Preparation of direct Z-scheme Bi2WO6/TiO2 heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H2 production

Direct Z-scheme Bi₂WO₆/TiO₂ heterojunction photocatalyst was prepared by one-step solvothermal method. The catalyst was characterized by XRD, TEM, XPS, UV–Vis DRS, photoluminescence spectroscopy and photoelectrochemical studies. The photocatalytic hydrogen production experiments show that Bi₂WO₆ did not generate H₂ and the H₂-production rate of TiO₂ is only 0.1 mmol⋅g⁻¹h⁻¹. The hydrogen production rate of the Bi₂WO₆/TiO₂ heterojunction photocatalyst reaches 12.9 mmol⋅g⁻¹h⁻¹, which is 129 times that of TiO₂. Compared with TiO₂, the enhanced H₂-production activity of the heterojunction catalyst can be attributed to the wider light absorption range and the efficient separation and migration of carriers at the close contact interface between Bi₂WO₆ and TiO₂. Based on the work functions of Bi₂WO₆, TiO₂ and their heterojunctions, combined with the results of electron paramagnetic resonance spectroscopy and Mott-Schottky measurements, the photocatalytic H₂ production mechanism of Z-scheme heterojunction Bi₂WO₆/TiO₂ was proposed. This work provides an easy and simple way to design a binary Z-scheme photocatalyst with efficient catalytic H₂-production activity without electron mediators.     

Photocatalytic hydrogen production enhancement of Z-Scheme CdS quantum dots/Ni2P/Black Ti3+–TiO2 nanotubes with dual-functional Ni2P nanosheets

The Z-Scheme CdS quantum dots/Ni₂P/Black Ti³⁺–TiO₂ nanotubes with dual-functional Ni₂P nanosheets are fabricated by a continuously electrospinning-annealing/reduction-chemical deposition method, there, the TiO₂ nanotubes are fabricated via electrospinning, subsequently, the 2D Ni₂P lamellas grow on the surface of nanotubes and the Ti³⁺/O_v ions are introduced by reduction, then CdS QDs are deposited on the surface of Ni₂P lamellas. Evaluated by the photocatalytic hydrogen production, the photocatalytic performance of Z-Scheme CdS QDs/Ni₂P/B–TiO₂(~3303.85 μmol/g h) exhibits an obvious enhancement of about ~70 folds than unmodified TiO₂. The main reasons for the HER enhancement are ascribed to that the Pt-like behavior 2D Ni₂P and Ti³⁺ ions can accelerate the photo-generated electrons diffusing into water and reduce H₂ activation barrier, the Z-Scheme heterojunction can accelerate the separating and transferring of photo-generated charge carriers, the O_v ions and hollow nanotubes can increase solar utilization, which can be supported by the electrochemical measurements.     

0D/2D heterojunction constructed by high-dispersity Mo-doped Ni2P nanodots supported on g-C3N4 nanosheets towards enhanced photocatalytic H2 evolution activity

Development of low cost and efficient non-noble-metal cocatalyst is still a hot topic to improve the activity of g-C₃N₄ in photocatalytic water splitting to produce H₂. As a potential cocatalyst in photocatalytic application, transition metal phosphides (TMPs) have been proved to greatly enhance the photocatalytic H₂ evolution performance comparable to noble metal Pt. Modifying TMPs by incorporation of hetero-metal has also been reported as an effective strategy for their electronic structure regulation and optimizing the intermediates absorption energy, however, which is rarely reported in the field of photocatalysis. Herein, the 0D/2D heterojunction is constructed by high-dispersity Mo-doped Ni₂P nanodots supported on g-C₃N₄ nanosheets, which exhibits the significantly improved photocatalytic H₂ evolution performance compared with that of Ni₂P/g-C₃N₄ and Pt/g-C₃N₄. Specifically, the optimal H₂ evolution rate reaches 67.6 μmol h⁻¹ over Mo–Ni₂P/g-C₃N₄ sample, which is 6.0 and 2.4 times higher than those of Pt/g-C₃N₄ and Ni₂P/g-C₃N₄, respectively. The fascinating result mainly stems from the improved separation efficiency of charge carriers and more effective electron donating reaction sites resulted from the electronic structure adjustment through doping Mo element into Ni₂P as cocatalyst. This work provides a valid evidence for the modification of cocatalyst to realize high H₂ evolution performance, opening up new opportunities and possibilities for the application of TMPs in the photocatalytic field.     

