Lixiang Zhang,Pan Li,Luping Feng,Xi Chen,Jiatian Jiang,Sheng Zhang,Anchao Zhang,Guofu Chen,Hua Wang
Visible-light-driven and ultra-stable CoS x /CdS photocatalysts were controllably fabricated by the ZIF-67-templated one-pot solvothermal route for highly efficient photocatalytic Cr(VI) reduction. It was discovered that the resulting CoS x /CdS composites could present different photocatalytic activities controllably depending on the CoS x -to-CdS molar ratios used. The one with 1/16 M ratio could display the highest photocatalytic reduction performance for Cr(VI) with the efficiency up to 100% within 30 min, which is 5.6-fold and 2.1-fold higher than that of pristine CoS x and CdS, respectively. Herein, the components of CoS x and CdS with well-matched energy-band structures might serve separately as the electrons donor and the holes quencher to prolong the lifetime of photogenerated electrons in CoS x /CdS composites. A direct Z-scheme heterojunction could be thus constructed for promoting the charge carrier transferring with the improved redox abilities, leading to the robust photocatalysis of CoS x /CdS photocatalyst. Moreover, the developed CoS x /CdS photocatalyst could present superior stability with the structure and activity well survived after five photocatalytic cycles. This work may pave the way towards the controllable construction of a direct Z-scheme photocatalytic system by synergistically combining two kinds of components with matched energy-band structures, achieving the enhanced photocatalysis for the wide applications in the environmental remediation field.
A visible-light-driven photoelectrochemical (PEC) sensor has been developed for probing Hg 2+ with “turn-on” signal output using hollow CoS x @CdS polyhedron as direct Z-scheme photocatalyst and Hg 2+ -recognition probe. The CoS x @CdS heterojunction photocatalysts were fabricated by growing CdS nanoparticles on the surface of cobalt sulfide (CoS x ) via one-pot solvothermal route using metal-organic frameworks (MOFs) of ZIF-67 polyhedrons as the sacrificial templates and cobalt precursors. It was discovered that the photocurrent responses of the CoS x @CdS-modified ITO electrodes could be specifically turned on by Hg 2+ , in contrast to these of the CoS x or CdS-modified ones showing no significant Hg 2+ -induced photocurrent. Under visible light irradiation, herein, the synergetic combination of CoS x and CdS components could improve the carriers transferring of PEC system. More importantly, the photocurrents of the PEC sensor could be greatly enhanced in the presence of Hg 2+ through the selective ion-exchange reaction to trigger the in-situ formation of a new Z-scheme heterojunction of CoS x @CdS/HgS photocatalysts, achieving the further promoted charge transferring and suppressed recombination of photogenerated electron-hole pairs. The developed double heterojunctions-based PEC sensors can detect Hg 2+ with the concentrations ranging from 0.010 to 1000 nM, which performances are much better than those of the current PEC analysis methods. Besides, such a MOF-templated one-pot construction route may pave the way toward the design of various direct Z-scheme heterojunction photocatalysts of PEC probes of great interest.
Qi-Rui Zhang,Yu-Long Wang,Zhi-Hao Deng,You-Long Chen,Si-Jing Ding,Liang Ma
Semiconductor junction shows greatly potential in photocatalysis due to the unique merits for charge separation, however the photocatalytic efficiency is still limited by the monotonous charge separation pathway and weak light absorption. Herein, multichannel charge separation driven by multiple internal electric fields (IEFs) has been proposed in ReS 2 /CoS x /CdS hollow nanostructures, which greatly improves the photocatalytic activity. By growing CdS nanoparticles on hollow ReS 2 /CoS x hybrids, the ReS 2 /CoS x /CdS ternary hybrids with Schottky junction (ReS 2 -CoS x ), type-I junction (ReS 2 -CdS), and Ohmic contact (CoS x -CdS) were constructed. The unique hollow structure and bandgap excitation endow the ReS 2 /CoS x /CdS hybrids with high light-harvesting efficiency across a broad spectrum from ultraviolet (UV) to near-infrared (NIR). Ultrafast transient absorption (TA) characterization elucidates the multi-interface charge transfer mechanisms, which involve electron transfer from CoS x to ReS 2 , from CdS to ReS 2 , from CdS to CoS x , and a possible sequential transfer from CdS to CoS x and then to ReS 2 . These pathways significantly prolong the lifetime of charge carriers and suppress charge recombination. Concurrently, the multiple IEFs facilitate charge separation and prevent back-transfer, further inhibiting charge recombination. The ReS 2 /CoS x /CdS hollow nanostructures exhibit remarkably enhanced photocatalytic activity, which is 15.00 and 15.36 times of pure CdS and ReS 2 , respectively, under visible light irradation (λ > 420 nm) with Na 2 S/Na 2 S 2 O 3 as the hole sacrificial agent. This study provides valuable insights for designing efficient photocatalysts based on semiconductor junction, and the synthesized materials show promising potential for solar-driven energy conversion applications.
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