Efficient Photocatalytic System Research Articles

A high-efficiency photocatalytic hydrogen evolution system based on nickel-quinoxaline dithiolate complexes and water-soluble CdSe quantum dots

Photocatalytic water splitting of water for hydrogen evolution is one of the effective methods to obtain clean hydrogen energy. In the present work, the following materials were synthesized: two nickel quinoxaline thiolate complexes [NBu4]2 [Ni(qdt)2] (1, Bu = n-butyl, qdt = quinoxaline-dithiol), [NBu4]2 [Ni(qdt)2(NO2)2] (2) and water-soluble MPA-CdSe quantum dots (MPA-CdSe QDs, MPA = 3-mercaptopropionic acid). Subsequently, an efficient three-component photocatalytic hybrid system for hydrogen evolution was developed and tested under visible light irradiation, in which one of the target complex 1 or 2 was used as the catalyst, triethylamine (TEA) was used as the sacrificial electron donor, and MPA-CdSe QDs were used as the light harvesting reagent. The turnover numbers (TON) for H2 evolution of 8974 (vs. complex 1) and 6532 (vs. complex 2) were obtained under the optimal conditions with TEA concentration of 5 %, pH = 12, and concentration of complex 1 or 2 of 1 × 10−5 mol L−1 after 13 h of irradiation (λ > 420 nm) in pure water. The mechanism investigation indicated that critical steps of hydrogen production was formation of hydride intermediates Ni(II)-H and Ni(I)-H spices, followed by the reaction of two Ni(II)-H or Ni(I)-H species with protons generating H2 molecules and regenerating the catalyst Ni(II).

In-situ synthesis of V2AlC@V2O5/TiO2 immobilized over honeycomb support with vanadium oxide electron transfer mediator for stimulating selective CO2 photoreduction through bi-reforming in a monolith reactor

Photocatalytic CO2 reduction to valuable chemicals and fuels is a practical approach for climate action; however, available photocatalysts and photoreactors are less efficient. In this work, well-designed V2AlC@V2O5 supported TiO2 and immobilized over honeycomb support for CO2 photoreduction in a monolith reactor have been investigated. The catalysts were loaded over the monolithic support using the sol-gel dip-coating method and found promising for higher light absorbance and charge separation. The performance of V2AlC@V2O5/TiO2 composite for photocatalytic CO2 reduction with water and bi-reforming of methanol was performed using a fixed bed and monolith photoreactor. Using V2AlC@V2O5/TiO2 with a fixed bed reactor and methanol–water mixture, a CO yield of 13.75 mmol g−1h−1 was produced, 26.39 and 38.19-fold higher than using water and pristine TiO2, respectively. Similarly, CH4 production was 1.97 and 12.33 folds higher than using water and TiO2 only, whereas, using water, production of H2 was not detected. The higher photoactivity of the composite with methanol was due to efficient photo-induced carrier separation due to the synergistic effect of V2AlC/V2O5 and more production of protons. Using a monolith photoreactor, CH4, CO and H2 production rates of 55.44, 35.51 and 1.638 mmol g−1h−1 were obtained, 166.50, 2.58 and 3.05 times more than those produced using a fixed bed reactor. This significantly higher photoactivity with monolith photoreactor was due to higher photon flux utilization with surface reactions, resulting in more production and utilization of photoinduced charge carriers. The highest QY after five consecutive cycles was 48.374, 25.358 and 1.51 % for CH4, CO and H2, which is 200.5, 2.54 and 3.87 folds higher than using the fixed bed, respectively. This work provides a new approach to designing and fabricating higher efficient and stable photocatalytic system for CO2 recycling, and it can be further employed for other energy-related applications.

