Coadsorption properties of CO2 and H2O on TiO2 rutile (110): A dispersion-corrected DFT study

Effect of Mn, N co-doped LiFePO4 on electrochemical and mechanical properties: A DFT study

In this study, the thermodynamic stability, embedding voltage, volume change rate, electronic structure properties, mechanical properties and lithium-ion diffusion characteristics of the Mn, N co-doped LiFePO4 material are investigated using a first-principles approach based on density generalization theory. The results show that the doped system has a low formation energy and the material meets the thermodynamic stability criteria. During the de-lithium process, the volume change rate of the doped material decreases and the cycling performance is improved, but the battery energy density decreases slightly. It is also found that the doping of N led to the transformation of the material from a p-type semiconductor to an N-type semiconductor, while the doping of Mn and N lead to the creation of impurity bands, narrowing of the band gap and an increase in conductivity. At the same time, Mn, N co-doping greatly improve the ductility of the material, suppress the generation of microcracks, and reduce the possibility of shear deformation. In addition, it is noteworthy that the lithium-ion diffusion energy barrier of the doped system is reduced, which predicts an increase in the diffusion rate of lithium ions in the doped system.

Self-Competitive Adsorption Behavior of Arsenic on the TiO2 Surface

TiO2 is a commonly used material to remove arsenic from drinking water by adsorption as well as photocatalytic oxidation (PCO). In the present paper, arsenic adsorption and PCO at different pH environments are studied on the (1 1 0) facet of rutile TiO2 (r-TiO2). A self-competitive adsorption (SCA) behavior of arsenic is observed; i.e., arsenic species compete to adsorb on the surface. Related DFT calculations are carried out to simulate adsorption. SCA behavior is the key to connecting calculation results with experimental results. Furthermore, PCO of arsenite is performed at different pH values. Of note, PCO is related to adsorption; namely, the adsorption process determines the whole PCO reaction speed. Therefore, SCA is also helpful for the PCO reaction. The SCA behavior is useful not only for arsenic on r-TiO2 but also for arsenic on anatase TiO2 (a-TiO2). It may be helpful to further study arsenic adsorption and PCO on other materials such as Fe2O3 and MnO2. The SCA behavior extends our understanding of arsenic and provides new insights into arsenic removal and its cycle in nature.

Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review

Solar fuel generation through CO₂ hydrogenation is the ultimate strategy to produce sustainable energy sources and alleviate global warming. The photocatalytic CO₂ conversion process resembles natural photosynthesis, which regulates the ecological systems of the earth. Currently, most of the work in this field has been focused on boosting efficiency rather than controlling the distribution of products. The structural architecture of the semiconductor photocatalyst, CO₂ photoreduction process, product analysis, and elucidating the CO₂ photoreduction mechanism are the key features of the photoreduction of CO₂ to generate C1 and C2 based hydrocarbon fuels. The selectivity of C1 and C2 products during the photocatalytic CO₂ reduction have been ameliorated by suitable photocatalyst design, co-catalyst, defect states, and the impacts of the surface polarisation state, etc. Monitoring product selectivity allows the establishment of an appropriate strategy to generate a more reduced state of a hydrocarbon, such as CH₄ or higher carbon (C2) products. This article concentrates on studies that demonstrate the production of C1 and C2 products during CO₂ photoreduction using H₂O or H₂ as an electron and proton source. Finally, it highlights unresolved difficulties in achieving high selectivity and photoconversion efficiency of CO₂ in C1 and C2 products over various nanostructured materials.

Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2 O

The design of robust, high-performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2 O. It is hypothesized that superior H2 O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2 . These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended π-conjugation. The as-synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar-energy conversion.

