Fabrication of heterostructured UIO-66-NH2 /CNTs with enhanced activity and selectivity over photocatalytic CO2 reduction

Developing photocatalysts with superior efficiency and selectivity is an important issue for photocatalytic converting CO₂. Hierarchically heterostructured one-dimensional nanomaterials represent a kind of promising catalysts for photocatalytic CO₂ reduction on account of the high surface area and synthetic effect between different components. Herein, we synthesized UIO-66-NH₂/carbon nanotubes (CNTs) heterostructures via a hydrothermal method, and investigated their photocatalytic performance. The element mapping, X-ray diffraction, and X-ray photoelectron spectroscopy collectively confirmed that the UIO-66-NH₂ was successfully loaded on the surface of the CNTs. The specific surface area of the UIO-66-NH₂/CNTs is 1.5 times higher than that of UIO-66-NH₂. The photocurrent and electrochemical impedance spectroscopy measurements showed that the CNTs could enhance the electron mobility and reduce the recombination of photogenerated electron-hole pairs, which was also confirmed by the Photoluminescence spectroscopy (PL). The CNTs can improve the conductivity of composites and the dispersion of UIO-66-NH₂, exposing more active sites, therefore the UIO-66-NH₂ can increase the absorption of carbon dioxide and thus enhance the selectivity. The composites remarkably promoted the separation and transition of electrons and thus improved the photocatalytic efficiency of CO₂ reduction. More importantly, it was found that the as-prepared composites suppress the hydrogen generation reaction during the CO₂ reduction process.     

Surface and interface engineering in CO2-philic based UiO-66-NH2-PEI mixed matrix membranes via covalently bridging PVP for effective hydrogen purification

We report on the fabrication of the defect-free mixed-matrix membrane (MMM) based on the polyethylenimine (PEI) matrix with uniformly dispersed metal-organic framework (MOF) filler UiO-66-NH₂, covalently bonded by polyvinylpyrrolidone (PVP). The key feature of the molecular level-controlled filler deposition in prepared UiO-66-NH₂-PVP-PEI membranes was bridging the MOF particles to the PEI polymer matrix via PVP polymer chains. Such an approach improved the polymer-filler interface interactions and boosted the MOF dispersion into the polymer matrix for higher MOF loadings up to 23 wt %. The overall membrane structure and properties were characterized using FTIR, XRD, TG, DSC, SEM and 3D optical profiler techniques. Obtained results revealed the uniform dispersion of UiO-66-NH₂, the strong polymer-filler interface interactions and entanglement of PEI with UiO-66-NH₂-PVP. Furthermore, the outstanding CO₂/H₂ separation performance was determined for the UiO-66-NH₂-PVP-PEI membrane with 18 wt % of MOF loading; the average CO₂ permeability of 394 Barrer and the separation factor of 12 for circa 100 h of the membrane testing overcome the 2008 Robeson reverse upper bound limit. Such improved CO₂/H₂ separation performance was achieved due to the combination of the diffusion-solution mechanism with the preferential adsorption of the CO₂ via the reversible bicarbonate reaction with amino groups of the UiO-66-NH₂ and PEI which acts as fixed CO₂ carrier sites in MMM structure.     

Enhanced charge transfer for efficient photocatalytic H2 evolution over UiO-66-NH2 with annealed Ti3C2Tx MXenes

The annealed Ti₃C₂T_x MXenes retained original layered morphology and gave rise to the formation of TiO₂ is anticipated to achieve improved photocatalytic hydrogen evolution performance as a noble-metal-free co-catalyst. In this work, a novel Ti₃C₂/TiO₂/UiO-66-NH₂ hybrid was rationally designed for the first time by simply introducing annealed Ti₃C₂T_x MXenes over water-stable Zr-MOFs (UiO-66-NH₂) precursors via a facile hydrothermal process. As expected, the rationally designed Ti₃C₂/TiO₂/UiO-66-NH₂ displayed significantly improvement in photocatalytic H₂ performance (1980 μmol·h⁻¹·g⁻¹) than pristine UiO-66-NH₂ under simulated sunlight irradiation. The excellent photocatalytic HER activity can be attributed to the formation of multi-interfaces in Ti₃C₂/TiO₂/UiO-66-NH₂, including Ti₃C₂/TiO₂/UiO-66-NH₂, Ti₃C₂/TiO₂ and Ti₃C₂/UiO-66-NH₂ interfaces, which constructed multiple pathways at the interfaces with Schottky junctions to accelerate the separation and transfer of charge carriers and endowed the accumulation of photo-generated electrons on the surface of Ti₃C₂. This work expanded the possibility of porous MOFs for the development of efficient photocatalytic water splitting using annealed MXenes.     