Enhanced hydrogen generation from methanol aqueous solutions over Pt/MoO3/TiO2 under ultraviolet light

The photocatalytic activity in hydrogen production from methanol reforming can be significantly enhanced by Pt/MoO₃/TiO₂ photocatalysts. Compared with Pt/P25, the photocatalytic activity of optimized Pt/MoO₃/TiO₂ shows an evolution rate of 169 μmol/h/g of hydrogen, which is almost two times higher than that of Pt/P25. XRD and Raman spectra show that MoO₃ are formed on the surface of TiO₂. It is found that with the bulk MoO₃ just formed, the catalyst shows the highest activity due to a large amount of heterojunctions and the high crystallinity of MoO₃. The HRTEM image showed a close contact between MoO₃ and TiO₂. It is proposed that the Z-scheme type of heterojunction between MoO₃ and TiO₂ is responsible for the improved photocatalytic activity. The heterojunction structure of MoO₃/TiO₂ does not only promote the charge separation, but also separates the reaction sites, where the oxidation (mainly on MoO₃) and reduction (on TiO₂) reactions occurred.     

Facile fabrication of titania-ordered cubic mesoporous carbon composite: Effect of Ni doping on photocatalytic hydrogen generation

Hitherto TiO₂ is the most popular catalyst for photocatalytic H₂ generation and reduction of organic pollutants due to its chemical inertness, high activity, and abundance. In this work, ordered mesoporous carbon CMK-8 supported TiO₂ nanoparticles loaded with non-noble metal Ni, denoted as NiTiO₂@CMK-8 are fabricated for application in photocatalytic H₂ generation. Our results demonstrate that the developed composite exhibit exceptional photocatalytic activity for H₂ generation (3556 μmol g⁻¹) under 300 W Xe lamp irradiation (with an external quantum efficiency of 37.9%), which is around 10 times higher than pure TiO₂ and 4 times that of TiO₂@CMK-8. The enhanced photocatalytic performance is attributed to the well-dispersed TiO₂ in the ordered mesoporous carbon structure of CMK-8. The performance is boosted by the black body-like light absorbance of CMK-8 and plasmonic effect of Ni. Enhanced UV–visible light absorbance, large surface area and the loaded Ni metal synergistically improve the charge-carrier kinetics to attain highly efficient photocatalytic H₂ generation. The NiTiO₂@CMK-8 composite shows enhanced activity for the reduction of 4-nitrophenol as well.     

Enhanced photocatalytic hydrogen evolution on TiO2 employing vanadium carbide as an efficient and stable cocatalyst

In an attempt to construct efficient and robust photocatalysts/systems for solar H₂ evolution from water splitting, the development of highly active and stable H₂ evolution cocatalysts is crucial yet remains a great challenge. Herein, we present that vanadium carbide (VC) can serve as an efficient cocatalyst when integrated with TiO₂ for photocatalytic H₂ evolution. With 15 wt% VC, the obtained TiO₂/VC (15 wt%) composite photocatalyst (denoted as TV15) shows the highest photocatalytic H₂ evolution rate of 521.4 μmol h⁻¹ g⁻¹, while the pristine TiO₂ hardly shows H₂ evolution activity. The apparent quantum efficiency (AQE) of H₂ evolution reaches up to 2.3% under light irradiation of 365 nm. Notably, the TV15 exhibits excellent photocatalytic stability for H₂ evolution over four cycles of continuous light irradiation of 20 h. The enhanced activity of TV15 can be attributed to the cocatalyst effects of VC, which can not only effectively capture the photogenerated electrons of TiO₂ to greatly enhance the charge separation efficiency but also significantly reduce the overpotential of H₂ evolution reaction, thus enhancing the photocatalytic activity of TiO₂/VC towards H₂ evolution. This work provides a new insight to rationally design and develop efficient photocatalysts using active and stable transition metal carbides as cocatalysts.     

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.     

Photocatalytic hydrogen evolution and antibiotic degradation by S-scheme ZnCo2S4/TiO2

In this study, ZnCo₂S₄ (ZCS) nanoparticles were coupled on the surface of TiO₂ by simple solvothermal method to form S-scheme heterojunction. Compared with ZCS and TiO₂, the photocatalytic performance of ZCS/TiO₂ under simulated sunlight is significantly improved, and its hydrogen evolution efficiency reaches 5580 μmol·g^?1·h^?1 with the apparent quantum efficiency (AQY) up to 11.5% at 420 nm, which is 88.3 times and 54.3 times that of TiO₂ and ZCS, respectively. Moreover, ZCS/TiO₂ also has excellent performance in the photocatalytic degradation of tetracycline (TC). The enhancement of photocatalytic performance of ZCS/TiO₂ is mainly due to S-scheme heterojunction. On the one hand, the S-scheme electron transfer path not only improves the electron-hole separation efficiency, but also improves the charge transfer efficiency. On the other hand, ZCS significantly enhances the visible light absorption of ZCS/TiO₂. The photocatalytic mechanism and S-scheme heterojunction structure is confirmed by XPS, EPR, ultraviolet photoelectron spectroscopy (UPS) and energy band structure. This work provides a new idea for designing and constructing S-scheme heterojunction to improve the performance of photocatalytic hydrogen evolution and TC degradation.     

