A p-n Junction by Coupling Amine-Enriched Brookite-TiO2 Nanorods with CuxS Nanoparticles for Improved Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction is a promising technology for reaching the aim of "carbon peaking and carbon neutrality", and it is crucial to design efficient photocatalysts with a rational surface and interface tailoring. Considering that amine modification on the surface of the photocatalyst could offer a favorable impact on the adsorption and activation of CO2, in this work, amine-modified brookite TiO2 nanorods (NH2-B-TiO2) coupled with CuxS (NH2-B-TiO2-CuxS) were effectively fabricated via a facile refluxing method. The formation of a p-n junction at the interface between the NH2-B-TiO2 and the CuxS could facilitate the separation and transfer of photogenerated carriers. Consequently, under light irradiation for 4 h, when the CuxS content is 16%, the maximum performance for conversion of CO2 to CH4 reaches at a rate of 3.34 µmol g-1 h-1 in the NH2-B-TiO2-CuxS composite, which is approximately 4 times greater than that of pure NH2-B-TiO2. It is hoped that this work could deliver an approach to construct an amine-enriched p-n junction for efficient CO2 photoreduction.

Co-embedding oxygen vacancy and copper particles into titanium-based oxides (TiO2, BaTiO3, and SrTiO3) nanoassembly for enhanced CO2 photoreduction through surface/interface synergy.

Photocatalytic CO2 reduction into valuable fuel and chemical production has been regarded as a prospective strategy for tackling with the issues of the increasing of greenhouse gases and shortage of sustainable energy. A composite photocatalysis system employing a semiconductor enriched with oxygen vacancy and coupled with metallic cocatalyst can facilitate charge separation and transfer electrons. In this work, mesoporous TiO2 and titanium-based perovskite oxides (BaTiO3 and SrTiO3) nanoparticle assembly incorporated with abundant oxygen vacancy and copper particles have been successfully synthesized for CO2 photoreduction. As an example, the TiO2 decorated with different amounts of Cu particles has an impact on photocatalytic CO2 reduction into CH4 and CO. Particularly, the optimal TiO2/Cu-0.1 exhibits nearly 13.5 times higher CH4 yield (22.27 µmol g-1 h-1) than that of pristine TiO2 (1.65 µmol g-1 h-1). The as-obtained BaTiO3/Cu-0.1 and SrTiO3/Cu-0.1 also show enhanced CH4 yields towards photocatalytic CO2 reduction compared with pristine ones. Based on the temperature programmed desorption (TPD) and photo/electrochemical measurements, the co-embedding of Cu particles and abundant oxygen vacancy into the titanium-based oxides could promote CO2 adsorption capacity as well as separation and transfer of photoinduced electron-hole pairs, and finally result in efficient CO2 photoreduction upon the TiO2/Cu, SrTiO3/Cu, and BaTiO3/Cu composites.

Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer.

Solar-driven photocatalytic H2 evolution could tackle the issue of fossil fuels-triggered greenhouse gas emission with sustainable clean energy. However, splitting water into hydrogen with high performance by a single semiconductor is challenging because of the poor charge separation efficiency. Herein, a novel ternary Cu@TiO2-Cu2O hybrid photocatalyst with multiple charge transfer channels has been designed for efficient solar-to-hydrogen evolution. Indeed, the ternary Cu@TiO2-Cu2O hybrid by coupling Cu@TiO2 with Cu2O nanoparticles shows highly-efficient photocatalytic hydrogen generation with rate of 12000.6 µmol·g-1·h-1, which is 4.4, 2.1, and 1.9 times higher than the pure TiO2 (2728.8 µmol·g-1·h-1), binary Cu@TiO2 (5595.5 µmol·g-1·h-1), and TiO2-Cu2O (6076.8 µmol·g-1·h-1) composite, respectively. In such a Cu@TiO2-Cu2O hybrid, the formed internal electric field in the TiO2-Cu2O p-n junction allows the electrons in Cu2O to migrate to TiO2, while the electrons in the CB of TiO2 could flow into Cu via the Schottky junction at the Cu@TiO2 interface. In this regard, a multiple charge transfer is achieved between the Cu@TiO2 and Cu2O, which facilitates promoted charge separation and results in the construction of electron-accumulated center (Cu) and hole-enriched surface (Cu2O). This p-n/Schottky junctions with steered charge transfer assists the hydrogen production upon the Cu@TiO2-Cu2O ternary photocatalyst.

Metallic Copper-Containing Composite Photocatalysts: Fundamental, Materials Design, and Photoredox Applications.

