Substantial Enhancement toward the Photocatalytic Activity of CdS

Subscriber access provided by Kaohsiung Medical University

Energy, Environmental, and Catalysis Applications

A Substantial Enhancement Towards the Photocatalytic Activity of CdS Quantum Dots by Photonic Crystal Supporting Films Ruifang Zhang, Fang Zeng, Fei Pang, and Jianping Ge ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14437 • Publication Date (Web): 19 Nov 2018 Downloaded from http://pubs.acs.org on November 21, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

A Substantial Enhancement Towards the Photocatalytic Activity of CdS Quantum Dots by Photonic Crystal Supporting Films

Ruifang Zhang, Fang Zeng, Fei Pang, Jianping Ge* Shanghai Key Laboratory of Green Chemistry and Chemical Processes School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, China E-mail: [email protected]

Abstract: The introduction of photonic crystal (PC) to semiconductor, usually appear in the form of inverse opal materials, has been proved to be an effective way to enhance the photocatalytic activity, but their enhancement factor is merely 2- to 4- fold in most previous reports. In this work, a supported thin film photocatalyst (CdS/SiO2-ETPTA), as a new PC based catalyst system, is prepared for hydrogen evolution under visible light, which presents an 6.4- to 8.8-fold activity compared to the same CdS quantum dots deposited on a non-PC film. This substantial enhancement originates from the high reflectivity of PC and absorption of reflected light by CdS, whose absorption edge exactly match the stopband of PC. Compared to the traditional inverse opal photocatalysts, the PC supported photocatalyst possesses many advantages including simplified procedures in synthesis, a substantial enhancement of activity, flexible modification with mature thin film techniques, good stability and easy regeneration in reaction.

Keywords: photonic crystal, CdS, quantum dots, photocatalyst, hydrogen evolution

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

Introduction Photonic crystals (PCs) are optic materials composed of alternate dielectric content, which have been broadly used in physical/chemical sensor,1-2 display unit,3-5 green printing,6-7 anti-counterfeiting identification,8-10 high performance chromatography,11 solar energy conversion12-13 and many other optical devices. Recently, photonic crystals with inverse opal (IO) structures, such as TiO2 IO, have been found valuable as photocatalysts because of the slow photon effect at the red edge of photonic stopband, the multiple light scattering within the macropores, and the enhanced mass transfer and surface reaction from pore structures. These structural effects are beneficial to the light absorption or the raise of surface activity, so that the IO photocatalysts will possess enhanced activity without the need of any chemical dopings and modifications. The first work of such photocatalyst is the anatase TiO2 IOs reported by Ozin in 2006, which showed a double rate for degradation of methylene blue under white light.14 Since then, great efforts have been paid to the synthesis of N-/F-doped TiO2 IOs,1516

Pt-/Au-/Ag-modified TiO2 IOs17-21 and other semiconductor IOs including ZnO,22-23 Fe2O3,24

ZnGa2O4,25 BiVO421, 26 and C3N4.27 Meanwhile, the enhancement of activity has been fully verified by photocatalytic degradation of organic compound,28-30 water splitting31-35 and reduction of CO2.36-37 Although these IO photocatalysts have attract great interests and point out a promising catalyst design, the enhancement of photocatalytic activity is merely 2- to 4- fold in practical reaction based on the reported research works. (Table S1, S2) The reason for the low enhancement of activity can be explained by the conflict impacts of photonic structures.38 On one hand, the PC structure will slow the photons at the red edge of its photonic stopband, which increase the light absorption and improve the activity. On the other hand, the PC structure will reflect the photons within the photonic stopband to decrease the activity. Only a precise tuning of photonic stopband to match the absorption edge of photocatalyst can allow the slow-photon-induced absorption enhancement to take the dominant role. Therefore, it is still a big challenge to achieve an IO-type PC photocatalyst with higher enhancement factor.


Page 3 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A possible solution to the above problem is the construction of “PC supported photocatalysts”, where the PC reflection and light absorption are separated in different materials. In this new framework, the slow photon effect is not required and the PC’s high reflectivity will no longer be a negative factor because it can act as a mirror to trap the photons into the photoactive materials.38 Compared to the IO photocatalyst, this separated design strategy can realize the production of large-size PC based photocatalysts with much simplified procedures and provide good flexibility to the combination of various semiconductors and PCs, which makes the PC supported photocatalyst a practically usable material. Recently, our group has developed a PC supported C3N4 photocatalyst, which leads to a 1.75fold reaction rate in degradation of Rhodamine B than the same C3N4 deposited on a non-PC support.39 It does not fully tap the potential of the PC supported photocatalyst because the graphitic C3N4 nanorods are not well coupled with PC for absorption enhancement. In this work, we shall report a PC supported thin film photocatalyst (CdS/SiO2-ETPTA) for highly efficient hydrogen evolution under visible light. (Figure 1) Thanks to the extra absorption of reflected light by CdS quantum dots (QDs) and strong coupling between PC and CdS layer, this supported photocatalyst presents 6.4- to 8.8-fold activity in hydrogen evolution compared to the same CdS QDs deposited on non-PC substrate. Systematic studies will prove that the matching between electronic bandgap (EBG) of semiconductor and photonic bandgap (PBG) of PC is the key to the enhancement of photocatalysis. Compared to the traditional IO photocatalyst, this new PC supported photocatalyst possesses many advantages including simplified procedures in synthesis of PC catalysts, a substantial enhancement of photocatalytic activity, flexible modification with mature thin film techniques, good stability in reaction and easy regeneration after reaction.

