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Article

g-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol

by
Menglong Zhang
,
Weizhe Wang
,
Fangliang Gao
* and
Dongxiang Luo
*
Institute of Semiconductors, South China Normal University, Guangzhou 510631, China
*
Authors to whom correspondence should be addressed.
Catalysts 2021, 11(4), 505; https://doi.org/10.3390/catal11040505
Submission received: 24 March 2021 / Revised: 12 April 2021 / Accepted: 13 April 2021 / Published: 16 April 2021
(This article belongs to the Special Issue Solar Fuels Production by Artificial Photosynthesis)
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Abstract

:
The outstanding optoelectronic performance and facile synthetic approach of metal halide perovskites has inspired additional applications well beyond efficient solar cells and light emitting diodes (LEDs). Herein, we present an alternative option available for the optimisation of selective and efficient oxidation of benzylic alcohols through photocatalysis. The materials engineering of hybrids based on formamidine lead bromide (FAPbBr3) and graphic carbon nitride (g-C3N4) is achieved via facile anti-solvent approach. The photocatalytic performance of the hybrids is highly reliant on weight ratio between FAPbBr3 and g-C3N4. Besides, the presence of g-C3N4 dramatically enhances the long-term stability of the hybrids, compared to metal oxides hybrids. Detailed optical, electrical and thermal studies reveal the proposed novel photocatalytic and stability behaviours arising in FAPbBr3 and g-C3N4 hybrid materials.

1. Introduction

As a promising family of semiconductor materials, organic–inorganic halide perovskites (OIHPs) have attracted massive attentions attributing to their potential applications in optoelectronic field. This can be summarised as several advantages of OIHPs over other typical semiconductor materials, including tunable band gap energy, low-cost and facile synthesising [1]. In addition, thanks to the superior light harvesting efficiency of OIHPs [2] halide perovskites-based solar cells have performed high solar energy conversion efficiency approached 25.2% (NERL, Best Research-Cell Efficiency Chart). While OIHPs-based conversion of solar energy continues to embody mainstream halide perovskites research, the potential applications toward photochemical processes remains rarely explored. The main issues are the poor stability of OIHPs, which would decompose and cause Pd leaking, especially in presence of polar solvent.
In addition to the perovskite, after it was triggered by the seminal work by Wang et al. [3] graphite carbon nitride (g-C3N4) is at present a prominent photoactive material within fundamental research among many candidates, because of the tunable band gap energy (by designing N-rich or C-rich C3N4) [4,5], stability under harsh chemical conditions [6] and metal-free. The high stability and poor solubility of g-C3N4 in general solvents allow its utilisations as an effective heterogeneous catalyst [7], particularly as photocatalyst for solar to chemical bond conversions, such as oxygen generation [8,9], hydrogen evolution [4,5,10] and overall water splitting [11]. On the other hand, OIHPs indicate potential capabilities to extend highly efficient light harvesting in visible wavelength region. While in aqueous systems, the instability nature of OIHPs generally limits their utilisations in typical photocatalytic processes including water splitting, CO2 reduction and degradation of organic pollutants. These limitations were commonly solved by using an oversaturated aqueous HX solution (X is depending on the halide ion in OIHPs) as sacrificial reagent, thus extended their applications to reduction of CO2 and oxidation of PEDOT [12]. A typical type-II band structure could be formed by FAPbBr3/C3N4, and it is expected to give an enhanced charge separation [13]. In addition, it was reported that the amine group (-NH2) of g-C3N4 could effectively bind to the surface and expose the steric hindrance -OH groups to prevent typical polar solvent including ethanol, methanol or isopropanol [14], thus optimising the stability of OIHPs. Furthermore, during the preparation of samples, it is unavoidable that the pristine g-C3N4 and OIHPs would be in presence in the as-prepared FAPbBr3/C3N4 hybrids, therefore the possible influence of pristine g-C3N4 on hybrids should also be considered due to its higher oxidation potential than FAPbBr3. Based on these highly interesting properties of g-C3N4 and OIHPs, constructing the FAPbBr3/C3N4 hybrids offers a path to exploit efficient selective and stable oxidation of alcohols to carbonyls, which is an important industrial organic reaction [15].
Herein we report the photocatalyst based on FAPbBr3/C3N4 for efficient and selective photoactivated oxidation of benzylic alcohol. Through utilisation of the band alignment of photogenerated electrons/holes in FAPbBr3/C3N4 hybrids, and modification of ratios between the two materials, the optimised photocatalytic performance under visible light is achieved. Besides, the photostability behaviour, optical, photochemical and thermal properties of FAPbBr3/C3N4 hybrids are demonstrated with details.

