2D MOFs enriched g-C3N4 nanosheets for highly efficient charge separation and photocatalytic hydrogen evolution from water

Here we report a 2D-2D heterostructure of g-C₃N₄/UMOFNs photocatalysts via mechanical grinding two kinds of two-dimensional nanosheets of g-C₃N₄ nanosheets and UMOFNs, which exhibits enhanced H₂ evolution from water with simulated solar irradiation. g-C₃N₄ nanosheets are in close contact with UMOFNs, and there is a certain interaction between them, showing the effect of superimposition on the two-dimensional layer. The 2D-2D heterostructure offers a maximal photocatalytic hydrogen production activity of 1909.02 μmol g⁻¹ h⁻¹ with 3 wt% of UMOFNs, which is 3-fold higher than that of g-C₃N₄ nanosheets (628.76 μmol g⁻¹ h⁻¹) and 15-flod higher than that of bulk g-C₃N₄ (124.30 μmol g⁻¹ h⁻¹). The significant increasement of photocatalysis is due to 2D-2D heterostructure possessing a short charge transfer distance and large contact area between g-C₃N₄ and UMOFNs. The highly dispersed NiO, CoO and π-π bonds in UMOFNs of 2D-2D structure also promote charge transfer and enhance the photocatalytic activity.     

A facile one-step strategy to construct 0D/2D SnO2/g-C3N4 heterojunction photocatalyst for high-efficiency hydrogen production performance from water splitting

Fabricating 0D/2D heterojunctions is considered to be an efficient mean to improve the photocatalytic activity of g-C₃N₄, whereas their applications are usually restricted by complex preparation process. Here, the 0D/2D SnO₂/g-C₃N₄ heterojunction photocatalyst is prepared by a simple one-step polymerization strategy, in which SnO₂ nanodots in-situ grow on the surface of g-C₃N₄ nanosheets. It shows the outstanding photocatalytic H₂ production activity relative to g-C₃N₄ under the visible light, which is due to the formation of 0D/2D heterojunction significantly contributing to the separation of photogenerated charge carriers. In particular, the H₂ production rate over the optimal SnO₂/g–C₃N₄–1 sample is 1389.2 μmol h⁻¹ g⁻¹, which is 6.06 times higher than that of g-C₃N₄ (230.8 μmol h⁻¹ g⁻¹). Meanwhile, the AQE value of H₂ production over the SnO₂/g–C₃N₄–1 sample reaches up to a maximum of 4.5% at 420 nm. This work develops a simple approach to design and fabricate g–C₃N₄–based 0D/2D heterojunctions for the high-efficiency H₂ production from water splitting.     

Highly efficient Bi2O3/MoS2 p-n heterojunction photocatalyst for H2 evolution from water splitting

The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi₂O₃/MoS₂ p-n heterojunction photocatalysts with tunable loading amount of Bi₂O₃ (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi₂O₃ and MoS_2, the Bi₂O₃/MoS₂ heterostructures displayed significantly superior performance for photocatalytic hydrogen (H₂) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi₂O₃/MoS₂ photocatalyst (10 μmol h⁻¹g⁻¹) with Bi₂O₃ content of 11 wt%, which was approximately ten times higher than pure Bi₂O₃ (1.1 μmol h⁻¹g⁻¹) and MoS₂ (1.2 μmol h⁻¹g⁻¹) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi₂O₃/MoS₂ heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.     

Fabrication of a Cu2-xSe/rGO heterojunction photocatalyst to achieve efficient photocatalytic H2 generation

The present study has successfully fabricated a Cu_2-xSe/rGO heterojunction for the first time using an in situ hot-injection method and employed it to produce photocatalytic hydrogen. The optimal Cu_2-xSe/3%rGO can achieve an efficient photocatalytic H₂ production at the rate 3123.48 μmol g⁻¹ h⁻¹, nearly 3.46 times higher than that of the pure Cu_2-xSe. The enhanced activity can be attributed to facilitated light absorption, up-regulated charge density, lower interfacial transfer resistance as well as a longer electron decay lifetime. In the meantime, the expanded specific surface area can create more active reaction sites, leading to the enhancement of photocatalytic peropeties. Besides, the mechanism of the Cu_2-xSe/rGO heterojunction's hydrogen production is proposed.     