Preparation, characterization and photocatalytic studies of defect pyrochlore, KMn0·33Te1·67O6 and its composite with g-C3N4

Skeletal materials belonging to the defect pyrochlore family have been the subject of considerable interest due to their remarkable properties. In this work, a highly efficient, stable and visible light active composite photocatalytic system consisting of defect pyrochlore of composition KMn0·33Te1·67O6 (KMnTeO) and g-C3N4 (g-CN) has been successfully prepared by simple physical mixing of pre-prepared KMnTeO and g-CN components synthesized in solid state and thermal treatment of low-cost melamine, respectively. Structural, morphological and optical properties of as-prepared catalysts were deduced from powder X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR), Raman, Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (FESEM-EDX), Transmission Electron Microscopy-High Resolution Transmission Electron Microscopy (TEM-HRTEM), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV–Vis DRS), X-ray Photoelectron Spectroscopy (XPS) and Photoluminescence (PL) measurements. The lattice parameter “a” of parent KMnTeO was obtained from Rietveld refinement of its powder XRD pattern. The FT-IR and Raman spectra of KMnTeO gave characteristic bands belonging to the defect pyrochlore structure. The photocatalytic activities of KMnTeO and composite KMnTeO-g-CN were evaluated by the degradation of methylene blue (MB). Scavenger experiments were carried out to identify the reactive species responsible for the degradation of MB. Furthermore, the reusability and stability of the photocatalysts were explored. The probable photocatalytic mechanism for MB degradation over the composite KMnTeO-g-CN was surmised according to the scavenger experiments. The work provides a new approach for the development of novel defect pyrochlore based composite photocatalysts to treat industrial wastewater containing organic pollutants.

Structurally disordered MoSe2 with rich 1T phase as a universal platform for enhanced photocatalytic hydrogen production

The improvement of surface reactivity in noble-metal-free cocatalysts is crucial for the development of efficient and cost-effective photocatalytic systems. However, the influence of crystallinity on catalytic efficacy has received limited attention. Herein, we report the utilization of structurally disordered MoSe2 with abundant 1T phase as a versatile cocatalyst for photocatalytic hydrogen evolution. Using MoSe2/carbon nitride (CN) hybrids as a case study, it is demonstrated that amorphous MoSe2 significantly enhances the hydrogen evolution rate of CN, achieving up to 11.37 μmol h−1, surpassing both low crystallinity (8.24 μmol h−1) and high crystallinity MoSe2 (3.86 μmol h−1). Experimental analysis indicates that the disordered structure of amorphous MoSe2, characterized by coordination-unsaturated surface sites and a rich 1T phase with abundant active sites at the basal plane, predominantly facilitates the conversion of surface-bound protons to hydrogen. Conversely, the heightened charge transfer capacity of the highly crystalline counterpart plays a minor role in enhancing practical catalytic performance. This approach is applicable for enhancing the photocatalytic hydrogen evolution performance of various semiconducting photocatalysts, including CdS, TiO2, and ZnIn2S4, thereby offering novel insights into the advancement of high-performance non-precious catalysts through phase engineering.

Facet-Dependent Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 Dual S-Scheme Photocatalyst as an Efficient Visible-Light-Driven Peroxymonosulfate Activator for Norfloxacin Degradation.

A lack of eco-friendly, highly active photocatalyst for peroxymonosulfate (PMS) activation and unclear environmental risks are significant challenges. Herein, we developed a double S-scheme Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 photocatalyst to activate PMS and investigated its impact on wheat seed germination. We observed an improvement in charge separation by depositing Fe2O3 on the (010) and (110) surfaces of BiVO4. This enhancement is attributed to the formation of a dual S-scheme charge transfer mechanism at the interfaces of Fe2O3/BiVO4(110) and BiVO4(010)/Fe2O3. By introducing PMS into the system, photogenerated electrons effectively activate PMS, generating reactive oxygen species (ROS) such as hydroxyl radicals (·OH) and sulfate radicals (SO4·-). Among the tested systems, the 20% Fe2O3/BiVO4/Vis/PMS system exhibits the highest catalytic efficiency for norfloxacin (NOR) removal, reaching 95% in 40 min. This is twice the catalytic efficiency of the Fe2O3/BiVO4/PMS system, 1.8 times that of the Fe2O3/BiVO4 system, and 5 times that of the BiVO4 system. Seed germination experiments revealed that Fe2O3/BiVO4 heterojunction was beneficial for wheat seed germination, while PMS had a significant negative effect. This study provides valuable insights into the development of efficient and sustainable photocatalytic systems for the removal of organic pollutants from wastewater.

