Efficient Photocatalytic CO₂ Reduction with High Selectivity for Ethanol by Synergistically Coupled MXene-Ceria and the Charge Carrier Dynamics

Abstract

The primary factors that govern the selectivity and efficacy of CO2 photoreduction are the degree of activation of CO2 on the active surface sites of photocatalysts and charge separation/transfer kinetics. In this context, the rational synthesis of heterostructured MXene-coupled CeO2-based photocatalysts with different loading concentrations of Ti3C2MXene via a one-step hydrothermal approach has been undertaken. These photocatalysts exhibit a shift in X-ray diffraction peaks to higher 2θ values and changes in stretching vibrations of 5 wt % Ti3C2MXene/CeO2(5-TC/Ce) that indicate interaction between Ti3C2MXene and CeO2. Moreover, XPS analysis confirms the presence of the Ce3+/Ce4+ states. A sharp band at 2335 cm–1 observed during the CO2 photoreduction process corresponds to bidentate b-CO3 2–, which facilitates the adsorption of CO2 at the surface of the catalyst as revealed by the TPD analysis. Furthermore, the Schryvers test and NMR analysis were undertaken to confirm the formaldehyde intermediate formation during CO2 photoreduction to C2H5OH. The decrease in emission intensity, reduced lifetimes (2.68 ns), and lower interfacial resistance, as revealed by PL, TR-PL, and EIS analysis, imply an efficient charge separation and charge transfer in the case of the Ti3C2MXene/CeO2 heterojunction. The decrease in the intensity of peaks in the EPR spectrum in the case of 5-TC/Ce further confirms efficient charge transfer kinetics across the interface. The optimized 5-TC/Ce shows CO2 reduction with a drastically enhanced yield of ethanol on the order of 6127 μmol g–1 at 5 h with 98% selectivity and 7.54% apparent quantum efficiency, which is 6-fold higher than that of ethanol produced by bare CeO2. Herein, CeO2 that acts as a redox couple (Ce3+/Ce4+) when coupled with MXene having a metallic nature that reduces the electron transfer resistance is in unison, enabling an enhanced mobilization of electrons. Thereby, the synergistic coupling of Ti3C2MXene with CeO2 leads to an efficient photoreduction of CO2 under visible light illumination.

Mechanistic Insight into the Defect-Engineered White Light Emission from the Single-Phase Orthovanadate Phosphor Synthesized by a Facile Rapid Microwave-Assisted Synthesis

“…When a defect arises, there is the possibility of many different bond lengths of V–O, and hence, these different types of V–O units with extensive vibrations lead to broadband owing to the overlapping of different vibration bands with an increase in reaction time and temperature owing to oxygen-related vacancies for asymmetric and symmetric V–O bands. Other peaks beyond 1000 cm –1 are due to impurities and adsorbed water and CO 2 molecules on the surface of the molecules. ,, All of the above observations show the presence of extensive defects, which are also reflected in the emission spectra.…”

“…High-resolution Ba 3d spectra (Figure a,d) exhibit two peaks that denote Ba 3d 3/2 and Ba 3d 5/2 . The fitting analysis shows that these peaks observed at 794 and 778.6 eV, respectively, suggest the +2 oxidation state of barium. , The XPS peak for BOV-60 consists of two near-lying peaks, which can be observed in the deconvoluted high-resolution spectra of barium. This is due to the presence of two different types of barium atoms, which may be due to different chemical environments upon creation of oxygen vacancy, as seen in BOV-60, confirming the higher degree of defects of the phosphors at higher synthesis time. ,, In the V 2p spectrum, the peaks appearing at 515.8 and 523.4 eV correspond to V 2p3/2 and V 2p1/2, respectively (Figure b,e), which implies that V exists in the +5 state.…”

“…The fitting analysis shows that these peaks observed at 794 and 778.6 eV, respectively, suggest the +2 oxidation state of barium. , The XPS peak for BOV-60 consists of two near-lying peaks, which can be observed in the deconvoluted high-resolution spectra of barium. This is due to the presence of two different types of barium atoms, which may be due to different chemical environments upon creation of oxygen vacancy, as seen in BOV-60, confirming the higher degree of defects of the phosphors at higher synthesis time. ,, In the V 2p spectrum, the peaks appearing at 515.8 and 523.4 eV correspond to V 2p3/2 and V 2p1/2, respectively (Figure b,e), which implies that V exists in the +5 state. A trace amount of vanadium also exists in the +4 state, as confirmed by a small peak at 521.9 eV; it may be explained by the fact that with oxygen vacancies, the two electrons left in place of oxygen can reduce the adjacent V +5 to V +4 in phosphors. ,,,, The peak for V +4 is more intense in the case of BOV-60 than that of BOV-5, which confirms the presence of oxygen vacancies in both and more reduction in V +5 to V +4 owing to more oxygen vacancies and hence more available unpaired electrons in BOV-60.…”

Diphosphorus Center Derived from Polyoxometalate for High-Energy Lithium Storage of MXene Nanosheets

“…The peaks at 234.2 ± 0.1/230.5 ± 0.1 eV are indexed to Mo δ+ of MoP 2 , the satellite peaks at 235.1 ± 0.1/231.8 ± 0.1 and 236.1 ± 0.1/233.0 ± 0.1 eV are corresponding to Mo(V) and Mo(VI) of MoO 3 phase. , It suggests that there are oxygen vacancies in the structure of MoO 3 , which can decrease the band gap of the material and promote the conductivity, and the exposed dangling bonds will provide more active sites. It can be seen from Figure e that a single signal peak appears at g = 2.0027 for Ti 3 C 2 T x and 0.1PMA@Ti 3 C 2 T x , which is assigned to C vacancy or O 2– free radical of Ti 3 C 2 T x structure. , There are emerging signal peaks appearing between the magnetic field from 3450 to 3800 G. The peak at g = 1.946 is indexed to Mo 5+ center atom of the distorted MoO 3 , and the signal peaks with the vertical mode g ⊥ = 1.932 and the parallel mode g ∥ = 1.906 are both indexed to Mo 5+ center atom of the defective MoO 6 octahedron Figure d shows the existence of a P–O bond, , which may be derived from the decomposition product of PMA, or the interaction between P and the surface terminal under the catalytic action of thermally driven.…”