Photoreduction of Aqueous Protons Coupling with Alcohol Oxidation on a S-Scheme Heterojunction Photocatalyst MnO/Carbon Nitride.

Crystalline carbon nitride (CCN), derived from amorphous polymeric CN, is considered as a new generation of metal-free photocatalyst because of its high crystallinity. In order to further promote the photocatalytic performance of CCN, p-type MnO nanoparticles are in situ synthesized and merged with n-type CCN through a one-pot process to form p-n heterojunction. The formed interfacial electric field between the semiconductors with different work functions efficiently breaks the coulomb interaction between MnO and CCN. The prepared catalysts exhibit drastically increased photocatalytic hydrogen evolution (PHE) activity integrated with oxidation of alkyl and aryl alcohols under irradiation of visible light. In the aqueous solution of benzyl alcohol (BzOH), the hydrogen generation rate over MnO/CCN (39.58 µmol h-1) is nearly 7 times and 37 times that of pure CCN (5.76 µmol h-1) and CN (1.06 µmol h-1), respectively, combining with oxidation of BzOH to benzaldehyde. This work proposes an avenue for in situ construction of a novel 2D material-based S-scheme heterojunction and extends its application in solar energy conservation and utilization.

Bifunctionalization of carbon nitride by incorporation of thiophene ring and polar nickel complex to promote photocatalytic activity for hydrogen evolution.

Photocatalytic performance of polymeric carbon nitride (CN) is primarily restricted by limited light utilization and poor charge separation efficiency. To this end, skeleton modification strategy was adopted by attaching thiophene ring and polar nickel complex (NiL) onto CN. The obtained bifunctionalized carbon nitride (TCN-NiL) displayed obviously elevated optical absorption and photoexcited charge separation efficiency. The NiL, with polar structure, plays as active sites like cocatalyst thus exhibited platinum-like H2 evolution activity from water splitting under visible light. The optimized photocatalytic H2 generation rate over TCN-NiL reached 136.7 µmol·h-1 without any cocatalyst, the highest rate reported so far in noble-metal-free CN-based catalysts, which is 5 times of that of CN loaded with 3 wt% Pt. Additionally, the maximum wavelength of performing H2 production capacity over TCN-NiL extends to 550 nm from 450 nm of CN, suggesting an excellent visible light absorption ability. This work provides a way for modifying CN to enhance the photocatalytic activities in a noble metal free system.

Anchoring nickel complex to g-C3N4 enables an efficient photocatalytic hydrogen evolution reaction through ligand-to-metal charge transfer mechanism.

The development of stable and efficient non-noble metal-based photocatalysts for water splitting is currently a key but challenging process for effective conversion and storage of sustainable energy. Here, we designed a new non-noble metal composite photocatalyst by covalently connecting nickel molecular ligand (NiL) to the graphitized carbon nitride (CN) framework for photocatalytic hydrogen evolution under visible light irradiation. Compared to CN, NiL-modified CN (NiL/CN) shows excellent photogenerated carrier migration rate. Without Pt as a co-catalyst, NiL/CN exhibits high photocatalytic activity (23.4 µmol h-1) with high stability. Experiments and theoretical calculations disclose that ligand-metal charge transfer (LMCT) mechanism plays a key role on the enhancement of photocatalytic activity. This work provides a promising method for future designing low-cost, high-performance photocatalysts for hydrogen production under solar light.

Photocatalytic hydrogen evolution over a nickel complex anchoring to thiophene embedded g-C3N4.

Evolution of hydrogen from water by utilizing solar energy and photocatalysts is one of the most promising ways to solve energy crisis. However, designing a cost-effective and stable photocatalyst without any noble metals is of vital importance for this process. Herein, an extremely active molecular complex cocatalyst NiL2(Cl)2 is successfully designed. After being covalently linked to thiophene-embedded polymeric carbon nitride (TPCN), the hybrid catalyst NiL2(Cl)2/TPCN exhibits extraordinary H2 production activity of 95.8 µmol h-1 without Pt (λ ≥ 420 nm), together with a remarkable apparent quantum yield of 6.68% at 450 nm. In such a composite catalyst, the embedded π-electron-rich thiophene-ring not only extends the π-conjugated system to enhance visible light absorption, but also promotes the charge separation through electron-withdrawing effect. It turns out that the CN covalent bonds formed between NiL2(Cl)2 and TPCN skeleton accelerate the transfer of electrons to the Ni active sites. Our finding reveals that the strategy of embedding π-electron-rich compounds to graphitic carbon nitride provides potentials to develop excellent photocatalysts. The strong covalent combination of molecular complexes cocatalyst onto organic semiconductors represents an important step towards designing noble-metal-free photocatalysts with superior activity and high stability for visible light driven hydrogen evolution.

