Photocatalytic Hydrogen Production over CdS Nanomaterials: An

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Photocatalytic Hydrogen Production over CdS Nanomaterials: An Interdisciplinary Experiment for Introducing Undergraduate Students to Photocatalysis and Analytical Chemistry Xin Li,*,†,‡ Yanping Deng,‡ Zhimin Jiang,†,‡ Rongchen Shen,†,‡ Jun Xie,†,‡ Wei Liu,‡ and Xiaobo Chen*,§

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†

College of Forestry and Landscape Architecture, Key Laboratory of Energy Plants Resource and Utilization, Ministry of Agriculture, South China Agricultural University, Guangzhou 510642, PR China ‡ College of Materials and Energy, South China Agricultural University, Guangzhou 510642, PR China § Department of Chemistry, University of Missouri−Kansas City, Kansas City, Missouri 64110, United States S Supporting Information *

ABSTRACT: Photocatalytic hydrogen generation over semiconductor photocatalysts has attracted considerable attention over the past few decades. This experiment is designed for sophomore- and higher-level undergraduates who are in the majors of materials chemistry, analytical chemistry, catalysis, or chemical engineering. In this experiment, CdS nanoparticles and nanosheets were first fabricated with a one-step directprecipitation reaction and a two-step precipitation−ion-exchange reaction, respectively, and then used as photocatalysts for visible-light hydrogen evolution from water, in the presence of noble-metal Pt nanoparticles as in situ cocatalysts and sodium sulfide and sulfite (Na2S/ Na2SO3) as sacrificial reagents. A gas chromatograph with a thermalconductivity detector (GC-TCD) was used to quantitatively monitor the produced hydrogen gas. This interdisciplinary experiment is expected to give students an introduction to nanomaterial synthesis, the general process of photocatalytic hydrogen generation, and the principles and use of instruments. Upon the completion of the experiment, students understand how chemistry can be utilized for renewable-energy applications. KEYWORDS: Second-Year Undergraduate, Upper-Division Undergraduate, Analytical Chemistry, Inorganic Chemistry, Laboratory Instruction, Photochemistry, UV−Vis Spectroscopy, Gas Chromatography, Materials Science, Interdisciplinary/Multidisciplinary

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applications of semiconductors and photocatalysis.8−19 For instance, Tatarko et al. and Chen et al. designed a cheap photocatalytic reactor and a simple parallel photochemical reactor for the remediation of the azo dye Congo Red and methylene blue in water for undergraduate students, respectively.9,18 Boffa et al. prepared sol−gel-derived TiO2 powders for the photodegradation of toluidine blue in solution using UV−vis light, thus effectively introducing undergraduate students to materials chemistry.15 Pitcher et al. described a simple demonstration of photocatalysis using the photodegradation of 2,6-dicholorophenolindophenol sodium salt (DCIP) over the commercially available TiO2.16 Stefanov et al. developed a relatively cheap and readily available 3D-printed gas-phase photocatalytic equipment for online monitoring of air-pollutant photodegradation, demonstrating the advanced scientific topics for chemical-engineering students.19 More

INTRODUCTION

Gradual depletion of fossil-oil resources and increasing environmental pollution due to the continuous burning of fossil oils have aroused the urgent need for the development of sustainable, renewable, and clean energy solutions. Over the past few decades, heterogeneous semiconductor photocatalysis has been widely considered as an appealing solution to simultaneously solve both the energy and environmental issues that threaten our future. In particular, since the discovery of photoelectrochemical water splitting by Fujishima and Honda in 1972,1 sustainable photocatalytic H2-fuel production from water, photocatalytic CO2 conversion, and environmental remediation over different semiconductors have attracted much attention.2−7 The concept and study of photocatalysis have also received increasing emphasis in undergraduate chemistry courses recently. Many teaching experiments and reactors about heterogeneous photocatalytic degradation and oxidation of pollutants have been reported, which help students to understand the basic chemistry, concepts, and extensive © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: January 29, 2019 Revised: April 21, 2019

