MoS2/CdS rod-like nanocomposites as high-performance visible light photocatalyst for water splitting photocatalytic hydrogen production

This study demonstrates a high-performance visible-light-driven photocatalyst for water splitting H₂ production. CdS nanorods (30 nm in diameters) with shorter radial transfer paths and fewer defects were prepared by a solvothermal method. To mitigate the recombination of electrons and holes, MoS₂ nanosheets with rich active sites were modified on the surface of CdS nanorods by a room-temperature sonication treatment. The photocatalytic water splitting tests show that the MoS₂/CdS nanocomposites exhibit excellent H₂ evolution rates. The highest H₂ evolution rates (63.71 and 71.24 mmol g^?1h^?1 in visible light and simulated solar light irradiation) was found at the 6% MoS₂/CdS nanocomposites, which was 14.61 times and 13.39 times higher than those of the corresponding pristine CdS nanorods in visible light and simulate solar light irradiation, respectively. The apparent quantum efficiency (AQE) of the 6% MoS₂/CdS nanocomposites at 420 nm was calculated to be 33.62%. The electrochemistry tests reveal that the enhanced photocatalytic activity is a result of extra photogenerated charge carries, greatly enhanced charge separation and transfer ability of the MoS₂/CdS composites. This study may give new insights for the rational design and facile synthesis of high-performance and cost-effective bimetallic sulfide photocatalysts for solar-hydrogen energy conversion.     

Efficient photocatalytic H2 evolution over Cu and Cu3P co-modified TiO2 nanosheet

Schottky junction and p-n heterojunction are widely employed to enhance the charge transfer during the photocatalysis process. Herein, Cu and Cu₃P co-modified TiO₂ nanosheet hybrid (Cu–Cu₃P/TiO₂) was fabricated using an in situ hydrothermal method. The ternary composite achieved the superior H₂ evolution rate of 6915.7 μmol g^?1 h^?1 under simulated sunlight, which was higher than that of Cu/TiO₂ (4643.4 μmol g^?1 h^?1) and Cu₃P/TiO₂ (6315.8 μmol g^?1 h^?1) and pure TiO₂ (415.7 μmol g^?1 h^?1). The enhanced activity can be attributed to the collaboration effect of Schottky junction and p-n heterojunction among Cu/TiO₂ and Cu₃P/TiO₂, which can harvest the visible light, reduce the recombination of charge carriers and lower the overpotential of H₂ evolution, leading to a fast H₂ evolution kinetics. This work develops a feasible method for the exploration of H₂ evolution photocatalyst with outstanding charge separation properties.     

Designing of a novel Mn0.2Cd0.8S@ZnO heterostructure with Type-II charge transfer path for efficient photocatalytic hydrogen evolution reaction

The development of photocatalysts with efficient hydrogen evolution activity has been the goal for sustainable hydrogen production. In this work, heterojunction composite photocatalyst is formed by hydrothermal coupling of ZnO and Mn_0.2Cd_0.8S. Compared with pure ZnO and Mn_0.2Cd_0.8S, the composite photocatalyst has the ability to provide more abundant active sites and better photogenerated carriers separation efficiency. The optimized composite photocatalyst shows a 9.36-fold increase in hydrogen evolution activity (4297.99 μmol g^?1 h^?1) compared to Mn_0.2Cd_0.8S (459.31 μmol g^?1 h^?1) and exhibits excellent cycling stability. Density functional theory calculations identifies Type-II charge transfer path in the composite photocatalyst, achieving effective separation in space of photogenerated electrons from holes and suppressing recombination within the semiconductor. The results show that the construction of Type-II heterojunction in this work achieves a significant enhancement of the hydrogen evolution activity of the photocatalyst by constructing carrier transport channels at the contact interface of the heterojunction.     