Oxygen vacancy induced Pt-decorated MOF photocatalyst for hydrogen production

The photocatalytic performance has remained challenging due to the rapid recombination of photoexcited electron-hole (e-h) pairs. To overcome this problem, creating oxygen vacancies on the surface of semiconductors has been an effective strategy. Herein, we report the effects of oxygen vacancies (Ov) on photocatalytic HER performance of Pt nanoparticles (NPs) anchored on UiO-66-NH₂. In contrast, under the same amount of Pt NPs, UiO-66-NH₂ with high oxygen vacancies (denoted as Pt/UN-Ovh) exhibit superior photocatalytic H₂ generation than the catalyst with low oxygen vacancies (denoted as Pt/UN-Ovl) under visible-light irradiation. Based on the experimental characterization and theoretical calculations, the high oxygen vacancies not only stabilize the Pt NPs on the substrate (UiO-66-NH₂), but also develop the strong interaction between Pt NPs and support thereby Pt NPs traps more electrons from substrate and provides protons for H₂ production inhibiting the electron-hole recombination. This work provides novel strategy for enhancing the photocatalysts performance of MOF based materials.     

UiO-66-NH2 functionalized cellulose nanofibers embedded in sulfonated polysulfone as proton exchange membrane

Metal–organic frameworks (MOFs) exhibit high proton conductivity, thermal stability, and offer immense flexibility in terms of tailoring their size. Owing to their unique characteristics, they are desirable candidates for proton conductors. Nevertheless, constructing ordered MOF proton channels in proton exchange membranes (PEMs) remains a formidable challenge. Herein, blend nanofibers of cellulose and UiO-66-NH₂ (Cell–UiO-66-NH₂) obtained via the electrospinning process were embedded in a sulfonated polysulfone matrix to obtain high-performance composite PEMs with an orderly arrangement of UiO-66-NH₂. Comprehensive characterization and membrane performance tests reveal that composite membrane with 5 wt% (nominal) UiO-66-NH₂ have revealed high proton conductivity of 0.196 S cm^?1 at 80 °C and 100% relative humidity. Meantime, the composite membrane exhibits a low methanol permeability coefficient (~5.5 × 10^?7 cm² s^?1). Moreover, the composite membrane exhibits a low swelling ratio (17.3%) even at 80 °C. The Cell–UiO-66-NH₂ nanofibers exhibit strong potential for use as a proton-conducting nanofiller in fuel-cell PEMs.     

Amino-group and space-confinement assisted synthesis of small and well-defined Rh nanoparticles as efficient catalysts toward ammonia borane hydrolysis

Hydrogen evolution from ammonia borane (AB) hydrolysis is of great importance considering the ever-increasing demand for green and sustainable energy. However, the development of a facile and efficient strategy to construct high-performance catalysts remains a grand challenge. Herein, we report an amino-group and space-confinement assisted strategy to fabricate Rh nanoparticles (NPs) using amino-functionalized metal-organic-frameworks (UiO-66-NH₂) as a NP matrix (Rh/UiO-66-NH₂). Owing to the coordination effect of amino-group and space-confinement of UiO-66-NH₂, small and well-distributed Rh NPs with a diameter of 3.38 nm are successfully achieved, which can be served as efficient catalysts for AB hydrolysis at room temperature. The maximum turnover frequency of 876.7 min^?1 is obtained by using the Rh/UiO-66-NH₂ with an optimal Rh loading of 4.38 wt% and AB concentration of 0.2 M at 25 °C, outperforming most of the previously developed Rh-based catalysts. The catalyst is also stable in repetitive cycles for five times. The high performance of this catalyst must be ascribed to the structural properties of UiO-66-NH₂, which enable the formation of small and well-dispersed Rh NPs with abundant accessible active sites. This study provides a simple and efficient method to significantly enhance the catalytic performance of Rh for AB hydrolysis.     

