NiRu-Mo2Ti2C3O2 as an efficient catalyst for alkaline hydrogen evolution reactions: the role of bimetallic site interactions in promoting Volmer-step kinetics.

The Volmer step in alkaline hydrogen evolution reactions (HERs), which supplies H* to the following steps by cleaving H-O-H bonds, is considered the rate-determining step of the overall reaction. The Volmer step involves water dissociation and adsorbed hydroxyl (*OH) desorption; Ru-based catalysts display a compelling water dissociation process in an alkaline HER. Unfortunately, the strong affinity of Ru for *OH blocks the active sites, resulting in unsatisfactory performance during HER processes. Hence, this study investigates a series of key descriptors (ΔG*H2O, ΔG*H-OH, ΔG*H, and ΔG*OH) of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt)-Ru/Mo2Ti2C3O2 to systematically explore the effects of bimetallic site interactions on the kinetics of the Volmer step. The results indicate that bimetallic catalysts effectively reduced the strong adsorption of *OH on Ru sites; especially, the NiRu diatomic state shows the highest electron-donating ability, which promoted the smooth migration of *OH from Ru sites to Ni sites. Therefore, Ru, Ni and MXenes are suitable to serve as water adsorption and dissociation sites, *OH desorption sites, and H2 release sites, respectively. Ultimately, NiRu/Mo2Ti2C3O2 promotes Volmer kinetics and has the potential to improve alkaline HERs. This work provides theoretical support for the construction of synergistic MXene-based diatomic catalysts and their wide application in the field of alkaline HERs.

In Situ Formation ZnIn2 S4 /Mo2 TiC2 Schottky Junction for Accelerating Photocatalytic Hydrogen Evolution Kinetics: Manipulation of Local Coordination and Electronic Structure.

Regulating electronic structures of the active site by manipulating the local coordination is one of the advantageous means to improve photocatalytic hydrogen evolution (PHE) kinetics. Herein, the ZnIn2 S4 /Mo2 TiC2 Schottky junctions are designed to be constructed through the interfacial local coordination of In3+ with the electronegative O terminal group on Mo2 TiC2 based on the different work functions. Kelvin probe force microscopy and charge density difference reveal that an electronic unidirectional transport channel across the Schottky interface from ZnIn2 S4 to Mo2 TiC2 is established by the formed local nucleophilic/electrophilic region. The increased local electron density of Mo2 TiC2 inhibits the backflow of electrons, boosts the charge transfer and separation, and optimizes the hydrogen adsorption energy. Therefore, the ZnIn2 S4 /Mo2 TiC2 photocatalyst exhibits a superior PHE rate of 3.12 mmol g-1 h-1 under visible light, reaching 3.03 times that of the pristine ZnIn2 S4 . This work provides some insights and inspiration for preparing MXene-based Schottky catalysts to accelerate PHE kinetics.

Single atom supported on MXenes for the alkaline hydrogen evolution reaction: species, coordination environment, and action mechanism.

The electrochemical hydrogen evolution reaction (HER) in alkaline media provides an environmentally friendly industrial application approach to replace traditional fossil energy. The search for efficient, low-cost, and durable active electrocatalysts is central to the development of this area. Transition metal carbides (MXenes) have been emerging as a new family of two-dimensional (2D) materials that have great potential in the HER. Herein, density functional theory calculations are performed to systematically explore the structural and electronic properties and alkaline HER performances of Mo-based MXenes, as well as the influence of species and the coordination environment of single atoms on the improvement of the electrocatalytic activity of Mo2Ti2C3O2. The results show that Mo-based MXenes (Mo2CO2, Mo2TiC2O2, and Mo2Ti2C3O2) exhibit excellent H binding ability, while slow water decomposition kinetics hinders their HER performance. Replacing the O-terminal of Mo2Ti2C3O2 with a Ru single-atom (RuS-Mo2Ti2C3O2) could promote the decomposition of water owing to the stronger electron-donating ability of the atomic state Ru. In addition, Ru could also improve the binding ability of the catalyst to H by adjusting the surface electron distribution. As a result, RuS-Mo2Ti2C3O2 exhibits excellent HER performance with a water decomposition potential barrier of 0.292 eV and a H adsorption Gibbs free energy of -0.041 eV. These explorations bring new prospects for single atoms supported on Mo-based MXenes in the alkaline hydrogen evolution reaction.

