Ultrathin Z-scheme 2D/2D N-doped HTiNbO5 nanosheets/g-C3N4 porous composites for efficient photocatalytic degradation and H2 generation under visible light

S-scheme NiO/C3N5 heterojunctions with enhanced interfacial electric field for boosting photothermal-assisted photocatalytic H2 and H2O2 production

Heterostructured visible-light-responsive photocatalysts represent a prospective approach to achieve efficient solar-to-chemical energy conversion. Herein, we propose a facile self-assembly technique to synthesize NiO nanoparticles/C3N5 nanosheets (NOCN) heterojunctions for hydrogen (H2) evolution catalysis and hydrogen peroxide (H2O2) production under visible light. In this regard, the black NiO nanoparticles (NPs) were tightly anchored on the surface of C3N5 nanosheets (CNNS) to construct S-scheme NOCN heterojunction, enabling efficient charge separation and high redox capability. Obtained results elucidated that the incorporated NiO NPs significantly promote light-harvesting efficiency and photo-to-thermal capacity over the NOCN composites. The enhanced photothermal effect facilitates the charge carrier transfer rate across the heterojunction and boosts the surface reaction kinetics. Accordingly, the photocatalytic performances of CNNS for H2 release and H2O2 production can be manipulated by introducing NiO NPs. The modified photocatalytic properties of NOCN composites are ascribed to the synergistic effects of all integrated components and the S-scheme heterojunction formation. Impressively, the high H2 evolution photocatalysis efficiency of NOCN nano-catalysts in seawater certifies their potential environmental applicability. Among all, the 12-NOCN nano-catalyst exhibits a higher photocatalytic efficiency for H2 release (112.2 μmol∙g-1∙h-1) and H2O2 production (91.2 μmol∙L-1∙h-1). Besides, the 12-NOCN nano-catalyst reveals excellent recyclability and structural stability. Additionally, the possible mechanism for photothermal-assisted photocatalysis is proposed. This work affords a feasible pathway to design photothermal-assisted S-scheme heterojunctions for diverse photocatalytic applications.

Carbonized polymer dots modified ZnIn2S4 microspheres for visible-light-driven hydrogen evolution promotion performance

To effectively separate electron-hole pairs produced by light, a heterojunction arrangement can be employed, thereby improving photocatalytic efficiency. In this study, a simple hydrothermal process is used to manufacture carbonized polymer dots/ZnIn2S4 (CPDs/ZIS) heterostructure, which enhances the light absorption and charge carrier lifetime in comparison to bare ZnIn2S4 (ZIS). Upon irradiation with visible light, the 3-CPDs/ZIS composite generates hydrogen at a rate of 133 μmol g-1 h-1, which is 8.9 times faster than that of pure ZIS. The addition of CPDs can increase the range of light that can be absorbed, extend the service life of the optical charge, increase the specific surface area, and promote charge separation and transmission, which could effectively accelerate the photocatalytic reduction reaction. The presence of CPDs results in the introduction of multiple transition energy states and a decrease in the H* adsorption free energy, which enhances the hydrogen evolution activity according to the theoretical calculation findings of density functional theory (DFT) and Gibbs free energy of the hydrogen evolution process. Combining theoretical calculations and experimental results, a direct Z-type heterojunction mechanism is proposed for the hydrogen evolution promotion effectiveness of CPDs/ZIS under visible light.

Boosted Photocatalytic Performance for Antibiotics Removal with Ag/PW12/TiO2 Composite: Degradation Pathways and Toxicity Assessment

