Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications

Our team studies hybrid nanostructures for clean energy and environments, focusing on nanocatalytic mechanisms to enhance efficiency, selectivity and scalability in solar to chemical conversion and environmental remediation via photocatalysis and electrocatalysis. Recent advances includes 2D nanomaterials, carbon-based nanocomposites and metabisulfite-based heterojunctions for the photoredox applications in hydrogen evolution, CO2 conversion, plastic reforming and organic synthesis, thus boosting solar to chemical efficiency and sustainability. My work has focused on creating advanced nanocatalysts for artificial photosynthesis and photothermal catalysis, achieving significant improvements in solar-driven hydrogen and syngas productions while revolving the fundamental surface chemistry and reaction mechanisms that drive sustainable energy conversions.

Our protocol exploits zinc copper sulfide over zinc cadmium sulfide between quick-throw, wurtzite and zincblende junctions and zinc copper sulfide electron reservoirs, enabling superior charge separations, visible light utilizations, and dual-function hydrogen evolutions and benzaldehyde productions with significantly enhanced efficiency. My future research focuses on designing advanced photocatalysts and electrocatalysts for carbon monoxide conversion, methane conversion, nitrate to ammonia transformation, hydrogen production and storage, biomass conversion, and plastic upcycling with the goal of achieving scalable, efficient, and sustainable solar to chemical energy applications of efficiency more than 5%To begin, place a 100 milliliter beaker on the work surface and pour 40 milliliters of ethylene glycol solution into it. Using a spatula, add zinc acetate dihydrate, cobalt acetate tetrahydrate and thioacetamide into the solution.

Subject the solution to ultrasonic treatment for 30 minutes. Then stir it continuously for four hours at ambient temperature. Transfer the resulting mixture into a 100 milliliter synthetic polymer lined stainless steel autoclave.

Then transfer the solution into a preheated oven and heat at 180 degrees Celsius for 12 hours. Using a centrifuge, collect the dark gray precipitate. Then, wash the precipitate three times, each with deionized water and ethanol.

Dry the washed dark gray sample in an oven overnight at 60 degrees Celsius to obtain a dark gray zinc cobalt sulfide powder. To synthesize zinc cadmium sulfide, pour 40 milliliters of deionized water into a 100 milliliter beaker. Using a spatula, add zinc acetate dihydrate, cadmium acetate dihydrate, sodium sulfide hydrate, and thioacetamide into the solution.

Subject the solution to ultrasonic treatment for 30 minutes, followed by stirring for three hours at ambient temperature. Next, add 0.2 molar sodium hydroxide aqueous solution dropwise into the stirred solution to adjust the pH to 7.0. Transfer the adjusted solution into a 100 milliliter synthetic polymer lined stainless steel autoclave.

Then, place the solution in an oven and heat it at 180 degrees Celsius for 24 hours. Using a centrifuge, collect the yellowish precipitate, then wash the precipitate three times each with deionized water and ethanol. Transfer the washed yellowish precipitate into an oven and dry it overnight at 60 degrees Celsius to obtain zinc cadmium sulfide solid powder.

To synthesize the photocatalyst, dissolve 4 milligrams of zinc cobalt sulfide and 0.196 grams of zinc cadmium sulfide into 40 milliliters of deionized water. After ultrasonication, collect the yellowish precipitate, then wash the sample three times, each with deionized water and ethanol. Transfer the washed yellowish precipitate into an oven and dry it overnight at 60 degrees Celsius.

The final product is a yellowish zinc cobalt sulfide and zinc cadmium sulfide solid powder. Add 20 milligrams of the synthesized photocatalyst and 60 milliliters of Benzyl alcohol aqueous solution into a 100 milliliter beaker. Place the beaker in an ultrasonic cleaner and perform ultrasonication for 30 minutes.

Then, transfer the solution into a three-necked top irradiation reactor cell and insert a magnetic stirrer bar. Maintain the solution under slow stirring throughout the entire reaction process. Next, connect a moisture trap to the downstream side of the reactor cell.

Then, connect the outlet to the gas sampling loop inlet of the gas chromatography system. Further, connect the gas sampling loop outlet to the reactor cell inlet to form a closed gas circulation system. Seal the reactor with a glass window.

Then, purge nitrogen gas at a flow rate of 50 milliliters per minute through the reactor for 30 minutes to remove all air inside. Now, turn on the peristaltic pump and set the flow rate to 20 milliliters per minute to circulate the nitrogen gas within the closed gas circulation system. Switch on the xenon lamp at 15 volts and position it so that the light passes through the glass window and reaches the solution inside the reactor.

Once the reaction is complete, using a 0.22 micrometer nylon syringe filter, filter one milliliter of the suspension. Dilute the filtered suspension with deionized water in a ratio of 1 to 9. Finally, use a high-performance liquid chromatography system equipped with a photodiode array detector and a high-performance 100 Angstrom column.

The high-resolution transmission electron microscopy images confirmed the coexistence of zincblende and wurtzite phases in zinc cadmium sulfide, and an interphase boundary clearly distinguished the two crystalline domains. The interphase structure of the zinc cobalt sulfide and zinc cadmium sulfide heterojunction was distinctly observed, demonstrating the successful incorporation of zinc cobalt sulfide on the zincblende and wurtzite interphases of zinc cadmium sulfide. The UV visible absorbance spectra showed that zinc cadmium sulfide had a higher absorbance in the visible region compared to zinc cobalt sulfide, and the zinc cobalt sulfide and zinc cadmium sulfide heterojunction exhibited slightly enhanced absorbance over zinc cadmium sulfide alone.

The optical band gap of zinc cadmium sulfide was calculated to be approximately 2.49 electron based on talk plot analysis. Nitrogen adsorption/desorption isotherms revealed that the zinc cobalt sulfide and zinc cadmium sulfide samples exhibited mesoporous characteristics, with a sharp increase in adsorption at relative pressure near 1.0. The pore size distribution of zinc cobalt sulfide and zinc cadmium sulfide, was concentrated primarily between 25 and 35 nanometers, confirming the mesoporous nature of the material.