Photocatalytic carbon dioxide reduction by copper oxide nanocluster-grafted niobate nanosheets (original) (raw)
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Current Opinion in Electrochemistry, 2020
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Catalysts
Copper oxide (Cu2O) is a potential material as a catalyst for CO2 reduction. Cu2O nanostructures have many advantages, including interfacial charge separation and transportation, enhanced surface area, quantum efficiency, and feasibility of modification via composite development or integration of the favorable surface functional groups. We cover the current advancements in the synthesis of Cu2O nanomaterials in various morphological dimensions and their photochemical and electrochemical applications, which complies with the physical enrichment of their enhanced activity in every application they are employed in. The scope of fresh designs, namely composites or the hierarchy of copper oxide nanostructures, and various ways to improve CO2 reduction performance are also discussed in this review. Photochemical and electrochemical CO2 transformations have received tremendous attention in the last few years, thanks to the growing interest in renewable sources of energy and green facile ch...
Nature Catalysis, 2019
he ever-increasing atmospheric concentrations of carbon dioxide (CO 2) are having a profound impact on the world's climate system 1. The need to control these CO 2 levels has led to intense research into alternative energy systems that do not rely on fossil fuels as a source of primary energy 2. Among the various approaches to help solve this problem is photocatalytic conversion of CO 2 to renewable fuels 3-5. The development of highly active, selective and stable photocatalysts are key requirements for the development of a practical CO 2 conversion process under the mildest conditions possible 6. There are, however, other requirements that have to be satisfied for the process to be commercially viable; the photocatalyst has to be earth-abundant, lowcost and non-toxic as well as able to absorb solar photons over a wide spectral range. In this regard, cuprous oxide (Cu 2 O) is a perfect choice. It has an anti-fluorite crystal structure and a direct band gap of 2 to 2.2 eV (ref. 7). As an electrocatalyst as well as a photocatalyst, it is well documented for CO 2 reduction powered by electric or visible light in aqueous media 6,8,9. Its narrow band gap and appropriate conduction and valence band energies make it an ideal material for aqueous CO 2 reduction 10,11. Unfortunately, its redox instability towards irreversible Cu 2 O → Cu + CuO disproportionation has hindered its use in aqueous electrocatalysis and photocatalysis 6. Many strategies designed to overcome this problem have not led to much success. These strategies include coupling an n-type semiconductor with p-type Cu 2 O in a Type II or Z-scheme configuration in addition to the use of different kinds of surface protection coating 5,12,13. In stark contrast, barely any research exists on gas-phase CO 2 photo reduction aimed at circumventing the aforementioned redox instability problem. In this context, the synthesis of Cu 2 O nanocubes has been reported by several methods, most of which can be classified into two categories. One uses Cu 2+ as the copper precursor (copper sulfate, copper chloride or copper acetate), and requires surfactant (SDS, PVP or cetyltrimethylammonium), weak reductant (hydroxylamine hydrochloride, sodium ascorbate or N 2 H 4) and a base (sodium hydroxide) 14-18. The other method involves pH controlled CuCl hydrolysis 19. The organic contamination introduced by the former and the pH sensitivity and instability of the latter, however, render these methods for making Cu 2 O nanocubes impractical for the gas-phase heterogeneous photocatalytic hydrogenation of CO 2. Described here, we present an approach based on surface chemistry engineering of morphologically well-defined Cu 2 O nanocubes to remedy this situation and bring Cu 2 O back into the running as a contender photocatalyst for converting CO 2 into synthetic fuels. Notably, the obtained nanocubes have surfaces comprising mixed oxidationstate copper Cu(0,I,II), oxygen vacancies [O] and hydroxyl groups OH that render the redox disproportionation reversible, thereby enabling high photocatalytic activity and stability towards the reverse watergas shift (RWGS) reaction, H 2 + CO 2 → CO + H 2 O. The synthesis, characterization and photocatalytic performance metrics of the Cu 2 O nanocubes are described and an insight into the surface chemistry underpinning the RWGS reaction is obtained by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results of this study bode well for future explorations of these Cu 2 O nanocubes as a practical CO 2 hydrogenation photocatalyst.
Nano letters, 2014
The production of renewable solar fuel through CO2 photoreduction, namely artificial photosynthesis, has gained tremendous attention in recent times due to the limited availability of fossil-fuel resources and global climate change caused by rising anthropogenic CO2 in the atmosphere. In this study, graphene oxide (GO) decorated with copper nanoparticles (Cu-NPs), hereafter referred to as Cu/GO, has been used to enhance photocatalytic CO2 reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (∼4-5 nm in size) in the GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron-hole pair recombination, further reduction of GO's bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between...