Photoelectrocatalytic nitrogen fixation with Vo-BiOBr/TiO2 heterostructured photoelectrode as photocatalyst

Photocatalytic or photoelectrocatalytic nitrogen fixation is considered as a very promising way to reduce energy requirements. Here, V_o-BiOBr/TiO₂ nanocomposite photoelectrode was constructed by modifying TiO₂ nanotube arrays with BiOBr nanosheets with oxygen vacancies (V_o) for photoelectrocatalytic nitrogen fixation. The oxygen vacancy promotes the adsorption and activation of N₂ on the catalyst surface. The Lewis basicity of nitrogen is enhanced by transferring the photogenerated electrons on the conduction band of BiOBr to the π anti-bonding orbit of N₂, which is more beneficial for the addition of protons. On the other hand, the heterojunction between TiO₂ and V_o-BiOBr facilitates the separation of photogenerated carriers. The photogenerated holes on the valence band of TiO₂ travelled to the counter electrode to produce oxygen at a negative potential, avoiding the further oxidation of NH₃. V_o-BiOBr/TiO₂ displays a high NH₃ production rate of 25.08 μg h^?1 cm^?2 at ?0.2 V which is 3.3 times higher than that of BiOBr/TiO₂. The synergistic effect between TiO₂ and V_o-BiOBr results in enhanced light absorption and higher photoelectrocatalytic efficiency for the N₂ reduction reaction.     

Hydrogen generation by photocatalytic reforming of glucose with heterostructured CdS/MoS2 composites under visible light irradiation

A binary heterostructured CdS/MoS₂ flowerlike composite photocatalysts was synthesized via a simple one-pot hydrothermal method. This photocatalyst demonstrated higher photocatalytic hydrogen production activity than pure MoS₂. The heterojunction formed between MoS₂ and CdS seems to promote interfacial charge transfer (IFCT), suppress the recombination of photogenerated electron–hole pairs, and enhance the hydrogen generation. Based on the good match between the conduction band (CB) edge of CdS and that of MoS₂, electrons in the CB of CdS can be transferred to MoS₂ easily through the heterojunction between them, which prevents the accumulation of electrons in the CB of CdS, inhibiting photocorrosion itself and greatly enhancing stability of catalyst. Hydrogen evolution reaction (HER) using Na₂S/Na₂SO₃ or glucose as sacrificial agents in aqueous solution was investigated. The ratio between CdS and MoS₂ plays an important role in the photocatalytic hydrogen generation. When the ratio between CdS and MoS₂ reaches 40 wt%, the photocatalyst showed a superior H₂ evolution rate of 55.0 mmol g⁻¹ h⁻¹ with glucose as sacrificial agent under visible light, which is 1.2 times higher than using Na₂S/Na₂SO₃ as sacrificial agent. Our experimental results demonstrate that MoS₂-based binary heterostructured composites are promising for photocorrosion inhibition and highly efficient H₂ generation.     

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.     

Promoted charge separation on 3D interconnected Ti3C2/MoS2/CdS composite for enhanced photocatalytic H2 production

The construction of heterojunction has been regarded as an effective way to promote photocatalytic H₂ evolution activity, in which an intimately interfacial contact between the materials forming heterojunction is a positive effect on enhancing activity. Herein, a ternary 3D interconnected nanocomposite Ti₃C₂/MoS₂/CdS was synthesized by a hydrothermal method. MoS₂ nanosheet with a vertically aligned structure grew on the surface of multi-layered Ti₃C₂ to form 3D Ti₃C₂/MoS₂ with tightly interfacial contact, which works as a cocatalyst for enhancing photocatalytic H₂ evolution. CdS as a photocatalyst covered the surface of Ti₃C₂/MoS₂ to absorb light energy. Benefitting to the synergistic effect between Ti₃C₂ and MoS₂, the Ti₃C₂/MoS₂ further accelerates electron transfer and inhibits the recombination of carriers. The H₂ evolution rate of Ti₃C₂/MoS₂/CdS reaches 15.2 mmol h^?1 g^?1 and the apparent quantum yield is 42.1% at λ = 420 nm. The result provides a useful insight for developing cocatalysts with new nanostructures via controlled interfacial engineering.     