Two-dimensional nitrides as highly efficient potential candidates for CO2 capture and activation

The performance of novel two-dimensional nitrides in carbon capture and storage (CCS) is analyzed for a broad range of pressures and temperatures. Employing an integrated theoretical framework where CO2 adsorption/desorption rates on the M2N (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) surfaces are derived from transition state theory and density functional theory based calculations, the present theoretical simulations consistently predict that, depending on the particular composition, CO2 can be strongly adsorbed and even activated at temperatures above 1000 K. For practical purposes, Ti2N, Zr2N, Hf2N, V2N, Nb2N, and Ta2N are predicted as the best suited materials for CO2 activation. Moreover, the estimated CO2 uptake of 2.32-7.96 mol CO2 kg-1 reinforces the potential of these materials for CO2 abatement.

Critical Role of Water and Oxygen Defects in C-O Scission during CO2 Reduction on Zn2GeO4(010)

Exploration of catalyst structure and environmental sensitivity for C-O bond scission is essential for improving the conversion efficiency because of the inertness of CO₂. We performed density functional theory calculations to understand the influence of the properties of adsorbed water and the reciprocal action with oxygen vacancy on the CO₂ dissociation mechanism on Zn₂GeO₄(010). When a perfect surface was hydrated, the introduction of H₂O was predicted to promote the scission step by two modes based on its appearance, with the greatest enhancement from dissociative adsorbed H₂O. The dissociative H₂O lowers the barrier and reaction energy of CO₂ dissociation through hydrogen bonding to preactivate the C-O bond and assisted scission via a COOH intermediate. The perfect surface with bidentate-binding H₂O was energetically more favorable for CO₂ dissociation than the surface with monodentate-binding H₂O. Direct dissociation was energetically favored by the former, whereas monodentate H₂O facilitated the H-assisted pathway. The defective surface exhibited a higher reactivity for CO₂ decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location. When the defective surface was hydrated, the reciprocal action for vacancy and surface H₂O on CO₂ dissociation was related to the vacancy type. The presence of H₂O substantially decreased the reaction energy for the direct dissociation of CO₂ on O_2c1- and O_3c2-defect surfaces, which converts the endoergic reaction to an exoergic reaction. However, the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate. When H₂O was present on the O_2c2-defect surface, both the barrier and reaction energy for direct dissociation were invariable. This result indicated that the introduction of H₂O had little effect on the kinetics and thermodynamics. Moreover, the H-assisted pathway was suppressed on all hydrated defect surfaces. These results provide a theoretical perspective for the design of highly efficient catalysts.

Environmental Effects on Zirconium Hydroxide Nanoparticles and Chemical Warfare Agent Decomposition: Implications of Atmospheric Water and Carbon Dioxide

Zirconium hydroxide (Zr(OH)₄) has excellent sorption properties and wide-ranging reactivity toward numerous types of chemical warfare agents (CWAs) and toxic industrial chemicals. Under pristine laboratory conditions, the effectiveness of Zr(OH)₄ has been attributed to a combination of diverse surface hydroxyl species and defects; however, atmospheric components (e.g., CO₂, H₂O, etc.) and trace contaminants can form adsorbates with potentially detrimental impact to the chemical reactivity of Zr(OH)₄. Here, we report the hydrolysis of a CWA simulant, dimethyl methylphosphonate (DMMP) on Zr(OH)₄ determined by gas chromatography-mass spectrometry and in situ attenuated total reflectance Fourier transform infrared spectroscopy under ambient conditions. DMMP dosing on Zr(OH)₄ formed methyl methylphosphonate and methoxy degradation products on free bridging and terminal hydroxyl sites of Zr(OH)₄ under all evaluated environmental conditions. CO₂ dosing on Zr(OH)₄ formed adsorbed (bi)carbonates and interfacial carbonate complexes with relative stability dependent on CO₂ and H₂O partial pressures. High concentrations of CO₂ reduced DMMP decomposition kinetics by occupying Zr(OH)₄ active sites with carbonaceous adsorbates. Elevated humidity promoted hydrolysis of adsorbed DMMP on Zr(OH)₄ to produce methanol and regenerated free hydroxyl species. Hydrolysis of DMMP by Zr(OH)₄ occurred under all conditions evaluated, demonstrating promise for chemical decontamination under diverse, real-world conditions.