Theoretical insights into effective electron transfer and migration behavior for CO2 reduction on the BiOBr(001) surfaces.

Carbon dioxide (CO2) activation by effective electrons has been regarded as the rather necessary first-step for a CO2 reduction reaction (CO2RR). In addition, the electron migration and photoreaction selectivity are closely associated with the dominant crystal surface of a catalyst. Therefore, it is very interesting and important to elucidate the electron transfer and charge density effects on the catalyst surface for the CO2RR. In this work, the dominant highly-active BiOBr(001) surfaces with Bi-, O- and Br-termination atoms are designed so that their electron distributions and CO2RR behaviors can be observed. The electron-rich sites on the BiOBr(001) surfaces, where more effective electrons will migrate to achieve the activation of the adsorbed CO2, are firstly confirmed by the electron density difference based on density functional theory calculations. Next, the CO2RR pathways at the electron-rich sites are investigated to explore the migration mechanism of effective photo-induced electrons. The results obtained reveal that if a larger number of electrons transfer to CO2, then less energy is needed to break the CO bond, and the formation of a *COOH intermediate corresponds to the ability of the surface to take part in protonation. Furthermore, the interface Bi atom can boost the transfer efficiency of effective electrons to CO2, but the exposed Br atom with a longer electron transfer distance, because of the steric hindrance of the interface Br atoms, makes it difficult for the electrons to migrate, resulting in it being harder to fracture the CO bond to benefit the formation of the HCOOH product. These findings should give deep insight into the migration behaviors of effective electrons for CO2 photoreduction on the BiOBr(001) surface and provide new perspectives for better understanding the structure-performance relationship at the molecular level.

Theoretical insights into photo-induced electron transfer at BiOX (X = F, Cl, Br, I) (001) surfaces and interfaces.

The electron transfer process (ETP) of a photocatalyst plays a crucial role in clarifying its photoelectrochemical catalytic mechanism. BiOX (X = F, Cl, Br, I) (001) surfaces display excellent photocatalytic performance due to the high separation efficiency of photogenerated electron-hole (e--h+) pairs in their own efficient internal electric field (IEF). The oxygen vacancies (OVs) on the surfaces could cause a change in localized electronic states, then improve the photocatalytic activity of BiOX. Here, the ETP at BiOX (001) surfaces with and without surface OVs were calculated and investigated using a DMol3 module based on density functional theory (DFT). The results showed that the electron transfer at the BiOX (001) surfaces and interfaces should be like this: firstly, the [-O-Bi-] layer at the interface received the photon energy, which made the electrons on the O atoms preferentially photo-induced to Bi atoms and left photo-induced holes on the interface O atoms. Then, the effective electrons on the interface Bi atoms were diffused to one- or multi- electron reactions, and at the same time, electrons from the bulk were transferred through the path of O → Bi → X → X → Bi → O on BiOX (001) surfaces under the IEF effect to interface O atoms, and consequently, maintain the stable proceeding of the photocatalytic reaction. More importantly, we found that the X atoms indeed played a key role in connecting the non-bonding interlayers of the BiOX nanocrystals and affecting the ETP on BiOX (001) surfaces as electron transmitters. The exploration of the OV introduction on BiOX (001) surfaces suggested that the OV-induced localized electronic states should increase the electron mobility and the charge carrier density to improve the photocatalytic activity of BiOX, especially for BiOCl and BiOBr. Our findings could provide new insight for deeply understanding the transfer and catalytic behaviour of photo-induced electrons at BiOX (001) surfaces and interfaces.

Adsorption mechanism of Ca2+, Mg2+, Fe3+, and Al3+ ions in phosphoric acid-nitric acid solution on 001 × 7 and S957 resins.