Surface oxygen vacancy facilitated Z-scheme MoS2/Bi2O3 heterojunction for enhanced visible-light driven photocatalysis-pollutant degradation and hydrogen production

An oxygen-vacancy rich, bismuth oxide (Bi₂O₃) based MoS₂/Bi₂O₃ Z-scheme heterojunction catalyst (2-BO-MS) was prepared in an autoclave hydrothermal method using ethanol and water. The performance of MoS₂/Bi₂O₃ catalyst was examined for photocatalytic hydrogen evolution, photoelectrochemical activity, and crystal violet (CV) dye degradation by comparing with pristine Bi₂O₃ and MoS₂. The hydrogen evolution performances of 2-BO-MS catalyst exhibited 3075.21 μmol g⁻¹ h⁻¹, which is 7.18 times higher than that of MoS₂ (428.14 μmol g⁻¹ h⁻¹). The XPS, XRD and HRTEM analyses covered that the superior photocatalytic performance of 2-BO-MS catalyst might have stemmed out due to the existence of oxygen vacancies, enhanced strong interfacial interaction between MoS₂ and Bi₂O₃ and specific surface area. The in-depth investigation has been performed for MoS₂/Bi₂O₃ Z-scheme heterojunction using several characterization techniques. Moreover, the photocatalytic mechanism for hydrogen evolution and photodegradation were proposed based on trapping experiment results. This results acquired using MoS₂/Bi₂O₃ Z-scheme heterojunction would be stepping stone for developing heterojunction catalyst towards attaining outstanding photocatalytic activity.     

Porous g-C3N4/TiO2 S-scheme heterojunction photocatalyst for visible-light driven H2-production and simultaneous wastewater purification

In this work, photocatalysts with a novel S-scheme heterojunction were fabricated by coupling MOF-derived TiO₂ with porous g-C₃N₄ (MTO/PCN). The S-scheme heterojunction with matching band gap possesses different advantageous properties, which can not only inhibit photo-generated charge recombination, but also reserve outstanding redox ability. As expected, superior hydrogen evolution efficiency of 40-MTO/PCN was obtained in a TEOA-containing aqueous solution and pure water, which were 5252.9 and 974.6 μmol h⁻¹ g⁻¹, respectively. Meanwhile, the hybrid can also serve as a bifunctional catalyst for H₂ generation (2137.3 μmol h⁻¹ g⁻¹) and organic contaminant removal (the RhB purification efficiency: 35.24%). This work furnishes a feasible method for devising bifunctional photocatalysts that can simultaneously produce hydrogen and purify wastewater to provide both energy-saving and environmental restoration functions.     

Efficient interfacial charge transfer of 2D/2D CoP/CdS heterojunction for extremely boosted photocatalytic H2 evolution performance

Constructing 2D/2D heterojunction photocatalysts has attracted great attentions due to their inherent advantages such as larger interfacial contact areas, short transfer distance of charges and abundant reaction active sites. Herein, 2D/2D CoP/CdS heterojunctions were successfully fabricated and employed in photocatalytic H₂ evolution using lactic acid as sacrificial reagents. The multiple characteristic techniques were adopted to investigate the crystalline phases, morphologies, optical properties and textual structures of heterojunctions. It was found that integrating 2D CoP nanosheets as cocatalysts with 2D CdS nanosheets by Co–S chemical bonds would significantly boost the photocatalytic H₂ evolution performances, and the 7 wt% 2D/2D CoP/CdS heterojunction possessed the maximal H₂ evolution rate of 92.54 mmol g^?1 h^?1, approximately 31 times higher than that of bare 2D CdS nanosheets. Photoelectrochemical, steady photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements indicated that there existed an effective charge separation and migration over 2D/2D CoP/CdS heterojunction, which then markedly lengthened the photoinduced electrons average lifetimes, retarded the recombination of charge carriers, and caused the dramatically boosted photocatalytic H₂ evolution activity. Moreover, the density functional theory (DFT) calculation further corroborated that the efficient charge transfer occurred at the interfaces of CoP/CdS heterojunction. This present research puts forward a promising strategy to engineer the 2D/2D heterojunction photocatalysts endowed with an appealing photocatalytic H₂ evolution performance.     

