Impurity Energy Levels Research Articles

Developing Rapid-Charging Li-S Batteries via "Target Catalysis" of Cations and Anions Modified Electrocatalyst.

The shuttle effect and sluggish sulfur reduction reaction have resulted in significantly low efficiency and poor high current cycling stability in lithium-sulfur batteries, impeding their practical applications. To address these challenges, the introduction of Ni cations into MoS2 grown on reduced graphene oxide (MoS2/rGO) induces the formation of impurity energy levels between the conduction and valence bands of MoS2. Additionally, the introduction of anionic Se expands the interlayer spacing, enhances intrinsic conductivity, and improves ion diffusion rates. Simultaneously introducing anionic and cationic species into the MoS2/rGO causes the center of the d-band to shift upward, reducing the occupancy of electrons in antibonding orbitals. This modification leads to a rearrangement of the electronic structure of Mo, accelerating the redox reactions of lithium polysulfides. It particularly enhances the binding energy and lowers the conversion energy barrier of Li2S4. Consequently, the Li||S coin cell with the Ni-MoSSe/rGO cathode demonstrates an initial capacity of 446 mAh g-1 at 20 C, with a remarkable capacity retention of ≈96.7% after 200 cycles. Moreover, even under high sulfur loading conditions (6.45 mg cm-2) and a low electrolyte/sulfur ratio (5.4 µL mg-2), it maintains a high areal capacity of 6.42 mAh cm-2.

Electronic and photocatalytic properties of Cu4 cluster-modified Ag/g-C3N4 single-atom catalysts: A hybrid DFT study

Increasing the active sites on the catalyst surface has been a key goal to increase the catalyst efficiency. This paper presents an efficient conversion of solar energy into chemical energy, realized by a Cu4 cluster-assisted single-atom catalyst (Ag-doped g-C3N4). The catalyst enhances charge transfer and light absorption, and the unique advantages of this approach in the field of photocatalysis are substantiated by density functional theory. Under the synergistic effect of Cu4 clusters, the electronic state density distribution of the Ag single-atom catalyst substrate is drastically altered, which realizes the increase of substrate active sites and rapid charge separation and transfer. Compared with the pristine substrate g-C3N4, the new electronic state distribution and the generation of impurity energy levels lead to the narrowing of the band gap from 2.77 to 1.83 eV, accelerating the transfer and separation of electrons and holes, and enlarging the visible light absorption range from 410 to 760 nm, thus improving the solar energy utilization. Despite the reduced band gap, the conduction and valance band edges of (Ag, Cu4) codoped g-C3N4 still have sufficient potential to split water. Therefore, to improve the photocatalytic performance under visible light, simultaneous codoping of the Ag single atom and Cu4 cluster on g-C3N4 is an effective strategy. The study provides theoretical support for further optimization of single-atom catalysts.

Mechanical and electrical properties of two-dimensional BN doped with carbon group elements: first-principles calculations

Abstract Research of low-dimensional nanomaterials provides a direction for solving the problems of energy and environmental pollution. In this work, the regulation mechanism of doping carbon group elements X (X = C, Si, Ge, Pb, Sn) on mechanical and electrical properties of 2D monolayer BN are investigated by first-principles calculations. Two doping sites were selected, replace B atoms (B15N16X) or N atoms (B16N15X). Lower relative enthalpies and the elastic constants, which conforming to the mechanical stability standard, fully prove the stability of the doping system. Compared with B15N16X, B16N15X has larger structural distortion, smaller elastic constants and modulus, and is more inclined to ductility. With the increase of atomic radius, the deformation degree increases and the elastic parameters decrease. C-doped by replacing B atoms improves the elastic mechanical properties of monolayer BN. Sn-doped and Pb-doped modulate the monolayer BN into ductility. More importantly, all doped configurations exhibit magnetism. The indirect band gap of the undoped system can also be modulated into a direct band gap, B15N16C, B16N15Si and B16N15Ge all have direct band gaps in the spin-down direction. Asymmetric impurity energy levels DOS further verify the magnetism of the reference system.

