Nickel Oxide in Combination with a Photoredox Catalyst for the

Research Article Cite This: ACS Sustainable Chem. Eng. 2019, 7, 11313−11322

pubs.acs.org/journal/ascecg

Nickel/Nickel Oxide in Combination with a Photoredox Catalyst for the Reductive Carboxylation of Unsaturated Hydrocarbons with CO2 under Visible-Light Irradiation Sandhya Saini,†,‡ Hari Singh,§ Pankaj Kumar Prajapati,†,‡ Anil K. Sinha,*,§ and Suman L. Jain*,† Chemical and Material Sciences Division and §Biofuel Division, CSIR-Indian Institute of Petroleum, Haridwar Road, Mohkampur, Dehradun 248005, India ‡ Academy of Scientific and Innovative Research, New Delhi 110001, India Downloaded via BUFFALO STATE on July 21, 2019 at 11:59:23 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

S Supporting Information *

ABSTRACT: Core−shell nickel/nickel oxide combined with ruthenium bipyridyl photoredox complex was found to be adept, reusable, and highly selective for the carboxylation of various aryl and olefinic compounds with carbon dioxide at ambient temperature under 20 W light-emitting diode light. The carboxylation of a range of aromatic hydrocarbons and olefins afforded excellent product yield under 1 atm pressure of carbon dioxide without adding any additive/cocatalyst. Importantly, in the case of styrenes, insertion of CO2 took place at the benzylic C−H, whereas in normal olefins it occurred at the terminal site selectively. Moreover, the developed photocatalyst was highly stable, which allowed it to be recycled successfully for subsequent runs with almost consistent efficiency. KEYWORDS: Photocatalytic carboxylation, CO2, Alkene, Nickel, Hybrid material

■

yield. Seo et al. performed direct β-selective carboxylation of styrene by using para-terphenyl and triethylamine under ambient pressure (1 atm) of CO2 in a continuous flow.16 Shimomaki et al. reported visible-light-assisted carboxylation of aryl halide with CO2 using Pd(OAc)2 and Ir(ppy)2(dtbpy)(PF6).17 The best results were found for 4-cyanostyrene with 95% conversion and 54% yield of the desired carboxylated product by using the combination of coordination complex of rhodium and [Ru(bpy)3]Cl2. However, the use of expensive and noble metals such as Rh and the formation of hydrogenated by-products make the process limited from practical viewpoints. Nickel oxide, a well-known semiconductor photocatalyst, because of its wide band gap (3.4 eV) can absorb under ultraviolet (UV) range of the solar spectrum.18 However, incorporation of Ni0 in NiO reduces the band gap and extends its efficiency in the visible region.19 Furthermore, the ferromagnetic nature of Ni and antiferromagnetic nature of NiO semiconductor causes the conductivity in the Ni/NiO semiconductor. Ni/NiO semiconductor has widely been used as a photocatalyst for various reactions, but it provided poor conversion for a faster electron−hole recombination rate. Hence, modification of semiconductor support by combining

INTRODUCTION Use of carbon dioxide (CO2) as a readily available, safer, and sustainable C1 source for the production of high-value chemicals has gained considerable interest in recent decades.1,2 Because of its higher stability both thermodynamically as well as kinetically, activation of CO2 is tedious and highly energyintensive.3−5 However, the single-electron reduction of CO2 through photocatalytic approach is feasible and has been extensively studied for artificial photosynthesis.6−8 Carboxylation of olefins with CO2 as a carboxylating agent has recently attracted enormous interest mainly because of the direct access of carboxylic acids that are otherwise prepared through conventional multistep formylation and oxidation reactions. The well-known methods for carboxylation of unsaturated compounds with CO2 mainly require the stoichiometric amount of organometallic reagents such as diethyl zinc and alkyl aluminum and generate copious amounts of hazardous metallic waste.9 Furthermore, catalytic carboxylation using transition-metal catalysts requires harsh reaction conditions, for example, higher temperature mainly because of the inert nature of CO2.10−12 Although photocatalytic carboxylation of unsaturated hydrocarbons involving singleelectron reduction under ambient conditions is an ideal approach,13 very few reports on this approach are known.14 Murata et al.15 proclamined Rh-catalyzed photochemical carboxylation with CO2 using tris(bipyridine)ruthenium(II) chloride to give carboxylated products in maximum 60−70% © 2019 American Chemical Society

Received: February 10, 2019 Revised: May 30, 2019 Published: June 3, 2019 11313

DOI: 10.1021/acssuschemeng.9b00824 ACS Sustainable Chem. Eng. 2019, 7, 11313−11322

Research Article

ACS Sustainable Chemistry & Engineering Scheme 1. Synthetic Route of [Ru(bpy)3]2+/Ni/NiO Photocatalyst

with the photoredox catalyst is considered to be an ideal approach which enhances the photocatalytic activity and also offers facile recovery and reusability of the photocatalyst.20 Recently, Jain and co-workers reported several hybrid systems comprising coordination complexes and photoactive semiconducting supports for light-assisted reduction of CO2 to methanol in remarkably improved yield, whereas the scope for other transformations remains unexplored.21,22 Thus, in continuation of our ongoing studies, herein we describe the first successful carboxylation of olefins with CO2 using a nickel/nickel oxide semiconductor grafted with ruthenium bipyridyl photoredox complex [Ru(bpy)3]2+ as catalyst under ambient temperature and pressure conditions using visible light (Scheme 1). The developed methodology offers the carboxylation of a range of aromatic and olefinic compounds, higher conversion, low-cost catalyst, reusable photocatalyst, and milder reaction conditions.