Novel triptycene-based microporous polymers decorated with Cd0.5Zn0.5S quantum dots to form 0D/3D heterojunction for efficient photocatalytic hydrogen evolution

A novel and porous triptycene-based microporous polymer (TMP) was synthesized through a palladium acetate-catalyzed Suzuki reaction, and then Cd_0.5Zn_0.5S quantum dots (CZS QDs) were homogeneously decorated onto the TMP by a facile in situ precipitation approach to fabricate a 0D/3D heterojunction for the first time. Characterizations indicate TMP with large specific surface area (809 m² g⁻¹) not only stabilizes CZS QDs but also provides abundant photocatalytic active sites, which can facilitate the activation and adsorption of H₂O molecules. The CZS QDs@TMP heterojunction possesses remarkably improved photocatalytic hydrogen evolution activity and outstanding photostability. The optimized CZS QDs@TMP-1 heterojunction exhibits highest hydrogen-producing rate of 81.33 mmol h⁻¹ g⁻¹, about 16.1 times higher than that of pristine CZS. The high photocatalytic activity of CZS QDs@TMP is due to several positive factors, such as high surface area, construction of n-n type heterostructures, tiny size effect of CZS QDs and close contact between 0D CZS QDs and 3D TMP, which will synergistically promote the visible-light response, boost the interfacial charge transfer and reduce the photocorrosion of CZS.     

Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS₂/g-C₃N₄ composite photocatalyst through decorating WS₂/g-C₃N₄ 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g⁻¹ h⁻¹ was obtained for such a specially designed CdSe/WS₂/g-C₃N₄ composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C₃N₄ NSs (0.43 mmol g⁻¹ h⁻¹), WS₂/g-C₃N₄ 2D/2D NSs (0.74 mmol g⁻¹ h⁻¹) and CdSe/g-C₃N₄ 0D/2D composites (0.96 mmol g⁻¹ h⁻¹), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS₂/g-C₃N₄ composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C₃N₄ NSs, CdSe QDs and WS₂ NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.     

Synergistic enhancement of photocatalytic H2 production by Ni decorated 2D bubble-like carbon nitride

In this paper, a novel 2D bubble-like g-C₃N₄ (B–CN) with a highly porous and crosslinked structure is successfully synthesized via a cost-effective bottom-up process. The as-prepared B–CN photocatalyst delivers a considerably expanded specific surface area and increased active sites. Moreover, the 2D bubble-like structure can afford shortened diffusion paths for both photogenerated charge carriers and reactants. As a result, the photocatalytic H₂ evolution rate of B–CN reached 268.9 μmol g^?1 h^?1, over 5 times more than that of bulk C₃N₄. The Ni ions were further deposited on B–CN as a cocatalyst to enhance the photocatalytic activity. Benefit from the synergy of 2D bubble-like structure and Ni species cocatalyst, recombination of photoinduced charges was greatly inhibited and the hydrogen evolution reaction (HER) was significantly accelerated. The resulted catalyst achieved a dramatically high H₂ evolution rate of 1291 μmol g^?1 h^?1. This work provides an alternative way to synthesize novel porous carbon nitride together with non-noble metal cocatalysts toward enhanced photocatalytic activity for H₂ production.     

CaH2-assisted structural engineering of porous defective graphitic carbon nitride (g-C3N4) for enhanced photocatalytic hydrogen evolution

