Photocatalytic H2 Generation Activity Research Articles

Fabrication of CoTiO3/MgIn2S4 S–scheme heterojunctions with efficient charge separation to enhance the photocatalytic activities of hydrogen generation and formaldehyde removal

The efficient separation of photoinduced charge carriers is a primary factor in the catalytic performance of photocatalysts. Constructing S-scheme heterojunctions is a prospective strategy to efficiently and spatially separate photoinduced charges while retaining strong oxidation and reduction capacities of the catalyst system. Herein, CoTiO3/MgIn2S4 (abbreviated x% CTO/MIS, where x% represents the mass ratio of CTO-to-MIS; x = 5, 10, 15, 20, and 25) heterojunctions were successfully synthesized using a hydrothermal method. These heterojunctions exhibited highly efficient and reusable visible-light photocatalytic properties for hydrogen (H2) generation and formaldehyde (HCHO) degradation. Notably, the 15 % CTO/MIS demonstrated an admirable H2 evolution activity of 631.77 μmol·g−1·h−1, with AQE = 2.25 % at λ = 420 nm, and an HCHO degradation rate of 67.18 %. The intermediate products generated during HCHO removal were identified applying in situ diffuse reflectance infrared Fourier transform spectroscopy. The exceptional catalytic performance of the synthesized materials was attributed to the boosted light absorption and utilization, rapidly separation, and transfer of photoproduced charge carriers, which resulted from the internal electric field of the S-scheme mechanism. Moreover, the S-scheme electron transfer pathway for the CTO/MIS catalyst system during the photocatalytic process was confirmed using electron spin resonance spectroscopy, free-radical capturing tests, density functional theory calculations, in situ X-ray photoelectron spectroscopy, and semiconductor energy band theory. The study offers an innovative perspective for establishing S-scheme heterojunctions with highly efficient and stable photocatalytic activity for H2 generation and HCHO removal.

Synthesis and application of Cu-CaTiO3-GO ternary composite: A new visible-light active multifunctional photocatalyst efficient towards antibiotic cefixime degradation and H2 evolution reaction

To combat the issues of energy scarcity and environmental pollution, a visible-light responsive, ternary photocatalyst (Cu-CaTiO3-GO) was fabricated, by photo-depositing Cu nanoparticles over a CaTiO3-GO binary composite. The physicochemical characteristics of Cu-CaTiO3-GO were investigated using XRD, HR-TEM, FE-SEM, EDS-mapping XPS, Raman, FT-IR, BET, EIS, UV–vis DRS, and PL techniques. In comparison with pristine CaTiO3, and binary composites (Cu-CaTiO3, CaTiO3-GO), the ternary hybrid exhibited superior photocatalytic activity for H2generation as well as antibiotic cefixime (CFX) degradation. Under LED light, the rate of H2 generation over Cu-CaTiO3-GO accumulated to 57.69 mmolh−1, while the photodegradation efficiency for CFX reached 94.1 % in 100 min with 53.4 % of TOC removal. The upgraded performance is credited to synergistic effects of Cu NPs (SPR effect), CaTiO3 (specialized cuboid-like morphology), and GO (high conductivity), co-existing in the trio-hybrid, which resulted in a greatly increased surface area, an expanded spectral response range, a stronger adsorption property, efficient charge migration and separation extent. Ternary catalyst performed well even in the 4 recycling tests (retaining 79.4 % CFX removal and 52.51 mmolh−1 H2 evolution efficiency). In Cu-CaTiO3-GO system, the electron transport channel (Cu → CaTiO3 → GO) with adequate band potentials effectively supports both photocatalytic oxidation and reduction. Photoelectrons are enriched and transferred by plasmonic Cu, and then captured by GO, an e- sink. This maximizes composite photo redox capability, rapidly generating active radicals (OH), and (O2-), degrading CFX to simpler molecules and reducing proton to H2. The effectiveness of Cu-CaTiO3-GO was even tested in the real water matrices. Besides, degradation intermediates of CFX were elucidated using LC-MS, and the decomposition pathway was suggested. Finally, the probable photocatalytic reaction mechanism was deduced for both the degradation and H2 generation processes. The current study proposes a non-noble transition metal-based perovskite-type photocatalytic material for both clean energy generation and wastewater treatment.

