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A series of ternary Ag/AgI-Ag 2 CO 3 photocatalysts synthesized using a facile coprecipitation method were employed to investigate their performances of Hg 0 removal in a wet scrubbing reactor. The hybrids were characterized by N 2 adsorption-desorption, XRD, SEM-EDS, HRTEM, XPS, DRS and ESR. The photocatalytic activities of Hg 0 removal were evaluated under fluorescent light. The results showed that AgI content, fluorescent light irradiation, reaction temperature all showed significant influences on Hg 0 removal. NO exhibited significant effect on Hg 0 removal in comparison to SO 2 . Among these ternary Ag/AgI-Ag 2 CO 3 hybrids, Ag/AgI(0.1)-Ag 2 CO 3 showed the highest Hg 0 removal efficiency, which could be ascribed to the effective separation of photogenerated electron-hole pairs between AgI and Ag 2 CO 3 and the surface plasmon resonance (SPR) effect in the visible region by metallic silver nanoparticles (Ag 0 NPs). The trapping studies of reactive radicals showed that the superoxide radicals ( O 2 − ) may play a key role in Hg 0 removal under fluorescent light. According to the experimental and characterization results, a possible photocatalytic oxidation mechanism for enhanced Hg 0 removal over Ag/AgI(0.1)-Ag 2 CO 3 hybrid under fluorescent light was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZnS/CdS was fabricated with type-II heterostructure by growing ZnS QDs on CdS NWs. • Low-bandgap CdS NWs and wide-bandgap ZnS QDs act separately as photosensitizer and Hg2+ probe. • A selective PEC sensor was developed for the analysis of Hg2+ with "turn-on" signal output. • Hg2+ induces the in-situ formation of HgS/ZnS/CdS with double type-II heterostructure. • The PEC sensor can detect Hg2+ with concentrations down to about 0.40 pM. An ultrasensitive and selective photoelectrochemical (PEC) platform has been developed for determining Hg2+ with "turn-on" signal output by synergistically using CdS nanowires (NWs) and ZnS quantum dots (QDs). CdS NWs was first prepared and then deposited with ZnS QDs to yield ZnS/CdS nanocomposite with type-II heterostructure. It was found that the as-constructed ZnS/CdS heterostructure can exhibit excellent photoelectrochemical characteristics by separately employing CdS NWs and ZnS QDs as the photosensitizer and Hg2+-recognition probe. What's more, the constructed analysis platform could display specifically enhanced photocurrent responses to Hg2+ under the visible light via the selective ion-exchange reaction. The in-situ formation of ternary HgS/ZnS/CdS could be thus expected with double type-II heterostructures so as to further enhance the transferring and separation of charges. A linear response can be achieved for Hg2+ in the concentration range from 0.0010 to 5.0 nM, with a detection limit of 0.40 pM. Moreover, the application feasibility of the developed sensor with ZnS/CdS heterostructure could be testified by detecting Hg2+ ions in environmental waters. Such a route of in-situ formation of double type-II heterostructure might promise the wide applications for designing different visible light-driven PEC sensors for probing heavy metals like Hg2+ with the "turn-on" signal output. [ABSTRACT FROM AUTHOR]

• A near-infrared-light-driven photoelectrochemical sensor is developed for probing Hg2+. • Bead chain-like Ag@Ag 2 S composites are prepared via one-step oil-bath route followed by photoreduction. • Ag 2 S and metallic Ag separately act as the sensitizer and Hg2+-recognition probe. • This PEC sensor can facilitate the detection of Hg2+ with concentrations down to 0.50 pM. A near-infrared (NIR) light-driven photoelectrochemical (PEC) sensing platform was established for the quantitative assay of Hg2+ using Ag@Ag 2 S nanocomposites. Ag 2 S quantum dots (QDs) with the bead-chain-like nanostructure were fabricated simply via one-step oil-bath route to be further deposited with metallic Ag through the photo-reduction method to yield Ag@Ag 2 S nanocomposites. It was found that Ag@Ag 2 S-based sensor could present more than twice larger PEC responses than the Ag 2 S-based one, due to the synergetic combination of metallic Ag with the surface plasmon resonance (SPR) effects and Ag 2 S QDs with the NIR-light-irradiated PEC properties. More importantly, the developed PEC sensor could display the photocurrent responses that are selectively inhibited in the presence of Hg2+ by forming Ag-Hg amalgam to accelerate the recombination of photo-induced electron-hole pairs. Under NIR light, it can detect Hg2+ in the concentrations linearly ranging from 0.0010 to 5.0 nM, with a limit of detection of about 0.50 pM. This work may guide a promising combination of Ag 2 S of NIR QDs with metallic Ag of SPR effects for designing various PEC sensing platforms for the complex environmental monitoring of different heavy-metal ions like Hg2+. [ABSTRACT FROM AUTHOR]

• A photoelectrochemical sensor was developed for the "signal-on" analysis of Hg2+. • Hollow CoS x @CdS polyhedrons were fabricated by ZIF-67-templated solvothermal route. • Direct Z-scheme CoS x @CdS photocatalysts were utilized as the recognition probes. • New Z-scheme heterojunction of CoS x @CdS/HgS was formed by the selective ion-exchange. • This PEC sensor can facilitate the detection of Hg2+ with concentrations down to 2.0 pM. A visible-light-driven photoelectrochemical (PEC) sensor has been developed for probing Hg2+ with "turn-on" signal output using hollow CoS x @CdS polyhedron as direct Z-scheme photocatalyst and Hg2+-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 Hg2+, in contrast to these of the CoS x or CdS-modified ones showing no significant Hg2+-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 Hg2+ 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 Hg2+ 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. [ABSTRACT FROM AUTHOR]

• A photoelectrochemical sensor was developed for the "signal-on" analysis of Hg2+. • Bead chain-like Ag 2 S were integrated with ZnS to be coated onto the ITO electrodes. • Ag 2 S and ZnS were utilized separately as the sensitizer and recognition probe. • Hg2+ can conduct a Zn-to-Hg exchange to form HgS/ZnS@Ag 2 S heterojunction. • This sensor can facilitate the detection of Hg2+ with concentrations down to 1.0 pM. A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg2+ by the synergetic combination of low-bandgap Ag 2 S and wide-bandgap ZnS quantum dots (QDs). Ag 2 S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag 2 S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag 2 S and ZnS QDs could act as the PEC sensitizer and Hg2+-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg2+ under the visible-light irradiation, presumably due to that Hg2+ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag 2 S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg2+ with concentrations ranging from 0.010–1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg2+ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg2+ evaluation. [ABSTRACT FROM AUTHOR]