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DOI: 10.1021/acs.jchemed.9b00087 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) in molecules. The bandgap of a solid corresponds to the HOMO−LUMO energy difference of a molecule. The photoexcited electrons and holes migrate to the surface of the CdS catalyst. If the surface of the CdS catalyst is loaded with Pt cocatalyst, the photoexcited electrons are collected by the Pt cocatalyst. As a result, the photogenerated electrons on Pt can reduce water to H2, whereas the holes accumulated on the surface of CdS can be consumed with sacrificial reagents (e.g., S2−/SO32−). A schematic of this process is shown in Figure 1.

recently, Xiong et al. used a TiO2-photocatalytic-oxidation process to treat methanol-containing wastewater, from which students can understand the basic principle of photocatalytic oxidation reactions and learn to assemble a specified apparatus for a chemical reaction and analytical methods.17 Interestingly, Rimoldi et al. demonstrated the application of irradiationinduced superhydrophilicity of TiO2 films to achieve surfacewetting properties for Master’s students.20 Impressively, Ma et al. also introduced a new graduate course called Photocatalysis: Principles and Applications into the physical-chemistry division at the University of Chinese Academy of Sciences (UCAS), which mainly involved the teaching materials, literature discussion, and student feedback.21 However, so far, few available experiments about photocatalytic H 2 evolution have been designed and developed for teaching undergraduates. In 2003, Koca developed a simple laboratory experiment for photocatalytic hydrogen production by direct sunlight.22 In that experiment, the volume of hydrogen evolved was determined from the displacement of liquid into the graduated pipet.20 The experiment nicely demonstrated that the different compositions of the CdS/ZnS photocatalysts exhibited significant effects on the volumes of hydrogen evolved.20 Notably, from a scientific point of view, the simple drainage gas-recovery technique was unfavorable for undergraduates to effectively utilize valuable laboratory skills, perform accurate analysis of H2, and understand the principles and use of instruments. As is well-known, CdS photocatalysts have long been considered to be one of the best H2-evolution photocatalysts and have gained increasing attention in the field of photocatalytic H2 generation.23−28 Typically, both the CdS photocatalyst and the cocatalysts play key roles in photocatalytic-H2evolution activity. Various nanostructures of CdS, including hierarchical porous 3D structures,29−31 2D nanosheets,25,27,28 1D nanowires−nanorods,26,32−34 and 0D nanoparticles− quantum dots35−37 have been, to date, explored in photocatalytic H2 generation. Meanwhile, various noble-metal and earth-abundant cocatalysts, such as Pt, MoS2, Ni3C, and NiS, have been employed to boost photocatalytic activity through better charge separation, facilitated H2-evolution kinetics, and reduced overpotentials.23−25,27,28,38 Herein, we design one photocatalytic-H2-evolution experiment based on the use of different CdS nanostructures, namely, 0D nanoparticles (NPs) and 2D nanosheets (NSs). We use this experiment to explain both the important energy applications of photocatalysis (e.g., the production of clean fuel, H2, from water using sunlight) and the importance of the dimension of the photocatalyst on the efficiency of H2 evolution. The 0D and 2D CdS photocatalysts were prepared with direct precipitation and a two-step precipitation−ionexchange reaction, respectively. Their photocatalytic-H2evolution activities under visible light were measured with a GC-TCD instrument. The general mechanism for photocatalytic H2 generation on CdS photocatalysts is as follows. In the first step, CdS absorbs light with energy larger than its bandgap (the bandgap of bulk CdS is 2.42 eV, 512 nm in wavelength; the students are asked to make this energy conversion and compare it with the bandgaps in the 0D and 2D CdS photocatalysts made in the experiment) and produces excited electrons (e−) and holes (h+) in the conduction and valence bands of CdS, respectively. The conduction and valence bands are the physics terms for the condensed materials or solids, which correspond to the

Figure 1. Schematic diagram of photocatalytic hydrogen evolution over nanostructured CdS photocatalysts under visible-light irradiation.