2. Result and Discussion

2.1. Structure and Morphologies

The FAPbBr3 and FAPbBr3/C3N4 samples are prepared using a modified facile anti-solvent precipitation method [16], with detailed procedure provided in the Supporting Information. Pristine g-C3N4 (JCPDS 87-1526) and FAPbBr3 (congruent with the previous report [17]) crystallise into their most thermodynamically stable graphite and cubic phase, respectively (Figure S1, Powder X-ray diffraction (PXRD)). The diffraction patterns of FAPbBr3/C3N4 are consistent with both phases, suggesting a successful synthesis of FAPbBr3/C3N4 hybrid. In the next, the morphologies of g-C3N4, FAPbBr3 and FAPbBr3/C3N4 samples prepared using modified anti-solvent method are confirmed by scanning electron microscopy (SEM), as it is shown in Figure S2a, the average size of FAPbBr3 synthesised from pure precursor solution (drying at 58 °C) is ca. 3 μm with its typical square morphology. On the other hand, the size of FAPbBr3 is dramatically reduced when using the same anti-solvent precipitation in presence of g-C3N4 as seed, this phenomenon was also observed in other FAPbBr3-involved nanohybrids, due to the extra nucleation sites [1,18,19]. For the FAPbBr3/C3N4 hybrids, the size of g-C3N4 is few tens micrometres and the decorated FAPbBr3 nanocrystals is few nanometres in size, from which the FAPbBr3 nanocrystals can hardly be identified using SEM due to the too small size (Figure S2). Thus, the high-resolution transmission electron microscopy (HRTEM) is employed to further investigate the crystal structure and morphology of as-prepared FAPbBr3/C3N4 hybrids. The g-C3N4 exhibits a typical plate-like morphology attributing to its graphite structure (Figure 1a,b), for contrast, darker spots of ca. 10 nm in size are observed on the g-C3N4 after the decoration of FAPbBr3 nanocrystals (Figure 1c,d), these darker spots are confirmed to be FAPbBr3 by select area electron diffraction (SAED, Figure 1c), in which the electron diffraction pattern from cubic crystal perovskite is consistent with the previous report [20]. In addition, the elemental formation was confirmed using SEM energy dispersive X-ray spectroscopy (EDX, Figure S3), the elements being detected were consistent with the predominant elements in g-C3N4 and FAPbBr3. Besides the morphological variation, no obvious chemical state differences of pristine are revealed by exploiting X-ray photoelectron spectroscopy (XPS) in the nanohybrid materials (Figure S4). As shown in Figure S4b, the XPS spectrum of g-C3N4 clearly records three peaks with different binding energies of 287.2 and 397.6 eV corresponding to the core level of C 1s and N 1s, respectively. Consistently, the binding energy of Pb 4f (Figure S4c) in FAPbBr3 is 137.4 and 142.3 eV, assigned to Pb 4f7/2 and Pb 4f5/2 [21]. The binding energy of Br 3d in FAPbBr3 (Figure S4d) at 67.2 and 68.1 eV, corresponding to Br 3d5/2 and Br 3d3/2 [22]. FAPbBr3 chemically reacts with C-NHx in C3N4 to generate C-N-Br bond due to the sp2-hybridised nitrogen in C3N4 [23,24,25]. In this manner of chemical bonding, the lone pair electrons provided by FAPbBr3 can neutralise the positive charge effect of hybridisation. The positive shift of binding energy of Br 3d in hybrids (Figure S4d) could support above reasoning. Similarly, it can be inferred that the positive shift of binding energy of Pb in hybrids (Figure S4c) is to balance the electron redistribution in hybrids. In addition, binding energy of Pb 4f and Br 3d presented shift toward greater energy after coupling with g-C3N4, this is accompanied by an increased electron density and enhanced electron-donating ability for FAPbBr3 side. As a result, an internal electric field undergoing electron transfer from FAPbBr3 to g-C3N4 is constructed, and accordingly, holes from g-C3N4 to FAPbBr3.