Selective Photocatalytic Oxidation of 5‐Hydroxymethylfurfural using Ce doped TiO2: A Crucial Role of Defective Sites

AbstractTransforming platform compounds with conventional catalysts, such as homogeneous and heterogeneous, into valuable chemicals encounters challenges associated with entailing high temperature/pressure and reusability during the reaction. To address these challenges, photocatalysis is one of the promising approaches, especially with visible‐light‐driven photocatalysts for selective transformation. A series of cerium‐doped TiO2 (CexTiO2; x=0.5, 1, 3 and 5 wt %) are prepared via a simple coprecipitation method for the cocatalyst‐free selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) under visible light illumination. Introducing Ce into the network to TiO2 generates impurity energy levels, reduces the band gap, and extends the spectral response range. This also causes slight distortion to the surface structure, thereby originating defective sites and various surface oxygen species, confirmed by X‐ray photoelectron spectroscopy and electron paramagnetic resonance studies. The HMF adsorption studies infer that HMF forms a surface complex with CeTiO2, facilitating the formation of ligand‐to‐metal charge transfer complex (LMCT) under visible light (~420 nm), which efficiently catalyzes the conversion of HMF (54.4 %) to DFF with a selectivity of >99 %. In‐situ DRIFTS and surface passivation studies provide insight into the interaction between HMF and surface acidic/basic sites along with hydroxyl groups of CeTiO2, which subsequently convert selectively to DFF.

Effect mechanism of Cd on band structure and photocatalytic hydrogen production performance of ZnS

ZnS is widely used in the photocatalytic decomposition of water to produce hydrogen due to its fast electron-hole pair generation and high negative potential. However, its absorption in the visible region is poor due to its wide band gap, and it has serious photogenerated carrier recombination problems. Herein, a shallow impurity energy level was introduced by doping the ZnS lattice with Cd. Due to its presence, electrons trying to return to the valence band are trapped and excited twice, suppressing the recombination of photogenerated carriers and greatly improving electron utilization. The Cd1.5-ZnS possesses a hydrogen production rate as high as 85722.20 μmol/g, which is 17 times higher than pure ZnS. Meanwhile, Cd1.5-ZnS has a narrower forbidden band and superior visible light absorption, and the serious photocorrosion problem of ZnS has been suppressed. This study provides a viable approach for the synthesis of photocatalysts with adjustable band gaps and enhanced hydrogen precipitation efficiency.

Nitrogen-doped ZnIn2S4 and TPA multi-dimensional synergistically enhance photocatalytic hydrogen production

To alleviate the environmental pollution and energy crisis caused by the excessive use of fossil fuels, photocatalytic water splitting to produce hydrogen is an important way to solve energy and environmental problems. Here, Nitrogen-doped ZnIn2S4 (N-ZIS) composite tungsten-based polyoxometalate (TPA) composites (denoted as N-ZIS/TPA) were synthesized by a one-step solvothermal method. The introduction of N3– instead of S2− in ZIS changes the internal electron arrangement of ZIS, improves the electronegativity of ZIS, and is conducive to the surface adsorption of positively charged H*. At the same time, the impurity energy level is generated at the valence band position, which narrows the band gap and broadens the light absorption range, thereby promoting photocatalytic hydrogen production. After compounding, due to the adjustable redox properties of TPA itself, the internal W6+ part is reduced to W4+, resulting in the coexistence of W6+ and W4+ in the composite material, which fully verifies the flow of interface electrons from N-ZIS to TPA. The close contact between N-ZIS and TPA and the built-in electric field’s driving force help achieve efficient interfacial charge transfer. At the same time, W6+/W4+ redox pairs were introduced to accelerate the separation of photogenerated electrons and holes. The photocatalytic hydrogen production rate of the best sample 1N-ZIS/TPA-15 is as high as 17345.53 μmol·g−1·h−1, which is 2.92 times that of N-ZIS (5940.08 μmol·g−1·h−1) and 8.03 times that of ZIS (2159.22 μmol·g−1·h−1). This study explores the design and construction of efficient s-type heterojunctions by adjusting the energy band position of ZnIn2S4 as a new strategy in the field of photocatalytic hydrogen production.