Apparently, the photocatalytic activity is synergistically dependent on the efficiency of the light absorption of the main photocatalyst (e.g., CdS), the charge-separation efficiency (the successive transfer rate after light absorption to the CdS surface and the charge separation from CdS to Pt), and the charge-transfer efficiency for the targeted reactions (e.g., the charge transfer from Pt to adsorbed water or H+ to drive the H2-evolution reaction).39 In the above process, there are also some unwanted competing pathways. For example, the photoexcited electrons and holes can recombine in the bulk of CdS to emit light or produce heat; therefore, the numbers of photoexcited electrons and holes reaching the surface will be reduced. Meanwhile, the photocatalytic activity will depend on the specific surface area of the photocatalyst and the cocatalyst. This is understandable because normally, larger surface areas result in higher activity. The bandgaps of 0D and 2D CdS are different, along with their different specific surface areas. Therefore, different activities are expected for the 0D and 2D CdS made in this experiment. The photocatalytic-H2-evolution activity of a photocatalyst is frequently expressed with the amount of H2 gas produced per hour using 1 g of photocatalyst, with the unit of moles per hour per gram (mol h−1 g−1). We expect that this experiment, which involves nanomaterial synthesis, photocatalytic reduction−oxidation reactions, H2 detection, and analysis of experimental results, will create considerable interest for nanomaterials chemistry, photochemistry, and renewable energy. This comprehensive experiment, as a live example of interdisciplinary chemical experiments that employ analytical instruments for cutting-edge research, is designed for sophomore- and higher-level undergraduates. B



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EXPERIMENTAL SECTION

the reactor and the suspension and assuming that no H2 gas was dissolved in the suspension), the amount of hydrogen produced per gram of catalyst was plotted with the illumination time, the photocatalytic-hydrogen-production rate was calculated, and the induction period for photocatalytic hydrogen production was estimated. In the GC, it is suggested that a molecular-sieve 5A column (i.d. of 0.3 cm, packed length of 1 m, 60−80 mesh) be used to measure the concentration of produced H2. It is also suggested that the injector, detector, and column temperatures be set at 100, 150, and 70 °C, respectively. The carrier gas was argon with a typical flow rate of 45 mL/min.

Chemicals

The chemicals used in this experiment include the following: deionized water (DI water), sodium sulfite (Alfa Aesar, >99.0%), sodium sulfide (Alfa Aesar, >99.0%), cadmium nitrate (Alfa Aesar, >99.0%), sodium hydroxide (Alfa Aesar, >99.0%), and hydrogen hexachloroplatinate(IV) (Alfa Aesar, >99.0%). Preparation of Two CdS Photocatalysts

CdS 0D nanoparticles and 2D nanosheets40,41 were synthesized with direct precipitation and a two-step precipitation− ion-exchange reaction, respectively.

Multiteam-Cooperation Option

The variables that can be tuned in this experiment include the following: the concentrations of the Na2S, Cd(NO3)2, and NaOH and their relative ratios in the synthesis of CdS 0D and 2D catalysts; the mass of the photocatalyst added to the reactor; the mass percentage of the Pt cocatalyst; the concentrations of the sacrificial reagents; and others. Students can be divided into a few teams; each team can focus on one major task: synthesis of different amounts of Na2S, Cd(NO3)2, and NaOH with different relative ratios; measurement of the photocatalytic-H2-evolution activity with different amounts of photocatalysts in solution (e.g., 5, 10, 15, 20, 25, and 50 mg); and measurement of the photocatalytic-H2-evolution activity over CdS photocatalysts loaded with different mass percentages of Pt cocatalysts (e.g., 0.1, 0.2, 0.5, 0.75, 1, 1.5, and 2%).