Photocatalyst is the core of photocatalysis and directly determines photocatalytic performance. However, low quantum efficiency and low utilization of solar energy are important technical problems in the application of photocatalysis. In this work, a series of polyoxometalates (POMs) [H3PW12O40] (PW12)-doped titanium dioxide (TiO2) nanofibers modified with various amount of silver (Ag) nanoparticles (NPs) were prepared by utilizing electrospinning/photoreduction strategy, and were labelled as x wt% Ag/PW12/TiO2 (abbr. x% Ag/PT, x = 5, 10, and 15, respectively). The as-prepared materials were characterized with a series of techniques and exhibited remarkable catalytic activities for visible-light degradation tetracycline (TC), enrofloxacin (ENR), and methyl orange (MO). Particularly, the 10% Ag/PT catalyst with a specific surface area of 155.09 m2/g and an average aperture of 4.61 nm possessed the optimal photodegradation performance, with efficiencies reaching 78.19% for TC, 93.65% for ENR, and 99.29% for MO, which were significantly higher than those of PW12-free Ag/TiO2 and PT nanofibers. Additionally, various parameters (the pH of the solution, catalyst usage, and TC concentration) influencing the degradation process were investigated in detail. The optimal conditions are as follows: catalyst usage: 20 mg; TC: 20 mL of 20 ppm; pH = 7. Furthermore, the photodegradation intermediates and pathways were demonstrated by HPLC-MS measurement. We also investigated the toxicity of products generated during TC removal by employing quantitative structure-activity relationship (QSAR) prediction through a toxicity estimation software tool (T.E.S.T. Version 5.1.2.). The mechanism study showed that the doping of PW12 and the modification of Ag NPs on TiO2 broadened the visible-light absorption, accelerating the effective separation of photogenerated carriers, therefore resulting in an enhanced photocatalytic performance. The research provided some new thoughts for exploiting efficient and durable photocatalysts for environmental remediation.

High-performance ZnIn2S4/Ni(dmgH)2 for photocatalytic hydrogen evolution: Ion exchange construction, photocorrosion mitigation, and efficiency enhancement by photochromic effect

In this work, a novel photocatalyst of ZnIn₂S₄/Ni(dmgH)₂ was designed by a simple chemical precipitation method and used to enhance hydrogen evolution under visible light irradiation. Along with vigorous discharges of hydrogen bubbles, an optimal rate of 36.3 mmol/g/h was reached under UV-Vis light for hydrogen evolution, nearly 4.9 times of the one from pure ZnIn₂S₄. The heterojunction exhibits steady hydrogen evolution capability and owns a high apparent quantum efficiency (AQE) of 20.45% under the monochromatic light at 420 nm. By coupling ZnIn₂S₄ with Ni(dmgH)₂, an extraordinary photochromic phenomenon was detected and attributed to the active Ni-S component in situ formed between the nickel and sulfur composites under light irradiation. The emerging sulfide benefits light absorption of the system and separation of photogenerated electron and hole pairs. Besides providing a promising photocatalyst for visible light hydrogen production, the present work is hoped to inspire new trends of catalytic medium designs and investigations.

Interfacial engineering of Ti3C2 MXene/CdIn2S4 Schottky heterojunctions for boosting visible-light H2 evolution and Cr(VI) reduction

Developing efficient heterojunction photocatalysts that have a high charge carrier separation rate and improved light-harvesting capacity is a crucial step in solving energy crisis and reducing environmental pollution. Herein, we synthesized few-layered Ti₃C₂ MXene sheets (MXs) by a manual shaking process, and combined with CdIn₂S₄ (CIS) to construct novel Ti₃C₂ MXene/CdIn₂S₄ (MXCIS) Schottky heterojunction through a solvothermal method. The strong interface between two-dimensional (2D) Ti₃C₂ MXene and 2D CIS nanoplates led to enhanced light-harvesting capacity and promoted charge separation rate. Additionally, the presence of S vacancies on the MXCIS surface helped to trap free electrons. The optimal sample, 5-MXCIS (with 5 wt% MXs loading), exhibited outstanding performance for photocatalytic hydrogen (H₂) evolution and Cr(VI) reduction under visible light due to the synergistic effect of enhanced light-harvesting capacity and charge separation rate. The charge transfer kinetics was thoroughly studied using multiple techniques. The reactive species of ^•O₂^-, ^•OH and h⁺ were generated in 5-MXCIS system, and e^- and ^•O₂^- radicals were found to be the main contributors to Cr(VI) photoreduction. Based on the characterization results, a possible photocatalytic mechanism for H₂ evolution and Cr(VI) reduction was proposed. On the whole, this work provides new insights into the design of 2D/2D MXene-based Schottky heterojunction photocatalysts for boosting photocatalytic efficiency.

