Researchers from Sun-Yat Sen University in China report in an open-access paper in ACS ES&T Engineering the development of a catalyst that destroys medications and other compounds already present in wastewater to generate hydrogen fuel, getting rid of a contaminant while producing something useful.

Herein, we are aiming to construct a dual-functional photocatalyst system which can degrade pollutants and simultaneously split water to generate hydrogen. We construct the Co₃O₄ modified {001}/{101}-TiO₂ (TC) nanosheets as the efficient dual-functional photocatalyst system. As a p-type semiconductor, Co₃O₄ construct a p–n junction with TiO₂ (n-type). And, the {001}/{101} facet of TiO₂ forms an intrinsic surface heterojunction.

The unique dual (p–n/surface) heterojunction structure enables the spatial separation of the charge carriers. The holes primarily accumulated on Co₃O₄ nanoparticles efficiently oxidize the pharmaceutical pollutants including enrofloxacin, ciprofloxacin, and ibuprofen, while the electrons accumulated on {101} facets of TiO₂ nanosheet can simultaneously reduce water molecules to generate hydrogen.

—Wu et al.

Wu et al. ACS EST Eng. 2021, 1, 3, 603-611

Harnessing the sun’s energy to split water to make hydrogen fuel is a promising renewable resource, but it is a slow process even when catalysts are used to speed it along. In some cases, alcohols or sugars are added to boost the rate of hydrogen production, but these chemicals are destroyed as hydrogen is generated, meaning the approach is not renewable.

In a separate strategy, researchers have tried using contaminants in wastewater to enhance hydrogen fuel generation. While titanium-based catalysts worked for both removing contaminants and generating hydrogen, the efficiencies were lower than expected for both steps because of their overlapping reaction sites.

One way to reduce such interferences is to make catalysts by fusing together different conductive metals, thus creating separate places for reactions to occur.

Corresponding author Chuanhao Li and colleagues wanted to combine cobalt oxide and titanium dioxide to create a dual-functioning catalyst that would break down common drugs in wastewater while also efficiently converting water into hydrogen for fuel.

To make the catalyst, the researchers coated nanoscale titanium dioxide crystals with a thin layer of cobalt oxide. Initial tests showed that this material didn’t produce much hydrogen, so as a next step, the team spiked this dual catalyst with 1% by weight of platinum nanoparticles—an efficient though expensive catalyst for generating hydrogen. In the presence of simulated sunlight, the platinum-impregnated catalyst degraded two antibiotics and produced substantial amounts of hydrogen.

Finally, the team tested their product on real wastewater, water from a river in China and deionized water samples. Under simulated sunlight, the catalyst stimulated hydrogen production in all three samples. The greatest amount of hydrogen was obtained from the wastewater sample.

The researchers say their catalyst could be a sustainable wastewater treatment option by generating hydrogen fuel at the same time.

The authors acknowledge funding from National Natural Science Foundation of China, Science and Technology Planning Project of Guangdong Province, Fundamental Research Funds for the Central Universities from Sun Yat-sen University and the Research Fund Program of Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology.

Resources

• Yaoyao Wu, Yuqiong Li, Hejing Hu, Guoshen Zeng, and Chuanhao Li (2021) “Recovering Hydrogen Energy from Photocatalytic Treatment of Pharmaceutical-Contaminated Water Using Co₃O₄ Modified {001}/{101}-TiO₂ Nanosheets” ACS ES&T Engineering 1 (3), 603-611 doi: 10.1021/acsestengg.1c00003