Synthesis of CdS Nanoparticles

In a typical synthesis run (molar ratio of Na2S/Cd(NO3)2 of 1.0), 20 mL of 0.25 M Na2S solution was added dropwise into 50 mL of 0.1 M Cd(NO3)2 aqueous solution under stirring. The yellow precipitates were collected by centrifugation or filtering, washed with distilled water and ethanol three times, and then dried in an oven at 100 °C for 20 min. Synthesis of CdS Nanosheets

Cd(NO3)2 aqueous solution (50 mL, 0.1 M) was added to 20 mL of 0.5 M NaOH solution at room temperature to form nanoporous Cd(OH)2 intermediates; then, 20 mL of 0.1 M Na2S solution was quickly poured into the solution under stirring to form 2D CdS nanosheets.40,41 The pale-yellow precipitates were collected by centrifugation or filtering, washed three times with ethanol and deionized water, and dried at 100 °C for 20 min.38−41

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HAZARDS Cadmium salts are carcinogens and may be fatal if swallowed. They should be handled with care. CdS is toxic and may damage the kidney, liver, or eyes. A protective face mask, a lab coat, and gloves should be worn to avoid inhalation or absorption when dealing with CdS and the CdS wastewater. All operations related to CdS should be carried out in a fume cupboard. Finally, the photocatalytic solution should be carefully filtered, the dried powders should be properly collected, and the liquid waste should be disposed following the waste-accumulation and -disposal guidance in the laboratory. Additionally, a xenon arc lamp has much stronger UV and visible light than that in the solar spectrum, which leads to greater damage to the experimental operators’ skin and eyes. Therefore, anti-ultraviolet polarized sunglasses, a face mask, and gloves have to be worn during the processes of photocatalytic H2 evolution.

Photocatalytic-H2-Evolution Procedure

The photocatalytic-H2-evolution-reaction experiment was performed in a 100 mL three-neck flat-bottom Pyrex flask at ambient pressure and temperature. A silicone rubber septum was used to seal the opening of the flask. A 350 W Xe arc lamp with a UV-cutoff filter (λ ≥ 420 nm) was used as the light source to trigger the photocatalytic reaction (19 cm away from the reactor). The focused-light intensity on the flask was ca. 160 mW cm−2. Notably, sunlight, normal desktop lamps, or LED lamps could also be used instead of a filtered Xe lamp, as they all contain visible light. In a typical experiment, 20 mg of photocatalysts was dispersed in a reactor containing 80 mL of an aqueous solution of Na2S (0.25 M) and Na2SO3 (0.25 M) under constant stirring and with an ultrasonic bath (Figure S1A). A suitable amount of H2PtCl6 powder was added to this suspension to make 1 wt % Pt loading on the CdS photocatalysts. This suspension was bubbled with N2 gas for 30 min to remove the dissolved oxygen to make sure that the system was under anaerobic conditions (Figure S1B). Then, the suspension was subjected to the visible-light irradiation (Figure S1C,D). After illumination for 1 h, 200 μL of evolved H2 gas was collected through a septum and analyzed using an online gas chromatograph (GC-9560, TCD, with Ar as the carrier gas; Figure S2). The reaction was continued for 2 h, and the amount of H2 gas produced was analyzed with GC frequently. By assuming that the response of the GC has a linear relationship with the concentration of H2 gas within the concentration range of photocatalytic hydrogen production, the concentration of H2 gas determined from the GC measurements was converted to the total amount of H2 gas produced in the reactor (paying attention to the volumes of