Realizing efficient exciton dissociation in an all-organic heterojunction photocatalyst for highly improved photocatalytic H2 evolution

Although graphitic carbon nitride is a promising photocatalyst in the field of energy conversion and environmental purification, the intrinsic properties like excitonic effects and sluggish charge transfer restrict further photocatalytic applications. To circumvent these limitations, the novel all-organic heterojunction photocatalysts were constructed by anchoring organic carbon dots (O-dots) on porous graphitic carbon nitride nanosheets (O-dots/CNS). Results demonstrated that excitons can be e?ectively dissociated into electrons and holes at the interface of O-dots/CNS heterojunction, followed by holes injected to O-dots and electrons accumulated in CNS to realize efficient charge separation. Consequently, the O-dots/CNS with the optimized hydrogen (H₂) evolution performance could be reached 1564.5 μmol h^?1g^?1 under the visible light irradiation. This work not only presents new ideas for rational design photocatalytic reaction system from exciton and charge carrier, but also broaden the applications of this new kind of organic dots in the field of energy conversion.     

Efficient photocatalytic hydrogen evolution on amorphous MoSx-modified CdS/KTaO3 heterojunctions under visible light irradiation

Constructing heterostructures with efficient charge separation is a promising route to improve photocatalytic hydrogen production. In this paper, MoS_x/CdS/KTaO₃ ternary heterojunction photocatalysts were successfully prepared by a two-step method (hydrothermal method and photo deposition method), which improved the photocatalytic hydrogen evolution activity. The results show that the rate of hydrogen evolution for the optimized photocatalyst is 2.697 mmol g^?1·h^?1under visible light, which is 17 times and 2.6 times of the original CdS (0.159 mmol g^?1 h^?1) and the optimal CdS/KTaO₃(1.033 mmol g^?1 h^?1), respectively, and the ternary photocatalyst also shows good stability. The improvement on photocatalytic hydrogen evolution performance can be attributed to the formation of heterojunction between the prepared composite materials, which effectively promotes the separation and migration of photo-generated carriers. Amorphous MoS_x acts as an electron trap to capture photogenerated electrons, providing active sites for proton reduction. This provides beneficial enlightenment for hydrogen production by efficiently utilizing sunlight to decompose water.     

Synergetic effect of carbon self-doping and TiO2 deposition on boosting the visible-light photocatalytic hydrogen production efficiency of carbon nitride

To improve the visible light utilization and photogenerated carriers separation, carbon self-doped carbon nitride (C-CN) supported TiO₂ photocatalysts were synthesized via a designed two-step strategy. After carbon self-doping, the colloid TiO₂ were in-situ deposited on C-CN surface and crystalized by calcination. Simultaneously, the bulk C-CN structure was thermally exfoliated to nanosheet morphology. This strategy ensured the saturated deposition of colloid TiO₂ nanoparticles on C-CN nanosheets to form well-constructed heterostructure with sufficient interfacial contact. The as-prepared TiO₂/C-CN (TCN) heterojunction photocatalysts showed enhanced visible light absorption capability, resulting in impressively high hydrogen production efficiency as 212.7 μmol h⁻¹, which was 10.8 times higher than that of CN. The remarkably enhanced photocatalytic performance may be mainly ascribed to synergetic effect of carbon self-doping and TiO₂ deposition on the improved visible light utilization and photogenerated carriers separation. The probable mechanism in such well-constructed heterojunction photocatalysts was proposed based on the structural analysis, electrical and photoelectrical properties, and photocatalytic process. The proposed strategy may be extended to the preparation of diverse heterojunction photocatalysts with excellent performance for solar energy conversion.     