Activation of CO2 by supported Cu clusters

CO₂ forms a bent, negative anion upon adsorption near a Cu₃ cluster supported on TiO₂.

Insights into the mechanism of the capture of CO2 by K2CO3 sorbent: a DFT study

The adsorption and reactions of CO₂ and H₂O on both monoclinic and hexagonal crystal K₂CO₃ were investigated using the density functional theory (DFT) approach.

The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface

CO₂ capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO₂ conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO₂ on rutile (110) surface. The calculated results demonstrate that CO₂ can be activated as CO₂ anions or CO₂ cation when the system contains excess electrons and holes. The electronic structure of the activated CO₂ is greatly changed, and the lowest unoccupied molecular orbital of CO₂ can be even lower than the conduction band minimum of TiO₂, which greatly facilities the CO₂ reduction. Meanwhile, the dissociation process of CO₂ undergoes an activated CO₂⁻ anion in bend configuration rather than the linear, while the long crossing distance of proton transfer greatly hinders the photocatalytic reduction of CO₂ on the rutile (110) surface. These results show the importance of the excess electrons on the CO₂ reduction process.

CO2 Capture and Conversion on Rutile TiO2(110) in the Water Environment: Insight by First-Principles Calculations

The conversion of CO2 by the virtue of sunlight has the great potential to produce useful fuels or valuable chemicals while decreasing CO2 emission from the traditional fossil fuels. Here, we use the first-principles calculations combined with the periodic continuum solvation model (PCSM) to explore the adsorption and reactivity of CO2 on rutile TiO2(110) in the water environment. The results exhibit that both adsorption structures and reactivity of CO2 are greatly affected by water coadsorption on rutile TiO2(110). In particular, the solvation effect can change the most stable adsorption configuration of CO2 and H2O on rutile TiO2(110). In addition, the detailed conversion mechanism of CO2 reduction is further explored in the water environment. The results reveal that the solvation effect cannot only greatly decrease the energy barrier of CO2 reduction but also affect the selectivity of the reaction processes. These results presented here show the importance of the aqueous solution, which should be helpful to understand the detailed reaction processes of photocatalysts.

Adsorption and interaction of CO2 on rutile TiO2(110) surfaces: a combined UHV-FTIRS and theoretical simulation study

P-polarized RAIR spectra of CO₂ adsorbed on reduced rutile TiO₂(110) surfaces as a function of CO₂ dosage and adsorption temperature. The incidence plane is along (a) the [001] azimuth and (b) the [11̄0] azimuth respectively.

Photocatalytic conversion of CO(2) into renewable hydrocarbon fuels: state-of-the-art accomplishment, challenges, and prospects

Photocatalytic reduction of CO2 into hydrocarbon fuels, an artificial photosynthesis, is based on the simulation of natural photosynthesis in green plants, whereby O2 and carbohydrates are produced from H2 O and CO2 using sunlight as an energy source. It couples the reductive half-reaction of CO2 fixation with a matched oxidative half-reaction such as water oxidation, to achieve a carbon neutral cycle, which is like killing two birds with one stone in terms of saving the environment and supplying future energy. The present review provides an overview and highlights recent state-of-the-art accomplishments of overcoming the drawback of low photoconversion efficiency and selectivity through the design of highly active photocatalysts from the point of adsorption of reactants, charge separation and transport, light harvesting, and CO2 activation. It specifically includes: i) band-structure engineering, ii) nanostructuralization, iii) surface oxygen vacancy engineering, iv) macro-/meso-/microporous structuralization, v) exposed facet engineering, vi) co-catalysts, vii) the development of a Z-scheme system. The challenges and prospects for future development of this field are also present.