Nickel complex co-catalyst confined by chitosan onto graphitic carbon nitride for efficient H2 evolution.

Developing earth-abundant H2-production heterogeneous photocatalysts with robust activity and stability has attracted great interests. Herein, a low-cost photocatalyst was prepared by binding nickel complex covalently from primary amines of chitosan (NiL) onto photosensitive carbon nitride nanosheets (CN) through electrostatic interaction. Introduction of NiL results in more efficient utilization of solar energy, photogenerated electrons' direct transfer and lower overpotential for water reduction. The optimized NiL3-CN photocatalyst shows the highest H2 evolution rate of 346 µmol g-1 h-1 under visible light irradiation and exhibits high stability during test. This work presents great potentials for sustainable conversion of solar energy, and sheds positive light on the development of heterogeneous photocatalysts via anchoring H2-evolving molecule catalysts confined by inexpensive macromolecules onto a semiconductor photosensitizer through a facile and valid method.

Boosting photocatalytic hydrogen evolution rate over carbon nitride through tuning its crystallinity and its nitrogen composition.

The photocatalytic activity of graphitic carbon nitride (CN) is mainly restricted by its high recombination rate of charge carriers and narrow visible light absorption. In the present work, nitrogen-deficient CN (NDCCN) nanosheets with high crystallinity were synthesized using molten salt (NaLiCO3) as an etching agent and high-temperature solvent. The electronic structure and energy band levels of the obtained NDCCN are optimized to extend its optical absorption and enhance separation efficiency of photo-generated charge carriers. With these changes, NDCCN displays high photocatalytic activity for hydrogen evolution under visible light illumination (111 µmol h-1), which is 4.6 times of that over pristine CN. This finding opens up a new window to simultaneously decrease nitrogen composition and increase crystallinity of carbon nitride for higher solar-light-driven hydrogen production efficiency.

Noble Metal-Free Photocatalysts Consisting of Graphitic Carbon Nitride, Nickel Complex, and Nickel Oxide Nanoparticles for Efficient Hydrogen Generation.

A facile and simple synthetic route is developed to prepare earth-abundant and noble metal-free hybrid photocatalysts, which are composed of graphitic carbon nitride (CN), nickel complex, and NiO x nanoparticles. Bimolecular nucleophilic substitution reaction was employed to attach a nickel complex onto a graphitic CN framework through covalent bonds to support its high loading and dispersion. NiO x nanoparticles were further incorporated into the catalysts to serve as a hole-transporting medium to improve the separation of photogenerated carriers for higher photocatalytic activity. Both yNiL/CN and yNiL/NiO x/CN exhibit superb H2 evolution activity. The optimum H2 evolution rate of the binary photocatalysts yNiL/CN reaches 303.3 µmol·h-1·g-1, whereas that of the ternary photocatalysts yNiL/NiO x/CN reaches 524.1 µmol·h-1·g-1, and the apparent quantum efficiency reaches 1.46% at 450 nm. This finding reveals that coordination of a nickel complex is significant in promoting photocatalytic performance, and the incorporation of NiO x nanoparticles as a hole-transporting medium is beneficial for separation of the photogenerated charge carriers. The novel hybrid system offers a new horizon for designing transition-metal complex-modified graphitic CN as noble metal-free and highly active photocatalysts for efficient visible light-driven hydrogen generation.

Triamterene-Grafted Graphitic Carbon Nitride with Electronic Potential Redistribution for Efficient Photocatalytic Hydrogen Evolution.

In this study, a photocatalyst with a distorted skeleton and synthesized by grafting triamterene onto graphitic carbon nitride (g-C3 N4 ) frameworks was prepared. The pteridine ring of the triamterene-based nitrogen-enriched organic structure functions as a trapped electron site owing to its inductive effect. The benzene ring in triamterene plays an important role in the even dispersion of electrons by a conjugative effect. Redistribution of the intramolecular electronic potential is caused by a synergistic effect between the pteridine and benzene rings of triamterene and promotes separation and migration of the photoinduced charge carriers. After coupling with triamterene, the π electrons of g-C3 N4 are relocated; that is, the intrinsic electronic and band structures of g-C3 N4 are effectively modulated. The modified polymeric photocatalyst shows a high photocatalytic H2 evolution rate of 157.5 µmol h-1 , a value that is 4.3 times higher than the H2 evolution rate of pristine g-C3 N4 (36.8 µmol h-1 ), with an apparent quantum efficiency of 9.7 % at λ=450 nm. The incorporation of triamterene into the g-C3 N4 frameworks significantly expands its π-delocalized system by redistribution of the electronic potential, expands the visible-light absorption range, and effectively promotes the separation and migration of photoinduced charge carriers. This strategy may provide a reference for promoting charge separation of g-C3 N4 through redistribution of the electronic potential and for synthesizing novel carbon nitride based semiconductors for efficient solar energy conversion into hydrogen.

