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[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]

Ultra-stable CoS x /CdS photocatalysts were fabricated by the ZIF-67-templated one-pot solvothermal route for photocatalytic Cr(VI) reduction under visible light. • CoS x /CdS composites were controllably fabricated by ZIF-67-templated solvothermal route. • Different photocatalytic activities were obtained depending on the CoS x -to-CdS molar ratios. • Highest visible-light photocatalysis for Cr(VI) reduction was expected with 100% efficiency. • Long-term stability could be maintained for the photocatalytic cycles. • A photocatalytic mechanism of direct Z-scheme heterojunction was proposed. 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. [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]

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]

An urchin-like LaPO 4 -based nanocomposite integrating Ag 3 PO 4 and Pd has been initially synthesized via a controllable self-assembly route, with enhanced photocatalysis and ultrastable structure for the synergistic hydrogen (H 2) evolution under sunlight. Citric acid was employed as a structure-mediated agent to guide the oriented growth of LaPO 4 along [101] facet at room temperature, showing the urchin-like 3D structure. Furthermore, Pd and Ag 3 PO 4 were coated in turn resulting in the Ag 3 PO 4 /Pd/LaPO 4 nanocomposite, in which Pd and Ag 3 PO 4 could act as the functions of electron receptor and electron donor in the photocatalysis, respectively. It was discovered that the as-developed nanocomposite could present the robust photocatalysis and stable morphology after consecutive uses. Based on the band structure analysis, a Z -scheme system of Ag 3 PO 4 /Pd/LaPO 4 was thereby proposed for the sunlight photocatalysis, as testified by DMPO spin trapping ESR spectra. Also, the photoluminescence and electrochemical impedance of nanocomposites were conducted, indicating that the improved carriers properties should be responsible mainly for the dramatically enhanced photocatalytic activities. Moreover, the outstanding photocatalytic performances of Ag 3 PO 4 /Pd/LaPO 4 were demonstrated in H 2 evolution (1084.3 μmol·g−1·h−1) under sunlight. Importantly, such a citric acid-controlled self-assembly route may pave the way toward the fabrication of multi-component photocatalyst tailored for the wide photocatalytic applications. Ag 3 PO 4 /Pd/LaPO 4 with strong synergistic effects and optimized photogenerated carriers properties performed efficient photocatalytic H 2 evolution via Z-scheme strategy. Unlabelled Image • A new Ag 3 PO 4 -Pd/LaPO 4 photocatalyst is synthesized with urchin-like 3D structure. • Pd and Ag 3 PO 4 increase the synergistic photocatalysis efficiency of nanocomposite. • Strong steric hindrance ensures a highly morphological and photocatalysis stability. • Z-scheme indicates high separation and transfer capacity of photogenerated carriers. • Ag 3 PO 4 -Pd/LaPO 4 shows outstanding photocatalytic hydrogen evolution activity. [ABSTRACT FROM AUTHOR]