Fabrication of black NiO/Sr2FeTaO6 heterojunctions with rapid interface charge transfer for efficient photocatalytic hydrogen evolution

Series of black NiO/Sr₂FeTaO₆ (NiO/SFT) composites were synthesized by the combined processes of hydrothermal method and calcination treatment. The formed NiO was deposited on the surface of Sr₂FeTaO₆ to form a closely interfacial contact, leading to the formation of NiO/Sr₂FeTaO₆ heterojunction. The resulted samples were fully characterized by XRD, TEM, XPS, and UV-Vis DRS to gain their microstructure, crystal phase, atomic states and optical absorption properties. Introducing narrow-bandgap semiconductor of black NiO in NiO/Sr₂FeTaO₆ heterojunctions exhibits two major advantages. On the one hand, coupling with black NiO can significantly increase the light harvesting capacity of Sr₂FeTaO₆. On the other hand, the formed NiO/Sr₂FeTaO₆ heterojunctions benefited the separation and transfer of photogenerated charge carriers, which was confirmed by photo-electrochemical measurement, PL and TR-PL spectra. The activity of as-prepared samples was evaluated by photocatalytic hydrogen (H₂) evolution (PHE) under visible light irradiation. The resulted NiO/SFT composites showed the improved PHE efficiency than that of NiO and Sr₂FeTaO₆, owing to the synergistic effects of synergistic effects of heterojunction formation for the efficient charge carrier transfer/separation and increased light harvesting capacity. However, the excess amount of NiO loaded in NiO/SFT composites will restrain the light harvesting of Sr₂FeTaO₆ component and decrease, leading to the decreased PHE activity. Our work provided an insight on the construction of high-efficiency heterojunction photocatalysts for PHE reaction.

Effects of Preparation Methods of Pd Supported on (001) Crystal Facets Exposed TiO2 Nanosheets for Toluene Catalytic Combustion

A series of TiO2 nanosheets-supported Pd catalysts were individually prepared by impregnation, deposition–precipitation, photo-deposition and in situ reduction by NaBH4. For comparison, Pd supported on P25 was prepared by the impregnation method. The experimental results show that the catalytic efficiency of the catalyst prepared with titanium dioxide nano sheet as the support is higher than that of the catalyst supported with P25. Its excellent properties are as follows: The resulting sample indicates that TiO2 nanosheets-supported Pd catalyst display an improved activity than Pd/P25, whose temperature of 100% complete conversion of toluene decreased by 40 ℃ at the most. The Pd particles on the catalyst synthesized by the light deposition method and the NaBH4 reduction method are more obvious, while the Pd particles on the catalyst synthesized by the immersion method and the deposition–precipitation method are less obvious, which shows that the latter two methods are more conducive to the dispersion of Pd. The good catalytic activity may be due to the better exposed mirror and dispersion of titanium dioxide nanosheets. This is mainly related to the exposed crystal plane of the nanosheet TiO2 (001), which made it easier to form the oxygen vacancy. Moreover, among all of the TiO2 nanosheets-supported Pd catalysts, Pd/TiO2 NS (TiO2 NS means TiO2 nanosheets) prepared by the impregnation method show the highest catalytic activity. The XRD results show that Pd prepared by impregnation is more dispersed and smaller. This is due to PdO being dispersed more efficiently than the others, leading to more Pd active sites.