Effects of CeO2 doping on the mechanical, infrared radiative, and thermophysical properties of Pr2Zr2O7 ceramics for potential thermal protective coatings

A series of Ce4+-doped Pr2Zr2O7 ceramics were produced using a solid reaction method to utilize novel ceramic materials as potential candidates for thermally protective coatings. The effects of Ce4+ doping on the phase composition and mechanical, infrared radiative, and thermophysical properties were studied in detail. The results indicated the good phase stability and sintering resistance of the Pr2(Zr1−xCex)2O7 ceramics. Moreover, Ce4+-doped Pr2Zr2O7 bulk materials exhibited higher infrared emissivity (0.904) at wavelengths of 3–5 μm and 1000 °C for Pr2(Zr0.5Ce0.5)2O7) owing to the introduction of impurity energy levels. Pr2(Zr0.7Ce0.3)2O7 exhibited an appropriate average coefficient of thermal expansion of 12.4 × 10−6 K−1 and a low thermal conductivity of 1.14 W m−1 K−1 at 1000 °C, owing to the reduction of lattice energy and the presence of more oxygen vacancies and substitution atoms.

Fluorine Doping Mediated Epitaxial Growth of NaREF4 on TiO2 for Boosting NIR Light Utilization in Bioimaging and Photodynamic Therapy

AbstractBy integrating TiO2 with rare earth upconversion nanocrystals (NaREF4), efficient energy transfer can be achieved between the two subunits under near‐infrared (NIR) excitation, which hold tremendous potential in the fields of photocatalysis, photodynamic therapy (PDT), etc. However, in the previous studies, the combination of TiO2 with NaREF4 is a non‐epitaxial random blending mode, resulting in a diminished energy transfer efficiency between the NaREF4 and TiO2. Herein, we present a fluorine doping‐mediated epitaxial growth strategy for the synthesis of TiO2‐NaREF4 heteronanocrystals (HNCs). Due to the epitaxial growth connection, NaREF4 can transfer energy through phonon‐assisted pathway to TiO2, which is more efficient than the traditional indirect secondary photon excitation. Additionally, F doping brings oxygen vacancies in the TiO2 subunit, which further introduces new impurity energy levels in the intrinsic band gap of TiO2 subunit, and facilitates the energy transfer through phonon‐assisted method from NaREF4 to TiO2. As a proof of concept, TiO2‐NaGdF4 : Yb,Tm@NaYF4@NaGdF4 : Nd@NaYF4 HNCs were rationally constructed. Taking advantage of the dual‐model up‐ and downconversion luminescence of the delicately designed multi‐shell structured NaREF4 subunit, highly efficient photo‐response capability of the F‐doped TiO2 subunit and the efficient phonon‐assisted energy transfer between them, the prepared HNCs provide a distinctive nanoplatform for bioimaging‐guided NIR‐triggered PDT.

Fluorine Doping Mediated Epitaxial Growth of NaREF4 on TiO2 for Boosting NIR Light Utilization in Bioimaging and Photodynamic Therapy.

By integrating TiO2 with rare earth upconversion nanocrystals (NaREF4), efficient energy transfer can be achieved between the two subunits under near-infrared (NIR) excitation, which hold tremendous potential in the fields of photocatalysis, photodynamic therapy (PDT), etc. However, in the previous studies, the combination of TiO2 with NaREF4 is a non-epitaxial random blending mode, resulting in a diminished energy transfer efficiency between the NaREF4 and TiO2. Herein, we present a fluorine doping-mediated epitaxial growth strategy for the synthesis of TiO2-NaREF4 heteronanocrystals (HNCs). Due to the epitaxial growth connection, NaREF4 can transfer energy through phonon-assisted pathway to TiO2, which is more efficient than the traditional indirect secondary photon excitation. Additionally, F doping brings oxygen vacancies in the TiO2 subunit, which further introduces new impurity energy levels in the intrinsic band gap of TiO2 subunit, and facilitates the energy transfer through phonon-assisted method from NaREF4 to TiO2. As a proof of concept, TiO2-NaGdF4 : Yb,Tm@NaYF4@NaGdF4 : Nd@NaYF4 HNCs were rationally constructed. Taking advantage of the dual-model up- and downconversion luminescence of the delicately designed multi-shell structured NaREF4 subunit, highly efficient photo-response capability of the F-doped TiO2 subunit and the efficient phonon-assisted energy transfer between them, the prepared HNCs provide a distinctive nanoplatform for bioimaging-guided NIR-triggered PDT.