Novel multi-channel anion exchange membrane based on poly ionic liquid-impregnated cationic metal-organic frameworks

The “trade-off” effect between hydroxide conductivity and dimensional stability is challenging issue for anion exchange membrane fuel cells (AEMFCs). In this study, the framework of UiO-66-NH₂ is for the first time applied to anion exchange membranes (AEMs). The robust pore walls of UiO-66-NH₂ with mechanical and structural durabilities protect the membrane from the excessive swelling effects (a swelling ratio of 7%). In addition, the framework of UiO-66-NH₂ is directly modified into (UiO-66-NH₂)⁺Cl⁻ as hydroxide conduction channels by anion stripping for the first time. And we construct well-organized ion nanochannels by the in-situ self-assembly of N,N,N′,N' -tetramethyl-1,6-hexanediamine (TMHDA) and allyl bromide within the highly ordered pores of (UiO-66-NH₂)⁺Cl⁻. The obtained QA@(UiO-66-NH₂)⁺Cl⁻ then incorporated into pristine membrane (QAPPO) to fabricate the novel multi-channel AEMs. The hydroxide conductivity of QA@(UiO-66-NH₂)⁺Cl⁻/PPO is up to 123 mS⋅cm⁻¹ at 80 °C, which is greatly improved compared to QAPPO pristine membrane.     

Highly efficient photocatalytic conversion of gas phase CO2 by TiO2 nanotube array sensitized with CdS/ZnS quantum dots under visible light

With the massive consumption of fossil fuels, energy crisis and effectively reducing CO₂ to curb global warming have become urgent and severe problems in the world. Photocatalytic conversion of CO₂ technology which can convert CO₂ into combustible compounds by using solar energy can solve both of the problems mentioned above. However, the photocatalytic conversion of CO₂ exhibits too low efficiency, especially under visible light. So, in order to improve the photocatalytic efficiency, the composite photocatalysts of TiO₂ nanotube array (TNTA) sensitized by CdS/ZnS quantum dots (QDs) were successfully prepared by anodization method and successive ionic layer adsorption and reaction (SILAR) method in this work. And the composite photocatalysts exhibited a high performance for photocatalytic conversion of gas-phase CO₂ to methanol under visible light. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), and X-ray photoelectric spectroscopy (XPS) were employed to characterize the ingredients and morphologies of the synthesized photocatalysts. And, UV–vis diffuse reflectance spectra (UV–Vis DRS) revealed that CdS/ZnS QDs enhanced the photo-absorption of composite photocatalyst in the visible light region. The main product methanol yield of CdS/ZnS-TNTA under visible light was 2.73 times that of bare TNTA when TNTA was treated by 10 SILAR cycles. Meanwhile, the product yield first increased before decreasing with the increase of the CO₂ flow rate. And the greatest product yield reached up to 255.49 nmol/(cm²-cat·h) with the increase of light intensity. The reaction mechanism was discussed in this paper. This high performance for photocatalytic reduction of CO₂ was primarily attributed to the CdS/ZnS QDs sensitization, which widens the response wavelength range of the catalyst to include visible light and partly inhibits the recombination of electron-hole pairs.     

Rational design of ZnO–CuO–Au S-scheme heterojunctions for photocatalytic hydrogen production under visible light

An integration of S-scheme heterojunction catalyst with surface plasmon resonance effect is the prime focus of current research activites in the field of visible light driven photocatalytic hydrogen (H₂) evolution. Herein, a sol-gel route is used to design a heterojunction of ZnO–CuO–Au. The effect of process parameters, including irradiation time, catalyst dose, and sacrificial reagents on the hydrogen evolution is studied. The S-scheme ZnO–CuO–Au heterojunction catalyst demonstrated high surface area, better optical absorption response in the visible part of light spectrum, and improved separation and transportion of charge carriers as verified by DRS, PL, and photoelectrochemical studies. The maximum H₂ evolution rateof ZnO–CuO–Au reaches 4655 μmolh⁻¹g⁻¹, which is 5 and 3.2 times higher than ZnO–CuO and Au–ZnO catalysts, respectively. A possible reason of this increase in H₂ evolution rate is inhibited recombination of charge carriers because of the S-scheme design to increase electrons with strong reduction potential and prolong lifetime, Au serves as an SPR source and conductive channel to swift the transfer of electrons and high density of active sites. This work offers innovative insight into designing plasmonic metals-modified S-scheme systems for solar fuel production.     