Selective removal of Ca2+ and Mg2+ ions using the 001 × 7 resin and Fe3+ and Al3+ ions using the S957 resin is able to achieve the deep purification of the phosphoric acid-nitric acid solution, but the adsorption behaviors of Fe3+ and Al3+ ions are seriously suppressed by phosphoric acid. In order to understand the interaction mechanism of separation processes and the influence of phosphoric acid, we first studied the bonding form of Ca2+, Mg2+, Fe3+, and Al3+ ions on 001 × 7 and S957 resins using FT-IR and XPS techniques; subsequently, quantum chemistry computation was carried out to further explore the bonding mechanism between the functional groups on resins and metal ions. FT-IR and XPS results reveal that for the adsorption process on the 001 × 7 resin, hydroxyls from sulfonic acid groups combine with Ca2+ and Mg2+ ions. Whereas Fe3+ and Al3+ ions are adsorbed on the S957 resin through an exchange reaction with hydroxyls on the phosphonic acid group but not on the sulfonic acid group. Quantum chemistry computation results reveal that the phosphonic acid group has a larger binding energy with Fe3+ and Al3+ ions. Thus, the S957 resin still presents great adsorption performance for Fe3+ and Al3+ ions despite the influence of dihydrogen phosphate ions in the phosphoric acid-nitric acid solution.

Promoted photocatalytic N2 fixation to ammonia over floatable TiO2/Bi/Carbon cloth through relay pathway.

The floatable photocatalyst at N2-water interface allows the adequate supply of N2 reactant and the utilization of photothermal energy for photocatalytic N2 fixation, however, the presence of non-volatile NO3- product poses a challenge to the stability as it easily covers the catalytic active sites. Herein, a floatable TiO2/Bi/CC (Carbon cloth) photocatalyst was designed, in which the non-volatile NO3- can be transformed to the volatile NH3 via the newly synergistic relay photocatalysis pathway (N2 â†’ NO3- â†’ NH3) between TiO2 (N2 â†’ NO3-) and Bi (NO3- â†’ NH3). Attractively, the spontaneous NO3- â†’ NO2- step occurs on Bi component to promote the relay pathway performing. Therefore, TiO2/Bi/CC system displays better long-term stability than TiO2/CC, and moreover, it achieves a higher NH3 yield of 8.28 mmol L-1 h-1 g-1 (i.e. 4.14 mmol h-1 m-2) than that 1.46 mmol L-1 h-1 g-1 for TiO2/Bi powder. Importantly, the N2 fixation products by TiO2/Bi/CC effectively promote lettuce growth and enhance lettuce nutrient contents, which further validates the feasibility of this system in large-scale application of crop cultivation.

Fe-Bi dual sites regulation of Bi2O2.33 nanosheets to promote photocatalytic nitrogen fixation activity.

In the process of photocatalytic ammonia synthesis, efficient activation of nitrogen molecules constitutes a fundamental challenge. During the N2 activation, the close interdependence between the acceptance and donation of electron results in their mutual limitation, leading to high energy barrier for N2 activation and unsatisfactory photocatalytic performance. This work decoupled the electron acceptance and donation processes by constructing Fe-Bi dual active sites, resulting in enhancing N2 activation through the high electron trapping ability of Fe3+ and strong electron donating ability of Bi2+. The photocatalytic nitrogen reduction efficiency of 3%Fe/Bi2O2.33 (118.71 µmol gcat-1h-1) is 5.3 times that of Bi2O2.33 (22.41 µmol gcat-1h-1). In-situ Fourier transform infrared (In situ FTIR) spectroscopy and density functional theory (DFT) calculations manifest that Fe3+-Bi2+ dual active sites work together to promote nitrogen adsorption and activation, and the reaction path is more inclined toward alternate hydrogenation path. N2 adsorption and activation properties are optimized by heteronuclear bimetallic active sites, which offers a new way for the rational design of nitrogen-fixing photocatalysts.

Enhanced photocatalytic hydrogen evolution of Ru/TiO2-x via oxygen vacancy-assisted hydrogen spillover process.