Creating electron traps in BiOBr nanosheet arrays by bulk-phase F doping to restrain carrier recombination for efficient photoelectrochemical water splitting system

Bismuth oxide semiconductors in the field of photoelectrochemical (PEC) water splitting face the problems of narrow photo response range and fast carrier compounding. On the basis of the above problems, we used a solvothermal method to prepare BiOBr nanosheet arrays (NSAs), which have a special structure that facilitates carrier transport. Subsequently, the F element was introduced into the bulk phase of BiOBr using a simple hydrothermal method. The results show that the BiOBr-F photoelectrode exhibits excellent photoelectrocatalysis performance under light and bias voltage. The photocurrent density of the BiOBr-F photoelectrode reached 28.35 μA cm−2 at 1.23 V vs. RHE, which is 2.01 times higher than that of the pure BiOBr, while a negative shift of the onset potential of 119 mV was obtained. The optical absorption tests show that the introduction of the F element forms an impurity energy level thereby extending the optical absorption range of BiOBr. Photoluminescence tests reveal that the introduction of F element effectively restricts the electron-hole pair recombination. This is due tothe fact that the F atoms replace some of the O atoms in BiOBr to create electron traps, thus forming a large number of electron-rich regions in the structure, which in turn reduces the electron-hole pair recombination. This work provides an effective solution to reduce the recombination between carriers by creating electron traps in semiconductor materials through bulk phase doping.

Enhanced broadband infrared radiation from rare earth orthochromites for High-Temperature radiative heat transfer

The development of broadband, high-performance infrared radiation materials is crucial for energy conservation and applications in aerospace and industrial sectors. Rare earth orthochromites, such as PrCrO3, exhibit good thermal stability and high infrared emissivity beyond the 6 μm wavelength range. However, their large bandgap limits their infrared emissivity before 6 μm, significantly impacting their potential applications. Herein, we have successfully enhanced the thermal emissivity of PrCrO3 by manipulating oxygen vacancies (OV) and accompanying impurity levels, leading to the synthesis of five rare earth orthochromites. Compared with pristine PrCrO3, co-doping of Ca, Co, and Mn introduced oxygen vacancies (OV) and impurity energy levels, effectively reducing the band gap and improving emissivity in the wavelengths below 6 μm. In particular, the infrared emissivity of (Pr0.3Y0.3Ca0.4)CrO3 in the wavelengths of 0.78–2.5 μm reaches 0.89, which is double than that of pristine PrCrO3. Furthermore, its thermal stability is excellent, as demonstrated by thermal shock experiments at 1500 ℃ for five cycles. More importantly, the developed orthochromites can be applied as a coating on substrates such as alumina ceramic sheets, exhibiting an average infrared emissivity of 0.95 and remarkable radiative heat transfer capability. This research contributes to the advancement of high-performance infrared radiation materials by vacancy engineering.

Tailoring electronic structure of stretchable freestanding single-crystal LaNiO3 thin film for enhanced oxygen evolution reaction

The comprehension of the electronic structure of an electrochemical catalyst, as a fundamental core content, has significantly accelerated advancements in competitive catalyst engineering since the adsorption and desorption abilities of an electrode are governed by its surface energy profile. However, achieving precise control over the electronic structure poses a significant challenge. Nanoporous materials, high-entropy systems, and layered double hydroxides frequently induce stoichiometric changes, leading to complexity such as electronic reconstruction, energy degeneracy disruption, and impurity energy levels. Here, we have successfully developed a stretchable freestanding single-crystal LaNiO3 thin film electrocatalyst enabling the accurate manipulation of the electronic structure on a large scale. Different from the rigid epitaxial heterostructure catalyst, we observed that with every 1 % increase in strain, the OER current of freestanding LaNiO3 is enhanced by ∼238 % compared to the pristine state. This is attributed to the dx2-y2 orbital occupation increasing by ∼7 %, and the eg-center decreasing by ∼0.05 eV, resulting in a weakened Ni-O adsorption.

Enhanced Photocatalytic Degradation by the Preparation of a Stable La-Doped FeTiO3 Photocatalyst: Experimental and DFT Study.