Experimental Section Materials: Tetraethylorthosilicate (TEOS, 98%), aqueous ammonia (28%) and Na2SO3 (AR) were purchased from Sinopharm Chemical Reagent Co. Ltd. Ethanol (99.9%) were purchased from J&K 3 ACS Paragon Plus Environment


Page 4 of 23

Co. Ltd. Trimethylolpropane ethoxylate triacrylate (ETPTA, Mn = 428), cadmium oxide (CdO, 99.9%), oleic acid (OA, 70%), 1-octadecene (ODE, 90%), sulfur powder, toluene (99.8%) were purchased from Sigma-Aldrich. Na2S·9H2O (99.9%) was purchased from Aladdin Co. Ltd. All chemicals were used directly as received without further treatment. Synthesis of CdS QDs: CdS quantum dots were prepared according to the reported procedure.40 Briefly, CdO (256 mg), OA (3 mL) and ODE (30 mL) were mixed by magnetic stirring in a threenecked flask, which was heated to 270 °C under nitrogen atmosphere to form a transparent and colorless solution. Sulfur (20-60 mg) dispersed in ODE (3 mL) was rapidly injected to the solution so that the temperature decreased to 250 °C immediately. The reaction was maintained at that temperature for 3 min until it was stopped by a rapid cooling and quenching. After being cooled down to room temperature, the reaction solution was diluted by toluene and methanol with volume ratio of 1:1, followed by the addition of excessive isopropanol to precipitate CdS QDs. The CdS QDs were separated from the solution by centrifugation at 9000 rpm for 10 min, and redispersed in toluene. The QDs were washed by precipitation with isopropanol and dispersion with toluene for another two times, and they were finally dispersed in toluene (10 mL) to form homogeneous solutions with CdS concentration ranging from 70 to 350 mg/mL. CdS QDs with average diameter of 2.7 nm, 4.5 nm and 5.5 nm, named as CdS1, CdS2 and CdS3, were prepared by decreasing the dosage of sulfur in the sequence of 60 mg, 40 mg and 20 mg. Preparation of SiO2-ETPTA PC film and CdS/PC photocatalyst: Monodisperse SiO2 particles were first synthesized by a modified Stöber method. The SiO2 particles (0.3 mL) were well dispersed in ethanol by sonication and then mixed with ETPTA (0.7 mL) containing photo initiator, 2-hydroxy-2methylpropiophenone (5%) to form a homogeneous dispersion. The mixture was heated to 90 °C for 2 hours to evaporate the ethanol content, which produced a supersaturated solution of SiO2 colloids (~ 1 mL). The liquid precursor was added to the center of a petri-dish with diameter of 6.6 cm and spun by a spin coater for 20 s with a speed of 1500 rpm to form a thin liquid film. The liquid precursor


Page 5 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spreading in the Petri-dish was transferred to a vacuumed desiccator and cured by UV light (365 nm, 4.8 mW/cm2) for 10 minutes to produce a PC film with specific reflection wavelength. Then, the CdS solution with different concentrations (1 mL) were loaded onto the SiO2-ETPTA PC film and vacuumed for several minutes in desiccator to form CdS/PC photocatalyst with CdS loading at 7 mg, 15 mg, 25 mg and 35 mg. Characterization: Transmission electron microscope (TEM) images were captured by a FEI Tecnai G2 F30 microscope operated at 300 kV. Scanning electron microscope (SEM) images were recorded by a Hitachi S-4800 scanning electron microscopy. The optical microscope (OM) images were taken on an Olympus BXFM reflection-type microscope operated in dark- field mode. UV-Vis absorption spectrum was measured by Shimadzu UV-2700. Reflection spectra were measured using an Ocean Optics Maya 2000 Pro spectrometer coupled to a six-around-one reflection/back scattering probe. Powder X-ray diffraction (XRD) patterns were measured on Rigaku Ultima IV X-ray diffractometer operated at 35 kV and 40 mA with Ni-filtered Cu-Kα radiation as X-ray beam source. Spin-coating was performed by a Laurell WS-650MZ spinner. Photocatalytic H2 production: First of all, the CdS/SiO2-ETPTA thin film photocatalyst was immersed in an aqueous solution (50 mL) of Na2S (0.25 mol/L) and Na2SO3 (0.25 mol/L) in quartz reactor, which was evacuated to remove air completely prior to irradiation and maintained at the low pressure state for hydrogen evolution. Then, the solution was irradiated under the visible light only (λ ≥ 420 nm) using a 300W Xe-lamp with a UV cutoff filter. The Xe lamp was placed right above the quartz reactor with a distance of 15 cm to the CdS/PC thin film photocatalyst, which was put at the bottom of the quartz reactor. The incident angle of light can be considered as 0°, and all the irradiation conditions were kept same for all experiments. The temperature of the reaction solution was maintained at 4 °C by a flow of cooling water during the reaction. The evolved H2 gas was sampled out at specific time and analyzed by gas chromatograph equipped with a thermal conductive detector



Page 6 of 23

(TCD) and a 5Å molecular sieve column. Due to the existence of sacrificial agent, the major oxidized product was Na2S2O3, and a small amount of element S and sulfate ions could also be detected.