Tailoring of Visible to Near-Infrared Active 2D MXene with Defect-Enriched Titania-Based Heterojunction Photocatalyst for Green H2 Generation.

A wide solar light absorption window and its utilization, long-term stability, and improved interfacial charge transfer are the keys to scalable and superior solar photocatalytic performance. Based on this objective, a noble metal-free composite photocatalyst is developed with conducting MXene (Ti3C2) and semiconducting cauliflower-shaped CdS and porous Cu2O. XPS, HRTEM, and ESR analyses of TiOy@Ti3C2 confirm the formation of enough defect-enriched TiOy (where y is < 2) on the surface of Ti3C2 during hydrothermal treatment, thus creating a third semiconducting site with enough oxygen vacancy. The final material, TiOy@Ti3C2/CdS/Cu2O, shows a broad absorption window from 300 to 2000 nm, covering the visible to near-infrared (NIR) range of the solar spectrum. Photocatalytic H2 generation activity is found to be 12.23 and 16.26 mmol g-1 h-1 in the binary (TiOy@Ti3C2/CdS) and tertiary composite (TiOy@Ti3C2/CdS/Cu2O), respectively, with good repeatability under visible-NIR light using lactic acid as the hole scavenger. A clear increase of efficiency by 1.53 mmol g-1 h-1 in the tertiary composite due to NIR light absorption supports the intrinsic upconversion of electrons, which will open a new prospective of solar light utilization. Decreased charge-transfer resistance from the EIS plot and a decrease in PL intensity established the improved interfacial charge separation in the tertiary composite. Compared to pure CdS, H2 generation efficiency is 29.6 times higher on the noble metal-free tertiary composite with an apparent quantum efficiency of 12.34%. Synergistic effect of defect-enriched TiOy formation, creation of proper dual p-n junction on a Ti3C2 sheet as supported by the Mott-Schottky plot, significant NIR light absorption, increased electron mobility, and charge transfer on the conductive Ti3C2 layer facilitate the drastically increased hydrogen evolution rate even after several cycles of repetition. Expectantly, the 2D MXene-based heterostructure with defect-enriched dual p-n junctions of desired interface engineering will facilitate scalable photocatalytic water splitting over a broad range of the solar spectrum.

Facile template-free fabrication of different micro/nanostructured In2O3 for photocatalytic H2 production from glucose solution

Indium oxide (In2O3) is a promising semiconductor used for various photocatalytic reactions, yet the green and template-free synthesizing the different micro/nanostructured In2O3 with tunable morphology is still full of challenge. In this study, the three morphological In2O3 with 3D micro-cubelike (In2O3-MC), 3D micro-ricelike (In2O3-MR), and 2D nano-platelike (In2O3-NP) were successfully fabricated through a facile hydrothermal strategy without any organic template additives. Owing to the enlarged specific surface area, promoted charge migration rate and suitable surface oxygen vacancies density, the unique 3D ricelike In2O3-MR exhibited the best photocatalytic H2 generation activity from biomass glucose solution, which was 1.9-fold and 1.7-fold higher than that of In2O3-MC and In2O3-NP under the same experimental conditions. In addition, the optimum photoactivity of In2O3-MR was achieved under the alkaline environment with pH = 11 and 1.0 wt% Pt cocatalyst loading, which was better than the most of previously reported In2O3-based photocatalysts. Simultaneously, the possible photocatalytic mechanism for solar H2 evolution from glucose solution was also discussed. Our work will bring about potential application in preparation of other photocatalysts with controlling morphology for renewable photocatalysis.

Spectroscopic Study on CdS/Ni/KNbO3: Confirming Ni Effect to Photocatalytic Activity.