Enhancing the photocatalytic hydrogen production of the ZnO–TiO2 heterojunction by supporting nanoscale Au islands

In this work, Au was loaded on the ZnO–TiO₂ heterojunction by the deposition-precipitation with urea method to boost its photocatalytic hydrogen production. The synthesized materials were characterized by TEM, ICP-OES, XRD, N₂ adsorption-desorption, UV–vis spectrophotometry, XPS, and (photo)electrochemical measurements. The TEM images confirmed the close contact between ZnO and TiO₂ nanoparticles and showed that although Au nanoparticles agglomerated in the form of islands; they were widely dispersed on the surface of the photocatalysts. Besides, the XPS characterization revealed the enhanced contribution by the metallic Au species as their amount was increased in the composite. The heterojunctions with different Au contents produced higher yield in the photocatalytic production of hydrogen, observing a maximum with the 2-wt.%- Au content (9.13 mmol g⁻¹), being this value 6 times higher than the results obtained with the ZnO–TiO₂ heterojunction. This improvement is associated with the synergistic interaction between the ZnO–TiO₂ heterojunction and Au islands that promoted the separation and transfer of charge carriers. Besides, the (photo)electrochemical characterization showed that the islands acted as “electronic reservoirs”, prolonging the lifetime of the photogenerated electron-hole pairs and creating surface or energy states at the Au/ZnO–TiO₂ heterojunction interface. These states helped improve the charge transfer processes by diminishing the recombination and increasing the photocatalytic hydrogen production.     

MoS2/CdS nanosheet-on-nanorod: An efficient photocatalyst for H2 generation from lactic acid decomposition

The CdS shows high selectivity on H₂ for photocatalytic lactic acid decomposition. However, the low efficiency caused by ultrafast charge recombination was not well addressed. Herein, MoS₂/CdS nanoheterostructure with intimate contact interface was synthesized in-situ and used as an efficient photocatalyst for H₂ generation. The optimum H₂ generation rate of MoS₂/CdS is 45.20 mmol g^?1 h^?1 which significantly boosts the activity of CdS (0.27 mmol g^?1 h^?1) by more than 167 folds. Band alignment of MoS₂ and CdS promoting charge transfer and separation contributes to the enhanced catalytic activity, which was well verified by multiple characterization approaches.     

Improving hole mobility with the heterojunction of graphitic carbon nitride and titanium dioxide via soft template process in photoelectrocatalytic water splitting

In this current work, we have prepared graphitic carbon nitride@titanium dioxide (g-C₃N₄@TiO₂) nanocomposite material via simple one-step soft template synthesis to improve the efficacy of charge separation in photoelectrocatalytic water splitting. The g-C₃N_4, a photoactive component was incorporated in varying amounts into TiO₂, and the resulting composites were confirmed to have improved photoelectrocatalytic activity over the bare-TiO₂. Under the optimal experimental condition, the 20 wt % g-C₃N₄@TiO₂ composite exhibited the highest photoelectrocatalytic activity. The g-C₃N₄ has an ability to absorb the incident photons, resulting in excitation of electrons between the frontier orbitals. These excited electrons move to TiO₂ via the interfacial border, hindering the recombination of the photo-induced electrons and holes and thus, improves the overall performance of the photocatalyst. The improved photoelectrocatalytic performance by g-C₃N₄@TiO₂ was ascribed to the overall impact of g-C₃N₄ that increased its absorptive spectrum into the visible region. As such, the presence of heterojunction in the prepared composite not only aided the separation of the photogenerated charge carriers but also maintained its strong oxidation and reduction capability in the photoelectrocatalytic water splitting.     

Step-scheme perylenediimide supramolecular nanosheet and TiO2 nanoparticle composites for boosted water splitting performance