Results and discussion Monodispersed CdS quantum dots (QDs) were first synthesized by a high-temperature reaction between CdO and sulfur in 1-octadecene with oleic acid as surfactant.40 (Figure 2) These CdS QDs could be well dispersed in non-polar solvents due to the wrapping of ligand OA on their surface. They had a typical zinc blend structure, which was proved by their X-ray diffraction patterns. (JCPDS #800019). By decreasing the dosage of sulfur from 60 mg to 20 mg, one could prepare CdS1, CdS2 and CdS3 QDs with diameter of 2.7 nm, 4.5 nm and 5.5 nm, as confirmed by TEM images and size distributions. The increase of particle size lead to the red-shift of absorption peak/shoulder from 380 nm, 404 nm to 423 nm. The flexible tuning of absorption brought great convenience to the selection of suitable CdS in the latter experiments, where the catalytic activity was optimized by bandgap matching of photocatalyst and photonic crystal supports. On the other hand, SiO2-ETPTA photonic crystal (PC) film was prepared by spin coating of SiO2 colloidal solution onto a Petri dish, followed by UV curing to fix the colloidal crystals. The key to this synthesis was the preparation of supersaturated ETPTA solution of SiO2 particles via selective evaporation of volatile solvent, after which the particles would automatically precipitate to form liquid photonic crystals in monomer and the liquid film could be quickly converted to polymeric photonic crystals by photo polymerization.41 Spin-coating helped to spread the liquid precursor uniformly on the substrate, so that a high quality PC film with adequately large size could be obtained to ensure repeatable activity for photocatalysis. The SiO2-ETPTA PC film showed an intense blue color and uniform reflection of incident light. (Figure 3a-3f) SEM images proved that the particles were orderly arranged in crystals. A lowmagnification SEM image with corresponding FFT pattern suggested that the photonic crystal was in 6 ACS Paragon Plus Environment

Page 7 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


long range order which ensured the uniform photonic properties throughout the film. (SI Figure S1) Meanwhile, the reflection changed regularly along the radial direction, which could be illustrated by 60 reflection signals measured from center to the edge of the film along the black, red and green lines. The reflection wavelengths were measured to be 450 to 470 nm with a deviation of 2.2%, and they usually followed a gently volcano trend along the radial direction. At the same time, the average reflection intensities of the film increased from 25% to 70% and then decreased to 45% along the radial direction. Therefore, the PC film was overall uniform in reflection wavelength with acceptable intensity fluctuations in radial direction, which reached a good balance between high crystallinity and large size for PC. The CdS QDs were then loaded onto the SiO2-ETPTA PC film by drop-casting to form a supported thin film photocatalyst (CdS/PC). (Figure 3g-3i) The hydrophobic CdS QDs could be well dispersed on the hydrophobic PC, which formed a dense particle film because the nanoparticles would be closely packed after the evaporation of solvent. Since the PC film has flat and smooth surface, the surface area of the whole thin film photocatalysts was simply determined by the deposited CdS quantum dots, which was measured to be around 7.8 m2/g for all three CdS quantum dots. (SI Figure S2) After the coating of CdS QDs, the PC film turned from blue to greenish yellow, which suggested that the CdS film was adequately thin to ensure the propagation of both the incident and reflected light. SEM images confirmed that the PC film was completely covered by the CdS layer with about 1 μm in thickness, which was consistent with the dosage of CdS. Through the ultraviolet photoelectron spectroscopy (UPS) measurement, the reduction potential of the photocatalytic system was calculated to be -1.7 eV according to the CB minimum, which was capable of reducing water to H2. (SI Figure S3) When the CdS/PC catalyst was applied to the photo reduction of water in the presence of Na2S and Na2SO3,42 it did present enhanced activity compared to the CdS QDs on non-PC support. For the convenience of comparison, the structural information and H2 evolution rate of all photocatalysts in this work were supplied in Table S3. Here, CdS3 QDs (15 mg) were deposited on a ETPTA film and