CoAl LDH in-situ derived CoAlP coupling with Ni2P form S-scheme heterojunction for efficient hydrogen evolution

Accelerating the separation and migration efficiency of photogenerated charge carriers and creating abundant active sites are the keys to the excellent H₂ production performance of photocatalysts. In this work, two strategies, the construction of S-scheme heterojunction and the introduction of active P species, were carried out based on polyhedral Ni-MOF-74 and layered CoAl LDH, in order to accelerate the separation and migration of electron-hole pairs as well as create rich active sites for more improved photocatalytic H₂ evolution performance. First, a delicate Ni-MOF-74/CoAl LDH S-scheme heterojunction was constructed, and then Ni-MOF-74/CoAl LDH was converted to CoAlP/Ni₂P S-scheme heterojunction. That is, the active P species was introduced based on the presence of S-scheme heterojunction. More importantly, Ni-MOF-74/CoAl LDH S-scheme heterojunction photocatalyst exhibits visible improvement in H₂ generation rate in comparison with single Ni-MOF-74 and CoAl LDH, which is attributed to the formation of S-scheme heterojunction undoubtedly. Further, CoAlP/Ni₂P S-scheme heterojunction shows more improved H₂ production performance than Ni-MOF-74/CoAl LDH, suggesting that P-modification is a high-efficiency means for enriching surface active sites and implementing the conversion of S-scheme heterojunction to S-scheme heterojunction.     

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.     

In-situ constructing cobalt incorporated nitrogen-doped carbon/CdS heterojunction with efficient interfacial charge transfer for photocatalytic hydrogen evolution

Designing an efficient heterojunction interface is an effective way to promote the electrons' transfer and improve the photocatalytic H₂ evolution performance. In this work, a novel hollow hybrid system of Co@NC/CdS has been fabricated and constructed. CdS nanospheres are anchored on the hollow-structured cobalt incorporated nitrogen-doped carbon (Co@NC) through a one-pot in-situ chemical deposition approach, forming an intimate interface and establishing an excellent channel to improve the electrons transfer and charge carriers separation between CdS and Co@NC cocatalyst, which immensely promotes the photocatalytic activity. The rate of photocatalytic H₂ evolution over hollow structured Co@NC/CdS heterojunction can be achieved 8.2 mmol g^?1 h^?1, which is about 45 times of pristine CdS nanospheres. The photocatalytic H₂ evolution mechanism has been investigated by the techniques of photoluminescence (PL) spectra, photocurrent-time (i-t) curves, electrochemical impedance spectroscopy (EIS) etc. This work aims to provide a new way in developing of high-performance advanced 3D heterojunction for photocatalytic hydrogen evolution.     

Hollow hexagonal NiSe–Ni3Se2 anchored onto reduced graphene oxide as efficient electrocatalysts for hydrogen evolution in wide-pH range

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni₃Se₂ nanosheets grown on reduced graphene oxide (NiSe–Ni₃Se₂/rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H₂SO₄, the NiSe–Ni₃Se₂/rGO possesses 112 mV to achieve 10 mA cm^?2 and a small Tafel slope (61 mV dec^?1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm^?2, and Tafel slopes are 103 and 92 mV dec^?1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni₃Se₂/rGO is better than that of NiSe–Ni₃Se₂. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst.     

In-situ photo-deposition CuO1−x cluster on TiO2 for enhanced photocatalytic H2-production activity

CuO_1?x cluster-modified TiO₂ (CuO_1?x/TiO₂) photocatalysts were prepared by an in-situ photoreduction deposition of Cu on TiO₂ powder support using copper acetate as a Cu source. The prepared samples without any Pt co-catalyst present an especially high photocatalytic H₂-evolution activity under solar light irradiation with 5% glycerol as sacrificial agent. The optimal CuO_1?x/TiO₂ catalyst with only 1 wt% CuO_1?x exhibits a high activity of 1725 μmol h^?1 g^?1 for H₂ evolution, which reaches 120 times that of TiO₂. The high photocatalytic activity of H₂ production is attributed to the highly dispersed CuO_1?x nano clusters on the surface of the TiO₂. In addition, Pt/CuO_1?x/TiO₂ was also prepared by loading Pt on CuO_1?x/TiO₂ sample, and its photocatalytic hydrogen evolution activity is enhanced 1.8 times compared with that of Pt/TiO₂ for overall water splitting reaction under solar light, demonstrating that a small amount CuO_1?x wondrously improves the photocatalytic activity of Pt/TiO₂ for overall water splitting reaction. This paper reports an economic and simple approach to prepare a photocatalyst with high hydrogen-production activity.     