The practical applications of graphitic carbon nitride (g-C₃N₄) for photocatalytic hydrogen evolution is strictly hindered by the low surface area, poor light harvesting capability and detrimental recombination of photoexcited charge carriers. Herein, using melamine as precursor and metal hydride (i.e., CaH₂) as active agent, we facilely incorporate various types of defects (i.e., nitrogen (N) vacancies (V_N), cyano groups (CN) and surface absorbed oxygen species(O_abs)) into g-C₃N₄ within a single step. The as-prepared material (denoted as MM-H) exhibits narrowed bandgap, promoted photoexcited electron-hole separation rate and facilitated charge transfer kinetics with enlarged BET surface area and massive porosity. As a result, a prominently enhanced photocatalytic H₂ productivity efficiency (1305.9 μmol h⁻¹g⁻¹) is shown on MM-H. This performance is better than that of g-C₃N₄ with CaH₂ post-treatment (617.3 μmol h⁻¹g⁻¹) and raw bulk-C₃N₄ (178.2 μmol h⁻¹g⁻¹). This work opens up a new dimension for designing high performance g–C₃N₄–based catalysts targeting various photocatalytic processes.     

Graphitic carbon nitride tetragonal hollow prism with enhanced photocatalytic hydrogen evolution

Graphitic carbon nitride tetragonal hollow prism (GCN-THP) with nitrogen vacancies was prepared by a simple two-step calcination method. Based on the characterizations of the as-prepared GCN-THP and the intermediate precursor, a possible mechanism was proposed for the formation of GCN-THP. The as-prepared GCN-THP exhibits superior activity and excellent stability during photocatalytic hydrogen evolution under visible light irradiation. The photocatalytic hydrogen evolution rate of GCN-THP was measured to be 1990 μmol g⁻¹ h⁻¹, which is 6.2 times as that of GCN. The enhanced photocatalytic activity could be attributed to unique 1D tetragonal hollow prism morphology and the presence of nitrogen vacancies in the as-prepared GCN-THP, which could increase the surface area, expand the visible light absorption, and promote the charge separation during photocatalytic hydrogen evolution. Our work could provide a new route to synthesize highly efficient photocatalysts with 1D hollow structures.     

Co3O4/CeO2 p-n heterojunction construction and application for efficient photocatalytic hydrogen evolution

The construction of p-n type heterojunction is an effective way to enhance the efficiency of photocatalytic hydrogen evolution. In this work, Co₃O₄/CeO₂ p-n heterojunction was construct by a simple hydrothermal method. This heterojunction mainly uses the internal electric field formed and accelerate the separation of electrons and holes in the opposite direction. In addition, according to SEM and TEM characterization, it was found that the granular cobalt oxide nanoparticles prepared by in-situ hydrothermal method were firmly and uniformly dispersed in cerium oxide, which effectively increased the active sites of hydrogen evolution. And combined with the BET results, it shows that the growth of cobalt oxide effectively increases the specific surface area and increases the active sites for hydrogen evolution. By exploring the hydrogen evolution capacity of different ratios of the complex, the test results showed that in all different ratios of the catalyst, CC-0.16 showed the best performance, and the hydrogen production efficiency reached 2298.52 μmol g⁻¹h⁻¹, which was 71 times that of nanobelt CeO₂ and 2.72 times that of Co₃O₄. According to the characterization results, the photocatalytic water splitting mechanism of the p-n heterojunction was proposed, and the charge transfer mechanism in the process was discussed in depth.     

Additional electron transfer channels of thermostable 0D Cs(Pb: Pt)Br3 perovskite quantum dots /2D accordion-like Ni-MOF nanojunction for photocatalytic H2 evolution

Overcoming the low charge transfer efficiency and poor photothermal stability of halide perovskite quantum dots (QDs) is the booster to achieve photocatalytic applications. In this paper, the Pt²⁺-doped CsPbBr₃ QDs/two-dimensional accordion-like Ni-MOF (CPPB QDs/Ni-MOF) composite was firstly synthesized by fixing the CPPB QDs into the pores of Ni-MOF. Electron separation and transfer efficiency were analyzed by PL spectra and electrochemical data. The photocatalyst exhibited outstanding photocatalytic performance in hydrogen (H₂) evolution. The optimal H₂ evolution efficiency of the composite reached 153.6 μmol h^?1, which was about 9 times than that of pure Ni-MOF and remained 134.8 μmol h^?1 after the cycle test. The splendid efficiency could be benefited from the advantages of 2D layered structure of Ni-MOF and the high charge separation and transmission efficiency of CPPB QDs. Finally, the mechanism of electron migration and additional electron transfer channels between composite interfaces was further demonstrated by density functional theory (DFT) calculations. The present work opens up a novel perspective for photocatalytic applications of doped halide perovskite QDs/Ni-MOF nanocomposites.     