2.2. Optical Features

The optical properties of g-C3N4, FAPbBr3 and FAPbBr3/C3N4 are characterised by UV-vis diffuse reflectance spectroscopy (DRUVS, Figure 2). Typical absorption edges and band gaps are exhibited for a series of materials: 441 nm (ca. 2.81 eV) for g-C3N4 and 560 nm (2.21 eV) for FAPbBr3, which are consistent with the previous reports.
In comparison to the pristine g-C3N4, a substantial enhancement of absorption capability is observed from FAPbBr3/C3N4 hybrids due to the adding of FAPbBr3, especially in the visible region. In addition, with respect to the pristine FAPbBr3, the hybrid materials exhibit a slight blue shift of ca. 15 nm, which could be attributed to the crystal size reduction [26]. FAPbBr3/C3N4 hybrid materials with 5, 10, 20 and 30 wt% of FAPbBr3 are prepared, elevating the weight ratio of FAPbBr3 in the hybrids leading to an increased visible region absorption.
In addition to the absorption spectrum, the emission of hybrid materials and pristine materials is determined by steady-state photoluminescence (PL) spectra to demonstrate the photophysical benefit of the formation of the hybrid system. Figure 3 presents PL spectra of g-C3N4, FAPbBr3 and FAPbBr3/C3N4 with different weight ratios, in which the pristine g-C3N4 and FAPbBr3 exhibit the typical PL emission peaks centred at ca. 442 and 562 nm, respectively. On the other hand, the FAPbBr3/C3N4 hybrids show obviously quenched PL emission intensity with respect to pristine g-C3N4, especially for the one loaded with 20% perovskite, suggesting that the photoinduced charge recombination rate occurring in the hybrids has been partially inhibited [7].

2.3. Photocatalytic Activity

The photocatalytic performances of the whole sample series are evaluated via selective photocatalytic oxidation of benzylic alcohol. Certain amounts (Supporting Information) of samples are put in an apolar solvent (trifluorotoluene) with molecular oxygen injection, and the Xe lamp with AM 1.5 G filter is then applied (100 mW cm−2) as a simulated solar illumination. For the photocatalytic activity test, the pristine FAPbBr3 (10 mg) and g-C3N4 (10 mg) are exploited as controls, giving the conversion rate of ca. 14.6% and 1.8% after an illuminated duration of 4 h (in 1.5 mL trifluorotoluene containing 0.1 mmol benzyl alcohol, saturated with oxygen), respectively (the photocatalytic conversion rate of samples and control groups are summarised in Table S1 under above conditions). As it is shown in Figure 4a for photoactivity results, the hybrids exhibit a substantial improvement compared to the pristine materials. About half-fold activity enhancement is obtained by adding 5 wt% of FAPbBr3, in comparison to pure FAPbBr3. The best performance of ca. 46.6% conversion rate (4 h illumination) is achieved from the hybrid with 20 wt% of FAPbBr3, which is approximately three-fold enhancement over pristine FAPbBr3 control group. The conversion rate of 10 mg 20 wt% FAPbBr3/C3N4 could be further enhanced to 69.5% with 8 h illumination (Figure 4b) at room temperature, which can be compared to that of FAPbBr3/TiO2 (10 mg, 8 h illumination at room temperature, 63% conversion rate, 99% selectivity) [19] and mpg-C3N4 (50 mg, 3 h illumination at 100 °C, 70% conversion rate, 68% selectivity) [27]. In addition, further increasing the FAPbBr3 weight ratio over 20 wt% will lead to a reduction of conversion rate. This could be due to two reasons: (1) The overloaded FAPbBr3 in hybrid reduces the g-C3N4 surface area available exposed to the reagent in apolar solvent; (2) the increased amount of FAPbBr3 nanocrystals indicates more interfaces and recombination centres, as it was observed in PL spectra (Figure 3). Based on both factors, excessive loading of FAPbBr3 will not be necessary for pursuing further optimisation of photocatalytic performance. Furthermore, adjusting the weight ratio between FAPbBr3 and g-C3N4 will not compromise the high selectivity (over 98% across all hybrids) for benzylic alcohol oxidation.
To further realise the photocatalytic process, electron spin resonance (ESR) spectroscopy is exploited to confirm the photo-induced reactive oxygen species, under simulated solar illumination. 5,5-Dimethy-1-Pyrroline N-oxide (DMPO) is employed as a trapping agent. Negligible signals from DMPO••O2− is observed in absence of illumination for hybrids (Figure 5). When the simulated illumination is applied, however, significantly increased ESR signals generated from DMPO••O2− are recorded, suggesting that the reduction of O2 to •O2− is triggered by photo-induced electrons from hybrids. Besides the •O2− signals, an additional ESR signal raised by nitroxide radical is observed, this could be attributed to the photo-induced cleavage of ring opening of DMPO••O2− [28]. The photocatalytic process of benzyl alcohol oxidation using OHIPs and hybrids is illustrated below in Figure 6. As demonstrated in previous reports [29,30], the generation of h+ and •O2− would lead to the formation of benzaldehyde. Another possible product form benzyl alcohol oxidation is benzoic acid, which would be formed in presence of ·OOH radicals. While in this work, no ·OOH radicals are monitored, resulting in the high selectivity of samples.