Hydrogen spillover effects will significantly improve the activity of photocatalytic hydrogen evolution reactions (HER), while their introduction and optimization require the construction of an excellent metal/support structure. In this study, we have synthesized Ru/TiO2-x catalysts with controlled oxygen vacancy (OVs) concentrations using a simple one-pot solvothermal method. The results show that Ru/TiO2-x3 with the optimal OVs concentration exhibits an unprecedentedly high H2 evolution rate of 13604 µmol·g-1·h-1, which was 45.7 and 2.2 times higher than that of TiO2-x (298 µmol·g-1·h-1) and Ru/TiO2 (6081 µmol·g-1·h-1). Controlled experiments, detailed characterizations, and theoretical calculations have revealed that the introduction of OVs on the carrier contributes to the hydrogen spillover effect in the metal/support system photocatalyst and that the process of hydrogen spillover in this system can be optimized by modulating the OVs concentration. This study proposes a strategy to decrease the energy barrier of hydrogen spillover and enhance photocatalytic HER activity. Moreover, it investigates the effect of OVs concentration on the hydrogen spillover effect in the photocatalytic metal/supports system.

Controllable Synthesis of BiOCl with Z-Scheme (001)/(110) Facet Homojunction and their Photocatalytic Killing Effect on HePG2 Cells in vitro.

In this study, a set of BiOCl with controllable ratios of (001) and (110) facets was prepared by adjusting the content of diethylene glycol (DEG) during the preparation process. The degradation experiment of bisphenol A (BPA) shows that under simulated sunlight, when the ratio of (001) to (110) is 0.61, BiOCl (BOC-2) has the best degradation activity, which can degrade 96.2% BPA within 20 min. After theoretical calculations and experimental characterization, a Z-scheme (001)/(110) facet homojunction is proposed. Then, three typical samples were selected to test the biological toxicity of HepG2 cells and the activity of killing HepG2 cells under ultraviolet light conditions. Studies have found that exposed facets play a more important role in the biotoxicity of BiOCl to cells; with a (001)/(110) ratio of 0.61, BOC-2 exhibits excellent endocytosis and phototoxicity but no obvious dark cytotoxicity, while with a (001)/(110) ratio of 0.15, BiOCl (BOC-4) has poor endocytosis and strong cytotoxicity under dark conditions. Through reactive oxygen species (ROS) and lactate dehydrogenase (LDH) assay detection, the process of photocatalytic killing cells of BOC-2 more looks like an apoptosis mechanism, while BOC-4 mainly causes cell necrosis.

Original self-assembled S-scheme BiOBr-(001)/Bi2SiO5/Bi heterojunction photocatalyst with rich oxygen vacancy for boosting CO2 reduction performance.

Photocatalysis CO2 reduction into high-value-added chemical feedstocks is desirable for simultaneously addressing the solar energy storage, CO2 excess and energy shortage issues. In this work, a kind of original S-scheme BiOBr-(001)/Bi2SiO5/Bi (OSB) heterostructure photocatalyst with rich oxygen vacancies is in-situ synthesized, which significantly promotes the photocatalytic CO2 reduction performance. Interestingly, the lower formation energy of oxygen vacancy exhibits the easy feasibility on the BiOBr-(001) surface via the assistant of ultrasound. There exists the highest photocatalytic CO2 reduction activity to CO of 234.05 µmol g-1h-1 for OSB-20 sample (ultrasound time: 20 min), higher 3.3 times than OSB-0 sample (without ultrasound). Combined with experimental and calculated results, the significative formation mechanism, widened light-response range, highly-efficient separation/transfer paths and improved redox-reduction abilities of photogenerated electron-hole pairs for S-scheme OSB-20 heterostructure are investigated and proposed. Our findings provide new insights for the construction and synthesis of the S-scheme Bi-based heterojunction photocatalyst system.

Improved visible light photocatalytic nitrogen fixation activity using a FeII-rich MIL-101(Fe): breaking the scaling relationship by photoinduced FeII/FeIII cycling.