The rapid photocarrier recombination limits the photocatalytic activity of iron titanate (FeTiO3) to be further improved. Developing novel approaches to inhibit the rapid recombination rate of the FeTiO3 photocatalysts is crucial for efficiently degrading pollutants in wastewater. Rare earth ions, with unique electron dispositions and large ion radii, could effectively inhibit photocarrier recombination. Herein, novel lanthanum (La)-doped FeTiO3 photocatalysts were designed and successfully synthesized. The photocatalytic performance of the 12 mol % La/FeTiO3 photocatalyst was superior in degrading tetracycline hydrochloride (TCH), methylene blue (MB), and brilliant blue (BB). These degradation rate constants (k) were 0.12358, 0.01357, and 0.03064 L mg-1 min-1, respectively, which were 12.83, 1.61, and 7.78 times that of pure FeTiO3. The photoelectronic tests and density functional theory (DFT) calculations revealed that the La 4f orbital forms an impurity energy level in the conduction band of FeTiO3. This level narrows the bandgap and acts as an electron acceptor, capturing photoexcited electrons and inhibiting the rapid recombination of photoexcited electron-hole pairs in FeTiO3. This work enhances the potential of FeTiO3 in the photocatalysis field and provides important insights into the efficient degradation of organic pollutants in wastewater.

Employing lattice compression spin polarization electric field for boosting degradation of mixed antibiotics in wastewater

Localized polarization electric field is a key factor affecting photocatalytic activity. In this study, the localized polarization electric field of lattice strain was introduced into the electronic structure of Bi2WO6 by using the high and low valence state doping method. The impurity energy level induced by lattice strain further affects the gap energy level. As an intermediate state for electron transfer, the gap level further promotes the dynamics of photo generated charges, reducing the band gap by 0.4 eV and improving the photoelectric performance by 60 %. Various tests and theoretical calculations have confirmed that the internal electric field of local polarization significantly improves the generation and transfer rate of photo-generated charges, thereby boosting catalytic activity. The removal ratios of ciprofloxacin (CIP) and tetracycline (TC) in the mixed wastewater reach 91.5 % and 97.1 % in 90 min, respectively. Cyclic tests have shown that the electronic structure control exhibits excellent stability with removal ratios of CIP and TC of 83.9 % and 85.7 %, respectively. Finally, the 8C of CIP and the 11C and 19O of TC are most susceptible to the attack of free radicals generated by lattice compression spin polarization electric fields based on the theoretical calculations of the Fukui function and the analysis of intermediates. This work provides new insights into the design of catalysts for efficient photo generated charge dynamics with lattice strain.

Preparation of amorphous Bi-Fe-O series semiconductor and its crystallization behavior and photocatalytic activity

In that research field of Bi-Fe-O series compounds, the design and development of amorphous Bi-Fe-O semiconductor with high photocatalytic activity and pure phase BiFeO3 with multiferroic properties are two major challenges. Herein, the amorphous Bi-Fe-O series semiconductor is prepared by mechanical alloying method using Fe2O3 and Bi2O3 as the raw materials, and the pure phase nano-BiFeO3 crystalline is subsequently obtained by heat treatment process. Meanwhile the microstructure, band gap structure and photocatalytic or electromagnetic activity of amorphous and crystallized Bi-Fe-O semiconductor are also investigated. The results show that after 25 h of mechanical alloying, the crystalline structure of Bi2O3 and Fe2O3 is destroyed, and the system is transformed into amorphous phase. Moreover, photocatalytic hydrogen production experiment shows that amorphous Bi-Fe-O semiconductor has the highest photocatalytic hydrogen production rate which is 4.03 μmol/g/h, due to more defects and impurity energy levels. In addition, pure phase nano-BiFeO3 crystalline can be obtained when the heat treatment temperature of amorphous Bi-Fe-O semiconductor is 600°C, which have the best ferroelectric properties. This work not only provides new ideas for the research and development of amorphous semiconductor, but also proposes a green method to prepare pure phase nano-BiFeO3 crystalline.

Rare earth induced lattice distortion of Bi2WO6 to effectively improve photocatalytic performance: Experimental and DFT calculations