Page 8 of 23

3 PC films (SI Figure S4) with increasing reflection intensities, which was controlled by the addition of different amounts of photo-initiator during the synthesis. Generally, a higher amount of initiator and a faster solidification lead to a lower reflection intensity, because the colloidal particles didn’t have adequate time to assemble into ordered structures before they were fixed. As the reflection increased in the sequence of 0%, 36%, 68% and 100%, the H2 evolution rate was measured to be 0.178, 0.48, 0.88 and 1.21 mmol·g-1·h-1. (Figure 4a, 4b) Apparently, all the PC supported photocatalysts had higher activity than the non-PC supported catalyst, and the highest enhancement factor reached 6.8. The increasing of activity along with the PC reflection intensity suggested that such enhancement was related to the absorption of reflected light from PC and the utilization of this energy to produce more photoelectrons for water reduction. In addition to the PC reflection intensity, the dosage of CdS QDs which controlled the thickness of CdS layer was another critical parameter to affect the photocatalytic activity. (Figure 4c, 4d) We had loaded 7-mg, 15-mg, 25-mg and 35-mg CdS quantum dots to the circular photonic crystal film with diameter of 6.6 cm and area of 0.00342 m2, and tested their hydrogen production. The “unit mass H2 evolution rate” were measured to be 1.09, 0.64, 0.35 and 0.11 mmol·g-1·h-1, and the “unit area H2 evolution rate” were measured to be 2.23, 2.81, 2.56 and 1.13 mmol·m-2·h-1, respectively. Here, a high loading of CdS QDs lead to a thicker CdS layer, which consumed the visible light reflected by PC layer and weakened the enhancement of photocatalytic activity. Meanwhile, a thicker CdS layer was also unfavorable to the surface reaction in photocatalysis, as only the exposed surface CdS QDs might contribute to the catalysis due to their hydrophobic characteristics. From the viewpoint of “unit mass H2 evolution rate”, the rate was monotonically enhanced from 0.11 to 1.09 mmol·g-1·h-1 when less CdS were loaded on PC, because both the exposed surface area of unit mass photocatalyst and the enhancement effect of PC support increased in this case. From the viewpoint of “unit area H2 evolution rate”, the rate first increased from 1.13 to 2.81 mmol·m-2·h-1, as the CdS loading decreased from 35 mg to 15 mg, because a thinner layer of CdS would allow the transmission of more reflected light and


Page 9 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


enhanced the absorption by surface photocatalyst. The rate then decreased to 2.23 mmol·m-2·h-1 when the CdS loading further decreased to 7 mg, because an extremely low loading of photocatalysts on a substrate with fixed area would lead to the decrease of photocatalytic activity eventually. Since the “unit area H2 evolution rate” was more valuable to judge the activity of photocatalyst film in practical reaction, the optimal dosage of CdS was determined to be 15 mg, which corresponded to 4.39 g/m2 loading of CdS on PC film. The separation of PC structure and photocatalysts into different materials brought convenience to the combination of different semiconductors and PCs, and the optimization of catalytic activity via matching their bandgaps. On one hand, we had prepared photocatalysts by deposition of CdS3 QDs (15 mg) on 4 PC supports (SI Figure S5) with reflection wavelength increased in the sequence of 420 nm, 451 nm, 520 nm and 590 nm. The corresponding enhancement of H2 evolution rate compared to CdS/non-PC decreased in the sequence of 7.24, 2.7, 1.7 and 1.4 fold as the reflection of PC gradually redshifted and deviated from the absorption of CdS. (Figure 5a, 5b) On the other hand, we had also prepared photocatalysts by deposition of CdS1, CdS2 and CdS3 QDs on the same PC supports with reflection at 420 nm. In this case, the enhancement factor increased in the sequence of 2.9, 6.4 and 8.8 fold as the absorption of CdS gradually redshifted to coincide with the reflection of PC. (Figure 5c, 5d) Both experiments indicated that the matching of photonic bandgap of PC and electronic bandgap of semiconductor would promote the absorption of reflected light and then lead to higher catalytic activity for photo reaction. Therefore, when the photocatalytic reaction was performed under monochromic irradiation to dermine the quatunm efficiency for PC and non-PC supported catalyst, the H2 evolution showed the highest enhancement with irradiation around 420 nm, where the incident light wavelength coincided with both the electronic and photonic bandgaps. (SI Figure S6) Based on the above investigations, a clear mechanism for the enhancement of photocatalysis by PC supporting film could be summarized as follows. Under irradiation of visible light, part of the incident light was absorbed by the CdS QDs film, which produced photoelectrons to reduce H+ in water to H2.