Enhanced photocatalytic hydrogen evolution over 0D/3D NiTiO3 nanoparticles/CdIn2S4 microspheres heterostructure photocatalyst

Constructing S-scheme heterojunction is regarded as an effective mode to motivate excellent photocatalytic performance for hydrogen generation. This paper prepares NiTiO₃/CdIn₂S₄ S-scheme heterostructure photocatalyst by hydrothermal method successfully. In the experiments, 20 wt% NiTiO₃/CdIn₂S₄ has the supreme photocatalytic activity with the H₂ generation rate of 5168.6 μmol g⁻¹ h⁻¹ and the apparent quantum yield (AQY) of 5.14% at 420 nm, approximately 7.7 times of pure CdIn₂S₄. Through the phase characterization analyses, NiTiO₃ and CdIn₂S₄ successfully compounded, with NiTiO₃ nanoparticles wrapping around CdIn₂S₄ microspheres to form the irregular clumps. Further analyses of performance reveal the larger specific surface area, wider absorption region, faster charge transfer rate, outstanding photostability and recyclability for 20 wt% NiTiO₃/CdIn₂S₄, all of which play the significant role in photocatalytic hydrogen evolution activity. Finally, a plausible S-scheme photocatalytic mechanism for NiTiO₃/CdIn₂S₄ is proposed. This study provides a novel and effective S-scheme photocatalyst for hydrogen generation from water splitting.     

Novel 2D Zn-porphyrin metal organic frameworks revived CdS for photocatalysis of hydrogen production

The main challenge of photocatalysis is how to improve the coefficient of utilization and conversion rate for solar energy. Herein, we report a composite photocatalyst related to a novel porphyrin metal organic frameworks (MOFs), in which cadmium sulfide nanoparticles (CdS NPs) are grown in situ on the surface of two-dimensional (2D) zinc porphyrin nanosheets (Zn-TCPP NSs) by hydrothermal method. Interestingly, Zn-TCPP NSs and CdS NPs form a Type II heterojunction structure, which reduces the photogenerated electron-hole recombination rate of CdS. Moreover, in the near-infrared region, the photo-excited electrons generated by Zn-TCPP NSs are transmitted to CdS NPs, so that cadmium sulfide can realize both visible light and near-infrared light for photocatalytic hydrogen production. The Zn-TCPP NSs not only has excellent light absorption capacity, but also has a unique frame design that effectively reduces the recombination rate of photoinduced electron hole pairs, thus improving the conversion rate of solar energy. As expected, the photocatalytic performance of the porphyrin MOFs modified materials is significantly enhanced compared to CdS NPs. The hydrogen production rate of the Pt@CdS NPs/Zn-TCPP NSs(C-Z-T) composite material in the visible light region is about 15.3 mmol g^?1 h^?1, which is 11 times for Pt@CdS NPs. Furthermore, the Pt@CdS NPs/Zn-TCPP NSs(C-Z-T) also has a considerable hydrogen production rate in the near-infrared region, such as 200 μmol g^?1 h^?1 at 600 nm, 90 μmol g^?1 h^?1 at 765 nm and 20 μmol g^?1 h^?1 at > 800 nm.     

Controllable fabrication of 3D porous carbon nitride with ultra-thin nanosheets templated by ionic liquid for highly efficient water splitting

Modifying the texture of carbon nitride to adjust its physicochemical performance is a fascinating method for achieving high photocatalytic activity. Herein, we synthesized 3D porous carbon nitride with ultra-thin nanosheets by using cyanuric acid-melamine supramolecular and ionic liquid as precursor and template, respectively. The ionic liquid adjusts the morphology of materials and induces the carbon residue into the porous channels owing to its incomplete degradation. The 3D porous framework makes carbon nitride reflect the enhanced surface area, exposes adequate reaction sites, and offers a pathway for charge transport. And carbon residue and ultra-thin nanosheets further promote the photogenerated carriers transport and reduce the recombination rate of charge carriers. Consequently, 3D porous carbon nitride with ultra-thin nanosheets exhibit outstanding and stable hydrogen evolution under visible light irradiation. Significantly, as-fabricated sample CN-100 reflects an improved H₂ generation rate, up to 17,028 μmol h^?1 g^?1, which is 12 times higher than that of CN (1412 μmol h^?1 g^?1). The present work offers a unique synthesis strategy to develop the novel photocatalyst with efficient photocatalytic performance.     