Adjusting the band gap of organic-inorganic composites by chemical bonding can effectively construct Step-scheme (S-scheme) heterojunctions, featuring properties of fast photogenerated charge migration and excellent photocatalytic performance. In this work, a novel perylene-3, 4, 9, 10-tetracarboxylicdiimide (PDI)-titanium dioxide (TiO₂) heterojunction is elaborately synthesized through simple solvent compounding method. The monodispersed spherical TiO₂ nanoparticles was prepared with the capping agents of oleylamine and oleic acid, and suffered by a ligand exchange process with nitrosonium tetrafluoroborate (NOBF₄) to remove oleylamine and oleic acid. The NOBF₄ ligands were further replaced by PDI super molecular nanosheets to obtain two dimensional (2D)-zero dimensional (0D) PDI-TiO₂ composites. TiO₂ nanoparticles are evenly anchored on the surface of PDI nanosheets with intimate contact. The PDI-TiO₂ composites has emerged considerably superior activity in hydrogen evolution. The highest hydrogen evolution rate for PDI-TiO₂composites with the PDI weight percentage of 2.4% was 9766 μmol h^?1 g^?1 under solar light irradiation, which is 2.56 times of TiO₂-NOBF₄ catalyst. Moreover, PDI-TiO₂ composites possess stoichiometric overall water splitting performance with H₂ and O₂ release rates of 238.20 and 114.18 μmol h^?1 g^?1. The superior photocatalytic performance of PDI-TiO₂ composites can be attributed to the dramatic increase in visible and NIR light absorption caused by π-π stacking structure of PDI, the prevented charge recombination by the S-scheme heterojunction, and the enhanced oxygen evolution by the stronger oxidation capability of PDI. PDI supramolecular nanosheets may work as a novel functional support for many types of semiconductor nanomaterials as graphene, which will display a wide range of application prospects in the energy and environmental fields.     

Chemical bath deposition synthesis of TiO2/Cu2O core/shell nanowire arrays with enhanced photoelectrochemical water splitting for H2 evolution and photostability

In this study, we have developed a facile chemical bath deposition (CBD) method to grow p-type Cu₂O nanoparticles on n-type TiO₂ nanowire arrays (TiO₂ NWAs) to fabricate TiO₂/Cu₂O core/shell heterojunction nanowire arrays (TiO₂/Cu₂O core/shell NWAs). When used as photoelectrode, the fabricated TiO₂/Cu₂O core/shell NWAs show improved photoelectrochemical (PEC) water splitting activity to pure TiO₂ NWAs. The effects of the CBD cycle times on the PEC activities have been studied. The TiO₂/Cu₂O core/shell heterojunction nanowire array photoelectrode prepared by cycling 5 times in the CBD process achieves the highest photocurrent of 2.5 mA cm^?2, which is 2.5 times higher than that of pure TiO₂ NWAs. In addition, the H₂ generation rate of this photoelectrode reaches to 32 μmol h^?1 cm^?2, 1.7 times higher than that of pure TiO₂ NWAs. Furthermore, the TiO₂/Cu₂O core/shell heterojunction nanowire array photoelectrode shows excellent photostability and achieves a stable photocurrent of over 2.3 mA cm^?2 during long light illumination time of 5 h. The enhanced photocatalytic activity of TiO₂/Cu₂O core/shell heterojunction nanowire array photoelectrode is attributed to the synergistic actions of TiO₂ and Cu₂O for improving visible light harvesting, and efficient transfer and separation of photogenerated electrons and holes.     

Deposition of CdS and Au nanoparticles on TiO2(B) spheres towards superior photocatalytic performance

TiO₂(B)/CdS/Au and TiO₂(B)/Au/CdS heterostructures were synthesized to investigate the effect of the selected deposition of CdS and Au nanoparticles (NPs) on H₂ generation. TiO₂(B) spheres (phase B) consisted of nanosheets were synthesized via a hydrothermal reaction. The deposition of CdS and Au NPs were carried out using wet-chemical method and a reduction reaction, respectively. The size and amount of Au and CdS NPs were adjusted to optimize the resulting properties and discuss the change of band gap. Two kinds of heterogeneous revealed different photocatalytic hydrogen generation which indicated the position of Au NPs affect the transfer of photogenerated carriers. The hydrogen production rate of TiO₂(B)/CdS/Au heterostructures reached up to 12100 μmol g⁻¹ h⁻¹, which is about 3.8 times of that of pure TiO₂(B) spheres. This is ascribed to the structure of heterostructures. CdS NPs increase the separation of photogenerated electrons and Au NPs accelerated the transfer of the electrons. The result provided a utilizable strategy for efficient photocatalysis H₂ generation.     