Herein, we report the structural and photophysical properties of CdS/Ni/KNbO3 composites with a quantum yield for photocatalytic H2 generation that is CdS and Ni amount dependent. The nonstoichiometric KNbO3 (1:1.1) structure indicates the defect at the K site, which is Ni-occupied during its deposit process. It exhibits a tendency like a Ni-doped characteristic up to 0.1 wt % Ni and then forms a Ni cluster in case the Ni amount exceeds 0.1 wt %. The related structural and photophysical properties of CdS/Ni/KNbO3 are examined with Fourier transform infrared, X-ray diffraction, ultraviolet-visible absorption, and luminescence spectral analysis. It demonstrates the CdS/Ni/KNbO3 composites to be an efficient light conversion caused by efficient charge/electron transfer between KNbO3 and CdS via doped Ni. The photocatalytic activity of CdS/Ni/KNbO3 exhibits a CdS and Ni amount dependency. The best photocatalytic activity for H2 generation is obtained with 0.1 wt % Ni and 2.9 wt % CdS as it gradually declines with the excess Ni amount than 0.1 wt % caused by a formed Ni cluster.

Effective graphene incorporation of strontium niobate–doped titanium oxide for photocatalytic hydrogen production

To meet the increasing global demand for clean energy and mitigate the impact of CO2 emissions on climate change, the production of photocatalytic hydrogen through water splitting is a compelling scientific and technological objective. Despite considerable efforts, the establishment of a reliable and highly efficient system for hydrogen generation powered by visible light remains challenging. In this study, we developed a solar-active strontium niobate-doped titanium oxide incorporated with graphene (Sr2Nb2O7–rGO–TiO2), characterized by various analytical techniques such as optical, morphological, HR-TEM, XPS, and XRD. Sr2Nb2O7–rGO–TiO2 demonstrated enhanced photocatalytic H2 evolution under solar irradiation without requiring precious-metal doping. The maximum H2 production performance rate of 1769 μmol/g/h was attained with the Sr2Nb2O7–rGO–TiO2 composites, significantly surpassing those of the bare (TiO2: 210 μmol/g/h, Sr2Nb2O7: 88 μmol/g/h) and binary (TiO2–rGO: 430 μmol/g/h, Sr2Nb2O7–rGO: 176 μmol/g/h, and Sr2Nb2O7–TiO2: 880 μmol/g/h) photocatalysts. The enhanced performance of the Sr2Nb2O7–rGO–TiO2 composite is attributable to the synergistic effect of rGO acting as an electron-transfer bridge. Thus, with the integration of rGO, absorption is attainable in an extended range up to 445 nm (2.90 eV), suggesting that the composite material could enable the catalyst to absorb more visible light. Additionally, the composite exhibited minor degradation after five consecutive cycles, demonstrating its excellent stability and reusability for hydrogen generation. Based on a comprehensive evaluation of the ESR and transient photocurrent response, a potential Z-scheme mechanism for the photocatalytic H2 generation activity over Sr2Nb2O7–rGO–TiO2 was suggested. The Z-scheme processability allows more electrons to contribute to the H2 evolution reduction. In this study, we developed a non-toxic, cost-effective, highly efficient, and recyclable photocatalyst for H2 production.

Construction of II-type and Z-scheme binding structure in P-doped graphitic carbon nitride loaded with ZnO and ZnTCPP boosting photocatalytic hydrogen evolution

A ternary heterostructure (ZnPPO) was constructed by loading ZnO and tetrakis (4-carboxyphenyl) zinc porphyrin (ZnTCPP) with P-doped g-C3N4 (PCN). In contrast to binary heterostructures (PCN-ZnO, ZnTCPP-ZnO and ZnTCPP-PCN) and single components (PCN, ZnTCPP and ZnO), ZnPPO has superior photocatalytic activity for H2 generation from water splitting. It is revealed that a binding structure of Ⅱ-type and Z-scheme has been constructed in ZnPPO, which plays a vital role in transferring photo-excited charge carriers. The significant enhancement of photocatalytic activity in ZnPPO is attributed to the effective transfer of photo-generated electrons and holes between the components of the ternary heterostructure.