Figure 1. XRD pattern of (a) RBN-2 photocatalyst and (b) Ni/NiO semiconductor.

■

RESULTS AND ISDCUSSION Synthesis and Characterization of Photocatalyst. The desired photocatalyst [Ru(bpy)3]2+/Ni/NiO(RBN-2) was prepared by the immobilization of [Ru(bpy)3]Cl2 on Ni/ NiO matrix as depicted in Scheme 1. The ruthenium concentration in the synthesized hybrid was found to be 0.27 wt % as determined by ICP-AES analysis. The crystalline nature and phases of the synthesized samples were determined using powder X-ray diffraction (XRD) (Figure 1). The higher intensity of the diffraction peaks in the diffractogram of Ni/NiO semiconductor confirms its crystalline nature. Furthermore, the diffraction peaks at 37°, 62°, and 79° corresponded to (111), (220), and (222) planes, respectively, confirming the presence of Ni2+ in a cubic NiO crystal (JCPDS card 78-0423).23 The peaks at 43° and 75° corresponding to (200) and (311) crystal planes are assigned to Ni0 as confirmed by JCPDS card no. 88-2326 (Figure 1b).24 After the immobilization, the constituent peaks of ruthenium were not observed in the diffractogram of the hybrid photocatalyst, which might be due to the poor loading of the complex. The presence of all characteristic peaks of Ni/NiO confirmed the occurrence of Ni2+ and Ni0 in the hybrid (Figure 1a).

UV−vis spectra were recorded from 200 to 800 nm for the [Ru(bpy)3]Cl2 complex, Ni/NiO semiconductor, and RBN-2 photocatalyst (Figure 2). In the case of the ruthenium complex, the characteristic absorbance peak at 287 nm revealed the bipyridine to bipyridine charge transfer (ππ*) in bipyridyl rings. Another peak at 453 nm showed the ruthenium to bipyridine charge transfer (dππ*), which further confirms its activity in the visible region (Figure 2a).25 The strong absorption at a wavelength of 345 nm was due to the intra 3d transitions of Ni2+ in the Ni/NiO semiconductor (Figure 2b).26 The increased intensity of absorbance at 286−380 and 400−580 nm confirms the successful immobilization of the Ru complex on Ni/NiO semiconductor (Figure 2c). Raman spectra of bare Ni/NiO and photocatalyst RBN-2 were used to determine the structure and electronic properties (Figure 3). Raman spectrum of Ni/NiO reveals the presence of characteristic intensity at 434, 495, 713, and 1075 cm−1 because of the vibrational signals of Ni−O bonds. Metallic Ni has no active vibrational mode; therefore, it is Raman inactive (Figure 3b). After the immobilization of the complex, the same trend with low intensity is obtained for the hybrid 11314


Research Article

ACS Sustainable Chemistry & Engineering

Figure 4. FT-IR plot of (a) Ru complex, (b) Ni/NiO semiconductor, and (c) RBN-2 photocatalyst.

Figure 2. UV−vis absorption plot of (a) Ru complex, (b) Ni/NiO, and (c) RBN-2.

The morphology and microstructure of the synthesized photocatalyst were estimated by high-resolution transmission electron microscopy (HR-TEM) (Figure 5). The photocatalyst

Figure 3. Raman spectra of (a) RBN-2 photocatalyst and (b) Ni/NiO semiconductor.

which verified the immobilization of ruthenium moiety on the semiconductor surface (Figure 3a). The changes in the chemical structure of the hybrid photocatalyst and semiconductor were evaluated by Fourier transform infrared spectroscopy (FT-IR) (Figure 4). The signals at 558 and 1162 cm−1 are assigned to stretching vibration of Ru−N and bending vibration of C−H bond in the Ru complex, respectively (Figure 4a). Furthermore, bands related to CN and CC bonds of the metal complex appeared at 1450 and 1619 cm−1, respectively.27 A broad signal at 3432 cm−1 is due to the moisture on the surface of the Ru complex. In the semiconductor, the emergence of peaks at 498 and 671 cm−1 is due to the Ni−O bending and Ni−O−H stretching vibration, respectively (Figure 4b).28 The remaining peaks at 1023, 1386, and 1633 cm−1 are attributed to the different vibrational modes of Ni−O bond in Ni/NiO, respectively (Figure 4b).29 The hybrid photocatalyst reveals slightly shifted vibration bands as compared to the semiconductor and complex, which confirms the successful immobilization and chemical interaction of the Ru complex units with the surface of porous Ni/NiO (Figure 4c).