Green synthesized carbon quantum dots as TiO2 sensitizers for photocatalytic hydrogen evolution

Carbon quantum dots (CQDs) have attracted growing interest due to their superior luminescent properties, which make them excellent photosensitizers for TiO₂. This study presents the green-synthesis of CQDs from edible mushroom Agaricus bisporus through microwave irradiation. In the study as-synthesized CQDs were used as a sensitizer for TiO₂ in photocatalytic hydrogen evolution in aqueous triethanolamine (sacrificial reagent) under visible-light irradiation. Photocatalytic hydrogen production activity of CQD-sensitized TiO₂ was found to be 472 μmol g⁻¹ h⁻¹ (without loading any noble metal co-catalyst) and 1458 μmol g⁻¹ h⁻¹ (with loading Pt co-catalyst). The study revealed that the CQDs from mushroom A. bisporus can be used as an efficient sensitizer for TiO₂ in photocatalytic hydrogen production.     

Hydrogen evolution using CdWO4 modified by BiFeO3 in the presence of potassium iodide; a combination of photocatalytic and non-photocatalytic water splitting

Novel heterogeneous structure of BiFeO₃–CdWO₄ with different molar ratios was applied for the photocatalytic hydrogen evolution in a self-designed externally UV/visible irradiated photoreactor in the presence of potassium iodide. The photocatalysts were synthesized by simple hydrothermal method and characterized by XRD, FE-SEM-mapping, TEM, UV–Vis DRS, PL, EIS, transient photocurrent and Mott-schottky techniques to identify the structural, optical and photoelectrochemical properties. The slope of Mott-schottky plots confirmed the p-type and n-type conductivity of the synthesized BiFeO₃ and CdWO₄, respectively. The p-n heterojunctions exhibited more efficiently light absorption, charge separation and electron mobility relative to the pure photocatalysts. We observed that coupling 40 mol% BiFeO₃ with CdWO₄ provided the best photocatalytic performance of hydrogen evolution, 268.90 μmol h⁻¹.g_cat⁻¹ from distilled water and 379.43 μmol h⁻¹.g_cat⁻¹ from 0.05 M KI aqueous solution. Iodine species increased H₂ evolution efficiency because of taking part in the charge transfer processes, either by scavenging excited holes or by direct reduction of H⁺ to H^• under UV irradiation. Fermi level equilibrium in the p-n heterojunction suggests the best interparticle charge transfer mechanism explaining how photoinduced electrons with superior energy states and desirable lifetime can be supplied to reduce H⁺ to H^•.     

Effect of tri-doping on H2 evolution under visible light irradiation on SrTiO3:Ni/Ta/La prepared by spray pyrolysis from polymeric precursor

Tri-doped photocatalyst, SrTiO₃:Ni/Ta/La, was prepared by spray pyrolysis from aqueous and polymeric precursor solutions. The third dopant, La³⁺, contributed to the BET surface area and porous morphology by preventing crystal growth, and increased the Ni²⁺/Ni³⁺ ratio by affecting the electron configuration in the lattice structure, which is closely related to the hydrogen evolution rate. The hydrogen evolution rate of the tri-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%)/La(0.3 mol%), was increased by about 60%–895.2 μmol g⁻¹ h⁻¹ from the value of 561.2 μmol g⁻¹ h⁻¹ for the co-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%), and was further enhanced to 2305.7 μmol g⁻¹ h⁻¹ when a polymeric precursor was used instead of an aqueous precursor in spray pyrolysis. The optimum additive content for polymeric precursor solution was 300 mol%.