Construction of porous ZnS/TiO2 S-scheme heterostructure derived from MOF-on-MOF with boosting photocatalytic H2-generation activity

The development of photocatalysts with synergistic effects is a crucial step in improving the utilization of clean energy for hydrogen generation. In this study, a novel porous ZnS/TiO2 heterostructure was successfully fabricated through the sulfuration of ZIF-8/NH2-MIL-125(Ti) using a one-pot hydrothermal method. Under simulated solar light, the as-prepared ZnS/TiO2 (5:1) heterostructure exhibited enhanced photocatalytic hydrogen production with a rate of 1718 μmol h−1 g−1, which is 4.8 times of ZnS and 38.8 times of TiO2, respectively. The construction of a S-scheme heterojunction between ZnS and TiO2 can enhance electron transfer and suppress electron-hole recombination, which is crucial for efficient photocatalysis. The photoelectrochemical test results were analyzed in detail to understand the photoinduced electron transfer process and the proposed photocatalytic mechanism. This work has significant potential for enhancing the solar hydrogen production performance of MOFs-derived heterojunction photocatalysts, providing a promising approach for clean energy generation.

Incorporating CdS and anchoring Pt single atoms into porphyrinic metal–organic frameworks for superior visible-light and sunlight-driven H2 evolution

Water splitting by photocatalytic semiconductors to produce hydrogen is considered one of the best ways to utilize solar energy. However, the recombination of electron-hole pairs in semiconductors such as cadmium sulfide (CdS) reduces the light-driven reaction efficiency. In addition, nanoparticles (NPs) of semiconductors tend to aggregate, resulting in decreased atom utilization. Rationally building composite photocatalysts by reducing nanoparticle aggregation and maximizing charge transport efficiency is thus seen as an attractive strategy for achieving high hydrogen evolution rates. Herein, we designed a new composite photocatalyst, CdS@PCN-222(Pt), by growing CdS in situ on a metal–organic framework (MOF) containing single Pt atoms. This catalyst exhibits an excellent hydrogen evolution activity of 71645 μmol/gCdS/h under visible light irradiation (λ ≥ 420 nm), which is around 110 times higher than pure CdS. Remarkably, CdS@PCN-222(Pt) also has an extremely high hydrogen evolution activity of 31326 μmol/gCdS/h under direct sunlight irradiation, far surpassing those of reported MOF-based photocatalysts. The charge-separation mechanisms were revealed by spectroscopic measurements, DFT calculations, and single crystal X-ray diffractions. The highly porous structure of PCN-222(Pt) results in the uniform distribution of CdS, and the anchored Pt single atoms achieve photo-induced electron transfer, inhibiting the recombination of photogenerated charge carriers. The results show that the synergistic effects between inorganic semiconductors and MOFs containing anchored single atoms enhance the photocatalytic activity for H2 generation under visible light and even sunlight. As a result, the findings offer important new perspectives that can be utilized in the design of high-performance composite photocatalysts in the future.

Construction of Zn vacancy mediated ZnS/Cu2−xS heterostructure via cation exchange reactions for broadband photocatalytic water splitting

Vacancy engineering has attracted great attention as the construction of defects can modify bandstructure and enhance photoabsorption ability by introducing additional vacancy energy levels, thereby achieving efficient photocatalytic H2 evolution activity. In this work, zinc-vacancy ZnS/Cu2−xS (ZnS-VZn/Cu2−xS) photocatalyst was successfully prepared by surface modification of ZnS-VZn. The presence of zinc vacancies endows visible light responsiveness of ZnS, which can be attributed to the two-photon absorption mechanism and demonstrated by the upward PL spectra. Cu2−xS would tightly anchor the surface of ZnS-VZn after the cation exchange reaction, which is good for the efficient transfer of charge carriers. Furthermore, Cu2−xS broadens the light absorption range of the ZnS-VZn/Cu2−xS composite and can generate more photoexcited charge carriers under visible light irradiation, resulting in outstanding photocatalytic H2 generation activity. As a result, the optimum photocatalytic H2 generation rate of 642.30 μmol g−1 h−1 was obtained over ZnS-VZn/Cu2−xS, which is 10.34 times higher than the pure ZnS-VZn. Additionally, ZnS-VZn/Cu2−xS composite exhibits excellent photostability over four cycles totaling 16 h and the charge transfer route is further confirmed by the in-situ XPS. The present work deepens the understanding of vacancy defects and provides a feasible method to rationally establish a semiconductor photocatalyst for efficient H2 generation from water splitting.