Figure 5. (a, b) TEM images; (c) EDX pattern of the hybrid RBN-2 photocatalyst.

exhibited lattice distances of 0.205 and 0.215 nm corresponding to the crystal planes (200) and (220) at 5 nm scale related to the Ni0 and Ni2+ (Figure 5b).30 The emergence of fine dark spots showed the grafting of ruthenium complex units on the surface. The presence of clear planes in the selected area electron diffraction (SAED) further verified the crystalline nature of the final photocatalyst (Figure 5a). Also, the existence of Ni, O, Ru, C, and N in the energy-dispersive Xray (EDX) confirmed the successful synthesis of the hybrid photocatalyst. Furthermore, the uniform distribution of all constituents in photocatalyst can be clearly seen in the elemental mapping (Figure 6). 11315


Research Article


material was found to be stable up to 800 °C, as shown in Figure 7b. The hybrid photocatalyst showed nearly similar weight loss pattern to the Ni/NiO, which suggested a much lower loading of the metal complex on Ni/NiO semiconductor (Figure 7c). X-ray photoelectron spectroscopy (XPS) was used to described surface chemical properties and interaction between the components (Figure 8). In XPS spectra of Ni, six peaks were observed in which three are related to Ni 2p1/2 and the remaining corresponded to Ni 2p3/2. The peaks at 874 and 857 eV are assigned to the Ni 2p1/2 and Ni 2p3/2, respectively, which suggested that nickel is present in the +2 oxidation state.31 The peaks at 868 and 856 eV authorized to Ni 2p1/2 and Ni 2p3/2 confirmed the existence of Ni0 in combination with NiO in the hybrid photocatalyst. Two satellite signals are also observed at 882 and 863 eV in the hybrid photocatalyst (Figure 8a). XPS spectra of O 1s showed a peak at 533 eV for Ni−OH because of the adsorbed water in the hybrid, whereas that at 531 eV is due to Ni−O−Ni bonding (Figure 8b). In N 1s spectra, two signals at 401 and 399 eV are observed for C N and C−N bonding, respectively, of the bipyridyl rings (Figure 8c).32 XPS spectra of C 1s showed two characteristic peaks at 288.8 and 284.8 eV. The peaks observed at 286 and 284 eV were assigned to ruthenium as Ru 3d3/2 and Ru 3d5/2, respectively (Figure 8d). The XPS survey scan revealed the existence of all desired elements, that is, Ru, Ni, O, N, and C, that confirmed the successful synthesis of the desired photocatalyst (Figure 8e). The surface properties of the semiconductor and photocatalyst were described by nitrogen adsorption−desorption theory known as Brunauer−Emmet−Teller (BET) (Figure 9).

Figure 6. Elemental mapping of (a) Ni, (b) O, (c) C, (d) N, (e) Ru, and (f) electron image for RBN-2 photocatalyst.

Thermograms of samples as determined by thermogravimetric analysis (TGA) and derivative thermal analysis (DTA) under a N2 environment in the temperature range from 30 to 800 °C are shown in Figure 7. For Ru complex, two weight losses are noticed in which the initial loss at 200 °C depicted the evaporation of the adsorbed water in the [Ru(bpy)2]Cl2 complex. A major peak at 420 °C can be attributed to the decay of the organic moieties of the metal complex (Figure 7a).25 For Ni/NiO, a steady and small weight loss was observed between 50 and 100 °C because of the removal of moisture and remaining organic substances. After that, the

Figure 7. TG/DTA of (a) [Ru(bpy)3]Cl2, (b) Ni/NiO, and (c) RBN-2 11316


Research Article


Figure 8. XPS pattern of (a) Ni 2p, (b) O 1s, (c) N 1s, (d) Ru 3d and C 1s, and (e) XPS survey for RBN-2 photocatalyst.

Figure 9. N2 adsorption−desorption isotherm of (a) Ni/NiO and (b) RBN-2 photocatalyst.

0.164 cm3/g, and 4.13 nm, respectively.33 The N2 adsorption− desorption isotherm of Ni/NiO revealed characteristic type IV

The surface area (SBET), mean pore volume (Vp), and average pore diameter (rp) of Ni/NiO were observed to be 163.2 m2/g, 11317