Semiconductor photocatalysis has long been regarded as a potential solution to tackle the energy and environmental challenges since the first discovery of water splitting by TiO2 almost 50 years ago. The past few years have seen a tremendous flurry of research interest in the modification of semiconductors because of their shortcomings in the aspects of solar harvesting, electron-hole pairs separation, and utilization of photogenerated carriers. Among the various strategies, the introduction of metallic copper into the photocatalysis system can not only enhance the absorption of sunlight and the separation efficiency of photogenerated electrons and holes, but also increase the adsorption ability of substrate and the number of active sites, so as to realize the high solar to chemical energy conversion efficiency. This review focuses on the rational design of copper-based composites and their applications in photoredox catalysis. First, the preparation methods of metallic copper-containing composites are discussed. Then, the applications of different types of copper-based composites in the photocatalytic removal of pollutants, splitting of water to hydrogen production, reduction of carbon dioxide, and conversion of organic matter are introduced. Finally, the opportunities and challenges in the design and synthesis of copper-based composites and their applications in the photocatalysis are prospected.

Facile polyol-triggered anatase-rutile heterophase TiO2-x nanoparticles for enhancing photocatalytic CO2 reduction.

Solar-driven CO2 photoreduction into fuels has great potential in addressing the environmental and energy crisis. Heterophase TiO2 has attracted increasing attention in photoenergy applications owing to its fascinating properties, but much more attention has been paid on photodegradation and photocatalytic water splitting than that of photocatalytic CO2 reduction. Herein, anatase-rutile heterophase TiO2 nanoparticles with oxygen vacancy (TiO2-x) were successfully synthesized by involving proper amounts of polyols (EG, DEG, TEG, etc.) into the reaction system. The heterophase TiO2-x nanoparticles could accelerate the electron-hole separation and exhibit superior photocatalytic activity for reducing CO2 into methane. This work offers an alternative approach to simply fabricate TiO2-x-based heterophase photocatalyst towards efficient CO2 photoreduction.

Cuprous ion (Cu+) doping induced surface/interface engineering for enhancing the CO2 photoreduction capability of W18O49 nanowires.

Solar-driven reduction of CO2 and H2O into fuels is a promising approach for addressing global warming and energy crisis. Herein, Cu+ doped W18O49 nanowires were prepared by a facile solvothermal method and applied in photocatalytic reduction of CO2. The composition and structure of pristine and Cu+ doped W18O49 samples have been characterized. It was found that the morphology of W18O49 nanowires was changed with increasing amounts of dopant. The photocatalytic CO2 reduction activity of W18O49 nanowires and the Cu+ doped W18O49 samples were evaluated using H2O as reducing agent. The strategy of Cu+ doping not only could affect the band edge position and the surface wettability, but also influenced separation of the photogenerated electron-hole pairs. It was found that Cu+ doping could introduce oxygen vacancy and change the conduction edge to a more negative position for W18O49 nanowires, which might be beneficial for the activation of CO2 and promote the following CO2 reduction. Furthermore, the higher separation efficiency of photogenerated electron-hole pairs with Cu+ doping could contribute to the CO2 photoreduction enhancement. In addition, the Cu+ doped W18O49 nanowires (Cu-W18O49-0.005) presented a relatively poor hydrophilic property, which might be beneficial for the adsorption of CO2 molecules and contribute to its superior photocatalytic CO2 reduction capability.

The synthesis of CB[8]/ZnO composites materials with enhanced photocatalytic activities.

Enhancing the separation of hole-electron pairs is one of the valid pathway to enhance the photocatalytic degradation performance of semiconductors. In this work, cucurbit[8]uril/zinc oxide (CB[8]/ZnO) composites were prepared. The structure, morphology, surface elements and optical properties of the composite are characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, thermogravimetric analysis, and specific surface area measurements. In the photocatalytic degradation of 500 mg/L reactive brilliant red X-3B and 400 mg/L reactive yellow X-RG solutions, the rate constant of the CB[8]/ZnO composite is six times that of pure ZnO. A possible photocatalytic degradation mechanism is proposed. Zn2+ ions chelate with the carbonyl group of CB[8] on the surface of CB[8]/ZnO. Under ultraviolet-visible light irradiation, the generated holes of ZnO are transferred to and trapped on the CB[8] units to facilitate the separation of electron-hole pairs, improving the photocatalytic performance of this system.

Promoting solar-to-hydrogen evolution on Schottky interface with mesoporous TiO2-Cu hybrid nanostructures.

Developing a highly efficient photocatalysis system based on a photocatalyst-cocatalyst host for the hydrogen evolution reaction has potential but is still challenging. Herein, we report enhanced splitting of water achieved by loading copper metal particles on mesoporous TiO2 microrods through involving of dual ligand agents into the reaction system. The composition, structure, and surface characteristics of the TiO2-Cu hybrid were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and nitrogen adsorption. The formation of a Schottky contact in the interface between the Cu metal and the n-type semiconductor TiO2 was confirmed experimentally by photo/electrochemical measurements. This Schottky junction, the TiO2-Cu hybrid photocatalyst, exhibited superior hydrogen evolution capability with rate of 6046 µmol g-1 h-1, which is 23 times higher than that of pristine TiO2 (260 µmol g-1 h-1). The experimental results demonstrated that efficient separation and transfer of photo-induced electron-hole pairs greatly contributed to the enhanced photocatalytic H2 evolution. The Schottky contact between Cu and TiO2 as well as cocatalyst characteristic of Cu play significant roles in preventing the recombination of electron-hole pairs and enhancing water splitting to form hydrogen. This study demonstrates a rational design to construct Schottky contacts in metal-semiconductor junctions to significantly boost their photocatalytic capacity.