The excellent visible light photocatalytic activity of bismuth-based photocatalysts has attracted the interest of many scholars at home and abroad. In this paper, rare earth (Sm, La, Ce, Eu) doped Bi2WO6 photocatalysts were prepared by a one-step hydrothermal method using bismuth nitrate and sodium tungstate as precursors. The microstructures and spectroscopic performances of prepared materials were investigated utilizing characterization methods, such as XRD, XPS, UV–vis, TEM, and N2 adsorption-desorption, etc., and the effluent removal performances were studied by using rhodamine B as a simulated degradation dye and the photodegradation mechanism was investigated in combination with DFT calculations. XRD indicates that the rare earth doping leads to the lattice distortion of the (131) crystal surface of Bi2WO6, and the relative amount of distortion is directly proportional to the photocatalytic activity; UV–vis spectra show that the absorption edge of Bi2WO6 is obviously red-shifted with the rare earth doping, and N2 adsorption-desorption curve show that the doped rare earths make the specific surface area of the sample effectively increased. Moreover, XPS spectrum suggests that the doped rare earth Ce and Eu often exist in the form of metastable oxidation states, and the transformation between Ce3+/Ce4+ and Eu2+/Eu3+ oxidation states is easy to form impurity energy levels between Bi2WO6, which make the energy level significantly enriched to broaden the absorption range and reduce band gap width of the material. DFT calculations further indicate that the rare earths successfully replace Bi sites. One of the main reasons for the improvement of photocatalytic activity is that rare earth doping is easier to replace Bi sites, leading to increased relative aberration; another one is that the arrangement of EVB and ECB in the photocatalytic mechanism is type-II, which contributes to red-shift of absorption edge and effective separation of electron-hole pairs in the photocatalytic process, thus improving the photocatalytic activity.

Mn-N codoped TiO2 nanotubes with enhanced photocatalytic activity: An integrated experimental and theoretical investigation

The efficient enhancement of the photocatalytic activity of TiO2 nanotubes under visible light remains a significant challenge in current research. This study, employing density functional theory, systematically investigates the impact of Mn-N co-doping on the morphology, electronic structure, and optical properties of Hydrothermal composite treatment of TiO2 nanotubes. The successful introduction of Mn-N co-doping into the nanotubes induces impurity energy levels, reducing the bandgap while enhancing absorption capability and reflectance of visible light. Mn and N are partially incorporated into the TiO2 lattice, resulting in a reduction of the bandgap from 2.98 eV to 2.81 eV. The degradation efficiency of methylene blue solution under UV light and visible light is improved by approximately 31 % and 25 %, respectively.

Bi & Mo co-doped In2S3 nano-foam blocks for boosted photocatalytic hydrogen generation

The design and construction of dual modifications on photocatalysts is a promising strategy to improve the photocatalytic properties. Herein, we fabricated the In2S3 nano-foam blocks with dual modifications of Bi & Mo co-doping and structure construction via a simple hydrothermal method to achieve an enhanced photocatalytic hydrogen generation. The results reveal that Bi & Mo co-doped In2S3 nano-foam blocks exhibit a high hydrogen generation rate of 5.45 mmol/g/h, which is 27 times that of bulk In2S3. Owing to the structural advantages, the enhanced specific surface area of the as-prepared nano-foam blocks improve the light harvesting efficiency of photocatalytic system. More importantly, the doped Bi and Mo atoms boost the improvement in the transfer and separation of photogenerated electrons and holes by introducing the impurity energy level. This work provides a reliable strategy for the design and fabrication of high-efficiency photocatalytic reaction system.

Monolayer BiOI doped with nonmetals (B, C, N, Si, P, S) to enhance photocatalytic hydrogen precipitation performance

Efficient photocatalysts play a crucial role in producing green and clean hydrogen energy. BiOI is a good material for photocatalytic hydrogen generation. However, the low position of the conduction band also affects its redox ability. We studied the electronic structure and hydrogen evolution reaction (HER) catalytic performance of six nonmetals doped BiOI based on the first principles calculation. The relationship between doping elements and catalytic performance was explained. We used the DFT + U method to find that the band gap values of X-BiOI (X = B, C, N, Si, P, S) are 1.99 eV, 1.23 eV, 1.73 eV, 2.08 eV, 1.40 eV and 1.77 eV, respectively. After nonmetal doping, the bottom position of the conduction band of BiOI rises, which enhances the reduction ability. Specifically, the impurity energy levels generated in the band gap of B and Si doped BiOI reduce the recombination rate of photogenerated carriers, and lower the work function to 5.62 eV and 5.45 eV, respectively. Studies on hydrogen production performance show that B-doped BiOI has the strongest reduction ability and the best catalytic effect, with the lowest ΔGH* (1.57 eV). This research provides some ideas for understanding nonmetal doped materials for the photocatalytic hydrogen evolution system.

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.