Research Article


loading afforded poor conversion of styrene, whereas the moderate loading (RBN-2 synthesized by using 50 mg of the complex with 1 g of support) exhibited the highest efficiency in terms of conversion to the corresponding carboxylated product (Table 1, entry 3). Moreover, in the end, the photocatalyst was separated from the reaction mixture by an external magnet and the resulting residue was analyzed by high-performance liquid chromatography (HPLC) to determine the conversion. On the basis of the above experiments, it was concluded that photocatalyst RBN-2, proton donor DMA, triethylamine, and visible illumination are key components for efficient transformation under the developed protocol. Furthermore, the carboxylation of various unsaturated hydrocarbons, that is, aromatic and aliphatic olefins and aromatic compounds with CO2 under optimized reaction medium, are carried out under the optimized experimental conditions. The data obtained from these experiments are summarized in Table 2. Among the different substrates studied, in styrenes (Table 2, entries 1−3 and 6) carboxylation occurred at the benzylic position of styrene, which is most likely due to the stability of the benzylic radical. The nature of the substituent present in the phenyl ring had a marginal effect on the reactivity to any significant extent and afforded almost similar conversion and product yields. However, in correlation to the existing literature report, the formation of linear products in aliphatic alkenes (Table 2, entries 4−5) is attributed to the steric factor.14 Accordingly, the formation of Ni-hydride species via light-assisted transfer of 2e− and 2H+ from triethylamine and DMA, respectively, followed by inclusion of the unsaturated moiety and carboxylation of the resulting organometallic intermediate with carbon dioxide provided linear carboxylated products.35 Furthermore, aromatic compounds such as benzene, bromobenzene, chlorobenzene, and toluene also showed moderate to higher conversion under the developed photocatalytic system (Table 2, entries 7−10). Importantly, in all cases, carboxylated products were obtained selectively without any evidence for the generation of by-products under the described photocatalytic conditions. Furthermore, the selective formation of para-carboxylated product from carboxylation of toluene under given experimental conditions may be specified on the basis of the steric hindrance at the ortho-position during the formation of reactive intermediate species. In addition, the lower reaction temperature during carboxylation (ambient temperature) favors the formation of the para-carboxylated product as suggested in the literature.36 Next, we checked the recycling of the synthesized hybrid RBN-2 photocatalyst. After reaction completion, the hybrid material could readily be recovered by an external magnet, then washed with ethyl alcohol, and dried at 60 °C in a vacuum oven for 8 h. The retrieved photocatalyst was subjected to the subsequent carboxylation of styrene with CO2 under optimized experimental conditions. The recovered material could be successfully reused for four successive runs with nearly consistent efficiency (Figure 10). Importantly, ICPAES analysis of recovered photocatalyst after the fourth run revealed 0.25 wt % ruthenium content, which is nearly equal to the fresh sample (0.27 wt %). Hence, it is proved that the photocatalyst possesses higher stability without any detectable leaching during the experiments. Furthermore, the heterogeneous nature of the photocatalyst was verified by performing a filtration test. The reaction was stopped after 8 h, and the photocatalyst was separated by filtration. The conversion as determined by HPLC was found

with H2 hysteresis loop and bottleneck-shaped pores (Figure 9a). Similarly, final material displayed type IV isotherm having hysteresis loop and slitlike pores.34 The BET surface area (SBET), mean pore volume, and average pore diameter (rp) of the hybrid were observed as 47.2 m2/g, 0.13 cm3/g, and 11.66 nm, respectively (Figure 9b). The decreased surface area and pore volume of the hybrid specified the deposition of Ru complex moieties at the surface, whereas increased average pore diameter suggested the distribution of complex units upon the outer surface of the pores. Photocatalytic Activity. The synthesized Ru complex, Ni/NiO, and hybrid [Ru(bpy)3]2+/Ni/NiO (RBN-2) photocatalysts were initially investigated for the carboxylation of styrene with CO2 under UV region irradiation by employing 20 W light-emitting diode (LED) white light under continuous stirring for 24 h using N,N-dimethylacetamide (DMA) as solvent that provides necessary protons and triethylamine (TEA) as electron provider. The intensity of LED light on the surface was 85 W/m2, as estimated by intensity meter. Among all photocatalysts, that is, [Ru(bpy)3]Cl2, Ni/NiO, and RBN-2, only hybrid ([Ru(bpy)3]2+/Ni/NiO) photocatalyst afforded the desired carboxylated product (Table 1, entries 1−3). This Table 1. Results for Optimization of Reaction Parametersa entry

catalyst

solvent

visible light

conv.b (%)

1 2 3 4 5i 5ii 5iii 5iv 5 6 7

Ru complex Ni/NiO RBN-2 RBN-2 RBN-2 RBN-2 RBN-2 RBN-2 RBN-1 RBN-3 RBN-4

DMA DMA DMA DMA DMF THF CH3CN H2O DMA DMA DMA

yes yes yes no yes yes yes yes yes yes yes

9 8 85 c 75 62 70 50 80 62 40

a

Reaction conditions: Photocatalyst (RBN-2: 14 mg, 0.01 mmol), styrene (0.5 mmol), TEA (2.4 mmol), DMA (4 mL), at room temperature under atmospheric pressure of CO2 in the presence of visible light irradiation using 20 W LED (λ > 400 nm), 24 h. b Conversion was determined by HPLC. cNo conversion observed.

finding suggested that the existence of both components, that is, ruthenium photosensitizer and Ni/NiO catalyst, is required for the present transformation. No reaction occurred in the dark, which further supported the photochemical nature of the reaction (Table 1, entry 4). Furthermore, different proton donor solvents, for example, N,N-dimethylformamide (DMF), methanol, ethanol, acetonitrile, and water were screened in place of DMA for the carboxylation of styrene under identical conditions (Table 1, entries 5i−iv). Among the various solvents tested, DMA was observed to be most efficient from the conversion and selectivity of the carboxylated product point of view (Table 1, entry 3). Hence, DMA was chosen as a solvent of choice in further experiments. Furthermore, in a blank run, no carboxylation proceeds without RBN-2 photocatalyst, even after the prolonged reaction time (48 h). Furthermore, among the different hybrid samples containing different loadings of ruthenium complex (RBN 1−4) studied, RBN-2 synthesized by using 50 mg of ruthenium complex was found to be efficient for the present transformation (Table 1, entries 6−8). The lower and excess ruthenium complex 11318