2.4. Stability Investigation

The aim of the photostability tests is to evaluate the potential influence of g-C3N4 on the FAPbBr3/C3N4 hybrids, since it may lead to different stability behaviour in comparison to that of typical FAPbBr3/metal oxide photocatalyst. The photostability of samples is initially demonstrated by repeating the photocatalytic cycles (4 h under illumination) with refilled reactant (benzylic alcohol) for six times. In terms of the pristine FAPbBr3 sample, the photoactivity loss is ca. 7.2% relative to its conversion rate in the first cycle, with a steady decreasing rate in the subsequent five cycles. In contrast, the FAPbBr3/C3N4 hybrids with different weight ratios presented similar photostability trend (Figure S5). For instance, the photoactivity loss of 20% FAPbBr3/C3N4 hybrids is ca. 16.9% after the first reaction cycle, and then the photoactivity remains stable from two to six reaction cycles (Figure 7a,b). The reduced photoactivity after reaction cycles in OIHPs-involved hybrids is a common phenomenon, it was typically concluded as that the product (benzaldehyde) offers higher polarity than the reactant (benzylic alcohol), and thus the illumination accelerates the dissolution of FAPbBr3 [19], which would partially explain the photoactivity decrease in both pure FAPbBr3 and hybrids. However, in comparison to the pristine FAPbBr3, FAPbBr3/C3N4 exhibits different trends of photostability (Figure 7a,b), suggesting that other factors should be considered in these photoactivated reactions.
Thus, in order to further realise the stability behaviours of FAPbBr3/C3N4, a comparison is made between FAPbBr3/C3N4 and FAPbBr3/WO3 hybrids (see Figures S6–S8 in supporting Information for details of the as-prepared FAPbBr3/WO3). WO3 has a similar band gap energy with that of C3N4 (ca. 2.81 eV). Besides, both of WO3 and C3N4 present plate-like morphology when prepared through common methods. Different from the FAPbBr3/C3N4, FAPbBr3/WO3 exhibits a steady photoactivity decreasing along with the six cycles, which is consistent with the behaviours of pristine FAPbBr3 and other typical OIHPs/metal oxides hybrids [30,31,32]. These results suggest that g-C3N4 should possibly be responsible for the FAPbBr3/C3N4 photostability behaviour instead of the construction of hybrids. Next, long-pass filter (420 nm, 450 nm and 500 nm) is applied on samples (FAPbBr3/C3N4, WO3/FAPbBr3 and FAPbBr3) to demonstrate the dependence of incident wavelength of light. When applying the long-pass filter (420 nm), the photostability of the three samples present photostability of similar trends, comparing to each of that under white light illumination, respectively. While relative to that under 420 nm long-pass filter, the FAPbBr3/C3N4 sample performs different trend of photostability (no dramatic conversion rate decreasing was found after first cycle) after employing the 450 nm (Figure 7c,d) or 500 nm long-pass filter (summarised in Table S2, supporting information). After 1 reaction cycles under illumination without filters, the conversion rate of FAPbBr3, FAPbBr3/WO3 and FAPbBr3/C3N4 decreased 7.2%, 7% and 16.9%, respectively. Then, FAPbBr3/C3N4 (20 wt%) exhibits outstanding photostability during two to six cycles, only less than 1% photoactivity loss, which can be compared to FAPbBr3 (19.2%) and FAPbBr3/WO3 (19%).
As it was known that g-C3N4 and FAPbBr3 would construct a typical type-II band structure, in which the holes migrate from the valance band (VB) of g-C3N4 to the VB of FAPbBr3 for benzylic alcohol oxidation reaction. During the preparation of samples, it is unavoidable that pristine g-C3N4 and FAPbBr3 would be in presence in the as-prepared FAPbBr3/C3N4 samples. The pristine g-C3N4 typically exhibits a higher oxidation potential than this type-II hybrid. When the energy of incident photons is greater than the band gap of pristine g-C3N4 (2.81 eV, 441 nm), the higher oxidation potential of g-C3N4 (with respect to FAPbBr3/C3N4) allows the oxidizing of N-H moieties into imines [33], which would partially consume the FA+(HC(NH2)2+) and Br− moieties in FAPbBr3, especially those on the surface of FAPbBr3 nanocrystals, thus resulting in decreasing of conversion rate after the first photocatalytic cycle. However, the oxidised N-H moieties typically present good tolerance to the typical polar solvent [14], therefore leading to the optimised photostability during the two to six cycles (Figure 7b). As a result, although the photoactivity FAPbBr3/C3N4 hybrids reduced 16.9% in the first cycle, only less than 1% conversion rate loss is recorded in the subsequent five cycles.
Furthermore, we compared the SEM images and XRD patterns of samples before and after the photocatalytic reactions. It should be noted that we focus on the possible morphology or crystal structure changes of FAPbB3, since the g-C3N4 is extremely chemically stable [34]. FAPbBr3 of few tens micrometre scale in size is prepared (by slowing the crystallisation process at lower temperature) for convenient morphology evaluation, because the nanocrystals are too small to be monitored using SEM. Before the photocatalytic reactions, the FAPbBr3 crystals present the typical cubic-like morphology with smooth surface (Figure 8a). The surface of pristine FAPbBr3 caved in (Figure 8b) after one photocatalytic reaction cycle, which could be due to the FA+ dissolution. On the other hand, interestingly, we observed stripes and intersected nanorods (red square frame in Figure 8c) on the surface of FAPbBr3 crystals when g-C3N4 is present. We believe this is highly possible to be the surface passivation attributing to the presence of g-C3N4 and thus preventing the photoactivity from dropping in the stability tests. In addition, there are no XRD patterns changes detected for these samples before and after photocatalysis, suggesting the samples mainly remain in their crystal structures.

