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A novel technique for photocatalytic removal of elemental mercury (Hg 0 ) using visible-light-driven Ag/AgBr-Ag 2 CO 3 hybrids was proposed. The ternary Ag/AgBr-Ag 2 CO 3 hybrids were synthesized by a simple modified co-precipitation method and characterized by N 2 adsorption-desorption, scanning electron microscope (SEM), X-ray diffraction (XRD), UV–vis diffused reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) techniques. The effects of AgBr content, fluorescent lamp (FSL) irradiation, solution temperature, SO 2 and NO on Hg 0 removal were investigated in detail. Furthermore, a possible reaction mechanism for higher Hg 0 removal was proposed, and the simultaneous removal of Hg 0 , SO 2 and NO was studied. The results showed that a high efficiency of Hg 0 removal was obtained by using Ag/AgBr-Ag 2 CO 3 hybrids under fluorescent lamp irradiation. The AgBr content, FSL irradiation, solution temperature, and SO 2 all exhibited significant effects on Hg 0 removal, while NO had slight effect on Hg 0 removal. The addition of Ca(OH) 2 demonstrated a little impact on Hg 0 removal and could significantly improve the SO 2 -resistance performance of Ag/AgBr(0.7)-Ag 2 CO 3 hybrid. The characterization results exhibited that hydroxyl radical ( OH), superoxide radical ( O 2 − ), hole (h + ), and Br 0 , were reactive species responsible for removing Hg 0 , and the h + played a key role in Hg 0 removal. [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]

[Display omitted] • Doping nitrogen into CoS x polyhedron via N 2 plasma treatment to yield N-CoS x. • CdS was controllably loaded on N-CoS x forming CdS/N-CoS x photocatalyst. • Surface wettability, conductivity and Fermi level of CoS x were tuned by plasma treatment. • Visible-light photocatalysis for Cr(VI) reduction was achieved with efficiency up to 100%. • A photocatalytic mechanism of direct Z-scheme heterojunction was proposed. A direct Z-scheme heterojunction has been constructed by loading cadmium sulfide (CdS) on cobalt sulfide doped with nitrogen (N-CoS x) by N 2 plasma treatment for efficient photocatalytic Cr(VI) reduction under visible light. It was discovered that the resulting CdS/N-CoS x nanocomposites could present different photocatalytic performances controllably depending on the plasma treatment time and CdS-to-N-CoS x ratios. Especially, the one with 5-min plasma treatment and 8/1 M ratio could exhibit the highest Cr(VI) photoreduction efficiency, which is over four and two folds higher than those of pristine N-CoS x and CdS, respectively. Herein, the plasma-assisted N doping could not only increase the surface wettability and conductivity of CoS x but also decrease its Fermi level for improving the photocatalytic Cr(VI) reduction. More importantly, a direct Z-scheme heterojunction could be constructed by the combination of CdS and N-CoS x with suitable band structures, which could further booster the charge separation and transferring, without sacrificing the redox capacity of photogenerated carriers. The enhanced photocatalytic activity and stability of CdS/N-CoS x nanocomposites could thereby be expected for Cr(VI) reduction, with the efficiency up to 100% within 25 min. Such a direct Z-scheme heterojunction created by the plasma treatment route may promise for the large-scale applications for the removal of various toxic pollutants in the environmental remediation field. [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 photocatalyst of Ag 2 S/AgI-Bi 2 S 3 /BiOI was synthesized with Z -scheme heterojunctions simply by the S2−-I− anion exchange route showing broad visible light response and enhanced photogenerated carriers properties. The yielded Ag 2 S/AgI-Bi 2 S 3 /BiOI could feature the reactive active sites of Bi 2 S 3 /BiOI and Ag 2 S/AgI heterojunctions, serving as the photogenerated electron donors and photogenerated electron acceptors, respectively. Ag bridges were generated to ensure the construction of Z -scheme strategy, which further improved the migration direction of charge carriers in nanocomposites. Moreover, the analysis of photoluminescence spectra and electrochemical impedance spectroscopy could testified the functions of heterojunctions, which dramatically achieved the enhanced separation and transferring capacity of photogenerated electron-hole pairs in photocatalyst, respectively. In addition, Ag 2 S/AgI-Bi 2 S 3 /BiOI with large specific surface area facilitated the efficient photocatalytic removal of salicylic acid (SA) (up to 89.2%) under visible light. Favorable photocatalytic production of hydrogen peroxide (H 2 O 2) were obtained in pure water driven by the visible light. Besides, by the results of capture experiments, DMPO spin trapping ESR spectra and band structures analysis, the Z -scheme manner of the nanocomposites could promote the reduction ability of photo-generated electrons so as to produce numerous ·O 2 − during the photocatalytic reactions toward the photocatalytic SA removal and H 2 O 2 production. Ag 2 S/AgI-Bi 2 S 3 /BiOI with broad visible light response and enhanced photogenerated carriers properties performed efficient photocatalytic salicylic acid removal via Z-scheme strategy. Unlabelled Image • Ag 2 S/AgI-Bi 2 S 3 /BiOI is synthesized by the S2−-I− anion exchange at room temperature. • The yielded Bi 2 S 3 /BiOI and Ag 2 S/AgI serve as different functions for photocatalysis. • Z-scheme indicates high separation and transfer capacity of photogenerated carriers. • Ag 2 S/AgI-Bi 2 S 3 /BiOI exhibits powerful visible light harvest for the SA removal. • The efficiently generation of H 2 O 2 could be expected in water under visible light. [ABSTRACT FROM AUTHOR]

Carbon nitride quantum dots (CNQDs) were doped into melamine (MA) and silver (Ag) matrix yielding CNQDs@MA−Ag nanocomposites by the supramolecular self‐assembly route. To our surprise, the resulting mesoporous nanocomposites could present different morphologies (i. e., nanowires, nanoflowers, and nanosheets) and especially tunable visible‐light photocatalysis performances depending on the percentages of CNQDs used. It was discovered that the CNQDs@MA−Ag ones with the pinecone‐like structure (containing 30 % CNQDs) could exhibit the strongest visible‐light photocatalysis for splitting water to yield H2O2 with a production efficiency of 39.82 μmol ⋅ g−1 h−1, which is more than ten‐fold higher than that of CNQDs alone. Herein, the nano‐scaled Ag could facilitate the increased light harvesting and the separation as well as transmission of electron‐hole pairs of CNQDs resulting in the enhanced visible‐light photocatalysis of nanocomposites. More importantly, the pinecone‐like ones might additionally enable more exposed active sites of photocatalysis and larger mesoporous specific area of contacting dissolved oxygen in water, leading to the higher photocatalytic efficiency of H2O2 generation. This CNQDs‐based fabrication strategy may open a new door towards the design of a variety of photocatalysts with different morphologies and tunable photocatalysis performances for the efficient splitting water toward H2O2 evolution under sunlight. [ABSTRACT FROM AUTHOR]