Rational Design of TaON/Potassium Poly(Heptazine Imide) Heterostructure for Multifunctional Environmental Remediation

AbstractTantalum oxynitride (TaON) has recently attracted much attention due to its excellent performance as a semiconductor. However, its shortage in separation of photogenerated charges hinders the wide application, which, fortunately, can be made up by forming heterojunctions with other photocatalysts. In this study, the rational design of an inorganic‐organic TaON/potassium poly (heptazine imide) (KPHI) heterojunction is reported to separate the photo charges on the two sides of this dyadic structure. The incorporation of 20 wt.% TaON into KPHI resulted not only in H2 generation but also in a wider set of environmental remediation applications under visible light, including Cr(VI) reduction and degradation of otherwise resilient antibiotics. 20TaON/KPHI effectively reduced 17.5 ppm Cr(VI) solution in 35 min under low‐power blue light irradiation with a rate constant which is ≈6 and 30 times higher than that of pristine KPHI and TaON, respectively. Moreover, the composite demonstrated a 2‐ and 40‐fold increase in H2 evolution rate in comparison to pure KPHI and TaON, respectively. This remarkable enhancement in photocatalytic activity is ascribed to the efficient electron‐hole separation and formation of an effective Z‐scheme heterojunction. This work offers a new paradigm for designing efficient photocatalytic systems for environmental applications under low‐power LED and natural sunlight.

Enhanced photocatalytic H2 evolution over conjugated polymer/Au@TiO2 ternary heterojunction under visible light: Enriched photons input from polymers

Exploring efficient and stable TiO2-based photocatalysts for visible-light H2 evolution remains a great challenge. Here, a novel ternary heterojunction (THSO/Au@TiO2) was successfully synthesized by a facile in-situ polymerization strategy, which showed highly enhanced photocatalytic activity towards H2 evolution under visible light. The optimized THSO/Au@TiO2-26 exhibited an excellent photocatalytic performance to H2 evolution (7504 μmol/g/h), which was 16.31, 416.89 and 1.81 times higher than that of THSO, TiO2 and THSO/TiO2 photocatalysts, respectively. This excellent performance should be attributed to the excellent visible light absorption ability of the polymer THSO, and the local surface plasmonic resonance effect of Au nanoparticles (Au NPs), promoting separation and transfer of photo-generated charge carriers. This work presents new insights for the design of efficient and rational TiO2-based photocatalytic systems to enhance photocatalytic performance towards H2 evolution under visible light.

Surface coordination induced a quasi p-n junction for efficient visible light driven degradation of tetracycline over hydroxyapatite

The removal of antibiotics from aquatic solutions remains a global environmental challenge. In this work, the photocatalytic removal of a typical antibiotic-tetracycline (TC) using hydroxyapatite (HAp) as a catalyst was investigated. It was impressive that TC could be efficiently degraded by HAp under visible light irradiation, even though both HAp and TC exhibited poor harvesting in visible light region. The experimental and theoretical explorations were undertaken to thoroughly investigate the underlying mechanism of visible light degradation of TC over HAp. The results indicated that the formed TC-HAp complexes via surface coordination played an important role as photosensitizers for the visible light response. Together with the formation of a quasi p-n junction via band alignment, the photogenerated electrons in the highest unoccupied molecular orbital (HOMO) of TC-HAp were excited to the lowest unoccupied molecular orbital (LUMO) and subsequently migrated to the conduction band of HAp to achieve the efficient charge separation. Superoxide radicals and holes were found to be the major active species for TC degradation. The toxicity evaluation showed that TC could be transferred to the lower toxic intermediates, and deep oxidation with prolonged reaction time was necessary to eliminate the toxicity of TC. This work demonstrates the surface coordination with subsequent quasi p-n junction mechanism of TC degradation over HAp under visible light, which will stimulate us to explore new efficient photocatalytic systems for the degradation of various contaminants.