3. Conclusions

In summary, a hybrid photocatalyst formed by g-C3N4 and FAPbBr3 is developed for highly stable and efficient photocatalytic oxidation of benzylic alcohol into aldehydes, which performs a three-fold enhancement in photocatalytic efficiency compared with pristine FAPbBr3. In addition, the uncommon photostability behaviour of FAPbBr3/C3N4 hybrids under white light illumination is realised by detailed comparing with metal oxide/FAPbBr3 hybrids and pristine FAPbBr3. As a result, although the coupled g-C3N4 would increase the photoactivity loss of hybrids in the original photocatalytic reactions, the photostability is dramatically enhanced in the subsequent reactions. We believe this would supply insights for OHIPs-involved optoelectronic applications toward the stability issues.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/catal11040505/s1, Figure S1. PXRD of FAPbBr3/C3N4 hybrids, where A = diffraction pattern from (110) of g-C3N4 (JCPDS# 87-1526), the rest of the diffraction patterns are consistent with FAPbBr3 from a previous report. Figure S2. SEM images of (a) prinstin FAPbBr3 crystals systhesis through anti-solovent method and their size distribution; (b)–(d) FAPbBr3/C3N4 hybrids materials. Figure S3. Selected area EDX analysis of the as-prepared FAPbBr3/C3N4 samples, with detailed elemental distribution. Figure S4. XPS spectrum of a C3N4/FAPbBr3 hybrids materials; (b) prinstine g-C3N4; (c–f) bind energy of Pb 4f orbitals, Br 3d orbitals, C 1s orbitals and N 1s orbitals, respectively. Figure S5. The photoactivity of C3N4/FAPbBr3 hybrids materials with respect to the photoactivity in the first cycle of each. The reaction conditions are consistent with other tests. Figure S6. HRTEM of (a) WO3 nanoplate and (b) WO3/FAPbBr3 hybrids materials. Figure S7. TEM-HAADF image and according elemental mapping of WO3/FAPbBr3 hybrids materials. Figure S8. PXRD of WO3/FAPbBr3 hybrids with different FAPbBr3 weight ratios, in which # = FAPbBr3 and * = WO3 (JCPDS# 43-1035), respectively. Table S1. Photocatalytic oxidation of benzylic alcohol using a series of samples. Table S2. Photocatalytic oxidation of benzylic alcohol using a series of samples with long-pass filter (420 nm, 450 nm and 500 nm).