Journal of Physical Chemistry C, 2016
This study reports on the solution combustion synthesis of two different ternary niobium oxides, namely, p-CuNb 2 O 6 and n-ZnNb 2 O 6. Such ternary oxides are attractive candidates in the "Holy Grail" search for efficient and stable semiconductors for solar energy conversion and environmental remediation. We demonstrate how this time-and energy-efficient method is capable of synthesizing high surface area and crystalline nanoparticles of the above compounds with enhanced optoelectronic properties. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV−visible and Raman spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure of these oxides was probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon to electron conversion efficiency vs wavelength). The obtained bandgap energy values (1.9 and 3.2 eV for the Cu-and Zn-containing compounds, respectively) were in reasonable agreement with those obtained via electronic structure calculations (2.07 and 3.53 eV). Finally, p-CuNb 2 O 6 showed promising activity for the PEC reduction of CO 2 , while n-ZnNb 2 O 6 was active for sulfite and water photooxidation. HCOOH, CH 3 OH, etc., produced by the photochemical or PEC conversion of CO 2. 4,8,9 The most extensively studied n-type metal oxide semiconductor is TiO 2 , mostly because of its robustness, outstanding stability in aqueous media, coupled with nontoxicity and earth abundance of its constituent elements. 10,11 However, the wide bandgap (3.0−3.2 eV) of this material limits its application in solar energy utilization processes. A plethora of other n-type oxide semiconductors (binary or even ternary oxides) have been applied as photoanodes (e.g., ZnO, WO 3 , Nb 2 O 5 , SrTiO 3). 12 On the other hand, p-type semiconductors Special Issue: Kohei Uosaki Festschrift
Synthesis of Cu2O nanocrystallites and their adsorption and photocatalysis behavior
Advanced Powder Technology, 2012
Cuprous oxide (Cu 2 O) nano-crystallites have been prepared via an electrochemical method by the anodic dissolution of copper in an alkaline solution of concentrated sodium chloride in a simple electrochemical cell. The effect of addition of glucose on the crystal size, structure and photocatalytic activity of Cu 2 O particles was studied. Photocatalytic decolorization of MeO in aqueous Cu 2 O suspensions was investigated. X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transformation infrared spectroscopy (FTIR) were used to characterize the samples. UV-vis Spectroscopy was employed to investigate the photocatalysis behavior of the Cu 2 O samples. The adsorption performance of the Cu 2 O samples showed that after adsorption of 2 h, the decolorization efficiencies of MO reached 11.81%, 95.24% and 56.53% for samples 1, 2 and 3, respectively, which proves that sample 2 has the highest adsorption capacity. The photocatalytic results showed that the as prepared Cu 2 O on the addition of 5 g/L glucose was the best sample since it was photostable and decolorized 98.7% of MeO solution in 30 min without any further decrease in the photocatalytic efficiency with increase in the irradiation time for 120 min. Higher concentrations of glucose lead to the decrease of photocatalytic efficiencies of the Cu 2 O particles.
ACS Energy Letters, 2016
Of the myriad electrode materials that have been used for electrochemical (EC) and photoelectrochemical (PEC) reduction of carbon dioxide in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This Perspective highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar chemical and morphological underpinnings in the in situ formation of copper nano-or microcubes on the (photo)cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in light of recent studies in the authors' laboratories and elsewhere. 46 range of electrode materials and electrolytes have been 47 deployed for the EC and PEC conversion of CO 2 ; many 48 reviews and book chapters exist. 6−13 In terms of sustainability 49 and process scalability, however, only a limited range of 50 candidates are worthy of serious consideration for technological 51 deployment. Thus, the use of earth-abundant and nontoxic 52 electrode materials has considerable appeal relative to noble 53 metals (e.g., Pt, Ru, Rh, etc.) or nonabundant elements (e.g., 54 Ga, In, etc.). Likewise, notwithstanding the limited solubility of 55 CO 2 in water (0.033 M at 298 K and 1 atm), the use of aqueous 56 electrolytes presents considerable practical advantages relative 57 to aprotic solvents and ionic liquids. Approaches involving 58 semiconductor suspensions and sacrificial reagents (the so-59 called "photocatalytic" (PC) processes), 14,15 while extremely 60 simple and attractive from an initial materials screening 61 perspective, will not be practical. For example, (a) the products 62
AppliedChem
The CO2 reduction by solar means has been discussed as an alternative to emission abatement, a fundamental topic for sustainable, carbon-free production in the future. However, the choice of efficient systems, starting with the catalysts, is still a critical issue, especially due to the poor activity of available options. Polyoxometalates have been extensively studied as promising photocatalysts due to their semiconducting properties. Nevertheless, the synthetic conditions of polyoxoniobate are stringent due to the low reaction activity of Nb species, the lack of soluble precursors, and the narrow pH range. Unlike the literature, in the present study, we report a simple polyoxoniobate synthesis method. This synthesis method has some remarkable features, such as low processing time and temperature and good activity and selectivity in the CO2 photoreduction process. The results revealed an outstanding efficiency for the CO2 reduction reaction with a high selectivity of CO2 to CO conve...
Applied Catalysis B: Environmental, 2012
Copper and iodine co-modified TiO 2 nanoparticles (Cu-I-TiO 2 ) were synthesized through a combined hydrothermal and wet-impregnation process. The structures and properties of the catalysts were characterized by XRD, BET, SEM/EDX, XPS, and UV-vis diffuse reflectance spectroscopy. Iodine ions were doped in the TiO 2 lattice by replacing Ti 4+ and, consequently, Ti 3+ was generated to balance the charge. Iodine doping reduced the TiO 2 crystal size and was responsible for visible light absorption. Cu species were found to deposit on the surface of TiO 2 and resulted in a slightly increased particle size. The activity of the Cu-I-TiO 2 catalyst was investigated by the photocatalytic reduction of CO 2 with water vapor, and CO was found to be the major reduction product with trace amounts of CH 4 generated. Under UV-vis irradiation, the activity of the co-modified catalyst (Cu-I-TiO 2 ) was higher than that of the single ionmodified catalysts (Cu-TiO 2 or I-TiO 2 ). Under visible light irradiation, the addition of Cu to I-TiO 2 did not lead to significant improvements in CO 2 reduction. Methyl chloride (CH 3 Cl) was detected as a reaction product when CuCl 2 was used as the precursor in the synthesis, thus suggesting that methyl radicals are reaction intermediates. When CuCl 2 was used as the Cu precursor, a three-fold increase in CO 2 photoreduction activity was observed, as compared to when Cu(NO 3 ) 2 was used as the Cu precursor. These differences in activities were probably due to enhanced Cu dispersion and the hole-scavenging effects of the Cl ions. However, the formation of by-products (e.g., CH 3 Cl) may be undesirable.