Multishelled hollow CaTiO3 cubes decorated with Co0.2Cd0.8S nanoparticles for efficient photocatalytic H2 evolution via S-scheme charge transfer

Rationally designing S-scheme heterostructures with boosted charge separation efficiency and superior redox ability is regarded as an appealing strategy to conquer the shortcomings of mono-component and conventional heterojunction photocatalysts. Herein, a novel hierarchical S-scheme heterostructured photocatalyst was constructed by integrating Co0.2Cd0.8S nanoparticles on multishelled hollow CaTiO3 cubes to substantially improve the photocatalytic hydrogen production activity. An internal electric field (IEF) is formed at the heterojunction interfaces owing to the significant disparity in Fermi level (EF) between Co0.2Cd0.8S and CaTiO3, accompanied by the energy band bending, which enables the S-scheme charge transport route in the Co0.2Cd0.8S/CaTiO3 heterostructure, as verified by electron paramagnetic resonance and theoretical calculations. Benefiting from the boosted separation efficiency and superior redox capability of photocarriers within the constructed S-scheme heterostructure, the optimized Co0.2Cd0.8S/CaTiO3 sample exhibited a significantly improved photocatalytic hydrogen evolution rate of 8.13 mmol h−1 g−1, far exceeding that of mono-component counterparts and previously reported Co0.2Cd0.8S- or CaTiO3-based photocatalysts. This study is anticipated to inspire the strategic development of other economical and efficient S-scheme photocatalytic systems with enhanced H2 evolution activity.

Peroxymonosulfate enhanced photocatalytic degradation of organic dye by metal-free TpTt-COF under visible light irradiation

Recently, the activation of persulfate (PDS) by non-metallic photocatalysts under visible light has attracted significant interest in applications in environmental remediation. This study presents a pioneering investigation into the combined application of the TpTt-COF and PMS for visible light degradation of organic dyes. Synthesized orange TpTt-COF monomers exhibit exceptional crystallinity, a 2D structure, and notable stability in harsh conditions. The broad visible light absorption around a wavelength of 708 nm. The TpTt-COF emerges as a promising candidate for photocatalytic dye degradation. The study addresses high charge recombination in the TpTt-COF, highlighting the crucial role of its electron donor and acceptor for the PMS activation. Comparative analyses against traditional photocatalytic materials, such as the metal-free carbon-based material g-C3N4 and transition metal-containing TiO2, demonstrate TpTt-COF's superior performance, generating diverse free radicals. In simulated experiments, the TpTt-COF's degradation rate surpasses PMS-combined g-C3N4 by 13.9 times. and 1.6 times higher than the TpTt-COF alone. Remarkably, the TpTt-COF maintains high activity under harsh environments. Investigations into the degradation mechanism and the TpTt-COF's reusability reveal its efficiency and stability. Under visible light, TpTt-COF facilitates efficient electron–hole separation. Combining the TpTt-COF with PMS produces various radicals, ensuring effective separation and a synergistic effect. Radical quenching experiments confirm the pivotal role of O2-· radicals, while ·OH and SO4-· radicals intensify the degradation. After five cycles, TpTt-COF maintains an impressive 83.2% degradation efficiency. This study introduces an efficient photocatalytic system mediated by PMS and valuable insights into governing mechanisms for organic pollutant degradation in water environments.

An Efficient Photocatalytic Oxygen Evolution System with the Coupling of Polyoxometalates with Bismuth Vanadate

