Different conformations, including planar, corrugated, as well as the deficient structure of the two-dimensional materials, play a relevant role in determining their catalytic reaction performances. Here, we systematically investigated the stabilities, electronic properties, and nitrogen activities capacity of various vacancy-modified g-C3N4 considering two different conformations (planar and corrugated) to explore the effects of nitrogen vacancy (NV) and conformations on the photocatalytic performance of g-C3N4 by means of density functional theory computations. Our results found that not only can the nitrogen vacancy (NV) promote separation efficiency of the photoinduced carriers in g-C3N4 but also the distortion conformation can activate more n → π* transitions of NV g-C3N4, resulting in a red shift of optical absorption spectra. More importantly, our results reveal that the corrugation configuration structure, compared to planar conformation, is much more favorable to photocatalytic nitrogen fixation reaction from the aspects of nitrogen absorption capacity and free-energy change, in which corrugation model with N2C vacancy has the smallest onset potential (1.32 V) for the most difficult step through the alternating pathway.

CeO2-based catalysts are potentially suitable for H2S-selective oxidation, but their practical application is limited due to the problem of sulfate formation. Herein, we report a facile citric acid-assisted hydrothermal process for the fabrication of porous Fe-doped CeO2 with flower-like morphology that can drastically promote the catalytic activities of CeO2 with high durability. Among the synthesized catalysts, the one with well-defined (110) and (100) planes is highly active for H2S-selective oxidation with H2S conversion and sulfur selectivity of almost 100% at 220 °C, superior to most of the reported Ce-based catalysts. Meanwhile, outstanding catalytic stability is achieved because the presence of Fe ions alleviates ceria deactivation due to sulfation. The results of systematic investigation prove that the doping of Fe not only raises the density of oxygen vacancies but also promotes the redox ability and oxygen activity of the catalyst. We conducted in situ DRIFTS (diffuse reflection infrared Fourier transform spectroscopy) experiments and density functional theory (DFT) calculations to disclose the reaction mechanism of H2S oxidation. The derived insights are important for the design of efficient ceria-related catalysts for practical applications.

Periodic density functional theory calculations have been performed to investigate the structures, the linear and second order nonlinear optical (NLO) properties of Zr-based UiO-66 metal−organic frameworks, in which the 1,4-benzene-dicarboxylate (BDC) linkers are functionalized by a series of isovalent substituents including −NH 2 , −OH, −SH, and halogen atoms. Our results show that the mixed phase will be formed for the case of the incorporation of a single hydroxyl or halogen atom, while it is more likely to synthesize the pure phase for the homodifunctionalized compounds. The ligand functionalization results in the appearance of the band gap states as well as the narrowing of the band gap. For the linear optical response, besides the redshift of the absorption edge, the ligand modification tends to increase the dielectric constant and enhance the optical anisotropy of UiO-66, especially when two −SH groups are incorporated into the BDC ligand. With regard to the NLO activity, the second harmonic generation (SHG) intensity of the pristine UiO-66 is comparable to that of KDP. The SHG response of UiO-66 can be effectively improved by the single-site substitution, and the obvious enhancement of the SHG activity is observed after introducing the sulfydryl group or the iodine atom. However, it is noted that the difunctionalizations by two −OH and −SH have a relatively weak impact on the SHG intensity because of the nearly centrosymmetric organization of the homodifunctionalized organic linkers. Among all derivatives, UiO-66-(SH) 2 is the most promising candidate for use as a near-infrared NLO material with a strong SHG effect (>20 pm/V) and good phase matchability. Furthermore, the primary origin of the SHG response for UiO-66 and its derivatives is determined by analyzing the band structure. This study reveals the possibility of designing NLO materials with outstanding performances based on the UiO-66-derived MOFs through rational functionalization of the organic linking unit.

Electrocatalytic nitrogen fixation using single-atom catalysts (SACs) offers a promising strategy for the sustainable production of NH3. On the basis of density functional theory, we systematically explored the potential for N2 electroreduction of single-atom catalysts (SACs) covering V, Nb, and Ta transition metal (TM) centers supported by graphene and g-C3N4 substrates. The single Nb-atom embedded on g-C3N4 nanosheet possesses outstanding nitrogen reduction reaction (NRR) catalytic activity and exhibits better performance than graphene with a considerably smaller maximum ΔG value (0.05 eV). The single Nb atom on g-C3N4 with more negative valence provides structural advantages for hosting empty d-orbitals for strong N2 and N2H adsorption, as well as more single d-electrons to further promote back-donation to activate the NN triple bond. This work may be helpful in developing more effective TM-based SACs for N2 reduction through varying substrate effect toward the same single-atom catalysts.

The industrial synthesis of NH 3 using Fe-or Ru-based catalysts usually requires harsh reaction conditions. It is desirable to develop catalysts that perform well at low temperature and pressure (250−400 °C, <2 MPa). The main challenge of low-temperature NH 3 synthesis is the dissociation of the extremely stable NN triple bond. Herein, we report the design of homogeneous single-atom Ru centers on an H-ZMS-5 (HZ) support with the Ru atoms individually anchored in the micropores of HZ, effectively boosting NH 3 synthesis under mild conditions via an associative pathway. Synchrotronbased near-edge X-ray absorption fine structure (NEXAFS) and in situ DRIFTS analyses show that N− groups are the primary intermediates, and DFT calculations further show that, unlike Ru nanoclusters, the cooperation of a single Ru atom and hydrogen species in HZ leads to N 2 hydrogenation rather than direct N 2 dissociation, and the indirect N−N bond dissociation occurs much more easily via the formation of the NHNH 3 * intermediate; the energy barrier for breaking the N−N bond keeps falling from 2.90 eV for *N 2 to 0.04 eV for *NHNH 3 , showing that N 2 hydrogenation is an effective way for sharp weakening of N−N bonds. Moreover, the rate-determining step is shifted from the dissociation of the NN triple bond to the formation of *N 2 H 2 . As a consequence, the single-atom 0.2 wt % Ru/H-ZSM-5 catalyst shows the highest NH 3 synthesis rate per gram of Ru (1.26 mol NH3 g Ru −1 h −1 at 300 °C and 1 MPa) among the Ru-based catalysts ever reported.