Research Article

ACS Sustainable Chemistry & Engineering Table 2. Photocatalytic Carboxylation of Unsaturated Olefins with CO2a

a

Reaction conditions: Photocatalyst (RBN-2), 14 mg (0.01 mmol), substrate (0.5 mmol), TEA (2.4 mmol), DMA (6 mL), room temperature and atmospheric pressure of CO2, visible-light irradiation using 20 W LED (λ > 400 nm), time 24 h. bConversion of the substrate to carboxylated product was determined by 1H NMR using relative conversion method with respect to substrate. cYield was determined by 1H NMR after esterification with TMSCHN2.

to be 38% after 8h. The filtrate so obtained was further irradiated under visible light up to 24 h. There was no further conversion observed, which indicated that the developed hybrid was quite stable without any noticeable leaching during the reaction. Furthermore, it was confirmed that the photocatalyst is vital for the present transformation, and in its absence, the reaction did not proceed. Furthermore, the advantage of the present system was established by its comparison with the existing photocatalytic carboxylation methods as summarized in Table 3. As mentioned earlier, the photocatalytic carboxylation of unsaturated hydrocarbons is less explored, and very few reports are known in this context. As clearly indicated in Table 3, the key features of the developed methodology are use of less expensive nickel catalyst, nonrequirement of additives, versatility toward a range of substrates, and easy recovery

and efficient reusability of the photocatalyst. These salient features establish the present methodology as more practical and applicable than the existing methodologies. The actual reaction pathway is unknown at this stage; however, analogous to the previous literature, a plausible path is depicted in Scheme 2. In the developed hybrid photocatalyst, ruthenium complex works as a photosensitizer which absorbs strongly in the visible range and transfers electrons from HOMO to LUMO. Triethylamine, a sacrificial electron donor, provided electrons in the HOMO of a photosensitizer.37 Subsequently, the excited electrons from the LUMO of Ru complex transfer into the low-energy CB of Ni/ NiO semiconductor. Similarly, under the visible illumination charge separation and electron transfer from VB to CB in NNO occurred, which created photogenerated holes and electrons, respectively. These photogenerated electrons in the 11319


Research Article


Scheme 2. Plausible Reaction Mechanism for the Carboxylation with CO2

RBN-1, RBN-2, RBN-3, and RBN-4 for 25, 50, 75, and 100 mg of Ru complex, respectively. Characterization Techniques. Morphological features of the materials were determined by using JEM-2100, a multipurpose, 200 kV analytical electron microscope. D8 advance powder X-ray diffractometer (Bruker) working with Cu Kα radiation (λ = 0.15418 nm) at 40 kV and 40 mA were used to analyze phase structures and crystalline properties of the materials. PerkinElmer-RX1-spectrophotometer was used to record FT-IR spectra of samples for identifying the different chemical bonds and interactions. UV−vis− NIR spectrometer (Lambda 9, PerkinElmer) equipped with a 10 mm quartz cell determined the absorption spectra of the photocatalysts using BaSO4 as a reference. Textural features of samples, that is, SBET, VP, and rp were approximated via nitrogen adsorption−desorption isotherm at 77 K using Micromeritics ASAP-2010. Chemical composition of the surface of samples were analyzed by X-ray photoelectron spectroscopy (XPES) using ESCA+ equipment (Scienta Omicron, GmbH). Thermal degradation patterns of samples were analyzed by using the techniques of thermogravimetric and differential thermal analyses between room temperature and 600 °C under N2 at the heating rate of 10 °C/min on the thermal analyzer (TA-SDT-Q-600). ICP-AES analysis was performed on DRE, PS3000 UV, Leeman Laboratories Inc., USA, to determine the ruthenium loading in the photocatalyst. The material was treated with concentrated nitric acid, filtered, and diluted with deionized water to 10 mL. Conversion of the substrate was determined by HPLC using Agilent Hi-Plex columns and RID-10A detector. Photocatalytic Carboxylation Experiment. In a general procedure of photocatalytic carboxylation experiment, unsaturated hydrocarbon (0.5 mmol), DMA (6 mL), and triethylamine (2.4 mmol) as an electron donor were added in a round-bottom flask of 100 mL capacity. The RB was purged with N2 environment to depart the air for 10 min and then with CO2 to saturate the solution. After that, 14 mg of RBN-2 (0.01 mmol) photocatalyst was added, and the vessel was closed tightly with a septum. The reaction mixture was continuously purged with CO2 until saturation. Subsequently, the reaction vessel was subjected to stirring under visible light (LED, 20 W, Model No. HP-FL-20 W-F, Hope LED Opto-Electric CO., Ltd.) for 24 h. The intensity of the LED source at the vessel was observed to be 85 W/m2 as measured by the intensity meter. After completion of the reaction, the photocatalyst was separated by an external magnet

Figure 10. Results of the recycling of the photocatalyst (RBN-2).