In this work, a coupling system consisting of bismuth vanadate (BiVO4) and cobalt-based polyoxometalates (Co-POMs) was developed to enhance the oxygen evolution reaction. Crystallization-driven self-assembly and the wet chemical synthesis method were deployed in synthesizing Co-POMs and monoclinic–tetragonal mixed–phase BiVO4, respectively. The introduction of Co-POMs into a BiVO4-containing mixture significantly enhanced the water oxidation reaction, with a more than twofold increment in the total amount of oxygen evolved. For instance, 461.2 µmol of oxygen was evolved from the system containing 20 mg of Co-POMs compared to 195 µmol of oxygen produced from a pristine BiVO4 system. This extraordinary improvement in the oxygen evolution reaction indicates the existence of a positive synergic effect between BiVO4 and Co-POMs, in which Co-POMs could act as effective cocatalysts to extract photogenerated charge carriers generated by BiVO4 and improve the charge transfer process. However, the amount of oxygen produced was slightly reduced to 440.7 µmol with an increase in AgNO3 loading from 30 mg to 60 mg. This unforeseen phenomenon could be elucidated by the shielding effect of silver particles, in which a higher AgNO3 loading led to a more prominent shielding effect. The presence of silver nanoparticles on post-reaction BiVO4 was confirmed by TEM and XPS analysis. This newly established process scheme provides an insight into the development of an efficient photocatalytic oxygen evolution system in realizing future commercial applications toward green energy production.

A binary dumbbell visible light driven photocatalyst for simultaneous hydrogen production with the selective oxidation of benzyl alcohol to benzaldehyde

Photocatalytic H2 production with selective oxidation of organic moieties in an aqueous medium is a fascinating research area. However, the rational design of photocatalysts and their photocatalytic performance are still inadequate. In this work, we efficiently synthesized the MoS2 tipped CdS nanowires (NWs) photocatalyst using soft templates via the two-step hydrothermal method for efficient H2 production with selective oxidation of benzyl alcohol (BO) under visible light illumination. The optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst exhibits the highest photocatalytic H2 production efficiency of 13.55 mmol g−1 h−1 with 99 % selective oxidation of BO, which was 42.34 and 2.21 times greater photocatalytic performance than that of pristine CdS NWs and MoS2/CdS NWs, respectively. The directional loading of MoS2 at the tips of CdS NWs (as compared to nondirectional MoS2 at CdS NWs) is the key factor towards superior H2 production with 99 % selective oxidation of BO and has an inhibitory effect on the photo corrosion of pristine CdS NWs. Therefore, the amazing enhancement in the photocatalytic performance and selectivity of optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst is due to the spatial separation of their photoexcited charge carriers through the Schottky junction. Moreover, the unique structure of the MoS2 flower at the tip of 1D CdS NWs offers separate active sites for adsorption and surface reactions such as H2 production at the MoS2 flower (confirmed by Pt photo deposition) and subsequently the selective oxidation of BO at the stem of CdS NWs. This rational design of a photocatalyst could be an inspiring work for the further development of an efficient photocatalytic system for H2 production with selective oxidation of BO (a strategy of mashing two potatoes with one fork).

In situ single iron atom doping on Bi2WO6 monolayers triggers efficient photo-fenton reaction

Developing an efficient photocatalytic system for hydrogen peroxide (H2O2) activation in Fenton-like processes holds significant promise for advancing water purification technologies. However, challenges such as high carrier recombination rates, limited active sites, and suboptimal H2O2 activation efficiency impede optimal performance. Here we show that single-iron-atom dispersed Bi2WO6 monolayers (SIAD-BWOM), designed through a facile hydrothermal approach, can offer abundant active sites for H2O2 activation. The SIAD-BWOM catalyst demonstrates superior photo-Fenton degradation capabilities, particularly for the persistent pesticide dinotefuran (DNF), showcasing its potential in addressing recalcitrant organic pollutants. We reveal that the incorporation of iron atoms in place of tungsten within the electron-rich [WO4]2− layers significantly facilitates electron transfer processes and boosts the Fe(II)/Fe(III) cycle efficiency. Complementary experimental investigations and theoretical analyses further elucidate how the atomically dispersed iron induces lattice strain in the Bi2WO6 monolayer, thereby modulating the d-band center of iron to improve H2O2 adsorption and activation. Our research provides a practical framework for developing advanced photo-Fenton catalysts, which can be used to treat emerging and refractory organic pollutants more effectively.