Author Contributions

Conceptualization, M.Z., W.W. and F.G.; Fomal analysis, M.Z. and W.W.; Writing—original draft, M.Z. and W.W.; Writing—review and editing, M.Z., W.W. and F.G.; Funding acquisition, M.Z., F.G. and D.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2020B1515020032, 2020B1515120022), the National Natural Science Foundation of China (Grant Nos. 62074060, 52002135), the Guangdong Science and Technology Plan (Grant No. 2019B040403003), the Pearl River Talent Recruitment Program (Grant No. 11804058), the Natural Science Foundation of Guangdong Province (Grant No. 2018A0303130199), the Program for Guangdong Introducing Innovative and Entrepreneurial Teams (2016ZT06C412) and the Scientific and Technological Plan of Guangdong Province, China (No. 2019B090905005).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) TEM image of the pristine g-C3N4 nanoplate; (b) HRTEM image of FAPbBr3/C3N4 hybrids; (c) FAPbBr3/C3N4 hybrids in which the FAPbBr3 nanocrystals are labelled by white circle with SAED on the right top in this image; (d) the lattice fringes of g-C3N4 (002) and FAPbBr3 (001), respectively.
Figure 1. (a) TEM image of the pristine g-C3N4 nanoplate; (b) HRTEM image of FAPbBr3/C3N4 hybrids; (c) FAPbBr3/C3N4 hybrids in which the FAPbBr3 nanocrystals are labelled by white circle with SAED on the right top in this image; (d) the lattice fringes of g-C3N4 (002) and FAPbBr3 (001), respectively.
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Figure 2. (a) UV-vis absorption spectrum of FAPbBr3/C3N4 hybrids materials with different weight ratio of FAPbBr3; (b) UV-vis diffuse reflectance spectrum and (c) digital photographs of FAPbBr3/C3N4 hybrids.
Figure 2. (a) UV-vis absorption spectrum of FAPbBr3/C3N4 hybrids materials with different weight ratio of FAPbBr3; (b) UV-vis diffuse reflectance spectrum and (c) digital photographs of FAPbBr3/C3N4 hybrids.
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Figure 3. PL spectrum of FAPbBr3/C3N4 hybrids materials with different weight ratio of FAPbBr3, g-C3N4 and FAPbBr3.
Figure 3. PL spectrum of FAPbBr3/C3N4 hybrids materials with different weight ratio of FAPbBr3, g-C3N4 and FAPbBr3.
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Figure 4. (a) Photocatalytic oxidation of benzylic alcohol to benzaldehyde over pristine FAPbBr3/C3N4 of different weight ratios, noted that the pure FAPbBr3 is of ca. 3 μm; (b) photocatalytic oxidation of benzylic alcohol using 20% FAPbBr3/C3N4 under different illumination durations, the data is averaged from 3 individual tests. Reaction conditions: photocatalyst (10 mg) and 0.1 mmol reactant, in trifluorotoluene (1.5 mL) saturated with oxygen before experiments, irradiated by AM 1.5G (ca. 100 mW cm−2) for 4 h each cycle, under room temperature.
Figure 4. (a) Photocatalytic oxidation of benzylic alcohol to benzaldehyde over pristine FAPbBr3/C3N4 of different weight ratios, noted that the pure FAPbBr3 is of ca. 3 μm; (b) photocatalytic oxidation of benzylic alcohol using 20% FAPbBr3/C3N4 under different illumination durations, the data is averaged from 3 individual tests. Reaction conditions: photocatalyst (10 mg) and 0.1 mmol reactant, in trifluorotoluene (1.5 mL) saturated with oxygen before experiments, irradiated by AM 1.5G (ca. 100 mW cm−2) for 4 h each cycle, under room temperature.