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TYPICAL RESULTS AND DISCUSSION The one-step reaction to form CdS 0D nanoparticles can be expressed as Na2S + Cd(NO3)2 → CdS (nanoparticles)↓ + 2NaNO3. The two-step precipitation−ion-exchange reaction to form CdS 2D nanosheets can be expressed as Cd(NO3)2 + Na(OH)2 → Cd(OH)2 (nanosheets)↓ + 2NaNO3 and Na2S + Cd(OH)2 (nanosheets)↓ → CdS (nanosheets)↓ + Na(OH)2. The typical structures and properties of the CdS 0D nanoparticles and 2D nanosheets synthesized in this experiment are shown in the Supporting Information. The crystalphase structure can be identified with powder-X-ray-diffraction (XRD) patterns (Figure S3, see also the information on the XRD technique in the Supporting Information). The microscale morphology of the CdS nanostructure can be observed with transmission electron microscopy (TEM, Figure S4). Their optical properties and the bandgaps can be determined C




Figure 2. (A) Reaction time courses and (B) average rates of H2 evolution over four different photocatalysts in aqueous solution: CdS NSs, CdS NPs, CdS NPs/2% Pt, and CdS NSs/2% Pt. The intercepts on the time scale of the dashed lines in (A) represent the induction time of each sample under visible-light illumination. Reaction conditions: 25 mg of catalyst; 80 mL of sacrificial-agent solution; light source, xenon lamp (350 W) with a UV-cutoff filter (λ ≥ 420 nm).

Similar measurements and analysis can be carried out to investigate how the photocatalytic-H2-evolution activity is affected by the preparation conditions of the CdS photocatalyst (e.g., the concentrations of the Na2S, Cd(NO3)2, and NaOH and their relative ratios in the synthesis of CdS 0D and 2D catalysts), the mass of the photocatalyst added to the reactor, the mass percentage of the Pt cocatalysts, and the concentrations of the sacrificial reagents, among others. A reasonable conclusion should be drawn from those observations. The explanations for the photocatalytic activity should consider the following factors: light absorption of the CdS photocatalyst (this can be done by measuring UV−visabsorption spectra), which is related to the size of the CdS photocatalyst; surface area; light scattering of the photocatalysts; surface polarization of the CdS catalysts; charge separation and overpotential reduction by the Pt cocatalyst; and others. Among these, students should pay attention to surface polarization. For example, the surface polarization can be affected by slight deviation of the stoichiometric 1:1 ratio of the Cd and S reagents during the synthesis, which will largely determine whether the surface bond-ending atoms are anionic (S2− ending) or cationic (Cd2+ ending).

with ultraviolet−visible (UV−vis)-absorption spectra (Figure S5, see also the fundamentals of UV−vis-absorption spectroscopy and the determination of the optical bandgap of semiconductors using UV−vis-absorption spectra in the Supporting Information). Examples of photocatalytic H2 evolution over two nanostructured CdS photocatalysts are shown in Figure 2. Control experiments without photocatalysts or irradiation reveal that no H2 is produced. Therefore, the produced H2 shown in Figure 2 is from the photocatalytic reactions. The increasing H2 production over time (displayed in Figure 2A) indicates the continuous production of H2 under visible-light irradiation. The average photocatalytic H2 activity can be obtained by calculating the slope of the line from the value at 2 to 0 h. Obviously, the activity increases in the order CdS NSs < CdS NPs < CdS NSs/2% Pt < CdS NPs/2% Pt. Surprisingly, the pure CdS NPs exhibit much higher photocatalytic-H2evolution activity compared with the previously reported activities of CdS nanosheets and nanorods.26 Under conditions of loading of the Pt cocatalysts, the rates of H2 evolution of CdS nanosheets and nanoparticles are enhanced by factors of 1.90 and 2.29, respectively. The higher activity of the nanoparticles can be explained by their smaller sizes and therefore larger surface areas for the photocatalytic hydrogenevolution reaction. The induction time can be obtained from the intercept on the time scale by extrapolating the line from the value at 2 to 1 h. Apparently, the induction time decreases as the photocatalytic activity increases. The decreased induction time is related to the gradual deposition of Pt nanoparticles on the CdS photocatalysts, which further boosts the photocatalytic H2 evolution. To further compare the H2evolution activity, the average H2-evolution rates over all CdS samples with and without Pt cocatalysts are displayed in Figure 2B. Clearly, loading suitable contents of Pt cocatalysts on the nano-CdS photocatalysts could greatly improve their photocatalytic-H2-evolution activity, indicating that the Pt NPs effectively improve the photocatalytic-H2-evolution activity. This improvement can be attributed to the effective collection of the photoexcited electrons by the Pt, the lower H2-evolution overpotential on Pt than on CdS, and the efficient separation of the photogenerated electrons from the holes that remain in the CdS to reduce the charge recombination.