Hydroxyapatite decorated TiO2 as efficient photocatalyst for selective reduction of CO2 with H2O into CH4

Efficient catalysts with high selectivity in products are highly desirable for photocatalytic CO₂ reduction. In this work, hydroxyapatite (HAP) decorated TiO₂ (HAP/TiO₂) were successfully fabricated via in-situ deposition of Ca(OH)₂ on rutile TiO₂ followed by a facile hydrothermal reaction. Comparing with TiO₂, HAP/TiO₂ exhibited significant enhancement (ca. 40 times) toward photocatalytic CO₂ reduction in the presence of H₂O with a >95% selectivity of CH₄. The characterizations revealed HAP possessed Lewis basic sites (O²⁻ in -PO₄^3- groups) and Lewis acidic sites (Ca²⁺ or OH⁻ vacancies), where Lewis basic sites could enhance the adsorption/activation of CO₂ and Lewis acidic sites facilitated the adsorption/dissociation of H₂O respectively, thus promoting the photocatalytic reduction and oxidation half-reactions of CO₂ and H₂O over Pt/TiO₂. The formation of much more stable intermediates over HAP/TiO₂ would be responsible for the high selectivity of CH₄. Moreover, photoelectrochemical and electrochemical characterizations revealed HAP could also promote the charge separation of TiO₂ and the charge transfer between TiO₂ and adsorbed species. The findings demonstrate HAP has a great potential as efficient assistant for photocatalytic CO₂ reduction with H₂O and will stimulate us to design novel semiconductor-based materials with tuned Lewis acidic and Lewis basic sites to achieve highly efficient photocatalysts.     

Facile strategy to fabricate Ni2P/g-C3N4 heterojunction with excellent photocatalytic hydrogen evolution activity

Transition metal phosphides are considered as the most prospective replacements for noble metal cocatalysts used for H₂ evolution during photocatalytic water splitting. In this work, Ni₂P/g-C₃N₄ composite photocatalyst was synthesized using a simple in-situ hydrothermal method by one step. Benefiting from the excellent light trapping, efficient transfer of charge carriers and strong stability of Ni₂P nanoparticles, as well as the stable interface contact between Ni₂P and g-C₃N₄, the Ni₂P/g-C₃N₄ exhibit greatly enhanced H₂ evolution performance during photocatalytic water splitting. The optimized H₂ evolution rate can reach 3344 μmol h^?1 g^?1 over 17.5 wt% Ni₂P/g-C₃N₄, which is 68.2 times greater than that of pure g-C₃N₄ and even much greater than that of 15 wt% Pt/g-C₃N₄. The apparent quantum efficiency (QE) is about 9.1% under 420 nm monochromatic. The enhancement mechanism was demonstrated in detail by transient photocurrent responses, photoluminescence spectra and electrochemical impedance spectroscopy. This work develops a facile strategy to fabricate transition metal phosphide/semiconductor heterojunction systems with potential application for photocatalytic H₂ evolution.     

Mesoporous g-C3N4 decorated by Ni2P nanoparticles and CdS nanorods together for enhancing photocatalytic hydrogen evolution

Ni₂P nanoparticles and CdS nanorods were grew together on a mesoporous g-C₃N₄ through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni₂P composite displays a high H₂ evolution rate with 2905.86 μmol g^?1 h^?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni₂P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni₂P. Meanwhile, Ni₂P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni₂P composite exerts good stability in 12-h cycles.     