The scaling relations between nitrogen adsorption and NHx destabilization are key challenges to the widespread adoption of the photocatalytic synthesis of ammonia. In this work, a FeII-rich MIL-101(Fe) (MIL-101(FeII/FeIII)) was synthesized using a one-step solvent thermal method with ethylene glycol (EG) as a reducing agent, which can break the scaling relationship by photoinduced FeII (high nitrogen adsorption ability) and FeIII (high NHz destabilization ability) cycling. XPS was used to detect the change in iron valence state in the MIL-101(FeII/FeIII) material. The photocatalytic nitrogen fixation efficiency of MIL-101(FeII/FeIII) under visible light without any sacrificial agent was 466.8 µmol h-1 g-1, five times that of MIL-101(Fe). After photocatalytic experiments, MIL-101(FeII/FeIII) retained an unchanged FeII/FeIII rate, indicating that this FeII/FeIII cycling can be maintained. DFT modeling of the FeII-rich MOF material showed that a FeII1 FeIII2 system has a higher N2 activation capacity than a FeIII3 system. The catalytic mechanism was further proved by in situ infrared spectra and N15 isotopic tracers. Therefore, the improvement of photocatalytic activity was mainly attributed to the change in the nitrogen adsorption capacity during the photoinduced FeII/FeIII cycling.

Two-dimensional/two-dimensional heterojunction-induced accelerated charge transfer for photocatalytic hydrogen evolution over Bi5O7Br/Ti3C2: Electronic directional transport.

Regulating electron density at the active site by electronic directional transport from special channels is an effective strategy to accelerate the reaction rate in photocatalytic water splitting. Here, a novel two dimensional/two dimensional (2D/2D) Bi5O7Br/Ti3C2 heterojunction with special interfacial charge transfer channel was fabricated successfully via in-situ growth of Bi5O7Br on the surface of ultrathin Ti3C2 by using a convenient hydrolysis method. The electrostatic attraction between Bi3+ cations and electronegative Ti3C2 ensures the construction of 2D/2D heterojunction and a strong intimate interface contact between Ti3C2 and Bi5O7Br, which establishes an electronic transport channel, and shortens the charge transport distance, assuring excellent bulk-to-surface and interfacial charge transfer abilities. Meanwhile, X-ray photoemission spectroscopy (XPS) and density functional theory (DFT) calculation revealed that the local electron density at the Ti3C2 active sites is remarkably increased because of the transfer of interfacial electrons from Bi5O7Br to Ti3C2, which is a key factor for enhancing the photocatalytic performance. Thus, the resultant Bi5O7Br/Ti3C2 exhibits significant improvement on the performance of photocatalytic hydrogen evolution under visible light irradiation. The hydrogen evolution reaction rate obtained on the optimized Bi5O7Br/Ti3C2 composite is 1.97 times higher than that of pristine Bi5O7Br. This work provides a new protocol for the construction of 2D/2D heterojunction photocatalytic systems and regulating electron density by electronic directional transporting.

Atomically dispersed Palladium-Ethylene Glycol- Bismuth oxybromide for photocatalytic nitrogen fixation: Insight of molecular bridge mechanism.

Performance of single-atom catalysis largely depends on the interaction between the metal and the supporter. Herein, ethylene glycol (EG) was used as a molecular bridge connecting Palladium (Pd) and bismuth oxybromide (BiOBr) to form atomically dispersed Pd catalyst (Pd-EG-BiOBr) for photocatalytic nitrogen fixation under ambient conditions. Compared with 0.20 wt% Pd-BiOBr, 0.20 wt% Pd-EG-BiOBr greatly promoted the photocatalytic nitrogen fixation activity, affording an ammonia formation rate of 124.63 µmol·h-1. The molecular bridge mechanism during catalyst formation and photocatalysis is speculated based on Transmission electron microscopy, In-situ Fourier transform infrared spectra, Electron spin resonance spectra, UV-vis diffuse reflectance spectra, Photoluminescence spectra and Density Functional Theory calculations. The results show that EG not only induces the formation of atomically dispersed Pd, but also enhances the electron density of Pd and activation capacity of nitrogen molecules. This work opens a new door to applications of atomically dispersed Pd supported catalysts for high efficiency photocatalytic nitrogen fixation.

Enhanced N2 photofixation activity of flower-like BiOCl by in situ Fe(III) doped as an activation center.