Adsorption and Separation of Ethyl Mercaptan from Methane by Hydroxyl Groups on the Surface of HTiNbO5-Nanosheets

Adsorption and separation of light mercaptan (R-SH, R = C₁-C₄) from methane gas can effectively improve the utilization efficiency of methane and the resource conversion of organic sulfide. To further investigate the effects of composition and structural characteristics of laminates on desulfurization performance, in this paper, a two-dimensional (2D) HTiNbO₅-nanosheet (HTiNbO₅-NS) was constructed. In addition, the hydrogen-bonding interaction between the exposed hydroxyl active sites on the surface of HTiNbO₅-NS and ethyl mercaptan (Et-SH) was constructed to realize the adsorption and separation of Et-SH from methane gas. The breakthrough adsorption capacity (C_ap (BT)) of HTiNbO₅-NS is 14.35 mg·g^-1 in a micro fixed bed with a space velocity of 6000 h^-1. The regeneration desulfurization rate (q) of the 10-cycle regeneration adsorption was ca. 96%. Furthermore, density functional theory (DFT) calculation results show that the S atoms of Et-SH and HTiNbO₅-NS with the terminal hydroxyl and bridge hydroxyl have electron cloud covering to form the hydrogen-bonding interaction. In addition, the formation details of this hydrogen-bond interaction are discussed. The effects of Ti on the microstructure, hydroxyl acid, hydroxyl content, surface area, and pore volume of nanosheets were studied to explain the reasons for the differences in the properties of the two kinds of nanosheets. This work broadens the design of 2D niobium-based efficient adsorbents for R-SH based on hydrogen-bonding interaction and is helpful to enrich the application of the hydrogen-bonding interaction.

2D/2D Heterojunction systems for the removal of organic pollutants: A review

Photocatalysis is considered to be an effective way to remove organic pollutants, but the key to photocatalysis is finding a high-efficiency and stable photocatalyst. 2D materials-based heterojunction has aroused widespread concerns in photocatalysis because of its merits in more active sites, adjustable band gaps and shorter charge transfer distance. Among various 2D heterojunction systems, 2D/2D heterojunction with a face-to-face contact interface is regarded as a highly promising photocatalyst. Due to the strong coupling interface in 2D/2D heterojunction, the separation and migration of photoexcited electron-hole pairs are facilitated, which enhances the photocatalytic performance. Thus, the design of 2D/2D heterojunction can become a potential model for expanding the application of photocatalysis in the removal of organic pollutants. Herein, in this review, we first summarize the fundamental principles, classification, and strategies for elevating photocatalytic performance. Then, the synthesis and application of the 2D/2D heterojunction system for the removal of organic pollutants are discussed. Finally, the challenges and perspectives in 2D/2D heterojunction photocatalysts and their application for removing organic pollutants are presented.

Ionic Liquid-Assisted Synthesis of Ag3PO4 Spheres for Boosting Photodegradation Activity under Visible Light

In this work, a simple chemical precipitation method was employed to prepare spherical-like Ag3PO4 material (IL-Ag3PO4) with exposed {111} facet in the presence of reactive ionic liquid 1-butyl-3-methylimidazole dihydrogen phosphate ([Omim]H2PO4). The crystal structure, microstructure, optical properties, and visible-light photocatalytic performance of as-prepared materials were studied in detail. The addition of ionic liquids played a crucial role in forming spherical-like morphology of IL-Ag3PO4 sample. Compared with traditional Ag3PO4 material, the intensity ratio of {222}/{200} facets in XRD pattern of IL-Ag3PO4 was significantly enhanced, indicating the main {111} facets exposed on the surface of IL-Ag3PO4 sample. The presence of exposed {111} facet was advantageous for facilitating the charge carrier transfer and separation. The light-harvesting capacity of IL-Ag3PO4 was larger than that of Ag3PO4. The photocatalytic activity of samples was evaluated by degrading rhodamine B (RhB) and p-chlorophenol (4-CP) under visible light. The photodegradation efficiencies of IL-Ag3PO4 were 1.94 and 2.45 times higher than that of Ag3PO4 for RhB and 4-CP removal, respectively, attributing to a synergy from the exposed {111} facet and enhanced photoabsorption. Based on active species capturing experiments, holes (h+), and superoxide radical (•O2−) were the main active species for visible-light-driven RhB photodegradation. This study will provide a promising prospect for designing and synthesizing ionic liquid-assisted photocatalysts with a high efficiency.