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Figure 5. ESR spectra of (a) FAPbBr3 and (b) 20% FAPbBr3/C3N4 hybrids.
Figure 5. ESR spectra of (a) FAPbBr3 and (b) 20% FAPbBr3/C3N4 hybrids.
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Figure 6. Schematic illustration of photo-catalytic reaction occurring on FAPbBr3/C3N4 hybrids.
Figure 6. Schematic illustration of photo-catalytic reaction occurring on FAPbBr3/C3N4 hybrids.
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Figure 7. (a) The conversion rate of 20% FAPbBr3/C3N4 and control groups under Xe lamp illumination for 6 cycles; (b) the conversion rate relative to the first cycle under Xe lamp illumination; (c,d) conversion rate for six cycles and conversion rate relative to the first cycle when applying a 450 nm long-pass filter, respectively. Reaction conditions: photocatalyst (10 mg) and 0.1 mmol reactant, trifluorotoluene (1.5 mL) saturated with oxygen before experiments, irradiated by AM 1.5 G (ca. 100 mW cm−2) for 4 h each cycle, under room temperature.
Figure 7. (a) The conversion rate of 20% FAPbBr3/C3N4 and control groups under Xe lamp illumination for 6 cycles; (b) the conversion rate relative to the first cycle under Xe lamp illumination; (c,d) conversion rate for six cycles and conversion rate relative to the first cycle when applying a 450 nm long-pass filter, respectively. Reaction conditions: photocatalyst (10 mg) and 0.1 mmol reactant, trifluorotoluene (1.5 mL) saturated with oxygen before experiments, irradiated by AM 1.5 G (ca. 100 mW cm−2) for 4 h each cycle, under room temperature.
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Figure 8. SEM image of (a) FAPbBr3 crystals prepared at 25 °C using anti-solvent method; (b) pristine FAPbBr3 crystals after the photocatalytic oxidation of benzylic alcohol; (c) FAPbBr3 crystals after the photocatalytic oxidation of benzylic alcohol when g-C3N4 is present.
Figure 8. SEM image of (a) FAPbBr3 crystals prepared at 25 °C using anti-solvent method; (b) pristine FAPbBr3 crystals after the photocatalytic oxidation of benzylic alcohol; (c) FAPbBr3 crystals after the photocatalytic oxidation of benzylic alcohol when g-C3N4 is present.
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Zhang, M.; Wang, W.; Gao, F.; Luo, D. g-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol. Catalysts 2021, 11, 505. https://doi.org/10.3390/catal11040505

AMA Style

Zhang M, Wang W, Gao F, Luo D. g-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol. Catalysts. 2021; 11(4):505. https://doi.org/10.3390/catal11040505

Chicago/Turabian Style

Zhang, Menglong, Weizhe Wang, Fangliang Gao, and Dongxiang Luo. 2021. "g-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol" Catalysts 11, no. 4: 505. https://doi.org/10.3390/catal11040505

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