Stimuli-responsive of magnetic metal-organic frameworks (MMOF): Synthesis,dispersion control,and its tunability into polymer matrix under the augmented-magnetic field for H2 separation and CO2 capturing applications

Single-crystal magnetic-responsive core-shell MOF by grafting Fe₃O₄ nanoparticles onto the UiO-66-NH₂ and their controlled embedding into gas separation mixed matrix membranes was reported. Obtained results confirmed the stimuli-responsive character of the MMOF during their dispersion of MMOF in a well-defined arrays structure in the PMMA matrix. Contrarily, an absence of a magnetic field results in the MMOF aggregation and sedimentation of the particles at the bottom of the membrane. Compared to the non-controlled ones, gas permeability increased by 26.2% for CO₂ and 76.67% for H_2, and selectivity increased 2.95 and 1.49 times for the CO₂/N₂ and H₂/CO₂ gas pairs, respectively. Moreover, obtained permeability-selectivity values for the H₂/CO₂ gas pairs overcome the appropriate modified 2008 Robeson upper bound.     

Metal (oxide) modified (M= Pd,Ag, Au and Cu) H2SrTa2O7 for photocatalytic CO2 reduction with H2O: The effect of cocatalysts on promoting activity toward CO and H2 evolution

Ag, Pd, Au, Cu₂O as cocatalysts were loaded on the layered H₂SrTa₂O₇ (HST) for photocatalytic CO₂ reduction with H₂O. The characterization revealed that cocatalysts loaded on the surface of HST can effectively promote the separation of photogenerated electrons and holes due to the formation of Schottky barrier or p-n junction, thus enhancing photocatalytic activity. Of note, Ag, Pd, Au, Cu₂O loading exhibited obviously different performance on promoting photocatalytic activity of HST toward CO evolution and H₂ evolution because of the different overpotentials of CO evolution and H₂ evolution on loaded photocatalysts. Cocatalysts with low overpotentials of CO or H₂ evolution act as active sites for CO or H₂ evolution, thus controlling the selectivity toward CO or H₂. The Au/HST exhibited high activity for only H₂ evolution (17.5 μmol g⁻¹ h⁻¹) due to relative low overpotential for H₂ evolution (0.67 V) while the Cu₂O/HST exhibited high activity only for CO evolution (0.23 μmol g⁻¹ h⁻¹) due to relative low overpotential for CO evolution (0.40 V). The Pd/HST sample exhibits high photocatalytic activity for both CO and H₂ evolution rates due to the low overpotential for CO and H₂ evolution, reaching 4.0 and 4.7 times of bare HST, respectively. This work here gives an in-depth understanding of the effect of cocatalysts on promoting photocatalytic activity and selectivity and can also give guidance to design photocatalysts with high activity and selectivity for photocatalytic CO₂ reduction with H₂O.     

Accelerated transfer and separation of charge carriers during the photocatalytic production of hydrogen over Au/ZrO2–TiO2 structures by interfacial energy states

Energy states and surface plasmon resonance (SPR) play an important role in photocatalytic processes and power generation energy, for they improve the separation, transport, and mobility of charge carriers. The creation of Au/semiconductor heterostructures with different amounts of Au forms energy states that can modulate surface plasmon excitation, interfacial charge transport and photocatalytic activity to generate hydrogen. However, the Au loading effect on the interfacial charge transport and photocatalysis of plasmonic Au/semiconductors is unclear. For this reason, in this study, Au/ZrO₂–TiO₂ materials with different Au loadings were synthesized and evaluated in the photocatalytic production of hydrogen. The results confirmed boosted photoactivity with increased gold loading up to 5 wt.%, obtaining four times more hydrogen production than with the base material. The (photo) electrochemical measurements revealed that the Au inclusion provoked the adjustment of Fermi level values associated with the variation of surface energy states at the Au/ZrO₂–TiO₂ interface, which can be related to the modulation of SPR. This phenomenon can be explained by two simultaneous effects: i) the creation of energy states at the Au/ZrO₂–TiO₂ interface that modify the Fermi level to more negative potentials with respect to the base material, in order to have photogenerated electrons with higher reducing power to catalyze the hydrogen production; and ii) the Au metallic nanoparticles with SPR act as electronic reservoirs that extend the life time of photogenerated electron-hole pairs, thus enhancing the separation of charge carriers and the mobility of photogenerated electrons.     