Carbon nanotubes-modified graphitic carbon nitride photocatalysts with synergistic effect of nickel(II) sulfide and molybdenum(II) disulfide co-catalysts for more efficient H2 evolution.

This work reports effective photocatalysts which are composed of carbon nitride (CN), carbon nanotubes (CNTs), MoS2 and NiS, for hydrogen evolution aiming at energy crises and environmental pollutions. The morphologies and optical properties of the photocatalysts were carefully characterized and their photocatalytic performance towards water reduction was studied afterwards. MoS2 and NiS exhibit a significant synergistic effect working as co-catalysts. Compared to MoS2/CN nanohybrid, carbon nanotubes and NiS improved the absorption of visible light and the separation of charge carriers effectively. NiS-MoS2/CNTs/CN catalyst exhibits high performance for H2 evolution and the optimized rate is 309.9 µmol·h-1·g-1 with no noble metals under visible light irradiation. The study demonstrates a non-noble metal photocatalyst system for effective generation of hydrogen with low cost.

Creating Graphitic Carbon Nitride Based Donor-π-Acceptor-π-Donor Structured Catalysts for Highly Photocatalytic Hydrogen Evolution.

Conjugated polymers with tailored donor-acceptor units have recently attracted considerable attention in organic photovoltaic devices due to the controlled optical bandgap and retained favorable separation of charge carriers. Inspired by these advantages, an effective strategy is presented to solve the main obstructions of graphitic carbon nitride (g-C3 N4 ) photocatalyst for solar energy conversion, that is, inefficient visible light response and insufficient separation of photogenerated electrons and holes. Donor-π-acceptor-π-donor polymers are prepared by incorporating 4,4'-(benzoc 1,2,5 thiadiazole-4,7-diyl) dianiline (BD) into the g-C3 N4 framework (UCN-BD). Benefiting from the visible light band tail caused by the extended π conjugation, UCN-BD possesses expanded visible light absorption range. More importantly, the BD monomer also acts as an electron acceptor, which endows UCN-BD with a high degree of intramolecular charge transfer. With this unique molecular structure, the optimized UCN-BD sample exhibits a superior performance for photocatalytic hydrogen evolution upon visible light illumination (3428 µmol h-1 g-1 ), which is nearly six times of that of the pristine g-C3 N4 . In addition, the photocatalytic property remains stable for six cycles in 3 d. This work provides an insight into the synthesis of g-C3 N4 -based D-π-A-π-D systems with highly visible light response and long lifetime of intramolecular charge carriers for solar fuel production.

Enhancing visible light photocatalytic activity of nitrogen-deficient g-C3N4 via thermal polymerization of acetic acid-treated melamine.

Nitrogen-deficient graphitic carbon nitride (CN-HAc) was synthesized by thermal condensation of acetic acid-treated melamine as a precursor. The nitrogen vacancies play a remarkable role on controlling the electronic structure of g-C3N4, such as extending the optical absorption and enhancing the separation efficiency of photogenerated charge carriers, resulting in the improvement of photocatalytic activity. The photocatalytic activity of the catalysts was evaluated by splitting water and degradation of rhodamine B (RhB) under visible light irradiation (λ>420nm). The average H2 evolution rate on CN-HAc is 24µmolh-1, which is about 5 times of that on pristine g-C3N4. Meanwhile, CN-HAc exhibits superior photocatalytic mineralization of RhB. The possible formation mechanism of nitrogen-deficient in the framework of g-C3N4 is proposed.

Carbonyl-Grafted g-C3 N4 Porous Nanosheets for Efficient Photocatalytic Hydrogen Evolution.

Carbonyl-grafted g-C3 N4 porous nanosheets (COCNPNS) were fabricated by means of a two-step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine-oxalic acid supramolecule as a precursor is key to synthesizing carbonyl-grafted g-C3 N4 . The bulk carbonyl-grafted g-C3 N4 (COCN) was further thermally etched onto porous nanosheets by O2 under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible-light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light-harvesting capability, under visible-light illumination (λ>420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 µmol h-1 , which is 26 times that of the p-CN obtained directly from thermal polycondensation of melamine.