Page 10 of 23

At the same time, part of the incident light propagated through the CdS thin film and interacted with the PC film. Visible light within the photonic bandgap would be entirely reflected towards the CdS layer. When the photonic bandgap (PBG) was close to the electronic bandgap (EBG) of CdS, the reflected light would be effectively absorbed by CdS, leading to the excitation of more photoelectrons and faster evolution of H2 gas. With proper design of bandgap structures, PC support would bring a substantial enhancement to the activity of many semiconductor photocatalysts. The CdS/PC photocatalyst showed stable activity when it was illuminated by visible light, and it could be regenerated to restore the activity to the original level. Considering the alternation of day and night, the long term stability of CdS2/PC1 photocatalysts were examined when the visible light was turned on and off by every 2 hours. (Figure 6a) The H2 evolution rate for the 4 cycles were measured to be 1.91, 1.84, 1.96 and 1.87 mmol·g-1·h-1, which suggested the photocatalysts possessed stable activity even the H2 evolution was interrupted for multiple times. On the other hand, this photocatalyst could be easily separated from the reaction system and regenerated to recover the original activity. After 3-hour reaction, the used CdS QDs were removed from the PC film and the same fresh CdS QDs were loaded to the PC film. (Figure 6b) The H2 evolution rate for the continuous 3 reactions were measured to be 2.23, 2.16, and 2.24 mmol·g-1·h-1, which confirmed the effective regeneration without any decline in catalytic activity. It was worth being noted that the supporting PC films were stable in structure even if the photocatalytic reactions were performed for multiple times, because the colloidal particles were fixed inside the ETPTA matrix and the hydrophobic polymer film wouldn‘t be corroded by water or irradiation. (SI Figure S7) The CdS/PC photocatalyst could be easily modified to boost the catalytic activity due to its compatibility to the well-developed thin film techniques. (Figure 7) For instance, a thin layer of Au nanoparticles could be coupled to CdS/PC film through ion sputtering to form Au/CdS/PC or CdS/Au/PC photocatalyst. Au itself was not a photocatalyst, because the Au/PC film showed no activity at all in the hydrogen production. (SI Figure S8) Instead, Au was widely used as cocatalyst in


Page 11 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


photocatalysis as it could quickly transfer the photoelectrons away from CdS and hinder the recombination of electron-hole pair to improve the photocatalytic activity. Here, the plasmonic effect of Au made little contribution to the enhancement of activity, because the plasmonic absorption didn‘t match the absorption of CdS QDs and the energy carried by the plasmonic electrons was inadequate to excite the electrons in the valance band of CdS. (SI Figure S9) The experimental results showed that the H2 evolution rate for Au/CdS/ETPTA and CdS/Au/ETPTA catalyst (0.77, 1.06 mmol·g-1·h-1) were higher than that of CdS/ETPTA (0.33 mmol·g-1·h-1). Accordingly, the H2 evolution rate for Au/CdS/PC and CdS/Au/PC catalyst (3.11, 3.76 mmol·g-1·h-1) were also higher than that of CdS/PC (2.11 mmol·g-1·h-1). Here, the CdS/Au/PC catalyst showed higher activity than the Au/CdS/ PC catalyst, because the light absorption and excitation of photoelectrons were more efficient when CdS was directly exposed to the irradiation without the covering of Au layer. Based on all the above control experiments, the H2 evolution rate got a 6.4-fold increase after replacing the ETPTA support with PC support, and it got an extra increase of 1.8 fold when Au layer is further coupled to it. Since the photocatalytic activity of current CdS QDs was close to most results in literature (Table S4), our experiments actually proved that the activity of CdS thin film catalyst could be easily increased by an order of magnitude just through coupling with PC support and deposition of Au.

Conclusion In summary, CdS QDs were deposited onto premade SiO2-ETPTA PC film to form a supported thin film photocatalyst (CdS/PC) for hydrogen evolution under visible light. The Petri-dish-size PC films with high crystallinity and uniform reflection ensured the repeatability of photocatalysis and feasibility of CdS/PC catalyst for practical application. The PC supported photocatalyst showed a substantial enhancement in activity due to the absorption of reflected light from PC and production of more photoelectrons. Systematic studies had proved that the matching between electronic bandgap (EBG) of semiconductor and photonic bandgap (PBG) of PC was the key to maximize the activity. The 11 ACS Paragon Plus Environment


Page 12 of 23

CdS/PC reported in this work usually possessed a 6.4- to 8.8-fold activity in H2 evolution compared to the CdS/non-PC catalyst. The enhancement factor rose to 11.4 when Au layer was deposited between CdS and PC through ion sputtering. It was worthy of being mentioned that the photonic crystal induced enhancement of photocatalytic activity was not limitted to semiconductor photocatalyst as it also worked for radical-related photocatalyst for organic reactions. (SI Figure S10) Compared to the traditional IO photocatalysts, the PC supported photocatalyst possessed many advantages including simplified procedures in large scale synthesis of PC based photocatalysts, a substantial enhancement of photocatalytic activity, flexible modification with mature thin film techniques, good stability in reaction and easy regeneration after reaction, all of which rendered it great potentials in solar energy utilization, environment protection and other green chemical processes.

Acknowledgements This work is supported by National Natural Science Foundation of China (21471058, 21671067), and Shuguang Program supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission (15SG21).

Supporting Information PC Supports with different intensities and wavelength, transmission spectra of related thin films, comparison of PC induced enhancement of photocatalytic activity in water splitting, CO2 reduction, degradation of organic compounds and other chemical reactions, comparison of H2 evolution catalyzed by CdS related photocatalysts in literature, summary of of all PC supported CdS photocatalysts and the corresponding H2 evolution rate, are supplied as Supporting Information


Page 13 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References 1.

Cai, Z. Y.; Kwak, D. H.; Punihaole, D.; Hong, Z. M.; Velankar, S. S.; Liu, X. Y.; Asher, S.

A., A Photonic Crystal Protein Hydrogel Sensor for Candida Albicans. Angew. Chem. Int. Ed. 2015, 54 (44), 13036-13040. 2.