In-situ upcycling of cadmium from wastewater into core–shell ZnS@Zn0.58Cd0.42S heterojunction photocatalyst for environmental purification and H2 evolution

Uncontrolled exploitation of heavy metals has caused environmental pollution and mineral resource depletion crises. The first-choice approach for addressing these issues is heavy metal upcycling. However, efficient retrieval and conversion of heavy metals from contaminated environments into high-value-added products remains challenging. Here, we developed a strategy to simultaneously achieve efficient accumulation (256 mg/g), magnetic separation (∼1 min), and directly in-site conversion of Cd2+ from wastewater into core–shell ZnS@Zn0.58Cd0.42S heterojunction photocatalysts (ZSC). Microalgae-derived yolk-shell microspheres containing multicomponent nanocores (Fe3O4 and ZnS) were developed to serve as adsorbent, magnetic carrier, and photocatalyst assembly platform to achieve Cd2+ upcycling into ZSC. In particularly, ZSC shows much higher photocatalytic activity for H2 generation and organic pollutant degradation than do commercial photocatalysts (P25-TiO2 and CdS) due to its greater utilization of solar energy and heterostructure. Altogether, we provide an appealing strategy for upcycling cadmium into high-performance heterojunction photocatalysts for environmental purification and clean energy generation.

Synergistic utilization of magnetic rGO/NiFe2O4-g-C3N4 S-Scheme heterostructure photocatalyst with enhanced charge carrier separation and transfer: A highly stable and robust photocatalyst for efficient solar fuel (hydrogen) generation

Graphitic-C3N4 is the prime photocatalyst for solar energy conversion applications owing to its inexpensive, non-toxic, low gap energy, chemical and thermal stability. Herein, a rGO/NiFe2O4-g-C3N4 (RNC-3) hybrid heterostructure photocatalyst was fabricated to realize the effective charge carrier transfer and efficient solar fuel (H2) generation. The photocatalytic H2 generation activity was evaluated under solar light irradiation in the presence of triethanolamine (TEOA) as a hole scavenger. The optimized co-catalysts loadings are 15 wt% and 3 wt% for NiFe2O4 and rGO, respectively. The results obtained show that RNC-3 hybrid heterostructure is an efficient and stable photocatalyst towards water-splitting and presented H2 generation activity of 11,817 μmolg-1h-1, approximately ∼4 and 76 times higher than NiFe2O4-g-C3N4 and g-C3N4 nanosheets, respectively. Notably, the solar-to-hydrogen (STH) conversion efficiency of 2.44% was achieved, prominently surpassing many reported g-C3N4-based materials. This outstanding performance can be related to the substantial band gap reduction from 2.75 to 2.48 eV and significant PL quenching was observed after the incorporation of NiFe2O4 and rGO, which dramatically improved charge carrier separation and transfer, thereby enhancing the photocatalytic performance. Furthermore, RNC-3 exhibits convenient magnetic recovery, practical reusability, and high activity, making it a potential visible-light responsive photocatalyst for efficient water-splitting applications.

Double-shelled CeO2 coupled CdZnS nanoparticles as an efficient heterojunction visible light photocatalyst for hydrogen evolution

Designing of novel semiconductor photocatalysts toward high-efficient catalytic H2 generation has played a potential role in developing sustainable energy. Here, nanostructured CeO2/CdZnS/ZnO composite material has been synthesized through simple hydrothermal process. The present photocatalyst exhibits high photocatalytic activity for H2 generation under visible light irradiation (λ > 420 nm). It can be possibly explained: First, the ZnO layer formed on double-shelled CeO2 hollow spheres (D-CeO2) by the priority adsorption of Zn2+ exhibits both efficient hole consumption and photo-corrosion inhibition. Second, superior charge separation and charge transfer efficiency originates from the Z-scheme CeO2/CdZnS heterojunction.

