu/Ti3C2Tx MXene Catalyst in Plasma Catalytic CO2 Hydrogenation

Plasma catalytic CO2 hydrogenation has emerged as a promising approach for converting CO2 into valuable chemicals such as CO, offering a potential solution to mitigate greenhouse gas emissions. In this study, we investigate the synergistic effect between plasma and a Cu/Ti3C2Tx MXene catalyst for CO2 hydrogenation via the reverse water gas shift (RWGS) reaction in a dielectric barrier discharge (DBD) reactor. Our findings reveal a significant enhancement in CO2 conversion (33.1%) and CO yield (31.9%) when using the Cu/Ti3C2Tx catalyst compared to plasma alone or with a Ti3C2Tx foam. Plasma treatment creates unsaturated Ti sites on the Ti3C2Tx surface, dramatically improving CO2 adsorption and activation, while Cu nanoparticles significantly enhances the activation and dissociation of H2 molecules on the catalyst surface. These surface adsorbed hydrogen species readily hydrogenate adsorbed CO2 molecules through the Langmuir-Hinshelwood mechanism. Furthermore, these surface hydrogen species can also participate in the conversion of gas-phase CO2 molecules through the Eley-Rideal pathway. This work sheds light on the synergistic plasma catalytic mechanism and provide insights for optimizing CO2 hydrogenation processes using MXene catalysts.

Pyridinic-N Coordination Effect on the Adsorption and Activation of CO2 by Single Vacancy Iron-Doped Graphene.

Graphene doped with different transition metals has been recently proposed to adsorb CO2 and help reduce the greenhouse effect. Iron-doped graphene is one of the most promising candidates for this task, but there is still a lack of full understanding of the adsorption mechanism. In this work, we analyze the electronic structure, geometry, and charge redistribution during adsorption of CO2 molecules by single vacancy iron-doped graphene by DFT calculations using the general gradient approximation of Perdew, Burke, and Ernzernhof functional (PBE) and the van der Waals density functional (vdW). To understand the impact of the pyridinic-N coordination of the iron atom, we gradually replaced the neighboring carbon atoms by nitrogen atoms. The analysis indicates that chemisorption and physisorption occur when the molecule is adsorbed in the side-on and end-on orientation, respectively. Adsorption is stronger when pyridinic-N coordination increases, and the vdW functional describes the chemical interactions and adsorption energy differently in relation to PBE without significant structural changes. The development of the chemical interactions with the change of coordination in the system is further investigated in this work with crystal overlap Hamilton population (COHP) analysis.

Oxygen vacancies-tuned BiOBr nanosheets for accelerating CO2 and Cr(VI) photoreduction

Unsatisfactory charge separation ability and insufficient active sites are the main factors leading to low efficiency for photocatalytic CO2 conversion and Cr(VI) reduction. Constructing surface defects to accelerate charge separation is an effective strategy for promoting photocatalytic process. Herein, the oxygen vacancies modulated BiOBr nanosheets were constructed by NaBH4 solution treatment. Density functional theory calculation results found that the formed oxygen vacancies would increase the electron density around Bi atoms near the oxygen vacancies, and inhibiting recombination of the photoinduced carriers. Besides, abundant oxygen vacancies can effectively enhance the adsorption of CO2 molecules. Therefore, the BiOBr with rich oxygen vacancies (BiOBr-ROV) shows higher evolution rates for CO (15.66 μmol g−1) and CH4 (0.22 μmol g−1) under irradiation of 300 W Xe lamp for 4 h compared with pristine BiOBr nanosheets (BiOBr) and BiOBr with deficient oxygen vacancies (BiOBr-DOV). The intermediate products in the CO2 reduction process have been detected by in-situ Fourier-transform infrared spectroscopy. Besides, the photodegradation activity of Cr(VI) over BiOBr-ROV is 98.65% under 80 min of irradiation, which is higher than that of BiOBr (78.01%) and BiOBr-DOV (53.67%). The work provides a new possibility to construct photocatalysts with high-performance for solar energy conversion.

A C21Ge two-dimensional material with high sensitivity and strong adsorption capacity for CO

Density functional theory (DFT) calculations were employed to investigate the adsorption of a single CO molecule on C21Ge (named due to the presence of 21 carbon atoms and 1 germanium atom in its structure). The study involved the determination of the most stable geometric structures, adsorption energies, adsorption heights, and density of states for the system, exploring the interactions between the adsorbed CO molecule and the substrate. The results revealed a high degree of CO adsorption on C21Ge, with adsorption energies of −1.34 eV and −1.33 eV for C atoms near the adsorption site and O atoms near the adsorption site, respectively. The adsorption distances were determined to be 2.89 Å and 3.04 Å, with the most stable adsorption sites identified as H3 and B3. The adsorption strength was slightly higher when C atoms were in proximity compared to O atoms. The high degree of hybridization between the density of states orbitals indicated strong interactions between the CO molecule and C21Ge, emphasizing the pronounced adsorption capability of C21Ge for CO.