Zhu, B.; Fu, Q.; Chen, K.; Ge, J., Liquid Photonic Crystals for Mesopore Detection. Angew.

Chem. Int. Ed. 2018, 57 (1), 252-256. 3.

Su Yeon, L.; Shin-Hyun, K.; Hyerim, H.; Jae Young, S.; Seung-Man, Y., Controlled

Pixelation of Inverse Opaline Structures towards Reflection-Mode Displays. Adv. Mater. 2014, 26 (15), 2391-2397. 4.

Yue, Y. F.; Kurokawa, T.; Haque, M. A.; Nakajima, T.; Nonoyama, T.; Li, X. F.; Kajiwara,

I.; Gong, J. P., Mechano-Actuated Ultrafast Full-Colour Switching in Layered Photonic Hydrogels. Nat. Commun. 2014, 5, 4659. 5.

Arsenault, A. C.; Puzzo, D. P.; Manners, I.; Ozin, G. A., Photonic-Crystal Full-Colour

Displays. Nat. Photonics 2007, 1 (8), 468-472. 6.

Bao, B.; Li, M. Z.; Li, Y.; Jiang, J. K.; Gu, Z. K.; Zhang, X. Y.; Jiang, L.; Song, Y. L.,

Patterning Fluorescent Quantum Dot Nanocomposites by Reactive Inkjet Printing. Small 2015, 11 (14), 1649-1654. 7.

Chen, K.; Fu, Q.; Ye, S.; Ge, J., Multicolor Printing Using Electric-Field-Responsive and

Photocurable Photonic Crystals. Adv. Funct. Mater. 2017, 27 (43), 1702825. 8.

Heo, Y.; Kang, H.; Lee, J.-S.; Oh, Y.-K.; Kim, S.-H., Lithographically Encrypted Inverse

Opals for Anti-Counterfeiting Applications. Small 2016, 12 (28), 3819-3826. 9.

Hu, H.; Tang, J.; Zhong, H.; Xi, Z.; Chen, C.; Chen, Q., Invisible Photonic Printing:

Computer Designing Graphics, UV Printing and Shown by a Magnetic Field. Sci. Rep. 2013, 3, 1484. 10. Fang, Y.; Ni, Y.; Leo, S.-Y.; Taylor, C.; Basile, V.; Jiang, P., Reconfigurable Photonic Crystals Enabled by Pressure-Responsive Shape-Memory Polymers. Nat. Commun. 2015, 6, 7416. 11. Fu, Q.; Zhu, B.; Ge, J., Hierarchically Structured Photonic Crystals for Integrated Chemical Separation and Colorimetric Detection. Nanoscale 2017, 9 (7), 2457-2463. 12. Chen, X. Q.; Ye, J. H.; Ouyang, S. X.; Kako, T.; Li, Z. S.; Zou, Z. G., Enhanced Incident Photon-to-Electron Conversion Efficiency of Tungsten Trioxide Photoanodes Based on 3D-Photonic Crystal Design. ACS Nano 2011, 5 (6), 4310-4318.



Page 14 of 23

13. Lv, L.; Lu, Q.; Ning, Y.; Lu, Z.; Wang, X.; Lou, Z.; Tang, A.; Hu, Y.; Teng, F.; Yin, Y.; Hou, Y., Self-Assembled TiO2 Nanorods as Electron Extraction Layer for High-Performance Inverted Polymer Solar Cells. Chem. Mater. 2015, 27 (1), 44-52. 14. Chen, J. I. L.; von Freymann, G.; Choi, S. Y.; Kitaev, V.; Ozin, G. A., Amplified Photochemistry with Slow Photons. Adv. Mater. 2006, 18 (14), 1915-1919. 15. Rahul, T. K.; Sandhyarani, N., Nitrogen-Fluorine Co-Doped Titania Inverse Opals for Enhanced Solar Light Driven Photocatalysis. Nanoscale 2015, 7 (43), 18259-18270. 16. Wang, T.; Yan, X.; Zhao, S.; Lin, B.; Xue, C.; Yang, G.; Ding, S.; Yang, B.; Ma, C.; Yang, G.; Yang, G., A Facile One-Step Synthesis of Three-Dimensionally Ordered Macroporous N-doped TiO2 with Ethanediamine as the Nitrogen Source. J. Mater. Chem. A 2014, 2 (37), 15611-15619. 17. Liu, J.; Liu, G.; Li, M.; Shen, W.; Liu, Z.; Wang, J.; Zhao, J.; Jiang, L.; Song, Y., Enhancement of Photochemical Hydrogen Evolution over Pt-Loaded Hierarchical Titania Photonic Crystal. Energy Environ Sci 2010, 3 (10), 1503-1506. 18. Zhang, Z.; Zhang, L.; Hedhili, M. N.; Zhang, H.; Wang, P., Plasmonic Gold Nanocrystals Coupled with Photonic Crystal Seamlessly on TiO2 Nanotube Photoelectrodes for Efficient Visible Light Photoelectrochemical Water Splitting. Nano Lett. 2013, 13 (1), 14-20. 19. Zhao, H.; Wu, M.; Liu, J.; Deng, Z.; Li, Y.; Su, B.-L., Synergistic Promotion of Solar-Driven H-2 Generation by Three-Dimensionally Ordered Macroporous Structured TiO2-Au-CdS Ternary Photocatalyst. Appl. Catal. B 2016, 184, 182-190. 20. Chen, Z.; Fang, L.; Dong, W.; Zheng, F.; Shen, M.; Wang, J., Inverse Opal Structured Ag/TiO2 Plasmonic Photocatalyst Prepared by Pulsed Current Deposition and Its Enhanced Visible Light Photocatalytic Activity. J. Mater. Chem. A 2014, 2 (3), 824-832. 21. Zhang, L.; Lin, C.-Y.; Valev, V. K.; Reisner, E.; Steiner, U.; Baumberg, J. J., Plasmonic Enhancement in BiVO4 Photonic Crystals for Efficient Water Splitting. Small 2014, 10 (19), 39703978. 22. Liu, J.; Jin, J.; Li, Y.; Huang, H.-W.; Wang, C.; Wu, M.; Chen, L.-H.; Su, B.-L., Tracing the Slow Photon Effect In a ZnO Inverse Opal Film for Photocatalytic Activity Enhancement. J. Mater. Chem. A 2014, 2 (14), 5051-5059. 23. Meng, S.; Li, D.; Wang, P.; Zheng, X.; Wang, J.; Chen, J.; Fang, J.; Fu, X., Probing Photonic Effect on Photocatalytic Degradation of Dyes Based on 3D Inverse Opal ZnO Photonic Crystal. RSC Adv. 2013, 3 (38), 17021-17028. 24. Xie, H.; Li, Y.; Jin, S.; Han, J.; Zhao, X., Facile Fabrication of 3D-Ordered Macroporous Nanocrystalline Iron Oxide Films with Highly Efficient Visible Light Induced Photocatalytic Activity. J. Phys. Chem. C 2010, 114 (21), 9706-9712. 14 ACS Paragon Plus Environment

Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25. Li, X.; Zhang, X.; Zheng, X.; Shao, Y.; He, M.; Wang, P.; Fu, X.; Li, D., A Facile Preparation of ZnGa2O4 Photonic Crystals with Enhanced Light Absorption and Photocatalytic Activity. J. Mater. Chem. A 2014, 2 (38), 15796-15802. 26. Zhou, M.; Wu, H. B.; Bao, J.; Liang, L.; Lou, X. W.; Xie, Y., Ordered Macroporous BiVO4 Architectures with Controllable Dual Porosity for Efficient Solar Water Splitting. Angew. Chem. Int. Ed. 2013, 52 (33), 8579-8583. 27. Sun, L.; Yang, M.; Huang, J.; Yu, D.; Hong, W.; Chen, X., Freestanding Graphitic Carbon Nitride Photonic Crystals for Enhanced Photocatalysis. Adv. Funct. Mater. 2016, 26 (27), 49434950. 28. Eftekhari, E.; Broisson, P.; Aravindakshan, N.; Wu, Z.; Cole, I. S.; Li, X.; Zhao, D.; Li, Q., Sandwich-Structured TiO2 Inverse Opal Circulates Slow Photons for Tremendous Improvement in Solar Energy Conversion Efficiency. J. Mater. Chem. A 2017, 5 (25), 12803-12810. 29. Liao, G.; Chen, S.; Quan, X.; Chen, H.; Zhang, Y., Photonic Crystal Coupled TiO2/Polymer Hybrid for Efficient Photocatalysis under Visible Light Irradiation. Environ. Sci. Technol. 2010, 44 (9), 3481-3485. 30. Sordello, F.; Duca, C.; Maurino, V.; Minero, C., Photocatalytic Metamaterials: TiO2 Inverse Opals. Chem. Commun. 2011, 47 (21), 6147-6149. 31. Waterhouse, G. I. N.; Wahab, A. K.; Al-Oufi, M.; Jovic, V.; Anjum, D. H.; Sun-Waterhouse, D.; Llorca, J.; Idriss, H., Hydrogen Production by Tuning the Photonic Band Gap with the Electronic Band Gap of TiO2. Sci. Rep. 2013, 3, 2849. 32. Zhang, J.; Li, L.; Wang, S.; Huang, T.; Hao, Y.; Qi, Y., Multi-Mode Photocatalytic Degradation and Photocatalytic Hydrogen Evolution of Honeycomb-Like Three-Dimensionally Ordered Macroporous Composite Ag/ZrO2. RSC Adv. 2016, 6 (17), 13991-14001. 33. Shang, L.; Tong, B. A.; Yu, H. J.; Waterhouse, G. I. N.; Zhou, C.; Zhao, Y. F.; Tahir, M.; Wu, L. Z.; Tung, C. H.; Zhang, T. R., CdS Nanoparticle-Decorated Cd Nanosheets for Efficient Visible Light-Driven Photocatalytic Hydrogen Evolution. Advanced Energy Materials 2016, 6 (3), 1501241. 34. Shi, R.; Cao, Y.; Bao, Y.; Zhao, Y.; Waterhouse, G. I. N.; Fang, Z.; Wu, L.-Z.; Tung, C.-H.; Yin, Y.; Zhang, T., Self-Assembled Au/CdSe Nanocrystal Clusters for Plasmon-Mediated Photocatalytic Hydrogen Evolution. Adv. Mater. 2017, 29 (27), 1700803. 35. Zhao, H.; Ding, X.; Zhang, B.; Li, Y.; Wang, C., Enhanced Photocatalytic Hydrogen Evolution along with Byproducts Suppressing over Z-Scheme CdxZn1-xS/Au/g-C3N4 Photocatalysts under Visible Light. Science Bulletin 2017, 62 (9), 602-609.