High and stable photoelectrochemical activity of ZnO/ZnSe/CdSe/Cu(x)S core-shell nanowire arrays: nanoporous surface with Cu(x)S as a hole mediator.

Advanced materials for electrocatalytic and photoelectrochemical water splitting are key for taking advantage of renewable energy. In this study, ZnO/ZnSe/CdSe/Cu(x)S core-shell nanowire arrays with a nanoporous surface were fabricated via ion exchange and successive ionic layer adsorption and reaction (SILAR) processes. The ZnO/ZnSe/CdSe/Cu(x)S sample displays a high photocurrent density of 12.0 mA cm(-2) under AM 1.5G illumination, achieves the highest IPCE value of 89.5% at 500 nm at a bias potential of 0.2 V versus Ag/AgCl, and exhibits greatly improved photostability. The functions of the ZnSe, CdSe, and Cu(x)S layers in the ZnO/ZnSe/CdSe/Cu(x)S heterostructure were clarified. ZnSe is used as a passivation layer to reduce the trapping and recombination of charge carriers at the interfaces of the semiconductors. CdSe functions as a highly efficient visible light absorber and builds heterojunctions with the other components to improve the separation and transportation of the photoinduced electrons and holes. Cu(x)S serves as a passivation layer and an effective p-type hole mediator, which passivates the defects and surface states of the semiconductors and forms p-n junctions with CdSe to promote the hole transportation at the semiconductor-electrolyte interface. The nanoporous surface of the ZnO/ZnSe/CdSe/Cu(x)S core-shell nanowire arrays, together with the tunnel transportation of the charge carriers in the thin films of ZnSe and CdSe, also facilitates the kinetics of photoelectrochemical reactions and improves the optical absorption as well.

Construction of ZnO/ZnS/CdS/CuInS2 core-shell nanowire arrays via ion exchange: p-n junction photoanode with enhanced photoelectrochemical activity under visible light.

ZnO/ZnS/CdS/CuInS2 core-shell nanowire arrays with enhanced photoelectrochemical activity under visible light were successfully prepared via ion exchange and hydrothermal methods. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis absorption, X-ray photoemission spectroscopy, and photoelectrochemical response. As a p-n junction photoanode, ZnO/ZnS/CdS/CuInS2 heterostructure shows much higher visible light photoelectrocatalytic activity toward water splitting than ZnO/ZnS/CdS and ZnO/ZnS films. The ZnO/ZnS/CdS/CuInS2 film with optimal constitution exhibits the highest photocurrent of 10.5 mA/cm(2) and the highest IPCE of approximately 57.7% at 480 nm and a bias potential of 0 V versus Ag/AgCl. The critical roles of CdS and ZnS in ZnO/ZnS/CdS/CuInS2 heterostructure were investigated. ZnS, as a passivation layer, suppresses the recombination of the photogenerated charge carriers at the interface of the oxide and CuInS2. CdS enhances the absorption of visible light and forms p-n junctions with CuInS2, which promotes the transport of charge carriers and retards the recombination of electrons and holes in CuInS2 to improve the photoelectrochemical performance of ZnO/ZnS/CdS/CuInS2 heterostructure.

Inlay of Bi2O2CO3 nanoparticles onto Bi2WO6 nanosheets to build heterostructured photocatalysts.

Surface-dispersive-type Bi2O2CO3/Bi2WO6 heterostructured nanosheets were successfully prepared via anion exchange in a hydrothermal process with the graphitic carbon nitride (g-C3N4) as a precursor of CO3(2-). The Bi2O2CO3 nanoparticles (with diameters about 5 nm) were highly homogeneously dispersed and inlaid in the single-crystalline Bi2WO6 nanosheets. The composites with intimate interfacial contacts between Bi2O2CO3 and Bi2WO6 exhibited superior visible light photocatalytic activity towards the degradation of rhodamine B (RhB). The composite nanosheets containing 7.86 wt% Bi2O2CO3 showed the best performance and the degradation rate of RhB was 6 times faster than that with the bare Bi2WO6. The dramatic enhancement of the photocatalytic activity of the Bi2O2CO3/Bi2WO6 photocatalysts can be attributed to the hetero-interfaces between Bi2O2CO3 and Bi2WO6, their intrinsically layered structure, two-dimensional morphology and the effective separation of the photoinduced carriers at the interfaces and in the semiconductors. This method can be used to design and prepare other Aurivillius heterostructured semiconductors for efficient light harvesting and energy conversion applications.