Photocatalytic nitrogen fixation has been considered to be a safe, green, eco-friendly, and sustainable technology. However, photoinduced activation of inert dinitrogen is an important factor hindering the development of this technology. Herein, in-situ Fe3+ doped flower-like BiOCl with highly active sites exposure was prepared by a solvent thermal method, which has excellent performance of N2 photofixation. Compared with virgin BiOCl with no nitrogen fixation activity, Fe-BiOCl reached 30 µmol·L-1·h-1 ammonia evolution rate under simulated sunlight without any sacrificial reagent. Characterization results demonstrated that the enhancement of N2 photofixation capacity was mainly attributed to the in-situ doped Fe3+ in BiOCl, the doped Fe3+ not only acts as a reaction center for N2 activation also as an "electron transfer bridge" trapping and migrating electrons from BiOCl to N2 molecules. Furthermore, the transformation of crystal facets from virgin BiOCl (001) to Fe-BiOCl (110) and (102) is more conducive for the exposure and accessibility of iron reactive sites. This work developed a potential strategy by in-situ introducing Fe3+ active sites in BiOCl semiconductor substrate, which establishes a good basis for the application of semiconductor catalysts in nitrogen fixation.

Preoxidation-assisted nitrogen enrichment strategy to decorate porous carbon spheres for catalytic adsorption/oxidation of methyl mercaptan.

Porous carbon spheres with high surface area and microporous structure were synthesized from alkyl phenols and formaldehyde via suspension polymerization and steam activation. The effects of air oxidation and ammonia solution heat treatment on the pore structure and surface chemistry of the carbon spheres were studied for catalytic oxidation of CH3SH. The structure property and surface chemistry of the obtained carbon spheres were characterized by N2 adsorption-desorption, FTIR, scanning electron microscopy, XRD, elemental analysis, X-ray photoelectron spectroscopy and Boehm titration, and then thermal analysis and gas chromatography-mass spectrometry were applied to investigate the catalytic oxidation product. Results show that the as-prepared microporous carbon spheres through direct ammonia treatment have a high surface area value of 1710 m2 g-1 and a total pore volume of 0.83 cm3 g-1. Moreover, the preoxidation-assisted nitrogen enrichment strategy not only increases the surface area and total pore volume of the carbon spheres, but also introduces more active nitrogen species such as pyridinic nitrogen and quaternary nitrogen, leading to the highest nitrogen content of 7.13 wt% and the highest CH3SH capacity of 622.8 mg g-1 due to the pyridinic nitrogen and quaternary nitrogen as function of catalysts. In addition, water and oxygen have a beneficial effect on CH3SH oxidation over the nitrogen modified carbon spheres, and the basic oxidation product is CH3SSCH3 that can be further oxidized into CH3SO2SCH3 according to DTG and GC/MS analysis. The great recycling stability after ten cycles with a reserved CH3SH capacity of 97% demonstrates that the porous carbon spheres obtained by preoxidation-assisted enriched nitrogen strategy are promising for catalytic oxidation of CH3SH.

Room-temperature hydrolysis fabrication of BiOBr/Bi12O17Br2 Z-Scheme photocatalyst with enhanced resorcinol degradation and NO removal activity.

BiOBr-based photocatalysts hold great promise in the application of organic wastewater treatment and air purification. However, the catalysis ability of photocatalyst is greatly limited by its poor reduction capacity and intrinsic high recombination rate of photo-generated charge carriers. In this work, a novel direct Z-scheme BiOBr/Bi12O17Br2 photocatalyst is prepared via a facile hydrolysis route at room temperature, which exhibits highly enhanced performance for resorcinol degradation and NO removal than pure Bi12O17Br2 and BiOBr. The formation of the direct Z-scheme heterojunction is substantiated by radical scavenging experiments and the analysis of electronic structure, and it benefits the photocatalytic reaction by accelerating the charge separation and improving the redox ability. Finally, the underlying photocatalytic mechanism is elucidated based on the band structure and radical scavenging experiments. This study provides a facile strategy for bismuth halide Z-scheme heterojunction constructing at room temperature and also sheds light on highly efficient photocatalysts designing.

Enhanced charge separation and increased oxygen vacancies of h-BN/OV-BiOCl for improved visible-light photocatalytic performance.