A ternary Ag/TiO2/CNT photoanode for efficient photoelectrochemical water splitting under visible light irradiation

A ternary Ag/TiO₂/CNT photoanode was prepared by grafting Ag nanoparticles on the surface of as-synthesized TiO₂/CNT nanocomposite for the photoelectrochemical (PEC) water splitting under visible light irradiance. The ternary composite photoanode was observed to generate four times higher photocurrent density compared to binary TiO₂/CNT nanocomposite under visible light irradiance. The Ag nanoparticles on the surface of nanocomposite act as a surface plasmon resonance (SPR) photosensitizer under visible light. The enhanced photocurrent density of Ag/TiO₂/CNT ternary photoanode is attributed to the increased light absorption in the visible region, decrease in band-bending and effective interfacial electron transfer due to the synergetic effect of Ag nanoparticles and CNTs. The enhanced charge transfer within the Ag/TiO₂/CNT was also confirmed by the electrochemical impedance spectroscopy. This work demonstrates a feasible route to improve the PEC performance of TiO₂ towards water splitting under sunlight irradiation.     

Enhanced visible light photocatalytic hydrogen evolution of Ta2O5 nanohoneycomb induced by plasmonic Au nanoparticle array

Polystyrene nanospheres in the sizes of 400, 200, and 100 nm were employed as a template to form hexagonal close-packed Ta₂O₅ nanohoneycombs (nHCs) by means of solution-based nanosphere lithography. Moreover, Au nanoparticle arrays with various diameters were further deposited on the Ta₂O₅ nHCs to achieve surface plasmon resonance (SPR) and enhance visible-light photocatalytic hydrogen evolution. Finite difference time domain (FDTD) simulation was performed and the result showed that the 100-nm Ta₂O₅ nHCs coupled with smaller Au nanoparticles exhibited more effective localized SPR effect to enclose the Ta₂O₅ photocatalyst. The photocatalytic hydrogen evolution results were consistent with those of FDTD simulation and photoelectrochemical tests. A concept of effective yield ratio is proposed to explain how the Au nanoparticle size and spacing affect the hydrogen evolution efficiency.     

Facile and green synthesis of titanate nanotube/graphene nanocomposites for photocatalytic H2 generation from water

A facile and green one-step method was used to prepare titanate nanotube/graphene (TNT/GR) photocatalysts via an alkaline hydrothermal process. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence emission spectroscopy. The photocatalytic performance was evaluated by H₂ generation from water splitting under Xe-lamp illumination. A significantly enhanced photocatalytic activity for H₂ evolution (12.1 μmol/h) was obtained over the compostion-optimized TNT/GR composite (with 1.0 wt% GR), two times higher than that of pure TNT (4.0 μmol/h). During hydrothermal reaction, the reduction of graphene oxide (GO) into GR without using any reducing agents and the formation of 1-D TNT were achieved simultaneously, which resulted in the direct growth of well-defined TNTs uniformly distributed on GR substrates.     

Construction of Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture for visible-light-driven hydrogen production

In this paper, a novel Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture has been successfully constructed by integrating Au/g-C₃N₄ plasmonic photocatalyst composite with 3D ZnIn₂S₄ nanosheet through a simple hydrothermal process. The Au nanoparticles were firstly anchored on the surface of pristine g-C₃N₄ material to get Au/g-C₃N₄ plasmonic photocatalyst. Ascribing to the surface plasmon resonance of Au nanoparticles, the obtained Au/g-C₃N₄ plasmonic photocatalyst shows a significant improved photocatalytic activity toward hydrogen production from water with visible light response comparing with pristine g-C₃N₄. Further combining Au/g-C₃N₄ plasmonic photocatalyst with 3D ZnIn₂S₄ nanosheet to construct a heterojunction composite. Owing to the synergistic effect of the surface plasmon resonance of Au nanoparticles in Au/g-C₃N₄ and the heterojunction structure in the interface of Au/g-C₃N₄ and ZnIn₂S₄, the prepared Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite shows an excellent photocatalytic activity toward hydrogen production from water with visible light response, which is around 7.0 and 6.3 times higher than that of the pristine C₃N₄ and Znln₂S₄ nanosheet, respectively. The present work might provide some insights for exploring other efficient heterojunction photocatalysts with excellent properties.     