Wide bandgap Bi2O2CO3-coupled Bi2MoO6 heterostructured hollow microspheres: one-pot synthesis and enhanced visible-light photocatalytic activity.

Hierarchical Bi2O2CO3/Bi2MoO6 heterostructured photocatalysts composed of nanoplatelets of Bi2O2CO3 and Bi2MoO6 were successfully prepared by a facile template-free solvothermal process. The microsphere-like Bi2O2CO3/Bi2MoO6 composites exhibited superior visible light photocatalytic activity towards degradation of rhodamine B. The highest degradation efficiency was observed on the material with the Bi/Mo molar ratio of 2.88/1, which can degrade 99% rhodamine B within 90 min, while only 44% rhodamine B was degraded over the pure Bi2MoO6 microspheres and 2% over the Bi2O2CO3 nanoplatelets. The dramatic enhancement in their photocatalytic performance of the Bi2O2CO3/Bi2MoO6 photocatalysts can be attributed to the high surface area and the effective separation of the photoinduced carriers at the interfaces and in the semiconductors. The photo-generated h+(VB) in the Bi2O2CO3/Bi2MoO6 photocatalysts turn out to be the dominant active species in the photocatalytic reaction. Importantly, Bi2O2CO3/Bi2MoO6 displayed visible-light photocatalytic activity for the destruction of E. coli (the percent kill is 99.09 in 60 min). In addition, the Bi2O2CO3/Bi2MoO6 composite was very stable during the reaction and can be used repeatedly. These features mean the present heterostructured photocatalyst can be applied in environmental remediation, and waste water disinfection.

Electrodeposition of polyaniline onto TiO2 nanoparticles/multiwalled carbon nanotubes for visible light photoelectrocatalysis.

In this study, polyaniline (PANI) was coated onto TiO2 nanoparticles/multiwalled carbon nanotubes (TiO2/MWCNTs) hybrid by electrochemical polymerization. Modification of TiO2/MWCNTs with PANI endows the resulted hybrid with visible light activity. The PANI/TiO2/MWCNTs hybrid shows remarkable photoelectrocatalytic activity for the degradation of RhB under visible light irradiation. The enhanced photocatalytic activity of the PANI/TiO2/MWCNTs hybrid originates from the effective charge transfer properties of the heterojunctions of PANI-TiO2 and TiO2-MWCNTs. The efficient charge transportation and high photoelectrocatalytic activity towards degradation of rhodamine B make this novel hybrid material promising for photocatalysis and for the development of photoelectrical devices.

Hydrothermal synthesis of Fe-doped NiO nanoplatelets with enhanced sensing property.

Ni(1-x)Fe(x)O (x = 0-0.05) nanoplatelets were synthesized by a facile hydrothermal process. The crystal structure and morphology of the samples were characterized by X-ray diffraction and field emission scanning electron microscopy. The incorporation and the valence state of Fe in NiO nanoplatelets were determined by X-ray photoelectron spectroscopy. Doping NiO nanoplatelets by Fe greatly improves their sensing performance. The Ni0.97Fe0.03O sensor showed the highest response up to 59.5 to 100 ppm ethanol at 280 degrees C, which is a 28.2-fold increase compared to the pure NiO nanoplatelets. The incorporation of Fe3+ into the lattice of NiO results in the decrease of the effective hole concentrations, which plays a key role for the enhancement of the sensing properties. Fe-dopant can be a promising substitute for the noble metal additives to fabricate gas sensors with much lower cost. Finally, the gas sensing mechanism was discussed.

Preparation and antibacterial property of waterborne polyurethane/Zn-Al layered double hydroxides/ZnO nanocomposites.

In this work, a novel environmental-friendly waterborne polyurethane/ZnAl-layered double hydroxides/ZnO nanoparticles composite (WPU/ZnAl-LDHs/ZnO) was synthesized via in-situ polymerization. ZnAl-LDHs and ZnAl-LDHs/ZnO were synthesized by refluxing in an oil bath. In order to disperse ZnAl-LDHs/ZnO homogeneously into WPU matrix, ZnAl-LDHs/ZnO was firstly functionalized by isophorone diisocyanate. The incorporated content of ZnAl-LDHs/ZnO in the composite has profound effect on such physical properties as mechanical strength, thermal stability and water swelling. It is demonstrated that appropriate amount of ZnAl-LDHs/ZnO with good dispersion in the WPU matrix significantly improves the physical performance of the composites. Finally, the antibacterial activity of the composite was tested against G(-) Escherichia coli and G(+) Staphylococcus aureus. The results indicate that WPU incorporated with ZnAl-LDHs/ZnO shows strong antibacterial activity upon contact.