The introduction of oxygen vacancies (OVs) on the surface of photocatalysts has already been proven to be an effective way to extend the light response to visible light and trap charge carriers, thereby promoting the photocatalytic performance. In this study, h-BN/OV-BiOCl composites were prepared using hexagonal boron nitride (h-BN) to further improve the visible-light photocatalytic activity of oxygen-vacancy-enriched bismuth oxychloride (OV-BiOCl). The composition and morphology of these materials were investigated, and the photocatalytic performance experiments showed that the introduction of h-BN could significantly improve the visible-light photocatalytic activity of OV-BiOCl, which was 1.7 and 1.4 times that of pure OV-BiOCl for the degradation of rhodamine B (RhB) and bisphenol A (BPA) when the h-BN content was 5 wt%, respectively. The role of h-BN was comprehensively investigated, and the results revealed that the presence of negatively charged h-BN could improve the separation efficiency of photoinduced electrons (e-) and holes (h+) by promoting the migration of positively charged h+ to the surface of the photocatalyst, as expected. Moreover, the oxygen vacancies in OV-BiOCl were increased in the presence of h-BN; this favored the activation of more adsorbed O2 for the oxidation of pollutants. Finally, a probable mechanism was proposed for the improved photocatalytic activity of the h-BN/OV-BiOCl composites. This study provides an insight into the roles of h-BN in oxygen-vacancy-enriched photocatalysts.

Enhanced photocatalytic reduction of CO2 to CO over BiOBr assisted by phenolic resin-based activated carbon spheres.

Photocatalytic reduction of CO2 using solar energy to decrease CO2 emission is a promising clean renewable fuel production technology. Recently, Bi-based semiconductors with excellent photocatalytic activity and carbon-based carriers with large specific surface areas and strong CO2 adsorption capacity have attracted extensive attention. In this study, activated carbon spheres (ACSs) were obtained via carbonization and steam activation of phenolic resin-based carbon spheres at 850 °C synthesized by suspension polymerization. Then, the BiOBr/ACSs sample was successfully prepared via a simple impregnation method. The as-prepared samples were characterized by XRD, SEM, EDX, DRS, PL, EIS, XPS, BET, CO2 adsorption isotherm and CO2-TPD. The BiOBr and BiOBr/ACSs samples exhibited high CO selectivity for photocatalytic CO2 reduction, and BiOBr/ACSs achieved a rather higher photocatalytic activity (23.74 µmol g-1 h-1) than BiOBr (2.39 µmol g-1 h-1) under simulated sunlight irradiation. Moreover, the analysis of the obtained results indicates that in this photocatalyst system, due to their higher micropore surface area and larger micropore volume, ACSs provide enough physical adsorption sites for CO2 adsorption, and the intrinsic structure of ACSs can offer effective electron transfer ability for a fast and efficient separation of photo-induced electron-hole pairs. Finally, a possible enhanced photocatalytic mechanism of BiOBr/ACSs was investigated and proposed. Our findings should provide new and important research ideas for the construction of highly efficient photocatalyst systems for the reduction of CO2 to solar fuels and chemicals.

Nitrogen-doped carbon quantum dots/Ag3PO4 complex photocatalysts with enhanced visible light driven photocatalytic activity and stability.

Novel nitrogen-doped carbon quantum dots/Ag3PO4 (NCQDs/Ag3PO4) complex photocatalysts were synthesized by a facile precipitation method at room temperature. The physical and chemical properties of Ag3PO4 and NCQDs/Ag3PO4 photocatalysts were detected through X-ray powder diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and electron spin resonance techniques. The as-prepared 3-NCQDs/Ag3PO4 composite exhibited much higher activity than the pure Ag3PO4 for eliminating methyl orange and bisphenol A solution under visible light (λ>420nm). Moreover, in the cyclic experiments, the 3-NCQDs/Ag3PO4 exhibited an excellent stability for the decolorization of methyl orange at some level. This suggested that NCQDs played an important role in the process of degradation. The function of NCQDs was discussed and a new mechanism was put forward for the degradation of methyl orange. The high activities and stability were attributed to the transfer of photogenerated charges through the vector of Ag3PO4→NCQDs→Ag in the photocatalytic process, leading to effective charge separation of Ag3PO4.