CB of the semiconductor converted CO2 into a radical anion (CO2•−).38 However, the unsaturated hydrocarbon substrate oxidized at the VB of the semiconductor and converted into the corresponding radical cation.39 Finally, the cation radical combines with reduced CO2 radical in the presence of protons derived from either DMA or TEA and afforded corresponding carboxylic acid (Scheme 2). Similar to the aromatic alkenes, aryl halides also have undergone free radical pathway and afforded carboxylic acids via coupling of reduced CO2 radical anion with phenyl radical cation as per the existing literature report.40

■

EXPERIMENTAL SECTION

Materials and Methods. Nickel nitrate hexahydrate was procured from Merck Millipore. Organosilane template octadecyl dimethyl (3-trimethoxysilylpropyl) ammonium chloride (ODAC), ruthenium(III) trichloride, and 2,2′-bipyridyl were bought from Sigma-Aldrich. The rest of the chemicals and reagents such as sodium hydroxide, hydrazine hydrate, sodium borohydride, styrene, 4chlorostyrene, 4-bromostyrene, 1-octene, 1-decene, 4-methylstyrene, benzene, bromobenzene, chlorobenzene, and toluene were bought from Alpha Across and used as received. Absolute ethanol and deionized water were used throughout the synthesis and reactions part. The Ni/NiO semiconductor was synthesized by following the reported organosilane-template-assisted chemical reduction method.41 Synthesis of [Ru(Cl2)3]+2/Ni/NiO (RBN-2) Photocatalyst. One gram of Ni/NiO dispersed in 10 mL of ethanol in a beaker was sonicated for 1 h. Then 50 mg of Ru(bpy)3Cl2 complex was added into the above suspension and stirred overnight or until dryness was achieved. The dried solution was washed three times with water followed by washing with ethanol and finally drying at 60 °C for 24 h. The as-prepared photocatalyst was used for the photocatalytic carboxylation of unsaturated hydrocarbons with CO2. The photocatalyst was optimized by the variation in ruthenium complex loading of 25, 75, and 100 mg over the Ni/NiO semiconductor. The synthesized photocatalysts with different Ru loadings were coded as

Table 3. Comparison of the Present Methodology with the Reported Photocatalytic Carboxylation of Styrene entry 1 2 3 4

catalyst/photoredox catalyst 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN)/ LNiBr2 (L = neocuproine) [Rh(4-CF3C6H4)2Cl]2/[Ru(bpy)3](PF6)2 para-terphenyl [Ru(bpy)3]+2/Ni-NiO

additive K2CO3 Cs2CO3 Ph3SiH

sacrificial electron donor diethyl-1,4-dihydro-2,6-dimethyl-3,5-pyridine dicarboxylate (Hantzsch ester) iPr2NEt 1,2,2,6,6-pentamethylpiperidine (PMP) Et3N

11320

solvent

conv. (%)

ref

DMF

54

14

DMA DMF DMA

67 87 89

15 16 this work


Research Article

ACS Sustainable Chemistry & Engineering and washed with ethanol followed by drying at 60 °C for 24 h in a vacuum oven. The separated photocatalyst was used for the recycling experiments. The conversion and yield of the carboxylic acids after methyl esterification with trimethylsilyl diazomethane (TMS-CHN2) was determined by 1H NMR by using relative conversion method concerning the substrate. The crude products were extracted with ethyl acetate followed by the usual workup to obtain the pure esters.

