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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] • 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 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]