Composite of formamidinium lead bromide perovskite FAPbBr3 with reduced graphene oxide (rGO) for efficient H2 evolution from HBr splitting

Solar hydrobromic acid (HBr) splitting using perovskite photocatalysts provides an attractive avenue to store solar energy into hydrogen (H2) and bromine (Br2), while an efficient photocatalytic system is still demanded. As for the semiconductor photocatalyst, formamidinium perovskites show some superiorities in structural stability, light adsorption and charge dynamics compared to their methylammonium counterparts, which are fitter for the photocatalysis process. Herein, the composite of formamidinium lead bromide perovskite (FAPbBr3) with reduced graphene oxide (rGO) is prepared using a facile photoreduction method. Under simulated sunlight irradiation (AM1.5G, 100 mW cm−2), this FAPbBr3/rGO composite (100 mg) demonstrates a noteworthy enhancement in photocatalytic H2 evolution activity of 386.7 μmol h−1, and it exhibits a notable stability with no significant decrease after 50 h of repeated tests. The single particle PL (photoluminescence) microscope is employed to study the charge dynamics, revealing that rGO in the composite effectively promotes the carrier separation. This work provides a highly efficient and stable photocatalyst for HBr splitting, and offers an effective modification strategy on lead bromide perovskites.

Salt-assisted construction of hydrophilic carbon nitride photocatalysts with abundant water molecular adsorption sites for efficient hydrogen production

Polymer carbon nitride (PCN), as an affordable and easily prepared photocatalyst, has acquired extensive attention for hydrogen production. However, bulk carbon nitride material exhibits poor dispersibility in water due to the relatively inert surface which limits its quantum efficiency in photocatalytic hydrogen production. In this study, a hydrophilic carbon nitride (HCN) is successfully synthesized by a novel salt-assisted heating process. The heightened water adsorption capacity may contribute additional active sites conducive to the photocatalytic hydrogen production reaction. Meanwhile, potassium ion doping and material size reduction greatly enhance the charge transfer and separation ability of HCN. Consequently, HCN exhibits highly efficient photocatalytic activity for hydrogen production, achieving a rate of 392 μmol·h−1, which is 16 times greater than that of pristine PCN. The simply developed synthetic strategy adopted here provides a novel concept for functionalizing carbon nitride and opening a distinct pathway for the construction of exceptionally efficient photocatalytic systems.

Synthesis, characterization, and photocatalytic activity for water remediation and hydrogen evolution of Zn(II) and Ni(II) bis(thiosemicarbazone) complexes

The extensive industrial use of organic dyes causes large amounts of these substances to arrive at water sources, so nowadays, organic compound removal from fresh water is a major concern. The use of photocatalysts is an interesting approach to solving this problem, with coordination compounds playing an outstanding role. We report the selective synthesis and characterization of three new dissymmetric bis(thiosemicarbazone) ligands and their nickel(II) and zinc(II) complexes, which have been fully characterized by several techniques. The photocatalytic activity of the six complexes for methyl orange degradation was also evaluated. All the complexes can degrade this organic dye, although the photoefficiency of the nickel compounds is, in general, higher than for the zinc ones, as the degradation is faster and they do not reach a plateau. Density functional theory calculations show a clear dependence of the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, as well as with the relative energies of these orbitals. On the other hand, the need for green fuels that do not produce the greenhouse effect is one of the major goals of modern life, and molecular hydrogen is one of the most promising ones. Considering the proven potential of bis(thiosemicarbazone) complexes to electrocatalyze H2 evolution recently reported in the literature, we also made some preliminary tests to investigate the potential of the nickel complexes to act as photocatalysts for water splitting. The results indicate that two of the complexes produce H2 in the conditions tested, so they could be used in the development of efficient photocatalytic systems for hydrogen evolution.

Methane sulfonic acid-assisted synthesis of g-C3N4/Ni2P/Ni foam: Efficient, stable and recyclable for photocatalytic nitrogen fixation under visible light