(3) Schneider, J.; Jia, H.; Muckerman, J. T.; Fujita, E. Thermodynamics and kinetics of CO2, CO, and H+ binding to the metal centre of CO2 reduction catalysts. Chem. Soc. Rev. 2012, 41, 2036−2051. (4) Chang, C.-F.; Chang, C.-Y.; Tsai, W.-T. Effects of burn-off and activation temperature on preparation of activated carbon from corn cob agrowaste by CO2 and steam. J. Colloid Interface Sci. 2000, 232, 45−49. (5) Goettmann, F.; Thomas, A.; Antonietti, M. Metal-free activation of CO2 by mesoporous graphitic carbon nitride. Angew. Chem., Int. Ed. 2007, 46, 2717−2720. (6) Habisreutinger, S. N.; Schmidt-Mende, L.; Stolarczyk, J. K. Photocatalytic reduction of CO2 on TiO2 and other semiconductors. Angew. Chem., Int. Ed. 2013, 52, 7372−7408. (7) Barton Cole, E.; Lakkaraju, P. S.; Rampulla, D. M.; Morris, A. J.; Abelev, E.; Bocarsly, A. B. Using a one-electron shuttle for the multielectron reduction of CO2 to methanol: kinetic, mechanistic, and structural insights. J. Am. Chem. Soc. 2010, 132, 11539−11551. (8) Low, J.; Zhang, L.; Zhu, B.; Liu, Z.; Yu, J. TiO2 Photonic crystals with localized surface photothermal effect and enhanced photocatalytic CO2 reduction activity. ACS Sustainable Chem. Eng. 2018, 6, 15653−15661. (9) Williams, C. M.; Johnson, J. B.; Rovis, T. Nickel-catalyzed reductive carboxylation of styrenes using CO2. J. Am. Chem. Soc. 2008, 130, 14936−14937. (10) Gaydou, M.; Moragas, T.; Julia-Hernandez, F.; Martin, R. Siteselective catalytic carboxylation of unsaturated hydrocarbons with CO2 and water. J. Am. Chem. Soc. 2017, 139, 12161−12164. (11) Huguet, N.; Jevtovikj, I.; Gordillo, A.; Lejkowski, M. L.; Lindner, R.; Bru, M.; Khalimon, A. Y.; Rominger, F.; Schunk, S. A.; Hofmann, P.; Limbach, M. Nickel-catalyzed direct carboxylation of olefins with CO2: one-pot synthesis of α,β-unsaturated carboxylic acid salts. Chem. - Eur. J. 2014, 20, 16858−16862. (12) Yu, B.; Diao, Z.-F.; Guo, C.-X.; He, L.-N. Carboxylation of olefins/alkynes with CO2 to industrially relevant acrylic acid derivatives. J. CO2 Util. 2013, 1, 60−68. (13) Yeung, C. S. Photoredox catalysis as a strategy for co2 incorporation: direct access to carboxylic acids from a renewable feedstock. Angew. Chem., Int. Ed. 2019, 58, 5492−5502. (14) Meng, Q.-Y.; Wang, S.; Huff, G. S.; König, B. Ligand-controlled regioselective hydrocarboxylation of styrenes with CO2 by combining visible light and nickel catalysis. J. Am. Chem. Soc. 2018, 140, 3198− 3201. (15) Murata, K.; Numasawa, N.; Shimomaki, K.; Takaya, J.; Iwasawa, N. Construction of a visible light-driven hydrocarboxylation cycle of alkenes by the combined use of Rh(I) and photoredox catalysts. Chem. Commun. 2017, 53, 3098−3101. (16) Seo, H.; Liu, A.; Jamison, T. F. Direct β-selective hydrocarboxylation of styrenes with CO2 enabled by continuous flow photoredox catalysis. J. Am. Chem. Soc. 2017, 139, 13969−13972. (17) Shimomaki, K.; Murata, K.; Martin, R.; Iwasawa, N. Visiblelight-driven carboxylation of aryl halides by the combined use of palladium and photoredox catalysts. J. Am. Chem. Soc. 2017, 139, 9467−9470. (18) Gondal, M.; Hameed, A.; Yamani, Z.; Arfaj, A. Photocatalytic transformation of methane into methanol under UV laser irradiation over WO3, TiO2 and NiO catalysts. Chem. Phys. Lett. 2004, 392, 372− 377. (19) Cui, E.; Lu, G. Enhanced surface electron transfer by fabricating a core/shell Ni@NiO cluster on TiO2 and its role on high efficient hydrogen generation under visible light irradiation. irradiation. Int. J. Hydrogen Energy 2014, 39, 8959−8968. (20) Hu, S.; Li, F.; Fan, Z.; Gui, J. Improved photocatalytic hydrogen production property over Ni/NiO/N−TiO2-x heterojunction nanocomposite prepared by NH3 plasma treatment. J. Power Sources 2014, 250, 30−39. (21) Kumar, P.; Mungse, H. P.; Khatri, O. P.; Jain, S. L. Nitrogendoped graphene-supported copper complex: a novel photocatalyst for

■

CONCLUSIONS The present paper demonstrates the use of a hybrid photocatalyst comprising a molecular complex and a semiconductor for carboxylation of unsaturated hydrocarbons with CO2 under visible illumination. From the different samples prepared, photocatalyst having moderate loading of ruthenium photosensitizer exhibited the highest efficiency. Furthermore, among the varieties of solvents, N,N-dimethylacetamide was observed to be the optimum proton donor solvent for efficient conversion. Furthermore, the use of triethylamine as a sacrificial electron donor was identified to be vital for efficient carboxylation of the substrates with CO2. The synthesized hybrid was readily recovered by an external magnet and recycled for a consecutive four runs without noticeable loss in the activity. More importantly, there was no leaching observed during the photochemical reactions. This is the first successful report on the use of hybrid photocatalyst for carboxylation with CO2 that may provide immense opportunities for carbon dioxide utilization to produce chemicals using an abundantly available, inexpensive, and renewable solar energy under ambient conditions.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.9b00824. 1 H and 13C NMR spectra of the carboxylated products (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*Phone: +911352525788. E-mail: [email protected] (S.L.J.). *E-mail: [email protected] (A.K.S.). ORCID

Suman L. Jain: 0000-0002-4198-040X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Director CSIR-Indian Institute of Petroleum, Dehradun, is kindly acknowledged for permitting publication of these data. S.S. and P.K.P. are grateful to the Council of Scientific and Industrial Research, New Delhi, for research fellowships. Analytical division of the Institute is acknowledged for providing analytical assistance.

■

REFERENCES

(1) Li, Y.; Cui, X.; Dong, K.; Junge, K.; Beller, M. Utilization of CO2 as a C1 building block for catalytic methylation reactions. ACS Catal. 2017, 7, 1077−1086. (2) Tortajada, A.; Juliá-Hernández, F.; Börjesson, M.; Moragas, T.; Martin, R. Transition-metal-catalyzed carboxylation reactions with carbon dioxide. Angew. Chem., Int. Ed. 2018, 57, 15948−15982. 11321