Direct Z-scheme ZnIn2S4 spheres and CeO2 nanorods decorated on reduced-graphene-oxide heterojunction photocatalysts for hydrogen evolution and photocatalytic degradation

Nanocomposite photocatalysts can potentially produce clean hydrogen (H2) and degrade organic pollutants such as tetracycline (TC). We present hydrothermally synthesized ternary composites of ZnIn2S4–CeO2 implanted into reduced graphene oxide (rGO) layers that outperform typical, expensive catalysts used in the hydrogen evolution reaction (HER). The structural morphology of the composite along with its H2 photocatalytic production and TC degradation ability are evaluated. The results reveal that the ZnIn2S4/rGO/CeO2 heterojunctions demonstrate higher photocatalytic activity for H2 generation and TC degradation than their bare and binary counterparts. The higher efficiency of the ZnIn2S4–rGO–CeO2 composite is attributable to the synergetic effect of rGO as an electron (e–)-transfer bridge, as evidenced by the photocurrent density and photoluminescence results. The ZnIn2S4/rGO/CeO2 ternary catalyst absorbs a wide range of wavelengths, diffuses and separates the photoinduced charge carriers quickly and efficiently, and slowly recombines e– and h+. The generated ternary composite material is then used to demonstrate plausible photocatalytic HER and degradation processes.

Plasmonic TiN nanobelts assisted broad spectrum photocatalytic H2 generation

The conversion of solar energy in a wide spectrum region to clean fuel, H2, remains a challenge in the field of photocatalysis. Herein, plasmonic TiN nanobelts, as a novel cocatalyst, were coupled with CdS nanoparticles to construct a 0D/1D CdS/TiN heterojunction. Utilization of the localized surface plasmon resonance (LSPR) effect generated from TiN nanobelts was effective in promoting light absorption in the near-infrared region, accelerating charge separation, and generating hot electrons, which can effectively improve the photocatalytic H2 generation activity of the 0D/1D CdS/TiN heterojunction over a wide spectral range. Furthermore, owing to the high metallicity and low work function, an ohmic-junction was formed between the CdS and TiN, favoring the transfer of hot electrons generated from TiN nanobelts the CdS nanoparticles, followed by the reaction with water to generate H2. Consequently, the 0D/1D CdS/TiN heterojunction demonstrated H2 generation activity even under light irradiation at 760 nm, while the pure CdS and Pt nanoparticles modified CdS presented no activity. This work opens a new insight into coupling plasmonic cocatalysts to realize full spectrum H2 production.

Porous CoxP nanosheets decorated Mn0.35Cd0.65S nanoparticles for highly enhanced noble-metal-free photocatalytic H2 generation

Incorporating 2D transition-metal phosphides into visible-light-driven semiconductors is fascinating for advancing novel photocatalysts. In this paper, porous CoxP nanosheets prepared by phosphating Co(OH)2 nanosheets are coupled with Mn0.35Cd0.65S nanoparticles for significantly boosted photocatalytic H2 evolution performance. The optimal CoxP/Mn0.35Cd0.65S hybrids show an excellent visible-light H2 production rate of 7188.9 μmol g−1h−1 upon visible light with an apparent quantum yield (AQY) of 18.9% at 420 nm. The H2 production rate of the 5% CoxP/Mn0.35Cd0.65S sample is about 257 times bare CdS and even 18 times higher than pristine Mn0.35Cd0.65S. This dramatic photocatalytic H2 generation activity is mainly ascribed to the efficient charge transfer and abundant active sites by introducing the porous CoxP nanosheets. The photocatalytic mechanism of the CoxP/Mn0.35Cd0.65S composites is investigated by the photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical, and photoelectrochemical (PEC) tests. This work presents a viable strategy to design a 2D/0D hybrid system containing porous cobalt phosphides nanosheets and MnCdS solid solutions for noble-metal-free photocatalytic application.