Photocatalytic nitrogen fixation is of great significance for solving the energy crisis and healthy development of the environment. However, photocatalysts have problems such as low activity, poor stability and difficult recovery, which seriously limit their application. Herein, we in situ synthesized g-C3N4/Ni2P/Ni three-dimensional reticulated foam photocatalysts (CNNPF) with excellent photocatalytic nitrogen fixation performance under visible light by a two-step methane sulfonic acid-assisted carbon nitride loading-calcined phosphatisation method, using nickel foam as the carrier and raw material. The results showed that the CNNPF had a stable three-dimensional network structure, and g-C3N4 was stably immobilized to the nickel foam skeleton with Ni2P. The best performance of CNNPF with ultrasonication for 2 h and phosphatisation for 1 h showed a high photocatalytic nitrogen fixation efficiency of up to 373 μmol·h−1·g−1, which was attributed to the Ni2P co-catalyst modification of g-C3N4 that led to the improvement of photogenerated electron-hole pair separation efficiency. Meanwhile, the three-dimensional network structure is favorable to provide more active sites for N2 adsorption and activation. In addition, the prepared material also has good stability and recyclability, and its nitrogen fixation efficiency was still maintained at 350 μmol·h−1·g−1 after five cycles. The present work provides a direction for the design of efficient and recyclable photocatalytic systems that show great potential in the field of economically sustainable nitrogen fixation.

Molten salt synthesis of 1T/2H mixed phase MoS2 for boosting photocatalytic H2 evolution via Schottky junction under EY-sensitized system

Clean H2 fuel obtained from the photocatalytic water splitting to hydrogen reaction could efficiently alleviate current energy crisis and the concomitant environmental pollution problems. Therefore, it is desirable to search for a highly efficient photocatalytic system to decrease the energy barrier of water splitting reaction. Herein, the 1T/2H mixed phase MoS2 sample with Schottky junction between contact interfaces is developed through molten salt synthesis for photocatalytic hydrogen production under a dye-sensitized system (Eosin Y-TEOA-MoS2) driven by the visible light. In mixed phase MoS2 sample, the photogenerated electrons of 2H-phase MoS2 migrated to the 1T-phase MoS2 are difficult to jump back because of the existence of Schottky barrier, which greatly suppresses the quenching of EY and therefore results in an enhanced hydrogen evolution performance. Therefore, the optimized MoS2 sample (MoS2-350) has an initial hydrogen evolution rate of 213 μmol h−1 and corresponding apparent quantum yield of 36.1 % at 420 nm, far higher than those of pure Eosin Y. It is strongly confirmed by the steady‐state/time-resolved photoluminescence (PL) spectra and transient photocurrent response experiments. With the assistance of Density functional theory (DFT) calculation, the function of Schottky junction in photocatalytic hydrogen evolution reaction is well explained. In addition, a new and universal method (SVM curve) of judging oxidation or reduction quenching for photosensitizers is proposed.

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin.

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP4+, where H2TMPyP4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP4+ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP4+-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex.

Enhanced photocatalytic performance of NH2-MIL-125(Ti)/SrTiO3 heterostructures by the piezoelectric effect of SrTiO3

Applying piezoelectric effect on modulating charge transport behavior was considered as one efficient strategy to make feasible charge separation in photocatalysts towards boosting hydrogen evolution performance. Here, with employing corona-poling treatment, SrTiO3 is converted to be a piezoelectric component in the constructed type II NH2-MIL-125(Ti)/SrTiO3 heterojunction. Since the piezoelectric field could tilt the band bending to a degree to be convenient for the charge transfer from SrTiO3 to NH2-MIL-125(Ti), it is also favorable to offer additional active sites on SrTiO3 to form dual reduction sites for the following piezo-photocatalytic reaction. Both the ameliorated surficial polarization and charge transfer trajectory in NH2-MIL-125(Ti)/SrTiO3 type II heterojunction are devoted to the boosted hydrogen production rate for NH2-MIL-125(Ti)/SrTiO3-0.1 (NM/STO-0.1), that is up to 1562.3 μmol h−1 g−1, 1.79 times higher than that of unpolarized NM/STO-0.1 (871.6 μmol h−1 g−1) and 2.35 times higher than that of NH2-MIL-125(Ti) (663.8 μmol h−1 g−1), respectively. This research reported initially the assistant of SrTiO3 with piezoelectric feature for enhanced performance photocatalytic hydrogen evolution, which could be one prominent strategy to achieve the reasonable design of efficient photocatalytic system.