Redox couple mediated charge carrier separation in g-C3N4/CuO photocatalyst for enhanced photocatalytic H2 production

Graphitic carbon nitride (g-C₃N₄) is one of the promising two-dimensional metal-free photocatalysts for solar water splitting. Regrettably, the fast electron-hole pair recombination of g-C₃N₄ reduces their photocatalytic water splitting efficiency. In this work, we have synthesized the CuO/g-C₃N₄ heterojunction via wet impregnation followed by a calcination method for photocatalytic H₂ production. The formation of CuO/g-C₃N₄ heterojunction was confirmed by XRD, UV–vis and PL studies. Notably, the formation of heterojunction not only improved the optical absorption towards visible region and also enhanced the carrier generation and separation as confirmed by PL and photocurrent studies. The photocatalytic H₂ production results revealed that CuO/g-C₃N₄ photocatalyst demonstrated the increased photocatalytic H₂ production rate than bare g-C₃N₄. The maximum H₂ production rate was obtained with 4 wt % CuO loaded g-C₃N₄ photocatalyst. Importantly, the rate of H₂ production was further improved by introducing simple redox couple Co²⁺/Co³⁺. Addition of Co²⁺ during photocatalytic H₂ production shuttled the photogenerated holes by a reversible conversion of Co²⁺ to Co³⁺ with accomplishing water oxidation. The effective shuttling of photogenerated holes decreased the election-hole pair recombination and thereby enhancing the photocatalytic H₂ production rate. It is worth to mention that the addition of Co²⁺ with 4 wt % CuO/g-C₃N₄ photocatalyst showed ∼7.5 and ∼2.0 folds enhanced photocatalytic H₂ production rate than bare g-C₃N₄/Co²⁺ and CuO/g-C₃N₄ photocatalysts. Thus, we strongly believe that the present simple redox couple mediated charge carrier separation without using noble metals may provide a new idea to reduce the recombination rate.     

Direct Z-scheme anatase/rutile bi-phase nanocomposite TiO2 nanofiber photocatalyst with enhanced photocatalytic H2-production activity

Design and preparation of direct Z-scheme anatase/rutile TiO₂ nanofiber photocatalyst to enhance photocatalytic H₂-production activity via water splitting is of great importance from both theoretical and practical viewpoints. Herein, we develop a facile method for preparing anatase and rutile bi-phase TiO₂ nanofibers with changing rutile content via a slow and rapid cooling of calcined electrospun TiO₂ nanofibers. The phase structure and composition, surface morphology, specific surface area, surface chemical composition and element chemical states of TiO₂ nanofibers were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). By a rapid cooling of 500 °C-calcined electrospun TiO₂ precursor, anatase/rutile bi-phase TiO₂ nanofibers with a roughly equal weight ratio of 55 wt.% anatase and 45 wt.% rutile were prepared. The enhanced H₂ production performance was observed in the above obtained anatase/rutile composite TiO₂ nanofibers. A Z-scheme photocatalytic mechanism is first proposed to explain the enhanced photocatalytic H₂-production activity of anatase/rutile bi-phase TiO₂ nanofibers, which is different from the traditional heterojunction electron–hole separation mechanism. This report highlights the importance of phase structure and composition on optimizing photocatalytic activity of TiO₂-based material.     

Cobalt sulfide quantum dots modified TiO2 nanoparticles for efficient photocatalytic hydrogen evolution

Cobalt sulfide quantum dots (CoSx QDs) modified TiO₂ nanoparticles are prepared with a precipitation-deposition method using TiO₂, cobalt acetate and sodium sulfide as the precursors. CoSx QD acts as an effective cocatalyst, which accelerates the transfer of the photo-generated electrons and serves as the active site for the reaction between electrons and H₂O, thus enhancing the separation of the e⁻/h⁺ pairs and the photocatalytic H₂ production activity of TiO₂. The amount of CoSx exhibits an optimum value at about 5% (mole ratio to TiO₂), at which the H₂ production rate achieves 838 μmol h⁻¹ g⁻¹ using ethanol as the sacrificial reagent. This exceeds that of the pure TiO₂ by more than 35 times.     

A 2D/1D TiO2 nanosheet/CdS nanorods heterostructure with enhanced photocatalytic water splitting performance for H2 evolution

TiO₂ with exposed (001) facets were composited with CdS nanorods to construct 2D/1D heterojunction. As comparison, P25 with mainly exposed (101) facets were employed to combine with CdS nanorods. The 2D/1D heterojunction of TiO₂ nanosheets and CdS nanorod displayed 3.7 times higher hydrogen generation than that of P25/CdS composites. The results indicated that TiO₂ with exposed (001) facets were favorable for enhancing the photocatalytic activity of CdS via optimizing the heterojunction between TiO₂ and CdS. Photoluminescence and photoelectrochemical characteristics results demonstrated that the 2D-TiO₂/1D-CdS heterojunction exhibits higher separation efficiency of photoinduced carriers and superior electron transfer ability. This work exemplifies that heterojunction modification is an effective strategy to improve the efficiency of the photocatalyst composites.