Efficient removal of heavy metal ions and organic dyes with cucurbit [8] uril-functionalized chitosan.

The development of a high-efficiency adsorption material is important for the simultaneous elimination of heavy metal ions and organic pollutants from wastewater. In the present work, a novel material was synthesized by grafting functionalized cucurbit [8] uril (CB[8]) onto chitosan (CS) chains via a CNC covalent bond (CB[8]-CS). This as-prepared material presented an unprecedented adsorption capacity. The maximum adsorption capacities (qm) were 1622.7 mg/g, 1172.7 mg/g, 1361.9 mg/g and 873.6 mg/g for the adsorption of reactive orange 5 (RO5), acidic blue 25 (AB25), reactive yellow 145 (RY145) and Pb2+ ions, respectively, which are far higher than the reported data. The simultaneous co-adsorption of dye and a heavy metal ion was tested with a mixed solution of 200 mg/L RO5 dye and Pb2+ ion, and the removal rates were 97% and 70% for RO5 and Pb2+, respectively. The adsorption mechanism was explored by means of the IR spectrum and the UV-vis diffuse reflection spectrum (DRS) together with theoretical calculations. The adsorption of dyes was mainly driven by the strong interaction between dye molecules and the hydrophobic cavity of CB[8], and the Pb2+ adsorption was mainly driven by the coordination of Pb2+ with the carbonyl of the CB[8] port and the amino group of chitosan. The ultrahigh adsorption capacity allows the use of CB[8]-CS as potential adsorbent for the simultaneous removal of heavy metal ions and organic dyes from aqueous solution.

Adsorption behavior and mechanism of acidic blue 25 dye onto cucurbit[8]uril: A spectral and DFT study.

The acidic blue 25 (AB25) dye was efficiently adsorbed by CB [8]; the saturated adsorption capacity (qexp) reached 434.8mg/g and was far higher than those of previous reported adsorbents. The Langmuir and Freundich isotherms were used to fit the equilibrium data, and the results showed that the Freundlich isotherm seemed to agree better with the AB25 adsorption. The adsorption kinetics followed the pseudo-second-order model. Calculated thermodynamic parameters showed that the adsorption of AB25 onto CB [8] was a spontaneous and enthalpy-driven process. The adsorption mechanism was explored by N2 adsorption-desorption, TG, FT-IR, UV-vis as well as MD simulation and DFT calculations. TG analysis revealed that a new inclusion complex was produced, and FT-IR,UV-vis spectrum and DFT calculations verify its structure. In this inclusion complex, the AB25 dye molecule inserted into cavities of CB [8] from portal, and the sulfonate and phenyl groups stayed in the hydrophobic cavity. TDDFT calculations indicated that all excitation arisen from π→π* transition.

Facile synthesis of highly efficient one-dimensional plasmonic photocatalysts through Ag@Cu2O core-shell heteronanowires.

A novel class of one-dimensional (1D) plasmonic Ag@Cu2O core-shell heteronanowires have been synthesized at room temperature for photocatalysis application. The morphology, size, crystal structure and composition of the products were investigated by XRD, SEM, TEM, XPS, and UV-vis instruments. It was found the reaction time and the amount of Ag nanowires play crucial roles in the formation of well-defined 1D Ag@Cu2O core-shell heteronanowires. The resultant 1D Ag@Cu2O NWs exhibit much higher photocatalytic activity toward degradation of organic contaminants than Ag@Cu2O core-shell nanoparticles or pure Cu2O nanospheres under solar light irradiation. The drastic enhancement in photocatalytic activity could be attributed to the surface plasmon resonance and the electron sink effect of the Ag NW cores, and the unique 1D core-shell nanostructure.

Visible-light-driven photoelectrochemical and photocatalytic performances of Cr-doped SrTiO3/TiO2 heterostructured nanotube arrays.

Well-aligned TiO2 nanotube arrays have become of increasing significance because of their unique highly ordered array structure, high specific surface area, unidirectional charge transfer and transportation features. However, their poor visible light utilization as well as the high recombination rate of photoexcited electron-hole pairs greatly limited their practical applications. Herein, we demonstrate the fabrication of visible-light-responsive heterostructured Cr-doped SrTiO3/TiO2 nanotube arrays by a simple hydrothermal method, which facilitate efficient charge separation and thus improve the photoelectrochemical as well as photocatalytic performances.