Synergistic Effect of the Sulfur Vacancy and Schottky Heterojunction on Photocatalytic Uranium Immobilization: The Thermodynamics and Kinetics

Abstract

Not only a critical matter in the nuclear fuel cycle but uranium is also a global contaminant with both radioactive and chemical toxicity. Reducing soluble hexavalent uranium [U(VI)] to relatively nonimmigrated tetravalent uranium [U(IV)] by photocatalytic technologies is recognized as a highly promising strategy for avoiding environmental pollution and re-extracting uranium resources from nuclear wastewater. Herein, we have designed a heterojunction photocatalyst constructed from the carbon aerogels (CA) and the CdS nanoflowers with an S-vacancy (CA@CdS-SV). With the S-vacancy and heterojunction being synergized, the U(VI) removal rate exceeded 97% in 40 min without the addition of any sacrificial agents. As impacted by the synergistic effects of the S-vacancy and heterojunction, thermodynamics and kinetics revealed that photogenerated electrons were first captured via shallow traps generated by vacancies on CdS-SV and then transferred to the CA surfaces through the heterojunction to realize the spatial separation of carriers, thereby achieving a satisfactory performance. This work is considered to underpin the improvement of U(VI) immobilization by exploiting the synergistic effect of vacancy engineering and the Schottky heterojunction from the perspective of thermodynamics and kinetics.

Sustainable Energy Resources for Driving Methane Conversion

“…One of the existing waste heat recovery methods mainly relies on thermoelectric generators (TEGs), which directly convert heat into electricity based on the “Seebeck effect.” Electronic devices such as solar cells, batteries, chips, and LED lights normally generate heat during operation, and the heat has to be directly dissipated to the ambient environment to prevent thermal runaway or can be recovered by TEGs for specific uses (e.g., driving an electrocatalytic CH 4 conversion process). Interestingly, thermoelectric materials have been also applied to electrocatalysis systems, leading to improved electrocatalytic performance, [ 148 ] and reaction pathways. [ 149 ] Thus, proof of concept research centering on the creative “integration” of thermoelectric materials and electrocatalytic CH 4 conversion technique is of great interest.…”

A comparative study on the linear scaling relations for the diffusion of S-vacancies on MoS2 and WS2

“…11 The importance of S-vacancies sites has also been recognized for other materials like CdS, where such sites improve the immobilization of uranium in the context of nuclear waste management. 12 To better understand the properties of S-vacancies, several works in literature have addressed different aspects of such sites, particularly on MoS 2 . Some works focus on their formation mechanism, 12 while others have been studying their electronic structures.…”

Dual Charge-Transfer Channels Harmonize Carrier Separation for Efficient U(VI) Photoreduction

“…Radioactive wastewater from the development of nuclear energy contains large amounts of dissolved hexavalent uranium [U­(VI)]. − The dissolved U­(VI) is highly mobile and can easily enter the ecosystem through aqueous medium and pose a potential hazard. − Fortunately, the conversion of highly soluble U­(VI) to tetravalent uranium [U­(IV)] with relatively low solubility by coupling adsorption with photocatalysis is considered an effective strategy to achieve a sustainable development of nuclear energy and environmental protection. − However, the large number of photogenerated electrons and holes that recombine during the photoreduction of U­(VI) can severely inhibit the catalytic activity of the photocatalyst, leading to the scarcity of reported photocatalysts that exhibit excellent catalytic activity for high concentrations of U­(VI). − Therefore, the design of a photocatalyst with effective spatial separation of carriers is of great practical importance for the efficient removal of U­(VI).…”