Porous graphitic carbon nitride with high concentration of oxygen promotes photocatalytic H2 evolution.

Porous structure design and the content regulation of heteroelements have been proved to be effective strategies to boost photocatalytic H2 generation activity of graphitic carbon nitride (g-C3N4) based photocatalyst. Herein, a series of porous graphitic carbon nitride with high concentration of oxygen (g-C3N4-O) photocatalysts were synthesized via in situ polymerization process using colloidal SiO2 as oxygen source. The content of oxygen within the g-C3N4-O photocatalysts could be tuned by adjusting the amount of added colloidal SiO2 during the preparation procedure. The introduced oxygen replaced two-coordinated nitrogen atom, influencing band edge position and localized electron distribution, thereby enhancing visible light harvesting and photoelectric conversion. As a result, the g-C3N4-O photocatalyst with an optimal oxygen content (8.39 wt%) showed 10.5 fold enhancement in H2 evolution rate compared to that of bulk g-C3N4, attributed to the porous structure and high concentration of incorporated oxygen.

Phase control of manganese sulfides during hydrothermal synthesis and their photocatalytic activity for H2 generation

We report a simple method to control phase formation in manganese sulfides during hydrothermal synthesis from aqueous solutions of manganese nitrate and thioacetamide without any additives or surfactants. In this work, MnS2, MnS or MnS2/MnS composites were obtained by adjusting the proportion of thioacetamide in the initial precursor mixture. The photocatalytic activities evaluated by H2 generation under ultraviolet light showed that MnS phase was found to be more active than the MnS2.

Promoting near-infrared photocatalytic activity of carbon-doped carbon nitride via solid alkali activation

Ultrabroad spectral absorption is required for semiconductor photocatalysts utilized for solar-to-chemical energy conversion. The light response range can be extended by element doping, but the photocatalytic performance is generally not enhanced correspondingly. Here we present a solid alkali activation strategy to synthesize near-infrared (NIR) light-activated carbon-doped polymeric carbon nitride (A-cPCN) by combining the copolymerization of melamine and 1,3,5-trimesic acid. The prepared A-cPCN is highly crystalline with a narrowed bandgap and enhanced efficiency in the separation of photogenerated electrons and holes. Under irradiation with NIR light (780 nm ≥ λ ≥ 700 nm), A-cPCN shows an excellent photocatalytic activity for H2 generation from water with rate of 165 µmol g−1 h−1, and the photo-redox activity for H2O2 production (109 µmol g−1 h−1) from H2O and O2, whereas no observed photocatalytic activity over pure PCN. The NIR photocatalytic activity is due to carbon doping, which leads to the formation of an interband level, and the alkali activation that achieved shrinking the transfer distance of photocarriers. The current synergistic strategy may open insights to fabricate other carbon-nitrogen-based photocatalysts for enhanced solar energy capture and conversion.

Microwave solvothermal synthesis of cubic MnS@Ag2S core-shell photocatalysts with improved charge separation and photocatalytic activity

Cubic α-MnS and core-shell MnS@Ag2S photocatalysts were successfully synthesized with a microwave-assisted solvothermal and ion-exchange approach. The morphology, phase, crystal/optical properties, charge separation and photocatalytic H2 generation activity of these photocatalysts were studied. The morphology of these MnS nanomaterials can be tuned from microsphere to microcubes by altering the reaction temperature and duration. A HRTEM image of the MnS@Ag2S photocatalyst reveals that the surface of cubic MnS is decorated with uniformly distributed Ag2S nanoparticles. The formation of Ag2S shell can effectively increase the carrier separation and photocatalytic activity of MnS-based photocatalysts. The rate of hydrogen production of the MnS@Ag2S photocatalyst becomes 2548 μmol g−1h−1, which is 3.7 times that of the MnS photocatalyst. Mn L3-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra were monitored in situ before and after exposure to light to investigate the interfacial charge-transfer behaviors within the MnS@Ag2S photocatalysts. The results confirm that photogenerated electrons transfer from MnS to Ag2S.