Controllable proton and CO2 photoreduction over Cu2O with various morphologies

Simultaneous photocatalytic reduction of water to H₂ and CO₂ to CO was observed over Cu₂O photocatalyst under both full arc and visible light irradiation (>420 nm). It was found that the photocatalytic reduction preference shifts from H₂ (water splitting) to CO (CO₂ reduction) by controlling the exposed facets of Cu₂O. More interestingly, the low index facets of Cu₂O exhibit higher activity for CO₂ photoreduction than high index facets, which is different from the widely-reported in which the facets with high Miller indices would show higher photoactivity. Improved CO conversion yield could be further achieved by coupling the Cu₂O with RuO_x to form a heterojunction which slows down fast charge recombination and relatively stabilises the Cu₂O photocatalyst. The RuO_x amount was also optimised to maximise the junction's photoactivity.     

Photocatalytic activity of Ag–TiO2-graphene ternary nanocomposites and application in hydrogen evolution by water splitting

TiO₂-graphene (P25-GR, PG) nanocomposite was fabricated with P25 and graphite oxide through a hydrothermal method, and then Ag nanoparticles (Ag NPs) was assembled in P25-GR (Ag-P25-GR, APG) under microwave-assisted chemical reduction. The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis) and Raman spectrum, respectively. The results showed that Ag NPs were well dispersed on the surface of PG with metallic state. The ternary Ag-P25-GR (APG) nanocomposites possessed the extended light absorption range and more efficient charge separation properties compared to binary P25-GR (PG). Methylene blue photodegradation experiment proved that surface plasmon resonance (SPR) phenomenon had an effect on photoreaction efficiency. The corresponding hydrogen evolution rate of APG prepared with 0.002 M AgNO₃ solution was 7.6 times than pure P25 and 2.7 times than PG in the test condition. The improved photocatalytic performance can be attributed to the presence of GR and SPR effect, leading to the longer lifetime of photo-generated electron–hole pairs and faster interfacial charge transfer rate. This work indicates that the photoactivity of ternary GR-based nanocomposites is superior to the binary one. We expected our work could give a new train of thought on exploration of GR-based nanocomposites.     

The one-pot synthesis of a ZnSe/ZnS photocatalyst for H2 evolution and microbial bioproduction

Low-cost photocatalysts are being developed for the conversion of visible light into H₂ and to drive CO₂ reduction. Hybrid photosynthesis is a promising approach to convert CO₂ and visible light into multicarbon compounds where a photocatalyst energizes the metabolism of an autotrophic microbe. Here, a heterostructure ZnSe/ZnS photocatalyst was synthesized by a simple one-pot method and evaluated for photocatalytic H₂ evolution (PHE) as well as for hybrid photosynthesis with the bioplastic-producing bacterium Ralstonia eutropha. ZnSe/ZnS nanoparticles exhibited a PHE 5.5 times higher than pure ZnSe. Photoluminescence and photoelectrochemical characterization of ZnSe/ZnS demonstrated more efficient charge separation probably caused by ZnS defects. Furthermore, ZnSe/ZnS improved 1.3 times bioplastic production from CO₂ by R. eutropha, which was not the case for pure ZnSe. These results show ZnSe/ZnS potential for both PHE as well as hybrid photosynthesis and provide insights on the photocatalytic reaction mechanisms involved when the two Zn-based materials are combined.     

Photocatalytic decomposition of formic acid and methyl formate on TiO2 doped with N and promoted with Au. Production of H2

The photo-induced vapor-phase decompositions of formic acid and methyl formate were investigated on pure, N-doped and Au-promoted TiO₂. Infrared (IR) spectroscopic studies revealed that illumination initiated the decomposition of adsorbed formate formed in the dissociation of formic acid and located mainly on TiO₂. The photocatalytic decompositions of formic acid and methyl formate vapor on pure TiO₂ occurred to only a limited extent. The deposition of Au on pure or doped TiO₂ markedly enhanced the extent of photocatalytic decomposition of formic acid. The main process was dehydrogenation to give H₂ and CO₂. The formation of CO occurred to only a very small extent. Addition of O₂ or H₂O to the formic acid decreased the CO level from ∼0.8% to ∼0.088%. Similar features were experienced in the photocatalytic decomposition of methyl formate, which dissociated in part to give surface formate. Experiments over Au deposited on N-doped TiO₂ revealed that the photo-induced decomposition of both compounds occurs even in visible light.