Research Article

ACS Sustainable Chemistry & Engineering CO2 reduction under visible light irradiation. RSC Adv. 2015, 5, 54929−54935. (22) Kumar, A.; Kumar, P.; Borkar, R.; Bansiwal, A.; Labhsetwar, N.; Jain, S. L. Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride supported heteroleptic iridium complex under visible light irradiation. Carbon 2017, 123, 371−379. (23) Sheela, T.; Nayaka, Y. A. Kinetics and thermodynamics of cadmium and lead ions adsorption on NiO nanoparticles. Chem. Eng. J. 2012, 191, 123−131. (24) Ramulifho, T.; Ozoemena, K. I.; Modibedi, R. M.; Jafta, C. J.; Mathe, M. K. Fast microwave-assisted solvothermal synthesis of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated MWCNTs: Pdbased bimetallic catalysts for ethanol oxidation in alkaline medium. Electrochim. Acta 2012, 59, 310−320. (25) Kumar, P.; Joshi, C.; Labhsetwar, N.; Boukherroub, R.; Jain, S. L. A novel Ru/TiO2 hybrid nanocomposite catalyzed photoreduction of CO2 to methanol under visible light. Nanoscale 2015, 7, 15258− 15267. (26) Qi, Y.; Qi, H.; Li, J.; Lu, C. Synthesis, microstructures and UV− vis absorption properties of β-Ni(OH)2 nanoplates and NiO nanostructures. J. Cryst. Growth 2008, 310, 4221−4225. (27) Adeloye, A. O.; Olomola, T. O.; Adebayo, A. I.; Ajibade, P. A. A high molar extinction coefficient bisterpyridyl homoleptic Ru(II) complex with trans-2-methyl-2-butenoic acid functionality: potential dye for dye-sensitized solar cells. Int. J. Mol. Sci. 2012, 13, 3511−3526. (28) Sonavane, A.; Inamdar, A.; Deshmukh, H.; Patil, P. Multicoloured electrochromic thin films of NiO/PANI. J. Phys. D: Appl. Phys. 2010, 43, 315102. (29) Lei, C.; Zhu, X.; Zhu, B.; Yu, J.; Ho, W. Hierarchical NiO−SiO2 composite hollow microspheres with enhanced adsorption affinity towards Congo red in water. J. Colloid Interface Sci. 2016, 466, 238− 246. (30) Patange, M.; Biswas, S.; Yadav, A.; Jha, S.; Bhattacharyya, D. Morphology-controlled synthesis of monodispersed graphitic carbon coated core/shell structured Ni/NiO nanoparticles with enhanced magnetoresistance. Phys. Chem. Chem. Phys. 2015, 17, 32398−32412. (31) Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W.; Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717−2730. (32) Agnès, C.; Arnault, J.-C.; Omnès, F.; Jousselme, B.; Billon, M.; Bidan, G.; Mailley, P. XPS study of ruthenium tris-bipyridine electrografted from diazonium salt derivative on microcrystalline boron doped diamond. Phys. Chem. Chem. Phys. 2009, 11, 11647− 11654. (33) Harraz, F.; Mohamed, R.; Shawky, A.; Ibrahim, I. Composition and phase control of Ni/NiO nanoparticles for photocatalytic degradation of EDTA. J. Alloys Compd. 2010, 508, 133−140. (34) Wen, W.; Wu, J.-M. Eruption combustion synthesis of NiO/Ni nanocomposites with enhanced properties for dye-absorption and lithium storage. ACS Appl. Mater. Interfaces 2011, 3, 4112−4119. (35) Yu, D.; Zhou, F.; Lim, D. S. W.; Su, H.; Zhang, Y. NHC-Ag/ Pd-catalyzed reductive carboxylation of terminal alkynes with CO2 and H2: A combined experimental and computational study for finetuned selectivity. ChemSusChem 2017, 10, 836−884. (36) Olah, G. A.; Török, B.; Joschek, J. P.; Bucsi, I.; Esteves, P. M.; Rasul, G.; Surya Prakash, G. K. Efficient chemoselective carboxylation of aromatics to arylcarboxylic acids with a superelectrophilically activated carbon dioxide-Al2Cl6/Al system. J. Am. Chem. Soc. 2002, 124 (38), 11379−11391. (37) Prajapati, P. K.; Singh, H.; Yadav, R.; Sinha, A. K.; Szunerits, S.; Boukherroub, R.; Jain, S. L. Core-shell Ni/NiO grafted cobalt(II) complex: An efficient inorganic nanocomposite for photocatalytic reduction of CO2 under visible light irradiation. Appl. Surf. Sci. 2019, 467, 370−381. (38) Bonin, J.; Chaussemier, M.; Robert, M.; Routier, M. Homogeneous photocatalytic reduction of CO2 to CO using iron(0) porphyrin catalysts: mechanism and intrinsic limitations. ChemCatChem 2014, 6, 3200−3207.

(39) Walling, C.; El-Taliawi, G. M.; Amarnath, K. Oxidation of styrene derivatives by peroxydisulfate(2-) ion-copper(II) in acetic acid and acetonitrile. reaction paths in oxidations via radical cations. J. Am. Chem. Soc. 1984, 106, 7573−7578. (40) Hou, J.; Li, J.-S.; Wu, J. Recent development of light-mediated carboxylation using CO2 as the feedstock. Asian J. Org. Chem. 2018, 7, 1439−1447. (41) Singh, H.; Rai, A.; Yadav, R.; Sinha, A. K. Glucose hydrogenation to sorbitol over unsupported mesoporous Ni/NiO catalyst. Mol. Catal. 2018, 451, 186−191.

11322


Nickel Oxide in Combination with a Photoredox Catalyst for the

Recommend Documents