Page 16 of 23

36. Wei, Y.; Jiao, J.; Zhao, Z.; Liu, J.; Li, J.; Jiang, G.; Wang, Y.; Duan, A., Fabrication of Inverse Opal TiO2-Supported Au@CdS Core-Shell Nanoparticles for Efficient Photocatalytic CO2 Conversion. Appl. Catal. B 2015, 179, 422-432. 37. Cao-Thang, D.; Yen, H.; Kleitz, F.; Trong-On, D., Three-Dimensional Ordered Assembly of Thin-Shell Au/TiO2 Hollow Nanospheres for Enhanced Visible-Light-Driven Photocatalysis. Angew. Chem. Int. Ed. 2014, 53 (26), 6618-6623. 38. Curti, M.; Schneider, J.; Bahnemann, D. W.; Mendive, C. B., Inverse Opal Photonic Crystals as a Strategy to Improve Photocatalysis: Underexplored Questions. J. Phys. Chem. Lett. 2015, 6 (19), 3903-3910. 39. Pang, F.; Jiang, Y.; Zhang, Y.; He, M.; Ge, J., Synergetic Enhancement of Photocatalytic Activity with a Photonic Crystal Film as a Catalyst Support. J. Mater. Chem. A 2015, 3 (43), 2143921443. 40. Yu, W. W.; Peng, X. G., Formation of High-Quality CdS and Other II-VI Semiconductor Nanocrystals in Noncoordinating Solvents: Tunable Reactivity of Monomers. Angew. Chem. Int. Ed. 2002, 41 (13), 2368-2371. 41. Yang, D.; Qin, Y.; Ye, S.; Ge, J., Polymerization-Induced Colloidal Assembly and Photonic Crystal Multilayer for Coding and Decoding. Adv. Funct. Mater. 2014, 24 (6), 817-825. 42. Wang, Z.; Liu, Z.; Chen, J.; Yang, H.; Luo, J.; Gao, J.; Zhang, J.; Yang, C.; Jia, S.; Liu, B., Self-Assembly of Three-Dimensional CdS Nanosphere/Graphene Networks for Efficient Photocatalytic Hydrogen Evolution. J. Energy Chem. 2018, DOI: 10.1016/j.jechem.2018.05.006.


Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figures and Captions

Figure 1. Enhancement of photocatalytic activity of CdS QDs by PC supporting film.

Figure 2. (a) Digital photo of CdS QDs dispersed in toluene and their (b) UV-Vis absorption, (c) XRD patterns, (d-f) TEM images and (g-i) size distribution.



Page 18 of 23

Figure 3. (a) Reflection peaks for inner, middle and outer regions of the PC film, and (b, c) evolution of reflection wavelengths and intensities along the radial direction. Digital photo, top view and crosssectional view of SEM images of (d-f) SiO2-ETPTA PC film and (g-i) CdS/PC thin film catalyst.


Page 19 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Reflection spectra of PC films with different intensities and (b) H2 evolution catalyzed by CdS3 QDs loaded on these films. (cat.1-cat.4) (c) Transmission spectra of CdS/PC films prepared by deposition of 7, 15, 25 and 35 mg of CdS3 QDs on the same PC films and (d) H2 evolution catalyzed by them. (cat.5-cat.8)



Page 20 of 23

Figure 5. (a) Reflection of 4 PC films with different reflection wavelength and absorption of CdS3 QDs loaded on PC. (b) Enhancements of H2 evolution rates comparing 4 CdS/PC to CdS/non-PC catalyst. (cat. 9-12, cat.1) (c) Absorption of CdS1, CdS2, CdS3 and reflection of PC1. (d) Comparison of H2 evolution rates for 3 CdS catalysts with and without PC support. (cat.13-16, 1, 17)


Page 21 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. (a) Time evolution of H2 production catalyzed by CdS2/PC1 (cat.22) when the visible light illumination is turned on and off in water reduction. (b) Time evolution of H2 production catalyzed by CdS2/PC1 (cat. 23) in the 1st run and the regenerated catalysts in the 2nd and 3rd run.



Page 22 of 23

Figure 7. Comparison of H2 evolution rates for CdS, Au/CdS, CdS/Au photocatalysts supported by ETPTA film (cat.15, 18, 19) and SiO2-ETPTA PC films (cat.16, 20, 21).


Page 23 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Content


Substantial Enhancement toward the Photocatalytic Activity of CdS

Recommend Documents