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CONCLUSION This experiment is intended for an undergraduate chemistry laboratory to provide students with a cutting-edge-renewableenergy-research experience through the study of the synthesis of nanostructured semiconductor photocatalysts and measurement of their photocatalytic-H2-production activities with the assistance of sacrificial reagents and Pt cocatalyst. More importantly, this experiment can create enthusiasm among students, allow them to learn various valuable laboratory skills and basic concepts of photocatalysis and nanotechnology, and enhance their capacity in fabricating and testing inorganic semiconductor nanomaterials. Additionally, the photocatalytic tests can introduce students to the high-sensitivity analytical method of gas chromatography and foster their understanding of photocatalytic-H2-evolution kinetics. In particular, for more advanced student, the morphology-dependent photocatalytic H2 production over various types of nano-CdS photocatalysts can be more carefully investigated through optimizing the parameters. With the aid of their supervisor, students can work D




(8) Yu, J. C.; Chan, L. Y. L. Photocatalytic degradation of a gaseous organic pollutant. J. Chem. Educ. 1998, 75, 750−751. (9) Bumpus, J. A.; Tricker, J.; Andrzejewski, K.; Rhoads, H.; Tatarko, M. Remediation of water contaminated with an azo dye: An undergraduate laboratory experiment utilizing an inexpensive photocatalytic reactor. J. Chem. Educ. 1999, 76, 1680−1683. (10) Herrera-Melian, J. A.; Dona-Rodriguez, J. M.; Rendon, E. T.; Vila, A. S.; Quetglas, M. B.; Azcarate, A. A.; Pariente, L. P. Solar photocatalytic destruction of p-nitrophenol: A pedagogical use of lab wastes. J. Chem. Educ. 2001, 78, 775−777. (11) Gravelle, S.; Langham, B.; Geisbrecht, B. Photocatalysis, a laboratory experiment for an integrated physical chemistry-instrumental analysis course. J. Chem. Educ. 2003, 80, 911−913. (12) Herrera-Melian, J. A.; Araña Mesa, J. A. Note on photocatalytic destruction of organic wastes: Methyl red as a substrate - Authors reply. J. Chem. Educ. 2005, 82, 526−526. (13) Romero, A.; Hernandez, G.; Suarez, M. F. Photocatalytic oxidation of sulfurous acid in an aqueous medium. J. Chem. Educ. 2005, 82, 1234−1236. (14) Soltzberg, L. J.; Brown, V. Note on photocatalytic destruction of organic wastes: Methyl red as a substrate. J. Chem. Educ. 2005, 82, 526−526. (15) Boffa, V.; Yue, Y. Z.; He, W. Sol-Gel Synthesis of a Biotemplated Inorganic Photocatalyst: A Simple Experiment for Introducing Undergraduate Students to Materials Chemistry. J. Chem. Educ. 2012, 89, 1466−1469. (16) Pitcher, M. W.; Emin, S. M.; Valant, M. A Simple Demonstration of Photocatalysis Using Sunlight. J. Chem. Educ. 2012, 89, 1439−1441. (17) Xiong, Q.; Luo, M. L.; Bao, X. M.; Deng, Y. R.; Qin, S.; Pu, X. M. Using Photocatalytic Oxidation and Analytic Techniques To Remediate Lab Wastewater Containing Methanol. J. Chem. Educ. 2018, 95, 131−135. (18) Chen, X.; Halasz, S. M.; Giles, E. C.; Mankus, J. V.; Johnson, J. C.; Burda, C. A Simple Parallel Photochemical Reactor for Photodecomposition Studies. J. Chem. Educ. 2006, 83, 265−267. (19) Stefanov, B. I.; Lebrun, D.; Mattsson, A.; Granqvist, C. G.; Ö sterlund, L. Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor. J. Chem. Educ. 2015, 92, 678−682. (20) Rimoldi, L.; Taroni, T.; Meroni, D. Wetting Modification by Photocatalysis: A Hands-on Activity To Demonstrate Photoactivated Reactions at Semiconductor Surfaces. J. Chem. Educ. 2018, 95, 2216− 2221. (21) Ma, J. H.; Guo, R. R. Engaging in Curriculum Reform of Chinese Chemistry Graduate Education: An Example from a Photocatalysis-Principles and Applications Course. J. Chem. Educ. 2014, 91, 206−210. (22) Koca, A.; Sahin, M. Photocatalytic hydrogen production by direct sunlight: A laboratory experiment. J. Chem. Educ. 2003, 80, 1314−1315. (23) Cheng, L.; Xiang, Q.; Liao, Y.; Zhang, H. CdS-Based photocatalysts. Energy Environ. Sci. 2018, 11, 1362−1391. (24) Li, Q.; Li, X.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J. CdS/ Graphene Nanocomposite Photocatalysts. Adv. Energy Mater. 2015, 5, 1500010. (25) Ma, S.; Xie, J.; Wen, J.; He, K.; Li, X.; Liu, W.; Zhang, X. Constructing 2D layered hybrid CdS nanosheets/MoS2 heterojunctions for enhanced visible-light photocatalytic H-2 generation. Appl. Surf. Sci. 2017, 391, 580−591. (26) Yuan, J.; Wen, J.; Gao, Q.; Chen, S.; Li, J.; Li, X.; Fang, Y. Amorphous Co3O4 modified CdS nanorods with enhanced visiblelight photocatalytic H2-production activity. Dalton Trans. 2015, 44, 1680−1689. (27) Ma, S.; Xu, X.; Xie, J.; Li, X. Improved visible-light photocatalytic H2 generation over CdS nanosheets decorated by NiS2 and metallic carbon black as dual earth-abundant cocatalysts. Chinese. J. Catal. 2017, 38, 1970−1980.

together to investigate the photocatalytic performance of CdS in a comprehensive manner. The integration of this laboratory experiment into their experimental courses can be adapted to a range of educational levels, from which undergraduate students may significantly benefit. The accumulated experience in the use of various instrumental techniques and in nanomaterial synthesis and photocatalysis is of great importance for students’ future studies and research. It is anticipated that this interdisciplinary experiment is suitable for undergraduate laboratory teaching.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.9b00087. Instructor notes, experimental procedure, and questions for students (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (X.L.). *E-mail: [email protected] (X.C.). ORCID

Xin Li: 0000-0002-4842-5054 Xiaobo Chen: 0000-0002-7127-4813 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS X.L. would like to thank the National Natural Science Foundation of China (51672089), the Special Funding on Applied Science and Technology in Guangdong (2017B020238005), the State Key Laboratory of Advanced Technology for Material Synthesis and Processing (Wuhan University of Technology, 2015-KF-7), State Scholarship Fund of China Scholarship Council (200808440114) and the Ding Ying Talent Project of South China Agricultural University for their support. X.C. appreciates the financial support from the U.S. National Science Foundation (DMR-1609061); the College of Arts and Sciences, University of MissouriKansas City; and the University of Missouri Research Board.

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Photocatalytic Hydrogen Production over CdS Nanomaterials: An

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