Rationally construct of CoSx/MoS2/g-C3N4 double heterojunction with promoting the separation of carriers for enhanced photocatalysis

g-C₃N₄ (CN) has attracted extensive attention in photocatalysis field, but its weak visible light absorption and rapid charge recombination limit its application. In this, MoS₂ and CoSx (ZIF67 derivatives) as cocatalyst grew on the surface of semiconductor CN in situ to construct CoSx/MoS₂/CN double heterojunction. Then the activities of photocatalytic hydrogen evolution and degradation MB were researched. The hydrogen production rate of 5%CoSx/MoS₂/CN-2 photocatalyst is 9800 μmol h^?1 g^?1 and is about 6.5 times as great as CN, 46 times than MoS₂ and 98 times than CoSx, respectively. Under natural sunlight and simulated sunlight, the degradation efficiency of MB is 99.95% and 99.50% after 4 h, respectively. Catalyst characterizations have pointed out that CoSx/MoS₂/CN catalyst has abundant active sites and larger specific surface area, which increase absorption of water and oxygen. At the same time, internal electric field and S vacancy enhance electrons transfer rate, which effectively inhibit the recombination of e^?-h⁺. This work provides a new idea into the creation of steady, high-efficiency and continuable photocatalytic catalyst for visible light.     

MoS2/Ti3C2 heterostructure for efficient visible-light photocatalytic hydrogen generation

The MoS₂/Ti₃C₂ catalyst with a unique sphere/sheet structure were prepared by hydrothermal method. The MoS₂/Ti₃C₂ heterostructure loading 30% Ti₃C₂ has a maximum hydrogen production rate of 6144.7  μmol g⁻¹ h⁻¹, which are 2.3 times higher than those of the pure MoS₂. The heterostructure maintains a high catalytic activity within 4 cycles. The heterostructure not only effectively reduce the recombination of photogenerated electrons and holes, but also provide more activation sites, which promotes the photocatalytic hydrogen evolution reaction (HER). These works can provide reference for the development of efficient catalysts in photocatalytic hydrogen evolution.     

The co-decorated TiO2 nanorod array photoanodes by CdS/CdSe to promote photoelectrochemical water splitting

A cascade structure of TiO₂/CdS/CdSe semiconductor heterojunction is synthesized using a three-step technique of facile hydrothermal growth for the enhancement of the photoelectrochemical performances. The optical and photoelectrochemical properties controlled by the deposition processing parameters have been investigated. It is shown that the patterns of semiconductor heterojunction enlarge the absorption range of solar spectra, and improve the properties of the photogenerated charge carriers describing separation and transportation, and reduce the interface resistance between the photoelectrode and electrolyte comparing with the pure TiO₂ and CdS-decorated TiO₂ nanorod array photoanodes. The higher photocurrent density and photoconversion efficiency are up to 4.23 mA cm⁻² and 4.2%, which are the 4.1 and 25.3 times superior than that of the pure TiO₂ photoanode. The hydrothermal growth time increment of CdSe yields greater photoelectrochemical water splitting performances. The underlying physics mechanisms have been discussed based on forming a type-Ⅱ energy band alignment structure.     

Boundary effect of Ag/TiO2 on catalytic H2O splitting for H2 production: A theoretical account

Ag supported on TiO₂ reveals advantages in photocatalytic H₂O splitting due to its synergistic effects for promoting the e^?/h⁺ separation. The structural and electronic characteristics of Ag/TiO₂, as well as adsorption and splitting of H₂O on different sites, were investigated employing the density functional theory calculations. The analysis of density of states and electrons densities evidenced the electron transfer and hybrid between Ag and TiO₂. The boundary was especially reactive toward the target species being the most active site, and thus electrons could be transferred to the adsorbate through the supported Ag atoms, leading to the generation of Schottky barrier, which inhibited the recombination of photogenerated electron-hole pairs. The O–H bond cleavage with the E_a of 2.18 eV was the rate-determining step for H₂ production on the Ag/TiO₂ boundary. Fukui functions indicated the outermost Ag cluster site on Ag/TiO₂ boundary exhibited high electron transferability and H₂ production tendency.